Structure and method for removing water granulated slag in downward gas extraction hole of water-containing thick coal seam

Abstract

The invention discloses a structure and method for removing water granulated slag in a downward gas extraction hole of a water-containing thick coal seam. The structure comprises a downward gas extraction unit and an upward gas extraction unit. The method comprises the following steps that the function relation between the hole bottom reaming radius r of the upward water and slag discharging hole and the reaming water pressure p is deduced; a downward gas extraction unit is constructed, and an upper gas extraction main pipe is connected; constructing an upward water and slag discharging hole, and reaming the bottom of the upward water and slag discharging hole, so that the upward water and slag discharging hole is communicated with the downward gas extraction unit; constructing an upward gas extraction unit, and connecting the upward gas extraction unit with a lower gas extraction main pipe; the downward gas extraction unit and the upward gas extraction unit conduct gas extraction, and water and slag in the downward gas extraction unit are naturally discharged through the upward water and slag discharging hole. According to the method, water granulated slag can be discharged at any time, electricity is not needed, water granulated slag in a plurality of downward drill holes can be discharged at a time, and therefore the extraction effect of the downward gas extraction drill holes is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of coal mine gas safety extraction technology, specifically relating to the structure and method for removing water slag from gas extraction holes in thick water-bearing coal seams. Background Technology

[0002] Coal seam gas drainage is an important technical measure for coal seam gas control, which can effectively reduce the occurrence of gas disasters. Among these measures, in-seam borehole gas drainage is a key step in controlling gas in a coal seam. For dipping coal seams, the return airway is generally located on the upper side, and the intake airway on the lower side. When drilling in-seam boreholes for gas drainage in the return airway, the boreholes are downward drainage holes; when drilling in-seam boreholes into the coal seam from the intake airway, these boreholes are upward drainage holes.

[0003] During upward drilling, water and coal dust (referred to as water slag) can be naturally discharged from the borehole by their own weight. However, during downward gas drainage drilling and long-term drainage, water slag is often difficult to discharge from the borehole. In dry coal seams, some water will diffuse within the coal seam or be pumped away in the form of water vapor. For water-bearing coal seams, water easily accumulates in the borehole during coal seam gas drainage. Coal dust generated during construction and stress disturbance also gradually remains in the gas drainage borehole, seriously affecting the effectiveness of borehole gas drainage.

[0004] Existing patents, such as "Integrated Device and Method for Automatic Discharge of Coal Seam Gas Extraction and Borehole Water (ZL201910293618)," "An Intelligent Drainage and Slag Removal System for Downward Drilling in Coal Mine Gas Extraction and Its Application (ZL201710797142)," and "Downward Extraction Drillhole Pressure Extraction System and Its Drainage Method (ZL2019107838120)," mainly involve opening the gas extraction borehole and draining water by inserting a pipe into the gas extraction pipe to draw water or by compressed air. The drawbacks are as follows: electricity is required, but it is difficult to use electricity freely underground and access points are not readily available; there are often hundreds or even thousands of boreholes along the return air roadway, resulting in low efficiency; for downward drilling in water-bearing coal seams, each extraction borehole uses a pipe suction method for drainage, which is inefficient; downward boreholes are easily refilled with water after drainage; pipe suction is difficult to effectively remove coal slag, easily causing pipeline blockage; for deeper downward gas extraction boreholes, air pressure is lost along the pipeline, making it difficult to effectively discharge water, and slag removal is even more difficult.

[0005] Therefore, it is necessary to develop a structure and method for removing water slag from downward gas extraction holes in thick water-bearing coal seams. This method can remove water slag at any time without electricity and can remove water slag from multiple downward boreholes at once, thereby significantly improving the extraction effect of downward gas extraction holes. Summary of the Invention

[0006] This invention provides a structure and method for removing water and slag from gas extraction holes in thick, water-bearing coal seams without the need for electricity, with good drainage and slag removal effects, and ensuring the normal operation of gas extraction.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a structure for removing water and slag from the downward gas extraction hole in a water-bearing thick coal seam, including a downward gas extraction unit (1) and an upward gas extraction unit (2); wherein the downward gas extraction unit (1) includes multiple downward gas extraction holes (4) and downward gas extraction branch pipes (8) installed in the downward gas extraction holes (4); the upward gas extraction unit (2) includes an upward drainage and slag discharge hole (5), an upward drainage and slag discharge pipe (14) installed in the upward drainage and slag discharge hole (5), multiple upward gas extraction holes (6), and upward gas extraction branch pipes (12) installed in the upward gas extraction holes (6); the length of the upward drainage and slag discharge hole (5) is longer than that of the upward gas extraction hole (6). R 1, R 1 is the coal seam gas extraction radius. The final hole position of the downward gas extraction hole (4) is located above the final hole position of the upward drainage and slag discharge hole (5). That is, the bottom position of the downward gas extraction hole (4) is higher than the bottom position of the upward drainage and slag discharge hole (5). After the bottom of the upward drainage and slag discharge hole (5) is enlarged, a cylindrical cavity (16) is formed. The cylindrical cavity (16) is simultaneously connected to the bottom of multiple downward gas extraction holes (4).

