Coal roadway gas extraction and roof cutting method based on directional fracturing

Abstract

The application discloses a coal roadway gas extraction and roof cutting method based on directional fracturing, and belongs to the field of underground coal mine gas extraction and surrounding rock control. Firstly, rock stratum analysis and calculation are performed, a borehole parallel to a coal roadway and equal in length to the coal roadway is constructed in an uphole roadway or a cross-cut, and a slot is cut, directional slot cutting in the borehole induces fracturing of a coal roadway roof, breaks the immediate roof of the coal roadway, cuts off stress transmission of the roof, reduces dynamic load strength, after mining of a working face is completed, the roof rock is broken, a hard roof normally collapses, and pressure relief is completed. Meanwhile, in the fracturing process, cracks expand from the coal roadway roof to a coal seam, a large number of cracks are generated in the coal seam, and the stored gas in the coal seam is more easily extracted, rapid excavation of a transportation roadway is realized, and gas outburst risk in the roadway excavation process is reduced. The application can improve roadway surrounding rock conditions, effectively reduce maintenance cost of a gob-side entry, improve gas extraction efficiency, and reduce roadway excavation risk, and has important significance for coal mine safety production.

Description

TECHNICAL FIELD

[0001] The present application relates to a coal roadway gas extraction and roof cutting method based on directional fracturing, and belongs to the technical field of coal mine underground gas extraction and surrounding rock control. BACKGROUND

[0002] With the continuous deepening of coal mining, coal resources are decreasing, in order to improve the utilization rate of resources, the gas extraction and surrounding rock control technology in coal mine has become the key to the safety production of coal mine. The traditional gas extraction method is low in efficiency under the condition of hard roof, and the risk of gas disaster is high, the accumulation of gas in the coal seam may cause explosion accident, which seriously threatens the safety of miners and the production efficiency of coal mine. The traditional surrounding rock control technology is directly supported under the dynamic load, which often causes the deformation of the surrounding rock of the roadway, and may also cause the collapse of the roadway, threatening the safety of personnel and equipment.

[0003] Therefore, it is of great significance to develop a new gas extraction combined with surrounding rock control technology, which can effectively control the surrounding rock pressure disaster of coal mine underground mining roadway and improve the efficiency of gas extraction. SUMMARY

[0004] The purpose of the present application is to provide a coal roadway gas extraction and roof cutting method based on directional fracturing. The method solves the problems of low efficiency of existing gas extraction method and high risk of gas disaster under the condition of hard roof.

[0005] The technical scheme of the present application: a coal roadway gas extraction and roof cutting method based on directional fracturing, first, rock analysis and calculation, construction of drill hole parallel to coal roadway and equal in length in uphill and downhill roadway or crosscut, and cutting groove, inducing coal roadway roof to fracture by directional cutting groove in drill hole, breaking the immediate roof of coal roadway, cutting off the stress conduction of roof, reducing the dynamic load strength, after the working face is mined, the roof rock is broken, the hard roof is normally collapsed, the pressure relief is completed, at the same time in the process of fracturing, the crack expands from the coal roadway roof to the coal seam, a large number of cracks are generated in the coal seam, the occurrence of gas in the coal seam is more easily extracted, the rapid excavation of the transportation roadway is realized, and the risk of gas outburst in the process of excavating roadway is reduced.

[0006] The foregoing coal roadway gas extraction and roof cutting method based on directional fracturing, the method specifically includes the following steps:

[0007] a. Analysis and calculation step: analyze the rock characteristics of the target coal seam roof, determine the appropriate fracturing position and direction, select reasonable drill hole radius and directional cutting groove angle, and then calculate the directional cutting groove section spacing D according to the formula t and the hydraulic fracturing drill hole spacing radius R;

