Borehole sealing device and method based on self-expanding gel and resistivity CT monitoring feedback

Abstract

This invention relates to the field of coal seam co-sealing, and discloses a sealing device and method based on self-expanding gel and resistivity CT monitoring feedback. The device includes a display, electrically connected to a PLC controller, which is electrically connected to a cement grouting pump and a self-expanding gel injection pump. A pressure sensor and a resistivity CT scanning host are sequentially connected to one side of each of the cement grouting pump and the self-expanding gel injection pump. The side of the pressure sensor is the coal seam, within which a first double-layer rivet bag and a second double-layer rivet bag are sequentially arranged, with rivets on the outer sides of both bags. Several electrode plates are arranged within the coal seam, the first double-layer rivet bag, and the second double-layer rivet bag. A gas extraction pipe is installed within the coal seam, and a compensating grouting pipe is connected to it. This invention improves the efficiency and concentration of gas extraction from coal seam boreholes.

Description

Technical Field

[0001] This invention relates to the field of coal seam co-sealing, and more specifically, to a sealing device and method based on self-expanding gel and resistivity CT monitoring feedback. Background Technology

[0002] As shallow coal resources gradually deplete, deep coal mining will become the norm in the industry. However, deep mining involves coal seams with high gas content and high pressure, posing a serious threat to mine safety. Statistics show that in a certain area, coalbed methane resources at depths greater than 2000m amount to approximately 36.81 trillion m³, with those at depths of 1000-2000m accounting for 61.2% of the total, possessing extremely high exploitation value. Achieving efficient coalbed methane development is crucial for ensuring mining safety, promoting comprehensive resource utilization, and contributing to environmental protection.

[0003] During coal seam mining operations, the original stress balance of the coal seam is disrupted, causing the surrounding coal to fracture under stress and eventually forming a fracture zone. After the completion of gas drainage and grouting boreholes, the disturbance during drilling and the pressure relief effect can create more fractures around the boreholes, severely impacting gas drainage efficiency. To address this issue, the industry has proposed using grouting to seal the boreholes, thereby improving gas drainage efficiency and concentration. However, traditional grouting methods mostly employ a one-time grouting process, resulting in less than ideal sealing effects and limited improvement in gas drainage.

[0004] Therefore, in order to improve the gas extraction efficiency and extraction concentration of coal seam boreholes, it is urgent to find a new method for sealing gas extraction boreholes to meet the needs of underground coal mine borehole sealing. However, there are currently no effective solutions to the problems existing in the relevant technologies. Summary of the Invention

[0005] To address the problems in related technologies, this invention proposes a sealing device and method based on self-expanding gel and resistivity CT monitoring feedback, in order to overcome the aforementioned technical problems existing in the prior art.

[0006] Therefore, the specific technical solution adopted by the present invention is as follows: According to one aspect of the present invention, a sealing device based on self-expanding gel and resistivity CT monitoring feedback is provided, comprising: The display is electrically connected to the PLC controller, which is in turn electrically connected to the cement grouting pump and the self-expanding gel injection pump. A pressure sensor and a resistive CT scanning host are sequentially connected to one side of each of the cement grouting pump and the self-expanding gel injection pump. The resistive CT scanning host is used for in-hole resistivity CT scanning and, combined with the expansion characteristics of the gel material and the interaction between the coal and rock gel, inversely determines the density and resistivity of the water-reacting self-expanding composite gel material. Based on the comparison between the density and resistivity and the acceptable density and resistivity thresholds, defect areas are identified. The side of the pressure sensor is a coal seam, within which a first double-layer rivet bag and a second double-layer rivet bag are sequentially installed. Two double-layer rivet bags are equipped with fixing components on their outer sides; based on feedback data from pressure sensors, cement-based grout is injected into the first and second double-layer rivet bags via a cement grouting pump; a water-swellable composite gel material is injected between the first and second double-layer rivet bags in a single injection via a self-expanding gel injection pump; several electrode plates are installed inside the coal seam, the first and second double-layer rivet bags, and electrode plate connecting wires are installed between the electrode plates; a gas extraction pipe is installed in the coal seam for extracting gas from the coal seam, and a compensation grouting pipe is connected in the coal seam to replenish the water-swellable composite gel material in the cracks and defect areas of the coal seam through secondary grouting.

[0007] Furthermore, in order to inject cement-based grout into the first double-layer rivet pouch and the second double-layer rivet pouch, and to inject water-swellable composite gel material between the first double-layer rivet pouch and the second double-layer rivet pouch, the cement grouting pump is connected to the pressure sensor and the resistive CT scanning host in sequence through the first grouting pipe; the self-swellable gel injection pump is connected to the pressure sensor and the resistive CT scanning host in sequence through the second grouting pipe.

