Method for improving permeability of coal measure strata in mountainous area through cooperation of hydraulic slotting and heat injection balance

Abstract

The invention discloses a method for improving permeability of a coal measure stratum in a mountainous area through cooperation of hydraulic slotting and heat injection balance. The method comprises the steps that a hole is drilled in the coal measure stratum in a tunnel and cleaned; the orifice is sealed and connected with a pipeline; high-pressure water-sand mixed liquid is injected for slotting and groove making, and deslagging and gas extraction are conducted; drilling retreating and multi-position slotting are conducted; after gas extraction, high-temperature and high-pressure steam is injected for permeability increasing, and synchronous extraction is conducted; the drill hole is sealed, the stratum is heated through waste heat, and extraction is monitored to reach the standard; and after the single hole is completed, repeated construction is conducted at the new position, and gas extraction is completed. According to the method, a hydraulic slotting and heat injection synergistic permeability increasing technology is adopted, five mechanisms of high-temperature steam deep penetration, hydraulic slotting pretreatment, high-pressure water preheating, abrasive enhanced cutting and synergistic permeability increasing are fused, a penetration channel is formed through slotting operation, steam penetrates into tiny holes of a coal seam for heating, and efficient desorption of gas is promoted; the cutting efficiency is improved through preheating and abrasive adding, the stratum pressure relief and gas extraction range is remarkably enlarged, the efficiency is improved, and the drilling cost and the safety risk are greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of gas extraction technology in coal-bearing formations, and in particular to a method for improving permeability in mountainous coal-bearing formations through hydraulic fracturing and coordinated heat injection. Background Technology

[0002] Tunneling through coal-bearing strata in mountainous areas faces severe challenges: these strata are characterized by high gas pressure, weak and fractured rock masses, and complex structures, which can easily lead to serious accidents such as coal and gas outbursts, unstable and collapsed surrounding rock, resulting in equipment damage, casualties, delays of several years, and even economic losses of hundreds of millions of yuan. Therefore, effective outburst suppression measures must be carried out before construction.

[0003] Existing gas outburst suppression technologies mainly draw on underground coal mining techniques, but their inherent defects are amplified under complex mountainous conditions: First, there's the intensive borehole drainage method, which involves drilling numerous holes in the coal seam to release gas slowly under its own pressure. While widely used, this requires drilling dozens or even hundreds of holes, resulting in construction periods lasting months and extremely high costs. Second, there's hydraulic fracturing technology, which uses high-pressure water to create fractures in the coal seam, improving gas flow. However, in structural coal formations, this method commonly suffers from severe fracturing fluid loss and uncontrollable fracture orientation. More importantly, the complex geological conditions, limited construction environment, and high risk of coupled disasters in mountainous coal-bearing strata exacerbate these limitations. Traditional methods have a small impact range per hole, long outburst suppression times, and high costs, failing to meet the core requirements of safe, economical, and rapid tunnel crossings, severely restricting the economic benefits and schedule control of engineering projects. Summary of the Invention

[0004] This invention provides a method for hydraulically cleaving and heat injection to improve permeability in coal-bearing strata in mountainous areas. This method addresses the technical problems of high gas pressure, weak and fractured rock mass, and complex geological conditions when tunnels pass through coal-bearing strata in mountainous areas. These problems include the difficulty in eliminating gas outbursts, the low efficiency and high cost of traditional methods, and the potential for serious safety accidents such as coal and gas outbursts and surrounding rock instability.

[0005] In view of the above technical problems, embodiments of the present invention provide a method for hydraulically slotted and heat-injected uniform permeability enhancement in mountainous coal-bearing strata, comprising:

[0006] S1. Drill boreholes into the coal-bearing strata within the tunnel and clean the boreholes;

[0007] S2. At the borehole opening, assemble the sealing device and connect the pipeline;

[0008] S3. Inject high-pressure water-sand mixture into the borehole to perform hydraulic cutting operations, forming multiple slots; discharge the residue and wastewater from the borehole, and simultaneously carry out gas extraction operations.

[0009] S4. Retract the hollow drill rod towards the borehole opening, make multiple cuts, and continuously extract gas from the borehole.