[0008] b. Drilling step: Based on the results of the above analysis and calculation, drill hydraulic fracturing holes in the coal seam roadway roof, and construct 1-3 hydraulic fracturing holes in the adjacent stone gate roadway, and evenly arrange them along the parallel direction of the trench. The drilling path is from the turn of the adjacent stone gate roadway roof to the coal roadway roof, and the depth range is the coal roadway length. The drilling hole spacing is calculated in step a;

[0009] c. Pre-determining the directional slotting section: First, use the drilling rig to push the drill pipe and slotting drill bit to open the directional slotting section at the calculated directional slotting section location, push out the drill pipe, and then push the packer into the directional slotting section. Pressurize the packer through the high-pressure water injection pipe;

[0010] d. Equipment installation steps: Place the hydraulic fracturing device, including the isolation section, high-pressure water pipeline, pressure gauge, and flow meter, into the predetermined position in the borehole;

[0011] e. Fracturing step: The high-pressure water injection pump is turned on, and roof cutting begins. The hydraulic fracturing device delivers high-pressure water for directional fracturing, forming a directional fracture network, breaking up the roof rock layer, and forming a gas migration channel of a certain width between the coal seam and the roof;

[0012] f. Gas extraction preparation steps: After hydraulic fracturing is completed, the top is cut and pressure relief begins. The hydraulic fracturing borehole is used as a gas extraction borehole. A gas extraction pipe is installed in the gas extraction borehole and connected to the surface gas extraction system;

[0013] g. Gas extraction steps: Start the gas extraction system and use the negative pressure generated by the extraction pump to extract the gas from the coal seam. Use flow meters and pressure gauges to monitor gas extraction parameters in real time, and adjust the extraction system operating parameters in a timely manner based on the monitoring results.

[0014] h. Support and mining steps: After the gas is controlled, support excavation is carried out in the transport tunnel, followed by normal mining. After the working face is mined, the pressure relief is completed.

[0015] In the aforementioned method for coal roadway gas extraction and top cutting based on directional fracturing, the formula for calculating the directional cutting groove spacing and the drilling hole spacing in step a is as follows:

[0016] (1) Directional slot spacing D t The calculation formula is:

[0017]

[0018] Compare the D calculated by the above two formulas (1) and (2) t The value is determined to be the minimum value calculated as the directional grooving segment spacing D t ;

[0019] In the above formula, Dt , directional groove spacing; E, elastic modulus of rock; λ, Poisson's ratio of rock; P1, injection pressure of high-pressure water injection pump; σ h , ground stress at the borehole; r w , the radius of the hydraulic fracturing borehole; σ t , rock tensile strength; Angle of internal friction of rock;

[0020] (2) The hydraulic fracturing borehole spacing is calculated according to the following formula (3):

[0021] R=L (3)

[0022] In the above formula (3), R is the radius of the hydraulic fracturing borehole spacing; L is the fracture deflection distance;

[0023] If only one hole is drilled, no calculation is required.

[0024] In the aforementioned coal roadway gas extraction and top cutting method based on directional fracturing, in the step a, the drilling diameter can be selected from 94, 96, 98, 115, and 120 mm, and the cutting angle range is 60°-90°.

[0025] In the aforementioned coal roadway gas extraction and roof cutting method based on directional fracturing, the high-pressure water injection pump has a pressure of 60-90 MPa and a flow rate of 90-150 L / min.

[0026] In the aforementioned coal roadway gas extraction and top cutting method based on directional fracturing, in the step c, the slotting sequence of each borehole is reversed, and each borehole has multiple directional slotting sections, and the slotting is performed sequentially from the bottom of the borehole from the inside to the outside. The length of the directional slot is d = 2r, where d is the length of the directional slot and r is the half length of the directional slot.

[0027] Beneficial effects of the present invention: Compared with the prior art, the method of the present invention has the following advantages:

[0028] 1. Solve the problems of material transportation efficiency and safety. The hydraulic fracturing drilling construction location of the present invention is in the stone gate adjacent to the working face. The drilling direction is parallel to the drift, and the construction is carried out in the rock layer. This not only improves the safety of construction personnel during drilling, but also reduces the transportation time of equipment. During the implementation process, it solves both safety and transportation problems, providing guarantees for safe and efficient production in the mine.

