A Collaborative Management Method for Multiple Disasters in the Triangular Zone of Coal Mining Faces Based on Directional Drilling

Abstract

This invention discloses a method for the coordinated management of multiple hazards in the triangular area of ​​a coal mining face based on directional drilling, comprising the following steps: S1, determining the stress concentration zone in the triangular area of ​​the coal mining face; S2, based on step S1, designing the control strata and spacing of the main and branch holes of the comb-shaped directional drilling; S3, dynamically analyzing geological conditions and continuously revising the branch hole exploration; S4, designing the number and length of the branch holes for segmented fracturing of the comb-shaped directional drilling, drilling the main holes of the comb-shaped directional drilling in the roof, and fracturing and modifying the branch holes; S5, determining the parameters for sealing and gas extraction after fracturing of the comb-shaped directional drilling; S6, dynamic control of gas extraction and real-time monitoring of mine pressure manifestation. This method achieves coordinated management of rockburst hazards in the triangular area at the end of the working face and gas extraction in the goaf, overcoming the problems of small treatment area and high cost of existing rockburst prevention and gas extraction boreholes.

Description

Technical Field

[0001] This invention relates to the field of coal mine disaster management technology, specifically to a method for the coordinated management of multiple disasters in a coal mining face, including the goaf, corner gas, and end triangle area, based on directional drilling. Background Technology

[0002] my country's coal seam geological conditions are complex, and most mines suffer from serious gas disasters. As the mining depth increases year by year, the risk of coal and gas outbursts is increasing, which also leads to frequent rockburst accidents, posing a major threat to the safe production of coal mines.

[0003] The combined dynamic disaster caused by the coupling effect of rockburst and coal and gas outburst is increasingly dangerous, more difficult to prevent and control, and more costly to manage. Rockburst can not only cause local roof collapses, but also induce abnormal gas outbursts in goaf areas, and even cause coal and gas outbursts. This coupled disaster phenomenon has already appeared in some mining areas in my country.

[0004] The coal seam and roof in the triangular area at the junction of the return airway and the working face cut are often in a state of elastic-plastic deformation. When the roof lithology is hard, the overhanging area of ​​the goaf roof on one side of the return airway is difficult to control effectively as the working face advances. Especially in mines with a tendency for rockbursts, the roof at the corner of the return airway is prone to forming a cantilever beam structure, making it difficult for the overhanging roof to collapse in an orderly manner. During mining, the roof beam in the triangular area may deform, break, or suddenly collapse, leading to a higher risk of local roof falls. At the same time, the upper corner of the return airway is also an area where gas easily accumulates and its concentration easily exceeds the limit at the working face. Gas from the goaf often escapes from the working face as rockbursts manifest, affecting mine production.

[0005] Extensive research has been conducted both domestically and internationally on the control of rockbursts and gas disasters. However, there are few comprehensive control methods for rockbursts and abnormal gas outbursts and accumulation in the triangular area at the end of the working face. Existing measures for the simultaneous control of coal seam rockbursts and gas disasters involve determining the borehole spacing and decompression radius, arranging a large number of short boreholes, and performing multiple water injections to plasticize the coal seam, alternating between water injection and gas extraction. However, these methods are complex, involve dense drilling, are not convenient to construct, and are not suitable for the triangular area at the end. They also cannot address the control of gas in the upper corner and goaf while simultaneously controlling the roof at the return air corner. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for the coordinated management of multiple disasters in the triangular area of ​​a coal mining face based on directional drilling. By designing and arranging comb-shaped directional long boreholes in the triangular area at the end of the working face, the main borehole and branch boreholes are located at specific strata. High-power fracturing pumps are used to fracture the entire section of the branch boreholes, thereby relieving pressure on the hard roof overlying the return air corner while expanding the fracture development in the gas-rich area and enhancing the gas extraction effect. This solves the problems of high cost of coordinated management of roof rockburst disasters in the triangular area at the end and gas in the upper corner and goaf, and the limited influence range of conventional extraction or pressure relief boreholes. It achieves source control of mine pressure and gas, thereby reducing costs, increasing efficiency, and ensuring safe production in coal mines.

[0007] A collaborative management method for multiple hazards in the triangular area of ​​a coal mining face based on directional drilling includes the following steps:

[0008] S1. Determine the stress concentration zone in the triangular area of ​​the coal mining face;

[0009] The lithology of the overlying rock at the working face end is analyzed, and stress data and gas emission data of the surrounding rock in the working face are collected during mining. The degree of gas and rockburst disaster in the triangular area is evaluated, and the stress concentration zone is determined.

[0010] Specifically, S11 collects geological data, mine pressure monitoring data, and gas data respectively through borehole columnar drilling, mine pressure stress monitoring system, and roadway gas monitoring system.

[0011] The mine pressure stress monitoring system includes a stress detector, a gas detector, and a signal acquisition station. The stress detector and the gas detector are respectively connected to the signal acquisition station. The stress detector is used to detect changes in overburden stress, the gas detector is used to detect changes in gas concentration, and the signal acquisition station is used to collect information when the stress detector senses a stress change signal and to monitor the gas concentration in real time.

