A coal mine multi-disaster collaborative treatment method based on ground horizontal well one-hole multi-use

Abstract

The application discloses a coal mine multi-disaster collaborative management method based on one-hole multi-purpose of a ground horizontal well, collects geological condition information of a coal seam, mine pressure appearance and roof falling of an adjacent working face; according to a key layer theory of the coal seam roof falling and a first weighting limit span, determines a main key layer and a sub key layer in 30-40 times of the coal seam mining height of the coal seam roof, and constructs a ground horizontal well drilling hole in the main key layer; connects a hydraulic fracturing tool string at the end of a fracturing oil pipe, and lowers the tool string into the ground horizontal well drilling hole, realizes coal seam gas / gas extraction, coal seam hard roof weakening and gangue disposal in a goaf behind a working face in one drilling hole, realizes collaborative management of coal seam gas / gas, hard roof and coal gangue multi-disasters, and solves the technical problems that gangue ground accumulation cannot be reduced, gas extraction amount of a single hole cannot be improved and the maximum grouting amount in the goaf cannot be realized by means of the roof falling process in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of coal mine production / coal mine disaster prevention and control, and relates to a method for the coordinated management of multiple disasters in coal mines, specifically a method for the coordinated management of multiple disasters in coal mines based on a single horizontal well with multiple uses. Background Technology

[0002] Due to the geological and sedimentary conditions of coal seams, some coal mining enterprises inevitably encounter various problems during coal seam mining, including gas disasters caused by excessive coalbed methane / gas content, severe mine pressure disasters caused by hard roofs, and a series of ecological and environmental problems caused by surface gangue accumulation induced by coal seam mining. Current methods for managing hard roofs include using directional long boreholes in the mine for segmented hydraulic fracturing to weaken the hard roof and achieve disaster prevention; for coalbed methane / gas management, methods include fracturing the coal seam using horizontal wells on the surface, followed by negative pressure extraction to reduce the coalbed methane / gas content and minimize gas-related safety hazards; and methods such as crushing and mixing surface gangue, then injecting the crushed gangue into the goaf through surface boreholes to manage surface gangue and reduce the ecological and environmental problems caused by surface gangue accumulation.

[0003] Several technical challenges arose during the resolution of these issues. For instance, in the implementation of segmented hydraulic fracturing for hard roof disaster control in coal mines, it was found that the hydraulic fracturing tool string, dragged forward or backward in the borehole, could cause wear on the packer's rubber sleeve if a slightly large sand or gravel particle appeared, leading to rapid sleeve wear during implementation. Furthermore, in coal seam gas extraction, it was discovered that current borehole gas extraction primarily utilizes full-bore gas extraction, directly installing negative pressure ventilation pipes at the wellhead. This results in inadequate gas extraction at deeper boreholes, especially in long boreholes (greater than 500 meters). Even after multi-segment fracturing and subsequent gas extraction, the extraction rate did not significantly increase. Therefore, there is an urgent need for a tool capable of targeted gas extraction to improve the gas extraction rate per borehole. During the injection of gangue slurry into the goaf, the current technology generally adopts the method of drilling and grouting after the collapsed rocks in the goaf have settled and stabilized. Therefore, the amount of grout injected is relatively small. How to achieve the maximum amount of grout injected into the goaf by taking advantage of the roof collapse process is an urgent problem to be solved.

[0004] To address the aforementioned issues, the three current methods for resolving safety and environmental problems in production are essentially independent operations. There is currently no method that can simultaneously achieve coordinated management of all three problems. There is an urgent need for a multi-hazard coordinated management method based on a single horizontal well for multiple uses.

[0005] Based on current technological improvements, a horizontal well can be drilled on the surface to simultaneously achieve coalbed methane / gas extraction, weakening and treating the hard roof of the coal seam, and filling and disposing of gangue in the goaf behind the working face, thus achieving the goals of solving technical problems, coordinating disaster management, and making full use of the borehole. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a multi-hazard management method for coal mines based on a single horizontal well, thereby solving the technical problem that existing methods and equipment cannot simultaneously reduce gangue accumulation on the ground, increase gas extraction from a single well, and maximize grouting volume in the goaf by utilizing the roof collapse process.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A collaborative management method for multiple disasters in coal mines based on the multi-purpose use of a single horizontal well, specifically including the following steps;

[0009] Step 1: Collect information on the geological conditions of the coal seam, the mine pressure manifestation of adjacent working faces, and the roof collapse situation;

[0010] The geological conditions information includes lithological parameters, thickness, physical and mechanical properties, coal seam gas content, and pressure of the coal seam and overlying strata.

[0011] The roof collapse situation includes periodic pressure data of the working face, initial pressure data, working face mine pressure distribution, roof collapse situation after coal seam mining, and the development of collapse zone, caving zone, and fracture zone.

[0012] Step 2: Based on the critical layer theory of coal seam roof collapse and the initial pressure limit span, calculate and determine the main critical layer and sub-critical layer within 30 to 40 times the coal seam mining height of the coal seam roof, and drill horizontal wells on the surface in the main critical layer.

[0013] Step 3: Connect the hydraulic fracturing tool string to the end of the fracturing tubing and lower it into the surface horizontal well borehole until it reaches the bottom of the surface horizontal well borehole;

[0014] Step 4: Move the hydraulic fracturing tool string to the first predetermined fracturing position;

[0015] Step 5: Insert high-density balls into the fracturing tubing. The high-density balls enter the hydraulic fracturing tool string, and start the large-displacement fracturing pump to carry out fracturing.

[0016] Step 6: Drag the hydraulic fracturing tool string backward to the next predetermined fracturing position, return to Step 5, until all predetermined fracturing positions in the horizontal well borehole have been completed, and completely remove the hydraulic fracturing tool string from the borehole.

[0017] Step 7: Connect the coalbed methane / gas extraction tool string to the end of the fracturing tubing and lower it to the first predetermined fracturing position. Connect the fracturing tubing orifice to the external negative pressure extraction pipeline for coalbed methane / gas extraction.

[0018] Step 8: Remove the external negative pressure extraction pipeline from the fracturing tubing orifice and retract the coalbed methane / gas extraction tool string to the next predetermined fracturing position. Connect the external negative pressure extraction pipeline at the fracturing tubing orifice for extraction until extraction is completed at all predetermined fracturing positions and completely withdraw the coalbed methane / gas extraction tool string.

[0019] Step 9: Start the working face mining in the coal seam. When the roof of the key layer collapses, drill a horizontal well to the surface and lower a slurry delivery pipeline. Use the roof horizontal well to fill the goaf with gangue slurry. When the filling pressure of the slurry in the slurry delivery pipeline rises to 100%, stop grouting and withdraw from the slurry delivery pipeline.

[0020] Step 10, repeat step 9 until the coal face is fully mined;

[0021] Step 11: Use materials such as concrete, loess, and sand to seal the horizontal well borehole on the ground.

[0022] This invention also includes the following technical features:

[0023] Step 2, specifically calculating and determining the main critical strata and subcritical strata within 30 to 40 times the mining height of the coal seam roof, includes the following sub-steps:

[0024] Step a.1: Based on the collected lithological parameters and physical and mechanical property parameters, the key strata theory is used to determine all key strata within 30 to 40 times the coal seam mining height of the coal seam roof.

[0025] Step a.2: Based on the collected mechanical parameters, calculate the initial compressive limit span of each critical layer under tensile stress or the initial compressive limit span under shear stress, and determine the maximum value among all calculation results. The critical layer containing the maximum value is the primary critical layer, and the other critical layers are all subcritical layers.

