Method for in-situ conversion of oil shale and carbon sequestration by injecting high-temperature carbon dioxide in cooperation with sodium gel capsules

Abstract

The application discloses a method for in-situ conversion of oil shale and carbon sequestration by injecting high-temperature carbon dioxide and sodium capsules, and belongs to the technical field of in-situ exploitation of fossil energy and carbon sequestration. The method comprises the following steps: firstly, determining a target development area and formulating a corresponding development strategy; secondly, performing fracturing reconstruction on an oil shale reservoir; thirdly, heating the oil shale reservoir and injecting supercritical carbon dioxide to perform displacement recovery; fourthly, injecting a sodium capsule suspension fluid into the oil shale reservoir to realize solid-phase geological sequestration; and finally, when oil and gas exploitation reaches an economic limit, all injection wells and production wells are closed, and final geological sequestration is completed. The method deeply integrates carbon dioxide geological sequestration technology and in-situ conversion of oil shale, significantly improves the recovery rate of oil shale, and simultaneously realizes geological sequestration of carbon dioxide, which is of great significance to carbon emission reduction and in-situ exploitation of fossil energy.

Description

Technical Field

[0001] This invention belongs to the field of in-situ extraction and carbon sequestration technology of fossil energy, specifically, it relates to a method for in-situ conversion and carbon sequestration of oil shale by injecting high-temperature carbon dioxide in conjunction with sodium capsules. Background Technology

[0002] Carbon dioxide geological sequestration is a process in which captured carbon dioxide is injected into underground geological structures such as deep saline aquifers and depleted oil and gas reservoirs through engineering techniques, and its long-term isolation from the atmosphere is achieved by using structural and strata-based sequestration mechanisms.

[0003] In the field of energy development, the application potential of carbon dioxide in the in-situ conversion of oil shale is gradually becoming apparent. Under high-temperature carbon dioxide injection conditions, it can not only promote the pyrolysis and conversion of organic matter in oil shale, but the special geological environment, such as the porous strata formed after high-temperature action, also provides favorable conditions for the geological sequestration of carbon dioxide. If the deep integration of carbon dioxide geological sequestration technology with the in-situ conversion and exploitation process of oil shale can be achieved, it is expected to simultaneously achieve the dual goals of improving oil and gas recovery and controlling carbon emissions, which is of great strategic significance for optimizing energy production models and building a low-carbon circular economy system.

[0004] The existing integrated in-situ mining and geological storage methods still have the following shortcomings: On the one hand, the storage and mining processes are often implemented in stages, failing to form a truly integrated operation mode, resulting in extended project cycles and increased costs; on the other hand, the storage mechanism mainly relies on formation adsorption or tectonic storage, which has limited storage efficiency, and there are environmental risks of carbon dioxide leakage and migration during long-term storage.

[0005] Therefore, further developing efficient and safe integrated technologies for in-situ mining and geological sequestration, improving geological sequestration efficiency and ensuring its long-term stability are of great significance for promoting the coordinated development of carbon sequestration technology and in-situ mining of fossil energy. Summary of the Invention

[0006] The purpose of this invention is to provide an integrated method for in-situ conversion and carbon sequestration of oil shale using high-temperature supercritical carbon dioxide injection combined with sodium capsules. This method simultaneously achieves efficient in-situ conversion and extraction of oil shale and stable mineralization and sequestration of carbon dioxide by injecting high-temperature supercritical carbon dioxide into the oil shale reservoir and using sodium capsules. This invention aims to improve the recovery rate of oil shale resources and the long-term safety of carbon dioxide geological sequestration, thereby solving the key problems of fragmented extraction and sequestration processes, low sequestration efficiency, and the susceptibility of carbon dioxide leakage and migration under long-term sequestration conditions in existing technologies.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules, comprising the following steps:

[0008] Step 1: Conduct geological exploration of the target development area to obtain oil shale reservoir parameters, deploy development wells based on the oil shale reservoir parameters, and determine the supercritical carbon dioxide injection parameters and sodium capsule deployment strategy.

[0009] Step 2: After drilling wells and completing the well network layout in the target development area, the oil shale reservoir is subjected to fracturing to form a fracture network;

[0010] Step 3: Heat the modified oil shale reservoir to the temperature at which kerogen undergoes thermal decomposition. When the oil shale reservoir temperature reaches the preset target temperature, inject supercritical carbon dioxide into the oil shale reservoir through injection wells to displace oil and gas products, and then extract the oil and gas products through production wells.

[0011] Step 4: After supercritical carbon dioxide injection is completed, sodium capsule suspension fluid is injected into the oil shale reservoir through the injection well. The sodium capsule suspension fluid is formed by dispersing sodium capsules and a dispersant in liquid carbon dioxide, wherein the mass concentration of sodium capsules is 3% to 8%. The dispersant is used to maintain the uniform dispersion of sodium capsules in liquid carbon dioxide. The sodium capsule wall material fails at a predetermined temperature and releases metallic sodium. The metallic sodium undergoes a reduction reaction with the surrounding supercritical carbon dioxide, 4Na + 3CO2 → C + 2Na2CO3, synthesizing solid carbon and sodium carbonate in situ, thus sealing carbon dioxide in the oil shale reservoir in solid form.