[0008] All the downward gas extraction branch pipes (8) are connected to an upper gas extraction main pipe (13) at the upper end. One end of the upper gas extraction main pipe (13) is closed and the other end is connected to an upper automatic water drainer (3). The upper gas extraction main pipe (13) is connected to the upper gas extraction trunk pipe (11) in the roadway through the upper connecting pipe (18).

[0009] The lower end of the upward drainage and slag discharge pipe (14) and the lower end of all the upward gas extraction branch pipes (12) are connected to a lower gas extraction main pipe (17). One end of the lower gas extraction main pipe (17) is closed and the other end is connected to a lower automatic water discharge device (9). The lower gas extraction main pipe (17) is connected to the lower gas extraction trunk pipe (10) in the roadway through the lower connecting pipe (15). A valve (7) is provided on the upward drainage and slag discharge pipe (14).

[0010] A method for removing water slag from a gas drainage hole in a thick, water-bearing coal seam is implemented using a structure for removing water slag from a gas drainage hole in a thick, water-bearing coal seam, and includes the following steps: S1. Derive the functional relationship between the enlargement radius r of the top drainage and slag discharge hole (5) and the enlargement water pressure p. S2. Construct the downward gas extraction unit (1) and connect it to the upper gas extraction trunk pipe (11). S3. Construct the upward drainage and slag-discharge hole (5). According to the functional relationship between the reaming radius r and the reaming water pressure p derived in step S1, reaming is carried out at the bottom of the upward drainage and slag-discharge hole (5) to connect the upward drainage and slag-discharge hole (5) with the downward gas drainage unit (1). S4. Construct the upward gas drainage unit (2) and connect the upward gas drainage unit (2) to the lower gas drainage main pipe (10). S5. Carry out gas drainage in the downward gas drainage unit (1) and the upward gas drainage unit (2). The water and slag in the downward gas drainage unit (1) are naturally discharged through the upward drainage and slag-discharge hole (5).

[0011] Step S1 specifically includes the following contents: When the drill rig constructs the upward drainage and slag-discharge hole (5), the final hole position is located below (including directly below and obliquely below) the final hole position of the designed downward gas drainage hole (4). After the hole is formed, the drill pipe is withdrawn, the drill bit is removed, and the hydraulic reaming drill bit is installed at the end of the drill pipe. By connecting the drill pipes one by one, the hydraulic reaming drill bit is pushed to the bottom of the hole for hydraulic reaming operation. Set a certain water pressure for the water pump. p Through the drill rig, control the forward and backward propulsion and rotation of the drill pipe to implement the hydraulic reaming operation, and the distance that the drill rig controls the drill pipe to advance forward along the center direction of the upward drainage and slag-discharge hole (5) is the reaming length. l During the reaming process, collect and weigh the coal chips discharged from the upward drainage and slag-discharge hole (5). The hole formed by reaming is approximately cylindrical. Calculate the reaming pressure through the equation. Calculate the reaming radius under the condition, where p is the reaming radius, m is the weight of the coal chips, r is the borehole radius, R is the density of coal, ρ is the reaming length. Based on this method, obtain the reaming radius under different reaming pressure conditions. The reaming pressure and the reaming radius are positively correlated, but follow the non-linear growth law of "fast first and then slow" and r = a l b p b (both a and b are rational numbers and a > 0, 0 < b < 1). a and b are obtained through on-site inspection. The reaming radius and the reaming pressure satisfy r = a p b functional relationship, p is the reaming pressure, that is, the water pressure.

