US20110197629A1 - Enhanced Natural Gas Liquid Recovery Process - Google Patents

Abstract

A method comprises receiving a hydrocarbon feed stream; separating the hydrocarbon feed stream into a heavy hydrocarbon rich stream and a recycle stream, wherein the recycle stream comprises a gas selected from the group consisting of carbon dioxide, nitrogen, air, and water; and separating the recycle stream into a natural gas liquids (NGL) rich stream and a purified recycle stream. A plurality of process equipment configured to receive a hydrocarbon feed stream, separate the hydrocarbon feed stream into a heavy hydrocarbon rich stream and a recycle stream comprising at least one C₃₊ hydrocarbon and a gas selected from the group consisting of carbon dioxide, nitrogen, air, and water, and separate the recycle stream into a NGL rich stream and a purified recycle stream.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• The present application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 12/122,336, filed May 16, 2008 by Eric Prim, and entitled “Natural Gas Liquid Recovery Process,” which claims priority to U.S. Provisional Patent Application Ser. No. 60/938,726, filed May 18, 2007 by Eric Prim, and entitled “NGL Recovery Process,” both of which are incorporated herein by reference as if reproduced in their entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
• Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
• Not applicable.
BACKGROUND
• Carbon dioxide (CO₂) is a naturally occurring substance in most hydrocarbon subterranean formations. Carbon dioxide also may be used for recovering or extracting oil and hydrocarbons from subterranean formations. One carbon dioxide based recovery process involves injecting carbon dioxide into an injection well, and recovering heavy hydrocarbons and perhaps some of the carbon dioxide from at least one recovery well. Carbon dioxide reinjection process also may produce natural gas liquids (NGLs).
SUMMARY
• In one aspect, the disclosure includes a method comprising receiving a hydrocarbon feed stream, separating the hydrocarbon feed stream into a heavy hydrocarbon rich stream and a carbon dioxide recycle stream, separating the carbon dioxide recycle stream into a NGL rich stream and a purified carbon dioxide recycle stream, and injecting the purified carbon dioxide recycle stream into a subterranean formation.
• In another aspect, the disclosure includes a plurality of process equipment configured to implement a method comprising receiving a recycle stream comprising at least one C₃₊ hydrocarbon and a gas selected from the group consisting of carbon dioxide, nitrogen, air, and water, and separating the recycle stream into a NGL rich stream and a purified recycle stream, wherein the NGL rich stream comprises less than about 70 percent of the C₃₊ hydrocarbons from the recycle stream.
• In a third aspect, the disclosure includes a method comprising selecting a first recovery rate for a NGL recovery process, estimating the economics of the NGL recovery process based on the first recovery rate, selecting a second recovery rate that is different from the first recovery rate, estimating the economics of the NGL recovery process based on the second recovery rate, and selecting the first recovery rate for the NGL recovery process when the estimate based on the first recovery rate is more desirable than the estimate based on the second recovery rate.
• In a fourth aspect, the disclosure includes a method comprising receiving a hydrocarbon feed stream; separating the hydrocarbon feed stream into a heavy hydrocarbon rich stream and a recycle stream, wherein the recycle stream comprises a gas selected from the group consisting of carbon dioxide, nitrogen, air, and water; and separating the recycle stream into a NGL rich stream and a purified recycle stream.
• In a fifth aspect, the disclosure includes a plurality of process equipment configured to receive a hydrocarbon feed stream; separate the hydrocarbon feed stream into a heavy hydrocarbon rich stream and a recycle stream comprising at least one C₃₊ hydrocarbon and a gas selected from the group consisting of carbon dioxide, nitrogen, air, and water; and separate the recycle stream into a NGL rich stream and a purified recycle stream.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a process flow diagram for an embodiment of a carbon dioxide reinjection process.
• FIG. 2 is a schematic diagram of an embodiment of a NGL recovery process.
• FIG. 3 is a chart depicting an embodiment of the relationship between the NGL recovery rate and the energy requirement.
• FIG. 4 is a schematic diagram of an embodiment of a NGL upgrade process.
• FIG. 5 is a process flow diagram for another embodiment of a reinjection process.
• FIG. 6 is a schematic diagram of another embodiment of a NGL recovery process.
• FIG. 7 is a flowchart of an embodiment of a NGL recovery optimization method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.
• Disclosed herein is a NGL recovery process that may be implemented as part of a carbon dioxide reinjection process to recover NGLs from a carbon dioxide recycle stream. When implementing a carbon dioxide reinjection process, the carbon dioxide is typically injected downhole into an injection well and a stream comprising hydrocarbons and carbon dioxide is generally recovered from a recovery well. The carbon dioxide may be separated from the heavy hydrocarbons and then recycled downhole, e.g., in the reinjection well. In some cases, the carbon dioxide recycle stream may comprise some NGLs, which may be recovered prior to injecting the carbon dioxide recycle stream downhole. The NGL recovery process may be optimized by weighing the NGL recovery rate against the amount of energy expended on NGL recovery.
• FIG. 1 illustrates an embodiment of a carbondioxide reinjection process100. The carbondioxide reinjection process100 may receive hydrocarbons and carbon dioxide from asubterranean hydrocarbon formation114, separate heavy hydrocarbons and some of the NGLs from the carbon dioxide, and inject the carbon dioxide downhole. As shown inFIG. 1, additional process steps may be included in the carbon dioxide reinjection process, such as compressing the carbon dioxide, dehydrating the carbon dioxide, and/or adding additional carbon dioxide to the carbon dioxide recycle stream. The specific steps in the carbondioxide reinjection process100 are explained in further detail below.
• The carbondioxide reinjection process100 may receive ahydrocarbon feed stream152 from asubterranean hydrocarbon formation114. Thehydrocarbon feed stream152 may be obtained from at least one recovery well as indicated by the upward arrow inFIG. 1, but also may be obtained from other types of wells. In addition, thehydrocarbon feed stream152 may be obtained from thesubterranean hydrocarbon formation114 using any suitable method. For example, if a suitable pressure differential exists between thesubterranean hydrocarbon formation114 and the surface, thehydrocarbon feed stream152 may flow to the surface via the pressure differential. Alternatively, surface and/or downhole pumps may be used to draw thehydrocarbon feed stream152 from thesubterranean hydrocarbon formation114 to the surface.
• Although the composition of thehydrocarbon feed stream152 will vary from one location to another, thehydrocarbon feed stream152 may comprise carbon dioxide, methane, ethane, NGLs, heavy hydrocarbons, hydrogen sulfide (H₂S), helium, nitrogen, water, or combinations thereof. The term “hydrocarbon” may refer to any compound comprising, consisting essentially of, or consisting of carbon and hydrogen atoms. The term “natural gas” may refer to any hydrocarbon that may exist in a gas phase under atmospheric or downhole conditions, and includes methane and ethane, but also may include diminishing amounts of C₃-C₈hydrocarbons. The term “natural gas liquids” or NGLs may refer to natural gases that may be liquefied without refrigeration, and may include C₃-C₈hydrocarbons. Both natural gas and NGL are terms known in the art and are used herein as such. In contrast, the term “heavy hydrocarbons” may refer to any hydrocarbon that may exist in a liquid phase under atmospheric or downhole conditions, and generally includes liquid crude oil, which may comprise C₉₊ hydrocarbons, branched hydrocarbons, aromatic hydrocarbons, and combinations thereof.
• Thehydrocarbon feed stream152 may enter aseparator102. Theseparator102 may be any process equipment suitable for separating at least one inlet stream into a plurality of effluent streams having different compositions, states, temperatures, and/or pressures. For example, theseparator102 may be a column having trays, packing, or some other type of complex internal structure. Examples of such columns include scrubbers, strippers, absorbers, adsorbers, packed columns, and distillation columns having valve, sieve, or other types of trays. Such columns may employ weirs, downspouts, internal baffles, temperature control elements, and/or pressure control elements. Such columns also may employ some combination of reflux condensers and/or reboilers, including intermediate stage condensers and reboilers. Alternatively, theseparator102 may be a phase separator, which is a vessel that separates an inlet stream into a substantially vapor stream and a substantially liquid stream, such as a knock-out drum, flash drum, reboiler, condenser, or other heat exchanger. Such vessels also may have some internal baffles, temperature control elements, and/or pressure control elements, but generally lack any trays or other type of complex internal structure commonly found in columns. Theseparator102 also may be any other type of separator, such as a membrane separator. In a specific embodiment, theseparator102 is a knockout drum. Finally, theseparator102 may be any combination of the aforementioned separators arranged in series, in parallel, or combinations thereof.
• Theseparator102 may produce aheavy hydrocarbon stream154 and a carbondioxide recycle stream156. Theheavy hydrocarbon stream154 may comprise most of the heavy hydrocarbons from thehydrocarbon feed stream152. In embodiments, theheavy hydrocarbon stream154 may comprise at least about 90 percent, at least about 95 percent, at least about 99 percent, or substantially all of the heavy hydrocarbons from thehydrocarbon feed stream152. Theheavy hydrocarbon stream154 may be sent to a pipeline for transportation or astorage tank104, where it is stored until being transported to another location or being further processed. In contrast, the carbondioxide recycle stream156 may comprise most of the carbon dioxide from thehydrocarbon feed stream152. In embodiments, the carbondioxide recycle stream156 may comprise at least about 90 percent, at least about 95 percent, at least about 99 percent, or substantially all of the carbon dioxide from thehydrocarbon feed stream152. Similarly, the carbondioxide recycle stream156 may comprise at least about 80 percent, at least about 90 percent, at least about 95 percent, or substantially all of the natural gas from thehydrocarbon feed stream152. All of the percentages referred to herein are molar percentages until otherwise specified.
• The carbondioxide recycle stream156 may enter acompressor106. Thecompressor106 may be any process equipment suitable for increasing the pressure, temperature, and/or density of an inlet stream. Thecompressor106 may be configured to compress a substantially vapor phase inlet stream, a substantially liquid phase inlet stream, or combinations thereof. As such, the term “compressor” may include both compressors and pumps, which may be driven by electrical, mechanical, hydraulic, or pneumatic means. Specific examples ofsuitable compressors106 include centrifugal, axial, positive displacement, turbine, rotary, and reciprocating compressors and pumps. In a specific embodiment, thecompressor106 is a turbine compressor. Finally, thecompressor106 may be any combination of the aforementioned compressors arranged in series, in parallel, or combinations thereof.
• Thecompressor106 may produce a compressed carbondioxide recycle stream158. The compressed carbondioxide recycle stream158 may contain the same composition as the carbondioxide recycle stream156, but at a higher energy level. The additional energy in the compressed carbondioxide recycle stream158 may be obtained from energy added to thecompressor106, e.g., the electrical, mechanical, hydraulic, or pneumatic energy. In embodiments, difference in energy levels between the compressed carbondioxide recycle stream158 and the carbondioxide recycle stream156 is at least about 50 percent, at least about 65 percent, or at least about 80 percent of the energy added to thecompressor106.
• The compressed carbondioxide recycle stream158 may enter adehydrator108. Thedehydrator108 may remove some or substantially all of the water from the compressed carbondioxide recycle stream158. Thedehydrator108 may be any suitable dehydrator, such as a condenser, an absorber, or an adsorber. Specific examples ofsuitable dehydrators108 include refrigerators, molecular sieves, liquid desiccants such as glycol, solid desiccants such as silica gel or calcium chloride, and combinations thereof. Thedehydrator108 also may be any combination of the aforementioned dehydrators arranged in series, in parallel, or combinations thereof. In a specific embodiment, thedehydrator108 is a glycol unit. Any water accumulated within or exiting from thedehydrator108 may be stored, used for other processes, or discarded.
• Thedehydrator108 may produce a dehydrated carbondioxide recycle stream160. The dehydrated carbondioxide recycle stream160 may contain little water, e.g., liquid water or water vapor. In embodiments, the dehydrated carbondioxide recycle stream160 may comprise no more than about 5 percent, no more than about 3 percent, no more than about 1 percent, or be substantially free of water.
• The dehydrated carbondioxide recycle stream160 may enter aNGL recovery process110. TheNGL recovery process110 may separate the dehydrated carbondioxide recycle stream160 into a NGLrich stream162 and a purified carbondioxide recycle stream164. The NGLrich stream162 may only comprise a portion of the total NGLs from the dehydrated carbondioxide recycle stream160. For example, the NGLrich stream162 may comprise less than about 70 percent, from about 10 percent to about 50 percent, or from about 20 percent to about 35 percent of the NGLs from the dehydrated carbondioxide recycle stream160. By taking a less aggressive cut of the NGLs and/or disregarding the recovery of methane, ethane, and optionally propane from the dehydrated carbondioxide recycle stream160, theNGL recovery process110 may produce a relatively high quality NGLrich stream162 with relatively little process equipment or energy. A specific example of a suitableNGL recovery process110 is shown inFIG. 2 and described in further detail below.
• As mentioned above, theNGL recovery process110 may produce a relatively high-quality NGLrich stream162. Specifically, while theNGL recovery process110 recovers only a portion, e.g., about 20 to about 35 percent, of the NGLs in the dehydrated carbondioxide recycle stream160, the resulting NGLrich stream162 is relatively lean with respect to methane and the acid gases. For example, the NGLrich stream162 may comprise most of the butane and heavier components from the dehydrated carbondioxide recycle stream160. For example, the NGLrich stream162 may comprise at least about 90 percent, at least about 95 percent, at least about 99 percent, or substantially all of the C₄₊ from the dehydrated carbondioxide recycle stream160. In an embodiment, the NGLrich stream162 may comprise at least about 20 percent, at least about 40 percent, at least about 60 percent, or at least about 70 percent of the C₃₊ from the dehydrated carbondioxide recycle stream160. In embodiments, the NGLrich stream162 may comprise no more than about 10 percent, no more than about 5 percent, no more than about 1 percent, or be substantially free of ethane. Similarly, the NGLrich stream162 may comprise no more than about 5 percent, no more than about 3 percent, no more than about 1 percent, or be substantially free of methane. Moreover, the NGLrich stream162 may comprise no more than about 5 percent, no more than about 3 percent, no more than about 1 percent, or be substantially free of acid gases, such as carbon dioxide or hydrogen sulfide. It will be realized that the composition of the NGLrich stream162 may be dependent on the dehydrated carbondioxide recycle stream160 composition. The examples provided below show the composition of the NGLrich stream162 for three different dehydrated carbondioxide recycle stream160 compositions. The NGLrich stream162 may be sent to a pipeline for transportation or a storage tank, where it is stored until being transported to another location or being further processed.
