Coal mining full-life-cycle coal, gas and heat combined development method

Abstract

The invention discloses a coal mining full-life-cycle coal, gas and heat combined development method which comprises the following steps: before coal mining, carrying out combined development on coal series gas and terrestrial heat in a coal series reservoir through a ground combined development well; in the coal mining process, coal seam gas is extracted through bottom drainage roadway gas extraction holes, circulating water pipes are arranged in an underground bottom drainage roadway or a coal face air return roadway and a transportation roadway, cold water is injected from the ground for cyclic heating while coal mining is conducted, and combined development of coal, gas and terrestrial heat is achieved; after coal mining, a goaf is filled and blocked to form a relatively closed mining influence body, coal gas and hot water in the mining influence body are extracted through the ground coal gas extraction hole and the geothermal energy extraction hole, and combined development of the coal gas and geothermal energy in the mining influence body is achieved. According to the application, transformation and upgrading of coal resource development from single energy acquisition to multi-energy collaborative, efficient and clean utilization are promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalbed methane, geothermal development and coal mining, and specifically relates to a method for the joint development of coal, gas and heat throughout the entire life cycle of coal mining. Background Art

[0002] Coal seams and their surrounding rocks are rich in coal-measure gas (including coalbed methane, coal-measure shale gas, and tight gas) and geothermal energy, providing a promising foundation for multi-energy co-mining. During traditional coal mining, coal-measure gas often escapes in large quantities due to untimely extraction, resulting in wasteful resources, serious safety hazards, and greenhouse gas emissions. Furthermore, the development and utilization of geothermal resources has not received sufficient attention, resulting in the waste of this clean energy and the high cost of using traditional cooling methods (such as air conditioning) during high-temperature coal mining operations.

[0003] Existing coal mining, coal-bearing gas, and geothermal development are mostly isolated operations based on subsystems and specific objectives. They lack systematic coordination and joint mechanisms, making it difficult to achieve complementary coupling between resources and maximize benefits. Furthermore, the mining process lacks a sustainable development path for residual energy in goafs, resulting in low efficiency in comprehensive resource utilization throughout the coal mine lifecycle. Therefore, a new model for multi-energy collaborative development, encompassing the entire pre-, mid-, and post-coal mining process, is needed: a method for the combined development of coal, gas, and heat throughout the entire coal mining lifecycle to achieve efficient and clean development of these multiple resources. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for the joint development of coal, gas and heat throughout the entire life cycle of coal mining, which runs through the entire process before, during and after coal mining. This method realizes the efficient and clean development of coal, gas and heat resources through a new model of collaborative development.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The method for the joint development of coal, gas and heat throughout the coal mining life cycle includes the following steps: (1) Before coal mining, the coal-bearing gas and geothermal energy in the coal-bearing reservoirs are jointly developed through ground joint development wells; (2) During coal mining, coal seam gas is extracted through gas extraction holes in the bottom extraction lanes. By arranging circulating water pipes in the underground bottom extraction lanes or the return air lanes and transport lanes of the coal mining face, cold water is injected from the ground for circulating heating while coal is being mined, thus realizing the joint development of coal, gas and geothermal energy. (3) After coal mining, the goaf is filled and sealed to form a relatively closed mining influence body. The coal-bearing gas and hot water in the mining influence body are extracted through the ground coal-bearing gas extraction holes and geothermal extraction holes to realize the joint development of coal-bearing gas and geothermal energy in the mining influence body.

[0006] The specific operation process of step (1) includes the following sub-steps: ① First, determine the well type for the combined development of coal-measure gas and geothermal energy. Based on the reservoir resource conditions, reservoir reformability, and stress sensitivity, determine the perforation layers for vertical and inclined wells, as well as the horizontal sections for horizontal wells, and then determine the perforation pattern. ② Implement drilling, completion, perforating and hydraulic fracturing operations for joint development wells; ③ For vertical wells, inclined wells and L-shaped horizontal wells, cold water is injected into the bottom of the joint development well through the cold water return pipe in the wellbore. For U-shaped horizontal wells, cold water is injected directly through the outer casing. The cold water absorbs heat from the surrounding formation while flowing in the casing of each well; ④ The joint development wells are dewatered and depressurized. The heated cold water and the original hot water in the reservoir are pumped out to the surface through the oil pipeline. During this period, the water injection rate is lower than the water production rate, so that the bottom hole pressure drops steadily. The coal-measure gas enters the wellbore from the reservoir and is produced to the surface through the outer casing; ⑤ After the development of coal-bearing gas is completed, continue to inject cold water into the joint development well, and extract the heated cold water and reservoir hot water through the oil pipeline for geothermal development.