[0012] S12. Input the data described in S11 into the pre-trained early warning neural network model for mine pressure disasters and gas outbursts to obtain the characteristics of the degree of gas and rockburst disasters in the triangular area, determine the stress concentration zone, and thus provide a basis for the stratigraphic layout of the main hole and branch holes of the comb-shaped directional drilling.

[0013] S2. Based on step S1, design the control layer positions and control spacing of the main holes and branch holes of the comb-shaped directional drilling.

[0014] Specifically, S21, based on the borehole measurement method, the positions of the three zones of overburden are observed through geological boreholes and borehole inspection instruments, or the height of the caving zone and fracture zone is calculated using empirical formulas or numerical simulations based on the height of the three zones of overburden caused by mining. The calculated height of the caving zone is a range, defined as h1~h2, and the height of the fracture zone is defined as h3~h4.

[0015] S22. According to step S21, design the layout layer positions of the main hole and branch holes of the comb-shaped directional drilling; and determine the layout spacing of the branch holes.

[0016] After coal seam mining, the overlying strata in the goaf gradually break, migrate, and subside, forming caving zones, fracture zones, and tortuous subsidence zones. The caving zones and fracture zones are affected by mining activities, resulting in well-developed fractures and localized gas enrichment, making them the core areas for gas extraction and remediation. The overlying strata in the fracture zones are generally hard and thick, making them less prone to collapse; these are the target strata for controlling rockbursts and addressing hazards such as roof collapses.

[0017] The main borehole of the comb-shaped directional drilling was designed within the fracture zone, and the controlled layer height was [missing information].

[0018] The branch holes in the comb-shaped directional drilling are designed to be located between the caving zone and the main borehole layer, and the height range of the branch holes is as follows:

[0019] The spacing L1 of the branch holes in the comb-shaped directional drilling is designed as follows: Based on the calculated values ​​of the effective gas extraction radius R1 after borehole fracturing and the effective influence radius R2 of hydraulic fracturing, the spacing L1 of the branch holes is determined to be twice the smaller value of R1 and R2 to avoid the treatment of blank areas.

[0020] Among them, the effective radius R1 of gas extraction after borehole fracturing:

[0021]

[0022]

[0023] In the formula: fr is the friction coefficient of the rock mass; σ0 is the internal friction angle of the coal (°); σ0 is the stress in the rock mass (MPa). c denoted as uniaxial compressive strength of the rock mass, MPa, and r0 as the radius of the borehole, m.

[0024] The effective radius of influence R2 of hydraulic fracturing is obtained by comparing empirical values ​​of the radius of influence under the same pumping pressure and fracturing injection time through testing methods such as stress reduction method or electromagnetic radiation method, combined with a large number of practical hydraulic fracturing experiments.

[0025] S23. Drilling: The drilling site is located on one side of the return airway of the working face. Comb-shaped directional boreholes are drilled in a direction perpendicular to the roadway according to the control spacing L1. The total length of the comb-shaped directional boreholes is determined according to the length of the working face.

[0026] S3. Dynamically analyze geological conditions and continuously revise the branch hole exploration;

[0027] Based on a comprehensive analysis and prediction of data from 3D seismic data, borehole columnar data, and existing tunnel geological structures, the following steps were taken: First, the geological structure characteristics of the fracturing area were determined using mining plan maps and geological profile prediction maps drawn from geological exploration boreholes. Second, contour maps of strata boundaries and seismic time profiles from 3D seismic interpretation of the area were collected to correct the strata structure. Finally, downhole measurement data was collected and overlaid with the 3D seismic interpretation results to ensure the accuracy of the target strata morphology. Then, during drilling, the drilling rig angle was adjusted based on the results of continuous correction through branch borehole exploration to control the drilling trajectory accuracy, ensuring that the drilling precision could be controlled within approximately 5 meters of the target fracturing location.

[0028] S4. Design the number and length of branch holes for segmented fracturing of comb-shaped directional drilling, carry out the drilling of the main hole of comb-shaped directional drilling in the top plate, and modify the fracturing of the branch holes.

[0029] Specifically, S41, based on the lithology and thickness of the target rock layer for fracturing, design the length of the branch holes of the comb-shaped directional drilling extending downward from the main hole of the comb-shaped directional drilling. Based on the effective influence radius R2 of hydraulic fracturing, determine the spacing between branch points as 2R2. Based on the length P of the main hole of the comb-shaped directional drilling in the fracturing section, determine the number of the branch holes as P / 2R2.

[0030] S42. According to step S3, the main hole and branch holes of the comb-shaped directional drilling are completed by using the drilling measurement while drilling equipment and the bottom hole motor drilling parameter adjustment system. The drilling method for the branch hole 28 at the end of the borehole adopts the side drilling branch method. Based on the branch design parameters, the drilling accuracy of the branch hole is strictly controlled by the drilling measurement while drilling and the bottom hole motor adjustment system.

[0031] Ultimately, the vertical error of the main hole of the comb-shaped directional drilling was controlled within ±0.5m, the horizontal error within ±2m, and the vertical error of the branch holes of the comb-shaped directional drilling within ±5m.

[0032] The construction of the branch holes at the end of the borehole is completed using a "reverse" process. The branch point is set at the design point by adjusting the facing angle of the motor at the bottom of the borehole.

