A method and system for cutting off and backfilling damaged areas in CO2 storage wells

Abstract

This invention discloses a method and system for cutting off and filling damaged areas in CO2 storage wellbores. The method includes cleaning the damaged area of ​​the CO2 storage wellbore to form a cavity, filling the cavity to form a first sealing layer, and filling the first sealing layer with sand to form a second sealing layer. This invention adopts a cut-off filling method, re-cleaning and filling the damaged area, breaking through the conventional "squeezing" repair approach, and thoroughly solving the current situation and potential hazards of the damaged area, laying the foundation for long-term CO2 storage. The method utilizes the filling pore structure for controllable sealing, leveraging the fluid seepage resistance and multi-interface Jamin effect within the pore structure to control the sealing resistance. This meets the requirements for re-injecting and storing CO2 in the oil layer, laying the foundation for long-term CO2 storage and control management.

Description

Technical Field

[0001] This invention relates to the field of wellbore damage repair technology, and in particular to a method and system for cutting off and filling damaged areas in CO2 buried wellbores. Background Technology

[0002] The most important concerns regarding CO2 storage are its stability and safety, specifically whether CO2 will gradually flow from the buried strata to the surface through damaged areas in the wellbore, causing CO2 leakage.

[0003] Figure 1 The diagram shows the structure of a CO2 storage wellbore, including a wellhead control valve, an injection wellhead, wellhead equipment, casing, and cement sheath. The casing located in the surface layer and near-surface rock layer is the surface casing, and the casing located at the lowest point of the near-surface rock layer and the buried oil layer is the technical casing. There is a cement sheath between the technical casing and the lowest point of the near-surface rock layer and the buried oil layer. A dense caprock is provided in the middle of the buried oil layer, and the perforations on the technical casing below the dense caprock serve as channels for CO2 injection into the formation.

[0004] Figure 2 This diagram illustrates the injection of CO2 into the buried oil layer via a CO2 burial wellbore. CO2 is injected from the injection wellhead, passes through the surface casing and the technical casing, and enters the buried oil layer through perforations in the technical casing. After CO2 is deposited in the CO2 burial wellbore, CO2 leakage is closely related to the cement sheath. The three leakage zones are: the second interface formed by cement sheath shrinkage and casing deformation; cracks and voids formed by damage to the cement sheath itself; and the third interface formed by formation stress compression and localized CO2 corrosion. Among these, damage to the cement sheath itself is the primary leakage area. Furthermore, with CO2 burial and the casing and formation stress stabilized, CO2 corrosion is approximately a single factor. Besides casing deformation and formation stress compression, CO2 penetration into the cement sheath and its gradual expansion are the main factors. CO2 corrosion primarily leads to the dissolution of alkaline minerals such as Ca(OH)2 and CSH in the cement sheath, which decompose to form CaCO3 precipitate. Simultaneously, the corrosion intensity of the cement sheath increases with increasing CO2 corrosion temperature, CO2 partial pressure, and corrosion time.

[0005] Currently, the main method for preventing CO2 corrosion and damage to cement sheaths is to improve the physical properties of conventional cement. For example, using flexible cement, expansive cement, and annular prestressing effectively reduces the risk of cement sheath seal failure. Adding other materials, such as latex, elastic particles, and polypropylene fibers, can also improve the mechanical properties of cement, reducing its elastic modulus or increasing its ultimate stress and strain. This method and technology are primarily effective for new wells; if a producing or abandoned well is used as a CO2 storage injection well, this method cannot be implemented.

[0006] For example, Figure 3 This diagram illustrates a typical damaged area in a CO2-bearing wellbore. The damaged area appears at the cement sheath of the casing, and multiple damaged areas exist. Currently, the best approach to address damaged areas in CO2-bearing wellbores is to repair the cement sheath, primarily by injecting different fluid systems for sealing. This includes methods such as repairing casing seal failures and repairing damaged cement sheaths. Specifically, systems of varying viscosities are injected into the damaged space to bond the voids and cracks, or the high viscosity is used to seal off CO2.

