Oil shale in-situ oxidation heat collection system and method

Abstract

The invention discloses an oil shale in-situ oxidation heat collection system and method, and belongs to the technical field of oil shale in-situ development and utilization. Comprising a well pattern structure and a ground power generation device. The well pattern structure comprises an injection well, a heat recovery well and a plurality of observation wells; an electromagnetic sensor is arranged in each observation well, the oil shale layer is fractured through hydraulic fracturing to form fractures, the injection well communicates with the heat recovery well, and nanometer magnetic induction particles are added into fracturing fluid to serve as a propping agent; the observation well is used for monitoring the distribution condition and the magnetic field intensity of the nano magnetic induction particles; organic matters and fixed carbon in the oil shale are directly oxidized to release heat in an underground in-situ state, low-temperature steam is used as a heat transfer fluid to extract heat energy released by oxidation of the oil shale for power generation, and the method can be used for development of oil gas resources of the oil shale and shale with medium and low maturity.

Description

Technical Field

[0001] The invention belongs to the technical field of in-situ development and utilization of oil shale, and relates to an in-situ oxidation heat recovery system and method for oil shale. Background Art

[0002] Oil shale is a fine-grained sedimentary rock containing solid organic matter (kerogen) and has high energy potential. At present, the development of oil shale mainly relies on open-pit mining and ground distillation technology. However, the existing mining model has many disadvantages and is limited by the mining depth. It is mainly concentrated on shallowly buried oil shale resources, and deep oil shale resources have not been effectively utilized. In order to solve this problem, domestic and foreign scholars have proposed a variety of in-situ mining technologies, but so far, large-scale industrial applications have not been achieved. The main reason is that the energy density of oil shale is low, and its calorific value is only about 30% of standard coal. In addition, most of the organic matter in oil shale exists in solid form, and the dense rock matrix dominated by clay minerals has a strong sealing property for its organic matter. The permeability of the solid matrix is ​​extremely low, and even if there is a small amount of liquid or gaseous organic matter, it is difficult to migrate and discharge. This makes it difficult for many in-situ mining methods to achieve ideal economic benefits.

[0003] In the process of oil and gas extraction, the degree of reservoir cracking and the oxidation exothermic process are important factors affecting the extraction efficiency and safety. Traditional reservoir monitoring methods mainly rely on seismic exploration, electromagnetic measurement, pressure monitoring and other means, but these methods have certain limitations in terms of resolution and real-time monitoring capabilities. In recent years, nanomagnetic particles, as an emerging functional material, have shown great potential in the field of reservoir monitoring. Nanomagnetic particles have unique physical and chemical properties, such as high specific surface area, adjustable magnetism and excellent biocompatibility, which enable them to perform superior performance in complex geological environments. After the nanomagnetic particles are injected into the reservoir, they can migrate with the expansion of cracks and the flow of fluids. Under the action of the external magnetic field, the particles generate response signals. By monitoring the changes in these signals, the degree of reservoir cracking can be reflected in real time.

[0004] In addition, in the process of oil and gas exploration and production, the temperature change inside the reservoir is crucial to optimize the mining plan and improve the recovery rate. However, traditional temperature detection methods are often limited by the complex downhole environment, and it is difficult to accurately and real-time monitor the temperature changes of the reservoir. The development of nanotechnology provides a new solution to this problem. Nanomagnetic particles have become an ideal temperature monitoring tool due to their unique magnetism and high sensitivity. When the temperature changes, the magnetic field strength of nanomagnetic particles will change significantly. By monitoring the change in magnetic field intensity, the temperature changes inside the reservoir can be indirectly reflected, thereby realizing accurate monitoring of temperature changes. This technology not only improves the accuracy and real-time performance of temperature monitoring, but also overcomes the limitations of traditional methods in complex downhole environments. Compared with traditional PIV particle technology, nanomagnetic particles have shown significant advantages in monitoring the cracking degree and temperature changes of reservoir fractures. Nanomagnetic particles are more sensitive to temperature changes and can monitor temperature changes inside cracks in real time. At the same time, nanomagnetic particles can be continuously monitored in real time through magnetic field detection technology, providing a stable data stream, while PIV technology usually requires intermittent capture of flow images. Nanomagnetic particles can enter smaller cracks and pores due to their tiny size, thus achieving higher spatial resolution. In addition, magnetic field detection technology can penetrate rocks to a certain depth and monitor the degree of cracking of deeper cracks. In high temperature and high pressure environments, nanomagnetic particles can maintain stable performance and are suitable for long-term monitoring tasks. Therefore, nanomagnetic particles have important technical advantages in reservoir monitoring and can provide new technical means to improve the efficiency and safety of oil and gas production.

[0005] Among the patents that have been published so far, patent publication number CN109736762A proposes a method for extracting shale oil and gas by in-situ catalytic oxidation of oil shale; patent publication number CN10477581A proposes a vacuum spiral tube nitrogen heater for underground in-situ conversion of oil shale; patent publication number CN109444020A proposes a device and method for observing the microscopic characteristics of rock fracture seepage based on 3D printing technology.

