CN115478830A - Permeability increasing method for low permeability coal seam - Google Patents
Permeability increasing method for low permeability coal seam Download PDFInfo
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- CN115478830A CN115478830A CN202211367031.1A CN202211367031A CN115478830A CN 115478830 A CN115478830 A CN 115478830A CN 202211367031 A CN202211367031 A CN 202211367031A CN 115478830 A CN115478830 A CN 115478830A
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- 239000003245 coal Substances 0.000 title claims abstract description 137
- 230000035699 permeability Effects 0.000 title claims abstract description 34
- 238000000034 method Methods 0.000 title claims abstract description 30
- 230000001965 increasing effect Effects 0.000 title claims abstract description 21
- 238000005553 drilling Methods 0.000 claims abstract description 109
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 66
- 238000002485 combustion reaction Methods 0.000 claims abstract description 52
- 238000004891 communication Methods 0.000 claims abstract description 26
- 239000007788 liquid Substances 0.000 claims abstract description 26
- 238000004880 explosion Methods 0.000 claims abstract description 11
- 239000000203 mixture Substances 0.000 claims abstract description 10
- 238000000605 extraction Methods 0.000 claims description 16
- 230000001737 promoting effect Effects 0.000 claims description 6
- 239000003034 coal gas Substances 0.000 claims description 5
- 238000005336 cracking Methods 0.000 claims description 4
- 238000005422 blasting Methods 0.000 claims description 3
- 230000003116 impacting effect Effects 0.000 claims description 3
- 238000012544 monitoring process Methods 0.000 claims description 3
- 230000002708 enhancing effect Effects 0.000 claims 1
- 239000007789 gas Substances 0.000 description 19
- 230000000694 effects Effects 0.000 description 4
- 239000012530 fluid Substances 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000011435 rock Substances 0.000 description 3
- 238000009826 distribution Methods 0.000 description 2
- 239000002360 explosive Substances 0.000 description 2
- 238000011065 in-situ storage Methods 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 238000005065 mining Methods 0.000 description 2
- 238000010276 construction Methods 0.000 description 1
- 238000004200 deflagration Methods 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- 238000001028 reflection method Methods 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
- E21B43/263—Methods for stimulating production by forming crevices or fractures using explosives
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B7/00—Special methods or apparatus for drilling
- E21B7/04—Directional drilling
- E21B7/046—Directional drilling horizontal drilling
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Abstract
The invention provides a permeability increasing method for a low permeability coal seam, which comprises the steps of drilling horizontal drill holes in sequence from the bottom of a roadway to the upper part of the roadway, and drilling a plurality of groups of vertical drill holes and lateral drill holes in the formed horizontal drill holes along the vertical direction upwards and the horizontal direction vertical to the horizontal drill holes; drilling a top plate horizontal well at the lower part of the top plate; drilling corresponding vertical communication holes upwards in each horizontal drilling hole on the uppermost layer, so that the vertical communication holes are communicated with the horizontal drilling holes on the uppermost layer and the horizontal section of the horizontal well of the top plate; plugging a horizontal drilling hole in a coal seam, and then putting a liquid combustion improver; pre-extracting the methane in the coal seam, closing a ground wellhead after the concentration of the extracted methane exceeds 80%, and igniting and detonating a methane-combustion improver mixture in the complex drilling network of the coal seam; and continuously carrying out combustion improver feeding and combustion explosion fracturing operation in the coal seam to promote the continuous expansion and extension of cracks around the complex drilling network. The method is simple to operate, low in implementation cost and remarkable in permeability increasing effect on the coal bed.
Description
Technical Field
The invention belongs to the technical field of coal safety mining and gas development, and particularly relates to a permeability increasing method for a low permeability coal bed.
