Coal mine low permeability sandstone ground water shutoff and water reduction method based on co2 sequestration utilization

Abstract

The application discloses a coal mine low-permeability sandstone ground water plugging and water reduction method based on sealing utilization, and specifically implements the following steps: step 1, arranging a ground injection well and a pumping and observing integrated well according to parameters of a treatment area; step 2, determining a drilling structure of the injection well and the pumping and observing integrated well; step 3, preparing a calcium hydroxide aqueous solution and an industrial waste gas CO2 aqueous solution; step 4, sequentially injecting the calcium hydroxide aqueous solution and the CO2 aqueous solution into the treatment area, and adjusting injection parameters and determining an end time through monitoring results of the pumping and observing integrated well in the injection process, and ending the water plugging and water reduction work. The application solves the problems of the prior art, such as large viscosity of a cement-based grouting material, difficulty in entering low-permeability sandstone micropores, only macroscopic fissure plugging, poor plugging effect, underground water pollution caused by chemical grouting and unreasonable application of industrial waste gas CO2.

Description

Technical Field

[0001] This invention belongs to the field of coal mine water hazard prevention and control. In the field of cross-disciplinary technology of storage and utilization, it involves based on Methods for water plugging and reduction on low-permeability sandstone surfaces in coal mines that are sealed and utilized. Background Technology

[0002] Low-permeability water-bearing rock strata are widely distributed in coal mines. These strata have low porosity and weak permeability. Existing water plugging and treatment technologies mostly adopt methods such as cement-based grouting, chemical grouting, or microbial mineralization.

[0003] However, existing technologies have the following significant drawbacks: cement-based grouting materials have high viscosity, making it difficult to penetrate the micropores of low-permeability sandstone, and can only seal macroscopic cracks with poor sealing effect; chemical grouting materials are costly and easily introduce corrosive ions, causing groundwater pollution; microbial mineralization processes are complex, costly, and have poor on-site adaptability, making them difficult to apply on a large scale in engineering projects. Meanwhile, a large amount of CO2 waste gas generated in industrial production is directly emitted, failing to achieve resource utilization and geological storage.

[0004] Therefore, it is necessary to propose a technical method that combines CO2 sequestration and utilization with water blocking and reduction in low-permeability sandstone in coal mines, so as to provide an integrated technical solution for coal mine water hazard control and carbon emission reduction. Summary of the Invention

[0005] The purpose of this invention is to provide a method based on The method for sealing and utilizing low-permeability sandstone in coal mines to plug and reduce water flow solves the problems of existing technologies, such as the high viscosity of cement-based grouting materials, which makes it difficult to penetrate the micropores of low-permeability sandstone and can only seal macroscopic cracks with poor sealing effect, groundwater pollution caused by chemical grouting, and the unreasonable use of industrial waste gas CO2.

[0006] The technical solution adopted in this invention is based on The method for water plugging and reduction on low-permeability sandstone surfaces in sealed and utilized coal mines shall be implemented according to the following steps: Step 1: Determine the layout of surface injection wells and integrated pumping and observation wells based on the parameters of the treatment area; Step 2: Determine the drilling structure of the injection well and the integrated pumping and observation well; Step 3: Prepare calcium hydroxide aqueous solution and industrial waste gas CO2 aqueous solution; Step 4: Inject calcium hydroxide aqueous solution and CO2 aqueous solution into the treatment area one after another. During the injection process, adjust the injection parameters and determine the end time by monitoring the results of the integrated pumping and observation well, and end the water blocking and water reduction work.

[0007] Preferably, the parameters of the treatment area include the length A of the treatment range, the thickness of the target aquifer, the permeability coefficient K of the target aquifer, and the hydrostatic pressure P1 of the target aquifer.

[0008] Preferably, in step 1, within the length A of the treatment area, the injection wells and the integrated pumping and observation wells are arranged in two parallel rows, and the row spacing M between the injection wells and the integrated pumping and observation wells is calculated according to formula (1): (1) Within the length A of the treatment area, multiple injection wells are set up in a row, and the distance L between two adjacent injection wells is calculated according to formula (2): (2) Where P2 is the injection pressure of the injection well, in MPa; K is the permeability coefficient of the target aquifer, in m / d; and L is the well spacing, in m. Within the length A of the treatment area, multiple integrated pumping and observation wells are set up in a row, and the distance N between two adjacent integrated pumping and observation wells is 1 / 2 of the distance L between injection wells.

