A system for exploiting shale oil of medium-low maturity

Abstract

The present application provides a kind of low maturity shale oil exploitation system, which uses nuclear energy generated by nuclear energy supply unit, chemical energy generated by chemical energy supply unit and geothermal energy generated by geothermal energy supply unit as the heat source of closed Brayton cycle module, so that the closed Brayton cycle module converts the heat energy generated by the above heat source into mechanical energy and electrical energy that can be used by double-horizontal well double-fracturing exploitation module using supercritical CO2 as working medium, thereby realizing the exploitation and processing of low maturity shale oil and the underground storage of CO2. This technology integrates multiple energy sources, improves energy utilization efficiency, reduces exploitation cost, and realizes environmental protection and sustainable development of resources.

Description

Technical Field

[0001] This invention relates to the field of energy extraction technology, and in particular to a shale oil extraction system for medium- and low-maturity shale. Background Technology

[0002] With rapid economic and industrial development, society's demand for fossil fuels has increased dramatically. Shale oil, as an unconventional new energy source, is characterized by its wide distribution, high reserves, and large thickness. The efficient development of unconventional oil and gas resources, represented by shale oil, is of great significance for alleviating energy shortages and ensuring energy security. The United States has achieved tremendous success in shale oil development through the shale revolution, realizing a transformation of its energy structure and significantly reducing its dependence on foreign oil consumption. my country, with its high dependence on imported crude oil, is making the vigorous promotion of the shale oil and gas industry crucial for ensuring national energy security and driving economic growth.

[0003] China possesses abundant shale oil resources, but the extraction of medium- and low-maturity shale oil faces numerous challenges, such as low levels of organic matter thermal evolution, low proportion of movable oil, and high proportion of unfractured kerogen. These challenges necessitate the application of in-situ underground heating and conversion technologies followed by fracturing and oil displacement techniques to achieve large-scale development and utilization. However, existing extraction technologies for medium- and low-maturity shale oil (including fracturing, oil displacement, and in-situ conversion technologies) suffer from high energy consumption, low efficiency, and significant environmental impact, thus hindering the development and utilization of medium- and low-maturity shale oil.

[0004] Therefore, there is an urgent need to develop a new type of shale oil extraction system with medium to low maturity to solve the above-mentioned technical problems. Summary of the Invention

[0005] In view of this, this application provides a medium-to-low maturity shale oil extraction system to solve the technical problems of high energy consumption, low efficiency and large environmental impact of existing medium-to-low maturity shale oil extraction technologies.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] To achieve the above technical objectives, this application adopts the following technical solution:

[0008] This invention provides a medium-to-low maturity shale oil extraction system, comprising:

[0009] The multi-energy coupled and coordinated power supply module includes a nuclear gas supply unit, a chemical energy supply unit and a geothermal energy supply unit arranged in parallel;

[0010] The closed-loop Brayton cycle module is connected to the multi-energy coupled and coordinated power supply module to receive heat sources generated from the nuclear gas supply unit, chemical energy supply unit and geothermal energy supply unit respectively, and converts thermal energy into mechanical energy and electrical energy using supercritical CO2 as the working medium.

[0011] The dual-horizontal-well dual-fracture production module is connected to a multi-energy coupled collaborative power supply module and a closed-loop Brayton cycle module, respectively, to extract and process medium- and low-maturity shale oil using mechanical and electrical energy and to perform underground CO2 storage.

[0012] Preferably, the nuclear power gas supply unit includes a power subunit, which includes a reactor, a first turbine, a first regenerator, a first cooler, and a compressor.

[0013] The reactor, the first turbine, and the first regenerator form a first closed loop through the first pipe, and the first regenerator, the first cooler, and the compressor form a second closed loop through the second pipe.

[0014] Preferably, the nuclear energy gas supply unit also includes a steam supply subunit connected to the power subunit pipeline. The steam supply subunit heats CO2 and water to a supercritical state through the heat source generated by the reactor, and injects supercritical CO2 and supercritical water alternately into the dual horizontal well dual fracturing production module through the power subunit.

[0015] Preferably, the chemical energy supply unit includes a heat-generating agent, which is used to react chemically with supercritical water to generate porous compounds; the chemical energy supply unit is used to input the heat generated by the chemical reaction into a closed Brayton cycle module and to store the porous compounds in shale reservoirs with medium to low maturity shale oil.

[0016] Preferably, the geothermal energy supply unit is used to transport part of the geothermal source provided by the geothermal layer located below the shale reservoir to the closed Brayton cycle module, while heating CO2 to a supercritical state through the remaining heat source and injecting the supercritical CO2 into the shale reservoir.

[0017] Preferably, the closed Brayton cycle module includes a multi-energy coupled heat source, a second turbine, a second regenerator, a second cooler, and a compressor. The multi-energy coupled heat source, the second turbine, and the second regenerator form a third closed loop through a third pipe, and the second regenerator, the second cooler, and the compressor form a fourth closed loop through a fourth pipe.

