Cross Reference to Related Application

[0001] This application claims priority to United States Provisional Patent Application Serial

No. 62/929,615 filed on November 1, 2019, the contents of which is incorporated herein by reference.

Field of the Invention

[0002] The following relates generally to drilling technology, and more particularly to systems and methods for downhole communications from a surface location to a bottom hole assembly.

Background of the Invention

[0003] In the oil, gas, and utility horizontal and directional drilling markets, specialized electronic equipment is deployed to perform functions near to the drill head. While these functions can include the switching of valves, solenoids and/or the operation of other mechanical devices, it is often the primary function of such electronic equipment to measure the orientation of the equipment and, accordingly, the position or survey of the wellbore, for use in controlling a drill string from the surface. An electronic system that is incorporated as a part of a bottom hole assembly (BHA) to measure the position of a wellbore proximal the drill head is commonly called a Measurement While Drilling (MWD) system.

[0004] It is not trivial to arrange communications between the surface and a downhole electric circuit such as a MWD system, a BHA controller, or some other downhole circuit within a wellbore deep beneath the surface of the earth. Deploying radio transceivers for this purpose tends to be ineffective because drill heads are typically operating from several tens to several thousands of meters beneath the surface of the earth, with the conductivity and density of the earth drastically attenuating radio waves before they can propagate more than a few meters underground.

[0005] It is known to accomplish communications from an MWD system to the surface

(“uphole communications”), by coding data into timed pressure fluctuations in the drilling fluid system. In some arrangements, the MWD system controls a downhole valve at timed intervals to choke off mudflow, with the timing of the choking representing a data bit or word. The resulting pulses from backpressure changes can be measured, timed, and decoded by surface equipment. The decoded data may represent drill head orientation and/or control feedback that can be displayed for an operator to review and use in the course of controlling the drilling system.

[0006] Communication from the surface to the MWD system (“downhole communications”) has tended to be more challenging than uphole communications. A typical downhole tool will be physically less able than a surface system to accommodate a powerful computer processor for handling decoding, signal filtration, and other signal processing requirements. Furthermore, the majority of the physical restrictions that can cause mud pressure drops are upstream of the MWD system. As a result, any fluctuations to the flow rate from surface that might have been hoped to induce reliably measurable pressure pulses downhole would have to be produced with a magnitude that is likely to unduly affect drilling itself. Additionally, in order to be unambiguously discemable by a MWD system downhole, such fluctuations would have to have long intervals, rendering the data rate to be low.

[0007] An alternative approach to downhole communications is to time the operation of the drilling fluid pumps to encode information for the MWD system. Monitoring “pump status” downhole is commonly done as a routine part of MWD operations; it is important for an MWD tool to know whether the fluid flow has been shut off and for how long it has been turned back on in order to properly read and time the transmission of data to surface. Monitoring pump status is commonly accomplished using a vibration sensor or a pressure transducer. Because of its common usage, this approach for downhole communications can be quite reliable. For example, in order to encode information using this channel, an operator at the surface controls the drilling fluid pumps according to several mud pump start and stop sequences. In this way, the downhole tool can, as part of monitoring pump status, detect and measure the time intervals between the starts and stops thereby to discern data encoded in the sequences.

[0008] However, using fluid flow fluctuations for encoding data tends to enable only very low data rates, typically as low as 1 to 3 bits per minute. Typical mud pumps can take several seconds to slow down and stop, which latency can limit the switching times and introducing uncertainty as to the timing at which exact stoppages and re-starts have occurred. Because some downhole electric circuits require 8-16 bits of data to be reliably transmitted down to them in order to recognize unambiguously that settings should be changed, downhole communications using this approach can occupy 10 minutes of rig time that could otherwise be fruitfully used for drilling itself. Faster methods of reliably downlinking are therefore desirable.

