Double-interface graded sealing method for carbon dioxide injection well and repairable grouting system

Abstract

The present application is suitable for the technical field of carbon dioxide geological storage, and provides a double-interface grading sealing method for carbon dioxide injection wells and a repairable grouting system. The system adopts a double-layer casing structure, the inner layer casing is a carbon dioxide conveying channel, and the annular space between the inner and outer layer casings is an independent grouting channel. The outer layer casing is provided with a first grouting hole and a second grouting hole, which correspond to the casing-cement ring interface and the cement ring-rock layer interface for targeted grouting, respectively. An interlayer packer is arranged along the well depth, and distributed optical fibers and annular pressure sensors are used for online monitoring. The method comprises wellbore preparation and double-layer casing running, primary cementing, first interface sealing, second interface sealing, sealing quality detection and baseline database establishment, and online monitoring and targeted repair during carbon dioxide injection. The present application can realize double-interface grading sealing of the wellbore, online monitoring throughout the life cycle, and repeated repair without stopping the well, and significantly improves the long-term sealing safety of carbon dioxide injection wells.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide geological storage technology, and particularly relates to a dual-interface graded sealing method for carbon dioxide injection wells and a repairable grouting system. Background Technology

[0002] Carbon capture, utilization, and storage (CCUS) is one of the core technologies for achieving large-scale carbon dioxide emission reduction and carbon sequestration throughout its entire life cycle. Among these technologies, subsea geological storage has become a major technical route for carbon dioxide sequestration due to its large storage capacity and distance from densely populated urban areas. In subsea geological carbon dioxide sequestration, the injection well is the only channel connecting the surface and underground reservoirs, and its sealing integrity is the core barrier to ensuring the safety of carbon dioxide sequestration. The U.S. Department of Energy's National Energy Technology Laboratory, in a series of technical reports from the National Risk Assessment Cooperation Project, pointed out that wellbore seal failure is one of the main sources of risk for carbon dioxide sequestration leakage, with micro-cracks at the casing-cement sheath interface being the primary leakage channel.

[0003] Currently, the sealing of subsea injection wells almost entirely relies on cement sheaths. However, due to limitations in their service environment, construction technology, and material properties, micro-cracks at the casing-cement sheath and cement sheath-formation interfaces are difficult to eliminate fundamentally. The formation and expansion of these cracks are mainly due to three factors: (1) Silicate cement undergoes volume shrinkage during hydration, and after initial setting, it forms micro-cracks between the outer wall of the casing and the inner wall of the cement sheath, as well as between the outer wall of the cement sheath and the formation rock wall. These are the initial channels for carbon dioxide leakage. (2) During carbon dioxide injection, the temperature and pressure of the wellbore fluctuate. Due to the difference in the expansion coefficients of the casing, cement layer, and formation rock wall, shear stress is generated at the interface, further exacerbating the expansion of the micro-cracks at the interface. (3) Supercritical carbon dioxide reacts with formation water to form a carbonic acid environment. The cement sheath will be corroded in this environment for a long time, leading to an increase in porosity and a decrease in interfacial bonding strength, ultimately resulting in irreversible degradation of sealing performance.

[0004] To address the above problems, existing technologies mainly seek improvements in the following two aspects:

[0005] One approach involves modifying the cement sheath material. This includes incorporating active components such as silica fume, fly ash, and nano-silica to enhance corrosion resistance, or adding expansive components like aluminum powder and magnesium oxide to compensate for cement shrinkage. However, these methods only repair micro-cracks within the cement sheath itself. For continuous micro-cracks formed at the casing-cement sheath and cement sheath-formation interfaces due to cement hydration shrinkage and thermo-pressure cyclic stress, the repair agent cannot reach the interfacial gaps or provide bonding reinforcement to the debonded interfaces. Furthermore, some studies explore replacing traditional silicate cement with novel cementing materials, but all material modification schemes are limited to the cement sheath itself and cannot address the micro-crack problem at the structural level.

[0006] Secondly, there are post-leakage remediation methods, including cement repair and chemical gel sealing. Cement slurry or chemical gel is injected through perforations or annular channels to form a solidified body in the gaps to seal the leakage channels. These methods are all passive remediation methods, and subsea operations require the use of drilling vessels, which is extremely costly. The sealing efficiency is also low, and repeated operations are required after the wellbore deteriorates repeatedly, making it impossible to achieve dynamic maintenance throughout the entire life cycle.

