Crushed soft coal and gas co-mining method based on underground coal extraction and pressure relief

Abstract

The invention provides a crushed soft coal and gas co-mining method based on underground coal extraction and pressure relief, and belongs to the technical field of coordinated development of coal and coal bed gas. Stress of a coal rock layer is effectively released through pressure relief extraction of a cross-layer coal extraction drill hole and a bedding coal extraction drill hole, coal bed gas extraction of a coal bed is promoted, and the coal bed gas extraction efficiency is improved. The hole sealing effect is improved through multiple times of slurry supplementing of the inorganic material, the extraction amount of underground coal bed gas is increased, and therefore co-extraction of crushed soft coal and coal bed gas is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of coordinated development of coal and coalbed methane, and specifically discloses a method for co - mining crushed soft coal and gas based on underground coal extraction and pressure relief. Background Technique

[0002] The poor permeability of crushed soft coal seams is the key factor restricting the treatment effect of coal seam gas. The advanced pre - drainage effect of surface coalbed methane wells in the planned area is poor. Conventional fracturing is difficult to form an effective seepage network and high - speed seepage channels in the coal seam, the extraction effect is extremely poor, the single - well output is low, and it is difficult to recover the cost. Summary of the Invention

[0003] The present invention provides a method for co - mining crushed soft coal and gas based on underground coal extraction and pressure relief, aiming to release the mining potential of crushed soft coal, improve the productivity of crushed soft coal mining, and improve the extraction effect, single - well output and economic benefits.

[0004] The above - mentioned method for co - mining crushed soft coal and gas based on underground coal extraction and pressure relief includes the following steps:

[0005] S1. For coal mines with crushed soft coal seam groups, according to exploration data, determine the first coal seam to be mined and the spatial position of the bottom gas - drainage roadway of the first coal seam to be mined;

[0006] S2. Optimize the design of the spatial position of the bottom gas - drainage roadway of the first coal seam to be mined, construct the bottom gas - drainage roadway of the first coal seam to be mined, and at the same time use it as the top gas - drainage roadway of the second coal seam to be mined;

[0007] S3. Construct the cross - layer borehole drill fields of the first coal seam to be mined and the second coal seam to be mined at the same time, and construct cross - layer coal - extraction boreholes;

[0008] S4. Use the cross - layer coal - extraction boreholes to conduct underground negative - pressure extraction on the first coal seam to be mined and the second coal seam to be mined until the coalbed methane content of the first coal seam to be mined and the second coal seam to be mined reaches the extraction standard;

[0009] S5. Conduct the infrastructure construction of the first coal seam to be mined, and construct the along - seam coal - extraction boreholes;

[0010] S6. Use the along - seam coal - extraction boreholes to conduct area - wide coverage coalbed methane extraction on the working face of the first coal seam to be mined until the coalbed methane content of the first coal seam to be mined reaches the extraction standard;

[0011] S7. Mine the coal on the working face of the first coal seam to be mined until the coal on the working face of the first coal seam to be mined is completely mined;

[0012] S8. Conduct the infrastructure construction of the next coal seam to be mined, and construct the along - seam coal - extraction boreholes;

[0013] S9. Use the bedding coal-digging boreholes to conduct regional full-coverage coalbed methane extraction on the working face of the next coal seam to be mined until the coalbed methane content of the next coal seam to be mined meets the extraction standard.

[0014] S10. Mine the coal on the working face of the next coal seam until the coal on the working face of the next coal seam to be mined is completely mined.

[0015] S11. Repeat steps S8 - S10 to achieve the co-mining of coal and coalbed methane in the soft and broken coal seam group.

[0016] In step S1, based on the exploration data, analyze the coal thickness, gas content, burial depth, and coal-rock mechanical properties of each coal seam to determine the first coal seam to be mined and the spatial position of the bottom gas drainage roadway of the first coal seam to be mined.

[0017] In step S3, the cross-cut coal-digging boreholes adopt the three-block two-injection sealing technology. Use three grouting bladder bags to seal the cross-cut coal-digging boreholes, forming an inner grouting section and an outer grouting section. The inner grouting section is filled with cement materials, and the outer grouting section is filled with inorganic flexible sealing materials.

[0018] The specific steps of the three-block two-injection sealing technology are as follows: The three grouting bladder bags are arranged in the cross-cut coal-digging borehole from the inside out, namely the inner bladder bag I, the middle bladder bag, and the outer bladder bag I. Install the inner grouting pipe I, the inner return slurry pipe I, the outer grouting pipe I, and the outer return slurry pipe I in the cross-cut coal-digging borehole. The inner grouting pipe I passes through the outer bladder bag I and the middle bladder bag and extends into the inner bladder bag I. One-way valves are installed on the part of the inner grouting pipe I located in the middle bladder bag and the inner bladder bag I. A blasting valve is installed on the part of the inner grouting pipe I located between the middle bladder bag and the inner bladder bag I. The inner return slurry pipe I passes through the outer bladder bag I and the middle bladder bag and extends between the middle bladder bag and the inner bladder bag I. The outer grouting pipe I passes through the outer bladder bag I and extends between the outer bladder bag I and the middle bladder bag. One-way valves are installed on the part of the outer grouting pipe I located in the outer bladder bag I. A blasting valve is installed on the part of the outer grouting pipe I located between the outer bladder bag I and the middle bladder bag. The outer return slurry pipe I passes through the outer bladder bag I and the middle bladder bag and extends between the middle bladder bag and the inner bladder bag I.

