Well and ground combined bottom plate comb-shaped hole hydraulic punching coal roadway strip gas pre-pumping method

Abstract

The invention relates to a well-ground combined bottom plate comb-shaped hole hydraulic punching coal roadway strip gas pre-extraction method which comprises the steps that according to the planned position of a coal roadway, an underground drill site is arranged, and coal seam bottom plate comb-shaped drill holes and well-ground communicating wells are designed; the well-ground communicating well is constructed to achieve communication between the ground and the underground drill site; aiming at any main hole, constructing a hole opening section of the main hole, and installing a gas-water separation device; constructing two opening sections of the main hole and branch holes; utilizing ground hydraulic punching equipment to perform hydraulic flushing on the branch holes through the well-ground communication well, and synchronously adopting a gas-water separation device to perform coal-water-gas separation; and all the main holes are constructed, and coal roadway strip gas is extracted underground. The coal seam floor comb-shaped drill holes are formed along the coal roadway strip, the well-ground combined hydraulic punching channel is constructed, the ground hydraulic punching capacity and the underground coal seam floor comb-shaped branch holes are combined, regional large-scale gas extraction is achieved, the cost for arranging the bottom drainage roadway is saved, and dense drilling in the bottom drainage roadway is avoided.

Description

Technical Field

[0001] This application relates to the field of coal mine gas drainage. Specifically, it relates to a method for pre-draining gas from coal roadway strips by hydraulic punching with comb-shaped holes in the floor through well-ground combination. Background Art

[0002] High-gas and coal and gas outburst mines are widely distributed. In high-gas and outburst coal seams, the coal body structure is generally severely damaged, with high coal seam gas content, high gas pressure, and low permeability, resulting in high costs and low efficiency of underground gas drainage, great difficulty in eliminating outbursts in coal seams, and severely restricting the safe and efficient production of coal.

[0003] Pre-draining coal seam gas is an important measure for preventing coal and gas outbursts. Coal roadway is the first roadway to be developed in the working face. Meeting the standard of pre-draining gas from coal roadway strips is the prerequisite for ensuring the safe and rapid driving of coal roadways and also the key point of the coal mine gas prevention task. In the prior art, developing dedicated gas drainage rock roadways and adopting various drilling methods to densely arrange holes and combining with hydraulic punching are the main methods to achieve the standard of pre-draining gas from crushed and soft coal roadway strips. However, there are problems such as high cost of rock roadway development and unfavorable drainage management due to dense hole arrangement. In addition, due to the limitations of conditions such as water, electricity, and space in coal mine roadways, the displacement of underground punching equipment is small, the pressure is low, and it is difficult to add abrasive jets, resulting in a small punching scale, which is difficult to meet the implementation of large-scale regional hydraulic punching of directional long boreholes and cannot achieve an ideal gas drainage effect. Summary of the Invention

[0004] To overcome at least one deficiency in the prior art, this application provides a method for pre-draining gas from coal roadway strips by hydraulic punching with comb-shaped holes in the floor through well-ground combination.

[0005] The method for pre-draining gas from coal roadway strips by hydraulic punching with comb-shaped holes in the floor through well-ground combination includes:

[0006] Step 1: According to the planned position of the coal roadway, arrange underground drill sites, and design comb-shaped boreholes in the coal seam floor and well-ground connection wells; the comb-shaped boreholes in the coal seam floor include multiple main holes, and each main hole is provided with multiple branch holes;

[0007] Step 2: Construct the well-ground connection well to achieve the connection between the ground and the underground drill site;

[0008] Step 3: For any main hole, construct an opening section of the main hole and install a gas-water separation device;

[0009] Step 4: Construct the second opening section of the main hole and the branch holes;

[0010] Step 5: Use ground hydraulic punching equipment to conduct hydraulic flushing on the branch holes through the well-ground connection well, and synchronously use the gas-water separation device to separate gas, water, and coal;

[0011] Step 6, return to Step 3, construct the next main hole until all main holes are constructed to drain the gas in the coal roadway strip underground.

[0012] In one embodiment, the extension direction of the main hole is consistent with the direction of the coal roadway strip; the inclination angle of the main hole is upward; the main hole horizon is arranged at a position of a first distance below the coal seam floor;

[0013] Among the multiple main holes, the main hole located at the central position is arranged along the center line of the coal roadway, and the other main holes are symmetrically arranged on both sides; each branch hole opens upward, and the end point of the branch hole is at a second distance from the roof of the target coal seam.

