In-situ CT-based carbon sequestration process cap damage and closure research experiment system and method

Abstract

The invention provides an in-situ CT (Computed Tomography)-based experimental system and an in-situ CT-based experimental method for researching the damage and closure of a cap layer in a carbon burying process, belongs to the technical field of carbon burying engineering, and aims to solve the key problems of microscopic damage, closure damage and the like of the cap layer in a CO2 burying process. A rock mechanical damage and CO2 closure evolution research experiment system capable of realizing an in-situ ground stress condition is designed, and a cover rock microcosmic damage caused by a CO2 injection process under the in-situ ground stress condition is obtained, and a cover breakthrough parameter during CO2 injection under the in-situ condition is obtained; and a high-precision digital rock core conforming to stratum characteristics is further established based on a real-time rock damage change result and CT scanning data, rock mechanical damage and closure change characteristics in the CO2 injection process are disclosed from two angles of experiments and simulation, and a theoretical support is provided for safe storage of CO2.

Description

Technical Field

[0001] This invention relates to the field of carbon storage engineering technology, and in particular to an experimental system and method for studying capillary damage and sealing in the carbon storage process based on in-situ CT. Background Technology

[0002] In recent years, with the proposal of the "dual carbon" goal, how to reduce carbon emissions and enhance carbon utilization has become the most pressing issue. CO2 capture and storage (CCS) is a recognized important way to achieve the "dual carbon" goal. It involves capturing, purifying, and injecting CO2 generated by industry and other sources into the target geological body for permanent storage. This method is considered the most promising way to reduce carbon emissions due to its large storage volume and low construction cost.

[0003] However, when a large amount of CO2 is injected into the target reservoir, it will migrate to the upper part of the reservoir under the action of buoyancy and accumulate at the bottom of the caprock of the target geological body. This causes abnormal pore pressure at the boundary between the reservoir and the caprock, which in turn causes damage and deformation of the rock mass of the upper caprock, induces the opening of fractures, and generates new fractures. This further causes CO2 to leak from the caprock, resulting in sealing failure and other consequences.

[0004] Therefore, there is an urgent need to explore the mechanical damage, failure, and sealing changes induced in the caprock during CO2 injection. Currently, my country is still in the early stages of CCS engineering implementation, and related technical methods have not yet been developed. This invention addresses the current technical bottlenecks in the industry and is expected to lay a foundation for the implementation and safety analysis of CO2 geological storage technology.

[0005] Among the existing authorized patents, the patent with publication number CN 107506534A, entitled "A Method for Evaluating Caprock Sealing Performance in Carbon Dioxide Flooding and Storage," calculates the carbon dioxide seepage velocity in the caprock by establishing a well logging response model for carbon dioxide geological storage bodies, a porosity and displacement pressure model, and a permeability and channel characteristic parameter fitting model. It also numerically simulates the reaction processes of different chemical substances in the caprock to determine the erosion resistance of different types of caprock, thereby comprehensively evaluating the caprock sealing capacity. This patent primarily focuses on different geological factors and establishes numerical models to simulate caprock sealing performance, which is innovative. However, this method uses a formation-scale benchmark to establish a relatively macroscopic calculation model, and does not consider damage to the microstructure and potential changes in sealing performance.

[0006] The patent CN 109033737 A, entitled "An Evaluation Method for Leakage Risk Zones in CO2 Geological Storage," utilizes refined geological and numerical models, combined with the concepts of fluid potential and potential gradient in hydrocarbon migration theory, to analyze the migration direction and accumulation areas of CO2. Based on the migration direction and distribution characteristics of CO2 within the storage body, and considering the sand body boundaries of the storage body, it predicts the lateral CO2 leakage risk. Based on the characteristics of caprock fracture pressure distribution and the dynamic pressure distribution within the storage body, it quantitatively studies the potential longitudinal leakage risk zones along the CO2 migration path using a proposed caprock fracture risk zone discrimination formula. This patent, also based on reservoir-scale analysis, primarily uses simulation to consider the potential migration direction and leakage pathways of CO2 under various conditions, thereby predicting and evaluating CO2 leakage risk. However, it provides relatively little consideration for the microscopic damage mechanisms during CO2 storage and the resulting impact on the sealing of the geological body.

[0007] Most studies on rock damage caused by CO2 injection explore the impact on rock structure and properties from the perspective of static chemical reactions, with no research on in-situ dynamic CO2 injection-induced caprock rock damage. In the process of evaluating caprock sealing, existing models mostly study the long-term CO2 storage efficiency from a macroscopic scale, without coupling the microscopic rock damage with CO2 seepage, and the seepage field-stress field mutual feedback evolution mechanism of CO2 escape process has not been revealed. In addition, the impact of changes in rock mechanical properties and rock mass structural damage caused by CO2 injection on the sealing of the caprock has not been clarified, and further in-situ microscopic research is needed to explore the mechanical damage and sealing changes of the caprock caused by CO2 injection. Summary of the Invention

[0008] To address the current lack of microscopic, in-situ consideration of the induced caprock damage characteristics and their impact on sealing performance during CO2 sequestration, this invention proposes an experimental system based on in-situ CT for studying caprock damage and sealing performance during carbon burial. This system can recreate formation stress and temperature conditions, simulating a series of mechanical damages and structural failures that may occur during CO2 sequestration, thereby causing real-time evolution of caprock sealing performance. Based on digital rock imaging data from in-situ CT at different time points, digital cores are reconstructed for in-situ simulation, which is then corroborated and supplemented with experimental results. This elucidates the mechanisms of microscopic changes in the caprock caused by CO2 injection and the evolution characteristics of sealing performance. The research findings are expected to solve key scientific problems in CO2 geological sequestration, overcoming the bottleneck of insufficient fundamental theory on rock damage and sealing evolution during CO2 geological sequestration from a microscopic perspective, and providing a scientific basis for CO2 sequestration safety and scheme optimization.