[0019] Open the one-way valves in the inner bladder bag I, the middle bladder bag, and the outer bladder bag I, and inject cement slurry into the three grouting bladder bags. The grouting bladder bags expand, forming an inner grouting section between the inner bladder bag I and the middle bladder bag and an outer grouting section between the middle bladder bag and the outer bladder bag I. After the grouting pressure reaches the preset value, open the blasting valve of the inner grouting pipe I. When the inner return slurry pipe I returns slurry, it indicates that the cement slurry fills the inner grouting section to form a solid sealing section. Then, open the blasting valve of the outer grouting pipe I and inject the prepared inorganic flexible sealing material into the outer grouting section until the outer return slurry pipe I returns slurry.

[0020] The bedding coal-digging boreholes adopt the composite pressure-sealing technology, including the low-pressure outer plug and high-pressure inner injection composite sealing technology and the inorganic nano-flexible material secondary pressure grouting technology.

[0021] The low-pressure external plugging and high-pressure internal injection composite hole sealing process includes the following steps:

[0022] t1. Lower the hole protection pipe to the bottom of the coal-digging borehole along the seam. The hole protection pipe consists of a solid pipe I + a screen pipe + a solid pipe II + a flange from inside to outside. The solid pipe I and the screen pipe are located in the support entity zone, and the solid pipe II extends from the support entity zone, the fracture development zone, the loose and broken zone to the hole opening and is connected to the flange.

[0023] t2. Use AB glue to plug between the loose and broken zone and the solid pipe II, and use AB glue to plug between the intersection of the fracture development zone and the support entity zone and the solid pipe II. Lower the external grouting pipe II and the external return slurry pipe II into the annulus between the hole protection pipe and the coal-digging borehole wall along the seam. Inject cement slurry into the annulus between the hole protection pipe and the coal-digging borehole wall through the external grouting pipe II. After the external return slurry pipe II returns slurry, wait for the cement slurry to solidify.

[0024] t3. Lower the bladder II, the internal grouting pipe II and the internal return slurry pipe II into the hole protection pipe. The bladder II is located at the intersection of the fracture development zone and the support entity zone. The internal grouting pipe II passes through the bladder II and extends into the last solid pipe II. A check valve is installed on the part of the internal grouting pipe II located inside the bladder II, and a blasting valve is installed on the part of the internal grouting pipe II located in the last solid pipe II. The internal return slurry pipe II passes through the bladder II and extends into the first screen pipe. Open the check valve of the internal grouting pipe II and inject cement slurry into the bladder II. The bladder II expands to seal the hole protection pipe. After the grouting pressure reaches the preset value, open the blasting valve of the internal grouting pipe II and inject cement slurry to the bottom of the hole, so that the cement slurry seeps into the coal wall and the coal seam fractures along the screen pipe. When the internal return slurry pipe II returns slurry, wait for coagulation.

[0025] t4. After the cement slurry in the hole protection pipe has finished waiting for coagulation, use a drill bit to drill through the bladder II and the cement in the hole protection pipe to the bottom of the hole. After the hole is formed, connect the gas drainage pipeline through the flange.

[0026] When the gas drainage concentration in the borehole decays to below the preset value, carry out secondary pressure grouting with inorganic nano-flexible materials, including the following steps:

[0027] t1. Lower the hole sealing pipe string with double bladders into the hole protection pipe. The inner bladder III is located at the intersection of the last screen pipe and the solid pipe I, and the outer bladder III is located in the loose and broken zone. The internal grouting pipe III passes through the outer bladder III and extends into the inner bladder III. Check valves are installed on the parts of the internal grouting pipe III located inside the outer bladder III and the inner bladder III, and a blasting valve is installed on the part of the internal grouting pipe III located between the outer bladder III and the inner bladder III. The internal return slurry pipe III passes through the outer bladder III and extends between the outer bladder III and the inner bladder III.

[0028] At t2, open the one-way valve of the inner grouting pipe III, and inject inorganic nano flexible material into the inner bladder III and the outer bladder III. The inner bladder III and the outer bladder III expand to seal the hole protection pipe. After the pressure reaches the preset value, open the blasting valve of the inner grouting pipe III, and inject inorganic nano flexible material between the inner bladder III and the outer bladder III until the inner return grouting pipe III returns the grout, so as to perform secondary pressure sealing on the cracks generated at the joint between the shrinkage and cracking after the first cement mortar solidifies and the coal seam borehole wall of the coal extraction borehole along the layer.

