Method for extracting coalbed methane from tectonic coal in coal mining area by stress release of double and single horizontal wells

Abstract

The present invention discloses a method for extracting coalbed methane from tectonic coal in a coal mining area by stress release through dual single-branch horizontal wells, belonging to the technical field of coalbed methane surface development and stress release gas extraction from protected layers in coal mining areas. Two horizontal wells with a "three-opening" wellbore structure are constructed at the middle position between the central axis of the coal mining face and the return air lane and the transport lane. The second opening and inclination section is drilled to the basic top hard rock layer of the mined coal seam at the final mining line position, and then a technical casing is lowered and cemented. The third opening horizontal well section is drilled along the basic top hard rock layer of the mined coal seam to the opening eye, and then a screen pipe is suspended and completed. During the mining process of the working face, a water ring vacuum pump is started at the wellhead of the horizontal well. By reasonably adjusting the extraction negative pressure, controlling the gas extraction rate and the CH4, O2, and CO content in the gas, the tectonic coal bed methane desorbed by stress release from the protected layer is extracted to the ground. This method can realize the extraction of tectonic coal bed methane from the protected layer by stress release during the entire mining process of the working face, significantly prolong the extraction time of a single well, and increase the cumulative CH4 extraction volume and economic benefits.

Description

Technical Field

[0001] The present invention relates to a method for extracting coalbed methane from tectonic coal in coal mining areas by stress release using double and single horizontal wells, and in particular to a method for utilizing the stress release of the upper tectonic coal reservoir generated during the mining process of the coal mining face to promote desorption of tectonic coalbed methane and increase permeability of the coal reservoir, thereby achieving long-term, efficient and economical extraction of tectonic coalbed methane from coal mining areas. The method belongs to the technical field of surface development of coalbed methane in coal mining areas and stress release gas extraction from protected layers. Background Art

[0002] my country is rich in coalbed methane resources. It is estimated that the geological resources of coalbed methane at a depth of less than 2000m are 36.8×10 12 m 3 , comparable to conventional natural gas resources, and primarily concentrated in coal mining areas with a high degree of coal and coalbed methane exploration. Large-scale development of coalbed methane in coal mining areas can alleviate my country's shortage of conventional oil and gas energy, reduce the risk of coal mine gas accidents, and reduce greenhouse gas emissions from coal mining operations, potentially generating significant economic, environmental, safety, and social benefits.

[0003] Due to the characteristics of high original ground stress, low permeability and great difficulty in hydraulic fracturing, it is difficult to achieve good coalbed methane extraction results using traditional vertical and horizontal well fracturing technologies. In order to comprehensively promote the exploration and development of tectonic coalbed methane resources within my country's coal mining areas, it is necessary to solve the problems of poor transformation effect of tectonic coal reservoirs using traditional vertical and horizontal well fracturing methods, poor wellbore stability of pressure-relieved coalbed methane vertical wells and directional wells, short extraction service time, and low economic benefits. Actively explore new technologies and methods for stress release mining of tectonic coalbed methane horizontal wells in coal mining areas to significantly improve the surface development of tectonic coalbed methane and the gas control effect of coal mining faces. Summary of the Invention

[0004] Technical problem: The purpose of the present invention is to overcome the problems of poor wellbore stability, short extraction service time, and low cumulative CH4 extraction volume of traditional unloading coalbed methane vertical wells and directional wells in coal mining areas, and to provide a method for extracting coalbed methane from tectonic coal in coal mining areas by stress release using dual single-branch horizontal wells. Two single-branch horizontal wells are used to realize the extraction of tectonic coalbed methane during the entire mining face recovery process and the extraction of coalbed methane from the goaf after the mining face is closed.

[0005] Technical solution: To achieve the above-mentioned purpose, the present invention provides a method for extracting coalbed methane from tectonic coal in a coal mining area by stress release using dual single horizontal wells, comprising the following steps:

[0006] (a) Based on the coal mining project plan, the mining area and the coal mining face design drawings, the location of the ground opening for the first single horizontal well is determined on the extension of the centerline of the coal mining face and the midline of the return air lane in the mining direction; the location of the ground opening for the second single horizontal well is determined on the extension of the centerline of the coal mining face and the midline of the transport lane in the mining direction;

[0007] (b) The first single horizontal well of the "three-split" wellbore structure is drilled on the ground. The first single horizontal well is vertically drilled in the first split vertical well section, and the surface casing is cemented; the second split inclined well section of the first single horizontal well is directionally drilled, and the well inclination angle is continuously increased during the drilling process. When the drilling reaches the basic top hard rock above the coal seam mined near the final mining line and located below the curved sinking zone formed by subsequent coal mining, the second split well inclination angle is controlled to be 90° to complete the drilling, and the technical casing of the first single horizontal well is lowered for cementing; the third split horizontal section of the first single horizontal well is drilled horizontally along the direction of the midline between the central axis of the coal mining working face and the return air lane. After drilling to the opening (cutting hole) position, the first single horizontal well is completed by the third split, and the prefabricated screen is hung in the first single horizontal well third split horizontal section by a screen hanger to complete the well;

