Working face initial mining period hydraulic fracturing top cutting drill hole arrangement method based on asymmetric three-hinged arch structure

Abstract

The invention belongs to the technical field of coal mining, and discloses a working face initial mining period hydraulic fracturing top cutting drill hole arrangement method based on an asymmetric three-hinged arch structure so as to solve the technical problems existing in initial mining period hard top plate treatment in the prior art. Comprising the steps that the position of a key layer is judged, the fracture distance of a hard roof of a working face is judged, the horizontal position of an upper roof fracture is determined based on an asymmetric three-hinged arch structure, the vertical height, namely the caving height h, of a hydraulic fracturing cut roof is determined, and fracturing holes of conventional straight holes are constructed in a working face open-off cut and transportation roadways and return air on the two sides. Fracturing holes in the cut holes are constructed perpendicular to the coal wall, drilling construction is conducted through drilling equipment, and the steps of conventional drilling fracturing, directional long drilling fracturing and the like are conducted respectively. According to the method, the rock mass strength is reduced, mine pressure disasters caused by overall caving of the large-area suspended roof are effectively controlled, frame pressing and rock burst disasters are avoided, the respective advantages of a conventional straight hole and a directional hole phase are fully played, and a guarantee is provided for safe and efficient stoping.

Description

Technical Field

[0001] The invention relates to the technical field of coal mining, and in particular to a method for arranging hydraulic fracturing and top cutting drilling holes in the initial mining period of a working face based on an asymmetric three-hinge arch structure. Background Art

[0002] At present, some coal mines have developed multiple layers of thick and hard roof on the upper part of the coal seam, which are characterized by high strength, large thickness, good integrity and strong self-bearing capacity. During the initial mining process, the working face is prone to form a large area of ​​suspended roof. The instantaneous collapse of a large area of ​​suspended roof will form a hurricane, posing a huge safety hazard to the mining of the working face.

[0003] At home and abroad, the main treatments for the hard roof in the initial mining period include blasting and cutting, hydraulic fracturing and cutting, CO2 fracturing and other technologies. However, the blasting method has a large amount of gunpowder, a high risk factor, and difficult approval procedures. The CO2 fracturing has high costs and produces harmful gases. Hydraulic fracturing and cutting technology is widely used in the treatment of hard roof. The hydraulic fracturing drilling arrangement for the hard roof of the working face in the initial mining period mainly adopts two methods: conventional straight holes and directional long holes. In comparison, conventional short straight holes have the characteristics of simple construction and low cost, and directional long holes have the characteristics of wide coverage and good fracturing effect. Most mines use conventional short straight holes to treat the hard roof in the initial mining period. The drilling angle, especially the horizontal coverage of the drilling hole, is determined by engineering analogy and experience, and the asymmetric fracture characteristics of the rock formation itself are not considered. As a result, the existing solutions cannot solve the phenomenon of large-area hanging roof in the initial mining period of the working face. The existing technology cannot solve the above technical problems. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problems existing in the prior art in the treatment of hard roof in the initial mining period, and to provide a method for arranging hydraulic fracturing and top cutting drilling holes in the initial mining period of a working face based on an asymmetric three-hinged arch structure.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The method for arranging hydraulic fracturing and top cutting drilling holes in the initial mining period of a working face based on an asymmetric three-hinge arch structure comprises the following steps:

[0007] Step 1: Determine the position of the key layer: Based on the rock columnar diagram of the coal seam, use the key layer theory formula (1) to calculate the load of the overlying rock layer on the first layer layer starting from the first layer roof above the coal seam. When the load of the n+1th layer is less than that of the nth layer, that is: (q n+1 )1<(q n )1, the n+1th layer is determined to be the key layer; then the n+1th layer is taken as the first layer to continue calculating the load of the overburden stratum on it, and the above process is repeated using formula (1) until (q n+1+m+1) n+1 <(q n+1+m ) n+1 When the load (q n+1+m ) n+1 is the load acting on the key layer;

[0008]

[0009] In the formula, q n is the load of each layer, kN; (q n ) i is the effect of the nth rock layer on the ith rock layer, kN; E is the elastic modulus of each rock layer, MPa; h is the thickness of each rock layer, m; γ is the bulk density of each rock layer, kN / m 3 ;

[0010] Step 2: Determine the breaking distance of the hard top plate of the working face, simplify the key layer into a fixed beam at both ends, and use formula (2) to calculate the breaking distance of the key layer:

[0011]

[0012] Where, L is the limit collapse step distance, m; R T is the tensile strength of the key layer, MPa; q is the upper load of the key layer, kN; h is the thickness of the key layer;

[0013] Step 3. Determine the horizontal position of the old roof fracture based on the asymmetric three-hinged arch structure: During the initial mining of the working face, the accumulated degree of tensile stress damage of the old roof under the influence of mining is different, resulting in the old roof with fixed supports at both ends not breaking in the middle, but breaking in the form of an asymmetric three-hinged arch. The horizontal position of the old roof fracture is the horizontal length l2 of the cut-eye side after the old roof roof breaks.