[0029] Taking the thickness of the support entity belt as 10m and the total thickness of the crack development zone and the loosening and fragmentation zone as 7m as an example, provide the specific parameters in the low-pressure external plugging and high-pressure internal injection composite hole sealing process and the secondary pressure grouting of inorganic nano flexible material;

[0030] The parameters in the low-pressure external plugging and high-pressure internal injection composite hole sealing process are as follows:

[0031] In step t1, the diameter of the coal extraction borehole along the layer is 245mm, the hole depth is 17m, and a hole protection pipe with a diameter of 160mm is lowered to the bottom of the hole. The hole protection pipe consists of 1 root of 160 solid pipe I + 3 roots of 160 screen pipes + 4 roots of 160 solid pipes II + 1 root of 160 flange short joint from the inside to the outside;

[0032] In step t2, at 500mm and 8m inside the hole from the hole opening of the hole protection pipe, use AB glue to seal respectively. The grouting pressure of the external grouting pipe II is 0.6 - 0.8MPa and it solidifies for 24 hours;

[0033] In step t3, lower the bladder II at 7m from the hole opening, and inject cement slurry through the inner grouting pipe II until the grouting pressure at the bottom of the hole is above 2MPa, and wait for setting for 24 hours;

[0034] When the gas extraction concentration in the borehole decays to less than 10%, perform secondary pressure grouting of inorganic nano flexible material, and the parameters are as follows:

[0035] In step t1, the distance between the inner bladder III and the hole opening is 15m, and the distance between the outer bladder III and the hole opening is 3m;

[0036] In step t2, the grouting pressure of injecting inorganic nano flexible material between the inner bladder III and the outer bladder III is 1.0 - 1.2Mpa.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] Through the pressure relief extraction of the cross-cut coal extraction borehole and the coal extraction borehole along the layer, the stress of the coal and rock stratum is effectively released, promoting the coal seam gas extraction of the coal seam. Using the multiple grouting of inorganic materials improves the hole sealing effect and the gas extraction volume of the underground coal seam gas, thereby realizing the co-mining of broken soft coal and coal seam gas. Brief Description of the Drawings

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings required for the description of the specific embodiments or the prior art. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0040] Figure 1 It is a flowchart of a method for co-mining crushed soft coal and gas based on underground coal mining for pressure relief.

[0041] Figure 2 It is a schematic diagram of a method for co-mining crushed soft coal and gas based on underground coal mining for pressure relief.

[0042] Figure 3 It is a schematic diagram of a hole-sealing process of "three plugs and two injections".

[0043] Figure 4 It is a schematic diagram of a composite hole-sealing process of low-pressure external plugging and high-pressure internal injection.

[0044] Figure 5 It is a schematic diagram of a secondary pressure grouting process of inorganic nano-flexible materials.

[0045] In the figure: 101 - the first coal seam to be mined; 102 - the second coal seam to be mined; 103 - the third coal seam to be mined; 104 - the fourth coal seam to be mined; 105 - the bottom / top extraction roadway; 106 - the ground surface.

[0046] 201 - the cross-cut drilling site; 202 - the cross-cut coal mining borehole; 203 - the longwall drilling site; 204 - the longwall coal mining borehole.

[0047] 301 - the inner bladder bag Ⅰ; 302 - the middle bladder bag; 303 - the outer bladder bag Ⅰ; 304 - the inner grouting pipe Ⅰ; 305 - the inner return slurry pipe Ⅰ; 306 - the outer grouting pipe Ⅰ; 307 - the outer return slurry pipe Ⅰ; 308 - the check valve; 309 - the blasting valve; 310 - the solid pipe Ⅰ; 311 - the screen pipe; 312 - the solid pipe Ⅱ; 313 - the flange; 314 - the AB glue; 315 - the outer grouting pipe Ⅱ; 316 - the outer return slurry pipe Ⅱ; 317 - the bladder bag Ⅱ; 318 - the inner grouting pipe Ⅱ; 319 - the inner return slurry pipe Ⅱ; 320 - the inner bladder bag Ⅲ; 321 - the outer bladder bag Ⅲ; 322 - the inner grouting pipe Ⅲ; 323 - the inner return slurry pipe Ⅲ. Specific Embodiments

[0048] The following will clearly and completely describe the technical solutions of the present invention with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0049] Example 1

