CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND

[0003] It can be desirable to detect the presence and/or extent of various events. For example, to obtain hydrocarbons from subterranean formations, wellbores are drilled from the surface to access the hydrocarbon-bearing formation. After drilling a wellbore to the desired depth, a production string is installed in the wellbore to produce the hydrocarbons from one or more production zones of the formation to the surface. The production of the fluids can be detected at the wellhead based on total flow of fluid. However, it can be difficult to determine where the fluid is inflowing into the wellbore when multiple productions zones are present and an extent of the fluid inflow (e.g., a fluid inflow rate).

BRIEF SUMMARY

[0004] In some embodiments, a method of determining the presence and/or extent of an event comprises determining a plurality of temperature features from a (e.g., a distributed) temperature sensing signal originating, determining one or more frequency domain features from an acoustic signal, and using at least one temperature feature of the plurality of temperature features and at least one frequency domain feature of the one or more frequency domain features to determine the presence and/or extent of the event at one or more locations.

[0005] In some embodiments, a method of determining the presence and/or extent of an event comprises determining a plurality of temperature features from a temperature sensing signal, determining one or more frequency domain features from an acoustic signal, and using at least one temperature feature of the plurality of temperature features and at least one frequency domain feature of the one or more frequency domain features to determine the presence and/or extent of the event at one or more locations. The plurality of temperature features comprise at least two of: a depth derivative of temperature with respect to depth, a temperature excursion measurement, a baseline temperature excursion, a peak-to-peak value, an autocorrelation, a Fast Fourier Transform (FFT) of the temperature sensing signal, a Laplace transform of the temperature sensing signal, a wavelet transform of the temperature sensing signal and/or of a derivative of the temperature sensing signal with respect to length (e.g., depth), or a derivative of flowing temperature with respect to length (depth), as described by Equation (1), a heat loss parameter, a time-depth derivative, or a depth-time derivative.

[0006] In some embodiments, a system of determining the presence and/or extent of an event (e.g., within a wellbore) comprises a processor, a memory, and an analysis program stored in the memory. The analysis program is configured, when executed on the processor, to receive a (e.g., distributed) temperature sensing signal and an acoustic signal, wherein the temperature sensing signal and the acoustic signal originated from the event (e.g., within the wellbore), determine a plurality of temperature features from the temperature sensing signal, determine one or more frequency domain features from the acoustics signal, and determine the presence and/or extent of the event at one or more locations (e.g., along the wellbore) using at least one temperature feature of the plurality of temperature features and at least one frequency domain feature of the one or more frequency domain features.

[0007] Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS [0008] For a detailed description of various exemplary embodiments, reference will now be made to the accompanying drawings in which: [0009] FIG. 1 is a schematic, cross-sectional illustration of a downhole wellbore environment according to some embodiments;

[0010] FIGS. 2A and 2B are a schematic, cross-sectional views of embodiments of a well with a wellbore tubular having an optical fiber inserted therein according to some embodiments;

[0011] FIG. 3 is a schematic view of an embodiment of a wellbore tubular with fluid inflow and sand ingress according to some embodiments;

[0012] FIG. 4 is a flow chart of a method for determining event (e.g., fluid inflow) locations (e.g., within a wellbore) according to some embodiments;

[0013] FIG. 5 is a flow diagram of a method of determining an extent of an event (e.g., a fluid inflow rate of a fluid inflow event) at one or more locations (e.g., within a wellbore) according to some embodiments;

[0014] FIG. 7 schematically illustrates a computer that may be used to carry out various methods according to some embodiments.

DETAILED DESCRIPTION

[0015] The following discussion is directed to various exemplary embodiments. However, one of ordinary skill in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

[0016] The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

[0017] Unless otherwise specified, any use of any form of the terms “connect,” “engage,” “couple,” “attach,” or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . “. Reference to up or down will be made for purposes of description with “up,” “upper,” “upward,” “upstream,” or “above” meaning toward the surface of the wellbore and with “down,” “lower,” “downward,” “downstream,” or “below” meaning toward the terminal end of the well, regardless of the wellbore orientation. Reference to inner or outer will be made for purposes of description with “in,” “inner,” or “inward” meaning towards the central longitudinal axis of the wellbore and/or wellbore tubular, and “out,” “outer,” or “outward” meaning towards the wellbore wall. As used herein, the term “longitudinal” or “longitudinally” refers to an axis substantially aligned with the central axis of the wellbore tubular, and “radial” or “radially” refer to a direction perpendicular to the longitudinal axis. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art with the aid of this disclosure upon reading the following detailed description of the embodiments, and by referring to the accompanying drawings.

[0018] As utilized herein, a ‘fluid inflow event’ includes fluid inflow (e.g., any fluid inflow regardless of composition thereof), gas phase inflow, aqueous phase inflow, and/or hydrocarbon phase inflow. The fluid can comprise other components such as solid particulate matter (e.g., sand, etc.) in some embodiments, as discussed in more detail herein.

[0019] Disclosed herein are systems and methods for detecting and/or characterizing an event, for example, determining the presence of an event, such as a fluid inflow event, at one or more locations, and/or an extent of the event, such as inflow quantities (e.g., within a subterranean wellbore). Other events can also be detected such as security events, transportation events, geothermal events, carbon capture and CO2 injection events, facility monitoring events, pipeline monitoring events, dam monitoring events, and the like. The systems allow for an identification of the event location(s) as well as the extent (e.g., inflow rates) at those locations using temperature features derived from temperature measurements as well as frequency domain features obtained from acoustic signals. As used herein, the term acoustic signals refers to signals representative of measurements of acoustic sounds, dynamic strain, vibrations, and the like, whether or not within the audible or auditory range.

[0020] In some embodiments, temperature features can be determined from temperature measurements taken along a length being monitored, such as a length of a wellbore. The temperature measurements can be used in a first or event identification/detection model that can provide an output indicative of event location(s), for example, fluid inflow locations along a wellbore. This can allow those locations with the event (e.g., fluid inflow) to be identified using temperature based measurements (e.g., from the wellbore). When combined with a (e.g., distributed) temperature sensing system that can provide distributed and continuous temperature measurements, the systems can allow for event (e.g., fluid inflow) locations to be tracked through time.

[0021] The systems described herein also allow for various frequency domain features to be obtained from an acoustic signal originating from the event (e.g., within the wellbore). The acoustic signals can be obtained using a distributed acoustic sensing (DAS) system that allows for continuous and distributed acoustic sensing. The acoustic signals can be taken along the same portions of the length (e.g., length of the wellbore) as the temperature measurements, thereby allowing for information about the events (e.g., fluid inflow events), to be determined using both the temperature features and the frequency domain features. In some embodiments, a second or extent model can be developed and used with one or more frequency domain features that can allow for the prediction of an extent of the event (e.g., fluid inflow rates for one or more fluids and/or fluid phases of a fluid inflow event).

[0022] When used together, the first or event identification model can allow the event locations to be determined using temperature features, and the second or extent model can allow for event (e.g., fluid inflow) extent (e.g., fluid inflow rates) to be determined at the one or more event locations. The second or event extent model can be used to verify or validate the event locations as determined from the first or event identification model. This can help to provide an improved event location determination for use in managing the event.

[0023] The second model can also be used to determine the event extents (e.g., fluid inflow rates of one or more fluids, fluid phases (e.g., combined gas glow, combined liquid flow, etc.), or both) from one or more locations (e.g., along the wellbore). The processing can be combined such that the second or event extent model may only be executed at the one or more locations as identified using the temperature features with the first or event identification model. The resulting event extents (e.g., fluid inflow rates) as determined from the second model can be used to provide an indication of the event extents at the one or more locations. The resulting event extent (e.g., fluid inflow rate) can also be normalized across the one or more locations to provide a relative contribution to the total event extent (e.g., fluid inflow rates) at the one or more locations. This information can be used along with independently measured extent values (e.g., actual fluid values (e.g., production rates)) to provide an improved determination of the actual event extents (e.g., fluid inflow rates) at one or more locations along the length being examined (e.g., one or more locations within the wellbore). This can allow for near real time information on the event to more effectively manage the event.

Overview

[0024] Disclosed herein are systems and methods for determining the presence and/or extent of events at one or more event locations, for example, within a subterranean wellbore, so that a wellbore operator may more effectively control the fluid production from the wellbore. The systems allow for an identification of the events and/or event extents at the event location(s) using temperature features derived from temperature measurements and acoustic features derived from acoustic measurements.

[0025] The new signal processing architecture disclosed herein allows for the identification of various events (e.g., the detection of the presence of the event at one or more locations). In some embodiments, the events can occur within a wellbore such as fluid inflow event (e.g., including fluid inflow detection, fluid inflow location determination, fluid inflow quantification, fluid inflow discrimination, etc.), fluid outflow detection (e.g., fluid outflow detection, fluid outflow quantification), fluid phase segregation, fluid flow discrimination within a conduit, well integrity monitoring, including in-well leak detection (e.g., downhole casing and tubing leak detection, leaking fluid phase identification, etc.), flow assurance (e.g., wax deposition), annular fluid flow diagnosis, overburden monitoring, fluid flow detection behind a casing, fluid induced hydraulic fracture detection in the overburden (e.g., micro-seismic events, etc.), sand detection (e.g., sand ingress, sand flows, etc.), and the like, each in real time or near real time in some embodiments. Other events can also be detected such as security events, transportation events, geothermal events, carbon capture and CO2 injection events, facility monitoring events, pipeline monitoring events, dam monitoring events, and the like.

[0026] As utilized herein, “fluid flow discrimination” indicates an identification and/or assignment of the detected fluid flow (e.g., single phase flow, mixed phase flows, time-based slugging, altering fluid flows, etc.), gas inflow, hydrocarbon liquid (e.g., ‘oil’) inflow, and/or aqueous phase (e.g., water) inflow, including any combined or multiphase flows or inflows. The methods of this disclosure can thus be utilized, in embodiments, to provide information on various events such as a fluid ingress and/or a fluid ingress point or location as well as flow regimes within a conduit rather than simply a location at which gas, water, or hydrocarbon liquid is present in the wellbore tubular (e.g., present in a flowing fluid), which can occur at any point above the ingress location as the fluid flows to the surface of the wellbore. In some embodiments, the system allows for a quantitative measurement of various fluid flows such as a relative concentration of in-well hydrocarbon liquid, water, and gas.

[0027] In some instances, the systems and methods can provide information in real time or near real time. As used herein, the term “real time” refers to a time that takes into account various communication and latency delays within a system, and can include actions taken within about ten seconds, within about thirty seconds, within about a minute, within about five minutes, or within about ten minutes of the action occurring. Various sensors ( e.g ., distributed temperature sensing sensors, distributed fiber optic acoustic sensors, etc.) can be used to obtain a distributed temperature signal and an acoustic signal at various points along a length being monitored, for example, along a wellbore. The distributed temperature sensing signal and the acoustic signal can then be processed using signal processing architecture with various feature extraction techniques (e.g., temperature feature extraction techniques, spectral feature extraction techniques) to obtain a measure of one or more temperature features, one or more frequency domain features, and/or combinations thereof that enable selectively extracting the distributed temperature sensing signals and acoustic signals of interest from background noise and consequently aiding in improving the accuracy of the identification of events, including, for example, the movement of fluids (e.g., gas inflow locations, water inflow locations, hydrocarbon liquid inflow locations, etc.) in real time. While discussed in terms of being real time in some instances, the data can also be analyzed at a later time at the same location and/or a displaced location.

[0028] As used herein, various frequency domain features can be obtained from the acoustic signal, and in some contexts, the frequency domain features can also be referred to herein as spectral features or spectral descriptors. In some embodiments, the spectral features can comprise other features, including those in the time domain, various transforms (e.g., wavelets, Fourier transforms, etc.), and/or those derived from portions of the acoustic signal or other sensor inputs. Such other features can be used on their own or in combination with one or more frequency domain features, including in the development of transformations of the features, as described in more detail herein.

[0029] In some embodiments, the distributed temperature sensing signals and the acoustic signal(s) can be obtained in a manner that allows for a signal to be obtained along a length of the sensor, for example, an entire wellbore or a portion of interest (e.g., a depth) thereof, a portion of a fiber in a security perimeter, the length of a portion thereof of a pipeline, or the like. In wellbore contexts, production logging systems utilize a production logging system (PLS) to determine flow profile in wells. However, since the PLS can be 10-20 meters long and the sensors are distributed along the length, sensors that are not at the front of the PLS are not actually taking measurements at the depth for which the measurements are recorded, and, thus, the data can be incorrect or incomplete over time. Furthermore, the flow can be altered by the mere presence of the PLS within the wellbore, so what is measured at the downstream end of the PLS is not an accurate reflection of what the profile/regime was before the tool disturbed the flow. Furthermore, as a PLS is typically run through a well once or a few times (down and then up once or a few times and out), and the sensors are exposed to the conditions at a given depth for only a very brief period of time (e.g., 4-5 seconds). Accordingly, while PLSs can provide an indication that certain events, such as downhole water inflow, may be occurring, they do not provide continuous measurements over prolonged durations of time that would be needed to study dynamic variabilities in production profdes over time.

[0030] Fiber optic distributed temperature sensors (DTS) and fiber optic distributed acoustic sensors (DAS) can capture distributed temperature sensing and acoustic signals, respectively, resulting from downhole events, such as wellbore events (e.g., gas inflow/flow, hydrocarbon liquid inflow/flow, water inflow/flow, mixed flow, leaks, overburden movement, and the like), as well as other background events. DTS and DAS can also be used to capture distributed temperature sensing and acoustic signals, respectively, from events, such as security events, transportation events, geothermal events, carbon capture and CO2 injection events, facility monitoring events, pipeline monitoring events, dam monitoring events, and the like. This allows for signal processing procedures that distinguish events and flow signals from other sources to properly identify each type of event. This in turn results in a need for a clearer understanding of the fingerprint of in-well event of interest (e.g., fluid inflow, water inflow, gas inflow, hydrocarbon liquid inflow, fluid flow along the tubulars, etc.) in order to be able to segregate and identify a signal resulting from an event of interest from other ambient background signals. As used herein, the resulting fingerprint of a particular event can also be referred to as an event signature, as described in more detail herein. In some embodiments, the temperature features and the acoustic features can each be used with a model (e.g., a machine learning model, multivariate model, etc.) to provide for detection, identification, and/or determination of the extents of various events. A number of different models can be developed and used to determine when and where certain events have occurred, for example, within a wellbore and/or the extents of such events.

[0031] The ability to identify various events (e.g., wellbore events, security events, transportation events, geothermal events, carbon capture and CO2 injection events, facility monitoring events, pipeline monitoring events, dam monitoring events, etc.) may allow for various actions or processes to be taken in response to the events. For example, reducing deferrals in wellbores resulting from one or more events such as water ingress and facilitating effective remediation relies upon accurate and timely decision support to inform the operator of the events. As another example, with respect to events within a wellbore, a well can be shut in, production can be increased or decreased, and/or remedial measures can be taken in the wellbore, as appropriate based on the identified event(s). As another example, the detection of a pipeline leak can allow the operator to develop a plan to fix the leak with minimal downtime in the pipeline. An effective response, when needed, benefits not just from a binary yes / no output of an identification/detection of in- well events but also from a measure of an extent, such as a relative amount of fluids (e.g., amount of gas inflow, amount of hydrocarbon liquid inflow, amount of water inflow, etc.) from each of the identified zones of events so that zones contributing the greatest fluid amount(s) can be acted upon first to improve or optimize production. The systems and methods described herein can be used, in applications, to identify the source of an event or problem, as well as additional information about the event (referred to herein as an “extent” of the event), such as a direction and amount of flow, and/or an identification of the type of problem being faced. For example, when an event comprising water inflow and a location thereof are detected, determination of an extent of the inflow event comprising a relative flow rate of the hydrocarbon liquid at the water inflow location may allow for a determination of whether or not to remediate, the type or method of remediation, the timing for remediation, and/or deciding to alter (e.g., reduce) a production rate from the well. For example, production zones can be isolated, production assemblies can be open, closed, or choked at various levels, side wells can be drilled or isolated, and the like. Such determinations can be used to improve on the drawdown of the well while reducing the production expenses associated with various factors such as produced water.