[0007] While existing repair techniques are theoretically feasible, their application results are often unsatisfactory. This is because the conditions of casing damage and cement sheath corrosion are highly complex, and the injected fluids typically have high viscosity, preventing them from penetrating small corrosion cracks, thus failing to achieve effective overall sealing. Considering the safety and long-term nature of CO2 burial, reliable and controllable technologies must be employed. Summary of the Invention

[0008] To address the technical problems existing in the prior art, this invention employs a cut-off filling method to re-clean and fill the damaged area, forming a stable cement sealing layer and a uniform sand filling layer. Water is then injected into the pore structure of the sand filling layer, and the gas is sealed using the principles of seepage resistance and multi-interface Jamin effect, achieving controllability in sealing time, sealing strength, and testing.

[0009] To achieve the above objectives, the present invention provides a method for repairing the damaged area of ​​a CO2 storage wellbore by cutting off and filling the defective zone, the method comprising:

[0010] Clean the damaged area of ​​the CO2 storage wellbore to form a cavity, and fill the cavity to form the first sealing layer;

[0011] A second sealing layer is formed by filling the first sealing layer with sand particles.

[0012] Furthermore, the cavity formed by cleaning the damaged area of ​​the CO2 storage wellbore is filled to form the first sealing layer, including,

[0013] A sealing layer is formed in the lower part of the damaged area of ​​the CO2 storage wellbore.

[0014] The casing, cement ring, and rock in the damaged area of ​​the CO2 storage well are ground into particles, and the particles are removed to create a cavity in the damaged area of ​​the CO2 storage well.

[0015] Flexible cement is injected to fill the cavity, forming the first sealing layer on the sealing layer.

[0016] Furthermore, injecting flexible cement to fill the cavity includes,

[0017] If the damaged area of ​​the CO2 storage wellbore is located in the buried oil layer or at the junction of the buried oil layer and the dense caprock, the height of the flexible cement filling exceeds 10m above the dense caprock.

[0018] If the damaged area of ​​the CO2 storage well is located above the dense capping layer, the height of the flexible cement filling should be greater than or equal to 5m.

[0019] Furthermore, the filling of sand particles to form a second sealing layer includes,

[0020] When filling with sand, add water to 1 / 3 to 1 / 2 the volume of the sand.

[0021] The sand particles are a mixture of three types of quartz sand: 200 mesh, 120 mesh, and 80 mesh, in a volume ratio of 1-5:10-20:20-30.

[0022] The height of the second sealing layer formed by filling with sand particles is greater than or equal to 50m.

[0023] Furthermore, the damaged area of ​​the CO2 storage well is fixed to the formation before a sealing layer is formed in the lower part of the sealed CO2 storage well.

[0024] This invention also provides a CO2 wellbore damage zone cut-off and backfilling repair system, the system comprising,

[0025] A tube grinder, including grinding components and a central column, is used to clean cavities formed in damaged areas of CO2-buried wellbores.

[0026] The grouting and sand filling device is a hollow tube with an inner diameter of less than 4cm. It is used to inject cement to fill the cavity to form the first sealing layer, and then fill the first sealing layer with sand to form the second sealing layer.

[0027] Furthermore, the tube grinding device structure specifically includes,

[0028] The grinding component is located at the lower end of the central column. The grinding component includes an upper support arm, a grinding block and a lower support arm. One end of the upper support arm is connected to the central column and the other end of the upper support arm is connected to the grinding block. There is a constant pressure spring inside the upper support arm to provide grinding pressure. One end of the lower support arm is connected to the central column and the other end of the lower support arm is connected to the grinding block.

[0029] The center column has a through hole structure, with an external thread at the upper end and a slide rail in the middle. An upper locking point is located at the upper end of the slide rail to lock the upper support arm. A lower locking point is located near the bottom of the center column to lock the lower support arm.

[0030] Furthermore, the upper locking point is connected to a cable, and the cable transmits signals to control the opening and closing of the upper locking point and / or the lower locking point;

[0031] There is also a blocking buckle near the bottom of the center column.