[0050] The common method for gas drainage in coal mines is still borehole drainage. By relieving pressure through coal mining boreholes underground, the drainage efficiency of coalbed methane is improved, which is an effective solution for gas drainage in soft and broken coal. Therefore, based on the new composite underground coal mining borehole sealing technology and combined with the construction of the top / bottom drainage roadway underground, a co - mining method for soft and broken coal and gas based on underground coal mining pressure relief is proposed. First, construct the cross - layer coal mining boreholes 202 of the top / bottom drainage roadway to carry out pressure relief drainage on the selected first mining coal seam 101 and the second mining coal seam 102. After the infrastructure projects such as the roadway of the first mining coal seam 101 are completed, construct the in - seam coal mining boreholes 204 for gas negative pressure drainage. The in - seam coal mining boreholes 204 of this coal seam should cover and drain the mining face. Area - type progressive boreholes and negative pressure drainage can be used. After the coal seam gas drainage in the mining face of the first mining coal seam 101 reaches the standard, coal mining is carried out. After the coal in the first mining coal seam 101 is mined, after the second mining coal seam 102 is pre - drained by the cross - layer coal mining boreholes 202 and pressure - relieved by the first mining coal seam 101, and after the infrastructure projects such as the roadway of the second mining coal seam 102 are completed, construct the in - seam coal mining boreholes 204 for gas negative pressure drainage. After the coal seam gas drainage reaches the standard, mine the coal in the second mining coal seam 102. After the pressure relief of the first and second mining coal seams, start the gas drainage of the third mining coal seam 103. After the coal seam gas drainage in the working face reaches the standard, carry out coal mining. In this way, the coordinated mining of coal and gas in soft and broken coal seam groups is realized.

[0051] Specifically, it includes the following steps.

[0052] S1. For coal mines with soft and broken coal seam groups, according to the exploration data, determine the first mining coal seam 101 and the spatial position of the bottom drainage roadway of the first mining coal seam 101.

[0053] In step S1, according to the exploration data, analyze the coal thickness, gas content, burial depth, and coal - rock mechanical properties of each coal seam to determine the first mining coal seam 101 and the spatial position of the bottom drainage roadway of the first mining coal seam 101.

[0054] S2. Optimize the design of the spatial position of the bottom drainage roadway of the first mining coal seam 101, and construct the bottom drainage roadway of the first mining coal seam 101, which also serves as the top drainage roadway of the second mining coal seam 102.

[0055] S3. At the same time, construct the cross - layer borehole drill sites 201 of the first mining coal seam 101 and the second mining coal seam 102, and construct the cross - layer coal mining boreholes 202.

[0056] In step S3, the three-block two-injection sealing process is adopted for the cross-layer coal-cutting borehole 202. Three grouting bladder bags are used to seal the cross-layer coal-cutting borehole 202, forming an inner grouting section and an outer grouting section. The inner grouting section is filled with cement material, and the outer grouting section is filled with inorganic flexible sealing material. The improved sealing process can completely achieve pressure sealing during sealing.

[0057] The specific steps of the three-block two-injection sealing process are as follows: The three grouting bladder bags are arranged in the cross-layer coal-cutting borehole from the inside to the outside in sequence, namely the inner bladder bag I 301, the middle bladder bag 302, and the outer bladder bag I 303. An inner grouting pipe I 304, an inner return slurry pipe I 305, an outer grouting pipe I 306, and an outer return slurry pipe I 307 are arranged in the cross-layer coal-cutting borehole 202. The inner grouting pipe I 304 passes through the outer bladder bag I 303 and the middle bladder bag 302 and extends into the inner bladder bag I 301. Check valves 308 are installed on the parts of the inner grouting pipe I 304 located in the middle bladder bag 302 and the inner bladder bag I 301. Blasting valves 309 are installed on the parts of the inner grouting pipe I 304 located between the middle bladder bag 302 and the inner bladder bag I 301. The inner return slurry pipe I 305 passes through the outer bladder bag I 303 and the middle bladder bag 302 and extends between the middle bladder bag 302 and the inner bladder bag I 301. The outer grouting pipe I 306 passes through the outer bladder bag I 303 and extends between the outer bladder bag I 303 and the middle bladder bag 302. Check valves 308 are installed on the parts of the outer grouting pipe I 306 located in the outer bladder bag I 303. Blasting valves 309 are installed on the parts of the outer grouting pipe I 306 located between the outer bladder bag I 303 and the middle bladder bag 302. The outer return slurry pipe I 307 passes through the outer bladder bag I 303 and the middle bladder bag 302 and extends between the middle bladder bag 302 and the inner bladder bag I 301;

[0058] Open the check valves 308 in the inner bladder bag I 301, the middle bladder bag 302, and the outer bladder bag I 303, and inject cement slurry into the three grouting bladder bags. The grouting bladder bags expand, forming an inner grouting section between the inner bladder bag I 301 and the middle bladder bag 302 and an outer grouting section between the middle bladder bag 302 and the outer bladder bag I 303. After the grouting pressure reaches the preset value, open the blasting valve of the inner grouting pipe I. When the inner return slurry pipe I returns slurry, it indicates that the inner grouting section is filled with cement slurry to form a solid sealing section. Then, open the blasting valve 309 of the outer grouting pipe I 304 and inject the prepared inorganic flexible sealing material into the outer grouting section until the outer return slurry pipe I 307 returns slurry. During the grouting process, the slurry begins to penetrate into the cracks around the borehole as the grouting pressure increases, thus achieving the sealing of the borehole.