[0008] Furthermore, to prevent backflow in the relevant pipelines, a first one-way valve is installed on the side of the first double-layer rivet bag, a third one-way valve is installed on the side of the second double-layer rivet bag, and a second one-way valve is installed inside the coal seam.

[0009] According to another aspect of the present invention, a sealing method based on self-expanding gel and resistivity CT monitoring feedback is also provided, comprising: Prepare a water-swellable composite gel material; install, set parameters, and test the electrode array and pressure sensor in the mining-affected area.

[0010] Based on feedback data from pressure sensors, cement-based grout is injected into the first and second double-layer rivet bags using a cement grouting pump to allow the first and second double-layer rivet bags to initially expand and solidify. A water-swellable composite gel material is then injected between the first and second double-layer rivet bags using a self-expanding gel injection pump.

[0011] By performing CT scanning of the resistivity within the pore using an electrode array and a resistive CT scanning host, and combining the swelling characteristics of the gel material with the interaction between the coal and rock gel interfaces, the density and resistivity of the water-swellable composite gel material were inverted.

[0012] Based on the comparison between the density and resistivity of the water-swellable composite gel material and the acceptable density and resistivity thresholds, defect areas were identified.

[0013] Gas is extracted from the coal seam using a gas extraction pipe; and a self-expanding composite gel material is injected into the cracks and defect areas of the coal seam through a secondary grouting process using a compensating grouting pipe.

[0014] Furthermore, the sealing method based on self-expanding gel and resistivity CT monitoring feedback also includes starting a cement grouting pump and injecting cement-based grout into the first double-layer rivet bag and the second double-layer rivet bag through the first grouting pipe, and using a fastener to puncture the outer woven bag and embed it into the coal wall; after the cement-based grout has initially set, starting a self-expanding gel injection pump and injecting water-reactive self-expanding composite gel material into the closed space between the first double-layer rivet bag and the second double-layer rivet bag through the second grouting pipe.

[0015] Furthermore, the water-swellable composite gel materials include cement, slag, quartz sand, acrylamide-sodium acrylate copolymer, nano-montmorillonite, sodium carboxymethyl cellulose, ammonium persulfate, and polycarboxylic acid compounds; the cement-based slurry includes cement and quartz sand.

[0016] Furthermore, the preparation of water-swellable composite gel materials includes: Cement, slag, quartz sand, acrylamide-sodium acrylate copolymer, nano-montmorillonite, sodium carboxymethyl cellulose, ammonium persulfate, and polycarboxylic acid are added to a constant temperature mixing tank and stirred under preset constant temperature and speed conditions to obtain a pregel slurry. The pregel slurry is allowed to stand for several minutes to remove air bubbles, resulting in a water-swellable composite gel material.

[0017] Furthermore, the density and resistivity of the water-swellable composite gel material were determined by inversion, including: Using an electrode array, resistivity scans were performed at multiple time points before, during, and after the injection of the water-swellable composite gel material and during the curing process to obtain the resistivity of the water-swellable composite gel material at different times. The resistivity of the water-swellable composite gel material under different expansion states and densities was determined through prior experiments to establish the relationship between resistivity and density in order to obtain the density of the water-swellable composite gel material. Specifically, for the two-phase medium of gel and coal-rock in the borehole, the potential field satisfies the Laplace equation; based on the initial conductivity of the gel, the expansion conductivity coefficient, the expansion factor, the interfacial porosity, and the conductivity of the coal-rock matrix, a coupled model of gel expansion and interfacial density is constructed; at the same time, in order to simultaneously invert the diffusion range and density, an objective function including data fitting terms, conductivity smoothing terms, diffusion range constraint terms, expansion factor constraint terms, and density constraint terms is constructed.

[0018] Furthermore, based on the comparison between the density and resistivity of the water-swellable composite gel material and the acceptable density and resistivity thresholds, the defect areas were identified as including: When the resistivity of the water-swellable composite gel material is outside the resistivity threshold range, the corresponding area is a defect area; when the density of the water-swellable composite gel material is higher than the qualified density and a preset geometric boundary occurs, the corresponding area is a defect area.

[0019] Furthermore, during the secondary grouting, the pressure is 1.0-1.2 MPa, the volume of grout is greater than the volume of the defect area, and CT scans are performed at a fixed frequency during the grouting process to track the grout filling situation in real time.