[0009] Preferably, in step 1, within the treatment area, the injection well is arranged in the direction of the natural flow of groundwater (D), and the integrated pumping and observation well is arranged opposite to the direction of the inflow.

[0010] Preferably, step 2 specifically involves: drilling injection wells and integrated pumping and observation wells according to the layout positions determined in step 1; drilling injection holes and integrated pumping and observation holes at the locations of the injection wells and integrated pumping and observation wells; installing casings in the injection holes and integrated pumping and observation holes; the range of the casings in the injection holes and integrated pumping and observation holes is from the hole opening to 2m below the top plate of the aquifer; and the effective water passage section is from the bottom of the casing to 5m below the bottom plate of the aquifer; the diameter of the bare hole in the effective water passage section is not less than 94mm; and a filter pipe is installed in the effective water passage section.

[0011] Preferably, in step 3, both the calcium hydroxide aqueous solution and the industrial waste gas CO2 aqueous solution are saturated solutions. The calcium hydroxide aqueous solution is prepared by adding water to quicklime, and the clear liquid at the top is taken after precipitation and filtration. The source of CO2 is industrial waste gas, and CO2 is injected into the water until the solution pH=4.

[0012] Preferably, in step 4, the calcium hydroxide aqueous solution and CO2 aqueous solution are injected sequentially into the treatment area as follows: The saturated aqueous solutions of Ca(OH)₂ and CO₂ prepared in step 3 are injected into the injection well sequentially. The injection pressure of the injection well is three times the hydrostatic pressure of the target aquifer. Ca(OH)₂ and CO₂ undergo the reaction shown in equation 3 within the rock pores, and the resulting CaCO₃ precipitates within the rock strata, sealing the tiny voids. Ca(OH)2+CO2=CaCO3↓+H2O (3).

[0013] Preferably, in step 4, adjusting the injection parameters based on the integrated well monitoring results during the injection process specifically involves: Simultaneously, water is pumped through the integrated pumping and monitoring well, with a monitoring time interval set to no more than 10 minutes. After the injection of Ca(OH)2 saturated aqueous solution begins, water is pumped through the integrated pumping and monitoring well according to the set monitoring time interval, and the pH and calcium ion concentration of the water sample are monitored. After the injection of Ca(OH)2 saturated aqueous solution, when the pH of the water sample is monitored to be >12 or the calcium ion concentration is monitored to be >400 mg / L, the injection of CO2 saturated solution begins, and monitoring continues. When the pH is monitored to be <10 or the calcium ion concentration is monitored to be <50 mg / L, the Ca(OH)2 saturated solution is re-injected, and the cycle is repeated until the end mechanism is reached.

[0014] Preferably, the termination mechanism in step 4 is as follows: when the single-hole pumping capacity of the integrated pumping well is less than 2m³. 3 When the water injection and pumping stop at / h, the water blocking and reduction work is completed.

[0015] The beneficial effects of this invention are: This invention eliminates the need for traditional large-particle, high-viscosity grouting materials or complex mineralization processes. Instead, it utilizes the in-situ reaction of saturated calcium hydroxide clarified solution with a saturated CO2 carbonate solution from industrial waste gas to fill the tiny voids in low-permeability rock formations with calcium carbonate crystals. This addresses the difficulty of grout diffusion in low-permeability rock formations from a material properties perspective. The simultaneous injection and extraction mode of the injection well and the integrated extraction and observation well creates a forced seepage field, ensuring precise and controllable sealing coverage. The integrated design of the extraction and observation wells eliminates the need for separate observation wells; the reaction progress can be determined by monitoring parameters such as pH value and calcium ion concentration, eliminating the need for tracers and significantly simplifying the construction process and reducing treatment costs. It organically combines CO2 sequestration and utilization with coal mine water hazard control, achieving permanent mineralization and sequestration of industrial waste gas CO2, resulting in significant safety, economic, and environmental benefits. The surface construction process is simple, highly controllable, and efficient, making it suitable for large-scale advanced water blocking and reduction projects in coal mines. After sealing, it significantly reduces formation permeability and greatly reduces water inflow at the mine face, demonstrating remarkable treatment effects. Attached Figure Description

[0016] Figure 1 This invention is based on A flowchart of a method for water plugging and reduction on low-permeability sandstone surfaces in sealed and utilized coal mines; Figure 2 This invention is based on A plan view of the layout of injection wells and integrated pumping and observation wells in the water plugging and reduction method for low-permeability sandstone surfaces in coal mines that are sealed and utilized; Figure 3 This invention is based on A cross-sectional view of the layout of injection wells and integrated pumping and observation wells in the water plugging and reduction method for low-permeability sandstone surfaces in coal mines that are sealed and utilized.