[0018] The closed Brayton cycle module also includes a generator, and the second turbine is connected to the generator via a fifth pipe.

[0019] Preferably, the dual-horizontal-well dual-fracture production module includes a gas injection well, a first oil production well, a second oil production well, and a collection well arranged sequentially at intervals. The gas injection well and the collection well both penetrate the caprock and shale reservoir sequentially along the underground direction and partially penetrate the geothermal layer. The first oil production well and the second oil production well both penetrate the caprock and partially penetrate the shale reservoir sequentially along the underground direction.

[0020] Preferably, the dual-horizontal-well dual-fracture production module further includes a first dual-pass pipeline and a second dual-pass pipeline, wherein the first dual-pass pipeline is located in the shale reservoir and the second dual-pass pipeline is located in the geothermal layer;

[0021] The collection well is connected to the gas injection well via a first double-pass pipeline, and both the first and second oil production wells are connected to the first double-pass pipeline; the collection well is also connected to the gas injection well via a second double-pass pipeline.

[0022] Preferably, the dual-horizontal-well dual-fracture production module further includes a first well valve, a second well valve, a third well valve, and a fourth well valve. The first well valve is installed on the first dual-way pipeline and located between the gas injection well and the first production well. The second well valve is installed on the first dual-way pipeline and located between the collection well and the second production well. The third well valve is installed on the second dual-way pipeline and located at the end closer to the gas injection well. The fourth well valve is installed on the second dual-way pipeline and located at the end closer to the collection well.

[0023] Preferably, the dual-horizontal-well dual-fracture production module also includes a CO2 storage unit connected to the collection well. The CO2 storage unit uses at least one of the following storage methods: structural storage, capillary storage, dissolution storage, and mineralization storage.

[0024] Beneficial Effects: This invention provides a system for the extraction of medium-to-low maturity shale oil. It utilizes nuclear energy from a nuclear gas supply unit, chemical energy from a chemical energy supply unit, and geothermal energy from a geothermal energy supply unit as heat sources for a closed-loop Brayton cycle module. This module uses supercritical CO2 as the working medium to convert the heat energy from these heat sources into mechanical and electrical energy usable by a dual-horizontal-well, dual-fracture extraction module. This enables the extraction and processing of medium-to-low maturity shale oil and the underground storage of CO2. By integrating multiple energy sources, this technology improves energy efficiency, reduces extraction costs, and simultaneously achieves environmental protection and sustainable resource development. Attached Figure Description

[0025] Figure 1 This is a structural block diagram of a low-to-medium maturity shale oil extraction system provided in Embodiment 1 of this application;

[0026] Figure 2 This is a schematic diagram of the structure of the power subunit in the medium-to-low maturity shale oil extraction system provided in Embodiment 1 of this application;

[0027] Figure 3 A schematic diagram of the energy supply mechanism of the chemical energy supply unit in the medium-to-low maturity shale oil extraction system provided in Embodiment 1 of this application;

[0028] Figure 4 This is a schematic diagram of the closed Brayton cycle module in the medium-to-low maturity shale oil extraction system provided in Embodiment 1 of this application;

[0029] Figure 5 This is a schematic diagram of the structure of the dual horizontal well dual fracturing production module in the medium-low maturity shale oil production system provided in Embodiment 1 of this application;

[0030] Figure 6 This is a schematic diagram of the method for extracting medium- and low-maturity shale oil using the medium- and low-maturity shale oil extraction system provided in Embodiment 1 of this application;

[0031] In the attached diagram: 11 - Reactor; 12 - First turbine; 13 - First regenerator; 14 - First cooler; 15 - Compressor; 21 - Multi-energy coupled heat source; 22 - Second turbine; 23 - Second regenerator; 24 - Second cooler; 25 - Compressor; 31 - Gas injection well; 32 - First production well; 33 - Second production well; 34 - Collection well; 35 - First dual-way pipeline; 36 - Second dual-way pipeline. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Low- to medium-maturity shale oils exhibit low levels of organic matter thermal evolution, with RO (vitrinite reflectance) typically ranging from 0.5% to 1.0%. They also have low proportions of retained hydrocarbons, mobile oil, and unpyrolyzed kerogen, indicating significant conversion potential. Therefore, in-situ underground heating conversion technology is required before fracturing and oil displacement technologies to achieve large-scale development and utilization (Wang et al., 2023; Wei et al., 2023). However, high energy consumption remains a critical issue for the large-scale development and utilization of continental shale oils, regardless of whether fracturing, oil displacement, or in-situ conversion technologies are employed.

