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

Abstract

The invention discloses a coal roadway gas extraction and roof cutting method based on directional fracturing, and belongs to the field of coal mine underground gas extraction and surrounding rock control. The method comprises the following steps: firstly, carrying out rock stratum analysis and calculation, constructing a drill hole which is parallel to a coal roadway and has the same length as the coal roadway from an uphill and downhill roadway or a cross-cut, cutting a groove, inducing a coal roadway roof to be fractured, crushing an immediate roof of the coal roadway, cutting off stress conduction of the roof and reducing dynamic load strength through a directional cutting groove in the drill hole, and after a working face is stoped, crushing roof rocks, and the hard top plate normally collapses, and pressure relief is completed. Meanwhile, in the fracturing process, cracks extend into the coal seam from the coal roadway roof, a large number of cracks are generated in the coal seam, occurrence gas in the coal seam is extracted more easily, rapid tunneling of the transportation roadway is achieved, and the gas outburst risk in the roadway tunneling process is reduced. The method not only can improve the surrounding rock condition of the roadway and effectively reduce the gob-side entry retaining maintenance cost, but also can improve the gas extraction efficiency and reduce the roadway tunneling risk, and is of great significance to coal mine safety production.

Description

Technical Field

[0001] The invention relates to a coal roadway gas extraction and roof cutting method based on directional fracturing, belonging to the technical field of underground coal mine gas extraction and surrounding rock control. Background Art

[0002] With the continuous deepening of coal mining, coal resources are becoming increasingly scarce. In order to improve the utilization rate of resources, underground coal mine gas extraction and surrounding rock control technology have become the key to coal mine safety production. Traditional gas extraction methods are inefficient under hard roof conditions, and the risk of gas disasters is high. Its accumulation in coal seams may cause explosion accidents, seriously threatening the lives of miners and the production efficiency of coal mines. Traditional surrounding rock control technology directly supports under dynamic loads, which often causes deformation of tunnel surrounding rocks and may also cause tunnel collapse, threatening the safety of personnel and equipment.

[0003] Therefore, the development of a new type of gas extraction combined with surrounding rock control technology can not only effectively control the surrounding rock pressure disasters in underground mining tunnels of coal mines, but also improve the efficiency of gas extraction, which is of great significance for the safe production of coal mines. Summary of the invention

[0004] The purpose of the present invention 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 methods and high risk of gas disasters under hard roof conditions.

[0005] The technical solution of the present invention is a method for gas extraction and roof cutting in a coal roadway based on directional fracturing. First, rock formation analysis and calculation are carried out, and boreholes parallel to and of the same length as the coal roadway are constructed and grooves are cut in the uphill and downhill roadways or stone gates. The directional grooves in the boreholes are used to induce fracturing of the coal roadway roof, break the direct roof of the coal roadway, cut off the stress conduction of the roof, and reduce the dynamic load strength. After the working face is mined, the roof rock is broken, and the hard roof collapses normally to complete the pressure relief. At the same time, during the fracturing process, the cracks extend from the coal roadway roof to the coal seam, causing a large number of cracks in the coal seam, making the gas in the coal seam easier to be extracted, thereby realizing rapid excavation of the transport roadway and reducing the risk of gas outburst during roadway excavation.

[0006] In the aforementioned method for coal roadway gas extraction and top cutting based on directional fracturing, the method specifically comprises the following steps:

[0007] a. Analysis and calculation steps: Analyze the rock characteristics of the target coal seam roof, determine the appropriate fracturing position 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;

[0008] b. Drilling step: According to the above analysis and calculation results, hydraulic fracturing holes are drilled in the roof of the coal seam roadway, and 1-3 hydraulic fracturing holes are constructed in the adjacent stone gate roadway, and are evenly arranged in the parallel direction of the slot. The drilling path is from the turning point of the adjacent stone gate roadway roof to the coal roadway roof, and the depth range is the length of the coal roadway. The spacing of the holes is calculated by step a;

