Deep coal seam no-roadway gas extraction and deep geothermal resource exploitation integrated method

Abstract

The application discloses a deep coal seam no-roadway gas extraction and deep geothermal resource exploitation integrated method, which comprises the following steps: S1, constructing a U-shaped well; S2, arranging a double-layer casing assembly in the U-shaped well; S3, arranging a plurality of annular packers on the double-layer casing assembly in the horizontal well section, and then connecting the double-layer casing assemblies in sections into an integrated whole; S4, performing hydraulic fracturing on the horizontal well section through the double-layer casing assembly; and S5, extracting gas through the double-layer casing assembly, and injecting cold water through the double-layer casing assembly, so that the high-temperature gas exchanges heat with the cold water, and the cold water is heated to become hot water. The application realizes deep coal seam no-roadway gas extraction and deep geothermal resource exploitation, solves the problem that deep coal seam gas is difficult to extract when shallow coal seams are exploited, reasonably exploits coal seam gas resources, reduces the gas extraction engineering quantity, and utilizes geothermal resources, thereby bringing more benefits to coal mines.

Description

Technical Field

[0001] This invention belongs to the field of gas disaster prevention and geothermal resource extraction technology, specifically involving an integrated method for deep coal seam gas extraction without roadways and deep geothermal resource extraction. Background Technology

[0002] As mining depth increases, coal seam gas content and formation temperature also rise. Mine gas hazards and heat damage severely impact the health of underground workers and the efficiency and safety of mine production. Therefore, effective prevention and control of mine gas hazards and heat damage is crucial for deep coal seam mining. In mining, coal seams are typically mined from top to bottom. Deep coal seams are often unmined or unminable. However, during mining, deep coal seam gas continuously enters the mine, increasing the pressure on gas control. Since there are no gas drainage tunnels in these deep seams, pre-excavating floor tunnels for gas drainage would significantly increase the workload. If gas control measures from the upper mining area can be used to drain deep coal seam gas, this not only reduces the amount of gas entering the mining area but also relieves pressure on the deep coal seam, creating favorable conditions for its mining. Deep coal seams contain large amounts of methane gas, which, due to the influence of underground temperatures, acquires high-temperature properties. During mining, this high-temperature gas not only poses safety hazards but also severely impacts the health of underground personnel due to the heat generated. This paper presents a deep coal seam thermal-gas co-mining regional disaster prevention and resource utilization system. This system can depressurize deep coal seams without significantly increasing the amount of engineering work, facilitating deep coal seam mining, while simultaneously collecting coalbed methane and geothermal resources. This not only aligns with the concept of sustainable development but also brings greater profits to coal mines. Summary of the Invention

[0003] The purpose of this invention is to provide an integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation, which solves the problem of gas control difficulties in deep coal seam areas, and not only exploits coalbed methane resources, but also utilizes geothermal resources.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: an integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation, comprising the following steps: S1. Construction of a U-shaped well, which includes, from left to right, a vertical well section at the injection end, a directional well section, a horizontal well section, and a vertical well section at the extraction end; S2. Arrange a double-layer casing assembly inside the U-shaped well; S3. Install several annular packers on the double-casing assembly in the horizontal well section, and then connect the double-casing assemblies of each section in series. S4. Hydraulic fracturing of the horizontal well section using a double-casing assembly; S5. Gas is extracted through a double-layer casing assembly, and cold water is injected through the same assembly. The high-temperature gas exchanges heat with the cold water, which then heats up and becomes hot water. The gas is drawn into the main gas pipeline by the ground gas extraction pump, and the hot water is stored in a central insulated water tank set up on the ground.

[0005] The double-casing assembly includes a vertical section double-casing at the injection end, a double-casing at the build-up section, a double-casing at the horizontal well section, and a vertical section double-casing at the extraction end. The lower end of the vertical section double-casing at the injection end is connected to the upper left end of the double-casing at the build-up section, the lower right end of the double-casing at the build-up section is connected to the left end of the double-casing at the horizontal well section, and the right end of the double-casing at the horizontal well section is connected to the lower end of the double-casing at the extraction end. Several annular packers are spaced along the left and right directions on the double casing of the horizontal well section. The upper end of the double casing of the vertical well section at the extraction end is equipped with a gas-water separation device. The outlet of the gas-water separation device is connected to the central insulated water storage tank. The gas outlet of the gas-water separation device is connected to the gas main pipeline through the surface gas drainage pump.

