A method for regional coal seam gas extraction in monoclinic structures

Abstract

The present invention relates to the technical field of coal seam gas drainage, and specifically relates to a method for regional coal seam gas drainage in a monoclinic structure, which includes: designing the working face of the coal seam by adopting the longwall mining method along the strike in view of the monoclinic structure background; constructing inclined drainage directional boreholes at the working face in the high part of the mine structure; designing and constructing large-diameter drainage directional boreholes at the low part of the mine structure according to the borehole construction data, and installing a gate valve at the orifice of the boreholes to control the drainage intensity. After the construction of the large-diameter drainage directional boreholes is completed, hydraulic fracturing is carried out, and the fractures formed by the hydraulic fracturing communicate with the drainage directional boreholes, effectively discharging the accumulated water in the drainage directional boreholes; after the accumulated water is discharged, the orifice gate valve is closed, and drainage is regularly carried out during the gas drainage process. The present invention can achieve regional drainage of coal seam gas in a monoclinic structure background, and can carry out gas drainage across several sections or even the scope of one level at a time, solving the technical problem that it is difficult to achieve regional drainage in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of coal seam gas drainage, and particularly relates to a method for regional coal seam gas drainage in a monoclinic structure. Background Art

[0002] Coal is an important energy mineral in China, accounting for more than 50% of China's energy market. A large amount of gas generated during coal mining poses a serious threat to the safe production of coal mines. Especially for coal and gas outburst mines, the types of gas disasters mainly include gas explosion, gas combustion and asphyxiation, and coal and gas outburst. The occurrence of any gas disaster directly threatens the lives of coal miners, and at the same time also hinders the normal production of coal mines and the sustainable, healthy and stable development of the coal industry. Therefore, strengthening the prevention and control of coal mine gas disasters is an important prerequisite and necessary way to ensure the safety of coal resources. Pre-drainage of coal seam gas is the fundamental strategy for preventing and controlling mine gas disasters, and it is necessary to strive to achieve the standard of coal seam gas drainage. At present, the main methods of gas drainage are surface well gas drainage and underground borehole gas drainage. Among them, underground borehole gas drainage mainly uses bedding or cross-cut boreholes for each coal mining face to gradually realize pre-drainage of gas in the coal roadway strip, pre-drainage of gas in the working face mining area, and pre-drainage of gas in the working face section; surface well drainage mainly uses "vertical + horizontal" boreholes constructed on the ground to drain coal seam gas underground.

[0003] At present, the construction of surface wells is difficult, costly, and time-consuming, making it difficult to achieve large-scale construction and use for large-scale gas drainage. The problems with underground borehole gas drainage are as follows: 1) For the pre-drainage of gas in the coal roadway strip, the gas pre-drainage in the working face extraction area, and the gas pre-drainage in the working face section of a single coal mining face, the borehole construction period is relatively short, making it difficult to achieve large-scale gas drainage in the coal seam. It can only drain a section, drive a section, drain a face, and extract a face, resulting in serious impacts on the mine production and the balance of the three reserves in the mine gas control; 2) Under the background of a monoclinic structure, the gas content in the coal seam gradually increases from the shallow part to the deep part of the coal, indicating that the time required for the gas drainage in the working face to meet the standard also gradually increases from the shallow part to the deep part. For example, if the time required for the first working face to meet the gas drainage standard is T0, then the time required for the next working face to meet the gas drainage standard is T0 + t1, and the time required for the next working face to meet the gas drainage standard is T0 + t1 + t2, and so on. Therefore, when draining and meeting the standard for each working face from the shallow part to the deep part, it is necessary to repeatedly consume the basic drainage time T0, resulting in a large waste of drainage time. At the same time, it is necessary to continuously carry out pre-drainage preparation work such as constructing drill sites, transporting drilling rigs, and drill pipes between various underground roadways, which will seriously waste effective construction time; 3) Mainly using ordinary short boreholes and directional boreholes (usually long boreholes), limited by the actual drill site setting conditions, roadway layout conditions, drilling rig performance, and construction process characteristics on site, it is difficult to achieve the pre-drainage of gas in the entire mining face and the entire coal roadway strip in one construction. For the entire mining face and the entire coal roadway strip, it is more often constructed in partitions and sections. Therefore, due to the overlap of boreholes between partitions and sections, there is a waste of borehole quantity. At the same time, it is very easy to cause gas drainage blank zones between partitions and sections due to the improper overlap of boreholes. On the one hand, this will have a great impact on the division of the later gas drainage evaluation unit. On the other hand, additional supplementary boreholes need to be constructed in the gas drainage blank zones, resulting in an increase in construction time and cost. In summary, the existing technology has the technical problem of being difficult to achieve regional drainage. Summary of the Invention