• In an embodiment, the NGLrich stream162 optionally may be processed in anNGL upgrade process170. TheNGL upgrade process170 may produce a relativelyheavy NGL stream172 that may be combined with theheavy hydrocarbon stream154. When combined, theheavy NGL stream172 and theheavy hydrocarbon stream154 may meet or exceed the pipeline and/or transportation thresholds or standards for a heavy hydrocarbon stream, as described in more detail with respect toFIG. 4. A relativelylight NGL stream174 may be sent to a pipeline for transportation or a storage tank, where it may be stored until transported to another location or further processed, as described in more detail with respect toFIG. 4. A specific example of a suitableNGL upgrade process170 is shown inFIG. 5 and described in further detail below.
• As mentioned above, theNGL recovery process110 may produce a purified carbondioxide recycle stream164. The purified carbondioxide recycle stream164 may comprise most of the carbon dioxide from the dehydrated carbondioxide recycle stream160, as well as some other components such as methane, ethane, propane, butane, nitrogen, and hydrogen sulfide. In embodiments, the purified carbondioxide recycle stream164 may comprise at least about 90 percent, at least about 95 percent, at least about 99 percent, or substantially all of the carbon dioxide from the dehydrated carbondioxide recycle stream160. In addition, the purified carbondioxide recycle stream164 may comprise at least about 90 percent, at least about 95 percent, at least about 99 percent, or substantially all of the methane from the dehydrated carbondioxide recycle stream160. As such, the purified carbondioxide recycle stream164 may comprise at least about 65 percent, at least about 80 percent, at least about 90 percent, or at least about 95 percent carbon dioxide. In embodiments, the purified carbondioxide recycle stream164 may comprise no more than about 10 percent, no more than about 5 percent, no more than about 1 percent, or be substantially free of C₃₊. Similarly, the purified carbondioxide recycle stream164 may comprise no more than about 20 percent, no more than about 10 percent, no more than about 5 percent, or be substantially free of C₂₊.
• The purified carbondioxide recycle stream164 may enter acompressor112. Thecompressor112 may comprise one or more compressors, such as thecompressor106 described above. In a specific embodiment, thecompressor112 is a turbine compressor. Thecompressor112 may compress the purified carbondioxide recycle stream164, thereby producing a carbondioxide injection stream168. The carbondioxide injection stream168 may contain the same composition as the purified carbondioxide recycle stream164, but at a higher energy level. The additional energy in the carbondioxide injection stream168 may be obtained from energy added to thecompressor112, e.g., the electrical, mechanical, hydraulic, or pneumatic energy. In some embodiments, the difference in energy levels between the carbondioxide injection stream168 and the purified carbondioxide recycle stream164 is at least about 50 percent, at least about 65 percent, or at least about 80 percent of the energy added to thecompressor112.
• In some embodiments, amakeup stream166 may be combined with either the purified carbondioxide recycle stream164 or the carbondioxide injection stream168. Specifically, as the carbondioxide reinjection process100 is operated, carbon dioxide and other compounds will be lost, e.g., by replacing the hydrocarbons in thesubterranean hydrocarbon formation114, by leakage into inaccessible parts of thesubterranean hydrocarbon formation114, and/or to other causes. Alternatively, it may be desirable to increase the amount of carbon dioxide and other compounds injected downhole. As such, themakeup stream166 may be combined with either the purified carbondioxide recycle stream164 and/or the carbondioxide injection stream168, for example in thecompressor112. Alternatively or additionally, themakeup stream166 may be combined with the carbondioxide recycle stream156, the compressed carbondioxide recycle stream158, the dehydrated carbondioxide recycle stream160, or combinations thereof. Themakeup stream166 may comprise carbon dioxide, nitrogen, methane, ethane, air, water, or any other suitable compound. In an embodiment, themakeup stream166 comprises at least 75 percent, at least 85 percent, or at least 95 percent carbon dioxide, nitrogen, methane, air, water, or combinations thereof. Finally, the carbondioxide injection stream168 may be sent to a carbon dioxide pipeline rather than being immediately injected downhole. In such a case, the carbondioxide injection stream168 may meet the carbon dioxide pipeline specifications. One example of a carbon dioxide pipeline specification is: at least about 95 percent carbon dioxide, substantially free of free water, no more than about 30 pounds of vapor-phase water per million cubic feet (mmcf) of product, no more than about 20 parts per million (ppm) by weight of hydrogen sulfide, no more than about 35 ppm by weight of total sulfur, a temperature of no more than about 120° F., no more than about four percent nitrogen, no more than about five percent hydrocarbons (wherein the hydrocarbons do not have a dew point exceeding about −20° F.), no more than about 10 ppm by weight of oxygen, and more than about 0.3 gallons of glycol per mmcf of product (wherein the glycol is not in the liquid state at the pressure and temperature conditions of the pipeline).
• FIG. 2 illustrates an embodiment of aNGL recovery process200. TheNGL recovery process200 may recover some of the NGLs from a carbon dioxide recycle stream described above. For example, theNGL recovery process200 may be implemented as part of the carbondioxide reinjection process100, e.g., by separating the dehydrated carbondioxide recycle stream160 into a NGLrich stream162 and a purified carbondioxide recycle stream164. Alternatively, theNGL recovery process200 may be implemented as a stand-alone process for recovering NGLs from a hydrocarbon containing stream.
• TheNGL recovery process200 may begin by cooling the dehydrated carbondioxide recycle stream160 in aheat exchanger202. Theheat exchanger202 may be any equipment suitable for heating or cooling one stream using another stream. Generally, theheat exchanger202 is a relatively simple device that allows heat to be exchanged between two fluids without the fluids directly contacting each other. Examples ofsuitable heat exchangers202 include shell and tube heat exchangers, double pipe heat exchangers, plate fin heat exchangers, bayonet heat exchangers, reboilers, condensers, evaporators, and air coolers. In the case of air coolers, one of the fluids comprises atmospheric air, which may be forced over tubes or coils using one or more fans. In a specific embodiment, theheat exchanger202 is a shell and tube heat exchanger.
• As shown inFIG. 2, the dehydrated carbondioxide recycle stream160 may be cooled using the cooled, purified carbondioxide recycle stream258. Specifically, the dehydrated carbondioxide recycle stream160 is cooled to produce the cooled carbondioxide recycle stream252, and the cooled, purified carbondioxide recycle stream258 is heated to produce the purified carbondioxide recycle stream164. The efficiency of the heat exchange process depends on several factors, including the heat exchanger design, the temperature, composition, and flowrate of the hot and cold streams, and/or the amount of thermal energy lost in the heat exchange process. In embodiments, the difference in energy levels between the dehydrated carbondioxide recycle stream160 and the cooled carbondioxide recycle stream252 is at least about 60 percent, at least about 70 percent, at least about 80, or at least about 90 percent of the difference in energy levels between the cooled, purified carbondioxide recycle stream258 and the purified carbondioxide recycle stream164.
• The cooled carbondioxide recycle stream252 then enters aNGL stabilizer204. TheNGL stabilizer204 may comprise aseparator206, acondenser208, and areboiler210. Theseparator206 may be similar to any of the separators described herein, such asseparator102. In a specific embodiment, theseparator206 is a distillation column. Thecondenser208 may receive an overhead254 from theseparator206 and produce the cooled, purified carbondioxide recycle stream258 and areflux stream256, which is returned to theseparator206. Thecondenser208 may be similar to any of the heat exchangers described herein, such asheat exchanger202. In a specific embodiment, thecondenser208 is a shell and tube, kettle type condenser coupled to a refrigeration process, and contains a reflux accumulator. As such, thecondenser208 may remove someenergy282 from thereflux stream256 and cooled, purified carbondioxide recycle stream258, typically by refrigeration. The cooled, purified carbondioxide recycle stream258 is substantially similar in composition to the purified carbondioxide recycle stream164 described above. Similarly, thereboiler210 may receive abottoms stream260 from theseparator206 and produce a sour NGLrich stream264 and a boil-upstream262, which is returned to theseparator206. Thereboiler210 may be like any of the heat exchangers described herein, such asheat exchanger202. In a specific embodiment, thereboiler210 is a shell and tube heat exchanger coupled to a hot oil heater. As such, thereboiler210 adds someenergy284 to the boil-upstream262 and the sour NGLrich stream264, typically by heating. The sour NGLrich stream264 may be substantially similar in composition to the NGLrich stream162, with the exception that the sour NGLrich stream264 has some additional acid gases, e.g.,acid gases270 described below.
• The sour NGLrich stream264 then may be cooled in anotherheat exchanger212. Theheat exchanger212 may be like any of the heat exchangers described herein, such asheat exchanger202. For example, theheat exchanger212 may be an air cooler as described above. A cooled, sour NGLrich stream266 may exit theheat exchanger212 and enter a throttlingvalve214. The throttlingvalve214 may be an actual valve such as a gate valve, globe valve, angle valve, ball valve, butterfly valve, needle valve, or any other suitable valve, or may be a restriction in the piping such as an orifice or a pipe coil, bend, or size reduction. The throttlingvalve214 may reduce the pressure, temperature, or both of the cooled, sour NGLrich stream266 and produce a low-pressure sour NGLrich stream268. The cooled, sour NGLrich stream266 and the low-pressure sour NGLrich stream268 have substantially the same composition as the sour NGLrich stream264, albeit with lower energy levels.
• The low-pressure sour NGLrich stream268 then may be sweetened in aseparator216. Theseparator216 may be similar to any of the separators described herein, such asseparators102 or206. In an embodiment, theseparator216 may be one or more packed columns that use a sweetening process to remove acid gases from the low-pressure sour NGLrich stream268. Suitable sweetening processes include amine solutions, physical solvents such as SELEXOL or RECTISOL, mixed amine solution and physical solvents, potassium carbonate solutions, direct oxidation, absorption, adsorption using, e.g., molecular sieves, or membrane filtration. Theseparator216 may produce the NGLrich stream162 described above. In addition, anyacid gases270 accumulated within or exiting from theseparator216 may be stored, used for other processes, or suitably disposed of. Finally, whileFIGS. 1 and 2 are described in the context of carbon dioxide reinjection, it will be appreciated that the concepts described herein can be applied to other reinjection processes, for example those using nitrogen, air, or water.
• FIG. 3 illustrates an embodiment of achart300 depicting the relationship between the NGL recovery rate and the energy expended to recover NGLs in the NGL recovery process. The NGL recovery rate may be a percentage recovery, and may represent the amount of C₃₊ in the carbon dioxide recycle stream that is recovered in the NGL rich stream. The energy requirement may be measured in joules (J) or in horsepower (hp), and may represent the energy required to generate the condenser energy and reboiler energy described above. If additional compressors are needed at any point in the carbon dioxide reinjection process than would be required in an otherwise similar carbon dioxide reinjection process that lacks the NGL recovery process, then the energy required to operate such compressors may be included in the energy requirement shown inFIG. 3.
• As shown bycurve302, the energy requirements may increase about exponentially as the NGLs are recovered at higher rates. In other words, substantially higher energy may be required to recover the NGLs at incrementally higher rates. For example, recovering afirst amount304 of from about 20 percent to about 35 percent of C₃₊ may require substantially less energy than recovering asecond amount306 of from about 40 percent to about 65 percent of C₃₊. Moreover, recovering thesecond amount306 of from about 40 percent to about 65 percent of C₃₊ may require substantially less energy than recovering athird amount308 of from about 70 percent to about 90 percent of C₃₊. Such significant reduction in energy requirements may be advantageous in terms of process feasibility and cost, where relatively small decreases in NGL recovery rates may require significantly less energy and process equipment, yielding significantly better process economics. Although the exact relationship of thecurve302 may depend on numerous factors especially the price of C₃₊, in an embodiment the economics of the NGL recovery process when the NGL recovery rate is in thesecond amount306 may be better than the economics of the NGL recovery process when the NGL recovery rate is in thethird amount308. Similarly, the economics of the NGL recovery process when the NGL recovery rate is in thefirst amount304 may be significantly better than the economics of the NGL recovery process when the NGL recovery rate is in thesecond amount306. Such a relationship is counterintuitive considering that in many other processes, the process economics generally improve with increased recovery rates.
• FIG. 4 illustrates an embodiment of aNGL upgrade process500. TheNGL upgrade process500 may separate a portion of the heavier components of the NGLrich stream162 for blending with theheavy hydrocarbon stream154. For example, theNGL upgrade process500 may be used to produce a relativelyheavy NGL stream172 for combining with theheavy hydrocarbon stream154 and a relativelylight NGL stream174 that may be sold and/or used as a NGL product. In general, theheavy hydrocarbon stream154 may sell for a higher price than the NGLrich stream162. By mixing at least a portion of the NGLrich stream162 with theheavy hydrocarbon stream154, theNGL upgrade process500 may be used to improve the economics and/or revenue from the NGL recovery process. As a result, theNGL upgrade process500 may be considered in the NGLrecovery optimization method400 described in more detail below.