[0009] Based on the above technical concept, the technical solution adopted by this invention is as follows:

[0010] One objective of this invention is to provide an experimental system for studying caprock damage and sealing in carbon burial processes based on in-situ CT. The experimental system includes a formation water injection system, a carbon dioxide injection system, a triaxial testing system for rock damage and sealing analysis, and an experimental controller. The pipelines of the formation water injection system, the carbon dioxide injection system, and the experimental controller are connected to the triaxial testing system for rock damage and sealing analysis via a three-way valve.

[0011] Different types of formation water were injected into the triaxial testing system for rock damage and sealing analysis through a formation water injection system to simulate the original fluid environment of the formation; CO2 was pumped into the triaxial testing system for rock damage and sealing analysis through a carbon dioxide injection system to simulate the migration and escape of CO2 in the formation during the carbon burial process, and the escape state of CO2 and the sealing changes of the caprock were analyzed through an experimental controller.

[0012] Based on the above technical solution, the formation water injection system further includes an ISCO injection pump A and a formation water container. The ISCO injection pump A and the formation water container are connected by a pressure-resistant metal pipeline. The outlet end of the pressure-resistant metal pipeline is connected to a three-way valve, and a one-way valve A and a pressure sensor A are installed at the outlet end of the pressure-resistant metal pipeline.

[0013] Based on the above technical solution, the carbon dioxide injection system further includes a kerosene bottle, an ISCO injection pump B, an intermediate container, and a CO2 cylinder. The kerosene bottle, ISCO injection pump B, and intermediate container are connected in sequence via pressure-resistant metal pipelines. A one-way valve A is installed on the pressure-resistant metal pipeline between the ISCO injection pump B and the intermediate container. The CO2 cylinder is connected to the intermediate container via a pressure-resistant metal pipeline. The intermediate container is connected to a three-way valve via a pressure-resistant metal pipeline. A one-way valve B and a pressure sensor B are installed at the outlet end of the intermediate container.

[0014] Based on the above technical solution, the triaxial testing system for rock damage and sealing analysis further includes a rotary dynamic seal joint, an adapter, a metal support frame, and a triaxial stress device. A three-way valve enters the rotary dynamic seal joint through a pipeline and is connected to the adapter at the top of the triaxial stress device via a high-strength metal cable. The bottom of the adapter is connected to the metal support frame, and a dedicated displacement differential sensor (LVDT) is installed between the adapter and the top cover plate of the triaxial stress device. The LVDT is used to realize the strain change of the experimental rock sample during CO2 injection and obtain the mechanical damage parameters of the experimental rock sample under in-situ conditions.

[0015] Based on the above technical solution, the triaxial testing system for rock damage and sealing analysis further includes an in-field X-ray generator and an X-ray signal receiver. The in-field X-ray generator scans the experimental rock sample inside the triaxial stress device, and the X-ray signal receiver obtains the original imaging results of the rock sample under the original formation temperature and pressure conditions.

[0016] Based on the above technical solution, the experimental system further includes an axial pressure and confining pressure loading system, which includes an axial pressure loading pump and a ring pressure loading pump. The axial pressure loading pump is connected to a three-way valve through a pressure-resistant metal pipeline, and the ring pressure loading pump is connected to a dynamic seal hydraulic rotary table through a pressure-resistant metal pipeline. A pressure sensor E is installed at the inlet end of the dynamic seal hydraulic rotary table.

[0017] Based on the above technical solution, a one-way valve D is further provided at the outlet end of the axial pressure loading pump, and pressure sensors C and D are provided at the inlet end of the three-way valve. Pressure sensor C is located on the pressure-resistant metal pipeline connecting the axial pressure loading pump and the three-way valve, and pressure sensor D is located on the pipeline connecting the experimental controller and the three-way valve.

[0018] Based on the above technical solution, the experimental system further includes a back pressure control and fluid collection system. The back pressure control and fluid collection system includes a back pressure pump and an oil-gas-water separator. The outlet of the triaxial stress device is connected to a back pressure valve through a high-pressure pipeline. The back pressure valve is connected to a back pressure pump that controls fluid overflow through a high-pressure pipeline. The outlet end of the back pressure valve is connected to the oil-gas-water separator through a pipeline. The oil-gas-water separator is connected to a gas flow meter, a water phase collection bottle, and a gas phase collection bottle through parallel pipelines.

[0019] Based on the above technical solution, a pressure sensor F and a one-way valve F are further installed on the high-pressure pipeline connecting the triaxial stress device and the back pressure valve.

[0020] 11. Another objective of this invention is to provide an experimental method for a research system based on in-situ CT to study capillary damage and sealing during carbon burial processes, characterized in that the experimental method includes the following steps:

[0021] Step 1: Pretreatment of experimental rock samples;

[0022] Step 2: Loading of confining pressure and formation temperature on experimental rock samples

[0023] The standard rock sample is loaded into the triaxial stress device. Then, check valves A, C, D, three-way valve, and F are closed, check valve E is opened, and the ring pressure loading pump is started to provide ring pressure to the experimental rock sample by injecting high-temperature hydraulic oil.