[0009] Another approach to downhole communications (both to and from surface) is what is conventionally called “EM Telemetry”. EM telemetry involves inducing electrical currents in the ground to carry data. In particular, when sending information down to the tool, an amplifier or current generator is arranged such that one electrode is connected to the rig or drill string and another is grounded to the earth in a location several hundred meters away. An AC voltage signal of either varying frequency or phase angle is then generated, causing a corresponding current to flow through the earth. Because elements of the current take all available paths, at least some of this current is detectable downhole. The downhole tool can thereby detect and measure the changes in current, frequency and/or phase angle, and decode such changes as data. This approach offers higher data rates than approaches referred to above. However, a principal drawback to this method is the need for an electrical discontinuity in the bottom hole assembly and sophisticated and high-powered electrical transmission equipment at the surface.

[0010] While various arrangements for downhole communications are known, improvements are desirable.

Summary of the Invention

[0011] In accordance with an aspect, there is provided a downhole communication receiver comprising: a sensor associated with a bottom hole assembly (BHA) of a drill string, the sensor producing electrical signals corresponding to axial behaviors of the BHA within a borehole; and a decoder in communication with the sensor for processing the electrical signals during signalling periods thereby to decode the axial behaviors as information.

[0012] In an embodiment, the axial behaviors of the BHA within the borehole comprise: accelerating, decelerating, and maintaining constant velocity within the borehole.

[0013] In an embodiment, the axial behaviors of the BHA within the borehole comprise: advancing, withdrawing, and remaining stationary within the borehole

[0014] In an embodiment, the sensor produces electrical signals corresponding to rates of the axial behaviors of the BHA within the borehole; and the decoder processes the electrical signals to decode the axial behaviors and the rates of the axial behaviors into the information for a downhole electric circuit.

[0015] In an embodiment, the decoder processes the electrical signals during signalling periods to determine that the BHA has been advanced or withdrawn a respective distance within the borehole, wherein the respective distance corresponds to respective information.

[0016] In an embodiment, the decoder processes the electrical signals during signalling periods to determine that the BHA has been advanced or withdrawn a threshold distance within the borehole during a particular time slot, wherein the particular time slot corresponds to respective information. [0017] In an embodiment, the particular time slot is one of eight (8) available time slots each corresponding to respective information.

[0018] In an embodiment, each time slot has a duration of two seconds.

[0019] In an embodiment, the decoder processes the electrical signals during signalling periods to determing that the BHA been advanced or withdrawn at a particular velocity within the borehole during a particular time slot, wherein the particular time slot corresponds to respective information. [0020] In an embodiment, the decoder is configured to process the electrical signals during signalling periods to determine whether the BHA has been moved axially in the borehole, wherein the respective state of the BHA having been moved or having not been moved during particular time slots corresponds to respective information.

[0021] In an embodiment, the decoder processes the electrical signals during signalling periods to determing that the BHA been advanced or withdrawn at or above a threshold velocity within the borehole during a particular time slot, wherein the particular time slot corresponds to respective information.

[0022] In an embodiment, the decoder decodes a predetermined unique combination of axial behaviors as an instruction for the decoder that a signalling period is commencing.

[0023] In an embodiment, the downhole communications receiver further comprises a vibration sensor in communication with the decoder for sensing vibration due to actuation of drill string fluid pumps thereby to detect commencement of a signaling period.

[0024] In an embodiment, the sensor comprises at least one inertial measurement unit (IMU).

[0025] In an embodiment, the sensor comprises at least one accelerometer.

[0026] In an embodiment, the downhole communications receiver further comprises at least one filter for fdtering out an influence of gravity on the at least one accelerometer.

[0027] In an embodiment, the downhole communications receiver further comprises a communication interface in communications with the decoder and the downhole electric circuit for conveying the information from the decoder to the downhole electric circuit.

[0028] In an embodiment, at least the decoder is a component of the downhole electric circuit.

[0029] In an embodiment, the decoder comprises: at least one microprocessor; and non- transitory processor-readable memory accessible by the at least one microprocessor and storing information in association with respective axial behaviors.