[0006] The double-layer casing of the injection end vertical shaft section, the double-layer casing of the directional drilling section, and the double-layer casing of the extraction end vertical shaft section have the same structure. They all include several sections of polyurethane insulated outer casing connected in series and several sections of polyurethane insulated inner casing connected in series. The inner circle of the polyurethane insulated outer casing and the outer circle of the polyurethane insulated inner casing are fixed together by a cross-shaped first connecting rod. The two ends of each section of polyurethane insulated outer casing and polyurethane insulated inner casing are staggered by 100mm and the first connecting rod is installed and fixed thereon.

[0007] The horizontal well section double casing consists of an outer slotted liner and an inner copper tube. The inner circle of the slotted liner and the outer circle of the copper tube are fixed together by a cross-shaped second connecting rod.

[0008] Each annular packer includes an installation cylinder, a water-absorbing and expanding rubber tube, two limiting rings, and several bow-shaped straighteners. The installation cylinder is coaxially fitted onto the slotted liner. The water-absorbing and expanding rubber tube and the two limiting rings are fitted onto the outer circumference of the installation cylinder. The two limiting rings are located at the left and right ends of the water-absorbing and expanding rubber tube, respectively. Multiple screws are provided around the circumference of the limiting rings. The screws pass through the limiting rings, the installation cylinder, and the slotted liner, fixing the installation cylinder to the slotted liner and simultaneously fixing the water-absorbing and expanding rubber tube to the installation cylinder. The bow-shaped straighteners are respectively set on the outer circumference of the installation cylinder on the left and right sides of the water-absorbing and expanding rubber tube. Several sets of positioning structures are evenly arranged along the circumference on the left and right sides of the installation cylinder. Each set of positioning structures includes two slots arranged at intervals. Each bow-shaped straightener is bent at both ends and inserted into the two slots of each set of positioning structures. The water-absorbing and expanding rubber tube is a multi-component system composed of an elastomer and a hydrophilic substance.

[0009] The gas-water separation device includes an external gas distribution pipe, an exhaust pipe, and a drainage insulation pipe. The lower end of the external gas distribution pipe is connected to the upper port of the polyurethane insulation outer sleeve of the double-layer casing of the extraction end vertical shaft section through a flange assembly. The upper port of the external gas distribution pipe is sealed, and the upper side of the external gas distribution pipe is connected to the exhaust pipe. The upper end of the polyurethane insulation inner sleeve of the double-layer casing of the extraction end vertical shaft section passes through the external gas distribution pipe and is connected to the drainage insulation pipe. The exhaust pipe is equipped with a gas integrated monitoring instrument and an exhaust control valve, and the drainage insulation pipe is equipped with a liquid integrated monitoring instrument and a drainage control valve. The surface gas extraction pump is installed on the exhaust pipe. The outlet of the exhaust pipe is connected to the gas main pipeline, and the outlet of the drainage insulation pipe is connected to the central insulation water storage tank.

[0010] The specific process of step S1 is as follows: vertically drill the injection end vertical shaft section and the extraction end vertical shaft section at the predetermined location, perform directional drilling at the bottom of the injection end vertical shaft section, then cement the injection end vertical shaft section, the extraction end vertical shaft section and the directional drilling section, after the cementing is completed, drill the horizontal well section, and finally complete the docking of the right end of the horizontal well section and the lower end of the extraction end vertical shaft section. The specific process of step S2 is as follows: Run in the injection end vertical shaft section double casing, the directional section double casing, the horizontal section double casing and the extraction end vertical shaft section double casing. The lower end of the injection end vertical shaft section double casing is connected to the upper left end of the directional section double casing. The extraction end vertical shaft section double casing is connected to a gas-water separation device on the ground. The gas-water separation device is connected to the central insulated water storage tank and the surface gas extraction pump.

[0011] The specific process of step S3 is as follows: First, put the installation sleeve of the annular packer onto the slotted liner. Then, put the water-absorbing expansion sleeve into the middle of the installation sleeve. Next, install two limiting rings to axially position the water-absorbing expansion sleeve. Use multiple screws to fix the limiting rings and the installation sleeve onto the slotted liner. Then, insert the bent parts at both ends of the bow-shaped centralizer into the two slots of a set of positioning structures. In the same way, fix and install the other bow-shaped centralizers into the corresponding two slots. The outward protruding part of the bow-shaped centralizer contacts the inner wall of the horizontal well section. Set the slotted liner and copper pipe along the center line of the horizontal well section. After all the annular packers are installed in the above manner, connect the left end of the horizontal well section double casing to the lower right end of the directional section double casing, and connect the right end of the horizontal well section double casing to the lower side of the extraction end vertical well section double casing.