[0006] However, the patent with publication number CN109736762A focuses on lowering the heating temperature and enhancing the catalytic effect, which is suitable for improving mining efficiency and energy utilization; the patent with publication number CN10477581A uses nitrogen heating, directly heats the injected nitrogen through the downhole combustion heat exchange system, focuses on nitrogen heating and in-well monitoring, and focuses on reducing heat loss and improving oil recovery rate. It is suitable for the development of deep and high-thickness oil shale, with low cost and small footprint; the patent with publication number CN109444020A is a 3D-printed transparent resin sample, servo motor controller, flow meter, solenoid valve and control motherboard, etc., which are used for observing seepage characteristics under laboratory conditions. Summary of the invention

[0007] The present invention overcomes the shortcomings of the prior art and proposes an oil shale in-situ oxidation heat recovery system and method. The present invention abandons the inherent mode of existing oil shale development and utilization technology that positions the product as oil and gas, directly oxidizes the organic matter and fixed carbon in the oil shale in an underground in-situ state to release heat, and uses low-temperature steam as a heat carrier fluid to extract the heat energy released by the oxidation of the oil shale for power generation. It can be used as a strategic reserve technology for the development of oil shale and medium and low maturity shale oil and gas resources.

[0008] In order to achieve the above object, the present invention is achieved through the following technical solutions: An oil shale in-situ oxidation heat recovery system comprises a well network structure and a ground power generation device; the well network structure comprises an injection well, a heat recovery well and a plurality of observation wells; the injection well and the heat recovery well penetrate the oil shale layer, and the depth of the observation well is determined according to the vertical distance from the wellhead of the observation well to the top plate of the oil shale layer; The wellhead of the injection well is connected with an oxygen injection device, a combustible gas injection device and an injection well temperature and pressure monitoring device; the wellhead of the heat production well is connected with a heat production well temperature and pressure monitoring device; an electromagnetic sensor is arranged in each observation well, the lower part of the electromagnetic sensor is in contact with the top plate of the oil shale layer, and the upper part of the electromagnetic sensor is connected with a high-sensitivity geomagnetic exploration device; the number of electromagnetic sensors arranged in each observation well is ≥1; the oil shale layer is fractured by hydraulic fracturing to form cracks, so that the injection well and the heat production well are connected, and nano-magnetic particles are added to the fracturing fluid as a proppant; the observation well is used to monitor the distribution of nano-magnetic particles and the magnetic field strength; The ground power generation device includes a dual-fluid heat exchanger, a flash evaporator and a generator; the dual-fluid heat exchanger is connected to the flash evaporator through a superheated water vapor transmission pipeline, the turbine on the flash evaporator drives the generator to generate electricity, the electricity generated by the generator is transformed by the transformer and then connected to the national power grid, the low-temperature and low-pressure condensed water after power generation re-enters the dual-fluid heat exchanger through the steam condensate water recovery pipeline after power generation, the dual-fluid heat exchanger is connected to the injection well through the low-temperature water reinjection pipeline, and the dual-fluid heat exchanger is connected to the heat production well through the heat production pipeline.

[0009] Furthermore, the injection wells and the heat production wells are arranged at a distance of 50-100 meters.

[0010] Furthermore, a downhole igniter control device is connected to the wellhead of the injection well.

[0011] Furthermore, an oxygen injection control valve is connected to the injection port of the oxygen injection device, and a combustible gas injection control valve is connected to the injection port of the combustible gas injection device.

[0012] Furthermore, a low-temperature water injection pump and a one-way valve are provided on the low-temperature water reinjection pipeline; and a hot water circulation pump is connected to the steam condensate water recovery pipeline after power generation.

[0013] Furthermore, electromagnetic sensors are evenly distributed at different depths and lateral positions in the observation well to comprehensively monitor the cracking of the oil shale layer.