[0032] The same signal processing described herein can be used to identify various events across a variety of industries. The systems can comprise similar real time signal processing architecture that allows for the identification of events using various signatures or models. Within these systems, various sensors (e.g., distributed temperature sensors, point temperature sensors, distributed fiber optic acoustic sensors, point acoustic sensors, etc.) can be used to obtain a sampling at various points along a path or length. The distributed temperature sensing signal and acoustic signals can then be processed using signal processing architecture with temperature feature and spectral feature extraction techniques, as detailed hereinbelow, to obtain temperature features and acoustic features, respectively, that enable selectively extracting the signals of interest from background noise.

[0033] Once obtained, the temperature and acoustic features can be used in various models in order to be able to segregate a noise resulting from an event of interest from other ambient background noise. Specific models can be determined for each event by considering one or more temperature features and/or acoustic features for known events. From these known events, the temperature and/or acoustic features specific to each event can be developed and signatures (e.g., having ranges or thresholds) and/or models can be established to determine a presence (or absence) of each event. Based on the specifics of each temperature and/or acoustic feature, the resulting signatures or models can be used to sufficiently distinguish between events to allow for a relatively fast identification of such events. The resulting signatures or models can then be used along with processed distributed temperature sensing and/or acoustic signal data to determine if an event is occurring at a point of interest along the path of the temperature and/or acoustic sensor(s). Any of the processing techniques disclosed herein can be used to initially determine a signature or model(s), and then process and compare the temperature and/or acoustic features in a sampled temperature sensing and/or acoustic signal with the resulting signatures or model(s).

[0034] Thus, temperature and acoustic signals in industries such as security (e.g., security, pipeline monitoring, etc.), energy (e.g., geothermal, etc.), transportation (e.g., railway monitoring, roadway monitoring, etc.), and facilities monitoring (e.g., monitoring equipment such as electric submersible pumps, wind turbines, compressors, dams, etc.) can benefit from the use of the systems and methods disclosed herein. For example, a pipeline can be monitored to detect temperature and/or acoustic signals along the length of a pipeline, using for example, a fiber attached to the pipeline, along with a DTS and/or DAS unit. The length of the fiber along the pipeline can be considered a path of the fiber as it passes from the receiver/generator (e.g., the DTS and/or DAS unit) along the pipeline. Various temperature and/or acoustic signatures can be detected based on temperature sensing and/or acoustic signals originating along the length of the pipeline and/or fiber. These signals can be processed to extract one or more temperature and/or spectral features, and signatures and/or model(s) of such events can be determined or developed. Once obtained, the signatures and/or model(s) can be used to process distributed temperature sensing and/or acoustic signals at various lengths along the path of the fiber and determine the presence or absence of the various events using the temperature and/or spectral features and the signatures and/or model(s).

[0035] Similarly, the temperature and/or acoustic monitoring techniques described herein can be used with one or more point sources, which can be individual or connected along a path. For example, a facility having industrial equipment can be monitored using the temperature and/or acoustic monitoring techniques described herein. For example, a facility having pumps, turbines, compressors, or other equipment can have a temperature and/or acoustic sensor(s) monitoring the piece of equipment. Signatures and/or model(s) of various events can be determined for each type of equipment and used to monitor and identify the state of the equipment. For example, a pump can be monitored to determine if the pump is active or inactive through the use of a temperature and/or acoustic signal and the temperature and/or spectral characteristics and/or model(s) determining the presence of an event as described herein. When multiple piece of equipment are present, a single distributed temperature sensor and/or acoustic sensor, such as a fiber, can be coupled to each piece of equipment. This configuration may allow a single interrogation unit to monitor multiple pieces of equipment using the analysis by resolving a length along the fiber for each piece of equipment. Thus, a distributed temperature and/or acoustic monitoring system may not require multiple processors correlating to individual pieces of equipment.

[0036] Similarly, pipelines can be monitored in a manner similar to the way the wellbores are monitored as disclosed herein. In this embodiment, the fiber may detect various events such as leaks, flow over a blockage or corrosion, and the like. This may allow for remote monitoring along the length of a pipeline.

[0037] Other types of industries can also benefit from the use of temperature and/or acoustic sensing to obtain temperature and/or acoustic signals that can be analyzed and matched to events using temperature and spectral feature extraction, respectively, as described hereinbelow. Any industry that experiences events that create temperature and/or acoustic signals can be monitored using the systems and methods as described herein. Further, when the signals are distributed across space, a single temperature and/or acoustic sensor, such as an optical fiber, can be used with a receiver unit to detect temperature and/or acoustic signals across the length or path of the sensor element, thereby enabling a single sensor to detect temperature sensing and/or acoustic signals across a wide area or path. In some embodiments, a point sensor such as a temperature thermocouple can be used to obtain a temperature from a location and used with the processes described herein to detect an event. In these embodiments, the signal may not be obtained from a wellbore. For example, the temperature and/or acoustic signals may be obtained from a nonwellbore source or from outside of a subterranean formation. Thus, the systems and processing techniques described herein can be used to identify events using temperature and/or acoustic features obtained from temperature sensing and/or acoustic signals across a variety of industries and locations.

[0038] Herein described are systems and methods for detecting (e.g., identifying) and characterizing events (e.g., wellbore events, security events, transportation events, geothermal events, carbon capture and CO2 injection events, facility monitoring events, pipeline monitoring events, dam monitoring events, etc.). In some embodiments, the wellbore events can comprise fluid inflow locations and/or fluid flow regimes within a conduit in the wellbore. In some embodiments, other wellbore events such as fluid outflow detection, fluid phase segregation, fluid flow discrimination within a conduit, well integrity monitoring, in-well leak detection, annular fluid flow diagnosis, overburden monitoring, fluid flow detection behind a casing, sand detection (e.g., sand ingress, sand flows, etc.), and the like can be detected. In some embodiments, events such as security events, transportation events, geothermal events, carbon capture and CO2 injection events, facility monitoring events, pipeline monitoring events, dam monitoring events, and the like can be detected. For example, temperature and/or acoustic signals can be used in security monitoring to detect open doorways, gaps or holes in a perimeter, or the like. Similarly, temperature and/or acoustic signals can be detected on railways to determine the presence of trains through friction based heating, and ice can be detected on railways or roadways through the use of the temperature and/or acoustic signals. Geothermal events, carbon capture events, and CO2 injection events can be similar to wellbore events with respect to geothermal fluid inflow, outflows, leaks, and the like. Pipelines can also be monitored for flow, leaks, blockages, and the like.

[0039] As described herein, temperature features and/or spectral descriptors or frequency domain features can be used with DTS temperature and/or DAS acoustic data processing, respectively, to provide for event detection and/or event extent determination. For example, the temperature and/or spectral features can be used with wellbore event detection/identification (e.g., fluid profiling, fluid inflow location detection, fluid phase discrimination such as the determination that the fluid at one or more locations such as the detected fluid inflow location comprises gas inflow, hydrocarbon liquid inflow, aqueous phase inflow, a combined fluid flow, and/or a time varying fluid flow such as slugging single or multiphase flow, and the like). In some embodiments, a first or event identification/detection model can be used for event identification. The first or event identification model can comprise one or more individual models, which can be the same or different as described in more detail herein. In some embodiments, the first or event identification model can comprise a plurality of sub-models such as a fluid flow model used for inflow fluid phase discrimination, which can allow for the determination of at least one of a gas phase inflow, an aqueous phase inflow, a hydrocarbon liquid phase inflow, and various combinational flow regimes in a wellbore. In some embodiments, the same or a different event identification models can be used to identify other events such as fluid flow phase discrimination to determine the composition of fluid flowing in a conduit. Suitable event detection model(s) can be developed for any of the events described herein.

[0040] Application of the signal processing techniques and one or more event detection models with DTS and/or DAS for wellbore events such as downhole surveillance can provide a number of benefits including improving reservoir recovery by monitoring efficient drainage of reserves through downhole fluid surveillance (e.g., production flow monitoring), improving well operating envelopes through identification of drawdown levels (e.g., gas, water, etc.), facilitating targeted remedial action for efficient well management and well integrity, reducing operational risk through the clear identification of anomalies and/or failures in well barrier elements. Similar advantages are also possible with other non-wellbore events.

[0041] In some embodiments, use of the systems and methods described herein may provide knowledge of the events and the locations experiencing various events, thereby potentially allowing for improved actions (e.g., remediation actions for wellbore events, security actions for security events, etc.) based on the processing results. The methods and systems disclosed herein can also provide information on the events. For example, for wellbore events, information about a variability of the amount of fluid inflow being produced by the different fluid influx zones as a function of different production rates, different production chokes, and downhole pressure conditions can be determined, thereby enabling control of fluid inflow. For fluid inflow events, embodiments of the systems and methods disclosed herein also allow for a computation of the relative concentrations of fluid ingress (e.g., relative amounts of gas, hydrocarbon liquid, and water in the inflow fluid) into the wellbore, thereby offering the potential for more targeted and effective remediation.

[0042] As disclosed herein, embodiments of the data processing techniques can use various sequences of real time digital signal processing steps to identify the temperature and/or acoustic signal resulting from various events from background noise, and allow real time detection of the events and their locations using distributed fiber optic temperature and/or acoustic sensor data as the input data feed.

[0043] One or more models can be developed using test data to provide a labeled data set used as input into the model. The resulting trained models can then be used to identify one or more signatures based on features of the test data and one or more machine learning techniques to develop correlations for the presence of various events. In the model development, specific events can be created in a test set-up, and the temperature and/or acoustic signals can be obtained and recorded to develop test data. The test data can be used to train one or more models defining the various events. The resulting model can then be used to determine one or more events. In some embodiments, actual field data can be used and correlated to actual events using inputs from, for example, other temperature sensors, other acoustic sensors, and/or other production sensors (e.g., pressure sensors, flow meters, optical sensors, etc.). The data can be labeled to create a training data set based on actual production situations. The data can then be used alone or in combination with the test data to develop the model(s).

[0044] As described herein, wellbore events are used as an example. However, as noted above, other events and event detection model(s) for the other events are also within the scope of this disclosure. As described herein, the systems and methods can be used to identify the presence and/or extent of one or more events. Various events can be determined using the system and method, such wellbore events including, without limitation, fluid outflow detection, fluid phase segregation, fluid flow discrimination within a conduit, well integrity monitoring, in well leak detection, annular fluid flow diagnosis, overburden monitoring, fluid flow detection behind a casing, , wax deposition events, sand detection (e.g., sand ingress, sand flows, etc.), security events, transportation events, geothermal events, carbon capture and CO2 injection events, facility monitoring events, pipeline monitoring events, dam monitoring events, and the like. Fluid flow can comprise fluid flow along or within a tubular within a wellbore such as fluid flow within a production tubular. Fluid flow can also comprise fluid flow from the reservoir or formation into a wellbore tubular. Such flow into the wellbore and/or a wellbore tubular can be referred to as fluid inflow. While fluid inflow may be separately identified at times in this disclosure, such fluid inflow is considered a part of fluid flow within the wellbore.

[0045] In some embodiments, temperature features and/or acoustic features can be determined from respective measurements taken along a length, for example, a length of a wellbore. In some embodiments, the temperature and/or acoustic measurements can be used with one or more temperature and/or acoustic signatures, respectively, to determine the presence of absence of an event. The signatures can comprise a number of thresholds or ranges for comparison with various temperature features. When the detected temperature features fall within the signatures, the event may be determined to be present. In some embodiments, the temperature measurements can be used in a first or event detection model that can provide an output indicative of the presence or absence of one or more events (and optionally also one or more event locations) along the length (e.g., along the length of the wellbore). This can allow events to be identified using temperature based measurements (e.g., from the wellbore). When combined with a distributed temperature sensing system that can provide distributed and continuous temperature measurements, the systems can allow for fluid inflow locations to be tracked through time. A second or event extent model can utilize one or more spectral features to determine an extent of the event at the one or more locations.

[0046] A DAS/DTS system of this disclosure will now be described with reference to a wellbore. As noted above, a hybrid DAS/DTS system of this disclosure can be applied in nonwellbore applications, and the following wellbore description should not be limiting.

[0047] Referring now to FIG. 1, a schematic, cross-sectional illustration of a downhole wellbore operating environment 101 according to some embodiments is shown. More specifically, environment 101 includes a wellbore 114 traversing a subterranean formation 102, casing 112 lining at least a portion of wellbore 114, and a tubular 120 extending through wellbore 114 and casing 112. A plurality of completion assemblies such as spaced screen elements or assemblies 118 may be provided along tubular 120 at one or more production zones 104a, 104b within the subterranean formation 102. In particular, two production zones 104a, 104b are depicted within subterranean formation 102 of FIG. 1; however, the precise number and spacing of the production zones 104a, 104b may be varied in different embodiments. The completion assemblies can comprise flow control devices such as sliding sleeves, adjustable chokes, and/or inflow control devices to allow for control of the flow from each production zone. The production zones 104a, 104b may be layers, zones, or strata of formation 102 that contain hydrocarbon fluids (e.g., oil, gas, condensate, etc.) therein.

[0048] In addition, a plurality of spaced zonal isolation devices 117 and gravel packs 122 may be provided between tubular 120 and the sidewall of wellbore 114 at or along the interface of the wellbore 114 with the production zones 104a, 104b. In some embodiments, the operating environment 101 includes a workover and/or drilling rig positioned at the surface and extending over the wellbore 114. While FIG. 1 shows an example completion configuration in FIG. 1, it should be appreciated that other configurations and equipment may be present in place of or in addition to the illustrated configurations and equipment. For example, sections of the wellbore 114 can be completed as open hole completions or with gravel packs without completion assemblies.

[0049] In general, the wellbore 114 can be formed in the subterranean formation 102 using any suitable technique (e.g., drilling). The wellbore 114 can extend substantially vertically from the earth's surface over a vertical wellbore portion, deviate from vertical relative to the earth's surface over a deviated wellbore portion, and/or transition to a horizontal wellbore portion. In general, all or portions of a wellbore may be vertical, deviated at any suitable angle, horizontal, and/or curved. In addition, the wellbore 114 can be a new wellbore, an existing wellbore, a straight wellbore, an extended reach wellbore, a sidetracked wellbore, a multi-lateral wellbore, and other types of wellbores for drilling and completing one or more production zones. As illustrated, the wellbore 114 includes a substantially vertical producing section 150 which includes the production zones 104a, 104b. In this embodiment, producing section 150 is an open-hole completion (i.e., casing 112 does not extend through producing section 150). Although section 150 is illustrated as a vertical and open-hole portion of wellbore 114 in FIG. 1, embodiments disclosed herein can be employed in sections of wellbores having any orientation, and in open or cased sections of wellbores. The casing 112 extends into the wellbore 114 from the surface and can be secured within the wellbore 114 with cement 111. [0050] The tubular 120 may comprise any suitable downhole tubular or tubular string (e.g., drill string, casing, liner, jointed tubing, and/or coiled tubing, etc.), and may be inserted within wellbore 114 for any suitable operation(s) (e.g., drilling, completion, intervention, workover, treatment, production, etc.). In the embodiment shown in Figure 2, the tubular 120 is a completion assembly string. In addition, the tubular 120 may be disposed within in any or all portions of the wellbore 114 (e.g., vertical, deviated, horizontal, and/or curved section of wellbore 114).

