CO2 recycling method for in-situ conversion of organic-rich shale with residual heat

Abstract

The method for residual heat recovery of CO2 injection cycle exploitation of organic-rich shale in-situ conversion belongs to the field of in-situ exploitation of organic-rich shale, and uses the organic-rich shale stratum after in-situ conversion process exploitation as a target area, uses the in-situ conversion existing development well pattern as a residual heat cycle exploitation channel, injects profile control liquid into the stratum to adjust the interface between supercritical CO2 and residual oil and gas products, injects CO2 at normal temperature with pressure greater than 8 MPa into the organic-rich shale stratum through an injection well, the temperature increases with the increase of injection depth, the organic-rich shale stratum heats and converts the CO2 into a supercritical state, the heat carried by the CO2, oil, gas and water mixture produced by a residual heat production well heats the in-situ conversion heat carrier and injects it into the in-situ conversion development well group adjacent to the organic-rich shale, the CO2 gas produced by the residual heat production well is cyclically injected into the injection well, and finally the CO2 is sealed in the stratum. The method changes oil and gas production into geothermal production, prolongs the engineering economic life.

Description

Technical Field

[0001] This invention belongs to the field of in-situ mining of organic-rich shale, specifically, it relates to a method for in-situ mining of residual heat after conversion of organic-rich shale using CO2 injection and recycling. Background Technology

[0002] my country possesses vast organic-rich shale resources, but their overall thermal evolution is relatively low. Studies suggest that the proportion of retained hydrocarbons is approximately 25%, while unconverted organic matter accounts for 40%–100%. Conventional horizontal well volumetric fracturing development techniques are not suitable, necessitating new technologies to address the extraction challenges of organic-rich shale. In-situ underground conversion technology refers to a development method that involves artificially heating shale reservoirs to 350℃–500℃ to in-situ decompose the solid organic matter and retained hydrocarbons within the shale into smaller molecule oil and gas, which is then extracted to the surface using advanced oil production techniques. Internationally, numerous oil companies and research institutions have successively developed more than ten in-situ conversion technologies for oil shale. Among them, the underground combustion in-situ conversion technology proposed by the U.S. Bureau of Mines and Occidental Petroleum (see patent document CA1113000A), Shell's ICP technology (see patent documents US8408294B2, US9644465B2), ExxonMobil's Electrofrac™ technology (see patent document AU2012332851A1), Israel Asia Technologies' TS method, and the CCR fluid heating technology proposed by U.S. shale oil companies (see patent document US7921907B2) have all been tested in the field. In response to the natural endowment of oil shale in my country, domestically developed self-generating heat in-situ conversion method (see patent document CN114017032B) and CO2 injection in-situ conversion method (see patent documents CN115306363A and CN218811531U) have been developed.

[0003] However, the above-mentioned technologies are only for the recovery of oil and gas resources in organic-rich shale. While the in-situ conversion of organic-rich shale produces a large amount of oil and gas, it also retains a large amount of heat in the shale formation, with temperatures reaching 400℃ to 500℃. By using technical means to extract this heat to the surface for in-situ conversion and recycling, the cost of in-situ conversion technology can be further reduced, which has great industrial application value.

[0004] Traditional geothermal extraction primarily uses water as the heat-carrying medium, circulating it into the formation to extract geothermal energy storage (refer to patent document CN115615106A). Water has advantages such as high heat capacity, high thermal conductivity, and thermal stability. However, its application is significantly limited for ultra-low permeability shale formations: ① High circulation flow is required for geothermal extraction. Deep, high-temperature shale reservoirs have low permeability, resulting in low water injectability and prominent issues with circulation and reinjection; ② High-speed water flow can erode formation rocks, causing the detachment of pore cement and the fragmentation of framework minerals, blocking the reservoir's pore throat structure and affecting the formation's conductivity; ③ Under high-temperature conditions, injected water will undergo geochemical reactions with minerals in the shale formation, leading to the dissolution and precipitation of sensitive minerals and the hydration and expansion of clay, reducing formation porosity and permeability, and affecting injection capacity and seepage rate; ④ Residual natural gas in the formation after in-situ conversion can cause the reservoir flow to be two-phase flow in the early stages of extraction, creating a fingering effect in the formation and affecting the initial extraction efficiency of geothermal development. In addition, insufficient natural water sources or concerns about the pollution of local water sources by ground-circulating water will also limit the application of water as a heat-carrying medium. Summary of the Invention