• TheNGL upgrade process500 may begin by passing the NGLrich stream162 into anNGL upgrade unit502. The NGLrich stream162 may be in the liquid phase after passing throughseparator216. TheNGL upgrade unit502 may comprise aseparator506, and areboiler510. While not illustrated inFIG. 4, some embodiments of theNGL upgrade unit502 also may comprise a condenser. Theseparator506 may be similar to any of the separators described herein, such asseparator102. In a specific embodiment, theseparator506 is a stripping column with apartial reboiler510, and theseparator506 may not comprise a condenser. The downcoming liquid phase may be provided by the liquid NGLrich stream162, which may be introduced at or near the top of theseparator506. In an embodiment, a condenser may be used to at least partially condenseoverhead stream524 to produce at least a portion of the downcoming liquid inseparator506. For example, the condenser may be similar to any of the heat exchangers described herein, such asheat exchanger202. Thereboiler510 may receive abottoms stream508 from theseparator506 and produce aheavy NGL stream514 and a boil-upstream512, which is returned to theseparator506 to provide the rising vapor phase within theseparator506. Thereboiler510 may be like any of the heat exchangers described herein, such asheat exchanger202. In a specific embodiment, thereboiler510 is a shell and tube heat exchanger coupled to a hot oil heater. As such, thereboiler510 adds someenergy516 to the boil-upstream512 and theheavy NGL stream514, typically by heating. Theheavy NGL stream514 may be substantially similar in composition to theheavy NGL stream172.
• Theheavy NGL stream514 then may be cooled in aheat exchanger518. Theheat exchanger518 may be any equipment suitable for heating or cooling one stream using another stream. Generally, theheat exchanger518 is a relatively simple device that allows heat to be exchanged between two fluids without the fluids directly contacting each other (i.e., indirect heat exchange). In an embodiment, heat integration that comprises using one or more streams in the overall process to cool theheavy NGL stream514, and thereby heating the one or more streams, may be used withheat exchanger518. Examples ofsuitable heat exchangers518 include shell and tube heat exchangers, double pipe heat exchangers, plate fin heat exchangers, bayonet heat exchangers, reboilers, condensers, evaporators, and air coolers. In the case of air coolers, one of the fluids comprise atmospheric air, which may be forced over tubes or coils using one or more fans. In a specific embodiment, theheat exchanger518 is a shell and tube heat exchanger with theheavy NGL stream514 passing on one side of the exchanger and a coolingfluid stream522 passing on the other. The cooled,heavy NGL stream172 may have substantially the same composition as theheavy NGL stream514, albeit with lower energy levels.
• Theoverhead stream524 fromseparator506 may comprise at least a portion of the lighter NGL components and may be cooled in anotherheat exchanger526. Theheat exchanger526 may be like any of the heat exchangers described herein, such asheat exchanger202. For example, theheat exchanger526 may be an air cooler as described above. The cooled,light NGL stream174 may have substantially the same composition as theoverhead stream524, albeit with lower energy levels.
• As shown inFIG. 4, one or more additional NGL input streams530,532 may be introduced into theNGL upgrade process500 upstream of theNGL upgrade unit502. The additional NGL input streams530,532 may comprise NGL streams from any suitable source, such as one or more additional recovery plants. The NGL input streams530,532 may be transported to theNGL upgrade unit502 by any suitable means. For example, the NGL input streams530,532 may be transported to theNGL upgrade unit502 through a pipeline or by truck. The additional NGL input streams530,532 may contain one or more acid gases and/or other contaminants. Depending on their compositions, the additional NGL input streams530,532 may be introduced at various input locations in the NGL recovery process. For example, an input location may comprise a point upstream of theseparator216 for an NGL input stream530 comprising acid gas components at or above a threshold level (e.g., a pipeline or storage threshold), thereby allowing for sweetening prior to being introduced to the downstream processes. As another example, an input location for anNGL input stream532 that comprises acid gas components below the threshold level may comprise a point downstream of theseparator216, thereby reducing the energy use of the overall recovery process. The use of one or more additional input streams may allow anNGL upgrade process500 to upgrade the NGL streams from a plurality of NGL recovery processes. For example, multiple NGL recovery processes and/or additional sources of NGL rich streams may feed the NGL product to a NGL upgrade process, thereby reducing the need to install an NGL upgrade process at each source of an NGL stream.
• In general, the NGL upgrade process may be used to separate a relativelyheavy NGL stream172 for blending with theheavy hydrocarbon stream154. The composition and flowrate of theheavy NGL stream172 may vary depending on the composition and flowrate of theheavy hydrocarbon stream154. As discussed above, theheavy hydrocarbon stream154 may be sent to a pipeline for transportation or a storage tank, where it is stored until being transported to another location or being further processed. Each of the downstream uses for theheavy hydrocarbon stream154 may have one or more thresholds and/or standards that theheavy hydrocarbon stream154 must meet in order to be transported or further processed. For example, pipelines may generally have standards setting thresholds for fluids passing through the pipeline, such as thresholds on vapor pressure (e.g., expressed as a Reid vapor pressure standard), carbon dioxide content, acid gas content (e.g., hydrogen sulfide content), and water content (e.g., a dew point standard). In an embodiment, the fluid transported in the pipeline may have a Reid vapor pressure of no more than about 20, no more than about 15, or no more than about 10. Accordingly, the composition and the flowrate of theheavy NGL stream172 may be controlled so that theheavy hydrocarbon stream154 may meet the transportation and/or further processing standards and/or threshold downstream of the mixing point between theheavy hydrocarbon stream154 and theheavy NGL stream172.
• In an embodiment, the composition and/or flowrate of theheavy NGL stream172 and thelight NGL stream174 may be controlled, at least in part, to allow thelight NGL stream174 to satisfy one or more transportation thresholds. Thelight NGL stream174 may be transported using a variety of transportation means and/or methods including, but not limited to, a pipeline and a tanker truck. Each transportation method may have one or more thresholds that thelight NGL stream174 may need to satisfy prior to being accepted for transportation. For example, a pipeline may have a heating value standard of between about 1,000 British thermal units per cubic foot (Btu/ft³) and about 1,200 Btu/ft³, or alternatively between about 1,050 Btu/ft³and about 1,100 Btu/ft³. In an embodiment, thelight NGL stream174 also may be subject to a dew point standard. As another example, tanker truck transportation may have a vapor pressure requirement that thelight NGL stream174 not exceed a vapor pressure of about 250 pounds per square inch gauge (psig) at a temperature of 100° F. Based on the applicable thresholds, the composition and the flowrate of theheavy NGL stream172 and thelight NGL stream174 may be controlled so that thelight NGL stream174 may meet the transportation thresholds, allowing thelight NGL stream174 to be transported for further use.
• FIG. 5 illustrates another embodiment of a carbondioxide reinjection process600. The process shown inFIG. 5 and the process ofFIG. 1 are similar, and those portions with similar numbering are described in more detail with respect toFIG. 1 above. In the interest of brevity, only those portions that differ fromFIG. 1 will be discussed with respect toFIG. 5.
• As can be seen inFIG. 5, the dehydration of the compressed carbondioxide recycle stream158 may be integrated with the NGL recovery/dehydration process610. The compressed carbondioxide recycle stream158 may enter a NGL recovery/dehydration process610. In an embodiment, the NGL recovery/dehydration process610 may comprise aseparator102 that produces multiple streams and allow one or more phases of the compressed carbondioxide recycle stream158 to be dehydrated without dehydrating the entirety of the compressed carbondioxide recycle stream158. This may allow for a reduction in the size of the dehydration unit and a reduction in the operating expense associated with the dehydrator. Further, the separate processing of the phases may allow the downstream processing units to receive each phase at a different location, which may further improve the process economics as described in more detail below with respect toFIG. 7.
• The compressed carbondioxide recycle stream158 may enter the NGL recovery/dehydration process610. The NGL recovery/dehydration process610 may dehydrate, process, and separate the compressed carbondioxide recycle stream158 into a NGLrich stream162 and a purified carbondioxide recycle stream164. The NGLrich stream162 may only comprise a portion of the total NGLs from the dehydrated carbondioxide recycle stream160. A specific example of a suitable NGL recovery/dehydration process610 is shown inFIG. 6 and described in further detail below.
• As mentioned above, the NGL recovery/dehydration process610 may produce a relatively high-quality NGLrich stream162. The NGLrich stream162 may have about the same composition as the NGLrich stream162 inFIG. 1. The NGLrich stream162 may be sent to a pipeline for transportation or a storage tank, where it is stored until transported to another location or further processed. In an embodiment, the NGL rich stream optionally may be processed in anNGL upgrade process170, as described in more detail above. TheNGL upgrade process170 may produce a relativelyheavy NGL stream172 that may be combined with theheavy hydrocarbon stream154. When combined, theheavy NGL stream172 and theheavy hydrocarbon stream154 may meet or exceed the pipeline and/or transportation properties for a heavy hydrocarbon stream. A relativelylight NGL stream174 may be sent to a pipeline for transportation or astorage tank104, where it may be stored until being transported to another location or being further processed. A specific example of a suitableNGL upgrade process170 is shown inFIG. 4 and described in further detail above.
• As mentioned above, the NGL recovery/dehydration process610 may produce a purified carbondioxide recycle stream164. The purified carbondioxide recycle stream164 may have about the same composition as the purified carbondioxide recycle stream164 inFIG. 1. The purified carbondioxide recycle stream164 may enter acompressor112. Thecompressor112 may comprise one or more compressors, such as thecompressor106 described above. In some embodiments, amakeup stream166 may be combined with either the purified carbondioxide recycle stream164 or the carbondioxide injection stream168. The resulting carbondioxide injection stream168 then may be injected into thesubterranean hydrocarbon formation114 or sent to a carbon dioxide pipeline.
• FIG. 6 illustrates an embodiment of a NGL recovery/dehydration process700. The NGL recovery/dehydration process700 may dehydrate and recover some of the NGLs from a carbon dioxide recycle stream. For example, the NGL recovery/dehydration process700 may be implemented as part of the carbondioxide reinjection process600, e.g., by separating the dehydrated carbondioxide recycle stream160 into a NGLrich stream162 and a purified carbondioxide recycle stream164.
• TheNGL recovery process700 may begin by cooling the compressed carbondioxide recycle stream158 in aheat exchanger702. Theheat exchanger702 may be any equipment suitable for heating or cooling one stream using another stream. Generally, theheat exchanger702 is a relatively simple device that allows heat to be exchanged between two fluids without the fluids directly contacting each other. Examples ofsuitable heat exchangers702 include shell and tube heat exchangers, double pipe heat exchangers, plate fin heat exchangers, bayonet heat exchangers, reboilers, condensers, evaporators, and air coolers. In the case of air coolers, one of the fluids comprises atmospheric air, which may be forced over tubes or coils using one or more fans. In a specific embodiment, theheat exchanger702 is a shell and tube heat exchanger.
• As shown inFIG. 6, the compressed carbondioxide recycle stream158 may be cooled using the cooled, purified carbondioxide recycle stream758. Specifically, the compressed carbondioxide recycle stream158 is cooled to produce the cooled carbondioxide recycle stream752, and the cooled, purified carbondioxide recycle stream758 is heated to produce the purified carbondioxide recycle stream164. The efficiency of the heat exchange process depends on several factors, including the heat exchanger design, the temperature, composition, and flowrate of the hot and cold streams, and/or the amount of thermal energy lost in the heat exchange process. In embodiments, the difference in energy levels between the compressed carbondioxide recycle stream158 and the cooled carbondioxide recycle stream752 is at least about 60 percent, at least about 70 percent, at least about 80, or at least about 90 percent of the difference in energy levels between the cooled, purified carbondioxide recycle stream758 and the purified carbondioxide recycle stream164.
• The cooled carbondioxide recycle stream752 then enters aseparator718. Theseparator718 may be similar to any of the separators described herein, such asseparator102. In a specific embodiment, theseparator718 is a three phase separator, which is a vessel that separates an inlet stream into three distinct phases such as a substantially vapor stream, a substantially first liquid stream (e.g., an organic liquid phase), and a substantially second liquid stream (e.g., an aqueous liquid phase). The first liquid stream may primarily comprise hydrocarbons and the second liquid stream may primarily comprise an aqueous fluid so that the first and second liquid streams are at least partially insoluble in each other and form two separable liquid phases. A three-phase separator may have some internal baffles and/or weirs, temperature control elements, and/or pressure control elements, but generally lacks any trays or other type of complex internal structure commonly found in columns. In an embodiment, theseparator718 may separate the cooled carbondioxide recycle stream752 into avapor recycle stream724, aliquid recycle stream728, and anaqueous fluid stream732. Theaqueous fluid stream732 exiting from thedehydrator722 may be stored, used for other processes, or discarded. Theaqueous fluid stream732 may first be treated to remove a portion of any hydrocarbons in the stream prior to storage, further use or process, or being discarded.
• The vapor recyclestream724 optionally may enter adehydrator720. Thedehydrator720 may remove some or substantially all of the water from thevapor recycle stream724. Thedehydrator720 may be any suitable dehydrator, such as a condenser, an absorber, or an adsorber. Specific examples ofsuitable dehydrators720 include refrigerators, molecular sieves, liquid desiccants such as glycol, solid desiccants such as silica gel or calcium chloride, and combinations thereof. Thedehydrator720 also may be any combination of theaforementioned dehydrators720 and722 arranged in series, in parallel, or combinations thereof. In a specific embodiment, thedehydrator720 is a glycol unit. Any water accumulated within or exiting from thedehydrator720 may be stored, used for other processes, or discarded.
