A system and method for propane-assisted CO2 flooding and produced gas treatment and reinjection.

Abstract

This invention belongs to the field of gas-driven oil recovery technology, specifically providing a system and method for propane-assisted CO2 flooding and produced gas treatment and reinjection, including a CO2 / propane injection subsystem and a produced gas treatment subsystem. This invention improves crude oil fluidity, reduces miscibility pressure, and increases reservoir recovery by adding propane to CO2. Furthermore, it designs a produced gas treatment and reinjection system for propane-assisted CO2 flooding technology, achieving propane reinjection and repurification of degraded gas sources under low-cost conditions, forming an economical and efficient reservoir CO2 injection and production system.

Description

Technical Field

[0001] This invention belongs to the field of gas-driven oil recovery technology, specifically relating to a system and method for propane-assisted CO2 flooding and produced gas treatment and reinjection. Background Technology

[0002] CO2, as a commonly used displacement medium in oilfield gas-driven development, is widely applied in reservoir development. CO2 flooding technology not only significantly improves oil recovery but also enables underground CO2 storage. On one hand, CO2 reduces crude oil viscosity and improves its fluidity by dissolving in it; on the other hand, CO2 has a strong extraction effect on light components in crude oil, and when temperature and pressure reach certain conditions, a miscibility effect occurs between oil and gas, thereby greatly enhancing the reservoir's mobilization capacity.

[0003] However, light hydrocarbon gases are often generated during reservoir development, with methane being the most abundant. Small amounts of light hydrocarbon gases have no economic value and are usually burned on-site to avoid direct emissions and environmental impact. However, during CO2 recycling and reinjection, the presence of methane affects the interphase interaction between CO2 and crude oil, weakening the oil displacement mechanisms such as CO2 viscosity reduction and crude oil expansion, increasing miscibility pressure, and adversely affecting CO2 development in the reservoir. Therefore, light hydrocarbon gases need to be treated. Meanwhile, as the application scope of CO2 flooding technology continues to expand, experts and researchers are adding various additives to CO2 to enhance the CO2 flooding effect and improve the stability and economy of the process, addressing increasingly complex application environments.

[0004] For example, Chinese patent CN108194065A provides a method for improving shale oil recovery using a carbon dioxide / co-solvent system. This method uses one of ethanol, isopropanol, acetone, or ethyl acetate as a co-solvent. CO2 / co-solvent is pressurized and mixed before being injected into the shale reservoir. After a period of well simmering, production is initiated, and this process is repeated multiple times. This method reduces crude oil viscosity by adding co-solvent, enhances the solubility of CO2 in crude oil, and reduces miscibility pressure. However, low co-solvent content cannot effectively reduce crude oil viscosity. Therefore, to effectively enhance the CO2 oil displacement effect, the amount of this type of co-solvent used is generally large. Furthermore, this method lacks a complete co-solvent recovery mechanism, both of which contribute to increased application costs.

[0005] Chinese patent CN117211743A discloses a skid-mounted device and method for self-circulating capture and reinjection of produced gas in a CO2 flooding process. The method involves preliminary separation and classification of the produced gas during CO2 flooding: direct reinjection, aerosol formation through feedstock addition, and oxygen-enriched combustion. The oxygen-enriched combustion method purifies the CO2 gas by supplying oxygen through an oxygen supply pipeline when the light hydrocarbon content in the CO2 gas is high, followed by ignition and combustion within the combustion chamber. This method solves the problem of high gas treatment costs associated with traditional membrane separation technologies. However, it does not consider the recovery and reuse of auxiliary agents added during CO2 development, therefore it is not suitable for scenarios involving CO2 reservoir development assisted by other media. Summary of the Invention

[0006] To address the current issues of produced gas treatment and auxiliary agent recovery in the application of CO2 enhanced oil recovery (EOR) technology in oilfields, this invention, based on the current application status of CO2 EOR and considering the potential of propane in assisted CO2 EOR, provides a system and method for propane-assisted CO2 EOR and produced gas treatment and reinjection. By adding propane to CO2, crude oil fluidity is improved, miscibility pressure is reduced, and reservoir recovery is increased. Furthermore, a produced gas treatment and reinjection system for propane-assisted CO2 EOR is designed, enabling propane reinjection and repurification of degraded gas sources under low-cost conditions, forming an economical and efficient reservoir CO2 injection and production system.

[0007] Propane, as a light hydrocarbon, can reduce crude oil viscosity and enhance CO2 solubility. Compared with methane, propane can effectively improve the interfacial tension between CO2 and crude oil, thereby reducing miscibility pressure. With a molecular weight similar to CO2, propane shows greater application potential in the development of low-permeability or tight oil reservoirs compared to other high-molecular-weight additives. Propane is gaseous at room temperature and pressure, and can be directly separated from crude oil under low pressure. Furthermore, propane can be liquefied at relatively low pressure, creating favorable conditions for low-cost recovery and purification, laying an economic foundation for its large-scale addition. Therefore, the propane-assisted CO2 flooding and produced gas treatment and reinjection system and method provided by this invention not only enhances the CO2 flooding effect and reduces costs while increasing efficiency, but also provides important support for the green development of oil fields, possessing significant technical and economic value.

[0008] The technical solution of the present invention is as follows:

[0009] To address the aforementioned problems, this invention provides a propane-assisted CO2 flooding and produced gas treatment and reinjection system, comprising a CO2 / propane injection subsystem and a produced gas treatment subsystem; the CO2 / propane injection subsystem is connected to the injection well, and the produced gas treatment subsystem is connected to the produced well.