[0012] Step S2 specifically includes the following contents: Construct a downward gas drainage hole (4) every certain distance using a drill rig. The spacing between two adjacent downward gas drainage holes (4) is determined by the drainage radius R 1 of the coal seam, and the drainage radius R1. Through on-site investigation, the distance between two adjacent downward gas extraction holes (4) is 2R1. After the construction of the downward gas extraction hole (4) is completed, the downward gas extraction branch pipe (8) is inserted into the downward gas extraction hole (4) and the hole is sealed by the two-plug-one-injection sealing process (two-plug-one-injection is a mature technology and will not be described in detail). After sealing for 24 hours, n downward gas extraction branch pipes (8) are connected to an upper gas extraction main pipe (13). One end of the upper gas extraction main pipe (13) is closed, and the other end is connected to the upper automatic water drainer (3). The closed end of the upper gas extraction main pipe (13) is higher than the end connected to the upper automatic water drainer (3) to facilitate drainage and slag removal. Finally, multiple upper gas extraction main pipes (13) are connected to the upper gas extraction trunk pipe (11).

[0013] Step S3 specifically includes the following: According to r=a p b The relationship was used to calculate the pore expansion pressure. p Hole enlargement radius under condition 1 r 1. Based on the hole enlargement radius r 1 and extraction radius R 1. Calculate the enlargement radius r 1. Number of downward gas extraction holes (4) n = r 1 / (2) R 1) +1), for the obtained n Round the value to the nearest integer, omitting the decimal. The drilling rig is used to construct the upward drainage and slag discharge holes (5), each n For each downward gas extraction hole (4), construct an upward drainage and slag discharge hole (5). The opening position of the upward drainage and slag discharge hole (5) is located at... n The downward gas extraction hole (4) is located at the center of the projection of the coal wall on the other side. The final position of the upward drainage and slag discharge hole (5) is located below the final position of the downward gas extraction hole (4) (including directly below and obliquely below). After the upward drainage and slag discharge hole (5) is completed, the drill rod is withdrawn, and the hydraulic reaming drill bit is installed at the end of the drill rod. By connecting the drill rods one by one, the hydraulic reaming drill bit is pushed to the bottom of the hole to create a cavity. The water pump pressure is set to p 1, its enlargement radius is r 1. The cylindrical cavity (16) formed by the enlarged hole can connect the bottom of the upward drainage and slag discharge hole (5) with the bottom of the downward gas extraction hole (4). After the enlarged hole is completed, the drill rod is removed.

[0014] Step S4 specifically includes the following:

[0015] After the upward drainage and slag discharge hole (5) is constructed, an upward gas extraction hole (6) is constructed at regular intervals using a drilling rig, with the upward drainage and slag discharge hole (5) as the center. The upward gas extraction hole (6) is parallel to the upward drainage and slag discharge hole (5), and the interval between two adjacent holes is 2. R 1. The length of the upward gas extraction hole (6) is smaller than that of the upward drainage and slag discharge hole (5). R 1. After the construction of the upward gas extraction hole (6) is completed, the upward gas extraction branch pipe (12) is installed in the upward gas extraction hole (6), and the upward drainage and slag discharge pipe (14) is installed in the upward drainage and slag discharge hole (5). The hole is sealed using a two-plug-one-injection sealing process (two-plug-one-injection is a mature technology and will not be described in detail). After sealing for 24 hours, the lower ends of the upward gas extraction branch pipe (12) and the upward drainage and slag discharge pipe (14) are connected to the lower gas extraction main pipe (17). A valve (7) is installed on the drainage and slag discharge pipe (14). During normal gas extraction, the valve (7) is closed and the upper drainage and slag discharge hole (5) does not participate in gas extraction. One end of the lower gas extraction main pipe (17) is closed and the other end is connected to the lower automatic water discharge device (9). The closed end of the lower gas extraction main pipe (17) is higher than the end connected to the lower automatic water discharge device (9) to facilitate drainage and slag discharge. Finally, multiple lower gas extraction main pipes (17) are connected to the lower gas extraction trunk pipe (10).

[0016] Step S5 specifically includes the following: For water-bearing coal seams, during the gas extraction process, water and coal dust (referred to as water slag) in the upward gas extraction hole (6) can be discharged naturally by their own weight. However, as the extraction time increases, water gradually accumulates in the downward gas extraction hole (4) under the action of extraction negative pressure. Coal slag generated during construction and stress disturbance also gradually remains in the downward gas extraction hole (4). Therefore, during the extraction process, the valve (7) on the upward drainage and slag discharge pipe (14) is manually opened at intervals. Water and coal dust generated during the extraction process of the downward gas extraction unit (1) are discharged. Under the action of gravity, the slag flows into the cylindrical cavity (16), and then into the upward drainage slag discharge hole (5) and the lower gas extraction main pipe (17). The coal slag and water in the lower gas extraction main pipe (17) are discharged through the lower automatic water discharge device (9). The gas enters the gas extraction main pipe through the lower gas extraction trunk pipe (10) and is finally discharged or utilized by the gas extraction pump. At certain intervals, the valve (7) on the upward drainage slag discharge pipe (14) is opened and closed according to this step, and the cycle is repeated continuously, so as to achieve the natural discharge of water and slag in the downward gas extraction hole (4).