[0017] As shown in the figure: B. Water injection hole, C. Integrated extraction and observation hole, E. Water-proof layer, F. Target aquifer. Detailed Implementation

[0018] The following detailed description is provided in conjunction with specific implementation methods.

[0019] Example 1 This invention is based on The process of water plugging and reduction method for low-permeability sandstone surface in sealed coal mines is as follows: Figure 1 As shown, the specific steps are as follows: Step 1: Determine the layout of surface injection wells and integrated pumping and observation wells based on the parameters of the treatment area; Step 2: Determine the drilling structure of the injection well and the integrated pumping and observation well; Step 3: Prepare calcium hydroxide aqueous solution and industrial waste gas CO2 aqueous solution; Step 4: Inject calcium hydroxide aqueous solution and CO2 aqueous solution into the treatment area one after another. During the injection process, adjust the injection parameters and determine the end time by monitoring the results of the integrated pumping and observation well, and end the water blocking and water reduction work.

[0020] Example 2 This invention is based on The process of water plugging and reduction method for low-permeability sandstone surface in sealed coal mines is as follows: Figure 1 As shown, the specific steps are as follows: Step 1: Determine the layout of surface injection wells and integrated pumping and observation wells based on the parameters of the treatment area, specifically as follows: The parameters of the treatment area include the length A of the treatment range, the thickness of the target aquifer, the permeability coefficient K of the target aquifer, and the hydrostatic pressure P1 of the target aquifer.

[0021] like Figure 2 and Figure 3 As shown, within the length A of the treatment area, the injection wells and the integrated pumping and observation wells are arranged in two parallel rows. The row spacing M between the injection wells and the integrated pumping and observation wells is calculated according to formula (1): (1) Within the length A of the treatment area, multiple injection wells are set up in a row, and the distance L between two adjacent injection wells is calculated according to formula (2): (2) Where P2 is the injection pressure of the injection well, in MPa; K is the permeability coefficient of the target aquifer, in m / d; and L is the well spacing, in m. Within the length A of the treatment area, multiple integrated pumping and observation wells are set up in a row, and the distance N between two adjacent integrated pumping and observation wells is 1 / 2 of the distance L between injection wells.

[0022] Within the treatment area, injection wells will be arranged in the direction of the natural flow of groundwater, D, and integrated pumping and observation wells will be arranged in the opposite direction of the flow. Step 2: Determine the drilling structure of the injection well and the integrated pumping and observation well; Step 3: Prepare calcium hydroxide aqueous solution and industrial waste gas CO2 aqueous solution; Step 4: Inject calcium hydroxide aqueous solution and CO2 aqueous solution into the treatment area one after another. During the injection process, adjust the injection parameters and determine the end time by monitoring the results of the integrated pumping and observation well, and end the water blocking and water reduction work.

[0023] Example 3 This invention is based on The process of water plugging and reduction method for low-permeability sandstone surface in sealed coal mines is as follows: Figure 1 As shown, the specific steps are as follows: Step 1: Determine the layout of surface injection wells and integrated pumping and observation wells based on the parameters of the treatment area, specifically as follows: The parameters of the treatment area include the length A of the treatment range, the thickness of the target aquifer, the permeability coefficient K of the target aquifer, and the hydrostatic pressure P1 of the target aquifer.

[0024] like Figure 2 As shown, within the length A of the treatment area, the injection wells and the integrated pumping and observation wells are arranged in two parallel rows. The row spacing M between the injection wells and the integrated pumping and observation wells is calculated according to formula (1): (1) Within the length A of the treatment area, multiple injection wells are set up in a row, and the distance L between two adjacent injection wells is calculated according to formula (2): (2) Where P2 is the injection pressure of the injection well, in MPa; K is the permeability coefficient of the target aquifer, in m / d; and L is the well spacing, in m. Within the length A of the treatment area, multiple integrated pumping and observation wells are set up in a row, and the distance N between two adjacent integrated pumping and observation wells is 1 / 2 of the distance L between injection wells.