[0032] Furthermore, the system also includes a fixing device.

[0033] The fixed device is a perforating projectile, including the projectile body, shaped charge liner, detonator, and telescopic tube.

[0034] The detonator is connected to the projectile body, the shaped charge liner is fixed inside the projectile body, and multiple telescopic tubes are provided and fixed to the shaped charge liner. The telescopic tubes have a through-hole structure.

[0035] Furthermore, the system also includes a packer, which comprises a body, a rubber ring, and a shielding top cover;

[0036] The top cover is threadedly connected to the main body, and there is a rubber ring on the upper and lower parts of the main body.

[0037] Compared with the prior art, the present invention provides a method and system for cutting off and filling damaged areas of CO2 buried wells, which has the following advantages:

[0038] (1) The present invention adopts the method of cutting and filling, which cleans and fills the damaged area again, breaks through the conventional idea of ​​"squeezing glue" repair, and completely solves the current situation and potential hidden dangers of the damaged area, laying the foundation for long-term CO2 storage.

[0039] (2) The present invention utilizes a method for controllable sealing by filling a pore structure. By utilizing the fluid seepage resistance within the pore structure and the multi-interface Jamin effect, the sealing resistance can be controlled.

[0040] (3) The method of the present invention can meet the requirements of injecting CO2 into the oil layer again and storing it, laying the foundation for long-term storage and control management of CO2.

[0041] (4) The operation mode of each device in the system of the present invention is reasonable and can effectively execute the method of the present invention, and has good application prospects. Attached Figure Description

[0042] Figure 1 A schematic diagram of the CO2 burial well shaft structure is shown;

[0043] Figure 2 A schematic diagram is shown showing the injection of CO2 into the reservoir through a CO2 storage wellbore for storage.

[0044] Figure 3 A schematic diagram of the damaged area in the CO2 storage wellbore is shown;

[0045] Figure 4 A flowchart of a method for cutting off and filling the damaged area of ​​a CO2 storage wellbore according to an embodiment of the present invention is shown;

[0046] Figure 5 This diagram illustrates a structural schematic of a cavity formed by cleaning a damaged area in a CO2 storage wellbore, as described in an embodiment of the present invention.

[0047] Figure 6 This diagram illustrates a structural schematic of repairing and sealing the damaged area of ​​a CO2-sealing wellbore in an embodiment of the present invention.

[0048] Figure 7a This diagram illustrates the forces acting on sand particles in the second sealing layer according to an embodiment of the present invention. Figure 7b This diagram illustrates the Jamin effect generated by the gas-liquid interface formed by sand particles and water in the second sealing layer.

[0049] Figure 8 This diagram illustrates a structural schematic of a CO2 wellbore damage zone cut-off and backfill repair system according to an embodiment of the present invention.

[0050] Figure 9a and Figure 9b A schematic diagram of the tube grinding device in an embodiment of the present invention is shown. Figure 9c A schematic diagram of the working state of the tube grinding machine is shown;

[0051] Figure 10a A schematic diagram of the fixing device in an embodiment of the present invention is shown. Figure 10b A schematic diagram of a telescopic tube in its extended state is shown. Figure 10c A schematic diagram of a telescopic tube being pushed into the formation is shown;

[0052] Figure 11 A schematic diagram of the packer in an embodiment of the present invention is shown;

[0053] Figure 12 A schematic diagram of the structure of a repeatedly buried CO2 wellbore in an embodiment of the present invention is shown. Detailed Implementation

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] like Figure 4 As shown, one embodiment of the present invention provides a method for repairing the damaged area of ​​a CO2 storage wellbore by cutting off and filling the damaged area. The method includes,

[0056] Step S101: Clean the damaged area of ​​the CO2 storage well to form a cavity, and fill the cavity to form the first sealing layer;

[0057] Step S102: Fill the first sealing layer with sand to form a second sealing layer.

[0058] The methods described in the above embodiments will be described in detail.