[0004] The present invention provides a method for regional coal seam gas drainage in a monoclinic structure, which solves the technical problem that it is difficult to achieve regional drainage in the existing technology.

[0005] The basic solution provided by the present invention is as follows: A method for regional coal seam gas drainage in a monoclinic structure, comprising:

[0006] S1. For the background of a monoclinic structure, design the working face of the coal seam using the longwall mining method along the strike;

[0007] S2. Conduct inclined drainage directional borehole construction in the working face at the high position of the mine structure;

[0008] S3. Design and construct large-diameter drainage directional boreholes at the low position of the mine structure according to the drilling construction data, and install gate valves at their orifices to control the drainage intensity. After the construction of the large-diameter drainage directional boreholes is completed, hydraulic fracturing is carried out. The fractures formed by hydraulic fracturing communicate with the extraction directional boreholes, effectively discharging the accumulated water in the extraction directional boreholes.

[0009] S4. After the accumulated water is discharged, close the orifice gate valve and regularly drain water during the gas extraction process.

[0010] The working principle and advantages of the present invention are as follows: First, for the coal seam gas in the background of monoclinic structure, regional extraction can be achieved. The so-called regional extraction means that the one-time extraction range of gas is not limited to one working face or one section, but can span several sections or even one level at a time for gas extraction; Second, it can effectively avoid the water lock effect and hydraulic plugging effect on coal seam gas extraction caused by the accumulated water in the borehole during and after the construction of the downward directional borehole, preventing the influence on the gas extraction effect; Third, during the extraction process of the borehole, the depressurized gas in the coal seam migrates along the borehole to the high position of the structure under the action of fluid potential and extraction negative pressure, while the water in the coal seam migrates along the borehole to the low position of the structure under the action of gravity, and gas-water separation can be automatically achieved in the borehole, effectively avoiding pumping water into the mine gas extraction pipeline and improving the extraction efficiency.

[0011] The present invention can achieve regional extraction of coal seam gas in the background of monoclinic structure, and can carry out gas extraction over a range spanning several sections or even one level at a time, solving the technical problem that it is difficult to achieve regional extraction in the prior art.

[0012] Furthermore, in S2, the spacing of the construction of the dip extraction directional boreholes is determined according to the extraction radius of the directional boreholes and the designed extraction time.

[0013] The beneficial effect is that reasonably determining the spacing of the construction of the dip extraction directional boreholes can improve the extraction range and efficiency.

[0014] Furthermore, in S2, wet operation is adopted for the construction of the directional boreholes.

[0015] The beneficial effect is that there is a competitive adsorption effect between water and coal seam gas, which is beneficial to the desorption of a large amount of coal seam gas.

[0016] Furthermore, in S2, after the borehole construction is completed, connection for extraction is carried out and a gas extraction metering device is installed at the orifice.

[0017] The beneficial effect is that the extracted gas can be measured in real time during the extraction process.

[0018] Furthermore, in S2, the construction length of the dip extraction directional boreholes ≤ 1000 m.

[0019] The beneficial effects are as follows: Generally, the designed dip length of the mine working face is 150 - 200 m, and the construction length of the listed dip drainage directional borehole ≤ 1000 m, which can improve the drainage efficiency.

[0020] Furthermore, in S3, the aperture of the large - diameter drainage directional borehole is not less than 200 mm. The elevation of the lowest point of the large - diameter drainage directional borehole trajectory gradually increases from the hole mouth to the hole bottom, with a slope between 2° and 5°, and the construction length of the large - diameter drainage directional borehole ≤ 2000 m.