[0010] S5. After a preset time of continuous gas extraction, implement heat injection to enhance permeability by delivering high-temperature and high-pressure steam into the borehole to facilitate heat exchange and promote the expansion of the slots; and simultaneously carry out gas extraction.

[0011] S6. Perform borehole sealing, use residual heat to heat the coal-bearing strata, continuously monitor gas concentration and extract gas until the gas concentration reaches the standard.

[0012] S7. Perform single-hole finishing, or select a new location in the coal-bearing strata to drill a hole, repeating steps S1 to S6 until the gas extraction of the entire coal-bearing strata is completed.

[0013] Optionally, step S1 further includes the following sub-steps:

[0014] S101. Debug the drilling rig in the tunnel and check the compatibility between the hollow drill rod and the drill bit;

[0015] S102. Adjust the drilling direction of the drilling rig to make the drilling rig drill directionally towards the coal seam on the side and above, so that the hollow drill rod penetrates the limestone layer and sandstone layer in sequence and extends into the coal seam until the drill bit reaches the mudstone layer and stops drilling.

[0016] S103. Remove rock debris from the borehole to ensure that no large pieces of rock debris remain in the borehole.

[0017] Optionally, step S2 further includes the following sub-steps:

[0018] S201. Install a borehole sealing device at the borehole opening to seal the inside of the borehole.

[0019] S202. Connect the outlet of the booster pump to the orifice sealing device through a pipeline. Connect the orifice sealing device to the hollow drill rod. Connect the inlet of the booster pump to the water-sand mixing tank through a pipeline.

[0020] S203. Connect the inlet end of the water-sand mixing box to the sand supply channel through a pipeline, and connect the outlet end of the water-sand mixing box to the heater. The heater is connected to the first water pump.

[0021] S204. Connect the water storage tank to the first water pump and the second water pump through pipelines respectively. Connect the outlet of the second water pump to the steam generator through pipelines. Pass the outlet of the steam generator through the orifice sealing device and connect it to the borehole.

[0022] S205. Connect the inlet of the gas-slag separation device to the orifice sealing device through a pipeline and connect it to the borehole. Connect the outlet of the gas-slag separation device to the gas extraction pipeline.

[0023] S206. Install a first check valve between the hollow drill rod and the booster pump, a second check valve between the sand supply channel and the water-sand mixing box, a third check valve between the steam generator and the borehole, and a fourth check valve between the gas-slag separation device and the borehole. After assembly, ensure that the first, second, third, and fourth check valves are all in the closed state.

[0024] Optionally, step S3 further includes the following sub-steps:

[0025] S301. Open the first check valve and the fourth check valve, start the heater and the first water pump, and the water in the water storage tank flows into the water-sand mixing tank after being heated by the heater.

[0026] S302. Open the second check valve and inject the sand in the sand supply channel into the water-sand mixing tank through the second check valve. Use the agitator in the water-sand mixing tank to mix the water and sand evenly.

[0027] S303. After the water-sand mixture in the water-sand mixing tank reaches the preset water level, start the booster pump. The booster pump pressurizes the water-sand mixture to 15~25MPa and then pumps it into the hollow drill pipe through the first check valve.

[0028] S304, High-pressure water-sand mixture is ejected from the opening on the hollow drill rod near the drill bit to cut the coal body around the borehole to form a slot;

[0029] S305. During the coal cutting process, the power of the first water pump, heater and booster pump is continuously adjusted to keep the water-sand mixing box always full of water-sand mixture. At the same time, the residue, wastewater and some gas in the borehole are discharged to the gas-slag separation device. The separated gas is extracted through the gas extraction pipeline, and the residue and wastewater remain in the gas-slag separation device.

[0030] S306. After the high-pressure water-sand mixture has been cutting for 1 hour, stop the operation of the first water pump, heater, and booster pump, and close the first and second check valves to stop the injection of sand and the cutting of coal.

[0031] S307. After the residue and wastewater in the borehole have been drained, close the fourth check valve and remove the borehole sealing device to complete the cutting work at this location.

