A method for grouting protection of a real pipe section of a gas ground extraction well in a mining area

Abstract

The application discloses a kind of real pipe section grouting protection methods of gas surface extraction well in mining area, to overcome the passive protection defects in the prior art mining area ground well protection technology, can be changed from passive resistance rock deformation into active regulation rock movement, reduce the deformation energy acting on wellbore from the root, realize the purpose of active control rock movement to protect wellbore;Based on the real-time monitoring and judgment of wellbore body strain, the timely capture and intervention of wellbore risk state can be realized, and the problem of intervention lag of traditional method can be solved;Through target area selection guided by key stratum theory and well layout design based on rock movement law, the grouting energy can be accurately applied to the key rock structure for controlling wellbore deformation, which can greatly improve the pertinence and efficiency of protection measures;Relying on the closed-loop control logic with "wellbore strain feedback" as the core, dynamic optimization and accurate stopping of grouting process can be realized, so that the protection effect can be evaluated in real time, the grouting amount is controllable, and the safety and economy of the project are improved.

Description

Technical Field

[0001] This invention relates to a protection method for gas surface extraction wells in mining areas. Specifically, it is a grouting protection method for the actual pipe section of a gas surface extraction well in mining areas, which is based on real-time monitoring and feedback of wellbore strain, dynamic triggering and control of grouting in the target rock strata delamination zone to achieve rock strata movement regulation and wellbore stress unloading. It belongs to the field of coal mine gas surface extraction engineering technology. Background Technology

[0002] Surface wells in mining-affected areas are a key engineering method for surface gas extraction in coal mines. They are vertically drilled into the overburden pressure relief zone of the coal seam to effectively extract pressure-relieved gas released during coal mining and gas enriched in the goaf. This dual function ensures safe coal mine production and facilitates the development and utilization of clean energy. However, with the widespread application of high-depth (thickness > 4m) fully mechanized mining technology in my country, the deformation and damage of the overburden "vertical three-zone" caused by mining has intensified dramatically. This has led to an unprecedented risk of breakage for surface wells traversing this area, severely restricting their long-term stable operation.

[0003] Currently, the protection of the solid casing section (i.e., the non-screen section, usually located at the top of the fracture zone and within the bending and subsidence zone) of surface wells in mining areas mainly adopts a "passive resistance" strategy, focusing on three aspects: first, strengthening the wellbore structure, such as using high-grade thick-walled casing; second, annular space compensation, i.e., increasing the borehole diameter to reserve space for deformation; and third, optimizing the cementing process, such as using tough cement slurry. However, under conditions of high mining height (>4m), the periodic fracturing and rotation of key overburden strata caused by the advancement of the working face can generate rock shear displacement on the order of tens to hundreds of millimeters. This displacement far exceeds the elastic deformation limit of steel, making the effect of simply strengthening the wellbore itself negligible; while excessively increasing the well diameter is limited by drilling technology and economic costs.

[0004] The fundamental limitation of existing protection technologies lies in their design philosophy, which attempts to make the wellbore "adapt" to or "resist" the large deformation of the rock strata that has already occurred, rather than "regulating" or "slowly releasing" the deformation energy acting on the wellbore from the source. The damage to surface wells in mining areas is essentially the result of the wellbore strain exceeding its material tolerance limits under the interaction of "rock strata-wellbore". Therefore, starting with controlling rock strata movement and reducing the deformation transmitted to the wellbore is a more fundamental "active control" approach.

[0005] Separation grouting technology provides a possibility for controlling rock strata movement. This technology injects grout into the separation fracture space formed in the mining overburden, and uses the support of the solidified grout to slow down the subsidence of the key layer, thereby affecting the entire overburden movement process. However, the direct application of traditional separation grouting technology to surface well protection has the following key technical problems: (1) Delayed grouting timing. The initiation of traditional separation grouting is mostly based on surface subsidence monitoring or empirical prediction, which cannot accurately capture the critical point when the stress state of the wellbore begins to deteriorate rapidly. It is often started only after the wellbore has been significantly damaged or even micro-fractured, missing the best time for protection intervention; (2) Decoupling of grouting target area and protection target. The selection of grouting layer fails to spatially couple with the movement of key rock strata that affect the stability of a specific wellbore (especially the key layer that controls the shear of the wellbore and the separation layer below it). The layout of grouting wells lacks quantitative design basis for specific well locations, resulting in the inefficiency of grouting effect to be transmitted to the well to be protected. If the grouting layer is selected as the key layer in the surface well screen pipe section, it will cause the grout to block the gas flow channel, resulting in surface well failure; (3) There is no closed-loop feedback between the grouting process and the well status. The grouting process is mainly controlled based on process parameters such as grouting pressure and flow rate, and it is impossible to know in real time the improvement effect of grouting measures on the stress and strain state of the protected object (well). There is no direct criterion from the well itself for when grouting reaches "sufficient" and "effective", which can easily lead to insufficient or excessive grouting. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a grouting protection method for the solid pipe section of a gas surface extraction well in a mining area. This method can transform the passive resistance to rock deformation into the active control of rock movement, thereby reducing the deformation energy acting on the wellbore from the source and achieving the purpose of actively controlling rock movement to protect the wellbore.