[0025] Within the treatment area, injection wells will be arranged in the direction of the natural flow of groundwater, D, and integrated pumping and observation wells will be arranged in the opposite direction of the flow. Step 2: Determine the drilling structure of the injection well and the integrated pumping and observation well. Specifically, follow the layout of the injection well and the integrated pumping and observation well as determined in Step 1, such as... Figure 3As shown, injection wells and integrated pumping and observation wells are drilled. Injection holes and integrated pumping and observation holes are drilled at the locations of the injection wells and integrated pumping and observation wells, respectively. The injection holes and integrated pumping and observation holes pass through the aquitard E and the target aquifer F from the ground to 5m below the bottom plate of the aquifer. Casings are installed in the injection holes and integrated pumping and observation holes. The range of the casings in the injection holes and integrated pumping and observation holes is from the hole opening to 2m below the top plate of the aquifer. The effective water passage section is from the bottom of the casing to 5m below the bottom plate of the aquifer. The diameter of the bare hole in the effective water passage section is not less than 94mm. A filter pipe is installed in the effective water passage section. Step 3: Prepare calcium hydroxide aqueous solution and industrial waste gas CO2 aqueous solution; Step 4: Inject calcium hydroxide aqueous solution and CO2 aqueous solution into the treatment area one after another. During the injection process, adjust the injection parameters and determine the end time by monitoring the results of the integrated pumping and observation well, and end the water blocking and water reduction work.

[0026] Example 4 This invention is based on The process of water plugging and reduction method for low-permeability sandstone surface in sealed coal mines is as follows: Figure 1 As shown, the specific steps are as follows: Step 1: Determine the layout of surface injection wells and integrated pumping and observation wells based on the parameters of the treatment area, specifically as follows: The parameters of the treatment area include the length A of the treatment range, the thickness of the target aquifer, the permeability coefficient K of the target aquifer, and the hydrostatic pressure P1 of the target aquifer.

[0027] like Figure 2 As shown, within the length A of the treatment area, the injection wells and the integrated pumping and observation wells are arranged in two parallel rows. The row spacing M between the injection wells and the integrated pumping and observation wells is calculated according to formula (1): (1) Within the length A of the treatment area, multiple injection wells are set up in a row, and the distance L between two adjacent injection wells is calculated according to formula (2): (2) Where P2 is the injection pressure of the injection well, in MPa; K is the permeability coefficient of the target aquifer, in m / d; and L is the well spacing, in m. Within the length A of the treatment area, multiple integrated pumping and observation wells are set up in a row, and the distance N between two adjacent integrated pumping and observation wells is 1 / 2 of the distance L between injection wells.

[0028] Within the treatment area, injection wells will be arranged in the direction of the natural flow of groundwater, D, and integrated pumping and observation wells will be arranged in the opposite direction of the flow. Step 2: Determine the drilling structure of the injection well and the integrated pumping and observation well. Specifically, follow the layout of the injection well and the integrated pumping and observation well as determined in Step 1, such as... Figure 3 As shown, injection wells and integrated pumping and observation wells are drilled. Injection holes and integrated pumping and observation holes are drilled at the locations of the injection wells and integrated pumping and observation wells, respectively. The injection holes and integrated pumping and observation holes pass through the aquitard E and the target aquifer F from the ground to 5m below the bottom plate of the aquifer. Casings are installed in the injection holes and integrated pumping and observation holes. The range of the casings in the injection holes and integrated pumping and observation holes is from the hole opening to 2m below the top plate of the aquifer. The effective water passage section is from the bottom of the casing to 5m below the bottom plate of the aquifer. The diameter of the bare hole in the effective water passage section is not less than 94mm. A filter pipe is installed in the effective water passage section. Step 3, prepare calcium hydroxide aqueous solution and industrial waste gas CO2 aqueous solution, specifically as follows: Both the calcium hydroxide aqueous solution and the industrial waste gas CO2 aqueous solution are saturated solutions. The calcium hydroxide aqueous solution is prepared by adding water to quicklime, and the clear liquid at the top is collected after precipitation and filtration. The CO2 source is industrial waste gas, and CO2 is injected into the water until the solution pH=4. Step 4: Inject calcium hydroxide aqueous solution and CO2 aqueous solution into the treatment area one after another. During the injection process, adjust the injection parameters and determine the end time by monitoring the results of the integrated pumping and observation well, and end the water blocking and water reduction work.

