Large-dip-angle'double-hard 'fully-mechanized caving face fracturing top cutting method based on thickener

Abstract

The invention discloses a large-dip-angle'double-hard 'fully mechanized caving face fracturing top cutting method based on a thickener, and relates to the technical field of large-dip-angle hard coal seam fracturing. The method comprises the following specific steps: determining technical parameters of viscous agent fracturing; topping presplitting drill holes are designed and arranged; selecting and preparing a thickening agent; carrying out viscous agent fracturing construction; and monitoring the fracturing effect and evaluating pressure relief. Through a customized thickener formula and a segmented packing fracturing process, the limitation of traditional blasting, water injection and hydraulic fracturing application scenarios is broken through, pressure relief treatment can be conducted on a large-dip-angle double-hard fully mechanized caving face, a crossheading roof rock stratum is made to generate cracks, a roof cantilever is cut off under stress during stoping advancing, it is guaranteed that a goaf roof caves smoothly, and the working efficiency is improved. And the goaf top suspending risk is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of large-dip-angle hard coal seam fracturing, and particularly relates to a large-dip-angle 'double-hard' fully mechanized caving face fracturing roof cutting method based on viscous agent. BACKGROUND

[0002] With the exploitation of coal resources in China, the mining problem of large-dip-angle 'double-hard' (both the roof rock and the coal seam have high strength) fully mechanized caving face is increasingly prominent. Because the coal seam dip angle of such working face is usually greater than 25° (even more than 35° for steeply inclined coal seam), and the roof rock of the crossheading is hard and complete, the roof of the goaf is prone to form a large area of suspended roof and cantilever structure, which not only leads to high stress on the working face and the roadway, causing serious deformation of the roadway, overloading of the support and other problems, but also may induce rock burst due to the sudden collapse of the suspended roof, seriously restricting safety production.

[0003] At present, the conventional technology for hard roof weakening and suspended roof control has significant limitations: although the blasting forced roof caving method can weaken the roof strength by pre-splitting, the explosive is difficult to obtain approval, has high cost and high risk coefficient, and is difficult to adapt to the complex construction environment of large-dip-angle working face; the water injection weakening method has limited effect on hard rocks such as sandstone and conglomerate, and the weakening range and degree are difficult to control, and has poor applicability under 'double-hard' geological conditions; the traditional hydraulic fracturing technology relies on water as the fracturing medium, has high requirements for rock permeability, and is prone to energy dispersion due to rapid liquid filtration in large-dip-angle boreholes, making it difficult to form a directional main crack, and there is a risk of water pollution, which is not suitable for 'double-hard' fully mechanized caving face.

[0004] Especially crucial is that the special geological conditions of large-dip-angle 'double-hard' fully mechanized caving face (difficult medium flow control caused by high dip angle, and large fracture resistance caused by 'double-hard' characteristics) make it difficult for existing technologies to achieve precise roof cutting: the three-dimensional crack system of the blasting method is prone to deviate from the designed direction in large-dip-angle rock layers, and the low-viscosity medium of the hydraulic fracturing method is difficult to maintain pressure in the crack under high stress environment, both of which cannot ensure that the roof falls along the predetermined path. Therefore, in view of the core problems of hard roof in the crossheading and difficult roof collapse in the goaf of large-dip-angle 'double-hard' fully mechanized caving face, a new type of fracturing roof cutting technology that is safe and efficient, highly directional and suitable for complex geological conditions is urgently needed to fill the application gap in this field. SUMMARY

[0005] In view of the above problems, the present application discloses a large-dip-angle 'double-hard' fully mechanized caving face fracturing roof cutting method based on viscous agent, which can perform pressure relief treatment on the working face, cause cracks in the roof rock of the crossheading, cut off the cantilever stress of the roof during the recovery and advancement, ensure the smooth collapse of the roof of the goaf, and reduce the risk of suspended roof in the goaf.