[0024] Close the three-way valve, check valve E, and check valve F. Use an external vacuum pump to evacuate the inside of the triaxial stress device to achieve a negative pressure state inside the experimental rock sample. Open check valve A, three-way valve, and check valve F. Start the ISCO injection pump A to drive formation water into the experimental rock sample. The rock sample is saturated with formation water when the outlet water flow stabilizes.

[0025] Open valve D (one-way valve) and start the axial pressure loading pump. Pump high-temperature hydraulic oil into the triaxial stress device to provide axial pressure simulation of the formation environment for the experimental rock sample. Then turn on the electric heating switch on the experimental controller to heat the hydraulic oil to the formation temperature and keep it stable.

[0026] Step 3: Conduct research on rock damage characteristics during in-situ CO2 injection.

[0027] After the formation temperature and pressure environment is established, the X-ray generator of the CT scanning system is activated to scan the experimental rock sample. The original imaging results of the rock sample under the original formation temperature and pressure conditions are obtained through the X-ray receiver. The microstructure of the original formation rock sample before the experiment is characterized to obtain the original distribution morphology of rock pore structure and micro fractures.

[0028] The initial stress-strain state of the experimental rock sample without CO2 injection was determined using a displacement differential sensor LVDT.

[0029] CO2 is released from the CO2 cylinder to the upper part of the intermediate container with a piston. The one-way valve B is closed to draw the kerosene into the ISCO injection pump B. The valves one-way valve B, one-way valve C, three-way valve, and one-way valve F are opened to start the ISCO injection pump B. The CO2 is driven into the experimental rock by driving the kerosene at the bottom of the piston of the intermediate container, thereby carrying out the CO2 injection-induced rock damage experiment.

[0030] The rock strain value under different pressures during the CO2 injection process is detected by a dedicated displacement differential sensor LVDT, thereby obtaining real-time stress-strain change characteristics;

[0031] Digital images of rocks at different times are acquired using an X-ray generator and a radiation receiver. The changes in the internal structure of the rocks are then obtained by inversion using post-processing software, including changes in the pore structure, deformation characteristics, cracks / fractures, etc., and are correlated with the established rock damage mechanics constitutive model to reveal the damage mechanism of the rocks from a microscopic perspective.

[0032] Step 4: Study the caprock sealing properties during CO2 sequestration.

[0033] Release CO2 from the CO2 cylinder to the upper part of the intermediate container with piston, close check valve B to draw kerosene from the kerosene container into ISCO injection pump B, open check valve B, check valve C, three-way valve, and check valve F, start ISCO injection pump B, and drive CO2 into the inlet end of the experimental rock sample by driving the kerosene at the bottom of the piston of the intermediate container.

[0034] By monitoring the outlet end of the experimental rock sample with an outlet flow meter, the current experiment can be stopped when the bubbles overflow uniformly and continuously at a certain pressure value. The pressure difference between the inlet and outlet ends of the experimental rock sample at this time is the CO2 breakthrough pressure of the rock sample at this time.

[0035] By analyzing the breakthrough changes in CO2 in caprock under different caprock conditions and different CO2 injection conditions, and corresponding CO2-induced rock damage characteristics, the sealing evolution characteristics of the caprock can be analyzed.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] This invention designs an experimental system for studying the evolution of rock mechanical damage and CO2 sealing under in-situ stress conditions. By acquiring the microscopic damage of caprock caused by CO2 injection under in-situ stress conditions, and obtaining breakthrough parameters of the caprock during CO2 injection under in-situ conditions, a high-precision digital core conforming to the stratigraphic characteristics is further established based on real-time rock damage changes and CT scan data. This system reveals the characteristics of rock mechanical damage and sealing changes during CO2 injection from both experimental and simulation perspectives, improving the accuracy of experimental results and the precision of simulation. This method has important theoretical and practical significance in the safety risk assessment and efficient carbon sequestration process. Attached Figure Description

[0038] Figure 1 This is a connection diagram of an experimental system for studying capillary damage and sealing during carbon burial based on in-situ CT.

[0039] Figure 2 The pressure change curves at the inlet and outlet are typical of the CO2 injection into rock breakthrough process.

[0040] Figure 3 This is an in-situ scan of rock damage / destruction imaging. (a) Three-dimensional reconstruction results of the rock sample; (b) Slice features at a certain location in the radial and axial directions.

[0041] Among them, 1. ISCO injection pump A; 2. Formation water container; 3. Check valve A; 4. Pressure sensor A; 5. Kerosene container; 6. ISCO injection pump B; 7. Check valve B; 8. Intermediate container; 9. CO2 cylinder; 10. Check valve C; 11. Pressure sensor B; 12. Axial pressure loading pump; 13. Check valve D; 14. Pressure sensor C; 15. Three-way valve; 16. Pressure sensor D; 17. Rotary dynamic seal joint; 18. Adapter accessories; 19. Metal support frame; 20. Displacement differential. 21. LVDT sensor; 22. Triaxial stress device; 23. X-ray generator; 24. X-ray receiver; 25. Experimental rock sample; 26. Metal base plate; 27. Dynamically sealed hydraulic rotary table; 28. Workbench; 29. ​​Pressure sensor E; 30. Ring pressure loading pump; 31. Check valve E; 32. Pressure sensor F; 33. Check valve F; 34. Back pressure valve; 35. Oil-gas-water separator; 36. Aqueous phase collection bottle; 37. Gas phase collection bottle; 38. Gas flow meter; 39. Back pressure pump; 30. Experimental controller. Detailed Implementation