[0010] The CO2 / propane injection subsystem includes an automatic feeding device and connected to it a propane storage tank, a CO2 storage tank, and a multi-stage pressurization module, which is connected to the injection well.

[0011] The produced gas treatment subsystem includes a gas-liquid separation module, a gas component separation module, and an oxygenation and combustion module.

[0012] Furthermore, the gas-liquid separation module includes a primary oil-gas separation device, a secondary oil-gas separation device, a primary produced gas tank, and a crude oil storage tank.

[0013] The primary oil-gas separation unit is connected to the production well, the secondary oil-gas separation unit, and the primary produced gas tank, respectively; the secondary oil-gas separation unit is connected to the primary produced gas tank and the crude oil storage tank, respectively.

[0014] The produced fluid from the production well undergoes initial separation into oil and gas phases through simple gravity separation in the primary oil-gas separator. The gas after the initial separation enters the primary produced gas tank, while the degassed crude oil (the liquid after the initial separation) enters the secondary oil-gas separator. In the secondary oil-gas separator, a second separation of oil and gas is completed. The crude oil (the liquid after the second separation) enters the crude oil storage tank connected to the secondary separator, while the gas after the second separation returns to the primary produced gas tank, cools, and then enters the next stage module.

[0015] The gas component separation module includes a purification sub-module, a component detection device, a component separation device, and a mixed reinjection gas tank, which are sequentially connected to the primary output gas tank.

[0016] The component detection device and component separation device are respectively connected to the secondary output gas tank.

[0017] Preferably, the purification submodule includes a first drying and dust removal device and a desulfurization device connected in sequence to pre-treat the produced gas (gas in the primary produced gas tank 9).

[0018] The mixed reinjection gas tank is also connected to the automatic feeding device in the CO2 / propane injection subsystem.

[0019] According to a preferred embodiment of the present invention, the component separation device achieves component separation under different scenarios at relatively low conditions by controlling the pressure and temperature within the chamber of the pretreated product gas based on the gas composition. The component separation device further includes a first gas detection sub-device to measure the gas content of the pretreated product gas to determine the component separation mode, optimize the separation steps, and reduce separation costs. Since the preferred propane and CO2 treatment conditions are low, the requirements for the component separation device are relatively weak.

[0020] The oxygenation combustion module includes a combustion device connected to the secondary output gas tank, and the combustion device is connected to a pure oxygen tank and a crude CO2 tank respectively.

[0021] The crude CO2 gas tank is connected to the CO2 storage tank in the CO2 / propane injection subsystem.

[0022] Preferably, a second drying and dust removal device is provided between the crude CO2 gas tank and the CO2 storage tank.

[0023] According to a preferred embodiment of the present invention, the combustion device includes an ignition device, a combustion chamber, and a second gas detection sub-device. Gas (mixed gas) in the secondary output gas tank enters the combustion device through a pipeline. The second gas detection sub-device analyzes the gas and controls the intake valve to match the amount of oxygen entering the combustion chamber. After ignition by the ignition device and complete combustion of the organic components, the gas passes the second gas detection sub-device's test again before entering the crude CO2 tank.

[0024] The oxygen-enriched combustion module also includes a water circulation heat exchange device, which transfers heat from the combustion device to the secondary oil-gas separation device through water circulation, thereby promoting the secondary separation of propane.

[0025] The automatic feeding device includes an intelligent feeding sub-device and a third gas detection sub-device. The intelligent feeding sub-device intelligently allocates the feeding ratio of CO2 and propane according to the reservoir conditions. The third gas detection sub-device detects the composition of the reinjected gas and controls the feeding of propane and CO2 storage tanks to change the composition of the reinjected gas.

[0026] The multi-stage booster module includes a primary booster device and a secondary booster device connected in sequence. The primary booster device is connected to an automatic feeding device, and the secondary booster device is connected to an injection well.

[0027] This invention also discloses a method for propane-assisted CO2 flooding and produced gas treatment and reinjection using the above-mentioned propane-assisted CO2 flooding and produced gas treatment and reinjection system, comprising:

[0028] S1. Set the ratio of propane to CO2 feed and inject it into the injection well through a multi-stage pressurization module;

[0029] S2. After the formation fluid is produced by the production well, the gas and liquid separated by the primary oil and gas separator enter the primary produced gas tank and the secondary oil and gas separator, respectively. The gas and liquid separated by the secondary oil and gas separator enter the primary produced gas tank and the crude oil storage tank, respectively.

[0030] S3. The gas in the primary output gas tank enters the component detection device through the purification submodule to identify the propane content.

[0031] When the propane content is ≥ M%, it enters the component separation device. The separated propane and CO2 gas enter the mixing and reinjection gas tank and the automatic feeding device in sequence. The remaining gas enters the secondary output gas tank.

[0032] When the propane content is <M%, it directly enters the secondary output gas tank;

[0033] S4. The gas in the secondary output gas tank enters the combustion device, and the oxygen amount is matched according to the gas composition. The gas after combustion enters the crude CO2 tank and CO2 storage tank in sequence.

[0034] Preferably, in step S1, different injection methods and injection ratios are selected according to different reservoir conditions.