[0029] Example 5 This invention is based on The process of water plugging and reduction method for low-permeability sandstone surface in sealed coal mines is as follows: Figure 1 As shown, the specific steps are as follows: Step 1: Determine the layout of surface injection wells and integrated pumping and observation wells based on the parameters of the treatment area, specifically as follows: The parameters of the treatment area include the length A of the treatment range, the thickness of the target aquifer, the permeability coefficient K of the target aquifer, and the hydrostatic pressure P1 of the target aquifer.

[0030] like Figure 2 As shown, within the length A of the treatment area, the injection wells and the integrated pumping and observation wells are arranged in two parallel rows. The row spacing M between the injection wells and the integrated pumping and observation wells is calculated according to formula (1): (1) Within the length A of the treatment area, multiple injection wells are set up in a row, and the distance L between two adjacent injection wells is calculated according to formula (2): (2) Where P2 is the injection pressure of the injection well, in MPa; K is the permeability coefficient of the target aquifer, in m / d; and L is the well spacing, in m. Within the length A of the treatment area, multiple integrated pumping and observation wells are set up in a row, and the distance N between two adjacent integrated pumping and observation wells is 1 / 2 of the distance L between injection wells.

[0031] Within the treatment area, injection wells will be arranged in the direction of the natural flow of groundwater, D, and integrated pumping and observation wells will be arranged in the opposite direction of the flow. Step 2: Determine the drilling structure of the injection well and the integrated pumping and observation well. Specifically, follow the layout of the injection well and the integrated pumping and observation well as determined in Step 1, such as... Figure 3 As shown, injection wells and integrated pumping and observation wells are drilled. Injection holes and integrated pumping and observation holes are drilled at the locations of the injection wells and integrated pumping and observation wells, respectively. The injection holes and integrated pumping and observation holes pass through the aquitard E and the target aquifer F from the ground to 5m below the bottom plate of the aquifer. Casings are installed in the injection holes and integrated pumping and observation holes. The range of the casings in the injection holes and integrated pumping and observation holes is from the hole opening to 2m below the top plate of the aquifer. The effective water passage section is from the bottom of the casing to 5m below the bottom plate of the aquifer. The diameter of the bare hole in the effective water passage section is not less than 94mm. A filter pipe is installed in the effective water passage section. Step 3, prepare calcium hydroxide aqueous solution and industrial waste gas CO2 aqueous solution, specifically as follows: Both the calcium hydroxide aqueous solution and the industrial waste gas CO2 aqueous solution are saturated solutions. The calcium hydroxide aqueous solution is prepared by adding water to quicklime, and the clear liquid at the top is collected after precipitation and filtration. The CO2 source is industrial waste gas, and CO2 is injected into the water until the solution pH=4. Step 4: Inject calcium hydroxide aqueous solution and CO2 aqueous solution into the treatment area in sequence. During the injection process, adjust the injection parameters and determine the timing of termination by monitoring the integrated pumping and observation wells to end the water blocking and reduction work. Specifically, the calcium hydroxide aqueous solution and CO2 aqueous solution are injected sequentially into the treatment area as follows: The saturated aqueous solutions of Ca(OH)2 and CO2 prepared in step 3 are injected into the injection well in sequence. The injection pressure of the injection well is three times the hydrostatic pressure of the target aquifer. Ca(OH)2 and CO2 undergo the reaction (3) in the pores of the rock strata, and the resulting CaCO3 precipitates in the rock strata to seal the tiny voids. Ca(OH)2+CO2=CaCO3↓+H2O (3).

[0032] The injection parameters are adjusted based on the monitoring results from the integrated pumping and observation well during the injection process, specifically as follows: Simultaneously, water is pumped through the integrated pumping and monitoring well, with a monitoring time interval set to no more than 10 minutes. After the injection of Ca(OH)2 saturated aqueous solution begins, water is pumped through the integrated pumping and monitoring well according to the set monitoring time interval, and the pH and calcium ion concentration of the water sample are monitored. After the injection of Ca(OH)2 saturated aqueous solution, when the pH of the water sample is monitored to be >12 or the calcium ion concentration is monitored to be >400 mg / L, the injection of CO2 saturated solution begins, and monitoring continues. When the pH is monitored to be <10 or the calcium ion concentration is monitored to be <50 mg / L, the Ca(OH)2 saturated solution is re-injected, and the cycle is repeated until the end mechanism is reached.