[0034] Under the "dual carbon" goal, promoting a low-carbon energy transition and adhering to the sustainable development strategy, nuclear energy and geothermal energy, as clean, low-carbon, and high-density energy sources, play an irreplaceable role in ensuring energy supply, promoting economic development, and addressing global climate change. Nuclear energy is not only used for power generation; it has made good progress in diversified applications for low-carbon transformation, such as nuclear steam supply, heating, hydrogen production, and seawater desalination. Geothermal energy, as a renewable energy source, is characterized by good stability and strong sustainability, and is an important component of the future energy structure.

[0035] CO2 enhanced oil recovery (EOR) technology, by injecting CO2 into the oil-bearing reservoir to maintain formation pressure, displaces crude oil into the production well, thereby increasing oil recovery. Simultaneously, CO2 geological sequestration (GSSR), as an important means of achieving carbon neutrality, can stably store CO2 underground for the long term, reducing greenhouse gas emissions. How to combine CO2 EOR with GSSR to achieve the dual goals of efficient oil and gas resource development and environmental protection is currently a hot research topic.

[0036] This application uses nuclear energy, geothermal energy, and pollution-free chemical energy as components of a new energy supply system, updating and iterating the thermal energy supply model that is mainly based on fossil energy. It also fully leverages the advantages and characteristics of each energy source to achieve coupled energy supply and synergistic complementarity. Furthermore, it organically combines emerging low-carbon chemical energy in-situ conversion of biothermal energy, CO2 pre-fracturing, high-pressure miscible CO2 flooding, and CO2 mineralization and storage technologies to jointly achieve the synergistic goal of green mining and carbon sequestration of continental shale oil.

[0037] The technical solution of the present invention will now be further described with reference to specific embodiments.

[0038] Example 1:

[0039] Please see Figure 1 , Figure 1 This is a structural block diagram of a medium-to-low maturity shale oil extraction system provided in Embodiment 1 of this application; wherein, the present invention provides a medium-to-low maturity shale oil extraction system, including a multi-energy coupled collaborative power supply module, a closed Brayton cycle module connected to the multi-energy coupled collaborative power supply module, and a dual horizontal well dual fracturing extraction module connected to the multi-energy coupled collaborative power supply module and the closed Brayton cycle module respectively;

[0040] Specifically, the multi-energy coupled collaborative power supply module includes a nuclear gas supply unit, a chemical energy supply unit, and a geothermal energy supply unit arranged in parallel; the closed Brayton cycle module is used to receive heat sources generated from the nuclear gas supply unit, the chemical energy supply unit, and the geothermal energy supply unit respectively, and converts thermal energy into mechanical energy and electrical energy using supercritical CO2 as the working medium; the dual horizontal well dual fracturing extraction module is used to extract and process medium- and low-maturity shale oil using mechanical energy and electrical energy and to perform underground CO2 storage.

[0041] Specifically, the basic principle of the nuclear power gas supply unit is to draw an appropriate amount of steam from the main steam header of the secondary loop of the nuclear island as a heating steam source, produce saturated steam for the tertiary loop through a steam converter, and then heat it to superheated steam through steam reheating with the main steam for external supply. The condensate from the heating steam is discharged into the corresponding feedwater heater or deaerator.

[0042] In this embodiment 1, the nuclear energy supply unit can utilize the thermal energy generated by the high-temperature gas-cooled reactor to supply continuously heated and alternately injected high-temperature supercritical CO2 and supercritical water vapor through the power subunit. That is, the nuclear energy supply unit heats low-temperature ordinary CO2 to a high-temperature and high-pressure state of supercritical CO2 using high-temperature water vapor, and injects the supercritical CO2 into shale reservoirs and geothermal layers with medium-to-low maturity shale oil through a gas injection process (including steam injection compressor 25 and steam injection pipeline), while simultaneously injecting supercritical water vapor into the shale reservoir.

[0043] Please see Figure 2 , Figure 2 This is a schematic diagram of the structure of the power subunit in the medium-low maturity shale oil extraction system provided in Embodiment 1 of this application; wherein, the nuclear power gas supply unit includes the power subunit, which includes a reactor 11, a first turbine 12, a first regenerator 13, a first cooler 14 and a compressor 15;

[0044] The reactor 11, the first turbine 12 and the first regenerator 13 form a first closed loop through the first pipe, and the first regenerator 13, the first cooler 14 and the compressor 15 form a second closed loop through the second pipe.

[0045] Specifically, reactor 11 is the energy source, releasing a large amount of thermal energy through nuclear reactions; the first turbine 12 plays the role of converting thermal energy into mechanical energy in the first closed loop, and the high-temperature working fluid from reactor 11 drives the first turbine 12 to rotate and do work; the first regenerator 13 is used to recover a portion of the heat from the working fluid discharged from the first turbine 12, thereby improving the thermal efficiency of the entire system; the first cooler 14 is used to cool the working fluid after passing through the first regenerator 13, thereby lowering its temperature; and the compressor 15 compresses the cooled working fluid, increasing its pressure to prepare it for re-entry into reactor 11.