[0007] To achieve the above objectives, the grouting protection method for the actual pipe section of the gas surface extraction well in this mining area specifically includes the following steps:

[0008] Step 1, Construction of Collaborative Protection Zone and Well Layout Design: Arrange grouting wells near the surface wells in the mining area within the coal mine working face to provide protection for the surface wells in the mining area. Based on the key layer theory, calculate and determine the depth of the target key layer and the delamination development zone below the target key layer, and control the final hole position of the grouting well to be below the delamination development zone below the target key layer.

[0009] Step 2, Install monitoring and grouting components: Deploy distributed fiber optic strain sensors in the actual pipe section of the surface well in the mining area, and construct a targeted grouting chamber at the bottom of the grouting well;

[0010] Step 3, Real-time monitoring and grouting trigger: During the coal mining process, the strain data of the surface well section in the mining area is acquired in real time. When the grouting conditions are met, a grouting trigger signal is generated for the delamination development area.

[0011] Grouting conditions are composite triggering conditions, requiring the simultaneous fulfillment of the following two conditions:

[0012] ① The maximum shear strain value of the wellbore, as monitored in real time, reaches the warning threshold determined based on the mechanical properties of the wellbore material;

[0013] ② The rock strata fracturing events detected by the microseismic monitoring system deployed around the coal mine working face have developed to within a predetermined distance below the target key layer;

[0014] Step 4, Targeted control of grouting and closed-loop grouting stop judgment: Start the grouting pump of the grouting well according to the grouting trigger signal, and carry out grouting operation in the delamination development area. During the grouting process, the well barrel strain is continuously monitored by distributed fiber optic strain sensors.

[0015] Grouting shall be stopped when one of the following conditions is met:

[0016] ① The maximum shear strain value of the wellbore monitored in real time has dropped below the safety threshold;

[0017] ② The grouting pressure rises to the set upper limit and the grouting flow rate remains below the lower limit.

[0018] Furthermore, in Step 1, two grouting wells are arranged in the direction parallel to the working face advance relative to the surface well in the mining area. The horizontal distance between each grouting well and the surface well in the mining area is 1.0 to 1.5 times the periodic pressure step distance of the roof. The horizontal distance between each grouting well and the return airway of the working face is 0.4 to 0.5 times the cut length.

[0019] Furthermore, the grouting operation is carried out in sequence: as the coal mine working face advances, when the working face enters the advanced influence range, if the grouting conditions are met, the grouting pump of the first grouting well near the working face cut is started to carry out grouting operations in the delamination development area until the grouting cessation conditions are met; as the coal mine working face continues to advance, after the coal mine working face has passed the surface well position in the mining area, if the grouting conditions are met, the grouting pump of the second grouting well near the working face stop line is started to carry out grouting operations in the delamination development area until the grouting cessation conditions are met.

[0020] Furthermore, in Step 1, the vertical distance between the final hole position at the bottom of the grouting well and the top of the surface well screen pipe section in the mining area is 2.0 to 4.0 times the mining height of the coal seam in the working face.

[0021] Furthermore, in Step 3, the warning threshold is set to 50-60% of the yield strain of the well casing material.

[0022] Furthermore, in Step 4, the grout used in the grouting operation is a composite grout with early strength and micro-expansion characteristics. The uniaxial compressive strength of the composite grout after solidification is not less than 5MPa, and the expansion rate after 28 days is controlled between 1.0% and 2.0%.

[0023] Furthermore, the composite slurry is composed of sulfoaluminate cement, fly ash, plastic fibers, and an expansion agent.

[0024] Furthermore, in Step 2, a targeted grouting chamber is constructed at the bottom of the grouting well. High-pressure cement injection is performed in the annulus above and below the screen pipe section of the grouting well to form an upper and lower seal.