[0006] A method for fracturing and cutting the top of a steeply inclined "double-hard" manhole cover based on a viscous agent, according to the present invention, includes the following steps:

[0007] S1. By conducting lithological tests on the roof, the compressive strength and elastic modulus of the roof rock are obtained. At the same time, by combining field measurements and theoretical analysis, the distribution of in-situ stress is clarified, thereby determining the initiation pressure of the fracturing layer.

[0008] S2. Determine the height of the caving zone based on the mining height, and clarify the vertical and horizontal positions of the viscous agent fracturing.

[0009] S3. In the working face roadway, at a specific distance from the coal wall on the side of the protective coal pillar, construct a row of pre-splitting holes along the roadway direction;

[0010] S4. Prepare a thickener according to the specific conditions of the fracturing layer;

[0011] S5. Fracturing boreholes in sequence, and using segmented sealing fracturing technology for individual boreholes, fracturing them segment by segment in a top-down order;

[0012] S6. By combining the monitoring data of the anchor cable force gauge, the observation results of the working face mine pressure, and various indicators such as the degree of roadway deformation reduction, the reduction of support load, the shortening of the roof collapse step distance, and the smoothness of coal discharge, the subsequent drilling parameters and fracturing parameters are dynamically adjusted.

[0013] Preferably, in S1, the formula for calculating the crack initiation pressure is:

[0014] P = 1.3(P* + R);

[0015] In the formula, P is the initiation pressure, MPa; P* is the self-weight stress, obtained through in-situ stress testing, or calculated by increasing the in-situ stress by 2.5 MPa for every 100m increase in depth; R is the tensile strength of the rock mass in the target stratum.

[0016] Preferably, in S2, the formula for calculating the height of the caving zone is:

[0017]

[0018] In the formula, h is the height of the caving zone; M is the mining height; K Z Kz is the residual expansion coefficient of the roof slab, with a value ranging from 1.1 to 1.5, and generally taken as 1.3.

[0019] Preferably, in S3, the pre-splitting holes are arranged 1-2 meters away from the protective coal pillar side coal wall, with the final hole direction facing the goaf, and the drilling inclination angle matching the coal seam inclination angle; the drilling diameter is 75-113mm, the hole spacing is 3-6m, and the hole depth is determined according to the actual thickness of the roof, ensuring that the final hole depth reaches the basic roof during drilling.

[0020] Preferably, in S4, the thickener is guar fracturing fluid with a viscosity of 50-500 mPa·s.

[0021] Preferably, in S5, the fracturing equipment includes a high-pressure pumping system, a water injection system, a perforator, and a flow and pressure monitoring system; the high-pressure pumping system includes a viscous agent pumping system and a breaker agent pumping system; the flow and pressure monitoring system includes a flow meter and a pressure gauge.

[0022] Fracturing methods include the following steps:

[0023] S51. Connect the equipment and check for a seal;

[0024] S52. Start the water injection system and inject the water in the water tank into the sealing device through the sealing device water injection pipe, so that the sealing device expands and fits tightly against the borehole wall.

[0025] S53. After sealing the hole, start the thickener pumping system to inject the prepared thickener from the thickener and proppant mixture tank into the fracturing area, so that the top plate will generate initial cracks and achieve crack initiation under high pressure.

[0026] S54. After the top plate fracturing is completed, shut down the viscous agent pumping system and inject the breaker from the breaker tank into the fracturing area through the breaker pumping system to degrade the viscous agent.

[0027] S55. After the rupture is completed, turn off the rupture agent pumping system and drain the degraded liquid. After observing that the liquid stops flowing out, drain the water from the sealing device and then remove the sealing device. This completes one fracturing cycle.

[0028] S56. Retract the sealing device to the next fracturing section and repeat steps S52 to S55, sealing and fracturing in sections from top to bottom.