[0026] Step a.1, which uses the critical stratum theory to determine all critical strata within 30 to 40 times the coal seam mining height of the roof, specifically includes the following sub-steps:

[0027] Step a.1.1: Take the first rock stratum above the coal seam as the current stratum;

[0028] Step a.1.2: Calculate the self-weight load of the current layer, and then calculate the force of each overlying rock layer above the current layer on the current layer in the direction away from the coal seam. If the calculation result of the current overlying rock layer is less than the calculation result of the previous overlying rock layer, stop the calculation and define the current overlying rock layer as the i-th key layer.

[0029] Step a.1.3: Take the i-th key layer as the current layer, and let i = i + 1, then execute step a.1.4;

[0030] Step a.1.4: Determine whether the current critical layer is within 30 to 40 times the coal seam mining height of the coal seam roof. If yes, proceed to step a.1.2; otherwise, end the process.

[0031] In step a.1.2, the self-weight load of the rock strata is determined by the following formula:

[0032] q n =γ n h n

[0033] in,

[0034] q n The self-weight load of the nth rock layer is expressed in kPa.

[0035] h n The thickness of the nth layer is expressed in meters (m).

[0036] γ n The density of the nth layer is expressed in kN / m³. 3 .

[0037] In step a.1.2, the forces exerted by each overlying rock layer on the current layer are determined by the following formula:

[0038]

[0039] In the formula:

[0040] q n | m+1 This represents the force exerted by the (m+1)th rock layer above the current layer on the current layer, in kPa.

[0041] E n Let be the elastic modulus of the nth rock layer, in GPa.

[0042] h n The thickness of the nth rock layer is expressed in meters (m).

[0043] h i The thickness of the i-th rock layer is expressed in meters.

[0044] E iLet be the elastic modulus of the i-th rock layer, in GPa;

[0045] γ i The density of the i-th layer is expressed in kN / m³. 3 ;

[0046] p m+1 The structural stress experienced by the (m+1)th layer is expressed in kPa.

[0047] Where i, m and n are all integers, and n≥1, i≥1, m≥n; the step size of i, n and m is 1.

[0048] In step a.2, the initial compression limit span under tensile stress is determined by the following formula:

[0049]

[0050] in:

[0051] l i,T , where is the ultimate span of the i-th critical layer under tensile stress, in meters;

[0052] R T The tensile strength of the rock stratum, expressed in Pa.

[0053] p represents the tectonic stress of the rock strata, with units of Pa.

[0054] q is the self-weight load of the rock strata, in Pa;

[0055] h represents the thickness of the rock strata, measured in meters (m).

[0056] In step a.2, the initial compression limit span under shear stress is determined by the following formula:

[0057]

[0058] in:

[0059] l i,T , where is the ultimate span of the i-th critical layer under shear stress, in meters;

[0060] R S The shear strength of the rock stratum is expressed in Pa.

[0061] p represents the tectonic stress of the rock strata, with units of Pa.

[0062] q is the self-weight load of the rock strata, in Pa;

[0063] h represents the thickness of the rock strata, in meters (m).

[0064] Step 2, drilling horizontal wells on the main critical layer, specifically includes the following:

[0065] Step b.1: Drill a hole on the ground using a single-hole drill, run the casing into the hole, cement the well, and wait for it to solidify.

[0066] The length of a single borehole is at least 20 meters, including the total length of the surface sand layer and the bedrock layer.

[0067] Step b.2: Drilling is carried out in the first borehole using a second borehole. Casing is then installed in the resulting second borehole, cemented, and allowed to solidify.

[0068] The second borehole reaches the upper part of the corresponding coal seam and is a vertical well borehole;

[0069] Step b.3: Drilling is carried out in the second borehole using a third borehole. Casing is run into the obtained third borehole, and partial cementing is performed to obtain a surface horizontal well.

[0070] The three-section drilling includes a build-up section and a horizontal well; the length of the casing installed in the three-section drilling is less than the length of the three-section drilling;

[0071] The diameter of the first drilling is greater than the diameter of the second drilling, and the diameter of the second drilling is greater than the diameter of the third drilling.

[0072] Step 5, specifically starting the large-displacement fracturing pump for fracturing, includes: gradually increasing the pump displacement to the maximum within 5 minutes, injecting high-pressure clean water into the fracturing tubing and maintaining it for at least 30 minutes, then gradually reducing the pump displacement until the pump is stopped, and recovering the high-density balls.

[0073] The hydraulic fracturing tool string includes a first sand-clearing pipe, a packer, a check valve, a second sand-clearing pipe, and a sand-swallowing shoe, which are connected in sequence and centrally.

[0074] Multiple water guide grooves are evenly opened along the circumference on the outer wall of the first and second sand cleaning pipes; a ball-throwing seat base is provided in the second sand cleaning pipe, which is coaxial with it. The ball-throwing seat base is cylindrical, and its inner cavity is two connected cavities. The two cavities are gradually expanding and gradually contracting along the axial direction.

[0075] The single-flow valve includes a housing. Multiple first annular grooves are equally spaced along the axial direction on the outer wall of the housing. A pair of first inclined supports are provided on the radially inner two side walls of each first annular groove. The ends of the pair of first inclined supports are close to the radially outer side of the first annular groove and the two first inclined supports form an obtuse angle. A first spring is sleeved inside the first annular groove and the first spring contacts the first inclined support.

[0076] A circular hole is provided at the center of the axial rear end of the sand-swallowing shoe.

[0077] The first annular groove is inclined relative to the shell.

[0078] The coalbed methane / gas extraction tool string includes an annular water supply and gas extraction pipe, a first composite packer, a composite check valve, a second composite packer, and a guide shoe connected in sequence at the center, forming an axial gas extraction channel;

[0079] The annular water supply and air extraction pipe includes an inner pipe and an outer pipe; the inner pipe and the outer pipe are coaxially arranged, and multiple connecting columns are arranged in the annular cavity between the inner pipe and the outer pipe, with the central axis of the connecting columns being parallel to the central axis of the inner pipe; the symmetrical side walls of the connecting columns are fixedly connected to the inner pipe and the outer pipe respectively, dividing the annular cavity into multiple first water injection channels.

[0080] The first or second composite packer includes an inner cylinder and an outer cylinder; the inner cylinder and the outer cylinder are coaxially arranged, and multiple connecting rods are arranged in the annular cavity between the inner and outer cylinders, with the central axis of the connecting rods parallel to the central axis of the inner cylinder; the symmetrical side walls of the connecting rods are fixedly connected to the inner cylinder and the outer cylinder respectively, dividing the annular cavity into multiple second water injection channels; the inner cylinder, the outer cylinder, and the connecting rods are all provided with radial through holes, which connect the inside of the inner cylinder and the outside of the outer cylinder, and a rubber sleeve is fitted on the outer side of the outer cylinder;

[0081] The composite flow valve includes a coaxially arranged outer shell and an inner shell. The outer wall of the inner shell is provided with a plurality of second annular grooves at equal intervals along the axial direction. Each second annular groove has a pair of second oblique supports on its radially outer side walls. The ends of the pair of second oblique supports are close to the radially outer side of the second annular groove and are at an obtuse angle. A second spring is sleeved inside the second annular groove and the second spring is in contact with the second oblique support.