[0030] In an embodiment, the information for the BHA controller comprises instructions for the downhole electric circuit.

[0031] According to another aspect, there is provided a method for downhole communications for a drilling system, the drilling system comprising a drill string having a bottom hole assembly (BHA) within a borehole, the BHA having a downhole electric circuit and an associated downhole communications receiver, the method comprising: determining information to be communicated to the downhole electric circuit; based on predetermined associations between different items of information for the downhole electric circuit and corresponding different inducible axial behaviors of the BHA within the borehole, selecting an inducible axial behavior corresponding to the determined information; and during a signaling period, from a surface location physically manipulating the drill string to induce the selected axial behaviour in the BHA, wherein based on the predetermined associations the downhole communications receiver senses and decodes the induced axial behavior as the information for the downhole electric circuit.

[0032] In an embodiment, the method further comprises: prior to the signaling period, from the surface location physically manipulating the drill string to induce a predetermined unique combination of axial behaviors in the BHA as an instruction for the downhole communications receiver that a signalling period is commencing.

[0033] In an embodiment, the selected axial behavior comprises advancing or withdrawing the

BHA a respective distance within the borehole, wherein the respective distance corresponds to respective information.

[0034] In an embodiment, the selected axial behavior comprises advancing or withdrawing the

BHA a threshold distance within the borehole dining a particular time slot, wherein the particular time slot corresponds to respective information.

[0035] In an embodiment, the selected axial behavior comprises advancing or withdrawing the

BHA at a particular velocity within the borehole during a particular time slot, wherein the particular time slot corresponds to respective information.

[0036] In an embodiment, the selected axial behavior comprises advancing or withdrawing the

BHA at or above a threshold velocity within the borehole during a particular time slot, wherein the particular time slot corresponds to respective information.

[0037] In an embodiment, the determined information comprises instructions for the downhole electric circuit.

[0038] Other aspects and embodiments will become apparent upon reading the following description.

Brief Description of the Drawings

[0039] Embodiments of the invention will now be described with reference to the appended drawings in which:

[0040] Figure 1 is a partially -sectioned and not-to-scale drawing of a borehole into which a drill string has been inserted, the drill string being axially manipulable within the borehole from a surface location to induce corresponding axial behaviour of a bottom hole assembly (BHA), according to an embodiment;

[0041] Figure 2 is an enlarged depiction of the BHA of Figure 1 and showing, schematically, a downhole electric circuit that is a BHA controller, a measurement-while-drilling (MWD) system in communication with the BHA controller, and a downhole communication receiver (DCR) in communication with the BHA controller, according to an embodiment; [0042] Figure 3 is a schematic diagram of an alternative embodiment of the BHA controller in which an alternative embodiment of a DCR is integrated with the alternative BHA controller;

[0043] Figure 4 is a plot showing the position of a drill string during physical manipulation from a surface location before and during a signaling period to induce a corresponding axial behaviour in the BHA, according to an embodiment;

[0044] Figures 5A is a plot showing induced axial behaviour - in this embodiment in terms of acceleration, deceleration and maintenance of constant velocity - of the BHA sensed by the DCR before and during the signaling period, according to an embodiment; and

[0045] Figures 5B, 5C and 5D are plots showing the real-time decoding of the sensed axial behavior of the BHA into decoded instruction data for the BHA controller.

Detailed Description

[0046] Figure 1 is a partially sectioned and not-to-scale drawing of a borehole 10 formed in the ground G. A drill string 20 extends from a draw works 40 located at the surface proximal to borehole 10 and continues through borehole 10 down to a bottom hole assembly (BHA) 30. BHA 30 includes a drill bit 32.

[0047] In this embodiment, draw works 40 can spool and unspool drill string 20 under the control of an operator or with the assistance of automation. By exercising control over draw works 40, drill string 20 can be manipulated with respect to borehole 10 to be axially either drawn outwards, urged inwards, or held in position. In embodiments, control over the spooling or unspooling by draw works 40, and thus of the axial manipulation of drill string 20 within borehole 20, can be exercised directly by a human operator, or using automation devices and techniques.