[0007] In summary, the current field of subsea carbon dioxide injection well sealing lacks a systematic solution that can simultaneously meet the three major requirements of "eliminating micro-cracks at dual interfaces, resisting long-term corrosion and degradation, and achieving low-cost in-situ repair during service life." Improvements in traditional cementing technology are mainly limited to material modification. There is an urgent need to introduce interdisciplinary technical approaches, constructing a novel sealing system from the perspective of geotechnical engineering interface strengthening and grouting reinforcement, integrating "active pre-sealing + dynamic repairability + wellbore-formation integration." Summary of the Invention

[0008] The purpose of this invention is to provide a dual-interface graded sealing method and a repairable grouting system for carbon dioxide injection wells, aiming to solve the problems mentioned in the background art.

[0009] The present invention is implemented as follows: a dual-interface repairable grouting system for carbon dioxide injection wells includes a double-layer casing structure and surface supporting equipment.

[0010] The double-layer casing includes an inner casing and an outer casing; the inner casing is a carbon dioxide delivery channel used to deliver supercritical carbon dioxide to the underground sealed storage layer; the annular space between the inner casing and the outer casing is a grouting channel, which is completely independent and sealed.

[0011] The outer casing has a two-stage grouting hole structure arranged along the well depth direction. The grouting hole structure includes a primary grouting hole and a secondary grouting hole. Both the primary and secondary grouting holes are equipped with one-way check valves at their openings. The primary grouting hole is a short hole structure that penetrates the outer casing wall and has its outlet facing the annular interface between the outer casing and the cement sheath, used to inject grout into the casing-cement sheath interface. The secondary grouting hole is an extended through-hole that penetrates both the outer casing and the cement sheath, with its end extending to the interface between the cement sheath and the wellbore rock strata, used to grout and reinforce the surrounding formation interface.

[0012] Interlayer packers are installed in sections along the well depth between the inner and outer casings, dividing the grouting channel into multiple independent grouting sections;

[0013] The outer wall of the outer sleeve is equipped with online monitoring equipment, which includes distributed optical fiber sensing cables and segmented annular pressure sensors.

[0014] The ground-based supporting equipment includes a wellhead multi-way control valve, a high-pressure grouting pump set, and a fiber optic monitoring terminal.

[0015] A further technical solution is provided in the primary grouting hole, which is a primary grouting channel. The primary grouting channel is a short guide pipe, which is fully welded to the outer sleeve, and the outer end face is flush with the outer wall of the outer sleeve.

[0016] The secondary grouting hole is equipped with an extended penetrating guide tube, the length of which is equal to the thickness of the cement ring.

[0017] A further technical solution is that the primary grouting holes and the secondary grouting holes are set at grouting sections every 10m along the well depth direction, and each section is set with four primary grouting holes and two secondary grouting holes, and the primary grouting holes and the secondary grouting holes are staggered in the circumferential direction.

[0018] A further technical solution is that the interlayer packer is an expansion rubber packer, the main body of which is a nitrile rubber cylinder resistant to supercritical carbon dioxide. It achieves setting and sealing by pressurizing the grouting channel and releases the pressure to unseal.

[0019] The interlayer packers are installed in sets every 100m along the wellbore depth.

[0020] A further technical solution is that the distributed optical fiber sensing cable is continuously bound and fixed along the outer sheath, covering all grouting and sealing sections throughout, for temperature detection and strain detection.

[0021] One to two annular pressure sensors are installed in each independent well section separated by the interlayer packer, mounted on the outer wall of the outer casing, to monitor the pressure at the casing-cement sheath interface.

[0022] Another objective of this invention is to provide a graded sealing method for a dual-interface carbon dioxide injection well, based on the aforementioned repairable dual-interface grouting system for carbon dioxide injection wells, comprising the following steps:

[0023] Step 1: Wellbore preparation and double casing installation;

[0024] After drilling is completed, the well is washed, the rock wall is repaired, and a double casing is installed.

[0025] Step 2: Initial cementing;

[0026] Pump carbon dioxide corrosion resistant cement slurry into the annular space between the outer casing and the wellbore rock strata. During the cementing process, maintain nitrogen positive pressure curing in the grouting channel until the cement sheath initially sets.