[0014] An oil shale in-situ oxidation heat recovery method is based on the oil shale in-situ oxidation heat recovery system and includes the following steps: S1. Wellbore layout connected to oil shale layer S1.1. Well pattern design: design the well pattern structure according to the geological structure of the oil shale layer; S1.2, Wellbore construction: Use directional drilling method to arrange injection wells, heat production wells and observation wells on the oil shale layer; S1.3. Use hydraulic fracturing to establish a fracture network in the oil shale layer: Add nano-magnetic particles as proppants to the fracturing fluid; Use the fracturing fluid to fracture the oil shale layer to form fractures, so that the injection well and the heat production well are connected; Before the fracturing operation, the image inside the oil shale layer was observed through high-sensitivity geomagnetic exploration equipment, and it was found that the concentration of nanomagnetic particles was 0, and the image did not show any information; as the fracturing operation gradually progressed, the concentration of nanomagnetic particles inside the oil shale layer gradually increased, and the high-sensitivity geomagnetic exploration equipment began to show preliminary images; when at least one crack image running through the injection well and the heat production well was observed, it was judged that the fracturing operation had successfully achieved the predetermined goal, and the crack had been formed and had effective connectivity; S2. Oil shale layer preheating and oxygen injection A mixture of combustible gas and oxygen is injected into the oil shale layer through an injection well until the temperature of the oil shale layer near the injection well reaches the ignition point of 350°C; and ignites at the bottom of the injection well to start preheating the oil shale layer; at this time, the injection of combustible gas is stopped and switched to pure oxygen injection; Whether the ignition point has been reached is determined by observing the magnetic field strength inside the oil shale layer using the high-sensitivity geomagnetic exploration equipment at the top of the well, and judging it through the attenuation curve and attenuation formula of the magnetic field strength with temperature; The attenuation formula is: In the formula, yes Magnetic field strength at temperature; yes is the initial magnetic induction intensity at the reference temperature; is the temperature; is the characteristic temperature constant; S3. Low temperature water injection and thermal energy collection S3.1. Low-temperature water injection: After the oil shale layer is heated by oxidation, low-temperature water below 50°C is injected through the injection well. During the flow of water in the oil shale layer, the water exchanges heat with the oil shale layer and is converted into high-temperature water vapor; S3.2, Steam collection: During the in-situ oxidation process of oil shale, the generated high-temperature water vapor flows to the heat production well through the fracture network in the oil shale layer, and the high-temperature water vapor is collected to the ground through the outlet of the heat production well; a dual-medium heat exchanger is used for heat exchange, and the heat of the high-temperature water vapor is released to drive the generator to generate electricity and convert it into electrical energy; The cooled steam after heat energy recovery is injected into the wellbore of the injection well through a dual-medium heat exchanger and then injected into the underground oil shale layer again.

[0015] The beneficial effects of the present invention compared with the prior art are as follows: 1. Efficient energy utilization: The present invention releases heat energy through an in-situ oxidation process and utilizes a low-temperature steam circulation system to convert the heat released underground into electrical energy, thereby significantly improving energy recovery efficiency and reducing energy waste.

[0016] 2. Low cost and environmental protection: Compared with the traditional oil and gas pyrolysis extraction technology, the present invention does not need to extract oil and gas, the process is simple, avoids damage to the environment, and greatly reduces the development cost, with strong economy and environmental friendliness.

[0017] 3. Wide applicability: The present invention is applicable to the development of deep oil shale resources, especially in areas where open-pit mining and distillation methods are difficult to apply. In addition, the technology can also be applied to the development and utilization of medium and low maturity shale oil and gas resources, broadening its scope of application.

[0018] 4. Low carbon dioxide emissions: The in-situ oxidation process of the present invention produces a high concentration of carbon dioxide, and the emissions are concentrated, which is convenient for subsequent treatment and can effectively reduce carbon dioxide emissions, meeting environmental protection requirements.

[0019] 5. Accurate monitoring and optimized control: By introducing nano-magnetic particles, the present invention can monitor the cracking situation inside the reservoir and the heat release process in the oxidation reaction in real time, optimize the heat recovery effect, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a connection schematic diagram of an oil shale in-situ oxidation heat recovery system of the present invention; Figure 2 Layout diagram of heat injection wells, heat production wells and observation wells; Figure 3 is the attenuation curve of magnetic field intensity with temperature; In the figure: 1- oil shale layer; 2- injection well; 3- heat production well; 4- dual-medium heat exchanger; 5- combustible gas injection device; 6- oxygen injection device; 7- downhole igniter control device; 8- injection well temperature and pressure monitoring device; 9- low-temperature water injection pump; 10- hot water circulation pump; 11- heat production well temperature and pressure monitoring device; 12- flash evaporator; 13- turbine; 14- generator; 15- transformer; 16- state power grid; 17- superheated steam transmission pipeline; 18- steam condensate recovery pipeline after power generation; 19- heat production pipeline; 20- one-way valve; 21- combustible gas injection control valve; 22- oxygen injection control valve; 23- low-temperature water reinjection pipeline; 24- downhole igniter; 25- injection well bottom temperature and pressure sensor; 26- heat production well bottom temperature and pressure sensor; 27- observation well; 28- high-sensitivity geomagnetic exploration equipment. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention is further described in detail in conjunction with the embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The technical solutions of the present invention are described in detail below in conjunction with the embodiments and the accompanying drawings, but the scope of protection is not limited thereto.

[0022] Example 1 See also Figure 1 and Figure 2 This embodiment proposes an oil shale in-situ oxidation heat recovery system, which includes a well network structure and a ground power generation device.

[0023] The well network structure includes injection wells 2, heat production wells 3 and multiple observation wells 27. The spacing between the injection wells 2 and the heat production wells 3 should be reasonably set according to the geological conditions of the oil shale layer 1, and the spacing is usually 50-100 meters. In this embodiment, the spacing between the injection wells 2 and the heat production wells 3 is 80 meters; the depths of the injection wells 2 and the heat production wells 3 should penetrate the oil shale layer 1 to ensure that the wellbore is completely connected to the oil shale layer 1 to achieve effective heat collection and gas injection. The depth of the observation well 27 is usually determined based on the vertical distance from the wellhead of the observation well 27 to the top plate of the oil shale layer 1, and its spatial orientation should avoid being arranged linearly with other wellbores to reduce interference between wellbores and improve the heat production effect.