[0048] As shown in Figure 1, axial manipulation of drill string 20 within borehole 10 from the surface induces a corresponding axial behaviour of the BHA 30 downhole. For example, if drill string 20 is being drawn outwards for a particular duration, BHA 30 will accordingly generally recede from the bottom of borehole 10 for the same duration. Similarly, if drill string 20 is being urged inwards for a particular duration, BHA 30 will accordingly generally move further towards or against the bottom of borehole 10 for the same duration. In addition, if drill string is being held in position for a duration, BHA 30 will be held in position for the duration.

[0049] It is well known to axially manipulate a drill string as described above for the purposes of re-orienting a drill bit according to a required change in drilling direction and/or for withdrawing a BHA from a borehole so that a component can be maintained or replaced. However, according to the present disclosure, systems and methods are provided for encoding information as axial manipulations of drill string 20, and for decoding the encoded information downhole for the use of a downhole electric circuit such as a BHA controller and/or a MWD system or some other downhole electric circuit or circuits or other kinds of electrical or electronic components intended to receive information.

[0050] In this embodiment, such encoded information is decoded downhole at BHA 30 by a downhole communications receiver 100 that senses the axial behaviours (back/forth linear movements and/or positions with respect to borehole 10 at particular times) that are induced in BHA 30 as a result of the axial manipulation of drill string 20 to encode the information. While not all axial behaviors induced in BHA 30 as the result of axial manipulation of drill string 20 will be intended to encode information, when axial behaviours are intended to encode information dining a signaling period, the encoded information can be decoded downhole and made available to a downhole electric circuit as operational information and/or instructions.

[0051] Figure 2 is an enlarged depiction of portions of BHA 30 and showing, schematically, a downhole electric circuit, in this embodiment a BHA controller 34, a measurement-while-drilling (MWD) system 36 in communication with BHA controller 34, and a downhole communication receiver (DCR) 100 in communication with BHA controller 34 thereby to provide decoded information to BHA controller 34, according to an embodiment.

[0052] In this embodiment, DCR 100 is physically associated with BHA 30 and includes a sensor 110 that produces electrical signals corresponding to the axial behaviors of BHA 30 within borehole 10. In this embodiment, sensor 110 is an accelerometer. Preferably, a filter is provided in conjunction with sensor 110 for filtering out the influence of gravity on sensor 110.

[0053] In alternative embodiments a sensor for producing electrical signals corresponding to the axial behaviors of BHA 30 within borehole 10 may be another form of inertial measurement unit (IMU) having multiple accelerometers or other sensors. In another embodiment, one or more components of MWD system 36 may serve double-duty as sensors for sensing the axial behaviors for decoding the axial behaviors into information. In yet another alternative embodiment a sensor for producing electrical signals corresponding to the axial behaviors of BHA 30 within borehole 10 may be an audio sensor for sensing a particular audio frequency, combination of frequencies, and/or magnitude of audio signals corresponding to an axial behavior of BHA 30. For example, while axially sliding within borehole 10, BHA 30 may scrape against an inner wall of borehole 10 thereby to generate downhole sounds that are not being generated while the BHA 30 is not axially sliding within borehole 10, and that are distinguishable from the scraping sounds that rotational movement alone of BHA 30 may generate. Various other kinds and combinations of sensors for sensing axial behaviors of BHA 30 and for producing electrical signals corresponding to such axial behaviors may be provided.

