A directional stereoscopic hydraulic fracturing caving method for large-inclination double-hard fully mechanized caving face

Abstract

The present application relates to the technical field of coal mining, in particular to a directional stereoscopic hydraulic fracturing caving method for large-inclination double-hard fully mechanized caving face, comprising the following steps: S1, determining basic information of the fully mechanized caving face; S2, determining fracturing technical parameters; S3, directional stereoscopic hydraulic fracturing borehole layout: arranging directional drilling boreholes and general drilling boreholes at the cementing surface of the hard layer according to the vertical drilling position and the horizontal drilling position of the directional stereoscopic hydraulic fracturing; S4, checking the sealing property of the borehole sealing; S5, directional stereoscopic hydraulic fracturing borehole construction: adopting staged fracturing; S6, directional stereoscopic hydraulic fracturing caving, forming a "coal body + fracture" composite structure in the roof rock and thick coal seam. The present application combines directional drilling hydraulic fracturing and general drilling hydraulic fracturing technology, forms directional stereoscopic hydraulic fracturing, and is suitable for the caving fully mechanized caving face with large-inclination coal seam and hard coal-rock interface.

Description

Technical Field

[0001] This invention relates to the field of coal mining technology, specifically to a directional three-dimensional hydraulic fracturing coal release method for a steeply inclined double-hard longwall face. Background Technology

[0002] In conventional coal mining, common methods to address the difficulty of fracturing the roof and coal seam include forced roof caving by blasting, water injection weakening, and hydraulic fracturing. Forced roof caving by blasting involves pre-drilling holes in the roof and filling them with explosives, using the energy from the explosion to create cracks and reduce roof strength. However, this method suffers from cumbersome approval processes for explosives, large construction workload, and high costs, and carries high risks such as explosions and gas ignition during underground operations. Water injection weakening relies on the dissolving and softening effect of water on the rock; however, its effectiveness is limited by the solubility of the rock itself, and it is difficult to precisely control the degree and extent of weakening, resulting in limited practical application. In contrast, hydraulic fracturing, with its advantage of creating directional cracks in the coal and rock strata using high-pressure water, can effectively reduce the strength of the coal and rock mass, increase the degree of fracture development, improve gas extraction conditions, and reduce roof accidents, making it a more commonly used technical method. A steep-angle, double-hard fully mechanized longwall caving face refers to a fully mechanized longwall caving face with a large coal seam dip angle (greater than 25°), a hard roof, hard coal quality, and a thick coal seam. This type of longwall caving face has unique geological characteristics. The large coal seam dip angle causes the coal to have a significant downward tendency under gravity, making it prone to coal wall spalling and support instability during mining. The hard coal quality and hard roof make coal crushing difficult and result in insufficient roof collapse, significantly impacting coal recovery rate and mining efficiency, and placing higher demands on mining technology. The application of conventional hydraulic fracturing technology in steeply inclined, double-hard fully mechanized longwall mining faces has revealed several drawbacks. Firstly, due to the large dip angle of the coal seam, the flow direction of high-pressure water after injection into the coal and rock mass is difficult to control, leading to disordered fracture propagation and an inability to form an effective fracture network in the predetermined direction, thus reducing the fracturing effect on the coal and rock mass. Secondly, the hardness of the coal and roof makes it difficult for conventional hydraulic fracturing pressure to overcome the rock mass strength, limiting the fracturing range and failing to fully break the coal and rock mass, thereby affecting coal extraction efficiency and coal recovery rate. Furthermore, while directional drilling and conventional short-hole hydraulic fracturing techniques can weaken the hard roof, their application in steeply inclined, double-hard fully mechanized longwall mining faces is limited by factors such as poor rock permeability leading to unstable fracturing effects and potential water pollution from fracturing fluid, making it difficult to meet the demands for efficient and safe mining in such special longwall mining faces. Summary of the Invention