[0007] The types of joint development wells include vertical wells, inclined wells, L-shaped horizontal wells and U-shaped horizontal wells; The specific operation process of step ② is as follows: drilling and completion operations are carried out, joint development wells penetrate the ground, horizontal sections of L-shaped and U-shaped horizontal wells are drilled to the preferred horizon, and vertical wells and inclined wells are drilled to at least 100 m below the main mining seam and the preferred horizon to ensure sufficient heat exchange; During the completion phase, the L-shaped horizontal well casings in L-shaped horizontal wells and U-shaped horizontal wells include surface casing, technical casing and production casing in sequence, and the vertical well casings in vertical wells, inclined wells and U-shaped horizontal wells include surface casing and production casing in sequence; Then perforation is carried out, and fracturing fluid and proppant are pumped into the coal-bearing gas reservoir through the ground and production casing to implement hydraulic fracturing.

[0008] The specific operation process of step ③ is as follows: For L-shaped horizontal wells, vertical wells and inclined wells, the cold water flowing out of the heat exchange station is injected into the bottom of the well through the ground and the cold water return pipe. For U-shaped horizontal wells, the cold water flowing out of the heat exchange station is directly injected into the outer casing through the ground. The cold water flows in the outer casing and absorbs the heat of the surrounding formation.

[0009] The specific operation process of step ④ is as follows: the heated cold water and the hot water produced by the coal-bearing gas reservoir are discharged from the ground through the oil pipeline, enter the heat exchange station through the water treatment device, and the heat is supplied to geothermal users. The coal-bearing gas is produced from the coal seam roof, the main mining coal seam and the coal seam floor to the outer casing, then produced to the ground and enters the gas gathering station, realizing the joint development of coal-bearing gas and geothermal energy.

[0010] The specific operation process of step ⑤ is as follows: after the development of coal-bearing gas is stopped, the L-shaped horizontal wells, vertical wells and inclined wells continue to inject the cold water flowing out of the heat exchange station into the bottom of the well through the ground and the cold water return pipe. The U-shaped horizontal wells continue to inject the cold water flowing out of the heat exchange station directly into the outer casing through the ground. After the cold water flows in the outer casing and absorbs the heat of the surrounding formations, it is discharged to the ground through the oil pipeline together with the hot water produced by the coal-bearing gas reservoir, and enters the heat exchange station through the water treatment device. The heat is supplied to geothermal users, realizing the continuous geothermal development of abandoned coal-bearing gas wells.

[0011] The specific operation process of step (2) includes the following sub-steps: ① Circulating water pipes are arranged in the bottom extraction lanes, return air lanes and transport lanes of the coal mining face and connected to the ground. The bottom extraction lanes are permanent lanes, and the circulating water pipes are metal pipes buried around the lane walls. The return air lanes and transport lanes of the coal mining face are temporary lanes, and the circulating water pipes are plastic hoses hung around the lanes except the bottom, and their positions are adjusted as the coal mining face moves; ② Before coal mining, extract coal seam gas through gas extraction holes in the bottom extraction tunnel; ③ While coal mining is being carried out in the cut, cold water is injected into the ground through the injection pipe. The cold water is heated in the tunnel and then discharged to the ground through the extraction pipe.

[0012] In step ①, the plastic hose is placed in the return air chute and the transport chute of the coal mining face; The specific operation process of step ③ is: while carrying out coal mining operations in the cut eye, the cold water flowing out of the heat exchange station is injected into the bottom extraction tunnel and the return air chute and transport chute of the coal mining working face through the cold water injection pipe via the ground, wellbore, underground tunnel, and connecting tunnel. After the cold water is circulated and heated, it flows into the water treatment device and heat exchange station through the hot water extraction pipe via the connecting tunnel, underground tunnel, wellbore, and ground. The heat is supplied to geothermal users to realize the joint development of coal, gas and geothermal energy.

[0013] The specific operation process of step (3) includes the following sub-steps: ①Fill and seal the coal mine goaf to construct a relatively closed mining impact body, including the collapse zone and upper and lower fault zones formed by coal mining collapse; ② Arrange surface coal-measure gas extraction boreholes, drill to the upper fault zone of the mining-affected body, and extract the residual coalbed methane in the mining-affected body, the shale gas in the rock formations of the collapse zone and fault zone, as well as the tight gas and the post-biogas generated by the continuous degradation of coal rock organic matter by microorganisms; ③ Arrange ground geothermal development boreholes, drill the boreholes to the lower part of the collapse zone of the mining-affected body, inject cold water into the mining-affected body through the cold water injection boreholes, and at the same time, groundwater flow replenishes water to the mining-affected body to form a mining-affected body reservoir. After heating, extract hot water through hot water extraction boreholes.