[0035] When considering reducing crude oil viscosity, the injection method and injection ratio are as follows:

[0036] When the crude oil viscosity is greater than or equal to 2000 mPa·s, the crude oil has poor fluidity and low injection capacity. Propane pre-injection is adopted to reduce the viscosity of crude oil and improve the injection capacity. Subsequently, propane and CO2 are mixed and injected. The amount of propane pre-injection is set according to the target formation reserves. Preferably, the proportion of propane in the mixed injection is 30% to 40%.

[0037] When the crude oil viscosity is less than 2000 mPa·s, a propane and CO2 mixed injection method is adopted, with the following preferred propane ratio:

[0038] ① When 2000 mPa·s > crude oil viscosity ≥ 500 mPa·s, the proportion of propane is 30%~40%;

[0039] ② When 500 mPa·s > crude oil viscosity ≥ 100 mPa·s, the proportion of propane is 20%~30%;

[0040] ③ When 100 mPa·s > crude oil viscosity ≥ 10 mPa·s, the proportion of propane is 15%~20%;

[0041] ④ When the crude oil viscosity is <10 mPa·s, the proportion of propane is less than 15%.

[0042] When considering reducing miscibility pressure, indoor high-temperature and high-pressure physical property experiments are required to determine the propane ratio based on the experimental results. The propane to CO2 feeding ratio set by the automatic feeding device is adjusted according to the above reservoir conditions, and the propane ratio can be gradually reduced as the reservoir is developed.

[0043] Preferably, in step S3, the gas in the mixed reinjection tank is pumped to the automatic feeding device. After detecting the propane content, the automatic feeding device adjusts the feeding ratio between the propane storage tank and the CO2 storage tank to meet the needs of different reservoirs at different development stages.

[0044] Preferably, in step S4, the heat generated by the combustion device is used to heat the secondary oil-gas separation device through a water circulation heat exchanger, thereby promoting propane volatilization and improving propane recovery rate.

[0045] In step S4, M% is a preset value, preferably 5-10. Based on the lower limit of propane content and related physical properties, the preferred component separation device of this invention has a pressure upper limit of 12 MPa and a temperature control range of -10 to 30°C, which has low requirements for equipment parameters and low separation cost. In field applications, the equipment parameter requirements can be further reduced by increasing the set M value.

[0046] The propane preferred in this invention is, on the one hand, a non-polar light hydrocarbon gas, and crude oil is mainly composed of non-polar hydrocarbons. The interactions between non-polar molecules are strong; therefore, propane and crude oil have good compatibility and are easily dissolved. When propane dissolves in crude oil, its low viscosity effectively reduces the crude oil viscosity, enhances its fluidity and mobility, weakens viscous fingering caused by differences in gas-liquid viscosity, and delays gas channeling. On the other hand, when the crude oil viscosity is low, the viscosity-reducing effect of propane weakens. A low proportion of propane can reduce CO2 miscibility pressure, enhance the CO2 oil displacement effect, and leverage the synergistic effect of both.

[0047] The advantages of this invention are:

[0048] 1. The propane used in this invention can not only dissolve well in crude oil, reduce crude oil viscosity, enhance crude oil fluidity, improve the mobility ratio, and improve the ability of CO2 to mobilize crude oil; but also reduce the minimum miscibility pressure between CO2 and crude oil, enhance the CO2 dissolution and extraction capacity, and improve crude oil recovery rate.

[0049] 2. The propane used in this invention is gaseous at room temperature and pressure with low liquefaction conditions. When produced alongside crude oil, it can naturally separate into oil and gas, and the subsequent separation of gas components requires low conditions, reducing equipment and separation costs. Compared to other additives, propane's high recovery rate allows for its large-scale addition in heavy oil development, effectively controlling costs while enhancing CO2 development efficiency.

[0050] 3. The produced gas treatment subsystem provided by this invention separates produced gas and crude oil through gravity separation and optimizes the produced gas treatment method based on the propane content measured by the component detection device. The simultaneous separation of propane and CO2, followed by adjustment of the reinjection gas ratio via an automatic feeding device, avoids the high costs and high parameters associated with single-component gas separation, achieving recycling. Furthermore, the oxygen-fueled combustion module designed in this invention achieves combustion of the mixed gas through precise oxygen ratio, converting organic gases into CO2. This simplifies operation and significantly reduces the processing cost of organic gases, enabling further optimization of degraded gas sources.

[0051] 4. This invention has a wide range of applications and can meet the development needs of reservoirs with different viscosities. Furthermore, the injection-production-processing-reinjection system designed in this invention is also applicable to different oil displacement media (pure propane, pure butane, and butane-assisted CO2, etc.) and different development modes (huff-and-puff development). Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the overall structure of a propane-assisted CO2 flooding and produced gas treatment and reinjection system according to the present invention.

[0053] Among them, 1-propane storage tank, 2-CO2 storage tank, 3-automatic feeding device, 4-first-stage pressurization device, 5-second-stage pressurization device, 6-injection well, 7-production well, 8-first-stage oil and gas separation device, 9-primary produced gas tank, 10-first drying and dust removal device, 11-desulfurization device, 12-component detection device, 13-component separation device, 14-mixed reinjection gas tank, 15-second-stage oil and gas separation device, 16-crude oil storage tank, 17-second-stage produced gas tank, 18-combustion device, 19-pure oxygen tank, 20-crude CO2 tank, 21-second drying and dust removal device, 22-water circulation heat exchange device, 23-construction reservoir. Detailed Implementation

[0054] The operation of the propane-assisted CO2 flooding and produced gas treatment and reinjection system of the present invention will now be described in full and detail with reference to the accompanying drawings.