[0003] To address the technical problems of insufficient coal and rock fracturing, unstable fracturing effects, and difficulty in meeting the requirements of efficient and safe mining when using conventional hydraulic fracturing technology in steeply inclined double-hard fully mechanized longwall faces, this invention provides a directional three-dimensional hydraulic fracturing coal release method for steeply inclined double-hard longwall faces. Directional drilling hydraulic fracturing is performed in the middle of the longwall face, while conventional drilling hydraulic fracturing is combined at both ends of the longwall face, in the return airway, and in the transport roadway, forming a directional three-dimensional hydraulic fracturing method. This significantly enhances the weakening effect of the double-hard layers, thereby improving the mining efficiency of the longwall face and reducing safety hazards. It achieves more environmentally friendly, safe, and efficient coal and roof release, and is particularly suitable for longwall faces with steeply inclined coal seams and hard coal-rock interfaces.

[0004] The technical solution of this invention is as follows: A directional three-dimensional hydraulic fracturing coal release method with a large-angle double-hard fully mechanized longwall face includes the following steps: S1. Determination of basic information of fully mechanized longwall face: Under the geological conditions of steeply inclined double-hard fully mechanized longwall face, obtain mechanical property data of roof strata, coal seam thickness, dip angle and mining height data, to provide a basis for subsequent directional three-dimensional hydraulic fracturing borehole layout; S2. Determination of fracturing technical parameters: Based on the mechanical property data of the roof strata, the fracturing initiation pressure at the bonding surface of the hard layer is calculated; the caving height is calculated based on the mining height of the coal seam; and the vertical and horizontal borehole positions for directional three-dimensional hydraulic fracturing are determined based on the caving height. S3. Directional three-dimensional hydraulic fracturing borehole layout: Based on the vertical and horizontal borehole positions of directional three-dimensional hydraulic fracturing, directional and conventional boreholes are arranged at the hard strata bonding surfaces in the return airway, transport roadway, and fully mechanized longwall face. Directional boreholes are used for fracturing in the middle of the fully mechanized longwall face, while conventional boreholes are used for fracturing at both ends of the fully mechanized longwall face, fracturing in the return airway, and fracturing in the transport roadway. S4. Drilling and sealing inspection: Push the sealing device to the pre-crack, use a high-pressure pump to pressurize and expand the sealing device to ensure that the sealing device can maintain pressure; S5. Directional three-dimensional hydraulic fracturing drilling: The retreating fracturing method is used to achieve segmented fracturing, and the changes in the initiation pressure of each fracturing segment are observed and controlled. S6. Directional three-dimensional hydraulic fracturing coal release: Directional weakening and fracturing of hard coal bodies in the roof strata, forming a composite structure of "coal body + fracture" in the roof strata and thick coal seams.

[0005] Furthermore, in S1, top rock samples were collected from the top rock layer of the steeply dipping double-hardened manhole cover, processed into standard specimens, and subjected to Brazilian splitting tests to test the tensile strength of the top rock layer.

[0006] Furthermore, in S2, the vertical borehole position is ensured based on the collapse height so that the direct top and the basic top fill the goaf after hydraulic fracturing, and the basic top is located above the advance support; the horizontal borehole position is determined by ensuring that the farthest fracturing position does not exceed the goaf.

[0007] Furthermore, in S3, the layout of directional drilling holes is optimized based on the lithology, thickness, and fracturing objectives at the bonding surface of the hard layer, ensuring that fractures can develop effectively and achieve the expected weakening effect.

[0008] Furthermore, in S3, the borehole spacing is determined to be 10-30m based on the lithology, thickness and fracturing requirements of the target stratum; multiple boreholes are designed according to the length of the fully mechanized longwall face and fracturing requirements, with each borehole having 5-20 fracturing segments.

[0009] Furthermore, in S3, conventional drilling adopts a vertical drilling layout.

[0010] Furthermore, in S4, by observing the borehole and monitoring the pressure gauge, the ability of the sealing device to maintain pressure is checked. If water flows out of the borehole, the sealing device and its connections are inspected to ensure that the sealing device is working properly.

[0011] Furthermore, in S5, if there is a discrepancy between the actual on-site measured fracturing pressure and the calculated fracturing pressure in S2, or if water backflow occurs at the orifice, the fracturing pressure and water flow rate are adjusted and controlled to ensure that the fracturing fracture can be effectively extended.