[0051] In this embodiment, the tubular 120 extends from the surface to the production zones 104a, 104b and generally provides a conduit for fluids to travel from the formation 102 (particularly from production zones 104a, 104b) to the surface. A completion assembly including the tubular 120 can include a variety of other equipment or downhole tools to facilitate the production of the formation fluids from the production zones. For example, zonal isolation devices 117 can be used to isolate the production zones 104a, 104b within the wellbore 114. In this embodiment, each zonal isolation device 117 comprises a packer (e.g., production packer, gravel pack packer, frac-pac packer, etc.). The zonal isolation devices 117 can be positioned between the screen assemblies 118, for example, to isolate different gravel pack zones or intervals along the wellbore 114 from each other. In general, the space between each pair of adjacent zonal isolation devices 117 defines a production interval, and each production interval may correspond with one of the production zones 104a, 104b of subterranean formation 102. [0052] The screen assemblies 118 provide sand control capability. In particular, the sand control screen elements 118, or other filter media associated with wellbore tubular 120, can be designed to allow fluids to flow therethrough but restrict and/or prevent particulate matter of sufficient size from flowing therethrough. The screen assemblies 118 can be of any suitable type such as the type known as “wire-wrapped”, which are made up of a wire closely wrapped helically about a wellbore tubular, with a spacing between the wire wraps being chosen to allow fluid flow through the filter media while keeping particulates that are greater than a selected size from passing between the wire wraps. Other types of filter media can also be provided along the tubular 120 and can include any type of structures commonly used in gravel pack well completions, which permit the flow of fluids through the filter or screen while restricting and/or blocking the flow of particulates (e.g. other commercially-available screens, slotted or perforated liners or pipes; sintered-metal screens; sintered-sized, mesh screens; screened pipes; prepacked screens and/or liners; or combinations thereof). A protective outer shroud having a plurality of perforations therethrough may be positioned around the exterior of any such filter medium.

[0053] The gravel packs 122 can be formed in the annulus 119 between the screen elements 118 (or tubular 120) and the sidewall of the wellbore 114 in an open hole completion. In general, the gravel packs 122 comprise relatively coarse granular material placed in the annulus to form a rough screen against the ingress of sand into the wellbore while also supporting the wellbore wall. The gravel pack 122 is optional and may not be present in all completions.

[0054] In some embodiments, one or more of the completion assemblies can comprise flow control elements such as sliding sleeves, chokes, valves, or other types of flow control devices that can control the flow of a fluid from an individual production zone or a group of production zones. The force on the production face can then vary based on the type of completion within the wellbore and/or each production zone (e.g., in a sliding sleeve completion, open hole completion, gravel pack completion, etc.). In some embodiments, a sliding sleeve or other flow controlled production zone can experience a force on the production face that is relatively uniform within the production zone, and the force on the production face can be different between each production zone. For example, a first production zone can have a specific flow control setting that allows the production rate from the first zone to be different than the production rate from a second production zone. Thus, the choice of completion type (e.g., which can be specified in a completion plan) can affect on the need for or the ability to provide a different production rate within different production zones.

[0055] Referring still to FIG. 1, a monitoring system 110 can comprise an acoustic monitoring system and/or a temperature monitoring system. The monitoring system 1110 can be positioned in the wellbore 114. As described herein, the monitoring system 110 may be utilized to detect or monitor fluid inflow event(s) into the wellbore 114. The various monitoring systems (e.g., acoustic monitoring systems, temperature monitoring systems, etc.) may be referred to herein as an “inflow detection system,” and/or an “inflow monitoring system.”

[0056] The monitoring system 110 comprises an optical fiber 162 that is coupled to and extends along tubular 120. In cased completions, the optical fiber 162 can be installed between the casing and the wellbore wall within a cement layer and/or installed within the casing or production tubing. Referring briefly to FIGS. 2A and 2B, optical fiber 162 of the monitoring system 110 may be coupled to an exterior of tubular 120 (e.g., such as shown in FIG. 2B) or an interior of tubular (e.g., such as shown in FIG. 2A). When the optical fiber 162 is coupled to the exterior of the tubular 120, as depicted in the embodiment of FIG. 2B, the optical fiber 162 can be positioned within a control line, control channel, or recess in the tubular 120. In some embodiments an outer shroud contains the tubular 120 and protects the optical fiber 162 during installation. A control line or channel can be formed in the shroud and the optical fiber 162 can be placed in the control line or channel (not specifically shown in FIGS. 2 A and 2B).

[0057] Referring again to FIG. 1, generally speaking, during operation of a the monitoring system, an optical backscatter component of light injected into the optical fiber 162 may be used to detect various conditions incident on the optical fiber such as acoustic perturbations (e.g., dynamic strain), temperature, static strain, and the like along the length of the optical fiber 162. The light can be generated by a light generator or source 166 such as a laser, which can generate light pulses. The light used in the system is not limited to the visible spectrum, and light of any frequency can be used with the systems described herein. Accordingly, the optical fiber 162 acts as the sensor element with no additional transducers in the optical path, and measurements can be taken along the length of the entire optical fiber 162. The measurements can then be detected by an optical receiver such as sensor 164 and selectively filtered to obtain measurements from a given depth point or range, thereby providing for a distributed measurement that has selective data for a plurality of zones (e.g., production zones 104a, 104b) along the optical fiber 162 at any given time. For example, time of flight measurements of the backscattered light can be used to identify individual zones or measurement lengths of the fiber optic 162. In this manner, the optical fiber 162 effectively functions as a distributed array of sensors spread over the entire length of the optical fiber 162, which typically across production zones 104a, 104b within the wellbore 114.

[0058] The light backscattered up the optical fiber 162 as a result of the optical backscatter can travel back to the source, where the signal can be collected by a sensor 164 and processed (e.g., using a processor 168). In general, the time the light takes to return to the collection point is proportional to the distance traveled along the optical fiber 162, thereby allowing time of flight measurements of distance along the optical fiber. The resulting backscattered light arising along the length of the optical fiber 162 can be used to characterize the environment around the optical fiber 162. The use of a controlled light source 166 (e.g., having a controlled spectral width and frequency) may allow the backscatter to be collected and any parameters and/or disturbances along the length of the optical fiber 162 to be analyzed. In general, the various parameters and/or disturbances along the length of the optical fiber 162 can result in a change in the properties of the backscattered light.

[0059] An acquisition device 160 may be coupled to one end of the optical fiber 162 that comprises the sensor 164, light generator 166, a processor 168, and a memory 170. As discussed herein, the light source 166 can generate the light (e.g., one or more light pulses), and the sensor 164 can collect and analyze the backscattered light returning up the optical fiber 162. In some contexts, the acquisition device 160 (which comprises the light source 166 and the sensor 164 as noted above), can be referred to as an interrogator. The processor 168 may be in signal communication with the sensor 164 and may perform various analysis steps described in more detail herein. While shown as being within the acquisition device 160, the processor 168 can also be located outside of the acquisition device 160 including being located remotely from the acquisition device 160. The sensor 164 can be used to obtain data at various rates and may obtain data at a sufficient rate to detect the acoustic signals of interest with sufficient bandwidth. While described as a sensor 164 in a singular sense, the sensor 164 can comprise one or more photodetectors or other sensors that can allow one or more light beams and/or backscattered light to be detected for further processing. In an embodiment, depth resolution ranges in a range of from about 1 meter to about 10 meters, or less than or equal to about 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 meter can be achieved. Depending on the resolution needed, larger averages or ranges can be used for computing purposes. When a high depth resolution is not needed, a system may have a wider resolution (e.g., which may be less expensive) can also be used in some embodiments. Data acquired by the monitoring system 110 (e.g., via fiber 162, sensor 164, etc.) may be stored on memory 170.

[0060] The monitoring system 110 can be used for detecting a variety of parameters and/or disturbances in the wellbore including being used to detect temperatures along the wellbore, acoustic signals along the wellbore, static strain and/or pressure along the wellbore, or any combination thereof.

[0061] In some embodiments, the monitoring system 110 can be used to detect temperatures within the wellbore. The temperature monitoring system can include a distributed temperature sensing (DTS) system. A DTS system can rely on light injected into the optical fiber 162 along with the reflected signals to determine a temperature and/or strain based on optical time-domain reflectometry. In order to obtain DTS measurements, a pulsed laser from the light generator 166 can be coupled to the optical fiber 162 that serves as the sensing element. The injected light can be backscattered as the pulse propagates through the optical fiber 162 owing to density and composition as well as to molecular and bulk vibrations. A portion of the backscattered light can be guided back to the acquisition device 160 and split of by a directional coupler to a sensor 164. It is expected that the intensity of the backscattered light decays exponentially with time. As the speed of light within the optical fiber 162 is known, the distance that the light has passed through the optical fiber 162 can be derived using time of flight measurements.

[0062] In both distributed acoustic sensing (DAS) and DTS systems, the backscattered light includes different spectral components which contain peaks that are known as Rayleigh and Brillouin peaks and Raman bands. The Rayleigh peaks are independent of temperature and can be used to determine the DAS components of the backscattered light. The Raman spectral bands are caused by thermally influenced molecular vibrations. The Raman spectral bands can then be used to obtain information about distribution of temperature along the length of the optical fiber 162 disposed in the wellbore.

[0063] The Raman backscattered light has two components, Stokes and Anti-Stokes, one being only weakly dependent on temperature and the other being greatly influenced by temperature. The relative intensities between the Stokes and Anti-Stokes components and are a function of temperature at which the backscattering occurred. Therefore, temperature can be determined at any point along the length of the optical fiber 162 by comparing at each point the Stokes and Anti-stokes components of the light backscattered from the particular point. The Brillouin peaks may be used to monitor strain along the length of the optical fiber 162.

[0064] The DTS system can then be used to provide a temperature measurement along the length of the wellbore during the production of fluids, including fluid inflow events. The DTS system can represent a separate system from the DAS system or a single common system, which can comprise one or more acquisition devices in some embodiments. In some embodiments, a plurality of fibers 162 are present within the wellbore, and the DAS system can be coupled to a first optical fiber and the DTS system can be coupled to a second, different, optical fiber. Alternatively, a single optical fiber can be used with both systems, and a time division multiplexing or other process can be used to measure both DAS and DTS on the same optical fiber. [0065] In an embodiment, depth resolution for the DTS system can range from about 1 meter to about 10 meters, or less than or equal to about 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 meter can be achieved. Depending on the resolution needed, larger averages or ranges can be used for computing purposes. When a high depth resolution is not needed, a system may have a wider resolution (e.g., which may be less expensive) can also be used in some embodiments. Data acquired by the DTS system 110 (e.g., via fiber 162, sensor 164, etc.) may be stored on memory 170.

[0066] While the temperature monitoring system described herein can use a DTS system to acquire the temperature measurements for a location or depth range in the wellbore 114, in general, any suitable temperature monitoring system can be used. For example, various point sensors, thermocouples, resistive temperature sensors, or other sensors can be used to provide temperature measurements at a given location based on the temperature measurement processing described herein. Further, an optical fiber comprising a plurality of point sensors such as Bragg gratings can also be used. As described herein, a benefit of the use of the DTS system is that temperature measurements can be obtained across a plurality of locations and/or across a continuous length of the wellbore 114 rather than at discrete locations.

[0067] The monitoring system 110 can comprise an acoustic monitoring system to monitor acoustic signals within the wellbore. The acoustic monitoring system can comprise a DAS based system, though other types of acoustic monitoring systems, including other distributed monitoring systems, can also be used.

[0068] During operation of a DAS system an optical backscatter component of light injected into the optical fiber 162 (e.g., Rayleigh backscatter) may be used to detect acoustic perturbations (e.g., dynamic strain) along the length of the fiber 162. The light backscattered up the optical fiber 162 as a result of the optical backscatter can travel back to the source, where the signal can be collected by a sensor 164 and processed (e.g., using a processor 168) as described herein. In general, any acoustic or dynamic strain disturbances along the length of the optical fiber 162 can result in a change in the properties of the backscattered light, allowing for a distributed measurement of both the acoustic magnitude (e.g., amplitude), frequency and, in some cases, of the relative phase of the disturbance. Any suitable detection methods including the use of highly coherent light beams, compensating interferometers, local oscillators, and the like can be used to produce one or more signals that can be processed to determine the acoustic signals or strain impacting the optical fiber along its length.

[0069] While the system 101 described herein can be used with a DAS system (e.g., DAS system 110) to acquire an acoustic signal for a location or depth range in the wellbore 114, in general, any suitable acoustic signal acquisition system can be used in performing embodiments of method 10 (see e.g., FIG. 1). For example, various microphones, geophones, hydrophones, or other sensors can be used to provide an acoustic signal at a given location based on the acoustic signal processing described herein. Further, an optical fiber comprising a plurality of point sensors such as Bragg gratings can also be used. As described herein, a benefit of the use of the DAS system 110 is that an acoustic signal can be obtained across a plurality of locations and/or across a continuous length of the wellbore 114 rather than at discrete locations.

[0070] The monitoring system 110 can be used to generate temperature measurements and/or acoustic measurements along the length of the wellbore. The resulting measurements can be processed to obtain various temperature and/or acoustic based features that can then be used to identify inflow locations, identify inflowing fluid phases, and/or quantify the rate of fluid inflow. Each of the specific types of features obtained from the monitoring system are described in more detail below.

[0071] Fluid can be produced into the wellbore 114 and into the completion assembly string. During operations, the fluid flowing into the wellbore may comprise hydrocarbon fluids, such as, for instance hydrocarbon liquids (e.g., oil), gases (e.g., natural gas such as methane, ethane, etc.), and/or water, any of which can also comprise particulates such as sand. However, the fluid flowing into the tubular may also comprise other components, such as, for instance steam, carbon dioxide, and/or various multiphase mixed flows. The fluid flow can further be time varying such as including slugging, bubbling, or time altering flow rates of different phases. The amounts or flow rates of these components can vary over time based on conditions within the formation 102 and the wellbore 114. Likewise, the composition of the fluid flowing into the tubular 120 sections throughout the length of the entire production string (e.g., including the amount of sand contained within the fluid flow) can vary significantly from section to section at any given time.

[0072] As the fluid enters the wellbore 114, the fluid can create acoustic signals and temperature changes that can be detected by the monitoring system such as the DTS system and/or the DAS systems as described herein. With respect to the temperature variations, the temperature changes can result from various fluid effects within the wellbore such as cooling based on gas entering the wellbore, temperature changes resulting from liquids entering the wellbore, and various flow related temperature changes as a result of the fluids passing through the wellbore. For example, as fluids enter the wellbore, the fluids can experience a sudden pressure drop, which can result in a change in the temperature. The magnitude of the temperature change depends on the phase and composition of the inflowing fluid, the pressure drop, and the pressure and temperature conditions. The other major thermodynamic process that takes place as the fluid enters the well is thermal mixing which results from the heat exchange between the fluid body that flows into the wellbore and the fluid that is already flowing in the wellbore. As a result, inflow of fluids from the reservoir into the wellbore can cause a deviation in the flowing well temperature profile.