[0059] The main components of the inorganic flexible sealing material are inorganic silicate base materials and self-made cationic nano-composite modifiers. The selected nano-materials have a spherical structure, a particle size of 20 - 80 nm, and a specific surface area ≥ 30 m 2 / g. Due to the differences in their structural morphologies, cationic nano-composite surfactants can form mixed micelles with special structures in the interlayers of silicates. At the same time, due to their spherical structures, they not only significantly increase the interlayer distance but also form a ball bearing effect in the silicate materials, improving their high-shear fluidity, facilitating pumping and grouting. Under low-shear conditions, they form a spatial cage structure, enhancing their thixotropic stability, increasing the water absorption and water retention of the materials, adjusting the hydrophilic-lipophilic properties of the material surface, changing the surface tension of the material, forming a stable and dense hydration layer on the material surface, enhancing its affinity with Ca 2+ , Mg 2+ etc., expanding the permeability of the sealing material, reducing the formation of foam in the sealing material, and enhancing the airtightness. The new inorganic nano-flexible hole-sealing material forms an inorganic gel when mixed with water, has strong water retention, does not solidify or shrink, and can achieve multiple slurry replenishments, extending the life and improving the efficiency of the gas drainage holes.

[0060] S4. Use the cross-layer coal-cutting borehole 202 to conduct underground negative pressure drainage on the first mining coal seam 101 and the second mining coal seam 102 until the gas content in the first mining coal seam 101 and the second mining coal seam 102 meets the drainage standard. At the same time, through the construction of the bottom drainage roadway and the coal-cutting pressure relief of the cross-layer coal-cutting borehole 202 in the first mining coal seam 101, the stress of the coal and rock strata is effectively released, the permeability of the coal and rock increases, and the gas drainage efficiency of the coal seam is improved.

[0061] S5. Carry out the infrastructure construction of the first mining coal seam and construct the along-layer coal-cutting borehole 204.

[0062] The along-layer coal-cutting borehole adopts a composite pressure-sealing hole technology, including a low-pressure external plugging and high-pressure internal injection composite sealing hole technology and an inorganic nano-flexible material secondary pressure slurry replenishment technology.

[0063] The low-pressure external plugging and high-pressure internal injection composite sealing hole technology includes the following steps:

[0064] t1. Lower the hole protection pipe to the bottom of the along-layer coal-cutting borehole 204. The hole protection pipe consists of a solid pipe I 310 + a screen pipe 311 + a solid pipe II 312 + a flange 313 from the inside out. The solid pipe I 310 and the screen pipe 311 are located in the support entity zone, and the solid pipe II 312 extends from the support entity zone, the fracture development zone, and the loose and broken zone to the hole opening and is connected to the flange 313;

[0065] At t2, AB glue 314 is used to seal between the loose and broken zone and the solid pipe II 312, and between the junction of the fissure-developed zone and the support solid zone and the solid pipe II 312. The outer grouting pipe II 315 and the outer slurry return pipe II 316 are arranged in the annulus between the protection hole pipe and the wall of the coal-digging borehole along the bedding. Cement slurry is injected into the annulus between the protection hole pipe and the wall of the coal-digging borehole along the bedding through the outer grouting pipe II 315. After the slurry returns through the outer slurry return pipe II 316, wait for the cement slurry to solidify. The purpose is to ensure the tightness of the low-pressure outer plugging and sealing area and withstand the pressure during the inner hole sealing in the high-pressure inner grouting and sealing area.

[0066] At t3, the inner bag II 317, the inner grouting pipe II 318 and the inner slurry return pipe II 319 are placed in the protection hole pipe. The bag II 317 is located at the junction of the fissure-developed zone and the support solid zone. The inner grouting pipe II 318 passes through the bag II 317 and extends into the last solid pipe II 310. A check valve 308 is installed on the part of the inner grouting pipe II 318 located inside the bag II 317, and a blasting valve 309 is installed on the part of the inner grouting pipe II 318 located in the last solid pipe II 310. The inner slurry return pipe II 319 passes through the bag II 317 and extends into the first screen pipe 311. Open the check valve 308 of the inner grouting pipe II 318 and inject cement slurry into the bag II 317. The bag II 317 expands to seal the protection hole pipe. After the grouting pressure reaches the preset value, open the blasting valve 309 of the inner grouting pipe II 318 and inject cement slurry to the bottom of the hole, so that the cement slurry seeps into the coal wall and the coal body fissures along the screen pipe 311. When the inner slurry return pipe II 319 returns slurry, wait for setting;

[0067] At t4, after the cement slurry in the protection hole pipe finishes setting, use a drill bit to drill through the bag II 317 and the cement in the protection hole pipe to the bottom of the hole. After the hole is formed, connect the drainage pipeline through the flange 313.

