CN115478830B - Low permeability coal seam permeability increasing method - Google Patents

Abstract

The invention provides a low permeability coal seam permeability increasing method, which comprises the steps of sequentially drilling horizontal drilling holes from the bottom of a roadway to the upper part of the roadway, and drilling a plurality of groups of vertical drilling holes and lateral drilling holes in the formed horizontal drilling holes along the vertical direction upwards and the horizontal direction vertical to the horizontal drilling holes; drilling a top plate horizontal well in the lower part of the top plate; corresponding vertical communication holes are drilled 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 on the top plate; plugging a horizontal drilling hole in a coal seam, and then adding a liquid combustion improver; pre-extracting methane in the coal bed, closing a ground wellhead after the concentration of extracted methane exceeds 80%, and igniting and detonating a methane-combustion improver mixture in a complex drilling network of the coal bed; and the combustion improver is continuously thrown and the explosion and cracking operation is continuously carried out in the coal seam, so that the continuous expansion and extension of cracks around the complex drilling network are promoted. The method is simple to operate, low in implementation cost and remarkable in permeability improvement effect on the coal seam.

Description

A method for increasing permeability of low-permeability coal seam

technical field

The invention belongs to the technical field of coal safety mining and gas development, and in particular relates to a method for increasing permeability of low-permeability coal seams.

Background technique

my country is a big country of coal production and consumption, and more than 50% of coal seams are high-gas coal seams, which are seriously affected by coal and gas outburst accidents. With the increase of mining depth, the risk of coal and gas outburst is increasing. Coal gas is a gas mixture dominated by methane, which not only causes hidden dangers in coal mine safety production, but also is an important clean energy, which belongs to typical unconventional natural gas. Therefore, effective gas extraction is not only the key to preventing coal and gas outbursts Measures are also an important technical link to realize the resource utilization of methane gas. my country's coal seam has the characteristics of high gas pressure, strong gas adsorption and low coal seam permeability. Therefore, it is necessary to adopt fracturing and permeability enhancement measures for coal seam to increase the gas permeability of coal seam, so as to realize effective gas extraction. At present, coal seam enhancement is mainly based on drilling pressure relief method, which uses the damage zone formed by stress release around the drilling hole to increase the permeability of coal seam, but this method has many problems such as limited range of permeability enhancement and small radius of effective gas extraction. , especially in soft coal seams with high shale content, the effect of fracturing and enhancing permeability is very limited. Therefore, it is necessary to upgrade the existing process methods, reform and innovate the existing technical system, and form an anti-permeability method suitable for low-permeability coal seams, so as to realize efficient extraction of coal gas and eliminate coal and gas in the production process of coal mines. Highlight accidents.

Contents of the invention

Aiming at the problems existing in the above-mentioned prior art, the present invention provides a method for increasing the permeability of low-permeability coal seams. The method is simple in operation, low in implementation cost, and has a remarkable anti-permeability effect on coal seams. At the same time, it can improve the efficiency of gas drainage. The method can effectively solve the problems of small coal seam fracturing range, limited anti-permeability effect and prone to gas disaster accidents existing in the existing coal seam anti-permeability technology, and can provide reliable technical support for the realization of coal gas resource utilization.

In order to achieve the above object, the present invention provides a method for increasing the permeability of low-permeability coal seams, which specifically includes the following steps;

Step 1: Construct a complex drilling network in the coal seam;

S11, aiming at the coal seam area with coal gas enrichment and high gas pressure, determine the multi-layer drilling position on the side of the air return roadway or the transportation roadway in parallel with the recovery working face;

S12, drilling horizontal drilling holes sequentially from the bottom of the roadway to the upper part of the roadway, after completing a group of horizontal drilling holes in the next layer, moving the drilling position vertically, and then performing the drilling operation of the horizontal drilling holes in the previous layer ;

S13, in the horizontal borehole that has been formed, along the length direction of the horizontal borehole, use the hydraulic jet sidetracking method to drill multiple sets of vertical boreholes and lateral drills in the vertical upward direction and in the horizontal direction perpendicular to the horizontal borehole Holes, using vertical drilling to connect the adjacent horizontal drillings on the upper and lower layers with each other, using lateral drilling to connect adjacent horizontal drillings on the same layer; in this process, using the Stress acts on the coal seam around the borehole, causing the coal seam to deform and rupture to form a borehole fissure zone, and a complex borehole network consisting of horizontal boreholes, vertical boreholes, and lateral boreholes is formed in the coal seam;

Step 2: Drill the horizontal well on the roof;