[0021] Furthermore, in S2, if regional coal seam gas drainage is carried out for the construction mine, before borehole construction on the ground, high - pressure grouting sealing is carried out on the fissures within the preset range near the borehole and within the preset depth near the ground, and at the same time, surface fissure water and atmospheric precipitation infiltration along the surface borehole fissures are intercepted.

[0022] The beneficial effects are as follows: Before borehole construction on the ground, high - pressure grouting sealing is carried out on the fissures within a certain range near the borehole and within a certain depth near the ground, which can ensure that the dip gas drainage borehole is air - tight; intercepting surface fissure water and atmospheric precipitation infiltration along the surface borehole fissures can prevent the generation of hydraulic plugging and water - locking effects during gas migration, and avoid affecting the gas drainage effect of the borehole.

[0023] Furthermore, in S2, a surface drainage well is constructed from the ground to the lowest point of the drainage area structure. At an appropriate position of the main well, a horizontal branch well is constructed towards the lowest point of the target coal seam structure and close to the dip drainage directional borehole. The elevation of the horizontal branch well does not exceed the elevation of the lowest point of the dip drainage directional borehole, and the trajectory of the horizontal branch well is straight.

[0024] The beneficial effects are as follows: Constructing a surface drainage well (borehole) from the ground to the lowest point of the drainage area structure, and constructing a horizontal branch well (borehole) from an appropriate position of the main well towards the lowest point of the target coal seam structure and close to the dip drainage directional borehole. At the same time, ensuring that the elevation of the horizontal branch well (borehole) does not exceed the elevation of the lowest point of the dip drainage directional borehole, and ensuring that the trajectory of the horizontal branch well (borehole) is straight can increase the drainage area and improve the drainage efficiency.

[0025] Furthermore, in S3, after the construction of the surface drainage well is completed, hydraulic fracturing is carried out on the target coal seam section. The fractures of the hydraulic fracturing connect the surface drainage well and the dip drainage directional borehole, effectively draining the borehole water accumulation during the construction and drainage processes of the dip drainage directional borehole and the coal seam water accumulation in the low - lying part of the structure.

[0026] The beneficial effects are as follows: After the construction of the surface drainage and extraction well is completed, hydraulic fracturing is carried out on the well section of the target coal seam to ensure that the fractures formed by the hydraulic fracturing effectively communicate the surface drainage and extraction well with the dip extraction directional borehole. Furthermore, the accumulated water in the borehole during the construction process and extraction process of the dip extraction directional borehole and the accumulated water in the coal seam at the structurally low position are effectively drained and extracted, ensuring the extraction effect of the dip extraction directional borehole. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 FIG. is a schematic layout diagram of the working face of the longwall mining method along the strike under the condition of a monoclinic structure, which is an embodiment of a method for regional coal seam gas extraction in a monoclinic structure according to the present invention.

[0028] Figure 2 FIG. is a plane layout diagram of regional gas extraction by dip extraction directional boreholes in Embodiment 1 of a method for regional coal seam gas extraction in a monoclinic structure according to the present invention.

[0029] Figure 3 FIG. is a schematic diagram of the orifice structure of the dip extraction directional borehole in Embodiment 1 of a method for regional coal seam gas extraction in a monoclinic structure according to the present invention.

[0030] Figure 4 FIG. is a schematic diagram of the orifice structure of the large-diameter drainage directional borehole in Embodiment 1 of a method for regional coal seam gas extraction in a monoclinic structure according to the present invention.

[0031] Figure 5 FIG. is a sectional view of the multi-coal seam layout of regional gas extraction by underground directional boreholes in Embodiment 1 of a method for regional coal seam gas extraction in a monoclinic structure according to the present invention.

[0032] Figure 6 FIG. is a schematic diagram of the distribution state of dip extraction directional boreholes during and after the driving process of the return airway and the conveyor roadway of Working Face A1 in Embodiment 1 of a method for regional coal seam gas extraction in a monoclinic structure according to the present invention.

[0033] Figure 7 FIG. is a schematic diagram of the distribution state of dip extraction directional boreholes during and after the driving process of the return airway and the conveyor roadway of Working Face A2 in Embodiment 1 of a method for regional coal seam gas extraction in a monoclinic structure according to the present invention.