[0059] Step 1: Fix the damaged area of ​​the CO2 storage well to the formation. Specifically, use a perforating gun to push the fixing device into the formation above the damaged area of ​​the CO2 storage well, thereby fixing the damaged area of ​​the CO2 storage well to the formation.

[0060] Step 2: Seal the lower part of the damaged area of ​​the CO2 storage wellbore to form a sealing layer;

[0061] Step 3: Grind the casing, cement ring, and rock in the damaged area of ​​the CO2 storage well into fine particles. Use hydraulic cleaning technology to carry these fine particles to the surface, cleaning the damaged area of ​​the CO2 storage well to create a cavity. Figure 5 The diagram shows the structure of the cavity. It can be seen that the wellbore, cement sheath and some of the formation rock in the damaged area of ​​the CO2 storage wellbore have been ground and cleaned. It can also be seen that the sealing layer is below the cavity and the fixing device is above the cavity.

[0062] Step 4: Inject flexible cement to fill the cavity.

[0063] If the damaged area of ​​the CO2 storage wellbore is located in the buried oil layer or at the junction of the buried oil layer and the dense caprock, the height of the flexible cement filling exceeds 10m above the dense caprock.

[0064] If the damaged area of ​​the CO2 storage well is located above a dense cap layer, the height of the flexible cement filling should be greater than or equal to 5m.

[0065] After the flexible cement solidifies, it forms the first sealing layer on the sealing layer;

[0066] Step 5: Fill the first sealing layer with sand to form a second sealing layer. The height of the second sealing layer formed by filling with sand is greater than or equal to 50m. The sand is a mixture of three types of quartz sand: 200 mesh, 120 mesh and 80 mesh, in a ratio of 1:3:8. Water, which accounts for 1 / 2 of the total volume of the sand, is also added during the filling process.

[0067] It should be noted that the filling sand is not limited to the specific conditions given in this embodiment. The volume of water used for filling the sand can be 1 / 3 to 1 / 2 of the sand volume. The sand is a mixture of three types of quartz sand, namely 200 mesh, 120 mesh and 80 mesh, in a volume ratio of 1-5:10-20:20-30.

[0068] Figure 6 The diagram shows a structural schematic for repairing the damaged area of ​​the CO2 storage wellbore. It can be seen that there are first and second sealing layers above the sealing layer. The first and second sealing layers do not fill the cavity, and the fixing device is located above the cavity.

[0069] In the CO2 burial wellbore damage repair method of this embodiment, the sand particles in the second sealing layer are not cemented. Therefore, when subjected to inward stress from the wellbore, the sand particles remain in close contact with the rock surface and will not form gaps. Figure 7a A schematic diagram of the forces acting on sand particles in the second sealing layer is shown. Injecting fluids such as water into the second sealing layer significantly increases seepage resistance. If micro-leaking CO2 enters the pores, a gas-liquid interface will form. As the number of gas-liquid interfaces within the pores increases, the Jamin effect intensifies, resistance increases, and sealing capacity improves. Figure 7b The diagram shows the Jamin effect generated by the gas-liquid interface formed by sand particles and water in the second sealing layer. Water exists between the sand particles, and the micro-leaking CO2 forms a CO2 gas block. The Jamin effect is reflected in the fact that the resistance in the multi-interface flow channel is much greater than the resistance in the single-phase water flow channel.

[0070] It should be noted that, obviously in Figure 5 and Figure 6 In this process, multiple damaged areas exist: one damaged area is located above the dense capping layer, one damaged area is partially above and partially below the dense capping layer, and one damaged area is located below the dense capping layer. This embodiment only grinds the damaged areas located above the dense capping layer, which saves on operating costs and reduces the volume of flexible cement and sand used for filling. Alternatively, the method described in this embodiment can be used to cut off and fill all damaged areas for repair.

[0071] like Figure 8 As shown, another embodiment of the present invention provides a CO2 wellbore damage zone cut-off and filling repair system, including a pipe grinder, a grouting and sand filling device, a fixing device, and a packer. The pipe grinder, grouting and sand filling device, fixing device, and packer are lowered into the tubing or the operation is completed.