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

[0010] d. Equipment installation steps: Place the hydraulic fracturing device at the predetermined position in the borehole. The device includes a sealing section, a high-pressure water pipeline, a pressure gauge, and a flow meter;

[0011] e. Fracturing step: Turn on the high-pressure water injection pump, and then start cutting the roof. The hydraulic fracturing device delivers high-pressure water for directional fracturing operations to form a directional fracture network, the roof rock layer is broken, and a gas migration channel of a certain width is formed between the coal seam and the roof;

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

[0013] g. Gas extraction steps: Start the gas extraction system, use the negative pressure generated by the extraction pump to extract the gas in the coal seam, use the flow meter and pressure gauge to monitor the gas extraction parameters in real time, and adjust the operation parameters of the extraction system in a timely manner according to 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 tunnel 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 tunnel gas extraction and top 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 tunnel gas extraction and top cutting method based on directional fracturing, in the step c, the grooving sequence of each borehole is reversed, and each borehole has multiple directional grooving sections, and the grooving is performed sequentially from the bottom of the borehole from the inside to the outside, and the directional grooving length is d=2r, d is the directional grooving length, and r is the half length of the directional grooving.

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

[0028] 1. Solve the problem of material transportation efficiency and transportation safety. The hydraulic fracturing drilling construction of the present invention is located 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, which not only improves the safety of construction personnel during drilling, but also reduces the transportation time of equipment. In the implementation process, it solves both the safety problem and the transportation problem, providing guarantee for safe and efficient production of mines.

[0029] 2. After the hydraulic fracturing equipment cuts the roof, the working face has not been mined yet 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 swelling 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 and solve the problem of stress imbalance when filling along the goaf to one side of the goaf.

[0030] 3. The innovation of the top cutting technology of the present invention compared with the traditional hydraulic fracturing top 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 top cutting position are easier to support and excavate, and the tunnel deformation is smaller.

[0031] 4. The present invention relates to a method for gas extraction. After the roof is cut, the cracks in the roof rock gradually expand and interconnect. 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 can be extracted, and the purpose of safe extraction can be achieved, changing the traditional idea of ​​gas extraction. The gas can be extracted while achieving pressure relief during roof cutting, and then the coal seam can be 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. When extracting gas at the stone gate, there is no need to arrange a gas extraction tunnel, which reduces the amount of excavation work, reduces production costs, improves the safety of gas extraction, and accelerates gas extraction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0035] Figure 2 It is a numbered illustration;

[0036] Figure 3 For drilling holes and pre-orientation slotting sections 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 section of the 110103 working face before mining, that is, after top cutting but not mining;

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

[0042] Fig. 9 This is a schematic diagram of directional grooving section fracturing;

[0043] Fig.10 This is a schematic diagram of crack diversion;

[0044] Fig.11 It is a flow chart of the whole process of coal tunnel 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 (advance head)-15; hydraulic fracturing drilling hole (gas extraction drilling hole)-16; 110101 filling-17; old top-18; No. 1 coal seam-19; direct Top-20; directional grooving section-21; drilling rig-22; temporary support-23; cut direct top-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 hole-42; isolation section-43; directional grooving-44; hydraulic fracturing expansion-45. DETAILED DESCRIPTION

[0046] The present invention is further described below in conjunction with the accompanying drawings and embodiments, 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: Analyze the rock characteristics of the target coal seam roof, determine the appropriate fracturing position and direction, and select a reasonable drilling radius and directional cutting angle. The drilling diameter can be 94, 96, 98, 115, 120 mm, and the cutting angle range is 60°-90°. Then calculate the directional cutting section spacing and hydraulic fracturing drilling spacing according to the listed formula.

[0049] (1) Calculation of the spacing between directional grooving sections

[0050] ①Estimated by the axial spacing of the groove section

[0051]

[0052] In the formula

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

[0054] E, elastic modulus of rock;

[0055] λ, Poisson’s ratio of rock;

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

[0057] σ h , in-situ stress at the borehole (MPa);

[0058] ② Calculate according to the optimal radial influence radius of the crack

[0059]

[0060] In the formula

[0061] D t , spacing of directional grooving sections (m);

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

[0063] λ, Poisson’s ratio;

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

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

[0066] Angle of internal friction of rock (°).