[0046] Specifically, the power subunit, through a first closed loop formed by the first pipeline, achieves the circulation of the high-temperature working fluid from reactor 11 to the first turbine 12 and then to the first regenerator 13, completing the conversion of thermal energy into mechanical energy and recovering some heat. The power subunit, through a second closed loop formed by the second pipeline, achieves the circulation of the working fluid through the first regenerator 13, the first cooler 14, and the compressor 15, completing the cooling and compression processes and preparing it for its next entry into the first closed loop. This design enables the nuclear power gas supply unit to operate efficiently and stably, providing the necessary energy support for the entire system.

[0047] In this embodiment 1, the nuclear energy gas supply unit also includes a steam supply subunit connected to the power subunit pipeline. The steam supply subunit heats CO2 and water to a supercritical state through the heat source generated by the reactor 11, and injects supercritical CO2 and supercritical water alternately into the dual horizontal well dual fracturing production module through the power subunit.

[0048] Specifically, the steam supply subunit and the power subunit are connected via pipelines, enabling the transfer and sharing of energy and matter. By utilizing the heat source generated by reactor 11 to heat CO2 and water to a supercritical state, this offers multiple advantages. Supercritical CO2 and water possess unique physical properties, such as high diffusivity, low viscosity, and good solubility, which can play a more effective role in subsequent extraction processes.

[0049] Alternating injection of supercritical CO2 and supercritical water into a dual-horizontal-well dual-fracture production module has the following advantages:

[0050] Improving extraction efficiency: Different supercritical fluids may have a synergistic effect on shale oil extraction, thereby more effectively displacing and extracting medium- and low-maturity shale oil;

[0051] Enhancing the effect of shale reservoir stimulation: Alternating injection can better improve the permeability and pore structure of shale reservoirs, which helps to increase oil and gas production.

[0052] In this Example 1, the chemical energy supply unit has the characteristics of being a fixed-point, small-scale unit. It adopts a new in-situ conversion and extraction approach with supercritical CO2 thermochemical conversion as the core, and combines the exothermic reaction of water as another heat source to provide direct heat for the in-situ conversion of organic matter in medium- and low-maturity shale oil.

[0053] Specifically, the chemical energy supply unit includes a heat-generating agent, which is used to react chemically with supercritical water to generate porous compounds; the chemical energy supply unit is used to input the heat generated by the chemical reaction into a closed Brayton cycle module and to store the porous compounds in shale reservoirs with medium to low maturity shale oil.

[0054] In this Example 1, the heat-generating agent is calcium oxide, the porous compound is calcium hydroxide, and the chemical energy supply unit combines core technologies such as calcium oxide powder surface coating modification, calcium oxide microspheres, calcium oxide hydroxyl injection liquid, and high-pressure air calcium oxide powder injection to store calcium oxide in shale reservoirs with medium to low maturity shale oil.

[0055] Please see Figure 3 , Figure 3 This is a schematic diagram of the energy supply mechanism of the chemical energy supply unit in the medium-to-low maturity shale oil extraction system provided in Embodiment 1 of this application; the specific energy supply mechanism of the chemical energy supply unit is as follows:

[0056] Following supercritical CO2 pre-fracturing, in-situ conversion and supercritical CO2 flooding of medium- and low-maturity shale oil are carried out. During this process, CO2 is injected into the shale reservoir, and calcium oxide powder, acting as an excellent heat generator, is injected into the reservoir. It reacts with subsequently injected high-pressure supercritical steam (H2O) to release heat, providing heat for the in-situ conversion of organic matter in the shale reservoir. Simultaneously, the reaction of calcium oxide with water produces porous calcium hydroxide (Ca(OH)2), which improves the permeability of the shale reservoir and fills the voids created by the pyrolysis of organic matter, increasing the stability of the shale reservoir. Furthermore, with increasing CO2 concentration, the steam further reacts to produce calcium carbonate (CaCO3), releasing both CO2 and calcium oxide (CaO), before the next cycle begins. The alternating injection of sufficient calcium oxide (CaO), supercritical steam, and supercritical CO2 ensures more complete CO2 flooding, while the exothermic reaction between calcium oxide and water continues to release heat in a cyclical manner. This allows for more complete in-situ conversion of organic matter and more thorough CO2 oil displacement. Near the later stages of CO2 oil displacement, calcium carbonate (CaCO3) is generated for mineralization and sequestration. A suitable ratio of nano-scale precipitating adsorbents is selected and injected along with the injected calcium oxide powder to reduce clogging of tiny pores.