[0020] The beneficial effects of this invention are as follows: 1. This invention uses a water-swellable composite gel material as the main sealing agent and cement-based material as the auxiliary sealing material. It is simple to operate, low in cost, safe, and effective. At the same time, it adopts a two-stage grouting method to effectively seal the secondary fractures caused by the desorption and flow of coal seam gas, which leads to the shrinkage of the coal matrix. This further improves the effect and concentration of coal seam borehole gas extraction.

[0021] 2. By combining resistivity CT scanning with borehole grouting, borehole sealing can effectively seal the roadway wall and the cracks around the borehole. At the same time, it can extract dynamic sealing throughout the entire process. It is simple to operate, low in cost, safe, and effective.

[0022] 3. The two-stage grouting method effectively seals secondary fractures caused by coal matrix shrinkage due to the desorption and flow of coal seam gas, significantly improving the efficiency and concentration of coal seam borehole gas extraction, saving coal seam gas extraction costs, and further improving coal seam mining efficiency. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the sealing device based on self-expanding gel and resistivity CT monitoring feedback according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the sealing device based on self-expanding gel and resistivity CT monitoring feedback according to an embodiment of the present invention; Figure 3 This is a flowchart of a sealing method based on self-expanding gel and resistivity CT monitoring feedback according to an embodiment of the present invention.

[0025] In the picture: 1. Display; 2. PLC controller; 3. Cement grouting pump; 4. Self-expanding gel injection pump; 5. Second grouting pipe; 6. First grouting pipe; 7. Pressure sensor; 8. Resistance CT scanning host; 9. First one-way valve; 10. First double-layer rivet bag; 11. Electrode sheet; 12. Second one-way valve; 13. Electrode connecting wire; 14. Fixing component; 15. Second double-layer rivet bag; 16. Third one-way valve; 17. Gas extraction pipe; 18. Self-expanding gel repair fluid; 19. Compensating grouting pipe; 01. Coal seam; 02. First compensating grouting pipe; 03. Second compensating grouting pipe. Detailed Implementation

[0026] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0027] According to embodiments of the present invention, a sealing device and method based on self-expanding gel and resistivity CT monitoring feedback are provided.

[0028] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments, such as... Figures 1-2As shown, according to an embodiment of the present invention, a sealing device based on self-expanding gel and resistivity CT monitoring feedback is provided, comprising: a display 1, which is electrically connected to a PLC controller 2, and the PLC controller 2 is electrically connected to a cement slurry injection pump 3 and a self-expanding gel injection pump 4 respectively; a pressure sensor 7 and a resistivity CT scanning host 8 are sequentially connected to one side of both the cement slurry injection pump 3 and the self-expanding gel injection pump 4, for in-hole resistivity CT scanning, and combined with the expansion characteristics of the gel material and the interaction between the coal and rock gel interfaces, the density and resistivity of the water-receiving self-expanding composite gel material are inverted, and the defect area is determined by comparing the results with the qualified density and resistivity thresholds; the side of the pressure sensor 7 is a coal seam 01, and a first double-layer rivet bag 10 and a second double-layer rivet bag 15 are sequentially arranged in the coal seam 01. A fastener 14, which can be a rivet or the like, is provided on the outside of the rivet bag 10 and the second double-layer rivet bag 15. Based on the feedback data of the pressure sensor 7, cement-based slurry is injected into the first double-layer rivet bag 10 and the second double-layer rivet bag 15. A water-swellable composite gel material is injected between the first double-layer rivet bag 10 and the second double-layer rivet bag 15 through a self-expanding gel injection pump 4. Several electrode plates 11 are provided in the coal seam 01, the first double-layer rivet bag 10 and the second double-layer rivet bag 15, and electrode connecting wires 13 are provided between the several electrode plates 11. A gas extraction pipe 17 is provided in the coal seam 01 for extracting gas from the coal seam 01. A compensation grouting pipe 19 is connected in the coal seam 01 to replenish the water-swellable composite gel material in the cracks and defect areas of the coal seam 01.

[0029] In one embodiment, the cement grouting pump 3 is connected to the pressure sensor 7 and the resistance CT scanning host 8 in sequence through the first grouting pipe 6; the self-expanding gel grouting pump 4 is connected to the pressure sensor 7 and the resistance CT scanning host 8 in sequence through the second grouting pipe 5, thereby enabling the injection of cement-based grout into the first double-layer rivet bag 10 and the second double-layer rivet bag 15, and the injection of water-reactive self-expanding composite gel material between the first double-layer rivet bag 10 and the second double-layer rivet bag 15.

[0030] In one embodiment, a first one-way valve 9 is provided on the side of the first double-layer rivet bag 10, a third one-way valve 16 is provided on the side of the second double-layer rivet bag 15, and a second one-way valve 12 is provided in the coal seam 01, thereby preventing backflow in the relevant pipelines.