[0017] Compared with related technologies, the present invention has the following beneficial effects by adopting the above technical solution: This invention drills upward drainage and slag discharge holes in the coal seam below downward gas extraction holes. Based on the theoretically derived relationship between the hole radius, coal density, and water pressure, hydraulic cavity creation is performed at the bottom of the upward drainage and slag discharge holes. The resulting near-cylindrical cavity connects to the bottom of several downward gas extraction holes. This allows the water and slag stored in the downward gas extraction holes to automatically flow into the near-cylindrical cavity by their own weight and ultimately be discharged through the upward drainage and slag discharge holes. This invention allows for one-time construction, enabling the immediate removal of water and slag from downward gas extraction holes without electricity. Furthermore, it can remove water and slag from multiple downward boreholes simultaneously, significantly improving the extraction efficiency of downward gas extraction boreholes. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0019] like Figure 1 As shown, the structure for removing water and slag from the downward gas extraction hole in the water-bearing thick coal seam of the present invention includes a downward gas extraction unit (1) and an upward gas extraction unit (2); wherein the downward gas extraction unit (1) includes multiple downward gas extraction holes (4) and downward gas extraction branch pipes (8) installed in the downward gas extraction holes (4); the upward gas extraction unit (2) includes an upward drainage and slag discharge hole (5), an upward drainage and slag discharge pipe (14) installed in the upward drainage and slag discharge hole (5), multiple upward gas extraction holes (6), and upward gas extraction branch pipes (12) installed in the upward gas extraction holes (6); the length of the upward drainage and slag discharge hole (5) is longer than that of the upward gas extraction hole (6). R 1, R 1 is the coal seam gas extraction radius. The final hole position of the downward gas extraction hole (4) is located above the final hole position of the upward drainage and slag discharge hole (5). That is, the bottom position of the downward gas extraction hole (4) is higher than the bottom position of the upward drainage and slag discharge hole (5). After the bottom of the upward drainage and slag discharge hole (5) is enlarged, a cylindrical cavity (16) is formed. The cylindrical cavity (16) is simultaneously connected to the bottom of multiple downward gas extraction holes (4).

[0020] All the downward gas extraction branch pipes (8) are connected to an upper gas extraction main pipe (13) at the upper end. One end of the upper gas extraction main pipe (13) is closed and the other end is connected to an upper automatic water drainer (3). The upper gas extraction main pipe (13) is connected to the upper gas extraction trunk pipe (11) in the roadway through the upper connecting pipe (18).

[0021] The lower end of the upward drainage and slag discharge pipe (14) and the lower end of all the upward gas extraction branch pipes (12) are connected to a lower gas extraction main pipe (17). One end of the lower gas extraction main pipe (17) is closed and the other end is connected to a lower automatic water discharge device (9). The lower gas extraction main pipe (17) is connected to the lower gas extraction trunk pipe (10) in the roadway through the lower connecting pipe (15). A valve (7) is provided on the upward drainage and slag discharge pipe (14).

[0022] A method for removing water slag from a gas drainage hole in a thick, water-bearing coal seam is implemented using a structure for removing water slag from a gas drainage hole in a thick, water-bearing coal seam, and includes the following steps: S1. Derive the functional relationship between the enlargement radius r of the top drainage and slag discharge hole (5) and the enlargement water pressure p. S2. Construct the downward gas extraction unit (1) and connect it to the upper gas extraction trunk pipe (11). S3. Construct the upward drainage and slag discharge hole (5). Based on step S1, derive the functional relationship between the hole enlargement radius r and the hole enlargement water pressure p. Enlarge the hole at the bottom of the upward drainage and slag discharge hole (5) so that the upward drainage and slag discharge hole (5) is connected to the downward gas extraction unit (1). S4. Construct the upward gas extraction unit (2) and connect the upward gas extraction unit (2) to the downward gas extraction trunk line (10). S5. The downward gas extraction unit (1) and the upward gas extraction unit (2) perform gas extraction. The water and slag in the downward gas extraction unit (1) are naturally discharged through the upward drainage and slag discharge hole (5).