[0027] Step 3: Primary interface sealing;

[0028] After the cement has initially set, a supercritical carbon dioxide-resistant expanding nitrile latex grout is pumped into the micro-gap at the casing-cement ring interface through the primary grouting hole at low pressure. After the grout has solidified, a flexible sealing layer is formed at the casing-cement ring interface.

[0029] Step 4: Secondary interface sealing;

[0030] After the flexible sealing layer has cured, nano-silicon-alkali activated mineral powder composite grout is pumped into the well wall rock strata outside the cement sheath through the secondary grouting hole. After the grout has cured, it forms a modified rock mass in the well wall rock strata.

[0031] Step 5: Seal quality inspection and baseline database establishment;

[0032] Sonic variable density logging is used to measure each independent well section along the wellbore. After the test is qualified, the online monitoring equipment is started to collect normal operating data and establish an initial benchmark database for each independent well section.

[0033] Step 6: Online monitoring and targeted remediation during carbon dioxide injection;

[0034] After the injection well is started, the online monitoring equipment continues to work, transmitting the detection results to the control unit in real time. When it is determined that the sealing performance of a certain part has deteriorated, an early warning is issued, and the corresponding grouting section is switched through the wellhead control valve to inject the corresponding sealing material for repair.

[0035] In a further technical solution, in step 3, the base material of the supercritical carbon dioxide-resistant expandable nitrile rubber latex is carboxylated nitrile rubber latex with a solid content of 50%, combined with a curing agent, an expansion agent, and an anti-carbon dioxide aging agent.

[0036] In a further technical solution, in step 4, the preparation sequence of the nano-silicon-alkali activated mineral powder composite slurry is as follows: first, water, NaOH, and retarder are stirred and dissolved; slag powder is added and stirred at 800 r / min for 10 min; finally, water glass and nano-silicon sol are added and stirred for 5 min until uniform; initial setting at room temperature is 6 h, final setting is 36 h, and compressive strength is ≥35 MPa.

[0037] In a further technical solution, in step 5, the evaluation criteria for acoustic variable density logging are as follows: record the amplitude of the first wave of acoustic waves. If the relative amplitude of the first wave is ≤20%, it is judged as a high-quality cementation of the flexible sealing layer; 20%~40% is qualified; and greater than 40% is unqualified.

[0038] The subsequent formation wave density display shows that if a continuous and clear formation wave phase axis is present on the VDL chart, the modified rock mass is considered to be well cemented; if the formation signal wave is weak or chaotic, the modified rock mass is considered to be poorly cemented.

[0039] A further technical solution involves a two-level judgment and graded alarm mechanism in step 6: when a single parameter fluctuates, it is only marked without triggering an alarm; if the annular pressure rises abnormally and is accompanied by a change in temperature at the corresponding location, it is determined to be a real leak and an alarm is triggered; after the warning signal is issued, there is no need to shut down the well. If the flexible sealing layer leaks, expandable nitrile latex slurry is re-injected for sealing; if the modified rock mass leaks, nano-silicon-alkali activated mineral powder composite slurry is re-injected for reinforcement. After the repair is completed, the sealing quality is re-tested.

[0040] The carbon dioxide injection well dual-interface graded sealing method and repairable grouting system provided in this invention have the following beneficial effects:

[0041] (1) Structurally eliminate the micro-cracks at the double interface: The casing-cement sheath gap is filled by the primary grouting hole, and the surrounding rock mass is reinforced by the secondary grouting hole, thus eliminating the core source of carbon dioxide leakage from the structure.

[0042] (2) Flexible sealing layer adapts to temperature and pressure cycle load: The flexible sealing layer has elastic deformation capability, which can absorb the interface deformation caused by temperature and pressure cycle. The interface can maintain complete sealing and the cyclic fatigue life is significantly improved compared with the traditional rigid interface.

[0043] (3) Synergistic effect of three anti-corrosion defenses: Three anti-corrosion defenses are set up. The outermost modified rock mass can first consume the leaked carbon dioxide and undergo a carbonization reaction to generate calcium carbonate to achieve self-compactment; the middle cement ring can be combined with corrosion-resistant components to enhance corrosion resistance; the inner nitrile latex flexible sealing layer itself has excellent resistance to carbon dioxide corrosion. The three defenses work together to greatly improve the sealing performance of the wellbore.

[0044] (4) In-situ targeted remediation without shutting down the well: In-situ remediation does not require the use of drilling vessels or well shutdown, which greatly saves maintenance costs. Multi-level barriers make the leakage process easy to monitor and detect, and deterioration can be identified in the early stages, avoiding sudden and serious leakage accidents and significantly reducing environmental and regulatory compliance risks.