[0024] The injection well 2 is used to inject oxygen, combustible gas and low-temperature water to stimulate the in-situ oxidation reaction of the oil shale layer; the wellhead of the injection well 2 is connected with an oxygen injection device 6, a combustible gas injection device 5, a downhole igniter control device 7 and an injection well temperature and pressure monitoring device 8; the injection port of the oxygen injection device 6 is connected with an oxygen injection control valve 22, and the injection port of the combustible gas injection device 5 is connected with a combustible gas injection control valve 21; the heat production well 3 is used to recover the heat generated by the in-situ oxidation process of the oil shale; the wellhead of the heat production well 3 is connected with a heat production well temperature and pressure monitoring device 11; the observation well 27 is used to monitor the distribution of nano-magnetic particles and the magnetic field strength, so as to reflect the cracking of the oil shale layer 1 and the heat release of the oxidation reaction. The injection well 2 and the heat production well 3 are connected through hydraulic fracturing technology. A downhole igniter 24 and a temperature and pressure sensor 25 at the bottom of the injection well 2 are arranged at the position where the bottom of the heat production well 3 is connected to the injection well 2, and a temperature and pressure sensor 26 at the bottom of the heat production well 3 is arranged at the position where the bottom of the heat production well 3 is connected to the injection well 2; an electromagnetic sensor is arranged in each observation well 27, the bottom of the electromagnetic sensor is in contact with the top plate of the oil shale layer 1, and the top of the electromagnetic sensor is connected to a high-sensitivity geomagnetic exploration device 28. The number of electromagnetic sensors arranged in each observation well 27 is ≥1; the electromagnetic sensors should be evenly distributed at different depths and lateral positions of the observation well 27 to ensure that the cracking of the oil shale layer 1 can be fully monitored; at the same time, the arrangement of the electromagnetic sensors should avoid areas that are prone to interference, such as the well wall, to ensure the accuracy and sensitivity of the signal.

[0025] The ground power generation device includes a dual-medium heat exchanger 4, a flash evaporator 12 and a generator 14. The flash evaporator 12 is arranged on the superheated water vapor delivery pipeline 17 connected to the dual-medium heat exchanger 4. The turbine 13 on the flash evaporator 12 drives the generator 14 to generate electricity. The electricity generated by the generator 14 is transformed by the transformer 15 and then connected to the national power grid 16. After the electricity is generated, the low-temperature and low-pressure condensed water re-enters the dual-medium heat exchanger 4 through the steam condensed water recovery pipeline 18 after power generation, and continues to receive the heat energy released by the oxidation of the oil shale layer 1.

[0026] The dual-medium heat exchanger 4 is connected to the injection well 2 through a low-temperature water reinjection pipeline 23, and a low-temperature water injection pump 9 and a one-way valve 20 are provided on the low-temperature water reinjection pipeline 23; the dual-medium heat exchanger 4 is connected to the heat production well 3 through a heat production pipeline 19; and a hot water circulation pump 10 is connected to the steam condensate water recovery pipeline 18 after power generation.

[0027] The dual-fluid heat exchanger 4 is an existing device that uses dual-fluid heat exchange technology to transfer heat from the superheated steam to the working fluid, and optimizes the heat energy conversion process through the efficient heat transfer characteristics of the dual working fluid. The design of the heat exchanger must ensure that the material has high temperature resistance and corrosion resistance to adapt to high temperature and high pressure working environments. The superheated steam is decompressed by the flash evaporator 12 to convert part of the steam into low-temperature and low-pressure steam, and the released heat is used to further heat the working fluid. The design of the flash evaporator 12 requires precise control of the decompression rate to ensure maximum heat recovery and energy conversion efficiency. As the final power conversion unit, the capacity design of the generator 14 should match the output capacity of the dual-fluid heat exchanger 4 to maximize the power output. The working efficiency of the generator 14 is closely related to the quality of the steam, so it needs to be optimized according to the specific system parameters during selection.

[0028] The temperature and pressure sensors in various places can monitor the working conditions in the wellbore in real time. Based on the real-time monitoring data, the injection amount of oxygen and water can be automatically adjusted according to the monitoring data to ensure the stable operation of the oil shale oxidation process and efficient heat recovery. Specifically, when the temperature or pressure in the wellbore is abnormal, the system will automatically adjust the injection amount of oxygen and water to ensure that the oxidation process is carried out under the optimal working conditions.

[0029] Example 2 This embodiment proposes an oil shale in-situ oxidation heat recovery method, based on an oil shale in-situ oxidation heat recovery system described in Example 1; and includes the following specific steps: S1, wellbore arrangement connected to oil shale layer 1 S1.1, well pattern design: design the well pattern structure according to the geological structure of the oil shale layer 1; S1.2. Wellbore construction: Directional drilling technology is used to arrange injection well 2, heat production well 3 and observation well 27 on the oil shale layer 1. The arrangement of injection well 2 and heat production well 3 must ensure that the wellbore penetrates the oil shale layer 1 and is accurately positioned.