• Thedehydrator720 may produce a dehydratedvapor recycle stream726. The dehydratedvapor recycle stream726 may contain little water, e.g., liquid water or water vapor. In embodiments, the dehydratedvapor recycle stream726 may comprise no more than about 5 percent, no more than about 3 percent, no more than about 1 percent, or be substantially free of water.
• Theliquid recycle stream728 from theseparator718 optionally may enter adehydrator722. Thedehydrator722 may remove some or substantially all of the water from theliquid recycle stream728. Thedehydrator722 may be any suitable dehydrator, such as a condenser, an absorber, or an adsorber. Suitable liquid-liquid separators such as hydro-cyclones and heater treaters also may be used. In an embodiment, the water in theliquid recycle stream728 may be in the form of hydrates (e.g., clathrate hydrates) and/or an emulsion. Suitable separators utilizing physical solvents, chemical solvents, and or heat may be used to break the hydrates and/or emulsion and separate the water from the remainingliquid recycle stream728 components. Specific examples ofsuitable dehydrators722 include hydro-cyclones, heater treaters, molecular sieves, liquid desiccants such as glycol, solid desiccants such as silica gel or calcium chloride, and combinations thereof. Thedehydrator722 also may be any combination of theaforementioned dehydrators722 arranged in series, in parallel, or combinations thereof. Any water accumulated within or exiting from thedehydrator722 may be stored, used for other processes, or discarded.
• Thedehydrator722 may produce a dehydratedliquid recycle stream730. The dehydratedliquid recycle stream730 may contain little water, e.g., liquid water or water vapor. In embodiments, the dehydratedliquid recycle stream730 may comprise no more than about 5 percent, no more than about 3 percent, no more than about 1 percent, or be substantially free of water.
• In an embodiment, only one of thedehydrators720,722 may be used. For example, any water contained in the cooled carbondioxide recycle stream752 may preferentially distribute to thevapor recycle stream724 or theliquid recycle stream728. By only using oneseparator720,722 on the stream containing the majority of the water, the dehydration requirements may be reduced, thereby reducing both the installation and operating costs associated with operating the dehydration system. In an embodiment in which only one dehydrator is used, the remaining stream may pass directly from theseparator718 to theseparator706. In an embodiment, bothdehydrators720,722 may be used, anddehydrators720,722 may comprise different types of dehydrators. For example,dehydrator720 may comprise a gas dehydration system whiledehydrator722 may comprise a unit designed to primarily perform a liquid-liquid phase separation. In an embodiment, bothdehydrators720,722 may be used and theseparator718 may be used to perform a first stage separation of any free water, thereby reducing the dehydration requirements. In still another embodiment, neitherdehydrator720,722 may be used and ratherseparator718 may be sufficient for removing any free water and thereby dehydrating the cooled carbondioxide recycle stream752 along with performing a first stage flash of the cooled carbondioxide recycle stream752 to allow the stream to be introduced to the NGL fractionator704 as separate streams. In yet another embodiment, thevapor recycle stream724 and theliquid recycle stream728 may be combined and passed to a single dehydrator.
• The dehydratedvapor recycle stream726 and the dehydratedliquid recycle stream730 then may enter aNGL fractionator704 as separate streams. In an embodiment, the dehydratedvapor recycle stream726 and the dehydratedliquid recycle stream730 may be fed to aseparator706 in the NGL fractionator704 at separate input locations. The ability to feed the dehydratedvapor recycle stream726 and the dehydratedliquid recycle stream730 at separate locations in theseparator706 may aid in the separation of the various components into theoverhead stream754 and the bottoms stream760. While the dehydratedvapor recycle stream726 is illustrated as entering theseparator706 above the dehydratedliquid recycle stream730, the dehydratedvapor recycle stream726 may entering theseparator706 below the dehydratedliquid recycle stream730, or enter at or near the same tray and/or location. In an embodiment, the dehydratedvapor recycle stream726 and the dehydratedliquid recycle stream730 may be combined prior to entering theNGL fractionator704.
• The NGL fractionator704 may comprise aseparator706, acondenser708, and areboiler710. Theseparator706 may be similar to any of the separators described herein, such asseparator102. In a specific embodiment, theseparator706 is a distillation column. In an embodiment, dehydratedvapor recycle stream726 may be introduced onto the tray and/or inlet location (e.g., when structured packing is used) with the closest matching vapor composition in the distillation column. Similarly, the dehydratedliquid recycle stream730 may be introduced onto the tray and/or inlet location with the closest matching liquid composition. Actual compositional measurements and/or process models may be used to match the dehydratedvapor recycle stream726 and the dehydratedliquid recycle stream730 to the appropriate trays and/or inlet location in the distillation column.
• Thecondenser708 may receive anoverhead stream754 from theseparator706 and produce the cooled, purified carbondioxide recycle stream758 and areflux stream756, which is returned to theseparator706. Thecondenser708 may be similar to any of the heat exchangers described herein, such asheat exchanger702. In a specific embodiment, thecondenser708 is a shell and tube, kettle type condenser coupled to a refrigeration process, and contains a reflux accumulator. As such, thecondenser708 may remove someenergy782 from thereflux stream756 and cooled, purified carbondioxide recycle stream758, typically by refrigeration. The cooled, purified carbondioxide recycle stream758 is substantially similar in composition to the purified carbondioxide recycle stream164 described above. Similarly, thereboiler710 may receive abottoms stream760 from theseparator706 and produce a sour NGLrich stream764 and a boil-upstream762, which is returned to theseparator706. Thereboiler710 may be like any of the heat exchangers described herein, such asheat exchanger702. In a specific embodiment, thereboiler710 is a shell and tube heat exchanger coupled to a hot oil heater. As such, thereboiler710 adds someenergy784 to the boil-upstream762 and the sour NGLrich stream764, typically by heating. The sour NGLrich stream764 may be substantially similar in composition to the NGLrich stream162, with the exception that the sour NGLrich stream764 has some additional acid gases, e.g.,acid gases770 described below.
• The sour NGLrich stream764 then may be cooled in anotherheat exchanger712. Theheat exchanger712 may be like any of the heat exchangers described herein, such asheat exchanger702. For example, theheat exchanger712 may be an air cooler as described above. A cooled, sour NGLrich stream766 exits theheat exchanger712 and enters a throttlingvalve714. The throttlingvalve714 may be an actual valve such as a gate valve, globe valve, angle valve, ball valve, butterfly valve, needle valve, or any other suitable valve, or may be a restriction in the piping such as an orifice or a pipe coil, bend, or size reduction. The throttlingvalve714 may reduce the pressure, temperature, or both of the cooled, sour NGLrich stream766 and produce a low-pressure sour NGLrich stream768. The cooled, sour NGLrich stream766 and the low-pressure sour NGLrich stream768 have substantially the same composition as the sour NGLrich stream764, albeit with lower energy levels.
• The low-pressure sour NGLrich stream768 then may be sweetened in aseparator716. Theseparator716 may be similar to any of the separators described herein, such asseparator102. In an embodiment, theseparator716 may be one or more packed columns that use a sweetening process to removeacid gases770 from the low-pressure sour NGLrich stream768. Suitable sweetening processes include amine solutions, physical solvents such as SELEXOL or RECTISOL, mixed amine solution and physical solvents, potassium carbonate solutions, direct oxidation, absorption, adsorption using, e.g., molecular sieves, or membrane filtration. Theseparator716 may produce the NGLrich stream162 described above. In addition, anyacid gases770 accumulated within or exiting from theseparator716 may be stored, used for other processes, or suitably disposed of. Finally, whileFIGS. 5 and 6 are described in the context of carbon dioxide recovery and/or reinjection, it will be appreciated that the concepts described herein can be applied to other recovery and/or reinjection processes, for example those using nitrogen, air, or water.
• As referenced above,FIG. 7 illustrates an embodiment of a NGLrecovery optimization method400. The NGLrecovery optimization method400 may be used to determine an improved or optimal project estimate for implementing the NGL recovery process and recovering NGLs at a suitable rate. As such, the NGL recovery process may be configured using appropriate equipment design based on the NGL recovery rate. Specifically, the NGLrecovery optimization method400 may design or configure the equipment size, quantity, or both based on an initial NGL recovery rate and required energy, and hence estimate the project feasibility and cost. Themethod400 may upgrade or improve the project estimate by iteratively incrementing the initial NGL recovery rate, re-estimating the project, and comparing the two estimates.
• Atblock402, themethod400 may select an initial NGL recovery rate. The initial NGL recovery rate may be relatively small, such as no more than about 20 percent recovery, no more than about 10 percent recovery, no more than about 5 percent recovery, or no more than about 1 percent recovery. Choosing the initial NGL recovery rate at a small percentage of the total NGL amount may result in a relatively low project estimate that may be increased gradually to reach improved estimates.
• Themethod400 then may proceed to block404, where the project equipment size may be determined based on the initial NGL recovery rate. Specifically, the size of the equipment described in the NGL recovery process and any additional compressors as described above may be determined. In addition, the pressure and temperature ratings and material compositions of such equipment may be determined atblock404, if desired.
• Themethod400 then may proceed to block406, where the project may be estimated. Project estimation may comprise an economic evaluation of the NGL recovery process, and may include the cost of obtaining, fabricating, and/or field constructing the equipment sized inblock404. In addition, project estimation may include the cost of operating and maintaining the NGL process, as well as the revenue generated by the sale or use of the products obtained by implementing the NGL process. As such, the project estimate may comprise the total project benefits (including production, sales, etc.) minus the total project capital and operating costs (including cost, equipment, etc.). In some embodiments, the project estimate may be based on an existing carbon dioxide reinjection plant that lacks the NGL recovery process.
• Themethod400 then may proceed to block408, where the recovery rate is incremented. The NGL recovery rate may be incremented by a relatively small percentage, for example no more than about 10 percent, not more than about 5 percent, or no more than about 1 percent. Themethod400 then may proceed to block410, which is substantially similar to block404. Themethod400 then may proceed to block412, which is substantially similar to block406.
• Themethod400 then may proceed to block414, where themethod400 may determine whether the project estimate has improved. For instance, themethod400 may compare the project estimate fromblock412 with the previous project estimate (either block406 or the previous iteration of block412) and determine whether the revised estimate is more economically desirable. Themethod400 may return to block408 when the condition atblock414 is met. Otherwise, themethod400 may proceed to block416.
• Atblock416, themethod400 may choose the previous project estimate as the final estimate. For example, themethod400 may select the previous NGL recovery rate (either block406 or the previous iteration of block412) instead of the estimate obtained atblock412. In some embodiments, the desired or optimum recovery rate selected atblock416 may represent a range of desirable or optimum points, as opposed to a single point. Accordingly, themethod400 may select the equipment sizing corresponding to the selected NGL recovery rate. The selected project estimate and sizing then may be used for the NGL recovery process. Of course, it will be appreciated that themethod400 may be revised to include a decremented, top-down estimation approach as opposed to an incremented, bottom-up estimation approach.
• Themethod400 may have several advantages over other project estimation methods. For example, process equipment of a specific size may be selected, and the corresponding recovery rate determined. Alternatively, a required recovery rate may be selected, and the equipment sized to achieve the recovery rate. However, it has been discovered that such approaches are inflexible and often yields suboptimal process economics. For example, relatively high NGL recovery rates will not lead to an improvement in process economics, e.g., because of the exponential increase in energy consumption. In contrast, themethod400 provides a flexible approach to determining a desirable or optimal project estimate.
• In an embodiment, the equipment size may be configured to allow for variations in recovery rates to accommodate changes in economic conditions, such as C₃₊ or energy pricing. Specifically, the equipment described herein can be sized above or below the desired or optimum amount to allow the processes described herein to operate at recovery rates slightly greater than or slightly less than the desirable or optimum point obtained inmethod400. As the process parameters and the energy requirements may be closely related, the ability of the process to continue to successfully operate under differing conditions may be reflected by constrained changes in the energy requirements of the process. When operating in thefirst amount304 or thesecond amount306 on thecurve302 inFIG. 3, significant increases or decreases in NGL recovery rate may be obtained with little change in the energy requirements. Such is not the case when operating in thethird amount308 on thecurve302 inFIG. 3, where significant increases or decreases in energy requirements yield only incremental changes in NGL recovery rate.
Example 1
• In one example, a process simulation was performed using theNGL recovery process200 shown inFIG. 2. The simulation was performed using the Hyprotech Ltd. HYSYS Process v2.1.1 (Build 3198) software package. TheNGL recovery process200 separated the dehydrated carbondioxide recycle stream160 into the purified carbondioxide recycle stream164, the NGLrich stream162, and theacid gas stream270. The specified values are indicated by an asterisk (*). The physical properties are provided in degrees Fahrenheit (F), psig, million standard cubic feet per day (MMSCFD), pounds per hour (lb/hr), U.S. gallons per minute (USGPM), and British thermal units per hour (Btu/hr). The material streams, their compositions, and the associated energy streams produced by the simulation are provided in tables 1, 2, and 3 below, respectively.