[0045] (5) Segmented independent grouting and targeted repair: The grouting channel is divided into multiple independent grouting segments by interlayer packers. With the help of a distributed online monitoring system, segmented detection, segmented grouting and targeted repair can be realized, avoiding problems such as grout cross-flow, uneven pressure and excessive sealing repair range throughout the well section. Attached Figure Description

[0046] Figure 1 This is a detailed view of the dual interfaces around the well.

[0047] Figure 2 This is a schematic diagram of the structure of the dual-interface repairable grouting system for carbon dioxide injection wells provided in an embodiment of the present invention;

[0048] Figure 3 A process flow diagram of the dual-interface graded sealing method for carbon dioxide injection wells provided in an embodiment of the present invention.

[0049] In the attached diagram: 1-Carbon dioxide injection pipeline; 2-High-pressure grouting pump set; 3-Fiber optic monitoring terminal; 4-Well wall rock strata; 5-Carbon dioxide delivery channel; 6-Grouting channel; 7-Cement sheath; 8-Primary grouting hole; 9-Secondary grouting hole; 10-Wellhead multi-way control valve. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0051] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0052] like Figure 1 and Figure 2 As shown, this is an embodiment of the carbon dioxide injection well dual-interface repairable grouting system provided by the present invention. It employs a double-casing structure, comprising an inner casing and an outer casing. The inner casing serves as a carbon dioxide delivery channel 5, used for the long-term, stable delivery of supercritical carbon dioxide to the underground sealing and storage layer. The annular space between the inner and outer casings is a grouting channel 6, which is entirely independent and sealed, and does not participate in the carbon dioxide delivery operation.

[0053] The outer casing has a two-stage grouting hole structure evenly arranged along the well depth direction, namely a primary grouting hole 8 and a secondary grouting hole 9. The orifices of the primary grouting hole 8 and the secondary grouting hole 9 are equipped with one-way check valves, which only allow the grouting slurry to flow outward and prevent carbon dioxide from flowing back into the grouting channel.

[0054] The primary grouting hole 8 is a short hole structure that only penetrates the outer wall of the outer casing. Its outlet is directly opposite the annular interface between the outer casing and the cement ring 7, and is used to fill the micro-gap at the casing-cement ring interface. The primary grouting hole 8 is provided with a primary grouting channel, which is a short guide tube that is fully welded to the outer casing, and its outer end face is flush with the outer wall of the outer casing.

[0055] The secondary grouting hole 9 is an extended penetrating through hole with an extended penetrating guide tube. The length of the guide tube is equal to the thickness of the cement sheath. The entire hole penetrates the outer casing and the cement sheath 7. The end of the hole extends to the interface between the cement sheath 7 and the well wall rock strata 4, allowing direct grouting reinforcement to the surrounding formation interface.

[0056] The guide pipes for both the primary grouting hole 8 and the secondary grouting hole 9 are double-layered casings, prefabricated in the factory and welded onto the casing, and lowered into the well along with the double-layered casing. Grouting sections are set every 10m along the well depth direction for the primary grouting hole 8 and the secondary grouting hole 9. Each section has four primary grouting holes 8 and two secondary grouting holes 9, and the primary grouting holes 8 and secondary grouting holes 9 are staggered circumferentially.

[0057] Interlayer packers are installed in sections along the well depth between the inner and outer casing, dividing the grouting channel into multiple independent grouting sections. The interlayer packers are expansion-type rubber packers, with a main body made of nitrile rubber resistant to supercritical carbon dioxide. After the wellbore is lowered into place, pressure is applied into the annular channel to achieve setting; depressurization releases the packer. The interlayer packers enable segmented grouting, segmented monitoring, and segmented targeted repair, avoiding problems such as grout cross-flow, uneven pressure, and excessively large sealing repair areas throughout the well. In this embodiment, one set of interlayer packers is installed every 100m along the wellbore depth, pre-installed at the designed depth of the annular channel during the factory prefabrication stage.

[0058] Online monitoring equipment, including distributed fiber optic sensing cables and segmented annular pressure sensors, is installed on the outer wall of the outer casing. The monitoring equipment is lowered into the wellbore along with the casing, and the cables are all routed to the fiber optic monitoring terminal 3 at the wellhead. The distributed fiber optic sensing cables are continuously bundled and fixed along the outer casing, covering all grouting and sealing sections.