[0031] like Figure 3 As shown, according to another embodiment of the present invention, a sealing method based on self-expanding gel and resistivity CT monitoring feedback is also provided, comprising: S1. Prepare a water-swellable composite gel material; in the mining-affected area, install, set parameters, and test the electrode array and pressure sensor 7.

[0032] S2. Based on the feedback data from the pressure sensor 7, cement-based grout is injected into the first double-layer rivet pouch 10 and the second double-layer rivet pouch 15 to allow the first double-layer rivet pouch 10 and the second double-layer rivet pouch 15 to initially expand and solidify; water-swellable composite gel material is injected between the first double-layer rivet pouch 10 and the second double-layer rivet pouch 15.

[0033] S3. The resistivity CT scan of the pore is performed by the electrode array and the resistivity CT scanning host 8. Combined with the expansion characteristics of the gel material and the interaction between the coal and rock gel interfaces, the density and resistivity of the water-swellable composite gel material are inverted.

[0034] S4. Based on the comparison results of the density and resistivity of the water-swellable composite gel material with the qualified density and resistivity threshold, the defect area is identified.

[0035] S5. Gas is extracted from coal seam 01 using gas extraction pipe 17; water-swellable composite gel material is added to the cracks and defect areas in coal seam 01 by secondary grouting using compensation grouting pipe 19. Figure 1 In the middle, 18 is a self-expanding gel repair solution. Figure 2 In the diagram, 02 is the first compensation grouting pipe, and 03 is the second compensation grouting pipe.

[0036] In one embodiment, the sealing method based on self-expanding gel and resistivity CT monitoring feedback further includes starting the cement grouting pump 3 and injecting cement-based grout into the first double-layer rivet bag 10 and the second double-layer rivet bag 15 through the first grouting pipe 6, and using the fastener 14 to puncture the outer woven bag and embed it into the coal wall; after the cement-based grout has initially set, starting the self-expanding gel injection pump 4 and injecting water-reactive self-expanding composite gel material into the closed space between the first double-layer rivet bag 10 and the second double-layer rivet bag 15 through the second grouting pipe 5.

[0037] In one embodiment, the water-swellable composite gel material contains cement, slag, quartz sand, acrylamide-sodium acrylate copolymer, nano-montmorillonite, sodium carboxymethyl cellulose, ammonium persulfate, and polycarboxylic acid compounds, while the cement-based slurry contains cement and quartz sand.

[0038] In one embodiment, the preparation of a water-swellable composite gel material includes: Cement, slag, quartz sand, acrylamide-sodium acrylate copolymer, nano-montmorillonite, sodium carboxymethyl cellulose, ammonium persulfate, and polycarboxylic acid are placed together in a constant temperature mixing tank and stirred under the set constant temperature and stirring rate to obtain a pregel slurry. The pregel slurry is left to stand for a certain period of time to allow the air bubbles to be expelled, and finally a water-swellable composite gel material is obtained.

[0039] In one embodiment, reversing the density and resistivity of the water-swellable composite gel material includes: Using an electrode array, resistivity scans were performed at multiple time points before, during, and after the injection of the water-swellable composite gel material and during the curing process. The resistivity of the material at different times was obtained. The resistivity of the water-swellable composite gel material under different expansion states and densities was measured in advance through experiments. The correlation between resistivity and density was established to obtain the density of the water-swellable composite gel material.

[0040] Specifically, for the two-phase medium of gel and coal-rock in the borehole, the potential field satisfies the Laplace equation; based on the initial conductivity of the gel, the expansion conductivity coefficient, the expansion factor, the interfacial porosity, and the conductivity of the coal-rock matrix, a coupled model of gel expansion and interfacial density is constructed; at the same time, in order to simultaneously invert the diffusion range and density, an objective function including data fitting terms, conductivity smoothing terms, diffusion range constraint terms, expansion factor constraint terms, and density constraint terms is constructed.

[0041] In one embodiment, based on the comparison between the density and resistivity of the water-swellable composite gel material and the acceptable density and resistivity thresholds, the defective areas are identified as including: When the resistivity of the water-swellable composite gel material is outside the resistivity threshold range, the corresponding area is a defect area; when the density of the water-swellable composite gel material is higher than the qualified density and a preset geometric boundary occurs, the corresponding area is a defect area.

[0042] In one embodiment, during secondary grouting, the pressure is 1.0-1.2 MPa, the volume of grout is greater than the volume of the defect area, and CT scans are performed at a fixed frequency during the grouting process to track the grout filling status in real time.

[0043] To facilitate understanding of the above technical solutions of the present invention, the working principle of the present invention in actual process will be described in detail below.