[0033] The termination mechanism is specifically defined as follows: when the pumping capacity of a single well in the integrated pumping and observation system is less than 2m³. 3 When the water injection and pumping stop at / h, the water blocking and reduction work is completed.

[0034] Example 6 Based on Example 5, this example selects a low-permeability water-bearing rock stratum at a depth of 400m in a coal mine as the target area for treatment, and implements it according to the following steps: 1. Arrange surface injection wells and integrated pumping and observation wells according to the parameters of the treatment area. A low-permeability aquifer with a depth of 400m in a coal mine is selected as the target treatment area. The treatment area length A is 1000m, the aquifer thickness is 100m, the maximum static head is 400m, and the aquifer permeability coefficient K=0.001m / d. Injection wells and integrated pumping and observation wells are arranged along the treatment direction, with a row spacing M of 80m, a single injection well spacing L of 380m, and an integrated pumping and observation well spacing N of 190m.

[0035] 2. Determine the drilling structure of the injection well and the integrated pumping and observation well. The casing of each well is placed 2m below the top plate of the aquifer from the wellhead. The effective water passage section is 5m below the bottom plate of the aquifer from the bottom of the casing. The diameter of the bare hole in the effective section is not less than 94mm. A filter pipe is installed in this section to prevent the well from collapsing due to prolonged water injection and pumping.

[0036] 3. Prepare calcium hydroxide aqueous solution and industrial waste gas CO2 aqueous solution. Both the prepared calcium hydroxide aqueous solution and CO2 aqueous solution are saturated solutions. The calcium hydroxide aqueous solution is prepared by adding water to quicklime. After precipitation and filtration, the clear liquid at the top is taken. The source of CO2 is industrial waste gas. CO2 is injected into the water until the solution pH=4.

[0037] 4. Saturated calcium hydroxide solution and saturated CO2 solution are injected sequentially into the treatment area. First, saturated Ca(OH)2 aqueous solution is injected, followed by saturated CO2 aqueous solution. The injection pressure of the injection well is three times the hydrostatic pressure of the target aquifer, i.e., 12 MPa. The two react in the pores of the rock strata according to Formula 3, so that calcium hydroxide and CO2 in the treatment area can fully generate calcium carbonate crystals, which fill the pores and microfractures of low-permeability sandstone in situ, achieving physical sealing of the strata. At the same time, CO2 is converted into stable calcium carbonate minerals, completing the geological sequestration of CO2. There is no secondary pollution or corrosive ion generation throughout the reaction process.

[0038] Ca(OH)2+ CO2= CaCO3↓ + H2O (3) 5. Adjust the injection parameters according to the monitoring results of the observation well. The monitoring parameters include water sample pH and calcium ion concentration. The monitoring time interval is no more than 10 minutes. After injecting Ca(OH)2 saturated solution, when pH>12 or calcium ion concentration>400mg / L, start injecting CO2 saturated solution. When pH<10 or calcium ion concentration<50mg / L, re-inject Ca(OH)2 saturated solution, and repeat the cycle.

[0039] 6. Determine the termination time based on the monitoring results of the observation wells, when the pumping rate of a single well is 2m³. 3 When the water injection and pumping stop at / h, the water blocking and reduction work is completed.

[0040] The measured water inflow in the corresponding underground working face area before treatment was 75m³. 3 After surface treatment, the water volume in the corresponding working area decreased to 18m³ / h. 3 The water reduction rate reached 76% per hour, achieving the goal of reducing water in low-permeability sandstone and also solidifying carbon dioxide, thus achieving the expected target effect.

Claims

1. Based on A method for water plugging and reduction on low-permeability sandstone surfaces in coal mines, characterized in that: The specific steps are as follows: Step 1: Determine the layout of surface injection wells and integrated pumping and observation wells based on the parameters of the treatment area; Step 2: Determine the drilling structure of the injection well and the integrated pumping and observation well; Step 3: Prepare calcium hydroxide aqueous solution and industrial waste gas CO2 aqueous solution; Step 4: Inject calcium hydroxide aqueous solution and CO2 aqueous solution into the treatment area one after another. During the injection process, adjust the injection parameters and determine the end time by monitoring the results of the integrated pumping and observation well, and end the water blocking and water reduction work.

2. The method based on claim 1 A method for water plugging and reduction on low-permeability sandstone surfaces in coal mines, characterized in that: The parameters of the treatment area include the length A of the treatment range, the thickness of the target aquifer, the permeability coefficient K of the target aquifer, and the hydrostatic pressure P1 of the target aquifer.