[0073] By obtaining the temperature in the wellbore, a number of temperature features can be obtained from the temperature measurements. The temperature features can provide an indication of one or more temperature trends at a given location in the wellbore during a measurement period. The resulting features can form a distribution of temperature results that can then be used with various models to identify one or more events within the wellbore at the location.

[0074] The temperature measurements can represent output values from the DTS system, which can be used with or without various types of pre-processing such as noise reduction, smoothing, and the like. When background temperature measurements are used, the background measurement can represent a temperature measurement at a location within the wellbore taken in the absence of the flow of a fluid. For example, a temperature profile along the wellbore can be taken when the well is initially formed and/or the wellbore can be shut in and allowed to equilibrate to some degree before measuring the temperatures at various points in the wellbore. The resulting background temperature measurements or temperature profile can then be used in determining the temperature features in some embodiments.

[0075] In general, the temperature features represent statistical variations of the temperature measurements through time and/or depth. For example, the temperature features can represent statistical measurements or functions of the temperature within the wellbore that can be used with various models to determine whether or not fluid inflow events have occurred. The temperature features can be determined using various functions and transformations, and in some embodiments can represent a distribution of results. In some embodiments, the temperature features can represent a normal or Gaussian distribution. In some embodiments, the temperature measurements can represent measurement through time and depth, such as variations taken first with respect to time and then with respect to depth or first with respect to depth and then with respect to time. The resulting distributions can then be used with models such as multivariate models to determine the presence of the fluid inflow events.

[0076] In some embodiments, the temperature features can include various features including, but not limited to, a depth derivative of temperature with respect to depth, a temperature excursion measurement, a baseline temperature excursion, a peak-to-peak value, a Fast Fourier transform (FFT), a Laplace transform, a wavelet transform, a derivative of temperature with respect to depth, a heat loss parameter, an autocorrelation, and combinations thereof.

[0077] In some embodiments, the temperature features can comprise a depth derivative of temperature with respect to depth. This feature can be determined by taking the temperature measurements along the wellbore and smoothing the measurements. Smoothing can comprise a variety of steps including filtering the results, de-noising the results, or the like. In some embodiments, the temperature measurements can be median filtered within a given window to smooth the measurements. Once smoothed, the change in the temperature with depth can be determined. In some embodiments, this can include taking a derivative of the temperature measurements with respect to depth along the longitudinal axis of the wellbore 114. The depth derivative of temperature values can then be processed, and the measurement with a zero value (e.g., representing a point of no change in temperature with depth) that have preceding and proceeding values that are non-zero and have opposite signs in depth (e.g., zero below which the value is negative and above positive or vice versa) can have the values assign to the nearest value. This can then result in a set of measurements representing the depth derivative of temperature with respect to depth.

[0078] In some embodiments, the temperature features can comprise a temperature excursion measurement. The temperature excursion measurement can comprise a difference between a temperature reading at a first depth and a smoothed temperature reading over a depth range, where the first depth is within the depth range. In some embodiments, the temperature excursion measurement can represent a difference between de-trended temperature measurements over an interval and the actual temperature measurements within the interval. For example, a depth range can be selected within the wellbore 114. The temperature readings within a time window can be obtained within the depth range and de-trended or smoothed. In some embodiments, the de-trending or smoothing can include any of those processes described above, such as using median filtering of the data within a window within the depth range. For median filtering, the larger the window of values used, the greater the smoothing effect can be on the measurements. For the temperature excursion measurement, a range of windows from about 10 to about 100 values, or between about 20-60 values (e.g., measurements of temperature within the depth range) can be used to median filter the temperature measurements. A difference can then be taken between the temperature measurement at a location and the de-trended (e.g., median filtered) temperature values. The temperature measurements at a location can be within the depth range and the values being used for the median filtering. This temperature feature then represents a temperature excursion at a location along the wellbore 114 from a smoothed temperature measurement over a larger range of depths around the location in the wellbore 114. [0079] In some embodiments, the temperature features can comprise a baseline temperature excursion. The baseline temperature excursion represents a difference between a de-trended baseline temperature profile and the current temperature at a given depth. In some embodiments, the baseline temperature excursion can rely on a baseline temperature profile that can contain or define the baseline temperatures along the length of the wellbore 114. As described herein, the baseline temperatures represent the temperature as measured when the wellbore 114 is shut in. This can represent a temperature profile of the formation in the absence of fluid flow. While the wellbore 114 may affect the baseline temperature readings, the baseline temperature profile can approximate a formation temperature profile. The baseline temperature profile can be determined when the wellbore 114 is shut in and/or during formation of the wellbore 114, and the resulting baseline temperature profile can be used over time. If the condition of the wellbore 114 changes over time, the wellbore 114 can be shut in and a new baseline temperature profile can be measured or determined. It is not expected that the baseline temperature profile is re-determined at specific intervals, and rather it would be determined at discrete times in the life of the wellbore 114. In some embodiments, the baseline temperature profile can be re-determined and used to determine one or more temperature features such as the baseline temperature excursion. [0080] Once the baseline temperature profile is obtained, the baseline temperature measurements at a location in the wellbore 114 can be subtracted from the temperature measurement detected by the temperature monitoring system 110 at that location to provide baseline subtracted values. The results can then be obtained and smoothed or de-trended. For example, the resulting baseline subtracted values can be median filtered within a window to smooth the data. In some embodiments, a window between 10 and 500 temperature values, between 50 and 400 temperature values, or between 100 and 300 temperature values can be used to median filter the resulting baseline subtracted values. The resulting smoothed baseline subtracted values can then be processed to determine a change in the smoothed baseline subtracted values with depth. In some embodiments, this can include taking a derivative of the smoothed baseline subtracted values with respect to depth along the longitudinal axis of the wellbore. The resulting values can represent the baseline temperature excursion feature.

[0081] In some embodiments, the temperature features can comprise a peak-to-peak temperature value. This feature can represent the difference between the maximum and minimum values (e.g., the range, etc.) within the temperature profile along the wellbore 114. In some embodiments, the peak-to-peak temperature values can be determined by detecting the maximum temperature readings (e.g., the peaks) and the minimum temperature values (e.g., the dips) within the temperature profile along the wellbore 114. The difference can then be determined within the temperature profile to determine peak-to-peak values along the length of the wellbore 114. The resulting peak-to-peak values can then be processed to determine a change in the peak-to- peak values with respect to depth. In some embodiments, this can include taking a derivative of the peak-to-peak values with respect to depth along the longitudinal axis of the wellbore 114. The resulting values can represent the peak-to-peak temperature values.

[0082] Other temperature features can also be determined from the temperature measurements. In some embodiments, various statistical measurements can be obtained from the temperature measurements along the wellbore 114 to determine one or more temperature features. For example, a cross-correlation of the temperature measurements with respect to time can be used to determine a cross-correlated temperature feature. The temperature measurements can be smoothed as described herein prior to determining the cross-correlation with respect to time. As another example, an autocorrelation measurement of the temperature measurements can be obtained with respect to depth. Autocorrelation is defined as the cross-correlation of a signal with itself. An autocorrelation temperature feature can thus measure the similarity of the signal with itself as a function of the displacement. An autocorrelation temperature feature can be used, in applications, as a means of anomaly detection for event (e.g., fluid inflow) detection. The temperature measurements can be smoothed and/or the resulting autocorrelation measurements can be smoothed as described herein to determine the autocorrelation temperature features.

[0083] In some embodiments, the temperature features can comprise a Fast Fourier transform (FFT) of the distributed temperature sensing (e.g., DTS) signal. This algorithm can transform the distributed temperature sensing signal from the time domain into the frequency domain, thus allowing detection of the deviation in DTS along length (e.g., depth). This temperature feature can be utilized, for example, for anomaly detection for event (e.g., fluid inflow) detection purposes. [0084] In some embodiments, the temperature features can comprise the Laplace transform of DTS. This algorithm can transform the DTS signal from the time domain into Laplace domain allows us to detect the deviation in the DTS along length (e.g., depth of wellbore 114). This temperature feature can be utilized, for example, for anomaly detection for event (e.g., fluid inflow) detection. This feature can be utilized, for example, in addition to (e.g., in combination with) the FFT temperature feature.

[0085] In some embodiments, the temperature features can comprise a wavelet transform of the distributed temperature sensing (e.g., DTS) signal and/or of the derivative of DTS with respect to depth, dT/dz. The wavelet transform can be used to represent the abrupt changes in the signal data. This feature can be utilized, for example, in inflow detection. A wavelet is described as an oscillation that has zero mean, which can thus make the derivative of DTS in depth more suitable for this application. In embodiments and without limitation, the wavelet can comprise a Morse wavelet, an Analytical wavelet, a Bump wavelet, or a combination thereof.

[0086] In some embodiments, the temperature features can comprise a derivative of DTS with respect to depth, or dT/dz. The relationship between the derivative of flowing temperature T/with respect to depth (L) (e.g., dT/dL) has been described by several models. For example, and without limitation, the model described by Sagar (Sagar, R., Doty, D. R, & Schmidt, Z. (1991, November 1). Predicting Temperature Profiles in a Flowing Well. Society of Petroleum Engineers, doi: 10.2118/19702-PA) which accounts for radial heat loss due to conduction and describes a relationship (Equation (1) below) between temperature change in depth and mass rate. The mass rate w _t is conversely proportional to the relaxation parameter A and, as the relaxation parameter A increases, the change in temperature in depth increases. Hence this temperature feature can be designed to be used, for example, in events comprising inflow quantification.

(1)

The formula for the relaxation parameter, A, is provided in Equation (2):

_c * average correction factor for one length interval g = acceleration of gravity, 32.2 ft/sec ² g _c = conversion factor, 32.2 ft-lbm/secMbf g _G = geothermal gradient, °F/ft A = specific enthalpy, Btu/lbm J — mechanical equivalent of heal, 778 ft-lbf/Btu k _an = thermal conductivity of material in annulus, Bto/D-ft-'F k _anw = thermal conductivity of gas in annulus, Btu/D-ft-°F k _anw = thermal conductivity of water in annulus,

Btu/D-ft-T k _cem = thermal conductivity of cement, Btu/D-ft-°F k _e = thermal conductivity of earth, Btu/D-ft-°F L = length of well from perforations, ft

L _in = length from perforation to Met, ft p = pressure, psi

P _wh =* wellhead pressure, psig q _gf = formation gas flow rate, scf/D q _ginj = injection gas flow rate, scf/D q _w = oil flow rate, STB/D q _w = water flow rate, STB/D Q = heat transfer between fluid and surrounding area, Btu/lbm r _ci = inside casing radius, in. r _co - outside casing radius, in. r _ti = inside tubing radius, in. r _t0 = outside tubing radius, in.

^F _wb ~ wellbore radius, in.

R _gL = gas/liquid ratio, scf/STB T = temperature, °F

T _bh = bottomhole temperature, °F T _c = casing temperature, °F T _e = surrounding earth temperature, °F T _ein = earth temperature at inlet, °F Tf = flowing fluid temperature, °F T _fin „ = flowing fluid temperature at inlet, °F T _h = cement/earth iaterface temperature, °F U = overall heat transfer coefficient, Bta/D*ft ² -°F v = fluid velocity, ft/sec V = volume w _I *= total mass flow rate, Ibm/sec Z * height from botom of hole, ft Z _in = height from botom of hole at Met, ft α = thermal diffusivity of earth, 0.04 ft ² /hr

YAPI ⁼ gravity, °API y _g - gas specific gravity (ajr«l) y _o = oil specific gravity y _w - water specific gravity θ » angle of inclination, degrees μ = Joule-Thomson coefficient [0087] In some embodiments, the temperature features can comprise a heat loss parameter. As described hereinabove, Sagar’s model describes the relationship between various input parameters, including the mass rate w _t and temperature change in depth dT _f /d _L . These parameters can be utilized as temperature features in a machine learning model which uses features from known cases (production logging results) as learning data sets, when available. These features can include geothermal temperature, deviation, dimensions of the tubulars 120 that are in the well (casing 112, tubing 120, gravel pack 122 components, etc.), as well as the wellbore 114, well head pressure, individual separator rates, downhole pressure, gas/liquid ratio, and/or a combination thereof. Such heat loss parameters can, for example, be utilized as inputs in a machine learning model for events comprising inflow quantification of the mass flow rate

Wt.

[0088] In some embodiments, the temperature features can comprise a time-depth derivative and/or a depth-time derivative. A temperature feature comprising a time-depth derivative can comprise a change in a temperature measurement at one or more locations across the wellbore taken first with respect to time, and a change in the resulting values with respect to depth can then be determined. Similarly, a temperature feature comprising a depth-time derivative can comprise a change in a temperature measurement at one or more locations across the wellbore taken first with respect to depth, and a change in the resulting values with respect to time can then be determined.

[0089] In some embodiments, the temperature features can be based on dynamic temperature measurements rather than steady state or flowing temperature measurements. In order to obtain dynamic temperature measurements, a change in the operation of the system (e.g., wellbore) can be introduced, and the temperature monitored using the temperature monitoring system. For example in a wellbore environment, the change in conditions can be introduced by shutting in the wellbore, opening one or more sections of the wellbore to flow, introducing a fluid to the wellbore (e.g., injecting a fluid), and the like. When the wellbore is shut in from a flowing state, the temperature profile along the wellbore may be expected to change from the flowing profile to the baseline profile over time. Similarly, when a wellbore that is shut in is opened for flow, the temperature profile may change from a baseline profile to a flowing profile. Based on the change in the condition of the wellbore, the temperature measurements can change dynamically over time. In some embodiments, this approach can allow for a contrast in thermal conductivity to be determined between a location or interval having radial flow (e.g., into or out of the wellbore) to a location or interval without radial flow. One or more temperature features can then be determined using the dynamic temperature measurements. Once the temperature features are determined from the temperature measurements obtained from the temperature monitoring system, one or more of the temperature features can be used to identify events along the length being monitored (e.g., within the wellbore), as described in more detail herein.

[0090] As described with respect to the temperature measurements, the inflow of fluids into the wellbore 114 an also create acoustic sounds that can be detected using the acoustic monitoring system such as a DAS system. Accordingly, the flow of the various fluids into the wellbore 114 and/or through the wellbore 114 can create vibrations or acoustic sounds that can be detected using acoustic monitoring system. Each type of inflow event such as the different fluid flows and fluid flow locations can produce an acoustic signature with unique frequency domain features.

