In-situ coupled thermal-chemical-biological coal mining system and method

Abstract

The present application belongs to the technical field of oil-rich coal mining, and particularly discloses a coal in-situ coupled mining system and method of heat-chemistry-biology; the present application forms fissures in the horizontal well by hydraulic fracturing, and injects proppants to divide the underground coal seam into regions, sets the packer connected with the electric heater at the region boundary, sets the branch pipeline in the injection well and the horizontal well, and sets the valve and the corresponding temperature sensor on the branch pipeline in each region of the horizontal well; the normal-temperature fluid is input into the injection well, and the electric heater is turned on, at this time, the packer expands to close the horizontal well, after pyrolysis of the coal seam, the electric heater is turned off, and the microbial aqueous solution is input, the viscosity of the mixture is reduced by using the degradation of the polycyclic aromatic hydrocarbon by the microorganism and the emulsification of the water-oil mixture, the tar adhered and retained in the coal seam and the rock pore wall is effectively collected, the viscosity of the mixture is reduced, and the tar recovery rate is improved.

Description

Technical Field

[0001] This invention belongs to the field of oil-rich coal mining technology, specifically relating to a coupled thermo-chemical-biological in-situ coal mining system and method. Background Technology

[0002] In-situ pyrolysis of underground coal is an emerging coal utilization technology with many advantages, such as less surface pollution, lower carbon emissions, increased exploitable depth, and avoidance of surface subsidence. Similar methods have been applied to oil shale with initial success, and in-situ pyrolysis of underground coal for extracting oil and gas resources has a promising future.

[0003] In the in-situ pyrolysis of oil-rich coal, the pyrolysis products first accumulate in horizontal wells and then flow into production wells under the transport of heat carrier gas. However, the tar products from coal pyrolysis contain a large amount of heavy aromatic hydrocarbons, which have undesirable characteristics such as high molecular weight, high viscosity, and easy coking. These heavy components tend to be retained and block the fractures in the coal seam, hindering the transport of oil and gas products and reducing the product recovery rate.

[0004] To address the technical challenge of the easy condensation of heavy components in tar, current research often focuses on the equation of state and viscosity-temperature curves of tar substances, aiming to ensure the fluidity and recoverability of the product mixture by rationally controlling external temperature and pressure. However, the actual underground in-situ pyrolysis process is complex, and the reliability of predicting actual underground conditions and product precipitation and transport is difficult to guarantee. Therefore, relying solely on physical control of the products to improve recovery rates is insufficient. Summary of the Invention

[0005] The purpose of this invention is to provide a coupled thermo-chemical-biological coal in-situ mining system and method to solve the problem that coal pyrolysis tar products are easily trapped and block the cracks in the coal seam during extraction, hindering transportation and reducing the product extraction rate.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a coupled thermo-chemical-biological in-situ coal mining system, comprising:

[0008] The system includes an injection well, a production well, a horizontal well, an electric heater, a packer, and branch pipelines. The electric heater is located near the injection well. Branch pipelines are used to introduce a nutrient-rich microbial solution. Both the injection and production wells are perpendicular to the underground coal seam and run parallel to each other. The horizontal well runs parallel to the surface, with one end connected to the bottom of the injection well and the other end connected to the bottom of the production well. Branch pipelines are installed within the injection and horizontal wells. The underground coal seam is divided into multiple zones horizontally. Each zone has a corresponding branch pipeline with a valve and a temperature sensor. The packer is installed at the zone boundary within the horizontal well. The electric heater is connected to the packer, allowing ambient temperature fluid to be introduced from the injection well into the horizontal well. When the electric heater is activated, the packer expands at the high temperature, sealing the zone boundary. The ambient temperature fluid is heated by the electric heater to become a high-temperature fluid, pyrolyzing the coal seam and releasing oil and gas products.

[0009] Furthermore, the packer is connected to the electric heater in the horizontal direction, and the packer is located on the side closer to the production well.

[0010] Furthermore, the length of each region is 10-20m.