[0014] In one embodiment, the well - to - surface communication well is an L - shaped directional well, connecting the ground and the underground drill site; the well - to - surface communication well includes a vertical section, a build - up section and a horizontal section, and the extension direction of the horizontal section is consistent with the direction of the coal roadway strip.

[0015] In one embodiment, Step 2, construct the well - to - surface communication well to achieve the connection between the ground and the underground drill site, including:

[0016] Step 21, conduct construction at the ground opening position, and the wellbore structure includes the first opening and the second opening; the first opening is constructed to a third distance below the bedrock surface, and the second opening constructs the vertical section, the build - up section and the horizontal section;

[0017] Step 22, according to the design point where the horizontal section extends to one side of the roadway, use a directional drilling rig to open a hole and drill at the point in the underground drill site to butt - joint the horizontal section and achieve the connection between the horizontal section and the underground drill site;

[0018] Step 23, lower a steel pipe casing from the ground, install a guide shoe at the end of the steel pipe casing. When the guide shoe completely extends out a fourth distance from one side of the roadway, stop lowering the casing, remove the guide shoe, and install a flange;

[0019] Step 24, conduct cementing on the completed well - to - surface communication well.

[0020] In one embodiment, Step 24, conduct cementing on the completed well - to - surface communication well, including:

[0021] Plug the two ends of the horizontal section with bagged polyurethane for sealing, and then use a quarter - inch grouting pipe and a gas guide pipe to grout and seal the annulus between the two ends of the bagged polyurethane;

[0022] Conduct conventional cement slurry cementing from the ground to form a cement sheath for the vertical section and the build - up section.

[0023] In one embodiment, Step 4, construct the second - opening section of the main hole and the branch holes, including:

[0024] The main holes are constructed in sequence from near to far, that is, after a section of the main hole is constructed, the drill bit is adjusted upward to drill the branched holes; after the branched holes are drilled, the drill returns to the main hole to drill the next section of the main hole until all the branched holes are drilled.

[0025] In one embodiment, in step 5, a ground hydraulic punching device is used to perform hydraulic flushing on the branched holes through the well-ground connection well, and a coal gas-water separation device is synchronously used for coal gas-water separation, including:

[0026] The coiled tubing workover rig on the ground is connected to the hydraulic punching tool string. The hydraulic punching tool string enters from the well-ground connection well, passes through the underground drill field, and reaches the starting position of the branched hole punching.

[0027] Multiple punching sections are set in the branched holes. For each punching section, the high-pressure pump is turned on, and high-pressure abrasive rotary jet punching is carried out by means of coiled tubing dragging. The punching displacement is 3-4 m 3 / min, and the sand addition concentration is 3%-5%;

[0028] During the punching process, coal, sand, water and gas enter the coal gas-water separation device for coal gas-water separation.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] 1. The present application arranges comb-shaped boreholes in the coal seam floor along the coal roadway strip, constructs a well-ground combined hydraulic punching channel, combines the ground hydraulic punching capacity with the underground coal seam floor comb-shaped branched holes, realizes regional large-scale gas drainage, saves the cost of arranging the bottom drainage roadway, and avoids intensive drilling in the bottom drainage roadway.

[0031] 2. The present application constructs a well-ground connection well, and uses a high-pressure pump with large displacement, high pressure and sand addition on the ground to perform high-intensity fixed-point punching and cavity forming on the underground coal seam floor comb-shaped branched holes. Compared with the conventional small-displacement and low-pressure punching underground, the punching distance is increased, the amount of coal punched out is increased, the coal seam gas pressure in the coal roadway strip is released to a greater extent, and the gas permeability is improved.