[0030] According to the thickness and range of the oil shale layer 1, the depth of the injection well 2 and the heat production well 3 is usually controlled at 300-1000 meters, and the depth of the observation well 27 is usually determined based on the depth from the wellhead to the top plate of the oil shale layer 1. The accuracy of the depth of each well should be ensured, and the drilling process should be tracked through a real-time monitoring system to avoid deviations.

[0031] Strict quality control measures should be implemented during the above construction process to ensure that the wellbore diameter, wellbore smoothness and wellbore stability meet the design requirements and avoid wellbore damage or fluid leakage due to wellbore instability.

[0032] After the wellbore construction is completed, each wellbore should be tested to verify the fluid transmission performance, pressure response and temperature distribution of the wellbore to ensure that each wellbore functions normally. Water or gas injection tests should be carried out on the injection well 2 to test the injectability and injection efficiency of the oil shale layer 1. Temperature and flow tests should be carried out on the heat production well 3 to ensure that heat can be effectively extracted. Pressure and temperature monitoring should be carried out on the observation well 27 to understand the status of the oil shale layer 1 in real time.

[0033] Then arrange the corresponding sensors and connect the various devices.

[0034] S1.3, Hydraulic fracturing: Use hydraulic fracturing technology to establish a fracture network in the oil shale layer 1. Through the action of fracturing fluid, the oil shale layer 1 is fractured to form fractures to ensure the connectivity between the injection well 2 and the thermal well 3. The formation of the fracture network helps the fluid flow in the oil shale layer 1 and enhances the permeability of the oil shale layer 1. Adding nano-magnetic particles as proppants in the fracturing fluid can not only enhance the stability of the fractures and keep the fractures open, but also improve the fluid dynamics during the fracturing process. Nano-magnetic particles are existing materials, such as magnetite (Fe3O4) nanoparticles or iron oxide (such as Fe2O3)-based nanoparticles.

[0035] Before the above-mentioned hydraulic fracturing, a detailed geological survey of the oil shale layer 1 must be conducted to evaluate the lithology, porosity, permeability and crack distribution of the oil shale layer 1. The selection of the fracturing fluid should be based on the characteristics of the oil shale layer 1. The fracturing fluid should have sufficient viscosity and fluidity to facilitate the injection of the liquid into the oil shale layer 1 and form cracks. Specifically, if the permeability of the oil shale layer 1 is low, a fracturing fluid with a higher viscosity needs to be selected; if there are certain natural cracks in the oil shale layer 1, a fracturing fluid with a lower viscosity can be selected.

[0036] During hydraulic fracturing, the pressure and flow rate of the injected liquid should be precisely controlled according to the specific conditions of the oil shale layer 1. Too high an injection pressure may cause the well wall to rupture, while too low a pressure may not effectively open the cracks. In the initial stage, the injection pressure should be gradually increased until the predetermined crack opening pressure is reached. At the same time, when controlling the injection pressure, attention should be paid to the stress state of the oil shale layer 1 to avoid damage to the oil shale layer 1 caused by excessive fracturing.

[0037] During the fracturing fluid injection process, it should be ensured that the fracturing fluid can be evenly distributed throughout the oil shale layer 1 so that the fracture network has good connectivity; through multi-stage injection and multiple fracturing, the fracture network can be gradually expanded to ensure that the injection well 2 and the heat production well 3 maintain sufficient connectivity.

[0038] The addition of the nano-magnetic particles enables the proppant to form a finer network structure in the cracks, thereby optimizing the connectivity of the cracks and improving the permeability of the oil shale layer 1; in addition, the nano-magnetic particles can also provide real-time crack change data through magnetic field monitoring technology, which is helpful for subsequent accurate evaluation of the fracturing effect.

[0039] Before the fracturing operation, the image inside the oil shale layer 1 was observed by the high-sensitivity geomagnetic exploration equipment 28, and it was found that the concentration of nanomagnetic particles was 0, and the image did not show any information. As the fracturing operation gradually progressed, the concentration of nanomagnetic particles inside the oil shale layer 1 gradually increased, and the high-sensitivity geomagnetic exploration equipment 28 began to show preliminary images. When at least one crack image running through the injection well 2 and the heat production well 3 is observed, it can be judged that the fracturing operation has successfully achieved the predetermined goal, and the crack has been formed and has effective connectivity.

[0040] S2. Preheating of oil shale layer 1 and oxygen injection A mixture of combustible gas and oxygen is injected into the oil shale layer 1 through the injection well 2 until the temperature of the oil shale layer 1 near the injection well 2 reaches the ignition point of 350°C; and ignites at the bottom of the injection well 2 to start preheating the oil shale layer 1. At this time, the injection of combustible gas is stopped and switched to pure oxygen injection.

[0041] Whether the ignition point has been reached is determined by using a highly sensitive geomagnetic exploration device 28 at the top of the observation well 27 to detect the magnetic field strength inside the oil shale layer 1, and by Figure 3 The attenuation curve of magnetic field intensity with temperature and the attenuation formula are used to make judgments; The attenuation formula is: In the formula, yes Magnetic field strength at temperature; is the initial magnetic flux density ( is the reference temperature); is the temperature; is a characteristic temperature constant that reflects the rate at which the magnetic field intensity decays.