[0042] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0043] Example 1

[0044] Existing methods for studying the sealing properties of caprocks after CO2 injection into target geological bodies mostly involve establishing macroscopic geological models and considering potential rock mass failure conditions. These methods predict the sealing properties of the caprock based on existing theoretical knowledge and methods. Another commonly used method is to conduct macroscopic experiments to study the series of mechanical and chemical changes in the rock mass caused by CO2 injection, thereby analyzing the potential sealing failure of the caprock. However, these methods have relatively low precision and lack the ability to investigate the impact of real-time rock mass damage and structural failure caused by CO2 injection under in-situ conditions on sealing properties from a microscopic perspective.

[0045] To address these issues, this invention proposes an experimental system for studying caprock damage and sealing in carbon burial processes based on in-situ CT. The experimental system includes a formation water injection system, a carbon dioxide injection system, a triaxial testing system for rock damage and sealing analysis, and an experimental controller 39. The pipelines of the formation water injection system, the carbon dioxide injection system, and the experimental controller 39 are connected to the triaxial testing system for rock damage and sealing analysis via a three-way valve 15.

[0046] The formation water injection system includes an ISCO injection pump A1 and a formation water container 2, which are connected by a pressure-resistant metal pipeline. The outlet of the pressure-resistant metal pipeline is connected to a three-way valve 15, and a one-way valve A3 and a pressure sensor A4 are installed at the outlet of the pressure-resistant metal pipeline. The formation water injection system can inject different types of formation water, thereby realizing the saturation process of rock samples and simulating the original fluid environment of the formation.

[0047] The ISCO injection pump A1 has a maximum operating pressure of 60 MPa and a maximum operating temperature of 80°C. It is connected via a high-pressure resistant metal pipe with a maximum pressure resistance of 80 MPa. The outlet is equipped with a check valve and a pressure gauge with a pressure range of 0–60 MPa and an accuracy of 0.1 MPa. Under normal pressure, fluids from different target reservoirs are loaded into the formation water container 2. First, the outlet end of the ISCO injection pump A1 in the formation water container 2 is closed, and the suction line of the container is closed. Then, the ISCO injection pump A1 is turned on to pump the fluid from the formation water container 2 into the experimental rock sample 24, saturating the core with formation fluid and thus achieving the original formation conditions. The main purpose of this system is to construct the original state of the formation, making CO2 sequestration more consistent with real working conditions.

[0048] The carbon dioxide injection system includes a kerosene bottle 5, an ISCO injection pump B6, an intermediate container 8, and a CO2 cylinder 9. The kerosene bottle 5, the ISCO injection pump B6, and the intermediate container 8 are connected in sequence via pressure-resistant metal pipelines. A one-way valve A3 is installed on the pressure-resistant metal pipeline between the ISCO injection pump B6 and the intermediate container 8. The CO2 cylinder 9 is connected to the intermediate container 8 via a pressure-resistant metal pipeline. The intermediate container 8 is connected to a three-way valve 15 via a pressure-resistant metal pipeline. A one-way valve B7 and a pressure sensor B11 are installed at the outlet end of the intermediate container 8.

[0049] The working pressure range of CO2 cylinder 9 is 0-7 MPa, the CO2 purity is 99.99%, the maximum working pressure of ISCO injection pump B6 is 60 MPa, the maximum working temperature is 80℃, and the maximum working pressure of intermediate container 8(8) with piston is 50 MPa, the maximum working temperature is 200℃.

[0050] The carbon dioxide injection system is used to realize the pumping and pressurization process of CO2, thereby simulating the migration and escape state of CO2 in the formation during carbon burial. Before CO2 injection, it needs to be released from CO2 cylinder 9 into the upper space of the piston in intermediate container 8. When CO2 needs to be injected, the one-way valve B7 is opened, and the kerosene that has been drawn in in advance is pumped in by ISCO injection pump B6, thereby pushing the piston in intermediate container 8 to provide high-pressure CO2 for the entire system.

[0051] The triaxial testing system for rock damage and sealing analysis is the core component of this system. It includes a rotary dynamic seal joint 17, an adapter 18, a metal support frame 19, and a triaxial stress device 21. A three-way valve 15 enters the rotary dynamic seal joint 17 through a pipeline and is connected to the adapter 18 on the top of the triaxial stress device 21 via a high-strength metal cable. The bottom of the adapter 18 is connected to the metal support frame 19, and a dedicated displacement differential sensor LVDT20 is installed between the adapter 18 and the top cover plate of the triaxial stress device 21. This sensor realizes the change in rock strain during CO2 injection and obtains in-situ rock mechanical damage parameters with a resolution of 0.1 μm. The experimental rock sample 24 is installed inside the triaxial stress device 21, and its bottom is connected to a metal base plate 25. The metal base plate 25 is connected to a dynamic seal hydraulic rotary table 26, which is mounted on a workbench 27.

[0052] The outer wall of the triaxial stress device 21 is made of a material with high X-ray penetrability to minimize the attenuation of X-rays and achieve high-precision imaging of the rock sample. The experimental rock sample 24 is installed inside the triaxial experimental system. The maximum size of the rock sample is φ25×100mm.

