Coal mine area coal bed gas one well multi-area, multi-area series continuous extraction method

Abstract

The present application belongs to the technical field of coal and coalbed methane coordinated development, and particularly relates to a coal mine area coalbed methane one-well multi-area and multi-area series connection continuous extraction method; according to the time-space relationship and mining sequence, the coal mine area is divided into a planning area, a preparation area, a mining area and a mined-out area; according to the time-space replacement relationship, the coalbed methane well is divided into a planning-preparation area coalbed methane well, a preparation-mining area coalbed methane well and a mining-mined-out area coalbed methane well, one-well multi-area and multi-area series connection continuous extraction; the present application improves the extraction life of the coal mine area coalbed methane well, maximizes the cost reduction and efficiency increase of coalbed methane extraction, breaks the spatial constraints of coal mining engineering and improves the coordinated development efficiency of coal and coalbed methane.

Description

Technical Field

[0001] This invention belongs to the field of coordinated development technology of coal and coalbed methane, specifically relating to a method for continuous extraction of coalbed methane from a single well in multiple zones and in series in a coal mining area. Background Technology

[0002] Increasing coal mine gas extraction and utilization is of significant practical and far-reaching importance for increasing clean energy supply, raising the proportion of clean energy consumption, and reducing greenhouse gas emissions. In recent years, thanks to the development of the coalbed methane industry, coal mine gas accidents have shown a decreasing trend year by year. However, gas accidents remain one of the most serious mine disasters.

[0003] Since 2010, coal mine gas extraction technology has gradually developed into a comprehensive management stage mainly based on regional extraction. The "three-zone linkage underground and surface three-dimensional extraction model" in key coal mining areas of Shanxi Province has gradually evolved into a "four-zone linkage (planning area, preparation area, mining area, and goaf area)" coal and coalbed methane co-extraction model (CN115341877A) covering all time periods, all strata, and all regions. In Shanxi Province, only high-rank coal in the southern Qinshui Basin has achieved commercial mining. Other areas are limited by geological conditions and low coalbed methane well production, preventing commercial mining. Despite more than ten years of technological exploration, high-rank coalbed methane in the southern Qinshui Basin still faces challenges such as low production capacity (only 37%) and low single-well output (profit of only 0.08 yuan / m³). 3 Due to issues such as [missing information], there are still a large number of low-yield wells in mature blocks that cannot effectively increase the gas production of a single well.

[0004] The "Four-Zone Linkage" Coalbed Methane Extraction Method (CN115341877A) divides the coal mining area into four extraction zones: a planning zone, a preparation zone, a mining-inducing zone, and a goaf zone. The planning zone employs surface pre-extraction, including surface pre-extraction vertical and horizontal wells. The preparation zone uses a combined surface and underground extraction method, connecting the underground directional long boreholes with the fracturing-affected zone of the surface mining-inducing vertical wells to increase permeability. The mining-inducing zone uses regionally progressive in-seam boreholes, high-level directional long boreholes, and cross-seam boreholes for underground extraction, while surface extraction utilizes surface mining-inducing vertical wells and surface mining-inducing L-shaped wells. The goaf zone is extracted through surface vertical wells. However, each extraction zone's wells are designed independently with a single function. Once a zone transitions to the next extraction zone, the coalbed methane wells are sealed and abandoned, resulting in significant waste of engineering costs. Therefore, under the overall design framework of multi-zone series connection, comprehensive consideration, optimization design, and exploration of innovative technologies for continuous extraction of coalbed methane wells in coal mining areas through multi-zone series connection will effectively improve the efficiency of coalbed methane wells in coal mining areas and achieve cost reduction and efficiency improvement. Summary of the Invention

[0005] This invention aims to address the problems of high cost and low returns in coalbed methane extraction, as well as the coordinated development of coal and coalbed methane in coal mining areas.

