CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional

Application No. 62/251,632 filed on November 5, 2015 and entitled "Process for Treating a Produced Water Stream" by James A. Keachie et al., which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] In the field of oil and gas exploration and production, the fluid material provided from underground reservoirs is generally termed "produced fluid". The produced fluid generally comprises naturally occurring dispersed and dissolved compounds, including the aromatic hydrocarbons desired, organic acids, phenols, and usually undesired gases and water, the water being generally termed 'produced water'.

[0003] The characteristics of produced water naturally vary, but generally contain a proportion of hydrocarbons. The oil-to-water ratio gradually decreases during production, leading to more water being produced than oil. This can lead to an oil-to-water ratio exceeding 1 :3, and produced water will normally be the largest single waste stream requiring disposal. Re-injection is not always feasible due to geographic and costs considerations, and increasing environmental restrictions in many jurisdictions now prevent the disposal of produced water with over 30 ppm hydrocarbons. Moreover, the environmental restrictions typically only cover dispersed hydrocarbons; they do not cover dissolved hydrocarbons or other organic components which would increase the Chemical Oxygen Demand (COD) of the water being disposed.

[0004] Thus, produced water generally undergoes at least some preliminary treatment to try and separate, and possibly recover the hydrocarbons as far as possible. One conventional treatment uses deoiling hydrocyclones as a first stage, which can recover a high amount of dispersed hydrocarbons, but has significant limitations associated with its operating envelope and the requirement for pressure to generate a centrifugal force, the primary driver of this operation. Also, the concentration and oil droplet sizes are critical in this technology, and where a pump is used upstream of the cyclone, the shearing effect on the oil droplets passing through the pump can reduce the efficiency significantly. [0005] Meanwhile, produced water flow rates also vary significantly across the life of a well or field. Even on a daily basis, the produced water flow rate can have a large variance. A deoiling hydrocyclone has best efficiency with a constant flow rate, and changes in flow rate of even 10 - 20% can affect its efficiency significantly. For these reasons, a produced water treatment process based on deoiling hydrocyclone may not be suitable to deal with increasing variants in produced water.

[0006] Other produced water treatment processes are known, generally based on gravity systems using additional gas or air injected to create a flotation effect, whereby small oil droplets are lifted to a surface for skimming out. These require a residence time in a suitable vessel in view of the increasing need to deal with produced water flow rate variants. As the commercial market is aiming to reduce residence time, and produce more compact oil production units, gravity based systems are increasingly required to try and provide better performance. This required increase in performance pushes gravity based systems to very high capability requirements, which can have an impact on reliability, operability and flexibility if design parameters change over a production field' s lifespan.

[0007] The publication "Treatment System of Produced Water with Supercritical

Carbon Dioxide" was delivered by Alsari A et al during the 2014 4th International Conference on Environment Science and Engineering was published in IPCEE vol68 (2014), pp40-44, and is incorporated herein by way of reference. This Alsari paper discusses a theoretical process for treating produced water based on extraction using supercritical carbon dioxide (hereinafter "SCC02") as an extracting agent. The process was simulated to calculate the system thermodynamic properties. The theoretical process was run at optimum conditions, which were found by running an optimisation routine on the main factors affecting the process. The conditions used were 32°C, 91 bar, and 1 : 1 mole of SCC02 to water, which resulted from the simulation process a recovery of 99% of the treated water.

[0008] However, this simulated process requires the use of an extraction column for the mass transfer of hydrocarbons in the water phase to the SCC02 phase. This results in a number of problems. Firstly, the physical size and therefore footprint of an extraction tower is generally large, even for small flow rates. Secondly, motion effects of floating offshore production vessels naturally significantly affect the balance and flows of streams in an extraction column, reducing the efficiency of an offshore extraction column. Thirdly, hydrocarbons and other contaminants that enter extraction columns from production can cause foaming, which can lead to fouling of the internal parts of the extraction column, leading to a reduction in the efficiency of the extraction column. In particular, solid contaminants are known to pose a significant problem. Lastly, the turndown associated with an extraction column can limit its effectiveness, and require special modifications or multiple extraction columns to deal with varying produced water flow rates.

[0009] Meanwhile, the Alsari A. et al paper also states a requirement for a 1 : 1 mole ratio of water to SCC02. This is a very high ratio, not only to provide enough SCC02 to flood an extraction column, but to be constantly replenished to supplement lost SCC02 after the extraction column.

[00010] Thus, the use of an extraction column to treat produced water even onshore requires a large OPEX and CAPEX for what seems to be a small operating envelope, even under best mode theoretical conditions.

[00011] Thus, there is a need in the art for a process for treating produced water based on non-theoretical conditions, in particular offshore conditions, and based on a significantly reduced OPEX and CAPEX.

SUMMARY

[00012] There is a system, process and apparatus for separating hydrocarbons from water using one or more supercritical fluids such as supercritical carbon dioxide.

[00013] In an embodiment, a process for separating hydrocarbons from water using supercritical carbon dioxide comprises at least the step of: providing the water and the supercritical carbon dioxide to a mixer to allow the hydrocarbons in the water to transfer to the supercritical carbon dioxide. Optionally, the mixer is a static mixer. Optionally the static mixer has at least first and second inlets and an outlet, and the static mixer is able to sustain supercritical carbon dioxide from the first inlet to the outlet.

[00014] In an embodiment, a process for separating hydrocarbons from water using supercritical carbon dioxide comprises at least the step of: co-currently mixing the water and the supercritical carbon dioxide to allow the hydrocarbons in the water to transfer to the supercritical carbon dioxide.

[00015] In an embodiment, a process for separating hydrocarbons from water using supercritical carbon dioxide comprises at least the steps of: adding one of the water and the supercritical carbon dioxide to the other, and agitating the so-formed mixture to allow the hydrocarbons in the water to transfer to the supercritical carbon dioxide.

