A drilling device and drilling method for underground gas hole

Abstract

The present invention discloses a drilling device and a drilling method for an underground gas hole. First, a casing hole is drilled in a drainage area, a sealing casing is sealed and fixed at the hole mouth, and then a drilling device is connected to the sealing casing. When drilling, a coolant is pressurized and injected into the borehole through a hollow drill rod to support the hole wall. After the hole in the rock formation section is penetrated, a wall-protecting mud is pressurized and injected into the rock formation to form a certain hydrostatic pressure in the hole, which can stabilize the rock wall. After entering the coal seam, clear water drilling is adopted. Water slag generated during the drilling process is separated by a water slag separation device to realize the secondary utilization of resources. When drilling to the final hole, the drainage pipeline is replaced under the pressurized state in the hole to carry out slow pressure reduction drainage. The slow pressure reduction drainage method can avoid the problem of speed-sensitive effect and blockage of the hole wall gap, reduce the attenuation efficiency of the gas amount in the gas hole, and improve the gas extraction amount.

Description

Technical Field

[0001] The invention relates to the technical field of underground gas extraction in coal mines, and in particular to an underground gas hole drilling device and a drilling method thereof. Background Art

[0002] Gas extraction in coal mines with high gas content can reduce the amount of gas outflow during mining, reduce gas hazards and various gas accidents, and is a preventive measure to ensure safe production. Gas extraction can reduce the burden of ventilation, solve gas problems that are difficult to solve with ventilation, and reduce ventilation costs. Especially for high-gas mines or mining areas, gas extraction is necessary in terms of safety, technology and economy.

[0003] Pre-extraction of coal seam gas in the coal seam and pre-extraction of coal seam gas by drilling holes through the bottom extraction lane are both important means of coal mine gas control and prevention of coal and gas outbursts. The coal body is depressurized by extraction and discharge drilling holes, and the gas pressure and gas content of the coal body are reduced by extraction, so as to achieve the purpose of eliminating outbursts and safe production. However, whether it is extraction of the coal seam, downward extraction of the top rock lane, or upward extraction of the bottom extraction lane, the phenomenon of deformation and collapse of the borehole will often occur during the extraction of coal seam gas, which greatly reduces the drilling rate, reduces the gas extraction efficiency, increases the extraction cost, and seriously limits the progress of gas extraction in the mine. Especially for pre-extraction of coal seam gas by drilling holes through the rock layer and the interface of the coal seam, stress concentration will occur because the borehole will pass through the interface of the rock layer and the coal seam, and the compressive strength and Poisson's ratio of the coal seam and the rock layer are different. The axis of the borehole and the normal of the interface must have a certain angle, so it is very easy to collapse the hole and get stuck, which seriously affects the extraction effect, and the extracted gas concentration is very low.

[0004] For example, in the top slab rock tunnel drilling field of Hudi Coal Industry of Jinmei Group, the down-hole drilling was carried out to pre-extract the strip gas of the 1301 track drift and the belt drift coal tunnel. During the actual drilling construction process, the phenomena of hole collapse, no slag return, and string holes occurred frequently. The drilling hole completion rate was only about 70%, and the concentration of a single hole was basically lower than 30% and decayed quickly. The flow rate of a 100-meter coal hole was only 0.03m 3 / min·hm, which is far from meeting the requirements of safe production in mines; even in the horizontal drilling and extraction of coal seams, there are still problems such as hole collapse, drill sticking, string holes, low concentration in a single hole, and rapid attenuation of gas volume in a single hole. It is necessary to improve them through new technical methods. Summary of the invention

[0005] In view of the problem that underground gas holes are prone to collapse in the prior art, the present invention provides an underground gas hole drilling device and a drilling method thereof, which improves the hole formation rate of the gas hole, improves the gas extraction efficiency, increases the gas extraction concentration, and reduces the extraction cost.

[0006] The present invention is achieved through the following technical solutions:

[0007] A drilling device for underground gas holes, comprising a drill rod, a pressure-maintaining valve, a tee pipe, a dynamic and static combined sealing device, a drilling rig and a water-slag separation device;

[0008] One end of the pressure-maintaining valve is connected to a sealing sleeve installed at the mouth of the gas hole, the other end of the pressure-maintaining valve is connected to the inlet of the tee pipe, the outlet of the tee pipe is connected to one end of the dynamic and static combined sealing device, and the water-slag outlet of the tee pipe is connected to the water-slag separation device;

[0009] The drill rod of the drilling rig passes through the dynamic and static combined sealing device, the tee pipe, the pressure maintaining valve and the sealing casing in sequence to drill into the coal and rock layer. The dynamic and static combined sealing device is used to seal the drill rod and the tee pipe and clamp the drill rod when disassembling the drill rod and drilling, so that the borehole is in a pressurized state.