[0091] As used herein, various frequency domain features can be obtained from the acoustic signal, and in some contexts, the frequency domain features can also be referred to herein as spectral features or spectral descriptors. The frequency domain features are features obtained from a frequency domain analysis of the acoustic signals obtained within the wellbore. The frequency domain features can be derived from the full spectrum of the frequency domain of the acoustic signal such that each of the frequency domain features can be representative of the frequency spectrum of the acoustic signal. Further, a plurality of different frequency domain features can be obtained from the same acoustic signal (e.g., the same acoustic signal at a location or depth within the wellbore), where each of the different frequency domain features is representative of frequencies across the same frequency spectrum of the acoustic signal as the other frequency domain features. For example, the frequency domain features (e.g., each frequency domain feature) can be a statistical shape measurement or spectral shape function of the spectral power measurement across the same frequency bandwidth of the acoustic signal. Further, as used herein, frequency domain features can also refer to features or feature sets derived from one or more frequency domain features, including combinations of features, mathematical modifications to the one or more frequency domain features, rates of change of the one or more frequency domain features, and the like. [0092] The frequency domain features can be determined by processing the acoustic signals from within the wellbore at one or more locations along the wellbore. As the acoustics signals at a given location along the wellbore contain a combination of acoustic signals, the determination of the frequency domain features can be used to separate and identify individual fluid inflow events. As an example, FIG. 3 illustrates sand 202 flowing from the formation 102 into the wellbore 114 and then into the tubular 120. As the sand 202 flows into the tubular 120, it can collide against the inner surface 204 of the tubular 120, and with the fiber 162 (e.g., in cases where the fiber 162 is placed within the tubular 120), in a random fashion. Without being limited by this or any particular theory, the intensity of the collisions depends on the effective mass and the rate of change in the velocity of the impinging sand particles 202, which can depend on a number of factors including, without limitation, the direction of travel of the sand 202 in the wellbore 114 and/or tubular 120. The resulting random impacts can produce a random, broadband acoustic signal that can be captured on the optical fiber 162 coupled (e.g., strapped) to the tubular 120. The random excitation response tends to have a broadband acoustic signal with excitation frequencies extending up to the high frequency bands, for example, up to and beyond about 5 kHz depending on the size of the sand particles 202. In general, larger particle sizes may produce higher frequencies. The intensity of the acoustic signal may be proportional to the concentration of sand 202 generating the excitations such that an increased broad band power intensity can be expected at increasing sand 202 concentrations. In some embodiments, the resulting broadband acoustic signals that can be identified can include frequencies in the range of about 5 Hz to about 10 kHz, frequencies in the range of about 5 Hz to about 5 kHz or about 50 Hz to about 5 kHz, or frequencies in the range of about 500 Hz to about 5 kHz. Any frequency ranges between the lower frequencies values (e.g., 5 Hz, 50 Hz, 500 Hz, etc.) and the upper frequency values (e.g., 10 kHz, 7 kHz, 5 kHz, etc.) can be used to define the frequency range for a broadband acoustic signal.

[0093] In addition to the sand entering the wellbore, fluid inflow at the location can also create acoustic signals along with fluid flowing axially or longitudinally through the wellbore. Background noise can also be present. Other acoustic signal sources can include fluid flow with or without sand 202 through the formation 102, fluid flow with or without sand 202 through a gravel pack 122, fluid flow with or without sand 202 within or through the tubular 120 and/or sand screen 118, fluid flow with sand 202 within or through the tubular 120 and/or sand screen 118, fluid flow without sand 202 into the tubular 120 and/or sand screen 118, gas / liquid inflow, hydraulic fracturing, fluid leaks past restrictions (e.g., gas leaks, liquid leaks, etc.) mechanical instrumentation and geophysical acoustic noises and potential point reflection noise within the fiber caused by cracks in the fiber optic cable / conduit under investigation. The combined acoustic signal can then be detected by the acoustic monitoring system. In order to detect one or more of these events, the acoustic signal can be processed to determine one or more frequency domain features of the acoustic signal at a depth in the wellbore.

[0094] In order to determine the frequency domain features, an acoustic signal can be obtained using the acoustic monitoring system during operation of the wellbore. The resulting acoustic signal can be optionally pre-processed using a number of steps. Depending on the type of DAS system employed, the optical data may or may not be phase coherent and may be pre-processed to improve the signal quality (e.g., denoised for opto-electronic noise normalization / de-trending single point-reflection noise removal through the use of median filtering techniques or even through the use of spatial moving average computations with averaging windows set to the spatial resolution of the acquisition unit, etc.). The raw optical data from the acoustic sensor can be received, processed, and generated by the sensor to produce the acoustic signal.

[0095] In some embodiments, a processor or collection of processors (e.g., processor 168 in FIG. 1) may be utilized to perform the optional pre-processing steps described herein. In an embodiment, the noise detrended “acoustic variant” data can be subjected to an optional spatial filtering step following the other pre-processing steps, if present. A spatial sample point filter can be applied that uses a filter to obtain a portion of the acoustic signal corresponding to a desired depth or depth range in the wellbore. Since the time the light pulse sent into the optical fiber returns as backscattered light can correspond to the travel distance, and therefore depth in the wellbore, the acoustic data can be processed to obtain a sample indicative of the desired depth or depth range. This may allow a specific location within the wellbore to be isolated for further analysis. The pre-processing may also include removal of spurious back reflection type noises at specific depths through spatial median filtering or spatial averaging techniques. This is an optional step and helps focus primarily on an interval of interest in the wellbore. For example, the spatial filtering step can be used to focus on a producing interval where there is high likelihood of sand ingress, for example. The resulting data set produced through the conversion of the raw optical data can be referred to as the acoustic sample data. [0096] The acoustic data, including the optionally pre-processed and/or filtered data, can be transformed from the time domain into the frequency domain using a transform. For example, a Fourier transform such as a Discrete Fourier transformations (DFT), a short time Fourier transform (STFT), or the like can be used to transform the acoustic data measured at each depth section along the fiber or a section thereof into a frequency domain representation of the signal. The resulting frequency domain representation of the data can then be used to provide the data from which the plurality of frequency domain features can be determined. Spectral feature extraction using the frequency domain features through time and space can be used to determine one or more frequency domain features.

[0097] The use of frequency domain features to identify inflow events and locations, inflow phase identification, and/or inflow quantities of one or more fluid phases can provide a number of advantages. First, the use of frequency domain features results in significant data reduction relative to the raw DAS data stream. Thus, a number of frequency domain features can be calculated and used to allow for event identification while the remaining data can be discarded or otherwise stored, and the remaining analysis can performed using the frequency domain features. Even when the raw DAS data is stored, the remaining processing power is significantly reduced through the use of the frequency domain features rather than the raw acoustic data itself. Further, the use of the frequency domain features can, with the appropriate selection of one or more of the frequency domain features, provide a concise, quantitative measure of the spectral character or acoustic signature of specific sounds pertinent to downhole fluid surveillance and other applications.

[0098] While a number of frequency domain features can be determined for the acoustic sample data, not every frequency domain feature may be used to identify inflow events and locations, inflow phase identification, and/or inflow quantities of one or more fluid phases. The frequency domain features represent specific properties or characteristics of the acoustic signals.

[0099] In some embodiments, combinations of frequency domain features can be used as the frequency domain features themselves, and the resulting combinations are considered to be part of the frequency domain features as described herein. In some embodiments, a plurality of frequency domain features can be transformed to create values that can be used to define various event signatures. This can include mathematical transformations including ratios, equations, rates of change, transforms (e.g., wavelets, Fourier transforms, other wave form transforms, etc.), other features derived from the feature set, and/or the like as well as the use of various equations that can define lines, surfaces, volumes, or multi-variable envelopes. The transformation can use other measurements or values outside of the frequency domain features as part of the transformation. For example, time domain features, other acoustic features, and non-acoustic measurements can also be used. In this type of analysis, time can also be considered as a factor in addition to the frequency domain features themselves. As an example, a plurality of frequency domain features can be used to define a surface (e.g., a plane, a three-dimensional surface, etc.) in a multivariable space, and the measured frequency domain features can then be used to determine if the specific readings from an acoustic sample fall above or below the surface. The positioning of the readings relative to the surface can then be used to determine if the event is present or not at that location in that detected acoustic sample.

[00100] The frequency domain features can include any frequency domain features derived from the frequency domain representations of the acoustic data. Such frequency domain features can include, but are not limited to, the spectral centroid, the spectral spread, the spectral roll-off, the spectral skewness, the root mean square (RMS) band energy (or the normalized subband energies / band energy ratios), a loudness or total RMS energy, a spectral flatness, a spectral slope, a spectral kurtosis, a spectral flux, a spectral autocorrelation function, or a normalized variant thereof.

[00101] The spectral centroid denotes the “brightness” of the sound captured by the optical fiber (e.g., optical fiber 162 shown in FIG. 1) and indicates the center of gravity of the frequency spectrum in the acoustic sample. The spectral centroid can be calculated as the weighted mean of the frequencies present in the signal, where the magnitudes of the frequencies present can be used as their weights in some embodiments.

[00102] The spectral spread is a measure of the shape of the spectrum and helps measure how the spectrum is distributed around the spectral centroid. In order to compute the spectral spread, Si, one has to take the deviation of the spectrum from the computed centroid as per the following equation (all other terms defined above):

(Eq. 2).

[00103] The spectral roll-off is a measure of the bandwidth of the audio signal. The

Spectral roll-off of the i ^th frame, is defined as the frequency bin ‘y’ below which the accumulated magnitudes of the short-time Fourier transform reach a certain percentage value (usually between 85% - 95%) of the overall sum of magnitudes of the spectrum.

[00104] where c=85 or 95. The result of the spectral roll-off calculation is a bin index and enables distinguishing acoustic events based on dominant energy contributions in the frequency domain (e.g., between gas influx and liquid flow, etc.).

[00105] The spectral skewness measures the symmetry of the distribution of the spectral magnitude values around their arithmetic mean.

[00106] The RMS band energy provides a measure of the signal energy within defined frequency bins that may then be used for signal amplitude population. The selection of the bandwidths can be based on the characteristics of the captured acoustic signal. In some embodiments, a sub-band energy ratio representing the ratio of the upper frequency in the selected band to the lower frequency in the selected band can range between about 1.5:1 to about 3:1. In some embodiments, the sub-band energy ratio can range from about 2.5:1 to about 1.8:1, or alternatively be about 2:1 The total RMS energy of the acoustic waveform calculated in the time domain can indicate the loudness of the acoustic signal. In some embodiments, the total RMS energy can also be extracted from the temporal domain after filtering the signal for noise. [00107] The spectral flatness is a measure of the noisiness / tonality of an acoustic spectrum. It can be computed by the ratio of the geometric mean to the arithmetic mean of the energy spectrum value and may be used as an alternative approach to detect broad-banded signals. For tonal signals, the spectral flatness can be close to 0 and for broader band signals it can be closer to 1.

[00108] The spectral slope provides a basic approximation of the spectrum shape by a linearly regressed line. The spectral slope represents the decrease of the spectral amplitudes from low to high frequencies (e.g., a spectral tilt). The slope, the y-intersection, and the max and media regression error may be used as features.

[00109] The spectral kurtosis provides a measure of the flatness of a distribution around the mean value.

[00110] The spectral flux is a measure of instantaneous changes in the magnitude of a spectrum. It provides a measure of the frame-to-frame squared difference of the spectral magnitude vector summed across all frequencies or a selected portion of the spectrum. Signals with slowly varying (or nearly constant) spectral properties (e.g., noise) have a low spectral flux, while signals with abrupt spectral changes have a high spectral flux. The spectral flux can allow for a direct measure of the local spectral rate of change and consequently serves as an event detection scheme that could be used to pick up the onset of acoustic events that may then be further analyzed using the feature set above to identify and uniquely classify the acoustic signal. [00111] The spectral autocorrelation function provides a method in which the signal is shifted, and for each signal shift (lag) the correlation or the resemblance of the shifted signal with the original one is computed. This enables computation of the fundamental period by choosing the lag, for which the signal best resembles itself, for example, where the autocorrelation is maximized. This can be useful in exploratory signature analysis / even for anomaly detection for well integrity monitoring across specific depths where well barrier elements to be monitored are positioned.

[00112] Any of these frequency domain features, or any combination of these frequency domain features (including transformations of any of the frequency domain features and combinations thereof), can be used to detect inflow events and locations, inflow phase identification, and/or inflow quantities of one or more phases within the wellbore. In an embodiment, a selected set of characteristics can be used to identify the presence or absence for each event, and/or all of the frequency domain features that are calculated can be used as a group in characterizing the presence or absence of an event. The specific values for the frequency domain features that are calculated can vary depending on the specific attributes of the acoustic signal acquisition system, such that the absolute value of each frequency domain feature can change between systems. In some embodiments, the frequency domain features can be calculated for each event based on the system being used to capture the acoustic signal and/or the differences between systems can be taken into account in determining the frequency domain feature values for each fluid inflow event between or among the systems used to determine the values and the systems used to capture the acoustic signal being evaluated.

[00113] One or a plurality of frequency domain features can be used to identify inflow events and locations, inflow phase identification, and/or inflow quantities of one or more phases. In some embodiments, one or a plurality of frequency domain features can also be used to detect inflow events and locations, inflow phase identification, and/or inflow quantities of one or more phases. In an embodiment, one, or at least two, three, four, five, six, seven, eight, etc. different frequency domain features can be used to detect inflow events and locations, inflow phase identification, and/or inflow quantities of one or more phases. The frequency domain features can be combined or transformed in order to define the event signatures for one or more events, such as, for instance, a fluid inflow event location or flowrate. While exemplary numerical ranges are provided herein, the actual numerical results may vary depending on the data acquisition system and/or the values can be normalized or otherwise processed to provide different results.

[00114] The systems described herein can be used with the temperature features and/or frequency domain features to determine the presence and/or extent of an event at one or more locations. Figure 4 illustrates a method 400 for detecting an event at one or more locations. The method can start at step 402 with a determination of temperature features and acoustic features originating from the event (e.g., within the wellbore). For example, for an event comprising fluid inflow, one or more fluids that can include gas, a liquid aqueous phase, a liquid hydrocarbon phase, and potentially other fluids as well as various combinations thereof can enter the wellbore at one or more locations along the wellbore. The temperature features can then be used to identify these inflow locations. Similarly, the temperature features can be utilized to determine the presence or absence of an event at one or more locations (e.g., along a length, such as, without limitation, along a pipeline, a security perimeter, an apparatus, a dam, etc.). As noted at step 404 and detailed further hereinbelow, the temperature features can be utilized with a first or event identification/detection model to provide an output of the first model and the be utilized with a second or event extent model to provide an output of the second model. As noted at step 406 and detailed further hereinbelow, the presence and/or extent of the event at the one or more locations can be determined using the output from the first or event identifi cation/ detection model, the output from the second or event extent model, or a combined output obtained using the output from the first or event identification model and the output from the second or event extent model. Although described as an “event extent” model, the second model can also be utilized as a (second) event identification/detection model to determine the presence or absence of the event at one or more locations along the length being monitored.

[00115] The temperature features can be determined using the temperature monitoring system to obtain temperature measurements along the length being monitored (e.g., the length of the wellbore). In some embodiments, a DTS system can be used to receive distributed temperature measurement signals from a sensor disposed along the length (e.g., the length of the wellbore), such as an optical fiber. The resulting signals from the temperature monitoring system can be used to determine one or more temperature features as described herein. In some embodiments, a baseline or background temperature profile can be used to determine the temperature features, and the baseline temperature profile can be obtained prior to obtaining the temperature measurements.