[0014]

[0015] Where, l2 is the horizontal length of the rock block on the cut side, m;

[0016] L is the sum of the length of the rock block near the working face, l1, and the length of the rock block near the cut-eye, l2, m;

[0017] K is the ratio of the length of the rock block on the side close to the working face, l1, to the length of the rock block on the side of the cut eye, l2;

[0018] Step 4: Determine the vertical height of the hydraulic fracturing cut top, i.e. the collapse height h:

[0019]

[0020] Where, M is the mining height of coal seam, m;

[0021] K Zis the residual expansion coefficient after the roof collapses;

[0022] Step 5: Design the layout parameters of the multi-level three-dimensional hydraulic fracturing and top cutting drilling holes of "conventional straight hole + directional long hole" during the initial mining period;

[0023] 5.1. Conventional straight-hole fracturing holes are constructed in the cut-hole of the working face and in the transport lanes and return air lanes on both sides. The fracturing holes in the cut-hole are constructed perpendicular to the coal wall, and the angle between the drill holes in the transport lane and return air lane and the coal wall is 45°-90°;

[0024] 5.2. The horizontal projection of the final hole position of the fracturing hole is not less than the horizontal position of the old top break determined in step 3; the vertical height of the final hole position of the fracturing hole is not less than the vertical height of the hydraulic fracturing cut top determined in step 4, and the elevation angle of the fracturing hole is determined to be in the range of 15-50°; the spacing between fracturing holes with the same elevation angle is in the range of 10m-20m, the fracturing holes are arranged in a fan shape in space, and the fracturing holes with different elevation angles are arranged alternately; the spacing between the fracturing points of a single hole is 3m or more;

[0025] 5.3. The reinforcement holes of the conventional straight holes are arranged in the middle of the working face, with a drilling spacing of 10-12m and an elevation angle greater than 60°. The vertical height of the final hole position of the reinforcement hole is not lower than the vertical height of the hydraulic fracturing top determined in step 4;

[0026] 5.4. The directional long hole is constructed in the transport tunnel or the return air tunnel. The vertical height of the flattened section of the directional long hole exceeds the vertical height of the hydraulic fracturing cut top determined in step 4. The horizontal length of the flattened section of the directional long hole covers the entire width of the working face. Two or more directional long holes are arranged within the horizontal position range of the old top break calculated in the formula in step 3. The vertical heights of the flattened sections of adjacent directional boreholes are equal, and the spacing is not less than 45m. The flattened section of the first directional long borehole close to the cut eye is no more than 20m away from the cut eye coal wall.

[0027] Step 6: Drilling is performed by drilling equipment, and conventional drilling fracturing and directional long drilling fracturing are performed respectively. During the construction, drilling parameters are monitored while drilling, drilling trajectory is controlled, and drilling quality is controlled to ensure that the drilling trajectory is in the target layer. According to the fracturing design, the roof segmented hydraulic fracturing construction is performed according to the workflow of tool string running, setting, dragging fracturing, and packer unsealing and recovery, and the fracturing construction of conventional straight holes and directional holes is completed;

[0028] Step 7: Use the automatic monitoring system of the fracturing pump group to monitor and record the pressure and flow parameters during the fracturing process to evaluate the effect of the staged hydraulic fracturing. Use a borehole peep instrument to explore the borehole after fracturing and observe the crack characteristics of the hole wall at the fracturing point. After the working face is mined, monitor the support resistance data before and after the working face enters the fracturing area, analyze the pressure strength, step distance, and dynamic load coefficient parameters, and further verify the fracturing effect.

[0029] Furthermore, in step 6, during the directional long drilling construction, the sealing device is expanded by continuously supplying water through the high-pressure pump to achieve sealing. After the pressure is further increased to reach the set pressure, the high-pressure water outlet device is opened to achieve the fracturing construction of the designed fracturing section; when the water injection pressure is greater than the rock formation fracture pressure, cracks are caused in the rock formation; after the first stage of fracturing construction is completed, the sealing device and the water outlet device are dragged to the designed position, and the second stage of fracturing construction is carried out, and the fracturing construction of the designed construction sections is completed in sequence, and three-dimensional continuous cracks are formed in adjacent fracturing sections.