[0010] Preferably, the water-slag separation device comprises a drainage pipe, a centrifugal water-slag separator and a slag storage cylinder;

[0011] Among them, the centrifugal water-slag separator is connected to the slag liquid output port of the three-way pipe through the water-slag inlet pipe, a drain pipe is arranged on the top of the centrifugal water-slag separator, the slag discharge port of the centrifugal water-slag separator is connected to the inlet of the slag storage drum through a gate valve, and a slag discharge gate valve is arranged at the outlet of the slag storage drum. When the water-slag is separated, the gate valve and the slag discharge gate valve are opened alternately.

[0012] Preferably, the drainage pipe is also provided with a water pressure regulating valve for adjusting the drainage rate and the pressure in the borehole.

[0013] Preferably, the centrifugal water-slag separator is a cylindrical structure, and the end of the water-slag inlet pipe is connected to the tangent point of the outer wall of the centrifugal water-slag separator, so that the water-slag entering the water-slag separator can perform centrifugal rotation along the cylinder wall.

[0014] Preferably, a booster valve is provided between the sealing sleeve and the pressure-maintaining valve, and a pressure gauge is provided on the booster valve;

[0015] The boost valve is a three-way valve, one end of which is connected to the sealing sleeve, and the pressurizing port is connected to the high-pressure water pump through a pipeline.

[0016] The present invention also provides a drilling method of a drilling device for a gas hole in a well, comprising the following steps:

[0017] S1. Drill a hole on the tunnel wall in the gas extraction area of ​​the bottom extraction tunnel, insert a sealing casing at the end of the hole and install a drilling device;

[0018] S2, start the drilling device to perform secondary drilling;

[0019] When the tunnel wall is a rock formation, the drilling is carried out by injecting wall protection mud into the hole through the drill rod to cool the slag removal liquid. After the hole passes through the coal-rock interface by a predetermined distance, the drilling is continued with clear water to cool the slag removal liquid until the hole is completed.

[0020] When the tunnel wall is a coal seam, the drilling is continued by injecting clean water into the hole under pressure through the drill pipe to cool the slag removal liquid until the hole is completed;

[0021] S3. Close the pressure-maintaining valve, and use the high-pressure water pump and the booster valve to replenish the pressure to keep the pressure in the hole unchanged. Then dismantle the drilling device, connect the drainage pipeline system, and reduce the pressure to drain the gas.

[0022] Preferably, in step S1, after the borehole is drilled for 5-50 m, a sealing casing is installed in the hole, and a sealing material is used to fill the gap between the sealing casing and the borehole.

[0023] Preferably, in step S2, the wall-protecting mud cooling and slagging liquid is injected under pressure through the drill pipe to perform drilling, so that the mud forms a layer of wall-protecting mud skin on the hole wall. After the borehole passes through the coal-rock interface by 2-20 meters, the wall-protecting mud cooling and slagging liquid is replaced with clean water cooling and slagging liquid, and drilling is continued until the end of the hole.

[0024] Preferably, in step S3, the drill rod is lengthened or removed section by section through the dynamic and static combined sealing device, and after the drill bit is pulled out of the pressure maintaining valve, the pressure maintaining valve is closed, the dynamic and static combined sealing device, the drilling rig and the water-slag separation device are disassembled, and the drainage pipeline system is connected to the end of the pressure maintaining valve.

[0025] Preferably, the specific method of reducing pressure to drain gas in step S3 is as follows: open the pressure-maintaining valve, start the drainage system, release water to reduce the pressure until the pressure in the hole reaches the set drainage pressure, and continue to drain gas at the set drainage pressure.