[0053] In this embodiment, the triaxial stress device is a common, conventional device in the industry. It consists of an outer cylindrical metal pressure-resistant shell and an inner rubber liner. The rock is placed inside the rubber liner, and a liquid is injected between the metal shell and the rubber liner to pressurize the liner. This pressure is then applied to the rock. This patent requires in-situ CT scanning; therefore, the outer shell of the triaxial device is made of a special metal, and the internal fluid is a non-X-ray absorbing fluid. The working principle is no different from that of a standard triaxial device.

[0054] This system serves as the primary reaction site after CO2 injection into the formation. It is used to investigate rock damage, deformation, and failure caused by multi-field coupling of fluid solidification at different stages after CO2 injection, thereby obtaining in-situ information on the rock damage mechanism and sealing characteristics. The system uses a dedicated displacement differential sensor LVDT20 to monitor the rock strain changes caused by stress changes during the CO2 injection process in real time, thereby establishing a stress-strain linkage relationship and establishing a rock mechanics constitutive equation. By changing the CO2 injection method, the system studies the breakthrough of CO2 in the target caprock, obtaining the CO2 breakthrough pressure changes at different injection stages and under different injection modes, thus corroborating the rock damage.

[0055] The triaxial testing system for rock damage and sealing analysis also includes an in-field X-ray generator 22 and an X-ray signal receiver. The in-field X-ray generator 22 and the X-ray signal receiver are symmetrically distributed on both sides of the triaxial stress device 21 for real-time scanning during the experiment. During the CO2 injection stage, the in-field X-ray generator 22 and the X-ray signal receiver acquire the digital imaging results of the rock in real time, and reconstruct the rock using a self-developed digital image inversion method to establish a gridded digital core. While revealing the changes in the rock's microstructure, in-situ simulations under simulated stratigraphic conditions are carried out to explore the evolution characteristics of rock sealing caused by damage. Combined with the experimental results, the system reveals the changes in rock damage and caprock sealing caused by CO2 injection.

[0056] The X-ray generator 22 is a three-dimensional X-ray microscope (with a resolution of up to 10-1 μm). Unlike ordinary projection micron CT systems that only use X-ray geometric magnification imaging, it can still achieve submicron resolution under the conditions of large working distance and no damage to the sample. The X-ray signal passes through the rock sample and is identified by the X-ray receiver 23 after attenuation. Based on the difference in the attenuation degree of X-rays by different minerals, a series of 2D grayscale images of rocks are obtained. Through relevant post-processing methods, the rock sample is restored with high precision under in-situ conditions. The digital rock sample is further extracted to simulate and calculate the sealing of the rock.

[0057] Example 2

[0058] Based on Embodiment 1, this embodiment further includes an axial pressure and confining pressure loading system. The axial pressure and confining pressure loading system includes an axial pressure loading pump 12 and a confining pressure loading pump 29. The axial pressure loading pump 12 is connected to a three-way valve 15 through a pressure-resistant metal pipeline. A one-way valve D13 and a pressure sensor C14 are installed on the pressure-resistant metal pipeline. The one-way valve D13 is located at the outlet end of the axial pressure loading pump 12, and the pressure sensor C14 is located at the inlet end of the three-way valve 15. The axial pressure loading pump 12 pumps high-temperature resistant hydraulic oil to the rotary dynamic sealing joint 17 at the top of the triaxial stress device 21. The axial pressure is applied to the rock sample by controlling the one-way valve D13 and the pressure sensor C14.

[0059] The ring pressure loading pump 29 is connected to the dynamic seal hydraulic rotary table 26 via a pressure-resistant metal pipeline. A one-way valve E30 is installed at the outlet end of the ring pressure loading pump 29, and a pressure sensor E28 is installed at the inlet end of the dynamic seal hydraulic rotary table 26. The ring pressure loading pump 29 also pumps high-temperature resistant and high X-ray permeable hydraulic oil into the dynamic seal hydraulic rotary table 26 to achieve ring pressure loading of rock samples. The working range of axial pressure and ring pressure is 0-40MPa. By heating the ring pressure loading hydraulic oil to reduce the reservoir temperature environment, the maximum temperature of this system can reach 150℃.

[0060] The axial pressure and confining pressure loading system is used to provide rocks with different geostress conditions and temperatures, thereby simulating the original state of the strata and increasing the accuracy and precision of the research. During the experiment, axial pressure and confining pressure are applied to the rock samples by axial pressure loading pump 12 and annular pressure loading pump 29. The formation temperature is simulated by heating the pressurized medium. During the CO2 injection stage, the in-field X-ray generator 22 and X-ray signal receiver acquire the digital imaging results of the rocks in real time. The rocks are reconstructed by a self-developed digital image inversion method to establish a gridded digital core. While revealing the changes in the microstructure of the rocks, in-situ simulations are carried out under simulated formation conditions to explore the evolution characteristics of rock sealing caused by damage. Combined with the experimental results, the rock damage and changes in caprock sealing caused by CO2 injection are revealed.