[0032] Optionally, step S4 further includes the following sub-steps:

[0033] S401. Retract the hollow drill rod 0.5~1m towards the borehole opening and reinstall the borehole sealing device;

[0034] S402. Repeat the hydraulic slit cutting and gas extraction work in step S3 until the drill bit is withdrawn to a distance of 0.3~0.6m from the bottom of the coal seam, and complete the last slit cutting to form multiple slots in the coal seam.

[0035] S403. After the cutting is completed, the residue and wastewater in the borehole are discharged, and the gas in the borehole is continuously extracted through the gas extraction pipeline.

[0036] Optionally, step S5 further includes the following sub-steps:

[0037] S501. After 8 to 12 hours of continuous gas extraction, stop extraction and close the fourth check valve, open the third check valve, start the second water pump and steam generator, so that the water in the water tank is sent to the steam generator through the second water pump to generate saturated steam at 250 to 300°C and 4 to 8.7 MPa.

[0038] S502. Saturated steam flows into the borehole through the third one-way valve, which increases the gas pressure inside the borehole. The high-pressure steam pressurizes the groove and heats the coal seam and surrounding rock strata, promoting the expansion of the groove.

[0039] S503. During the high-pressure steam injection process, continuously monitor the gas pressure inside the borehole. Once the pressure inside the borehole reaches 6-8 MPa, open the fourth check valve to discharge residue and wastewater and extract gas.

[0040] S504. After the pressure inside the borehole drops below 4MPa, close the fourth check valve and continue to inject steam to increase the pressure. Repeat this cycle to maintain the pressure inside the borehole.

[0041] Optionally, step S6 further includes the following sub-steps:

[0042] S601. After continuously injecting steam for 4 to 6 hours, stop the operation of the second water pump and steam generator, close the second and fourth check valves, stop steam injection, seal the borehole, and use the residual heat in the borehole to fully heat the coal-bearing strata.

[0043] S602. After the borehole is sealed for 2 to 4 hours, open the fourth check valve to discharge the condensate to the gas-slag separation device, and at the same time extract the separated gas through the gas extraction pipeline.

[0044] S603. When the extracted gas concentration is below 15%, stop extraction and close the fourth one-way valve, and repeat steps S5 and S6; if the gas concentration is still below 15% after heating, the gas extraction of the borehole is completed.

[0045] Optionally, step S7 further includes the following sub-steps:

[0046] S701. After the drilling operation is completed, the borehole shall be sealed with sealing material;

[0047] S702. In the coal-bearing strata next to the borehole, select a new location to drill a borehole, and repeat steps S1 to S6 until the gas extraction of the entire coal-bearing strata is completed.

[0048] S703. Under the synergistic effect of hydraulic fracturing and coal seam heating, the decompression range and gas extraction range of coal-bearing strata are expanded.

[0049] This invention constructs a three-in-one coal-bearing formation gas enhancement technology system through the spatiotemporal orderly synergy of hydraulic fracturing and high-temperature heat injection, which integrates "mechanical fracturing, thermal permeability enhancement, and stress regulation." This system breaks through the efficiency bottleneck of traditional single physical or chemical permeability enhancement modes. The beneficial effects of this invention are specifically reflected in the following aspects:

[0050] First, the deep penetration and efficient heat exchange of high-temperature steam: The injected high-temperature steam molecules carry high energy and can penetrate deep into the tiny pores and fissures of the coal seam. Through condensation heat exchange reactions, the coal seam temperature is significantly increased, thereby reducing the gas adsorption capacity. Due to the capillary condensation characteristics of steam, it preferentially condenses within the micropores of the coal, thus ensuring the smooth output of desorbed gas and not hindering gas extraction. This deep penetration and efficient heat exchange mechanism greatly improves the heating efficiency of the coal seam and the gas desorption rate.

[0051] Secondly, hydraulic slotting pretreatment enhances steam permeability: Addressing the limited permeability of steam in tight coal seams, this invention first creates multiple slots in the coal seam through high-pressure hydraulic slotting. These slots serve as channels for steam permeation, allowing subsequently injected steam to penetrate deeper into the coal seam, achieving a wider heating effect. This pretreatment method not only expands the heating range of the steam but also significantly improves the efficiency and coverage of gas extraction.