[0012] Furthermore, in S5, when directional drilling and hydraulic fracturing are carried out in the middle of the fully mechanized mining face, the cracks are directionally extended along the bonding surface of the hard layer by means of temporary plugging and diversion technology, forcibly cutting the bonding surface between the hard layers to form a through main crack with a length of 20-50m.

[0013] Furthermore, in S5, the dual-lane conventional drilling hydraulic fracturing adopted at both ends of the fully mechanized longwall face is replaced by hydraulic fracturing using vertically drilled holes, which forms dense branch fractures at both ends, expands the weakening range, covers the directional fracturing blind zone, and reduces the overall stress concentration factor of the fully mechanized longwall face to 1.5-2.0.

[0014] The beneficial effects of this invention are as follows: This invention provides a directional, three-dimensional hydraulic fracturing coal release method for steeply inclined, double-hard fully mechanized longwall faces. By organically combining directional drilling and conventional drilling fracturing techniques, it solves the problems of disordered fracture propagation direction and insufficient fracturing effect in traditional hydraulic fracturing techniques under steeply inclined, hard coal and rock conditions. This directional, three-dimensional hydraulic fracturing coal release method first precisely designs the borehole spatial layout according to the geological conditions of the fully mechanized longwall face. It adopts a three-dimensional borehole layout, arranging directional and conventional boreholes in the return airway, transport roadway, and the bonding surface of the hard strata in the fully mechanized longwall face. This ensures complete coverage of the hard roof by the fracturing range and effectively controls the flow path of high-pressure water in the steeply inclined coal and rock mass, allowing the fracture network to expand stably in the predetermined direction. By employing a retreating fracturing method to achieve segmented fracturing, the overall weakening effect of the hard coal and rock mass is significantly enhanced. This not only greatly improves the roof's venting performance and increases coal recovery rate but also eliminates the safety hazards associated with blasting methods. Meanwhile, based on the principle of hydraulic fracturing, this technology avoids the complex approval process and environmental pollution risks of traditional blasting operations. It has advantages such as simple construction, high safety, and strong adaptability, providing a brand-new technical solution for the safe and efficient mining of steeply inclined double hard coal seams, which improves the economic benefits of coal mining while ensuring operational safety. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a cross-sectional view of the directional drilling hydraulic fracturing arrangement of the present invention.

[0017] Figure 2 This is a cross-sectional view of the hydraulic fracturing arrangement of conventional drilling in this invention.

[0018] In the diagram, 1-Roof strata; 2-Thick coal seam; 3-Transport roadway; 4-Ordinary drill hole; 5-Directional drill hole; 6-Safety release; 7-Center; 8-Fracturing device; 9-Packer; 10-Check valve; 11-Ball seat; 12-Motor; 13-Oil pump; 14-Water tank; 15-High voltage power line; 16-Valve; 17-Flow meter; 18-Pressure gauge; 19-Sealing device water inlet; 20-Fracturing zone; 21-Sealing device. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0020] Those skilled in the art will know that in coal mines, the bonding surface of hard strata usually refers to the contact surface of hard rock strata between the coal seam and the roof or floor. Due to differences in lithology (such as the boundary between hard rock strata such as sandstone and limestone and the coal seam), these contact surfaces are prone to forming stress concentration zones, leading to problems such as difficulty in roof collapse or floor bulging.

[0021] Those skilled in the art will know that for fully mechanized longwall mining faces, coal seams with a thickness of more than 5 meters are considered thick coal seams.