[0025] Compared with existing technologies, the grouting protection method for the solid pipe section of the gas extraction well in this mining area aims to overcome the passive protection defects of existing surface well protection technologies in mining areas. It can transform from passively resisting rock deformation to actively regulating rock movement, thereby reducing the deformation energy acting on the wellbore from the root. Based on real-time monitoring and judgment of the wellbore's strain, it can realize timely capture and intervention of the wellbore's risk status, solving the problem of delayed intervention in traditional methods. Through target area selection guided by the key layer theory and well layout design based on rock movement laws, the grouting energy can be precisely applied to the key rock structure controlling the wellbore deformation, which can significantly improve the pertinence and efficiency of protection measures. Relying on the closed-loop control logic with "wellbore strain feedback" as the core, it can realize dynamic optimization and precise stopping of the grouting process, so that the protection effect can be evaluated in real time and the grouting volume can be controlled, improving the safety and economy of the project. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the plan layout of the grouting protection surface well of the present invention;

[0027] Figure 2 This is a schematic diagram of the stratum cross-section of the grouting protection surface well of the present invention.

[0028] In the diagram: 1. Surface well in the mining area; 2. Grouting well; 3. Horizontal distance between the grouting well and the return airway of the working face; 4. Horizontal distance between the surface well in the mining area and the grouting well in the direction of working face advancement; 5. Goaf; 6. Mined coal seam; 7. Vertical distance from the end position of the grouting well to the top of the screen pipe of the surface well; 8. Target key layer; 9. Delamination development zone; 10. Solid pipe section of the surface well in the mining area; 11. Distributed fiber optic strain sensor; 12. Screen pipe section of the surface well in the mining area; 13. Screen pipe section of the grouting well; 14. Solid pipe section of the grouting well; 100. Coal mine working face; 101. Working face cut-out; 102. Working face stop-mining line; 103. Working face intake airway; 104. Working face return airway; 105. Working face cut-out length. Detailed Implementation

[0029] The present invention will be further described below using the 81203 working face of a coal mine as an example, in conjunction with the accompanying drawings.

[0030] like Figure 1 As shown, the grouting protection method for the solid pipe section of the gas surface extraction well in this mining area specifically includes the following steps:

[0031] Step 1, Engineering data collection and parameter determination: At least one grouting well (2) is arranged around the surface well (1) in the mining area of ​​the coal mine working face (100) to provide protection for the surface well (1), and the final hole position of the grouting well (2) is located below the delamination development zone (9) below the target key layer (8).

[0032] Example 81203: Coal seam mining height M=4.5m, working face cut length L1=250m. Based on on-site mine pressure observation and theoretical analysis, the periodic pressure step distance L of the roof of this working face is... p Approximately 15m. The surface section 10 of the pre-protected mining area surface well 1 is located 100m above the coal seam roof to the surface. Through analysis of the columnar, lithological, and mechanical parameters (compressive strength, elastic modulus, and layer thickness) of the overburden, and calculations based on the key layer theory, it was determined that there is a medium-grained sandstone layer with a thickness of 8.2m at approximately 135m above the coal seam roof. Its fracture distance is much greater than that of other rock layers, and it is the main key layer controlling the movement of the rock layer where the surface section 10 of the mining area surface well is located. Therefore, it is identified as the target key layer 8. The rock layer below the target key layer 8 is the delamination development zone 9. It is expected that the delamination development zone 9 will form a significant delamination zone during the mining process.

[0033] To protect the surface well 1 located within the mining-affected zone of the working face, the grouting well 2 is specifically arranged as follows:

[0034] Well site surface deployment such as Figure 1 As shown, two grouting wells 2 are arranged near the surface well 1 in the mining area, parallel to the direction of the working face advance, on both sides of the surface well 1. The horizontal distance between the two grouting wells 2 and the return airway 104 of the working face (number 3 in the figure) is designed to be 0.45L1 = 0.45 × 250m = 112.5m, where L1 is the cut-in length. The horizontal distance between the first grouting well 2 closest to the working face cut-in 101 and the surface well 1 in the mining area (number 4 in the figure) is designed to be 1.5L. p =1.5×15m = 22.5m. The horizontal distance between the second grouting well 2 near the stop line 102 of the working face and the surface well 1 in the mining area is also designed to be 22.5m.