Background
China is a large country for coal production and consumption, and more than 50% of coal seams are high-gas coal seams and are seriously influenced by coal and gas outburst accidents. With the increase of mining depth, the coal and gas outburst risk is increased. The coal gas is a gas mixture mainly containing methane, which not only causes potential safety production hazards of coal mines, but also is an important clean energy source, and belongs to typical unconventional natural gas, so that the effective gas extraction is not only a key measure for preventing and treating coal and gas outburst, but also an important technical link for realizing resource utilization of the gas. The coal seam in China has the characteristics of high gas pressure, strong gas adsorption, low coal seam permeability and the like, so that cracking permeability-increasing measures need to be adopted for the coal seam, the air permeability of the coal seam is increased, and effective gas extraction is realized. At present, the permeability of a coal seam is mainly increased by a drilling pressure relief method, and a damaged zone formed by stress release around a drill hole is utilized to improve the permeability of the coal seam, but the method has the problems of limited permeability increasing range, small effective gas extraction radius and the like, and particularly has a very limited fracturing permeability increasing effect in a soft coal seam with high argillaceous content. Therefore, the existing process method needs to be upgraded and reformed, the existing technical system is innovated, and an anti-reflection method suitable for a low permeability coal bed is formed, so that the high-efficiency extraction of coal gas is realized, and accidents such as coal and gas outburst in the production process of a coal mine are eliminated.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a permeability increasing method for a low permeability coal seam, which has the advantages of simple operation process, low implementation cost, obvious permeability increasing effect on the coal seam, and capability of improving gas extraction efficiency.
In order to achieve the purpose, the invention provides a permeability increasing method for a low permeability coal seam, which specifically comprises the following steps;
the method comprises the following steps: constructing a complex drilling network of the coal bed;
s11, determining the positions of multilayer drilling holes on the side surface in a return airway or a transportation airway in a mode parallel to a stope face aiming at the coal gas enrichment and high gas pressure coal seam area;
s12, sequentially drilling horizontal drill holes from the bottom of the roadway to the upper part of the roadway, after the next layer of horizontal drill holes are completed, vertically moving the positions of the drill holes, and then performing drilling operation of the upper layer of horizontal drill holes;
s13, drilling a plurality of groups of vertical drill holes and lateral drill holes in the formed horizontal drill holes along the length direction of the horizontal drill holes in a hydraulic jet sidetracking mode along the vertical direction and the horizontal direction vertical to the horizontal drill holes, communicating the adjacent horizontal drill holes of the upper layer and the lower layer with the vertical drill holes, and communicating the adjacent horizontal drill holes of the same layer with the lateral drill holes; in the process, stress released in the drilling operation process is applied to the coal seam around the drill hole, so that the coal seam deforms and fractures to form a drill hole fracture zone, and a complex drill hole network consisting of horizontal drill holes, vertical drill holes and lateral drill holes is formed in the coal seam;
step two: drilling a roof horizontal well on the ground;
drilling a top plate horizontal well at the lower part of a top plate in a ground drilling mode, and enabling the horizontal section of the top plate horizontal well to be parallel to the coal bed;
step three: communicating the roof horizontal well with the complex drilling network of the coal seam;
after the top plate horizontal well is drilled, drilling corresponding vertical communication holes upwards in each horizontal drilling hole on the uppermost layer in a hydraulic jet sidetracking mode, enabling the vertical communication holes to be communicated with the horizontal drilling holes on the uppermost layer and the horizontal section of the top plate horizontal well, and forming a complex drilling network-vertical communication holes-top plate horizontal well interconnected complex well pattern channel in the coal bed and the top plate;
step four: feeding a liquid combustion improver;
plugging horizontal drilling holes in the coal seam in an underground transportation roadway or a return airway, then putting a liquid combustion improver into the coal seam from the ground through a top horizontal well, so that the liquid combustion improver enters the coal seam through the top horizontal well and a vertical communication hole, flows into each region of the coal seam through horizontal drilling holes, vertical drilling holes and lateral drilling holes in the coal seam, and meanwhile, part of the liquid combustion improver enters the coal seam through cracks around the drilling holes;
step five: blasting and cracking;
pre-extracting methane in the coal seam through a top plate horizontal well, monitoring the concentration of the methane in real time, closing a ground wellhead of the top plate horizontal well after the concentration of the extracted methane exceeds 80%, then performing electric shock ignition on the methane-combustion improver mixture in the complex drilling network of the coal seam, igniting and detonating the methane-combustion improver mixture in the complex drilling network of the coal seam, impacting the coal seam by utilizing high air pressure generated in the combustion and explosion process of the methane and the combustion improver, promoting the coal seam around the complex drilling network to form large-scale cracks, and further communicating crack zones formed around the complex drilling network due to stress release;
step six: constructing a multi-scale methane extraction system;
and repeating the fourth step and the fifth step for multiple times, continuously carrying out combustion improver feeding and combustion explosion fracturing operation in the coal seam, promoting the continuous expansion and extension of cracks around the complex drilling network, further increasing the complexity and the extension distance of the cracks, and finally forming a natural crack-large-scale crack-coal seam complex drilling network-vertical communication hole-roof horizontal well multi-scale methane extraction system in the coal seam.