[0029] 2. After the hydraulic fracturing equipment cuts the roof, the working face has not yet been mined, and the roof rock becomes more broken. When the working face is mined, the gangue on the roof will fall as it is mined. The rock's crushing and expansion properties and the control of the support device are used to achieve stress balance of the surrounding rock. This is different from the traditional filling into the goaf. The broken rock on the roof after cutting the roof can cooperate with the filling material to reinforce the goaf, solving the problem of stress imbalance when filling along the goaf to one side of the goaf.

[0030] 3. The innovation of the roof cutting technology of the present invention compared with traditional hydraulic fracturing roof cutting is that: before the working face is mined, the roof is broken in advance to achieve local stress transfer of the roof; during mining, the roof rock falls as it is mined; after the working face is mined, due to the stress transfer of the roof, the tunnels adjacent to the roof cutting position are easier to support and excavate, and the tunnel deformation is smaller.

[0031] 4. The present invention is a method for gas extraction. After the roof is cut, the cracks in the roof rock gradually expand and penetrate each other. At the same time, the roof rock is broken under the action of high-pressure water, and the roof rock layer sinks and deforms, forming a pressure relief space of a certain width between the coal seam and the roof, thereby effectively improving the stress state and migration channel of the gas in the coal seam. At this time, the gas is extracted, and the purpose of safe extraction can be achieved, changing the traditional idea of ​​gas extraction. The gas is extracted while achieving pressure relief when the roof is cut, and then the coal seam is directly mined, solving the problem of difficult extraction in traditional gas extraction tunnels.

[0032] 5. The present invention combines directional hydraulic fracturing to achieve roof cutting. By shortening the long cantilever beam in the goaf, the stress condition of the side tunnels in the goaf is improved, the stress of the tunnel surrounding rock is transferred, the mine pressure is alleviated, and the original stress transfer path is changed, which is beneficial to the support of the roof and the two sides, solves the problems of roof bulging and coal wall spalling, and achieves the purpose of pressure relief.

[0033] 6. The present invention is a new type of gas extraction method. By extracting gas at the stone gate, there is no need to arrange a gas extraction tunnel, which reduces the amount of excavation engineering, lowers production costs, improves the safety of gas extraction, and accelerates gas extraction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the layout diagram of the mining area tunnels;

[0035] Figure 2 It is a numbered illustration;

[0036] Figure 3 It is a section for drilling holes and pre-orienting grooves based on BB profiles;

[0037] Figure 4 To pressurize the packer based on the BB profile;

[0038] Figure 5 It is a hydraulic fracturing diagram based on BB section;

[0039] Figure 6 For gas extraction based on BB profile;

[0040] Figure 7 This is the AA cross-section of the 110103 working face before mining, that is, after top cutting but not mining;

[0041] Figure 8 This is the AA cross-section of the 110103 working face after mining, that is, mining was carried out after the top was cut;

[0042] Figure 9 This is a schematic diagram of fracturing in the directional groove section;

[0043] Figure 10 Schematic diagram of crack turning;

[0044] Figure 11 This is a flow chart of the entire process of coal roadway extraction and top cutting method based on directional fracturing.

[0045] Explanation of reference numerals: transport up the mountain - 1; track up the mountain - 2; return air up the mountain - 3; regulating air door - 4; 11 machine track stone door - 5; 11 return air stone door - 6; 12 return air stone door - 7; 12 machine track stone door - 8; 110102 return air lane - 9; 110102 transport lane (110103 return air lane) - 10; 110101 goaf - 11; stop mining line - 12; 110102 goaf - 13; 110102 filling - 14; 110103 transport lane (tunneling head) - 15; hydraulic fracturing drilling hole (gas extraction drilling hole) - 16; 110101 filling - 17; old roof - 18; No. 1 coal seam - 19; direct Roof-20; directional grooving section-21; drilling rig-22; temporary support-23; cut direct roof-24; 110103 filling-25; 110103 goaf-26; hydraulic fracturing-27; high-pressure water pipe-28; water tank-29; high-pressure water injection pump-30; pressure gauge and flow meter-31; gas extraction pipe-32; gas monitor-33; gas flow meter-34; gas extraction pump-35; gas tank-36; high-pressure pump-37; pressure gauge-38; water injection pipe-39; water injection head (gas injection head)-40; elastic membrane-41; water outlet-42; isolation section-43; directional grooving-44; hydraulic fracturing expansion-45. DETAILED DESCRIPTION