[0011] Furthermore, two parallel, interconnected horizontal wells are constructed between the injection well and the production well, located in the middle and bottom of the underground coal seam, respectively. Branch pipelines are installed in both the injection well and the two horizontal wells, and valves are installed in each area of ​​the branch pipelines in each of the two horizontal wells, along with temperature sensors corresponding to the valves. Packers connected to electric heaters are installed at the boundaries of the areas within each horizontal well.

[0012] Furthermore, a gas heater is installed at the entrance of the horizontal well, a formation temperature sensor is installed inside the horizontal well, and the produced well is connected to a gas concentration detector.

[0013] Secondly, the present invention provides a coupled thermo-chemical-biological in-situ coal mining method, and a coupled thermo-chemical-biological in-situ coal mining system based on any one of the above-mentioned methods, comprising:

[0014] Injection wells and production wells are drilled from the surface into the underground coal seam, and a horizontal well is drilled between the injection wells and the production wells; the underground coal seam is divided into zones along the horizontal direction;

[0015] Hydraulic fracturing is performed by injecting fracturing agent into the underground coal seam through the injection well to form fractures in the underground coal seam, and then injecting proppant.

[0016] Branch pipelines are laid in the injection well and the horizontal well. A valve and a corresponding temperature sensor are installed in each area of ​​the horizontal well. A packer connected to an electric heater is placed at the junction of the first area and the second area.

[0017] Ambient temperature fluid is introduced into the horizontal well from the injection well, and the electric heater is turned on at the same time. Under the high temperature of the electric heater, the packer expands and seals the boundary of the area. The ambient temperature fluid is heated by the electric heater and becomes a high temperature fluid, which pyrolyzes the coal seam and releases oil and gas products.

[0018] After the coal in the first zone is completely pyrolyzed, the electric heater is turned off, the packer temperature decreases, the seal on the horizontal well is released, and the oil and gas products are collected to the surface through the production well.

[0019] The packer is advanced to the boundary between the second and third zones, and the electric heater is restarted to seal and pyrolyze the coal seam in the second zone.

[0020] Temperature is detected in each area using temperature sensors. Valves in the first area are opened to allow a microbial aqueous solution containing nutrients to be introduced, flushing the fractures in the first area and extracting residual tar products. Some of the tar products flow out of the production well along with the oil and gas products in the second area and are collected.

[0021] Repeat the above steps until pyrolysis and tar collection are completed in all coal seam areas.

[0022] Furthermore, the introduced room-temperature fluid is nitrogen or carbon dioxide.

[0023] Furthermore, the valves on the branch pipelines are controlled by corresponding temperature sensors. When the temperature sensor in a region detects that the temperature of the coal seam in the region is lower than the temperature that microorganisms can tolerate, the corresponding valve opens. When the temperature in the next region is also lower than the temperature that microorganisms can tolerate, the valve closes and the corresponding valve in the next region opens.

[0024] Furthermore, the microorganisms can tolerate temperatures of 30-50°C.

[0025] Furthermore, the microorganism is Pseudomonas aeruginosa; the nutrients include carbon, nitrogen and phosphorus sources.

[0026] The present invention has at least the following beneficial effects:

[0027] 1. This invention involves hydraulic fracturing to create fractures in a horizontal well and injecting proppant to divide the underground coal seam into zones. A packer connected to an electric heater is placed at the zone boundaries. Branch pipelines are installed in both the injection well and the horizontal well. Each branch pipeline in the horizontal well is equipped with a valve and a corresponding temperature sensor. Ambient temperature fluid is introduced into the injection well, and the electric heater is turned on. At this point, the packer expands, sealing the horizontal well. After pyrolysis of the coal seam, the electric heater is turned off, and a microbial aqueous solution is introduced. Utilizing the degradation of polycyclic aromatic hydrocarbons (PAHs) and the emulsification of the water-oil mixture by the microorganisms, the viscosity of the produced mixture is reduced. This effectively collects tar adhering to and remaining on the coal seam and rock pore walls, thereby reducing the mixture viscosity and increasing tar recovery rate.