[0012] The specific process of step S4 is as follows: clean water is injected into the annular cavity of the polyurethane insulation outer casing and the polyurethane insulation inner casing of the double-layer casing of the injection end vertical well section. The clean water enters between the outer circle of the copper pipe and the inner circle of the slotted liner. The clean water also flows into the space between the slotted liner and the inner wall of the horizontal well section through the holes and slots on the slotted liner. After 72 hours of water injection, the water-absorbing expansion rubber sleeve begins to expand. After another 72 hours, the water-absorbing expansion rubber sleeve is fully expanded. The outer circle of the expanded water-absorbing expansion rubber sleeve seals the annulus between the inner wall of the horizontal well section and the outer circle of the slotted liner, thus dividing the horizontal well section into several segments. Next, the upper end of the double-casing in the extraction section of the vertical shaft is sealed. Fracturing fluid is injected into the annular cavity of the polyurethane-insulated outer casing and the polyurethane-insulated inner casing of the injection section of the vertical shaft. In several small sections separated by the annular packer, the pressure of the fracturing fluid gradually increases. The weakest section in each section begins to fracture first. As the fracture extends deeper, the pressure required for the fracture to continue to extend in this section will be greater than the initiation pressure of the weakest section. At this point, the weakest section begins to fracture. In the horizontal well, fractures will be initiated in a stepwise manner in order of strength, from the weakest section to the second weakest section, resulting in relatively uniform fracture development in the horizontal well. Fracturing ends when the fracture extension stabilizes.

[0013] The specific process of step S5 is as follows: The upper port of the polyurethane insulation outer casing of the injection end vertical shaft section is sealed; the upper port of the polyurethane insulation outer casing of the extraction end vertical shaft section is opened and connected to the gas-water separation device. Coal seam gas carrying heat enters the slotted liner through coal seam fractures under pressure differential. The gas flows under the promotion of the coal seam gas pressure gradient. Softened cold water is continuously injected from the polyurethane insulation inner casing of the injection end vertical shaft section. When the cold water reaches the copper pipe in the horizontal shaft section, the high-temperature gas outside the copper pipe transfers heat to the cold water through the copper pipe. The cold water in the copper pipe gradually heats up during its flow in the horizontal shaft section. When the water in the copper pipe flows to the bottom of the extraction end vertical shaft section, the water temperature reaches its highest value. The temperature of the water and gas in the double-layer casing of the extraction end vertical shaft section will gradually decrease. During the process, insulation measures are implemented. The slotted liner for gas extraction is replaced with a polyurethane insulated outer casing, and the inner casing for water circulation is replaced with a polyurethane insulated inner casing. When gas and water reach the gas-water separation device, the gas monitoring instrument on the exhaust pipe monitors the pressure, temperature, and flow rate of the gas in real time, and the liquid monitoring instrument on the drainage insulated pipe monitors the pressure, temperature, and flow rate of the hot water in real time. Finally, the gas is drawn into the main gas pipeline by the surface gas extraction pump, and the gas from the extraction shaft sections of various areas in the mine also flows into the main gas pipeline. Hot water flows to the central insulated water storage tank through the drainage insulated pipe, and the hot water circulating from the extraction shaft sections of various areas in the mine is also injected into the central insulated water storage tank for storage. The hot water in the central insulated water storage tank is then extracted and used in various parts of the mine.

[0014] By adopting the above technical solution, the present invention has the following technical effects compared with the prior art: (1) Based on the U-shaped well for coalbed methane extraction in mining areas, this invention provides a double-casing structure arranged along the U-shaped well. The outer casing extracts gas, and the inner casing is for water circulation. The heat brought out by the extracted gas after coal seam fracturing is transferred to the inner casing. The heat is brought to the surface for utilization by water circulation, thereby realizing the co-extraction of heat and gas in deep coal seams and regional disaster prevention.

[0015] (2) The gas-water separation device realizes the separation of gas and water in the double-layer casing. The gas-water separation device is equipped with control valves and comprehensive monitoring instruments (thermometer, pressure gauge and flow meter) to monitor the status of gas and circulating water.

[0016] (3) The central insulated water storage tank is set on the ground and its location is as close as possible to the vertical shaft section of the extraction end of the U-shaped well in each area. The central insulated water storage tank is connected to the diversion device of each area through the drainage insulated pipe. The hot water circulating in the inner casing of the U-shaped well is concentrated and stored in the central insulated water storage tank.

[0017] (4) Two limiting rings on the annular packer are used to limit the axial (left-right) position of the water-absorbing and expanding rubber sleeve. Screws fix the limiting rings, the mounting sleeve, and the slotted liner to position the annular packer. Several bow-shaped centering plates ensure that the double-layer casing in the horizontal well section is centered within the horizontal well section. The water-absorbing and expanding rubber sleeve is a multi-component system composed of an elastomer and a hydrophilic substance. After 72 hours of water injection, the water-absorbing and expanding rubber sleeve begins to expand. The fully expanded rubber sleeve seals the annulus between the inner wall of the horizontal well section and the slotted liner, dividing the horizontal well section into several small segments.