[0012] Step 5: After oil and gas recovery is completed, shut down the injection well and production well to achieve dual solid-state and supercritical carbon dioxide sequestration.

[0013] Furthermore, the development well pattern adopts an inverted five-point well pattern, including one injection well located in the center and four production wells located at the vertices of the square. Both the injection well and the production wells are vertical wells, and the distance between the injection wells and the production wells is 15m to 50m.

[0014] Furthermore, the injection parameters for supercritical carbon dioxide include injection pressure, bottom hole temperature during injection, injection flow rate, and cumulative injection volume. The injection pressure of supercritical carbon dioxide is typically controlled at 1.1 to 1.3 times the original pressure of the oil shale reservoir to ensure effective injection of supercritical carbon dioxide, achieve miscible displacement, and improve recovery. Based on reservoir permeability, fracture development, and injection capacity testing, the injection flow rate is typically controlled at 2.0 m³ / h to avoid excessively high flow rates leading to viscous fingering, gas channeling, or uncontrolled fracture propagation. 3 / h~3.0m 3 Within the range of / h. The cumulative injection rate of the supercritical carbon dioxide is determined by the formula A preliminary estimate was made, among which The estimated cumulative volume of carbon dioxide to be injected is expressed in meters. 3 ; The area controlled by the well network is expressed in meters (m²). 2 ; The effective thickness of the oil shale is expressed in meters (m). Porosity of oil shale after fracturing; This represents the oil saturation of oil shale. The expected recovery rate (determined based on existing technologies such as oilfield statistical methods, indoor water-drive oil testing methods, and core analysis methods); It is the carbon dioxide displacement coefficient (generally 1.5 to 2.5, determined through numerical simulation or analogy, reflecting the volume displacement relationship between supercritical carbon dioxide and crude oil).

[0015] Furthermore, the sodium capsule deployment strategy includes: dispersing sodium capsules at a mass concentration of 3.0% to 8.0% in liquid carbon dioxide under conditions where the bottom-hole temperature reaches 430℃ to 450℃, forming a sodium capsule suspension; the discharge rate of the sodium capsule suspension is controlled at 1.5m³. 3 / h~2.0m 3 / h, while adjusting the injection rate and combining real-time monitoring of oil and gas products with the temperature-controlled release characteristics of sodium capsules, the molar ratio of metallic sodium to carbon dioxide at various locations in the oil shale reservoir is kept below 4:3 to prevent local excess of metallic sodium and ensure that metallic sodium can react completely at all locations.

[0016] Furthermore, the sodium capsule comprises a metallic sodium core and three sequentially coated wall materials. The first wall material is a sodium stearate passivation film with a thickness of 0.1µm to 0.5µm; the second wall material is a thermosensitive layer composed of ethyl cellulose with an average molecular weight of 80,000 Da to 120,000 Da and a thickness of 15µm to 25µm. The thermal response failure temperature of the thermosensitive layer corresponds to the thermal decomposition reaction temperature of kerogen in oil shale reservoirs, which ranges from 430℃ to 450℃; the third wall material is a phenolic resin composite coating doped with 5wt% to 15wt% nano-silica with a thickness of 3µm to 8µm.

[0017] Furthermore, the method for preparing the sodium capsule includes:

[0018] Under inert gas protection, metallic sodium is melted and prepared into sodium microparticles with a particle size of 50µm to 150µm; under inert gas protection, the sodium microparticles are subjected to surface passivation treatment to form a sodium stearate passivation film; using fluidized bed coating technology, a temperature-sensitive layer composed of ethyl cellulose is coated on the surface of the sodium stearate passivation film; and a phenolic resin composite coating with a mass fraction of 5wt% to 15wt% nano-silica is formed on the outside of the temperature-sensitive layer through in-situ polymerization.

[0019] Furthermore, the sodium capsule suspension fluid is composed of the following components by mass percentage: 3.0% to 8.0% sodium capsules, 0.015% to 0.16% dispersant, and the balance being liquid carbon dioxide, wherein the dispersant is perfluorooctyl ethyl acrylate.

[0020] Furthermore, in step 4, the sodium capsules have a particle size distribution of 80µm to 180µm. This particle size range is designed to ensure that the sodium capsules have effective fluidity in the fracture network of oil shale reservoirs, while maintaining their settling stability in suspended fluids.

[0021] Furthermore, in step 4, the supercritical carbon dioxide participating in the reduction reaction includes the previously injected supercritical carbon dioxide and the supercritical carbon dioxide formed by the conversion of liquid carbon dioxide in the sodium capsule suspension fluid due to reservoir temperature and pressure conditions.

[0022] Furthermore, in step 2, hydraulic fracturing is carried out by explosive fracturing to form a fracture network in the oil shale reservoir; in step 3, the oil shale reservoir is heated by electric heating to a temperature range of 430℃ to 450℃.