[0082] The outer shell is provided with multiple sets of radial air extraction channels at equal intervals along the axial direction, and the radial air extraction channels in each set are evenly distributed along the circumference; the end face of the outer shell is provided with axial through holes evenly distributed along the circumference, the axial through holes are connected to the first water injection channel, and the axial through holes and the radial air extraction channels are offset in the circumference.

[0083] Step 8 involves opening the wellhead sealing cover of the first water injection channel, releasing the pressure in the expanded first and second composite packers, and removing the coalbed methane / gas extraction tool string from the borehole.

[0084] Compared with the prior art, the beneficial technical effects of this invention are:

[0085] (I) The method of the present invention can realize coalbed methane / gas extraction, weakening of hard roof of coal seam and disposal of gangue in goaf behind working face in one borehole, realizing the coordinated management of multiple disasters such as coalbed methane / gas, hard roof and gangue, and solving the technical problem that existing methods and equipment cannot simultaneously reduce gangue ground accumulation, increase gas extraction volume of single borehole and realize maximum grouting volume in goaf by means of roof collapse process.

[0086] (II) The method described in this invention realizes multiple uses of a surface horizontal well drilling. From the perspective of improving the quality and efficiency of mining production, considering the construction cost of a surface horizontal well, it greatly reduces the cost of disaster management in production and improves work efficiency.

[0087] (III) The method of the present invention is carried out entirely on the ground, which avoids the safety hazards caused by workers working underground. Furthermore, the ground operation does not affect the underground operation and can be carried out simultaneously, thus improving the overall operation efficiency.

[0088] (IV) This invention adds two sand-cleaning pipes to the existing hydraulic fracturing tool string for removing large pieces of sand and gravel, further reducing the wear of sand and gravel on the packer in the borehole; and improves the original guide shoe so that the guide shoe has the function of swallowing and returning sand.

[0089] (V) This invention improves the extraction pipeline, packer and one-way extraction valve on the basis of the existing coalbed methane / gas extraction tool string, so that the coalbed methane / gas can achieve fixed-point double-sealed one-way coalbed methane / gas extraction, improve the ability of coalbed methane directional extraction, and the utilization rate of single-hole gas extraction. Attached Figure Description

[0090] Figure 1 This is a schematic diagram of the overall construction process technology of the present invention.

[0091] Figure 2 This is a schematic diagram of the hydraulic fracturing tool string in this invention;

[0092] Figure 3 For this Figure 2 Sectional view of AA;

[0093] Figure 4 This is a schematic diagram of the one-way valve in a sealed state according to the present invention;

[0094] Figure 5 This is a schematic diagram of the structure of a one-way valve in the present invention, which is in an open state and contains water in the channel;

[0095] Figure 6 This is a schematic diagram illustrating the expansion effect of the packer in the hydraulic fracturing tool string of the present invention;

[0096] Figure 7 This is a schematic diagram of the structure of the coalbed methane / gas extraction tool string in this invention;

[0097] Figure 8 for Figure 7 BB section view;

[0098] Figure 9 for Figure 7 CC section view;

[0099] Figure 10 for Figure 7 DD section view;

[0100] Figure 11 A schematic diagram of a composite flow valve in the open state with gas in the channel;

[0101] Figure 12 A comparison chart showing the actual borehole gas production obtained using extraction tools and the simulated gas production obtained using theoretical simulation.

[0102] Figure 13 This diagram illustrates the crack propagation effect after hydraulic fracturing of the roof strata and the fracture effect of the roof strata in the goaf.

[0103] The meanings of the labels in the figure are as follows: First sand removal pipe 1, packer 3, check valve 2, packer 4, second sand removal pipe 5, sand intake shoe 6, water guide channel 7, ball-dropping seat base 8, fracturing tubing 9, annular water supply and air extraction pipe 10, first composite packer 11, composite check valve 12, second composite packer 13, guide shoe 14, forming axial air extraction channel 15;

[0104] Housing 201, first annular groove 202, first inclined support 203, first spring 204;

[0105] Inner pipe 1001, outer pipe 1002, connecting column 1003, first water injection channel 1004;

[0106] Inner cylinder 1101, outer cylinder 1102, connecting rod 1103, second water injection channel 1104, radial through hole 1105, rubber sleeve 1106;

[0107] The outer shell 1201, the inner shell 1202, the second annular groove 1203, the second inclined support 1204, the second spring 1205, the radial air extraction channel 1206, and the axial through hole 1207.

[0108] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0109] It should be noted that, unless otherwise specified, all components in this invention are those known in the art.

[0110] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0111] This invention provides a method for collaborative management of multiple disasters in coal mines based on a single horizontal well with multiple uses, specifically including the following steps;

[0112] Step 1: Collect information on the geological conditions of the coal seam, the mine pressure manifestation of adjacent working faces, and the roof collapse situation;

[0113] Geological condition information includes lithological parameters, thickness, physical and mechanical properties of the coal seam and overlying strata, coal seam gas content, and pressure.

[0114] The roof collapse situation includes the periodic pressure data of the working face, the initial pressure data, the distribution of mining pressure in the working face, the roof collapse situation after coal seam mining, and the development of the collapse zone, caving zone, and fracture zone.

[0115] Step 2: Based on the critical layer theory of coal seam roof collapse and the initial pressure limit span, calculate and determine the main critical layer and sub-critical layer within 30 to 40 times the coal seam mining height of the coal seam roof, and drill horizontal wells on the surface in the main critical layer.

[0116] Step 3: Connect the hydraulic fracturing tool string to the end of the fracturing tubing and lower it into the surface horizontal well borehole until it reaches the bottom of the surface horizontal well borehole;

[0117] Step 4: Move the hydraulic fracturing tool string to the first predetermined fracturing position;

[0118] Step 5: Insert high-density balls into the fracturing tubing 9. The high-density balls enter the hydraulic fracturing tool string, and start the large-displacement fracturing pump to carry out fracturing.

[0119] Step 6: Drag the hydraulic fracturing tool string backward to the next predetermined fracturing position, return to Step 5, until all predetermined fracturing positions in the horizontal well borehole have been completed, and completely remove the hydraulic fracturing tool string from the borehole.

[0120] Step 7: Connect the coalbed methane / gas extraction tool string to the end of the fracturing tubing 9 and lower it to the first predetermined fracturing position. Connect the orifice of the fracturing tubing 9 to the external negative pressure extraction pipeline for coalbed methane / gas extraction.

[0121] Step 8: Remove the external negative pressure extraction pipeline from the 9th orifice of the fracturing tubing, and retract the coalbed methane / gas extraction tool string to the next predetermined fracturing position. Connect the external negative pressure extraction pipeline at the 9th orifice of the fracturing tubing to perform extraction until extraction is completed at all predetermined fracturing positions, and completely withdraw the coalbed methane / gas extraction tool string.

[0122] Step 9: Start the working face mining in the coal seam. When the roof of the key layer collapses, drill a horizontal well to the surface and lower a slurry delivery pipeline. Use the roof horizontal well to fill the goaf with gangue slurry. When the filling pressure of the slurry in the slurry delivery pipeline rises to 100%, stop grouting and withdraw from the slurry delivery pipeline.

[0123] Step 10, repeat step 9 until the coal face is fully mined;

[0124] Step 11: Use materials such as concrete, loess, and sand to seal the horizontal well borehole on the ground.

[0125] In the above technical solution, in step 4, when running the fracturing tubing 9 and hydraulic fracturing tool string into the horizontal well borehole, the vertical section is run directly. In the horizontal section, water needs to be injected into the annulus between the fracturing tubing and the casing every 30 meters. The injected water returns from inside the fracturing tubing 9. The water injection also cleans the sand and gravel between the casing and the fracturing tubing 9. Large pieces of sand and gravel return to the fracturing tubing through the sand-absorbing shoe and exit the wellhead from the fracturing tubing.