[0032] 3. The present application performs hydraulic punching on the ground, but the coal, water and gas ejected and broken by the upward punching of the branched holes flow downward into the main hole of the comb-shaped hole, and then return to the mature coal, gas and water separation and treatment system underground for real-time treatment, avoiding the problems that the broken coal and rock debris have a long migration distance, a large height difference, and cannot leave the bottom of the hole in time under the action of the pressure difference, and there is no need to arrange a mud pit and a gas drainage pipeline on the ground. Description of the Drawings

[0033] The present application can be better understood by referring to the description given below in conjunction with the accompanying drawings. The drawings, together with the following detailed description, are included in this specification and form a part of this specification. In the drawings:

[0034] Figure 1 It shows the flow chart of the method for pre-draining the gas in the coal roadway strip by hydraulic punching with comb-shaped holes in the floor of the well-ground combined method;

[0035] Figure 2 It shows the design schematic diagram of the comb-shaped boreholes in the coal seam floor and the well-ground connection wells;

[0036] Figure 3 It shows the schematic diagram of the branch holes;

[0037] Figure 4 It shows the schematic diagram of the well-ground connection wells;

[0038] Figure 5 It shows the schematic diagram of the cementing of the horizontal section of the well-ground connection wells;

[0039] Figure 6 It shows the schematic diagram of the construction of the main hole;

[0040] Figure 7 It shows the schematic diagram of the hydraulic flushing of the branch holes;

[0041] Figure 8 It shows the schematic diagram after the hydraulic flushing of all the branch holes of the main hole. Specific embodiments

[0042] In the following, the exemplary embodiments of the present application will be described in conjunction with the accompanying drawings. For clarity and conciseness, not all features of the actual embodiments are described in the specification. However, it should be understood that many embodiment-specific decisions may be made during the development of any such actual embodiment to achieve the specific goals of the developer, and these decisions may vary with different embodiments.

[0043] Here, it should also be noted that in order to avoid obscuring the present application with unnecessary details, only the device structures closely related to the solution of the present application are shown in the drawings, and other details less related to the present application are omitted.

[0044] It should be understood that the present application is not limited to the described embodiments only due to the following description with reference to the drawings. In this document, where feasible, the embodiments can be combined with each other, features can be replaced or borrowed between different embodiments, and one or more features can be omitted in one embodiment.

[0045] The embodiments of the present application provide a method for pre-draining the gas in the coal roadway strip by hydraulic punching with comb-shaped holes in the floor of the well-ground combined method, Figure 1 It shows the flow chart of the method for pre-draining the gas in the coal roadway strip by hydraulic punching with comb-shaped holes in the floor of the well-ground combined method, see Figure 1 , and the method includes:

[0046] Step 1: According to the planned position of the coal roadway, arrange underground drill sites, and design comb-shaped boreholes in the coal seam floor and wellbore-ground connection wells; the comb-shaped boreholes in the coal seam floor include multiple main holes, and each main hole is provided with multiple branch holes.

[0047] Here, according to the position of the coal seam roadway in the working face designed according to the coal mine excavation plan, use the opened cross-cut for uncovering coal in the underground to arrange the underground drill site; the cross-cut for uncovering coal is a rock roadway developed for uncovering the coal seam.

[0048] Figure 2 The design schematic diagrams of the comb-shaped boreholes in the coal seam floor and the wellbore-ground connection wells are shown. The extension direction of the main holes is consistent with the direction of the coal roadway strip to ensure covering the gas drainage range of the coal seam in the coal roadway strip (15 m outside the contour lines on both sides of the roadway); the inclination angle of the main holes is upward, which is beneficial to the backflow of the coal slag during subsequent hydraulic punching and to avoid water accumulation in the holes; the main hole layer is arranged at a position 3 - 7 m below the coal seam floor;

[0049] Among the multiple main holes, the main hole located in the central position is arranged along the center line of the coal roadway, and the other main holes are symmetrically arranged on both sides. The distance between the other main holes and the center line of the coal roadway is 10 m; each branch hole opens upward, and the end point of the branch hole is 0.5 m away from the roof of the target coal seam. The multiple branch holes are evenly arranged with a spacing of 10 - 20 m. Figure 3 The schematic diagram of the branch holes is shown.

[0050] The wellbore-ground connection well is an L-shaped directional well that connects the ground and the underground drill site; the wellbore-ground connection well includes a vertical section, a build section, and a horizontal section, and the extension direction of the horizontal section is consistent with the direction of the coal roadway strip. Figure 4 The schematic diagram of the wellbore-ground connection well is shown.

[0051] According to the layout of the underground drill site, design the opening position of the main hole and the end hole position of the wellbore-ground connection well, and keep the elevation the same to facilitate their connection through pipelines.