[0028] 2. This invention can improve the energy utilization rate of underground pyrolysis: First, the downhole heating fluid avoids heat loss during transmission; second, segmented pyrolysis can avoid heat waste caused by short circuits in the horizontal well; and finally, the heating power can be adjusted in real time using a temperature measurement-closed-loop control system. Attached Figure Description

[0029] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0030] Figure 1 This is a schematic diagram of a single horizontal well layout;

[0031] Figure 2 A schematic diagram of the microbial aqueous solution rinsing process;

[0032] Figure 3 This is a schematic diagram of a dual-horizontal-well layout;

[0033] Figure 4 This is a schematic diagram of the microbial secondary oil recovery process;

[0034] Reference numerals in the attached diagram: 1. Upper boundary of coal seam; 2. Underground coal seam; 3. Lower boundary of coal seam; 4. Fracture; 5. Injection well; 6. Production well; 7. Horizontal well; 8. Electric heater; 9. Packer; 10. Branch pipeline; 11. Valve; 12. Temperature sensor; 13. Area boundary; 14. Formation temperature detector; 15. Gas concentration detector; 16. Gas heater. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0036] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this invention is for describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0037] Example 1

[0038] like Figure 1 As shown, a coupled thermo-chemical-biological in-situ coal mining system includes:

[0039] 5. Injection well; 6. Production well; 7. Horizontal well; 8. Electric heater; 9. Packer; 10. Branch pipeline;

[0040] Both injection well 5 and extraction well 6 are opened perpendicular to the underground coal seam 2, and the opening directions of injection well 5 and extraction well 6 are parallel; horizontal well 7 is opened parallel to the ground surface, with one end of horizontal well 7 connected to the bottom end of injection well 5 and the other end of horizontal well 7 connected to the bottom end of extraction well 6.

[0041] Branch pipes 10 are installed in injection well 5 and horizontal well 7; underground coal seam 2 is divided into multiple areas along the horizontal direction, and a valve 11 is installed on the corresponding branch pipe 10 in each area, and a temperature sensor 12 corresponding to the valve 11 is installed in each area; packer 9 is installed at the area boundary 13 in horizontal well 7, and electric heater 8 is connected to packer 9.

[0042] As a further improvement of the present invention, the packer 9 is connected to the electric heater 8 in the horizontal direction, with the electric heater 8 located on the side closer to the injection well 5 and the packer 9 located on the side closer to the production well 6.

[0043] Packer 9 is an expansion packer, and the sealing components are made of materials that deform under heat, such as metal, rubber, or shape memory polymer.

[0044] Electric heater 8 is a resistance heater, and the resistance wire used for heating is made of Ni-Cr or Fe-Cr-Al alloy. The heating power of electric heater 8 is adjusted in real time using PID control based on the measured temperature of each zone.

[0045] As a further improvement of the present invention, the length of each region is 10-20m.

[0046] As a further improvement of the present invention, for areas with thicker coal seams, two parallel, through horizontal wells 7 are opened between the injection well 5 and the production well 6. The two parallel horizontal wells 7 are respectively opened in the middle and bottom of the underground coal seam 2. Branch pipes 10 are provided in both the injection well 5 and the two horizontal wells 7. Each area of ​​the branch pipes 10 is equipped with a valve 11 and a temperature sensor 12 corresponding to the valve. Packers 9 connected to electric heaters 8 are respectively set at the area boundary 13 in each horizontal well 7.

[0047] As a further improvement of the present invention, in view of the small coal seam area and the fact that microorganisms are not sensitive to environmental temperature requirements, a gas heater 16 is installed at the inlet of the horizontal well 7, a formation temperature sensor 14 is installed inside the horizontal well 7, and the production well 6 is connected to a gas concentration detector 15.

[0048] Example 2

[0049] A coupled thermo-chemical-biological in-situ coal mining method includes:

[0050] S1: Drill injection well 5 and production well 6 from the surface into the underground coal seam 2, and drill a horizontal well 7 between injection well 5 and production well 6; divide the underground coal seam 2 into areas along the horizontal direction, and drill directional boreholes at the boundary 13 of the areas along the normal direction of the plane formed by the horizontal well 7 and injection well 5 for subsequent hydraulic fracturing and placement of packers 9.