[0054] In this embodiment, DCR 100 also includes a decoder 120 in communication with sensor 110. Decoder 120 processes electrical signals from sensor 110 to decode the axial behaviors of BHA 30 as sensed by sensor 110 as information for BHA controller 34. In this embodiment, decoder 120 includes a microprocessor and non-transitory processor-readable memory accessible by the at least one microprocessor, and a timer for enabling decoder 120 to perceive intervals and decode information using time and/or time slots. The memory stores a predefined relationship between information conveyable to BHA controller 34 and respective axial behaviors. In this way, the axial behaviors sensed by sensor 110 can, as part of the decoding, be translated by the microprocessor to information based on the predefined relationship embodied in the memory. In embodiments, decoder 120 includes a plurality of microprocessor and/or microprocessor cores for handling decoding and information retrieval accordingly. In this embodiment, DCR 100 includes a communication interface 130 in communications with decoder 120 and BHA controller 34 for conveying the information gleaned during the decoding to BHA controller 34. Depending on the implementation, communication interface 130 may handle communications protocols as between DCR 100 and BHA controller 34, or may simply convey electrical signals corresponding to the decoded information along to an input port of BHA controller 34. Such decoded information might be operational information for BHA controller 36 or instructions for BHA controller 34 to modify operation of BHA 30 and/or to convey information from MWD system 36 uphole to the surface, or to react to the information in some other way.

[0055] Figure 3 is a schematic diagram of an alternative embodiment of BHA controller 34A in which an alternative embodiment of a DCR 100A is integrated as part of the alternative BHA controller 34A. In this embodiment, at least decoder 120A is a component of alternative BHA controller 34A. That is, in this embodiment, decoder 120A is software stored in memory of BHA controller 34A and executable on a processor of BHA controller 34A for configuring BHA controller 34A to conduct decoding as part of the overall systemic operations of BHA controller 34A.

[0056] Figure 4 is a plot showing the position of drill string 20 during physical manipulation from a surface location such as at draw works 40 before and during a signaling period to induce a corresponding axial behaviour in BHA 30, according to an embodiment. The following is applicable to operation of either decoder 120 or decoder 120A, though the following description will refer only to decoder 120 for ease of understanding.

[0057] In this embodiment, decoder 120 decodes a predetermined unique combination of axial behaviors as an instruction for decoder 120 that a signaling period will commence. It will be appreciated that, as described above, axial manipulation of drill string 20 inducing axial behavior of BHA 30 within borehole 10 will not always necessarily be for signaling purposes. As such, it is useful to inform decoder 120 when a signaling period is about to commence, so that decoder 120 can regard axial behaviors sensed by sensor 110 in response to axial behavior occurring during a signaling period as potentially decodable information, but can otherwise regard such axial behaviors as informationally meaningless. Furthermore, in this embodiment, a vibration sensor that is part of MWD system 36 communicates, via BHA controller 34, with decoder 120. The vibration sensor indicates that a threshold amount of vibration is being sensed in drill string 20, with such vibration being a result of actuation of drill string fluid pumps. This indication of vibration can be used to signal decoder 120 to begin listening for an initiation sequence that itself indicates the commencement of a signaling period is imminent. Such an initiation sequence might be expected within, for example, one minute of sensing the vibration.

[0058] An example initiation sequence serving as an instruction for decoder 120 that a signaling period will commence is shown in the plot of Figure 4. Initially, drill string 20 is held axially stationary at draw works 40. At a time T=0 seconds, drill string 20 is drawn outwards by 2-3 meters and then held axially stationary. Then, at a time T=2 seconds, drill string 20 is urged inwards back to its initial position. Then, at a time T=4 seconds, drill string 20 is drawn outwards again by 2-3 meters and then held axially stationary. Then at a time T=4 seconds, drill string 20 is urged inwards back to its initial position.

[0059] Figures 5A is a plot showing induced axial behaviour - in this embodiment in terms of acceleration and deceleration in each of two directions (inwards, outwards), and maintenance of constant velocity - of BHA 30 sensed by DCR 100 before and during a signaling period, according to an embodiment. In response to the axial behaviors induced in BHA 300 by the drawing outwards, holding stationary, and urging inwards of drill string 20 described above, sensor 110 of DCR 100 produces corresponding electrical signals. With sensor 110 being an accelerometer, the corresponding electrical signals are themselves indicative of sensed axial behaviors including acceleration and deceleration in each of two directions (inwards, outwards), along with maintenance of a constant velocity at particular times (including, for example, zero velocity). For example, the accelerometer may be configured to output the different signals under different acceleration conditions shown in Table 1, below.