[0006] This invention provides the following technical solution: a method for continuous extraction of coalbed methane from a single well in multiple zones and in series in a coal mining area. Based on the spatiotemporal relationship and the order of mining, the coal mining area is divided into a planning zone, a preparation zone, a mining-initiated zone, and a goaf zone. Based on the spatiotemporal succession relationship, the coalbed methane wells are divided into coalbed methane wells in the planning-preparation zone, coalbed methane wells in the preparation-mining-initiated zone, and coalbed methane wells in the mining-goaf zone, and continuous extraction is performed from a single well in multiple zones and in series in a series.

[0007] Furthermore, the well type of the coalbed methane wells in the planning-preparation area is vertical coalbed methane wells. In the planning area, a network of vertical coalbed methane wells in the planning-preparation area is arranged parallel to the central axis of the planned coal mining face for fracturing and extraction. After the coal mining area is converted to the preparation area, the vertical coalbed methane wells in the planning-preparation area take over from the coalbed methane wells in the planning area. During the main roadway excavation, long boreholes along the coal seam are drilled along the excavation direction to connect and depressurize the fracturing-affected area of ​​the vertical coalbed methane wells in the planning-preparation area. Before the roadway is excavated, the planned working face is subjected to secondary fracturing. During the roadway excavation, ordinary boreholes along the coal seam are drilled underground to connect the fracturing fracture end area of ​​the vertical coalbed methane wells in the planning-preparation area with the unconnected affected area. The underground long boreholes along the coal seam and ordinary boreholes along the coal seam are used to enhance the extraction of gas, realizing the pre-extraction of coalbed methane in the planning area and the enhanced underground extraction of surface fracturing in the preparation area.

[0008] Furthermore, the well type of the coalbed methane wells in the planning-preparation area is horizontal coalbed methane wells. In the planning area, a network of horizontal coalbed methane wells is arranged parallel to the central axis of the planned coal mining face for fracturing and extraction. The horizontal landing point of the horizontal coalbed methane wells in the planning-preparation area is less than 10m from the cut-off point of the working face, and the target point of the horizontal coalbed methane wells in the planning-preparation area is less than 10m from the stop-mining line of the working face. After the extraction area of ​​the horizontal coalbed methane wells in the planning-preparation area is converted into the preparation area, the horizontal coalbed methane wells in the planning-preparation area will replace the coalbed methane wells in the planning area. In the preparation area, long boreholes along the coal seam are drilled along the direction of excavation during the main roadway excavation to connect and relieve pressure in the fracturing-affected area of ​​the planned-preparation area coal seam gas horizontal well. Before the roadway is excavated, secondary fracturing is carried out on the planned working face. During the roadway excavation, ordinary boreholes along the coal seam are drilled underground to connect the fracturing fracture end area of ​​the planned-preparation area coal seam gas horizontal well with the unconnected affected area. The underground long boreholes along the coal seam and ordinary boreholes along the coal seam are used to enhance gas extraction, realizing the pre-extraction of coal seam gas in the planned area and the enhanced underground extraction of surface fracturing in the preparation area.

[0009] Furthermore, the well type of the coalbed methane wells in the preparation-mining zone is a vertical coalbed methane well. In the planning area, a network of vertical coalbed methane wells in the preparation-mining zone is arranged parallel to each other along the working face within a range of 30-40m from the return airway. The target coal seam section is fracturing on the surface through the vertical coalbed methane wells in the preparation-mining zone. After fracturing, the wellheads of the vertical coalbed methane wells in the preparation-mining zone are sealed, and enhanced negative pressure extraction is carried out underground. The extraction equipment is dismantled before the coal seam is mined. After the coal seam is mined, the working face is transformed into a mining zone, and the vertical coalbed methane wells in the preparation zone are replaced by the coalbed methane wells in the mining zone. The wellheads of the vertical coalbed methane wells in the preparation zone are opened, and surface negative pressure extraction equipment is installed. Negative pressure extraction is carried out on the surface without fracturing, and coalbed methane is extracted by utilizing the pressure relief caused by coal seam mining disturbance.