[0008] (c) The second single horizontal well of the "three-opening" wellbore structure is drilled on the ground. The first vertical section of the second single horizontal well is drilled vertically, and the surface casing is cemented; the second inclined section of the second single horizontal well is directionally drilled, and the well inclination angle is continuously increased during the drilling process. When the drilling reaches the basic top hard rock above the coal seam mined near the final mining line and located at the top of the fracture zone formed by subsequent coal mining, the second well inclination angle is controlled to be 90° to complete the drilling, and the technical casing of the second single horizontal well is lowered for cementing; the third horizontal section of the second single horizontal well is drilled horizontally along the direction of the center axis of the coal mining working face and the center line of the transport tunnel with geological guidance. After drilling to the cutting position, the second single horizontal well is drilled and the third opening is completed. The prefabricated screen is hung by the screen hanger in the second single horizontal well third opening horizontal section to complete the well;

[0009] (d) A gas production wellhead is installed on the ground of the first single horizontal well, the gas production wellhead is connected to the gas production pipeline, and the first single horizontal well gas pipeline rotary valve, the first single horizontal well gas flow meter, and the first single horizontal well water ring vacuum pump are installed on the gas pipeline; a gas production wellhead is installed on the ground of the second single horizontal well, the gas production wellhead is connected to the gas production pipeline, and the second single horizontal well gas pipeline rotary valve, the second single horizontal well gas flow meter, and the second single horizontal well water ring vacuum pump are installed on the gas pipeline;

[0010] (e) During the coal seam extraction and recovery process at the coal mining face, as the goaf is formed, the stress of the overlying first and second structural coal seams is gradually released and the coalbed methane of the structural coal is desorbed. The water ring vacuum pump of the second single horizontal well and the water ring vacuum pump of the first single horizontal well are started successively, and the wellhead negative pressure of the first and second single horizontal wells during extraction is adjusted in a timely manner according to the gas production rate and the volume percentage of CH4, O2, and CO in the produced gas, so as to achieve stress release, desorption, and continuous extraction of coalbed methane in the first and second structural coal seams during the entire process of coal mining at the coal mining face, significantly increasing the extraction service time and cumulative extracted gas volume of the first and second single horizontal wells;

[0011] (f) When the coal mining face is mined to the final mining line, the transport tunnel, return air tunnel and goaf are completely closed, and the desorbed gas from the goaf of the coal mining face and the first structural coal seam and the second structural coal seam within the influence range of the stress release of the mined coal seam are continuously extracted, thereby further extending the extraction service time and cumulative extracted gas volume of the first single horizontal well and the second single horizontal well.

[0012] In step (a), the ground opening locations of the first single horizontal well and the second single horizontal well are located outside the coal mining working face and close to the track tunnel and the return air tunnel. At the same time, the ground opening locations of the first single horizontal well and the second single horizontal well are required to have flat terrain and convenient transportation conditions, meeting the conditions for the construction of the first single horizontal well and the second single horizontal well and the ground construction of the extraction well site.

[0013] In step (b), the first single horizontal well (the first opening is vertically drilled to 10m below the interface between the Quaternary loose layer and the bedrock, and the well is cemented after the J55 steel grade surface casing is run, and the G-grade oil well cement is injected, and the cementing cement slurry returns to the surface from the annulus between the first opening well wall and the surface casing; the first single horizontal well is directional drilled in the second opening inclination section using a single-bend screw drill bit, the well inclination angle is continuously increased during the drilling process, and the well inclination full angle change rate is controlled to be less than 5° / 30m, after the second opening is completed, the J55 steel grade technical casing is run, and then the G-grade oil well cement is injected for cementing, and the cementing cement slurry returns to 150m above the basic top hard rock at the bottom of the curved subsidence zone from the annulus between the second opening well wall and the technical casing; the first single horizontal well is drilled in the basic top hard rock using a geosteering drilling tool in the third opening horizontal section, and after the third opening is completed, a prefabricated screen of N80 steel grade is hung by a screen hanger to complete the well;

[0014] The prefabricated screen tube has an inner diameter of ≥150 mm and a wall thickness of ≥9 mm. It is processed by spiral punching, has a hole diameter of ≥10 mm, and a hole density of 16 to 20 holes / m2.