[0014] In step ③, after the water in the reservoir of the mining-affected body fully absorbs heat, the hot water in the mining-affected body is extracted through the hot water extraction borehole. After being pumped out of the ground, it enters the water treatment device and the heat exchange station in turn. The heat is supplied to geothermal users, realizing the joint development of coal-bearing gas and geothermal energy.

[0015] This application includes three stages: the joint development of coal-measure gas and geothermal energy before coal mining, the joint development of coal, gas and geothermal energy during coal mining, and the joint development of coal-measure gas and geothermal energy after coal mining. Before coal mining, the coal-measure gas in the coal seam and its surrounding rock is developed through ground coal-measure gas and geothermal joint development wells; at the same time, the geothermal energy is circulated and developed through the injection of ground cold water, heat exchange in the wellbore, and hot water extraction from oil pipes. During coal mining, while mining, various methods are used to extract coal seam gas, and the geothermal energy is circulated and developed, and the heat damage of the coal mine is controlled by injecting ground cold water into permanent tunnel buried pipes for heat exchange, and by mobile hoses for heat exchange in the coal mining working face air lane and machine lane. After coal mining, the coal mine goaf is filled and sealed to form a relatively closed mining influence body. The coal-measure gas in the mining influence body is then extracted through ground drilling, and a mining influence body reservoir is formed through groundwater runoff replenishment or ground cold water injection. After heating, hot water is extracted through ground drilling. Based on the depth of coal mining and geothermal temperature, the ground heat of different temperatures is utilized in a graded manner. This achieves the coordinated development and efficient utilization of coal, gas, and heat throughout the entire coal mining life cycle, promotes the transformation and upgrading of coal resource development from a single energy source to the coordinated, efficient, and clean utilization of multiple energy sources, and provides key technical support for the construction of a new energy system that combines green development of coal resources and multi-energy complementarity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Flowchart of the present invention.

[0017] Figure 2 Schematic diagram of the structure of the L-shaped horizontal well in the joint development method of the present invention.

[0018] Figure 3 This is a schematic diagram of the structure of the vertical well in the joint development method of the present invention.

[0019] Figure 4 It is a structural schematic diagram of the inclined well in the joint development method of the present invention.

[0020] Figure 5 It is a structural schematic diagram of the U-shaped horizontal well in the joint development method of the present invention.

[0021] Figure 6 It is a structural schematic diagram of the joint development of coal and geothermal energy in coal mining according to the present invention.

[0022] Figure 7 This is a schematic diagram of the structure of the joint development of coal-measure gas and geothermal energy after coal mining in the present invention. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are further described below with reference to the accompanying drawings.

[0024] like Figure 1-7 As shown in the figure, the method of joint development of coal, gas and heat throughout the life cycle of coal mining includes the following steps: (1) Joint development of coal-measure gas and geothermal energy before coal mining. Specifically, before coal mining, the coal-measure gas and geothermal energy in the coal-measure reservoir are jointly developed through a joint development well on the ground; The specific operation process includes the following sub-steps: ① Determine the well type, perforation layer and method. Specifically, first determine the well type for the joint development of coal-measure gas and geothermal energy. According to the reservoir resource conditions, reservoir reformability and stress sensitivity, determine the perforation layer of vertical wells, inclined wells and the horizontal layer of horizontal wells, and then determine the perforation method. The types of joint development wells include vertical wells, inclined wells, L-type horizontal wells and U-type horizontal wells. In vertical wells, such as Figure 3 As shown, a vertical well extends vertically downward through the overlying rock strata, coal seam roof 12, main mining coal seam 13, and coal seam floor 14. A gas gathering station 2, water treatment device 3, and heat exchange station 4 are located on the ground 1. The hot water outlet of the heat exchange station 4 is connected to the heat supply inlet of a geothermal user 5, and the cold water return port of the heat exchange station 4 is connected to the cold water return port of the geothermal user 5. The water outlet of the water treatment device 3 is connected to the water inlet of the heat exchange station 4. The air inlet of the gas gathering station 2 is connected to an exhaust pipe, which is connected to an outer casing 11. The outer casing 11 is arranged along the vertical well. The water inlet of the water treatment device 3 is connected to an oil pipe 10, and the cold water return port of the heat exchange station 4 is connected to a cold water return pipe 9. The oil pipe 10 and the cold water return pipe 9 are arranged within the outer casing 11. The vertical well includes surface casing 6 and production casing 8.