[0035] like Figure 2As shown, the final borehole of grouting well 2 needs to penetrate the delamination development zone 9 below the target key layer 8. To ensure that the grouting operation does not affect the gas extraction function of the surface well screen section 12 of the mining area surface well 1 located in the fracture zone, the vertical distance ΔH (number 7 in the figure) between the bottom of the final borehole of grouting well 2 and the top of the surface well screen section 12 of the mining area is designed to be 4M = 4 × 4.5m = 18m.

[0036] Step 2, Install monitoring and grouting components: Install distributed fiber optic strain sensors 11 for real-time monitoring of wellbore strain in the actual pipe section 10 of the surface well 1 in the mining area, and construct a targeted grouting chamber at the bottom of the grouting well 2.

[0037] In this embodiment, during the casing installation process of the surface well 1 in the mining area, distributed fiber optic strain sensors 11 for real-time monitoring of wellbore strain are simultaneously laid in the surface well section 10 of the mining area. The distributed fiber optic strain sensors 11 use Φ3mm tight-fitting sensing optical cables, which are tightly fixed to the outer wall of the casing using equally spaced special clamps. The sensors are connected to a BOTDR / A demodulator on the surface, enabling continuous, distributed measurement of axial strain and shear strain along the entire length of the wellbore.

[0038] Example 2: Grouting well 2 adopts a two-section well structure: such as Figure 2 As shown, in the first stage, a Φ311mm drill bit was used to drill through the Quaternary loose layer to 50m below the stable bedrock surface, and a Φ244.5mm technical casing was run in and cemented to seal the aquifer. In the second stage, a Φ165.1mm drill bit was used to drill to the designed final depth. After completion, a combined grouting string was run in, the main body of which was a Φ114.3mm N80 steel grade casing. In the section corresponding to the delamination development zone 9, it was replaced with a grouting well screen section 13 of the same outer diameter. After the string reached the predetermined depth, high-pressure cementing was performed in the annulus above and below the grouting well screen section 13 to form a seal at both ends, thereby constructing a targeted grouting chamber that precisely restricts and guides the grouting channel to the delamination development zone 9.

[0039] Step 3, Real-time monitoring and grouting trigger: During the 100-meter longwall mining process in the coal mine working face, the strain data of the well shaft of the surface well section 10 in the mining area is obtained in real time. When the grouting conditions are met, a grouting trigger signal is generated for the delamination development area (9).

[0040] Grouting conditions are composite triggering conditions, requiring the simultaneous fulfillment of the following two conditions:

[0041] ① The maximum shear strain value of the wellbore, as monitored in real time, reaches the warning threshold determined based on the mechanical properties of the wellbore material;

[0042] ② The rock strata rupture event height detected by the microseismic monitoring system deployed around the coal mine working face (100) has developed to within a predetermined distance range below the target key layer (8).

[0043] During the longwall mining process in this embodiment, distributed fiber optic strain sensors 11 transmit real-time strain data from the wellbore. For the N80 grade steel casing of surface well 1 in the mining area, with an API standard minimum yield strength of 552 MPa and a steel elastic modulus of 210 GPa, the corresponding theoretical yield strain is approximately 0.263%. A warning threshold ε is set. c It is 55% of the yield strain, i.e., ε c = 0.263% × 55% ≈ 0.145%.

[0044] When the coal mine working face 100 advanced to approximately 18m from the surface well 1 in the mining area (entering the advanced influence range), the distributed fiber optic strain sensor 11 reported that the maximum shear strain of the solid pipe section 10 of the surface well in the mining area continued to increase to 0.15%, exceeding the warning threshold ε. c If the rock strata fracture event detected by the microseismic monitoring system deployed around the coal mine working face 100 has developed to within 20m below the target key layer 8, the controller generates a grouting trigger signal and starts the grouting pump of the first grouting well 2 near the working face cut 101.

[0045] Step 4, Targeted control of grouting and closed-loop grouting judgment: Start the grouting pump of grouting well 2 according to the grouting trigger signal, and carry out grouting operation in the delamination development zone 9. During the grouting process, the well barrel strain is continuously monitored by distributed optical fiber strain sensor (11).

[0046] Grouting shall be stopped when one of the following conditions is met:

[0047] ① The maximum shear strain value of the wellbore monitored in real time has dropped below the safety threshold;

[0048] ②When the grouting pressure rises to the upper limit of the set pressure and the grouting flow rate remains below the lower limit, it indicates that the delamination space has been basically filled.