[0018] (5) Compared to simultaneous fracturing of the entire horizontal well section, the annular packer reduces the contact area between the fracturing fluid and the wellbore, increasing the pressure on the wellbore under the same fracturing fluid pressure conditions, making the fractures easier to propagate. During simultaneous fracturing of the entire horizontal well section, inter-fracture interference occurs between adjacent fracture propagation zones, inhibiting the fracture length in the middle area and making it difficult to form effective fractures. The annular packer prevents fracture initiation at the point where the outer circumference of the water-absorbing expansion sleeve contacts the horizontal well section, and separates the fracture development zones on both sides of the water-absorbing expansion sleeve, reducing the inter-fracture interference effect, forming more effective fractures, and improving the fracturing effect.

[0019] In summary, this invention is based on sound principles, features a novel design, has low construction costs, and generates significant benefits. It enables tunnel-free gas extraction from deep coal seams and the exploitation of deep geothermal resources. This solves the problem of gas extraction difficulties in deep coal seams when mining shallow coal seams, rationally exploits coalbed methane resources, reduces the amount of gas extraction work, and utilizes geothermal resources, bringing more revenue to coal mines. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the cross-sectional structure of the double-layer casing in the injection end vertical shaft section, the double-layer casing in the directional drilling section, and the double-layer casing in the extraction end vertical shaft section of the present invention. Figure 3 This is a schematic diagram of the cross-sectional structure of the double-layer casing in the injection end vertical shaft section, the double-layer casing in the directional drilling section, and the double-layer casing in the extraction end vertical shaft section of the present invention. Figure 4 This is a schematic cross-sectional view of the double-layer casing in the horizontal well section of the present invention. Figure 5 This is a schematic diagram of the annular packer in this invention; Figure 6 This is a schematic diagram of the air-water separation device in this invention. Detailed Implementation

[0021] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0022] like Figures 1-6 As shown, the integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation of the present invention includes the following steps: S1. Construct a U-shaped well, which includes, from left to right, a vertical well section 1 at the injection end, a directional section 31, a horizontal well section 32, and a vertical well section 3 at the extraction end; S2. Arrange a double-layer casing assembly inside the U-shaped well; S3. Install several annular packers 7 on the double-layer casing assembly in the horizontal well section 32, and then connect the double-layer casing assemblies of each section in series. S4. Hydraulic fracturing of horizontal well section 32 using a double-casing assembly; S5. Gas is extracted through the double-layer casing assembly, and cold water is injected through the double-layer casing assembly at the same time. The high-temperature gas exchange heat with the cold water, and the cold water is heated to become hot water. The gas is drawn into the gas main pipeline 10 by the ground gas extraction pump 12, and the hot water is stored in the central insulated water storage tank 11 set on the ground.

[0023] The double-casing assembly includes a vertical section double-casing 2 at the injection end, a double-casing 4 at the directional drilling section, a double-casing 5 at the horizontal well section, and a vertical section double-casing 6 at the extraction end. The lower end of the vertical section double-casing 2 at the injection end is connected to the upper left end of the double-casing 4 at the directional drilling section, the lower right end of the double-casing 4 at the directional drilling section is connected to the left end of the double-casing 5 at the horizontal well section, and the right end of the double-casing 5 at the horizontal well section is connected to the lower end of the double-casing 6 at the extraction end. Several annular packers 7 are spaced apart on the horizontal well section double casing 5 in the left and right direction. The upper end of the vertical well section double casing 6 at the extraction end is equipped with a gas-water diversion device 8. The outlet of the gas-water diversion device 8 is connected to the central insulated water storage tank 11. The gas outlet of the gas-water diversion device 8 is fed into the gas main pipeline 10 through the surface gas drainage pump 12.

[0024] The structures of the double-layer casing 2 in the injection end vertical shaft section, the double-layer casing 4 in the directional drilling section, and the double-layer casing 6 in the extraction end vertical shaft section are the same. They all include several sections of polyurethane insulated outer casing 21 connected in series and several sections of polyurethane insulated inner casing 22 connected in series. The inner circle of the polyurethane insulated outer casing 21 and the outer circle of the polyurethane insulated inner casing 22 are fixed together by a cross-shaped first connecting rod 23. The two ends of each section of polyurethane insulated outer casing 21 and polyurethane insulated inner casing 22 are staggered by 100mm and the first connecting rod 23 is installed and fixed.

[0025] The horizontal well section double casing 5 includes an outer slotted liner 51 and an inner copper tube 52. The inner circle of the slotted liner 51 and the outer circle of the copper tube 52 are fixed together by a cross-shaped second connecting rod 53.