[0005] The purpose of this invention is to provide a method for CO2 injection and recycling to exploit the residual heat after in-situ conversion of organic-rich shale, thereby solving the problems of high energy consumption and carbon emissions in in-situ conversion technology of organic-rich shale. This method can improve the recycling of residual heat in organic-rich shale formations after in-situ conversion, further reduce the cost of shale oil extraction, and at the same time, achieve efficient and safe storage of CO2 in the formation after in-situ conversion of organic-rich shale.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for in-situ conversion of organic-rich shale using CO2 recycling, the method comprising the following steps:

[0007] Step 1: Determine the target area for residual heat from in-situ conversion of organic-rich shale in CO2 recycling mining. The target area is the organic-rich shale formation after mining by in-situ conversion process, and the average temperature of the formation exceeds 250°C.

[0008] Step 2: Utilize the existing development well network in situ as a residual heat circulation exploitation channel, convert the existing heat injection wells in the development well network in situ as injection wells and the production wells as residual heat production wells, and run insulated oil pipes in the residual heat production wells.

[0009] Step 3: Inject profile control fluid into the organic-rich shale formation to adjust the interface between supercritical CO2 and residual oil and gas products in the formation;

[0010] Step 4: Using a compressor, ambient temperature CO2 with a pressure greater than 8MPa is injected into the organic-rich shale formation after in-situ conversion through the injection well. As the injection depth increases, the temperature rises, and the organic-rich shale formation heats the CO2. When the temperature reaches 31.1℃, the CO2 is converted into a supercritical state, and the pressure and temperature changes at the bottom of the injection well and the residual heat production well are monitored in real time.

[0011] Step 5: Using a heat exchanger, the heat carried by the mixture of CO2, oil, gas and water produced in the residual heat production well is used to heat the in-situ conversion heat transfer medium. The heated in-situ conversion heat transfer medium is then injected into the adjacent organic-rich shale in-situ conversion development well group to realize the recycling of the formation residual heat after in-situ conversion. The mixture of CO2, oil, gas and water produced in the residual heat production well is separated, and the CO2 gas is circulated and injected into the injection well.

[0012] Step Six: Geothermal resource development is completed, equipment is recovered, and injection wells and residual heat production wells are cemented and sealed.

[0013] Furthermore, in step two, the heat-insulating oil pipe adopts SY-T 5324-94 prestressed heat-insulating oil pipe. The old heat-insulating oil pipe that is pulled out after gas injection and heat recovery in the well can continue to be used in the next round of gas injection and heat recovery when its apparent thermal conductivity is less than 1.2 times that of the new heat-insulating oil pipe.

[0014] Furthermore, in step three, PI optimization decision-making technology is used to determine the type and dosage of profile control agent.

[0015] Furthermore, in step three, bulky particles and polymeric weak gels are used together as profile control agents. Bulky particle suspension and polymeric weak gel suspension are sequentially injected into the organic-rich shale formation. Bulky particle suspension forms a bulky particle suspension layer, and polymeric weak gel suspension forms a polymeric weak gel suspension layer. The bulky particle suspension layer uses bulky particles with a diameter of 1mm to 3mm or 3mm to 5mm, wherein the bulky particles are GP series ground crosslinked prepolymers, and the polymeric weak gel is zwitterionic polymer FT-213.