[0126] In step 5, the high-density ball is a lightweight, high-strength sphere that can withstand pressures of over 40 MPa. It can float in water and enter the deepest part of the pipe, the ball-setting base 8, with the water flow, to achieve the sealing of the entire pipe and increase the water pressure inside the pipe.

[0127] In step 9, the high wear-resistant ceramic slurry conveying pipeline is lowered for two reasons: first, to improve the wear resistance of the pipeline and prevent the slurry from running out of the borehole due to the large amount of gangue slurry transported; second, to use the compression or pressure caused by the fracture of the key layer to the ceramic pipeline to make the discharge port move in time as the working face moves forward, thereby further increasing the amount of slurry injected into the goaf.

[0128] The raw material for producing gangue slurry is mainly gangue generated during coal mining and discharged to the surface. After primary and secondary crushing, it is made into particles with a diameter of less than 10mm, and then mixed with water to make gangue slurry, which is then filled into the goaf. This method primarily treats solid waste such as gangue generated during coal mining at the lowest operating cost. When the gangue slurry flows into the fracture zone of the critical fracture layer, smaller particles can be filled into the goaf along the fracture development zone. When the slurry flows behind the working face, the filling support helps to prevent the gangue slurry in the goaf from contaminating the coal face, ultimately achieving goaf filling and large-scale gangue slurry treatment.

[0129] In step 10, a 100% increase in slurry filling pressure indicates that the cracks in the goaf have been completely filled, and slurry filling can proceed to the next location.

[0130] Specifically, step 2, calculating and determining the main critical strata and subcritical strata within 30 to 40 times the mining height of the coal seam roof, includes the following sub-steps:

[0131] Step a.1: Based on the collected lithological parameters and physical and mechanical property parameters, the key strata theory is used to determine all key strata within 30 to 40 times the coal seam mining height of the coal seam roof.

[0132] Step a.2: Based on the collected mechanical parameters, calculate the initial compressive limit span of each critical layer under tensile stress or the initial compressive limit span under shear stress, and determine the maximum value among all calculation results. The critical layer containing the maximum value is the primary critical layer, and the other critical layers are all subcritical layers.

[0133] Specifically, step a.1, which uses the key strata theory to determine all key strata within 30 to 40 times the coal seam mining height of the coal seam roof, includes the following sub-steps:

[0134] Step a.1.1: Take the first rock stratum above the coal seam as the current stratum;

[0135] Step a.1.2: Calculate the self-weight load of the current layer, and then calculate the force of each overlying rock layer above the current layer on the current layer in the direction away from the coal seam. If the calculation result of the current overlying rock layer is less than the calculation result of the previous overlying rock layer, stop the calculation and define the current overlying rock layer as the i-th key layer.

[0136] Step a.1.3: Take the i-th key layer as the current layer, and let i = i + 1, then execute step a.1.4;

[0137] Step a.1.4: Determine whether the current critical layer is within 30 to 40 times the coal seam mining height of the coal seam roof. If yes, proceed to step a.1.2; otherwise, end the process.

[0138] Specifically, in step a.1.2, the self-weight load of the rock strata is determined by the following formula:

[0139] q n =γ n h n

[0140] in,

[0141] q n The self-weight load of the nth rock layer is expressed in kPa.

[0142] h n The thickness of the nth layer is expressed in meters (m).

[0143] γ n The density of the nth layer is expressed in kN / m³. 3 .

[0144] Specifically, in step a.1.2, the forces exerted by the overlying rock layers above the current layer on the current layer are determined by the following formula:

[0145]

[0146] In the formula:

[0147] q n | m+1 This represents the force exerted by the (m+1)th rock layer above the current layer on the current layer, in kPa.

[0148] E n Let be the elastic modulus of the nth rock layer, in GPa.

[0149] h n The thickness of the nth rock layer is expressed in meters (m).

[0150] h i The thickness of the i-th rock layer is expressed in meters.

[0151] E i Let be the elastic modulus of the i-th rock layer, in GPa;

[0152] γ i The density of the i-th layer is expressed in kN / m³. 3 ;

[0153] p m+1 The structural stress experienced by the (m+1)th layer is expressed in kPa.

[0154] Where i, m and n are all integers, and n≥1, i≥1, m≥n; the step size of i, n and m is 1.

[0155] Specifically, in step a.2, the initial compression limit span under tensile stress is determined by the following formula:

[0156]

[0157] in:

[0158] l i,T , where is the ultimate span of the i-th critical layer under tensile stress, in meters;

[0159] R T The tensile strength of the rock stratum, expressed in Pa.

[0160] p represents the tectonic stress of the rock strata, with units of Pa.

[0161] q is the self-weight load of the rock strata, in Pa;

[0162] h represents the thickness of the rock strata, in meters (m).

[0163] Specifically, in step a.2, the initial compression limit span under shear stress is determined by the following formula:

[0164]

[0165] in:

[0166] l i,T , where is the ultimate span of the i-th critical layer under shear stress, in meters;

[0167] R S The shear strength of the rock stratum is expressed in Pa.

[0168] p represents the tectonic stress of the rock strata, with units of Pa.

[0169] q is the self-weight load of the rock strata, in Pa;

[0170] h represents the thickness of the rock strata, in meters (m).

[0171] Specifically, step 2, drilling horizontal wells on the main key layer, includes the following:

[0172] Step b.1: Drill a hole on the ground using a single-hole drill, run the casing into the hole, cement the well, and wait for it to solidify.

[0173] The length of the first borehole should be at least 20 meters, including the total length of the surface sand layer and the bedrock layer.

[0174] Step b.2: Drilling is carried out in the first borehole using a second borehole. Casing is then installed in the resulting second borehole, cemented, and allowed to solidify.

[0175] The second borehole reaches directly to the upper part of the corresponding coal seam and is a vertical well borehole;

[0176] Step b.3: Drilling is carried out in the second borehole using a third borehole. Casing is run into the obtained third borehole, and partial cementing is performed to obtain a surface horizontal well.

[0177] Three-section drilling includes a build-up section and a horizontal well; the length of the casing installed in a three-section drilling section is less than the length of the three-section drilling section.

[0178] The diameter of the first drilling is greater than the diameter of the second drilling, and the diameter of the second drilling is greater than the diameter of the third drilling.

[0179] In the above technical solution, this cementing process ensures stable end pressure for subsequent drilling and prevents casing retraction during fracturing operations, thus guaranteeing borehole stability. Furthermore, the casing length does not extend into the fracturing or gas extraction area.

[0180] Specifically, in step 5, starting the large-displacement fracturing pump for fracturing includes: gradually increasing the pump displacement to the maximum within 5 minutes, injecting high-pressure clean water into the fracturing tubing 9 and maintaining it for at least 30 minutes, then gradually reducing the pump displacement until the pump is stopped, and recovering the high-density balls.

[0181] Specifically, the hydraulic fracturing tool string includes a first sand-clearing pipe 1, a packer 3, a check valve 2, a packer 4, a second sand-clearing pipe 5, and a sand-swallowing shoe 6, which are connected in sequence and centrally.