[0022] Example 1 refer to Figures 1-2 Taking the 1901 fully mechanized longwall face of a certain mine as an example, a directional three-dimensional hydraulic fracturing coal release method for a steeply inclined double-hard fully mechanized longwall face is provided, including the following steps: S1. Basic Information of the Longwall Coal Mine (LLC) Face: The coal seams in the 1901 LCC face are all steeply dipped (dipping angle greater than 25°). The immediate roof is limestone, dark gray, with a cryptocrystalline structure. The rock is dense and hard (f=9), belonging to hard rock strata. According to the principle of LCC mining, the hard rock strata need to be loosened and weakened in advance. Complete rock samples (roof rock samples) of the main lithology of the roof were collected from the roof stratum 1 of the 1901 LCC face. After collection, they were processed into standard specimens and subjected to Brazilian splitting tests to test their tensile strength. The tensile strength of roof stratum (hard roof limestone) 1 was found to be 4.4 MPa.

[0023] The coal seam being mined is the No. 9 coal seam, which is thick coal seam 2. The 1901 fully mechanized longwall face is the first fully mechanized longwall face to be mined in the No. 9 coal seam. The average vertical depth of the 1901 fully mechanized longwall face from the surface is 389.5m, the maximum vertical depth is 459.6m, the length of the 1901 fully mechanized longwall face is 280m, the strike length is 1060m, the average coal seam dip angle is 27°, the average coal thickness is 6m, the mining height is 2.8m, and the coal release height is 3.2m.

[0024] S2. Determination of fracturing technical parameters: Based on the mechanical parameters of the roof strata 1 of the fully mechanized longwall face and the mining height, the fracturing pressure P was calculated to be 18.2 MPa and the caving height h was 9.3 m. The formula for calculating the initiation pressure is: P = 1.3(P* + R). P is the crack initiation pressure, in MPa. P* is the self-weight stress of the rock mass, measured in MPa. P* is obtained through in-situ stress testing, or it can be roughly calculated by the fact that the in-situ stress increases by approximately 2.5 MPa for every 100m increase in depth. R represents the tensile strength of the target stratum rock mass, in MPa. The formula for calculating the collapse height is: , h represents the collapse height, in meters (m). M represents the mining height, in meters (m). K Z Kz is the residual expansion coefficient of the top plate, and its value is 1.1-1.5. In this embodiment, it is 1.3.

[0025] The vertical and horizontal borehole locations for directional hydraulic fracturing are determined based on the collapse height; the vertical borehole locations are ensured to fill the goaf after hydraulic fracturing, with the direct roof and main roof filling the goaf, and the main roof breaking off above the advance support; the horizontal borehole locations are determined by ensuring that the furthest fracturing location does not exceed the goaf.

[0026] S3. Layout of directional three-dimensional hydraulic fracturing boreholes: Based on the vertical and horizontal borehole positions of directional three-dimensional hydraulic fracturing, directional boreholes 5 and conventional boreholes 4 are arranged at the hard strata bonding surfaces of the return airway, transport roadway 3, and the fully mechanized longwall face. Directional boreholes 5 are used for fracturing in the middle of the fully mechanized longwall face, while conventional boreholes 4 are used for fracturing at both ends of the fully mechanized longwall face and for fracturing in both roadways (return airway and transport roadway 3). The target fracturing layers for both directional boreholes 5 and conventional boreholes 4 are at the hard strata bonding surfaces, and the arrangement and number are designed according to the stratum height of the hard strata bonding surfaces. S31. Drill holes 4 in the return airway using conventional drilling. The return airway is approximately 1200m long, with two rows of standard drill holes (4). Each row has 8m spacing between holes, and each row contains 150 standard drill holes (4), for a total of 300 holes across both rows. The total drilling length is 6000m, and the drilling is done vertically. The parameters for the standard drill holes (4) are as follows: 1-1# is drilled 1-2m away from the upper side of the return airway in the roof of transport roadway 3, and drilled inward in the direction of the return airway. The horizontal angle of the ordinary drill hole 4 is 60° and the hole depth is 20m. Based on the situation of the interbedded rock, 1-2#, 4 ordinary drilling holes are arranged 1-1.5m below the interbedded rock on the lower side, with an angle of 30° with the side wall. The vertical angle of the ordinary drilling holes 4 is 10° and the hole depth is 20m.