[0044] The preparation process of the water-swellable composite gel material is as follows: The proportions of cement are 40% to 50%, slag 10% to 20%, quartz sand 15% to 25%, acrylamide-sodium acrylate copolymer 1.0% to 5.0%, nano-montmorillonite 0.5% to 2.0%, sodium carboxymethyl cellulose 0.2% to 0.5%, ammonium persulfate 0.05% to 0.2%, and polycarboxylate 0.5% to 1.5%. First, all these raw materials are added to a constant-temperature mixing tank. Under constant temperature conditions of 30℃ to 40℃, the mixture is stirred at a stirring speed of 500 r / min for 5 minutes to obtain a uniform pre-gel slurry. Next, the stirred slurry is left to stand for 10 minutes to allow air bubbles to escape, thus ensuring the uniformity of the slurry. Simultaneously, cement slurry is prepared for the initial shaping of the composite structure. Cement and quartz sand are mixed in an appropriate ratio to form a cement slurry with good fluidity, ensuring that the cement slurry can be smoothly filled into the mold of the double-layer rivet bag for the initial expansion and shaping of the first double-layer rivet bag 10 and the second double-layer rivet bag 15, forming a stable expansion structure.

[0045] II. Pre-treatment of Boreholes in Mining-Affected Areas: High-pressure hydraulic slotting technology is used for borehole pre-treatment in mining-affected areas. By increasing the slotting pressure to 30-35 MPa, the slotting depth is ensured to be 10-15 times the borehole radius, while the slotting thickness is controlled within the range of 80-100 mm, forming a thickened disc-shaped slot to enhance the coverage of mining-affected fractures. After slotting, high-pressure air is used to clean the coal slag inside the borehole, ensuring no residual impurities remain, thus preventing impurities from affecting the adhesion of subsequent gel materials.

[0046] III. Installation and Testing of the Encapsulation Device: The device was installed and fixed. The gas extraction pipe 17 was made of antistatic steel braid with a diameter of 89mm. The electrode array used 12 flexible copper electrodes with a circumference of 15mm. The electrode leads, i.e., the electrode connecting wires 13, were led out of the drill hole through a waterproof sealing sleeve and connected to the resistance CT scanning host 8. The device was then installed and fixed. Finally, the parameters of the electrode array, gas concentration sensor, oxygen concentration sensor, pressure sensor 7, liquid level sensor, resistance CT scanning host 8, PLC controller 2, and system were set. The specific parameter settings were: minimum gas extraction concentration ≥20%, safe oxygen concentration ≤8%, minimum gel injection pressure ≥1.5MPa, minimum liquid level ≥10%, and real-time CT scanning. Tests and inspections were then conducted.

[0047] IV. Constructing a multi-field coupled inversion model. First, for the borehole gel ( ) and coal and rock ( For a two-phase medium, the potential field satisfies the Laplace equation:

[0048] Among them, the divergence operator The potential function describes the degree of divergence of a vector field at a point in space. Indicates the conductivity distribution. Defined by the coupled model of gel swelling and interfacial density:

[0049] In the formula, The initial conductivity of the gel is represented by k, and the expansion-conductivity coefficient is represented by k. Indicates the expansion factor. Indicates the interfacial porosity. This indicates the electrical conductivity of the coal and rock matrix.

[0050] To simultaneously invert the diffusion range and density, an objective function with multiple regularization terms is constructed:

[0051] In the formula, This represents the measured potential of the electrode array. This represents the signal obtained from a model or numerical calculation. This refers to the diffusion coefficient, interface parameters, or characteristic parameters of a certain type of medium in a real system. The gradient of the parameter field is typically used to smooth constraints. Indicates the time-dependent inflation factor. Representing different regularization coefficients, This represents the prior estimate of the diffusion range and expansion factor, where D represents the density index.

[0052] Among them, the closer the density index D is to 1, the higher the density. The specific formula is as follows:

[0053] In the formula, This represents the variance of conductivity in the gel region. This indicates the gel conductivity.