[0182] Multiple water guide grooves 7 are evenly opened along the circumference on the outer wall of the first sand cleaning pipe 1 and the second sand cleaning pipe 5; a ball-throwing sealing base 8 is provided in the second sand cleaning pipe 5, which is coaxial with it. The ball-throwing sealing base 8 is cylindrical, and its inner cavity is two connected cavities. The two cavities are gradually narrowing and gradually expanding along the axial direction.

[0183] The single-flow valve 2 includes a housing 201. Multiple first annular grooves 202 are equally spaced along the axial direction on the outer wall of the housing 201. Each first annular groove 202 has a pair of first inclined supports 203 on its radially inner two side walls. The ends of the pair of first inclined supports 203 are close to the radially outer side of the first annular groove 202 and the two first inclined supports 203 form an obtuse angle. A first spring 204 is sleeved inside the first annular groove 202 and contacts the first inclined support 203.

[0184] A circular hole is provided at the center of the axial rear end of the sand-swallowing shoe 6.

[0185] See Figure 2 The components of the hydraulic fracturing tool string with sand and gravel filtration function are connected by threaded connections. A cross-sectional view of the second sand-cleaning pipe 5 is shown below. Figure 3As shown, the pipe itself is thicker than the fracturing tubing 9 and the packer 4. This is to avoid the borehole wall directly abrading the outer rubber sleeve of the packer. The thicker pipe diameter can also form a better scraping effect with the borehole wall, removing some larger sand particles in advance. There are some water guide grooves 7 on the outside of the first sand cleaning pipe 1 and the second sand cleaning pipe 5, which can effectively allow clean water to pass through the first sand cleaning pipe 1 and the second sand cleaning pipe 5. The first sand cleaning pipe 1 and the second sand cleaning pipe 5 push the larger sand particles in front of them forward with the help of water. The water injected from the casing annulus returns to the fracturing tubing 9 from the sand swallowing shoe. With the help of the water thrust, the large sand particles in front of the first sand cleaning pipe 1 and the second sand cleaning pipe 5 are sent into the sand swallowing shoe 6, and then come out from the wellhead with the return water. This achieves the purpose of cleaning the large sand particles in front of the tool string during the forward movement of the hydraulic fracturing tool string.

[0186] During the retraction of the tool string, water needs to be injected into the fracturing tubing 9. The water flows out from the sand-absorbing shoe 6, and then passes through the water guide grooves 7 of the first sand-cleaning pipe 1 and the second sand-cleaning pipe 5 in sequence. The water returns to the wellhead through the annulus in the casing and fracturing tubing 9. With the help of the water flushing, large sand and gravel particles that appear during the retraction of the first sand-cleaning pipe 1 and the second sand-cleaning pipe 5 are discharged from the wellhead along with the returned water. This realizes the function of cleaning large sand and gravel during the tool string insertion and withdrawal process.

[0187] The packer 4 is cylindrical with multiple water passage holes on its wall. It is wrapped with a highly elastic rubber sleeve. When the water pressure inside the packer 4 reaches 3MPa, the rubber sleeve begins to expand. When the pressure reaches 5MPa, the rubber sleeve can reach its maximum expansion capacity and fit with the hole wall to form a set seal. Once the pressure decreases, the expanded rubber sleeve begins to shrink back until it returns to its original state.

[0188] In the check valve 2, when there is no external discharge pressure, the first spring 204 is seated on the first inclined support 203, forming a seal against the inner channel. When the external discharge pressure reaches 5MPa, the first spring 204 leaves the first inclined support 203 to form a water outlet channel. Once the pressure is less than 5MPa, the first spring 204 returns to the first inclined support 203 to seal the channel, preventing external water from returning to the check valve 2. Figure 4 The first spring 204 and the first inclined support 203 in the flow valve 2 are in close contact, and external water cannot enter the central channel through the channel. Figure 5 The water pressure from the inside to the outside in the flow valve 2 is greater than 5MPa, causing the first spring 204 to be in a state away from the first inclined support 203, and the channel contains flowing water.

[0189] In step 6, when it is necessary to retract the fracturing tool string, water needs to be injected into the fracturing tubing 9 and injected into the casing through the sand-absorbing shoe 6. The water is then returned through the annulus between the fracturing tool string and the casing 15, which carries away the large sand and gravel particles in the annulus and discharges them from the wellhead.

[0190] In step 5, the function of the ball-setting seat 8 is that when no ball is being thrown, the seat is open and water can pass through or return through the seat. However, in order for the packer 4 to achieve pressure increase, the pressure inside the entire tool string needs to be increased. By throwing a high-density ball, the water flows into the ball-setting seat 8 and completely seals the ball-setting seat 8, thus achieving pressure increase inside the tool string.

[0191] Specifically, the first annular groove 202 is inclined relative to the shell 201.

[0192] Specifically, the coalbed methane / gas extraction tool string includes an annular water supply and gas extraction pipe 10, a first composite packer 11, a composite check valve 12, a second composite packer 13, and a guide shoe 14 connected in sequence at the center, forming an axial gas extraction channel 15.

[0193] The annular water supply and air extraction pipe 10 includes an inner pipe 1001 and an outer pipe 1002; the inner pipe 1001 and the outer pipe 1002 are coaxially arranged, and a plurality of connecting posts 1003 are arranged in the annular cavity between the inner pipe 1001 and the outer pipe 1002, the central axis of the connecting post 1003 is parallel to the central axis of the inner pipe 1001; the symmetrical side walls of the connecting post 1003 are fixedly connected to the inner pipe 1001 and the outer pipe 1002 respectively, dividing the annular cavity into a plurality of first water injection channels 1004;

[0194] The first composite packer 11 or the second composite packer 13 includes an inner cylinder 1101 and an outer cylinder 1102. The inner cylinder 1101 and the outer cylinder 1102 are coaxially arranged. Multiple connecting rods 1103 are arranged in the annular cavity between the inner cylinder 1101 and the outer cylinder 1102. The central axis of the connecting rods 1103 is parallel to the central axis of the inner cylinder 1101. The symmetrical side walls of the connecting rods 1103 are fixedly connected to the inner cylinder 1101 and the outer cylinder 1102 respectively, dividing the annular cavity into multiple second water injection channels 1104. The inner cylinder 1101, the outer cylinder 1102 and the connecting rods 1103 are all provided with a radial through hole 1105. The radial through hole 1105 connects the inside of the inner cylinder 1101 and the outside of the outer cylinder 1102. A rubber sleeve 1106 is fitted on the outside of the outer cylinder 1102.

[0195] The composite flow valve 12 includes a coaxially arranged outer shell 1201 and inner shell 1202. The outer wall of the inner shell 1201 is provided with a plurality of second annular grooves 1203 at equal intervals along the axial direction. Each second annular groove 1203 has a pair of second oblique supports 1204 on its radially outer two side walls. The ends of the pair of second oblique supports 1204 are close to the radially outer side of the second annular groove 1203 and are at an obtuse angle. A second spring 1205 is sleeved inside the second annular groove 1203 and contacts the second oblique support 1204.

[0196] Multiple sets of radial air extraction channels 1206 are provided at equal intervals along the axial direction on the outer shell 1202, and the radial air extraction channels 1206 in each set are evenly distributed in the circumferential direction; axial through holes 1207 are provided on the end face of the outer shell 1202 and are evenly distributed in the circumferential direction. The axial through holes 1207 are connected to the first water injection channel 1004, and the axial through holes 1207 and the radial air extraction channels 1206 are staggered in the circumferential direction.