[00016] In another embodiment, a process for separating hydrocarbons from water using supercritical carbon dioxide comprises at least the step of: bringing together the water and the supercritical carbon dioxide to allow the hydrocarbons in the water to transfer to the supercritical carbon dioxide, and separating the so-formed stream in a multiphase separator to provide a separate hydrocarbon-rich supercritical carbon dioxide stream and a separate hydrocarbon-lean produced water stream.

[00017] In an embodiment, a process for separating hydrocarbons from water using supercritical carbon dioxide comprises at least the step of: bringing together the water and the supercritical carbon dioxide to allow the hydrocarbons in the water to transfer to the supercritical carbon dioxide, reducing the supercritical conditions of the so formed hydrocarbon-rich supercritical carbon dioxide stream to cause a phase change in the carbon dioxide to provide a gaseous carbon dioxide stream and a recovered hydrocarbon stream, recovering the carbon dioxide for recycling, and replenishing the carbon dioxide with treated exhaust gas.

[00018] In an embodiment, a process for separating hydrocarbons from water using supercritical carbon dioxide comprises at least the step of: bringing together the water and the supercritical carbon dioxide to allow the hydrocarbons in the water to transfer to the supercritical carbon dioxide, and separating the so-formed stream to provide a separate hydrocarbon-rich supercritical carbon dioxide stream and a separate hydrocarbon-lean produced water stream, and injecting the hydrocarbon-lean produced water stream into a well wholly or substantially without depressurization.

[00019] Optionally, the water is produced water and provided as a produced water stream, optionally a hydrocarbon-rich produced water stream.

[00020] Optionally, the supercritical carbon dioxide is provided, either before, concurrently, or after providing the water.

[00021] Optionally, any so formed mixed supercritical carbon dioxide and water stream is passed into a separator.

[00022] Optionally, any so formed mixed supercritical carbon dioxide and water in the separator is separated into a separate hydrocarbon-rich supercritical carbon dioxide stream and a separate hydrocarbon-lean produced water stream.

[00023] Optionally, the supercritical conditions of the supercritical carbon dioxide stream after any separator are reduced to cause a phase change in the carbon dioxide, to provide a gaseous carbon dioxide stream and a recovered hydrocarbon stream.

[00024] In an embodiment, a process for separating hydrocarbons from water using supercritical carbon dioxide for treating a hydrocarbon-rich produced water stream to provide a hydrocarbon-lean produced water stream and a recovered hydrocarbon stream, the process comprises at least the steps of: (a) providing a static mixer having at least first and second inlets and an outlet, and able to sustain supercritical carbon dioxide from the first inlet to an outlet;

(b) providing a hydrocarbon-rich produced water stream into the first inlet of the static mixer;

(c) providing, either before, concurrently, or after step (b), a supercritical carbon dioxide stream into the second inlet of the static mixer;

(d) mixing the hydrocarbon-rich produced water stream and the supercritical carbon dioxide stream to wholly or substantially allow the hydrocarbons in the hydrocarbon- rich produced water stream to transfer to the supercritical carbon dioxide stream, to provide a mixed hydrocarbon-rich supercritical carbon dioxide and hydrocarbon-lean produced water stream;

(e) providing a supercritical carbon dioxide and hydrocarbon-lean produced water stream multiphase separator;

(f) passing the mixed hydrocarbon-rich supercritical carbon dioxide and hydrocarbon-lean produced water stream from the outlet of the static mixer into the separator;

(g) separating the mixed hydrocarbon-rich supercritical carbon dioxide and hydrocarbon-lean produced water stream in the separator, to provide a separate hydrocarbon- rich supercritical carbon dioxide stream and a separate hydrocarbon-lean produced water stream; and

(h) reducing the supercritical conditions of the separate hydrocarbon-rich supercritical carbon dioxide stream to cause a phase change in the carbon dioxide, to provide a gaseous carbon dioxide stream and a recovered hydrocarbon stream.

[00025] Optionally said process further comprises recovering the gaseous carbon dioxide stream for recycling into the supercritical carbon dioxide stream; and replenishing the supercritical carbon dioxide stream with one or more of the group comprising: treated exhaust gas, sweetened amine gas, permeate gas, carbon dioxide producing well gas, and carbon dioxide injection gas.

[00026] Optionally the process further comprises injecting the hydrocarbon-lean produced water stream into a well wholly or substantially without depressurization.

[00027] In an embodiment, an apparatus to separate hydrocarbons from water using one or more supercritical fluids such as supercritical carbon dioxide comprises a mixer able to mix the water and the supercritical carbon dioxide to wholly or substantially allow the hydrocarbons in the water to transfer to the supercritical carbon dioxide.

[00028] In an embodiment, an apparatus to treat a hydrocarbon-rich produced water stream to provide a hydrocarbon-lean produced water stream and a recovered hydrocarbon stream comprises:

(i) a static mixer having at least a first inlet for a supercritical carbon dioxide stream and a second inlet for a hydrocarbon-rich produced water stream, and an outlet, and able to sustain supercritical carbon dioxide from the first inlet to an outlet and mix the hydrocarbon-rich produced water stream and the supercritical carbon dioxide stream to wholly or substantially allow the hydrocarbons in the hydrocarbon-rich produced water stream to transfer to the supercritical carbon dioxide stream, to provide a mixed hydrocarbon-rich supercritical carbon dioxide and hydrocarbon-lean produced water stream;

(ii) a supercritical carbon dioxide and hydrocarbon-lean produced water stream separator able to separate the mixed hydrocarbon-rich supercritical carbon dioxide and hydrocarbon-lean produced water stream, to provide a separate hydrocarbon-rich supercritical carbon dioxide stream and a separate hydrocarbon-lean produced water stream; and

(iii) one or more phase changers to reduce the supercritical conditions of the separate hydrocarbon-rich supercritical carbon dioxide stream to cause a phase change in the carbon dioxide, to provide a gaseous carbon dioxide stream and a recovered hydrocarbon stream.