[0023] Compared with existing technologies, the advantages of the high-temperature carbon dioxide injection combined with sodium capsule in-situ conversion and carbon sequestration of oil shale proposed in this invention are as follows:

[0024] First, this invention employs a high-temperature carbon dioxide injection combined with sodium capsule in-situ conversion and carbon sequestration method for oil shale. In the process of recovering oil shale, metallic sodium reacts with supercritical carbon dioxide in a reduction reaction: 4Na + 3CO₂ → C + 2Na₂CO₃. This reaction converts carbon dioxide into solid carbon and sodium carbonate, fixing the carbon dioxide in solid form within the reservoir. Compared to conventional geological sequestration, this method eliminates the long-term environmental risks of carbon dioxide leakage and migration, achieving near-permanent carbon sequestration.

[0025] Second, the present invention employs a method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules, which is used to develop and harvest oil shale. The reaction between metallic sodium and supercritical carbon dioxide releases a large amount of heat, which can provide heat to the oil shale reservoir and accelerate the thermal decomposition of kerogen.

[0026] Third, the method of high-temperature carbon dioxide injection combined with sodium capsule in-situ conversion and carbon sequestration of oil shale is used in this invention to develop and harvest oil shale; since metallic sodium and carbon dioxide produce solid carbon and sodium carbonate, which can fill the developed micro-cracks to a certain extent, thereby reducing the phenomenon of carbon dioxide leakage.

[0027] Fourth, this invention not only achieves physical sequestration of carbon dioxide, but also chemical mineralization sequestration (solid carbon and sodium carbonate) through the chemical reaction between metallic sodium and carbon dioxide, forming a dual physical and chemical sequestration mechanism. Even with a relatively limited content of metallic sodium, the reaction products can still significantly improve sequestration stability, prevent carbon dioxide leakage, and ensure long-term sequestration safety.

[0028] A further advantage is that the present invention uses an inverted five-point well pattern as the development well pattern, which can effectively control drilling costs and ensure energy return rate. While taking into account drilling costs, the in-situ conversion utilization rate remains at a high level. The sodium capsule of the present invention adopts a three-layer composite wall material design, which realizes effective encapsulation of metallic sodium, stable transportation in underground high-temperature environment and controllable release under target temperature and pressure conditions. Attached Figure Description

[0029] The accompanying drawings are provided to further illustrate the invention and form part of this application. The illustrative embodiments and descriptions thereof are used to understand the invention and do not constitute an undue limitation thereof. In the drawings:

[0030] Figure 1 Flowchart of a method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules;

[0031] Figure 2 Well location distribution map for the method of in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules;

[0032] Figure 3 Schematic diagram of the principle of the method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules;

[0033] Figure 4 A graph showing the oil recovery rate of oil shale using a method of in-situ conversion and carbon sequestration of oil shale with high-temperature carbon dioxide injection and sodium capsules.

[0034] Figure 5 A geological storage efficiency diagram of in-situ conversion and carbon sequestration of oil shale using a method of high-temperature carbon dioxide injection combined with sodium capsules;

[0035] Figure labels: 1-Injection well; 2-Production well; 3-Sodium capsule suspension fluid; 4-Supercritical carbon dioxide; 5-Oil and gas products; 6-Surface separation system; 7-Electric heater. Detailed Implementation

[0036] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, this invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions of this invention and actual circumstances. To avoid obscuring the essence of this invention, well-known methods, processes, flows, components, and circuits are not described in detail.

[0037] Figure 1 A flowchart of a method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules is shown. Figure 3 A schematic diagram illustrating the principle of a method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules. Figure 1 and Figure 3 As shown, this invention proposes a method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules. The method first involves fracturing the oil shale reservoir through explosive fracturing to create a fracture network. After the fracture network is formed, an electric heater 7 heats the oil shale reservoir to a predetermined temperature. Then, supercritical carbon dioxide 4 is injected into the oil shale reservoir through injection well 1, and production well 2 is opened to produce oil and gas products 5. Subsequently, sodium capsule suspension 3 is injected into the oil shale reservoir through injection well 1 to react with the supercritical carbon dioxide 4. Finally, all injection wells 1 and production wells 2 are closed when oil and gas production reaches the economic limit (i.e., the production threshold at which the operating cost of oil and gas extraction exceeds the sales revenue of the produced oil and gas), completing the geological sequestration of carbon dioxide. During extraction, the oil and gas products 5 are separated and processed by a surface separation system 6. It should be noted that the surface separation system 6 is derived from the oil and gas separation system widely used in oil shale oil and gas development. Since the technical principles and applications are well known in the industry, they will not be described in detail here.

[0038] The method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules specifically includes:

[0039] Step 1: Identify the target development area and formulate corresponding development strategies:

[0040] A thorough investigation of resource assessment and geological exploration data in the target development area was conducted to obtain oil shale reservoir parameters, including geological reserves, burial depth, effective thickness, organic matter abundance, porosity, and oil saturation. Based on these parameters and considering economic and environmental factors, the target development area was determined. Furthermore, based on relevant data from the target development area, the injection parameters for supercritical carbon dioxide 4, the sodium capsule deployment strategy, and the well network layout were determined.