Using the ground drilling method, drill a roof horizontal well at the lower part of the roof, and make the horizontal section of the roof horizontal well parallel to the coal seam;

Step 3: Connect the horizontal well on the roof and the complex drilling network in the coal seam;

After the roof horizontal well is drilled, the hydraulic jet sidetracking method is used to drill the corresponding vertical communication holes in the uppermost horizontal boreholes, so that the vertical communication holes connect the uppermost horizontal boreholes with the roof horizontal wells. Horizontal section, and form a complicated well network channel in the coal seam and the roof in which the complex drilling network-vertical connecting holes-roof horizontal wells are interconnected;

Step 4: put in liquid combustion accelerant;

Block the horizontal boreholes in the coal seam in the underground transportation lane or return air lane, and then put liquid combustion-supporting agent into the coal seam from the ground through the roof horizontal well, so that the liquid combustion-supporting agent enters the coal seam through the roof horizontal well and vertical communication holes In the coal seam, it flows into various areas of the coal seam through horizontal drilling, vertical drilling and lateral drilling, and at the same time, part of the liquid combustion aid enters the interior of the coal seam through the cracks around the drilling holes;

Step five: detonation and cracking;

The methane in the coal seam is pre-drained through the roof horizontal well, and the methane concentration is monitored in real time. After the methane concentration exceeds 80%, the surface wellhead of the roof horizontal well is closed, and then the methane-combustion agent in the complex drilling network of the coal seam The mixture is ignited by electric shock, ignites and detonates the methane-combustion agent mixture in the complex drilling network of the coal seam, and uses the high pressure generated during the combustion and explosion of methane and combustion accelerant to impact the coal seam, prompting the formation of large-scale cracks in the coal seam around the complex drilling network, and Further communication of fractured zones surrounding complex borehole networks due to stress relief;

Step 6: Build a multi-scale methane extraction system;

Steps 4 and 5 are repeated several times, and continuous injection of combustion aids and explosion fracturing operations in the coal seam promotes the continuous expansion and extension of cracks around the complex drilling network, further increases the complexity and extension distance of cracks, and finally forms in the coal seam Natural fractures-large-scale fractures-coal seam complex drilling network-vertical connecting holes-roof horizontal well multi-scale methane drainage system.

Further, in order to monitor the drainage process more comprehensively, in step five, while monitoring the methane concentration, the components of methane are also monitored synchronously.

As a preference, in step 1, the thickness of the coal seam in the coal seam region is not less than 2m.

Further, in order to obtain a better anti-reflection effect, in S11 in step 1, ensure that the drilling positions of different layers are at different heights from the bottom of the roadway.

In the present invention, firstly, multiple layers of horizontal boreholes are drilled in the coal seam area, and the vertical boreholes are used to connect the adjacent horizontal boreholes of the upper and lower layers to each other, and the lateral boreholes are used to connect the adjacent horizontal boreholes of the same layer. If the holes are connected to each other, a complex drilling network can be formed in the coal seam, which provides a coal seam internal communication channel for later coal seam fracturing and permeability enhancement; secondly, the roof horizontal well can be drilled in the area where the roof is located, and the rock formation where the roof is located can be used The stable structure forms a stable wellbore, which in turn can ensure the stability of the main section of the fluid injection channel, and provides a strong guarantee for the subsequent liquid combustion aid to be fully injected into various parts of the coal seam; then, use vertical communication holes to connect The horizontal wells on the roof and the horizontal drilling holes in the uppermost layer finally form a complex well network channel in which the complex drilling network-vertical drilling-vertical connecting holes-horizontal wells on the roof are connected to each other. The azimuths are connected to each other, which greatly enhances the uniformity of fracture distribution, effectively increases the range of fracture, and makes the fracture effect better. In addition, this kind of well pattern channel can make the coal seam communicate with various channels and fluids. The main section of the injection channel is fully connected, which effectively ensures that the subsequent liquid combustion accelerant can be more fully injected into each area inside the coal seam, and is conducive to further entering the cracks inside the coal seam in each area; then, the horizontal drilling is blocked Afterwards, the injection of liquid combustion accelerant into the complex well pattern channel through the horizontal well on the roof can ensure that the hydraulic combustion accelerant can fully enter all parts of the complex well pattern channel, which is conducive to saving the amount of liquid combustion accelerant. The hydraulic combustion accelerant in the coal seam can also drive part of the methane in the cracks into the main channel, which can help improve the gas extraction efficiency; finally, after the liquid combustion accelerant is put in, the methane in the complex drilling network of the coal seam will be ignited- Combustion additive mixture can make full use of the methane in the coal seam for in-situ ignition and detonation, so that large-scale cracks can be formed by the high-pressure impact of detonation and then a fracture zone. This method has a significant effect on improving the permeability of the coal seam. It only needs to put the combustion accelerant into the coal seam and ignite it. The operation process is simple and more economical.