[0067] According to the above two formulas, two D t The minimum value is determined as the spacing D of the directional grooving segment. t .

[0068] (2) Calculation of hydraulic fracturing borehole spacing (no calculation is 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 top rock layer (m);

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

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

[0088] μ, viscosity (MPa·s).

[0089] R=L

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

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

[0092] S2: According to the above analysis results, hydraulic fracturing holes are drilled in the roof of the coal seam roadway. 1-3 hydraulic fracturing holes are constructed in the adjacent stone gate roadway and evenly arranged in the parallel direction of the slot. The drilling path is from the adjacent stone gate roadway roof to the coal roadway roof. The depth range is the length of the coal roadway. The spacing of the holes is obtained through the above calculation.

[0093] S3: Predetermine the directional groove section (fracturing point). The groove opening sequence of each borehole is reversed, and each borehole has multiple directional groove sections. The groove section spacing is obtained through the above calculation, 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 bit, 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 length of the directional groove is d=2r, r is the half length of the directional groove (m).

[0094] S4: Connect the hydraulic fracturing device. The device includes a packer, a high-pressure water pipe, a pressure gauge and a flow meter. The pressure gauge and flow meter monitor the pressure changes and the flow rate changes of the high-pressure water in the fracturing process in real time, and adjust the pressure and flow of the high-pressure water flow according to the preset pressure to ensure that the fracturing process is carried out stably in the predetermined direction and achieve the expected fracturing effect. Considering the filtration loss, change of direction and multi-crack expansion during the crack propagation process, and considering a certain margin coefficient, the pressure of the high-pressure water injection pump is determined to be 60-90MPa and the flow rate is 90-150L / min.

[0095] S5: Turn on 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 flow first flows along the high-pressure water pipe to the sealing section for water injection fracturing. The high-pressure water flow cuts and crushes the roof rock to form a directional fracture network. As the fracturing progresses, the cracks gradually expand and penetrate each other. At the same time, the roof rock is crushed under the action of high-pressure water, and the roof rock layer sinks and deforms, forming a through-guided fracture between the coal seam and the roof, thereby effectively improving the stress state and migration channel of gas in the coal seam.

[0096] S6: After the hydraulic fracturing is completed, the top cutting is also completed, 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 ground gas extraction system.

[0097] S7: Start the gas extraction system and use the negative pressure generated by the extraction pump to extract the gas in the coal seam. As hydraulic fracturing acts on the roof and completes the top cutting, the roof is broken to form cracks. The cracks in the roof provide a good migration channel for gas, greatly improving the efficiency of gas extraction. During the gas extraction process, the gas extraction flow, concentration, pressure and other parameters are monitored in real time, and the operating parameters of the extraction system are adjusted in time according to the monitoring results to achieve safe, efficient and stable gas extraction.

[0098] S8: After the gas is controlled, support excavation is carried out in the transport tunnel, followed by normal mining. Roof cutting and pressure relief is to cut off the roof in advance. At this time, the working face has not been mined, and the roof rock becomes more broken. When the working face is mined, the gangue of the roof will fall as it is mined. The purpose of anchor net 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 recovery working face is 110101→110102→110103. 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 outburst volume 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 of the 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 decreases from west to east. The direct top 20 of the No. 1 coal seam 19 is generally muddy siltstone. The borehole diameter is selected to be 100mm, and two hydraulic fracturing boreholes are opened. At the same time, the cutting angle ɑ=75°.