[0010] Furthermore, the vertical coalbed methane well in the preparation-mining area adopts a two-section wellbore structure, with the second section drilled to 30m below the bottom plate of the target coal seam. The segmented cementing method is adopted, with the segmented cementing position being the location of the largest fracture zone above the top plate of the target coal seam. The upper part of the second section's production casing is connected to the production casing of the target coal seam section using a drillable sliding sleeve and an external compression packer. The drainage and gas production tubing is connected to the wellhead using a wellhead hanger.

[0011] Furthermore, the well type of coalbed methane well in the mining-goaf area is a vertical coalbed methane well; after the goaf area is sealed for 2-3 years, the vertical coalbed methane well in the preparation-mining-moving area is cleared and converted into a coalbed methane well in the mining-goaf area, with only one well left in each goaf area for negative pressure extraction.

[0012] Furthermore, the well type of the coalbed methane well in the mining-goaf area is an L-shaped horizontal well. In the mining area, a network of L-shaped horizontal wells is arranged parallel to each other along the working face within a range of 30-40m from the return airway. A surface negative pressure extraction device is installed at the wellhead of the L-shaped horizontal wells in the mining-goaf area. Negative pressure extraction is performed on the surface without fracturing, utilizing the pressure relief caused by coal seam mining to extract coalbed methane. After the coal seam is mined out, the wellhead of the L-shaped horizontal wells in the mining-goaf area is sealed, and the working face is converted from the mining area to the goaf area. After the goaf area is sealed for 2-3 years, the wellhead of the L-shaped horizontal wells in the mining-goaf area is opened, and the L-shaped horizontal wells in the mining-goaf area replace the coalbed methane wells in the mining area. The horizontal sections of the L-shaped horizontal wells in the mining-goaf area are then cleared.

[0013] Furthermore, the total length L of the horizontal section of the L-shaped horizontal well in the mining-goaf coalbed methane area is divided into two parts: the first section is 0.4 L long and the second section is 0.6 L long. The horizontal well section is designed to be arranged along the downdip direction of the monoclinal with an inclination angle of 1° to 2°. In the longitudinal direction, the fracture zone is divided into three parts: the upper, middle and lower parts of the fracture zone. The horizontal well section of the L-shaped horizontal well is located in the lower middle part of the fracture zone in the longitudinal direction. The first section of the horizontal well section is arranged in the middle of the fracture zone. The second section of the horizontal well section is arranged in the lower part of the fracture zone.

[0014] Compared with the prior art, the advantages of the present invention are:

[0015] This invention provides a method for continuous extraction of coalbed methane (CBM) from a single well in multiple zones or in series within a coal mining area. Under the overall design framework of multi-zone series extraction, it comprehensively considers and optimizes the design, exploring and innovating a continuous extraction technology for CBM wells in coal mining areas. This effectively improves the efficiency of CBM wells and achieves cost reduction and efficiency improvement. Simultaneously, the continuous extraction technology can effectively break the spatial constraints of coal mining engineering; the coal mining engineering can assist this technology in overcoming extraction limits through mining operations. The spatiotemporal coordination and complementary advantages between the coal mining engineering and the continuous extraction technology significantly improve coal recovery rate and CBM extraction rate, greatly increasing the economic benefits for enterprises. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a single well with multiple zones and multiple zones connected in series.

[0017] Figure 2 Schematic diagram of vertical well deployment for coalbed methane in the planning-preparation area;

[0018] Figure 3 Schematic diagram of coalbed methane horizontal well deployment in the planning-preparation area;

[0019] Figure 4 Schematic diagram of vertical well deployment for coalbed methane in the preparation-mining area;

[0020] Figure 5 A schematic diagram of the shaft structure for a vertical coalbed methane well in the preparation-mining area;

[0021] Figure 6 A schematic diagram of the deployment of L-shaped horizontal wells for coalbed methane in the mining-goaf area;

[0022] Figure 7 This is a schematic diagram of the stratigraphic arrangement of the horizontal section of an L-shaped horizontal well in a coalbed methane well in a mining-goaf area;

[0023] Figure 8 This is a schematic diagram of the wellbore structure of an L-shaped horizontal well for coalbed methane in a mining-goaf area.