[00116] In some embodiments, a plurality of temperature features can be determined from the temperature measurements, and the plurality of temperature features can comprise at least two of: a depth derivative of temperature with respect to depth, a temperature excursion measurement, a baseline temperature excursion, a peak-to-peak value, a fast Fourier transform, a Laplace transform, a wavelet transform, a derivative of temperature with respect to length (e.g., depth), a heat loss parameter, an autocorrelation, as detailed hereinabove, and/or the like. Other temperature features can also be used in some embodiments. The temperature excursion measurement can comprise a difference between a temperature reading at a first depth, and a smoothed temperature reading over a depth range, where the first depth is within the depth range. The baseline temperature excursion can comprise a derivative of a baseline excursion with depth, where the baseline excursion can comprise a difference between a baseline temperature profile and a smoothed temperature profile. The peak-to-peak value can comprise a derivative of a peak-to- peak difference with depth, where the peak-to-peak difference comprises a difference between a peak high temperature reading and a peak low temperature reading with an interval. The fast Fourier Transform can comprise an FFT of the distributed temperature sensing signal. The Laplace transform can comprise a Laplace transform of the distributed temperature sensing signal. The wavelet transform can comprise a wavelet transform of the distributed temperature sensing signal or of the derivative of the distributed temperature sensing signal with respect to length (e.g., depth). The derivative of the distributed temperature sensing signal with respect to length (e.g., depth) can comprise the derivative of the flowing temperature with respect to depth. The heat loss parameter can comprise one or more of the geothermal temperature, a deviation, dimensions of the tubulars that are in the well, well head pressure, individual separator rates, downhole pressure, gas/liquid ratio, or the like. The autocorrelation can comprise a cross-correlation of the distributed temperature sensing signal with itself. [00117] Once the temperature features are obtained, the temperature features can be used with a first or event (e.g., fluid inflow) identification model to identify the presence of the event at one or more locations. In some embodiments, the first or event identification model can accept a plurality of temperature features as inputs. In general, the temperature features are representative of feature at a particular location (e.g., a depth resolution portion of the optical fiber along the length being monitored, e.g., along a length of the wellbore) along the length. The first or event identification model can comprise one or more models configured to accept the temperature features as input(s) and provide an indication of whether or not there is an event at the particular location along the length. The output of the first or event identification model can be in the form of a binary yes/no result, and/or a likelihood of an event (e.g., a percentage likelihood, etc.). Other outputs providing an indication of an event are also possible. In some embodiments, the first or event identification model can comprise a multivariate model, a machine learning model using supervised or unsupervised learning algorithms, or the like.

[00118] In some embodiments, the first or event identification model can comprise a multivariate model. A multivariate model allows for the use of a plurality of variables in a model to determine or predict an outcome. A multivariate model can be developed using known data on events along with temperature features for those events to develop a relationship between the temperature features and the presence of the event at the locations within the available data. One or more multivariate models can be developed using data, where each multivariate model uses a plurality of temperature features as inputs to determine the likelihood of an event occurring at the particular location along the length.

[00119] In some embodiments, the first or event identification model can comprise one or more multivariate models. The multivariate model can use multivariate equations, and the multivariate model equations can use the temperature features or combinations or transformations thereof to determine when an event is present. The multivariate model can define a threshold, decision point, and/or decision boundary having any type of shapes such as a point, line, surface, or envelope between the presence and absence of the specific event. In some embodiments, the multivariate model can be in the form of a polynomial, though other representations are also possible. The model can include coefficients that can be calibrated based on known event data. While there can be variability or uncertainty in the resulting values used in the model, the uncertainty can be taken into account in the output of the model. Once calibrated or tuned, the model can then be used with the corresponding temperature features to provide an output that is indicative of the occurrence of an event.

[00120] The multivariate model is not limited to two dimensions (e.g., two temperature features or two variables representing transformed values from two or more temperature features), and rather can have any number of variables or dimensions in defining the threshold between the presence or absence of the event. When used, the detected values can be used in the multivariate model, and the calculated value can be compared to the model values. The presence of the event can be indicated when the calculated value is on one side of the threshold and the absence of the event can be indicated when the calculated value is on the other side of the threshold. In some embodiments, the output of the multivariate model can be based on a value from the model relative to a normal distribution for the model. Thus, the model can represent a distribution or envelope and the resulting temperature features can be used to define where the output of the model lies along the distribution at the location along the length being monitored (e.g., along the length of the wellbore). Thus, each multivariate model can, in some embodiments, represent a specific determination between the presence of absence of an event at a specific location along the length. Different multivariate models, and therefore thresholds, can be used for different events, and each multivariate model can rely on different temperature features or combinations or transformations of temperature features. Since the multivariate models define thresholds for the determination and/or identification of events, the multivariate models and first or event identification model using such multivariate models can be considered to be temperature based event signatures for each type of event.

[00121] In some embodiments, the first or event identification model can comprise a plurality of models. Each of the models can use one or more of the temperature features as inputs. The models can comprise any suitable model that can relate one or more temperature features to an occurrence of an event (e.g., a likelihood of the event, a binary yes/no output, etc.). The output of each model can then be combined to form a composite or combined output. The combined output can then be used to determine if an event has occurred, for example, by comparing the combined output with a threshold value (e.g., a fluid inflow threshold). The determination of the occurrence of an event can then be based on the comparison of the combined output with the threshold value. [00122] As an example, the first or event identification model can comprise a plurality of multivariate models, each using a plurality of temperature features as described above. The output of the multivariate models can include a percentage likelihood of the occurrence of an event at the particular location at which each model is applied. The resulting output values can then be used in a function such as a simple multiplication, a weighted average, a voting scheme, or the like to provide a combined output. The resulting output can then be compared to a threshold to determine if an event has occurred. For example, a combined output indicating that there is greater than a fifty percent likelihood of an event at the particular location can be taken as an indication that the event has occurred at the location of interest.

[00123] In some embodiments, the first or event identification model can also comprise other types of models. In some embodiments, a machine learning approach comprises a logistic regression model. In some such embodiments, one or more temperature features can be used to determine if an event is present at one or more locations of interest. The machine learning approach can rely on a training data set that can be obtained from a test set-up or obtained based on actual temperature data from known events. The one or more temperature features in the training data set can then be used to train the first or event identification model using machine learning, including any supervised or unsupervised learning approach. For example, the first or event identification model can be a neural network, a Bayesian network, a decision tree, a logistical regression model, a normalized logistical regression model, or the like. In some embodiments, the first or event identification model can comprise a model developed using unsupervised learning techniques such a k-means clustering and the like.

[00124] In some embodiments, the model(s) can be developed and trained using a logistic regression model. As an example for training of a model used to determine the presence or absence of an event, the training of the model can begin with providing the one or more temperature features to the logistic regression model corresponding to one or more reference data sets in which event(s) are present. Additional reference data sets can be provided in which event(s) are not present. The one or more temperature features can be provided to the logistic regression model, and a first multivariate model can be determined using the one or more frequency domain features as inputs. The first multivariate model can define a relationship between a presence and an absence of the events. [00125] Once the model is trained, the first or event identification model can be used to determine the presence or absence of an event at one or more locations along the length (e.g., the length of the wellbore) in step 406. The temperature features determined for each location along the length can be used with the first or event identification model. The output of the first or event identification model can provide an indication of the presence of an event at each location for which the temperature features are obtained. When the output indicates that an event has occurred at a given location, an output can be generated indicating the presence of the event. The process can be repeated along the length to provide an event profile, which can comprise an indication of the events at one or more locations along the length being monitored.

[00126] In some embodiments, the event outputs from the first or event identification model can be presented as a profile along a length on an output device. The outputs can be presented in the form of an event profile depicted along an axis with or without a schematic. The event profile can then be used to visualize the event locations, which can allow for various processes to be carried out. For example, for events comprising inflow, the fluid inflow locations can be compared to the producing zones within a completion to understand where fluid is entering the wellbore. In some embodiments, fluid inflow can be detected at locations other than a producing zone, which may provide an indication that a remediation procedure is needed within the wellbore.

[00127] Also disclosed herein is a process for validating the event locations from the first or event identification model using the temperature features and/or determining an extent of the event (e.g., a quantity of fluid (e.g., a liquid) entering the wellbore, blockage within a pipeline, etc.) at the one or more event locations identified by the first or event identification model. The second or event extent model can use one or more frequency domain features in one or more event models to predict an extent of the event(s) (e.g., a quantity or flow rate of one or more fluids and/or fluid phases into the wellbore, amount of leakage from a pipeline, etc.). For example, when the event comprises fluid inflow in a wellbore, the second or event extent model can be used to predict the inflow rates of one or more fluids including a gas, an aqueous liquid, a hydrocarbon liquid, or another fluid within the wellbore. In some embodiments, the second or event extent model can be used to predict the inflow rate of a fluid phase such as a gas phase and/or a liquid phase (e.g., including a liquid aqueous phase and a hydrocarbon liquid phase). [00128] In some embodiments, the frequency domain features can be used with a second or event extent model to predict a fluid inflow rate, such as a liquid flowrate into the wellbore. The second or event extent model can relate a fluid inflow rate of one or more phases (e.g., including a total liquid flow rate) to one or more frequency domain features. In some embodiments, the second or event extent model can accept one or more frequency domain features as inputs. In general, the frequency domain features are representative of feature at a particular location (e.g., a depth resolution portion of the optical fiber along the length, e.g., the length of the wellbore) along the length. The second model can comprise one or more models configured to accept the frequency domain features as input(s) and provide an indication of an extent of the event (e.g., a fluid inflow rate) at the location. When the event comprises fluid inflow, for example, the output of the second or event extent model can be, for example, in the form of a flow rate of one or more fluids and/or fluid phases. In some embodiments, the second or event extent model can comprise a multivariate model, a machine learning model using supervised or unsupervised learning algorithms, or the like.

[00129] In some embodiments, a second or event extent model can be developed using a machine learning approach. In some such embodiments, a single frequency domain feature (e.g., spectral flatness, RMS bin values, etc.) can be used to determine if the event is present at each location of interest. In some embodiments, the supervised learning approach can be used to determine a model of the event extent (e.g., inflow rate of one or more fluids and/or fluid phases, such as gas inflow rate, a hydrocarbon inflow rate, a water inflow rate, a total gas phase inflow rate, and/or a total liquid phase (e.g., a liquid aqueous phase and a liquid hydrocarbon phase) inflow rate).

[00130] In some embodiments, the second or event extent model can be trained using a labeled data set, which can be obtained using a test apparatus such as a test flow set-up and/or field data that is labeled using other instrumentation to identify the extent of an event. Using testing data as an example, the method of developing the second or event extent model can include determining one or more frequency domain features from the acoustic signal for at least a portion of the data from the plurality of tests. The one or more frequency domain features can be obtained across the portion of length where event occurs. The second or event extent model can then be trained using the frequency domain features from the tests. The training of the second or event extent model can use machine learning, including any supervised or unsupervised learning approach. For example, the second or event extent model can be a neural network, a Bayesian network, a decision tree, a logistical regression model, a normalized logistical regression model, k-means clustering or the like.

[00131] In some embodiments, the second or event extent model can be developed and trained using a logistic regression model. As an example for training of a model used to determine the extent of an event comprising fluid inflow (e.g., to determine the fluid inflow rate), the training of the second or event extent model can begin with providing one or more frequency domain features to the logistic regression model corresponding to one or more event tests where known event extents have been measured. Similarly, one or more frequency domain features can be provided to the logistic regression model corresponding to one or more tests where no event is present. A first multivariate model can be determined using the one or more frequency domain features as inputs. The first multivariate model can define a relationship between a presence and an absence of the event and/or event extent.

[00132] In the second or event extent model, the multivariate model equations can use the frequency domain features or combinations or transformations thereof to determine when a specific event extent (e.g., a specific fluid inflow rate or fluid inflow rate for a fluid phase) is present. The multivariate model can define a threshold, decision point, and/or decision boundary having any type of shapes such as a point, line, surface, or envelope between the presence and absence of the event extent (e.g., the specific fluid inflow rate or fluid inflow rate for a phase). In some embodiments, the multivariate model can be in the form of a polynomial, though other representations are also possible. When models such a neural networks are used, the thresholds can be based on node thresholds within the model. As noted herein, the multivariate model is not limited to two dimensions (e.g., two frequency domain features or two variables representing transformed values from two or more frequency domain features), and rather can have any number of variables or dimensions in defining the threshold between the presence or absence of the event (e.g., fluid inflow) and the specific event extents (e.g., fluid inflow rates for one or more fluids and/or fluid phases). Different multivariate models can be used for various event extents (e.g., inflow rate for each fluid type and/or fluid inflow phase), and each multivariate model can rely on different frequency domain features or combinations or transformations of frequency domain features. [00133] Whether a test system or in-situ sensors are used to obtain data on the event extents (e.g., inflow rates), collectively referred to as “reference data”, one or more models can be developed for the determination of the event extents (e.g., inflow rates) using the reference data. The model(s) can be developed by determining one or more frequency domain features from the acoustic signal for at least a portion of the reference data. The training of the model(s) can use machine learning, including any supervised or unsupervised learning approach. For example, one or more of the model(s) can be a neural network, a Bayesian network, a decision tree, a logistical regression model, a normalized logistical regression model, k-means clustering, or the like. [00134] The one or more frequency domain features used in the second or event extent model can comprise any frequency domain features noted hereinabove as well as combinations and transformations thereof. For example, In some embodiments, the one or more frequency domain features comprise a spectral centroid, a spectral spread, a spectral roll-off, a spectral skewness, an RMS band energy, a total RMS energy, a spectral flatness, a spectral slope, a spectral kurtosis, a spectral flux, a spectral autocorrelation function, combinations and/or transformations thereof, or any normalized variant thereof. In some embodiments, the one or more frequency domain features comprise a normalized variant of the spectral spread (NVSS) and/or a normalized variant of the spectral centroid (NVSC).

[00135] The output of the second or event extent model can comprise an indication of the event extent (e.g., the flow rate of one or more fluids and/or fluid phases). For example, for events comprising fluid inflow, the total liquid inflow rate at a location can be determined from the second or event extent model. The resulting output can be compared to the output of the first or event identification model to allow the event (e.g., fluid inflow) location determination to be based both on the first or event identification model using the temperature features and the second or event extent model using the frequency domain features. The final output can be a function of both the output from the first or event identification model and the second or event extent model. In some embodiments, the outputs can be combined as a product, weighted product, ratio, or other mathematical combination. Other combinations can include voting schemes, thresholds, or the like to allow the outputs from both models to be combined. As an example, if the output from either model is zero, then the event identification at the location would also indicate that there is no event at the location. In this example, one model can indicate that an event is present, but the other model can indicate that no event is present. The final result can indicate that no event is present. When both models indicate that the event is present, the final combined output can provide a positive indication of the event at the location. It is noted that the output of the second or event extent model can provide one or more indications of event extents (e.g., a fluid inflow rate of one or more fluids and/or fluid phases). While this output is distinct from the output of the first or event identification model, the two outputs can be combined to improve the accuracy of the event location identification.

[00136] Also described herein are methods and systems for using the combined or hybrid approach to determining event extents (e.g., fluid inflow rates) at the one or more locations at which an event (e.g., fluid inflow) is identified. In these embodiments, the outputs of the first or event identification model and the second or event extent model can be used together to help to determine an event extent (e.g., an inflow rate of one or more fluids and/or fluid phases) along the length being monitored (e.g., within the wellbore). In some embodiments, the outputs of the two models can be combined to form a final event presence and/or event extent determination. In some embodiments, the first or event identification model can be used to identify the one or more locations at which the event (e.g., fluid inflow) is occurring, and the second or event extent model can then be used to determine the event extent (e.g., fluid inflow rates) at the identified locations, which can occur without combining the outputs of the two models.