[0054] Finally, by using an electrode array to perform CT scans of the resistivity within the borehole, and to study the expansion characteristics of the gel material and the interaction between the coal and rock-gel interface, a three-dimensional image of the diffusion range and density of the sealing material around the borehole was obtained. Specifically, the resistivity was scanned at multiple time points before, during, and after gel injection using an electrode array within the borehole. Based on this data, the resistivity of the gel material under different expansion states and densities was accurately measured through experiments. The relationship between resistivity and density was established, and the expansion characteristics of the gel and the interfacial mechanical and electrical interactions with the coal and rock were also studied. Finally, the collected data is input into a nonlinear iterative inversion algorithm. This algorithm can quantitatively invert and evaluate the sealing structure and gel material's functional state in the mining-affected area, calculate the true three-dimensional resistivity distribution around the borehole, and then transform the inverted resistivity distribution into a three-dimensional density image of the sealing material. This allows for a clear and intuitive assessment of the gel's diffusion range and density. Based on the discrepancy between the measured response data and the numerical model calculation results, the algorithm iteratively corrects the model parameters, gradually bringing the calculation results closer to the measured results and obtaining the optimal parameter solution that best matches the actual working conditions. The nonlinear iterative inversion algorithm is collaboratively completed by the monitoring device, data processing unit, and calculation analysis unit. Its specific algorithm steps include the following processes: 1. Monitoring data collection: By setting up monitoring devices inside boreholes or around the sealing structure in the mining-affected area, physical response data of the sealing area can be collected in real time. These data include resistivity change signals, strain response signals, and seepage-related parameters. The collected data is then transmitted to the data processing unit.

[0055] 2. Initial parameter settings: In the calculation and analysis unit, the initial values ​​of the parameters to be inverted are set according to the specific form of the sealing structure, the type of gel material, and the actual conditions of the surrounding rock. At the same time, the corresponding physical constraint parameters are input to limit the range of reasonable values ​​of the parameters.

[0056] 3. Forward modeling and response prediction: The computational analysis unit constructs a forward model of the physical field of the sealing area based on the current model parameters, and performs numerical calculations on the diffusion, expansion and densification process of the gel material in the borehole and crack to obtain the corresponding predicted physical response results.

[0057] 4. Objective function construction and error evaluation: The predicted physical response results obtained in step 3 are compared with the measured physical response data obtained in step 1, and an objective function including data fitting terms and multiple physical constraint terms is constructed. It is used to evaluate the deviation between the current model parameters and the actual state.

[0058]

[0059] In the formula, The physical response obtained from monitoring Model response results.

[0060] 5. Parameter update and iterative calculation: Based on the changing trend of the objective function, the model parameters are updated, and steps 3 to 4 above are repeated to form a nonlinear iterative calculation process, so that the objective function value gradually decreases.

[0061] 6. Convergence judgment and result output: When the objective function changes by a certain amount or the model parameter update reaches the pre-set convergence condition, the iterative calculation stops and the model parameters obtained by inversion and the corresponding physical field response results are output. These results can be used to present the diffusion state, expansion behavior and densification degree of the sealing region.

[0062] 7. Feedback control: The results obtained from the inversion are transmitted to the control unit. These results are used to evaluate and adjust the sealing process parameters and subsequent construction plans, so as to achieve dynamic feedback and optimized control of the sealing effect.

[0063] In the specific application scenario of this invention, the monitoring data of the mining-affected area is used as the inversion constraint. The physical state of the sealing area is dynamically inverted using a nonlinear iterative inversion algorithm to achieve a quantitative assessment of the sealing effect, providing a basis for subsequent process adjustments and structural optimization.

[0064] V. Sealing: Start the cement grouting pump 3 to inject cement-based grout into the inner layer through the first grouting pipe 6. Fill the first double-layer rivet bag 10 through the first one-way valve 9 and the second double-layer rivet bag 15 through the third one-way valve 16. Then the first double-layer rivet bag 10 and the second double-layer rivet bag 15 expand, and the fixing piece 14 punctures the outer woven bag and embeds into the coal wall. The pressure sensor 7 provides real-time feedback data to control the cement grout injection. After the cement grout has initially set, inject the self-expanding gel repair liquid 18 into the sealed space between the two bags through the second grouting pipe 5. Use a pulsed circulation grouting method with a grouting time of 2 minutes and a 1-minute pause to prevent premature expansion of the gel from causing pipeline blockage.

[0065] VI. Resistivity CT Scan: Dynamic scanning is used for the sealing pores. Monitor 1 displays the CT images to determine the presence of defect areas. The judgment is based on dynamic scanning to identify sealing defect areas. By performing resistivity CT scans within the pores at different time points, the real-time inverted three-dimensional resistivity images are compared with the indoor calibrated acceptable density and resistivity thresholds. Areas with abnormally low resistivity (indicating incomplete curing) or abnormally high resistivity (indicating cavitation or shrinkage detachment), or uneven or discontinuous geometric boundaries in high-density areas, are identified as defect areas.

[0066] 7. Connect the gas extraction pipe 17 into the extraction system for gas extraction.