[0026] Compared with the prior art, the present invention has the following beneficial technical effects:

[0027] The drilling device for an underground gas hole provided by the present invention comprises a sealing casing which is sealingly installed at the mouth of the gas hole, the sealing casing is connected to one end of a tee pipe, the other end of the tee pipe is connected to a dynamic-static combined sealing device, the dynamic-static combined sealing device is connected to a drilling rig, and when drilling, a cooling slag removal liquid is pressurized into the hole through a hollow drill rod to cool the drill bit, thereby playing a certain supporting role on the hole wall, solving the problem of hole wall collapse, and improving the gas extraction concentration. The drill rod dynamic seal is in the dynamic-static combined sealing device, and when the drill rod is installed or removed, the pressure loss in the hole is avoided, thereby causing the hole wall to collapse. The water slag generated during the drilling process enters the water slag separation device, which is controlled by a valve to separate the water slag without reducing the pressure in the hole, thereby ensuring the porosity of the gas hole.

[0028] The present invention provides a method for drilling a gas hole in a well. First, a sealing casing is lowered into a first borehole in a drainage area, and then a drilling device is connected to the sealing casing. During the second borehole drilling, a hollow drill rod is used to pressurize the borehole and inject wall-protecting mud to cool the slag removal liquid. When the borehole passes through the coal-rock interface, the wall-protecting mud forms a layer of wall-protecting mud on the hole wall to support the hole wall. At the same time, the wall-protecting mud cooling slag removal liquid forms a certain hydrostatic pressure in the hole, which can stabilize the rock wall. After entering the coal seam, clear water drilling is adopted. When drilling to the end hole, the drainage pipeline is replaced under the pressurized state in the hole to carry out slow pressure reduction drainage. The slow pressure reduction drainage method can avoid the problem of speed-sensitive effect and blockage of the hole wall gap, and reduce the attenuation efficiency of the gas amount in the gas hole. At the same time, positive pressure drainage is adopted to increase the concentration of gas and also increase the gas extraction amount. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a diagram showing the use status of the drilling device of the present invention;

[0030] Figure 2 It is a structural diagram of the residue leaf separation device of the present invention.

[0031] In the figure: 1. drill rod; 2. rock mass; 3. sealing material; 4. sealing casing; 5. pressure maintaining valve; 6. tee pipe; 7. dynamic and static combined sealing device; 8. water-slag separation device; 9. water pressure regulating valve; 10. drain pipe; 11. centrifugal water-slag separator; 12. water-slag inlet pipe; 13. gate valve; 14. slag storage cylinder; 15. slag discharge gate valve; 16. slag discharge port; 17. drilling rig. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below in conjunction with the accompanying drawings, which are intended to explain the present invention rather than to limit it.

[0033] See also Figure 1 and Figure 2 A drilling device for underground gas holes includes a drill rod 1, a sealing casing 4, a pressure-maintaining valve 5, a tee pipe 6, a dynamic and static combined sealing device 7, a drilling rig 17 and a water-slag separation device.

[0034] Among them, the drill rod 1 is connected to the drilling rig 17. The drill rod 1 is a hollow structure. When drilling, coolant will be pressurized and supplied to the hole in the coal rock layer through the inner hole of the drill rod 1 to cool the drill bit at the end of the drill rod 1. At the same time, the coolant can flush the cut rock chips out of the drill hole and play a role in supporting the hole wall.

[0035] The sealing sleeve 4 is sealed and sleeved on the mouth of the gas hole, the mouth of the sealing sleeve 4 is connected to one end of the pressure-maintaining valve 5, the other end of the pressure-maintaining valve 5 is connected to the inlet of the tee pipe 6, the outlet of the tee pipe 6 is connected to one end of the dynamic-static combined sealing device 7, and the drill pipe 1 of the drilling rig 17 passes through the dynamic-static combined sealing device 7, the tee pipe 6, the pressure-maintaining valve 5 and the sealing sleeve 4 in sequence to drill the coal seam.

[0036] The pressure-maintaining valve 5 is in a normally open state during the drilling process, and the drill rod 1 passes through the pressure-maintaining valve 5 for drilling operations. When the drilling is completed, the three-way pipe 6, the static combined sealing device 7 and the drilling rig 17 need to be disassembled and the gas drainage pipeline replaced. At this time, the pressure-maintaining valve is in a closed state, which is used to keep the borehole in a pressurized state to prevent the gas hole from collapsing.

[0037] The dynamic and static combined sealing device 7 is used to seal the drill pipe and the tee pipe 6 during the process of disassembling and assembling the drill pipe 1 and drilling, so that the borehole is in a pressurized state. The dynamic and static combined sealing device 7 is a pressurized operating sealing device, preferably an oil field pressurized operating sealing device.