[0057] Specifically, supercritical CO2, with its low viscosity and high diffusivity, can more easily penetrate the micropores and natural fractures in rocks, forming a more complex and extensive artificial fracture network, thereby increasing the effective permeability and conductivity of shale reservoirs. The use of supercritical CO2 in shale oil pre-fracturing technology offers advantages such as strong fracture-creating ability, reduced damage to shale reservoirs, enhanced oil and gas flowability, reduced rock fracturing pressure, and improved fracturing fluid flowback efficiency.

[0058] Specifically, the in-situ conversion technology for medium- and low-maturity shale oil involves heating the kerogen in shale reservoirs using underground heating equipment or high-temperature fluids, causing the kerogen to pyrolyze in situ to generate shale oil and shale gas. Finally, the generated oil and gas are lifted to the surface using conventional extraction methods. This technology results in a high degree of recovery of medium- and low-maturity shale oil and gas resources, improves the displacement efficiency of shale oil and gas, and produces high-quality shale oil from in-situ heated shale oil.

[0059] Specifically, CO2 flooding technology refers to the technique of injecting CO2 into shale reservoirs to maintain formation pressure, displacing crude oil into production wells, and improving oil recovery by utilizing the inherent properties of CO2. Supercritical CO2 can effectively extract and vaporize light hydrocarbons in crude oil. As extraction and vaporization deepen, the mixture approaches or reaches a miscible state, significantly reducing interfacial tension and dramatically improving oil displacement efficiency. During CO2 flooding, a large amount of CO2 dissolves in the crude oil. When the pressure decreases, the solubility of CO2 in the crude oil decreases, and the volume of CO2 expands. At this point, the crude oil flows into the production well mainly due to the elastic expansion energy of the separated CO2; this process is known as CO2 dissolved gas flooding.

[0060] In this embodiment 1, the geothermal energy supply unit has the characteristics of underground coverage. It uses geothermal energy as the heat source for in-situ conversion technology of low-maturity shale oil and designs a CO2 geological storage and heat extraction-energy storage integrated utilization system. Among them, the geothermal energy supply unit uses supercritical CO2 as fracturing fluid and heat extraction medium to carry out reservoir creation and mining of dry hot rock.

[0061] Specifically, the geothermal energy supply unit is used to transport part of the geothermal source provided by the geothermal layer located below the shale reservoir to the closed Brayton cycle module, while using the remaining heat source to heat CO2 to a supercritical state and inject supercritical CO2 into the shale reservoir.

[0062] In this embodiment 1, the closed-loop Brayton cycle module can improve the heat source conversion efficiency of medium and low maturity shale oil and increase the flexibility of the cycle system. The closed-loop Brayton cycle module can be combined with various forms of heat sources to construct a multi-heat source coupled cycle system, using supercritical CO2 as the work medium to directly participate in heat absorption, thereby meeting the heating needs of three heat sources: nuclear energy, geothermal energy, and chemical energy.

[0063] Please see Figure 4 , Figure 4 This is a schematic diagram of the structure of a closed Brayton cycle module in a medium-to-low maturity shale oil extraction system provided in Embodiment 1 of this application; wherein, the closed Brayton cycle module includes a multi-energy coupled heat source 21, a second turbine 22, a second regenerator 23, a second cooler 24, and a compressor 25. The multi-energy coupled heat source 21, the second turbine 22, and the second regenerator 23 form a third closed loop through a third pipe, and the second regenerator 23, the second cooler 24, and the compressor 25 form a fourth closed loop through a fourth pipe;

[0064] The closed Brayton cycle module also includes a generator 26, and the second turbine 22 is connected to the generator 26 via a fifth pipe.

[0065] Specifically, the multi-energy coupled heat source 21 provides heat for the entire cycle; the second turbine 22 rotates and does work under the action of the high-temperature and high-pressure working fluid, and is connected to the generator 26 through the fifth pipe to convert the mechanical energy generated by the turbine into electrical energy output; the second regenerator 23 is used to recover part of the heat of the working fluid discharged from the second turbine 22 to improve the thermal efficiency of the system; the second cooler 24 is used to cool the working fluid after passing through the second regenerator 23; the compressor 25 compresses the cooled working fluid to increase its pressure and prepare it to re-enter the cycle.

[0066] Furthermore, the third closed loop realizes the circulation of the high-temperature and high-pressure working fluid from the heat source to the turbine and then to the regenerator, completing the conversion of thermal energy into mechanical energy and recovering some of the heat; the fourth closed loop realizes the circulation of the working fluid through the regenerator, cooler and compressor 25, completing the cooling and compression process, and preparing it to enter the third closed loop again.

[0067] Please see Figure 5 , Figure 5 This is a schematic diagram of the structure of the dual-horizontal-well dual-fracture extraction module in the medium-low maturity shale oil extraction system provided in Embodiment 1 of this application; the dual-horizontal-well dual-fracture extraction module extracts both medium-low maturity shale oil and medium-deep geothermal energy by reasonably controlling four well valves, while simultaneously achieving underground CO2 sequestration.