[0015] In step (c), the second single horizontal well is vertically drilled to 10 m below the interface between the Quaternary loose layer and the bedrock, and is completed. After the J55 steel grade surface casing is run, G-grade oil well cement is injected for cementing, and the cementing cement slurry returns to the surface from the annulus between the first opening well wall and the surface casing; the second single horizontal well is directionally drilled in the second opening inclination section using a single-bend screw drill bit, and the well inclination angle is continuously increased during the drilling process, and the full angle change rate of the well inclination is controlled to be less than 5° / 30 m. After the second opening is completed, the J55 steel grade technical casing is run, and then G-grade oil well cement is injected for cementing, and the cementing cement slurry returns to 150 m above the basic top hard rock at the top of the fracture zone from the annulus between the second opening well wall and the technical casing; the second single horizontal well is drilled in the basic top hard rock using a geological guidance drilling tool in the third opening horizontal section, and after the third opening is completed, a prefabricated screen of N80 steel grade is hung by a screen hanger to complete the well.

[0016] The inner diameter of the ground prefabricated screen tube is ≥150mm, the wall thickness is ≥9mm, and it is processed by spiral punching. The hole diameter is ≥10mm, and the hole density is 16 holes / m2 to 20 holes / m2.

[0017] In step (d), the inner diameter of the gas production pipeline is ≥150 mm; the first single horizontal well gas flow meter and the second single horizontal well gas flow meter are electromagnetic vortex gas flow meters, and the effective measurement range of the gas flow rate is 4 m 3 / min~40m 3 / min, and can realize cumulative flow storage and real-time display; the first single horizontal well water ring vacuum pump adopts a mode of one running and one standby, and the second single horizontal well water ring vacuum pump adopts a mode of one running and one standby to ensure continuous extraction of tectonic coalbed methane.

[0018] In step (e), the wellhead negative pressure during extraction should be controlled at -0.06MPa to -0.03MPa; when the volume percentage of CH4 in the extracted gas is lower than 50% and the volume percentage of O2 is higher than 1%, the extraction intensity should be reduced, the volume percentage of CH4 in the produced gas should be increased, and the volume percentages of O2 and CO in the produced gas should be reduced; when the volume percentage of CH4 in the negative pressure extracted gas is higher than 80% and the volume percentage of O2 is lower than 0.2%, the extraction intensity should be increased, and the output rate of pure CH4 in the extracted gas should be increased by appropriately reducing the volume percentage of CH4 in the produced gas.

[0019] In step (f), the transport tunnel and the return air tunnel are closed by building a closed wall and applying cement, and the thickness of the closed wall is ≥1.5m; during the process of continuous extraction of coalbed methane from the goaf and the first structural coal seam and the second structural coal seam by the first single horizontal well and the second single horizontal well, when the volume percentage of CH4 in the negative pressure extraction output gas is lower than 20% and the volume percentage of CO is greater than 0.0024%, the first single horizontal well and the second single horizontal well stop negative pressure extraction or start to adopt intermittent negative pressure extraction.

[0020] Beneficial effects: Due to the adoption of the above technical solution, the present invention overcomes the problems of poor wellbore stability of traditional unloading coalbed methane vertical wells and directional wells, short extraction service time, low cumulative CH4 extraction volume, and poor economic benefits of ground extraction of coalbed methane from coal mining faces, and proposes a method for extracting coalbed methane from tectonic coal in coal mining areas by stress release using dual single-branch horizontal wells. Two single-branch horizontal wells are used to realize the extraction of tectonic coal from the coal mining face during the entire recovery process and the extraction of coalbed methane from the goaf after the coal mining face is closed. First, two single-branch horizontal wells are used to extract the coalbed methane resources desorbed during the stress release of tectonic coal in the curved subsidence zone and fracture zone above the coal mining face; second, after the horizontal and vertical displacement of the coal strata above the goaf causes the termination of the single horizontal well and the closure of the mining face, two single-branch horizontal wells can still be used to continuously extract the coalbed methane in the goaf. The main advantages compared with the existing technology are:

[0021] ① Two single horizontal wells can realize the coordinated exploitation of tectonic coalbed methane resources in the curved subsidence zone and fracture zone, significantly improving the tectonic coalbed methane extraction rate in the stress release zone;

[0022] ② It can realize stress release and coalbed methane extraction during the entire mining process of the coal face, significantly extending the extraction time of coalbed methane wells and greatly increasing the cumulative CH4 extraction volume of coalbed methane wells;

[0023] ③ Two single horizontal wells can be used to extract coalbed methane from the closed goaf of the coal mining face, achieving the function of "one well for multiple uses";

[0024] ④ The technology and process are simple, the project implementation cost is low, and the economic, environmental and social benefits are good. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a plan view of the double and single horizontal wells used in the present invention for stress release extraction of tectonic coal in a coal mining area before coalbed methane recovery.