[0049] In this embodiment, the grouting pump of the first grouting well 2, located near the working face cut 101, is activated. A high-performance composite grout with early strength and micro-expansion characteristics is injected into the delamination development zone 9 through the solid pipe section 14 and the screen pipe section 13 of the grouting well. The high-performance composite grout is composed of sulfoaluminate cement and fly ash mixed at a mass ratio of 1:1, with 0.1% plastic fiber (to improve crack resistance) and 8% expansion agent (to generate active support force), and a water-cement ratio of 0.45. Experiments show that the uniaxial compressive strength of the high-performance composite grout after 28 days reaches 8.2 MPa, with an expansion rate of 1.5%. According to the in-situ stress test, the minimum principal stress in the delamination development zone 9 is about 4.8 MPa, and the fracturing pressure is about 14 MPa. Therefore, the upper limit of the grouting pressure P is set to 3.36 MPa (0.7 × 4.8 MPa ≈ 3.36 MPa), and the lower limit is set to 9.8 MPa (0.7 × 14 MPa = 9.8 MPa). In actual operation, the grouting pressure P is controlled between 2.0 and 3.0 MPa, which can ensure the effective diffusion of grout and prevent the rock layer from being fractured or the grout from being lost ineffectively.

[0050] After grouting began, the wellbore strain, grouting pressure P, and grouting flow rate Q were monitored simultaneously in real time. Approximately 2 hours into grouting, the cumulative grouting volume V reached 180 m³. 3 At this point, the maximum shear strain value of the wellbore fed back by the distributed fiber optic strain sensor 11 gradually decreased from 0.15% at the time of triggering to 0.10%, which is already below the set warning threshold ε. c Once the grouting conditions are met, the controller issues a stop grouting command and shuts down the grouting pump of the first grouting well 2.

[0051] After grouting in the first grouting well 2 was stopped, the shaft strain was monitored again using a distributed fiber optic strain sensor (11). When the coal mine working face 100 advanced about 30m past the surface well 1 in the mining area, the shaft strain rose again and reached the set warning threshold ε due to the re-compaction and settlement of the rock strata behind the goaf. c Furthermore, if the microseismic monitoring system deployed around the coal mine working face 100 detects that the rock stratum fracturing event has developed to within 20m below the target critical stratum 8, the controller will generate a grouting trigger signal again and start the grouting pump of the second grouting well 2, located near the working face stop line 102, to perform grouting operations in the delamination development zone 9 to cope with the subsidence impact behind the goaf. Under the coordinated protection of the closed-loop control logic of "strain over-limit trigger → grouting intervention → strain falling back to the safe range and stopping grouting" of the two grouting wells 2, the peak strain of the wellbore of the surface well 1 in the mining area can be effectively controlled below the safe threshold throughout the entire mining period.

[0052] The grouting protection method for the actual pipe section of the gas extraction well in this mining area coordinates the spatial relationship between the surface well and the grouting well, and constructs a triggering mechanism based on real-time monitoring of the well body strain. This triggers targeted grouting for the delamination of key rock strata, and uses the real-time change feedback of well body strain to evaluate the protection effect and decide on the termination of grouting, thereby achieving active control of rock strata movement and coordinated unloading of well body stress.

[0053] The grouting protection method for the solid pipe section of the gas extraction well in this mining area involves directly deploying distributed fiber optic strain sensors on the solid pipe section of the surface well in the mining area to be protected. This enables real-time sensing of the wellbore's "health status." The grouting trigger condition is set when the wellbore strain reaches a warning threshold determined based on the mechanical properties (yield strain) of the pipe material. This can capture the critical point of deterioration of the wellbore's stress state and achieve timely grouting intervention. Scientifically designed grouting well locations and grouting layers ensure that the grout-formed support can efficiently act on key rock strata structures that affect wellbore stability, and that grouting does not affect the development of fracture zones and gas flow in the surface well screen pipe section. A real-time feedback closed loop between the grouting process and the wellbore's safety status is established. The criterion for stopping grouting is when the real-time monitored wellbore strain value drops below the safety threshold. At the same time, grouting pressure and flow rate criteria (sudden pressure increase, sharp flow decrease) are used as protective grouting stop conditions. This enables real-time quantitative evaluation of the protection effect and dynamic and precise control of the grouting volume, avoiding under-grouting or over-grouting.