Table 1

[0060] Different accelerometers, inertial measurement units (IMU), or other kinds of sensor usable for sensing axial behaviors will provide different schemas of electrical signals for doing so. [0061] Figures 5B, 5C and 5D are plots showing the real-time decoding of the sensed axial behavior of BHA 30 by decoder 120, based on electrical signals from sensor 110, into decoded information. The data plotted in Figure 5A is first integrated into calculated velocity (plotted in Figure 5B), and then integrated again to derive a calculated position (plotted in Figure 5C). In this embodiment, sensor 110 produces electrical signals corresponding to rates of the axial behaviors of the BHA within the borehole so that decoder 120 can process the electrical signals to decode the axial behaviors and the rates of the axial behaviors into the information for the BHA controller. In this way, position can be accurately calculated using not just the fact and timing of accelerating or decelerating in a particular direction, but the rate at which such accelerating or decelerating is happening over time. Referring to Figure 5C, prior to time To of a signaling period, the calculated positions correspond to the initiation sequence described above in connection with Figure 4. Decoder 120 recognizes the decoded initiation sequence as an instruction that a signaling period will commence at time To. Time To is the beginning of the corresponding signaling period.

[0062] In this embodiment, decoder 120 processes the electrical signals during the signaling period to determine that the BHA has been advanced or withdrawn a threshold distance within the borehole during a particular time slot, with the particular time slot corresponding to respective information. The threshold distance may be a sufficient distance, given the system, for ensuring the difference between a minor inadvertent movement and a deliberate axial manipulation can be discerned by DCR 100. For example, the selected threshold distance might be three (3) meters.

[0063] In this embodiment, a base-8 schema is used, wherein the particular time slot is one of eight (8) available time slots each corresponding to respective information. The durations of the time slots may be any decided-upon value, such as either one second or two or three seconds each, provided that the duration is sufficient for enabling axial manipulation of drill string 20 to be done to reliably and predictibly align with a desired time slot.

[0064] Table 2 shows time slots during a signalling period for each of two examples, the first of the examples having time slots that are two seconds in duration, and the second of the examples having time slots that are three seconds in duration. The actual duration of the time slots chosen for a given implementation must coordinated as between the DCR 100 and the operator or system that is to axially manipulate drill string 20 for signaling.

Table 2

[0065] A data structure having the information depicted in Table 2 is stored in memory within

DCR 100 thereby to facilitate translating movement of BHA 30 determined by decoder 120 during a particular time slot within the signaling period into corresponding information for BHA 30. Other bases may be used depending on the needs of the system and its operations.

[0066] Various techniques for indicating the end of a signaling period or its continuance may be used. A single word of information may be all that is desired to send downhole to BHA controller 34 in a given instance, but it may be desired to send multiple words of information sequentially in a given instance. Therefore, in this embodiment, DCR 100 is configured to regard a window of time corresponding to 8 time slots passing with no detected movement of BHA 30 by sensor 110 as an indication that communication has ended for the time being. When this occurs, decoder 120 of DCR 100 is entitled to thereafter regard any axial behavior of BHA 30 as sensed by sensor 110 not to be encoding any information. However, in order for more communications to be done at a later time, an initialization sequence such as that described above may again be induced from the surface for detection by decoder 120. On the other hand, so long as valid movement (i.e. a threshold amount of movement such as, for example, 3 metres) is induced during one of the time slots, decoder 120 will continue to decode and to be vigilant during the next window of 8 time slots, thereby extending successive signaling periods.