[0061] Example 3

[0062] Based on Embodiment 2, this embodiment further includes a back pressure control and fluid collection system. The back pressure control and fluid collection system includes a back pressure pump 38 and an oil-gas-water separator 34. The outlet of the triaxial stress device 21 is connected to a back pressure valve 33 via a high-pressure pipeline. The back pressure valve 33 is connected to the back pressure pump 38, which controls fluid overflow, via a high-pressure pipeline. The outlet of the back pressure valve 33 is connected to the oil-gas-water separator 34 via a pipeline. The oil-gas-water separator 34 is connected to a gas flow meter 37, a water phase collection bottle 35, and a gas phase collection bottle 36 via parallel pipelines to quantitatively obtain parameters such as the mass of water and the volume of gas at the outlet. The back pressure valve 33 has a maximum operating pressure of 50 MPa and a maximum operating temperature of 100°C. The oil-gas-water separator 34 has a maximum operating temperature of 80°C. The gas flow meter 37 has a maximum operating temperature of 150°C. The water phase collection bottle 35 and the gas phase collection bottle 36 have a maximum operating temperature of 100°C.

[0063] A pressure sensor F31 and a one-way valve F32 are installed on the high-pressure pipeline connecting the triaxial stress device 21 and the back pressure valve 33. The back pressure control and fluid collection system is mainly used to apply back pressure to the rock outlet and collect the outlet fluid.

[0064] Example 4

[0065] This embodiment uses an abandoned oil reservoir in Block X of the Ordos Basin as the target carbon burial geological body. The caprock of this target geological body is selected as an example, and a formation core sample (24) is selected as the experimental sample. Formation water is used as the original saturated fluid. The target formation temperature is T0, the overlying strata pressure is Pv, and the formation pressure is P0. Figure 1 The experimental system deployment describes the research methods for studying caprock damage and sealing during CO2 injection, including the following steps:

[0066] Step 1: Rock sample pretreatment

[0067] Stratigraphic cores were selected for drilling, cutting, and grinding to create standard cylindrical rock samples for this study. The size of the standard rock samples can be adjusted based on the scanning accuracy of the CT system.

[0068] Since the target geological body is the overburden layer of an abandoned oil reservoir, the presence of formation oil is ignored. The permeability, pore volume, and porosity of the target rock sample are determined in accordance with the standard "SY / T5336—2006 Core Analysis Method".

[0069] Standard rock samples drilled from the same core column were selected for rock mechanics testing to obtain the strength and mechanical parameters (elastic modulus, Poisson's ratio, etc.) of the rock samples under the initial formation conditions.

[0070] Step 2: Loading of confining pressure and formation temperature on experimental rock samples 24

[0071] The standard rock sample is loaded into the triaxial stress device 21, and then check valves A3, C10, D13, 15, and F32 are closed. Check valve E30 is opened, and the ring pressure loading pump 29 is started to provide ring pressure to the experimental rock sample 24 by injecting high-temperature hydraulic oil.

[0072] Close the three-way valve 15, check valve E30, and check valve F32. Use an external vacuum pump to evacuate the triaxial stress device 21 to create a negative pressure state inside the experimental rock sample 24. Open the check valve A3, three-way valve 15, and check valve F32. Start the ISCO injection pump A1 to displace formation water into the experimental rock sample 24. The rock sample is saturated with formation water when the outlet flow rate stabilizes.

[0073] Open the check valve D13 and start the axial pressure loading pump 12. Similarly, pump high-temperature resistant hydraulic oil into the triaxial stress device 21 to provide axial pressure simulation of the formation environment for the experimental rock sample 24. Then, turn on the electric heating switch on the experimental controller 39 to heat the hydraulic oil to the formation temperature and keep it stable.

[0074] Step 3: Conduct research on rock damage characteristics during in-situ CO2 injection.

[0075] After the formation temperature and pressure environment is established, the X-ray generator 22 of the CT scanning system is activated to scan the experimental rock sample 24. The original imaging results of the rock sample under the original formation temperature and pressure conditions are obtained through the X-ray receiver 23. The microstructure of the original formation rock sample before the experiment is characterized, and the original distribution morphology of rock pore structure and micro-fractures is obtained. Figure 3 (a) and Figure 3 (b) can be used as the original control group for the later CO2 injection process;

[0076] At this time, the initial stress-strain state of the experimental rock sample 24 without CO2 injection is calibrated using the displacement differential sensor LVDT20.

[0077] CO2 is released from CO2 cylinder 9 to the upper part of intermediate container 8 with piston. Check valve B7 is closed to draw kerosene into ISCO injection pump B6. Check valves B7, C10, 15, and F32 are opened to start ISCO injection pump B6. CO2 is driven into the experimental rock by driving the kerosene at the bottom of the piston of intermediate container 8, thereby carrying out CO2 injection-induced rock damage experiment.

[0078] The LVDT20 displacement differential sensor was used to detect rock strain values ​​under different pressures during CO2 injection, thereby obtaining real-time stress-strain variation characteristics. Figure 2 (as shown);

[0079] In addition, digital images of rocks at different times are obtained based on X-ray generator 22 and X-ray receiver 23, and the changes in the internal structure of the rocks are obtained by inversion based on post-processing software, including changes in the pore structure, deformation characteristics, cracks / fractures, etc., and correspond to the established rock damage mechanical constitutive model, revealing the damage mechanism of the rocks from a microscopic perspective.