[0034] Figure 8 FIG. is one of the schematic diagrams of Embodiment 2 of a method for regional coal seam gas extraction in a monoclinic structure according to the present invention.

[0035] Figure 9 FIG. is the second schematic diagram of Embodiment 2 of a method for regional coal seam gas extraction in a monoclinic structure according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] The following is a more detailed description through specific embodiments:

[0037] Example 1

[0038] The embodiment of a method for gas drainage from regional coal seams with a monoclinic structure of the present invention is basically as follows:

[0039] S1. In view of the monoclinic structure background, the longwall mining method along the strike is adopted to design the working face of the coal seam. The working face of the coal seam is designed by the longwall mining method along the strike, and the schematic layout diagram of the working face design is as Figure 1 (Schematic layout diagram of the working face of the longwall mining method along the strike under the condition of monoclinic structure) shown.

[0040] S2. Inclined extraction directional boreholes are constructed at the high position of the mine structure working face.

[0041] In this embodiment, the implementation process includes the following aspects:

[0042] Firstly, at the high position of the mine structure, the existing return airway, material roadway of the working face or a specially excavated roadway is used for the construction of inclined extraction directional boreholes in the coal seam, as shown in the appendix Figure 2 (Schematic plane layout diagram of regional gas drainage by inclined extraction directional boreholes). The aperture of the inclined extraction directional borehole is ≥96 mm. The inclined extraction directional borehole is a downward borehole. The coal seam firmness coefficient is ≥0.8, and the coal seam is a thin coal seam or medium-thick coal seam;

[0043] Secondly, generally, the designed inclined length of the mine working face is 150 - 200 m. The construction length of the inclined extraction directional boreholes listed in this embodiment is ≤1000 m. After the borehole construction is completed, it is timely sealed, and a tee is installed at the hole mouth, as shown in the appendix Figure 3 (Schematic diagram of the hole mouth structure of the inclined extraction directional borehole). Gate valves 1 and 2 are installed at the front and upper ports of the tee. Gate valve 1 is connected to the gas drainage pipeline of the mine. A gas drainage metering device is installed on the drainage pipeline, and the gas drained can be measured in real time during the drainage process;

[0044] Thirdly, the spacing of the inclined extraction directional borehole construction is determined according to the extraction radius of the directional borehole and the designed extraction time to reasonably determine the spacing of the inclined extraction directional borehole construction and improve the extraction range and efficiency. The directional borehole construction adopts wet operation. According to relevant research, there is a competitive adsorption effect between water and coal seam gas, which is beneficial to the desorption of a large amount of coal seam gas. The water pressure used in the inclined extraction directional borehole construction is calculated based on the target depth of the borehole and the slag discharge resistance, etc., to meet the requirements of borehole slag discharge and leave a safety factor of 1.5 times.

[0045] S3. According to the borehole construction data, large-aperture drainage directional boreholes are designed and constructed at the low position of the mine structure, and gate valves are installed at their hole mouths to control the drainage intensity. After the construction of the large-aperture drainage directional boreholes is completed, hydraulic fracturing is carried out. The fractures formed by the hydraulic fracturing communicate with the extraction directional boreholes to effectively drain the accumulated water in the extraction directional boreholes.

[0046] In this embodiment, the implementation process includes the following aspects:

[0047] First, after the construction of the inclined drainage directional boreholes is completed, large-diameter drainage directional boreholes are designed and constructed at the low position of the mine structure based on the construction data of each inclined drainage directional borehole (especially the position data of the end hole points), and a gate valve 3 is installed at its orifice to control the drainage and drainage intensity. As shown in the Figure 4 (Schematic diagram of the orifice structure of the large-diameter drainage directional borehole), the large diameter of the large-diameter drainage directional borehole means that the borehole diameter is not less than 200 mm. The elevation of the lowest point of the trajectory of the large-diameter drainage directional borehole gradually increases from the orifice to the bottom hole, and the slope is not less than 2 degrees and not more than 4 degrees. The trajectory of the large-diameter drainage directional borehole should be close to the inclined drainage directional borehole;