Description of drawings

Fig. 1 is the construction schematic diagram of complex borehole network of coal seam among the present invention;

Fig. 2 is the structural representation of drilling the roof horizontal well on the ground in the present invention;

Fig. 3 is the structural representation of the complex drilling network connecting the roof horizontal well and the coal seam among the present invention;

Fig. 4 is the drop-in schematic diagram of liquid combustion accelerant among the present invention;

Fig. 5 is a schematic diagram of the detonation and cracking operation in the present invention.

In the figure: 1. Horizontal drilling, 2. Vertical drilling, 3. Lateral drilling, 4. Roof, 5. Horizontal well on the roof, 6. Coal seam, 7. Vertical communication hole, 8. Liquid combustion aid, 9. Surface wellhead, 10. Large-scale fractures.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

The present invention provides a method for increasing the permeability of low-permeability coal seams. Firstly, a complex borehole network is drilled in the coal seam 6, then a roof horizontal well 5 is drilled in the roof 4 from the ground, and finally a horizontal well 1 is drilled upwards in the horizontal borehole 1. The vertical communication hole 7 connected with the roof horizontal well 5; the liquid combustion aid 8 is put into the roof horizontal well 5 on the ground, and the liquid combustion aid 8 enters the complex drilling network of the coal seam through the roof horizontal well 5, and is connected with the coal seam complex The methane mixes within the borehole network to form an explosive multiphase fluid. By igniting the combustible and explosive multi-phase fluid in the complex drilling network, the explosion occurs inside the complex drilling network, impacts the coal seam around the complex drilling network, forms cracks, and produces a large-scale stress release area in the coal seam 6, and in the coal seam 6 Form a complex drilling network-artificial fractures-natural fractures interconnected high-conductivity channels, so as to realize the multi-dimensional and multi-level permeability enhancement reconstruction of low-permeability coal seams, and achieve the purpose of low-permeability coal seam enhancement, specifically including the following steps;

Step 1: Construct the coal seam complex drilling network, as shown in Figure 1 to Figure 4;

S11, aiming at the coal seam area with coal gas enrichment and high gas pressure, determine the multi-layer drilling position on the side of the air return roadway or the transportation roadway in parallel with the recovery working face;

S12, drilling horizontal boreholes 1 sequentially from the bottom of the roadway to the upper part of the roadway, after completing a group of horizontal boreholes 1 in the next layer, moving the drilling position vertically, and then proceeding to the previous layer of horizontal boreholes 1 Drill job;

S13, in the horizontal borehole 1 that has been formed, along the length direction of the horizontal borehole 1, a plurality of sets of vertical boreholes 2 are drilled vertically upward and in a horizontal direction perpendicular to the horizontal borehole 1 by means of hydraulic jet sidetracking And lateral boreholes 3, utilize vertical boreholes 2 to connect the horizontal boreholes 1 adjacent to the upper and lower layers, utilize lateral boreholes 3 to communicate with each other adjacent horizontal boreholes 1 of the same layer; in this process, Since the drilling operation will cause the release of coal seam stress, in this way, the released stress can be used to act on the coal seam 6 around the drill hole, so that the coal seam 6 is deformed and ruptured to form a borehole fracture zone, and the coal seam 6 is formed by horizontal drilling. Complex drilling network composed of hole 1-vertical drilling 2-lateral drilling 3;

Step 2: Drill the horizontal well on the roof;

As shown in Figure 2, the roof horizontal well 5 is drilled at the lower part of the roof 4 by using the ground drilling method, and the horizontal section of the roof horizontal well 5 is parallel to the coal seam 6; due to the high strength of the roof 4 and the stable rock structure, the roof water When the flat well 5 passes through the top plate 4, it is easy to form a stable wellbore;

Step 3: Connect the horizontal well on the roof and the complex drilling network in the coal seam;

As shown in Figure 3, after the horizontal well 5 on the roof is drilled, the corresponding vertical communication holes 7 are drilled upwards in the horizontal drilling holes 1 on the uppermost layer by means of hydraulic jet sidetracking, so that the vertical communication holes 7 are connected to the uppermost level. The horizontal section of the horizontal borehole 1 in the upper layer and the roof horizontal well 5 forms a complex well pattern channel in which a complex drilling network-vertical communication holes 7-roof horizontal well 5 are connected to each other in the coal seam 6 and the roof 4; In this way, the coal seam 6 communicates with the ground through the vertical communication hole 7 and the horizontal well 5 in the roof, thereby providing a channel for later coal seam fracturing enhancement and gas drainage;