[0027] S32. Ordinary drilling holes 4 are arranged in transport tunnel 3. Transport roadway 3 is approximately 1200m long, with two rows of conventional drill holes 4. Each row has 8m spacing between holes, and each row contains 150 conventional drill holes 4, for a total of 300 holes across both rows. The total drilling length is 6750m, and the drilling is done vertically. The parameters of the conventional drill holes 4 are as follows: Holes 1-3 are drilled 1.5-2m from the lower side of transport roadway 3 on the roof of the roadway, and drilled inward in the direction of transport roadway 3. The horizontal angle of the conventional drill holes 4 is 60° and the hole depth is 20m. 1-4# are drilled on the upper side. According to the interbedded rock situation, conventional drill holes 4 are arranged in the second layer of interbedded rock. The horizontal direction of conventional drill holes 4 is at an angle of 30° with the coal wall, and the hole depth is 25m.

[0028] S32. Arrange 5 directional drilling holes in the middle of the fully mechanized longwall face. The layout of directional drilling borehole 5 was optimized based on the lithology, thickness, and fracturing objective at the bonding surface of the hard strata, ensuring effective fracture development and achieving the desired weakening effect. Specifically, the directional drilling site was located 360m from the 1901 cut-in. Considering that the goaf (stress reduction zone) of coal seam 5 is above the fully mechanized longwall face on the side adjacent to transport roadway 3 (lower roadway), while the goaf face on the side adjacent to return airway (upper roadway) is above solid coal, and the longwall face itself has an inclination angle, the roof of the goaf on the upper roadway side is more prone to collapse. Therefore, the designed directional drilling borehole 5 was slightly denser on the lower roadway side and slightly sparser on the upper roadway side. Combined with the coal release interval within the longwall face, the horizontal spacing of directional drilling borehole 5 was determined to be 30-40m. Directional drilling boreholes 1, 2, 3, 4, and 5 were designed, with the target layer being the bonding surface (hard strata bonding surface) of the 2.56m roof stratum 1 and thick coal seam 2. The length of directional drilling borehole 5 was determined based on the thickness of the coal seam traversed on site. In order to weaken the coal and rock mass and improve the top coal venting effect, each directional drilling hole 5 has 20 fracturing sections. The specific number of directional drilling holes 5 needs to be determined based on the fracturing effect.

[0029] Under the condition of thick coal seams with steep inclination, the trajectory design of directional drilling borehole 5 needs to be more precise to adapt to the inclination characteristics and thickness variations of thick coal seams, ensure that the borehole can accurately reach the target fracturing layer, i.e. the bonding surface of the hard layer, while reducing the ineffective extension of the borehole, reducing material consumption, avoiding engineering hazards such as adjacent roadways and goaf areas, and ensuring construction safety.

[0030] A combination of directional drilling hole 5 and conventional drilling hole 4 was used to achieve directional three-dimensional hydraulic fracturing hole layout.

[0031] S4. Drilling and sealing inspection: Push the sealing device 21 to the pre-crack, use a high-pressure pump to pressurize and expand the sealing device 21 to ensure that the sealing device 21 can maintain pressure. Equipment such as directional drilling, conventional drilling, and sealing device 21 are transported to the fully mechanized longwall face. Figure 1As shown, the directional drilling fracturing tool is obtained by sequentially connecting the safety release handle 6, centralizer 7, fracturizer 8, packer 9, check valve 10, and ball seat 11 of the directional drilling fracturing equipment; Figure 2 As shown, a conventional drilling fracturing tool is obtained by sequentially connecting the motor 12, oil pump 13, water tank 14, high-voltage wire 15, valve 16, flow meter 17, and pressure gauge 18 of the conventional drilling fracturing equipment. High-pressure water is injected into the sealing port 19 to expand the sealing device 21 or packer 9, fracturing the hard, bonded surface of the fracturing zone 20. This ensures that the sealing device 21 or packer 9 can maintain pressure. The sealing device 21's ability to maintain pressure is checked by observing the borehole and monitoring the pressure gauge. If water flows out of the borehole, the sealing device and its connections are inspected to ensure that the sealing device 21 is functioning properly.