[0068] When the gas drainage concentration in the borehole decays to below the preset value, use inorganic nano flexible materials for secondary pressure-bearing hole sealing and slurry replenishment, including the following steps:

[0069] At t1, a hole-sealing pipe string with double bags is lowered into the protection hole pipe. The inner bag III 320 is located at the junction of the last screen pipe 311 and the solid pipe I 310, and the outer bag III 321 is located in the loose and broken zone. The inner grouting pipe III 322 passes through the outer bag III 321 and extends into the inner bag III 320. Check valves 308 are installed on the parts of the inner grouting pipe III 322 located inside the outer bag III 321 and the inner bag III 320, and a blasting valve 309 is installed on the part of the inner grouting pipe III 318 located between the outer bag III 321 and the inner bag III 320. The inner slurry return pipe III 323 passes through the outer bag III 321 and extends between the outer bag III 321 and the inner bag III 320;

[0070] At t2, open the one-way valve 308 of the inner grouting pipe III 322, and inject the inorganic nano flexible material into the inner bladder III 320 and the outer bladder III 321. The inner bladder III 320 and the outer bladder III 321 expand to block the hole protection pipe. After the pressure reaches the preset value, open the blasting valve 309 of the inner grouting pipe III 322, and inject the inorganic nano flexible material between the inner bladder III 320 and the outer bladder III 321 until the inner return grouting pipe III 323 returns grout, so as to perform secondary pressure sealing on the cracks generated at the joint between the shrinkage cracks and the bedding coal extraction borehole wall after the first cement mortar solidifies.

[0071] S6. Use the bedding coal extraction borehole 204 to perform regional full-coverage coalbed methane extraction on the working face of the first coal seam 101 until the coalbed methane content of the first coal seam 101 reaches the extraction standard.

[0072] S7. Mine the coal on the working face of the first coal seam 101 until the coal on the working face of the first coal seam 101 is mined out.

[0073] S8. Carry out the infrastructure construction of the next coal seam to be mined, and construct the bedding coal extraction borehole 204.

[0074] S9. Use the bedding coal extraction borehole 204 to perform regional full-coverage coalbed methane extraction on the working face of the next coal seam to be mined until the coalbed methane content of the next coal seam to be mined reaches the extraction standard.

[0075] S10. Mine the coal on the working face of the next coal seam until the coal on the working face of the next coal seam to be mined is mined out.

[0076] S11. Repeat steps S8 - S10 to realize the co-mining of coal and coalbed methane in the soft broken coal seam group.

[0077] Due to the coal mining of the first coal seam 101, pressure relief is achieved for the second coal seam 102, which is beneficial to the coalbed methane extraction of the second coal seam 102. After the coalbed methane gas extraction on the working face reaches the standard, the mining of the working face of the second coal seam 102 is carried out. In this way, the co-mining of coal and coalbed methane in the coal seam group is realized by cycling.

[0078] Embodiment 2

[0079] Taking the thickness of the support entity belt as 10m and the total thickness of the crack development zone and the loosening and fragmentation zone as 7m as an example, provide the specific parameters in the low-pressure external plugging and high-pressure internal injection composite sealing process and the secondary pressure grouting with inorganic nano flexible material;

[0080] The parameters in the low-pressure external plugging and high-pressure internal injection composite sealing process are:

[0081] In step t1, the diameter of the coal-digging borehole 204 along the bedding is 245 mm, and the hole depth is 17 m. A hole-protecting pipe with a diameter of 160 mm is lowered to the bottom of the hole. The hole-protecting pipe consists of, from the inside out, 1 piece of 160 solid pipe Ⅰ + 3 pieces of 160 screen pipes + 4 pieces of 160 solid pipe Ⅱ + 1 piece of 160 flange short joint;

[0082] In step t2, at 500 mm and 8 m inside the hole from the hole opening of the hole-protecting pipe, AB glue 314 is used for plugging respectively. The grouting pressure of the outer grouting pipe Ⅱ 315 is 0.6 - 0.8 MPa, and it solidifies for 24 hours;

[0083] In step t3, a bladder bag Ⅱ 317 is lowered at 7 m from the hole opening, and the grouting pressure of injecting cement slurry to the bottom of the hole through the inner grouting pipe Ⅱ 318 is above 2 MPa, and it waits for setting for 24 hours;

[0084] When the gas drainage concentration in the borehole decays to less than 10%, secondary pressure grouting with inorganic nano flexible material is carried out. The parameters are as follows:

[0085] In step t1, the distance from the inner bladder bag Ⅲ 320 to the hole opening is 15 m, and the distance from the outer bladder bag Ⅲ 321 to the hole opening is 3 m;

[0086] In step t2, the grouting pressure of injecting inorganic nano flexible material between the inner bladder bag Ⅲ 320 and the outer bladder bag Ⅲ 321 is 1.0 - 1.2 Mpa.