[0023] Step S1 specifically includes the following: When drilling the upward drainage and slag removal hole (5), the final hole position is located below (including directly below and obliquely below) the designed final hole position of the downward gas extraction hole (4). After drilling, the drill rod is withdrawn, the drill bit is removed, and the hydraulic reaming drill bit is installed at the end of the drill rod. By connecting the drill rods one by one, the hydraulic reaming drill bit is pushed to the bottom of the hole for hydraulic reaming operation. The water pump is set to a certain water pressure. p The hydraulic reaming operation is carried out by controlling the drill rod to advance and rotate. The distance that the drill rod advances forward along the center direction of the drainage and slag discharge hole (5) controlled by the drill rig is the length of the reaming operation. l During the hole enlargement process, the coal dust discharged from the upward drainage and slag discharge hole (5) is collected and weighed. The hole formed by the enlargement is approximately cylindrical. Calculate the reaming pressure p The enlargement radius under the given conditions, where r Where m is the radius of the borehole and m is the weight of the coal dust. R Where is the borehole radius, ρ For the density of coal, lis the reaming length; based on this method, the reaming radius under different reaming pressure conditions is obtained. The reaming pressure is positively correlated with the reaming radius, but follows a non-linear growth law of "fast first and then slow" and r = a p b (both a and b are rational numbers, a > 0, 0 < b < 1), and a and b are obtained through on-site inspection. The relationship between the reaming radius and the reaming pressure satisfies r = a p b functional relationship, where p is the reaming pressure, that is, the water pressure.

[0024] Step S2 specifically includes the following content: A downward gas drainage hole (4) is constructed by a drill at a certain interval. The distance between two adjacent downward gas drainage holes (4) is determined by the drainage radius R 1 of the coal seam. The drainage radius R 1 is obtained through on-site inspection. The distance between two adjacent downward gas drainage holes (4) is 2R1; after the construction of the downward gas drainage hole (4) is completed, the downward gas drainage branch pipe (8) is inserted into the downward gas drainage hole (4), and the two-block-one-injection sealing process is used for sealing (the two-block-one-injection is a mature technology and will not be elaborated in detail). After 24 hours of sealing, n downward gas drainage branch pipes (8) are connected to an upper gas drainage main pipe (13). One end of the upper gas drainage main pipe (13) is closed, and the other end is connected to an upper automatic water drainer (3). The closed end of the upper gas drainage main pipe (13) is higher than the end connected to the upper automatic water drainer (3) to facilitate drainage and slag removal. Finally, multiple upper gas drainage main pipes (13) are connected to the upper gas drainage trunk pipe (11).

[0025] Step S3 specifically includes the following content: According to the relationship of r = a p b , the reaming pressure p 1 under the condition is calculated, and based on the reaming radius r 1 and the drainage radius r 1, the number of downward gas drainage holes (4) included in the reaming radius R 1 is calculated ( r = n = r 1 / (2 R 1) + 1), and the obtained n value is rounded, and the decimal part is omitted; An upward drainage and slag removal hole (5) is constructed by a drill. For each n downward gas drainage hole (4), an upward drainage and slag removal hole (5) is constructed. The opening position of the upward drainage and slag removal hole (5) is located at nThe downward gas extraction hole (4) is located at the center of the projection of the coal wall on the other side. The final position of the upward drainage and slag discharge hole (5) is located below the final position of the downward gas extraction hole (4) (including directly below and obliquely below). After the upward drainage and slag discharge hole (5) is completed, the drill rod is withdrawn, and the hydraulic reaming drill bit is installed at the end of the drill rod. By connecting the drill rods one by one, the hydraulic reaming drill bit is pushed to the bottom of the hole to create a cavity. The water pump pressure is set to p 1, its enlargement radius is r 1. The cylindrical cavity (16) formed by the enlarged hole can connect the bottom of the upward drainage and slag discharge hole (5) with the bottom of the downward gas extraction hole (4). After the enlarged hole is completed, the drill rod is removed.