[0041] The well pattern layout adopts an inverse five-point well pattern as the development well pattern. Figure 2This diagram illustrates the well location distribution in the in-situ conversion and carbon sequestration method for oil shale using high-temperature carbon dioxide injection combined with sodium capsules. The inverted five-point well network includes one injection well (1) at the center and four production wells (2) at the vertices of the square. Temperature and pressure sensors and electric heaters (7) are installed in all injection wells (1) and production wells (2). The injection parameters for supercritical carbon dioxide (4) include injection pressure, bottom hole temperature during injection, injection flow rate, and cumulative injection volume. The injection pressure of supercritical carbon dioxide (4) is typically controlled at 1.1–1.3 times the original pressure of the oil shale reservoir to ensure effective injection, achieve miscible displacement, and improve recovery. Based on reservoir permeability, fracture development, and injection capacity testing, the injection flow rate is typically controlled at 2.0 m³ / s to avoid excessively high flow rates leading to viscous fingering, gas channeling, or uncontrolled fracture propagation. 3 / h~3.0m 3 Within the range of / h. The cumulative injection rate of the supercritical carbon dioxide is determined by the formula A preliminary estimate was made, among which The estimated cumulative volume of carbon dioxide to be injected is expressed in meters. 3 ; The area controlled by the well network is expressed in meters (m²). 2 ; The effective thickness of the oil shale is expressed in meters (m). Porosity of oil shale after fracturing; This represents the oil saturation of oil shale. The expected recovery rate (determined based on existing technologies such as oilfield statistical methods, indoor water-drive oil testing methods, and core analysis methods); The carbon dioxide displacement coefficient (typically 1.5–2.5, determined through numerical simulation or analogy, reflecting the volumetric displacement relationship between supercritical carbon dioxide and crude oil) is used. The sodium capsule deployment strategy involves injecting sodium capsule suspension fluid 3 after the supercritical carbon dioxide 4 is injected. The injection displacement of sodium capsule suspension fluid 3 is typically 1.5 m³ / s. 3 / h~2.0m 3 / h, and throughout the process, the molar ratio of metallic sodium to carbon dioxide in all parts of the oil shale reservoir is always kept to be less than 4:3.

[0042] Preferably, the temperature and pressure sensors in the injection well 1 and the production well 2 monitor the temperature and pressure in the oil shale reservoir in real time. When the bottom hole temperature reaches the range of 430℃ to 450℃, supercritical carbon dioxide 4 is injected. After the supercritical carbon dioxide 4 injection is completed, sodium capsule suspension 3 is injected.

[0043] Preferably, the reverse five-point well pattern adopts vertical wells, with the well spacing between injection well 1 and production well 2 being 15m to 50m. This effectively controls drilling costs while ensuring energy return on investment.

[0044] Step 2: Stimulate the oil shale reservoir:

[0045] Due to the dense and low-permeability characteristics of oil shale, the conductivity of oil shale reservoirs is extremely poor, requiring reservoir stimulation to ensure smooth flow channels for supercritical carbon dioxide 4 and oil and gas products 5.

[0046] Preferably, the oil shale reservoir stimulation employs explosive fracturing to create a fracture network within the oil shale reservoir, ensuring unobstructed flow pathways. Explosive fracturing is an existing reservoir fracturing technology, and its specific process will not be explained in detail here.

[0047] Preferably, the oil shale reservoir, after reservoir modification, greatly improves the displacement efficiency and recovery rate of oil and gas.

[0048] Step 3: Heating the oil shale reservoir and injecting supercritical carbon dioxide for displacement recovery:

[0049] After the oil shale reservoir stimulation is completed, the reservoir is heated to a temperature range of 430℃ to 450℃. Then, supercritical carbon dioxide 4 is injected from injection well 1 to displace the oil and gas products 5. Finally, the oil and gas products 5 are extracted from production well 2.

[0050] Preferably, the method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium encapsulation involves heating the oil shale reservoir using electric heaters 7 in injection well 1 and production well 2, with the heating temperature ranging from 430℃ to 450℃. 430℃ to 450℃ is the optimal temperature window for the efficient pyrolysis of kerogen in oil shale to generate liquid hydrocarbons; within this temperature range, supercritical carbon dioxide 4 also exhibits good diffusion capacity and hydrocarbon dissolution and extraction performance; and within this temperature range, the reaction rate between metallic sodium and carbon dioxide is rapid.

[0051] Preferably, the method of injecting high-temperature carbon dioxide in conjunction with sodium capsules for in-situ conversion and carbon sequestration of oil shale can further fracture the oil shale reservoir by injecting supercritical carbon dioxide, thereby expanding the fracture network.

[0052] Preferably, in the method of high-temperature carbon dioxide injection combined with sodium capsule in-situ conversion and carbon sequestration of oil shale, the extracted oil and gas will be separated in the surface separation system 6, and the separated oil and gas products 5 will be processed separately.

[0053] Preferably, in the method of in-situ conversion and carbon sequestration of oil shale by injecting high-temperature carbon dioxide in conjunction with sodium capsules, supercritical carbon dioxide 4 can also act as a slug to prevent the sodium capsules from reacting with the oil and gas products 5.

[0054] Compared with existing technologies, taking the above measures has the following advantages:

[0055] Carbon dioxide has a high affinity for organic matter, and it can mobilize crude oil in the adsorbed and miscible state in shale organic matter. Supercritical carbon dioxide can expand and create new fractures, improving the conductivity of oil shale reservoirs. Supercritical carbon dioxide can also act as a slug to prevent sodium capsules from contacting oil and gas products.