[0087] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for mining crushed soft coal and gas based on underground coal digging and pressure relief, characterized in that: The steps include: S1, for coal mines with broken and soft coal seams, determine the first mining coal seam and the spatial location of the bottom extraction lane of the first mining coal seam based on exploration data; S2, optimize the spatial position of the bottom extraction tunnel of the first mining coal seam, construct the bottom extraction tunnel of the first mining coal seam, and simultaneously serve as the top extraction tunnel of the second mining coal seam; S3, constructing through-layer drilling sites for the first and second mining coal seams at the same time, and constructing through-layer coal-digging drilling holes; S4, using a through-layer coal drilling borehole to perform underground negative pressure extraction on the first mining coal seam and the second mining coal seam until the coal seam gas content of the first mining coal seam and the second mining coal seam reaches the extraction standard; S5, carry out the infrastructure construction of the first mining coal seam, and drill holes along the seam; S6, using the coal-digging drilling holes along the seam to conduct regional full coverage coal-bed methane extraction on the working face of the first mining coal seam, until the coal-bed methane content of the first mining coal seam reaches the extraction standard; S7, mining the coal at the working face of the first mining coal seam until all the coal at the working face of the first mining coal seam is mined; S8, carrying out the infrastructure construction of the next coal seam to be mined, and drilling holes along the seam; S9, using the coal drilling holes along the seam to carry out regional full coverage coalbed methane extraction on the working face of the next coal seam to be mined, until the coalbed methane content of the next coal seam to be mined reaches the extraction standard; S10, mining the coal at the working face of the next coal seam until all the coal at the working face of the next coal seam is mined; S11, loop steps S8-S10 to realize the co-mining of coal and coalbed methane in the broken and soft coal seam group.

2. The method for mining crushed soft coal and gas based on underground coal excavation and pressure relief according to claim 1 is characterized in that: In step S1, the thickness, gas content, burial depth, and mechanical properties of coal and rock of each coal seam are analyzed based on the exploration data to determine the first mining coal seam and the spatial position of the bottom extraction lane of the first mining coal seam.

3. The method for mining crushed soft coal and gas based on underground coal digging and pressure relief according to claim 1 is characterized in that: In step S3, the through-layer coal drilling hole adopts a three-blocking and two-injection sealing process, and three grouting bags are used to seal the through-layer coal drilling hole to form an inner grouting section and an outer grouting section. The inner grouting section is filled with cement material, and the outer grouting section is filled with inorganic flexible sealing material.

4. The method for mining crushed soft coal and gas based on underground coal digging and pressure relief according to claim 3 is characterized in that: Three grouting bags are arranged in sequence from the inside to the outside in the through-layer coal drilling hole, namely the inner bag I, the middle bag, and the outer bag I. In the through-layer coal drilling hole, the inner grouting pipe I, the inner return grouting pipe I, the outer grouting pipe I, and the outer return grouting pipe I are arranged. The inner grouting pipe I passes through the outer bag I and the middle bag and extends into the inner bag I. The part of the inner grouting pipe I located in the middle bag and the inner bag I is installed with a one-way valve. The inner grouting pipe I is located between the middle bag and the inner bag I. The portion of the outer bag is equipped with a bursting valve, the inner return grouting pipe I passes through the outer bag I and the middle bag to extend between the middle bag and the inner bag I, the outer grouting pipe I passes through the outer bag I to extend between the outer bag I and the middle bag, the portion of the outer grouting pipe I located inside the outer bag I is equipped with a one-way valve, the portion of the outer grouting pipe I located between the outer bag I and the middle bag is equipped with a bursting valve, the outer return grouting pipe I passes through the outer bag I and the middle bag to extend between the middle bag and the inner bag I; Open the one-way valves in the inner bag I, the middle bag and the outer bag I, inject cement slurry into the three grouting bags, and the grouting bags will expand to form an inner grouting section between the inner bag I and the middle bag, and an outer grouting section between the middle bag and the outer bag I. After the grouting pressure reaches the preset value, open the bursting valve of the inner grouting pipe I. When the inner return grouting pipe I returns grouting, it means that the cement slurry fills the inner grouting section to form a solid sealing section. Then open the bursting valve of the outer grouting pipe I, and inject the configured inorganic flexible sealing material into the outer grouting section until the outer return grouting pipe I returns grouting.

5. The method for mining crushed soft coal and gas based on underground coal digging and pressure relief according to claim 4 is characterized in that: The composite pressure sealing process is used in the seam coal drilling process, including the low-pressure external plugging and high-pressure internal injection composite sealing process and the inorganic nano-flexible material secondary pressure grouting process.