[0026] Figure 2 This is a plan view of the process of extracting coalbed methane from tectonic coal in a coal mining area by stress release of double and single horizontal wells according to the present invention.

[0027] Figure 3This is a drilling trajectory diagram of the first single horizontal well on the cross section of the central axis of the coal mining face and the midline of the return air lane before mining in the present invention.

[0028] Figure 4 This is a diagram of the drilling trajectory of the first single horizontal well on the cross section of the central axis of the coal mining face and the midline of the return air lane during the mining process of the present invention.

[0029] Figure 5 This is a drilling trajectory diagram of the second single horizontal well on the cross section of the central axis of the coal mining face and the middle line of the transport tunnel before mining in the present invention.

[0030] Figure 6 This is a drilling trajectory diagram of the second single horizontal well on the cross section of the central axis of the coal mining face and the middle line of the transport tunnel during the mining process of the present invention.

[0031] In the figure: 1-coal mining face; 2-coal mining face central axis; 3-transport tunnel; 4-return air tunnel; 5-center line between the coal mining face central axis and the transport tunnel; 6-center line between the coal mining face central axis and the return air tunnel; 7-1-first single-branch horizontal well; 7-2-second single-branch horizontal well; 8-1-inclination section of the first single-branch horizontal well; 8-2-inclination section of the second single-branch horizontal well; 9-1-technical casing of the first single-branch horizontal well; 9-2-technical casing of the second single-branch horizontal well; 10-final production line; 11-opening hole; 12-1-third-split horizontal section of the first single-branch horizontal well; 12-2-third-split horizontal section of the second single-branch horizontal well; 13-1-screen of the horizontal well section of the first single-branch horizontal well; 13-2-screen of the horizontal well section of the second single-branch horizontal well; 14-1-screen suspension of the first single-branch horizontal well Hanger; 14-2-second single horizontal well screen hanger; 15-working face airflow direction; 16-track main tunnel; 17-return air main tunnel; 18-1-first single horizontal well water ring vacuum pump; 18-2-second single horizontal well water ring vacuum pump; 19-1-first single horizontal well gas flowmeter; 19-2-second single horizontal well gas flowmeter; 20-1-first single horizontal well gas pipeline rotary valve; 20-2-second single horizontal well gas pipeline rotary valve; 21-hydraulic support; 22-goaf; 23-mined coal seam; 24-1-first structural coal seam; 24-2-second structural coal seam; 25-mined coal seam floor; 26-mined coal seam direct roof; 27-mined coal seam basic top hard rock layer; 28-caving zone; 29-fracture zone; 30-bend subsidence zone. DETAILED DESCRIPTION

[0032] An embodiment of the present invention will be further described below with reference to the accompanying drawings:

[0033] like Figure 1 As shown, the method for extracting coalbed methane from tectonic coal in a coal mining area by stress release of dual single horizontal wells of the present invention has the following specific steps:

[0034] (a) According to the coal mining engineering plan, the mining area and the coal mining working face (1) design drawing, the position of the ground opening of the first single horizontal well (7-1) is determined on the extension section of the mining direction between the central axis (2) of the coal mining working face and the middle line (6) of the return air lane (4), and the position of the ground opening of the second single horizontal well (7-2) is determined on the extension section of the mining direction between the central axis (2) of the coal mining working face and the middle line (5) of the transport lane (3); the ground opening positions of the first single horizontal well (7-1) and the second single horizontal well (7-2) are located outside the coal mining working face (1) and close to the positions of the track lane (16) and the return air lane (17). At the same time, the ground opening positions of the first single horizontal well (7-1) and the second single horizontal well (7-2) are required to have flat terrain and convenient transportation conditions, so as to meet the conditions for the construction of the first single horizontal well (7-1) and the second single horizontal well (7-2) and the ground construction of the extraction well site.