[0033] Repeat step S42 until the branch hole at the beginning of the construction borehole is completed, thus completing the drilling process of the main hole and branch holes of the comb-shaped directional drilling.

[0034] S43. Branch segment fracturing modification: The fracturing tool string is transported by a directional drilling machine to the junction between the branch hole at the end of the main hole of the comb-shaped directional drilling and the main hole, which is the design position of the first stage of fracturing.

[0035] like Figure 5As shown, the fracturing tool string includes a release device, packer 1, flow restrictor, packer 2, and guide shoe. A double-seal single-clamp process with two packers is used, with packing performed on both sides before and after the intersection of the main borehole and the branch borehole in the comb-shaped directional drilling. After fracturing is completed, pressure is released and drainage is performed, thus completing the fracturing modification of the branch borehole.

[0036] Preferably, the fracturing fluid used in the staged fracturing in S4 is clean water, and the pumping pressure is maintained at 13MPa to 25MPa.

[0037] S44. Using a backward-dragging fracturing tool string, the process of S43 is repeated continuously to complete the fracturing of all the branch holes, thereby forming multiple fracturing sections. When the high-pressure fracturing fluid reaches 3MPa, the packer is fully set. After the pressure is further increased to 5MPa, the flow restrictor is opened to realize the fracturing construction of the fracturing section. During the fracturing construction, the high-pressure fracturing fluid is continuously injected into the roof rock layer, causing the water pressure acting on the rock layer to gradually increase. When the pressure is greater than the rock layer fracturing pressure, the elastic residual energy of the rock layer is released in the form of kinetic energy, which manifests as rock mass compression and fracturing, causing vibration and other dynamic phenomena. This promotes the formation of a new fracture system in the rock layer, destroys the overall integrity of the rock layer, and reduces its strength. In turn, a three-dimensional fracture network is generated in the hard rock layer, which optimizes the treatment of the overburden rock of the rock burst and adds gas migration channels in the mining fracture zone.

[0038] S5. Determination of parameters for sealing and gas extraction after fracturing comb-shaped directional drilling.

[0039] S51. The borehole diameter is determined by the drilling capacity of the drilling rig and the diameter of the fracturing tool string, which is crucial for determining the negative pressure and sealing parameters for gas extraction in comb-shaped directional boreholes. The concentration and pressure of the gas to be extracted from the fracture zone of the comb-shaped directional borehole in the roof are relatively low. After overcoming the borehole friction resistance and local resistance, the residual negative pressure in the long directional borehole at the top needs to be much lower than the negative pressure in the stope to achieve the goal of high-flow extraction. Based on the designed gas mixing volume per borehole, borehole diameter, borehole length, and borehole deformation, the required extraction negative pressure for gas extraction in the fracture zone of the long directional borehole can be estimated. The initial cross-section of the borehole is considered circular. The resistance value that needs to be overcome for gas extraction can be calculated by referring to the formula for calculating the resistance of the extraction pipeline, with some parameters corrected. The local resistance is estimated based on 15% of the straight pipe resistance loss. The formula for calculating the resistance of the extraction pipeline is: Hm = 9.81gQ 2 gγgL / (KgD 5 )

[0040] Where: Hm—pipeline frictional resistance, Pa;

[0041] L—Length of the negative pressure section pipeline, in meters;

[0042] Q—Flow rate of mixed gas in the extraction pipe, m3 / h;

[0043] γ — the density ratio of the mixed gas to air;

[0044] K – A coefficient related to pipe diameter;

[0045] D—Inner diameter of the extraction / discharge tube, in cm;

[0046] The negative pressure of normal coal seam extraction borehole is 13 kPa. Based on field experience, gas extraction in the goaf is considered open extraction.

[0047] Preferably, the extraction negative pressure is generally less than 13 kPa.

[0048] S52. Top plate comb-shaped directional drilling: A welded steel pipe with a total length of not less than 30m is placed at the borehole opening position as a sealing pipe, and the length of the sealing section is slightly less than the total length of the sealing pipe; the required sealing length should be 15m to 30m according to field experience; preferably, the sealing agent is polyurethane or malathion, and the sealing agent is cement mortar or yellow mud.

[0049] S53. Connect the comb-shaped directional borehole in the top plate to the extraction pipeline system. Install a gas pressure gauge and an electronic flow monitor on the borehole pipe. Adjust the negative pressure of the extraction system and observe the pressure gauge reading. When the pressure gauge reading is stable and consistent with the negative pressure adjusted by the extraction system, it proves that the borehole is well sealed. Otherwise, return to repeat S52 to increase the sealing depth and quality until the sealing result is good.

[0050] S6. Dynamic control of gas extraction and real-time monitoring of mine pressure manifestation;

[0051] The influence range of hydraulic fracturing in comb-shaped directional boreholes in the roof was continuously explored using the transient electromagnetic method after fracturing to determine the fracturing effect. During the mining process, the comb-shaped directional boreholes gradually penetrated into the goaf, and the boreholes at the end of the rock strata deformed and collapsed, resulting in a reduction in the effective extraction length of the boreholes. Therefore, the extraction system was adjusted to dynamically change the negative pressure and reduce the energy loss of extraction.