[0026] Each annular packer 7 includes an installation cylinder 71, a water-absorbing and expanding rubber cylinder 72, two limiting rings 73, and several bow-shaped straightening plates 75. The installation cylinder 71 is coaxially fitted onto the slotted liner 51. The water-absorbing and expanding rubber cylinder 72 and the two limiting rings 73 are both fitted onto the outer circumference of the installation cylinder 71. The two limiting rings 73 are located at the left and right ends of the water-absorbing and expanding rubber cylinder 72, respectively. Multiple screws 74 are provided circumferentially on the limiting rings 73. The screws 74 pass through the limiting rings 73, the installation cylinder 71, and the slotted liner 51 in sequence, fixing the installation cylinder 71 to the slotted liner 51. At the same time, the water-absorbing and expanding rubber tube 72 is fixed on the mounting tube 71; the bow-shaped straightening pieces 75 are respectively set on the outer circle of the mounting tube 71 on the left and right sides of the water-absorbing and expanding rubber tube 72. The left and right sides of the mounting tube 71 are provided with several sets of positioning structures evenly arranged in the circumferential direction. Each set of positioning structures includes two slots 76 arranged at intervals on the left and right. Each bow-shaped straightening piece 75 is bent at both ends and inserted into the two slots 76 of each set of positioning structures; the water-absorbing and expanding rubber tube 72 is a multi-component system composed of elastomer and hydrophilic material.

[0027] The gas-water separation device 8 includes an external gas distribution pipe 86, an exhaust pipe 87, and a drainage and insulation pipe 9. The lower end of the external gas distribution pipe 86 is connected to the upper port of the polyurethane insulation outer sleeve 21 of the double-layer casing 6 in the vertical shaft section of the extraction end via a flange assembly 81. The upper port of the external gas distribution pipe 86 is sealed, and the upper side of the external gas distribution pipe 86 is connected to the exhaust pipe 87. The upper end of the polyurethane insulation inner sleeve 22 of the double-layer casing 6 in the vertical shaft section of the extraction end passes through the external gas distribution pipe 86 and is connected to the drainage and insulation pipe 9. The exhaust pipe 87 is equipped with a gas integrated monitoring instrument 82 and an exhaust control valve 83. The drainage and insulation pipe 9 is equipped with a liquid integrated monitoring instrument 84 and a drainage control valve 85. The surface gas extraction pump 12 is installed on the exhaust pipe 87. The outlet of the exhaust pipe 87 is connected to the gas main pipeline 10, and the outlet of the drainage and insulation pipe 9 is connected to the central insulated water storage tank 11.

[0028] The specific process of step S1 is as follows: vertically drill the injection end vertical shaft section 1 and the extraction end vertical shaft section 3 at the predetermined location, perform directional drilling at the bottom of the injection end vertical shaft section 1, then cement the injection end vertical shaft section 1, the extraction end vertical shaft section 3 and the directional drilling section 31, after the cementing is completed, drill the horizontal shaft section 32, and finally complete the docking of the right end of the horizontal shaft section 32 and the lower end of the extraction end vertical shaft section 3. The specific process of step S2 is as follows: 2, 4, 5, and 6 are installed in the injection end vertical shaft section double casing, 4 in the directional drilling section double casing, 5 in the horizontal shaft section double casing, and 6 in the extraction end vertical shaft section. The lower end of the injection end vertical shaft section double casing 2 is connected to the upper left end of the directional drilling section double casing 4. A gas-water separation device 8 is connected to the extraction end vertical shaft section double casing 6 on the ground. The gas-water separation device 8 is connected to the central insulated water storage tank 11 and the surface gas extraction pump 12, respectively.

[0029] The specific process of step S3 is as follows: First, put the mounting sleeve 71 of the annular packer 7 onto the slotted liner 51. Then, put the water-absorbing and expanding rubber sleeve 72 onto the middle of the mounting sleeve 71. Next, install two limiting rings 73 to axially position the water-absorbing and expanding rubber sleeve 72. Use multiple screws 74 to fix the limiting rings 73 and the mounting sleeve 71 to the slotted liner 51. Then, insert the bent parts at both ends of the bow-shaped straightening plate 75 into the two slots 76 of a set of positioning structures, and repeat the same process. He fixed the bow-shaped centralizer 75 into the corresponding two slots 76. The outward protruding part of the bow-shaped centralizer 75 contacts the inner wall of the horizontal well section 32. The slotted liner 51 and copper pipe 52 are set along the center line of the horizontal well section 32. After all the annular packers 7 are installed in the above operation method, the left end of the horizontal well section double casing 5 is connected to the lower right end of the directional section double casing 4, and the right end of the horizontal well section double casing 5 is connected to the lower side of the extraction end vertical well section double casing 6.