[0048] Second, after the construction of the large-diameter drainage directional borehole is completed, hydraulic fracturing is carried out on it. After the fracturing is completed, a collapse-proof screen pipe is lowered in time to ensure that the fractures formed by the hydraulic fracturing communicate with the inclined drainage directional borehole, and ensure that the accumulated water and sediment in the inclined drainage directional borehole are effectively discharged through the large-diameter drainage directional borehole. It is also necessary to decide whether to carry out secondary fracturing, tertiary fracturing, etc. according to the communication situation of the borehole fractures. Among them, during the drainage process, gate valve 1 needs to be closed, and gate valve 2 and gate valve 3 need to be opened;

[0049] Third, during the first drainage process, clean water is injected into the hole of the inclined drainage directional borehole through gate valve 2 to wash the inclined drainage directional borehole again to ensure that the extraction borehole is unobstructed. After the water and slag in the inclined drainage directional borehole are discharged, close gate valve 3 and gate valve 2 at the orifice, open gate valve 1 for gas extraction, and regularly carry out gate drainage according to the steps in "Second" during the extraction process of the inclined drainage directional borehole.

[0050] S4. After the accumulated water is discharged, close the orifice gate valve and regularly drain water during the gas extraction process.

[0051] It should be noted that for the above technical solution, it is possible to carry out regional extraction of single coal seam gas or regional extraction of multiple coal seam gases at the same time. The sectional view is as shown in the Figure 5 (Sectional view of the layout of multiple coal seams for regional gas extraction by underground directional boreholes), and the specific implementation process also includes the following steps:

[0052] S11. After the gas drainage in the A1 working face reaches the standard, the return airway and the transport roadway of the A1 working face can be driven. During the driving of the return airway, the down-dip directional drainage boreholes successively exposed on its lower side are re-sealed and connected for extraction, and the up-dip directional drainage boreholes successively exposed on its upper side are grouted and sealed (the sealing length is not less than 2 / 3 of the width of the isolation coal pillar between the working faces). During the driving of the transport roadway, the down-dip directional drainage boreholes successively exposed on its lower side are re-sealed and connected for extraction, and the up-dip directional drainage boreholes successively exposed on its upper side are grouted and sealed in sequence (the sealing length is not more than 0.5 m). As shown in Figure 6 Figure (Schematic diagram of the distribution state of the dip directional drainage boreholes during and after the driving of the return airway and the transport roadway of the A1 working face), so during the driving of the roadway and the coal mining in the A1 working face, the dip directional drainage boreholes left in the coal mining area of the A1 working face can continue to extract the coal seam gas in the coal mining area of the A1 working face, and the remaining boreholes can continue to extract the coal seam gas of the remaining working faces A2, A3... An;

[0053] S12. After the coal mining in the A1 working face is completed and the gas drainage in the A2 working face reaches the standard, the return airway and the transport roadway of the A2 working face can be driven. During the driving of the return airway, the down-dip directional drainage boreholes successively exposed on its lower side are re-sealed and connected for extraction, and the up-dip directional drainage boreholes successively exposed on its upper side are grouted and sealed (the sealing length is not less than 2 / 3 of the width of the isolation coal pillar between the working faces). During the driving of the transport roadway, the down-dip directional drainage boreholes successively exposed on its lower side are re-sealed and connected for extraction, and the up-dip directional drainage boreholes successively exposed on its upper side are grouted and sealed in sequence (the sealing length is not more than 0.5 m). As shown in Figure 7 Figure (Schematic diagram of the distribution state of the dip directional drainage boreholes during and after the driving of the return airway and the transport roadway of the A2 working face), so during the driving of the roadway and the coal mining in the A2 working face, the dip directional drainage boreholes left in the coal mining area of the A2 working face can continue to extract the coal seam gas in the coal mining area of the A2 working face, and the remaining boreholes can continue to extract the coal seam gas of the remaining working faces A3, A4... An;

[0054] S13. By analogy, the gas drainage of all working faces in the A wing is completed.