[0030] Furthermore, in step 6, during conventional drilling construction, drilling construction is carried out according to the drilling design. After the hole is formed, the fracturing tool is sent to the designed section and water is injected and pressurized by a manual pump to cause the packer rubber tube to expand and seal the hole. The high-pressure pump is turned on to start water injection construction. When the water injection pressure is greater than the rock breaking pressure, the original cracks will expand and new crack networks will be generated in the target layer. After the fracturing time is reached, the first stage of fracturing construction is completed, and the fracturing string is withdrawn to the second stage of fracturing according to the designed fracturing spacing. The second stage of fracturing construction continues to start, and the fracturing construction of the entire hole is completed in sequence.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention innovates the arrangement method of hydraulic fracturing and top cutting drilling for the hard roof in the initial mining stage of the working face. The method can effectively solve the problem of strong mine pressure that may occur in the initial mining stage of the working face and the subsequent side drift, and fracture and weaken the hard roof rock layer above the cutting eye to destroy the integrity of the rock layer, thereby reducing the strength of the rock mass, prompting the roof to collapse in time, reducing the area of ​​the suspended roof, realizing the transfer and release of high concentrated stress, and effectively controlling the mine pressure disaster caused by the overall collapse of a large area of ​​suspended roof, avoiding the occurrence of frame crushing and impact ground pressure disasters, giving full play to the respective advantages of conventional straight holes and directional holes, and providing guarantees for achieving safe and efficient mining. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the process of the present invention.

[0034] Figure 2 The 2102 working surface layout diagram provided for an embodiment of the present invention.

[0035] Figure 3 The stratum column diagram of the 2102 working face provided in the embodiment of the present invention.

[0036] Figure 4 A plan view of the drilling arrangement at the initial mining stage of a working face provided in an embodiment of the present invention.

[0037] Figure 5 A cross-sectional arrangement diagram of drilling holes in the initial mining stage of a working face provided in an embodiment of the present invention.

[0038] Figure 6An asymmetric three-hinge arch structure for the initial breaking of the working surface top plate provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0040] The method for arranging hydraulic fracturing and top cutting drilling holes in the initial mining period of a working face based on an asymmetric three-hinge arch structure comprises the following steps:

[0041] Step 1: Determine the position of the key layer and determine the position of the key layer and its upper load: According to the rock column diagram of the coal seam, use the key layer theory formula (1) to calculate the load of the overlying rock layer on the first layer layer from the first layer roof above the coal seam layer by layer. When the load of the n+1th layer is less than that of the nth layer, that is: (q n+1 )1<(q n )1, the n+1th layer is determined to be the key layer; then the n+1th layer is taken as the first layer to continue calculating the load of the overburden stratum on it, and the above process is repeated using formula (1) until (q n+1+m+1 ) n+1 <(q n+1+m ) n+1 When the load (q n+1+m ) n+1 is the load acting on the key layer;

[0042]

[0043] In the formula, q n is the load of each layer, kN; (q n ) i is the effect of the nth rock layer on the ith rock layer, kN; E is the elastic modulus of each rock layer, MPa; h is the thickness of each rock layer, m; γ is the bulk density of each rock layer, kN / m 3 .

[0044] Step 2: Determine the breaking distance of the hard top plate of the working surface:

[0045]

[0046] Where, L is the limit collapse step distance, m; R T is the tensile strength of the key layer, MPa; q is the upper load of the key layer, kN; h is the thickness of the key layer.

[0047] Step 3: Determine the horizontal position of the old roof fracture based on the asymmetric three-hinged arch structure: During the initial mining of the working face, the old roof has different degrees of accumulated tensile stress damage under the influence of mining, resulting in the old roof with fixed supports at both ends not breaking in the middle, but breaking in the form of an asymmetric three-hinged arch. The horizontal position of the old roof fracture is the horizontal length l2 of the cut-eye side after the old roof roof fractures:

[0048]

[0049] Where, l2 is the horizontal length of the rock block on the cut side, m;

[0050] L is the sum of the length of the rock block near the working face, l1, and the length of the rock block near the cut-eye, l2, m;

[0051] K is the ratio of the length of the rock block on the side close to the working face, l1, to the length of the rock block on the side of the cut eye, l2;

[0052] Step 4: Determine the vertical height of the hydraulic fracturing cut top, i.e. the collapse height h:

[0053]

[0054] Where, M is the mining height of coal seam, m;

[0055] K Z is the residual expansion coefficient after the roof collapses;

[0056] Step 5: Design the layout parameters of the multi-level three-dimensional hydraulic fracturing and top-cutting drilling holes of "conventional straight holes + directional long holes" during the initial mining period.