[0051] S2: Hydraulic fracturing is performed by injecting fracturing agent into the underground coal seam 2 through injection well 5, forming a certain distribution of fractures 4 in the underground coal seam 2, and then proppant is injected.

[0052] S3: A branch pipeline 10 is laid in the injection well 5 and the horizontal well 7 for subsequent introduction of a microbial solution containing nutrients; a valve 11 and a temperature sensor 12 corresponding to the valve 11 are installed in each area of ​​the branch pipeline 10 in the horizontal well 7; the opening and closing of the valve 11 is controlled by the corresponding temperature sensor 12; a packer 9 connected to an electric heater 8 is placed at the junction of the first area and the second area;

[0053] S4: Normal temperature fluid is introduced into horizontal well 7 from injection well 5, and electric heater 8 is turned on at the same time; at the high temperature of electric heater 8, packer 9 expands and seals the boundary 13 of the area; at the same time, the normal temperature fluid is heated into high temperature fluid by electric heater 8, which efficiently heats this part of the coal seam in the relatively closed area and releases oil and gas products.

[0054] S5: After the coal in the first zone is completely pyrolyzed, the electric heater 8 is turned off. With the continuous flow of room temperature fluid, the temperature of the packer 9 decreases, the seal on the horizontal well 7 is released, and the oil and gas products are collected to the surface through the production well 6.

[0055] S6: Push the packer 9 to the boundary between the second and third zones, and restart the electric heater 8 to seal and pyrolyze the coal seam in the second zone;

[0056] S7: Temperature is detected in each area using temperature sensor 12. When the temperature in the first area drops to a level tolerable for microorganisms, valve 11 in the first area opens, allowing a microbial aqueous solution containing nutrients to be introduced into the coal seam. This flushes the fissures in the first area and extracts any residual tar products. Figure 2 As shown. This portion of the tar products subsequently flowed out along with the oil and gas products from the second region and were collected in production well 6.

[0057] S8: Repeat the above steps until pyrolysis and tar collection are completed in all coal seam areas.

[0058] The room-temperature fluid introduced in step S4 is either nitrogen or carbon dioxide.

[0059] As a further improvement of this invention, the microorganism used to degrade coal tar is *Pseudomonas aeruginosa*. Nutrients include carbon, nitrogen, and phosphorus sources. A certain amount of oxygen is dissolved in the aqueous solution of the microorganisms to ensure their normal growth and metabolism.

[0060] As a further improvement of the present invention, the branch pipe 10 is an insulated pipe; the valve 11 on the branch pipe 10 is controlled by a corresponding temperature sensor 12. When the temperature sensor 12 in a region detects that the coal seam temperature in the region is lower than the temperature that microorganisms can tolerate, the corresponding valve 11 opens. When the temperature in the next region is also lower than the temperature that microorganisms can tolerate, the valve 11 is closed, and the corresponding valve 11 in the next region is opened.

[0061] As a further improvement of the present invention, the microorganisms can tolerate a temperature of 30-50°C.

[0062] As a further improvement of the present invention, the ambient temperature fluid introduced into the injection well 5 can be replaced by the pyrolysis gas collected in the production well 6.

[0063] Example 3

[0064] For areas with thin coal seams, a combined thermal-chemical-biological in-situ coal mining method includes the following steps:

[0065] S1: Drill injection well 5 and production well 6 from the surface into the underground coal seam 2, and drill a horizontal well 7 connecting injection well 5 and production well 6; divide the underground coal seam 2 into regions along the horizontal direction, with each region being a pyrolysis sub-region every 15m. Perform directional drilling at the region boundary 13 for subsequent hydraulic fracturing and placement of packers 9;

[0066] S2: Hydraulic fracturing is performed by injecting fracturing agent into the underground coal seam 2 through injection well 5, forming a certain distribution of fractures 4 in the underground coal seam 2, and then proppant is injected.