[0029] Compared with existing technologies, the advantages of the large-angle "double-hard" manhole cover fracturing and top-cutting method based on viscous agents disclosed in this invention are:

[0030] This invention addresses the core challenges of roof collapse and stress concentration under steep inclination (greater than 25°) geological conditions characterized by a suspended roof. It utilizes viscous agent fracturing technology to achieve directional roof cutting, overcoming the limitations of traditional blasting, water injection, and hydraulic fracturing in this scenario. The high viscosity of the viscous agent reduces filtration loss and maintains intra-fracture pressure in steep boreholes, ensuring the formation of directional master fractures under high stress. This forces the roof to collapse along the designed path, effectively eliminating the risk of rockbursts caused by large-area suspended roofs and cantilever structures. Viscosity agent fracturing eliminates the need for explosives, avoiding the approval difficulties and high risks associated with blasting methods and reducing safety hazards in complex construction environments at steep inclination faces. Furthermore, the viscous agent system can be degraded by a breaker, reducing groundwater pollution. Compared to traditional hydraulic fracturing, it is more environmentally friendly and meets the requirements of green mining.

[0031] This invention utilizes a customized viscous agent formulation and segmented fracturing process. The "top-down segmented fracturing" technology, designed for steeply inclined boreholes, addresses the challenges of controlling medium flow in inclined rock formations, ensuring sufficient fracturing in each segment. The accompanying dedicated pumping and monitoring system (flow and pressure monitoring, anchor bolt force gauges, etc.) provides real-time feedback on construction results, facilitating dynamic optimization of drilling and fracturing parameters and adapting to complex geological conditions. Compared to blasting, it reduces the costs of explosives and safety management; compared to traditional hydraulic fracturing, it reduces water consumption and subsequent treatment costs. By shortening the roof collapse step, mitigating roadway deformation, and reducing support load, it reduces downtime for face maintenance, improves coal delivery smoothness, ensures safe and efficient mining of steeply inclined "double-hard" fully mechanized faces, and significantly improves production efficiency. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of 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, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 This is a system diagram of a large-angle "double-hard" manhole cover fracturing and top cutting method based on a viscous agent, provided for an embodiment of the present invention.

[0034] Figure 2 This is a drilling layout diagram.

[0035] In the diagram: 1- Thickener and proppant mixture tank; 2- Debriding agent tank; 3- Water tank; 4- Flow and pressure monitoring system; 5- First high-pressure pipeline; 6- Second high-pressure pipeline; 7- Third high-pressure pipeline; 8- Fourth high-pressure pipeline; 9- Fifth high-pressure pipeline; 10- First valve; 11- Second valve; 12- Third valve; 13- Fourth valve; 14- Fifth valve; 15- Fracturing zone; 16- Sealer; 17- Drill hole; 18- Sealer water injection pipe. Detailed Implementation

[0036] The specific embodiments of the present invention will be briefly described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] Figures 1-2 A preferred embodiment of the present invention is shown and analyzed in detail.

[0038] This invention discloses a method for fracturing and cutting the top of a large-angle "double-hard" manhole cover based on a viscous agent, comprising the following steps:

[0039] S1. Through lithological testing of the roof rock, key mechanical parameters such as compressive strength and elastic modulus are obtained. Simultaneously, combined with field measurements and theoretical analysis, the stress distribution is clarified. Based on this fundamental data, mature rock mechanics theories and numerical simulation methods are used to accurately calculate the pressure required for roof crack initiation. The formula for calculating the crack initiation pressure is:

[0040] P = 1.3(P* + R);

[0041] In the formula, P is the initiation pressure, MPa; P* is the self-weight stress, obtained through in-situ stress testing, or calculated by increasing the in-situ stress by 2.5 MPa for every 100m increase in depth; R is the tensile strength of the rock mass in the target stratum.

[0042] S2. Determine the height of the caving zone based on the mining height, and clarify the vertical and horizontal positions of the viscous fracturing. In the vertical direction, ensure that the depth of borehole 17 is precisely controlled to ensure that the direct roof and the basic roof can fully fill the goaf when the viscous fracturing is completed. In the horizontal direction, the broken roof position of the basic roof should be located directly above the advanced support, while ensuring that the farthest fracturing point does not exceed the goaf area.