[0068] Specifically, the dual-horizontal-well dual-fracture production module includes a gas injection well 31, a first oil production well 32, a second oil production well 33, and a collection well 34 arranged in sequence at intervals. Both the gas injection well 31 and the collection well 34 penetrate the caprock and shale reservoir in sequence along the underground direction and partially penetrate the geothermal layer. Both the first oil production well 32 and the second oil production well 33 penetrate the caprock and partially penetrate the shale reservoir in sequence along the underground direction.

[0069] Preferably, the dual-horizontal-well dual-fracture production module further includes a first dual-pass pipeline 35 and a second dual-pass pipeline 36, wherein the first dual-pass pipeline 35 is located in the shale reservoir and the second dual-pass pipeline 36 is located in the geothermal layer;

[0070] The collection well 34 is connected to the gas injection well 31 through the first double-pass pipeline 35, and the first oil production well 32 and the second oil production well 33 are both connected to the first double-pass pipeline 35; the collection well 34 is also connected to the gas injection well 31 through the second double-pass pipeline 36.

[0071] Preferably, the dual-horizontal-well dual-fracture production module further includes a first well valve, a second well valve, a third well valve, and a fourth well valve. The first well valve is installed on the first dual-pass pipeline 35 and located between the gas injection well 31 and the first oil production well 32. The second well valve is installed on the first dual-pass pipeline 35 and located between the collection well 34 and the second oil production well 33. The third well valve is installed on the second dual-pass pipeline 36 and located at the end near the gas injection well 31. The fourth well valve is installed on the second dual-pass pipeline 36 and located at the end near the collection well 34.

[0072] In this embodiment 1, the dual-horizontal-well dual-fracture production module also includes a CO2 storage unit connected to the collection well 34. The CO2 storage unit includes at least one of the following storage methods: structural storage (characterized by large storage capacity and mature technology), capillary storage (characterized by relatively stable storage and high efficiency), dissolution storage (characterized by simple dissolution and low leakage risk), and mineralization storage (characterized by the most stable storage and strong scalability).

[0073] Specifically, structural sequestration refers to the use of the sealing properties of underground geological structures to sequester carbon dioxide, forming carbon dioxide storage reservoirs similar to oil and gas reservoirs; capillary sequestration refers to the use of tiny underground capillary structures to adsorb carbon dioxide molecules, fixing them to achieve long-term sequestration; dissolution sequestration utilizes the solubility of carbon dioxide to dissolve it in solvents (such as groundwater) in ionic form to achieve sequestration; and mineralization sequestration utilizes chemical reactions to convert carbon dioxide into stable carbonate minerals, achieving long-term stable carbon dioxide sequestration.

[0074] Please see Figures 5 to 6 , Figure 6 This is a schematic flowchart illustrating a method for extracting medium- and low-maturity shale oil using a system provided in Embodiment 1 of this application; specifically, the method includes the following steps:

[0075] The first step is site selection and assessment: Select areas with abundant shale oil resources and suitable geological conditions, conduct detailed geological exploration and resource assessment, and determine the location, thickness, and quality of shale oil layers.

[0076] The second step involves the nuclear power plant's steam supply unit. Heating steam generated at the nuclear power plant is introduced into the nuclear power steam supply unit to heat the demineralized water, converting it into qualified steam. This steam is then piped to industrial users. The nuclear power plant uses reactor 11 to heat the primary coolant. The heated primary feedwater flows through the steam generator (SG) to heat the secondary feedwater, converting it into saturated steam. Most of this steam enters turbine generator set 26 for power generation, while the remaining steam is introduced into the nuclear power steam supply unit to heat the demineralized water, ultimately converting it into qualified steam that is sent to external industrial users.

[0077] The mechanism by which the nuclear power gas supply unit supplies high-temperature supercritical carbon dioxide (SCO2) is actually to heat low-temperature ordinary CO2 to a high-temperature and high-pressure state of supercritical CO2 through high-temperature water vapor, and then inject the gas into the formation through the steam injection process, namely the steam injection compressor 25 and the steam injection pipeline.

[0078] The third step involves the chemical energy supply unit's modification of the shale reservoir: In the shale reservoir, after supercritical CO2 pre-fracturing, in-situ conversion and supercritical CO2 oil displacement are carried out. At this time, the shale reservoir is filled with CO2, and calcium oxide powder, as an excellent heat generator, is injected into the shale reservoir. It reacts with the subsequently injected high-pressure water vapor (H2O) to release heat, providing heat for the in-situ conversion of organic matter. At the same time, after calcium oxide reacts with water, it generates porous calcium hydroxide (Ca(OH)2), which not only improves the permeability of the shale reservoir but also fills the voids generated after the pyrolysis of organic matter in the shale reservoir, increasing the stability of the shale reservoir. Meanwhile, as the CO2 concentration increases, it will further react with water vapor to generate calcium carbonate (CaCO3), releasing CO2 and calcium oxide (CaO) simultaneously, and then proceed to the next cycle.