[0052] During the mining process, real-time monitoring data such as roadway roof displacement and roof stress gauge were collected, along with gas concentration in the extraction pipeline and working face. The rockburst and gas extraction treatment effects before and after fracturing were recorded and compared.

[0053] Preferably, the length of the main hole of the comb-shaped directional drilling ranges from 200m to 2000m, the length of the branch holes of the comb-shaped directional drilling ranges from 40 to 150m, and the number of branch holes of the comb-shaped directional drilling is 3 to 10.

[0054] Preferably, the comb-shaped directional drilling segmented hydraulic fracturing technology in S4 guides the drilling through branch holes and seals the holes with two packers. The segmented fracturing technology of "overall setting and step-by-step unsealing" in the open hole achieves directional control of the fracturing fracture extension direction, fully relieves the pressure on the target rock layer, forms a three-dimensional fracture network, and effectively controls the collapse of the roof.

[0055] Preferably, the fracturing fluid used in the segmented hydraulic fracturing in S4 is clean water, and the pumping pressure is maintained at 13MPa to 25MPa.

[0056] Preferably, the gas extraction parameters for the comb-shaped directional borehole in S5 include borehole length, borehole diameter, extraction negative pressure, extraction time, extraction flow rate, and extraction concentration. The sealing materials and parameters include sealing agent, borehole casing, sealing length, and sealing strength.

[0057] Preferably, the influence range of hydraulic fracturing is usually determined by sampling and measuring the change in total moisture content of the coal seam. However, conventional sampling is labor-intensive and sampling of soft and fractured coal seams is often difficult. Therefore, transient electromagnetic profiling is used to investigate the change in water content within the radial range of the borehole before and after fracturing. If the water content is uniform, the resistivity contour lines are layered. In the water-rich area, the resistivity value decreases, and the contour lines are distorted and deformed. Based on the change in water content within a certain radial range continuously detected along the borehole axis, the influence radius of hydraulic fracturing is determined.

[0058] Compared with the prior art, the advantages of the present invention are as follows:

[0059] 1. This invention provides a method for the coordinated management of multiple disasters in the triangular area of ​​a working face based on a directional borehole with multiple uses. It achieves the coordinated management of rockburst disasters in the triangular area at the end of the working face and gas extraction in the goaf. This overcomes the problems of small treatment area, large workload, high cost, and mutual interference of existing technologies for rockburst prevention and gas extraction boreholes.

[0060] (1) Fracturing channels are developed between the caving zone and the fracture zone, resulting in gas enrichment. However, the fractures in the upper part of the caving zone are mainly delamination fractures, while the fractures in the middle and lower parts are mostly fractures. The caving zone is more easily compacted by the top fracture zone, making borehole maintenance difficult and the extraction cycle short, resulting in low gas extraction efficiency. Therefore, gas extraction is carried out through comb-shaped branch holes of directional boreholes.

[0061] (2) The overlying rock in the fracture zone is usually hard, thick, and has few original fractures, making it difficult to collapse and prone to end-to-end overhang. However, if extraction boreholes are arranged in this layer, although the gas extraction effect is limited, the borehole quality is high and the borehole stability is strong. This layer is also the best treatment area for pressure relief boreholes. Therefore, the pressure relief of the hard roof is weakened by the comb-shaped main hole of the directional hole, and gas extraction is carried out by the branch holes.

[0062] (3) Based on directional drilling, the main hole and the branch hole play different roles in specific strata. The main body of the borehole formed by the branch hole and the main hole has a better gas extraction effect. After mining, the branch hole that goes deep into the goaf fails due to the collapse of the roof. The main hole and the remaining comb-shaped branch hole can be retained for a longer time for effective extraction.

[0063] (4) By using a high-power fracturing pump group to perform segmented hydraulic fracturing of comb-shaped directional boreholes in the top plate, the multi-effect coupling of borehole pressure relief and fracturing to generate three-dimensional fractures will be achieved under the guidance of the branch holes. This effectively increases the fractures of the target rock mass, releases the pressure accumulated in the overlying rock, and weakens the impact tendency.

[0064] (5) At the same time, the top plate comb-shaped directional drilling hydraulic fracturing is carried out by injecting clean water to relieve pressure, which is green and environmentally friendly. The drilling management and maintenance are convenient during extraction, and regional treatment can be achieved according to the drilling length. Attached Figure Description

[0065] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0066] Figure 1 This is a flowchart of the operation steps of the present invention;

[0067] Figure 2 This is a longitudinal perspective view of the segmented hydraulic fracturing hole layout of a single comb-shaped directional borehole in the roof before mining in this invention;

[0068] Figure 3 This is a longitudinal perspective view of the segmented hydraulic fracturing hole layout of a single comb-shaped directional borehole in the roof during the mining process of this invention;

[0069] Figure 4 This is a top view of the multi-stage fracturing arrangement of comb-shaped directional drilling holes in the top plate in this invention.

[0070] Figure 5 This is a schematic diagram of the first branch segment of a single comb-shaped directional borehole in the top plate in this invention.