[0056] Step 4: Inject sodium capsule suspension fluid 3:

[0057] After the supercritical carbon dioxide 4 injection is completed, sodium capsule suspension fluid 3 is injected.

[0058] Preferably, in the method of high-temperature carbon dioxide injection combined with sodium capsule in-situ conversion and carbon sequestration of oil shale, the wall material of the sodium capsule will gradually fail at a temperature of 430℃~450℃, releasing sodium metal to react with carbon dioxide.

[0059] Preferably, in the method of high-temperature carbon dioxide injection combined with sodium capsule in-situ conversion and carbon sequestration of oil shale, metallic sodium and carbon dioxide mainly undergo the reaction 4Na + 3CO2 → C + 2Na2CO3.

[0060] The supercritical carbon dioxide 4 in the reaction is composed of injected supercritical carbon dioxide 4 and supercritical carbon dioxide 4 converted from liquid carbon dioxide in the sodium capsule suspension fluid 3 due to temperature and pressure changes in the oil shale reservoir.

[0061] Preferably, in the method for in-situ conversion and carbon sequestration of oil shale using sodium capsules with high-temperature carbon dioxide injection, the sodium capsules are prepared as follows: a three-layer wall material is constructed using a sequential encapsulation process. The first layer involves the melting of metallic sodium using a high-temperature melting furnace or resistance heating furnace. After the metallic sodium is completely melted, sodium particles ranging from 50µm to 150µm are obtained using a microreactor method. It should be noted that the "microreactor method" typically refers to microreactor technology, a process enhancement technology based on miniaturized channels (typically with characteristic sizes of 10µm to 1000µm) to achieve continuous flow chemical reactions. This technology, through its high specific surface area, precise heat and mass transfer control, and intrinsically safe design, is widely used in pharmaceuticals, fine chemicals, and energy materials. The entire process is conducted under the protection of an inert gas (such as argon) to effectively isolate air and ensure operational safety and product purity. Subsequently, surface passivation treatment was performed: In an argon-protected glove box, the obtained sodium particles were placed in a dry reactor, and an anhydrous ethanol solution of stearic acid with a molar concentration of 0.2 mol / L to 0.5 mol / L (the amount of stearic acid was 5% to 10% of the mass of metallic sodium) was added. The reaction was carried out at 70℃ to 80℃ with continuous stirring for 1 to 2 hours, allowing the stearic acid to react with the surface of metallic sodium to form a sodium stearate passivation film. After the reaction was completed, the system was cooled, washed with anhydrous ethanol, filtered, and then dried at 40℃ to 50℃ under an argon atmosphere for 2 to 4 hours, finally forming the first layer of the wall material sodium stearate passivation film. The sodium stearate passivation film is typically 0.1µm to 0.5µm thick. Its function is to isolate metallic sodium from direct contact with subsequent coating materials, prevent side reactions during storage and coating, and improve the stability of the microsphere surface. The second layer involves using fluidized bed coating technology (a very mature existing technology) to coat the passivated sodium microspheres with a temperature-sensitive layer composed of ethyl cellulose. By controlling the average molecular weight of the ethyl cellulose (e.g., selecting a type with a molecular weight of 80,000 Da to 120,000 Da) and the coating thickness (preferably 15µm to 25µm), its glass transition temperature (Tg) or softening point can be adjusted to the trigger window of the target oil shale reservoir. For example, by selecting ethyl cellulose with a molecular weight of 100,000 Da and controlling the coating thickness to 20 µm, the thermal response failure temperature can be stabilized within the range of 430℃ to 450℃. The third layer: In order to enhance the mechanical strength of the sodium capsule during underground transportation, a phenolic resin composite coating with a mass fraction of 5 wt% to 15 wt% nano-silica is coated on the outside of the temperature-sensitive layer through an in-situ polymerization process. The preferred coating thickness is 3 µm to 8 µm. This layer thickness can provide sufficient protection while avoiding the thermal response performance of the temperature-sensitive layer due to excessive coating thickness.

[0062] Furthermore, after the sodium capsules are prepared, the finished product with a particle size distribution of 80µm to 180µm is obtained by sieving. This particle size range is designed to ensure that the capsules have effective fluidity in the fracture network of oil shale reservoirs, while maintaining their sedimentation stability in suspended fluids. Subsequently, the thermally triggered release performance needs to be verified in a reactor simulating the temperature and pressure conditions of oil shale. It can only be put into use after the release rate reaches 90%.

[0063] Furthermore, qualified sodium capsules are uniformly dispersed in liquid carbon dioxide at a mass concentration of 3.0%–8.0% (the percentage of sodium capsule mass to the total mass of the suspension) together with a dispersant (perfluorooctyl ethyl acrylate) to form a stable, pumpable suspension. The composition (mass percentage) of the sodium capsule suspension is as follows: sodium capsules 3.0%–8.0%, dispersant 0.015%–0.16%, liquid carbon dioxide 91.84%–96.985%, and the sum of the mass percentages of all components is 100%.