Optionally, the apparatus may include one or more stages or sections for recovery of the one or more supercritical fluids such as supercritical carbon dioxide.

[00029] Such stages or sections may include one or more of the group comprising:

C02/hydrocarbon separators, water/C02 separators, valves, phase changers, heat exchangers, compressors, mixers, and a combination of same.

[00030] Optionally there are one or more entry valves for changing the properties of one or more of the streams prior to their entry into any separator.

[00031] Optionally, one or more heat exchangers are for heat exchange between two or more of the streams in the apparatus, more optionally to increase the efficiency of the apparatus and/or to better align the properties of one or more of the streams prior to their subsequent use or action.

[00032] In one embodiment, the apparatus includes a valve and water/C02 separator able to separate the hydrocarbon-lean produced water stream to provide a carbon dioxide stream and a water stream.

[00033] In another embodiment, the apparatus includes three cascading water/C02 separators able to increasingly separate the hydrocarbon-lean produced water stream to provide two or more carbon dioxide stream and a water stream.

[00034] Optionally, the apparatus includes one or more carbon dioxide stages or sections able to recycle one or more of the so formed carbon dioxide streams into a supercritical carbon dioxide stream, optionally for use with the present process, apparatus, and systems.

[00035] Such stages or sections may include one or more of the group comprising: valves, phase changers, heat exchangers, compressors, mixers, and a combination of same.

[00036] Optionally, the apparatus includes one or more carbon dioxide replenishment stages or sections, optionally in combination with one or more of the carbon dioxide stages or sections able to recycle one or more of the so formed carbon dioxide streams into a supercritical carbon dioxide stream.

[00037] The various aspects described herein can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects can optionally be provided in combination with one or more of the optional features of the other aspects described herein. Also, optional features described in relation to one example can typically be combined alone or together with other features in different examples.

[00038] Various examples and aspects will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary embodiments and aspects and implementations. The processes, systems, and methods are also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the spirit and scope of the present processes, systems, and methods. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes.

[00039] Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present processes, systems, and methods. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present processes, systems, and methods.

[00040] In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of, "consisting", "selected from the group of consisting of, "including", or "is" preceding the recitation of the composition, element or group of elements and vice versa.

[00041] All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

[00042] The systems and processes described herein can be better understood with reference to the following detailed description together with the appended illustrative drawings in which like elements are numbered the same:

[00043] Figure 1 depicts a schematic diagram of an example of the process according to an embodiment.

[00044] Figure 2 depicts a schematic diagram of an example of a more developed process according to an embodiment.

DETAILED DESCRIPTION

[00045] The present description relates to separating hydrocarbons from water using a supercritical fluid or fluids such as supercritical carbon dioxide, in particular processes and apparatus for treating a hydrocarbon-rich produced water stream to provide a hydrocarbon- lean produced water stream, and a recovered hydrocarbon stream.

[00046] The present description broadly relates to processes for separating hydrocarbons from water with greater efficiency using one or more supercritical fluids such as supercritical carbon dioxide, particularly for but not limited to, upstream oil and gas applications.

[00047] The present processes, systems, and methods are useable with any water that contains hydrocarbons desired to be recovered. The present processes, systems, and methods are not limited by the nature or source of the hydrocarbons and water, or the amount of hydrocarbons in the water.

[00048] In the field of providing fluid material mainly comprising desired hydrocarbons from underground reservoirs, generally termed "produced fluid", other components, in particular water, are often a part of the produced fluid. Such water is known in the art as "produced water" and is termed as such hereinafter.

[00049] An example of such water provided as a stream can be termed a hydrocarbon- rich produced water stream, which could be provided from an upstream production separation system, optionally onshore, or optionally offshore.

[00050] Produced water conditions are generally dependent on any upstream separation process, and are thus usually different for every location and application.

[00051] The water can be pressurized, optionally in the range 50 - 100 barg. Optionally the water is already pressurized because of its upstream process conditions. Conventional oil and gas processing typically operates an upstream separation process at a pressure in the range 2 - 20 barg, although LNG separation may be at a higher pressure, and downstream processing may be at a lower pressure.

[00052] The temperature of the water, in particular produced water from an upstream production separation unit, may be at a temperature which needs to be either heated or cooled prior to provision to the present processes, systems, and methods.

[00053] A number of supercritical fluids are known, where a substance can be taken to a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. These include carbon dioxide, water, nitrous oxide and some hydrocarbons and organic compounds. The commonest is supercritical carbon dioxide, but the present processes, systems, and methods may use any suitable single or combination of supercritical fluids, and all references herein to supercritical carbon dioxide extend to any suitable single or combination of supercritical fluids.

[00054] Supercritical carbon dioxide (hereinafter "SCC02") is a fluid state of carbon dioxide when it is held at or above its critical temperature (304.25K) and critical pressure (72.9 atm or 7.35 MPa). t is a known solvent, and it can be provided using a carbon dioxide compressor and a suitable heat exchanger such as a supercritical cooler. The provision and nature of SCC02 are well known in the art, and it is known that its fluid state properties can be tuned to achieve different solvent properties.