[0055] like Figure 1 As shown, a propane-assisted CO2 flooding and produced gas treatment and reinjection system includes a CO2 / propane injection subsystem and a produced gas treatment subsystem; the CO2 / propane injection subsystem is connected to the injection well, and the produced gas treatment subsystem is connected to the production well.

[0056] The CO2 / propane injection subsystem is used to regulate gas composition and compress gas, and includes a propane storage tank 1, a CO2 storage tank 2, an automatic feeding device 3, a primary pressurization device 4, and a secondary pressurization device 5. The automatic feeding device 3 is connected to the propane storage tank 1, the CO2 storage tank 2, and the primary pressurization device 4, respectively. The primary pressurization device 4 is connected in sequence to the secondary pressurization device 5 and the injection well 6.

[0057] The propane storage tank 1 and CO2 storage tank 2 store propane and CO2 for injection into the formation, respectively.

[0058] The automatic feeding device 3 can set and adjust the gas ratio according to reservoir conditions and development methods. The automatic feeding device 3 includes an intelligent feeding sub-device and a third gas detection sub-device, which can detect the composition of the reinjected gas and change the composition of the reinjected gas by intelligently distributing the feeding ratio of propane storage tank 1 and CO2 storage tank 2 to meet the injection ratio.

[0059] The primary booster 4 and the secondary booster 5 can boost the gas to the injection pressure in two stages to meet the injection pressure requirements.

[0060] The produced gas treatment subsystem includes a gas-liquid separation module, a gas component separation module, and an oxygenation and combustion module.

[0061] The gas-liquid separation module is used to achieve gas-liquid separation of the produced fluid, including a primary oil-gas separation device 8, a primary produced gas tank 9, a secondary oil-gas separation device 15, and a crude oil storage tank 16; the primary oil-gas separation device 8 is connected to the producing well 7, the secondary oil-gas separation device 15, and the primary produced gas tank 9 respectively; the secondary oil-gas separation device 15 is connected to the primary produced gas tank 9 and the crude oil storage tank 16 respectively;

[0062] The primary oil-gas separator 8 separates the naturally degassed product fluid into two phases, oil and gas, through gravity separation. The gas after the primary separation enters the primary product gas tank 9, and the liquid after the primary separation enters the secondary oil-gas separator 15.

[0063] The secondary oil-gas separation device 15 promotes the secondary separation of propane in the liquid after the primary separation by means of heating, thereby improving the propane recovery rate. The gas after secondary separation enters the primary produced gas tank 9, and the liquid after secondary separation enters the crude oil storage tank 16.

[0064] The gas component separation module is used for output processing and manufacturing, including a first drying and dust removal device 10, a desulfurization device 11, a component detection device 12, a component separation device 13, and a mixed reinjection gas tank 14 connected in sequence to the primary output gas tank 9, and a secondary output gas tank 17 connected to the component detection device 12 and the component separation device 13 respectively.

[0065] The first drying and dust removal device 10 and the desulfurization device 11 are used to achieve the drying, dust removal and desulfurization of the produced gas.

[0066] The component detection device 12 performs propane component detection on the pretreated output gas to determine the gas delivery pipeline.

[0067] The component separation device 13 includes a first gas detection sub-device, which measures the content of the pretreated product gas to determine the component separation mode, optimize the separation steps, and reduce separation costs. The component separation device 13 performs component separation on the pretreated product gas by controlling temperature and pressure. The use of a mixed separation method for propane and CO2 avoids the harsh conditions, complex operations, and high costs associated with single-component separation. The separated propane and CO2 enter the mixed reinjection gas tank 14, while the remaining gas enters the secondary product gas tank 17.

[0068] The mixed reinjection gas tank 14 is connected to the automatic feeding device 3. Propane and CO2 are reinjected into the construction reservoir 23 after the gas ratio is adjusted by the automatic feeding device 3.

[0069] The oxygen-enriched combustion module is used for the combustion of organic gases and includes a combustion device 18 connected to the secondary product gas tank 17, and a pure oxygen tank 19 and a crude CO2 tank 20 respectively connected to the combustion device 18. The crude CO2 tank 20 is connected to the CO2 storage tank 2 through a second drying and dust removal device 21. The combustion device 18 exchanges heat with the secondary oil-gas separator 15 through a water circulation heat exchange device 22.

[0070] The combustion device 18 includes an ignition device, a combustion chamber, and a second gas detection sub-device. After analyzing the gas, the second gas detection sub-device controls the oxygen supply to the chamber by adjusting the inlet valve of the pure oxygen tank 19. After ignition by the ignition device, the organic components are fully combusted. After passing the second gas detection sub-device's test, the gas enters the crude CO2 tank 20 and returns to the CO2 storage tank 2 after passing through the second drying and dust removal device 21.

[0071] The water circulation heat exchange device 22 conducts the heat generated by the combustion device 18 to the secondary oil-gas separator 15, promoting the volatilization and recovery of propane.

[0072] A method for propane-assisted CO2 oil displacement and produced gas treatment and reinjection using the above-mentioned propane-assisted CO2 oil displacement and produced gas treatment and reinjection system is as follows.

[0073] S1. Based on the crude oil viscosity and development method, the feeding ratio is set by the automatic feeding device 3. CO2 and propane in the storage tank are pumped into the automatic feeding device 3 and the ratio is adjusted. Then, they are pressurized to the set injection pressure by the first-stage pressurization device 4 and the second-stage pressurization device 5 and injected into the injection well 6.