[0052] Furthermore, the preheating effect of high-pressure water reduces heat loss: the injected high-pressure water is preheated before cutting the coal seam, which not only enhances the water's impact cutting ability but also simultaneously preheats the coal seam. This preheating reduces the coal seam's ability to absorb methane and increases the amount of methane desorbed. When steam is subsequently injected, because the coal body already has a certain initial temperature, heat loss and condensation rate are effectively controlled, thus achieving better coal seam heating and methane extraction efficiency.

[0053] Furthermore, the addition of abrasive enhances cutting and permeability: by adding sand as an abrasive to the high-pressure water, the cutting ability of the water jet is significantly enhanced. This enhanced water jet can expand the coverage area of ​​the hydraulic cuts, achieving a more uniform permeability enhancement effect in the coal seam. The combination of directional and uniform permeability enhancement further improves the efficiency and stability of gas extraction.

[0054] Finally, the synergistic effect significantly expands the depressurization and gas extraction range: Compared with traditional hydraulic slotting technology or direct borehole gas extraction technology, this invention significantly expands the depressurization and gas extraction range of coal-bearing strata through the synergistic effect of hydraulic slotting and coal seam heating. This synergistic effect not only improves gas extraction efficiency but also effectively increases the construction spacing between adjacent boreholes, significantly reducing the total amount of drilling work and costs. Simultaneously, it reduces the occurrence of safety issues such as blowouts and excessive gas levels, providing strong support for the safe, economical, and rapid passage of tunnels through coal-bearing strata. Attached Figure Description

[0055] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 This is a construction system layout diagram of a method for hydraulic slotting combined with heat injection to improve permeability in mountainous coal-bearing strata according to an embodiment of the present invention;

[0057] Figure 2 This is a schematic diagram of the installation structure of the hollow drill rod and drill bit of a drilling rig in one embodiment of the present invention;

[0058] Figure 3 This is a schematic diagram of the construction method of multiple boreholes and the gas extraction range in one embodiment of the present invention.

[0059] The reference numerals in the accompanying drawings are as follows:

[0060] 1-Mudstone layer, 2-Coal seam, 3-Sandstone layer, 4-Limestone layer, 5-Borehole, 6-Slotted groove, 7-Hollow drill rod, 8-Drill bit, 9-Borehead sealing device, 101-First check valve, 102-Second check valve, 103-Third check valve, 104-Fourth check valve, 11-Booster pump, 12-Water-sand mixing box, 13-Sand supply channel, 14-Heater, 151-First water pump, 152-Second water pump, 153-Third water pump, 154-Fourth water pump, 16-Water storage tank, 17-Steam generator, 18-Gas-slag separation device, 19-Gas extraction pipeline, 20-Tunnel, 21-Opening, 22-Gas extraction range. Detailed Implementation

[0061] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0062] In the description of this invention, it should be understood that the terms "longitudinal," "radial," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0063] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0064] like Figures 1 to 3 As shown, one embodiment of the present invention provides a method for hydraulically slotted and heat-injected uniform permeability enhancement in mountainous coal-bearing strata, comprising:

[0065] S1. Drill borehole 5 into the coal-bearing strata in tunnel 20 and clean the borehole 5.

[0066] In one embodiment, step S1 further includes the following sub-steps:

[0067] S101. In tunnel 20, debug the drilling rig (drilling and cutting integrated equipment) and check the compatibility between the hollow drill rod 7 and the drill bit 8.

[0068] S102. Adjust the drilling direction of the drilling rig to make the drilling rig drill directionally towards the coal seam 2 on the side and above, so that the hollow drill rod 7 penetrates the limestone layer 4 and the sandstone layer 3 in sequence and extends into the coal seam 2 until the drill bit 8 reaches the mudstone layer 1 and stops drilling.

[0069] S103. Remove rock debris from borehole 5 to ensure that no large pieces of rock debris remain in borehole 5.

[0070] S2. At the opening of borehole 5, assemble the sealing device and connecting pipeline.

[0071] In one implementation, step S2 further includes the following sub-steps:

[0072] S201. Install a hole sealing device 9 at the hole opening of borehole 5 to seal the inside of borehole 5.