[0032] S5. Directional three-dimensional hydraulic fracturing drilling construction: The retreating fracturing method is adopted (fracturing segment by segment from the bottom of the hole until the entire construction is completed). The segmented fracturing is achieved by combining packer 9, directional drilling fracturing tools and ordinary drilling fracturing tools. Under the conditions of thick coal seam and large dip angle, segmented fracturing requires precise observation and control of the initiation pressure change of each fracturing segment. If there is a difference between the actual initiation pressure detected on site and the calculated value of the initiation pressure, or if water backflow occurs at the wellhead, the fracturing pressure and water flow rate should be adjusted and controlled immediately to ensure that the fracturing fracture can be effectively extended, while avoiding excessive damage to the thick coal seam 2 and affecting mining safety. When performing directional drilling and hydraulic fracturing in the middle of the fully mechanized longwall face, the cracks are directionally extended along the bonding surface of the hard strata by combining with the temporary plugging and diversion technology, forcibly cutting the bonding surface between the hard strata to form a through main crack with a length of 20-50m. The hydraulic fracturing at both ends of the fully mechanized longwall face is carried out by drilling vertical holes to form dense branch fractures at both ends (increasing the density by 2-3 times), expanding the weakening range and covering the blind zone of directional fracturing. Through hydraulic fracturing, the overall stress concentration factor of the fully mechanized longwall face is reduced (from 3.0 to 1.5-2.0), preventing the directional fractures in the middle from closing due to excessive stress difference. S6. Directional three-dimensional hydraulic fracturing and coal release: The roof stratum 1 is directionally weakened and the hard coal body is fractured. High-pressure water is injected to form vertical through cracks in the roof stratum 1, which destroys its overall bending strength, reduces the overhang length of the roof, and the fracturing water seeps into the natural fissures along the vertical through cracks, expands the crack branches, and forms a "coal body + crack" composite structure. This causes the roof stratum 1 to collapse in stages and in an orderly manner, avoids large-scale sudden collapse, and uses the formed crack network to disperse the concentrated stress in the mining area, reduce the periodic pressure intensity, and reduce the risk of rockburst.

[0033] After hydraulic fracturing, vertical and inclined fractures are formed in the thick coal seam 2. The fracture network runs through the coal body, dividing the intact coal block into a loose structure. The fracturing water seeps into the natural fractures of the coal body and further expands the fracture opening through mechanical behavior, thus forming a "coal body + fracture" composite structure, which significantly improves the coal body's releaseability.

[0034] Directional three-dimensional hydraulic fracturing increases the fracture density at the bonding surface of the hard coal seam and improves the connectivity of the fracture network, thereby enabling hydraulic fracturing for coal and roof caving, increasing the efficiency of caving and improving coal mine production efficiency. In thick coal seams and steeply inclined mining environments, this directional three-dimensional hydraulic fracturing method can more effectively improve roof caving performance, reduce roof resistance to mining operations, and increase coal recovery and production efficiency, which is of great significance for ensuring efficient and safe coal mining. For thick coal seam mining, it can effectively solve the problems of large coal seam thickness and high roof pressure. For steeply inclined mining, it can adapt to the inclined characteristics of the coal seam, prevent safety hazards caused by uneven roof collapse, and ensure the smooth progress of the mining process.