[0067] S3: A branch pipeline 10 is laid in the injection well 5 and the horizontal well 7. A valve 11 and a temperature sensor 12 corresponding to the valve 11 are installed in each area of ​​the horizontal well 7. The opening and closing of the valve 11 is controlled by the corresponding temperature sensor 12. The packer 9 connected to the electric heater 8 is placed at the junction of the first area and the second area.

[0068] S4: Atmospheric nitrogen gas is introduced into horizontal well 7 from injection well 5, and electric heater 8 is turned on simultaneously. Under the high temperature of electric heater 8, packer 9 expands, sealing the boundary 13 of the area. The atmospheric nitrogen gas is heated by electric heater 8 into high-temperature nitrogen gas, with the heating temperature set at 600℃. When the temperature reaches the specified temperature of 600℃, electric heater 8 switches to heat preservation mode. This efficiently heats this part of the coal seam within a relatively enclosed area. Since the heated high-temperature nitrogen gas does not flow directly to production well 6 through horizontal well 7, but diffuses into the coal seam through the fractures 4 formed by hydraulic fracturing, its heat can be fully utilized, improving energy utilization efficiency.

[0069] S5: After the coal in the first zone is completely pyrolyzed, the electric heater 8 is turned off. With the continuous introduction of nitrogen at room temperature, the temperature of the packer 9 decreases, the seal on the horizontal well 7 is released, and the oil and gas products generated in the early pyrolysis are collected to the surface through the horizontal well 7 and the production well 6.

[0070] S6: Push the packer 9 to the boundary between the second and third zones, and restart the electric heater 8 to seal and pyrolyze the coal seam in the second zone;

[0071] S7: When the temperature in the first region drops to 40℃, the valve 11 in the region, controlled by the corresponding temperature sensor 12, opens, and the Pseudomonas aeruginosa culture medium containing nutrients is introduced into the horizontal well 7. Carried by high-temperature nitrogen gas, it enters the coal seam in the first region to flush the fractures 4 and extract the residual coal tar. This tar product then flows out with the oil and gas products in the second region and is collected in the production well 6.

[0072] S8: Repeat the above steps until pyrolysis and tar collection are completed in all coal seam areas.

[0073] Example 4

[0074] like Figure 3 As shown, for areas with thick coal seams, a coupled thermal-chemical-biological in-situ coal mining method includes the following steps:

[0075] S1: Drill injection well 5 and production well 6 from the surface into the underground coal seam 2. Drill two parallel, continuous horizontal wells 7 between injection well 5 and production well 6, located in the middle and bottom of the underground coal seam 2. Divide the underground coal seam 2 into pyrolysis sub-regions every 15m. Conduct directional drilling at the boundary 13 of the regions for subsequent hydraulic fracturing and placement of packers 9.

[0076] S2: Hydraulic fracturing is performed by injecting fracturing agent into the underground coal seam 2 through injection well 5, forming a certain distribution of fractures 4 in the underground coal seam 2, and then proppant is injected.

[0077] S3: A branch pipeline 10 is laid in the injection well 5 and the two horizontal wells 7. The branch pipeline 10 is equipped with a valve 11 in each pyrolysis sub-region in the horizontal well 7. The opening and closing of the valve 11 is controlled by the corresponding temperature sensor 12. The packer 9 connected to the electric heater 8 is placed at the junction of region 1 and region 2.

[0078] S4: Atmospheric-temperature nitrogen gas is introduced into the horizontal well 7 from the injection well 5, and the electric heater 8 is turned on simultaneously. Under the high temperature of the electric heater 8, the packer 9 expands, sealing the boundary 13 of the area. The atmospheric-temperature nitrogen gas is heated by the electric heater 8 into high-temperature nitrogen gas, with the heating temperature set at 600℃. When the temperature reaches the specified temperature of 600℃, the electric heater 8 switches to heat preservation mode. This efficiently heats this part of the coal seam within a relatively enclosed area. Since the heated hot fluid does not flow directly from the horizontal well 7 to the production well 6, but diffuses into the coal seam through the fractures 4 formed by hydraulic fracturing, its heat can be fully utilized, improving energy utilization efficiency.