[0035] (b) The first single horizontal well (7-1) of the "three-opening" wellbore structure is drilled vertically in the first vertical well section of the first single horizontal well (7-1), and the surface casing is cemented; the second inclined section (8-1) of the first single horizontal well is drilled directionally, and the well inclination angle increases continuously during the drilling process. When the well is drilled to the basic top hard rock above the mining coal seam (23) near the final mining line (10) and located below the curved sinking zone (30) formed by subsequent coal mining, the second well inclination angle is controlled to be 90° to complete the drilling, and the first single horizontal well is lowered. The well casing (9-1) is cemented; the first single horizontal well three-opening horizontal section (12-1) is drilled horizontally along the middle line (6) of the coal mining face center axis (2) and the return air channel (4) in a geologically oriented manner. After drilling to the opening hole (11), the first single horizontal well (7-1) is drilled and completed. A prefabricated screen (13-1) is hung on the first single horizontal well three-opening horizontal section (12-1) using a screen hanger (14-1) to complete the well; the first single horizontal well (7-1) is drilled vertically to the Quaternary loose layer and bedrock. The drilling was completed 10m below the interface, and after running J55 steel grade surface casing, G grade oil well cement was injected for cementing. The cementing cement slurry returned to the surface from the annulus between the first opening well wall and the surface casing. The first single horizontal well (7-1) was drilled in the second opening with a single-bend screw drill bit. During the drilling process, the well inclination angle increased continuously, and the full angle change rate of the well inclination was controlled to be less than 5° / 30m. After the second opening was completed, J55 steel grade technical casing was run, and then G grade oil well cement was injected for cementing. The cementing cement slurry returned to the surface from the annulus between the second opening well wall and the technical casing (9-1). The annulus returns to 150m above the basic top hard rock at the bottom of the curved sinking zone (30); the first single horizontal well (7-1) is drilled in the basic top hard rock by using a geological guidance drill tool in the three-split horizontal section (12-1); after the three-split drilling is completed, a prefabricated screen pipe (13-1) made of N80 steel grade is hung by a screen pipe hanger (14-1) to complete the well; the surface prefabricated screen pipe (13-1) has an inner diameter of ≥150mm and a wall thickness of ≥9mm, and is processed by spiral drilling, with a hole diameter of ≥10mm and a hole density of 16 holes / m to 20 holes / m.

[0036] (c) The second single horizontal well (7-2) of the "three-opening" wellbore structure is drilled on the ground. The first vertical well section of the second single horizontal well (7-2) is vertically drilled and the surface casing is cemented. The second inclined section (8-2) of the second single horizontal well is directionally drilled. The well inclination angle increases continuously during the drilling process. When the drilling reaches the basic top hard rock above the mining coal seam (23) near the final mining line (10) and located at the top of the fracture zone (29) formed by subsequent coal mining, the second well inclination angle is controlled to 90 degrees to complete the drilling and then the second single horizontal well is lowered. The technical casing (9-2) is cemented; the second single horizontal well three-split horizontal section (12-2) is drilled horizontally along the middle line (5) of the coal mining working face center axis (2) and the transport tunnel (3) in a geologically oriented manner. After drilling to the opening hole (11), the second single horizontal well (7-2) is drilled for three times and completed. The prefabricated screen (13-2) is hung on the second single horizontal well three-split horizontal section (12-2) by using the screen hanger (14-2) to complete the well; the second single horizontal well (7-2) is drilled vertically once to the Quaternary loose layer and the bedrock. The drilling was completed 10m below the interface, and after running J55 steel grade surface casing, G grade oil well cement was injected for cementing. The cementing cement slurry returned to the surface from the annulus between the first opening well wall and the surface casing. The second single horizontal well (7-2) was directional drilled with a single-bend screw drill bit in the second opening and inclination section. During the drilling process, the well inclination angle increased continuously, and the full angle change rate of the well inclination was controlled to be less than 5° / 30m. After the second opening was completed, J55 steel grade technical casing was run, and then G grade oil well cement was injected for cementing. The cementing cement slurry returned to the surface from the annulus between the second opening well wall and the technical casing (9-2). The annulus returns to 150m above the basic top hard rock at the top of the fracture zone (29); the second single horizontal well (7-2) three-opening horizontal section (12-2) is drilled in the basic top hard rock using a geological guidance drill tool, and after the three-opening is completed, a prefabricated screen pipe (13-2) of N80 steel grade is hung by a screen pipe hanger (14-2) to complete the well; the ground prefabricated screen pipe (13-2) has an inner diameter of ≥150mm and a wall thickness of ≥9mm, and is processed by spiral drilling, with a hole diameter of ≥10mm and a hole density of 16 holes / m to 20 holes / m.

[0037] (d) A gas production wellhead is installed on the ground of the first single horizontal well (7-1), which is connected to a gas production pipeline. The gas pipeline is equipped with a first single horizontal well gas pipeline rotary valve (20-1), a first single horizontal well gas flow meter (19-1), and a first single horizontal well water ring vacuum pump (18-1). A gas production wellhead is installed on the ground of the second single horizontal well (7-2), which is connected to a gas production pipeline. The gas pipeline is equipped with a second single horizontal well gas pipeline rotary valve (20-2), a second single horizontal well gas flow meter (19-2), and a second single horizontal well water ring vacuum pump (18-2); the inner diameter of the gas production pipeline is ≥150mm; the first single horizontal well gas flow meter (19-1) and the second single horizontal well gas flow meter (19-2) are electromagnetic vortex gas flow meters, and the effective measurement range of the gas flow rate is 4m 3 / min~40m 3 / min, and can realize cumulative flow storage and real-time display; the first single horizontal well water ring vacuum pump (18-1) adopts a mode of one running and one standby, and the second single horizontal well water ring vacuum pump (18-2) adopts a mode of one running and one standby to ensure continuous extraction of tectonic coalbed methane.