[0080] The digital core reconstruction techniques and methods are as follows:

[0081] Based on multi-scale digital images and pore size distribution characteristics of rocks obtained from in-situ CT CO2 injection-induced rock micro-damage experiments, an Enhanced Super-Resolution Generative Adversarial Network (EDSRGAN) was constructed using deep learning principles. The EDSRGAN algorithm was systematically trained using a large amount of pore / fracture structure data from a rock pore / fracture structure database, maximizing the recovery of pore and fracture structure details in CT slices. This breakthrough overcomes the original resolution limit of CT scanning equipment, achieving refined reconstruction of the pore / fracture structure of dense caprock. Furthermore, topology fitting was performed on the multi-scale digital imaging using a self-programmed (Python) system to construct multi-scale digital cores and rock fracture structures, and a pore network model was extracted.

[0082] The series of digital rock images obtained during the experiment can serve as the basis for in-situ simulation. Based on the digital imaging post-processing method implemented by the above-mentioned self-programmed program, the digital rock images are reconstructed to obtain digital rock cores considering the CO2 injection process under the conditions described above. Different stress states and CO2 injection methods are applied to the digital rock cores to simulate rock deformation and stress damage characteristics. The simulation results are mutually verified and supplemented with the experimental results, thereby revealing the rock damage mechanism of the CO2 injection process under in-situ conditions.

[0083] Step 4: Study the caprock sealing properties during CO2 sequestration.

[0084] CO2 is released from CO2 cylinder 9 to the upper part of intermediate container 8 with piston. Check valve B7 is closed to draw kerosene from kerosene container 5 into ISCO injection pump B6. Check valves B7, C10, 15, and F32 are opened to start ISCO injection pump B6. CO2 is driven into the inlet of experimental rock sample 24 by driving the kerosene at the bottom of the piston of intermediate container 8.

[0085] According to the standard method of SY / T 5748-2020, select the initial pressure difference at the inlet and outlet of the experimental rock sample and adjust the pressure at the inlet and outlet. Set the back pressure at the outlet through the back pressure pump connected by the back pressure valve. The back pressure is usually set to be 0.5 MPa higher than the saturated vapor pressure at the experimental temperature.

[0086] Similarly, based on the standard method of SY / T 5748-2020, the constant pressure time t and the pressure interval P during the CO2 injection process were selected, and CO2 was injected from low to high according to the pressure interval P. During the experiment, the net confining pressure was always kept equal to the effective overburden pressure P. v The selection criteria for initial pressure difference, experimental pressure interval, and constant time are shown in Tables 1 and 2 below.

[0087] Table 1. Initial Pressure Differential Selection Table

[0088]

[0089] Table 2. Experimental pressure intervals and constant pressure schedules

[0090]

[0091] By monitoring the outlet end of the experimental rock sample with an outlet flow meter, the current experiment can be stopped when the bubbles overflow uniformly and continuously at a certain pressure value. The pressure difference between the inlet and outlet ends of the experimental rock sample at this time is the CO2 breakthrough pressure of the rock sample at this time.

[0092] By analyzing the breakthrough changes in CO2 in caprock under different caprock conditions and different CO2 injection conditions, and corresponding CO2-induced rock damage characteristics, the sealing evolution characteristics of the caprock can be analyzed.

[0093] Based on in-situ CT scan images, digital cores were reconstructed at different stages of the reaction to quantitatively characterize changes in rock pore / fracture structure, obtain the mechanical damage characteristics of the rock during CO2 breakthrough, and simulate the diffusivity of CO2 during breakthrough under in-situ conditions. The simulation principle and process followed the national standard GB / T29172-2012 Core Analysis Methods, and the simulation parameters were obtained from rock property testing experiments of the target strata. The basic principle for obtaining the diffusion coefficient is as follows: CO2 gas is introduced into one diffusion chamber at each end of the rock sample, and nitrogen gas is introduced into the other. Under constant temperature and pressure conditions, the concentration of CO2 gas changes with time. By testing the concentration of CO2 gas in the two diffusion chambers at different times, the diffusion coefficient of CO2 gas in the rock can be obtained. Through multiple sets of diffusion experiments, the CO2 diffusion coefficient of the rock was calculated, the diffusion capacity of the caprock was analyzed, and the sealing characteristics of the caprock were studied.

[0094] Based on the experimental breakthroughs in pressure, rock damage, and real-time evolution characteristics of diffusivity, the sealing life and diffusion risk of CO2 in the target caprock were obtained, thus laying a theoretical foundation for the safety of CO2 sequestration in the target geological block.

[0095] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention, enabling those skilled in the art to understand and apply it. However, it should not be construed that the specific implementation of the invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. An experimental system for studying capillary damage and sealing during carbon burial based on in-situ CT, characterized in that, The experimental system includes a formation water injection system, a carbon dioxide injection system, a triaxial testing system for rock damage and sealing analysis, and an experimental controller. The pipelines of the formation water injection system, the carbon dioxide injection system, and the experimental controller are connected to the triaxial testing system for rock damage and sealing analysis via a three-way valve. Different types of formation water were injected into the triaxial testing system for rock damage and sealing analysis through a formation water injection system to simulate the original fluid environment of the formation; CO2 was pumped into the triaxial testing system for rock damage and sealing analysis through a carbon dioxide injection system to simulate the migration and escape of CO2 in the formation during the carbon burial process, and the escape state of CO2 and the sealing changes of the caprock were analyzed through an experimental controller.