[0057] 5.1. Conventional straight-hole fracturing holes are constructed in the cut-outs of the working face and in the transport lanes and return air lanes on both sides. The fracturing holes in the cut-outs are constructed perpendicular to the coal wall, and the angle between the drill holes in the transport lanes and return air lanes and the coal wall is 45°-90°.

[0058] 5.2. The horizontal projection of the final hole position of the fracturing hole shall not be less than the horizontal position of the old top break determined in step 3; the vertical height of the final hole position of the fracturing hole shall not be less than the vertical height of the hydraulic fracturing top determined in step 4, and the elevation angle of the fracturing hole shall be determined to be in the range of 15-50°; the spacing between fracturing holes with the same elevation angle shall be in the range of 10m-20m, and the fracturing holes shall be arranged in a fan shape in space, and the fracturing holes with different elevation angles shall be arranged alternately. The spacing between the fracturing points of a single hole shall be 3m or more.

[0059] 5.3. The reinforcement holes of the conventional straight holes are arranged in the middle of the working face, with a drilling spacing of 10-12m and an elevation angle greater than 60°. The vertical height of the final hole position of the reinforcement hole is not lower than the vertical height of the hydraulic fracturing top determined in step 4.

[0060] 5.4. The directional long hole is constructed in the transport tunnel or return air tunnel. The vertical height of the flattened section of the directional long hole exceeds the vertical height of the hydraulic fracturing cut top determined in step 4. The horizontal length of the flattened section of the directional long hole covers the entire width of the working face. Two or more directional long holes are arranged within the horizontal position range of the initial break of the old top calculated in the formula in step 3. The vertical heights of the flattened sections of adjacent directional boreholes are equal, and the spacing is not less than 45m. The flattened section of the first directional long borehole close to the cut eye is no more than 20m away from the cut eye coal wall.

[0061] Step 6: Drilling construction is carried out by drilling equipment, and conventional drilling fracturing and directional long drilling fracturing are performed respectively. During the construction, drilling parameters are monitored while drilling, drilling trajectory is controlled, and drilling quality control is performed to ensure that the drilling trajectory is in the target layer. According to the fracturing design, the roof segmented hydraulic fracturing construction is carried out according to the work flow of tool string lowering, sealing, dragging fracturing, and packer unsealing and recovery to complete the fracturing construction of conventional straight holes and directional holes.

[0062] Step 7: Use the automatic monitoring system of the fracturing pump group to monitor and record the pressure and flow parameters during the fracturing process to evaluate the effect of the staged hydraulic fracturing. Use a borehole peep instrument to explore the borehole after fracturing and observe the crack characteristics of the hole wall at the fracturing point. After the working face is mined, monitor the support resistance data before and after the working face enters the fracturing area, analyze the pressure strength, step distance, and dynamic load coefficient parameters, and further verify the fracturing effect.

[0063] Embodiment 1:

[0064] The present invention is used for the first mining working face of a certain mine. The first mining coal seam is the No. 2 coal seam with an average burial depth of 480m. Multiple layers of thick and thin interlayered hard roof are developed on the upper part of the coal seam. The rock type is mainly powder and fine sandstone. The overall performance is high in strength, large in thickness, good in integrity, and strong in self-bearing capacity.

[0065] Combine the following Figure 1 Describe the technical route diagram of the present invention.

[0066] First, collect geological data of the study area, conduct on-site surveys underground, and select suitable fracturing construction sites to avoid affecting the normal production of the mine.

[0067] Step 1: Determine the position of the key layer and the initial breaking distance of the old top, and determine the position of the key layer and its upper load:

[0068]

[0069] In the formula, q n is the load of each layer, kN; (q n ) iis the effect of the nth rock layer on the ith rock layer, kN; E is the elastic modulus of each rock layer, MPa; h is the thickness of each rock layer, m; γ is the bulk density of each rock layer, kN / m 3 .

[0070] The physical and mechanical parameters were measured and the elastic modulus of the rock layer in the upper 0-4.8m layer of the coal seam was 26GPa, and the rock layer bulk density was 23.9kN / m 3 ; The elastic modulus of the rock layer at 4.8-22.43m is 26GPa, and the rock layer density is 24.8kN / m 3 Therefore, from formula (1), we can get that (q2)1<(q1)1, that is, the medium-grained sandstone at the 4.8~22.43m layer on the top of the 2102 working face is the key layer.