[0016] Furthermore, in step four, temperature and pressure sensors are driven into the organic-rich shale formation every 20m along the line connecting the injection well and the residual heat production well to ensure that the bottom hole pressure of the injection well and the residual heat production well is greater than 8MPa and the bottom hole temperature is greater than 35℃, while ensuring that the formation fluid pressure at the bottom of the well and the organic-rich shale formation is the same.

[0017] Furthermore, in step five, the in-situ conversion heat transfer medium includes nitrogen, water vapor, air, and CO2.

[0018] Furthermore, in step six, the end of the recycling process of residual formation heat after in-situ conversion is determined by evaluating the energy return rate curve. The recycling of residual formation heat after in-situ conversion is terminated when the energy return rate decreases.

[0019] Furthermore, after step six, CO2 is sealed inside the organic-rich shale formation.

[0020] Furthermore, in the CO2 injection and circulation mining method for residual heat after in-situ transformation of organic-rich shale, the formation pressure of the organic-rich shale formation is checked at 10-day intervals after well sealing, and the well sealing is considered reliable if the pressure drop is less than 2% after four months.

[0021] Through the above design scheme, the present invention can bring the following beneficial effects:

[0022] 1. In-situ conversion of organic-rich shale formations with residual heat enhancement is used as a new energy utilization method. This effectively utilizes existing in-situ conversion well networks and surface facilities, and in the later stages of in-situ conversion development, transforms oil and gas extraction into geothermal extraction, thus extending the economic life of the project.

[0023] 2. This invention proposes a technology that uses CO2 as a heat-carrying medium to extract residual heat from organic-rich shale formations after in-situ conversion. This technology fully utilizes the heat capacity characteristics of CO2 in different phases to improve heat extraction and heat exchange efficiency. At the same time, combined with CO2 geological storage technology, a large amount of CO2 is buried in the gas reservoir during geothermal extraction, reducing greenhouse gas emissions. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the invention and form part of this invention. The illustrative embodiments and descriptions thereof are used to understand the invention and do not constitute an undue limitation thereof. In the drawings:

[0025] Figure 1 This is a general layout diagram of the CO2 recycling mining in-situ conversion residual heat system for organic-rich shale in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the well network layout for the CO2 circulating mining in-situ conversion residual heat system of organic-rich shale in an embodiment of the present invention;

[0027] Figure 3 This is a cross-sectional view of the residual heat mining zone of the CO2 circulating mining in-situ conversion residual heat system for organic-rich shale in an embodiment of the present invention;

[0028] Figure 4 This is a temperature diagram of the residual heat system for in-situ conversion of organic-rich shale in a CO2 recycling mining embodiment of the present invention;

[0029] Figure 5This is a schematic diagram of the surface injection and heat exchange system of the CO2 cyclic mining in-situ conversion residual heat system for organic-rich shale in an embodiment of the present invention.

[0030] The markings in the diagram are as follows: 1-Injection well; 2-Residual heat production well; 3-Overburden; 4-Organic shale formation; 5-Underlying layer; 6-Insulated tubing; 7-Downhole heater; 8-CO2 drive section; 9-Polymer weak gel suspension layer; 10-Swelling particle suspension layer; 11-High permeability zone; 12-CO2, oil, gas, and water mixture drive section; 13-Compressor; 14-Oil-gas separator; 15-Heat exchanger; 16-In-situ conversion working fluid gas source; 17-CO2 gas source.