2. The experimental system for studying capillary damage and sealing during carbon burial based on in-situ CT according to claim 1, characterized in that, The formation water injection system includes an ISCO injection pump A and a formation water container. The ISCO injection pump A and the formation water container are connected by a pressure-resistant metal pipeline. The outlet end of the pressure-resistant metal pipeline is connected to a three-way valve, and a one-way valve A and a pressure sensor A are installed at the outlet end of the pressure-resistant metal pipeline.

3. The experimental system for studying capillary damage and sealing during carbon burial based on in-situ CT according to claim 2, characterized in that, The carbon dioxide injection system includes a kerosene bottle, an ISCO injection pump B, an intermediate container, and a CO2 cylinder. The kerosene bottle, ISCO injection pump B, and intermediate container are connected in sequence via pressure-resistant metal pipelines. A one-way valve A is installed on the pressure-resistant metal pipeline between the ISCO injection pump B and the intermediate container. The CO2 cylinder is connected to the intermediate container via a pressure-resistant metal pipeline. The intermediate container is connected to a three-way valve via a pressure-resistant metal pipeline. A one-way valve B and a pressure sensor B are installed at the outlet end of the intermediate container.

4. The experimental system for studying capillary damage and sealing during carbon burial based on in-situ CT according to claim 3, characterized in that, The triaxial testing system for rock damage and sealing analysis includes a rotary dynamic seal joint, an adapter, a metal support frame, and a triaxial stress device. A three-way valve enters the rotary dynamic seal joint through a pipeline and is connected to the adapter at the top of the triaxial stress device via a high-strength metal cable. The bottom of the adapter is connected to the metal support frame, and a dedicated displacement differential sensor (LVDT) is installed between the adapter and the top cover plate of the triaxial stress device. The LVDT is used to realize the strain change of the experimental rock sample during CO2 injection, thereby obtaining the mechanical damage parameters of the experimental rock sample under in-situ conditions.

5. The experimental system for studying capillary damage and sealing during carbon burial based on in-situ CT according to claim 4, characterized in that, The triaxial testing system for rock damage and sealing analysis also includes an in-field X-ray generator and an X-ray signal receiver. The in-field X-ray generator scans the experimental rock samples inside the triaxial stress device, and the X-ray signal receiver obtains the original imaging results of the rock samples under the original formation temperature and pressure conditions.

6. The experimental system for studying capillary damage and sealing in carbon burial process based on in-situ CT according to claim 5, characterized in that, The experimental system also includes an axial pressure and confining pressure loading system, which includes an axial pressure loading pump and a ring pressure loading pump. The axial pressure loading pump is connected to a three-way valve through a pressure-resistant metal pipeline, and the ring pressure loading pump is connected to a dynamic seal hydraulic rotary table through a pressure-resistant metal pipeline. A pressure sensor E is installed at the inlet end of the dynamic seal hydraulic rotary table.

7. The experimental system for studying capillary damage and sealing during carbon burial based on in-situ CT according to claim 6, characterized in that, A check valve D is installed at the outlet end of the axial pressure loading pump, and pressure sensors C and D are installed at the inlet end of the three-way valve. Pressure sensor C is located on the pressure-resistant metal pipeline connecting the axial pressure loading pump and the three-way valve, and pressure sensor D is located on the pipeline connecting the experimental controller and the three-way valve.

8. The experimental system for studying capillary damage and sealing in carbon burial process based on in-situ CT according to claim 6, characterized in that, The experimental system also includes a back pressure control and fluid collection system, which includes a back pressure pump and an oil-gas-water separator. The outlet of the triaxial stress device is connected to a back pressure valve via a high-pressure pipeline. The back pressure valve is connected to a back pressure pump that controls fluid overflow via a high-pressure pipeline. The outlet of the back pressure valve is connected to the oil-gas-water separator via a pipeline. The oil-gas-water separator is connected to a gas flow meter, a water phase collection bottle, and a gas phase collection bottle via parallel pipelines.

9. The experimental system for studying capillary damage and sealing in carbon burial process based on in-situ CT according to claim 8, characterized in that, A pressure sensor F and a one-way valve F are installed on the high-pressure pipeline connecting the triaxial stress device and the back pressure valve.

10. The experimental method of the experimental system for studying capillary damage and sealing in carbon burial process based on in-situ CT according to any one of claims 1-9, characterized in that, The experimental method includes the following steps: Step 1: Pretreatment of experimental rock samples; Step 2: Loading of confining pressure and formation temperature on experimental rock samples The standard rock sample is loaded into the triaxial stress device. Then, check valves A, C, D, three-way valve, and F are closed, check valve E is opened, and the ring pressure loading pump is started to provide ring pressure to the experimental rock sample by injecting high-temperature hydraulic oil. Close the three-way valve, check valve E, and check valve F. Use an external vacuum pump to evacuate the inside of the triaxial stress device to achieve a negative pressure state inside the experimental rock sample. Open check valve A, three-way valve, and check valve F. Start the ISCO injection pump A to drive formation water into the experimental rock sample. The rock sample is saturated with formation water when the outlet water flow stabilizes. Open valve D (one-way valve) and start the axial pressure loading pump. Pump high-temperature hydraulic oil into the triaxial stress device to provide axial pressure simulation of the formation environment for the experimental rock sample. Then turn on the electric heating switch on the experimental controller to heat the hydraulic oil to the formation temperature and keep it stable. Step 3: Conduct research on rock damage characteristics during in-situ CO2 injection; Step 4: Study the sealing properties of the cap layer during the CO2 sequestration process.

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