[0067] It will be appreciated that various communications protocols may be established based on the downhole sensing and decoding of information that has been encoded in induced axial behaviour of drill string 20, as disclosed herein. For example, a simple protocol might be established for ensuring an operator can be assured that information has been communicated reliably and predictably, for enabling the operator to correct for an error in information previously sent, and/or for clearing information previously communicated. Such a protocol might include making use of an uphole communications technology using a different physical and/or electrical transport technology as a feedback mechanism, so that one could receive confirmation at the surface that the correct information had indeed been communicated correctly downhole via the induced axial behaviour described herein. Such feedback might be in the form of measurements made by MWD system 36 indicative of, for example, a desired change in direction of BHA 30 or some other operational feedback.

[0068] A method for downhole communications according to this disclosure may be done by a human operator interacting with draw works 40 to axially manipulate drill string 30, or with the help of automation. Initially, information to be communicated to BHA controller 34 is determined. For example, it may be desired to communicate particular instructions to BHA controller 34. Then, if being done by a human operator interfacing with draw works 40, the operator would consult a table - perhaps writen on a card or displayed on a computer accessible to the operator - that would associate particular axial manipulations that could done and at what timing, with particular predetermined data words or entire predetermined complete combinations of data words. DCR 100 would have been preconfigured with the same associations, as stored in memory of decoder 120 or in another downhole location accessible to decoder 120. As such, based on such predetermined associations between different items of information for BHA controller 34 and corresponding different predetermined inducible axial behaviors of BHA 30 within borehole 10, an inducible axial behavior corresponding to the determined information would be selected.

[0069] As described above, in this embodiment, prior to the signaling period, the operator axially manipulates drill string 20 to induce a predetermined unique combination of axial behaviors in BHA 30 as an instruction for DCR 100 that a signalling period is commencing.

[0070] During a signaling period, in this embodiment, the operator would cause the physical manipulation of drill string 20 to induce the selected axial behaviour in the BHA 30. The operator controlling draw works 40 would instruct draw works 40 to spool or unspool drill string 20 at particular times and intervals. Based on the predetermined associations DCR 100 would sense and decode the induced axial behavior as the information for BHA controller 34.

[0071] As described above, in this embodiment, the selected axial behavior comprises advancing or withdrawing the BHA a threshold distance within the borehole during a particular time slot, wherein the particular time slot corresponds to respective information to be communication. The threshold distance would be configured prior to operation depending on the physical needs of the system for unambiguously conveying information in a system where a smaller than the threshold amount of axial movement might be likely to occur without deliberate manipulation. In this embodiment, the threshold distance is be three (3) meters. It will be appreciated that the information to be conveyed might be instructions and/or other information desired to be communicated to BHA controller 30. [0072] Although embodiments have been described with reference to the drawings, those of skill in the art will appreciate that variations and modifications may be made without departing from the spirit, scope and purpose of the invention as defined by the appended claims.

[0073] For example, rather than DCR 100 detecting a threshold amount of movement during a particular time slot during a signaling period, DCR 100 may be configured to perceive information received in another physical manner. In one example, decoder 120 may be configured to process the electrical signals from sensor 110 during signalling periods to determine that BHA 30 has been advanced or withdrawn a respective distance within the borehole, wherein the respective distance corresponds to respective information. Table 3 below shows an example association between such respective distances and corresponding information. The first of the distances in Table 3 corresponds to an example threshold distance of three (3) meters for, as described above, unambiguously conveying information in systems where a smaller than the threshold amount of axial movement might be likely to occur without deliberate manipulation.

Table 3

[0074] In the event that a system can be operationally configured such that negligible axial movement is likely to occur without deliberate manipulation, the threshold amount might be set to zero (0) meters or some other small amount.