[0031] Throughout the accompanying drawings, the same or similar reference numerals denote the same or similar elements. Detailed Implementation

[0032] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, this invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions of this invention and actual circumstances. To avoid obscuring the essence of this invention, well-known methods, processes, flows, and elements are not described in detail. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] The geothermal extraction technology of this invention is based on traditional geothermal extraction technology. However, the differences in heat source and geological conditions between the organic-rich shale after in-situ conversion and the target strata of traditional geothermal extraction technology determine the limitations of traditional geothermal extraction technology when applied to the residual heat extraction project of organic-rich shale after in-situ conversion. First, the temperature of traditional heat source strata is stable over a long time scale. Therefore, traditional geothermal extraction only measures the temperature parameters of the strata during the geological exploration stage. However, the heat of organic-rich shale comes from the treatment of the strata by the in-situ conversion process. During the heat extraction process, the strata temperature has a gradient difference, thus requiring real-time monitoring of the bottom hole and underground temperature during the extraction process to meet the heat extraction requirements. Secondly, traditional geothermal technologies typically target formations with high thermal conductivity, where the main channels for heat transfer are natural or artificial fractures. The surface area of ​​these fractures is sufficient to meet the heating requirements of the heat transfer medium. However, organic-rich shale has poor thermal conductivity, and larger fractures reduce the transit time of the heat transfer medium in the heat source formation. Furthermore, residual oil and gas in the formation can generate two-phase flow with supercritical CO2, leading to a fingering effect. Therefore, to increase the sweep efficiency of supercritical CO2 and improve heat extraction efficiency, this invention adds a formation profile adjustment process to the traditional heat extraction technology.

[0034] In summary, this invention proposes a method for in-situ conversion of residual heat in organic-rich shale through CO2 injection and recycling, which can effectively improve energy recovery efficiency and reduce the development cost of organic-rich shale.

[0035] This invention proposes a method for exploiting residual heat from in-situ conversion of organic-rich shale using CO2 injection. This method primarily involves injecting CO2 into the organic-rich shale formation 4 after in-situ conversion, where the supercritical CO2 formed by heating the formation 4 serves as a heat-carrying medium. This process exploits the residual heat from the in-situ conversion of the organic-rich shale to assist in heating the in-situ conversion formation. Furthermore, the characteristics of supercritical CO2 are utilized during the heat extraction process to extract residual oil and gas, ultimately achieving the goals of improving oil and gas recovery, reducing engineering costs, extending engineering life, and storing CO2 greenhouse gases. Figure 3 and Figure 4 The diagrams show the residual heat extraction zone profile of the CO2-cycle mining system for in-situ conversion of organic-rich shale and the temperature schematic diagram of the CO2-cycle mining system for in-situ conversion of organic-rich shale.

[0036] like Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, the residual heat method after in-situ transformation of organic-rich shale through CO2 injection recycling specifically includes:

[0037] Identify target areas for in-situ conversion of residual heat in organic-rich shale using CO2 recycling;

[0038] This invention is based on the in-situ conversion process of organic-rich shale. The target area is the organic-rich shale stratum 4 after in-situ conversion mining. The stratum, burial depth, thickness, and sealing properties determine the heat-carrying medium's sweep range and energy return rate of the heat recovery process. Fully understanding the target block and stratum is the first step in carrying out the residual heat method after in-situ conversion of organic-rich shale through CO2 injection cycle mining.

[0039] The geological conditions of the target area are as follows:

[0040] The selected strata are organic-rich shale strata 4, which have been mined using in-situ conversion technology;

[0041] The average temperature of the selected strata exceeds 250℃;

[0042] The selected formation has a complete injection-production well network;

[0043] The selected strata have a burial depth of less than 3000m.

[0044] Modify the existing well network system for in-situ conversion of organic-rich shale;

[0045] The existing downhole facilities are designed to serve in-situ conversion processes. Their injection and production capabilities, methods, and insulation performance may not necessarily meet the requirements of CO2 injection and circulation mining of organic-rich shale after in-situ conversion and residual heat treatment. Therefore, it is necessary to modify the existing well network system for injection and production and insulation performance.

[0046] Furthermore, the existing development well network will be converted in situ into gas injection well 1, and the original production well will be converted into residual heat production well 2. Insulated oil pipe 6 will be installed in residual heat production well 2 to reduce heat loss in the wellbore of residual heat production well 2 during residual heat extraction.