[0073] S202. Connect the outlet of the booster pump 11 to the orifice sealing device 9 through a pipeline. The orifice sealing device 9 is connected to the hollow drill rod 7. Connect the inlet of the booster pump 11 to the water-sand mixing box 12 through a pipeline.

[0074] S203. Connect the inlet end of the water-sand mixing box 12 to the sand supply channel 13 through a pipeline, and connect the outlet end of the water-sand mixing box 12 to the heater 14. The heater 14 is connected to the first water pump 151.

[0075] S204. Connect the water storage tank 16 to the first water pump 151 and the second water pump 152 through pipelines respectively. Connect the outlet of the second water pump 152 to the steam generator 17 through pipelines. Pass the outlet of the steam generator 17 through the orifice sealing device 9 and connect it to the borehole 5.

[0076] S205. Connect the inlet of the gas-slag separation device 18 to the orifice sealing device 9 through a pipeline and connect it to the borehole 5. Connect the outlet of the gas-slag separation device 18 to the gas extraction pipeline 19.

[0077] S206. Install a first check valve 101 (with its inlet facing the booster pump 11) between the hollow drill rod 7 and the booster pump 11. Install a second check valve 102 (with its inlet facing the sand supply channel 13) between the sand supply channel 13 and the water-sand mixing box 12. Install a third check valve 103 (with its inlet facing the steam generator 17) between the steam generator 17 and the borehole 5. Install a fourth check valve 104 (with its inlet facing the borehole 5) between the gas-slag separation device 18 and the borehole 5. After assembly, ensure that the first check valve 101, the second check valve 102, the third check valve 103 and the fourth check valve 104 are all in the closed state.

[0078] S3. Inject the high-pressure water-sand mixture into borehole 5 to perform hydraulic cutting operations, forming multiple slots 6; discharge the residue and wastewater in borehole 5, and simultaneously carry out gas extraction operations.

[0079] In one implementation, step S3 further includes the following sub-steps:

[0080] S301. Open the first check valve 101 and the fourth check valve 104, start the heater 14 and the first water pump 151, and the water in the water storage tank 16 flows into the water-sand mixing tank 12 after being heated by the heater 14.

[0081] S302. Open the second check valve 102 and inject the sand in the sand supply channel 13 into the water-sand mixing box 12 through the second check valve 102. Use the agitator in the water-sand mixing box 12 to mix the water and sand evenly.

[0082] S303. After the water-sand mixture in the water-sand mixing tank 12 reaches the preset water level, start the booster pump 11. The booster pump 11 pressurizes the water-sand mixture to 15~25MPa and then pumps it into the hollow drill rod 7 through the first one-way valve 101.

[0083] S304. High-pressure water-sand mixture is ejected from the opening 21 near the drill bit 8 on the hollow drill rod 7 to cut the coal body around the borehole 5 to form a slot 6.

[0084] S305. During the coal cutting process, the power of the first water pump 151, heater 14, and booster pump 11 is continuously adjusted to ensure that the water-sand mixing box 12 is always filled with water-sand mixture. At the same time, the residue, wastewater, and some gas in the borehole 5 are discharged to the gas-slag separation device 18. The separated gas is extracted through the gas extraction pipeline 19, while the residue and wastewater remain in the gas-slag separation device 18.

[0085] S306. After the high-pressure water-sand mixture has been cutting for 1 hour, stop the operation of the first water pump 151, heater 14, and booster pump 11, and close the first check valve 101 and the second check valve 102 to stop the injection of sand and the cutting of coal.

[0086] S307. After the residue and wastewater in the borehole 5 have been drained, close the fourth one-way valve 104 and remove the borehole sealing device 9 to complete the cutting work at this position.

[0087] S4. Retract the hollow drill rod 7 towards the borehole opening, make multiple cuts, and continuously extract gas from the borehole 5.

[0088] In one implementation, step S4 further includes the following sub-steps:

[0089] S401. Retract the hollow drill rod 7 0.5~1m towards the borehole opening and reinstall the borehole sealing device 9.

[0090] S402. Repeat the hydraulic cutting and gas extraction work in step S3 until the drill bit 8 is withdrawn to a distance of 0.3~0.6m from the bottom of the coal seam 2, and complete the last cutting to form multiple slots 6 in the coal seam 2.