[0059] Temperature and strain detection can be achieved. One to two annular pressure sensors are installed in each independent well section separated by the interlayer packer, mounted on the outer wall of the outer casing, to monitor the pressure at the casing-cement sheath interface; the leakage at the interface between the cement sheath 7 and the well wall rock strata 4 is determined by a fiber optic sensing system, using both temperature and strain parameters, in conjunction with the pressure at the casing-cement sheath interface.

[0060] The monitoring system can continuously collect annular pressure, casing strain, interface temperature and leakage anomaly signals in real time, realizing all-weather online monitoring of wellbore sealing status, anomaly identification and accurate location of deteriorated leakage sections.

[0061] The ground-based supporting equipment includes a wellhead multi-way control valve 10, a high-pressure grouting pump set 2, a carbon dioxide injection pipeline 1, and a fiber optic monitoring terminal 3.

[0062] like Figure 3 The diagram illustrates a dual-interface staged sealing method for carbon dioxide injection wells according to an embodiment of the present invention. Based on the aforementioned system, it includes the following steps:

[0063] Step 1: Wellbore preparation and double casing installation;

[0064] Drilling operations were carried out to the target storage layer. After drilling to the designed depth, drilling fluid was circulated to flush the well and remove cuttings from the wellbore. A caliper was run to check the regularity of the wellbore, and a scraper was used to correct the rock wall to ensure its regularity. Double casing was run in, with the inner casing serving as an independent carbon dioxide delivery channel 5. The outer casing was pre-fabricated with primary grouting holes 8, secondary grouting holes 9, and a one-way check valve.

[0065] Step 2: Initial cementing;

[0066] Carbon dioxide corrosion resistant cement slurry is pumped into the annular space between the outer casing and the wellbore rock strata. The cement slurry rises to the predetermined height. During cementing, the grouting channel is continuously maintained under positive nitrogen pressure for 48 hours until the initial setting strength of the cement sheath reaches 3.5 MPa. During the setting period, the tubing string must not be disturbed to ensure uniform solidification of the cement sheath. Nitrogen supply is then stopped, and the grouting channel is subjected to water pressure testing and diameter checks section by section to ensure that there is no cement blockage in the primary and secondary grouting holes.

[0067] Step 3: Primary interface sealing;

[0068] Stop all operations and wait for the cement to initially set, forming a cement ring 7 with a certain strength. At this time, the cement ring is not completely cured, and certain cracks are generated between the outer casing and the well wall rock layer 4 due to cement hydration shrinkage.

[0069] The high-pressure grouting pump set 2 is connected to the primary grouting hole 8 in the grouting channel 6. Through the primary grouting hole 8, an expandable nitrile latex grout resistant to supercritical carbon dioxide is pumped into the gap at low pressure. The grouting pressure is controlled within the range of lower than the formation fracturing pressure and higher than the annular pressure. The grout slowly expands and solidifies in the micro-cracks, filling all the micro-cracks and forming a continuous, flexible, and tough sealing layer.

[0070] The base material of the supercritical carbon dioxide-resistant expanding nitrile butadiene latex slurry is carboxyl-based nitrile butadiene latex with a solid content of 50%, combined with curing agents, expanding agents, and anti-carbon dioxide aging agents. After curing, the slurry has a volume expansion rate of 15%~30%, a temperature resistance of ≥80℃, and a strength retention rate of ≥90% after long-term immersion in supercritical carbon dioxide environment. It initially sets in 4 hours at room temperature and finally sets in 24 hours, with a compressive strength of ≥12MPa.

[0071] Step 4: Secondary interface sealing;

[0072] After the flexible sealing layer has cured, nano-silicon-alkali activated mineral powder composite grout is pumped into the well wall rock stratum 4 outside the cement sheath 7 through the secondary grouting hole 9. A step-by-step pressurization permeation grouting process is used to diffuse the grout into the pores and micro-fractures of the surrounding rock mass. After the grout cures, a modified rock mass will be formed, which will significantly improve the overall impermeability and mechanical strength of the well wall rock stratum 4.

[0073] The preparation sequence of the nano-silica-alkali activated mineral powder composite slurry is as follows: first, dissolve water, NaOH, and retarder by stirring; then add slag powder and stir at 800 r / min for 10 min; finally, add water glass and nano-silica sol and stir for 5 min until homogeneous. Initial setting at room temperature is 6 h, final setting is 36 h, and the compressive strength is ≥35 MPa.