[0030] The specific process of step S4 is as follows: clean water is injected into the annular cavity of the polyurethane insulation outer sleeve 21 and polyurethane insulation inner sleeve 22 of the double-layer casing 2 of the vertical well section at the injection end. The clean water enters between the outer circle of the copper pipe 52 and the inner circle of the slotted liner 51. The clean water also flows into the space between the slotted liner 51 and the inner wall of the horizontal well section 32 through the holes and slots on the slotted liner 51. After 72 hours of water injection, the water-absorbing expansion sleeve 72 begins to expand. After another 72 hours, the water-absorbing expansion sleeve 72 is fully expanded. The outer circle of the expanded water-absorbing expansion sleeve 72 seals the annulus between the inner wall of the horizontal well section 32 and the outer circle of the slotted liner 51, thus dividing the horizontal well section 32 into several sections. Next, the upper end of the double-casing 6 in the vertical shaft section of the extraction end is sealed. Fracturing fluid is injected into the annular cavity of the polyurethane insulated outer casing 21 and polyurethane insulated inner casing 22 in the vertical shaft section of the injection end. In several small sections separated by the annular packer 7, the pressure of the fracturing fluid gradually increases. The weakest section in each section starts to fracture first. As the fracture extends deeper, the pressure required for the fracture to continue to extend in this section will be greater than the initiation pressure of the weakest section. At this time, the weakest section begins to fracture. The horizontal well will form a step-by-step fracture initiation in the order of the weakest section, the weakest section, the second weakest section, and so on, so that the fracture development in the horizontal well is relatively uniform. When the fracture expansion is stable, the fracturing ends.

[0031] The specific process of step S5 is as follows: The upper port of the polyurethane insulation outer casing 21 of the injection end vertical shaft section 1 is closed; the upper port of the polyurethane insulation outer casing 21 of the extraction end vertical shaft section 3 is opened and connected to the gas-water separation device 8; the heated coal seam gas enters the slotted liner 51 through the coal seam fractures under the action of pressure difference; the gas flows under the promotion of the coal seam gas pressure gradient; softened cold water is continuously injected from the polyurethane insulation inner casing 22 of the injection end vertical shaft section 1; when the cold water reaches the copper pipe 52 of the horizontal shaft section 32, the high-temperature gas outside the copper pipe 52 transfers heat to the cold water through the copper pipe 52; the cold water in the copper pipe 52 gradually heats up during the flow in the horizontal shaft section 32; when the water in the copper pipe 52 flows to the bottom of the extraction end vertical shaft section 3, the water temperature reaches its highest value; the temperature of the water and gas in the double-layer casing 6 of the extraction end vertical shaft section gradually decreases; at this time, the extraction... Insulation measures are implemented, with the slotted liner 51 for gas extraction replaced by a polyurethane insulated outer sleeve 21, and the inner sleeve for water circulation replaced by a copper pipe 5252 replaced by a polyurethane insulated inner sleeve 22. When gas and water reach the gas-water separation device 8, the gas comprehensive monitoring instrument 82 on the exhaust pipe 87 monitors the pressure, temperature, and flow rate of the gas in real time, and the liquid comprehensive monitoring instrument 84 on the drainage insulation pipe 9 monitors the pressure, temperature, and flow rate of the hot water in real time. Finally, the gas is drawn into the main gas pipeline 10 by the surface gas extraction pump 12, and the gas from the extraction shaft section 3 in each area of ​​the mine also flows into the main gas pipeline 10. Hot water flows through the drainage insulation pipe 9 to the central insulation water storage tank 11, and the hot water circulating from the extraction shaft section 3 in each area of ​​the mine is also injected into the central insulation water storage tank 11 for storage. The hot water in the central insulation water storage tank 11 is then extracted and used in various parts of the mine.

[0032] The above embodiments illustrate the basic principles and features of the present invention, but are merely preferred embodiments and are not limited to these embodiments. Those skilled in the art, inspired by this patent, can make many modifications and improvements without departing from the spirit and scope of the claims, all of which fall within the scope of protection of the present invention. Therefore, the scope of this patent and its protection should be determined by the appended claims.