[0038] (e) During the mining process of the coal seam (23) at the coal mining face (1), as the goaf (22) is formed, the stress of the overlying first structural coal seam (24-1) and the second structural coal seam (24-2) is gradually released and the structural coal seam gas is desorbed, the second single horizontal well water ring vacuum pump (18-2) and the first single horizontal well water ring vacuum pump (18-1) are started in succession, and the first single horizontal well water ring vacuum pump is adjusted in time according to the gas production rate and the volume percentage of CH4, O2 and CO in the produced gas. The wellhead negative pressure during extraction of the horizontal well (7-1) and the second single horizontal well (7-2) realizes stress release, desorption and continuous extraction of coalbed methane from the first structural coal seam (24-1) and the second structural coal seam (24-2) during the entire extraction process of the coal mining working face (1), significantly increasing the extraction service time and cumulative extracted gas volume of the first single horizontal well (7-1) and the second single horizontal well (7-2); the wellhead negative pressure during extraction should be controlled at -0.06MPa to -0.03MPa. When the volume percentage of CH4 in the extracted gas is lower than 50% and the volume percentage of O2 is higher than 1%, the extraction intensity should be reduced, the volume percentage of CH4 in the produced gas should be increased, and the volume percentages of O2 and CO in the produced gas should be reduced; when the volume percentage of CH4 in the negative pressure extracted gas is higher than 80% and the volume percentage of O2 is lower than 0.2%, the extraction intensity should be increased, and the output rate of pure CH4 in the extracted gas should be increased by appropriately reducing the volume percentage of CH4 in the produced gas.

[0039] (f) After the coal mining face (1) is mined to the final mining line (10), the transport tunnel (3), the return air tunnel (4) and the goaf (22) are completely closed, and the desorbed gas of the first structural coal seam (24-1) and the second structural coal seam (24-2) within the mining stress release influence range of the goaf (22) of the coal mining face (1) and the mined coal seam (23) is continuously extracted, thereby further extending the extraction service time and cumulative extraction gas volume of the first single horizontal well (7-1) and the second single horizontal well (7-2); the transport tunnel (3) and the return air tunnel (4) are constructed by The sealing wall is sealed by applying cement, and the thickness of the sealing wall is ≥1.5m; during the process of continuous extraction of coalbed methane from the goaf (22) and the first structural coal seam (24-1) and the second structural coal seam (24-2) by the first single horizontal well (7-1) and the second single horizontal well (7-2), when the volume percentage of CH4 in the negative pressure extraction output gas is lower than 20% and the volume percentage of CO is greater than 0.0024%, the first single horizontal well (7-1) and the second single horizontal well (7-2) stop negative pressure extraction or start to adopt intermittent negative pressure extraction.