[0043] The formula for calculating the height of the landslide zone is:

[0044]

[0045] In the formula, h is the height of the caving zone; M is the mining height; KZ Kz is the residual expansion coefficient of the roof slab, with a value ranging from 1.1 to 1.5, and generally taken as 1.3.

[0046] S3. Within the working face roadway, at a distance of 1-2 meters from the protective coal pillar side wall, construct a row of pre-splitting holes along the roadway direction. The final hole direction should face the goaf. The dip angle of borehole 17 should match the dip angle of the coal seam, i.e., the dip angle of borehole 17 should be slightly less than the dip angle of the coal seam by 5°-10°, to increase the area where the target roof can be fractured. The diameter of borehole 17 is 75-113mm, the hole spacing is 3-6m, and the hole depth is determined according to the actual thickness of the roof. During drilling, ensure that the final hole depth reaches the basic roof.

[0047] S4. Prepare a thickener according to the specific conditions of the fracturing layer. The thickener viscosity must be significantly higher than water to effectively reduce filtration loss, minimize seepage into the coal face and goaf, and ensure the efficiency of the fracturing fluid; it should be non-toxic, harmless, and flame-retardant, complying with coal mine safety regulations; it should degrade within a set time after fracturing to reduce the impact on subsequent roof collapse and coal release; its viscosity should decrease during pumping for easy flow, and recover upon entering the fracture to maintain fracture-creating capacity; it should maintain stable performance under underground temperature and pressure conditions. Specifically, for dense, low-permeability layers (such as shale and dense sandstone), due to their dense lithology, small pores, and low filtration loss, a high-viscosity thickener is required to drive the fracture depth and carry proppant into the microfracture network; for medium-to-high permeability layers (such as conventional sandstone and carbonate rocks), due to good pore connectivity (permeability > 1 mD) and rapid filtration leading to insufficient energy, a low-filtration-loss thickener should be selected, meaning a suitable thickener should be prepared based on the specific characteristics of the fracturing layer. Guar fracturing fluid with a viscosity of 50-500 mPa·s can be used as a thickener to ensure good sand-carrying capacity and plugging performance during fracturing.

[0048] S5. Fracturing boreholes 17 sequentially, employing segmented isolation fracturing technology for each borehole 17, fracturing segment by segment from top to bottom. The fracturing equipment includes a high-pressure pumping system, a water injection system, a borehole sealer 16, and a flow and pressure monitoring system 4. Based on the fracturing pressure calculated in S1, a high-pressure pumping system specifically designed for viscous liquids is configured to ensure high displacement stability and wear resistance, overcoming the flow resistance of the viscous agent and achieving high-pressure delivery of 10-30 MPa. The borehole sealer 16 is an expansion-type high-pressure sealer 16, its material must be resistant to the corrosion of the viscous agent to ensure reliable sealing during high-pressure pumping and prevent leakage of the viscous agent along the borehole wall. Pipelines and valves use large-diameter, low-resistance high-pressure steel pipes and high-pressure resistant ball valves to reduce pressure loss during viscous agent delivery. The high-pressure pumping system includes a viscous agent pumping system and a breaker pumping system; the flow and pressure monitoring system 4 includes a flow meter and a pressure gauge.

[0049] Fracturing methods include the following steps:

[0050] S51. Connect the equipment and check for a seal;

[0051] S52. Start the water injection system and inject the water in the water tank 3 into the sealing device 16 through the sealing device water injection pipe 18, so that the sealing device 16 expands and tightly fits the wall of the borehole 17.

[0052] S53. After sealing the borehole, start the thickener pumping system to inject the prepared thickener from the thickener and proppant mixture tank 1 into the fracturing zone 15, causing the top plate to generate initial cracks and initiate fracturing under high pressure. For dense, low-permeability layers that require proppant, the proppant and thickener are mixed in the thickener and proppant mixture tank 1 and then injected together into the fracturing zone 15.

[0053] S54. After the top plate fracturing is completed, the viscous agent pumping system is turned off, and the breaker is injected from the breaker tank 2 into the fracturing area 15 through the breaker pumping system to degrade the viscous agent.