Claims

1. An integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation, characterized in that: Includes the following steps: S1. Construction of a U-shaped well, which includes, from left to right, a vertical well section at the injection end, a directional well section, a horizontal well section, and a vertical well section at the extraction end; S2. Arrange a double-casing assembly in the U-shaped well; the double-casing assembly includes a double-casing in the injection end vertical section, a double-casing in the build-up section, a double-casing in the horizontal section, and a double-casing in the extraction end vertical section; the lower end of the double-casing in the injection end vertical section is connected to the upper left end of the double-casing in the build-up section, the lower right end of the double-casing in the build-up section is connected to the left end of the double-casing in the horizontal section, and the right end of the double-casing in the horizontal section is connected to the lower end of the double-casing in the extraction end vertical section; S3. Install several annular packers on the double-layer casing assembly in the horizontal well section. The double-layer casing in the horizontal well section includes an outer slotted liner and an inner copper tube. The inner circle of the slotted liner and the outer circle of the copper tube are fixed together by a cross-shaped second connecting rod. Then, connect the double-layer casing assemblies of each section in series. S4. Hydraulic fracturing of the horizontal well section using a double-casing assembly; S5. Gas is extracted through a double-casing assembly, and cold water is injected through the same assembly. The high-temperature gas exchanges heat with the cold water. The upper port of the polyurethane insulation outer casing of the injection end vertical shaft section is sealed, and the upper port of the polyurethane insulation outer casing of the extraction end vertical shaft section is opened and connected to the gas-water separation device. The heated coal seam gas enters the slotted liner through the coal seam fracture under the action of pressure difference. The gas flows under the promotion of the coal seam gas pressure gradient. Softened cold water is continuously injected from the polyurethane insulation inner casing of the injection end vertical shaft section. When the cold water reaches the copper pipe in the horizontal shaft section, the high-temperature gas outside the copper pipe transfers heat to the cold water through the copper pipe. The cold water in the copper pipe gradually heats up during the flow in the horizontal shaft section. Cold water is heated to become hot water, and the gas is drawn into the main gas pipeline by the gas extraction pump on the ground. The hot water is stored in a central insulated water storage tank set up on the ground.

2. The integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation according to claim 1, characterized in that: Several annular packers are spaced along the left and right directions on the double casing of the horizontal well section. The upper end of the double casing of the vertical well section at the extraction end is equipped with a gas-water separation device. The outlet of the gas-water separation device is connected to the central insulated water storage tank. The gas outlet of the gas-water separation device is connected to the gas main pipeline through the surface gas drainage pump.

3. The integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation according to claim 2, characterized in that: The double-layer casing of the injection end vertical shaft section, the double-layer casing of the directional drilling section, and the double-layer casing of the extraction end vertical shaft section have the same structure. They all include several sections of polyurethane insulated outer casing connected in series and several sections of polyurethane insulated inner casing connected in series. The inner circle of the polyurethane insulated outer casing and the outer circle of the polyurethane insulated inner casing are fixed together by a cross-shaped first connecting rod. The two ends of each section of polyurethane insulated outer casing and polyurethane insulated inner casing are staggered by 100mm and the first connecting rod is installed and fixed thereon.

4. The integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation according to claim 3, characterized in that: Each annular packer includes an installation cylinder, a water-absorbing and expanding rubber tube, two limiting rings, and several bow-shaped straighteners. The installation cylinder is coaxially fitted onto the slotted liner. The water-absorbing and expanding rubber tube and the two limiting rings are fitted onto the outer circumference of the installation cylinder. The two limiting rings are located at the left and right ends of the water-absorbing and expanding rubber tube, respectively. Multiple screws are provided around the circumference of the limiting rings. The screws pass through the limiting rings, the installation cylinder, and the slotted liner, fixing the installation cylinder to the slotted liner and simultaneously fixing the water-absorbing and expanding rubber tube to the installation cylinder. The bow-shaped straighteners are respectively set on the outer circumference of the installation cylinder on the left and right sides of the water-absorbing and expanding rubber tube. Several sets of positioning structures are evenly arranged along the circumference on the left and right sides of the installation cylinder. Each set of positioning structures includes two slots arranged at intervals. Each bow-shaped straightener is bent at both ends and inserted into the two slots of each set of positioning structures. The water-absorbing and expanding rubber tube is a multi-component system composed of an elastomer and a hydrophilic substance.

5. The integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation according to claim 4, characterized in that: The gas-water separation device includes an external gas distribution pipe, an exhaust pipe, and a drainage insulation pipe. The lower end of the external gas distribution pipe is connected to the upper port of the polyurethane insulation outer sleeve of the double-layer casing of the extraction end vertical shaft section through a flange assembly. The upper port of the external gas distribution pipe is sealed, and the upper side of the external gas distribution pipe is connected to the exhaust pipe. The upper end of the polyurethane insulation inner sleeve of the double-layer casing of the extraction end vertical shaft section passes through the external gas distribution pipe and is connected to the drainage insulation pipe. The exhaust pipe is equipped with a gas integrated monitoring instrument and an exhaust control valve, and the drainage insulation pipe is equipped with a liquid integrated monitoring instrument and a drainage control valve. The surface gas extraction pump is installed on the exhaust pipe. The outlet of the exhaust pipe is connected to the gas main pipeline, and the outlet of the drainage insulation pipe is connected to the central insulation water storage tank.