[0079] Sufficient calcium oxide (CaO), supercritical steam, and supercritical CO2 are injected alternately in a cyclical manner to ensure more complete CO2 oil displacement. Simultaneously, the exothermic reaction between calcium oxide and water continues to release heat in a cyclical manner. This makes the in-situ conversion more complete and the oil displacement more thorough. Near the later stage of CO2 oil displacement, calcium carbonate (CaCO3) is generated for mineralization and storage. A suitable ratio of nano-sized precipitants and adsorbents is selected and injected along with the injected calcium oxide powder to reduce the clogging of tiny pores.

[0080] The fourth step is the development of geothermal energy by the geothermal energy supply unit: Geothermal energy resources are developed beneath shale reservoirs, combining CO2-enhanced geothermal systems with multi-branch well fracturing technology and plume geothermal systems for modification and innovation. CO2 is used as the heat extraction medium for geothermal extraction, and then the high-temperature CO2 is used for further processing. 2注入 In shale reservoirs, it provides heat and CO2 sources for pre-fracturing, heating, and oil displacement processes.

[0081] The fifth step is to construct a multi-energy coupled and coordinated cycle system: install a closed Brayton cycle system, using supercritical CO2 as the work medium to directly participate in heat absorption, thereby meeting the heating needs of three heat sources: nuclear energy, geothermal energy, and chemical energy, improving the heat source conversion efficiency, and increasing the flexibility of the cycle system.

[0082] Step 6, the preparation stage for the dual-horizontal-well dual-fracture production module to extract medium- and low-maturity shale oil: close the second well valve (B) and the fourth well valve (D), open the first well valve (A) and the third well valve (C), supply power and heat from the surface nuclear power plant, inject a large amount of high-temperature and high-pressure supercritical CO2 fluid into the upper shale reservoir and the lower medium-deep geothermal layer, simultaneously achieving fracturing and fracture creation and communication between the geothermal layer and the shale reservoir, and initially preheating the geothermal layer to prepare for in-situ conversion.

[0083] Step 7, the first sub-step of the dual-horizontal-well dual-fracture production module for in-situ conversion and gas injection-driven oil recovery of medium- and low-maturity shale oil: Open the third well valve (C) and the fourth well valve (D), and close the first well valve (A) and the second well valve (B). A large amount of low-temperature CO2 is injected into the underlying geothermal layer. A significant portion of the CO2 carries geothermal energy through the previously fractured fissures and is transferred to the shale reservoir for full-coverage heating. The remaining high-temperature CO2 is collected in collection well 34 for initial oil recovery and cover heating.

[0084] Step 8, the second sub-step of the dual-horizontal-well dual-fracture production module for in-situ conversion and gas injection-driven oil recovery of medium-to-low maturity shale oil: Opening the first well valve (A) and the second well valve (B), and closing the third well valve (C) and the fourth well valve (D). The upper horizontal well is densely perforated and finely cut, releasing calcium oxide in batches. The nuclear power plant then continuously supplies a large amount of high-temperature steam, which reacts with the calcium oxide in an exothermic reaction, accelerating the pyrolysis of kerogen. The generated calcium hydroxide improves reservoir properties and reacts with injected carbon dioxide to form calcium carbonate precipitate, which is then decomposed back into carbon dioxide and calcium oxide under high-temperature conditions. This cycle not only ensures thorough in-situ conversion but also accelerates the miscibility of shale oil with CO2, allowing the first and second production wells 32 and 33, located between the steam injection well and the collection well 34, to continuously produce oil, improving shale oil recovery. Below, high-temperature CO2 carrying heat enters the shale reservoir along artificial fractures, further expanding the fracture system.

[0085] Step 9: CO2 mineralization and sequestration in the later stage of the dual-horizontal-well dual-fracture production module – geothermal heat extraction stage: The high-temperature CO2 collected in collection well 34 will continue to be supplied to the shale reservoir for oil displacement, accelerating the displacement of the remaining oil. At the same time, it will accelerate the mineralization of CO2 to form calcium carbonate precipitate or continue to circulate in the reaction, thereby achieving permanent sequestration. The remaining extracted high-temperature CO2 can be used for geothermal heating and other purposes to provide heating for the oilfield base.

[0086] Step 10, CO2 geological sequestration: During the mining process, the generated CO2 is injected into the shale reservoir through a steam injection process to achieve CO2 geological sequestration and reduce greenhouse gas emissions.