[00055] In contrast to the use of an extraction column, the present description provides a first efficient process for separating hydrocarbons from water using SCC02 by simply providing the water and SCC02 to a mixer to allow the hydrocarbons in the water to transfer to the SCC02. Optionally, the mixer is a static mixer, and more optionally a static mixer which has at least first and second inlets and outlets. Optionally the mixer includes one or more pre-mixing chambers or areas such that mixing may occur either in a pre-mixer area, or within the main mixer or in a combination of same, prior to an outlet.

[00056] In a second way, the present description provides an efficient process for separating hydrocarbons from water using SCC02 by co-currently mixing the water and SCC02 to allow the hydrocarbons in the water to transfer to the SCC02.

[00057] Co-current mixing can be provided by a range of suitable apparatus which is simpler in construction and use than an extraction column, and which can more easily accommodate changes of flow rates, and which has stability of mixing for upstream oil and gas applications.

[00058] Co-current mixing can be carried out using one or more eductors, for example an eductor/injector/jet pump/ejector arrangement, to mix the water 5 and SCC02 to allow the hydrocarbons in the water to transfer to the SCC02. This method can utilise lift and non-lift type eductors.

[00059] Co-current mixing can also be carried out in dynamic or static mixers, optionally involving one or more inputs and outputs with a flow or flows of material thereinbetween, generally to provide a so formed mixed stream.

[00060] Optionally, the co-current mixing is provided by a mixer, optionally a static mixer, and more optionally a static mixer which has at least first and second inlets and outlets. Static mixers are able to provide continuous mixing of two or more fluid materials, and typically include one or more helical elements that can produce patterns of flow division and radial mixing in a manner known in the art. Static mixers include plate type mixers, generally comprising a series of plates or baffles at different arrangements or angles along the longitudinal axis, able to achieve mixing and blending of the inputted materials. A particular advantage of a static mixer is that a certain degree of motion of the mixer, such as when located offshore, and in particular on a vessel such as a production vessel, does not affect the mixing achieved within the mixer.

[00061] The mixer or other apparatus used to provide the co-current mixing can sustain

SCC02 from its input to at least one output. The conditions required for SCC02 are defined above, and maintaining carbon dioxide above its critical temperature and pressure are achievable alongside the pressure and temperature requirements for any hydrocarbon production separation system.

[00062] The present description also provides an efficient process for separating hydrocarbons from water using SCC02 by adding one of the water and the SCC02 to the other, and agitating the so-formed mixture to allow the hydrocarbons in the water to transfer to the supercritical carbon dioxide. The addition of one of the water and the SCC02 to the other may be carried out in any suitable apparatus or vessel, including a tank or reservoir, able to sustain SCC02 in its supercritical condition from an inlet to an outlet. Agitation of the so-formed mixture may be achieved using one or more stirrers, paddles, blades or other moveable or rotatable devices, able to encourage the interaction of the water and the SCC02 to allow the mass transfer of the hydrocarbons out of the water and into SCC02, optionally over a time period.

[00063] The mixture of water such as processed water and SCC02 formed by the mixing or mixer or addition described above, can then be provided to a water/SCC02 separator, able to maintain the supercritical conditions for the SCC02.

[00064] Separators used in the oil and gas processing fields are well known in the art, and generally comprise a pressure vessel used for separating an input material into at least two components, optionally three or more components. The components can be separated based on their phase or constitution. Oil and gas separators are known in the art, and are generally categorised into gas-liquid 2-phased separators or oil/gas/water 3-phase separators. They can include a preliminary stage or zone, and one or more baffles or weirs or other separation devices able to achieve separation of the two or more components, and provide them to one or more suitable and generally separate outlets from the separator. Density difference is the driving force of gravity separation, but other parameters such as viscosity and surface tension can also have an effect.

[00065] The present disclosure also includes a process for separating hydrocarbons from water using SCC02 by bringing together the water and the SCC02 to allow the hydrocarbons in the water to transfer to SCC02, there is an improvement in easily separating the so-formed stream in a multiphase water/SCC02 separator, to provide a separate hydrocarbon-rich SCC02 stream, and a separate hydrocarbon-lean produced water stream.

[00066] Optionally, multiphase water/SCC02 separator is a multiphase gravity separator, ore optionally a 3-phase gravity separator. Optionally, there are one or more separate SCC02 streams provided directly into the separator to assist distribution, polishing, etc.

[00067] Considering Stokes' Law, the density and viscosity differences between the hydrocarbon-rich SCC02 component and the hydrocarbon-lean water component will create a boundary layer thereinbetween, thus allowing both components to be separated and provided to separate outlets from the water/SCC02 separator. The density and viscosity of SCC02 and water are approximately 560kg/m ³ 0.0465cP, and 1000-1 100kg/m ³ 0.8 - lcP respectively. The water properties will depend on specific produced water composition.

[00068] Optionally, the so-formed stream provided to the multiphase water/SCC02 separator is the so-formed mixed stream described hereinabove, although the present processes, systems, and methods provide for one or more other water and SCC02 streams being provided.

[00069] The required residence time in the water/SCC02 separator may depend upon the flow conditions and other parameters of the input material, and could range from less than one minute to more than one minute. Any solids that enter the water/SCC02 separator may be maintained in the hydrocarbon-lean processed well stream due to their viscosity, and can either accumulate in the water/SCC02 separator for easy collection and removal, or may be drawn out of the separator with the hydrocarbon-lean produced water stream, for easy removal by filters or gravity devices, either continuously or in batch processes, as desired or necessary.

[00070] The process parameters of the water/SCC02 separator used can maintain the

SCC02 in its supercritical form (i.e. within the supercritical conditions defined above) from its input to its output, so that the hydrocarbons transferred into the SCC02 are maintained therewith through the water/SCC02 separator.