[00137] Figure 5 illustrates a flow chart for a method 500 of determining the presence and/or extent of an event. At step 502, the temperature features can be determined using any of the processes and systems as described herein. In some embodiments, a DTS system can be used to obtain distributed temperature sensing signal along the length being monitored (e.g., along a length within the wellbore). The DTS system can provide distributed temperature measurements along the length over time. A baseline temperature can be stored for the length as described herein and used along with the temperature measurements to determine the temperature features. The temperature features can include any of those described herein including a depth derivative of temperature with respect to depth, a temperature excursion measurement, a baseline temperature excursion, a peak-to-peak value, a fast Fourier transform, a Laplace transform, a wavelet transform, a derivative of temperature with respect to length (e.g., depth), a heat loss parameter, an autocorrelation, a statistical measure of a variation with respect to time and/or distance, as detailed hereinabove, or a combination thereof. [00138] At step 504, one or more frequency domain features can be obtained from an acoustic signal originating along the length being monitored (e.g., within the wellbore). The frequency domain features can be determined using any of the processes and systems as described herein. In some embodiments, a DAS system can be used to obtain a distributed acoustic signal along the length being monitored (e.g., within the wellbore). The acoustic signals obtained from the DAS system can then be processed to determine one or more frequency domain features as described herein. In some embodiments, the frequency domain features can comprise at least one of: a spectral centroid, a spectral spread, a spectral roll-off, a spectral skewness, an RMS band energy, a total RMS energy, a spectral flatness, a spectral slope, a spectral kurtosis, a spectral flux, a spectral autocorrelation function, or any combination thereof, including combinations and modifications thereof.

[00139] The temperature features and the frequency domain features can then be used to determine a presence and/or extent of one or more events (e.g., a fluid inflow at one or more locations in a wellbore and/or a fluid inflow rate thereof) at one or more locations along the length being monitored in step 506. The temperature features and the frequency domain features can be used in several ways to determine the presence and/or the extent of the one or more events along the length being monitored. In some embodiments, the temperature features can be used in the first or event identification model to obtain an identification of one or more locations along the length having the event. Any of the models and methods of using the temperature features within the models as described herein can be used in step 406 to determine the one or more event (e.g., fluid inflow) locations. The output of the first or event identification model can provide an indication of one or more locations along the length being monitored (e.g., along the length of the wellbore) having an event.

[00140] The frequency domain features can be used in the second or event extent model to obtain an indication of the event extent (e.g., fluid inflow rate for one or more fluids and/or fluid phases) at the one or more locations along the length (e.g., the wellbore). In some embodiments, the second or event extent model can be limited to being executed at the one or more locations identified by the first or event identification model. The second or event extent model can then predict the event extent(s) (e.g., fluid inflow rates of one or more fluids and/or fluid phases) at the one or more locations. The event extent(s) (e.g., fluid inflow rates) can then be representative of the event extents at the one or more locations along the length (e.g., the wellbore).

[00141] In some embodiments, the output of the first or event identification model and the second or event extent model can be combined to provide a combined output from the first or event identification model and the second or event extent model. The resulting combined output can then be used to determine an event extent (e.g., a fluid inflow rate) at the one or more locations along the length being monitored (e.g., the wellbore) as identified by the first or event identification model. The combined output can be determined as a function of the output of the first or event identification model and the output of the second or event extent model. Any suitable functions can be used to combine the outputs of the two models. This can include formulas, products, averages, and the like, each of which can comprise one or more constants or weightings to provide the final output. The ability to determine the event extent(s) as a function of the output of both models can allow for either model to override the output of the other model. For example, if the first or event identification model indicates that a location along the length being monitored has an event, but the second or event extent model indicates no event, the resulting combined output may be considered to indicate that there is no event at that location. Similarly, if the first or event identification model indicates a non-zero but low likelihood of an event at a location, the output can serve as a weighting to any event extents determined by the second or event extent model. Thus, the use of the hybrid model approach can provide two separate ways to verify and determine the event extents along the length (e.g., fluid inflow rates into the wellbore).

[00142] In some embodiments, both the temperature features and the frequency domain features can then be used in a single model to determine a presence and/or extent of one or more events at one or more locations along the length being monitored in step 506. The temperature features and the frequency domain features can be used in an event identification model as inputs to obtain an identification of one or more locations along the length having the event. In this embodiment, the test data for both temperature features and frequency domain features can be used to train a model using any of the models and techniques described herein. Once trained using one or more temperature features and one or more frequency domain features, the resulting features determined for a time interval can be used as inputs into the model. The output of the event identification model can provide an indication of one or more locations along the length being monitored (e.g., along the length of the wellbore) having an event. The same model or a second model can then be used to obtain an indication of the event extent (e.g., fluid inflow rate for one or more fluids and/or fluid phases) at the one or more locations along the length (e.g., the wellbore). The second model can be separate in some embodiments. In other embodiments, the first model may provide an output including both the locations of one or more events and the extent of such events.

[00143] The resulting output of the models can be an indication of an event at one or more locations along the length. The event prediction can be for one or more events (e.g., one or more fluids (e.g., a gas, an aqueous liquid, a hydrocarbon liquid, etc.) and/or a fluid phase (e.g., a gas phase, a liquid phase, etc.)). The event extents can be used as indicated by the model in their form as output by the model. In some embodiments, the total event extents can be normalized across the one or more locations having the event. This can allow for a determination of a relative proportion of the event at each of the identified locations. This can be useful for understanding where the contributions to an event are occurring along the length, irrespective of the absolute event extent along the length.

[00144] In some embodiments, the event extents can be refined by using an independent measure of the event extent (e.g., fluid flow rate from the wellbore as measured at logging tool above the producing zones, a wellhead, surface flow line, or the like). Thus, as depicted in FIG. 5, method 500 can further comprise optional step 508 of independently measuring an event extent. For example, when the event comprises fluid inflow and the event extent comprises the fluid inflow rate, the fluid production rate can be measured by a standard fluid flowrate measurement tool that is not associated with the acoustic monitoring system or the temperature monitoring system within the wellbore. For example, the fluid production rate can be measured with various flow meters. The fluid production rate can comprise an indication of the fluid flow rates of one or more fluids and/or one or more fluid phases. The resulting event extent (e.g., fluid production rate) information can then be combined with the output of the combined models as described herein. In some embodiments, the resulting normalized event extents can be used with the actual event extents (e.g., production rates) to allocate the actual event extent (e.g., production rates) across the one or more event (e.g., fluid) inflow locations along the length being monitored (e.g., within the wellbore). Thus, method 500 of FIG. 5 can further comprise optional step 510 of allocating the event extent across the one or more locations. As an example, for events comprising fluid inflow and event extents comprising fluid inflow rates at one or more locations, if the models indicate that thirty percent of a liquid phase inflow rate is occurring at a first location and seventy percent is occurring at a second location, the actual production rate can be allocated so that thirty percent of the produced liquid phase flowrate is attributed to the first location and the remaining seventy percent of the liquid phase flow rate is flowing into the wellbore at the second location. The allocations can be made for one or more of the fluid inflow rates and/or fluid phase inflow rates, where the actual production rates for the fluids and/or fluid phases can be used with the corresponding model outputs for one or more fluids and/or fluid phases. The allocation process can allow for an improved accuracy for the determination of fluid inflow rates at the one or more locations along the wellbore.

[00145] Any of the systems and methods disclosed herein can be carried out on a computer or other device comprising a processor (e.g., a desktop computer, a laptop computer, a tablet, a server, a smartphone, or some combination thereof), such as the acquisition device 160 of Figure 1. FIG. 6 illustrates a computer system 680 suitable for implementing one or more embodiments disclosed herein such as the acquisition device or any portion thereof. The computer system 680 includes a processor 682 (which may be referred to as a central processor unit or CPU) that is in communication with memory devices including secondary storage 684, read only memory (ROM) 686, random access memory (RAM) 688, input/output (I/O) devices 690, and network connectivity devices 692. The processor 682 may be implemented as one or more CPU chips. [00146] It is understood that by programming and/or loading executable instructions onto the computer system 680, at least one of the CPU 682, the RAM 688, and the ROM 686 are changed, transforming the computer system 680 in part into a particular machine or apparatus having the novel functionality taught by the present disclosure. It is fundamental to the electrical engineering and software engineering arts that functionality that can be implemented by loading executable software into a computer can be converted to a hardware implementation by well- known design rules. Decisions between implementing a concept in software versus hardware typically hinge on considerations of stability of the design and numbers of units to be produced rather than any issues involved in translating from the software domain to the hardware domain. Generally, a design that is still subject to frequent change may be preferred to be implemented in software, because re-spinning a hardware implementation is more expensive than re-spinning a software design. Generally, a design that is stable that will be produced in large volume may be preferred to be implemented in hardware, for example in an application specific integrated circuit (ASIC), because for large production runs the hardware implementation may be less expensive than the software implementation. Often a design may be developed and tested in a software form and later transformed, by well-known design rules, to an equivalent hardware implementation in an application specific integrated circuit that hardwires the instructions of the software. In the same manner as a machine controlled by a new ASIC is a particular machine or apparatus, likewise a computer that has been programmed and/or loaded with executable instructions may be viewed as a particular machine or apparatus.

[00147] Additionally, after the system 680 is turned on or booted, the CPU 682 may execute a computer program or application. For example, the CPU 682 may execute software or firmware stored in the ROM 686 or stored in the RAM 688. In some cases, on boot and/or when the application is initiated, the CPU 682 may copy the application or portions of the application from the secondary storage 684 to the RAM 688 or to memory space within the CPU 682 itself, and the CPU 682 may then execute instructions of which the application is comprised. In some cases, the CPU 682 may copy the application or portions of the application from memory accessed via the network connectivity devices 692 or via the I/O devices 690 to the RAM 688 or to memory space within the CPU 682, and the CPU 682 may then execute instructions of which the application is comprised. During execution, an application may load instructions into the CPU 682, for example load some of the instructions of the application into a cache of the CPU 682. In some contexts, an application that is executed may be said to configure the CPU 682 to do something, e.g., to configure the CPU 682 to perform the function or functions promoted by the subject application. When the CPU 682 is configured in this way by the application, the CPU 682 becomes a specific purpose computer or a specific purpose machine.

[00148] The secondary storage 684 is typically comprised of one or more disk drives or tape drives and is used for non-volatile storage of data and as an over-flow data storage device if RAM 688 is not large enough to hold all working data. Secondary storage 684 may be used to store programs which are loaded into RAM 688 when such programs are selected for execution. The ROM 686 is used to store instructions and perhaps data which are read during program execution. ROM 686 is a non-volatile memory device which typically has a small memory capacity relative to the larger memory capacity of secondary storage 684. The RAM 688 is used to store volatile data and perhaps to store instructions. Access to both ROM 686 and RAM 688 is typically faster than to secondary storage 684. The secondary storage 684, the RAM 688, and/or the ROM 686 may be referred to in some contexts as computer readable storage media and/or non-transitory computer readable media.

[00149] I/O devices 690 may include printers, video monitors, electronic displays (e.g., liquid crystal displays (LCDs), plasma displays, organic light emitting diode displays (OLED), touch sensitive displays, etc.), keyboards, keypads, switches, dials, mice, track balls, voice recognizers, card readers, paper tape readers, or other well-known input devices.

[00150] The network connectivity devices 692 may take the form of modems, modem banks, Ethernet cards, universal serial bus (USB) interface cards, serial interfaces, token ring cards, fiber distributed data interface (FDDI) cards, wireless local area network (WLAN) cards, radio transceiver cards that promote radio communications using protocols such as code division multiple access (CDMA), global system for mobile communications (GSM), long-term evolution (LTE), worldwide interoperability for microwave access (WiMAX), near field communications (NFC), radio frequency identity (RFID), and/or other air interface protocol radio transceiver cards, and other well-known network devices. These network connectivity devices 692 may enable the processor 682 to communicate with the Internet or one or more intranets. With such a network connection, it is contemplated that the processor 682 might receive information from the network, or might output information to the network (e.g., to an event database) in the course of performing the above-described method steps. Such information, which is often represented as a sequence of instructions to be executed using processor 682, may be received from and outputted to the network, for example, in the form of a computer data signal embodied in a carrier wave. [00151] Such information, which may include data or instructions to be executed using processor 682 for example, may be received from and outputted to the network, for example, in the form of a computer data baseband signal or signal embodied in a carrier wave. The baseband signal or signal embedded in the carrier wave, or other types of signals currently used or hereafter developed, may be generated according to several known methods. The baseband signal and/or signal embedded in the carrier wave may be referred to in some contexts as a transitory signal.

[00152] The processor 682 executes instructions, codes, computer programs, scripts which it accesses from hard disk, floppy disk, optical disk (these various disk based systems may all be considered secondary storage 684), flash drive, ROM 686, RAM 688, or the network connectivity devices 692. While only one processor 682 is shown, multiple processors may be present. Thus, while instructions may be discussed as executed by a processor, the instructions may be executed simultaneously, serially, or otherwise executed by one or multiple processors. Instructions, codes, computer programs, scripts, and/or data that may be accessed from the secondary storage 684, for example, hard drives, floppy disks, optical disks, and/or other device, the ROM 686, and/or the RAM 688 may be referred to in some contexts as non-transitory instructions and/or non-transitory information.

[00153] In an embodiment, the computer system 680 may comprise two or more computers in communication with each other that collaborate to perform a task. For example, but not by way of limitation, an application may be partitioned in such a way as to permit concurrent and/or parallel processing of the instructions of the application. Alternatively, the data processed by the application may be partitioned in such a way as to permit concurrent and/or parallel processing of different portions of a data set by the two or more computers. In an embodiment, virtualization software may be employed by the computer system 680 to provide the functionality of a number of servers that is not directly bound to the number of computers in the computer system 680. For example, virtualization software may provide twenty virtual servers on four physical computers. In an embodiment, the functionality disclosed above may be provided by executing the application and/or applications in a cloud computing environment. Cloud computing may comprise providing computing services via a network connection using dynamically scalable computing resources. Cloud computing may be supported, at least in part, by virtualization software. A cloud computing environment may be established by an enterprise and/or may be hired on an as-needed basis from a third party provider. Some cloud computing environments may comprise cloud computing resources owned and operated by the enterprise as well as cloud computing resources hired and/or leased from a third party provider.

[00154] In an embodiment, some or all of the functionality disclosed above may be provided as a computer program product. The computer program product may comprise one or more computer readable storage medium having computer usable program code embodied therein to implement the functionality disclosed above. The computer program product may comprise data structures, executable instructions, and other computer usable program code. The computer program product may be embodied in removable computer storage media and/or non-removable computer storage media. The removable computer readable storage medium may comprise, without limitation, a paper tape, a magnetic tape, magnetic disk, an optical disk, a solid state memory chip, for example analog magnetic tape, compact disk read only memory (CD-ROM) disks, floppy disks, jump drives, digital cards, multimedia cards, and others. The computer program product may be suitable for loading, by the computer system 680, at least portions of the contents of the computer program product to the secondary storage 684, to the ROM 686, to the RAM 688, and/or to other non-volatile memory and volatile memory of the computer system 680. The processor 682 may process the executable instructions and/or data structures in part by directly accessing the computer program product, for example by reading from a CD-ROM disk inserted into a disk drive peripheral of the computer system 680. Alternatively, the processor 682 may process the executable instructions and/or data structures by remotely accessing the computer program product, for example by downloading the executable instructions and/or data structures from a remote server through the network connectivity devices 692. The computer program product may comprise instructions that promote the loading and/or copying of data, data structures, files, and/or executable instructions to the secondary storage 684, to the ROM 686, to the RAM 688, and/or to other non-volatile memory and volatile memory of the computer system 680.