[0052] Step 2: Construct the wellbore-ground connection well to achieve the connection between the ground and the underground drill site. Specifically, it includes the following steps:

[0053] Step 21: Conduct construction at the opening position on the ground. The wellbore structure includes the first opening and the second opening; in the first opening, construct to 10 - 15 m below the bedrock surface, with a bit size of Φ241.3 mm, and set the casing size of Φ193.7 mm, and conduct conventional cementing; in the second opening, construct the vertical section, the build section, and the horizontal section, with a bit size of Ф171.4 mm, and drill the end hole of the horizontal section to 10 m away from the underground roadway; after the second opening is completed, displace the wellbore mud with gas-based fluid;

[0054] Step 22: According to the designed point position where the horizontal section extends to one side of the roadway, use a directional drilling rig to conduct opening drilling at the point position in the underground drill site, dock with the horizontal section, and achieve the connection between the horizontal section and the underground drill site;

[0055] Step 23: Lower a steel pipe casing into the ground. The size of the steel pipe casing is Ф139.7mm. An underreamer is installed at the end of the steel pipe casing. When the underreamer completely extends 30 cm out of one side of the roadway, stop lowering the casing, remove the underreamer, and install a flange.

[0056] Step 24: Cement the completed wellbore connecting well.

[0057] Specifically, Figure 5 Fig. shows the schematic diagram of cementing the horizontal section of the wellbore connecting well. Cementing of the wellbore connecting well is divided into two steps.

[0058] First step: In the underground drill field, use the "two plugs and one injection" method to grout and seal the holes in the horizontal section. Polyurethane bags are respectively stuffed at both ends of the horizontal section for plugging, and then the annular space between the two polyurethane bags is grouted and sealed using a quarter-inch grouting pipe and a gas guide pipe.

[0059] Conventionally grout and cement the well from the ground to form a cement sheath in the vertical well section and the build-up section. Thus, the wellbore connecting well is constructed and connected to the underground drill field.

[0060] Step 3: For any main hole, construct an open-hole section of the main hole and install a gas-water separation device.

[0061] Figure 6 Fig. shows the schematic diagram of main hole construction. The borehole is located in the stable rock stratum at the coal seam floor, is a small-angle upward hole, the distance from the coal seam floor is controlled within 3 - 7m, the size of the first-opening bit is Ф120mm, drill for 25 - 30m, ream to Ф200mm, lower a Ф139.7mm casing, and grout and cement the casing.

[0062] After the completion of the first-opening structure, install a coal, water, and gas separation device at the hole mouth. The coal, water, and gas separation device is a commonly used device for underground gas drainage, including a four-way device. Its upper channel is provided with a gas extraction outlet, which is connected to the underground negative-pressure gas drainage system. The lower channel is provided with coal and water outlets, and the coal slag and water are led out to the nearby sedimentation tank through a conveying pipe. The left and right channels are respectively connected to the wellbore connecting well end and the comb-shaped hole end at the coal seam floor. Under the premise that the space in the underground drill field permits, the separation device with a large volume and large-diameter channels is selected in this application to facilitate the handling of a large amount of returned coal, water, and gas under the condition of large-displacement hydraulic punching in a multi-hole area.

[0063] Step 4: Construct the second open-hole section of the main hole and the branch holes.

[0064] Specifically, the main hole is constructed sequentially from near to far, that is, after constructing a section of the main hole, adjust the drill bit upward to drill the branch hole; after the branch hole is drilled, retreat to the main hole to drill the next section of the main hole until all branch holes are drilled.

[0065] Use a directional drilling rig at the underground drilling site to construct the second open - hole section to the starting point of the first branch hole. The bit size for the second open - hole is Ф120mm. To facilitate subsequent hydraulic flushing and slag discharge, the main hole section of the second open - hole can be reamed to Ф200mm.

[0066] Select a positive displacement motor with a 1.75° bend angle. At the starting point of the branch hole, adjust the bending direction of the bit to build an inclined branch hole upwards. Stop drilling when the branch hole reaches 0.5m above the coal seam roof, and withdraw the underground drilling tools.

[0067] Step 5: Use the ground hydraulic flushing equipment to conduct hydraulic flushing of the branch hole through the well - to - surface communication well, and synchronously use a gas - water separation device to separate coal, gas, and water.