Step 4: put in liquid combustion accelerant;

As shown in Figure 4, the horizontal borehole 1 in the coal seam 6 is blocked in the underground transportation lane or the return air lane, and then the liquid combustion accelerant 8 is injected into the coal seam 6 from the ground through the roof horizontal well 5 to make the liquid combustion accelerant 8 Enter the coal seam 6 through the roof horizontal well 5 and the vertical communication hole 7, and flow into each area of the coal seam 6 through the horizontal borehole 1, the vertical borehole 2 and the lateral borehole 3 inside the coal seam 6, and at the same time, make part of the liquid combustion The agent 8 enters the interior of the coal seam 6 through the cracks around the borehole;

Step five: detonation and cracking;

As shown in Figure 5, the methane in the coal seam 6 is pre-drained through the roof horizontal well 5, and the methane concentration is monitored in real time. After the methane concentration exceeds 80%, the surface wellhead 9 of the roof horizontal well 5 is closed, and then the The methane-combustible mixture in the complex drilling network of the coal seam is ignited by electric shock, and the methane-combustible mixture in the complex drilling network of the coal seam is ignited, and the high pressure generated during the combustion and explosion of methane and the combustion Large-scale fractures 10 are formed in the coal seam 6 around the borehole network, and further communicate the fracture zone formed by stress release around the complex borehole network;

Step 6: Build a multi-scale methane extraction system;

Steps 4 and 5 were repeated several times, and the combustion accelerant and explosion fracturing operations were continuously carried out in coal seam 6 to promote the continuous expansion and extension of cracks around the complex drilling network, further increasing the complexity and extension distance of cracks, and finally in coal seam 6. A multi-scale methane drainage system is formed in the natural fractures-large-scale fractures 10-coal seam complex drilling network-vertical communication holes 7-roof horizontal wells 5.

In order to monitor the extraction process more comprehensively, in step five, while monitoring the methane concentration, the methane components are also monitored simultaneously.

As a preference, in step one, the thickness of the coal seam 6 in the coal seam area is not less than 2m.

In order to obtain a better anti-reflection effect, in S11 in step 1, ensure that the drilling positions of different layers are at different heights from the bottom of the roadway.

In the present invention, firstly, multiple layers of horizontal boreholes are drilled in the coal seam area, and the vertical boreholes are used to connect the adjacent horizontal boreholes of the upper and lower layers to each other, and the lateral boreholes are used to connect the adjacent horizontal boreholes of the same layer. If the holes are connected to each other, a complex drilling network can be formed in the coal seam, which provides a coal seam internal communication channel for later coal seam fracturing and permeability enhancement; secondly, the roof horizontal well can be drilled in the area where the roof is located, and the rock formation where the roof is located can be used The stable structure forms a stable wellbore, which in turn can ensure the stability of the main section of the fluid injection channel, and provides a strong guarantee for the subsequent liquid combustion aid to be fully injected into various parts of the coal seam; then, use vertical communication holes to connect The horizontal wells on the roof and the horizontal drilling holes in the uppermost layer finally form a complex well network channel in which the complex drilling network-vertical drilling-vertical connecting holes-horizontal wells on the roof are connected to each other. The azimuths are connected to each other, which greatly enhances the uniformity of fracture distribution, effectively increases the range of fracture, and makes the fracture effect better. In addition, this kind of well pattern channel can make the coal seam communicate with various channels and fluids. The main section of the injection channel is fully connected, which effectively ensures that the subsequent liquid combustion accelerant can be more fully injected into each area inside the coal seam, and is conducive to further entering the cracks inside the coal seam in each area; then, the horizontal drilling is blocked Afterwards, the injection of liquid combustion accelerant into the complex well pattern channel through the horizontal well on the roof can ensure that the hydraulic combustion accelerant can fully enter all parts of the complex well pattern channel, which is conducive to saving the amount of liquid combustion accelerant. The hydraulic combustion accelerant in the coal seam can also drive part of the methane in the cracks into the main channel, which can help improve the gas extraction efficiency; finally, after the liquid combustion accelerant is put in, the methane in the complex drilling network of the coal seam will be ignited- Combustion additive mixture can make full use of the methane in the coal seam for in-situ ignition and detonation, so that large-scale cracks can be formed by the high-pressure impact of detonation and then a fracture zone. This method has a significant effect on improving the permeability of the coal seam. It only needs to put the combustion accelerant into the coal seam and ignite it. The operation process is simple and more economical.