[0071] Step 2: Before the first collapse of the 2102 working face, the mechanical structure of the upper roof should be a fixed-support beam structure. According to the limit collapse step distance of the fixed-support beam, it can be known that:

[0072]

[0073] Where, L is the limit collapse step distance, m; R T is the tensile strength of the key layer, which is taken as 7.01MPa; q is the upper load of the key layer, which is taken as 730kN; h is the thickness of the key layer, which is taken as 17.63m.

[0074] Under unfractured conditions, the initial collapse step distance of the 2102 first mining face was 77m.

[0075] Step 3: Determine the horizontal position of the old roof fracture based on the asymmetric three-hinged arch structure: During the initial mining of the working face, the old roof has different degrees of accumulated tensile stress damage under the influence of mining, resulting in the old roof with fixed supports at both ends not breaking in the middle, but breaking in the form of an asymmetric three-hinged arch. The horizontal position of the old roof fracture is the horizontal length l2 of the cut-eye side after the old roof roof fractures:

[0076]

[0077] Where, l2 is the length of the rock block on the cut side, m;

[0078] L is the sum of the length of the rock block on the side close to the working face, l1, and the length of the rock block on the side of the cutting eye, l2, which is 77m.

[0079] K is the ratio of the length of the rock block on the side close to the working face, l1, to the length of the rock block on the side of the cutting eye, l2, which is taken as 1.5.

[0080] Therefore, the horizontal position of the old roof break, that is, the horizontal length l2 of the cut-eye side after the old roof top breaks, should be within the range of 30.8m based on the geological conditions.

[0081] Step 4: Determine the vertical height of the hydraulic fracturing cut top, i.e. the collapse height h:

[0082]

[0083] Where M is the mining height of the coal seam, which is 3.56m.

[0084] K Z It is the residual expansion coefficient after roof collapse and is taken as 1.15.

[0085] The vertical height of the hydraulic fracturing cut top was determined to be 23.7m.

[0086] Step 5: Design the layout parameters of the multi-level three-dimensional hydraulic fracturing and top-cutting drilling holes of "conventional straight holes + directional long holes" during the initial mining period.

[0087] 5.1. Conventional straight-hole fracturing holes are constructed in the cut-hole of the working face and in the transport lanes and return air lanes on both sides. The fracturing holes in the cut-hole are constructed perpendicular to the coal wall, and the angle between the drill holes in the transport lane and return air lane and the coal wall is 45°-90°;

[0088] 5.2. The horizontal projection of the final hole position of the fracturing hole is not less than the horizontal position of the old top break determined in step 3; the vertical height of the final hole position of the fracturing hole is not less than the vertical height of the hydraulic fracturing cut top determined in step 4, and the elevation angle of the fracturing hole is determined to be in the range of 15-50°; the spacing between fracturing holes with the same elevation angle is in the range of 10m-20m, the fracturing holes are arranged in a fan shape in space, and the fracturing holes with different elevation angles are arranged alternately; the spacing between the fracturing points of a single hole is 3m or more;

[0089] 5.3. The reinforcement holes of the conventional straight holes are arranged in the middle of the working face, with a drilling spacing of 10-12m and an elevation angle greater than 60°. The vertical height of the final hole position of the reinforcement hole is not lower than the vertical height of the hydraulic fracturing top determined in step 4;

[0090] 5.4. The directional long hole is constructed in the transport tunnel or the return air tunnel. The vertical height of the flattened section of the directional long hole exceeds the vertical height of the hydraulic fracturing cut top determined in step 4. The horizontal length of the flattened section of the directional long hole covers the entire width of the working face. Two or more directional long holes are arranged within the horizontal position range of the initial break of the old top calculated in the formula of step 3. The vertical heights of the flattened sections of adjacent directional boreholes are equal, and the spacing is not less than 45m. The flattened section of the first directional long borehole close to the cut eye is no more than 20m away from the cut eye coal wall.

[0091] A total of 16 conventional straight-hole fracturing holes S are arranged in the 2102 working face cut, with a drilling spacing of 20m. 17 conventional straight-hole fracturing holes L are arranged, with a drilling spacing of 20m. 5 conventional straight-hole fracturing holes B are arranged, with a drilling spacing of 10m. 7 conventional straight-hole reinforcement holes N are arranged, with a drilling spacing of 10m. The vertical height of the final hole position of the reinforcement hole N is not less than the vertical height of the hydraulic fracturing cut top determined in step 4, 23.7m.