[0054] S55. After the rupture is completed, turn off the rupture agent pumping system and drain the degraded liquid. After observing that the liquid stops flowing out, drain the water from the wellbore 16 and then remove the wellbore 16. This completes one fracturing cycle. This fracturing cycle can be repeated as needed until the expected fracturing effect is achieved.

[0055] S56. Retract the sealing device 16 to the next fracturing section and repeat steps S52 to S55, sealing and fracturing in sections from top to bottom.

[0056] S6. Combining monitoring data from anchor bolt force gauges, working face mine pressure observation results, and various indicators such as the degree of roadway deformation mitigation, support load reduction, roof collapse step shortening, and coal discharge smoothness, the subsequent borehole parameters and fracturing parameters are dynamically adjusted to continuously optimize the fracturing effect and improve the safety and efficiency of coal mining. Judging the effectiveness of roof cutting and pressure relief requires comprehensive verification through the coordinated changing trends of multi-dimensional data on "stress-deformation-production" (such as stress reduction, deformation mitigation, and collapse rules). The core basis for stopping fracturing is the "ineffective fracturing" or "loss of control risk" reflected by abnormal data, requiring dynamic decision-making in conjunction with real-time monitoring to ensure safe and efficient fracturing.

[0057] Reference Figure 1 and Figure 2 Using the above methods, taking the 4312 fully mechanized longwall face of a certain mine as an example, in order to ensure that the overhang of the goaf in the 4312 fully mechanized longwall face does not exceed the regulations, it is necessary to construct pre-splitting boreholes 17 in the transport roadway and return air roadway of the fully mechanized longwall face, fill them with viscous agent, and carry out pressure relief treatment on the roof to create cracks in the roof strata of the roadway. When the longwall advances, the roof cantilever is cut off by force, so as to achieve the effect of pre-splitting the roof of the working face and ensure the smooth collapse of the roof in the goaf.

[0058] The fully mechanized longwall mining face operates at a 26° dip angle. The No. 3 coal seam being mined is a thick seam. The average vertical depth of the working face from the surface is 595m, the working face length is 185.9m, the strike length is 951.7m, and the average coal thickness is 8.4m. The immediate roof is limestone, dark gray in hardness, with a cryptocrystalline structure. The rock is dense and hard (f=9), classifying it as a hard stratum. According to the principles of top-coal caving mining, the hard, thick coal and rock must be loosened and weakened beforehand.

[0059] First, complete rocks of the main lithology that make up the roof were collected from the roof strata of the working face. After collection, they were processed into standard specimens and subjected to Brazilian splitting test to test their tensile strength. The tensile strength of the hard roof limestone was found to be 5.48 MPa.

[0060] Secondly, based on the obtained mechanical parameters of the roof strata and the roadway depth, the target coal and rock fracturing pressure P was calculated to be 26.6 MPa, and the caving zone height h was 24 m. Since the basic roof fracture position should be located above the advance support after hydraulic fracturing, and the furthest fracturing position should not exceed the goaf, the horizontal position was determined to be 20 m to 30 m based on the actual site conditions.

[0061] Then, as Figure 2 As shown, in the working face roadway, two meters away from the protective coal pillar side coal wall, a row of pre-splitting holes is constructed along the roadway direction, with the final hole direction facing the goaf. The drilling angle of hole 17 is 60°; the hole depth is 40m, the diameter is 75mm, and the hole spacing is 6m. When drilling, ensure that the final hole depth reaches the basic top.

[0062] After the completion of borehole 17, the thickener was prepared. Based on the actual fracturing requirements, the viscosity of the thickener was controlled at 500 mPa·s to ensure that it has good sand-carrying capacity and plugging performance during the fracturing process.