[0038] The water-slag separation device 8 includes a water pressure regulating valve 9 , a drain pipe 10 , a centrifugal water-slag separator 11 and a slag storage cylinder 14 .

[0039] Among them, a water-slag inlet pipe 12 is provided on the centrifugal water-slag separator 11, one end of the water-slag inlet pipe 12 is connected to the centrifugal water-slag separator 11, and the other end of the water-slag inlet pipe 12 is connected to the slag liquid outlet of the three-way pipe 6. The water slag enters the centrifugal water-slag separator 11 through the water-slag inlet pipe 12 for water-slag separation.

[0040] The centrifugal water-slag separator 11 is a cylindrical structure, and the lower end is a truncated cone structure. A drain pipe 10 is provided at the top of the centrifugal water-slag separator 11, and a water pressure regulating valve 9 is provided at the outlet of the drain pipe 10. The water pressure regulating valve 9 can adjust the pressure in the gas hole during the drilling operation to prevent the processed hole from collapsing due to pressure reduction during the drilling process. The outlet of the water pressure regulating valve 9 is connected to a water storage tank, and the discharged water is precipitated and purified in the water storage tank for secondary use.

[0041] The end of the water-slag inlet pipe 12 is connected to the tangent point of the outer wall of the centrifugal water-slag separator 11. The water-slag enters the centrifugal water-slag separator 11 under pressure, and the water rotates and flows along its side wall. The slag is precipitated to the bottom of the centrifugal water-slag separator 11, thereby realizing centrifugal separation of the water-slag. The separated water is discharged to the water storage tank through the drain pipe.

[0042] The bottom outlet of the centrifugal water-slag separator 11 is provided with a gate valve 13, the outlet of the gate valve 13 is connected to the inlet of the slag storage cylinder 14, and the bottom outlet of the slag storage cylinder 14 is provided with a slag discharge gate valve 15, which is connected to the slag discharge port.

[0043] After the water slag is separated in the centrifugal water slag separator 11, the gate valve 13 is opened, and the slag enters the slag storage cylinder 14 through the gate valve 13. Since the slag discharge gate valve 15 is closed, the pressure in the borehole will not be reduced, thereby avoiding the collapse of the gas hole caused by the pressure reduction.

[0044] After the slag enters the slag storage tube 14, the gate valve 13 is closed, and then the slag discharge gate valve 15 is opened to discharge the slag from the slag discharge port 16. During this process, since the gate valve 13 is closed, the pressure in the borehole will not be reduced, thereby avoiding the collapse of the gas hole caused by the pressure reduction.

[0045] Furthermore, in order to prevent the gas hole pressure from decreasing during the disassembly of the drilling rig 17 and the slag removal process, the disassembly of the drill rod and the extraction of gas, a booster valve is provided between the sealing casing 4 and the pressure maintaining valve. The booster valve is a three-way valve, the inlet end of which is connected to the sealing casing 4, the outlet end of which is connected to the pressure maintaining valve 5, the pressurization port of which is connected to the high-pressure water pump through a liquid pipeline, and the coolant is pressurized and injected into the gas hole through the liquid pipeline to adjust the pressure in the gas hole.

[0046] Furthermore, in order to facilitate monitoring of the pressure in the gas hole, a pressure gauge is provided on the pressure-maintaining valve 5 for checking the pressure in the gas hole.

[0047] The drilling device provided by the present invention comprises a sealing sleeve which is sealed and installed at the hole mouth position, the sealing sleeve is connected to one end of the tee pipe, the other end of the tee pipe is connected to the dynamic and static combined sealing device, the dynamic and static combined sealing device is connected to the drilling rig, and when drilling, the hole is pressurized and injected with cooling slag removal liquid through the hollow drill rod to cool the drill bit, thereby extending the service life of the drill bit and at the same time playing a certain supporting role on the hole wall to solve the problem of hole wall collapse. The drill rod dynamic seal is in the dynamic and static combined sealing device, and when installing or disassembling the drill, the pressure reduction loss in the hole is avoided, thereby causing the hole wall to collapse. The water slag generated during the drilling process enters the water slag separation device, which is controlled by a valve to separate the water slag without reducing the pressure in the hole, thereby ensuring the porosity of the gas hole.