[0072] The grouting and sand filling device is a hollow tube with an inner diameter of less than 4 cm. After the grinding tool cleans the damaged area of ​​the CO2-buried well barrel to form a cavity, the grouting and sand filling device is connected to the tubing and lowered down. It is used to inject cement to fill the cavity to form the first sealing layer, and then fill the first sealing layer with sand to form the second sealing layer.

[0073] like Figure 9a As shown, the grinding tool includes a central column and grinding components, used to clean the cavity formed in the damaged area of ​​the CO2-buried wellbore. The grinding components are located at the lower end of the central column and include an upper support arm, grinding blocks, and a lower support arm. One end of the upper support arm is connected to the central column, and the other end is connected to the grinding blocks. A constant pressure spring is located inside the upper support arm to provide grinding pressure to the grinding blocks. One end of the lower support arm is connected to the central column, and the other end is connected to the grinding blocks. There are a total of 6 grinding blocks, evenly distributed axially. The central column has a through-hole structure, with external threads at the upper end and a slide rail in the middle. Figure 9bAs shown, an upper locking point is provided at the upper end of the slide rail, which is used to lock the upper support arm. A lower locking point is provided near the bottom of the center column, which is used to lock the lower support arm. The upper locking point is connected to a cable, and the cable transmits signals to control the opening and closing of the upper locking point and / or the lower locking point. A blocking buckle is also provided near the bottom of the center column.

[0074] During the operation of the tube grinding machine, the tubing string is fixed to the external thread and lowered into the damaged area of ​​the CO2 storage well. Figure 9c The diagram illustrates the working state of the grinding tool. As the grinding tool is lowered along the tubing string, the abrasive blocks retract to be close to the central column. In the initial grinding stage, the cable control signal opens the upper locking point, causing the upper support arm to move downwards within the slide until it contacts the casing. Using the pressure of the constant-pressure spring, the central column rotates to grind the casing, cement sheath, and rock in the damaged area of ​​the CO2-bearing wellbore into particles. During grinding, cement slurry is injected into the tubing string. The slurry flows into the central column, reaches the packer, and then returns, flushing the grinding particles back to the surface. The cement slurry also cools the grinding surface. During the grinding process, the tubing string is raised and lowered slowly and uniformly to ensure even grinding of the entire designed grinding section. In the later stages of grinding, the upper support arm fully extends, ending the grinding process. Finally, the cable control signal opens the lower locking point, connecting the upper support arm to the blocking buckle. The abrasive blocks and lower support arm hang naturally, and then the grinding tool is lifted along the tubing string to retrieve it.

[0075] like Figure 10a As shown, the fixing device is a perforating projectile, including a projectile body, a shaped charge liner, a detonator, and a telescopic tube. The detonator is connected to the projectile body, the shaped charge liner is fixed inside the projectile body, and multiple telescopic tubes are fixed to the shaped charge liner. The telescopic tubes have a through-hole structure. The shaped charge liner is used to store explosives, the detonator is used to detonate the explosives, and the telescopic tubes are used to fix the casing. When the perforating projectile is placed in the perforating gun and detonated, the explosive gases are ejected along the through-holes, and the telescopic tubes are pushed into the ground by the explosive gases. Figure 10b A schematic diagram of a telescopic tube in its extended state is shown. The telescopic tube includes a first section, a middle section, and a last section, all of which are through-hole cylinders. Relatively speaking, the first section has the smallest cross-sectional area and the longest length, the middle section has a moderate cross-sectional area and a moderate length, and the last section has the largest cross-sectional area and the shortest length. The first section is connected to the middle section, and the middle section is connected to the last section. The first section has an outlet, and there is a blocking surface at the connection between the middle and last sections. For example, Figure 10c A schematic diagram of a telescopic tube being inserted into the formation is shown. It can be seen that the first, middle, and last sections extend. After the detonator ignites the explosive, the explosive gas is ejected along the through-hole. The blocking surface is secured to the casing. The middle section extends into the cement ring, and the first section, after entering the formation and creating a hole, forms an opening in the rock. In this embodiment, the opening diameter of the shaped charge liner is 61mm, meaning the maximum outer diameter of the last section of the telescopic tube can reach 61mm, maximizing the supporting force. The extension length of the first, middle, and last sections is 120mm, allowing the telescopic tube to effectively penetrate to a depth of 100mm, penetrating the cement ring, pushing into the formation, embedding itself in the rock, and providing effective support.