[0092] In the auxiliary transport tunnel and main transport tunnel of the 2102 working face, 7 conventional straight-hole fracturing holes C are arranged, with a drilling distance of 10m. 2 conventional straight-hole fracturing holes A are arranged, with a drilling distance of 10m.

[0093] In addition, a drilling site and two directional long holes are arranged in the main transport tunnel of the 2102 working face. The target layer is 25m. The vertical height of the flattened sections of adjacent directional drill holes is equal. The drilling spacing is 50m. The flattened section of the first directional long drill hole close to the cut eye is no more than 20m away from the cut eye coal wall. The drilling construction parameters are shown in Tables 1 and 2; the plan and cross-section diagrams of the drilling design layout are shown in Figure 2 , 3 shown.

[0094] Table 1 Long drilling construction parameters

[0095]

[0096] Table 2 Short drilling construction parameters

[0097]

[0098]

[0099] 6) Fracturing construction.

[0100] Optimize drilling equipment for drilling construction, conduct drilling parameter monitoring, drilling trajectory control and drilling quality control during construction to ensure that the drilling trajectory is in the target layer.

[0101] Conventional short borehole drilling construction uses two ZDY3200LPS drilling rigs and supporting drilling rig platforms with a hole diameter of 60mm. The construction sequence is: D. The two drilling rigs are located in the main and auxiliary transport lanes respectively to construct C hole and A hole in turn; ② After the main and auxiliary transport drilling construction is completed, the drilling rig enters the cutting eye to alternately construct the working hole, S hole, and N hole; ③ During the drilling construction, the fracturing construction of S hole, L hole, C hole and A hole is alternately carried out at intervals.

[0102] The directional long hole drilling construction uses ZDY12000 drilling rig and supporting drilling rig platform, with a hole diameter of 120mm. The hole mouth is opened 120mm and drilled to the direct top, the second hole is expanded to 193mm, and the 153mm casing is lowered to cross the rock layer 10m. After the casing is solidified, it is drilled to the final hole according to the designed trajectory.

[0103] The conventional straight hole and directional hole combination technology is used for fracturing construction. Conventional short borehole fracturing uses a water injection steel pipe to push the sealer to the first stage of the designed fracturing position, and a manual pump is used to pressurize the sealer to achieve the hole sealing. The fracturing pump is turned on and high-pressure water is injected through the water injection pipeline. The single-hole multiple fracturing operation is completed by the reverse single-hole multi-stage fracturing method. The fracturing layer is the direct top and part of the basic top. There are 63 conventional short boreholes for fracturing construction, among which: L hole is fracturing every 3m, and the single hole is fracturing for 9 sections: S hole is fracturing every 3m, and the single hole is fracturing for 8 sections: A hole is fracturing every 3m, and the single hole is fracturing for 7 sections: C hole is fracturing every 3m, and the single hole is fracturing for 10 sections; B hole is fracturing every 3m, and the single hole is fracturing for 17 sections.

[0104] Directional long-hole fracturing uses a drilling rig to deliver the guide device, sealing device, water outlet device and oil pipe to the first designed fracturing position, and turns on the high-pressure pump to inject high-pressure water to cause the sealing device to expand and seal, thus sealing the hole. Continue to inject high-pressure water, open the water outlet device to start fracturing, and use the "double-seal single-card multi-point drag fracturing process" to complete single-hole fracturing, and the fracturing layer is the basic top. This fracturing construction has two long directional long holes, of which the No. 1 hole is 381m deep, the fracturing spacing is 30m, and a total of 8 fracturing sections; the No. 1 hole is 330m deep, the fracturing spacing is 15m, and a total of 16 fracturing sections.

[0105] 7) Effect test

[0106] During the fracturing process, water flow occurred near the hole or near the anchor cable. Some recorded photos were selected for analysis, and it can be seen that during the fracturing process, water flow from the adjacent hole and increased dripping or continuous water flow from the anchor cable occurred, and the water flow from the anchor cable was mainly distributed in the fracturing borehole orifice area, indicating that the increased water flow from the anchor cable was due to the penetration of the fracturing cracks.