[0026] Step S4 specifically includes the following: After the upward drainage and slag discharge hole (5) is constructed, an upward gas extraction hole (6) is constructed at regular intervals using a drilling rig, with the upward drainage and slag discharge hole (5) as the center. The upward gas extraction hole (6) is parallel to the upward drainage and slag discharge hole (5), and the interval between two adjacent holes is 2. R 1. The length of the upward gas extraction hole (6) is smaller than that of the upward drainage and slag discharge hole (5). R 1. After the construction of the upward gas extraction hole (6) is completed, the upward gas extraction branch pipe (12) is installed in the upward gas extraction hole (6), and the upward drainage and slag discharge pipe (14) is installed in the upward drainage and slag discharge hole (5). The hole is sealed using a two-plug-one-injection sealing process (two-plug-one-injection is a mature technology and will not be described in detail). After sealing for 24 hours, the lower ends of the upward gas extraction branch pipe (12) and the upward drainage and slag discharge pipe (14) are connected to the lower gas extraction main pipe (17). A valve (7) is installed on the drainage and slag discharge pipe (14). During normal gas extraction, the valve (7) is closed and the upper drainage and slag discharge hole (5) does not participate in gas extraction. One end of the lower gas extraction main pipe (17) is closed and the other end is connected to the lower automatic water discharge device (9). The closed end of the lower gas extraction main pipe (17) is higher than the end connected to the lower automatic water discharge device (9) to facilitate drainage and slag discharge. Finally, multiple lower gas extraction main pipes (17) are connected to the lower gas extraction trunk pipe (10).

[0027] Step S5 specifically includes the following: For water-bearing coal seams, during the gas extraction process, water and coal dust (referred to as water slag) in the upward gas extraction hole (6) can be discharged naturally by their own weight. However, as the extraction time increases, water gradually accumulates in the downward gas extraction hole (4) under the action of extraction negative pressure. Coal slag generated during construction and stress disturbance also gradually remains in the downward gas extraction hole (4). Therefore, during the extraction process, the valve (7) on the upward drainage and slag discharge pipe (14) is manually opened at intervals. Water and coal dust generated during the extraction process of the downward gas extraction unit (1) are discharged. Under the action of gravity, the slag flows into the cylindrical cavity (16), and then into the upward drainage slag discharge hole (5) and the lower gas extraction main pipe (17). The coal slag and water in the lower gas extraction main pipe (17) are discharged through the lower automatic water discharge device (9). The gas enters the gas extraction main pipe through the lower gas extraction trunk pipe (10) and is finally discharged or utilized by the gas extraction pump. At certain intervals, the valve (7) on the upward drainage slag discharge pipe (14) is opened and closed according to this step, and the cycle is repeated continuously, so as to achieve the natural discharge of water and slag in the downward gas extraction hole (4).

[0028] The above embodiments illustrate the basic principles and features of the present invention, but are merely preferred embodiments and are not limited to these embodiments. Those skilled in the art, inspired by this patent, can make many modifications and improvements without departing from the spirit and scope of the claims, all of which fall within the scope of protection of the present invention. Therefore, the scope of this patent and its protection should be determined by the appended claims.

Claims

1. A structure for removing water and slag from a gas extraction well in a thick, water-bearing coal seam, characterized in that: It includes a downward gas extraction unit (1) and an upward gas extraction unit (2); wherein the downward gas extraction unit (1) includes multiple downward gas extraction holes (4) and downward gas extraction branch pipes (8) installed in the downward gas extraction holes (4); the upward gas extraction unit (2) includes an upward drainage and slag discharge hole (5), an upward drainage and slag discharge pipe (14) installed in the upward drainage and slag discharge hole (5), multiple upward gas extraction holes (6), and upward gas extraction branch pipes (12) installed in the upward gas extraction holes (6); the upward drainage and slag discharge hole (5) is longer than the upward gas extraction hole (6). R 1, R 1 is the coal seam gas extraction radius. The final hole position of the downward gas extraction hole (4) is located above the final hole position of the upward drainage and slag discharge hole (5). That is, the bottom position of the downward gas extraction hole (4) is higher than the bottom position of the upward drainage and slag discharge hole (5). After the bottom of the upward drainage and slag discharge hole (5) is enlarged, a cylindrical cavity (16) is formed. The cylindrical cavity (16) is simultaneously connected to the bottom of multiple downward gas extraction holes (4).

2. The structure for removing water slag from the gas extraction hole in a thick, water-bearing coal seam according to claim 1, characterized in that: All the downward gas extraction branch pipes (8) are connected to an upper gas extraction main pipe (13) at the upper end. One end of the upper gas extraction main pipe (13) is closed and the other end is connected to an upper automatic water drainer (3). The upper gas extraction main pipe (13) is connected to the upper gas extraction trunk pipe (11) in the roadway through the upper connecting pipe (18).