6. The integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation according to claim 5, characterized in that: The specific process of step S1 is as follows: vertically drill the injection end vertical shaft section and the extraction end vertical shaft section at the predetermined location, perform directional drilling at the bottom of the injection end vertical shaft section, then cement the injection end vertical shaft section, the extraction end vertical shaft section and the directional drilling section, after the cementing is completed, drill the horizontal well section, and finally complete the docking of the right end of the horizontal well section and the lower end of the extraction end vertical shaft section. The specific process of step S2 is as follows: Run in the injection end vertical shaft section double casing, the directional section double casing, the horizontal section double casing and the extraction end vertical shaft section double casing. The lower end of the injection end vertical shaft section double casing is connected to the upper left end of the directional section double casing. The extraction end vertical shaft section double casing is connected to a gas-water separation device on the ground. The gas-water separation device is connected to the central insulated water storage tank and the surface gas extraction pump.

7. The integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation according to claim 6, characterized in that: The specific process of step S3 is as follows: First, put the installation sleeve of the annular packer onto the slotted liner. Then, put the water-absorbing expansion sleeve into the middle of the installation sleeve. Next, install two limiting rings to axially position the water-absorbing expansion sleeve. Use multiple screws to fix the limiting rings and the installation sleeve onto the slotted liner. Then, insert the bent parts at both ends of the bow-shaped centralizer into the two slots of a set of positioning structures. In the same way, fix and install the other bow-shaped centralizers into the corresponding two slots. The outward protruding part of the bow-shaped centralizer contacts the inner wall of the horizontal well section. Set the slotted liner and copper pipe along the center line of the horizontal well section. After all the annular packers are installed according to the above steps, connect the left end of the horizontal well section double casing to the lower right end of the directional section double casing, and connect the right end of the horizontal well section double casing to the lower side of the extraction end vertical well section double casing.

8. The integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation according to claim 7, characterized in that: The specific process of step S4 is as follows: clean water is injected into the annular cavity of the polyurethane insulation outer casing and the polyurethane insulation inner casing of the double-layer casing of the injection end vertical well section. The clean water enters between the outer circle of the copper pipe and the inner circle of the slotted liner. The clean water also flows into the space between the slotted liner and the inner wall of the horizontal well section through the holes and slots on the slotted liner. After 72 hours of water injection, the water-absorbing expansion rubber sleeve begins to expand. After another 72 hours, the water-absorbing expansion rubber sleeve is fully expanded. The outer circle of the expanded water-absorbing expansion rubber sleeve seals the annulus between the inner wall of the horizontal well section and the outer circle of the slotted liner, thus dividing the horizontal well section into several segments. Next, the upper end of the double-casing in the extraction section of the vertical shaft is sealed. Fracturing fluid is injected into the annular cavity of the polyurethane-insulated outer casing and the polyurethane-insulated inner casing in the injection section of the vertical shaft. In several small sections separated by the annular packer, the pressure of the fracturing fluid gradually increases. The weakest section in each section begins to fracture first. As the fracture extends deeper, the pressure required for the fracture to continue to extend in this section will be greater than the initiation pressure of the weakest section. At this point, the weakest section begins to fracture. In the horizontal well, fractures will be initiated in a stepwise manner in order of strength, from the weakest section to the second weakest section, resulting in relatively uniform fracture development in the horizontal well. Fracturing ends when the fracture extension stabilizes.

9. The integrated method for deep coal seam gas extraction without roadways and deep geothermal resource exploitation according to claim 8, characterized in that: The specific process of step S5 is as follows: When the water in the copper pipe flows to the bottom of the extraction shaft section, the water temperature reaches its highest value. The temperature of the water and gas in the double-layer casing of the extraction shaft section will gradually decrease. At this time, insulation measures are taken. The slotted liner for gas extraction is replaced with a polyurethane insulated outer casing, and the inner casing for water circulation is replaced with a polyurethane insulated inner casing. When the gas and water reach the gas-water separation device, the gas comprehensive monitoring instrument on the exhaust pipe monitors the pressure, temperature, and flow rate of the gas in real time, and the liquid comprehensive monitoring instrument on the drainage insulation pipe monitors the pressure, temperature, and flow rate of the hot water in real time. Finally, the gas is drawn into the gas main pipeline by the gas extraction pump on the ground. The gas from the extraction shaft sections in various areas of the mine also flows into the gas main pipeline. The hot water flows to the central insulation water tank through the drainage insulation pipe. The hot water circulating from the extraction shaft sections in various areas of the mine is also injected into the central insulation water tank for storage. The hot water in the central insulation water tank is then extracted to various parts of the mine for use.

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