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

[0113]

[0114] In the formula

[0115] D t , spacing of 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) determines the spacing of the directional groove segments, and 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 is required if only one borehole is drilled)

[0124] ① Calculated according to the deflection distance of the crack

[0125]

[0126] In the above three formulas

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

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

[0129] θ, deflection angle (°), 15°;

[0130] 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;

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

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

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

[0134] h, thickness of the immediate top rock layer (m), 4.09m;

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

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

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

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

[0139] Based on the calculations of (1) and (2), the spacing of the directional grooves is finally determined to be D t =12.5m, the number of directional cuts is 16, and the spacing between hydraulic fracturing holes is 11m.

[0140] S2: According to the above analysis results, hydraulic fracturing boreholes 16 are drilled in the roof of the coal seam roadway. Two hydraulic fracturing boreholes 16 are constructed in the adjacent stone gate roadway, evenly arranged in the parallel direction of the slot, with a spacing of 11m between the two boreholes. The drilling path is from the 12-machine track stone gate 8 roadway roof to the coal roadway roof, with a depth range of the coal roadway length, and the spacing of the boreholes is obtained through the above calculation.

[0141] S3: Predetermine the directional groove section (fracturing point) 21. The groove opening sequence of each borehole adopts the reverse type, 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 rod and the groove drill bit, open the directional groove section 21 at the calculated directional groove position, and push out the drill rod. Then push the packer into the borehole groove, and pressurize the packer through the high-pressure water injection pipe 39, so as 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 device. The device includes a packer, a high-pressure water pipe 28, a pressure gauge and a flow meter 31. The pressure gauge and the flow meter 31 monitor the pressure changes and the flow rate changes of the high-pressure water in the fracturing process in real time, and adjust the pressure and flow of the high-pressure water flow according to the preset pressure to ensure that the fracturing process is carried out stably in the predetermined direction and achieve the expected fracturing effect. Considering the filtration loss, change of direction and multi-crack expansion during the crack propagation process, and considering a certain surplus coefficient, the pressure of the high-pressure water injection pump is determined to be 60-90MPa and the flow rate is 90-150L / min.

[0143] S5: Turn on the high-pressure water injection pump 30, and the hydraulic fracturing device delivers high-pressure water for directional fracturing. During the fracturing process, the high-pressure water flow first flows along the high-pressure water pipe to the sealing section 43 for water injection fracturing. The high-pressure water flow cuts and crushes the roof rock to form a directional fracture network. As the fracturing progresses, the cracks gradually expand and penetrate each other. At the same time, the roof rock is crushed under the action of high-pressure water, and the roof rock layer sinks and deforms, forming a through-guided fracture between the coal seam and the roof, thereby effectively improving the stress state and migration channel of gas in the coal seam.

[0144] S6: Hydraulic fracturing completed, hydraulic fracturing fluid consumption 1.53m 3 The time consumed is 17 minutes. The hydraulic fracturing device is replaced 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 in the No. 1 coal seam to the ground gas tank 36, and 3490m of gas was extracted.3 .

[0146] S8: After the gas is controlled, support excavation is carried out in the 110103 transport tunnel (excavation head) 15, followed by normal mining. The roof is cut off in advance to relieve pressure. At this time, the 110103 working face has not been mined, and the roof rock becomes more broken. When the 110103 working face is mined, the gangue of the roof will fall as it is mined. The purpose of anchor net 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 for improving mine safety and efficiency. By performing hydraulic fracturing drilling construction in parallel to the direction of the chute in the 12-machine rail stone gate 8, the construction safety is guaranteed and the equipment transportation time is reduced. The method realizes top cutting through directional hydraulic fracturing, improves the stress condition of the side tunnel of the goaf, alleviates the mine pressure, changes the stress transmission path, and is conducive to support. After the top is cut, the top plate rock is broken and falls as it is mined, achieving the stress balance of the surrounding rock and solving the stress imbalance problem of the 110103 filling material 25. At the same time, the method breaks the top plate rock under the action of high-pressure water, improves the gas migration channel, and realizes safe and efficient gas extraction. Finally, gas is extracted at the 12-machine rail stone gate 8, which reduces the workload of the gas extraction tunnel, improves the safety of gas extraction, and accelerates the efficiency of gas extraction.