Further, in order to more comprehensively monitor the extraction process, in the fifth step, the methane concentration is monitored, and meanwhile, the methane components are synchronously monitored.
Preferably, in step one, the thickness of the coal seam in the coal seam area is not less than 2m.
Further, in order to obtain a better anti-reflection effect, in step one, in S11, it is ensured that the heights of the drilling positions of different layers from the bottom of the roadway are different.
According to the method, firstly, a plurality of layers of horizontal drill holes are drilled in a coal seam area, the upper horizontal drill hole and the lower horizontal drill hole are communicated with each other through the vertical drill holes, the adjacent horizontal drill holes in the same layer are communicated with each other through the lateral drill holes, so that a complex drill hole network can be formed in the coal seam, and a coal seam internal communication channel is provided for later-stage coal seam fracturing and permeability increasing; secondly, drilling a top plate horizontal well in the area where the top plate is located, and forming a stable borehole by utilizing the characteristic of stable structure of the rock stratum where the top plate is located, so that the stability of the main body section of the fluid injection channel can be ensured, and a powerful guarantee is provided for the fact that a subsequent liquid combustion improver can be fully injected into each part in the coal seam; then, the vertical communication holes are used for connecting the horizontal hole of the top plate and the horizontal hole of the uppermost layer, so that a complex well pattern channel with a complex drilling network, the vertical drilling hole, the vertical communication hole and the horizontal hole of the top plate which are mutually communicated is finally formed, the complex well pattern channel can enable all directions of a coal bed to be mutually communicated, the uniformity of the distribution of fracturing cracks is greatly enhanced, the fracturing range is effectively enlarged, and the fracturing effect is better; then, after the horizontal drilling hole is plugged, the liquid combustion improver is put into the complex well pattern channel through the top plate horizontal well, so that the hydraulic combustion improver can be ensured to fully enter each part of the complex well pattern channel, the consumption of the liquid combustion improver is favorably saved, and moreover, the hydraulic combustion improver entering the fracture can drive part of methane in the fracture to the main channel, so that the gas extraction efficiency can be favorably improved; finally, igniting and detonating the methane-combustion improver mixture in the complex drilling network of the coal seam after the liquid combustion improver is put in, and carrying out in-situ ignition and explosion by fully utilizing the methane in the coal seam, so that large-scale cracks can be formed by utilizing high-pressure impact of the explosion and further a fissure zone is formed.
Drawings
FIG. 1 is a schematic diagram of the construction of a complex drilling network of a coal seam according to the present invention;
FIG. 2 is a schematic structural view of a ground roof-drilling horizontal well according to the present invention;
FIG. 3 is a schematic structural diagram of a complex drilling network for communicating a roof horizontal well with a coal seam according to the present invention;
FIG. 4 is a schematic diagram of the delivery of a liquid oxidizer in accordance with the present invention;
fig. 5 is a schematic view of the deflagration-initiated operation of the present invention.
In the figure: 1. horizontal drilling, 2 vertical drilling, 3 lateral drilling, 4 roof, 5 roof horizontal well, 6 coal bed, 7 vertical communication hole, 8 liquid combustion improver, 9 ground well mouth, 10 large-scale crack.
Detailed Description
The invention will be further explained with reference to the drawings.