Claims (3)

1. The permeability-increasing method for the low permeability coal seam is characterized by comprising the following steps of;

step one: constructing a complex drilling network of the coal seam;

s11, aiming at a coal bed region with high gas concentration and high gas pressure of a coal bed, determining multi-layer drilling positions on the side surface in a return air roadway or a transport roadway in a mode parallel to a stope face;

s12, sequentially drilling horizontal drilling holes (1) from the bottom of a roadway to the upper part of the roadway, vertically upwards moving the drilling positions after completing a group of horizontal drilling holes (1) on the next layer, and then performing drilling operation on the horizontal drilling holes (1) on the upper layer;

s13, in the formed horizontal drilling holes (1), drilling a plurality of groups of vertical drilling holes (2) and lateral drilling holes (3) along the length direction of the horizontal drilling holes (1) in a hydraulic jet sidetrack mode along the vertical direction and the horizontal direction perpendicular to the horizontal drilling holes (1), communicating the upper layer of adjacent horizontal drilling holes (1) and the lower layer of adjacent horizontal drilling holes (1) with each other by using the vertical drilling holes (2), and communicating the same layer of adjacent horizontal drilling holes (1) with each other by using the lateral drilling holes (3); in the process, stress released in the drilling operation process is used for acting on the coal bed (6) around the drill hole, so that the coal bed (6) is deformed and broken to form a drill hole fracture zone, and a complex drilling network consisting of horizontal drill holes (1) -vertical drill holes (2) -lateral drill holes (3) is formed in the coal bed (6);

step two: drilling a top plate horizontal well on the ground;

drilling a roof horizontal well (5) at the lower part of the roof (4) in 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: a roof horizontal well and a complex drilling network of the coal seam are communicated;

after the roof horizontal well (5) is drilled, a hydraulic jet sidetrack drilling mode is adopted to drill corresponding vertical communication holes (7) upwards in each horizontal drilling hole (1) at the uppermost layer, so that the vertical communication holes (7) are communicated with horizontal sections of the horizontal drilling holes (1) at the uppermost layer and the roof horizontal well (5), and complex drilling network-vertical communication holes (7) -complex well pattern channels in which the roof horizontal well (5) are mutually communicated are formed in the coal seam (6) and the roof (4);

step four: adding a liquid combustion improver;

plugging horizontal drilling holes (1) in a coal bed (6) in a downhole transportation roadway or a return air roadway, then throwing a liquid combustion improver (8) into the coal bed (6) from the ground through a roof horizontal well (5), enabling the liquid combustion improver (8) to enter the coal bed (6) through the roof horizontal well (5) and a vertical communication hole (7), enabling the liquid combustion improver to flow into each area of the coal bed (6) through the horizontal drilling holes (1), the vertical drilling holes (2) and the lateral drilling holes (3) in the coal bed (6), and enabling part of the liquid combustion improver (8) to enter the coal bed (6) through cracks around the drilling holes;

step five: cracking by burning and explosion;

pre-extracting methane in a coal bed (6) through a roof horizontal well (5), monitoring the concentration of methane in real time, closing a ground wellhead (9) of the roof horizontal well (5) after the concentration of extracted methane exceeds 80%, then performing electric shock ignition on a methane-combustion improver mixture in a complex drilling network of the coal bed, igniting and detonating the methane-combustion improver mixture in the complex drilling network of the coal bed, and utilizing high air pressure generated in the combustion explosion process of the methane and the combustion improver to impact the coal bed (6), so as to promote the coal bed (6) around the complex drilling network to form large-scale cracks (10), and further communicating crack zones around the complex drilling network due to stress release;

monitoring the methane concentration and simultaneously monitoring the components of methane;

step six: constructing a multi-scale methane extraction system;

repeating the steps four and five for a plurality of times, continuously carrying out combustion improver throwing and blasting fracturing operation in the coal seam (6), promoting 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 holes (7) -roof horizontal well (5) multi-scale methane extraction system in the coal seam (6).

2. A low permeability coal seam anti-reflection method according to claim 1, wherein in step one the thickness of the coal seam (6) in the coal seam area is not less than 2m.

3. A low permeability coal seam anti-reflection method according to claim 1 or claim 2 wherein in step S11 it is ensured that the heights of different layer drill positions from the bottom of the tunnel are different.

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