[00155] In some contexts, the secondary storage 684, the ROM 686, and the RAM 688 may be referred to as a non-transitory computer readable medium or a computer readable storage media. A dynamic RAM embodiment of the RAM 688, likewise, may be referred to as a non-transitory computer readable medium in that while the dynamic RAM receives electrical power and is operated in accordance with its design, for example during a period of time during which the computer system 680 is turned on and operational, the dynamic RAM stores information that is written to it. Similarly, the processor 682 may comprise an internal RAM, an internal ROM, a cache memory, and/or other internal non-transitory storage blocks, sections, or components that may be referred to in some contexts as non-transitory computer readable media or computer readable storage media.

[00156] Having described various systems and methods, certain embodiments can include, but are not limited to:

[00157] In a first embodiment, a method of determining a presence or extent of an event comprises: determining a plurality of temperature features from a temperature sensing signal; determining one or more frequency domain features from an acoustic signal; and using at least one temperature feature of the plurality of temperature features and at least one frequency domain feature of the one or more frequency domain features to determine a presence or extent of the event at one or more locations.

[00158] A second embodiment can include the method of the first embodiment, wherein the one or more events comprise one or more wellbore events, and wherein the one or more wellbore events comprise one or more of: a fluid inflow, a fluid outflow, a fluid phase segregation, a fluid flow discrimination within a conduit, a well integrity monitoring, an in-well leak detection, an annular fluid flow, an overburden monitoring, a fluid flow detection behind a casing, a fluid induced hydraulic fracture detection in an overburden, a sand ingress, a wax deposition, or a sand flow along a wellbore.

[00159] A third embodiment can include the method of the first or second embodiment, wherein the one or more events comprise one or more security events, transportation events, geothermal events, carbon capture and C02 injection events, facility monitoring events, pipeline monitoring events, or dam monitoring events.

[00160] A fourth embodiment can include the method of any one of the first to third embodiments, wherein the plurality of temperature features comprises a depth derivative of temperature with respect to depth.

[00161] A fifth embodiment can include the method of any one of the first to fourth embodiments, wherein the plurality of temperature features comprises a temperature excursion measurement, wherein the temperature excursion measurement comprises a difference between a temperature reading at a first depth and a smoothed temperature reading over a depth range, wherein the first depth is within the depth range.

[00162] A sixth embodiment can include the method of any one of the first to fifth embodiments, wherein the plurality of temperature features comprises a baseline temperature excursion, wherein the baseline temperature excursion comprises a derivative of a baseline excursion with depth, wherein the baseline excursion comprises a difference between a baseline temperature profile and a smoothed temperature profile.

[00163] A seventh embodiment can include the method of any one of the first to sixth embodiments, wherein the plurality of temperature features comprises a peak-to-peak value, wherein the peak-to-peak value comprises a derivative of a peak-to-peak difference with depth, wherein the peak-to-peak difference comprises a difference between a peak high temperature reading and a peak low temperature reading with an interval.

[00164] An eighth embodiment can include the method of any one of the first to seventh embodiments, wherein the plurality of temperature features comprises an autocorrelation, wherein the autocorrelation is a cross-correlation of the temperature sensing signal with itself. [00165] A ninth embodiment can include the method of any one of the first to eighth embodiments, wherein the plurality of temperature features comprises a Fast Fourier Transform (FFT) of the temperature sensing signal.

[00166] A tenth embodiment can include the method of any one of the first to ninth embodiments, wherein the plurality of temperature features comprises a Laplace transform of the temperature sensing signal.

[00167] An eleventh embodiment can include the method of any one of the first to tenth embodiments, wherein the plurality of temperature features comprises a wavelet transform of the temperature sensing signal or a wavelet transform of the derivative of the temperature sensing signal with length (e.g., depth).

[00168] A twelfth embodiment can include the method of the eleventh embodiment, wherein the wavelet comprises a Morse wavelet, an analytical wavelet, a Bump wavelet, or a combination thereof.

[00169] A thirteenth embodiment can include the method of any one of the first to twelfth embodiments, wherein the plurality of temperature features comprises a derivative of flowing temperature with respect to depth.

[00170] A fourteenth embodiment can include the method of any one of the first to thirteenth embodiments, wherein the plurality of temperature features comprises a heat loss parameter. [00171] A fifteenth embodiment can include the method of any one of the first to fourteenth embodiments, wherein the plurality of temperature features comprise a time-depth derivative, a depth-time derivative, or both.

[00172] A sixteenth embodiment can include the method of any one of the first to fifteenth embodiments, wherein the one or more frequency domain features comprise at least one of: a spectral centroid, a spectral spread, a spectral roll-off, a spectral skewness, an RMS band energy, a total RMS energy, a spectral flatness, a spectral slope, a spectral kurtosis, a spectral flux, or a spectral autocorrelation function. [00173] A seventeenth embodiment can include the method of any one of the first to sixteenth embodiments, wherein using the at least one temperature feature and the at least one frequency domain feature comprises: using the at least one temperature feature in a first model; using the at least one frequency domain feature of the one or more frequency domain features in a second model; combining an output from the first model and an output from the second model to form a combined output; and determining a presence or extent of the event based on the combined output.

[00174] An eighteenth embodiment can include the method of the seventeenth embodiment, wherein the first model comprise one or more multivariate models, and wherein the output from each multivariate model of the one or more multivariate model comprises an indication of the presence of the event at one or more locations .

[00175] A nineteenth embodiment can include the method of the eighteenth embodiment, wherein the second model comprises a regression model, and wherein the output from the regression model comprises an indication of the presence or extent of the event at the one or more locations.

[00176] A twentieth embodiment can include the method of the nineteenth embodiment, wherein combining the output from the first model with the output from the second model comprises determining the combined output as a function of: 1) the output from the first model, and 2) the output from the second model.

[00177] A twenty first embodiment can include the method of any one of the first to twentieth embodiments, further comprising: receiving an independent indication of extent of the event; and allocating a portion of the event extent to the one or more locations based on the event extent at the one or more locations based on the combined output.

[00178] A twenty second embodiment can include the method of any one of the first to twenty first embodiments, further comprising: receiving the temperature sensing signal from a sensor comprising a fiber optic based temperature sensor or receiving the acoustic signal from a sensor comprising a fiber optic based acoustic sensor.

[00179] A twenty third embodiment can include the method of the twenty second embodiment, wherein the fiber optic based temperature sensor or the fiber optic based acoustic sensor is disposed in a wellbore. [00180] A twenty fourth embodiment can include the method of any one of the first to twenty third embodiments, further comprising: denoising and calibrating the temperature sensing signal prior to determining the one or more temperature features; or normalizing the one or more temperature features prior to determining the presence of the one or more events.

[00181] In a twenty fifth embodiment, a method of determining a presence or extent of an event comprises:

[00182] determining a plurality of temperature features from a temperature sensing signal, wherein the plurality of temperature features comprise at least two of: a depth derivative of temperature with respect to depth, a temperature excursion measurement, a baseline temperature excursion, or a peak-to-peak value, an autocorrelation, a Fast Fourier Transform (FFT) of the temperature sensing signal, a Laplace transform of the temperature sensing signal, a wavelet transform of the temperature sensing signal or of a derivative of the temperature sensing signal with respect to length (e.g., depth), or a derivative of flowing temperature with respect to length (depth), as described by Equation (1), a heat loss parameter, a time-depth derivative, or a depthtime derivative; determining one or more frequency domain features from an acoustic signal originated in the wellbore; and using at least one temperature feature of the plurality of temperature features and at least one frequency domain feature of the one or more frequency domain features to determine the presence or extent of the event at one or more locations.

[00183] A twenty sixth embodiment can include the method of the twenty fifth embodiment, wherein the one or more events comprise one or more wellbore events, and wherein the one or more wellbore events comprise one or more of: a fluid inflow, a fluid outflow, a fluid phase segregation, a fluid flow discrimination within a conduit, a well integrity monitoring, an in-well leak detection, an annular fluid flow, an overburden monitoring, a fluid flow detection behind a casing, a sand ingress, a wax deposition, or a sand flow along a wellbore.

[00184] A twenty seventh embodiment can include the method of the twenty fifth embodiment, wherein the one or more events comprise one or more security events, transportation events, geothermal events, carbon capture and C02 injection events, facility monitoring events, pipeline monitoring events, or dam monitoring events.

[00185] A twenty eighth embodiment can include the method of the twenty fifth embodiment, wherein the one or more events comprises a fluid inflow at one or more locations. [00186] A twenty ninth embodiment can include the method of the twenty eighth embodiment, wherein the fluid inflow is a liquid inflow at the one or more locations.

[00187] A thirtieth embodiment can include the method of the twenty ninth embodiment, wherein the liquid inflow comprises an aqueous liquid, a hydrocarbon liquid, or a combination of both an aqueous liquid and a hydrocarbon liquid.

[00188] A thirty first embodiment can include the method of any one of the twenty fifth to thirtieth embodiments, wherein the temperature excursion measurement comprises a difference between a temperature reading at a first depth and a smoothed temperature reading over a depth range, wherein the first depth is within the depth range.

[00189] A thirty second embodiment can include the method of any one of the twenty fifth to thirty first embodiments, wherein the baseline temperature excursion comprises a derivative of a baseline excursion with depth, wherein the baseline excursion comprises a difference between a baseline temperature profile and a smoothed temperature profile.

[00190] A thirty third embodiment can include the method of any one of the twenty fifth to thirty second embodiments, wherein the peak-to-peak value comprises a derivative of a peak-to- peak difference with depth, wherein the peak-to-peak difference comprises a difference between a peak high temperature reading and a peak low temperature reading with an interval.

[00191] A thirty fourth embodiment can include the method of any one of the twenty fifth to thirty third embodiments, wherein the one or more frequency domain features comprise at least one of: a spectral centroid, a spectral spread, a spectral roll-off, a spectral skewness, an RMS band energy, a total RMS energy, a spectral flatness, a spectral slope, a spectral kurtosis, a spectral flux, or a spectral autocorrelation function.

[00192] A thirty fifth embodiment can include the method of any one of the twenty fifth to thirty fourth embodiments, wherein using the at least one temperature feature and the at least one frequency domain feature comprises: using the at least one temperature features in a first model; using at least one frequency domain feature of the one or more frequency domain features in a second model; combining an output from the first model and an output from the second model to form a combined output; and determining a presence or extent of the event at the one or more locations based on the combined output.

[00193] A thirty sixth embodiment can include the method of the thirty fifth embodiment, wherein the first model comprise one or more multivariate models, and wherein the output from each multivariate model of the one or more multivariate model comprises an indication of the presence or absence of the event at one or more locations along the wellbore.

[00194] A thirty seventh embodiment can include the method of the thirty fifth embodiment, wherein the second model comprises a regression model, and wherein the output from the regression model comprises an indication of a presence or an extent thereof at the one or more locations.

[00195] A thirty eighth embodiment can include the method of the thirty fifth embodiment, wherein combining the output from the first model with the output from the second model comprises determining the combined output as a function of: 1) the output from the first model, and 2) the output from the second model.

[00196] A thirty ninth embodiment can include the method of any one of the twenty fifth to thirty eighth embodiments, further comprising: receiving an independent indication of an event extent; and allocating a portion of the event extent to the one or more locations based on the determined event extent at the one or more locations based on the combined output.

[00197] In a fortieth embodiment, a system of determining a presence or extent of an event comprises:

[00198] a processor; a memory; and an analysis program stored in the memory, wherein the analysis program is configured, when executed on the processor, to: receive a temperature sensing signal and an acoustic signal; determine a plurality of temperature features from the temperature sensing signal; determine one or more frequency domain features from the acoustics signal; and determine a presence or extent of the event at one or more locations using at least one temperature feature of the plurality of temperature features and at least one frequency domain feature of the one or more frequency domain features.

[00199] A forty first embodiment can include the system of the fortieth embodiment, wherein the analysis program is further configured to: use the at least one temperature features in a first model; use at least one frequency domain feature of the one or more frequency domain features in a second model; combine an output from the first model and an output from the second model to form a combined output; and determine a presence or extent of the event at the one or more locations based on the combined output.

[00200] A forty second embodiment can include the system of the forty first embodiment, wherein the first model comprises one or more multivariate models, and wherein the output from each multivariate model of the one or more multivariate model comprises an indication of the one or more locations.

[00201] A forty third embodiment can include the system of any one of the fortieth to forty second embodiments, wherein the second model comprises a regression model, and wherein the output from the regression model comprises an indication an extent of the event at the one or more locations.

[00202] A forty fourth embodiment can include the system of the forty first embodiment, wherein the analysis program is further configured to: combine the output from the first model with the output from the second model as a function of: 1) the output from the first model, and 2) the output from the second model.

[00203] A forty fifth embodiment can include the system of any one of the fortieth to forty fourth embodiments, wherein the analysis program is further configured to: receive an independent indication of an event extent; and allocate a portion of the event extent to the one or more locations based on the determined event extent at the one or more locations based on the combined output.

[00204] A forty sixth embodiment can include the system of any one of the fortieth to forty fifth embodiments, wherein the plurality of temperature features comprise at least two of: a depth derivative of temperature with respect to depth, a temperature excursion measurement, a baseline temperature excursion, or a peak-to-peak value, an autocorrelation, a Fast Fourier Transform (FFT) of the temperature sensing signal, a Laplace transform of the temperature sensing signal, a wavelet transform of the temperature sensing signal or of a derivative of the temperature sensing signal with respect to length (e.g., depth), or a derivative of flowing temperature with respect to length (depth), as described by Equation (1), a heat loss parameter, a time-depth derivative, or a depth-time derivative.

[00205] A forty seventh embodiment can include the system of any one of the fortieth to forty sixth embodiments, wherein the temperature excursion measurement comprises a difference between a temperature reading at a first depth and a smoothed temperature reading over a depth range, wherein the first depth is within the depth range.

[00206] A forty eighth embodiment can include the system of any one of the fortieth to forty seventh embodiments, wherein the baseline temperature excursion comprises a derivative of a baseline excursion with depth, wherein the baseline excursion comprises a difference between a baseline temperature profile and a smoothed temperature profile.

[00207] A forty ninth embodiment can include the system of any one of the fortieth to forty eighth embodiments, wherein the peak-to-peak value comprises a derivative of a peak-to-peak difference with depth, wherein the peak-to-peak difference comprises a difference between a peak high temperature reading and a peak low temperature reading with an interval.

[00208] A fiftieth embodiment can include the system of any one of the fortieth to forty ninth embodiments, wherein the one or more frequency domain features comprise at least one of: a spectral centroid, a spectral spread, a spectral roll-off, a spectral skewness, an RMS band energy, a total RMS energy, a spectral flatness, a spectral slope, a spectral kurtosis, a spectral flux, or a spectral autocorrelation function.

[00209] The embodiments disclosed herein have included systems and methods for detecting and/or characterizing sand ingress and/or sand transport within a subterranean wellbore, or a plurality of such wellbores. Thus, through use of the systems and methods described herein, one may more effectively limit or avoid sand ingress and accumulation with a wellbore so as to enhance the economic production therefrom.

[00210] While exemplary embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.