Claims

1. A method for extracting coalbed methane from tectonic coal in coal mining areas by stress release of double and single horizontal wells, characterized in that The following steps are involved: (a) Based on the coal mining engineering plan, the mining area and the design drawing of the coal mining face (1), the position of the ground opening of the first single horizontal well (7-1) is determined on the extension of the mining direction between the central axis (2) of the coal mining face and the first middle line (6) of the return air lane (4), and the position of the ground opening of the second single horizontal well (7-2) is determined on the extension of the mining direction between the central axis (2) of the coal mining face and the second middle line (5) of the transport lane (3); (b) The first single horizontal well (7-1) of the "three-opening" wellbore structure is drilled on the ground. The first single horizontal well (7-1) is vertically drilled in the first vertical section and the surface casing is cemented. The second inclined section (8-1) of the first single horizontal well is directionally drilled. The well inclination angle increases continuously during the drilling process. When the well is drilled to the basic top hard rock above the mining coal seam (23) near the final mining line (10) and located below the curved sinking zone (30) formed by subsequent coal mining, the second well inclination angle is controlled to be 90 degrees to complete the drilling and the well is lowered. The first single horizontal well technical casing (9-1) is cemented; the first single horizontal well three-split horizontal section (12-1) is drilled horizontally along the center axis (2) of the coal mining face and the first middle line (6) of the return airway (4) in a geologically oriented manner; after drilling to the opening hole (11), the first single horizontal well (7-1) is drilled and completed, and the first single horizontal well screen pipe hanger (14-1) is used to hang the first single horizontal well horizontal section screen pipe (13-1) in the first single horizontal well three-split horizontal section (12-1) to complete the well; (c) The second single horizontal well (7-2) of the "three-opening" wellbore structure is drilled on the ground. The first vertical well section of the second single horizontal well (7-2) is vertically drilled and the surface casing is cemented. The second inclined section (8-2) of the second single horizontal well is directionally drilled. The well inclination angle increases continuously during the drilling process. When the well is drilled to the basic top hard rock above the mining coal seam (23) near the final mining line (10) and at the top of the fracture zone (29) formed by subsequent coal mining, the second well inclination angle is controlled to 90 degrees to complete the drilling and the first well is lowered. The second single horizontal well technical casing (9-2) is cemented; the second single horizontal well three-way horizontal section (12-2) is drilled horizontally along the direction of the second middle line (5) between the central axis (2) of the coal mining working face and the transport tunnel (3) using geological guidance. After drilling to the opening hole (11), the second single horizontal well (7-2) is drilled and completed. The second single horizontal well screen hanger (14-2) is used to hang the second single horizontal well horizontal section screen (13-2) in the second single horizontal well three-way horizontal section (12-2) to complete the well; (d) A gas production wellhead is installed on the ground of the first single horizontal well (7-1), the gas production wellhead is connected to the gas production pipeline, and the gas pipeline is installed with a first single horizontal well gas pipeline rotary valve (20-1), a first single horizontal well gas flow meter (19-1), and a first single horizontal well water ring vacuum pump (18-1); a gas production wellhead is installed on the ground of the second single horizontal well (7-2), the gas production wellhead is connected to the gas production pipeline, and the gas pipeline is installed with a second single horizontal well gas pipeline rotary valve (20-2), a second single horizontal well gas flow meter (19-2), and a second single horizontal well water ring vacuum pump (18-2); (e) During the mining process of the coal seam (23) at the coal mining face (1), as the goaf (22) is formed, the stress of the overlying first structural coal seam (24-1) and the second structural coal seam (24-2) is gradually released and the structural coal seam gas is desorbed, the second single horizontal well water ring vacuum pump (18-2) and the first single horizontal well water ring vacuum pump (18-1) are started successively, and the wellhead negative pressure of the first single horizontal well (7-1) and the second single horizontal well (7-2) during extraction is adjusted in time according to the gas production rate and the volume percentage of CH4, O2 and CO in the produced gas, so as to achieve the stress release, desorption and continuous extraction of the coal seam gas of the first structural coal seam (24-1) and the second structural coal seam (24-2) during the whole mining process of the coal mining face (1), and significantly increase the extraction service time and cumulative extracted gas volume of the first single horizontal well (7-1) and the second single horizontal well (7-2); (f) After the coal mining face (1) is mined to the final mining line (10), the transport tunnel (3), the return air tunnel (4) and the goaf (22) are completely closed, and the desorbed gas from the first structural coal seam (24-1) and the second structural coal seam (24-2) within the mining stress release influence range of the goaf (22) of the coal mining face (1) and the mined coal seam (23) is continuously extracted, thereby further extending the extraction service time and cumulative extraction gas volume of the first single horizontal well (7-1) and the second single horizontal well (7-2).

2. The method for extracting coalbed methane from tectonic coal in a coal mining area by stress release of dual and single horizontal wells according to claim 1 is characterized in that: In step (a), the ground opening positions of the first single horizontal well (7-1) and the second single horizontal well (7-2) are located outside the coal mining face (1) and close to the track tunnel (16) and the return air tunnel (17). At the same time, the ground opening positions of the first single horizontal well (7-1) and the second single horizontal well (7-2) are required to have flat terrain and convenient transportation conditions, meeting the conditions for the construction of the first single horizontal well (7-1) and the second single horizontal well (7-2) and the ground construction of the extraction well site.

3. The method for extracting coalbed methane from tectonic coal in a coal mining area by stress release of dual and single horizontal wells according to claim 1 is characterized in that: In step (b), the first single horizontal well (7-1) is vertically drilled to 10 m below the interface between the Quaternary loose layer and the bedrock, and is completed. After the J55 steel grade surface casing is lowered, G grade oil well cement is injected for cementing. The cementing cement slurry returns to the surface from the annulus between the first opening well wall and the surface casing; the second opening of the first single horizontal well (7-1) is directionally drilled using a single-bend screw drill bit. During the drilling process, the well inclination angle is continuously increased, and the full angle change rate of the well inclination is controlled to be less than 5° / 30 m. After the second opening is completed, the J55 steel grade technical casing is lowered, and then G grade oil well cement is injected for cementing. The cementing cement slurry returns to 150 m above the basic top hard rock at the bottom of the curved subsidence zone (30) from the annulus between the second opening well wall and the first single horizontal well technical casing (9-1). m; the first single horizontal well three-split horizontal section (12-1) is drilled in the basic top hard rock using a geological steering drill tool. After the three-split drilling is completed, the first single horizontal well screen pipe hanger (14-1) is used to hang the N80 steel grade first single horizontal well horizontal section screen pipe (13-1) to complete the well.