• TABLE 1
  Material Streams

  			Cooled,
  	Dehydrated	Cooled CO2	Purified CO2
  	CO2Recycle	Recycle	Recycle
  Name	Stream 160	Stream 252	Stream 258
  Vapor Fraction	0.9838	0.9392	1.0000
  Temperature (F.)	104.0*	45.00*	4.011
  Pressure (psig)	340.0*	335.0	330.0
  Molar Flow (MMSCFD)	17.00*	17.00	15.88
  Mass Flow (lb/hr)	8.049e+04	8.049e+04	7.254e+04
  Liquid Volume Flow	218.1	218.1	192.3
  (USGPM)
  Heat Flow (Btu/hr)	−2.639e+08	−2.658e+08	−2.577e+08
  	Purified CO2	Sour NGL	Cooled Sour
  	Recycle	Rich Stream	NGL Rich
  Name	Stream 164	264	Stream 266
  Vapor Fraction	1.0000	0.00000	0.0000
  Temperature (F.)	97.39	202.6	120.0*
  Pressure (psig)	325.0	340.0	635.3*
  Molar Flow (MMSCFD)	15.88	1.119	1.119
  Mass Flow (lb/hr)	7.254e+04	7947	7947
  Liquid Volume Flow	192.3	25.84	25.84
  (USGPM)
  Heat Flow (Btu/hr)	−2.558e+08	−8.443e+06	−8.862e+06

  	Low-Pressure
  	Sour NGL
  	Rich Stream	Acid Gas	NGL Rich
  Name	268	Stream 270	Stream 162
  Vapor Fraction	0.0000	1.0000	0.0000
  Temperature (F.)	120.9	100.0*	111.8
  Pressure (psig)	200.3*	5.304*	185.3*
  Molar Flow (MMSCFD)	1.119	0.1030	1.016
  Mass Flow (lb/hr)	7947	446.4	7501
  Liquid Volume Flow	25.84	1.100	24.74
  (USGPM)
  Heat Flow (Btu/hr)	−8.862e+06	−1.083e+06	−7.779e+06

• TABLE 2
  Stream Compositions

  			Cooled,
  	Dehydrated	Cooled CO2	Purified CO2
  	CO2Recycle	Recycle	Recycle
  Name	Stream 160	Stream 252	Stream 258
  Comp Mole Frac (H2S)	0.0333*	0.0333	0.0327
  Comp Mole Frac (Nitrogen)	0.0054*	0.0054	0.0058
  Comp Mole Frac (CO2)	0.7842*	0.7842	0.8359
  Comp Mole Frac (Methane)	0.0521*	0.0521	0.0558
  Comp Mole Frac (Ethane)	0.0343*	0.0343	0.0348
  Comp Mole Frac (Propane)	0.0406*	0.0406	0.0313
  Comp Mole Frac (i-Butane)	0.0072*	0.0072	0.0022
  Comp Mole Frac (n-Butane)	0.0171*	0.0171	0.0015
  Comp Mole Frac (i-Pentane)	0.0058*	0.0058	0.0000
  Comp Mole Frac (n-Pentane)	0.0057*	0.0057	0.0000
  Comp Mole Frac (n-Hexane)	0.0070*	0.0070	0.0000
  Comp Mole Frac (n-Octane)	0.0071*	0.0071	0.0000
  Comp Mole Frac (H2O)	0.0000*	0.0000	0.0000
  	Purified CO2	Sour NGL	Cooled Sour
  	Recycle	Rich Stream	NGL Rich
  Name	Stream 164	264	Stream 266
  Comp Mole Frac (H2S)	0.0327	0.0421	0.0421
  Comp Mole Frac (Nitrogen)	0.0058	0.0000	0.0000
  Comp Mole Frac (CO2)	0.8359	0.0500	0.0500
  Comp Mole Frac (Methane)	0.0558	0.0000	0.0000
  Comp Mole Frac (Ethane)	0.0348	0.0281	0.0281
  Comp Mole Frac (Propane)	0.0313	0.1728	0.1728
  Comp Mole Frac (i-Butane)	0.0022	0.0789	0.0789
  Comp Mole Frac (n-Butane)	0.0015	0.2388	0.2388
  Comp Mole Frac (i-Pentane)	0.0000	0.0887	0.0887
  Comp Mole Frac (n-Pentane)	0.0000	0.0866	0.0866
  Comp Mole Frac (n-Hexane)	0.0000	0.1063	0.1063
  Comp Mole Frac (n-Octane)	0.0000	0.1077	0.1077
  Comp Mole Frac (H2O)	0.0000	0.0000	0.0000
  	Low-
  	Pressure
  	Sour NGL
  	Rich	Acid Gas	NGL Rich
  Name	Stream 268	Stream 270	Stream 162
  Comp Mole Frac (H2S)	0.0421	0.4568	0.0000
  Comp Mole Frac (Nitrogen)	0.0000	0.0000	0.0000
  Comp Mole Frac (CO2)	0.0500	0.5432	0.0000
  Comp Mole Frac (Methane)	0.0000	0.0000	0.0000
  Comp Mole Frac (Ethane)	0.0281	0.0000	0.0309
  Comp Mole Frac (Propane)	0.1728	0.0000	0.1903
  Comp Mole Frac (i-Butane)	0.0789	0.0000	0.0869
  Comp Mole Frac (n-Butane)	0.2388	0.0000	0.2630
  Comp Mole Frac (i-Pentane)	0.0887	0.0000	0.0977
  Comp Mole Frac (n-Pentane)	0.0866	0.0000	0.0954
  Comp Mole Frac (n-Hexane)	0.1063	0.0000	0.1171
  Comp Mole Frac (n-Octane)	0.1077	0.0000	0.1186
  Comp Mole Frac (H2O)	0.0000	0.0000	0.0000

• TABLE 3
  Energy Streams

  	Name	Heat Flow (Btu/hr)
  	CondenserQ Energy Stream 282	1.469e+06
  	ReboilerQ Energy Stream 284	1.152e+06

Example 2
• In another example, the process simulation was repeated using a different dehydrated carbondioxide recycle stream160. The material streams, their compositions, and the associated energy streams produced by the simulation are provided in tables 4, 5, and 6 below, respectively.