[0024] In the diagram: 1-Planned-Preparation Area Coalbed Methane Vertical Well; 2-Long Borehole Along the Coal Seam; 3-Ordinary Borehole Along the Coal Seam; 4-Main Roadway; 5-Planned-Preparation Area Coalbed Methane Horizontal Well; 6-Preparation-Mining Area Coalbed Methane Vertical Well; 7-Return Airway; 8-Drillable Sliding Sleeve; 9-External Compression Packer; 10-Target Coal Seam; 11-Production Casing for Target Coal Seam Section; 12-Hanger; 13-Upper Part of Production Casing in Second-Stage Section; 14-Mining-Goaf Area Coalbed Methane L-Shaped Horizontal Well; 14.1-Vertical Well Section; 14.2-Horizontal Well Section; 15-Coal Pillar; 16-Slotted Casing; 17-Second-Stage Production Casing; 18-Goaf Production Casing; 19-Drainage and Gas Production Pipeline; X-Coal Seam Mining Direction. Detailed Implementation

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] like Figure 1 As shown, a method for continuous extraction of coalbed methane (CBM) from a single well in multiple zones and in series in coal mining areas is proposed. Based on spatiotemporal relationships and the sequence of mining operations, the coal mining area is divided into a planning zone, a preparation zone, a mining-initiated zone, and a goaf zone. Based on spatiotemporal succession, CBM wells are further divided into planning-preparation zone CBM wells, preparation-mining-initiated zone CBM wells, and mining-initiated zone CBM wells, enabling continuous extraction from a single well in multiple zones and in series. Through the design and implementation of multi-purpose wells, the extraction life of CBM wells in coal mining areas is improved, achieving cost reduction and efficiency enhancement, and breaking the spatial constraints of coal mining engineering.

[0027] In the planning area, surface pre-extraction vertical wells and surface pre-extraction horizontal wells are generally used for extraction; in the preparation area, surface fracturing wells and downhole extraction wells are generally used for extraction; two types of wells are designed.

[0028] like Figure 2As shown: The well type of the coalbed methane wells in the planning-preparation area is vertical coalbed methane wells; in the planning area, a network of vertical coalbed methane wells 1 is arranged parallel to the central axis of the planned coal mining face for fracturing and extraction; after the extraction area of ​​vertical coalbed methane wells 1 in the planning-preparation area is converted into the preparation area, vertical coalbed methane wells 1 in the planning-preparation area will take over from the coalbed methane wells in the planning area and become the coalbed methane wells in the preparation area. During the excavation of the main roadway 4, boreholes 2 along the length of the coal seam are drilled along the excavation direction to extract coalbed methane from the coal seam in the planning-preparation area. The fracturing-affected area of ​​vertical coalbed methane well 1 is connected and depressurized to achieve regional depressurization and extraction. Before tunneling, secondary fracturing is carried out on the planned working face. During tunneling, ordinary borehole 3 is drilled underground along the coal seam to connect the fracturing fracture end area of ​​vertical coalbed methane well 1 in the planned-preparation area with the unconnected affected area. The gas extraction is enhanced by using long borehole 2 and ordinary borehole 3 along the coal seam underground, so as to achieve pre-extraction of coalbed methane in the planned area and enhanced underground extraction of surface fracturing in the preparation area.