4. The method for extracting coalbed methane from tectonic coal in a coal mining area by stress release of dual and single horizontal wells according to claim 3 is characterized by: The first single horizontal well horizontal well section screen pipe (13-1) has an inner diameter of ≥150 mm and a wall thickness of ≥9 mm, is processed by spiral drilling, has a hole diameter of ≥10 mm, and a hole density of 16 holes / m to 20 holes / m.

5. The method for extracting coalbed methane from tectonic coal in coal mining areas by stress release of dual and single horizontal wells according to claim 1 is characterized in that: In step (c), the second single horizontal well (7-2) is vertically drilled to 10 m below the interface between the Quaternary loose layer and the bedrock, and is completed. After the J55 steel grade surface casing is lowered, G grade oil well cement is injected for cementing. The cementing cement slurry returns to the surface from the annulus between the first opening well wall and the surface casing; the second single horizontal well (7-2) is directionally drilled using a single-bend screw drill bit in the second opening inclination section. During the drilling process, the well inclination angle is continuously increased, and the full angle change rate of the well inclination is controlled to be less than 5° / 30 m. After the second opening is completed, the J55 steel grade technical casing is lowered, and then G grade oil well cement is injected for cementing. The cementing cement slurry returns to 150 m above the basic top hard rock at the top of the fracture zone (29) from the annulus between the second opening well wall and the second single horizontal well technical casing (9-2). m; the second single horizontal well three-split horizontal section (12-2) is drilled in the basic top hard rock using a geological steering drill tool. After the third split is completed, the second single horizontal well screen pipe hanger (14-2) is used to hang the N80 steel grade second single horizontal well horizontal section screen pipe (13-2) to complete the well.

6. The method for extracting tectonic coalbed methane from coal mining areas by stress release of dual and single horizontal wells according to claim 5, characterized in that: The second single horizontal well horizontal well section screen pipe (13-2) has an inner diameter of ≥150 mm and a wall thickness of ≥9 mm, is processed by spiral drilling, has a hole diameter of ≥10 mm, and a hole density of 16 holes / m2 to 20 holes / m2.

7. The method for extracting tectonic coalbed methane from coal mining areas by stress release of dual and single horizontal wells according to claim 1 is characterized in that: In step (d), the inner diameter of the gas production pipeline is ≥150 mm; the first single horizontal well gas flow meter (19-1) and the second single horizontal well gas flow meter (19-2) are electromagnetic vortex gas flow meters, and the effective measurement range of the gas flow rate is 4m 3 / min~40 m 3 / min, and realize the cumulative flow storage and real-time display; the first single horizontal well water ring vacuum pump (18-1) adopts the mode of one running and one standby, and the second single horizontal well water ring vacuum pump (18-2) adopts the mode of one running and one standby to ensure the continuous extraction of tectonic coalbed methane.

8. The method for extracting tectonic coalbed methane from coal mining areas by stress release of dual and single horizontal wells according to claim 1 is characterized by: In step (e), the wellhead negative pressure during extraction should be controlled at -0.06 MPa to -0.03 MPa; when the volume percentage of CH4 in the extracted gas is lower than 50% and the volume percentage of O2 is higher than 1%, the extraction intensity should be reduced, the volume percentage of CH4 in the produced gas should be increased, and the volume percentages of O2 and CO in the produced gas should be reduced; when the volume percentage of CH4 in the negative pressure extracted gas is higher than 80% and the volume percentage of O2 is lower than 0.2%, the extraction intensity should be increased, and the output rate of pure CH4 in the extracted gas should be increased by appropriately reducing the volume percentage of CH4 in the produced gas.

9. The method for extracting coalbed methane from tectonic coal in a coal mining area by stress release of dual and single horizontal wells according to claim 1, characterized in that: In step (f), the transport tunnel (3) and the return air tunnel (4) are closed by building a closed wall and applying cement, and the thickness of the closed wall is ≥1.5 m; during the process of continuous extraction of coalbed methane from the goaf (22) and the first structural coal seam (24-1) and the second structural coal seam (24-2), when the volume percentage of CH4 in the negative pressure extraction output gas is lower than 20% and the volume percentage of CO is greater than 0.0024%, the first single horizontal well (7-1) and the second single horizontal well (7-2) stop the negative pressure extraction or start to adopt an intermittent negative pressure extraction method.

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