[0067] 8. Secondary grouting: After a certain period of extraction, the coal matrix shrinks and cracks increase due to the desorption and flow of coalbed methane. The self-expanding composite gel grout (i.e., self-expanding gel repair liquid 18) is slowly injected at low pressure through the compensation grouting pipe 19. The injection pressure is 1.0-1.2 MPa, and the grouting volume is 1.2 times the defect volume. Real-time CT scanning is performed during the grouting process to track the grout filling status.

[0068] 9. Continue gas extraction until the extraction work is completed.

[0069] This invention's sealing method uses a water-swellable composite gel material as the main sealing agent. After injection, this material slowly absorbs water and expands, tightly filling the fissures around the borehole to form a tight seal. An electrode array is pre-embedded within the sealing section. After sealing, a resistivity CT scan of the borehole is performed using the electrode array to retrieve a three-dimensional image of the diffusion range and density of the sealing material around the borehole. If a sealing defect is found, secondary grouting can be performed through a pre-embedded grouting pipe until the CT image is complete. This invention discloses a sealing device and method based on self-swellable gel and resistivity CT monitoring feedback. Using a water-swellable composite gel material as the main sealing agent and cement-based material as an auxiliary sealing material, it is simple to operate, low in cost, highly safe, and effective. The water-swellable composite gel material is injected once between the first double-layer rivet bag 10 and the second double-layer rivet bag 15 via a self-swellable gel injection pump 4, and then supplemented into the fissures and defect areas within the coal seam 01 through secondary grouting, achieving a two-stage grouting method. The two-stage grouting method effectively seals the secondary fractures caused by coal matrix shrinkage due to the desorption and flow of coal seam gas, further improving the efficiency and concentration of coal seam borehole gas extraction.

[0070] Combining resistivity CT scanning with borehole grouting effectively seals fissures on the roadway walls and around the borehole. This dynamic sealing method allows for the entire extraction process and is characterized by its simplicity, low cost, high safety, and excellent results. Furthermore, the two-stage grouting approach effectively seals secondary fissures caused by coal matrix shrinkage due to the desorption and flow of coal seam gas, further improving the efficiency and concentration of coal seam borehole gas extraction.

[0071] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "screw connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0072] 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, 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 sealing device based on self-expanding gel and resistivity CT monitoring feedback, characterized in that, include: PLC controller (2) and cement grouting pump (3) and self-expanding gel injection pump (4) electrically connected thereto. The cement grouting pump (3) and the self-expanding gel injection pump (4) are connected in sequence to a pressure sensor (7) and a resistance CT scanning host (8). The resistance CT scanning host (8) is used for CT scanning of the resistivity in the borehole. Combined with the expansion characteristics of the gel material and the interaction between the coal and rock gel interface, the density and resistivity of the water-swelling composite gel material are inverted. Based on the comparison results of the density and resistivity with the qualified density and resistivity threshold, the defect area is determined. The side of the pressure sensor (7) is a coal seam (01). A gas extraction pipe (17), a first double-layer rivet bag (10) and a second double-layer rivet bag (15) are arranged in sequence in the coal seam (01). Fixing members (14) are arranged on the outside of the first double-layer rivet bag (10) and the second double-layer rivet bag (15). Based on the feedback data from the pressure sensor (7), cement-based grout is injected into the first double-layer rivet bag (10) and the second double-layer rivet bag (15) by the cement grouting pump (3); The self-expanding gel injection pump (4) injects water-swelling composite gel material into the space between the first double-layer rivet bag (10) and the second double-layer rivet bag (15) in one go. A plurality of electrode plates (11) are provided in the coal seam (01), the first double-layer rivet bag (10) and the second double-layer rivet bag (15), and the electrode plates (11) are connected to the pressure sensor (7) through electrode plate connecting lines (13); The coal seam (01) is connected to a compensation grouting pipe (19), which replenishes the cracks and defect areas in the coal seam (01) with water-swellable composite gel material through secondary grouting.

2. The sealing device based on self-expanding gel and resistivity CT monitoring feedback according to claim 1, characterized in that, The cement grouting pump (3) is connected to the pressure sensor (7) and the resistance CT scanning host (8) in sequence through the first grouting pipe (6); The self-expanding gel injection pump (4) is connected in sequence to the pressure sensor (7) and the resistance CT scanning host (8) through the second injection pipe (5).

3. The sealing device based on self-expanding gel and resistivity CT monitoring feedback according to claim 2, characterized in that, The first double-layer rivet bag (10) is provided with a first one-way valve (9) on its side, the second double-layer rivet bag (15) is provided with a third one-way valve (16) on its side, and the coal seam (01) is provided with a second one-way valve (12).