The invention provides a permeability increasing method for a hypotonic coal seam, which comprises the steps of firstly drilling a complex drilling network in a coal seam 6, then drilling a top plate horizontal well 5 in a top plate 4 from the ground, and finally upwards drilling a vertical communication hole 7 communicated with the top plate horizontal well 5 in a horizontal drilling hole 1; and (3) putting a liquid combustion improver 8 into the ground roof horizontal well 5, wherein the liquid combustion improver 8 enters the coal seam complex drilling network through the roof horizontal well 5 and is mixed with methane in the coal seam complex drilling network to form combustible and explosive multiphase fluid. By igniting combustible and explosive multiphase fluid in the complex drilling network, the complex drilling network is exploded, the coal seam around the complex drilling network is impacted, cracks are formed, a large-range stress release area is generated in the coal seam 6, and high-flow-guide-capacity channels communicated with the complex drilling network, artificial cracks and natural cracks are formed in the coal seam 6, so that multidimensional and multi-level permeability-increasing transformation of a low-permeability coal seam is realized, and the purpose of permeability increasing of the low-permeability coal seam is achieved;
the method comprises the following steps: constructing a complex drilling network of the coal seam, as shown in figures 1 to 4;
s11, determining the positions of multilayer drilling holes on the side surface in a return airway or a transportation airway in a mode parallel to a stope face aiming at the coal gas enrichment and high gas pressure coal seam area;
s12, sequentially drilling horizontal drill holes 1 from the bottom of the roadway to the upper part of the roadway, after finishing a group of horizontal drill holes 1 on the next layer, vertically moving the drill hole positions, and then performing drilling operation on the horizontal drill holes 1 on the previous layer;
s13, drilling a plurality of groups of vertical drill holes 2 and lateral drill holes 3 in the formed horizontal drill holes 1 along the length direction of the horizontal drill holes 1 in a hydraulic jet sidetracking mode along the vertical direction and the horizontal direction vertical to the horizontal drill holes 1, communicating the upper layer of horizontal drill holes 1 with the lower layer of adjacent horizontal drill holes 2, and communicating the same layer of adjacent horizontal drill holes 1 with the lateral drill holes 3; in the process, the stress of the coal seam is released due to the drilling operation, so that the released stress can be applied to the coal seam 6 around the drill hole, the coal seam 6 is deformed and broken, a drill hole fracture zone is formed, and a complex drill hole network consisting of a horizontal drill hole 1, a vertical drill hole 2 and a lateral drill hole 3 is formed in the coal seam 6;
step two: drilling a roof horizontal well on the ground;
as shown in fig. 2, a top plate horizontal well 5 is drilled at the lower part of a top plate 4 by adopting a ground drilling mode, and the horizontal section of the top plate horizontal well 5 is parallel to a coal seam 6; because the strength of the top plate 4 is high, the rock stratum structure is stable, and a stable borehole is easily formed when the top plate horizontal well 5 penetrates through the top plate 4;
step three: communicating the roof horizontal well with the complex drilling network of the coal seam;
as shown in fig. 3, after the roof horizontal well 5 is drilled, drilling a corresponding vertical communication hole 7 upwards in each horizontal drilling hole 1 on the uppermost layer by adopting a hydraulic jet sidetracking manner, so that the vertical communication hole 7 is communicated with the horizontal section of the horizontal drilling hole 1 on the uppermost layer and the horizontal section of the roof horizontal well 5, and forming a complex drilling network-vertical communication hole 7-roof horizontal well 5 interconnected complex well pattern channel in the coal seam 6 and the roof 4; by adopting the mode, the coal bed 6 is communicated with the ground through the vertical communication hole 7 and the horizontal well 5 in the top plate, so that a channel is provided for coal bed fracturing permeability increase and gas extraction in the later period;
step four: feeding a liquid combustion improver;
as shown in fig. 4, a horizontal borehole 1 in a coal seam 6 is plugged in an underground transportation roadway or a return airway, then a liquid combustion improver 8 is put into the coal seam 6 from the ground through a roof horizontal well 5, so that the liquid combustion improver 8 enters the coal seam 6 through the roof horizontal well 5 and a vertical communication hole 7, flows into each area of the coal seam 6 through the horizontal borehole 1, a vertical borehole 2 and a lateral borehole 3 in the coal seam 6, and meanwhile, part of the liquid combustion improver 8 enters the coal seam 6 through cracks around the borehole;
step five: blasting and cracking;
as shown in fig. 5, pre-extracting methane in a coal seam 6 through a roof horizontal well 5, monitoring the methane concentration in real time, closing a ground wellhead 9 of the roof horizontal well 5 after the extracted methane concentration exceeds 80%, then performing electric shock ignition on a methane-combustion improver mixture in a coal seam complex drilling network, igniting and detonating the methane-combustion improver mixture in the coal seam complex drilling network, impacting the coal seam 6 by using high air pressure generated in the combustion and explosion process of the methane and the combustion improver, promoting the coal seam 6 around the complex drilling network to form large-scale cracks 10, and further communicating crack zones formed around the complex drilling network due to stress release;
step six: constructing a multi-scale methane extraction system;
and repeating the fourth step and the fifth step for multiple times, continuously carrying out combustion improver feeding and combustion explosion fracturing operation in the coal seam 6, promoting the continuous expansion and extension of cracks around the complex drilling network, further increasing the complexity and the extension distance of the cracks, and finally forming a natural crack-large-scale crack 10-coal seam complex drilling network-vertical communication hole 7-roof horizontal well 5 multi-scale methane extraction system in the coal seam 6.