[0064] Furthermore, the preparation method of the sodium capsule suspension is as follows: First, a measured amount of liquid carbon dioxide is injected into a high-pressure sealed container. Then, a measured amount of dispersant is added under stirring conditions to fully dissolve or disperse the dispersant in the liquid carbon dioxide. Finally, measured amounts of sodium capsules are gradually added, and the mixture is circulated and mixed to form a uniform and stable suspension. It should be noted that the entire preparation process must be carried out under high pressure to ensure that the carbon dioxide remains liquid at the operating temperature.

[0065] Furthermore, the sodium capsule suspension uses liquid carbon dioxide as the continuous phase and maintains positive pressure under injection pressure to ensure that the entire transportation process is in an anhydrous environment. After entering the oil shale reservoir, the hydrophobic coating on the outer layer of the sodium capsule (i.e., a phenolic resin composite coating doped with 5wt% to 15wt% nano-silica) effectively blocks formation water before reaching the trigger temperature of 430℃ to 450℃. Moreover, at high temperatures, the reaction rate between supercritical carbon dioxide 4 and metallic sodium is much faster than that of water vapor, thus ensuring that metallic sodium preferentially undergoes a mineralization reaction with carbon dioxide and avoids side reactions with water, ensuring a safe and efficient process.

[0066] The specific injection volume of sodium capsule suspension fluid 3 should take into account economic costs.

[0067] Preferably, the method for in-situ conversion and carbon sequestration of oil shale by injecting high-temperature carbon dioxide and using sodium capsules is characterized by injection rate control, microcapsules, self-sealing of micro-fractures by solid carbon and sodium carbonate, and real-time monitoring of products by a surface separation system. This ensures that the molar ratio of metallic sodium to carbon dioxide in the oil shale reservoir is always less than 4:3, preventing local excess of metallic sodium and ensuring that metallic sodium reacts completely in all locations.

[0068] Compared with existing technologies, taking the above measures has the following advantages:

[0069] Sodium metal reacts with supercritical carbon dioxide to convert carbon dioxide into carbon and sodium carbonate, thus sealing the carbon dioxide in solid form within the oil shale reservoir. Compared to conventional geological sequestration, this method eliminates the long-term environmental risks of carbon dioxide migration and leakage, achieving near-permanent carbon sequestration. The reaction between sodium metal and carbon dioxide is exothermic, which can replenish the heat of the oil shale reservoir and accelerate the pyrolysis reaction, promoting the generation of oil and gas. The excess of carbon dioxide compared to sodium metal can prevent the waste of sodium metal. The carbon and sodium carbonate solids produced by the reaction of sodium metal and carbon dioxide can also fill the developed microfractures to a certain extent, preventing carbon dioxide leakage.

[0070] Step 5: After oil and gas recovery is completed, shut down all injection wells 1 and production wells 2 to complete the final geological sequestration.

[0071] Once oil and gas extraction reaches its economic limit (i.e., the production threshold at which the operating cost of oil and gas extraction exceeds the sales revenue of the produced oil and gas), extraction ceases. All wellheads are then closed to complete geological sealing.

[0072] The method of high-temperature carbon dioxide injection combined with sodium capsule in-situ conversion and carbon sequestration of oil shale ultimately achieves dual physical and chemical sequestration.

[0073] Compared with existing technologies, taking the above measures has the following advantages:

[0074] Carbon dioxide injection into underground geological sequestration reduces carbon emissions during oil shale mining and mitigates environmental pollution; two-phase sequestration has a larger sequestration capacity than conventional sequestration and eliminates problems such as carbon dioxide migration, achieving permanent sequestration.

[0075] Example 1:

[0076] This case study selects the oil shale in the Songliao Basin of China as the research object. The geological parameters of the target development area are as follows: the target oil shale layer has a burial depth of 800m, an oil content of 6%, a porosity of 8%, and a permeability of 1.000mD, belonging to a typical low-porosity, low-permeability oil shale reservoir. In addition, the well pattern covers an area of ​​100m (length) × 60m (width), the effective thickness of the oil shale reservoir is 10m, the oil saturation measured by core analysis is 30%, the expected recovery rate is 60%, the porosity after fracturing is 16%, and the carbon dioxide displacement coefficient is taken as 2.

[0077] In the first phase, based on the obtained parameters of the target oil shale reservoir, a reverse five-point well pattern was selected as the development well pattern, including one injection well (1) and four production wells (2), with a vertical well depth of 850m and a well spacing of 20m. Figure 2 As shown; the preliminary estimate of the cumulative injection volume of supercritical carbon dioxide 4 is at least 3456 m³. 3 .

[0078] In the second stage, the oil shale reservoir is subjected to blasting and fracturing to form a fracture network. The permeability of the fractures generated by the fracturing is 75 mD.

[0079] In the third stage, the oil shale reservoir was heated electrically to 430℃~450℃ (heating rate 5℃ / h~10℃ / h). Once the temperature reached the 430℃~450℃ range, supercritical carbon dioxide 4 was injected for displacement at a flow rate of 2m³. 3 / h, production well 2 is started to recover oil and gas products 5. Further, after recovery, oil and gas products 5 are separated in the surface separation system 6, where they are processed separately.