[0197] In the above technical solution, the cross-section of the composite flow valve 12 is as follows: Figure 10 As shown, the outermost layer of the outer shell is composed of a closed-type breathable filter membrane. The radial air extraction channel 1206 on the outer shell is the outermost channel for drawing gas from the outside into the inside. However, the gas can only enter the inside from the outside, and the gas inside cannot escape from the inside to the outside. The seal is achieved by means of the second spring 1205 and the second inclined support 1204.

[0198] Figure 11 This is a schematic diagram of the effect of the one-way suction valve 24 during suction. When the negative pressure in the radial suction channel 1206 reaches 8 kPa, the second spring 1205 moves away from the second inclined support 1204, opening the suction channel. Gas enters the radial suction channel 1206 from the outside through the opened channel to achieve suction. Once the negative pressure value is less than 5 kPa, the second spring 1205 returns to the second inclined support 1204, sealing the channel, and the gas in the radial suction channel 1206 cannot diffuse from the inside to the outside.

[0199] In addition, ensuring that the composite flow valve in the gas extraction tool covers the position of the flow valve is necessary to enable the extraction tool to completely seal the fractured area, so that the extraction tool can effectively extract the coalbed methane / gas discharged from the fracture.

[0200] The main operation of the coalbed methane / gas extraction tool string involves injecting water pressure into the first water injection channel 1004 in the annular water supply and extraction pipe 10. The water pressure then passes through the second water injection channel 1104 in the first composite packer 11 and the axial through hole 1207 in the composite check valve 12 to reach the second composite packer 13. As the pressure continues to rise, when it reaches 3 MPa, the first composite packer 11 and the second composite packer 13 begin to set. When the pressure reaches 5 MPa, the first composite packer 11 and the second composite packer 13 are completely set. Then, the water supply channel is closed, so that the pressure inside the channel remains constant, and the first composite packer 11 and the second composite packer 13 remain in a set state. After the first composite packer 11 and the second composite packer 13 are fully set, negative pressure gas extraction is achieved through the axial extraction channel 15. When the negative pressure reaches 5 kPa, the second spring 1205 in the composite check valve 12 begins to leave the second inclined support 1204, opening the channel from the extraction pipeline to the outside of the extraction tool string. When the negative pressure reaches 8 kPa, the extraction channel of the composite check valve 12 is fully opened, and the coalbed methane / gas enters the radial extraction channel 1206 of the extraction tool string from the fracturing fracture obtained in step 5. Then, it enters the axial extraction channel 15 through the composite check valve 12 and finally reaches the wellhead, realizing the extraction of coalbed methane / gas underground.

[0201] The first composite packer 11 and the second composite packer 13 have the same structure.

[0202] Specifically, step 8 involves opening the wellhead sealing cover of the first water injection channel 1004, releasing the pressure in the expanded first composite packer 11 and second composite packer 13, and removing the coalbed methane / gas extraction tool string from the borehole.

[0203] Simulation example:

[0204] To verify the gas extraction effect, the theoretical daily gas production of the borehole was predicted using the production simulation software CBM-SIM with reference to the coal seam reservoir parameters in Table 1. Simultaneously, the coalbed methane / gas extraction tool string of this invention was used to perform single-section coalbed methane / gas extraction in a borehole of a mine in the Huaibei area. The gas production of both methods is as follows: Figure 12 As shown, the better the fit between the two, the better the borehole extraction effect. This borehole extraction has achieved the ideal effect. Figure 12 The comparison results show that the extraction effect of this borehole in this section is in good agreement with the expectations, and the extraction effect of this coalbed methane / gas extraction tool string is good.

[0205] Table 1 Reservoir parameters of gas-bearing coal seams

[0206]

[0207]

[0208] Actual test example:

[0209] Case background brief:

[0210] A coal seam in a mine in Huaibei is buried at a depth of approximately 800 meters. The mined coal seam is designated as No. 8, with a thickness of 3.00 meters and an average methane content of approximately 10.00 m³. 3 This is a high-gas coal mine. The current mining face is numbered 8003. Experience from the adjacent 8001 face shows a hard roof within 60 meters above the coal seam, resulting in periodic pressure intervals of approximately 18-30 meters and initial pressure intervals of approximately 30-60 meters during coal seam advancement. During these periodic pressure intervals, the fully mechanized mining face experiences significant support resistance, severe spalling and blasting of the coal wall, and some hydraulic supports have experienced cylinder bursts and support seizures due to intense mine pressure. During coal seam mining, the amount of gangue produced is approximately 10% of the coal output. The annual production capacity of a single working face is 4 million tons per year, and the total gangue output of the entire mine is approximately 400,000 tons per year. There is an urgent need to manage the corresponding amount of gangue; otherwise, surface stockpiling would be necessary, causing damage to the surface ecological environment. This invention addresses the problems of a hard roof, high coal seam gas levels, and surface gangue stockpiling in this mine, achieving good remediation results. The specific implementation steps are as follows:

[0211] Implementation plan:

[0212] Step 1: Collect information on the geological conditions of the coal seam, the mine pressure manifestation of adjacent working faces, and the roof collapse situation;

[0213] Geological condition information includes lithological parameters, thickness, physical and mechanical properties of the coal seam and overlying strata, coal seam gas content, and pressure.

[0214] The roof collapse situation includes the periodic pressure data of the working face, the initial pressure data, the distribution of mining pressure in the working face, the roof collapse situation after coal seam mining, and the development of the collapse zone, caving zone, and fracture zone.

[0215] Step 2: Based on the critical layer theory of coal seam roof collapse, calculate and determine the main critical layer and sub-critical layer within 30 to 40 times the coal seam mining height of the coal seam roof, and drill horizontal wells on the surface in the main critical layer.

[0216] The process of drilling a horizontal well on the surface consists of three drilling operations. The first drilling operation has a diameter of 244.5 mm and a length of 25 meters, covering the total length of the surface sand layer and the bedrock layer. After the first drilling operation is completed, the casing for the first drilling operation is run in and cemented (the casing is bonded to the formation using concrete or other bonding materials). After cementing is completed, the second drilling operation (diameter 177.8 mm) begins. The diameter of the second drilling operation is generally smaller than that of the first drilling operation. The second drilling operation reaches the upper part of the corresponding coal seam and is a vertical well. After the second drilling operation is completed, cementing is performed. After the cementing is completed and solidified, the third drilling operation (diameter 139.7 mm) begins with an even smaller diameter, continuing until the final length of the horizontal well is reached. Casing is then run in and cemented (not necessarily for the entire length; this depends on the stability of the borehole).

[0217] Step 3: Connect the hydraulic fracturing tool string to the end of the fracturing tubing and lower it into the surface horizontal well borehole until it reaches the bottom of the surface horizontal well borehole;

[0218] The hydraulic fracturing tool string is lowered into the casing. In the vertical well section, the tool string can be lowered directly. When it reaches the horizontal section, the annulus pipeline is cleaned every 30 meters.

[0219] The specific steps are as follows: water is injected into the annulus of the fracturing tubing and casing. The injected water returns from inside the fracturing tubing. The water injection also cleans up the sand and gravel between the casing and the fracturing tubing. Large pieces of sand and gravel return to the fracturing tubing through the sand-absorbing shoe and then exit the wellhead from the fracturing tubing.

[0220] Step 4: Move the hydraulic fracturing tool string to the first predetermined fracturing position;

[0221] Step 5: Insert high-density balls into the fracturing tubing. The high-density balls enter the hydraulic fracturing tool string, and start the large-displacement fracturing pump to carry out fracturing.