[0074] S2. After the fluid is produced from the production well 7, it undergoes primary oil and gas separation in the primary oil and gas separation unit 8. The gas after primary separation enters the primary production gas tank 9, and the liquid after primary separation enters the secondary oil and gas separation unit 15 for secondary oil and gas separation. The gas after secondary separation also enters the primary production gas tank 9, and the liquid after secondary separation enters the crude oil storage tank 16.

[0075] S3. The produced gas in the primary produced gas tank 9 passes through the first drying and dust removal device 10, the desulfurization device 11, and the component detection device 12 in sequence via pipelines. The component detection device 12 measures the content of the pretreated produced gas. Based on the gas composition, considering the gas partial pressure law and related gas properties, the following corresponding treatment methods can be selected:

[0076] When the propane content is ≥ M%, it enters the component separation device 13 for cooling and pressurization to achieve the liquefaction and separation of the remaining propane and CO2. The separated propane and CO2 gas enter the mixing and reinjection gas tank 14 and are connected to the automatic feeding device 3 through pipelines. As propane and CO2 are separated, the propane content gradually decreases. When the propane content is < M% or reaches the preferred upper limit of temperature and pressure, the remaining gas is pushed from the component separation device 13 to the secondary output gas tank 17.

[0077] When the propane content is <M%, it directly enters the secondary output gas tank 17.

[0078] The M% mentioned above is a preset value, and the preferred M value in this invention is 5-10. Based on the lower limit of propane content and related physical properties, the preferred component separation device 13 of this invention has an upper pressure limit of 12 MPa and a temperature control range of -10 to 30°C, which has low requirements for equipment parameters and low separation costs. In field applications, the equipment parameter requirements can be further reduced by increasing the set M value. Methane and propane liquefaction conditions are extremely harsh, and liquefaction will not occur within the preferred temperature and pressure range.

[0079] The gas in the mixed reinjection gas tank 14 is pumped to the automatic feeding device 3. The automatic feeding device 3 can also adjust the composition of the reinjection gas through the propane storage tank 1 and the CO2 storage tank 2 to meet the needs of different reservoirs at different development stages.

[0080] S4. The secondary product gas tank 17 is connected to the combustion device 18. Based on the gas composition in the secondary product gas tank 17, the oxygen content is matched to ensure the organic gases in the mixed gas are burned in the combustion device 18, purifying the CO2 gas. The burned gas enters the crude CO2 tank 20, and after drying and deoxygenation, it returns to the CO2 storage tank 2. The heat generated by the combustion device 18 supplies heat to the secondary oil-gas separator 15 through the water circulation heat exchanger 22, promoting propane volatilization and improving propane recovery rate.

[0081] Specific implementation process:

[0082] The propane and CO2 ratio of the automatic feeding device 3 is set according to the reservoir characteristics and development method. Propane and CO2 gases in propane storage tank 1 and CO2 storage tank 2 are transported to the automatic feeding device 3 and adjusted to the preset ratio. The injection gas that meets the ratio passes through the primary pressurization device 4 and the secondary pressurization device 5 in sequence, pressurizes to the injection pressure, and is injected into the formation through the injection well 6.

[0083] Formation fluid is produced from production well 7 and undergoes initial separation and degassing in the primary oil-gas separator 8. The primary oil-gas separator 8 separates the degassed crude oil (liquid after initial separation) and the gas after initial separation through gravity separation, and then transports them to the secondary oil-gas separator 15 and the primary produced gas tank 9, respectively. The secondary oil-gas separator 15 performs secondary separation through heating and other means to further promote the volatilization of propane, and then separates the oil and gas through gravity separation. The crude oil (liquid after secondary separation) enters the crude oil storage tank 16, while the gas after secondary separation also enters the primary produced gas tank 9.

[0084] The produced gas in the primary produced gas tank 9 passes through the first drying and dust removal device 10 to remove moisture and solid impurities, and then passes through the desulfurization device 11 to remove H2S gas, thus completing the pretreatment of the produced gas.

[0085] After pretreatment, the output gas is analyzed by component detection device 12 to determine the propane content, which is then compared with a preset value M%. When the propane content is ≥ M%, it enters component separation device 13. Component separation device 13 liquefies the main components of propane and CO2 by adjusting the temperature and pressure. When the propane content is < M% or the preferred temperature and pressure upper limit is reached, gas-liquid separation is performed. The liquefied propane and CO2 are transported to mixing and reinjection gas tank 14, while the remaining gas is transported to secondary output gas tank 17.

[0086] After the pretreated output gas is tested by the component detection device 12 to determine the propane content, when the propane content is <M%, it directly enters the secondary output gas tank 17.

[0087] The gas in the secondary output gas tank 17 is a mixture of CO2 and organic gases. It is transported via pipeline to the combustion device 18. A second gas detection sub-device within the combustion device 18 measures the organic gas content and matches the required oxygen quantity for combustion. Oxygen is transported from the pure oxygen tank 19 to the combustion device 18 via pipeline, ignited by the ignition device, and the organic gases are fully combusted and converted into CO2. The CO2 is pushed to the crude CO2 tank 20 and, after passing through the second drying and dust removal device 21, returned to the CO2 storage tank 2. The heat generated by the combustion device 18 is utilized by the secondary oil-gas separator 15 through the water circulation heat exchanger 22.