[0068] Specifically, Figure 7 The figure shows a schematic diagram of hydraulic flushing of the branch hole. First, connect the well - to - surface communication well end to the coal, water, and gas separation device to form a hydraulic flushing channel that is connected above and below the well. Use pipe fittings that match the casing flange at the well - to - surface communication well end and one end of the coal, water, and gas separation device. The outer diameter of the pipe fittings is not less than Ф139.7mm.

[0069] Then, use the ground equipment for hydraulic flushing. The ground equipment includes a coiled tubing service truck, a high - pressure pump, a sand - mixing truck, and a liquid tank. The flushing tool string includes a guide shoe, a spray gun, and a safety joint. A rotatable nozzle is installed on the spray gun. The ground coiled tubing operation machine is connected to the hydraulic flushing tool string. The hydraulic flushing tool string enters from the well - to - surface communication well, passes through the underground drilling site, and reaches the starting position of flushing the branch hole. The starting position of flushing is the point where each branch hole meets the target coal seam.

[0070] Multiple flushing sections are set in the branch hole. For each flushing section, start the high - pressure pump on the ground with a large displacement, high pressure, and sand - adding function, and use the coiled tubing dragging method to conduct high - pressure abrasive rotary jet flushing. The flushing displacement is 3 - 4m 3 / min, and the sand - adding concentration is 3% - 5%. The spacing between multiple flushing sections is 0.5 - 1m. The flushing time is determined according to the amount of coal powder returned. Ensure that the coal output of each flushing section is not less than 2t. When the coal return volume reaches the requirement, communicate in real - time between the wellhead and the underground, stop adding sand, reduce the displacement, push the tool to the next flushing section, increase the displacement, add sand, and continue flushing.

[0071] During the flushing process, coal, sand, water, and gas enter the gas - water separation device for coal, gas, and water separation.

[0072] During the flushing of the branch hole, according to the coal powder return situation at the wellhead, timely disturb the coal and sand in the hole by pulling up and pushing down the coiled tubing operation, which is beneficial to the normal discharge of coal, sand, water, and gas.

[0073] After the branch hole flushing is completed, withdraw the flushing tool to the vertical well section of the well - to - surface communication well, and remove the pipe fittings connecting the well - to - surface communication well end and the coal, water, and gas separation device.Figure 8 It shows a schematic diagram after hydro-flushing all the branch holes of the main hole.

[0074] Step 6: Return to Step 3 to construct the next main hole until all the main holes are constructed, and extract the gas in the underground coal roadway strip.

[0075] For all the main holes arranged in the coal roadway strip and their included branch holes, repeat Steps 3 to 5 in sequence, with alternating operations underground and on the ground to complete the hydro-punching.

[0076] For the comb-shaped holes in the coal seam floor completed by the combined underground and surface hydro-punching, remove the pipe fittings connecting the wellbore-ground communication well end to the coal, water, and gas separation device, install a sealing plug, and use the underground negative-pressure gas drainage system to continuously drain the gas from the boreholes.

[0077] In summary, the present application has the following beneficial effects:

[0078] 1. The present application arranges comb-shaped boreholes in the coal seam floor along the coal roadway strip, constructs a combined underground and surface hydro-punching channel, combines the surface hydro-punching capacity with the underground comb-shaped branch holes in the coal seam floor, realizes regional large-scale gas drainage, saves the cost of arranging bottom drainage roadways, and avoids intensive drilling in the bottom drainage roadways.

[0079] 2. The present application constructs a wellbore-ground communication well, and uses a high-pressure pump with large displacement, high pressure, and sand addition on the ground to perform high-intensity fixed-point punching and cavity formation on the underground comb-shaped branch holes in the coal seam floor. Compared with the conventional small-displacement and low-pressure punching underground, the punching distance is increased, the amount of coal punched out is increased, the gas pressure of the coal seam in the coal roadway strip is released to a greater extent, and the permeability is improved.

[0080] 3. The present application performs hydro-punching on the ground, but the coal, water, and gas ejected and broken by the upward branch hole punching flow downward into the main hole of the comb-shaped hole, and then return to the mature coal, gas, and water separation and treatment system underground for real-time treatment, avoiding the problems that the broken coal and rock debris have a long migration distance, a large height difference, and cannot leave the bottom of the hole in time under the action of the pressure difference, and there is no need to arrange a slurry pond and gas drainage pipelines on the ground.