Claims

1. A method for coal roadway gas extraction and top cutting based on directional fracturing, characterized in that: First, rock formation analysis and calculation are carried out, and holes and grooves are cut in parallel to and of the same length as the coal roadway in the uphill and downhill tunnels or stone gates. The directional grooves in the drill holes are used to induce fracturing of the coal roadway roof, break the direct roof of the coal roadway, cut off the stress conduction of the roof, and reduce the dynamic load strength. After the working face is mined, the roof rock is broken, and the hard roof collapses normally to complete the pressure relief. At the same time, during the fracturing process, the cracks extend from the coal roadway roof to the coal seam, causing a large number of cracks in the coal seam. The gas in the coal seam is easier to be extracted, realizing rapid excavation of the transport roadway and reducing the risk of gas outbursts during roadway excavation.

2. A method for coal roadway gas extraction and top cutting based on directional fracturing according to claim 1, characterized in that: The method specifically comprises the following steps: a. Analysis and calculation steps: Analyze the rock characteristics of the target coal seam roof, determine the appropriate fracturing position 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: According to the above analysis and calculation results, hydraulic fracturing holes are drilled in the roof of the coal seam roadway, and 1-3 hydraulic fracturing holes are constructed in the adjacent stone gate roadway, and are evenly arranged in the parallel direction of the slot. The drilling path is from the turning point of the adjacent stone gate roadway roof to the coal roadway roof, and the depth range is the length of the coal roadway. The spacing of the holes is calculated by step a; c. Pre-determining the directional slotting section steps: first, use the drilling rig to push the drill pipe and the slotting drill bit to open the directional slotting section at the calculated directional slotting section position, push out the drill pipe, and then push the packer into the directional slotting section, and pressurize the packer through the high-pressure water injection pipe; d. Equipment installation steps: Place the hydraulic fracturing device at the predetermined position in the borehole. The device includes a sealing section, a high-pressure water pipeline, a pressure gauge, and a flow meter; e. Fracturing step: Turn on the high-pressure water injection pump, and then start cutting the roof. The hydraulic fracturing device delivers high-pressure water for directional fracturing operations to form a directional fracture network, the roof rock layer is broken, and a gas migration channel of a certain width is formed between the coal seam and the roof; f. Gas extraction preparation steps: After the hydraulic fracturing is completed, the top cutting is completed and the pressure relief begins. The hydraulic fracturing borehole is used as a gas extraction borehole, and a gas extraction pipe is installed in the gas extraction borehole and connected to the ground gas extraction system; g. Gas extraction steps: Start the gas extraction system, use the negative pressure generated by the extraction pump to extract the gas in the coal seam, use the flow meter and pressure gauge to monitor the gas extraction parameters in real time, and adjust the operation parameters of the extraction system in a timely manner according to 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.

3. A method for coal roadway gas extraction and top cutting based on directional fracturing according to claim 2, characterized in that: The formula for calculating the directional grooving spacing and drilling spacing in step a is as follows: (1) Directional slot spacing D t The calculation formula is: Compare the D calculated by the above two formulas (1) and (2) t The value is determined to be the minimum value of the directional grooving segment spacing D. t ; In the above formula, D t , 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; (2) The hydraulic fracturing borehole spacing is calculated according to the following formula (3): R=L (3) In the above formula (3), R is the radius of the hydraulic fracturing borehole spacing; L is the fracture deflection distance; If only one hole is drilled, no calculation is required.

4. A method for coal roadway gas extraction and top cutting based on directional fracturing according to claim 2, 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°.

5. A method for coal roadway gas extraction and top cutting based on directional fracturing according to claim 2, 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.

6. A method for coal roadway gas extraction and top cutting based on directional fracturing according to claim 2, characterized in that: In the step c, each drilling and grooving sequence is reversed, and each drilling hole has multiple directional grooving sections, and the grooving is performed from the bottom of the drilling hole from the inside to the outside. The directional grooving length is d=2r, d is the directional grooving length, and r is the half length of the directional grooving.

Images