[0071] Figure label:

[0072] 1-Sealing pipe; 2-Main hole of comb-shaped directional drilling; 3-Branch hole of comb-shaped directional drilling; 4-Fracturing and setting position of branch hole; 5-Target stratum; 6-Old roof; 7-Direct roof; 8-Coal seam; 9-Fractured zone; 10-Fractured zone; 11-Collapse zone; 12-Transport roadway; 13-Corner; 14-Goaf; 15-Roof comb-shaped directional drilling 1; 16-Roof comb-shaped directional drilling 2; 17-Drilling site 1; 18-Drilling site 2; 19-Return airway; 20-Drill hole left after drilling by directional drilling rig; 21-Push tubing; 22-Branch hole at the beginning of the borehole; 23-Release handle; 24-Packer 1; 25-Flow restrictor; 26-Packer 2; 27-Guide shoe; 28-Branch hole at the end of the borehole. Detailed Implementation

[0073] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0074] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0075] like Figures 1 to 5 As shown, a method for collaborative management of multiple hazards in the triangular area of ​​a coal mining face based on directional drilling includes the following steps:

[0076] S1. Determine the stress concentration zone in the triangular area of ​​the coal mining face;

[0077] The lithology of the overlying rock at the working face end is analyzed, and stress data and gas emission data of the surrounding rock in the working face are collected during mining. The degree of gas and rockburst disaster in the triangular area is evaluated, and the stress concentration zone is determined.

[0078] Specifically, S11 collects geological data, mine pressure monitoring data, and gas data respectively through borehole columnar drilling, mine pressure stress monitoring system, and roadway gas monitoring system.

[0079] The mine pressure stress monitoring system includes a stress detector, a gas detector, and a signal acquisition station. The stress detector and the gas detector are respectively connected to the signal acquisition station. The stress detector is used to detect changes in overburden stress, the gas detector is used to detect changes in gas concentration, and the signal acquisition station is used to collect information when the stress detector senses a stress change signal and to monitor the gas concentration in real time.

[0080] S12. Input the data described in S11 into the pre-trained early warning neural network model for mine pressure disasters and gas outbursts to obtain the characteristics of the degree of gas and rockburst disasters in the triangular area, determine the stress concentration zone, and thus provide a basis for the stratigraphic layout of the main hole 2 and branch holes of the comb-shaped directional drilling.

[0081] S2. Based on step S1, design the layout layers of the main hole 2 and branch holes of the comb-shaped directional drilling, and the layout spacing of the comb-shaped directional drilling.

[0082] Specifically, S21, based on the borehole measurement method, the positions of the three overburden zones are observed through geological boreholes and borehole inspection instruments, or the height of the caving zone 11 and the fracture zone 9 is numerically simulated using empirical formulas for the height of the three overburden zones during mining, or flac3d or UDEC software. The calculated height is a range, and the height range of the caving zone 11 is defined as h1~h2, and the height range of the fracture zone 9 is h3~h4.

[0083] like Figure 2 and Figure 3 As shown in Table 1, based on the stratigraphic information and the lithology and thickness of the rock strata displayed in the borehole columnar section, the height of the caving zone (i.e., the caving zone) and the height of the fracture zone (i.e., the fissure zone) are calculated using the recommended formulas in the "Guidelines for Coal Pillar Retention and Coal Mining in Buildings, Water Bodies, Railways and Main Shafts".

[0084] Table 1. Empirical formulas for calculating the height of caving zones and fault zones.

[0085]

[0086] Note: M - mining height, m; n - number of coal seams; H a - Maximum height of the landslide zone, m; H c - Maximum height of the fault zone, in meters (m).

[0087] S22. According to step S21, design the layout layer positions of the main hole 2 and branch holes of the comb-shaped directional drilling; and determine the layout spacing of the branch holes.

[0088] After coal seam mining, the overlying strata of goaf 14 gradually fractured, migrated, and subsided, forming caving zones, fracture zones, and tortuous subsidence zones. The caving zone 11 to fracture zone 9 were affected by mining activities, resulting in fully developed fracture 10. This area has localized gas enrichment and is the core area for gas extraction and remediation. Meanwhile, the overlying strata of fracture zone 9 are generally hard and thick, making them less prone to collapse. This is the target stratum for controlling rockbursts and addressing hazards such as roof collapse at the end of the goaf.

[0089] Among them, weak rock strata refer to mudstone, argillaceous sandstone, etc. with a uniaxial compressive strength of 10-20 MPa; medium-hard rock strata refer to sandstone, argillaceous limestone, sandy mudstone, sandy shale, shale, etc. with a uniaxial compressive strength of 20-40 MPa; hard rock strata refer to quartz sandstone, limestone, sandy mudstone, conglomerate, etc. with a uniaxial compressive strength of 40-80 MPa; and thick rock strata refer to rock strata with a thickness greater than 3 m.

[0090] The comb-shaped directional drilling main borehole 2 is designed within fracture zone 9, and the controlled layer height is [missing information]. The branch hole layer is designed between the caving zone 11 and the main hole layer, and the layer height range of the branch hole is [missing information].

[0091] By designing the main borehole 2 of the comb-shaped directional drilling in the fracture zone 9, and the branch borehole in the caving zone 11 between the main borehole and the branch borehole, and further optimizing the layer design based on the fracturing effect of the high-power fracturing pump group, a single borehole can be used for multiple purposes and multiple disasters can be managed in a coordinated manner.