[0047] Furthermore, if the old insulated tubing 6, which is pulled out after gas injection and heat recovery using SY-T 5324-94 prestressed insulated tubing, has an apparent thermal conductivity that is less than 1.2 times that of the new insulated tubing 6, then its thermal insulation performance is considered reliable and it can be used in the next round of gas injection and heat recovery.

[0048] Furthermore, the existing development well network will be converted in situ into gas injection well 1 and production wells into residual heat production well 2, making full use of the thermal insulation performance of the original injection wells by converting the injection and production wells.

[0049] Adjusting the supercritical CO2 drive interface:

[0050] Because organic-rich shale formation 4 inevitably contains some residual oil and gas, this residual oil and gas will form a two-phase flow with the injected supercritical CO2. During displacement, the viscosity differences between the phases will cause a fingering effect. Simultaneously, due to the heterogeneity of organic-rich shale formation 4 and the large voids created by artificial fracturing, residual heat blocks with varying permeability exist. The fingering effect and the unstable displacement interface caused by permeability differences will reduce the sweep efficiency of supercritical CO2 and decrease thermal recovery. Therefore, a small amount of profile control agent needs to be added to the formation to adjust the interface between supercritical CO2 and residual oil and gas products, preventing gas channeling in the formation after supercritical CO2 injection and ensuring that large amounts of high-temperature formations are not swept away.

[0051] Furthermore, PI optimization decision-making technology is used to design and determine the type and dosage of profile control agent;

[0052]

[0053] q represents the daily injection rate of the gas injection well, in meters (m³). 3 ·d -1 ;

[0054] μ represents the dynamic viscosity of the fluid, with units of mPa·s;

[0055] k represents formation permeability, in μm. 2 ;

[0056] h represents the formation thickness, in meters (m).

[0057] t represents the well shut-in test time, in seconds;

[0058] c represents the overall compression coefficient, in Pa. -1 ;

[0059] r e This indicates the control radius of the water control well, in meters (m).

[0060] Selection of profile control agents: Profile control agents are selected based on four criteria: formation temperature, formation water salinity, PI value of the injection well, and cost. Calculation of profile control agent dosage:

[0061] W=βh f ΔPI

[0062] In the formula:

[0063] W indicates the dosage of profile control agent, in tons (t) or cubic meters (m). 3 ;

[0064] β represents the dosage coefficient, in t·MPa -1 ·m -1 or m 3 ·MPa -1 ·m -1 ;

[0065] h f Indicates the thickness of the gas injection layer, in meters (m).

[0066] ΔPI represents the planned increase in PI value of the injection well before and after profile adjustment, in MPa.

[0067] Furthermore, in the organic-rich shale formation 4, bulky particles and polymeric weak gels are used together as profile control agents. A suspension of bulky particles and a suspension of polymeric weak gels are sequentially injected into the organic-rich shale formation 4. The bulky particle suspension forms a bulky particle suspension layer 10, and the polymeric weak gel suspension forms a polymeric weak gel suspension layer 9. The bulky particle suspension layer 10 uses bulky particles with diameters of 1mm to 3mm or 3mm to 5mm, which rapidly advance in high-permeability zones 11 such as formation fractures and large pores. The residual oil, gas, and water mixed with CO2 at its front forms a CO2, oil, gas, and water mixture dispersal section 12. The polymeric weak gel suspension layer 9 forms a weak gel in distant formations, playing a profile control role. A stable propulsion interface forms at the rear of the polymeric weak gel suspension layer 9, and the supercritical CO2 after the propulsion interface forms the CO2 dispersal section 8. The bulky particles are GP series surface cross-linked prepolymers, and the polymeric weak gel is the zwitterionic polymer FT-213. Conventional geothermal development, due to the relatively homogeneous strata without cracks or large pores, does not require the injection of two-stage profile control agents. In-situ transformation of the strata by high-temperature fluid convection heating results in a denser formation without severe fingering effects, also eliminating the need for profile control agents.