[0074] Step 5: Seal quality inspection and baseline database establishment;

[0075] Sonic variable density logging (CBL / VDL) was used to measure each independent section along the wellbore segment by segment to quantitatively evaluate the cementation quality of the flexible sealing layer and qualitatively evaluate the cementation quality of the modified rock mass. Specifically, the amplitude of the first sonic wave was recorded to quantitatively evaluate the cementation quality of the flexible sealing layer: a relative amplitude of ≤20% was considered excellent cementation, 20%~40% was acceptable, and greater than 40% was unacceptable. Subsequent formation wave variable density displays were recorded to qualitatively evaluate the cementation quality of the modified rock mass: if a continuous and clear formation wave phase axis appeared on the VDL chart, the modified rock mass was considered well cemented; if the formation signal wave was weak or chaotic, the modified rock mass was considered poorly cemented.

[0076] After passing the inspection, the online monitoring equipment is activated to continuously collect data such as temperature, strain, and annular pressure of each segment under normal operating conditions for 72 hours, and to establish an initial benchmark database for each independent well section.

[0077] Step 6: Online monitoring and targeted remediation during carbon dioxide injection;

[0078] Once the injection well begins operation, carbon dioxide is pumped in, and the online monitoring equipment operates continuously. The monitoring results...

[0079] Data is transmitted to the control unit, where the system analyzes the deteriorated areas. Distributed fiber optic sensing cables acquire real-time temperature and strain fields in the wellbore, while annular pressure sensors monitor the pressure at the casing-cement sheath interface in each independent well section. The surface demodulation system analyzes the data and automatically compares it with a benchmark database.

[0080] The early warning system employs a two-level judgment and graded alarm mechanism. When a single parameter experiences a small fluctuation, it is only marked without triggering an alarm. If the annular pressure rises abnormally, accompanied by a change in temperature at the corresponding location, the system determines it as a real leak and subsequently issues an alarm. The ground-based fiber optic monitoring terminal 3 receives the early warning signal and, based on the system prompts, determines the type of failure interface and identifies the specific grouting section number and depth location where deterioration has occurred.

[0081] When the online monitoring equipment detects a decrease in the sealing performance of a certain part, it issues an early warning. Upon receiving the warning signal, there is no need to shut down the well. The wellhead control valve is switched to the grouting channel of the corresponding layer, and the corresponding sealing material is injected again. When the flexible sealing layer leaks, expandable nitrile latex grout is injected to repair the leak. When the modified rock mass leaks, nano-silicon-alkali activated mineral powder composite grout is injected again to reinforce the outer rock mass. After the repair is completed, the sealing quality is retested. Once the standard is met, the system continues to operate, realizing the full life cycle repeatable repair of the wellbore sealing system.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dual-interface repairable grouting system for carbon dioxide injection wells, characterized in that, Includes a double-layer casing structure and ground-based supporting equipment; The double-layer casing includes an inner casing and an outer casing; the inner casing is a carbon dioxide delivery channel used to deliver supercritical carbon dioxide to the underground sealed storage layer; the annular space between the inner casing and the outer casing is a grouting channel, which is completely independent and sealed. The outer casing has a two-stage grouting hole structure arranged along the well depth direction. The grouting hole structure includes a primary grouting hole and a secondary grouting hole. Both the primary and secondary grouting holes are equipped with one-way check valves at their openings. The primary grouting hole is a short hole structure that penetrates the outer casing wall and has its outlet facing the annular interface between the outer casing and the cement sheath, used to inject grout into the casing-cement sheath interface. The secondary grouting hole is an extended through-hole that penetrates both the outer casing and the cement sheath, with its end extending to the interface between the cement sheath and the wellbore rock strata, used to grout and reinforce the surrounding formation interface. Interlayer packers are installed in sections along the well depth between the inner and outer casings, dividing the grouting channel into multiple independent grouting sections; The outer wall of the outer sleeve is equipped with online monitoring equipment, which includes distributed optical fiber sensing cables and segmented annular pressure sensors. The ground-based supporting equipment includes a wellhead multi-way control valve, a high-pressure grouting pump set, and a fiber optic monitoring terminal.