[0092] The layout spacing L1 of the branch holes 3 of the comb-shaped directional drilling is designed as follows: Based on the calculated values ​​of the effective gas extraction radius R1 after borehole fracturing and the effective influence radius R2 of hydraulic fracturing, the layout spacing L1 of the branch holes is determined to be twice the smaller value of R1 and R2 to avoid the blank area affected by the treatment.

[0093] Among them, the effective radius R1 of gas extraction after borehole fracturing:

[0094]

[0095]

[0096] In the formula: fr is the friction coefficient of the rock mass; σ0 is the internal friction angle of the coal (°); σ0 is the stress in the rock mass (MPa). c denoted as uniaxial compressive strength of the rock mass, MPa, and r0 as the radius of the borehole, m.

[0097] The effective radius of influence R2 of hydraulic fracturing is obtained by comparing empirical values ​​of the radius of influence under the same pumping pressure and fracturing injection time through testing methods such as stress reduction method or electromagnetic radiation method, combined with a large number of practical hydraulic fracturing experiments.

[0098] S23. Drilling: The drilling site is located on one side of the return airway 19 of the working face. Comb-shaped directional drilling is carried out in a direction perpendicular to the roadway according to the control spacing L1. The total length of the comb-shaped directional drilling is determined according to the length of the working face.

[0099] S3. Dynamic analysis of geological conditions, and continuous correction of the branch hole exploration during the construction process;

[0100] Dynamic analysis of geological conditions was conducted based on 3D seismic data, borehole columnar data, and geological structural features revealed by existing tunnels. First, the geological structural features of the fracturing area were determined using mining plan maps and geological profile prediction maps drawn from geological exploration boreholes. Second, contour maps of strata boundaries and seismic time profiles from 3D seismic interpretation of the area were collected to correct the strata structure. Finally, downhole measurement data was collected and overlaid with the 3D seismic interpretation results to ensure the accuracy of the target strata morphology. Furthermore, during drilling operations, the drilling rig angle was adjusted based on the results of continuous correction through branch borehole exploration to control the drilling trajectory accuracy, ensuring that the construction precision could be controlled within approximately 5 meters of the fracturing target location.

[0101] S4. Design the number and length of branch holes for segmented fracturing of comb-shaped directional drilling, drill the main hole 2 of the comb-shaped directional drilling in the top plate, and modify the branch holes for fracturing.

[0102] Specifically, S41, based on the lithology and thickness of the target rock layer for fracturing, design the branch hole 3 of the comb-shaped directional drilling extending downward from the main hole 2 of the comb-shaped directional drilling. Based on the effective influence radius R2 of hydraulic fracturing, determine the spacing between branch points as 2R2. Based on the length P of the main hole of the comb-shaped directional drilling in the fracturing section, determine the number of branch holes as P / 2R2.

[0103] Figure 2 and Figure 3 As shown, there is a branch hole fracturing and sealing position 4 on one side of the target rock stratum 5. The old roof 6, the immediate roof 7 and the coal seam 8 are arranged in sequence. The main hole 2 of the comb-shaped directional drilling is designed to be 500m to 600m long. The horizontal section is branched every 60m, and a total of 5 branch holes of the comb-shaped directional drilling are constructed. The length of the branch hole 3 of the comb-shaped directional drilling is designed to be 40m to 60m.

[0104] S42. According to step S3, the drilling of the main hole 2 and branch holes of the comb-shaped directional drilling is completed by using the drilling measurement while drilling equipment and the bottom hole motor drilling parameter adjustment system. The drilling method for the branch hole 28 at the end of the borehole adopts the side drilling branch method. Based on the branch design parameters, the drilling accuracy of the branch hole is strictly controlled by the drilling measurement while drilling and the bottom hole motor adjustment system.

[0105] Ultimately, the vertical error of the main hole 2 of the comb-shaped directional drilling was controlled within ±0.5m, the horizontal error within ±2m, and the vertical error of the branch hole 3 of the comb-shaped directional drilling was controlled within ±5m.

[0106] The construction of the branch holes at the end of the borehole is completed using a "reverse" process. The branch point is set at the design point by adjusting the facing angle of the motor at the bottom of the borehole.

[0107] Repeat step S42 until the first branch hole 22 of the construction borehole is completed, thus completing the drilling process of the main hole 2 and the branch holes of the comb-shaped directional drilling.

[0108] S43. Branch segment fracturing modification: The fracturing tool string is transported by a directional drilling machine to the junction between the branch hole at the end of the main hole 2 of the comb-shaped directional drilling and the main hole, which is the design position for the first stage of fracturing.

[0109] Multiple comb-shaped directional drilling holes in the top plate for segmented fracturing, such as... Figure 4 As shown, it includes transport roadway 12, corner 13, goaf 14, roof comb-shaped directional borehole 15, roof comb-shaped directional borehole 2 16, drilling site 1 17, drilling site 2 18, and return airway 19.

[0110] like Figure 5 As shown, the borehole 20 left after drilling by the directional drilling rig. The fracturing tool string includes a push tubing 21, a branch hole 22 at the beginning of the borehole, a release 23, a packer 124, a flow restrictor 25, a packer 26, a guide shoe 27, and a branch hole 28 at the end of the borehole. A double-seal single-clamp process with two packers is used, with packing performed on both sides before and after the intersection of the main borehole 2 and the branch hole in the comb-shaped directional drilling. After the fracturing operation is completed, the pressure is released and the water is drained, completing the fracturing modification of the branch hole.