[0046] The present invention will be further described below with reference to the accompanying drawings and examples, but they are not intended to limit the present invention.

[0047] An embodiment of the present invention: A method for coal roadway gas extraction and top cutting based on directional fracturing includes the following steps:

[0048] S1: Analyzing the rock characteristics of the target coal seam roof, determining the appropriate fracturing position and direction, selecting reasonable drilling radius and directional slot angle, drilling diameter can be selected as 94, 96, 98, 115, 120 mm, slot angle range is 60°-90°, then calculating the directional slot section spacing and hydraulic fracturing drilling spacing according to the listed formula.

[0049] (1) Directional slot section spacing calculation

[0050] ① According to the slot section axial spacing estimation

[0051]

[0052] In the formula

[0053] D t , directional slot spacing (m);

[0054] E, elastic modulus of rock;

[0055] λ, Poisson's ratio of rock;

[0056] P1, high-pressure water injection pump water injection pressure (MPa);

[0057] σ h , borehole stress (MPa);

[0058] ② According to the optimal radial influence radius calculation of the crack

[0059]

[0060] In the formula

[0061] D t , directional slot section spacing (m);

[0062] r w , the radius of the hydraulic fracturing drilling (m);

[0063] λ, Poisson's ratio;

[0064] P1, high-pressure water injection pump water injection pressure (MPa);

[0065] σ t , tensile strength of rock (MPa);

[0066] Internal friction angle of rock (°).

[0067] According to the above two formulas, two D t values are calculated and compared, and the minimum value is determined as the spacing D t of the directional slot section.

[0068] (2) Calculation of hydraulic fracturing borehole spacing (no calculation required if only one borehole is drilled)

[0069] Calculated by the deflection distance of the crack

[0070] The deflection angle θ is the angle between the cutting direction and the maximum horizontal principal stress, θ = 90° - ɑ = 90° - 75° = 15°.

[0071] The crack deflection distance refers to the vertical distance from the crack propagation path to the maximum horizontal principal stress of the borehole when the crack propagation path is parallel to the maximum horizontal principal direction, and is represented by L.

[0072] According to fracture mechanics

[0073]

[0074] Deflection distance

[0075]

[0076] In the above three formulas,

[0077] L, crack deflection distance (m);

[0078] θ, deflection angle (°);

[0079] r, half length of directional groove (m);

[0080] fracture toughness of rocks;

[0081] σ h , in-situ stress at the borehole (MPa);

[0082] σ1, maximum horizontal principal stress (MPa);

[0083] σ3, minimum horizontal principal stress (MPa);

[0084] K, permeability coefficient (m / s);

[0085] h, thickness of the immediate roof rock layer (m);

[0086] ΔP, pressure difference between the hydraulic fracturing borehole and the rock formation (MPa);

[0087] q, fracturing fluid displacement (m 3 / s);

[0088] μ, viscosity (MPa·s).

[0089] R=L

[0090] R, hydraulic fracturing drilling spacing radius (m).

[0091] By the calculation of (1) and (2), the spacing D of the directional grooving segments is finally determined. t and hydraulic fracturing borehole spacing R.