In order to more comprehensively monitor the extraction process, in the fifth step, the methane concentration is monitored, and meanwhile, the methane components are synchronously monitored.
Preferably, in step one, the thickness of the coal seam 6 in the coal seam area is not less than 2m.
In order to obtain better anti-reflection effect, in S11 in the step one, the heights of the drilling positions of different layers from the bottom of the roadway are ensured to be different.
According to the method, firstly, a plurality of layers of horizontal drill holes are drilled in a coal seam area, the upper layer of adjacent horizontal drill holes and the lower layer of adjacent horizontal drill holes are communicated with each other through the vertical drill holes, the adjacent horizontal drill holes in the same layer are communicated with each other through the lateral drill holes, so that a complex drill hole network can be formed in the coal seam, and a coal seam internal communication channel is provided for later-stage coal seam fracturing and permeability increasing; secondly, drilling a top plate horizontal well in the area where the top plate is located, and forming a stable borehole by utilizing the characteristic of stable structure of the rock stratum where the top plate is located, so that the stability of the main body section of the fluid injection channel can be ensured, and a powerful guarantee is provided for the fact that a subsequent liquid combustion improver can be fully injected into each part in the coal seam; then, the vertical communication holes are used for connecting the horizontal hole of the top plate and the horizontal hole of the uppermost layer, so that a complex well pattern channel with a complex drilling network, the vertical drilling hole, the vertical communication hole and the horizontal hole of the top plate which are mutually communicated is finally formed, the complex well pattern channel can enable all directions of a coal bed to be mutually communicated, the uniformity of the distribution of fracturing cracks is greatly enhanced, the fracturing range is effectively enlarged, and the fracturing effect is better; then, after the horizontal drilling hole is plugged, the liquid combustion improver is put into the complex well pattern channel through the top plate horizontal well, so that the hydraulic combustion improver can be ensured to fully enter each part of the complex well pattern channel, the consumption of the liquid combustion improver is favorably saved, and moreover, the hydraulic combustion improver entering the fracture can drive part of methane in the fracture to the main channel, so that the gas extraction efficiency can be favorably improved; finally, igniting and detonating the methane-combustion improver mixture in the complex drilling network of the coal seam after the liquid combustion improver is put in, and fully utilizing the methane in the coal seam to carry out in-situ ignition and explosion, so that a large-scale crack can be formed by high-pressure impact of explosion and further a fractured zone is formed.