[0111] Preferably, the fracturing fluid used in the staged fracturing in S4 is clean water, and the pumping pressure is maintained at 13MPa to 25MPa.

[0112] S44. Using a backward-dragging fracturing tool string, the process of S43 is repeated continuously to complete the fracturing of all the branch holes, thereby forming multiple fracturing sections. When the high-pressure fracturing fluid reaches 3MPa, the packer is fully set. After the pressure is further increased to 5MPa, the flow restrictor is opened to realize the fracturing construction of the fracturing section. During the fracturing construction, the high-pressure fracturing fluid is continuously injected into the roof rock layer, causing the water pressure acting on the rock layer to gradually increase. When the pressure is greater than the rock layer fracturing pressure, the elastic residual energy of the rock layer is released in the form of kinetic energy, which manifests as rock mass compression and fracturing, causing vibration and other dynamic phenomena, causing the rock layer to generate a new fracture system, destroying the overall integrity of the rock layer and reducing its strength. This generates a three-dimensional fracture network 10 in the hard rock layer, optimizes the treatment of the overburden rock of the rock burst, and adds a gas migration channel modification in the mining fracture zone 9.

[0113] S5. Determination of parameters for sealing and gas extraction after fracturing comb-shaped directional drilling.

[0114] S51. The borehole diameter is determined by the drilling capacity of the drilling rig and the diameter of the fracturing tool string, which is crucial for determining the negative pressure and sealing parameters for gas extraction in comb-shaped directional boreholes. The gas concentration and pressure to be extracted in the comb-shaped directional borehole fracture zone 9 of the roof are relatively low. After overcoming borehole friction resistance and local resistance, the residual negative pressure in the long directional borehole at the top needs to be significantly lower than the stope negative pressure to achieve the goal of high-flow extraction. Based on the designed gas mixing volume per borehole, borehole diameter, borehole length, and borehole deformation, the required extraction negative pressure for gas extraction in the long directional borehole fracture zone 9 can be estimated. The initial cross-section of the borehole is considered circular. The resistance value to be overcome for gas extraction can be calculated using the formula for calculating the resistance of the extraction pipeline, with some parameters adjusted accordingly. The local resistance is estimated based on 15% of the straight pipe resistance loss. The formula for calculating the resistance of the extraction pipeline is: Hm = 9.81gQ. 2 gγgL / (KgD 5 )

[0115] Where: Hm—pipeline frictional resistance, Pa;

[0116] L—Length of the negative pressure section pipeline, in meters;

[0117] Q—Flow rate of mixed gas in the extraction pipe, m3 / h;

[0118] γ — the density ratio of the mixed gas to air;

[0119] K – A coefficient related to pipe diameter;

[0120] D—Inner diameter of the extraction / discharge tube, in cm;

[0121] The negative pressure of normal coal seam extraction borehole is 13 kPa. Based on field experience, the gas extraction in the goaf is an open extraction method. Preferably, the extraction negative pressure is generally less than 13 kPa.

[0122] S52. The high negative pressure during extraction from the comb-shaped directional drilling in the top plate necessitates higher sealing quality. A welded steel pipe with a total length of not less than 30m is lowered at the borehole opening as sealing pipe 1, with the sealing section length slightly shorter than the total length of sealing pipe 1. Based on field experience, the required sealing length should be 15m to 30m. Preferably, the sealing agent is polyurethane or malathion, and the sealing agent is cement mortar or yellow mud.

[0123] S53. Connect the comb-shaped directional borehole to the extraction pipeline system. Install a gas pressure gauge and an electronic flow monitor on the borehole pipe. Adjust the negative pressure of the extraction system and observe the pressure gauge reading. When the pressure gauge reading is stable and consistent with the adjusted negative pressure of the extraction system, it proves that the borehole is well sealed. Otherwise, return to repeat S52 to increase the sealing depth and quality until the sealing result is good.

[0124] S6, dynamic control of gas extraction and real-time monitoring of mine pressure manifestation.

[0125] The influence range of hydraulic fracturing in comb-shaped directional boreholes was continuously explored using the transient electromagnetic method after fracturing to determine the fracturing effect. During the mining process, the comb-shaped directional boreholes gradually penetrated into the goaf 14. The boreholes at the end of the rock strata deformed and collapsed, resulting in a reduction in the effective extraction length of the boreholes. Consequently, the extraction system was adjusted to dynamically change the negative pressure and reduce extraction energy loss.

[0126] During the mining process, real-time monitoring data such as roadway roof displacement and roof stress gauge were collected, along with gas concentration in the extraction pipeline and working face. The rockburst and gas extraction treatment effects before and after fracturing were recorded and compared.