[0092] S2: Based on the above analysis, drill hydraulic fracturing holes in the coal seam roadway roof. Construct one to three hydraulic fracturing holes in the adjacent stone gate roadway, evenly spaced parallel to the runway. The drilling path is from the adjacent stone gate roadway roof to the coal roadway roof, with a depth range equal to the coal roadway length. The spacing between the holes is calculated above.

[0093] S3: Predetermine the directional groove section (fracturing point). The groove opening sequence of each borehole adopts a reverse method, and each borehole has multiple directional groove sections. The groove section spacing is calculated as above, and the grooves are opened from the bottom of the borehole from the inside to the outside. Operation steps: First, use the drilling rig to push the drill pipe and the groove drill bit to open the directional groove section at the calculated directional groove section position, and push out the drill pipe. Then push the packer into the directional groove section, and pressurize the packer through the high-pressure water injection pipe to achieve the purpose of sealing the directional groove section. The directional groove length is d = 2r, where r is the half length of the directional groove (m).

[0094] S4: Connect the hydraulic fracturing equipment. This equipment includes a packer, high-pressure water pipe, pressure gauge, and flow meter. The pressure gauge and flow meter monitor the pressure changes and high-pressure water flow rate during the fracturing process in real time. They adjust the pressure and flow rate of the high-pressure water flow according to the preset pressure to ensure that the fracturing process proceeds stably along the predetermined direction and achieves the desired fracturing effect. Taking into account filtration loss, direction change, and multi-fracture expansion during crack propagation, as well as a certain margin factor, the pressure of the high-pressure water injection pump is determined to be 60-90 MPa and the flow rate is 90-150 L / min.

[0095] S5: Start the high-pressure water injection pump, and the hydraulic fracturing device delivers high-pressure water for directional fracturing. During the fracturing process, the high-pressure water first flows along the high-pressure water pipe to the sealed section for water fracturing. The high-pressure water cuts and fragments the roof rock, forming a directional fracture network. As fracturing progresses, the fractures gradually expand and interconnect. Simultaneously, the roof rock is shattered by the high-pressure water, causing the roof rock layer to sink and deform, forming a continuous guide fracture between the coal seam and the roof, effectively improving the stress state and migration pathways of gas in the coal seam.

[0096] S6: After hydraulic fracturing is complete, the top is cut and the hydraulic fracturing borehole is used as a gas extraction borehole. A gas extraction pipe is installed in the gas extraction borehole and connected to the surface gas extraction system.

[0097] S7: The gas extraction system is activated, using the negative pressure generated by the extraction pump to extract gas from the coal seam. As hydraulic fracturing acts on the roof and completes roof shearing, the roof fractures and forms cracks. These cracks provide excellent pathways for gas migration, significantly improving gas extraction efficiency. During the gas extraction process, parameters such as gas flow rate, concentration, and pressure are monitored in real time. Based on these monitoring results, the extraction system's operating parameters are adjusted to ensure safe, efficient, and stable gas extraction.

[0098] S8: After gas control is complete, support excavation is carried out in the transport tunnel, followed by normal mining. Roof cutting and pressure relief involves removing the roof in advance, before the working face is mined, and the roof rock becomes more fragmented. When the working face is mined, the roof gangue will fall as it is mined. The purpose of anchor wire support in the transport tunnel is to ensure the safety and stability of the working face.

[0099] The method of the present invention is described in detail below by taking a certain mine as an example.

[0100] The mining sequence of the No. 1 coal seam mining face is 110101→110102→110103, and double-wing mining is adopted. The strike length of the 110103 working face is 200m. The No. 1 coal seam is a low-gas coal seam with a relative gas emission of 6.5m 3 / t, 110103 working face is located in the west wing mining area of ​​this mine, with a burial depth of 400m, an average coal seam thickness of 2.4m, a dip angle of 3-8°, and an average dip angle of 5°. The working face adopts the strike longwall retreat mining method, and uses hydraulic fracturing technology for top cutting. The advancement method to the next section working face is to leave a lane along the air, carry out drilling construction at the 12 machine track stone gate 8, and carry out gas extraction based on top cutting and pressure relief.