[0025] The inclined shaft includes an upper straight section perpendicular to the ground and a lower inclined section that passes through the overlying rock layer, the coal seam roof 12, the main mining coal seam 13 and the coal seam floor 14 in sequence. The upper straight section and the lower inclined section are interconnected. In the inclined shaft, Figure 4 As shown, the gas gathering station 2, water treatment device 3, and heat exchange station 4 are installed on the ground 1. The hot water outlet of the heat exchange station 4 is connected to the heat supply inlet of the geothermal user 5, and the cold water return outlet of the heat exchange station 4 is connected to the cold water return outlet of the geothermal user 5. The water outlet of the water treatment device 3 is connected to the water inlet of the heat exchange station 4. The air inlet of the gas gathering station 2 is connected to an exhaust pipe, which is connected to an outer casing 11. The outer casing 11 is arranged along the inclined well. The water inlet of the water treatment device 3 is connected to an oil pipe 10. The cold water return outlet of the heat exchange station 4 is connected to a cold water return pipe 9. The oil pipe 10 and the cold water return pipe 9 are installed in the outer casing 11. The upper straight section includes surface casing 6 and production casing 8.

[0026] The L-shaped horizontal well includes a vertical section perpendicular to the ground and a horizontal section arranged in the coal seam roof 12, and the vertical section and the horizontal section are connected to each other; in the L-shaped horizontal well, Figure 2 As shown, the corresponding gas gathering station 2, water treatment device 3, and heat exchange station 4 are installed on the ground 1. The hot water outlet of the heat exchange station 4 is connected to the heat supply inlet of the geothermal user 5, and the cold water return port of the heat exchange station 4 is connected to the cold water return port of the geothermal user 5. The water outlet of the water treatment device 3 is connected to the water inlet of the heat exchange station 4. The air inlet of the gas gathering station 2 is connected to an exhaust pipe, which is connected to an outer casing 11. The outer casing 11 is arranged along the L-shaped horizontal well. The water inlet of the water treatment device 3 is connected to an oil pipeline 10, and the cold water return port of the heat exchange station 4 is connected to a cold water return pipe 9. The oil pipeline 10 and the cold water return pipe 9 are arranged in the outer casing 11. The L-shaped horizontal well includes surface casing 6, technical casing 7, and production casing 8.

[0027] The U-shaped horizontal well includes an L-shaped horizontal well on the left and a vertical well on the right. The vertical well on the right goes vertically downward from the ground and sequentially passes through the overlying rock layer, the coal seam roof 12, the main mining coal seam 13 and the coal seam floor 14. The L-shaped horizontal well includes a vertical section vertically downward from the ground and a horizontal section set in the coal seam roof 12. The vertical section and the horizontal section are connected to each other. The right end of the horizontal section of the L-shaped horizontal well is connected to the vertical well through a cavitation. In the U-shaped horizontal well, as shown in FIG. Figure 5 As shown, the corresponding gas gathering station 2, water treatment device 3 and heat exchange station 4 are arranged on the ground 1, the hot water outlet of the heat exchange station 4 is connected to the heat inlet of the geothermal user 5, the cold water return port of the heat exchange station 4 is connected to the cold water return port of the geothermal user 5, the outlet of the water treatment device 3 is connected to the water inlet of the heat exchange station 4, the air inlet of the gas gathering station 2 is connected to the exhaust pipe, the exhaust pipe is connected to the outer casing 11, the outer casing 11 is arranged along the vertical well, the water inlet of the water treatment device 3 is connected to the oil pipe 10, the oil pipe 10 is arranged in the outer casing 11, and the bottom end of the oil pipe 10 extends to the cavitation site, the cold water return port of the heat exchange station 4 is connected to the cold water return pipe 9, and the cold water return pipe 9 is connected to another outer casing 111 arranged in the L-shaped horizontal well, the L-shaped horizontal well includes a surface casing 6, a technical casing 7 and a production casing 8, and the vertical well includes a surface casing 6 and a production casing 8.