3. The method based on claim 2 A method for water plugging and reduction on low-permeability sandstone surfaces in coal mines, characterized in that: In step 1, within the length A of the treatment area, the injection wells and the integrated pumping and observation wells are arranged in two parallel rows, and the row spacing M between the injection wells and the integrated pumping and observation wells is calculated according to formula (1): （1） Within the length A of the treatment area, multiple injection wells are set up in a row, and the distance L between two adjacent injection wells is calculated according to formula (2): （2） Where P2 is the injection pressure of the injection well, in MPa; K is the permeability coefficient of the target aquifer, in m / d; and L is the well spacing, in m. Within the length A of the treatment area, multiple integrated pumping and observation wells are set up in a row, and the distance N between two adjacent integrated pumping and observation wells is 1 / 2 of the distance L between injection wells.

4. The method based on claim 3 A method for water plugging and reduction on low-permeability sandstone surfaces in coal mines, characterized in that: In step 1, within the treatment area, the injection well is arranged in the direction of the natural flow of groundwater, D, and the integrated pumping and observation well is arranged opposite to the direction of the inflow.

5. The method based on claim 4 A method for water plugging and reduction on low-permeability sandstone surfaces in coal mines, characterized in that: Step 2 specifically involves drilling injection wells and integrated pumping and observation wells according to the layout positions determined in Step 1. Injection holes and integrated pumping and observation holes are drilled at the locations of the injection wells and integrated pumping and observation wells, respectively. Casing is installed in the injection holes and integrated pumping and observation holes. The range of the casing in the injection holes and integrated pumping and observation holes is from the hole opening to 2m below the top plate of the aquifer, and from the bottom of the casing to 5m below the bottom plate of the aquifer, which is the effective water passage section. The diameter of the bare hole in the effective water passage section is not less than 94mm, and a filter pipe is installed in the effective water passage section.

6. The method based on claim 5 A method for water plugging and reduction on low-permeability sandstone surfaces in coal mines, characterized in that: In step 3, both the calcium hydroxide aqueous solution and the industrial waste gas CO2 aqueous solution are saturated solutions. The calcium hydroxide aqueous solution is prepared by adding water to quicklime, and the clear liquid at the top is taken after precipitation and filtration. The source of CO2 is industrial waste gas, and CO2 is injected into the water until the solution pH=4.

7. The method based on claim 6 A method for water plugging and reduction on low-permeability sandstone surfaces in coal mines, characterized in that: In step 4, the calcium hydroxide aqueous solution and CO2 aqueous solution are injected sequentially into the treatment area as follows: The saturated aqueous solutions of Ca(OH)₂ and CO₂ prepared in step 3 are injected into the injection well sequentially. The injection pressure of the injection well is three times the hydrostatic pressure of the target aquifer. Ca(OH)₂ and CO₂ undergo the reaction shown in equation 3 within the rock pores, and the resulting CaCO₃ precipitates within the rock strata, sealing the tiny voids. Ca(OH)2+CO2=CaCO3↓+H2O (3).

8. The method based on claim 7 A method for water plugging and reduction on low-permeability sandstone surfaces in coal mines, characterized in that: In step 4, adjusting the injection parameters based on the integrated well monitoring results during the injection process specifically involves: Simultaneously, water is pumped through the integrated pumping and monitoring well, with a monitoring time interval set to no more than 10 minutes. After the injection of Ca(OH)2 saturated aqueous solution begins, water is pumped through the integrated pumping and monitoring well according to the set monitoring time interval, and the pH and calcium ion concentration of the water sample are monitored. After the injection of Ca(OH)2 saturated aqueous solution, when the pH of the water sample is monitored to be >12 or the calcium ion concentration is monitored to be >400 mg / L, the injection of CO2 saturated solution begins, and monitoring continues. When the pH is monitored to be <10 or the calcium ion concentration is monitored to be <50 mg / L, the Ca(OH)2 saturated solution is re-injected, and the cycle is repeated until the end mechanism is reached.

9. The method based on claim 8 A method for water plugging and reduction on low-permeability sandstone surfaces in coal mines, characterized in that: The termination mechanism in step 4 is specifically: when the single-hole pumping capacity of the integrated pumping well is less than 2m³. 3 When the water injection and pumping stop at / h, the water blocking and reduction work is completed.

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