Claims (4)
1. A permeability increasing method for a low permeability coal seam is characterized by comprising the following steps;
the method comprises the following steps: constructing a complex drilling network of a coal seam;
s11, determining the positions of multilayer drilling holes on the side surface in a return airway or a transportation airway in a mode parallel to a stope face aiming at the coal gas enrichment and high gas pressure coal seam area;
s12, sequentially drilling horizontal drill holes (1) from the bottom of the roadway to the upper part of the roadway, vertically moving the positions of the drill holes after the next layer of horizontal drill holes (1) is finished, and then performing drilling operation on the upper layer of horizontal drill holes (1);
s13, drilling a plurality of groups of vertical drill holes (2) and lateral drill holes (3) in the formed horizontal drill holes (1) along the length direction of the horizontal drill holes (1) in a hydraulic jet sidetracking mode along the vertical direction and the horizontal direction perpendicular to the horizontal drill holes (1), communicating the upper layer of horizontal drill holes (1) and the lower layer of horizontal drill holes (2) with each other, and communicating the same layer of horizontal drill holes (1) with each other by using the lateral drill holes (3); in the process, stress released in the drilling operation process is applied to the coal seam (6) around the drill hole, so that the coal seam (6) deforms and breaks to form a drill hole fracture zone, and a complex drill hole network consisting of a horizontal drill hole (1), a vertical drill hole (2) and a lateral drill hole (3) is formed in the coal seam (6);
step two: drilling a roof horizontal well on the ground;
drilling a roof horizontal well (5) at the lower part of the roof (4) by adopting a ground drilling mode, and enabling the horizontal section of the roof horizontal well (5) to be parallel to the coal seam (6);
step three: communicating the roof horizontal well with the complex drilling network of the coal seam;
after the roof horizontal well (5) is drilled, drilling corresponding vertical communication holes (7) upwards in each horizontal drilling hole (1) on the uppermost layer in a hydraulic jet sidetracking mode, enabling the vertical communication holes (7) to communicate the horizontal drilling holes (1) on the uppermost layer with the horizontal section of the roof horizontal well (5), and forming a complex drilling network-vertical communication holes (7) -complex well network channels communicated with the roof horizontal well (5) in the coal seam (6) and the roof (4);
step four: putting a liquid combustion improver;
plugging a horizontal drilling hole (1) in a coal seam (6) in an underground transportation roadway or a return airway, then putting a liquid combustion improver (8) into the coal seam (6) from the ground through a roof horizontal well (5), enabling the liquid combustion improver (8) to enter the coal seam (6) through the roof horizontal well (5) and a vertical communication hole (7), and enabling the liquid combustion improver (8) to flow into each area of the coal seam (6) through the horizontal drilling hole (1) in the coal seam (6), a vertical drilling hole (2) and a lateral drilling hole (3), and meanwhile enabling part of the liquid combustion improver (8) to enter the coal seam (6) through cracks around the drilling hole;
step five: blasting and cracking;
pre-extracting methane in a coal seam (6) through a roof horizontal well (5), monitoring the methane concentration in real time, closing a ground wellhead (9) of the roof horizontal well (5) after the extracted methane concentration exceeds 80%, then performing electric shock ignition on a methane-combustion improver mixture in a coal seam complex drilling network, igniting and detonating the methane-combustion improver mixture in the coal seam complex drilling network, impacting the coal seam (6) by utilizing high air pressure generated in the combustion and explosion process of the methane and the combustion improver, promoting the coal seam (6) around the complex drilling network to form large-scale cracks (10), and further communicating crack zones formed around the complex drilling network due to stress release;
step six: constructing a multi-scale methane extraction system;
and repeating the fourth step and the fifth step for multiple times, continuously carrying out combustion improver feeding and combustion explosion fracturing operation in the coal seam (6), promoting the continuous expansion and extension of cracks around the complex drilling network, further increasing the complexity and the extension distance of the cracks, and finally forming a multi-scale methane extraction system comprising natural cracks, large-scale cracks (10), the complex drilling network of the coal seam, vertical communication holes (7) and a roof horizontal well (5) in the coal seam (6).
2. The permeability reducing method for a low permeability coal seam according to claim 1, wherein in the fifth step, the methane concentration is monitored and simultaneously the methane component is monitored.
3. A method of enhancing permeability of a low permeability coal seam as claimed in claim 1 or claim 2 wherein in step one the thickness of the coal seam (6) in the region of the coal seam is not less than 2m.
4. The permeability reducing method for the low permeability coal seam according to claim 3, wherein in step one, in S11, the heights of drilling positions of different layers from the bottom of the roadway are ensured to be different.
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| CN110173238A (en) * | 2019-05-27 | 2019-08-27 | 中国矿业大学(北京) | The anti-reflection extraction of high seam three-dimensional roadway layout networking explosion thick gas method entirely |
| CN112761588A (en) * | 2021-01-22 | 2021-05-07 | 中国矿业大学 | Shale reservoir methane in-situ combustion-explosion fracturing and combustion improver safe feeding cooperative control method |
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