[0088] The reinjection gas, composed of propane and CO2, in the mixed reinjection gas tank 14 is pumped to the automatic feeding device 3 via the reinjection pipeline. The automatic feeding device 3 measures the ratio of propane to CO2. When the ratio does not meet the preset ratio, propane storage tank 1 and CO2 storage tank 2 are added to adjust the ratio. When the preset ratio is met, the reinjection gas is pressurized to the required injection pressure through the primary pressurization device 4 and the secondary pressurization device 5, and then injected into the formation through the injection well 6, completing the reinjection of the produced gas.

[0089] Example 1

[0090] The viscosity of crude oil in reservoir H is 500 mPa·s. I1 and P1 are the gas injection well and the production well, respectively.

[0091] Wells I1 and P1 employ a propane-assisted CO2 flooding and produced gas treatment and reinjection system, such as Figure 1 As shown, it includes a CO2 / propane injection subsystem and a produced gas treatment subsystem;

[0092] Based on the characteristics of reservoir H, the propane content of the automatic feeding device 3 is set to 30%, and the propane content M% of the component detection device 12 is set to 5%. Propane and CO2 gas in propane storage tank 1 and CO2 storage tank 2 are transported to the automatic feeding device 3 and adjusted to a propane content of 30%. They then pass through the primary pressurization device 4 and the secondary pressurization device 5 in sequence, pressurizing to an injection pressure of 10 MPa, and are injected into the formation through injection well 6 (I1).

[0093] Formation fluid is produced from production well 7 (P1) and enters the primary oil-gas separator 8 for initial separation, undergoing natural degassing at ambient temperature and pressure. After degassing, under the influence of gravity, the liquid after the initial separation enters the secondary oil-gas separator 15, while the gas after the initial separation is transported to the primary produced gas tank 9. The secondary oil-gas separator 15 performs secondary separation by heating to 60°C and stirring, further promoting propane volatilization. When no further gas separation occurs, oil and gas are separated by gravity. The liquid (crude oil) after the secondary separation enters the crude oil storage tank 16 for subsequent processing, while the gas after the secondary separation also enters the primary produced gas tank 9.

[0094] The produced gas in the primary produced gas tank 9 passes through the first drying and dust removal device 10 to remove moisture and solid impurities, and then passes through the desulfurization device 11 to remove H2S gas, thus completing the pretreatment of the produced gas.

[0095] The pretreated product gas, after being measured by component detection device 12, has a propane content of 24%, which is greater than the preset value M%. It then enters component separation device 13. Component separation device 13 liquefies the main components of propane and CO2 by adjusting the temperature and pressure. When liquefaction ceases, the propane content in the gas phase is measured to be below the preset value M%. At this point, the temperature is 0°C and the pressure is approximately 10 MPa. The liquefied propane and CO2 after gas-liquid separation are transported to mixing and reinjection gas tank 14, while the remaining gas is transported to secondary product gas tank 17.

[0096] The mixed gas in the secondary output gas tank 17 is transported to the combustion device 18. The second gas detection sub-device within the combustion device 18 measures the organic gas content and matches the required oxygen quantity for combustion. Oxygen is transported from the pure oxygen tank 19 to the combustion device 18 via pipeline, ignited by the ignition device, and the organic gas is fully combusted and converted into CO2 gas. The CO2 is pushed to the crude CO2 tank 20 and, after passing through the second drying and dust removal device 21, returned to the CO2 storage tank 2. The heat generated by the combustion device 18 is utilized by the secondary oil-gas separator 15 through the water circulation heat exchanger 22.

[0097] The reinjected gas in the mixed reinjection gas tank 14 is pumped to the automatic feeding device 3 via the reinjection pipeline. Its propane content is measured to be 28%, which does not meet the preset ratio. Propane is added through the propane storage tank 1 to adjust the propane content to 30%. After meeting the preset ratio, the reinjected gas is pressurized to the required injection pressure of 10 MPa by the first-stage pressurization device 4 and the second-stage pressurization device 5, and then injected into the construction reservoir 23 through the injection well 6 (I1) to complete the reinjection of the produced gas.

[0098] Example 2

[0099] The crude oil viscosity of reservoir Y is 25 mPa·s, and it is a saturated reservoir. I2 and P2 are gas injection well and production well, respectively.

[0100] Wells I2 and P2 employ a propane-assisted CO2 flooding and produced gas treatment and reinjection system, such as Figure 1 As shown, it includes a CO2 / propane injection subsystem and a product gas treatment subsystem; the automatic feeding device 3 is set to have a propane content of 15%, and the component detection device 12 is set to have a propane content M% of 5%.

[0101] Propane and CO2 gas from propane storage tank 1 and CO2 storage tank 2 are transported to automatic feeding device 3 and adjusted to a propane content of 15%. They then pass through primary pressurization device 4 and secondary pressurization device 5 in sequence, pressurizing to 15 MPa, and are injected into the formation through injection well 6 (I2).

[0102] Formation fluid is produced through production well 7 and undergoes initial separation and degassing in primary oil and gas separation unit 8. Primary oil and gas separation unit 8 separates the degassed crude oil (liquid after initial separation) and gas after initial separation through gravity separation, and then transports them to secondary oil and gas separation unit 15 and primary produced gas tank 9, respectively.