[0079] S5: After the coal in the first zone is completely pyrolyzed, the electric heater 8 is turned off. With the continuous introduction of nitrogen at room temperature, the temperature of the packer 9 decreases, the seal on the horizontal well 7 is released, and the oil and gas products generated in the early pyrolysis are collected to the surface through the horizontal well 7 and the production well 6.

[0080] S6: Advance the packer 9 to the boundary between the second and third zones, and restart the electric heater 8 to seal and pyrolyze the coal seam in the second zone.

[0081] S7: When the temperature in the first region drops to 40℃, the valve 11 in the region, controlled by the corresponding temperature sensor 12, opens, and the Pseudomonas aeruginosa culture medium containing nutrients is introduced into the horizontal well 7. Carried by high-temperature nitrogen gas, it enters the coal seam in the first region to flush the fractures 4 and extract the residual coal tar. This tar product then flows out with the oil and gas products in the second region and is collected in the production well 6.

[0082] S8: Repeat the above steps until all coal seam areas have completed pyrolysis and tar collection.

[0083] Example 5

[0084] like Figure 4 As shown, for situations where the coal seam area is small and the microorganisms are not sensitive to environmental temperature requirements, the specific operating steps are as follows:

[0085] In the underground coal seam 2, an injection well 5, a production well 6, and a horizontal well 7 connecting the two are drilled. A gas heater 16 is installed at the inlet of the horizontal well 7. Fracturing fluid is injected to form fractures 4 in the coal seam, and proppant is injected to fill the fractures 4. First, room temperature nitrogen is injected into the formation, and at the same time, the gas heater 16 is turned on to heat the coal seam for pyrolysis. Oil and gas products are collected in the production well 6. When the gas concentration detector 15 detects that the concentration of pyrolysis gas in the produced gas in the production well 6 is lower than a certain set value, the gas heater 16 is turned off. Room temperature nitrogen is continuously introduced or switched to liquid water for waste heat recovery. The waste heat of the underground coal seam 2 heats the room temperature nitrogen into high temperature nitrogen and the liquid water into superheated steam. When the formation temperature sensor 14 detects that the formation temperature has dropped to a temperature that microorganisms can tolerate, a microbial aqueous solution containing nutrients is injected into the injection well 5 to flush the coal seam for secondary oil recovery. The aqueous solution containing dissolved tar is collected in the production well 6.

[0086] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A coupled thermo-chemical-biological in-situ coal mining system, characterized in that, include: Injection well (5), production well (6), horizontal well (7), electric heater (8), packer (9), branch pipeline (10); the electric heater (8) is located on the side close to the injection well (5); the branch pipeline (10) is used to introduce a microbial solution containing nutrients; Both the injection well (5) and the extraction well (6) are opened perpendicular to the underground coal seam (2), and the opening directions of the injection well (5) and the extraction well (6) are parallel; the horizontal well (7) is opened parallel to the ground, one end of the horizontal well (7) is connected to the bottom end of the injection well (5), and the other end of the horizontal well (7) is connected to the bottom end of the extraction well (6). Branch pipelines (10) are installed in the injection well (5) and the horizontal well (7); the underground coal seam (2) is divided into multiple areas along the horizontal direction, and a valve (11) is installed on the corresponding branch pipeline (10) in each area, and a temperature sensor (12) corresponding to the valve (11) is installed in each area; the packer (9) is installed at the boundary (13) of the area in the horizontal well (7), and the electric heater (8) is connected to the packer (9). Normal temperature fluid is introduced from the injection well (5) into the horizontal well (7). When the electric heater (8) is turned on, the packer (9) can expand under the high temperature of the electric heater (8) to seal the boundary (13) of the area; the normal temperature fluid is heated by the electric heater (8) to become a high temperature fluid, pyrolyzes the coal seam, and releases oil and gas products.

2. The coupled thermo-chemical-biological coal mining system according to claim 1, characterized in that, The packer (9) is connected to the electric heater (8) in the horizontal direction, and the packer (9) is located on the side close to the production well (6).