[0029] like Figure 3 As shown: The well type of the coalbed methane wells in the planning-preparation area is horizontal coalbed methane wells; in the planning area, a network of 5 horizontal coalbed methane wells in the planning-preparation area is arranged parallel to the central axis of the planned coal mining face for fracturing and extraction; the horizontal landing point of the 5 horizontal coalbed methane wells in the planning-preparation area is less than 10m away from the cut-off point of the working face, and the target point of the 5 horizontal coalbed methane wells in the planning-preparation area is less than 10m away from the stop-mining line of the working face; after the extraction area of ​​the 5 horizontal coalbed methane wells in the planning-preparation area is converted into the preparation area, the 5 horizontal coalbed methane wells in the planning-preparation area will take over from the coalbed methane wells in the planning area. During the excavation of the main roadway 4, a long borehole 2 along the coal seam is constructed along the excavation direction to connect and depressurize the fracturing-affected area of ​​the planned-preparation area coalbed methane horizontal well 5, achieving the purpose of regional depressurization and extraction. Before the roadway is excavated, the planned working face is subjected to secondary fracturing. During the roadway excavation, a conventional borehole 3 along the coal seam is constructed underground to connect the fracturing fracture end area of ​​the planned-preparation area coalbed methane horizontal well 5 with the unconnected affected area. The underground long borehole 2 along the coal seam and the conventional borehole 3 along the coal seam are used to enhance gas extraction, realizing the pre-extraction of coalbed methane in the planned area and the enhanced underground extraction of surface fracturing in the preparation area.

[0030] In the preparation zone, negative pressure extraction is generally carried out using surface fracturing wells and downhole extraction wells, while in the mining zone, negative pressure extraction is generally carried out using mining vertical wells.

[0031] Laterally, the gas-conducting fracture zone is divided into three zones: the lateral fracture zone, the "O"-shaped fracture zone, and the recompacted zone. Numerical simulations were conducted using the working face height, key overlying strata structure, and mining depth as influencing factors on the development morphology of the three zones. A fitting formula was established to calculate the range of the "O"-shaped fracture zone. Vertical coalbed methane wells were then arranged parallel to each other along the working face within a range of 7.30-40m from the return airway.

[0032] like Figure 4 As shown: The well type of the coalbed methane well in the preparation-mining zone is a vertical coalbed methane well; in the planning area, a network of 6 vertical coalbed methane wells in the preparation-mining zone is arranged parallel to each other along the working face within a range of "30~40m" from the return airway 7; the target coal seam 10 section is fracturing on the surface through the vertical coalbed methane wells in the preparation-mining zone 6; after fracturing, the wellhead of the vertical coalbed methane wells in the preparation-mining zone 6 is sealed, and enhanced negative pressure extraction is carried out underground; the drainage equipment is dismantled before the coal seam is mined; after the coal seam is mined, the working face is transformed into the mining zone, and the vertical coalbed methane wells in the preparation-mining zone 6 are replaced by the coalbed methane wells in the mining zone; the wellhead of the vertical coalbed methane wells in the preparation-mining zone 6 is opened, and surface negative pressure extraction equipment is installed; negative pressure extraction is carried out on the surface without fracturing, and coalbed methane is extracted by utilizing the pressure relief caused by coal seam mining disturbance.

[0033] After the preparation zone coalbed methane vertical well 6 is replaced by the coalbed methane well in the mining zone, in order to improve the negative pressure extraction effect of the coalbed methane well in the mining zone, the production casing below the external compression packer 9 can be perforated to expand the coalbed methane diffusion channel area.

[0034] like Figure 5 As shown: To meet the coalbed methane extraction requirements of the preparation and mining areas, the vertical well 6 in the preparation-mining area adopts a two-section wellbore structure. The first section uses a 444.5mm drill bit and has a surface casing diameter of 377.7mm, which is cemented. The second section has a wellbore diameter of 325mm and is drilled to a depth of 30m below the bottom plate of the target coal seam 10. To extend the service life of the vertical well 6 in the preparation-mining area, ensure stability, and improve gas production, a segmented cementing method is adopted. The segmented cementing location is the position of the largest fracture zone above the top plate of the target coal seam 10. The upper part of the production casing 13 in the second section is connected to the production casing 11 of the target coal seam 10 section using a drillable sliding sleeve 8 and an external compression packer 9. The drainage and gas production tubing 19 is connected to the wellhead using a wellhead hanger 12. The diameter of the second section production casing is 244.5mm or 193.7mm.