3. The structure for removing water slag from the gas extraction hole in a thick, water-bearing coal seam according to claim 2, characterized in that: The lower end of the upward drainage and slag discharge pipe (14) and the lower end of all the upward gas extraction branch pipes (12) are connected to a lower gas extraction main pipe (17). One end of the lower gas extraction main pipe (17) is closed and the other end is connected to a lower automatic water discharge device (9). The lower gas extraction main pipe (17) is connected to the lower gas extraction trunk pipe (10) in the roadway through the lower connecting pipe (15). A valve (7) is provided on the upward drainage and slag discharge pipe (14).

4. A method for removing water and slag from a gas drainage hole in a thick, water-bearing coal seam, implemented using the structure for removing water and slag from a gas drainage hole in a thick, water-bearing coal seam as described in claim 3, characterized in that: Includes the following steps: S1. Derive the functional relationship between the enlargement radius r of the top drainage and slag discharge hole (5) and the enlargement water pressure p. S2. Construct the downward gas extraction unit (1) and connect it to the upper gas extraction trunk pipe (11). S3. Construct the upward drainage and slag discharge hole (5). Based on step S1, derive the functional relationship between the hole enlargement radius r and the hole enlargement water pressure p. Enlarge the hole at the bottom of the upward drainage and slag discharge hole (5) so that the upward drainage and slag discharge hole (5) is connected to the downward gas extraction unit (1). S4. Construct the upward gas extraction unit (2) and connect the upward gas extraction unit (2) to the downward gas extraction trunk line (10). S5. The downward gas extraction unit (1) and the upward gas extraction unit (2) perform gas extraction. The water and slag in the downward gas extraction unit (1) are naturally discharged through the upward drainage and slag discharge hole (5).

5. The method for removing water and slag from the gas extraction hole in a thick, water-bearing coal seam according to claim 4, characterized in that: Step S1 specifically includes the following: When the final hole position during the construction of the upward drainage and slag discharge hole (5) by the drill rig is below (including directly below and obliquely below) the final hole position of the designed downward gas drainage hole (4), after the hole is formed, the drill pipe is withdrawn, the drill bit is removed, the hydraulicized reaming bit is installed at the end of the drill pipe, and the hydraulicized reaming bit is pushed to the bottom of the hole for hydraulic reaming operation by successively connecting the drill pipes; a certain water pressure is set for the water pump. p The hydraulic reaming operation is carried out by controlling the forward and backward movement and rotation of the drill pipe by the drill rig. The distance that the drill rig controls the drill pipe to advance forward along the central direction of the upward drainage and slag discharge hole (5) is the length of the reaming. l During the reaming process, the coal chips discharged from the upward drainage and slag discharge hole (5) are collected and weighed. The hole formed by the reaming is approximately cylindrical. The reaming pressure is calculated by the equation The reaming radius under the condition of p is calculated, where r is the reaming radius, m is the weight of the coal chips, R is the borehole radius, ρ is the density of the coal, l is the reaming length, ; Based on this method, the reaming radii under different reaming pressure conditions are obtained. The reaming pressure and the reaming radius are positively correlated, but follow the non-linear growth law of "fast first and then slow" and r = a p b (both a and b are rational numbers and a > 0, 0 < b < 1). a and b are obtained through on-site investigation. The reaming radius and the reaming pressure satisfy the functional relationship r = a p b where p is the reaming pressure, that is, the water pressure.

6. The method for removing water and slag from a gas extraction well in a thick, water-bearing coal seam according to claim 5, characterized in that: Step S2 specifically includes the following: At regular intervals, a downward gas extraction hole (4) is drilled using a drilling rig. The spacing between two adjacent downward gas extraction holes (4) is determined by the extraction radius of the coal seam. R 1. Determine the sampling radius. R 1. Through on-site investigation, the distance between two adjacent downward gas extraction holes (4) is 2R1. After the construction of the downward gas extraction hole (4) is completed, the downward gas extraction branch pipe (8) is inserted into the downward gas extraction hole (4) and the hole is sealed by the two-plug-one-injection sealing process (two-plug-one-injection is a mature technology and will not be described in detail). After sealing for 24 hours, n downward gas extraction branch pipes (8) are connected to an upper gas extraction main pipe (13). One end of the upper gas extraction main pipe (13) is closed, and the other end is connected to the upper automatic water drainer (3). The closed end of the upper gas extraction main pipe (13) is higher than the end connected to the upper automatic water drainer (3) to facilitate drainage and slag removal. Finally, multiple upper gas extraction main pipes (13) are connected to the upper gas extraction trunk pipe (11).