[0107] The pressure curve of directional long drilling is analyzed by taking the 8th section of D1 hole and the 4th section of D2 hole as examples. First, the high-pressure water injection pump is turned on, and the water expansion packer is slowly injected. The water injection pressure shows a step-like growth law, and the maximum increase is 28.8MPa. Suddenly, there is a significant pressure drop, indicating that the rock formation has broken. After the pressure drop, it enters the stable pressure maintenance stage and maintains for a period of time. Then, an instantaneous pressure drop occurs again, and then it starts to rise and recover, indicating that the rock strength of the rock formation has weakened. There were 3 pressure drops during the fracturing process, indicating that the hydraulic fracturing construction in this section has effectively destroyed the integrity of the roof, formed cracks in the rock mass and fully extended, and achieved the engineering construction effect. After the fracturing construction, the in-hole peek effect is good, the adjacent hole has obvious water discharge, and the fracturing treatment effect is good.

[0108] After the rock formation is damaged by hydraulic fracturing, the initial mining structure of the upper roof is simplified as a mechanical model with one end fixed and the other end simply supported, that is, one end is fixed above the coal wall, and the other end forms a simply supported end due to the existence of the fracturing cracks. Therefore, by converting the roof fixed beam structure into a simply supported beam structure, the roof on the cut side collapses in advance, reducing the initial pressure step distance of the working face, reducing the pressure intensity, and protecting the safe and efficient mining during the initial release of the working face.

[0109] Based on the above analysis, when no hydraulic fracturing roof weakening measures were taken for the 2102 working face, the mechanical model calculated that the initial collapse step was 77m, which could easily cause strong pressure and even dynamic disasters on the working face. Theoretical calculations show that the reasonable range of hydraulic fracturing in the vertical direction of the working face is the basic top of the medium-grained sandstone and the sub-critical layer of the mudstone layer. The effective fracturing section in the horizontal direction is reasonably arranged within 30.8m from the cut-eye side of the working face.

[0110] In order to solve the problem of large-area hanging roof on the hard roof in the initial mining stage, a combination of conventional straight holes and directional holes is used to fracture and weaken the hard roof rock layer above the cut eye, destroy the integrity of the rock layer, thereby reducing the strength of the rock mass, prompting the roof to collapse in time, reducing the hanging roof area, achieving the transfer and release of high-concentration stress, and effectively controlling the stress and energy conditions for the occurrence of strong mine pressure disasters. After the fracturing construction, the in-hole peek effect is good, the adjacent holes have obvious water discharge, and the fracturing treatment effect is good. It can be seen that the multi-level hydraulic fracturing top cutting drilling arrangement method for the initial mining of the thick hard roof working face determined by this patent is feasible.

Claims

1. A method for arranging hydraulic fracturing and top cutting drilling holes in the initial mining period of a working face based on an asymmetric three-hinge arch structure, characterized in that: The following steps are involved: Step 1: Determine the position of the key layer: Based on the rock columnar diagram of the coal seam, use the key layer theory formula (1) to calculate the load of the overlying rock layer on the first layer layer starting from the first layer roof above the coal seam. When the load of the n+1th layer is less than that of the nth layer, that is: (q n+1 )1<(q n )1, the n+1th layer is determined to be the key layer; then the n+1th layer is taken as the first layer to continue calculating the load of the overburden stratum on it, and the above process is repeated using formula (1) until (q n+1+m+1 ) n+1 <(q n+1+m ) n+1 When the load (q n+1+m ) n+1 is the load acting on the key layer; In the formula, q n is the load of each layer, kN; (q n ) i is the effect of the nth rock layer on the ith rock layer, kN; E is the elastic modulus of each rock layer, MPa; h is the thickness of each rock layer, m; γ is the bulk density of each rock layer, kN / m 3 ; Step 2: Determine the breaking distance of the hard top plate of the working face, simplify the key layer into a fixed beam at both ends, and use formula (2) to calculate the breaking distance of the key layer: Where, L is the limit collapse step, m; RT is the tensile strength of the key layer, MPa; q is the upper load of the key layer, kN; h is the thickness of the key layer; Step 3, determine the horizontal position of the old roof fracture based on the asymmetric three-hinged arch structure: during the initial mining of the working face, the old roof has different degrees of accumulated tensile stress damage under the influence of mining, resulting in the old roof with fixed supports at both ends not being fractured in the middle, but being fractured in the form of an asymmetric three-hinged arch. The horizontal position of the old roof fracture is the horizontal length l2 of the cut-eye side after the old roof roof fractures; Where, l2 is the horizontal length of the rock block on the cut side, m; L is the sum of the length of the rock block near the working face side l1 and the length of the rock block near the cut-eye side l2, m; K is the ratio of the length of the rock block near the working face side l1 to the length of the rock block near the cut-eye side l2; Step 4: Determine the vertical height of the hydraulic fracturing cut top, i.e. the collapse height h: Where, M is the mining height of coal seam, m; K Z is the residual expansion coefficient after the roof collapses; Step 5: Design the layout parameters of the multi-level three-dimensional hydraulic fracturing and top cutting drilling holes of "conventional straight hole + directional long hole" during the initial mining period; 5.