• TABLE 4
  Material Streams

  			Cooled,
  	Dehydrated	Cooled CO2	Purified CO2
  	CO2Recycle	Recycle	Recycle
  Name	Stream 160	Stream 252	Stream 258
  Vapor Fraction	0.9874	0.9286	1.0000
  Temperature (F.)	104.0*	60.00*	22.77
  Pressure (psig)	685.3*	680.3	590.0
  Molar Flow	20.00*	20.00	18.86
  (MMSCFD)
  Mass Flow (lb/hr)	8.535e+04	8.535e+04	7.780e+04
  Liquid Volume Flow	258.0	258.0	232.2
  (USGPM)
  Heat Flow (Btu/hr)	−2.741e+08	−2.760e+08	−2.683e+08
  	Purified CO2	Sour NGL	Cooled Sour
  	Recycle	Rich Stream	NGL Rich
  Name	Stream 164	264	Stream 266
  Vapor Fraction	1.0000	0.00000	0.0000
  Temperature (F.)	87.48	290.7	120.0*
  Pressure (psig)	585.0	600.0	635.3*
  Molar Flow	18.86	1.139	1.139
  (MMSCFD)
  Mass Flow (lb/hr)	7.780e+04	7552	7552
  Liquid Volume Flow	232.2	25.83	25.83
  (USGPM)
  Heat Flow (Btu/hr)	−2.663e+08	−7.411e+06	−8.371e+06
  	Low-Pressure
  	Sour NGL
  	Rich Stream	Acid Gas	NGL Rich
  Name	268	Stream 270	Stream 162
  Vapor Fraction	0.0000	1.0000	0.0000
  Temperature (F.)	120.5	100.0*	118.6
  Pressure (psig)	200.3*	5.304*	185.3*
  Molar Flow	1.139	0.02943	1.110
  (MMSCFD)
  Mass Flow (lb/hr)	7552	141.2	7411
  Liquid Volume Flow	25.83	0.3421	25.49
  (USGPM)
  Heat Flow (Btu/hr)	−8.371e+06	−5.301e+05	−7.841e+06

• TABLE 5
  Stream Compositions

  			Cooled,
  	Dehydrated	Cooled CO2	Purified CO2
  	CO2Recycle	Recycle	Recycle
  Name	Stream 160	Stream 252	Stream 258
  Comp Mole Frac (H2S)	0.0004*	0.0004	0.0004
  Comp Mole Frac (Nitrogen)	0.0153*	0.0153	0.0162
  Comp Mole Frac (CO2)	0.6592*	0.6592	0.6975
  Comp Mole Frac (Methane)	0.1813*	0.1813	0.1922
  Comp Mole Frac (Ethane)	0.0620*	0.0620	0.0620
  Comp Mole Frac (Propane)	0.0411*	0.0411	0.0275
  Comp Mole Frac (i-Butane)	0.0064*	0.0064	0.0017
  Comp Mole Frac (n-Butane)	0.0179*	0.0179	0.0024
  Comp Mole Frac (i-Pentane)	0.0040*	0.0040	0.0000
  Comp Mole Frac (n-Pentane)	0.0049*	0.0049	0.0000
  Comp Mole Frac (n-Hexane)	0.0030*	0.0030	0.0000
  Comp Mole Frac (n-Octane)	0.0045*	0.0045	0.0000
  Comp Mole Frac (H2O)	0.0000*	0.0000	0.0000
  	Purified CO2	Sour NGL	Cooled Sour
  	Recycle	Rich Stream	NGL Rich
  Name	Stream 164	264	Stream 266
  Comp Mole Frac (H2S)	0.0004	0.0008	0.0008
  Comp Mole Frac (Nitrogen)	0.0162	0.0000	0.0000
  Comp Mole Frac (CO2)	0.6975	0.0250	0.0250
  Comp Mole Frac (Methane)	0.1922	0.0000	0.0000
  Comp Mole Frac (Ethane)	0.0620	0.0613	0.0613
  Comp Mole Frac (Propane)	0.0275	0.2670	0.2670
  Comp Mole Frac (i-Butane)	0.0017	0.0836	0.0836
  Comp Mole Frac (n-Butane)	0.0024	0.2751	0.2751
  Comp Mole Frac (i-Pentane)	0.0000	0.0697	0.0697
  Comp Mole Frac (n-Pentane)	0.0000	0.0858	0.0858
  Comp Mole Frac (n-Hexane)	0.0000	0.0527	0.0527
  Comp Mole Frac (n-Octane)	0.0000	0.0790	0.0790
  Comp Mole Frac (H2O)	0.0000	0.0000	0.0000
  	Low-
  	Pressure
  	Sour NGL
  	Rich	Acid Gas	NGL Rich
  Name	Stream 268	Stream 270	Stream 162
  Comp Mole Frac (H2S)	0.0008	0.0315	0.0000
  Comp Mole Frac (Nitrogen)	0.0000	0.0000	0.0000
  Comp Mole Frac (CO2)	0.0250	0.9685	0.0000
  Comp Mole Frac (Methane)	0.0000	0.0000	0.0000
  Comp Mole Frac (Ethane)	0.0613	0.0000	0.0629
  Comp Mole Frac (Propane)	0.2670	0.0000	0.2740
  Comp Mole Frac (i-Butane)	0.0836	0.0000	0.0858
  Comp Mole Frac (n-Butane)	0.2751	0.0000	0.2824
  Comp Mole Frac (i-Pentane)	0.0697	0.0000	0.0716
  Comp Mole Frac (n-Pentane)	0.0858	0.0000	0.0881
  Comp Mole Frac (n-Hexane)	0.0527	0.0000	0.0541
  Comp Mole Frac (n-Octane)	0.0790	0.0000	0.0811
  Comp Mole Frac (H2O)	0.0000	0.0000	0.0000

• TABLE 6
  Energy Streams

  	Name	Heat Flow (Btu/hr)
  	CondenserQ Energy Stream 282	1.884e+06
  	ReboilerQ Energy Stream 284	2.211e+06

Example 3
• In a third example, the process simulation was repeated using a different dehydrated carbondioxide recycle stream160. The material streams, their compositions, and the associated energy streams produced by the simulation are provided in tables 7, 8, and 9 below, respectively.

• TABLE 7
  Material Streams

  			Cooled,
  	Dehydrated	Cooled CO2	Purified CO2
  	CO2Recycle	Recycle	Recycle
  Name	Stream 160	Stream 252	Stream 258
  Vapor Fraction	1.0000	0.9988	1.0000
  Temperature (F.)	104.0*	30.00*	4.617
  Pressure (psig)	340.0*	335.0	330.0
  Molar Flow	17.00*	17.00	16.82
  (MMSCFD)
  Mass Flow (lb/hr)	8.083e+04	8.083e+04	7.968e+04
  Liquid Volume Flow	203.4	203.4	199.5
  (USGPM)
  Heat Flow (Btu/hr)	−3.016e+08	−3.032e+08	−3.025e+08
  	Purified CO2	Sour NGL	Cooled Sour
  	Recycle	Rich Stream	NGL Rich
  Name	Stream 164	264	Stream 266
  Vapor Fraction	1.0000	0.00000	0.0000
  Temperature (F.)	76.45	199.4	120.0*
  Pressure (psig)	325.0	340.0	635.3*
  Molar Flow	16.82	0.1763	0.1763
  (MMSCFD)
  Mass Flow (lb/hr)	7.968e+04	1153	1153
  Liquid Volume Flow	199.5	3.894	3.894
  (USGPM)
  Heat Flow (Btu/hr)	−3.009e+08	−1.278e+06	−1.340e+06
  	Low-Pressure
  	Sour NGL
  	Rich Stream	Acid Gas	NGL Rich
  Name	268	Stream 270	Stream 162
  Vapor Fraction	0.0000	1.0000	0.0000
  Temperature (F.)	120.4	100.0*	115.4
  Pressure (psig)	200.3*	5.304*	185.3*
  Molar Flow	0.1763	0.01048	0.1659
  (MMSCFD)
  Mass Flow (lb/hr)	1153	48.82	1105
  Liquid Volume Flow	3.894	0.1188	3.776
  (USGPM)
  Heat Flow (Btu/hr)	−1.340e+06	−1.653e+05	−1.175e+06

• TABLE 8
  Stream Compositions

  			Cooled,
  	Dehydrated	Cooled CO2	Purified CO2
  	CO2Recycle	Recycle	Recycle
  Name	Stream 160	Stream 252	Stream 258
  Comp Mole Frac (H2S)	0.0031*	0.0031	0.0030
  Comp Mole Frac (Nitrogen)	0.0008*	0.0008	0.0008
  Comp Mole Frac (CO2)	0.9400*	0.9400	0.9493
  Comp Mole Frac (Methane)	0.0219*	0.0219	0.0222
  Comp Mole Frac (Ethane)	0.0156*	0.0156	0.0157
  Comp Mole Frac (Propane)	0.0116*	0.0116	0.0088
  Comp Mole Frac (i-Butane)	0.0015*	0.0015	0.0002
  Comp Mole Frac (n-Butane)	0.0031*	0.0031	0.0001
  Comp Mole Frac (i-Pentane)	0.0007*	0.0007	0.0000
  Comp Mole Frac (n-Pentane)	0.0006*	0.0006	0.0000
  Comp Mole Frac (n-Hexane)	0.0005*	0.0005	0.0000
  Comp Mole Frac (n-Octane)	0.0006*	0.0006	0.0000
  Comp Mole Frac (H2O)	0.0000*	0.0000	0.0000
  	Purified CO2	Sour NGL	Cooled Sour
  	Recycle	Rich Stream	NGL Rich
  Name	Stream 164	264	Stream 266
  Comp Mole Frac (H2S)	0.0030	0.0094	0.0094
  Comp Mole Frac (Nitrogen)	0.0008	0.0000	0.0000
  Comp Mole Frac (CO2)	0.9493	0.0500	0.0500
  Comp Mole Frac (Methane)	0.0222	0.0000	0.0000
  Comp Mole Frac (Ethane)	0.0157	0.0000	0.0000
  Comp Mole Frac (Propane)	0.0088	0.2794	0.2794
  Comp Mole Frac (i-Butane)	0.0002	0.1265	0.1265
  Comp Mole Frac (n-Butane)	0.0001	0.2985	0.2985
  Comp Mole Frac (i-Pentane)	0.0000	0.0713	0.0713
  Comp Mole Frac (n-Pentane)	0.0000	0.0617	0.0617
  Comp Mole Frac (n-Hexane)	0.0000	0.0482	0.0482
  Comp Mole Frac (n-Octane)	0.0000	0.0550	0.0550
  Comp Mole Frac (H2O)	0.0000	0.0000	0.0000
  	Low-
  	Pressure
  	Sour NGL
  	Rich Stream	Acid Gas	NGL Rich
  Name	268	Stream 270	Stream 162
  Comp Mole Frac (H2S)	0.0094	0.1584	0.0000
  Comp Mole Frac (Nitrogen)	0.0000	0.0000	0.0000
  Comp Mole Frac (CO2)	0.0500	0.8416	0.0000
  Comp Mole Frac (Methane)	0.0000	0.0000	0.0000
  Comp Mole Frac (Ethane)	0.0000	0.0000	0.0000
  Comp Mole Frac (Propane)	0.2794	0.0000	0.2970
  Comp Mole Frac (i-Butane)	0.1265	0.0000	0.1345
  Comp Mole Frac (n-Butane)	0.2985	0.0000	0.3174
  Comp Mole Frac (i-Pentane)	0.0713	0.0000	0.0758
  Comp Mole Frac (n-Pentane)	0.0617	0.0000	0.0656
  Comp Mole Frac (n-Hexane)	0.0482	0.0000	0.0512
  Comp Mole Frac (n-Octane)	0.0550	0.0000	0.0584
  Comp Mole Frac (H2O)	0.0000	0.0000	0.0000