[0091] S403. After the cutting is completed, the residue and wastewater in the borehole 5 are discharged, and the gas in the borehole 5 is continuously extracted through the gas extraction pipeline 19.

[0092] S5. After a preset time of continuous gas extraction, heat injection is carried out to enhance permeability by delivering high-temperature and high-pressure steam into borehole 5 to facilitate heat exchange and promote the expansion of the slot 6; and gas extraction is carried out simultaneously.

[0093] In one implementation, step S5 further includes the following sub-steps:

[0094] S501. After 8 to 12 hours of continuous gas extraction, stop extraction and close the fourth check valve 104, open the third check valve 103, and start the second water pump 152 and the steam generator 17. The water in the water storage tank 16 is sent to the steam generator 17 through the second water pump 152 to generate saturated steam at 250 to 300°C and a pressure of 4 to 8.7 MPa.

[0095] S502, saturated steam flows into borehole 5 through the third one-way valve 103, which increases the gas pressure in borehole 5. The high-pressure steam pressurizes the groove 6 and heats the coal seam 2 and the surrounding rock strata, promoting the expansion of the groove 6.

[0096] S503. During the high-pressure steam injection process, continuously monitor the gas pressure inside borehole 5. After the pressure inside borehole 5 reaches 6~8MPa, open the fourth one-way valve 104 to discharge residue and wastewater and extract gas.

[0097] S504. After the pressure inside the hole drops below 4MPa, close the fourth check valve 104 and continue to inject steam to increase the pressure. Repeat this cycle to maintain the pressure inside the borehole 5.

[0098] S6. Seal borehole 5, use residual heat to heat the coal-bearing strata, continuously monitor the gas concentration and extract the gas until the gas concentration reaches the standard.

[0099] In one implementation, step S6 further includes the following sub-steps:

[0100] S601. After continuously injecting steam for 4 to 6 hours, stop the operation of the second water pump 152 and the steam generator, and close the second one-way valve 102 and the fourth one-way valve 104 to stop steam injection. Seal the borehole 5 and use the residual heat in the borehole 5 to fully heat the coal-bearing strata. After the temperature of the coal-bearing strata rises, its adsorption of gas decreases, thereby achieving the purpose of increasing gas production.

[0101] S602. After sealing borehole 5 for 2 to 4 hours, open the fourth one-way valve 104 to discharge the condensate to the gas-slag separation device 18, and at the same time extract the separated gas through the gas extraction pipeline 19.

[0102] S603. When the extracted gas concentration is below 15%, stop extraction and close the fourth one-way valve 104, and repeat steps S5 and S6. If the gas concentration is still below 15% after heating, the gas extraction of borehole 5 is completed.

[0103] S7. Perform single-hole finishing, or select a new location in the coal-bearing strata to drill borehole 5, and repeat steps S1 to S6 (multi-hole construction) until the gas extraction of the entire coal-bearing strata is completed.

[0104] In an implementation, such as Figure 3As shown, step S7 further includes the following sub-steps:

[0105] S701. After the drilling operation of hole 5 is completed, hole 5 shall be sealed with sealing material.

[0106] S702. In the coal-bearing strata next to borehole 5, select a new location to drill borehole 5, and repeat steps S1 to S6 until the gas extraction of the entire coal-bearing strata is completed; ultimately achieving the goal of balanced permeability enhancement of the coal-bearing strata.

[0107] S703. Under the synergistic effect of hydraulic fracturing and coal seam 2 heat injection, the pressure relief range and gas extraction range of the coal-bearing strata 22 are significantly expanded.

[0108] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for balancing and dehydrating coal measures strata in mountainous areas by hydraulic slotting and heat injection, characterized in that, The method comprises the following steps: S1, drilling a borehole (5) in the coal measure stratum in the tunnel and cleaning the borehole (5); S2, assembling a sealing device and connecting pipeline at the borehole mouth of the borehole (5); S3, injecting a high-pressure water-sand mixed liquid into the borehole (5) to perform a hydraulic slotting operation to form a plurality of slot grooves (6); discharging the residue and waste water in the borehole (5) and simultaneously performing a gas extraction operation; S4, withdrawing the hollow drill rod (7) towards the borehole mouth to perform multi-position slotting and continuously extract the gas in the borehole (5); S5, after continuously extracting the gas for a preset time length, performing heat injection to increase the permeability, conveying high-temperature and high-pressure steam into the borehole (5) to perform heat exchange and promote the expansion of the slot grooves (6); and simultaneously performing gas extraction; S6, sealing the borehole, heating the coal measure stratum by using the residual heat, continuously monitoring the gas concentration and extracting the gas until the gas concentration reaches the standard; S7, performing a single-hole finishing or drilling a borehole at a new position in the coal measure stratum and repeating steps S1 to S6 until the gas extraction of the entire coal measure stratum is completed.