[0068] Efficiently utilize the residual heat from the extracted formation:

[0069] To improve heat utilization and reduce heat loss during energy conversion in the energy storage process, the method proposed in this invention is carried out simultaneously with the in-situ conversion oil recovery project. It utilizes heat exchange to maximize the use of residual heat to heat the in-situ conversion working medium. Through a high-efficiency, high-pressure heat exchanger 15, the heat carried by the high-temperature CO2, oil, gas, and water mixture produced in the residual heat production well 2 is used to heat the in-situ conversion heat transfer medium. This heat transfer medium is then injected into the adjacent organic-rich shale in-situ conversion development well group, achieving the recycling of residual heat from the formation after in-situ conversion. Meanwhile, the CO2, oil, gas, and water mixture produced in the residual heat production well 2 is separated, and the CO2 gas is circulated and injected into the gas injection well 1; see... Figure 5 .

[0070] Dynamic control of heat extraction processes:

[0071] To ensure full utilization of extracted heat, a widely applicable assessment model for residual heat extraction in organic-rich shale formations needs to be established. This model analyzes the formation's heat reserves using computer modeling by considering parameters such as formation thickness, area, rock specific heat capacity, and the thermal conductivity of the overlying layer 3 and underlying layer 5. The extracted heat per unit time is controlled by adjusting the injected supercritical CO2 gas flow rate. The production flow rate of residual heat production well 2 is positively correlated with the injected supercritical CO2 flow rate. The output heat is calculated based on the specific heat capacity of the produced material, assuming a heat exchange efficiency of 80%. To meet the heating requirements of the in-situ conversion working fluid, real-time monitoring of changes in parameters such as wellbore bottom temperature and formation pressure is necessary.

[0072] Furthermore, taking the line connecting injection well 1 and residual heat production well 2 as the axis, temperature and pressure sensors are driven into the formation every 20m. It is required to ensure that the bottom hole pressure is greater than 8MPa and the bottom hole temperature is greater than 35℃, while ensuring that the bottom hole fluid pressure and the formation fluid pressure are the same.

[0073] The heat extraction process has ended.

[0074] Based on the residual heat exploitation assessment model of organic-rich shale formations and the dynamic changes in energy return rate obtained from real-time injection and production parameters, the process is terminated when the energy return curve declines. The energy return rate is (total compressible energy of the injected medium + thermal energy + chemical energy) / (total compressible energy of the produced gas + thermal energy + chemical energy).

[0075] Sealing the well ensures effective CO2 storage:

[0076] After the process is completed, the downhole heater 7 and the heat-insulating tubing 6 are recovered, the surface equipment is cleaned and tidied up, cement mortar is used for sealing, and regular inspections are carried out after the sealing is completed to monitor the sealing status of the injection and production wells.

[0077] Furthermore, the formation pressure is checked every 10 days after well sealing, and the well sealing is considered reliable if the pressure drop is less than 2% after four months.

[0078] Example

[0079] This example selects organic-rich shale strata 4 in Fuyu, China as the construction area.

[0080] The well network in this area follows the "reverse seven-point" layout commonly used in oil extraction: a central injection well (1) surrounded by six residual heat production wells (2) arranged in a regular hexagon. Initial drilling used an X385mm four-wing drill bit to a depth of 10m, followed by the installation of surface casing. Subsequently, an X215.9mm roller cone drill bit was used to drill to a depth of 500m. The first reaming operation used an X311mm roller cone drill bit, reaming the section from 0 to 500m. The second reaming operation used an X346mm scraper drill bit, reaming the section from 0 to 500m. (See...) Figure 1 and Figure 2 .

[0081] The organic-rich shale stratum 4 in this area is located 500m underground, with a total porosity of 28.65%, a matrix permeability of 0.01md, and a fracture permeability of 100md.