[0080] In the fourth stage, qualified sodium capsules were uniformly dispersed in liquid carbon dioxide at a mass concentration of 3.0% along with a dispersant to prepare sodium capsule suspension fluid 3. Then, at a concentration of 1.8m... 3 The sodium capsule is injected into the oil shale reservoir at a rate of / h. After injection, the sodium capsule wall material gradually fails, releasing metallic sodium. The metallic sodium reacts with supercritical carbon dioxide 4, fixing the supercritical carbon dioxide 4 in the oil shale reservoir in the solid form of carbon and sodium carbonate, while also heating the oil shale reservoir.

[0081] In the fifth stage, after oil and gas recovery reaches the economic limit (i.e., the production threshold at which the operating cost of oil and gas extraction exceeds the sales revenue of the produced oil and gas), injection well 1 and production well 2 are shut down to complete the geological sequestration of carbon dioxide. The final recovery rate is 65%, and the carbon sequestration is 1.65 t / m³. 3 .

[0082] Example 2:

[0083] This case study selects the oil shale in the southern Ordos Basin as the research object. The geological parameters of the target development area are as follows: the target oil shale layer is buried at a depth of 850m, with an oil content of 6.5%, porosity of 9%, and permeability of 0.15mD. In addition, the well pattern covers an area of ​​100m (length) × 60m (width), the effective thickness of the oil shale reservoir is 12m, the oil saturation measured by core analysis is 35%, the expected recovery rate is 65%, the porosity after fracturing is 17%, and the carbon dioxide displacement coefficient is taken as 2.5.

[0084] The operating steps are the same as in Example 1. Operating parameters: vertical well depth of the inverted five-point well pattern is 900m, well spacing is 20m, supercritical carbon dioxide injection pressure is controlled at 1.2 times the original pressure of the oil shale reservoir, and injection flow rate is 2.6m³ / h. 3 / h, the preliminary estimate of the cumulative injection volume of supercritical carbon dioxide 4 is at least 6961.5m³. 3Sodium capsule suspension 3 is prepared by uniformly dispersing 5.5% (w / w) sodium capsules and a dispersant in liquid carbon dioxide; the injection displacement of the sodium capsule suspension is 1.7 m³ / h. 3 / h; heating temperature 430℃~450℃ (electric heating, heating rate 5℃ / h~10℃ / h). Final recovery rate 61%, carbon sequestration 1.72t / m³. 3 .

[0085] Example 3:

[0086] This case study selects the Maoming Basin oil shale as the research object. The geological parameters of the target development area are as follows: the target oil shale layer has a burial depth of 800m, an oil content of 6.2%, a porosity of 1.56%, and a permeability of 0.05mD. In addition, the well network covers an area of ​​100m (length) × 60m (width), the effective thickness of the oil shale reservoir is 12m, the oil saturation measured by core analysis is 35%, the expected recovery rate is 63%, the porosity after fracturing is 9%, and the carbon dioxide displacement coefficient is 2.5.

[0087] The operating steps are the same as in Example 1. Operating parameters: vertical well depth of the inverted five-point well pattern is 850m, well spacing is 20m, supercritical carbon dioxide injection pressure is controlled at 1.2 times the original pressure of the oil shale reservoir, and injection flow rate is 2.4m³ / h. 3 / h, the preliminary estimate of the cumulative injection volume of supercritical carbon dioxide 4 is at least 3572.1 m³ / h. 3 Sodium capsule suspension 3 is prepared by uniformly dispersing 8% (by mass) sodium capsules and a dispersant in liquid carbon dioxide; the injection displacement of sodium capsule suspension 3 is 1.6 m³ / s. 3 / h; heating temperature 430℃~450℃ (electric heating, heating rate 5℃ / h~10℃ / h). Final recovery rate 62%, carbon sequestration 1.52t / m³. 3 .

[0088] Comparative Example 1:

[0089] The method is the same as described in Example 1, except that step 4 is not performed, that is, sodium capsule suspension fluid 3 is not injected, and after displacement by supercritical carbon dioxide 3, it is directly geologically sealed.

[0090] Compare the recovery rate and geological storage efficiency of Example 1 and Comparative Example 1, see Figure 4 and Figure 5 . Figure 4 The diagram shows the oil recovery rate of the in-situ conversion and carbon sequestration method for oil shale using high-temperature carbon dioxide injection combined with sodium capsules. Figure 5The diagram shows the geological storage efficiency of the high-temperature carbon dioxide injection combined with sodium capsule in-situ conversion and carbon sequestration method for oil shale. The results show that the recovery rate of the high-temperature carbon dioxide injection combined with sodium capsule in-situ conversion and carbon sequestration method in Example 1 in this target development area is 65%, which is more than one year faster than the conventional oil shale mining method in Comparative Example 1. The carbon sequestration of the oil shale using the high-temperature carbon dioxide injection combined with sodium capsule in-situ conversion and carbon sequestration method in Example 1 is 1.65 t / m³. 3 Compared to the conventional geological sequestration method in Comparative Example 1, the carbon sequestration capacity is approximately 0.9 t / m³. 3 An increase of nearly 83.3%.