[00071] Optionally, the water provided after separation from the hydrocarbons, such as any hydrocarbon-lean water stream, is suitable for disposal. Where this water or water stream includes a higher than ambient amount of carbon dioxide, the stream may be passed into one or more suitable water/C02 separators, optionally at one or more reduced pressure over one or more stages, to recover the carbon dioxide, optionally for recycling back into a process as described herein as a source of carbon dioxide for the provision of the SCC02, and a final water stream. Any depressurisation may be provided over one or more stages, such as two stages, which improves the recovery of the carbon dioxide and improves the efficiency of the recycling carbon dioxide by reducing the recompression requirement compared to the use of a single stage depressurisation. That is, where some or all of the carbon dioxide can be recovered at an elevated pressure, optionally the same as or slightly less than the pressure of a phase separator, then less recompression is required to recycle the carbon dioxide back into the SCC02 stream.

[00072] The hydrocarbon-lean water has been found to have a significantly reduced hydrocarbon content of both dispersed and dissolved constituents. This hydrocarbon-lean water can be discharged into the sea at near atmospheric conditions. Thus, the present processes, systems, and methods have achieved the objective of extracting hydrocarbons from water to allow the disposal of the water thereafter in a manner that meets environmental regulations.

[00073] The hydrocarbon-lean water stream provided at the end of any such carbon dioxide separation stage or stages at or around ambient temperature, such as 25-40° C, and may be a source of cooling medium for cooling one or more hotter streams in another part of a process of the present processes, systems, and methods, such as hotter carbon dioxide as it leaves one or more compressors used to compress carbon dioxide being recycled to a suitable pressure.

[00074] In the same way, the hydrocarbon-rich water, such as produced water, provided for the present processes, systems, and methods may be at a suitable temperature to act as a cooling medium for cooling hot gases from a compressor such as hot carbon dioxide leaving one or more of its compressors as discussed hereinabove.

[00075] Any and all such heat exchanges are designed to reduce the energy demand on the rest of the process.

[00076] The process for separating hydrocarbons from water using supercritical carbon dioxide can use the hydrocarbon-lean produced water stream for injection into a well, wholly or substantially without depressurisation. By not depressurizing the hydrocarbon-lean water stream, the process provides a high pressure water stream that can result in a more efficient water injection process for enhanced oil recovery and the like. The present processes, systems, and methods can conserve energy which would otherwise be lost through conventional systems that depressurise a produced water stream. The present processes, systems, and methods can conserve the power already utilised to increase the pressure to the operating pressure required for the present processes, systems, and methods.

[00077] According to Mosavat and Torabi, 2014, it is also known that injecting CO2- saturated water into oil producing reservoirs will increase oil recovery. The present processes, systems, and methods may provide a hydrocarbon-lean produced water stream that has a high CO2 content, optionally CC^-saturated. Thus, the present processes, systems, and methods may further provide the use of a CC^-saturated hydrocarbon-lean produced water stream for injection into a well, wholly or substantially without depressurization.

[00078] Furthermore, the present processes, systems, and methods can provide a hydrocarbon-lean produced water stream for injection into a well from which typical well fouling contaminants such as hydrocarbons which can plug formations or provide sustenance to souring bacteria, have been removed.

[00079] The hydrocarbon-lean produced water stream provided by the present processes, systems, and methods for injection into a well may be injected into any suitable well, being the well from which the produced water stream is derived, or a different well, and 'directly' back into such a well, or indirectly after one or more other processes, treatments, or storage.

[00080] The SCC02 required at the beginning of the process may be provided from any suitable source. Conveniently, some or all of the carbon dioxide provided by one or more of the steps of a process is recycled to provide a source of carbon dioxide for the SCC02 required.

[00081] Even with full carbon dioxide recycling, it is possible that the SCC02 required at the beginning of the process will need to be replenished, typically due to the loss of carbon dioxide when one or more steps or stages described herein, such as a remainder still being dissolved in the hydrocarbon-lean water stream for disposal. One source of SCC02 for replenishment could be provided by a suitable tank or reservoir or other storage vessel of either SCC02, or a carbon dioxide source that requires being made supercritical. However, where room in any production system is limited, in particular on offshore vessels, it is difficult in the restricted space already existing on an offshore or floating production system to provide a new and separate SCC02 or carbon dioxide reservoir or tank.

[00082] Thus, in another way, it has been found that in a process for separating hydrocarbons from water using supercritical carbon dioxide comprising at least the step of replenishing the supercritical carbon dioxide stream with one or more of the group comprising: treated exhaust gas, sweetened amine gas, permeate gas, carbon dioxide producing well gas, and carbon dioxide injection gas.

[00083] Treated exhaust gas may be provided by any upstream or downstream production system in a manner known in the art, generally from power generation. A side stream of a flue gas could be taken for further treatment, such as a cooling stage, an amine extraction stage (to remove the C02 from water vapour, oxygen, nitrogen and any nitrious oxides produced from combustion The C02 can be recovered from amine via conventional methods of regeneration.

[00084] An alternative source of carbon dioxide is from a natural gas sweetening system. Sour gas recovered from the regeneration of amine from a sweetening process could be treated using a solid desiccant system, or alternatively to remove any ]¾S contamination from the carbon dioxide.

[00085] An alternative source of carbon dioxide is permeate gas of a carbon dioxide membrane removal system. The permeate gas can be of sufficient quality to utilize immediately after the membrane system. Further treatment may be required to increase the carbon dioxide purity which can be carried out largely based on the methods outlined above.

[00086] An alternative source of carbon dioxide will be from existing carbon dioxide flood systems, typically being carbon dioxide from a carbon dioxide producing well or a carbon dioxide injection system.

[00087] By replenishing the carbon dioxide for the process based on one or more of the above, i.e. a co-product in the upstream production system or an existing available source, little additional space is required to provide a suitable carbon dioxide source, providing further efficiency in the present process.