7. The method for removing water and slag from a gas extraction well in a thick, water-bearing coal seam according to claim 6, characterized in that: Step S3 specifically includes the following: According to r=a p b The relationship was used to calculate the pore expansion pressure. p Hole enlargement radius under condition 1 r 1. Based on the hole enlargement radius r 1 and extraction radius R 1. Calculate the enlargement radius r 1. Number of downward gas extraction holes (4) n = r 1 / (2) R 1) +1), for the obtained n Round the value to the nearest integer, omitting the decimal. The drilling rig is used to construct the upward drainage and slag discharge holes (5), each n For each downward gas extraction hole (4), construct an upward drainage and slag discharge hole (5). The opening position of the upward drainage and slag discharge hole (5) is located at... n The downward gas extraction hole (4) is located at the center of the projection of the coal wall on the other side. The final position of the upward drainage and slag discharge hole (5) is located below the final position of the downward gas extraction hole (4) (including directly below and obliquely below). After the upward drainage and slag discharge hole (5) is completed, the drill rod is withdrawn, and the hydraulic reaming drill bit is installed at the end of the drill rod. By connecting the drill rods one by one, the hydraulic reaming drill bit is pushed to the bottom of the hole to create a cavity. The water pump pressure is set to p 1, its enlargement radius is r 1. The cylindrical cavity (16) formed by the enlarged hole can connect the bottom of the upward drainage and slag discharge hole (5) with the bottom of the downward gas extraction hole (4). After the enlarged hole is completed, the drill rod is removed.

8. The method for removing water and slag from a gas extraction well in a thick, water-bearing coal seam according to claim 7, characterized in that: Step S4 specifically includes the following: After the upward drainage and slag discharge hole (5) is constructed, an upward gas extraction hole (6) is constructed at regular intervals using a drilling rig, with the upward drainage and slag discharge hole (5) as the center. The upward gas extraction hole (6) is parallel to the upward drainage and slag discharge hole (5), and the interval between two adjacent holes is 2. R 1. The length of the upward gas extraction hole (6) is smaller than that of the upward drainage and slag discharge hole (5). R 1. After the construction of the upward gas extraction hole (6) is completed, the upward gas extraction branch pipe (12) is installed in the upward gas extraction hole (6), and the upward drainage and slag discharge pipe (14) is installed in the upward drainage and slag discharge hole (5). The hole is sealed using a two-plug-one-injection sealing process (two-plug-one-injection is a mature technology and will not be described in detail). After sealing for 24 hours, the lower ends of the upward gas extraction branch pipe (12) and the upward drainage and slag discharge pipe (14) are connected to the lower gas extraction main pipe (17). A valve (7) is installed on the drainage and slag discharge pipe (14). During normal gas extraction, the valve (7) is closed and the upper drainage and slag discharge hole (5) does not participate in gas extraction. One end of the lower gas extraction main pipe (17) is closed and the other end is connected to the lower automatic water discharge device (9). The closed end of the lower gas extraction main pipe (17) is higher than the end connected to the lower automatic water discharge device (9) to facilitate drainage and slag discharge. Finally, multiple lower gas extraction main pipes (17) are connected to the lower gas extraction trunk pipe (10).

9. The method for removing water slag from a gas extraction well in a thick, water-bearing coal seam according to claim 8, characterized in that: Step S5 specifically includes the following: For water-bearing coal seams, during the gas extraction process, water and coal dust (referred to as water slag) in the upward gas extraction hole (6) can be discharged naturally by their own weight. However, as the extraction time increases, water gradually accumulates in the downward gas extraction hole (4) under the action of extraction negative pressure. Coal slag generated during construction and stress disturbance also gradually remains in the downward gas extraction hole (4). Therefore, during the extraction process, the valve (7) on the upward drainage and slag discharge pipe (14) is manually opened at intervals. Water and coal dust generated during the extraction process of the downward gas extraction unit (1) are discharged. Under the action of gravity, the slag flows into the cylindrical cavity (16), and then into the upward drainage slag discharge hole (5) and the lower gas extraction main pipe (17). The coal slag and water in the lower gas extraction main pipe (17) are discharged through the lower automatic water discharge device (9). The gas enters the gas extraction main pipe through the lower gas extraction trunk pipe (10) and is finally discharged or utilized by the gas extraction pump. At certain intervals, the valve (7) on the upward drainage slag discharge pipe (14) is opened and closed according to this step, and the cycle is repeated continuously, so as to achieve the natural discharge of water and slag in the downward gas extraction hole (4).

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