4. A sealing method based on self-expanding gel and resistivity CT monitoring feedback, wherein the sealing device based on self-expanding gel and resistivity CT monitoring feedback described in claim 3 is used to achieve sealing, characterized in that, include: Preparation of a water-swellable composite gel material; In the area affected by mining, the electrode array and the pressure sensor (7) are installed, their parameters are set, and they are tested and inspected. Based on the feedback data from the pressure sensor (7), cement-based grout is injected into the first double-layer rivet bag (10) and the second double-layer rivet bag (15) by the cement grouting pump (3) so that the first double-layer rivet bag (10) and the second double-layer rivet bag (15) initially expand and solidify; water-reactive self-expanding composite gel material is injected into the space between the first double-layer rivet bag (10) and the second double-layer rivet bag (15) in one go by the self-expanding gel injection pump (4); The resistivity CT scan of the pore is performed by the electrode array and the resistivity CT scanning host (8), and the density and resistivity of the water-swelling composite gel material are inverted by combining the swelling characteristics of the gel material with the interaction of the coal and rock gel interface. Based on the comparison between the density and resistivity of the water-swellable composite gel material and the qualified density and resistivity thresholds, the defect area was identified. Gas is extracted from the coal seam (01) using the gas extraction pipe (17); water-swellable composite gel material is added to the cracks and defect areas in the coal seam (01) by secondary grouting using the compensation grouting pipe (19).

5. The sealing method based on self-expanding gel and resistivity CT monitoring feedback according to claim 4, characterized in that, It also includes starting the cement grouting pump (3) and injecting cement-based grout into the first double-layer rivet bag (10) and the second double-layer rivet bag (15) through the first grouting pipe (6), and using the fastener (14) to puncture the outer woven bag and embed it into the coal wall; After the cement-based grout has initially set, the self-expanding gel injection pump (4) is started and water-swelling composite gel material is injected into the closed space between the first double-layer rivet bag (10) and the second double-layer rivet bag (15) through the second grouting pipe (5).

6. The sealing method based on self-expanding gel and resistivity CT monitoring feedback according to claim 4, characterized in that, The water-swellable composite gel material includes cement, slag, quartz sand, acrylamide-sodium acrylate copolymer, nano-montmorillonite, sodium carboxymethyl cellulose, ammonium persulfate, and polycarboxylic acid system. The cement-based slurry includes cement and quartz sand.

7. The sealing method based on self-expanding gel and resistivity CT monitoring feedback according to claim 6, characterized in that, The preparation of the water-swellable composite gel material includes: Cement, slag, quartz sand, acrylamide-sodium acrylate copolymer, nano-montmorillonite, sodium carboxymethyl cellulose, ammonium persulfate, and polycarboxylic acid are added to a constant temperature mixing tank and stirred under preset constant temperature and speed conditions to obtain a pregel slurry. The pregel slurry was left to stand for several minutes to remove air bubbles, resulting in a water-swellable composite gel material.

8. The sealing method based on self-expanding gel and resistivity CT monitoring feedback according to claim 4, characterized in that, The density and resistivity of the water-swellable composite gel material described in the inverse analysis include: Using an electrode array, resistivity scans were performed at multiple time points before and after injection and during the curing process of the water-swellable composite gel material to obtain the resistivity of the water-swellable composite gel material at different times. The resistivity of the water-swellable composite gel material under different expansion states and densities was measured in advance through experiments, and the relationship between resistivity and density was established to obtain the density of the water-swellable composite gel material. Among them, for the two-phase medium of gel and coal rock in the borehole, the potential field satisfies the Laplace equation; Based on the initial electrical conductivity of the gel, the expansion electrical conductivity coefficient, the expansion factor, the interfacial porosity, and the electrical conductivity of the coal and rock matrix, a coupled model of gel expansion and interfacial density is constructed. At the same time, in order to simultaneously invert the diffusion range and density, an objective function is constructed that includes a data fitting term, an electrical conductivity smoothing term, a diffusion range constraint term, an expansion factor constraint term, and a density constraint term.

9. The sealing method based on self-expanding gel and resistivity CT monitoring feedback according to claim 4, characterized in that, The comparison between the density and resistivity of the water-swellable composite gel material and the acceptable density and resistivity thresholds identifies the defective areas as follows: When the resistivity of a water-swellable composite gel material is outside the resistivity threshold range, the corresponding region is a defect area. When the density of a water-swellable composite gel material is higher than the acceptable density and a preset geometric boundary occurs, the corresponding area is a defect area.

10. The sealing method based on self-expanding gel and resistivity CT monitoring feedback according to claim 4, characterized in that, In the secondary grouting, the pressure is 1.0-1.2 MPa, the volume of grout is greater than the volume of the defect area, and CT scans are performed at a fixed frequency during the grouting process to track the grout filling situation in real time.

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