3. The coupled thermo-chemical-biological coal mining system according to claim 1, characterized in that, The length of each region is 10-20m.

4. The coupled thermo-chemical-biological coal mining system according to claim 1, characterized in that, Two parallel horizontal wells (7) are opened between the injection well (5) and the production well (6). The two parallel horizontal wells (7) are opened in the middle and bottom of the underground coal seam (2), respectively. Branch pipelines (10) are installed in both the injection well (5) and the two horizontal wells (7). Each area of ​​the branch pipeline (10) is equipped with a valve (11) and a temperature sensor (12) corresponding to the valve. Packers (9) connected to electric heaters (8) are installed at the boundary (13) of each area in each horizontal well (7).

5. The coupled thermo-chemical-biological coal mining system according to claim 1, characterized in that, A gas heater (16) is installed at the inlet of the horizontal well (7), a formation temperature sensor (14) is installed inside the horizontal well (7), and the production well (6) is connected to a gas concentration detector (15).

6. A method for in-situ coal mining coupled with thermo-chemical-biological processes, characterized in that, A coupled thermo-chemical-biological coal mining system based on any one of claims 1-5 includes: Drill injection wells (5) and extraction wells (6) from the surface into the underground coal seam (2), and drill a horizontal well (7) between the injection wells (5) and extraction wells (6); divide the underground coal seam (2) into areas along the horizontal direction; Hydraulic fracturing is performed by injecting fracturing agent into the underground coal seam (2) through injection well (5) to form fractures (4) in the underground coal seam (2) and then injecting proppant. Branch pipes (10) are laid in the injection well (5) and the horizontal well (7). A valve (11) and a temperature sensor (12) corresponding to the valve (11) are installed in each area of ​​the branch pipe (10) in the horizontal well (7). A packer (9) connected to an electric heater (8) is placed at the junction of the first area and the second area. Ambient temperature fluid is introduced into horizontal well (7) from injection well (5), and electric heater (8) is turned on at the same time. Under the high temperature of electric heater (8), packer (9) expands and seals the boundary (13) of the area. Ambient temperature fluid is heated by electric heater (8) and becomes high temperature fluid, which pyrolyzes the coal seam and releases oil and gas products. After the coal in the first zone is completely pyrolyzed, the electric heater (8) is turned off, the temperature of the packer (9) decreases, the seal on the horizontal well (7) is released, and the oil and gas products are collected to the surface through the production well (6). The packer (9) is pushed to the boundary between the second and third zones, and the electric heater (8) is turned on again to seal and pyrolyze the coal seam in the second zone; Temperature detection is performed in each area by temperature sensor (12), valve (11) in the first area is opened, and microbial aqueous solution containing nutrients is introduced to flush the fractures in the first area, extract the residual tar products, and some tar products flow out of the production well (6) together with the oil and gas products in the second area and are collected. Repeat the above steps until pyrolysis and tar collection are completed in all coal seam areas.

7. The method for in-situ coal mining coupled with thermo-chemical-biological processes according to claim 6, characterized in that, The introduced fluid at room temperature is either nitrogen or carbon dioxide.

8. The method for in-situ coal mining coupled with thermo-chemical-biological processes according to claim 6, characterized in that, The valve (11) on the branch pipeline (10) is controlled by the corresponding temperature sensor (12). When the temperature sensor (12) in the area detects that the temperature of the coal seam in the area is lower than the temperature that microorganisms can tolerate, the corresponding valve (11) is opened. When the temperature of the next area is also lower than the temperature that microorganisms can tolerate, the valve (11) is closed and the valve (11) corresponding to the next area is opened.

9. A method for in-situ coal mining coupled with thermo-chemical-biological processes according to claim 6, characterized in that, The microorganisms can tolerate temperatures of 30-50℃.

10. A method for in-situ coal mining coupled with thermo-chemical-biological processes according to claim 6, characterized in that, The microorganism is Pseudomonas aeruginosa; the nutrients include carbon, nitrogen and phosphorus sources.

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