[0048] The gas hole drilling method provided by the present invention is described in detail below.

[0049] A method for drilling a gas hole underground comprises the following steps:

[0050] S1. Drill a hole in the coal seam or rock stratum in the gas extraction area of ​​the bottom extraction lane, and seal the hole casing 4 at the mouth of the hole. The specific method is as follows:

[0051] First, use a 120mm drill bit to drill 5-50m upward at a certain angle in the rock layer 2 of the top plate of the bottom extraction tunnel, or drill horizontally in the coal rock layer, insert a sealing casing 4 into the hole, fill the sealing material 3 between the sealing casing and the hole, and seal and fix the sealing casing. The sealing and fixing should meet the pressure requirements in the hole.

[0052] S2. Connect a drilling device to the end of the sealing casing 4.

[0053] The end of the sealing casing 4 is connected to the pressure-maintaining valve 5, the other end of the pressure-maintaining valve is connected to the tee 6, the other end of the tee 6 is connected to the dynamic-static combined sealing device 7, the slag liquid outlet of the tee 6 is connected to the water-slag separation device, the drilling rig 17 is arranged at the other end of the dynamic-static combined sealing device 7, and the drill rod of the drilling rig 17 passes through the dynamic-static combined sealing device 7 and extends into the casing hole.

[0054] S3, start the drilling device to perform secondary drilling

[0055] When the tunnel wall is a rock formation, the drill pipe is used to pressurize the hole to inject wall protection mud cooling and slag removal liquid to drill. After the hole passes through the coal-rock interface for a certain distance, clean water is used to cool the slag removal liquid until the end of the hole.

[0056] When the tunnel wall is a coal seam, the drilling is continued by injecting clean water into the hole under pressure through the drill pipe to cool the slag removal liquid until the hole is completed;

[0057] During the drilling process, a drill rod is installed through the dynamic and static combined sealing device 7 to control the drilling depth of the hole, and the water-slag separation device separates the discharged water-slag.

[0058] The details are as follows:

[0059] The drill bit diameter used in the second drilling is smaller than that in the first drilling. In the second drilling, a drill bit with a diameter of 94 mm is used to drill according to the designed trajectory to the final hole of the designed length.

[0060] During the drilling process, the drilling machine 17 supplies 1.5-10MPa cooling and slag removal liquid into the coal and rock formation hole through the hollow drill rod 1, which is used to cool the drill bit and flush out the rock debris generated during drilling. At the same time, the cooling and slag removal liquid can balance the hole wall and formation pressure to prevent the hole wall from falling off and collapsing. The dynamic and static combined sealing device 7 can seal the drill rod 1 and the sealing casing 4 when drilling, replacing the drill rod and the drill rod joint, to prevent the pressure in the hole from being lower than the predetermined pressure, causing the hole to collapse.

[0061] The predetermined pressure is greater than the gas decomposition pressure and less than the formation pressure.

[0062] When drilling in rock formations, wall-protecting mud is used to cool the slag removal liquid. The wall-protecting mud is injected under pressure through the drill pipe. Because the mud can form a supporting and protective mud skin on the hole wall, the injection of the wall-protecting mud generates a certain hydrostatic pressure in the hole, which can stabilize the rock wall and prevent the hole from collapsing. In addition, the mud can also fill the gaps in the drill wall tightly, forming a dense mud skin with very low permeability, avoiding water leakage on the inner wall of the hole and maintaining a certain water pressure in the hole, which helps to maintain the stability of the hole wall. In addition, the mud has a high viscosity. Through the circulation of the mud, the cut and broken soil and stone debris can be suspended and discharged out of the hole along with the mud, playing the role of carrying slag and discharging soil. At the same time, since the mud circulates as a flushing fluid, it has a cooling and lubricating effect on the drill bit, reducing the wear of the drill bit.

[0063] After the borehole passes through the coal-rock interface 2-20 meters, clean water pressure drilling is used until the end of the hole.

[0064] When entering the coal seam, clean water is injected as a coolant through the drill pipe under pressure to carry out drilling operations until the end of the hole. Clean water is used as a coolant to avoid filling the gaps in the hole wall, which will prevent the gas from being discharged. The drilling allows the discharged water slag to enter the water slag separation device for separation.