[0082] The following examples are further illustrated with reference to the accompanying drawings.

[0083] The CO2 circulation mining method for residual heat recovery after in-situ conversion of organic-rich shale is based on a CO2 circulation mining system for residual heat recovery after in-situ conversion of organic-rich shale. This system includes an injection well 1, a residual heat production well 2, an insulated tubing 6, a downhole heater 7, a compressor 13, an oil-gas separator 14, a heat exchanger 15, an in-situ conversion working fluid source 16, and a CO2 source 17. The CO2 source 17 and the CO2 separation end of the oil-gas separator 14 are both connected to the inlet end of the compressor 13 via pipelines. The downhole heater 7 is located at... In injection well 1, heat-insulating oil pipe 6 is installed in residual heat production well 2. Injection well 1 is connected to the gas outlet of compressor 13 through a static pressure valve. Residual heat production well 2 is connected to the heat-carrying medium inlet of heat exchanger 15 through a pipeline. Inlet of oil-gas separator 14 is connected to heat-carrying medium outlet of heat exchanger 15 through a pipeline. In-situ conversion working medium gas source 16 is connected to the heated medium inlet of heat exchanger 15 through a pipeline. CO2 outlet of oil-gas separator 14 is connected to CO2 gas source 17 through a pipeline.

[0084] Room temperature CO2 with a pressure greater than 8 MPa enters through injection well 1. As the injection depth increases, the temperature rises. The high-temperature organic-rich shale formation 4 heats the CO2 to a certain temperature. When the temperature reaches 31.1℃, the CO2 transforms into a supercritical state. Afterward, with the help of profile control agents, the supercritical CO2 working medium will gradually and smoothly advance in the organic-rich shale formation 4. During the advancement, it exchanges heat with the organic-rich shale formation 4 and drives the residual oil and gas to the residual heat production well 2. Compared with traditional water medium, supercritical CO2 can absorb more heat and bring it to the surface. The high-temperature CO2, oil, gas, and water mixture produced from residual heat production well 2 enters heat exchanger 15. Through heat exchanger 15, the heat carried by the CO2, oil, gas, and water mixture produced from residual heat production well 2 heats the in-situ conversion heat transfer medium (the in-situ conversion working medium used in the Fuyu in-situ conversion project is high-temperature nitrogen). Different heating effects can be achieved by controlling the ratio and flow rate of the CO2, oil, gas, and water mixture input to heat exchanger 15 to the in-situ conversion working medium. The cooled CO2, oil, gas, and water mixture enters oil-gas separator 14, where it is separated into CO2 and combustible oil / gas. The oil / gas flows back to the oil / gas collection tank, while the CO2 is recycled and injected into injection well 1. The energy return rate curve is constantly monitored. The heat recovery process ends when the energy return rate begins to decline. After the process ends, the downhole heater 7 and insulated tubing 6 are recovered, surface equipment is cleaned and tidied, the well is sealed with cement mortar, and a regular inspection system is established to monitor the sealing status of the injection and production wells over the long term. After well sealing, the formation pressure should be checked every 10 days. Well sealing is considered reliable if the pressure drop is less than 2% after four months.