[0063] Next, after the thickener is prepared, the fracturing operation phase begins. For example... Figure 1As shown, the fracturing equipment includes a high-pressure pumping system, a water injection system, a perforator 16, and a flow and pressure monitoring system 4. The high-pressure pumping system includes a thickener pumping system and a breaker pumping system. The thickener pumping system includes a thickener and proppant mixture tank 1, whose output end is connected to the fracturing zone 15 via a first high-pressure pipeline 5, on which a first valve 10 is installed. The breaker pumping system includes a breaker tank 2, whose output end is connected to the fracturing zone 15 via a second high-pressure pipeline 6, on which a second valve 11 is installed. The first high-pressure pipeline 5 and the second high-pressure pipeline 6 are connected together to a third high-pressure pipeline 7, one end of which extends into the fracturing zone 15, and the other end is equipped with a third valve 12 for discharging the degraded thickener. The water injection system includes a water tank 3. A fourth high-pressure pipeline 8 is installed at the output end of the water tank 3. A fourth valve 13 is installed on the fourth high-pressure pipeline 8. The fourth high-pressure pipeline 8 is connected to the sealing device 16 through a fifth high-pressure pipeline 9. One end of the fifth high-pressure pipeline 9 is connected to the water injection pipe 18 of the sealing device, and the other end is equipped with a fifth valve 14 for discharging water from the sealing device 16. The flow and pressure monitoring system 4 includes a flow meter and a pressure gauge. The flow and pressure monitoring system 4 is respectively installed on the first high-pressure pipeline 5, the second high-pressure pipeline 6, and the fourth high-pressure pipeline 8.

[0064] The fracturing method includes the following steps:

[0065] First, connect the relevant equipment in a standardized manner to ensure that all connection parts are well sealed and there is no risk of leakage.

[0066] During fracturing operations, the fourth valve 13 is opened while all other valves are closed. Water from the water tank 3 is injected into the sealer 16 through the sealer injection pipe 18, causing the sealer 16 to expand and tightly adhere to the borehole wall 17. After sealing, the fourth valve 13 is immediately closed. Next, the first valve 10 is opened, and the prepared thickener is injected from the thickener and proppant mixture tank 1 into the fracturing zone 15, causing initial cracks to form in the roof under high pressure. Subsequently, the thickener is allowed to remain in the cracks for a period of time to fully exert its fracturing effect and effectively fracture the hard roof. Due to the high viscosity of the thickener, even at large dip angles, leakage is effectively reduced, ensuring the fracturing effect.

[0067] After the top plate fracturing is completed, close the first valve 10 and open the second valve 11 to inject the breaker from the breaker tank 2 into the fracturing zone 15 to break down and degrade the viscous agent. After breaking down the viscous agent, close the second valve 11 and open the third valve 12 to drain the degraded liquid. After observing that no liquid is flowing out, close the third valve 12 and open the fifth valve 14 to drain the water from the sealer 16. When no water flows out of the pipeline at the fifth valve 14, remove the sealer 16, thus completing one fracturing cycle. The above fracturing cycle can be repeated as needed until the desired fracturing effect is achieved.

[0068] Retract the sealing device 16 to the next fracturing section and repeat the above steps, sealing and fracturing in sections from top to bottom.

[0069] Finally, the fracturing effect is evaluated and parameters are dynamically adjusted. Combining real-time monitoring data from the anchor bolt force gauge, working face mine pressure observation results (including support resistance, piston shrinkage, etc.), and comprehensive indicators such as the degree of roadway deformation mitigation, support load reduction, roof collapse step shortening, and coal discharge smoothness, a comprehensive and systematic dynamic adjustment is made to subsequent borehole parameters (such as borehole location, diameter, depth, and inclination angle) and fracturing parameters (such as fracturing pressure, thickener viscosity, and breaker dosage) to continuously optimize the fracturing effect and improve the safety and efficiency of coal mining.