[0035] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A directional three-dimensional hydraulic fracturing coal release method for a steeply inclined double-hard coal-bearing face, characterized in that, Includes the following steps: S1. Determination of basic information of fully mechanized longwall face: Under the geological conditions of steeply inclined double-hard fully mechanized longwall face, obtain mechanical property data of roof strata, coal seam thickness, dip angle and mining height data, to provide a basis for subsequent directional three-dimensional hydraulic fracturing borehole layout; S2. Determination of fracturing technical parameters: Based on the mechanical property data of the roof strata, the fracturing initiation pressure at the bonding surface of the hard layer is calculated; the caving height is calculated based on the mining height of the coal seam; and the vertical and horizontal borehole positions for directional three-dimensional hydraulic fracturing are determined based on the caving height. S3. Directional three-dimensional hydraulic fracturing borehole layout: Based on the vertical and horizontal borehole positions of directional three-dimensional hydraulic fracturing, directional and conventional boreholes are arranged at the hard strata bonding surfaces in the return airway, transport roadway, and fully mechanized longwall face. Directional boreholes are used for fracturing in the middle of the fully mechanized longwall face, while conventional boreholes are used for fracturing at both ends of the fully mechanized longwall face, fracturing in the return airway, and fracturing in the transport roadway. S4. Drilling and sealing inspection: Push the sealing device to the pre-crack, use a high-pressure pump to pressurize and expand the sealing device to ensure that the sealing device can maintain pressure; S5. Directional three-dimensional hydraulic fracturing drilling: The retreating fracturing method is used to achieve segmented fracturing, and the changes in the initiation pressure of each fracturing segment are observed and controlled. S6. Directional three-dimensional hydraulic fracturing and coal release: Directional weakening and fracturing of hard coal bodies in the roof strata, forming a composite structure of "coal body + fracture" in the roof strata and thick coal seams; In S2, the formula for calculating the initiation pressure is: P = 1.3 (P +R), where P is the crack initiation pressure, in MPa; P P represents the self-weight stress of the rock mass, expressed in MPa. The stress is obtained through in-situ stress testing, or it can be roughly calculated by the fact that the in-situ stress increases by approximately 2.5 MPa for every 100m increase in depth; R is the tensile strength of the rock mass in the target stratum, in MPa; In S2, the vertical borehole position is determined based on the collapse height to ensure that the direct roof and the main roof fill the goaf after hydraulic fracturing, and the main roof collapse position is located above the advance support; the horizontal borehole position is determined by ensuring that the farthest fracturing position does not exceed the goaf. In S3, the layout of directional drilling holes is optimized based on the lithology, thickness, and fracturing purpose at the bonding surface of the hard layer to ensure that the fractures can develop effectively and achieve the expected weakening effect. In S3, conventional drilling adopts a vertical drilling layout; In S5, the dual-lane conventional drilling hydraulic fracturing at both ends of the fully mechanized longwall face is replaced by hydraulic fracturing using vertically drilled holes, which forms dense branch fractures at both ends, expands the weakening range, covers the directional fracturing blind zone, and reduces the overall stress concentration factor of the fully mechanized longwall face to 1.5-2.

0. In S5, when directional drilling and hydraulic fracturing are carried out in the middle of the fully mechanized mining face, the cracks are directionally extended along the bonding surface of the hard layer by means of temporary plugging and diversion technology, which forcibly cuts the bonding surface between the hard layers and forms a through main crack with a length of 20-50m.

2. The method for directional three-dimensional hydraulic fracturing and coal release with a large-angle double-hardened coal-bearing face as described in claim 1, characterized in that, In S1, top rock samples were collected from the top rock layer of the steeply dipping double-hardened manhole cover and processed into standard specimens for Brazilian splitting tests to test the tensile strength of the top rock layer.

3. The method for directional three-dimensional hydraulic fracturing and coal release with a large-angle double-hardened coal-bearing face as described in claim 1, characterized in that, In S3, the borehole spacing is determined to be 10-30m based on the lithology, thickness and fracturing requirements of the target stratum; multiple boreholes are designed according to the length of the fully mechanized longwall face and the fracturing requirements, with each borehole having 5-20 fracturing segments.

4. The method for directional three-dimensional hydraulic fracturing and coal release with a large-angle double-hardened coal-bearing face as described in claim 1, characterized in that, In S4, the ability of the sealing device to maintain pressure is checked by observing the borehole and monitoring the pressure gauge. If water flows out of the borehole, the sealing device and its connections are checked to ensure that the sealing device is working properly.

5. The method for directional three-dimensional hydraulic fracturing and coal release with a large-angle double-hardened coal-bearing face as described in claim 1, characterized in that, In S5, if there is a discrepancy between the actual on-site measured fracturing pressure and the calculated fracturing pressure in S2, or if water backflow occurs at the orifice, the fracturing pressure and water flow rate are adjusted and controlled to ensure that the fracturing fracture can be effectively extended.

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