[0222] Start the high-displacement fracturing pump and gradually increase it to the maximum pump displacement within 5 minutes. Inject high-pressure clean water into the fracturing tubing 9 and maintain it for at least 30 minutes. Then gradually reduce the pump displacement until the pump is stopped and the high-density balls are recovered.

[0223] Step 6: Drag the hydraulic fracturing tool string backward to the next predetermined fracturing position, return to Step 5, until all predetermined fracturing positions in the horizontal well borehole have been completed, and completely remove the hydraulic fracturing tool string from the borehole.

[0224] Step 7: Connect the coalbed methane / gas extraction tool string to the end of the fracturing tubing and lower it to the first predetermined fracturing position. Connect the 9th orifice of the fracturing tubing to the external negative pressure extraction pipeline for coalbed methane / gas extraction.

[0225] Step 8: Remove the external negative pressure extraction pipeline from the 9th orifice of the fracturing tubing, and retract the coalbed methane / gas extraction tool string to the next predetermined fracturing position. Connect the external negative pressure extraction pipeline at the 9th orifice of the fracturing tubing to perform extraction until extraction is completed at all predetermined fracturing positions, and completely withdraw the coalbed methane / gas extraction tool string.

[0226] When the working face in the coal seam begins to advance, when the roof of the key layer collapses, a slurry delivery pipeline is drilled into the horizontal well on the surface and filled with gangue slurry into the goaf using the roof horizontal well. When the filling pressure of the slurry in the slurry delivery pipeline rises to 100%, the grouting is stopped and the slurry delivery pipeline is withdrawn.

[0227] A 100% increase in slurry filling pressure indicates that the cracks in the goaf have been completely filled, and slurry filling can proceed to the next location.

[0228] Step 10, repeat step 9 until the coal face is fully mined;

[0229] Step 11: Use materials such as concrete, loess, and sand to seal the horizontal well borehole on the ground.

[0230] Figure 13 The diagram illustrates the effect of using this borehole for gangue slurry filling. The gangue slurry flows from the borehole along the fractures of the key stratum and fills the goaf fractures above and below, including spaces created above the key stratum and uncompacted spaces below. It may also flow into the goaf behind the longwall mining face. These spaces, when filled, can accommodate a considerable amount of gangue. This provides a good solution for handling surface gangue and avoiding ecological damage caused by gangue stockpiling. In particular, this solution utilizes previous boreholes in the project, saving a significant amount of construction and surface compensation costs.

Claims

1. A method for collaborative management of multiple disasters in coal mines based on the multi-purpose use of a single horizontal well, specifically including the following steps; Step 1: Collect information on the geological conditions of the coal seam, the mine pressure manifestation of adjacent working faces, and the roof collapse situation; The geological conditions information includes lithological parameters, thickness, physical and mechanical properties, coal seam gas content, and pressure of the coal seam and overlying strata. The roof collapse situation includes periodic pressure data of the working face, initial pressure data, working face mine pressure distribution, roof collapse situation after coal seam mining, and the development of collapse zone, caving zone, and fracture zone. Step 2: Based on the critical layer theory of coal seam roof collapse and the initial pressure limit caving distance, calculate and determine the main critical layer and sub-critical layer within 30 to 40 times the coal seam mining height of the coal seam roof, and drill horizontal wells on the surface in the main critical layer. Step 3: Connect the hydraulic fracturing tool string to the end of the fracturing tubing and lower it into the surface horizontal well borehole until it reaches the bottom of the surface horizontal well borehole; Step 4: Move the hydraulic fracturing tool string to the first predetermined fracturing position; Step 5: Insert high-density balls into the fracturing tubing (9). The high-density balls enter the hydraulic fracturing tool string, and start the large-displacement fracturing pump for fracturing. Step 6: Drag the hydraulic fracturing tool string backward to the next predetermined fracturing position, return to Step 5, until all predetermined fracturing positions in the horizontal well borehole have been completed, and completely remove the hydraulic fracturing tool string from the borehole. Step 7: Connect the coalbed methane / gas extraction tool string to the end of the fracturing tubing (9) and lower it to the first predetermined fracturing position. Connect the orifice of the fracturing tubing (9) to the external negative pressure extraction pipeline for coalbed methane / gas extraction. Step 8: Remove the external negative pressure extraction pipeline from the orifice of the fracturing tubing (9), and move the coalbed methane / gas extraction tool string to the next predetermined fracturing position. Connect the external negative pressure extraction pipeline at the orifice of the fracturing tubing (9) to perform extraction until extraction is completed at all predetermined fracturing positions and completely withdraw the coalbed methane / gas extraction tool string. Step 9: Start the working face mining in the coal seam. When the roof of the key layer collapses, drill a hole to the surface horizontal well and lower a slurry delivery pipeline. Use the roof horizontal well to fill the goaf with gangue slurry. When the filling pressure of the slurry in the slurry delivery pipeline rises to 100%, stop grouting and withdraw from the slurry delivery pipeline. Step 10, repeat step 9 until the coal face is fully mined; Step 11: Use concrete, loess, and sand to seal the horizontal well borehole on the ground.

2. The coal mine multi-hazard collaborative management method based on a single horizontal well for multiple uses as described in claim 1, characterized in that, Step 2, specifically calculating and determining the main critical strata and subcritical strata within 30-40 times the mining height of the coal seam roof, includes the following sub-steps: Step a.1: Based on the collected lithological parameters and physical and mechanical property parameters, the key strata theory is used to determine all key strata within 30 to 40 times the coal seam mining height of the coal seam roof. Step a.2: Based on the collected physical and mechanical property parameters, calculate the initial compressive limit span of each critical layer under tensile stress or under shear stress, and determine the maximum value among all calculation results. The critical layer containing the maximum value is the primary critical layer, and the other critical layers are all subcritical layers.

3. The coal mine multi-hazard collaborative management method based on a single horizontal well for multiple uses as described in claim 2, characterized in that, Step a.1, which uses the critical stratum theory to determine all critical strata within 30-40 times the coal seam mining height of the roof, specifically includes the following sub-steps: Step a.1.1: Take the first rock stratum above the coal seam as the current stratum; Step a.1.2: Calculate the self-weight load of the current layer, and then calculate the force of each overlying rock layer above the current layer on the current layer in the direction away from the coal seam. If the calculation result of the current overlying rock layer is less than the calculation result of the previous overlying rock layer, stop the calculation and define the current overlying rock layer as the i-th key layer. Step a.1.3: Take the i-th key layer as the current layer, and let i = i + 1, then execute step a.1.4; Step a.1.4: Determine whether the current critical layer is within 30 to 40 times the coal seam mining height of the coal seam roof. If yes, proceed to step a.1.2; otherwise, end the process.

4. The coal mine multi-hazard collaborative management method based on a single horizontal well for multiple uses as described in claim 3, characterized in that, In step a.1.2, the self-weight load of the rock strata is determined by the following formula: in, For the first The self-weight load of the rock strata, in units of ; For the first The thickness of the layer, in units of ; For the first The density of the layer, in units of .

5. The coal mine multi-hazard collaborative management method based on a single horizontal well for multiple uses as described in claim 3, characterized in that, In step a.1.2, the forces exerted by each overlying rock layer on the current layer are determined by the following formula: In the formula: This represents the force exerted by the (m+1)th rock layer above the current layer on the current layer, in kPa. Let be the elastic modulus of the nth rock layer, in GPa. The thickness of the nth rock layer is expressed in meters (m). For the first i Thickness of the rock strata, in meters; For the first i The elastic modulus of the rock strata, expressed in GPa. For the first i The density of the layer is expressed in kN / m³. 3 ; The structural stress experienced by the (m+1)th layer is expressed in kPa. in, i m and n are all integers, and n≥1. i ≥1, m≥n; i The step size for the values ​​of n and m is 1.