[0101] S1: The No. 1 coal seam 19 has a simple structure and a large variation in coal seam thickness. It is a mostly mineable coal seam and occasionally contains a layer of interbedded gangue. It is a relatively stable coal seam and its thickness becomes thinner from west to east. The direct top 20 of the No. 1 coal seam 19 is generally muddy siltstone. The drill hole diameter is selected as 100mm, and two hydraulic fracturing drill holes are opened. At the same time, the cutting angle ɑ=75° is determined.

[0102] (1) Calculation of spacing between directional groove sections (fracturing points)

[0103] ① Estimate according to the axial spacing formula of the groove section

[0104]

[0105] In the formula

[0106] D t , spacing between directional grooving sections (m).

[0107] E, elastic modulus of muddy siltstone (GPa), 1.95GPa=19500Pa.

[0108] λ, Poisson’s ratio of argillaceous siltstone, 0.25.

[0109] P1, injection pressure of high-pressure water injection pump (MPa), 60MPa.

[0110] σ h , in situ stress at the borehole (MPa), σh=γh, bulk density of muddy siltstone γ=26000N / m 3 , burial depth h = 400m, calculated to be 10.4MPa.

[0111] Then D t =13.870m

[0112] ②Calculate according to the optimal radial influence radius of the crack

[0113]

[0114] In the formula

[0115] D t , spacing between directional grooving sections (m);

[0116] r w , radius of hydraulic fracturing borehole (m), 0.05m;

[0117] λ, Poisson's ratio, 0.25;

[0118] σ v , in situ stress at the borehole (MPa), σh=γh, bulk density of muddy siltstone γ=26000N / m 3 , burial depth h = 400m, calculated to be 10.4MPa.

[0119] σ t , tensile strength of argillaceous siltstone (MPa), 1MPa;

[0120] Internal friction angle of muddy siltstone (°), 25°.

[0121] Then D t =12.517m

[0122] According to the above D t The minimum value calculated by the two formulas of (directional groove segment spacing) is used to determine the spacing of the directional groove segments. The spacing of the directional groove segments is D t =12.5m, then the number of directional grooving sections is 200÷12.5=16.

[0123] (2) Calculation of hydraulic fracturing boreholes (no calculation required if only one borehole is drilled)

[0124] ① According to the deflection distance of the crack

[0125]

[0126] In the above three formulas

[0127] R, hydraulic fracturing borehole spacing radius (m);

[0128] L, crack deflection distance (m);

[0129] θ, deflection angle (°), 15°;

[0130] σ h , stress at the borehole (MPa), σh=γh, the bulk density of argillaceous siltstone γ=26000 N / m 3 , buried depth h=400 m, calculated 10.4 MPa;

[0131] σ1, maximum horizontal principal stress (MPa), 25 MPa;

[0132] σ3, minimum horizontal principal stress (MPa), 8.3 MPa;

[0133] K, permeability coefficient (m / s), 7×10 -9 m / s;

[0134] h, the thickness of the immediate roof (m), 4.09 m;

[0135] ΔP, the pressure difference between the hydraulic fracturing borehole and the rock formation (MPa);

[0136] q, fracturing fluid discharge (m 3 / s), 90 L / min=0.0015 m 3 / s;

[0137] μ, viscosity (MPa·s), 1×10 -8 MPa·s.

[0138] The hydraulic fracturing borehole spacing radius R is calculated as 5.848 m, and the hydraulic fracturing borehole spacing D is 2R=2×5.848=11.696 m, so the borehole spacing is taken as 11 m.

[0139] According to the calculation of (1) and (2), the final determination of the directional slot spacing is D t =12.5 m, and the number of directional slots is 16, and the hydraulic fracturing borehole spacing is 11 m.