2. The method of balancing and dehydrating the coal measures strata in mountainous area by hydraulic slotting and heat injection synergy according to claim 1, characterized in that, The step S1 further comprises the following sub-steps: S101, debugging the drilling machine in the tunnel (20) and checking the adaptability of the hollow drill rod (7) and the drill bit (8); S102, adjusting the drilling direction of the drilling machine to make the drilling machine directionally drill upwards to the coal seam, so that the hollow drill rod (7) penetrates the limestone layer (4), the sandstone layer (3) and extends into the coal seam (2) in sequence, and stops drilling when the drill bit (8) reaches the mudstone layer (1); S103, discharging the rock debris in the borehole to ensure that there is no large rock debris remaining in the borehole.

3. The method of balancing and dehydrating coal measures strata in mountainous areas by hydraulic slotting and heat injection synergy according to claim 2, characterized in that, The step S2 further comprises the following sub-steps: S201, installing a borehole sealing device (9) at the borehole mouth of the borehole (5) to seal the inside of the borehole (5); S202, connecting the outlet of the booster pump (11) to the borehole sealing device (9) through the pipeline, connecting the borehole sealing device (9) and the hollow drill rod (7), connecting the inlet of the booster pump (11) to the water-sand mixing box (12) through the pipeline; S203, connecting the inlet end of the water-sand mixing box (12) to the sand supply channel (13) through the pipeline, connecting the outlet end of the water-sand mixing box (12) to the heater (14), and connecting the heater (14) to the first water pump (151); S204, connecting the water storage tank (16) to the first water pump (151) and the second water pump (152) through the pipeline, connecting the outlet of the second water pump (152) to the steam generator (17) through the pipeline, and connecting the outlet of the steam generator (17) to the borehole (5) through the borehole sealing device (9); S205, connecting the inlet of the gas residue separation device (18) to the borehole sealing device (9) through the pipeline and connecting the borehole (5), and connecting the outlet of the gas residue separation device (18) to the gas extraction pipeline (19). S206, install a first one-way valve (101) between the hollow drill rod (7) and the booster pump (11), install a second one-way valve (102) between the sand supply channel (13) and the water-sand mixing tank (12), install a third one-way valve (103) between the steam generator (17) and the drill hole (5), install a fourth one-way valve (104) between the gas residue separation device (18) and the drill hole (5), after assembly, the first one-way valve (101), the second one-way valve (102), the third one-way valve (103) and the fourth one-way valve (104) are all in the closed state.

4. The method of balancing and dehydrating the coal measures strata in mountainous area by hydraulic slotting and heat injection synergy according to claim 3, characterized in that, The step S3 further includes the following sub-steps: S301, open the first one-way valve (101) and the fourth one-way valve (104), start the heater (14) and the first water pump (151), the water in the water storage tank (16) is heated by the heater (14) and then flows into the water-sand mixing tank (12); S302, open the second one-way valve (102), inject the sand in the sand supply channel (13) into the water-sand mixing tank (12) through the second one-way valve (102), and mix the water and sand uniformly by using the stirrer in the water-sand mixing tank (12); S303, after the water-sand mixture in the water-sand mixing tank (12) reaches a preset water level, start the booster pump (11), the booster pump (11) pressurizes the water-sand mixture to 15-25 MPa and then pumps it into the hollow drill rod (7) through the first one-way valve (101); S304, the high-pressure water-sand mixture is ejected from the opening (21) of the hollow drill rod (7) close to the drill bit (8), and the coal body around the drill hole (5) is cut to form a slot (6); S305, during the cutting of the coal body, the power of the first water pump (151), the heater (14) and the booster pump (11) is continuously adjusted so that the water-sand mixing tank (12) is always filled with water-sand mixture, and at the same time, the residue and waste water in the drill hole (5) and part of the gas are discharged to the gas residue separation device (18), the separated gas is extracted through the gas extraction pipeline (19), and the residue and waste water remain in the gas residue separation device (18); S306, after the high-pressure water-sand mixture continuously cuts for 1 hour, stop the work of the first water pump (151), the heater (14) and the booster pump (11), and close the first one-way valve (101) and the second one-way valve (102), stop the injection of sand and the cutting of the coal body; S307, after the residue and waste water in the drill hole (5) are discharged, close the fourth one-way valve (104) and remove the borehole sealing device (9), and the slotting work at this position is completed.