6. The coal mine multi-hazard collaborative management method based on a single horizontal well for multiple uses as described in claim 2, characterized in that, In step a.2, the initial compressive limit span under tensile stress is determined by the following formula: in: For the first The ultimate slump of the critical layer under tensile stress, in meters; The tensile strength of the rock stratum, expressed in Pa. The tectonic stress of the rock strata is expressed in Pa. This represents the self-weight load of the rock strata, in Pa. The thickness of the rock strata is expressed in meters (m).

7. The coal mine multi-hazard collaborative management method based on a single horizontal well for multiple uses as described in claim 2, characterized in that, In step a.2, the initial ultimate sag under shear stress is determined by the following formula: in: For the first The ultimate slump of the critical layer under shear stress, in meters; The shear strength of the rock stratum is expressed in Pa. The tectonic stress of the rock strata is expressed in Pa. This represents the self-weight load of the rock strata, in Pa. The thickness of the rock strata is expressed in meters (m).

8. The method for collaborative management of multiple disasters in coal mines based on a single horizontal well with multiple uses, as described in claim 1, is characterized in that... Step 2, drilling horizontal wells on the main critical layer, specifically includes the following: Step b.1: Drill a hole on the ground using a single-hole drill, run the casing into the hole, cement the well, and wait for it to solidify. The length of a single borehole is at least 20 meters, including the total length of the surface sand layer and the bedrock layer. Step b.2: Drilling is carried out in the first borehole using a second borehole. Casing is then installed in the resulting second borehole, cemented, and allowed to solidify. The second borehole reaches the upper part of the corresponding coal seam and is a vertical well borehole; Step b.3: Drilling is carried out in the second borehole using a third borehole. Casing is run into the obtained third borehole, and partial cementing is performed to obtain a surface horizontal well. The three-section drilling includes a build-up section and a horizontal well; the length of the casing installed in the three-section drilling is less than the length of the three-section drilling; The diameter of the first drilling is greater than the diameter of the second drilling, and the diameter of the second drilling is greater than the diameter of the third drilling.

9. The method for collaborative management of multiple disasters in coal mines based on a single horizontal well with multiple uses, as described in claim 1, is characterized in that... In step 5, starting the large-displacement fracturing pump for fracturing specifically includes: gradually increasing the pump displacement to the maximum within 5 minutes, injecting high-pressure clean water into the fracturing tubing (9) and maintaining it for at least 30 minutes, then gradually reducing the pump displacement until the pump is stopped and the high-density balls are recovered.

10. The coal mine multi-hazard collaborative management method based on a single horizontal well for multiple uses as described in claim 1, characterized in that, The hydraulic fracturing tool string includes a first sand-clearing pipe (1), a packer one (3), a check valve (2), a packer two (4), a second sand-clearing pipe (5), and a sand-swallowing guide shoe (6) that are connected in sequence and centrally connected. Multiple water guide grooves (7) are evenly provided on the outer walls of the first sand cleaning pipe (1) and the second sand cleaning pipe (5) along the circumference; a ball-throwing seat base (8) is provided in the second sand cleaning pipe (5) and is coaxial with it. The ball-throwing seat base (8) is cylindrical and its inner cavity is two connected cavities. The two cavities are gradually narrowing and gradually expanding along the axial direction. The single-flow valve (2) includes a housing (201). A plurality of first annular grooves (202) are equally spaced along the axial direction on the outer wall of the housing (201). A pair of first oblique supports (203) are provided on the radial inner side walls of each first annular groove (202). The ends of the pair of first oblique supports (203) are close to the radial outer side of the first annular groove (202) and the two first oblique supports (203) form an obtuse angle. A first spring (204) is sleeved inside the first annular groove (202) and the first spring (204) contacts the first oblique support (203). The sand-swallowing shoe (6) has a circular hole at the center of its axial rear end.

11. The coal mine multi-hazard collaborative management method based on a single horizontal well for multiple uses as described in claim 10, characterized in that, The first annular groove (202) is inclined relative to the housing (201).

12. The coal mine multi-hazard collaborative management method based on a single horizontal well for multiple uses as described in claim 1, characterized in that, The coalbed methane / gas extraction tool string includes an annular water supply and gas extraction pipe (10), a first composite packer (11), a composite check valve (12), a second composite packer (13), and a guide shoe (14) connected in sequence at the center, forming an axial gas extraction channel (15). The annular water supply and air extraction pipe (10) includes an inner pipe (1001) and an outer pipe (1002); the inner pipe (1001) and the outer pipe (1002) are coaxially arranged, and a plurality of connecting columns (1003) are provided in the annular cavity between the inner pipe (1001) and the outer pipe (1002), the central axis of the connecting column (1003) is parallel to the central axis of the inner pipe (1001); the symmetrical side walls of the connecting column (1003) are fixedly connected to the inner pipe (1001) and the outer pipe (1002) respectively, dividing the annular cavity into a plurality of first water injection channels (1004). The first composite packer (11) or the second composite packer (13) includes an inner cylinder (1101) and an outer cylinder (1102); the inner cylinder (1101) and the outer cylinder (1102) are coaxially arranged, and a plurality of connecting rods (1103) are arranged in the annular cavity between the inner cylinder (1101) and the outer cylinder (1102), the central axis of the connecting rods (1103) being parallel to the central axis of the inner cylinder (1101); the connecting rods (1103) are parallel to each other. The two side walls are fixedly connected to the inner cylinder (1101) and the outer cylinder (1102) respectively, dividing the annular cavity into multiple second water injection channels (1104); the inner cylinder (1101), the outer cylinder (1102) and the connecting rod (1103) are provided with radial through holes (1105), the radial through holes (1105) connect the inside of the inner cylinder (1101) and the outside of the outer cylinder (1102), and the outer cylinder (1102) is fitted with a rubber sleeve (1106). The composite flow valve (12) includes a coaxially arranged outer shell (1201) and inner shell (1202). The outer wall of the inner shell (1202) is provided with a plurality of second annular grooves (1203) at equal intervals along the axial direction. Each of the second annular grooves (1203) is provided with a pair of second oblique supports (1204) on its radially outer side walls. The ends of the pair of second oblique supports (1204) are close to the radially outer side of the second annular groove (1203) and are at an obtuse angle. A second spring (1205) is sleeved inside the second annular groove (1203) and the second spring (1205) is in contact with the second oblique support (1204). The outer shell (1201) is provided with multiple sets of radial air extraction channels (1206) at equal intervals along the axial direction, and the radial air extraction channels (1206) in each set are evenly distributed in the circumferential direction; the end face of the outer shell (1201) is provided with axial through holes (1207) evenly distributed in the circumferential direction, the axial through holes (1207) are connected to the first water injection channel (1004), and the axial through holes (1207) and the radial air extraction channels (1206) are offset in the circumferential direction.

13. The coal mine multi-hazard collaborative management method based on a single horizontal well for multiple uses as described in claim 12, characterized in that, The specific operation of step 8 is as follows: open the wellhead sealing cover of the first water injection channel (1004), release the pressure in the first composite packer (11) and the second composite packer (13) after expansion, and remove the coalbed methane / gas extraction tool string from the borehole.

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