[0091] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all embodiments here. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules, characterized in that, Includes the following steps: Step 1: Conduct geological exploration of the target development area to obtain oil shale reservoir parameters, deploy development wells based on the oil shale reservoir parameters, and determine the supercritical carbon dioxide injection parameters and sodium capsule deployment strategy. Step 2: After drilling wells and completing the well network layout in the target development area, the oil shale reservoir is subjected to fracturing to form a fracture network; Step 3: Heat the modified oil shale reservoir to the temperature at which kerogen undergoes thermal decomposition. When the oil shale reservoir temperature reaches the preset target temperature, inject supercritical carbon dioxide into the oil shale reservoir through injection wells to displace oil and gas products, and then extract the oil and gas products through production wells. Step 4: After supercritical carbon dioxide injection is completed, sodium capsule suspension fluid is injected into the oil shale reservoir through the injection well; the sodium capsule suspension fluid is formed by dispersing sodium capsules and a dispersant in liquid carbon dioxide, wherein the mass concentration of sodium capsules is 3% to 8%; the dispersant is used to maintain the uniform dispersion of sodium capsules in liquid carbon dioxide; the sodium capsule wall material fails at a predetermined temperature and releases metallic sodium; the metallic sodium undergoes a reduction reaction with the surrounding supercritical carbon dioxide to generate solid carbon and sodium carbonate; Step 5: After oil and gas recovery is completed, shut down the injection well and production well to achieve dual solid-state and supercritical carbon dioxide sequestration; The injection parameters for supercritical carbon dioxide include injection pressure, bottom hole temperature during injection, injection flow rate, and cumulative injection volume. The injection pressure of supercritical carbon dioxide is controlled at 1.1 to 1.3 times the original pressure of the oil shale reservoir, the bottom hole temperature during injection is 430℃ to 450℃, and the injection flow rate is controlled at 2.0 m³ / min. 3 / h to 3.0m 3 Within the range of / h; the cumulative injection rate of supercritical carbon dioxide is from To make an estimate, among which The estimated cumulative volume of carbon dioxide to be injected is expressed in meters. 3 ; The area controlled by the well network is expressed in meters (m²). 2 ; The effective thickness of the oil shale is expressed in meters (m). Porosity of oil shale after fracturing; This represents the oil saturation of oil shale. The expected recovery rate; The displacement coefficient for carbon dioxide ranges from 1.5 to 2.

5. The sodium capsule comprises a sodium metal core and three sequentially coated wall layers. The first wall layer is a sodium stearate passivation film with a thickness of 0.1µm to 0.5µm. The second wall layer is a thermosensitive layer composed of ethyl cellulose with an average molecular weight of 80,000 Da to 120,000 Da and a thickness of 15µm to 25µm. The thermal failure temperature of the thermosensitive layer corresponds to the thermal decomposition reaction temperature of kerogen in oil shale reservoirs, which ranges from 430℃ to 450℃. The third wall layer is a phenolic resin composite coating doped with 5wt% to 15wt% nano-silica with a thickness of 3µm to 8µm.

2. The method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules according to claim 1, characterized in that, The development well network adopts an inverted five-point well network, including one injection well located in the center and four production wells located at the vertices of the square. Both the injection well and the production wells are vertical wells, and the distance between the injection wells and the production wells is 15m to 50m.

3. The method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules according to claim 1, characterized in that, The sodium capsule deployment strategy includes: injecting sodium capsule suspension fluid into an oil shale reservoir at a temperature of 430℃~450℃ at an injection rate of 1.5m³ / h~2.0m³ / h; by controlling the injection rate and combining the temperature-controlled release characteristics of the sodium capsule with real-time monitoring of oil and gas products, the molar ratio of metallic sodium to carbon dioxide participating in the reaction at various locations within the oil shale reservoir is kept less than 4:

3.

4. The method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules according to claim 1, characterized in that, The method for preparing the sodium capsule includes: melting metallic sodium under inert gas protection and preparing sodium microparticles with a particle size of 50µm to 150µm; performing surface passivation treatment on the sodium microparticles under inert gas protection to form a sodium stearate passivation film; coating the surface of the sodium stearate passivation film with a temperature-sensitive layer composed of ethyl cellulose using fluidized bed coating technology; and forming a phenolic resin composite coating with a mass fraction of 5wt% to 15wt% nano-silica on the outside of the temperature-sensitive layer through an in-situ polymerization process.

5. The method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules according to claim 1, characterized in that, The sodium capsule suspension fluid is composed of the following components by mass percentage: 3.0% to 8.0% sodium capsules, 0.015% to 0.16% dispersant, and the balance being liquid carbon dioxide, wherein the dispersant is perfluorooctyl ethyl acrylate.

6. The method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules according to claim 1 or 5, characterized in that, In step 4, the particle size distribution of the sodium capsules is between 80µm and 180µm.

7. The method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules according to claim 1, characterized in that, In step 4, the supercritical carbon dioxide participating in the reduction reaction includes the previously injected supercritical carbon dioxide and the supercritical carbon dioxide formed by the transformation of liquid carbon dioxide in the sodium capsule suspension fluid due to the temperature and pressure conditions of the oil shale reservoir.

8. The method for in-situ conversion and carbon sequestration of oil shale using high-temperature carbon dioxide injection combined with sodium capsules according to claim 1, characterized in that, In step 2, hydraulic fracturing is performed using explosive fracturing to create a fracture network in the oil shale reservoir. In step 3, the oil shale reservoir is heated using electric heating to a temperature range of 430℃ to 450℃.

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