[0075] Furthermore, the processing of axial behavior may be done in a manner that decodes information based on derived velocity, and does not have to be done solely based on derived position. For example, velocity data over time, derived by processing accelerometer data through a single integration step, can be sufficient for decoding axial behavior into information, such that double integrating such accelerometer data to derive position data as described above would not be required. As such, the decoder would be configured to process the electrical signals during signalling periods to determine that the BHA has been moved axially at a respective velocity with the borehole, with the respective axial velocity corresponding to respective information. Determination that the BHA has moved at a particular axial velocity during a particular time slot during the signaling period would indicate a respective item of information. Table 4 below shows an example association between such respective velocities and corresponding information. It will be appreciated that the particular Velocities and Information are shown for ease of understanding; a given implementation may require that there be larger steps between velocities, and/or that different information be represented.

Table 4

[0076] The downhole communications systems and methods described herein may be used for initiating a communications session. Alternatively or in some combination, the downhole communications systems and methods may be used to send feedback or confirmation messages, or other information such as instructions, in response to a downhole component having itself initiated such a communications session. The method and/or means by which communications are sent uphole does not have to be the same as the method and/or means by which communications for the same communications are sent downhole. For example, whereas downhole communications for a communication session may be done at least by using the methods and systems disclosed herein, uphole communications for the same communication session may be done using, for example, time pressure fluctuations in drilling fluid. Variations are possible.

[0077] In a given signaling scheme, non-movement of a BHA during a particular time slot of a signaling period may itself represent a respective piece of information.

[0078] While particular examples of data words and signaling protocols have been provided herein, alternatives are possible. Furthermore, depending on needs and costs, a given system will preferably be provided with the capability of being configured in the field. Such configuration might contemplate the need for a system to operate according to particular conditions that might be different were the system to be operated elsewhere and/or under different conditions. For example, rather than providing an instruction set of eight (8) possible instructions as described above, it may be useful to configure the system in the field to operate according to a reduced instruction set of fewer possible instructions, or to operate according to an expanded instruction set of greater possible instructions. By enabling modifications of the instruction set according to what is needed in the field at the time, provision of axial manipulations may be simplified for an operator, or access to a greater range of instructions by way of a greater range of possible axial manipulations may be offered. In an embodiment, multiple instruction sets might be stored in DCR 100, with each instruction set offering at least one instruction that would, once received by DCR 100, instruct DCR 100 to switch from the present instruction set to one of the other instruction sets. Such would be useful for adapting to changed ground conditions without necessarily requiring fully withdrawing BHA 30 for manual configuration. In such an example, one of the instructions in an eight-instruction instruction set might be made available for enabling DCR 100 to be instructed to operate according to a predetermined sixteen- instruction instruction set. In turn, the sixteen-instruction instruction set might make available an instruction for enabling DCR 100 to operate according to the reduced, eight-instruction instruction set. Variations and alternatives are possible.

[0079] While the downhole electric circuit in embodiments described in detail herein is a BHA controller, the present disclosure contemplates use of the systems and techniques described herein for providing information to other kinds of downhole electric circuits, combinations of circuits, or other components the receive or relay information and that may be incorporated into a drilling system. [0080] In embodiments described herein, a threshold distance travelled during a particular time slot is used as the determinant as to whether that time slot was being used for signalling. However, in an alternative embodiment, a particular threshold velocity of axial movement achieved during a time slot may be used as the determinant as to whether that time slot was chosen for signalling. In this way, to detect a signal occurring during a time slot, the distance the BHA was caused to axially move during a time slot could be any amount, including a small amount, provided that the speed with which it was caused to axially move reached or exceeded a threshold velocity. In addition to the distance itself not being determinative in such an embodiment, deriving velocity from acceleration data received from an accelerometer would require only a single integration process, rather than a double integration process. It will be appreciated that processing of the electrical signals could be done so as to calculate average speed during a time slot, so the decoder could then determine if the average speed during the time slot exceeded a threhold velocity. This approach would have the potential to enable the receiver to filter out certain short and unintended (those that were not intended to be induced) spikes in velocity by somewhat averaging them out. Alternatively, processing of the electrical signals could be done so that if the velocity of the BHA at any time during a time slot exceeded the threshold velocity, the decoder would register that the time slot was indeed being used for signaling.