[0042] The mixing ratio of the injected combustible gas and oxygen needs to be precisely adjusted according to the properties, temperature and heat extraction requirements of the oil shale layer 1 to ensure that the combustible gas can burn stably and achieve the expected temperature increase effect. During this process, the gas injection pressure and flow rate in the well need to be continuously monitored to avoid uneven gas injection or too fast temperature increase of the oil shale layer 1 due to excessive or too small flow rate. When the temperature of the oil shale layer 1 reaches 350°C, the injection of combustible gas is stopped and replaced with pure oxygen. At this time, the injection flow rate and pressure of pure oxygen need to be precisely controlled to ensure that the temperature of the oil shale layer 1 is further increased and remains stable. During the gas injection process, real-time temperature monitoring is required through the injection well bottom temperature and pressure sensor 25 to ensure that the temperature distribution of the oil shale layer 1 is uniform and avoid local overheating or temperature fluctuations. If the temperature is too high or too low, the gas injection parameters should be adjusted in time to ensure the safety and effectiveness of the operation.

[0043] During the entire preheating process of the oil shale layer 1, strict safety monitoring measures need to be implemented, especially in key links such as gas injection, ignition, and temperature monitoring. The injected mixed gas and pure oxygen have certain flammability and explosion risks, so gas leakage monitoring and fire prevention measures must be strengthened to ensure that the working environment meets safety requirements and prevent fire or explosion accidents.

[0044] The attenuation of the magnetic field intensity inside the oil shale layer 1 is monitored by the high-sensitivity geomagnetic exploration equipment 28 above the observation well 27, and the attenuation degree of the magnetic field intensity generated by the nano-magnetic particles inside the oil shale layer 1 as the temperature changes is detected. The relationship between the magnetic field intensity and the temperature of the oil shale layer 1 is calculated and analyzed in real time according to the preset magnetic field intensity attenuation curve and attenuation formula to accurately monitor the change of the temperature of the oil shale layer 1. Pure oxygen is injected into the oil shale layer 1 through the injection well 2. Oxygen reacts with organic matter and fixed carbon in the oil shale layer 1 to release a large amount of heat energy. The oxidation reaction gradually expands around the wellbore to form a high-temperature porous rock structure, thereby providing ideal conditions for subsequent thermal energy collection. The flow rate and pressure of pure oxygen injection need to be precisely adjusted to ensure that oxygen can fully react with organic matter in the oil shale layer 1, while avoiding damage to the structure of the oil shale layer 1 or excessive oxidation.

[0045] During the pure oxygen injection process, the injection pressure and flow rate need to be precisely controlled. Too high an injection pressure may cause the oil shale layer 1 to rupture, while too low a pressure may not be able to push the oxygen to fully contact with the reactants in the oil shale layer 1. The uniform distribution of pure oxygen is also the key to ensuring the stable progress of the oxidation reaction. Multiple injection wells 2 should be designed according to the distribution of the oil shale layer 1 to ensure that the oxygen can be effectively expanded to the entire oil shale layer 1 area.

[0046] During the pure oxygen injection process, the temperature of the oil shale layer 1 and the progress of the oxidation reaction need to be monitored in real time by high-precision geomagnetic exploration equipment 28 above the observation well 27. Too high or too low temperature will affect the efficiency of the oxidation reaction, so it is necessary to ensure that the temperature is always maintained in the optimal range.

[0047] During the entire pure oxygen injection process, safety monitoring needs to be strengthened, especially monitoring of gas leakage and temperature. Therefore, gas leakage detection equipment needs to be installed to prevent accidents. At the same time, the heat generated by the oxidation reaction needs to be kept within a safe range to avoid excessively high temperatures from damaging the structure of the oil shale layer 1.

[0048] By adjusting the injection rate and pressure of pure oxygen, the stability of the oxidation reaction is ensured, and local overheating or insufficient oxygen supply is prevented, thereby ensuring uniform release of heat in the oil shale layer 1 and maximizing the energy utilization efficiency in the oil shale layer 1.

[0049] S3. Low temperature water injection and thermal energy collection S3.1. Low-temperature water injection: After the oil shale layer 1 is oxidized and heated, low-temperature water (temperature is usually controlled below 50°C) is injected. During the flow of water in the oil shale layer 1, the water effectively exchanges heat with the oil shale layer 1 and is converted into high-temperature steam.

[0050] In the above process, the injection temperature of low-temperature water is required to be precisely controlled to ensure that the water temperature does not exceed the set maximum temperature so as not to affect the thermal stability of the oil shale layer 1; the flow rate and rate of injected water should be dynamically adjusted according to the temperature, permeability and oxidation process of the oil shale layer 1 to ensure that water can flow evenly through the oil shale layer 1 to maximize the heat conversion efficiency.