[0140] S2: Based on the above analysis, hydraulic fracturing borehole 16 is drilled in the coal seam roadway roof. Two hydraulic fracturing boreholes 16 are constructed in the adjacent stone gate roadway, evenly spaced parallel to the runway, with a spacing of 11 meters between the two boreholes. The drilling path is from the 12-track stone gate 8 roadway roof to the coal roadway roof, with a depth range equal to the coal roadway length. The borehole spacing is calculated above.

[0141] S3: Predetermine the directional groove section (fracturing point) 21. The groove opening sequence of each borehole adopts a reverse method, and 16 directional groove sections 21 are opened in each borehole. The groove section spacing is 12.5m, and the grooves are opened from the bottom of the borehole from the inside to the outside. Operation steps: First, use the drilling rig 22 to push the drill pipe and the groove drill bit to open the directional groove section 21 at the calculated directional groove position, and push out the drill pipe. Then push the packer into the borehole groove, and pressurize the packer through the high-pressure water injection pipe 39 to achieve the purpose of sealing the directional groove section 21. The length of the directional groove is d = 2r = 2×150mm = 300mm.

[0142] S4: Connect the hydraulic fracturing system. This system includes a packer, high-pressure water pipe 28, a pressure gauge, and a flow meter 31. The pressure gauge and flow meter 31 monitor the pressure changes and high-pressure water flow rate during the fracturing process in real time. They adjust the pressure and flow rate of the high-pressure water flow according to the preset pressure to ensure that the fracturing process proceeds stably along the predetermined direction and achieves the desired fracturing effect. Taking into account filtration loss, direction change, and multi-fracture expansion during crack propagation, as well as a certain margin factor, the pressure of the high-pressure water injection pump is determined to be 60-90 MPa and the flow rate is 90-150 L / min.

[0143] S5: The high-pressure water injection pump 30 is turned on, and the hydraulic fracturing device delivers high-pressure water for directional fracturing. During the fracturing process, the high-pressure water first flows along the high-pressure water pipe to the sealing section 43 for water fracturing. The high-pressure water cuts and crushes the roof rock, forming a directional fracture network. As the fracturing progresses, the fractures gradually expand and interconnect. Simultaneously, the roof rock is crushed by the high-pressure water, causing the roof rock layer to sink and deform, forming a continuous guide fracture between the coal seam and the roof, effectively improving the stress state and migration pathways of gas in the coal seam.

[0144] S6: Hydraulic fracturing completed, hydraulic fracturing fluid consumption 1.53m 3 It takes 17 minutes to replace the hydraulic fracturing device with a gas extraction device. The hydraulic fracturing borehole 16 is used as the gas extraction borehole 16. A gas extraction pipe is installed in the gas extraction borehole 16 and connected to the ground gas extraction system.

[0145] S7: Gas extraction was carried out to extract the gas from the No. 1 coal seam to the surface gas tank 36, and 3490m of gas was extracted.3 .

[0146] S8: After gas control is complete, support excavation is carried out in the 110103 transport tunnel (excavation head) 15, followed by normal mining. Roof cutting and pressure relief involves removing the roof in advance. At this time, the 110103 working face has not yet been mined, and the roof rock has become more broken. When the 110103 working face is mined, the roof gangue will fall as it is mined. The purpose of anchor wire support in the 110103 transport tunnel is to ensure the safety and stability of the working face.

[0147] The present invention is a gas extraction method that improves mine safety and efficiency. By performing hydraulic fracturing drilling construction parallel to the direction of the chute inside the 12-machine track stone gate 8, it not only ensures construction safety but also reduces equipment transportation time. This method achieves top cutting through directional hydraulic fracturing, improves the stress conditions of the side tunnels in the goaf, alleviates mine pressure, changes the stress transmission path, and is beneficial to support. After top cutting, the top plate rock is broken and falls as it is mined, achieving stress balance in the surrounding rock and solving the stress imbalance problem of the 110103 filling material 25. At the same time, this method breaks the top plate rock under the action of high-pressure water, improves the gas migration channel, and achieves safe and efficient gas extraction. Finally, by extracting gas at the 12-machine track stone gate 8, the workload of the gas extraction tunnel is reduced, the safety of gas extraction is improved, and the efficiency of gas extraction is accelerated.