[0028] ② Implement drilling, completion, perforation and hydraulic fracturing operations for the joint development wells; specifically, implement drilling and completion operations, with the joint development wells penetrating the ground 1, the horizontal sections of the L-type and U-type horizontal wells being drilled to the preferred stratum, and the vertical wells and inclined wells being drilled to at least the main mining coal seam 13 and 100 m below the preferred stratum to ensure sufficient heat exchange. During the completion phase, the L-type horizontal well casings in the L-type horizontal wells and the U-type horizontal wells include surface casing 6, technical casing 7 and production casing 8 in sequence, and the vertical wells in the vertical wells, inclined wells and U-type horizontal wells include surface casing 6 and production casing 8 in sequence; then, perforation is implemented, and fracturing fluid and proppant are pumped into the coal-bearing gas reservoir through the ground 1 and production casing 8 to implement hydraulic fracturing.

[0029] ③ Cold water is injected into the surface 1 and circulated for heating. Specifically, for vertical wells, inclined wells and L-shaped horizontal wells, cold water is injected into the bottom of the joint development well through the cold water return pipe 9 in the wellbore 19. For U-shaped horizontal wells, cold water is directly injected through the outer casing 11. The cold water absorbs the heat of the surrounding formations while flowing in the casings of various wells. Furthermore, for L-shaped horizontal wells, vertical wells and inclined wells, the cold water flowing out of the heat exchange station 4 is injected into the bottom of the well through the surface 1 and the cold water return pipe 9. For U-shaped horizontal wells, the cold water flowing out of the heat exchange station 4 is directly injected into the outer casing 11 through the surface 1. The cold water flows in the outer casing 11 and absorbs the heat of the surrounding formations.

[0030] ④ Drainage and pressure reduction, joint development of coal-bearing gas and geothermal energy. Specifically, the joint development wells are drained and pressure reduced, and the heated cold water and the original hot water in the reservoir are pumped out of the ground 1 through the oil pipe 10. During this period, the water injection volume is lower than the water production volume, so that the bottom hole pressure drops steadily, and the coal-bearing gas enters the wellbore 19 from the reservoir and is produced on the ground 1 through the outer casing 11; further, the heated cold water and the hot water produced from the coal-bearing gas reservoir are discharged from the ground 1 through the oil pipe 10 together, and enter the heat exchange station 4 through the water treatment device 3. The heat is supplied to the geothermal users 5. The coal-bearing gas is produced from the main coal seam 13, the coal seam roof 12 and the coal seam floor 14 to the outer casing 11, and then produced on the ground 1 and enters the gas gathering station 2, realizing the joint development of coal-bearing gas and geothermal energy.

[0031] ⑤ Continue geothermal energy development after coal-measure gas development. Specifically, after coal-measure gas development is completed, continue to inject cold water into the joint development well, and extract the heated cold water and reservoir hot water through the oil pipe 10 for geothermal development. Furthermore, after coal-measure gas development is stopped, the L-shaped horizontal wells, vertical wells, and inclined wells continue to inject the cold water flowing out of the heat exchange station 4 into the well bottom through the ground 1 and the cold water return pipe 9. The U-shaped horizontal wells continue to inject the cold water flowing out of the heat exchange station 4 directly into the outer casing 11 through the ground 1. The cold water flows in the outer casing 11 and absorbs heat from the surrounding formations. After that, it is discharged from the ground 1 through the oil pipe 10 together with the hot water produced by the coal-measure gas reservoir. It enters the heat exchange station 4 through the water treatment device 3, and the heat is supplied to the geothermal users 5, realizing the continuous geothermal development of abandoned coal-measure gas wells.

[0032] (2) Joint development of coal and geothermal energy in coal mining. Specifically, during the coal mining process, coal seam gas is extracted through the gas extraction holes 18 in the bottom extraction tunnel 17. By arranging circulating water pipes in the underground bottom extraction tunnel 17 or the return air tunnel and transportation tunnel of the coal mining face, cold water is injected from the ground 1 for circulating heating during coal mining, thereby realizing the joint development of coal, gas and geothermal energy. The specific operation process of step (2) includes the following sub-steps: ① Laying of water pipes in the bottom extraction tunnel 17 and the coal mining face tunnel. Specifically, circulating water pipes are laid in the bottom extraction tunnel 17, the return air tunnel of the coal mining face, and the transport tunnel underground in the coal mine and connected to the ground 1. The bottom extraction tunnel 17 is a permanent tunnel, and the circulating water pipes are metal pipes buried around the tunnel walls. The return air tunnel and the transport tunnel of the coal mining face are temporary tunnels, and the circulating water pipes are plastic hoses hung around the tunnel except at the bottom, and their positions are adjusted as the coal mining face moves. The plastic hoses are installed in the return air chute 22 and the transport chute 23 of the coal mining face. ② Before coal mining, coal seam gas is extracted through the bottom extraction lane 17. Specifically, before coal mining, coal seam gas is extracted through the gas extraction holes 18 in the bottom extraction lane 17; ③ Simultaneously with coal mining, cold water is injected into the surface 1 for circulation and heating to develop geothermal energy. Specifically, while coal mining is underway, cold water is injected underground through an injection pipe. The cold water is heated in the roadway and then discharged to the surface 1 through an extraction pipe. Furthermore, while coal mining is underway, cold water flowing out of the heat exchange station 4 is injected through the cold water injection pipe 15 via the surface 1, shaft 19, underground roadway 20, and connecting roadway 21 into the bottom extraction roadway 17, as well as the return air chute 22 and transport chute 23 of the coal mining face. After circulation and heating, the cold water flows through the hot water extraction pipe 16, connecting roadway 21, underground roadway 20, shaft 19, and surface 1 into the water treatment device 3 and heat exchange station 4. Heat is then supplied to geothermal users 5, achieving the combined development of coal, gas, and geothermal energy.