[0051] The injected low-temperature water should fully exchange heat with the heat in the oil shale layer 1, so that the water gradually heats up during the flow and is converted into high-temperature water vapor; the uniformity of the water flow and the stability of the oil shale layer 1 are crucial, and it is necessary to ensure that the flow of water in the oil shale layer 1 is not blocked, and that the pressure and temperature changes are within a safe range; in addition, the purity of the water must also meet certain standards to avoid the negative impact of impurities in the water on the permeability of the oil shale layer 1 and the heat recovery process.

[0052] S3.2. Steam collection: During the in-situ oxidation process of oil shale, the generated high-temperature water vapor flows to the heat production well 3 through the fracture network in the oil shale layer 1, and the high-temperature water vapor is collected to the ground through the outlet of the heat production well 3; to ensure the efficiency and stability of high-temperature water vapor collection, the temperature and pressure of the high-temperature water vapor must be monitored in real time.

[0053] During the flow of high-temperature water vapor, the temperature, pressure and flow rate of high-temperature water vapor are accurately controlled through a real-time data monitoring system to ensure that the high-temperature water vapor always remains in the best state to achieve the most efficient thermal energy collection.

[0054] S3.3, heat recovery: The high-temperature steam generated during the in-situ oxidation of oil shale is heat exchanged by a dual-medium heat exchanger 4, and the heat of the high-temperature steam is released to drive the generator 14 to generate electricity and converted into electrical energy. The system realizes the recycling of high-temperature steam.

[0055] In the process of in-situ oxidation heat recovery of oil shale, the cooling steam after heat energy recovery is injected into the wellbore of the injection well 2 through the dual-medium heat exchanger 4, and then injected into the underground oil shale layer 1 again to utilize the heat released by the underground rock layer. This process can effectively reduce energy waste and further improve the utilization efficiency of thermal energy.

[0056] S4. Wellbore rotation and repeated heat recovery When the temperature of the high-temperature water vapor at the outlet of the heat production well 3 drops to a predetermined threshold, the current injection and heat production operations are stopped, and the wellbore rotation operation is performed. Specifically, the original injection well 2 is converted into the heat production well 3, and the original heat production well 3 is converted into the injection well 2, and the observation well 27 remains unchanged, so as to continue the oxidation reaction and heat energy collection, ensuring the continuity of heat energy collection and the stability of system operation. After the rotation operation, the above-mentioned oxidation heat release and injection of low-temperature water heat production process are repeated until the organic matter and fixed carbon in the oil shale layer 1 are completely oxidized and all available heat energy is recovered.

[0057] S5. Completion of heat extraction and closure of the wellbore When all the organic matter and fixed carbon in the oil shale layer 1 are oxidized and the recoverable heat energy in the oil shale layer 1 is fully recovered, the injection of oxygen and water is stopped. Then, the injection well 2, the heat production well 3 and the observation well 27 are closed in accordance with safety regulations to prevent wellbore collapse or pollutant leakage, thereby ensuring the safe closure of the oil shale layer 1.

[0058] Specifically, by real-time monitoring of parameters such as oxygen concentration, temperature change, and gas composition in the oil shale layer 1, it is confirmed that the oxidation of organic matter and fixed carbon has reached the predetermined standard, ensuring that the recoverable heat energy in the oil shale layer 1 is fully recovered. After the oxidation reaction is completed, the injection of oxygen and water is stopped immediately. The cessation of gas and water injection should be precisely controlled to avoid the injection of excessive gas or water, and to prevent unnecessary energy loss and environmental impact. After stopping gas and water injection, the pressure and temperature of the oil shale layer 1 may change. Therefore, it is necessary to monitor the changes in pressure and temperature of the oil shale layer 1 in real time, and take appropriate adjustment measures to ensure the stability of the oil shale layer 1.

[0059] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific embodiments of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the present invention, which should be regarded as belonging to the present invention and the scope of patent protection determined by the submitted claims.

Claims

1. An oil shale in-situ oxidation heat recovery system, characterized in that: It comprises a well network structure and a ground power generation device; the well network structure comprises an injection well (2), a heat production well (3) and a plurality of observation wells (27); the depths of the injection well (2) and the heat production well (3) penetrate the oil shale layer (1), and the depth of the observation well (27) is determined according to the vertical distance from the wellhead of the observation well (27) to the top plate of the oil shale layer (1); The wellhead of the injection well (2) is connected to an oxygen injection device (6), a combustible gas injection device (5) and an injection well temperature and pressure monitoring device (8); the wellhead of the heat production well (3) is connected to a heat production well temperature and pressure monitoring device (11); an electromagnetic sensor is arranged in each observation well (27), the lower part of the electromagnetic sensor is in contact with the top plate of the oil shale layer (1), and the upper part of the electromagnetic sensor is connected to a high-sensitivity geomagnetic exploration device (28); the number of electromagnetic sensors arranged in each observation well (27) is ≥1; the oil shale layer (1) is hydraulically fractured to form a crack, so that the injection well (2) and the heat production well (3) are connected, and nano-magnetic particles are added to the fracturing fluid as a proppant; the observation well (27) is used to monitor the distribution of the nano-magnetic particles and the magnetic field strength; The ground power generation device comprises a dual-medium heat exchanger (4), a flash evaporator (12) and a generator (14); the dual-medium heat exchanger (4) is connected to the flash evaporator (12) via a superheated water vapor transmission pipeline (17); the turbine (13) on the flash evaporator (12) drives the generator (14) to generate electricity; the electricity generated by the generator (14) is transformed by a transformer (15) and then connected to the national power grid (16); low-temperature and low-pressure condensed water after power generation re-enters the dual-medium heat exchanger (4) via a post-power generation steam condensed water recovery pipeline (18); the dual-medium heat exchanger (4) is connected to the injection well (2) via a low-temperature water reinjection pipeline (23); and the dual-medium heat exchanger (4) is connected to the heat recovery well (3) via a heat recovery pipeline (19).