2. The dual-interface repairable grouting system for carbon dioxide injection wells according to claim 1, characterized in that, The primary grouting hole is provided with a primary grouting channel, which is a short guide pipe that is fully welded to the outer sleeve, and the outer end face is flush with the outer wall of the outer sleeve. The secondary grouting hole is equipped with an extended penetrating guide tube, the length of which is equal to the thickness of the cement ring.

3. The dual-interface repairable grouting system for carbon dioxide injection wells according to claim 1, characterized in that, The primary and secondary grouting holes are set at grouting sections every 10m along the well depth direction. Each section is set with four primary grouting holes and two secondary grouting holes. The primary and secondary grouting holes are staggered in the circumferential direction.

4. The dual-interface repairable grouting system for carbon dioxide injection wells according to claim 1, characterized in that, The interlayer packer is an expansion rubber packer, the main body of which is a nitrile rubber cylinder resistant to supercritical carbon dioxide. It achieves setting and sealing by pressurizing the grouting channel and releases the pressure to unseal. The interlayer packers are installed in sets every 100m along the wellbore depth.

5. The dual-interface repairable grouting system for carbon dioxide injection wells according to claim 2, characterized in that, The distributed optical fiber sensing cable is continuously bound and fixed along the outer sheath, covering all grouting and sealing sections, and is used for temperature detection and strain detection. One to two annular pressure sensors are installed in each independent well section separated by the interlayer packer, mounted on the outer wall of the outer casing, to monitor the pressure at the casing-cement sheath interface.

6. A method for staged sealing of a carbon dioxide injection well at two interfaces, based on the repairable grouting system for a carbon dioxide injection well at two interfaces as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Wellbore preparation and double casing installation; After drilling is completed, the well is washed, the rock wall is repaired, and a double casing is installed. Step 2: Initial cementing; Pump carbon dioxide corrosion resistant cement slurry into the annular space between the outer casing and the wellbore rock strata. During the cementing process, maintain nitrogen positive pressure curing in the grouting channel until the cement sheath initially sets. Step 3: Primary interface sealing; After the cement has initially set, a supercritical carbon dioxide-resistant expanding nitrile latex grout is pumped into the micro-gap at the casing-cement ring interface through the primary grouting hole at low pressure. After the grout has solidified, a flexible sealing layer is formed at the casing-cement ring interface. Step 4: Secondary interface sealing; After the flexible sealing layer has cured, nano-silicon-alkali activated mineral powder composite grout is pumped into the well wall rock strata outside the cement sheath through the secondary grouting hole. After the grout has cured, it forms a modified rock mass in the well wall rock strata. Step 5: Seal quality inspection and baseline database establishment; Sonic variable density logging is used to measure each independent well section along the wellbore. After the test is qualified, the online monitoring equipment is started to collect normal operating data and establish an initial benchmark database for each independent well section. Step 6: Online monitoring and targeted remediation during carbon dioxide injection; After the injection well is started, the online monitoring equipment continues to work, transmitting the detection results to the control unit in real time. When it is determined that the sealing performance of a certain part has deteriorated, an early warning is issued, and the corresponding grouting section is switched through the wellhead control valve to inject the corresponding sealing material for repair.

7. The dual-interface staged sealing method for carbon dioxide injection wells according to claim 6, characterized in that, In step 5, the evaluation criteria for acoustic variable density logging are as follows: record the amplitude of the first wave of acoustic waves. If the relative amplitude of the first wave is ≤20%, it is judged as a high-quality cementation of the flexible sealing layer; 20%~40% is qualified; and greater than 40% is unqualified. The subsequent formation wave density display shows that if a continuous and clear formation wave phase axis is present on the VDL chart, the modified rock mass is considered to be well cemented; if the formation signal wave is weak or chaotic, the modified rock mass is considered to be poorly cemented.

8. The dual-interface staged sealing method for carbon dioxide injection wells according to claim 6, characterized in that, In step 6, a two-level judgment and graded alarm mechanism is adopted: when a single parameter fluctuates, it is only marked and no alarm is triggered; if the annular pressure rises abnormally and is accompanied by a change in temperature at the corresponding location, it is judged as a real leak and an alarm is triggered; after the warning signal is issued, there is no need to shut down the well. If the flexible sealing layer leaks, expandable nitrile latex slurry is re-injected for sealing. If the modified rock mass leaks, nano-silicon-alkali activated mineral powder composite slurry is re-injected for reinforcement. After the repair is completed, the sealing quality is re-tested.

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