6. The method for mining crushed soft coal and gas based on underground coal digging and pressure relief according to claim 5, characterized in that: The low-pressure external plugging and high-pressure internal injection composite sealing process includes the following steps: t1, in the seam coal drilling hole, the hole protection pipe is lowered to the bottom of the hole. The hole protection pipes are solid pipe I + screen pipe + solid pipe II + flange from the inside to the outside. The solid pipe I and the screen pipe are located in the supporting solid zone, and the solid pipe II extends from the supporting solid zone, the fracture development zone, and the loose and broken zone to the hole mouth and is connected to the flange; t2, AB glue is used to seal between the loose and broken zone and the solid pipe II, and AB glue is used to seal between the intersection of the fracture development zone and the supporting solid zone and the solid pipe II. The external grouting pipe II and the external grouting pipe II are placed under the annulus between the hole protection pipe and the wall of the coal-cutting borehole in the layer. Cement slurry is injected into the annulus between the hole protection pipe and the wall of the coal-cutting borehole in the layer through the external grouting pipe II. After the cement slurry is returned to the external grouting pipe II, wait for the cement slurry to solidify; t3, put bag II, inner grouting pipe II and inner return grouting pipe II in the hole protection pipe, bag II is located at the junction of the fracture development zone and the supporting solid zone, inner grouting pipe II passes through bag II and extends to the last solid pipe II, the part of inner grouting pipe II located in bag II is installed with a one-way valve, the part of inner grouting pipe II located in the last solid pipe II is installed with a bursting valve, inner return grouting pipe II passes through bag II and extends to the first screen pipe, open the one-way valve of inner grouting pipe II, inject cement slurry into bag II, bag II expands and blocks the hole protection pipe, after the grouting pressure reaches the preset value, open the bursting valve of inner grouting pipe II, inject cement slurry to the bottom of the hole, so that the cement slurry penetrates into the coal wall and coal body cracks along the screen pipe, and wait for solidification after the inner return grouting pipe II returns grouting; t4. After the cement slurry in the hole protection tube has finished solidifying, use a drill bit to drill through the bag II and cement in the hole protection tube to the bottom of the hole. After the hole is formed, the pumping pipeline is connected through the flange.

7. The method for mining crushed soft coal and gas based on underground coal excavation and pressure relief according to claim 6, characterized in that: When the gas extraction concentration in the borehole decays to below the preset value, the inorganic nano-flexible material is used for secondary pressure grouting, including the following steps: t1, a sealing pipe string with double bags is lowered into the hole protection pipe, the inner bag III is located at the junction of the last screen pipe and the solid pipe I, the outer bag III is located in the loose and broken zone, the inner grouting pipe III passes through the outer bag III and extends into the inner bag III, the part of the inner grouting pipe III located in the outer bag III and the inner bag III is installed with a one-way valve, the part of the inner grouting pipe III located between the outer bag III and the inner bag III is installed with a bursting valve, and the inner return grouting pipe III passes through the outer bag III and extends between the outer bag III and the inner bag III; t2, open the one-way valve of the inner grouting pipe III, inject inorganic nano-flexible material into the inner bag III and the outer bag III, the inner bag III and the outer bag III expand to seal the hole protection pipe, after the pressure reaches the preset value, open the bursting valve of the inner grouting pipe III, inject inorganic nano-flexible material between the inner bag III and the outer bag III, return grout to the inner return grouting pipe III, and perform secondary pressure sealing on the cracks generated at the junction of the shrinkage and cracking of the cement mortar after the first cement mortar solidifies and the wall of the coal drilling along the layer.

8. The method for mining crushed soft coal and gas based on underground coal excavation and pressure relief according to claim 7, characterized in that: The thickness of the supporting solid zone is 10m, and the total thickness of the fracture development zone and loose fracture zone is 7m; The parameters of the low-pressure external plugging and high-pressure internal injection composite sealing process are: In step t1, the diameter of the coal drilling hole is 245mm, the hole depth is 17m, and a hole protection pipe with a diameter of 160mm is installed to the bottom of the hole. The hole protection pipes are 1 160 solid pipe I + 3 160 screen pipes + 4 160 solid pipe II + 1 160 flange short connection from inside to outside; In step t2, AB glue is used to seal the hole protection pipe at 500mm and 8m from the hole mouth respectively, and the grouting pressure of the outer grouting pipe II is 0.6-0.8MPa, and solidification takes 24 hours; In step t3, a bag II is placed 7 m away from the hole mouth, and cement slurry is injected through the inner grouting pipe II until the grouting pressure at the bottom of the hole is above 2 MPa, and the grouting is allowed to solidify for 24 hours; When the gas extraction concentration in the borehole decays to below 10%, the inorganic nano-flexible material is used for secondary pressure grouting, and the parameters are: In step t1, the distance between the inner bag III and the orifice is 15m, and the distance between the outer bag III and the orifice is 3m; In step t2, the grouting pressure of the inorganic nano flexible material injected between the inner bag III and the outer bag III is 1.0-1.2 MPa.

Images