[0055] In this embodiment, there are the following advantages:

[0056] (1) Regional advance extraction can be achieved for monocline coal seam gas. The so-called regional extraction means that the gas extraction range is not limited to one mining tunnel, one mining working face, or one section, but is carried out across several sections or even a horizontal range at one time, which solves the problem of insufficient advance gas control in one tunnel or one face of the mine. At the same time, it also solves the problem of no place to construct the gas extraction drilling hole in the coal seam of the next working face due to the lack of preparation of the mining tunnel in the shallow working face of the mine;

[0057] (2) Large-aperture drainage directional drilling and fracturing can effectively prevent water and slag accumulation in the hole during the directional drilling process and the extraction process, which will have a water lock effect and hydraulic plugging effect on coal seam gas extraction, thereby avoiding affecting the gas extraction effect;

[0058] (3) During the extraction process of the directional drilling hole for inclined extraction, the depressurized gas that seeps from the coal seam into the directional drilling hole for inclined extraction rapidly moves along the drilling hole to the high part of the structure (hole mouth) under the action of fluid potential, density and extraction negative pressure. The water that seeps into the drilling hole moves along the drilling hole to the low part of the structure under the action of gravity, and the gas-water separation is automatically achieved in the extraction drilling hole, effectively avoiding the pumping of water into the mine gas extraction pipeline to prevent the extraction efficiency from being affected;

[0059] (4) The directional drilling trajectory for inclined extraction directly passes through multiple mining faces, including the mining area and the excavation tunnel of each mining face. Except for the opening section, the drilling trajectory is basically parallel to each other and evenly arranged along the inclination in each working face. There is no blank area for gas extraction, and there is no waste of drilling volume due to the connection of boreholes;

[0060] (5) Regional gas extraction directional drilling can be carried out in one tunnel, and gas extraction can be carried out in multiple sections or even in one level of coal seam at one time, avoiding the need to move directional drilling rigs and drill rods back and forth between multiple tunnels at different levels underground, effectively reducing construction preparation time and transportation safety accidents;

[0061] (6) When the gas extraction of a certain working face reaches the standard, the inclined extraction directional drilling holes left in the working face recovery area revealed during the excavation of the upper and lower tunnels can still be efficiently utilized to continue to extract the gas in the working face recovery area. There is no need to construct gas extraction drilling holes in the working face recovery area, so that the working face can be extracted while recovering, thereby improving the recovery efficiency. At the same time, the remaining inclined extraction directional drilling holes in the lower part of the working face can still be used for efficient and advanced extraction of coal seam gas in the lower unrecovered area. In this way, when the recovery of the previous working face is completed, the coal seam gas of the next working face has sufficient time to achieve the standard of extraction, realizing continuous recovery of the working face and improving the production efficiency of the mine;

[0062] (7) When the drilling arrangement is as shown in the attached Figure 5When the multi - coal - seam layout is as shown, the mining of Coal Seam 1 is carried out first. The mining of Coal Seam 1 can effectively relieve the pressure of adjacent Coal Seam 2 and Coal Seam 3. With such an arrangement, the inclined drainage directional boreholes in Coal Seam 2 and Coal Seam 3 can achieve regional high - efficiency drainage of the pressure - relieved gas in Coal Seam 2 and Coal Seam 3. In this way, the rapid drainage of gas in Coal Seam 2 and Coal Seam 3 reaches the standard, and at the same time, it effectively prevents the gas from the pressure - relieved Coal Seam 2 and Coal Seam 3 from flowing into the mining space of Coal Seam 1 along the mining cracks of Coal Seam 1, resulting in gas over - limit in the mining space of Coal Seam 1.

[0063] Embodiment 2

[0064] The difference from Embodiment 1 is only that, as shown in Attachment Figure 8 and Attachment Figure 9 In this embodiment, for a production mine (a mine with complete second - phase project), the simulation of the borehole layout of the regional coal - seam gas drainage directional boreholes is as shown in Attachment Figure 4 In S2, if regional coal - seam gas drainage is carried out for a construction mine, before borehole construction on the ground, high - pressure grouting is used to seal the fissures within the preset range near the borehole and within the preset depth near the ground, and at the same time, the surface fissure water and atmospheric precipitation infiltration along the surface borehole fissures are intercepted, which can ensure that the inclined gas drainage boreholes are air - tight, prevent the generation of hydraulic plugging and water - locking effects due to gas migration, and avoid affecting the gas drainage effect of the boreholes; at the same time, a ground drainage well is constructed from the ground to the lowest point of the structure in the drainage area, and a horizontal branch well is constructed from an appropriate position of the main well to the lowest point of the structure of the target coal seam and close to the inclined drainage directional borehole. The elevation of the horizontal branch well does not exceed the elevation of the lowest point of the inclined drainage directional borehole, and the trajectory of the horizontal branch well is straight, which can increase the scope of the drainage area and improve the drainage efficiency.