[0065] The water slag enters the three-way pipe through the pressure-maintaining valve 5, and enters the centrifugal water-slag separator 11 from the three-way pipe 6 for water-slag separation. The separated water enters the water pressure regulating valve 9 and is discharged to the water storage tank. At the same time, the drainage volume is adjusted by adjusting the opening of the water pressure regulating valve 9 to maintain the pressure in the hole and avoid the collapse of the hole wall.

[0066] When the amount of slag in the centrifugal water-slag separator 11 reaches a certain amount, open the gate valve 13, close the slag discharge gate valve 15, and discharge the slag into the chip storage bucket 14 while maintaining the pressure in the hole. Close the gate valve 13, open the slag discharge gate valve 15, and the slag is discharged from the slag discharge port 16. When the slag discharge is completed, close the slag discharge gate valve 15, and repeat this step until the end of the hole.

[0067] During the process of removing slag or installing drill pipe, it is easy to cause a certain pressure drop in the hole. The pressure in the hole is monitored in real time through the pressure valve. When the pressure is lower than the preset pressure, the liquid pipeline is connected through the booster valve to pressurize the hole and inject liquid to keep the pressure in the hole at the preset pressure.

[0068] During the installation of the drill pipe, the water pressure regulating valve 9 is closed to prevent the pressure in the hole from decreasing.

[0069] S4. While keeping the pressure in the borehole unchanged, dismantle the drilling device and connect the drainage pipeline system.

[0070] The drill pipe is removed section by section through the dynamic and static combined sealing device 7. After the drill bit is pulled out of the pressure-maintaining valve 5, the pressure-maintaining valve 5 is closed, the dynamic and static combined sealing device 7, the drilling rig 17 and the water-slag separation device 8 are disassembled, and the drainage pipeline system is connected to the end of the pressure-maintaining valve 5.

[0071] S5. Open the pressure-maintaining valve 5, start the drainage system, release water to reduce the pressure until the pressure in the hole reaches the set drainage pressure, and continue gas drainage at the set drainage pressure.

[0072] During the drainage process, when the pressure in the gas hole is lower than the preset pressure, the pressure is increased through the booster valve to prevent the hole wall from collapsing. At the same time, the pressure in the gas hole can also be adjusted by adjusting the waterproofing amount.

[0073] During the drainage process, when the reservoir pressure drops below the critical desorption pressure, methane gas is desorbed from the inner surface of the microvoids in the coal matrix, diffuses into the coal fracture system due to the difference in gas concentration, and finally flows into the pores in the form of Darcy flow and is produced through the drainage pipeline system.

[0074] Among them, desorption is the prerequisite for coalbed methane drainage, and pressure reduction is the prerequisite for desorption. It can be seen that whether ground drilling coalbed methane can occur depends on whether the coalbed methane can be depressurized and desorbed. Using positive pressure drainage to change the existing negative pressure drainage can greatly increase the concentration and extraction volume of the drainage gas, while avoiding the problem of blockage of the hole wall gap caused by the speed-sensitive effect, and prolonging the drainage time.

[0075] The present invention provides a method for drilling an underground gas hole. First, a casing hole is drilled in a drainage area, a sealing casing is sealed and fixed at the hole mouth, and then a drilling device is connected to the sealing casing. When drilling, a hollow drill rod is used to pressurize the borehole and inject wall-protecting mud to cool the slag liquid, which plays a role in supporting the hole wall. After the borehole passes through the coal-rock interface, clean water drilling is adopted. The water slag generated during the drilling process is separated by a water-slag separation device to achieve secondary utilization of resources. When drilling to the final hole, the drainage pipeline is replaced in the pressurized state in the hole to carry out slow pressure reduction drainage. The slow pressure reduction drainage method can avoid the problem of speed-sensitive effect and blockage of the hole wall gap, reduce the attenuation efficiency of the gas amount in the gas hole, and improve the gas concentration and extraction amount.