1. Conventional straight-hole fracturing holes are constructed in the cut-hole of the working face and in the transport lanes and return air lanes on both sides. The fracturing holes in the cut-hole are constructed perpendicular to the coal wall, and the angle between the drill holes in the transport lane and return air lane and the coal wall is 45°-90°; 5.

2. The horizontal projection of the final hole position of the fracturing hole is not less than the horizontal position of the old top break determined in step 3; the vertical height of the final hole position of the fracturing hole is not less than the vertical height of the hydraulic fracturing cut top determined in step 4, and the elevation angle of the fracturing hole is determined to be in the range of 15-50°; the spacing between fracturing holes with the same elevation angle is in the range of 10m-20m, the fracturing holes are arranged in a fan shape in space, and the fracturing holes with different elevation angles are arranged alternately; the spacing between the fracturing points of a single hole is 3m or more; 5.

3. The reinforcement holes of the conventional straight holes are arranged in the middle of the working face, with a drilling spacing of 10-12m and an elevation angle greater than 60°. The vertical height of the final hole position of the reinforcement hole is not lower than the vertical height of the hydraulic fracturing top determined in step 4; 5.

4. The directional long hole is constructed in the transport tunnel or the return air tunnel. The vertical height of the flattened section of the directional long hole exceeds the vertical height of the hydraulic fracturing cut top determined in step 4. The horizontal length of the flattened section of the directional long hole covers the entire width of the working face. Two or more directional long holes are arranged within the horizontal position range of the old top break calculated in the formula in step 3. The vertical heights of the flattened sections of adjacent directional boreholes are equal, and the spacing is not less than 45m. The flattened section of the first directional long borehole close to the cut eye is no more than 20m away from the cut eye coal wall. Step 6: Drilling is performed by drilling equipment, and conventional drilling fracturing and directional long drilling fracturing are performed respectively. During the construction, drilling parameters are monitored while drilling, drilling trajectory is controlled, and drilling quality is controlled to ensure that the drilling trajectory is in the target layer. According to the fracturing design, the roof segmented hydraulic fracturing construction is performed according to the workflow of tool string running, setting, dragging fracturing, and packer unsealing and recovery, and the fracturing construction of conventional straight holes and directional holes is completed; Step 7: Use the automatic monitoring system of the fracturing pump group to monitor and record the pressure and flow parameters during the fracturing process to evaluate the effect of the staged hydraulic fracturing. Use a borehole peep instrument to explore the borehole after fracturing and observe the crack characteristics of the hole wall at the fracturing point. After the working face is mined, monitor the support resistance data before and after the working face enters the fracturing area, analyze the pressure strength, step distance, and dynamic load coefficient parameters, and further verify the fracturing effect.

2. According to the method for arranging hydraulic fracturing and top cutting drilling holes in the initial mining period of a working face based on an asymmetric three-hinged arch structure as described in claim 1, in the step 6, during the directional long drilling construction, the sealing device is caused to expand by continuously supplying water through a high-pressure pump to achieve sealing, and after the pressure is continuously increased to reach the set pressure, the high-pressure water outlet device is opened to achieve the fracturing construction of the designed fracturing section; when the water injection pressure is greater than the rock formation fracture pressure, cracks are caused to form in the rock formation; after the first stage of fracturing construction is completed, the sealing device and the water outlet device are dragged to the designed position, and the second stage of fracturing construction is carried out, and the fracturing construction of the designed construction sections is completed in sequence, and three-dimensional continuous cracks are formed in adjacent fracturing sections.

3. According to the method for arranging hydraulic fracturing and top cutting drilling holes in the initial mining period of a working face based on an asymmetric three-hinged arch structure as described in claim 1, in the step 6, in conventional drilling construction, drilling construction is carried out according to the drilling design, and after the hole is formed, the fracturing tool is sent to the designed section and water is injected and pressurized by a manual pump to cause the packer rubber cylinder to expand and seal the hole, and the high-pressure pump is turned on to start water injection construction. When the water injection pressure is greater than the rock breaking pressure, the original cracks will expand and new crack networks will be generated in the target layer. After the fracturing time is reached, the first stage of fracturing construction is completed, and the fracturing string is withdrawn to the second stage of fracturing according to the designed fracturing spacing, and the second stage of fracturing construction is continued to start, and the fracturing construction of the entire hole is completed in sequence.

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