• TABLE 9
  Energy Streams

  	Name	Heat Flow (Btu/hr)
  	CondenserQ Energy Stream 282	6.236e+06
  	ReboilerQ Energy Stream 284	5.666e+06

Example 4
• In a fourth example, a process simulation was performed using the NGL recovery/dehydration process700 shown inFIG. 6. The simulation was performed using the Bryan Research and Engineering ProMax software package. The NGL recovery/dehydration process700 separated the compressed carbondioxide recycle stream158 into the purified carbondioxide recycle stream164, the NGLrich stream162, and theacid gas stream770. The specified values are indicated by an asterisk (*). The material streams, their compositions, and the associated energy streams produced by the simulation are provided in tables 10, 11, and 12 below, respectively.

• TABLE 10
  Material Streams

  	Compressed		Purified
  	Carbon	Cooled Carbon	Carbon
  	Dioxide	Dioxide	Dioxide
  	Recycle	Recycle	Recycle
  Name	Stream 158	Stream 752	Stream 164
  Temperature (° F.)	110	55	72.0898
  Pressure (psig)	535	532	526.909
  Mole Fraction Vapor (%)	100	97.1149	100
  Mole Fraction Light Liquid (%)	0	2.63789	0
  Mole Fraction Heavy Liquid (%)	0	0.247192	0
  Molecular Weight (lb/lbmol)	34.5734	34.5734	33.2372
  Molar Flow (lbmol/hr)	143.165	143.165	136.153
  Vapor Volumetric Flow (ft3/hr)	1369.35	1144.29	1217.29
  Liquid Volumetric Flow (gpm)	170.725	142.665	151.766
  Std Vapor Volumetric Flow	1.30389	1.30389	1.24003
  (MMSCFD)
  Std Liquid Volumetric Flow (sgpm)	16.1721	16.1721	14.7954
  Enthalpy (Btu/hr)	−1.54233E+07	−1.55479E+07	−1.49692E+07
  Net Ideal Gas Heating Value	512.476	512.476	391.24
  (Btu/ft3)
  	Cooled,
  	Purified
  	Carbon
  	Dioxide	Dehydrated
  	Recycle	Vapor Recycle	NGL Rich
  Name	Stream 758	Stream 726	Stream 162
  Temperature (° F.)	−4.70484	54.9077	121.117
  Pressure (psig)	529.909	531	438.3
  Mole Fraction Vapor (%)	100	99.9993	0
  Mole Fraction Light Liquid (%)	0	0.000671338	100
  Mole Fraction Heavy Liquid (%)	0	0	0
  Molecular Weight (lb/lbmol)	33.2372	33.941	65.1996
  Molar Flow (lbmol/hr)	136.153	138.957	5.97957
  Vapor Volumetric Flow (ft3/hr)	880.68	1140.73	10.8305
  Liquid Volumetric Flow (gpm)	109.799	142.221	1.35029
  Std Vapor Volumetric Flow	1.24003	1.26557	0.0544597
  (MMSCFD)
  Std Liquid Volumetric Flow (sgpm)	14.7954	15.4591	1.2954
  Enthalpy (Btu/hr)	−1.50938E+07	−1.51048E+07	−405001
  Net Ideal Gas Heating Value	391.24	463.982	3359.57
  (Btu/ft3)
  		Sour NGL	Cooled, Sour
  	Aqueous Fluid	Rich Stream	NGL Rich
  Name	Stream 732	764	Stream 766
  Temperature (° F.)	54.9077	262.193	120
  Pressure (psig)	531	531.909	521.909
  Mole Fraction Vapor (%)	0	0	0
  Mole Fraction Light Liquid (%)	100	100	100
  Mole Fraction Heavy Liquid (%)	0	0	0
  Molecular Weight (lb/lbmol)	18.2988	63.2785	63.2785
  Molar Flow (lbmol/hr)	0.354052	6.58207	6.58207
  Vapor Volumetric Flow (ft3/hr)	0.103218	14.3659	11.2331
  Liquid Volumetric Flow (gpm)	0.0128688	1.79107	1.40049
  Std Vapor Volumetric Flow	0.00322458	0.0599471	0.0599471
  (MMSCFD)
  Std Liquid Volumetric Flow (sgpm)	0.013039	1.36091	1.36091
  Enthalpy (Btu/hr)	−43829.7	−468892	−508612
  Net Ideal Gas Heating Value	0.450311	3053.71	3053.71
  (Btu/ft3)

  		Low-Pressure
  		Sour NGL
  		Rich Stream
  	Name	768	Acid Gases 770
  	Temperature (° F.)	120.145	120
  	Pressure (psig)	441.3	12.3041
  	Mole Fraction Vapor (%)	0	100
  	Mole Fraction Light Liquid (%)	100	0
  	Mole Fraction Heavy Liquid (%)	0	0
  	Molecular Weight (lb/lbmol)	63.2785	42.366
  	Molar Flow (lbmol/hr)	6.58207	0.645859
  	Vapor Volumetric Flow (ft3/hr)	11.2586	147.542
  	Liquid Volumetric Flow (gpm)	1.40367	18.3949
  	Std Vapor Volumetric Flow	0.0599471	0.00588224
  	(MMSCFD)
  	Std Liquid Volumetric Flow (sgpm)	1.36091	0.0667719
  	Enthalpy (Btu/hr)	−508612	−106053
  	Net Ideal Gas Heating Value	3053.71	9.39946
  	(Btu/ft3)

• TABLE 11
  Stream Compositions

  	Compressed		Purified
  	Carbon	Cooled Carbon	Carbon
  	Dioxide	Dioxide	Dioxide
  	Recycle	Recycle	Recycle
  Name	Stream 158	Stream 752	Stream 164
  Comp Molar Flow H2S (lbmol/hr)	0	0	0
  Comp Molar Flow Nitrogen	5.42488	5.42488	5.42487
  (lbmol/hr)
  Comp Molar Flow CO2(lbmol/hr)	78.374	78.374	77.7679
  Comp Molar Flow Methane	46.8833	46.8833	46.8831
  (lbmol/hr)
  Comp Molar Flow Ethane (lbmol/hr)	5.04264	5.04264	4.97376
  Comp Molar Flow Propane (lbmol/hr)	2.60218	2.60218	1.06689
  Comp Molar Flow i-Butane	0.632167	0.632167	0.0262049
  (lbmol/hr)
  Comp Molar Flow n-Butane	1.01441	1.01441	0.0106494
  (lbmol/hr)
  Comp Molar Flow i-Pentane	0.543958	0.543958	2.47836E−05
  (lbmol/hr)
  Comp Molar Flow n-Pentane	0.27933	0.27933	6.5645E−06
  (lbmol/hr)
  Comp Molar Flow n-Hexane	1.94061	1.94061	6.8325E−08
  (lbmol/hr)
  Comp Molar Flow n-Heptane	0	0	0
  (lbmol/hr)
  Comp Molar Flow H2O (lbmol/hr)	0.427428	0.427428	1.88221E−05
  Comp Molar Flow Diethyle Amine	0	0	0
  (lbmol/hr)
  	Cooled,
  	Purified
  	Carbon
  	Dioxide	Dehydrated
  	Recycle	Vapor Recycle	NGL Rich
  Name	Stream 758	Stream 726	Stream 162
  Comp Molar Flow H2S (lbmol/hr)	0	0	0
  Comp Molar Flow Nitrogen	5.42487	5.41324	5.81573E−09
  (lbmol/hr)
  Comp Molar Flow CO2(lbmol/hr)	77.7679	77.1797	1.75658E−06
  Comp Molar Flow Methane	46.8831	46.6143	2.21379E−05
  (lbmol/hr)
  Comp Molar Flow Ethane (lbmol/hr)	4.97376	4.89657	0.068452
  Comp Molar Flow Propane (lbmol/hr)	1.06689	2.39516	1.53245
  Comp Molar Flow i-Butane	0.0262049	0.529946	0.605608
  (lbmol/hr)
  Comp Molar Flow n-Butane	0.0106494	0.799268	1.00312
  (lbmol/hr)
  Comp Molar Flow i-Pentane	2.47836E−05	0.345064	0.543843
  (lbmol/hr)
  Comp Molar Flow n-Pentane	6.5645E−06	0.161123	0.279274
  (lbmol/hr)
  Comp Molar Flow n-Hexane	6.8325E−08	0.622204	1.9405
  (lbmol/hr)
  Comp Molar Flow n-Heptane	0	0	0
  (lbmol/hr)
  Comp Molar Flow H2O (lbmol/hr)	1.88221E−05	0.000761257	0.0062375
  Comp Molar Flow Diethyle Amine	0	0	7.30571E−05
  (lbmol/hr)
  		Sour NGL	Cooled, Sour
  	Aqueous Fluid	Rich Stream	NGL Rich
  Name	Stream 732	764	Stream 766
  Comp Molar Flow H2S (lbmol/hr)	0	0	0
  Comp Molar Flow Nitrogen	7.93825E−06	5.94147E−09	5.94147E−09
  (lbmol/hr)
  Comp Molar Flow CO2(lbmol/hr)	0.00385078	0.602328	0.602328
  Comp Molar Flow Methane	0.000125243	2.25954E−05	2.25954E−05
  (lbmol/hr)
  Comp Molar Flow Ethane (lbmol/hr)	1.31496E−05	0.0688655	0.0688655
  Comp Molar Flow Propane (lbmol/hr)	6.92895E−06	1.53528	1.53528
  Comp Molar Flow i-Butane	4.43906E−07	0.605962	0.605962
  (lbmol/hr)
  Comp Molar Flow n-Butane	1.35201E−06	1.00376	1.00376
  (lbmol/hr)
  Comp Molar Flow i-Pentane	3.68843E−07	0.543932	0.543932
  (lbmol/hr)
  Comp Molar Flow n-Pentane	1.57397E−07	0.279323	0.279323
  (lbmol/hr)
  Comp Molar Flow n-Hexane	1.94686E−07	1.9406	1.9406
  (lbmol/hr)
  Comp Molar Flow n-Heptane	0	0	0
  (lbmol/hr)
  Comp Molar Flow H2O (lbmol/hr)	0.350046	0.00199881	0.00199881
  Comp Molar Flow Diethyle Amine	0	0	0
  (lbmol/hr)