[00088] The hydrocarbon-rich SCC02 stream from any phase separator can optionally be heated, optionally by one or more of the higher temperature streams in part of the present process such as recycled hot carbon dioxide provided from a carbon dioxide compressor, to be depressurised in one or more stages to achieve a phase change in the carbon dioxide in order to provide as gaseous carbon dioxide stream in one or more stages, and a recovered hydrocarbon stream in one or more stages.

[00089] The depressurization may occur over one or more stages, generally by passage through one or more pressure reduction valves, and entering one or more C02/hydrocarbon separators at a reduced pressure and/or an increased temperature beyond the critical temperate and critical pressure of SCC02, in order to create a phase change. In this way, the hydrocarbon-rich SCC02 is converted into gaseous C02 and liquid hydrocarbons, which can easily be separated in a suitable separator, in particular a two-phase separator. The carbon dioxide gas will be wholly or substantially free from other components, and easily removable through one or more exits, often at or near the top of the separator optionally for subsequent recycle into the process. Meanwhile, the liquid hydrocarbon stream can be recovered, and returned back into the production system at elevated pressure.

[00090] An apparatus for carrying out the present methods and processes may comprise components known to those of skill in the man, such as a mixer, optionally a static mixer, as discussed herein, and a multiphase separator, optionally a multiphase gravity separator, able to separate a mixed hydrocarbon-rich supercritical carbon dioxide and hydrocarbon-lean produced water stream, to provide a separate hydrocarbon-rich supercritical carbon dioxide stream and a separate hydrocarbon-lean produced water stream. The phase changers able to reduce the supercritical conditions of the separate hydrocarbon-rich supercritical carbon dioxide stream to cause a phase change in the carbon dioxide may be any one or combination of pressure and temperature changers, including heat exchangers, valves, reducers, etc.

[00091] Referring now to figure 1, a preferred embodiment of a process for separating hydrocarbons from water using SCC02 is shown to include a source of produced water 20 that passes through a pump 22 to increase its pressure before being provided to a static mixer 26 through a first inlet 24.

[00092] The produced water 20 can be provided from an upstream production separation system (not shown) and is intended to be provided at a pressure above 50 barg, optionally greater than 70 barg, into the static mixer 26. The temperature of the produced water 20 may require heating or cooling to a suitable entry temperature into the static mixer 26, generally being the same or similar to the entry temperature of the SCC02 described hereinafter, generally being approximately 30°C.

[00093] Figure 1 also shows a source of SCC02 30 being supplied through a second inlet 32 to the static mixer 26. As described above, the supercritical conditions for SCC02 are generally 73 barg at approximately 31°C, and the source of SCC02 in the example shown in figure 1 will be described hereinafter.

[00094] It is possible for the produced water stream 20 to be provided in a continuous or batch form, and to have a constant or variable flowrate. It is possible for the SCC02 source 30 to be provided in a continuous or batch form, and to have a constant or variable flowrate. Optionally, the flowrate of the SCC02 stream 30 and the produced water stream 20 are wholly or substantially similar, and they are provided into the static mixer 26 wholly or substantially simultaneously. However, the present processes, systems, and methods allow the design of the static mixer 26 to be such that one of the said streams is provided either before, concurrently or after one of the other streams.

[00095] The static stream 26 achieves continuous mixing of the produced water stream

20 and the SCC02 30 by the internal design of the static mixer 26 to wholly or substantially allow the hydrocarbons in the hydrocarbon-rich produced water stream to transfer to the SCC02 stream 30, to provide at an outlet 34 of the static mixer 26, a mixed hydrocarbon-rich supercritical carbon dioxide and hydrocarbon-lean produced water stream 40. As described above, the conditions of the static mixer 26 are such that the supercritical conditions of the SCC02 are maintained from the inlet 32 to the outlet 34, such that the SCC02 component of the mixed stream 40 is maintained in its supercritical state.

[00096] The mixed stream 40 is provided through an inlet 44 to a multiphase water/SCC02 separator, being a 3-phase gravity separator 42 in this example 5. The 3-phase separator 42 may have any suitable internal arrangement and design, including a pre- separation zone for preliminary phase separation. Typically, a 3 -phase separator includes one or more baffles, and one or more weirs, such as the weir 46 shown in figure 1, to create, provide and/or control liquid levels or interface levels.

[00097] Considering Stokes' Law, the density and viscosity differences between the hydrocarbon-rich SCC02 component of the mixed stream and the droplet size of the SCC02 40, and the hydrocarbon-lean produced water component of the mixed stream 40, will create a boundary layer (not shown) thereinbetween. The boundary layer is below the height of the relevant internal weir 46, so that the 3 -phase separator 42 will separate the mixed stream 40 to provide a separate hydrocarbon-rich SCC02 stream 50 through a first outlet 52 of the 3- phase separator 42, and a separate hydrocarbon-lean produced water stream 54 through a second outlet 56 of the 3-phase separator 42.

[00098] Optionally, the 3-phase separator 42 includes a third gaseous outlet 58 to maintain the temperature and pressure at the required supercritical levels in the separator 42.

[00099] One or more SCC02 streams could be provided into the 3-phase separator 42 to help distribution or polishing therein. One possible SCC02 stream is a side stream 31 from the source of SCCO2 30.

[000100] The hydrocarbon-lean produced water stream 54 is saturated with carbon dioxide, while still having a pressure and temperature of the supercritical conditions of the SCC02 described above. Figure 1 shows passing the hydrocarbon-lean produced water stream 54 through a control value 60 and through an inlet 62 into a first water/C02 separator 64. The control valve 60 reduces the pressure of the hydrocarbon-lean produced water stream 54, such that carbon dioxide can be separated in the first separator 64 into a final water stream 66 through a bottom outlet of the first separator 64, and a carbon dioxide stream 70 through a top outlet 72 of the first separator 64.