[0103] The secondary oil-gas separation unit 15 heats the fluid to 60°C and then performs secondary separation by stirring to further promote the volatilization of propane. Then, the oil and gas are separated by gravity. The crude oil (liquid after secondary separation) enters the crude oil storage tank 16, while the gas after secondary separation also enters the primary production gas tank 9.

[0104] The produced gas in the primary produced gas tank 9 passes through the first drying and dust removal device 10 to remove moisture and solid impurities, and then passes through the desulfurization device 11 to remove H2S gas, thus completing the pretreatment work.

[0105] In the initial stage of production, the main product is pure crude oil. After degassing, the main components of the produced fluid are crude oil and light hydrocarbon gases saturated in the crude oil, with almost no injected gas. At this time, the pre-treated produced gas is measured by component detection device 12 to have a propane content of only 3%, and it directly enters the secondary produced gas tank 17. After being converted into CO2 by adding oxygen and combustion in the combustion device 18, it is returned to the CO2 storage tank 2 after passing through the crude CO2 tank 20 and the second drying and dust removal device 21.

[0106] After a period of displacement, the content of injected gas in the produced gas gradually increases. When the propane content is ≥ M%, the produced gas enters the component separation unit 13. The component separation unit 13 liquefies propane and CO2 by adjusting the temperature and pressure. The liquefied propane and CO2 are transported to the mixed reinjection gas tank 14, while the remaining gas is transported to the secondary produced gas tank 17.

[0107] The mixed gas in the secondary output gas tank 17 contains CO2 and organic gases. After being burned with oxygen in the combustion device 18, it is converted into CO2 and then returned to the CO2 storage tank 2 after passing through the crude CO2 tank 20 and the second drying and dust removal device 21.

[0108] The heat generated by the combustion device 18 is utilized by the secondary oil-gas separator 15 through the water circulation heat exchange device 22.

[0109] The reinjection gas, composed of propane and CO2, in the mixed reinjection gas tank 14 is pumped to the automatic feeding device 3 via the reinjection pipeline. The automatic feeding device 3 measures the ratio of propane to CO2 and adjusts the ratio by adding gas through the propane storage tank 1 and the CO2 storage tank 2. When the preset ratio is met, the reinjection gas is pressurized to the required injection pressure through the primary pressurization device 4 and the secondary pressurization device 5, and then injected into the formation through the injection well 6, completing the reinjection of the produced gas.

[0110] Example 3

[0111] The viscosity of crude oil in reservoir Z is 10 mPa·s, and the formation pressure is 16 MPa. I3 and P3 are gas injection well 6 and production well 7, respectively. The miscibility pressure of CO2 and crude oil was measured to be about 18 MPa by indoor high temperature and high pressure PVT test. When 35% propane was added, the miscibility pressure dropped to 15.5 MPa.

[0112] Wells I3 and P3 employ a propane-assisted CO2 flooding and produced gas treatment and reinjection system, such as... Figure 1 As shown, it includes a CO2 / propane injection subsystem and a produced gas treatment subsystem;

[0113] Based on the characteristics of reservoir H, the propane content of the automatic feeding device 3 is set to 35%, and the propane content M% of the component detection device is set to 5%. Propane and CO2 gas in propane storage tank 1 and CO2 storage tank 2 are transported to the automatic feeding device 3 and adjusted to a propane content of 35%. After passing through the primary pressurization device 4 and the secondary pressurization device 5, they are injected into the construction reservoir 23 through injection well 6 (I3).

[0114] Formation fluid is produced from production well 7 (P3) and enters the primary oil-gas separator 8 for initial separation, where natural degassing occurs at ambient temperature and pressure. After degassing, under the action of gravity, the liquid after the initial separation enters the secondary oil-gas separator 15, while the gas after the initial separation is transported to the primary produced gas tank 9. The secondary oil-gas separator 15 performs secondary separation by heating the fluid to 60°C and stirring, further promoting the volatilization of propane. When no more gas separation occurs, oil and gas are separated by gravity. The crude oil (the liquid after the secondary separation) enters the crude oil storage tank 16 for further processing, while the gas after the secondary separation also enters the primary produced gas tank 9.

[0115] The produced gas in the primary produced gas tank 9 passes through the first drying and dust removal device 10 to remove moisture and solid impurities, and then passes through the desulfurization device 11 to remove H2S gas, thus completing the pretreatment work.

[0116] The pretreated product gas, after being measured by component detection device 12, has a propane content of 30%, which is greater than the preset value M%, and then enters the component separation device 13. The component separation device 13 liquefies the main components of propane and CO2 by adjusting the temperature and pressure. When liquefaction ceases, the propane content in the gas phase is measured to be lower than the preset value M%, at which point the temperature is 0°C and the pressure is approximately 10 MPa. The liquefied propane and CO2 after gas-liquid separation are transported to the mixing and reinjection gas tank 14, while the remaining gas is transported to the secondary product gas tank 17.

[0117] The mixed gas in the secondary output gas tank 17 is transported to the combustion device 18. The second gas detection sub-device within the combustion device 18 measures the organic gas content and matches the required oxygen quantity for combustion. Oxygen is transported from the pure oxygen tank 19 to the combustion device 18 via pipeline, ignited by the ignition device, and the organic gas is fully combusted and converted into CO2 gas. The CO2 is pushed to the crude CO2 tank 20 and, after passing through the second drying and dust removal device 21, returned to the CO2 storage tank 2. The heat generated by the combustion device 18 is utilized by the secondary oil-gas separator 15 through the water circulation heat exchanger 22.