2. The oil shale in-situ oxidation heat recovery system according to claim 1, characterized in that: The injection well (2) and the heat production well (3) are arranged at a distance of 50-100 meters.

3. The oil shale in-situ oxidation heat recovery system according to claim 1, characterized in that: A downhole igniter control device (7) is connected to the wellhead of the injection well (2).

4. The oil shale in-situ oxidation heat recovery system according to claim 1, characterized in that: The injection port of the oxygen injection device (6) is connected to an oxygen injection control valve (22), and the injection port of the combustible gas injection device (5) is connected to a combustible gas injection control valve (21).

5. The oil shale in-situ oxidation heat recovery system according to claim 1, characterized in that: A low-temperature water injection pump (9) and a one-way valve (20) are provided on the low-temperature water reinjection pipeline (23); and a hot water circulation pump (10) is connected to the steam condensate water recovery pipeline (18) after power generation.

6. The oil shale in-situ oxidation heat recovery system according to claim 1, characterized in that: The electromagnetic sensors are evenly distributed at different depths and lateral positions of the observation well (27) for comprehensively monitoring the cracking conditions of the oil shale layer (1).

7. An oil shale in-situ oxidation heat recovery method, characterized in that: An oil shale in-situ oxidation heat recovery system based on any one of claims 1 to 6, comprising the following steps: S1. Wellbore arrangement connected to oil shale layer (1) S1.1, well pattern design: design the well pattern structure according to the geological structure of the oil shale layer (1); S1.2, wellbore construction: using directional drilling method, an injection well (2), a heat extraction well (3) and an observation well (27) are arranged on the oil shale layer (1); S1.

3. Establishing a fracture network in the oil shale layer (1) by hydraulic fracturing: adding nano-magnetic particles as proppants to the fracturing fluid; fracturing the oil shale layer (1) with the fracturing fluid to form fractures, thereby connecting the injection well (2) and the heat production well (3); before the fracturing operation, observing the image inside the oil shale layer (1) with a high-sensitivity geomagnetic exploration device (28), finding that the concentration of nano-magnetic particles is 0, and the image does not show any information; as the fracturing operation gradually advances, the concentration of nano-magnetic particles inside the oil shale layer (1) gradually increases, and the high-sensitivity geomagnetic exploration device (28) begins to show a preliminary image; when at least one fracture image running through the injection well (2) and the heat production well (3) is observed, it is determined that the fracturing operation has successfully achieved the predetermined goal, and the fracture has been formed and has effective connectivity; S2. Oil shale layer (1) Preheating and oxygen injection A mixture of combustible gas and oxygen is injected into the oil shale layer (1) through an injection well (2) until the temperature of the oil shale layer (1) near the injection well (2) reaches an ignition point of 350°C; and the mixture is ignited at the bottom of the injection well (2) to start preheating the oil shale layer (1); at this time, the injection of combustible gas is stopped and replaced with injection of pure oxygen; Whether the ignition point has been reached is determined by detecting the magnetic field strength inside the oil shale layer (1) through a high-sensitivity geomagnetic exploration device (28) at the top of the observation well (27), and judging by the attenuation curve of the magnetic field strength with temperature and the attenuation formula; The attenuation formula is: In the formula, yes Magnetic field strength at temperature; yes is the initial magnetic induction intensity at the reference temperature; is the temperature; is the characteristic temperature constant; S3. Low temperature water injection and thermal energy collection S3.1, low-temperature water injection: after the oil shale layer 1 is oxidized and heated, low-temperature water below 50° C. is injected through the injection well (2). During the flow of water in the oil shale layer (1), the water exchanges heat with the oil shale layer (1) and is converted into high-temperature water vapor; S3.2, steam collection: during the in-situ oxidation process of oil shale, the generated high-temperature water vapor flows to the heat production well (3) through the fracture network in the oil shale layer (1), and the high-temperature water vapor is collected to the ground through the outlet of the heat production well (3); a dual-medium heat exchanger (4) is used for heat exchange, and the heat of the high-temperature water vapor is released to drive the generator (14) to generate electricity, thereby converting it into electrical energy; The cooled steam after heat energy recovery is injected into the wellbore of the injection well (2) through the dual-medium heat exchanger (4), and then injected into the underground oil shale layer (1) again.

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