[0065] In addition, after the construction of the ground drainage well in S3, hydraulic fracturing is carried out on the well section of the target coal seam. The cracks formed by the hydraulic fracturing connect the ground drainage well and the inclined drainage directional borehole, effectively draining the borehole water accumulation during the construction and drainage process of the inclined drainage directional borehole and the coal seam water accumulation in the low - lying part of the structure, ensuring the drainage effect of the inclined drainage directional borehole.

[0066] The above are only embodiments of the present invention. Common general knowledge such as specific structures and characteristics known in the art is not described in detail herein. Those of ordinary skill in the art know all the common general knowledge in the technical field to which the invention pertains before the filing date or the priority date, are able to obtain all the prior art in this field, and have the ability to apply conventional experimental means before this date. Those of ordinary skill in the art can, under the inspiration given in this application, complete and implement this solution in combination with their own abilities. Some typical well-known structures or well-known methods should not become an obstacle for those of ordinary skill in the art to implement this application. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope claimed in this application shall be subject to the content of its claims, and the specific implementation manners and the like recorded in the specification can be used to interpret the content of the claims.

Claims

1. A method for regional coal seam gas extraction in monoclinic structures, characterized in that, Including: S1. For the background of monoclinic structure, design the working face of the coal seam by using the longwall mining method along the strike; S2. Conduct inclined drainage directional drilling construction at the working face in the high part of the mine structure; S3. According to the drilling construction data, design and construct large-diameter drainage directional drilling in the low part of the mine structure, and install a gate valve at its orifice to control the drainage intensity. After the construction of the large-diameter drainage directional drilling is completed, conduct hydraulic fracturing. The fractures formed by the hydraulic fracturing communicate with the drainage directional drilling, effectively discharging the accumulated water in the drainage directional drilling; S4. After the accumulated water is discharged, close the orifice gate valve and regularly drain water during the gas drainage process; In S2, if regional coal seam gas drainage is carried out for a newly-built mine, before drilling construction on the ground, conduct high-pressure grouting sealing on the fractures within the preset range near the drilling and within the preset depth range near the ground, and at the same time cut off the infiltration of surface fissure water and atmospheric precipitation along the surface hole fractures; In S2, construct a ground drainage well from the ground to the lowest point of the drainage area structure. At an appropriate position of the main well, construct a horizontal branch well towards the lowest point of the target coal seam structure and close to the inclined drainage directional drilling. The elevation of the horizontal branch well does not exceed the elevation of the lowest point of the inclined drainage directional drilling, and the trajectory of the horizontal branch well is straight; In S3, after the construction of the ground drainage well is completed, conduct hydraulic fracturing on the well section of the target coal seam. The fractures formed by the hydraulic fracturing communicate the ground drainage well with the inclined drainage directional drilling, effectively draining the accumulated water in the drilling during the construction and drainage process of the inclined drainage directional drilling and the accumulated water in the coal seam in the low part of the structure; 2. The regional coal seam gas drainage method for monoclinic structures according to claim 1, characterized in that, In S2, the spacing of the inclined drainage directional drilling construction is determined according to the drainage radius of the directional drilling and the designed drainage time; 3. The regional coal seam gas extraction method for monoclinic structures according to claim 2, characterized in that, In S2, wet operation is adopted for the directional drilling construction; 4. The regional coal seam gas drainage method for monoclinic structures as claimed in claim 3, characterized in that, In S2, the construction length of the inclined drainage directional drilling is ≤1000m; 5. The method for regional coal seam gas extraction for monoclinic structures according to claim 4, characterized in that, In S3, the aperture of the large-diameter drainage directional drilling is not less than 200mm. The elevation of the lowest point of the large-diameter drainage directional drilling trajectory gradually increases from the orifice to the bottom of the hole, and the slope is between 2 degrees and 5 degrees. The construction length of the large-diameter drainage directional drilling is less than or equal to 2000m.

Images