[0081] The above are only various embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claimed rights.

Claims

1. A method for pre-extracting gas from coal lane strips by hydraulic punching of comb-shaped holes in the floor of a well and ground, characterized in that: include: Step 1: Arrange the underground drilling site according to the planned location of the coal roadway, and design the comb-shaped drill holes on the coal seam floor and the well-ground connecting well; the comb-shaped drill holes on the coal seam floor include a plurality of main holes, and each main hole is provided with a plurality of branch holes; Step 2: construct a well-ground connecting well to achieve connection between the ground and the underground drilling site; Step 3, for any main hole, construct an opening section of the main hole and install a gas-water separation device; Step 4, construct the second opening section of the main hole and the branch hole; Step 5, using ground hydraulic punching equipment to hydraulically flush the branch holes through the well-ground connecting well, and simultaneously using a gas-water separation device to separate the coal, water and gas; Step 6, return to step 3 and construct the next main hole until all main holes are completed and the coal lane strip gas is extracted underground.

2. The method according to claim 1, characterized in that The extension direction of the main hole is consistent with the direction of the coal roadway strip; the inclination angle of the main hole is inclined upward; the main hole layer is arranged at a position of a first distance below the coal seam floor; The central main hole among the multiple main holes is arranged along the center line of the coal roadway, and the other main holes are symmetrically arranged on both sides; each branch hole is opened upward, and the terminal point of the branch hole is the second distance from the target coal seam roof.

3. The method according to claim 1, characterized in that The well-to-ground connecting well is an L-shaped directional well, connecting the ground and the underground drilling site; the well-to-ground connecting well includes a vertical well section, a deflection section and a horizontal section, and the extension direction of the horizontal section is consistent with the direction of the coal roadway strip.

4. The method according to claim 1, characterized in that Step 2: construct a well-ground connecting well to achieve the connection between the ground and the underground drilling site, including: Step 21, construction is performed at the surface opening position, and the wellbore structure includes a first opening and a second opening; the first opening is constructed to a third distance below the bedrock surface, and the second opening is constructed to construct a vertical well section, a deflection section, and a horizontal section; Step 22, according to the design point where the horizontal section extends to the side of the tunnel, a directional drill is used in the underground drilling site to drill a hole at the point, and the horizontal section is connected to the underground drilling site to achieve the connection between the horizontal section and the underground drilling site; Step 23, lower the steel pipe casing from the ground, install the guide shoe at the end of the steel pipe casing, and when the guide shoe is fully extended out of the tunnel by a distance of one fourth, stop lowering the casing, remove the guide shoe, and install the flange; Step 24, cementing the completed well-ground connecting well.

5. The method according to claim 4, characterized in that Step 24, cementing the completed well-ground connecting well, includes: The two ends of the horizontal section are respectively plugged with bagged polyurethane for plugging, and then the annulus between the bagged polyurethane at both ends is grout-sealed using a four-point grouting pipe and an air guide pipe; Conventional cementing is carried out from the ground to form cement sheaths in the vertical well section and the deflection section.

6. The method according to claim 1, characterized in that Step 4, constructing the second opening section of the main hole and the branch hole, including: The main hole is constructed from near to far, that is, after one section of the main hole is constructed, the drill bit is adjusted upward to drill the branch hole; after the branch hole is drilled, it returns to the main hole to drill the next section of the main hole until all the branch holes are drilled.

7. The method according to claim 1, characterized in that Step 5, using the ground hydraulic punching equipment to hydraulically flush the branch holes through the well-ground connecting well, and simultaneously using the gas-water separation device to separate the coal, water and gas, including: The surface coiled tubing operation machine is connected to the hydraulic punching tool string, which enters from the well-ground connecting well, passes through the downhole drilling site, and reaches the starting position of the branch hole punching; The branch hole is provided with a plurality of punching sections. For each punching section, a high-pressure pump is turned on and a high-pressure abrasive rotary jet punching is performed by means of continuous tubing dragging. The punching displacement is 3 to 4 m 3 / min, the sand concentration is 3% to 5%; During the punching process, coal, sand, water and gas enter the gas-water separation device for coal-water-gas separation.

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