[0127] The principle of this invention is to design and arrange comb-shaped directional boreholes in the triangular area at the end of the working face, so that the main borehole 2 and the branch boreholes are located in specific strata, that is, the main borehole is arranged in the hard rock layer of the fracture zone 9, which ensures the quality and service life of the borehole. The comb-shaped branch boreholes extending from the main borehole connect the gas-rich area between the fracture zone 9 and the collapse zone 11, thereby enhancing the gas extraction range. The branch boreholes are fracturing in their entirety using a high-power fracturing pump set. The hydraulic fracturing of the comb-shaped directional boreholes increases the fractures 10 and weak surfaces of the overlying hard rock layer. The fracturing water injection can reduce the cohesion between rock layers. After high pressure water is used, a water wedge is formed, which can increase the weak surfaces of the fractures 10 in the rock. The strength of the rock will be significantly reduced after fracturing, so that the roof of the corner 13 will collapse in time, thereby reducing the exposed and collapsed area of ​​the roof. While achieving stress transfer and release in the overburden, the fracture channels generated by hydraulic fracturing increase the rock strata fractures between the main borehole and branch boreholes, improving the permeability of the rock strata and the gas extraction efficiency in the goaf A area, and reducing the risk of gas exceeding the limit in the upper corner 13. This achieves the goal of multi-purpose drilling, cost reduction, and efficiency improvement. The method of this invention is simple and easy to operate, fully utilizing the multiple functions of drilling and avoiding the repetitiveness and waste inherent in existing drilling techniques.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for collaborative management of multiple hazards in the triangular area of ​​a coal mining face based on directional drilling, comprising the following steps: S1. Determine the stress concentration zone in the triangular area of ​​the coal mining face; S2. Based on step S1, design the control layer positions and control spacing of the main holes and branch holes of the comb-shaped directional drilling. S3. Dynamically analyze geological conditions and continuously revise the branch hole exploration; S4. Design the number and length of branch holes for segmented fracturing of comb-shaped directional drilling, carry out the drilling of the main hole of comb-shaped directional drilling in the top plate, and modify the fracturing of the branch holes; S5. Determination of parameters for sealing and gas extraction after fracturing comb-shaped directional drilling. S6. Dynamic control of gas extraction and real-time monitoring of mine pressure manifestation; In step S1, the lithology of the overlying rock at the working face end is analyzed, and stress data and gas emission data of the surrounding rock in the working face during mining are collected to evaluate the degree of gas and rockburst disaster in the triangular area and determine the stress concentration zone; S11, geological data, mine pressure monitoring data and gas data are collected through borehole columnar drilling, mine pressure stress monitoring system and roadway gas monitoring system respectively; S12, the data in S11 are input into the pre-trained mine pressure disaster and gas emission early warning neural network model to obtain the degree characteristics of gas and rockburst disaster in the triangular area, determine the stress concentration zone, and thus provide a basis for the stratigraphic layout of the main hole and branch holes of comb-shaped directional drilling; In step S2, S21, the height of the collapse zone and fracture zone is calculated; S22, based on step S21, the layout layer positions of the main hole and branch holes of the comb-shaped directional drilling are designed; and the layout spacing of the branch holes is determined. The main borehole of the comb-shaped directional drilling is designed within the fracture zone, and the height of the controlled layer is [missing information]. The branch hole layer is designed between the caving zone and the main hole layer, and the layer height range of the branch hole is [missing information]. ; In the formula: H1 is the height of the controlled layer; h1 is the minimum height of the caving zone; h2 is the maximum height of the caving zone; h3 is the minimum height of the fracture zone; h4 is the maximum height of the fracture zone.

2. The method for coordinated management of multiple disasters in the triangular area of ​​a coal mining face based on directional drilling as described in claim 1, characterized in that: Based on the calculated values ​​of the effective gas extraction radius R1 after borehole fracturing and the effective influence radius R2 of hydraulic fracturing, the control spacing L1 of the branch holes is determined.

3. The method for coordinated management of multiple disasters in the triangular area of ​​a coal mining face based on directional drilling as described in claim 2, characterized in that: Effective radius R1 for gas extraction after borehole fracturing: In the formula: fr is the friction coefficient of the rock mass; The internal friction angle of coal is denoted as , in degrees (°). The stress in the rock mass is expressed in MPa. denoted as uniaxial compressive strength of the rock mass, MPa, and r0 as the radius of the borehole, m.

4. The method for coordinated management of multiple disasters in the triangular area of ​​a coal mining face based on directional drilling according to claim 3, characterized in that: It also includes step S23, drilling construction: the construction site is on one side of the return air roadway of the working face, and comb-shaped directional drilling is carried out in a direction perpendicular to the roadway according to the control spacing L1. The total length of the comb-shaped directional drilling is determined according to the length of the working face.

5. The method for coordinated management of multiple disasters in the triangular area of ​​a coal mining face based on directional drilling according to claim 1, characterized in that: In step S3, the geological conditions are dynamically analyzed based on 3D seismic data, borehole columnar data, and the geological structural features revealed by existing tunnels.

6. The method for coordinated management of multiple disasters in the triangular area of ​​a coal mining face based on directional drilling according to claim 1, characterized in that: In step S4, S41, based on the lithology and thickness of the target rock layer, design the length of the branch holes of the comb-shaped directional drilling extending downward from the main hole of the comb-shaped directional drilling; S42, according to step S3, complete the drilling of the main hole and branch holes of the comb-shaped directional drilling; S43, fracturing and modifying the branch section; S44, using a backward dragging fracturing tool string, continuously repeat the process of S43 to complete the fracturing of all the branch holes.

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