Claims

1. A method for coal roadway gas extraction and roof cutting based on directional fracturing, characterized by: First, rock formation analysis and calculation are performed. Drill holes and grooves are drilled parallel to and equal in length to the coal roadway in the uphill and downhill tunnels or stone gates. Directional grooves in the drill holes are used to induce fracturing of the coal roadway roof, breaking the direct roof of the coal roadway, cutting off stress transmission in the roof, and reducing dynamic load strength. After the working face is mined, the roof rock is broken, and the hard roof collapses normally, completing pressure relief. Simultaneously, during the fracturing process, cracks extend from the coal roadway roof into the coal seam, creating a large number of cracks in the coal seam. This makes it easier to extract the gas in the coal seam, enabling rapid excavation of the transport roadway and reducing the risk of gas outbursts during excavation. The method specifically comprises the following steps: a. Analysis and calculation steps: Analyze the rock characteristics of the target coal seam roof to determine the appropriate fracturing location and direction, and select a reasonable drilling radius and directional cutting angle. Then calculate the directional cutting segment spacing D according to the formula t and hydraulic fracturing borehole spacing radius R; b. Drilling step: Based on the results of the above analysis and calculation, drill hydraulic fracturing holes in the coal seam roadway roof, and construct 1-3 hydraulic fracturing holes in the adjacent stone gate roadway, and evenly arrange them along the parallel direction of the trench. The drilling path is from the turn of the adjacent stone gate roadway roof to the coal roadway roof, and the depth range is the coal roadway length. The drilling hole spacing is calculated in step a; c. Pre-determining the directional slotting section: First, use the drilling rig to push the drill pipe and slotting drill bit to open the directional slotting section at the calculated directional slotting section location, push out the drill pipe, and then push the packer into the directional slotting section. Pressurize the packer through the high-pressure water injection pipe; d. Equipment installation steps: Place the hydraulic fracturing device, including the isolation section, high-pressure water pipeline, pressure gauge, and flow meter, into the predetermined position in the borehole; e. Fracturing step: The high-pressure water injection pump is turned on, and roof cutting begins. The hydraulic fracturing device delivers high-pressure water for directional fracturing, forming a directional fracture network, breaking up the roof rock layer, and forming a gas migration channel of a certain width between the coal seam and the roof; f. Gas extraction preparation steps: After hydraulic fracturing is completed, the top is cut and pressure relief begins. The hydraulic fracturing borehole is used as a gas extraction borehole. A gas extraction pipe is installed in the gas extraction borehole and connected to the surface gas extraction system; g. Gas extraction steps: Start the gas extraction system and use the negative pressure generated by the extraction pump to extract the gas from the coal seam. Use flow meters and pressure gauges to monitor gas extraction parameters in real time, and adjust the extraction system operating parameters in a timely manner based on the monitoring results. h. Support and mining steps: After the gas is controlled, support excavation is carried out in the transport tunnel, followed by normal mining. After the working face is mined, the pressure relief is completed.

2. A method for coal roadway gas extraction and top cutting based on directional fracturing according to claim 1, characterized in that: In the step a, the drilling diameter can be selected from 94, 96, 98, 115, and 120 mm, and the grooving angle range is 60°-90°.

3. The method for coal roadway gas extraction and top cutting based on directional fracturing according to claim 1, characterized in that: The high-pressure water injection pump has a pressure of 60-90 MPa and a flow rate of 90-150 L / min.

4. The method for coal roadway gas extraction and roof cutting based on directional fracturing according to claim 1, characterized in that: In the step c, the order of grooving each hole is reversed, and each hole has multiple directional groove sections, and the grooves are cut from the bottom of the hole from the inside to the outside. The length of the directional groove is d=2r, where d is the length of the directional groove and r is the half length of the directional groove.

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