[0076] Figure 11 A schematic diagram of the packer is shown. The packer includes a main body, rubber rings, and a shielding top cover. The shielding top cover is threadedly connected to the main body. There is a rubber ring at the top and bottom of the main body. The packer used in this embodiment is a Y421 type packer. The purpose of the packer is to prevent cement, debris, etc., from entering the bottom sleeve during later work.

[0077] An embodiment of the present invention also provides the working process of cutting off and filling the damaged area of ​​a CO2 storage well in the above-described method and system for repair. The CO2 storage well is 2000m deep, with a bottom temperature of 60°C, a bottom pressure of 15MPa, and a top depth of 1900m for the dense caprock.

[0078] (1) Preparatory work

[0079] The location of the damaged area in the CO2-bearing wellbore was confirmed using a pressurized wellbore integrity test, specifically within the 1500-1600m section of the CO2-bearing wellbore. Prior to the test, the CO2 injection perforations at the bottom of the oil layer had been pressure-sealed, ensuring that the stored CO2 gas would not flow into the wellbore in large quantities under high pressure differential. The pressure inside the wellbore met the requirements for normal downhole operations.

[0080] (2) Insert packer

[0081] The Y421 packer was lowered to a depth of 1650m, and the top cover was opened to form a packing layer.

[0082] (3) Fix the upper sleeve

[0083] The fixed device was lowered to a depth of 1450m. Within the range of 1445-1450m, holes were evenly drilled around the perimeter, and a total of 10 telescopic tubes were evenly pushed into the formation.

[0084] (4) Tube grinding machine operation

[0085] The grinding tool is lowered to a depth of 1630m, and grinding is carried out within the 1450-1630m range. Once the grinding tool is in place, the locking point is opened, and the grinding tool enters the working state. The tubing is slowly and evenly raised and lowered to uniformly grind the casing, cement sheath, and some rock layers within the 1450-1630m section. If the grinding blocks fail, a signal is sent to the ground, and the tubing is raised to replace the grinding blocks. This process continues until the entire section is ground. Then, the locking point is opened, and the grinding tool is lifted along the tubing to retrieve it.

[0086] (5) Grinding section filling

[0087] The grouting and sand filling device is lowered to a depth of 1640m (or stopped after encountering resistance upon contact with the bottom cover), and flexible cement is injected. The filling height is designed to be 100m, that is, filled to a depth of 1540m. After standing for 24 hours, the first sealing layer is formed.

[0088] After the cement has initially solidified, sand is added as filling. The sand is a mixture of 200-mesh, 120-mesh, and 80-mesh quartz sand in a 1:3:8 ratio. The filling height is designed to be 100m, i.e., filling to a depth of 1440m. Water, accounting for half the total volume of the sand, is added during the filling process. During filling, the tubing string can be raised and lowered, using its weight to compress the sand particles, making them adhere tightly to the rock wall and forming a second sealing layer. This completes the cut-off filling and repair of the damaged area of ​​the CO2 burial well.

[0089] (6) Reuse

[0090] After CO2 has been stored for a certain period of time (e.g., 30 years), if it is necessary to inject CO2 into the formation again, the first and second sealing layers need to be opened to form an injection channel. Figure 12 The diagram shows the structure of a wellbore for repeated CO2 storage. The first sealing layer, the second sealing layer, and the isolation layer are destroyed to form a CO2 storage channel. CO2 is injected from the wellhead, which can realize the re-injection and storage of CO2 into the oil layer.