[0033] (3) Joint development of coal-bearing gas and geothermal energy after coal mining. Specifically, after coal mining, the goaf 25 is filled and sealed to form a relatively closed mining-affected body 29. The coal-bearing gas and hot water in the mining-affected body 29 are extracted through the coal-bearing gas extraction holes 26 and geothermal extraction holes on the ground, thereby realizing the joint development of coal-bearing gas and geothermal energy in the mining-affected body 29.

[0034] The specific operation process of step (3) includes the following sub-steps: ① Fill and seal the coal mine goaf 25 to construct a relatively closed mining impact body 29, including the collapse zone and upper and lower fault zones formed by collapse after coal mining; ② Extraction of coal-measure gas from mining-affected body 29. Specifically, arrange a surface coal-measure gas extraction borehole 1, drill the borehole to the upper fault zone of mining-affected body 29, and extract the residual coalbed methane, shale gas in the rock formations of the collapse zone and fault zone, tight gas, and post-biogas generated by continuous degradation of coal rock organic matter by microorganisms within mining-affected body 29; ③ Recharge water to the mining-affected body 29 reservoir and extract hot water. Specifically, a geothermal development borehole is arranged on the surface 1 and drilled to the lower part of the collapse zone of the mining-affected body 29. Cold water is injected into the mining-affected body 29 through the cold water injection borehole 27. Simultaneously, groundwater flow replenishes water to the mining-affected body 29, forming a reservoir of the mining-affected body 29. After heating, hot water is extracted through the hot water extraction borehole 28. Furthermore, after the water in the reservoir of the mining-affected body 29 has fully absorbed heat, the hot water in the mining-affected body 29 is extracted through the hot water extraction borehole 28. After being pumped out of the surface 1, it enters the water treatment device 3 and the heat exchange station 4 in sequence. The heat is supplied to the geothermal user 5, realizing the joint development of coal-measure gas and geothermal energy.

[0035] There are two types of circulating water pipes. One type is the metal pipe used in permanent tunnels such as the bottom extraction tunnel 17 and is buried around the tunnel wall. The other type is the plastic hose used in temporary tunnels such as the return air tunnel and transport tunnel of the coal mining face and is hung around the tunnel except the bottom. The position is adjusted as the coal mining face moves.

[0036] The mining-affected body 29 includes a geological body formed by coal mining, which can enrich residual coal-measure gas and has a certain fracture space, including a collapse zone and upper and lower fault zones formed by collapse after coal mining.

[0037] The coal-bearing gas includes coalbed methane in residual coal, shale gas and tight gas in collapse zones and fault zone strata, as well as post-biogas generated by continuous degradation of coal rock organic matter by microorganisms. The hot water includes water injected into the mining-affected body 29 through the ground 1 geothermal development borehole and heated, and water supplied to the mining-affected body 29 through groundwater runoff and heated.

[0038] Geothermal resources include shallow (<200 m), middle (200-3000 m) and deep (>3000 m) hydrothermal geothermal resources with different temperatures.