  		Low-Pressure
  		Sour NGL
  		Rich Stream
  	Name	768	Acid Gases 770
  	Comp Molar Flow H2S (lbmol/hr)	0	0
  	Comp Molar Flow Nitrogen	5.94147E−09	0
  	(lbmol/hr)
  	Comp Molar Flow CO2(lbmol/hr)	0.602328	0.602272
  	Comp Molar Flow Methane	2.25954E−05	2.56258E−07
  	(lbmol/hr)
  	Comp Molar Flow Ethane (lbmol/hr)	0.0688655	0.000254578
  	Comp Molar Flow Propane (lbmol/hr)	1.53528	0.00159919
  	Comp Molar Flow i-Butane	0.605962	0.00016306
  	(lbmol/hr)
  	Comp Molar Flow n-Butane	1.00376	0.000353691
  	(lbmol/hr)
  	Comp Molar Flow i-Pentane	0.543932	3.41627E−05
  	(lbmol/hr)
  	Comp Molar Flow n-Pentane	0.279323	2.16905E−05
  	(lbmol/hr)
  	Comp Molar Flow n-Hexane	1.9406	4.4341E−05
  	(lbmol/hr)
  	Comp Molar Flow n-Heptane	0	0
  	(lbmol/hr)
  	Comp Molar Flow H2O (lbmol/hr)	0.00199881	0.0411157
  	Comp Molar Flow Diethyle Amine	0	4.17895E−20
  	(lbmol/hr)

• TABLE 12
  Energy Streams

  	Name	Heat Flow (Btu/hr)
  	Condenser Energy Stream 782	320524
  	Reboiler Energy Stream 784	253961

Example 5
• In a fifth example, the process simulation was continued for theNGL upgrade process500 shown inFIG. 4. The simulation was performed using the Aspen Tech. HYSYS Version 7.2 (previously Hyprotech Ltd. HYSYS) software package. TheNGL upgrade process500 separates the NGLrich stream162 into theheavy NGL stream172 and thelight NGL stream174. In the following tables and results, the low-pressure sour NGLrich stream268 has the composition as determined by the simulation model of the low-pressure sour NGLrich stream768 from Example 4. Similarly, theacid gas stream270 has the composition as determined by the simulation model of theacid gas stream770 from Example 4. In addition, the NGLrich stream162 has the composition as determined by the simulation model of the NGLrich stream162 from Example 4. The material streams, their compositions, and the associated energy streams produced by the simulation are provided in tables 13, 14, and 15 below, respectively.

• TABLE 13
  Material Streams

  	Low-Pressure
  	Sour NGL
  	Rich Stream	Acid Gas	NGL Rich
  Name
  	268	Stream 270	Stream 162
  Vapor Fraction	0.0000	1.0000	0.0000
  Temperature (F.)	120.145	120.0	94.16
  Pressure (psig)	441.3	12.3041	250.0
  Molar Flow (MMSCFD)	0.321888	5.8822e−002	1.019
  Mass Flow (lb/hr)	416.5033	27.362473	7567
  Standard Liquid Volume	46.6598	2.2893	840.0
  Flow (barrel/day)
  Heat Flow (Btu/hr)	−508612	−106053	−7.920e+006

  				Cooled,
  	Overhead	Heavy NGL	Light NGL	HeavyNGL
  Name	Stream
  524	Stream 514	Stream 174	Stream 172
  Vapor Fraction	1.0000	0.0000	0.0000	0.0000
  Temperature	185.7	270.6	134.0	100.0
  (F.)
  Pressure (psig)	160.0	165.0	155.0	160.0
  Molar Flow	0.3687	0.6507	0.3687	0.6507
  (MMSCFD)
  Mass Flow	2186	5381	2186	5381
  (lb/hr)
  Standard	266.4	576.5	266.4	576.5
  Liquid
  Volume Flow
  (barrel/day)
  Heat Flow	−2.029e+006	−4.885e+006	−2.367e+006	−5.478e+006
  (Btu/hr)

• TABLE 14
  Stream Compositions

  		Low-Pressure
  		Sour NGL
  		Rich Stream	Acid Gas	NGL Rich
  	Name	268	Stream 270	Stream 162
  	Comp Mole Frac (H2S)			0.0000
  	Comp Mole Frac (Nitrogen)			0.0000
  	Comp Mole Frac (CO2)	0.09151	0.93251	0.0000
  	Comp Mole Frac (Methane)	0.00000	0.00000	0.0000
  	Comp Mole Frac (Ethane)	0.01046	0.00039	0.0027
  	Comp Mole Frac (Propane)	0.23325	0.00248	0.1653
  	Comp Mole Frac (i-Butane)	0.09206	0.00025	0.0756
  	Comp Mole Frac (n-Butane)	0.15250	0.00055	0.2423
  	Comp Mole Frac (i-Pentane)	0.08264	0.00005	0.1092
  	Comp Mole Frac (n-Pentane)	0.04244	0.00003	0.0915
  	Comp Mole Frac (n-Hexane)	0.29483	0.00007	0.2943
  	Comp Mole Frac (n-Heptane)	0.00000	0.00000	0.0191
  	Comp Mole Frac (n-Octane)	—	—	0.0000
  	Comp Mole Frac (H2O)	0.00030	0.06366	0.0000

  				Cooled,
  	Overhead	Heavy NGL	Light NGL	Heavy NGL
  Name	Stream 524	Stream 514	Stream 174	Stream 172
  Comp Mole Frac (H2S)	0.0000	0.0000	0.0000	0.0000
  Comp Mole Frac (Nitrogen)	0.0000	0.0000	0.0000	0.0000
  Comp Mole Frac (CO2)	0.0000	0.0000	0.0000	0.0000
  Comp Mole Frac (Methane)	0.0000	0.0000	0.0000	0.0000
  Comp Mole Frac (Ethane)	0.0075	0.0000	0.0075	0.0000
  Comp Mole Frac (Propane)	0.4547	0.0013	0.4547	0.0013
  Comp Mole Frac (i-Butane)	0.1330	0.0431	0.1330	0.0431
  Comp Mole Frac (n-Butane)	0.2751	0.2236	0.2751	0.2236
  Comp Mole Frac (i-Pentane)	0.0486	0.1435	0.0486	0.1435
  Comp Mole Frac (n-Pentane)	0.0359	0.1230	0.0359	0.1230
  Comp Mole Frac (n-Hexane)	0.0437	0.4363	0.0437	0.4363
  Comp Mole Frac (n-Heptane)	0.0013	0.0292	0.0013	0.0292
  Comp Mole Frac (n-Octane)	0.0000	0.0000	0.0000	0.0000
  Comp Mole Frac (H2O)	0.0000	0.0000	0.0000	0.0000

• TABLE 15
  Energy Streams

  	Name	Heat Flow (Btu/hr)
  	Reboiler Energy Stream 516	25.4 × 103
  	Cooling Fluid Stream 522	39.72 × 103

• At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art 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. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R₁, and an upper limit, R_u, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R₁+k*(R_u−R₁), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, e.g., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. 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. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that 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 disclosure. The discussion of a reference in the disclosure is not an admission that it is prior art, especially any reference that has a publication date after the priority date of this application. The disclosure of all patents, patent applications, and publications cited in the disclosure are hereby incorporated by reference, to the extent that they provide exemplary, procedural, or other details supplementary to the disclosure.
• While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might 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.
• In addition, 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 coupled or 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.

Claims (25)

1. A method comprising:

receiving a hydrocarbon feed stream;

separating the hydrocarbon feed stream into a heavy hydrocarbon rich stream and a recycle stream, wherein the recycle stream comprises a gas selected from the group consisting of carbon dioxide, nitrogen, air, and water; and

separating the recycle stream into a natural gas liquids (NGL) rich stream and a purified recycle stream.

2. The method ofclaim 1, further comprising injecting the purified recycle stream into a subterranean formation.

3. The method ofclaim 1, further comprising:

separating the recycle stream into a vapor recycle stream and a liquid recycle stream; and

dehydrating the vapor recycle stream.

4. The method ofclaim 3, further comprising dehydrating the liquid recycle stream.

5. The method ofclaim 1, further comprising:

separating the recycle stream into a vapor recycle stream and a liquid recycle stream; and

dehydrating the liquid recycle stream.

6. The method ofclaim 1, further comprising separating the recycle stream into a vapor recycle stream and a liquid recycle stream, wherein the vapor recycle stream and the liquid recycle stream are fed to the separation of the recycle stream as separate streams.

7. The method ofclaim 6, wherein separating the vapor recycle stream and the liquid recycle stream comprises using a three-phase separator.

8. The method ofclaim 1, further comprising dehydrating at least a portion of the recycle stream prior to separating the recycle stream into the NGL rich stream and the purified recycle stream.

9. The method ofclaim 1, wherein separating the recycle stream comprises:

separating the recycle stream into the purified recycle stream and a sour NGL rich stream; and

sweetening the sour NGL rich stream, thereby producing the NGL rich stream.

10. The method ofclaim 9, further comprising:

cooling the sour NGL rich stream prior to sweetening the sour NGL rich stream; and

throttling the sour NGL rich stream prior to sweetening the sour NGL rich stream.

11. The method ofclaim 9, wherein the NGL rich stream comprises no more than about 5 percent acid gases.

12. The method ofclaim 1, further comprising:

separating the NGL rich stream into a heavy NGL stream and a light NGL stream; and

mixing the heavy NGL stream with the heavy hydrocarbon rich stream.

13. The method ofclaim 12, further comprising:

separating the recycle stream into a vapor recycle stream and a liquid recycle stream, wherein the vapor recycle stream and the liquid recycle stream are fed to the separation of the recycle stream as separate streams; and

dehydrating at least one of the vapor recycle stream and the liquid recycle stream.

14. The method ofclaim 12, wherein the heavy hydrocarbon rich stream has a Reid vapor pressure of less than 6 after being mixed with at least a portion of the heavy NGL stream.

15. The method ofclaim 12, wherein the light NGL stream has an energy content of between about 1,000 British thermal units per cubit foot (Btu/ft³) and about 1,200 Btu/ft³.

16. The method ofclaim 12, wherein the light NGL stream has a vapor pressure of less than about 250 pounds per square inch gauge (psig) at a standard temperature.

17. The method ofclaim 12, further comprising:

combining a second NGL rich stream with the NGL rich stream prior to separating the NGL rich stream; and

separating the second NGL rich stream along with the NGL rich stream to form the heavy NGL stream and the light NGL stream.

18. A plurality of process equipment configured to:

receive a hydrocarbon feed stream;

separate the hydrocarbon feed stream into a heavy hydrocarbon rich stream and a recycle stream comprising at least one C₃₊ hydrocarbon and a gas selected from the group consisting of carbon dioxide, nitrogen, air, and water; and

separate the recycle stream into a natural gas liquid (NGL) rich stream and a purified recycle stream.

19. The process equipment ofclaim 18, further configured to:

separate the NGL rich stream into a heavy NGL stream and a light NGL stream; and

mix at least a portion of the heavy NGL stream with the heavy hydrocarbon rich stream.

20. The process equipment ofclaim 18, wherein the NGL rich stream comprises less than about 70 percent of the C₃₊ hydrocarbons from the recycle stream.

21. The process equipment ofclaim 18, wherein the NGL rich stream comprises from about 10 percent to about 50 percent of the C₃₊ hydrocarbons from the recycle stream.

22. The process equipment ofclaim 18, wherein the process equipment configured to separate the recycle stream into the NGL rich stream and the purified recycle stream is configured to:

separate the recycle stream into a vapor recycle stream and a liquid recycle stream; and

separate the vapor recycle stream and the liquid recycle stream into the NGL rich stream and the purified recycle stream.

23. The process equipment ofclaim 22, wherein the recycle stream is separated in a separator, and wherein the vapor recycle stream and the liquid recycle stream enter the separator as separate streams.

24. The process equipment ofclaim 19, wherein the heavy hydrocarbon rich stream has a Reid vapor pressure of less than 6 at a temperature of about 100° F. after being mixed with the heavy NGL stream.

25. The process equipment ofclaim 19, further configured to:

combine a second NGL rich stream with the NGL rich stream prior to separating the NGL rich stream; and

separate the second NGL rich stream along with the NGL rich stream to form the heavy NGL stream and the light NGL stream.

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