[000101] The control valve 60 may be able to reduce the pressure in the first separator 64 to wholly or substantially ambient pressure, and the final water stream 66 may be for direct disposal inline with local environment regulations.

[000102] In an alternative arrangement, the control valve 60 does not fully reduce the pressure of the hydrocarbon-lean produced water stream 54 to ambient pressure, such that the final water stream 66 provided is still at an elevated pressure, and can be potentially injected directly into a well or wellbore (not shown) at the elevated pressure, (or further alternatively fed to a water injection system for further pressure increase). The final water stream 66 is already at a high pressure, possibly at the required high pressure for well injection, saving overall energy by its direct use. [000103] It may also be advantageous to inject a water stream saturated with carbon dioxide into a well for purposes of enhanced oil recovery as discussed above. The final water stream 66 may have a high carbon dioxide saturation already.

[000104] It is beneficial to recover the carbon dioxide stream 70, as discussed hereinafter.

[000105] The hydrocarbon-rich SCC02 stream 50, optionally at an above ambient temperature such as about 50°C, passes through a first heat exchanger 80 (discussed hereinafter), control valve 82, and through an inlet 86 into a C02/hydrocarbon separator 84. The control valve 82 is a pressure reduction valve which reduces the pressure of the hydrocarbon-rich SCC02 stream 50, optionally to an intermediate pressure such as 25-35 barg, so that in the C02/hydrocarbon separator 84, there is a phase change in the carbon dioxide to provide a gaseous carbon dioxide stream 88 through a top outlet 90, and a recovered hydrocarbon stream 92 through a bottom outlet 94.

[000106] The recovered hydrocarbon stream 92 has been found to be of sufficient high quality that it can be returned to a processing system at the required system pressure, such as the upstream processing system, and/or be provided for one or more other uses, optionally at a pressure through a control valve 96. The hydrocarbon recovery may provide an overall increase in the total oil recovery from the associated production process, and therefore the hydrocarbon source, as well as increased revenue for the operator, and decreased costs, both for chemical usage, and the additional steps required for conventional produced water treatment.

[000107] The carbon dioxide stream 88 can be combined with the carbon dioxide stream 70 from the first separator 64, and provided into a first C02 compressor 98 to provide a recycled pressurised carbon dioxide stream 100. Where the first carbon dioxide stream 70 is already at an above ambient pressure, then a part of the carbon dioxide streams being fed into the first compressor 98 is already at an above ambient pressure, reducing the overall energy required for the recompression of the carbon dioxide being recycled, thereby increasing the efficiency of the overall process shown in figure 1. The pressure of the recycled pressurised carbon dioxide stream 100 may be at or close to 75 barg, such that it is close to the critical pressure required to achieve supercritical carbon dioxide at a later stage.

[000108] The recycled carbon dioxide stream 100 can then pass through the first heat exchanger 80. As the recycled carbon dioxide stream 100 is at an elevated temperature after its compression, its passage through the first heat exchanger 80 helps to heat the hydrocarbon-rich SCC02 stream 50, thereby providing at least some of the energy required to change the temperature of the SCC02 in the hydrocarbon-rich SCC02 stream 50 (as part of generating the phase change and thus separation in the subsequent C02/hydrocarbon separator 84 as described above). The cooler recycled C02 stream 102 provided from the first heat exchanger 80 passes to a gate 104 through a first inlet 106. The gate 104 includes a second inlet 108 for the provision of any replenishing C02 from a C02 source 110 and a pre- treatment 112 stage.

[000109] The C02 source 1 10 may be a separate reservoir or tank. Optionally, the C02 source 1 10 is treated exhaust gas, in particular exhaust fuel gas provided from an upstream processing system, or another source as discussed above. The output C02 stream 114 from the gate 104 is then provided into a supercritical cooler 116 known in the art to cool the C02 to the required critical temperature (generally in the range 30 - 35 °C) to condense the C02 into SCC02 at the critical pressure and so provide the SCC02 stream 30 described above.

[000110] The example process shown in figure 1 includes a number of benefits and advantages described herein separately, which can be combined together as described to provide a more beneficial and more advantageous process, including a number of synergistic efficiencies, while still requiring a minimal number of apparatus and components.

[000111] The example also process can be applied to a suitable offshore vessel to treat downstream hydrocarbon-rich produced water without being effected by the vessels' motion through the use of a static mixer, and with substantial or complete carbon dioxide recycling, providing suitable final streams for subsequent uses as discussed hereinafter.

[000112] Figure 2 shows another exemplary system, partly based on the example shown in figure 1 and developed therefrom. Referring to figure 2, there is a source of produced water to provide a produced water stream 20 into a pump 22 and then into a static mixer 26 through first inlet 24. A second inlet 32 of the static mixer 26 provides a source of SCC02 30, and the static mixer 26 achieves co-current mixing of the input streams to allow the hydrocarbons in the produced water 20 to transfer to the SCC02.

[000113] The static mixer 26 provides a mixed hydrocarbon-rich SCC02 and hydrocarbon-lean produced water stream 40 through an outlet 34, which passes into a SCC02/water multiphase separator 42, able to separate the mixed stream 40 into a separate hydrocarbon-rich SCC02 stream 50 and a separate hydrocarbon-lean produced water stream 54 through respective outlets 52 and 56. The hydrocarbon-rich SCC02 stream 50 passes through a second heat exchanger 80a and a control valve 82 to be provided into a C02/hydrocarbon separator 84 through an inlet 86. Reduced pressure through the control valve 82, and some heating of the hydrocarbon-rich SCC02 stream 50 in the second heat exchanger 80a, allows a phase change of the carbon dioxide to occur in the C02/hydrocarbon separator 84, to provide a top first carbon dioxide recycle stream 88 through a top outlet, and a bottom recovered hydrocarbon stream 92 which is available for recovery and use through a control valve 96 as described above.