[0118] The reinjected gas in the mixed reinjection gas tank 14 is pumped to the automatic feeding device 3 via the reinjection pipeline. Its propane content is measured to be 60%, which does not meet the preset ratio. Carbon dioxide is added through the CO2 storage tank 2 to adjust the propane content to 35%. After meeting the preset ratio, the reinjected gas is pressurized to the required injection pressure through the primary pressurization device 4 and the secondary pressurization device 5, and then injected into the formation through the injection well 6 (I3) to complete the reinjection of the produced gas.

Claims

1. A system for propane-assisted CO2 flooding and produced gas treatment and reinjection, characterized in that, It includes a CO2 / propane injection subsystem and a produced gas processing subsystem; the CO2 / propane injection subsystem is connected to the injection well, and the produced gas processing subsystem is connected to the produced well; The CO2 / propane injection subsystem includes an automatic feeding device and connected to it a propane storage tank, a CO2 storage tank, and a multi-stage pressurization module, which is connected to the injection well. The produced gas treatment subsystem includes a gas-liquid separation module, a gas component separation module, and an oxygenation and combustion module. The gas-liquid separation module includes a primary oil-gas separation device, a secondary oil-gas separation device, a primary produced gas tank, and a crude oil storage tank; the primary oil-gas separation device is connected to the production well, the secondary oil-gas separation device, and the primary produced gas tank; the secondary oil-gas separation device is connected to the primary produced gas tank and the crude oil storage tank. The gas component separation module includes a purification submodule, a component detection device, a component separation device, and a mixed reinjection gas tank, which are sequentially connected to the primary produced gas tank; the component detection device and the component separation device are respectively connected to the secondary produced gas tank. The oxygenation combustion module includes a combustion device connected to the secondary output gas tank, and the combustion device is connected to a pure oxygen tank and a crude CO2 tank respectively. The crude CO2 gas tank is connected to the CO2 storage tank in the CO2 / propane injection subsystem; The mixed reinjection gas tank is connected to the automatic feeding device in the CO2 / propane injection subsystem.

2. The propane-assisted CO2 flooding and produced gas treatment and reinjection system according to claim 1, characterized in that, The oxygen-enriched combustion module also includes a water circulation heat exchange device, which transfers heat from the combustion device to the secondary oil-gas separator through water circulation.

3. The propane-assisted CO2 flooding and produced gas treatment and reinjection system according to claim 1, characterized in that, The component separation device further includes a first gas detection sub-device; The combustion device includes an ignition device, a combustion chamber, and a second gas detection sub-device; The automatic feeding device includes an intelligent feeding sub-device and a third gas detection sub-device.

4. The propane-assisted CO2 flooding and produced gas treatment and reinjection system according to claim 1, characterized in that, The purification submodule includes a first drying and dust removal device and a desulfurization device connected in sequence. A second drying and dust removal device is installed between the crude CO2 gas tank and the CO2 storage tank.

5. The propane-assisted CO2 flooding and produced gas treatment and reinjection system according to claim 1, characterized in that, The multi-stage booster module includes a primary booster device and a secondary booster device connected in sequence. The primary booster device is connected to an automatic feeding device, and the secondary booster device is connected to an injection well.

6. A method for propane-assisted CO2 flooding and produced gas treatment and reinjection using the propane-assisted CO2 flooding and produced gas treatment and reinjection system according to any one of claims 1-5, characterized in that, include: S1. Set the ratio of propane to CO2 feed and inject it into the injection well through a multi-stage pressurization module; S2. After the formation fluid is produced by the production well, the gas and liquid separated by the primary oil and gas separator enter the primary produced gas tank and the secondary oil and gas separator, respectively. The gas and liquid separated by the secondary oil and gas separator enter the primary produced gas tank and the crude oil storage tank, respectively. S3. The gas in the primary output gas tank enters the component detection device through the purification submodule to identify the propane content. When the propane content is ≥ M%, it enters the component separation device. The separated propane and CO2 gas enter the mixing and reinjection gas tank and the automatic feeding device in sequence. The remaining gas enters the secondary output gas tank. When the propane content is <M%, it directly enters the secondary output gas tank; M% is a preset value for propane content; S4. The gas in the secondary output gas tank enters the combustion device, and the oxygen amount is matched according to the gas composition. The gas after combustion enters the crude CO2 tank and CO2 storage tank in sequence.

7. The method according to claim 6, characterized in that, In step S1, when considering reducing crude oil viscosity, the injection method is as follows: When the crude oil viscosity is greater than or equal to 2000 mPa·s, propane pre-injection is used first, followed by propane and CO2 mixed injection. When the crude oil viscosity is less than 2000 mPa·s, propane and CO2 are injected together.

8. The method according to claim 7, characterized in that, When 2000 mPa·s > crude oil viscosity ≥ 500 mPa·s, the proportion of propane is 30%~40%; When 500 mPa·s > crude oil viscosity ≥ 100 mPa·s, the proportion of propane is 20%~30%; When 100 mPa·s > crude oil viscosity ≥ 10 mPa·s, the proportion of propane is 15%~20%; When the crude oil viscosity is <10 mPa·s, the proportion of propane is less than 15%.

9. The method according to claim 6, characterized in that, M is 5~10.

10. The method according to claim 9, characterized in that, The component separation device has a pressure limit of 12 MPa and a temperature control range of -10 to 30°C.

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