Claims

1. A method for grouting protection of the solid pipe section of a gas surface extraction well in a mining area, characterized in that, Specifically, the following steps are included: Step 1, Construction of Collaborative Protection Zone and Well Layout Design: Arrange grouting wells (2) near the surface well (1) in the mining area of ​​the coal mine working face (100) to provide protection for the surface well (1). Based on the key layer theory, calculate and determine the depth of the target key layer (8) and the delamination development zone (9) below the target key layer (8). Control the final hole position of the grouting well (2) to be below the delamination development zone (9) below the target key layer (8). Step 2, Install monitoring and grouting components: Install distributed fiber optic strain sensors (11) in the actual pipe section (10) of the surface well in the mining area (1), and construct a targeted grouting chamber at the bottom of the grouting well (2); Step 3, Real-time monitoring and grouting trigger: During the mining process of the coal mine working face (100), the strain data of the well shaft of the surface well section (10) in the mining area is obtained in real time. When the grouting conditions are met, a grouting trigger signal is generated for the delamination development area (9). Grouting conditions are composite triggering conditions, requiring the simultaneous fulfillment of the following two conditions: ① The maximum shear strain value of the wellbore, as monitored in real time, reaches the warning threshold determined based on the mechanical properties of the wellbore material; ②The rock strata fracturing event height detected by the microseismic monitoring system deployed around the coal mine working face (100) has developed to within the predetermined distance range below the target key layer (8); Step 4, Targeted control of grouting and closed-loop grouting judgment: Start the grouting pump of the grouting well (2) according to the grouting trigger signal, and carry out grouting operation in the delamination development zone (9). During the grouting process, the well barrel strain is continuously monitored by the distributed optical fiber strain sensor (11). Grouting shall be stopped when one of the following conditions is met: ① The maximum shear strain value of the wellbore monitored in real time has dropped below the safety threshold; ② The grouting pressure rises to the set upper limit and the grouting flow rate remains below the lower limit.

2. The grouting protection method for the solid pipe section of a gas surface extraction well in a mining area according to claim 1, characterized in that, In Step 1, two grouting wells (2) are arranged in front of and behind the surface well (1) in the mining area along the direction parallel to the working face advance. The horizontal distance between each grouting well (2) and the surface well (1) in the mining area is 1.0 to 1.5 times the periodic pressure step distance of the roof. The horizontal distance between each grouting well (2) and the return airway (104) of the working face is 0.4 to 0.5 times the cut length.

3. The grouting protection method for the solid pipe section of a gas surface extraction well in a mining area according to claim 2, characterized in that, Grouting operations are carried out in sequence: As the coal mine working face (100) advances, when the coal mine working face (100) enters the advanced influence range, if the grouting conditions are met, the grouting pump of the first grouting well (2) near the working face cut (101) is started to carry out grouting operations in the delamination development area (9) until the grouting stop conditions are met; as the coal mine working face (100) continues to advance, after the coal mine working face (100) passes the well position of the surface well (1) in the mining area, if the grouting conditions are met, the grouting pump of the second grouting well (2) near the working face stop line (102) is started to carry out grouting operations in the delamination development area (9) until the grouting stop conditions are met.

4. The grouting protection method for the solid pipe section of a gas surface extraction well in a mining area according to claim 1, 2, or 3, is characterized in that, In Step 1, the vertical distance between the final hole position at the bottom of the grouting well (2) and the top of the surface well screen section (12) in the mining area is 2.0 to 4.0 times the mining height of the coal seam in the working face.

5. The grouting protection method for the solid pipe section of a gas surface extraction well in a mining area according to claim 1, 2, or 3, is characterized in that, In Step 3, the warning threshold is set to 50-60% of the yield strain of the well casing material.

6. The grouting protection method for the solid pipe section of a gas surface extraction well in a mining area according to claim 1, 2, or 3, is characterized in that, In Step 4, the grout used in the grouting operation is a composite grout with early strength and micro-expansion characteristics. The uniaxial compressive strength of the composite grout after solidification is not less than 5MPa, and the expansion rate after 28 days is controlled between 1.0% and 2.0%.

7. The grouting protection method for the solid pipe section of a gas surface extraction well in a mining area according to claim 6, characterized in that, The composite grout is composed of sulfoaluminate cement, fly ash, plastic fibers and an expansion agent.

8. The grouting protection method for the solid pipe section of a gas surface extraction well in a mining area according to claim 1, 2, or 3, is characterized in that, In Step 2, a targeted grouting chamber is constructed at the bottom of the grouting well (2). High-pressure cementing is performed in the annulus above and below the grouting well screen pipe section (13) to form an upper and lower seal.

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