[000114] In one enhancement, the hydrocarbon-lean produced water stream 54 passes through a first stage control valve 60a into a first stage water/5 C02 separator 64a. The first stage control valve 60a depressurises the hydrocarbon-lean produced water stream 54 between the critical pressure required for SCC02, i.e. approximately 73 barg, to a first intermediate pressure, such as in the range 25 - 35 barg, to provide from the first stage water/C02 separator 64a a second recycle carbon dioxide stream 70a through a top outlet 72a, and an intermediate pressure produced water stream 120 through a bottom outlet 122, which passes through a second stage control valve 124 and into a second stage water/C02 separator 126 through an inlet 128. The second stage control valve 124 reduces the pressure further, such that there is a second stage depressurisation and separation of the carbon dioxide from the produced water. The second stage separator 126 provides a top carbon dioxide stream 130 through a top outlet 132, which passes into a first carbon dioxide compressor 134 to provide a compressed carbon dioxide stream 136, which passes through a third heat exchanger 138 and into a gas/liquid separator 140 through an inlet 142.

[000115] The second stage separator 126 also provides a bottom reduced pressure produced water stream 146 through a bottom outlet 148, which also passes through the third heat exchanger 138 to provide a final ambient or near ambient pressure produced water stream 150 ready for disposal, such as overboard.

[000116] The final produced water stream 150 can be suitably discharged or disposed of at near atmospheric conditions and within local environmental regulations. Any residuals in the final produced water stream 150 will mainly be any fine solids that have been carried through the process, and any still dissolved carbon dioxide. Any net change in carbon dioxide in the overall process, such as in the final produced water stream 150, should be negligible from the produced water that entered the process 20, but it is possible that some carbon dioxide can be lost, and hence the possible need for replenishment as discussed herein.

[000117] Optionally the final water stream 150 passes through a produced water cooler 152 discussed hereinafter to provide a cooler final water stream 153.

[000118] The third heat exchanger 138 can be used to help cool the compressed C02 stream 136, being at an elevated temperature after its passage through the first compressor 134, thereby removing the requirement for external cooling.

[000119] The gas/liquid separator 140 provides a final bottom discharge stream 154 for disposal with the final produced water stream 150, and a third recycle carbon dioxide stream 156.

[000120] Figure 2 shows a carbon dioxide manifold 160 able to accept the first, second and third carbon dioxide recycle streams 88, 70a and 156 respectively, optionally equalising their input conditions, in particular any different pressures, prior to combining the streams into a single recycle stream 162 which passes into a second carbon dioxide compressor 164. The second compressor 164 provides a compressed recycle carbon dioxide stream 168, which passes through the second heat exchanger 80a to heat the hydrocarbon-rich SCC02 stream 50 in the same manner as the heat exchanger 80 shown in figure 1, and which provides a cooler recycle carbon dioxide stream 170 into the gate 104 through a first inlet. Through a second inlet of the gate 104, there is provided a replenishing source of carbon dioxide 172, optionally through a pre-treatment stage 174 if required. The outlet stream 176 of the gate 104 can pass through a fourth heat exchanger 178 prior to passage through a supercritical cooler 116 to provide the source of the SCC02 stream 30 as described hereinbefore.

[000121] The fourth heat exchanger 178 provides another source of cooling for the recycle carbon dioxide stream 176 to maximise the efficiency of the overall process. Optionally the fourth heat exchanger 178 is the produced water cooler 152.

[000122] In another alternative arrangement, the produced water cooler 152 can be located on the inlet source of the produced water stream 20 to provide cooling of this stream.

[000123] The enhanced example process shown in figure 2 again includes a number of benefits and advantages described herein separately, which can be combined together as described to provide a more beneficial and more advantageous process, including a number of synergistic efficiencies, while still requiring a minimal number of apparatus and components. The enhanced example process shown in figure 2 can be applied to a suitable offshore vessel as discussed above. The enhanced example process shown in figure 2 is further beneficial by 5 using multi-stage depressurisation of the hydrocarbon-lean water stream, and a number of heat-exchanges between streams to improve the overall efficiency of the process.

[000124] While various embodiments in accordance with the principles disclosed herein have been shown and described above, modifications thereof may be made by one skilled in the art without departing from the spirit and the teachings of the disclosure. The embodiments described herein are representative only and are not intended to be limiting. Many variations, combinations, and modifications are possible and are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Accordingly, the scope of protection is not limited by the description set out above, but is defined by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention(s). Furthermore, any advantages and features described above may relate to specific embodiments, but shall not limit the application of such issued claims to processes and structures accomplishing any or all of the above advantages or having any or all of the above features.

[000125] Additionally, the section headings used herein are provided for consistency with the suggestions under 37 C.F.R. 1.77 or to otherwise provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings might refer to a "Field," the claims should not be limited by the language chosen under this heading to describe the so-called field. Further, a description of a technology in the "Background" is not to be construed as an admission that certain technology is prior art to any invention(s) in this disclosure. Neither is the "Summary" to be considered as a limiting characterization of the invention(s) set forth in issued claims. Furthermore, any reference in this disclosure to "invention" in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of the claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.

[000126] Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Use of the term "optionally," "may," "might," "possibly," and the like with respect to any element of an embodiment means that the element is not required, or alternatively, the element is required, both alternatives being within the scope of the embodiment(s). Also, references to examples are merely provided for illustrative purposes, and are not intended to be exclusive.

[000127] While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted or not implemented.

[000128] Also, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.