[0076] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A drilling device for underground gas holes, characterized in that: It comprises a drill rod (1), a pressure-maintaining valve (5), a three-way pipe (6), a dynamic and static combined sealing device (7), a drilling rig (17) and a water-slag separation device (8); One end of the pressure-maintaining valve (5) is connected to a sealing sleeve (4) installed at the mouth of the gas hole, the other end of the pressure-maintaining valve (5) is connected to an inlet of a three-way pipe (6), the outlet of the three-way pipe (6) is connected to one end of a dynamic and static combined sealing device (7), and the water-slag outlet of the three-way pipe (6) is connected to a water-slag separation device (8); The drill rod (1) of the drilling rig passes through the dynamic and static combined sealing device (7), the tee pipe (6), the pressure retaining valve (5) and the sealing casing (4) in sequence to drill into the coal and rock layer. The dynamic and static combined sealing device (7) is used to seal the drill rod and the tee pipe (6) and clamp the drill rod when disassembling the drill rod and drilling a hole, so that the hole is in a pressurized state. The water-slag separation device comprises a drainage pipe (10), a centrifugal water-slag separator (11) and a slag storage cylinder (14); The centrifugal water-slag separator (11) is connected to the slag liquid outlet of the three-way pipe (6) through a water-slag inlet pipe (12), a drainage pipe (10) is arranged on the top of the centrifugal water-slag separator (11), the slag outlet of the centrifugal water-slag separator (11) is connected to the inlet of the slag storage cylinder (14) through a gate valve (13), and a slag discharge gate valve (15) is arranged at the outlet of the slag storage cylinder (14). When the water-slag is separated, the gate valve (13) and the slag discharge gate valve (15) are opened alternately; The drainage pipe (10) is also provided with a water pressure regulating valve (9) for regulating the drainage rate and the pressure in the borehole; The drilling method of the underground gas hole drilling device comprises the following steps: S1. Drill a hole on the wall of the gas extraction area of ​​the bottom extraction tunnel, insert a sealing casing (4) into the end of the hole and install a drilling device; S2, start the drilling device to perform secondary drilling; When the tunnel wall is a rock layer, the wall-protecting mud cooling and slag-discharging liquid is injected into the hole by the drill pipe to form a layer of wall-protecting mud skin on the hole wall. After the hole passes through the coal-rock interface for 2-20 meters, the wall-protecting mud cooling and slag-discharging liquid is replaced with clean water cooling and slag-discharging liquid, and drilling continues until the end of the hole; When the tunnel wall is a coal seam, the drilling is continued by injecting clean water into the hole under pressure through the drill pipe to cool the slag removal liquid until the hole is completed; S3, close the pressure-maintaining valve (5), and use the high-pressure water pump and the booster valve to replenish the pressure to keep the pressure in the hole unchanged, dismantle the drilling device, connect the drainage pipeline system, and reduce the pressure to drain the gas; The drill rod is lengthened or removed section by section through the dynamic and static combined sealing device (7), and after the drill bit is pulled out of the pressure-maintaining valve (5), the pressure-maintaining valve (5) is closed, the dynamic and static combined sealing device (7), the drilling rig (17) and the water-slag separation device (8) are disassembled, and the drainage pipeline system is connected to the end of the pressure-maintaining valve (5); The gas drainage method by reducing pressure is as follows: opening the pressure-maintaining valve (5), starting the drainage system, releasing water to reduce the pressure until the pressure in the hole reaches the set drainage pressure, and continuously draining the gas by positive pressure drainage under the set drainage pressure, so as to increase the concentration and extraction volume of the gas, and avoid the problem of blockage of the hole wall gap caused by the speed-sensitive effect, thereby extending the drainage time; During the drainage process, when the pressure in the gas hole is lower than the preset pressure, the pressure is increased through the booster valve to control the drainage pressure.

2. The underground gas hole drilling device according to claim 1, characterized in that: The centrifugal water-slag separator (11) is of a cylindrical structure, and the end of the water-slag inlet pipe (12) is connected to the tangent point of the outer wall of the centrifugal water-slag separator (11), so that the water-slag entering the water-slag separator can perform centrifugal rotation along the cylinder wall.

3. The underground gas hole drilling device according to claim 1, characterized in that: A pressure boosting valve is also provided between the sealing sleeve (4) and the pressure maintaining valve (5), and a pressure gauge is also provided on the pressure boosting valve; The booster valve is a three-way valve, one end of which is connected to the sealing sleeve (4), and the pressurizing port is connected to the high-pressure water pump through a pipeline.

4. The underground gas hole drilling device according to claim 1, characterized in that: In step S1, after the borehole is drilled 5-50 m, a sealing casing (4) is installed in the hole, and a sealing material is used to fill the gap between the sealing casing (4) and the borehole.

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