[0091] First, circulating cement slurry is used to return the filling sand to the surface. Under pressure-maintaining control, a drill bit slightly smaller than the inner diameter of the casing is used to drill through the filling cement sheath until the aluminum ball at the top of the lowered cap is destroyed (surface monitoring shows the mud flowing downwards at an accelerated rate). The packer is then removed by running the tubing string, at which point the wellbore is ready for re-burying. A CO2 injection line is connected to the wellhead for re-injection.

[0092] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for repairing the damaged area of ​​a CO2 storage wellbore by cutting off and filling the damaged area, characterized in that, The method includes, Clean the damaged area of ​​the CO2 storage wellbore to form a cavity, and fill the cavity to form the first sealing layer; A second sealing layer is formed by filling the first sealing layer with sand particles. This process involves cleaning the damaged area of ​​the CO2-buried wellbore to create a cavity, and filling the cavity to form the first sealing layer. A sealing layer is formed in the lower part of the damaged area of ​​the CO2 storage wellbore. The casing, cement ring, and rock in the damaged area of ​​the CO2 storage well are ground into particles, and the particles are removed to create a cavity in the damaged area of ​​the CO2 storage well. Flexible cement is injected to fill the cavity, forming the first sealing layer on the sealing layer; The filling of sand particles to form the second sealing layer includes, When filling with sand, add water to 1 / 3 to 1 / 2 the volume of the sand. The sand particles are a mixture of three types of quartz sand: 200 mesh, 120 mesh, and 80 mesh, in a volume ratio of 1-5:10-20:20-30. The height of the second sealing layer formed by filling with sand particles is greater than or equal to 50m.

2. The method according to claim 1, characterized in that, Injecting flexible cement to fill cavities includes, If the damaged area of ​​the CO2 storage wellbore is located in the buried oil layer or at the junction of the buried oil layer and the dense caprock, the height of the flexible cement filling exceeds 10m above the dense caprock. If the damaged area of ​​the CO2 storage well is located above the dense capping layer, the height of the flexible cement filling should be greater than or equal to 5m.

3. The method according to any one of claims 1-2, characterized in that, Before forming a sealing layer in the lower part of the CO2 burial wellbore damage zone, the CO2 burial wellbore damage zone is also fixed to the formation.

4. A CO2 wellbore damage zone cut-off and backfilling repair system, used to implement the method as described in any one of claims 1-3, characterized in that, The system includes, A tube grinder, including grinding components and a central column, is used to clean cavities formed in damaged areas of CO2-buried wellbores. The grouting and sand filling device is a hollow tube with an inner diameter of less than 4cm. It is used to inject cement to fill the cavity to form the first sealing layer, and then fill the first sealing layer with sand to form the second sealing layer.

5. The system according to claim 4, characterized in that, The tube grinding device structure specifically includes: The grinding component is located at the lower end of the central column. The grinding component includes an upper support arm, a grinding block and a lower support arm. One end of the upper support arm is connected to the central column and the other end of the upper support arm is connected to the grinding block. There is a constant pressure spring inside the upper support arm to provide grinding pressure. One end of the lower support arm is connected to the central column and the other end of the lower support arm is connected to the grinding block. The center column has a through hole structure, with an external thread at the upper end and a slide rail in the middle. An upper locking point is located at the upper end of the slide rail to lock the upper support arm. A lower locking point is located near the bottom of the center column to lock the lower support arm.

6. The system according to claim 5, characterized in that, The upper locking point is connected to a cable, and the cable transmits signals to control the opening and closing of the upper locking point and / or the lower locking point; There is also a blocking buckle near the bottom of the center column.

7. The system according to claim 4, characterized in that, The system also includes a fixing device. The fixed device is a perforating projectile, including the projectile body, shaped charge liner, detonator, and telescopic tube. The detonator is connected to the projectile body, the shaped charge liner is fixed inside the projectile body, and multiple telescopic tubes are provided and fixed to the shaped charge liner. The telescopic tubes have a through-hole structure.

8. The system according to claim 4, characterized in that, The system also includes a packer, which comprises a body, a rubber ring, and a shielding top cover; The top cover is threadedly connected to the main body, and there is a rubber ring on the upper and lower parts of the main body.

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