[0039] This application includes three stages: the joint development of coal-measure gas and geothermal energy before coal mining, the joint development of coal, gas and geothermal energy during coal mining, and the joint development of coal-measure gas and geothermal energy after coal mining. Before coal mining, the coal-measure gas in the coal seam and its surrounding rock is developed through a ground-level coal-measure gas and geothermal joint development well 1; at the same time, the geothermal energy is circulated and developed by injecting cold water from the ground 1, exchanging heat in the wellbore 19, and extracting hot water from the oil pipe 10. During coal mining, while mining, various methods are used to extract coal seam gas, and the geothermal energy is circulated and developed by injecting cold water from the ground 1 into permanent tunnel buried pipes for heat exchange, and exchanging heat with mobile hoses in the coal mining working face ventilation lane and machine lane, and the heat damage in the coal mine is controlled. After coal mining, the goaf 25 of the coal mine is filled and sealed to form a relatively closed mining-affected body 29. The coal-bearing gas in the mining-affected body 29 is then extracted through a borehole on the ground 1. A reservoir of the mining-affected body 29 is formed through groundwater runoff or cold water injection from the ground 1. After heating, hot water is extracted through a borehole on the ground 1. Based on the depth of coal mining and geothermal temperature, the mined geothermal energy of different temperatures is graded and utilized on the ground 1. This achieves the coordinated development and efficient utilization of coal, gas, and heat throughout the entire life cycle of coal mining, promotes the transformation and upgrading of coal resource development from single energy acquisition to multi-energy coordinated, efficient, and clean utilization, and provides key technical support for the construction of a new energy system that combines green development of coal resources with multi-energy complementarity.

[0040] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for the combined development of coal, gas, and heat throughout the entire life cycle of coal mining, characterized by: The steps include: (1) Before coal mining, the coal-bearing gas and geothermal energy in the coal-bearing reservoirs are jointly developed through ground joint development wells; (2) During coal mining, coal seam gas is extracted through gas extraction holes in the bottom extraction lanes. By arranging circulating water pipes in the underground bottom extraction lanes or the return air lanes and transport lanes of the coal mining face, cold water is injected from the ground for circulating heating while coal is being mined, thus realizing the joint development of coal, gas and geothermal energy. (3) After coal mining, the goaf is filled and sealed to form a relatively closed mining influence body. The coal-bearing gas and hot water in the mining influence body are extracted through the ground coal-bearing gas extraction holes and geothermal extraction holes to realize the joint development of coal-bearing gas and geothermal energy in the mining influence body.

2. The method for the combined development of coal, gas and heat during the entire life cycle of coal mining according to claim 1, characterized in that: The specific operation process of step (1) includes the following sub-steps: ① First, determine the well type for the combined development of coal-measure gas and geothermal energy. Based on the reservoir resource conditions, reservoir reformability, and stress sensitivity, determine the perforation layers for vertical and inclined wells, as well as the horizontal sections for horizontal wells, and then determine the perforation pattern. ② Implement drilling, completion, perforating and hydraulic fracturing operations for joint development wells; ③ For vertical wells, inclined wells and L-shaped horizontal wells, cold water is injected into the bottom of the joint development well through the cold water return pipe in the wellbore. For U-shaped horizontal wells, cold water is injected directly through the outer casing. The cold water absorbs heat from the surrounding formation while flowing in the casing of each well; ④ The joint development wells are dewatered and depressurized. The heated cold water and the original hot water in the reservoir are pumped out to the surface through the oil pipeline. During this period, the water injection rate is lower than the water production rate, so that the bottom hole pressure drops steadily. The coal-measure gas enters the wellbore from the reservoir and is produced to the surface through the outer casing; ⑤ After the development of coal-bearing gas is completed, continue to inject cold water into the joint development well, and extract the heated cold water and reservoir hot water through the oil pipeline for geothermal development.

3. The method for the combined development of coal, gas and heat during the entire life cycle of coal mining according to claim 2, characterized in that: The types of joint development wells include vertical wells, inclined wells, L-shaped horizontal wells and U-shaped horizontal wells; The specific operation process of step ② is as follows: drilling and completion operations are carried out, joint development wells penetrate the ground, horizontal sections of L-shaped and U-shaped horizontal wells are drilled to the preferred horizon, and vertical wells and inclined wells are drilled to at least 100 m below the main mining seam and the preferred horizon to ensure sufficient heat exchange; During the completion phase, the L-shaped horizontal well casings in L-shaped horizontal wells and U-shaped horizontal wells include surface casing, technical casing and production casing in sequence, and the vertical well casings in vertical wells, inclined wells and U-shaped horizontal wells include surface casing and production casing in sequence; Then perforation is carried out, and fracturing fluid and proppant are pumped into the coal-bearing gas reservoir through the ground and production casing to implement hydraulic fracturing.

4. The method for the combined development of coal, gas and heat during the entire life cycle of coal mining according to claim 3, characterized in that: The specific operation process of step ③ is as follows: For L-shaped horizontal wells, vertical wells and inclined wells, the cold water flowing out of the heat exchange station is injected into the bottom of the well through the ground and the cold water return pipe. For U-shaped horizontal wells, the cold water flowing out of the heat exchange station is directly injected into the outer casing through the ground. The cold water flows in the outer casing and absorbs the heat of the surrounding formation.