[0070] The above description of the disclosed embodiments enables those skilled in the art to make and use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit and scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for fracturing and top-cutting a large-angle "double-hard" manhole cover based on a viscous agent, characterized in that, Includes the following steps: S1. By conducting lithological tests on the roof, the compressive strength and elastic modulus of the roof rock are obtained. At the same time, by combining field measurements and theoretical analysis, the distribution of in-situ stress is clarified, thereby determining the initiation pressure of the fracturing layer. S2. Determine the height of the caving zone based on the mining height, and clarify the vertical and horizontal positions of the viscous agent fracturing. S3. In the working face roadway, at a specific distance from the coal wall on the side of the protective coal pillar, construct a row of pre-splitting holes along the roadway direction; S4. Prepare a thickener according to the specific conditions of the fracturing layer; S5. Fracturing boreholes (17) in sequence, and using segmented sealing fracturing technology for each borehole (17), fracturing segment by segment in a top-down order; S6. Based on the monitoring data of the anchor bolt cable force gauge, the observation results of the working face mine pressure, and various indicators such as the degree of roadway deformation reduction, the reduction of support load, the shortening of the roof collapse step distance, and the smoothness of coal discharge, the subsequent drilling (17) parameters and fracturing parameters are dynamically adjusted.

2. The method for fracturing and top-cutting a large-angle "double-hard" manhole cover based on a viscous agent according to claim 1, characterized in that, In S1, the formula for calculating the crack initiation pressure is: P = 1.3(P* + R); In the formula, P is the initiation pressure, MPa; P* is the self-weight stress, obtained through in-situ stress testing, or calculated by increasing the in-situ stress by 2.5 MPa for every 100m increase in depth; R is the tensile strength of the rock mass in the target stratum.

3. The method for fracturing and top-cutting a large-angle "double-hard" manhole cover based on a viscous agent according to claim 1, characterized in that, In S2, the formula for calculating the height of the caving zone is: In the formula, h is the height of the caving zone; M is the mining height; K Z Kz is the residual expansion coefficient of the roof slab, with a value ranging from 1.1 to 1.5, and generally taken as 1.

3.

4. The method for fracturing and top-cutting a large-angle "double-hard" manhole cover based on a viscous agent according to claim 1, characterized in that, In S3, the pre-splitting holes are arranged 1-2 meters away from the coal wall on the side of the protective coal pillar, and the final hole direction is towards the goaf. The inclination angle of the borehole (17) matches the inclination angle of the coal seam. The diameter of the borehole (17) is 75-113mm, the spacing between holes is 3-6m, and the hole depth is determined according to the actual thickness of the roof. When drilling, ensure that the final hole depth reaches the basic roof.

5. The method for fracturing and top-cutting a large-angle "double-hard" manhole cover based on a viscous agent according to claim 1, characterized in that, In S4, the thickener is guar fracturing fluid with a viscosity of 50-500 mPa·s.

6. The method for fracturing and top-cutting a large-angle "double-hard" manhole cover based on a viscous agent according to claim 1, characterized in that, In S5, the fracturing equipment includes a high-pressure pumping system, a water injection system, a sealing device (16), and a flow and pressure monitoring system (4); the high-pressure pumping system includes a viscous agent pumping system and a breaker agent pumping system; the flow and pressure monitoring system (4) includes a flow meter and a pressure gauge; Fracturing methods include the following steps: S51. Connect the equipment and check for a seal; S52. Start the water injection system and inject the water in the water tank (3) into the sealing device (16) through the sealing device water injection pipe (18), so that the sealing device (16) expands and tightly fits the borehole (17) wall. S53. After the sealing is completed, start the thickener pumping system and inject the prepared thickener from the thickener and proppant mixture tank (1) into the fracturing area (15) so that the top plate generates initial cracks under high pressure and achieves crack initiation. S54. After the top plate fracturing is completed, shut down the viscous agent pumping system and inject the breaker from the breaker tank (2) into the fracturing area (15) through the breaker pumping system to degrade the viscous agent. S55. After the rupture is completed, turn off the rupture agent pumping system and drain the degraded liquid. After observing that the liquid stops flowing out, drain the water in the sealing device (16) and then remove the sealing device (16). This completes one fracturing cycle. S56. Retract the sealing device (16) to the next fracturing section and repeat steps S52 to S55 to seal and fracture in sections from top to bottom.

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