[0085] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for in-situ transformation of organic-rich shale using CO2 recycling, characterized in that, The method includes the following steps: Step 1: Determine the target area for residual heat from in-situ conversion of organic-rich shale in CO2 recycling mining. The target area is the organic-rich shale stratum (4) after mining by in-situ conversion process, and the average temperature of the stratum exceeds 250℃. Step 2: Utilize the existing development well network in situ as a residual heat circulation mining channel, convert the existing development well network in situ as injection wells (1) and production wells as residual heat production wells (2), and run insulated oil pipes (6) into the residual heat production wells (2). Step 3: Inject profile control fluid into the organic-rich shale formation (4) to adjust the interface between supercritical CO2 and residual oil and gas products in the formation; Step 4: Using compressor (13), room temperature CO2 with a pressure greater than 8MPa is injected into the organic-rich shale formation (4) after in-situ transformation through injection well (1). As the injection depth increases, the temperature rises. The organic-rich shale formation (4) heats the CO2. When the temperature reaches 31.1℃, the CO2 is transformed into a supercritical state. The pressure and temperature changes at the bottom of injection well (1) and residual heat production well (2) are monitored in real time. Step 5: Through heat exchanger (15), the heat carried by the CO2, oil, gas and water mixture produced in the residual heat production well (2) is used to heat the in-situ conversion heat transfer medium, and the heated in-situ conversion heat transfer medium is injected into the adjacent organic shale in-situ conversion development well group to realize the recycling of the formation residual heat after in-situ conversion. The CO2, oil, gas and water mixture produced in the residual heat production well (2) is separated and CO2 gas is circulated and injected into the injection well (1). Step 6: Geothermal resource development ends, equipment is recovered, and cement is used to seal the injection well (1) and the residual heat production well (2).

2. The method for in-situ transformation of organic-rich shale using CO2 injection and recycling, as described in claim 1, is characterized in that... In step two, the heat-insulating oil pipe (6) adopts SY-T 5324-94 prestressed heat-insulating oil pipe. The old heat-insulating oil pipe (6) that is pulled out after gas injection and heat recovery in the well can continue to be used in the next round of gas injection and heat recovery when its apparent thermal conductivity is less than 1.2 times that of the new heat-insulating oil pipe (6).

3. The method for in-situ transformation of organic-rich shale using CO2 injection and recycling, as described in claim 1, is characterized in that... In step three, the PI optimization decision-making technique is used to determine the type and dosage of profile control agent.

4. The method for in-situ transformation of organic-rich shale using CO2 recycling as described in claim 1 or 3, characterized in that, In step three, bulky particles and polymeric weak gel are used as profile control agents. Bulky particle suspension and polymeric weak gel suspension are injected sequentially into the organic-rich shale formation (4). Bulky particle suspension forms a bulky particle suspension layer (10), and polymeric weak gel suspension forms a polymeric weak gel suspension layer (9). The bulky particle suspension layer (10) uses bulky particles with a diameter of 1 mm to 3 mm or 3 mm to 5 mm. The bulky particles are GP series ground crosslinked prepolymers, and the polymeric weak gel is zwitterionic polymer FT-213.

5. The method for in-situ transformation of organic-rich shale using CO2 injection and recycling, as described in claim 1, is characterized in that... In step four, taking the line connecting the injection well (1) and the residual heat production well (2) as the axis, temperature and pressure sensors are driven into the organic-rich shale formation (4) every 20m to ensure that the bottom pressure of the injection well (1) and the residual heat production well (2) is greater than 8MPa and the bottom temperature is greater than 35℃, while ensuring that the formation fluid pressure at the bottom of the well and the organic-rich shale formation (4) is the same.

6. The method for in-situ transformation of organic-rich shale after CO2 injection and recycling, as described in claim 1, is characterized in that... In step five, the in-situ conversion heat transfer medium includes nitrogen, water vapor, air, and CO2.

7. The method for in-situ transformation of organic-rich shale using CO2 injection and recycling, as described in claim 1, is characterized in that... In step six, the end of the recycling process of residual formation heat after in-situ conversion is determined by evaluating the energy return rate curve. The recycling process of residual formation heat after in-situ conversion ends when the energy return rate decreases.

8. The method for in-situ transformation of organic-rich shale using CO2 injection and recycling, as described in claim 1, is characterized in that... After step six, CO2 is sealed inside the organic-rich shale strata (4).

9. The method for in-situ transformation of organic-rich shale using CO2 injection and recycling, as described in claim 1, is characterized in that... After sealing the well, the formation pressure of the organic-rich shale formation (4) is checked every 10 days. The well sealing is considered reliable if the pressure drop is less than 2% after four months.

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