5. The method for the combined development of coal, gas and heat during the entire life cycle of coal mining according to claim 4, characterized in that: The specific operation process of step ④ is as follows: the heated cold water and the hot water produced by the coal-bearing gas reservoir are discharged from the ground through the oil pipeline, enter the heat exchange station through the water treatment device, and the heat is supplied to geothermal users. The coal-bearing gas is produced from the coal seam roof, the main mining coal seam and the coal seam floor to the outer casing, then produced to the ground and enters the gas gathering station, realizing the joint development of coal-bearing gas and geothermal energy.

6. The method for the combined development of coal, gas and heat during the entire life cycle of coal mining according to claim 5, characterized in that: The specific operation process of step ⑤ is as follows: after the development of coal-bearing gas is stopped, the L-shaped horizontal wells, vertical wells and inclined wells continue to inject the cold water flowing out of the heat exchange station into the bottom of the well through the ground and the cold water return pipe. The U-shaped horizontal wells continue to inject the cold water flowing out of the heat exchange station directly into the outer casing through the ground. After the cold water flows in the outer casing and absorbs the heat of the surrounding formations, it is discharged to the ground through the oil pipeline together with the hot water produced by the coal-bearing gas reservoir, and enters the heat exchange station through the water treatment device. The heat is supplied to geothermal users, realizing the continuous geothermal development of abandoned coal-bearing gas wells.

7. The method for the combined development of coal, gas and heat during the entire life cycle of coal mining according to claim 1, characterized in that: The specific operation process of step (2) includes the following sub-steps: ① Circulating water pipes are arranged in the bottom extraction lanes, return air lanes and transport lanes of the coal mining face and connected to the ground. The bottom extraction lanes are permanent lanes, and the circulating water pipes are metal pipes buried around the lane walls. The return air lanes and transport lanes of the coal mining face are temporary lanes, and the circulating water pipes are plastic hoses hung around the lanes except the bottom, and their positions are adjusted as the coal mining face moves; ② Before coal mining, extract coal seam gas through gas extraction holes in the bottom extraction tunnel; ③ While coal mining is being carried out in the cut, cold water is injected into the ground through the injection pipe. The cold water is heated in the tunnel and then discharged to the ground through the extraction pipe.

8. The method for the combined development of coal, gas and heat during the entire life cycle of coal mining according to claim 7, characterized in that: In step ①, the plastic hose is placed in the return air chute and the transport chute of the coal mining face; The specific operation process of step ③ is: while carrying out coal mining operations in the cut eye, the cold water flowing out of the heat exchange station is injected into the bottom extraction tunnel and the return air chute and transport chute of the coal mining working face through the cold water injection pipe via the ground, wellbore, underground tunnel, and connecting tunnel. After the cold water is circulated and heated, it flows into the water treatment device and heat exchange station through the hot water extraction pipe via the connecting tunnel, underground tunnel, wellbore, and ground. The heat is supplied to geothermal users to realize the joint development of coal, gas and geothermal energy.

9. The method for the combined development of coal, gas and heat during the entire life cycle of coal mining according to claim 1, characterized in that: The specific operation process of step (3) includes the following sub-steps: ①Fill and seal the coal mine goaf to construct a relatively closed mining impact body, including the collapse zone and upper and lower fault zones formed by coal mining collapse; ② Arrange surface coal-measure gas extraction boreholes, drill to the upper fault zone of the mining-affected body, and extract the residual coalbed methane in the mining-affected body, the shale gas in the rock formations of the collapse zone and fault zone, as well as the tight gas and the post-biogas generated by the continuous degradation of coal rock organic matter by microorganisms; ③ Arrange ground geothermal development boreholes, drill the boreholes to the lower part of the collapse zone of the mining-affected body, inject cold water into the mining-affected body through the cold water injection boreholes, and at the same time, groundwater flow replenishes water to the mining-affected body to form a mining-affected body reservoir. After heating, extract hot water through hot water extraction boreholes.

10. The method for the combined development of coal, gas and heat during the entire life cycle of coal mining according to claim 9, characterized in that: In step ③, after the water in the reservoir of the mining-affected body fully absorbs heat, the hot water in the mining-affected body is extracted through the hot water extraction borehole. After being pumped out of the ground, it enters the water treatment device and the heat exchange station in turn. The heat is supplied to geothermal users, realizing the joint development of coal-bearing gas and geothermal energy.

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