[0087] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0088] This method achieves green mining by coupling multiple energy sources. Based on the existing closed-loop Brayton cycle in this field, this method combines supercritical CO2 Brayton cycle and multi-energy coupling system. Through the dual-horizontal-well dual-fracture mining mode, it can extract both medium- and low-maturity shale oil and medium- and deep geothermal energy, while simultaneously achieving underground CO2 storage.

[0089] This invention provides a method for improving shale oil recovery and CO2 geological sequestration using a multi-energy coupled synergistic power supply system. This method optimizes energy utilization efficiency and reduces extraction costs by integrating nuclear, geothermal, and chemical energy, while providing a new solution for environmental protection and sustainable resource development. Through supercritical CO2 Brayton cycle technology, it achieves efficient shale oil extraction and geological carbon dioxide sequestration, possessing significant industrial application value and environmental benefits.

[0090] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A system for the extraction of low to medium maturity shale oil, the system comprising: The application relates to a multi-energy coupling and collaborative energy supply module, a closed Brayton cycle module and a double-horizontal-well double-fracturing exploitation module. The multi-energy coupling and collaborative energy supply module comprises a nuclear energy gas supply unit, a chemical energy supply unit and a geothermal energy supply unit arranged side by side. The double-horizontal-well double-fracturing exploitation module is connected with the multi-energy coupling and collaborative energy supply module and the closed Brayton cycle module, and is used for exploiting and processing middle-low maturity shale oil and underground storing CO2 by mechanical energy and electric energy. The nuclear energy gas supply unit comprises a power subunit and a steam supply subunit in communication with the power subunit. The power subunit comprises a reactor, a first turbine, a first regenerator, a first cooler and a compressor. The reactor, the first turbine and the first regenerator form a first closed loop through a first pipeline. The first regenerator, the first cooler and the compressor form a second closed loop through a second pipeline.

2. The system for producing oil from low to medium mature shale of claim 1, wherein, The steam supply subunit heats CO2 and water to supercritical state by the heat source generated by the reactor, and alternately injects supercritical CO2 and supercritical water into the double-horizontal-well double-fracturing exploitation module through the power subunit. The chemical energy supply unit comprises a heat generating agent.

3. The system for producing oil from low to medium mature shale of claim 1, wherein, The heat generating agent is used for generating porous compounds by chemical reaction with supercritical water.

4. The system for producing oil from low to medium mature shale of claim 3, wherein, The chemical energy supply unit inputs the heat source generated by chemical reaction into the closed Brayton cycle module, and stores the porous compounds into the shale reservoir with middle-low maturity shale oil. The geothermal energy supply unit transports part of geothermal source provided by a geothermal layer below the shale reservoir into the closed Brayton cycle module, and heats CO2 to supercritical state by the remaining heat source, and injects supercritical CO2 into the shale reservoir. The closed Brayton cycle module comprises a multi-energy coupling heat source, a second turbine, a second regenerator, a second cooler and a compressor. The multi-energy coupling heat source, the second turbine and the second regenerator form a third closed loop through a third pipeline. The second regenerator, the second cooler and the compressor form a fourth closed loop through a fourth pipeline. The closed Brayton cycle module further comprises a generator. The second turbine is further connected with the generator through a fifth pipeline. The double-horizontal-well double-fracturing exploitation module comprises an injection well, a first oil production well, a second oil production well and a collection well arranged in sequence and at intervals. The injection well and the collection well penetrate the cap rock and the shale reservoir in sequence and partially penetrate the geothermal layer along the ground direction. The first oil production well and the second oil production well penetrate the cap rock in sequence and partially penetrate the shale reservoir along the ground direction. The double-horizontal-well double-fracturing exploitation module further comprises a first double-pass pipeline and a second double-pass pipeline. The first double-pass pipeline is arranged in the shale reservoir. The second double-pass pipeline is arranged in the geothermal layer. The collection well is communicated with the gas injection well through the first double-passage pipeline, and the first oil production well and the second oil production well are communicated with the first double-passage pipeline; the collection well is also communicated with the gas injection well through the second double-passage pipeline.

5. The system for producing oil from low to medium mature shale of claim 4, wherein, The double-horizontal well double-fracturing exploitation module further comprises a first well valve, a second well valve, a third well valve and a fourth well valve, the first well valve is installed on the first double-passage pipeline and located between the gas injection well and the first oil production well, the second well valve is installed on the first double-passage pipeline and located between the collection well and the second oil production well; the third well valve is installed on the second double-passage pipeline and located at one end close to the gas injection well, and the fourth well valve is installed on the second double-passage pipeline and located at one end close to the collection well.

6. The system for producing oil from low to medium mature shale of claim 3, wherein, The double-horizontal well double-fracturing exploitation module further comprises a CO2 storage unit communicated with the collection well, and the storage mode of the CO2 storage unit comprises at least one of the following: tectonic storage, capillary storage, dissolution storage and mineralization storage.

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