5. The method of balancing and dehydrating the coal measures strata in mountainous area by hydraulic slotting and heat injection synergy according to claim 4, characterized in that, The step S4 further includes the following sub-steps: S401, retract the hollow drill rod (7) by 0.5-1 m towards the borehole, and reinstall the borehole sealing device (9); S402, repeat the hydraulic slotting and gas extraction work in step S3 until the drill bit (8) is retracted to 0.3-0.6 m from the floor of the coal seam (2), complete the last slotting, and form a plurality of slots (6) in the coal seam (2); S403. After the cutting is completed, the residue and wastewater in the borehole (5) are discharged, and the gas in the borehole (5) is continuously extracted through the gas extraction pipeline (19).

6. The method of balancing and dehydrating the coal measures strata in mountainous area by hydraulic slotting and heat injection synergy according to claim 5, characterized in that, Step S5 further includes the following sub-steps: S501. After 8 to 12 hours of continuous gas extraction, stop extraction and close the fourth check valve (104), open the third check valve (103), start the second water pump (152) and the steam generator (17), so that the water in the water tank (16) is sent to the steam generator (17) through the second water pump (152) to generate saturated steam at 250 to 300°C and 4 to 8.7 MPa. S502, saturated steam flows into the borehole (5) through the third one-way valve (103), which increases the gas pressure inside the borehole (5). The high-pressure steam pressurizes the groove (6) and heats the coal seam (2) and the surrounding rock strata, promoting the expansion of the groove (6). S503. During the high-pressure steam injection process, continuously monitor the gas pressure inside the borehole (5). After the pressure inside the borehole (5) reaches 6~8MPa, open the fourth check valve (104) to discharge the residue and wastewater and extract the gas. S504. After the pressure inside the hole drops below 4MPa, close the fourth check valve (104) and continue to inject steam to increase the pressure. Repeat this cycle to maintain the pressure inside the borehole (5).

7. The method of balancing and dehydrating coal measures strata in mountainous areas by hydraulic slotting and heat injection synergy according to claim 6, characterized in that, Step S6 further includes the following sub-steps: S601. After continuously injecting steam for 4 to 6 hours, stop the operation of the second water pump (152) and the steam generator (17), and close the second check valve (103) and the fourth check valve (104) to stop the steam injection, seal the borehole (5), and use the residual heat in the borehole (5) to fully heat the coal-bearing strata. S602. After sealing the borehole (5) for 2 to 4 hours, open the fourth check valve (104) to discharge the condensate to the gas-slag separation device (18) and extract the separated gas through the gas extraction pipeline (19). S603. When the gas concentration is below 15%, stop the extraction and close the fourth check valve (104), and repeat steps S5 and S6. If the gas concentration is still below 15% after heating, the gas extraction of the borehole is completed.

8. The method of balancing and dehydrating the coal measures strata in mountainous area by hydraulic slotting and heat injection synergy according to claim 7, characterized in that, Step S7 further includes the following sub-steps: S701. After the drilling operation is completed, the borehole (5) is sealed with sealing material. S702. In the coal-bearing strata next to borehole (5), select a new location to drill a borehole and repeat steps S1 to S6 until the gas extraction of the entire coal-bearing strata is completed. S703. Under the synergistic effect of hydraulic fracturing and coal seam heating, the pressure relief range and gas extraction range of coal-bearing strata (22) are expanded.

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