[0035] Using the mining water-conducting fracture zone calculation formula recommended in the "Specifications for Coal Pillar Retention and Coal Mining in Buildings, Water Bodies, Railways and Main Shafts" and the "Trial Regulations for Mine Hydrogeology", the development height of the overburden gas-conducting fracture zone is predicted, and the maximum value is used as the basis for the location of the second cementing well.

[0036] The segmented cementing method is as follows: Before cementing, pressurize and open the external compression packer 9, insert the drillable ball of the drillable sleeve 8 into the sleeve, so that the cement slurry outlet on the sleeve is fully exposed, and cement slurry is injected on the surface for cementing. After the cementing operation is completed and the cement slurry has reached the cementing requirements, the drill string is lowered to mill off the drillable ball, thus completing the segmented cementing.

[0037] After well completion, hydraulic jetting and perforation fracturing were used to perform surface fracturing on section 10 of the target coal seam. After fracturing, the surface wellhead was sealed, and enhanced negative pressure extraction was carried out downhole. Before coal seam recovery, the pumping unit and oil rods and other drainage equipment were removed, and the wellhead was sealed.

[0038] In mining-affected areas, two types of wells are generally used for extraction: vertical wells and L-shaped horizontal wells. In goaf areas, vertical wells are generally used for extraction.

[0039] The well type for coalbed methane wells in the mining-goaf area is a vertical coalbed methane well. After the goaf area is sealed for 2-3 years, the vertical coalbed methane well 6 in the preparation-mining-moving area will be cleared and converted into a mining-goaf coalbed methane well. To save costs and increase extraction volume, only one well will be left in each goaf area for negative pressure extraction. To avoid water accumulation in the goaf area affecting the extraction effect, wells in the goaf area with higher elevations should be retained for extraction. If the gas production channel is blocked due to the collapse of the goaf roof, a smaller drill bit will be used to drill and clear the goaf section of the gas well to a depth of 10m below the bottom of the target coal seam 10.

[0040] like Figure 6 As shown: The well type of the coalbed methane wells in the mining-goaf area is an L-shaped horizontal well; in the mining-affected area, a network of 14 L-shaped horizontal wells is arranged parallel to each other within a range of 7"30~40m from the return airway along the working face; surface negative pressure extraction equipment is installed at the wellhead of the 14 L-shaped horizontal wells in the mining-affected area, and negative pressure extraction is carried out on the surface without fracturing, utilizing the pressure relief and extraction of coalbed methane by coal seam mining disturbance; coal seam return After mining is completed, the wellhead of the L-shaped horizontal well 14 in the mining-goaf area is sealed, and the mining face is converted from the mining area to the goaf area. After the goaf area is sealed for 2-3 years, the wellhead of the L-shaped horizontal well 14 in the mining-goaf area is opened, and the L-shaped horizontal well 14 in the mining-goaf area is replaced by the coalbed methane well in the mining area. The horizontal section 14.2 of the L-shaped horizontal well 14 in the mining-goaf area is cleared.

[0041] like Figure 7 As shown: The total length L of the horizontal section 14.2 of the L-shaped horizontal well 14 in the mining-goaf area is divided into two parts: the first section is 0.4 L long and the second section is 0.6 L long. The horizontal section 14.2 is designed to be arranged along the downdip direction of the monoclinal with a dip angle of 1° to 2°. The fracture zone is divided into three parts in the longitudinal direction: the upper, middle and lower parts of the fracture zone. The horizontal section 14.2 of the L-shaped horizontal well is located in the lower middle part of the fracture zone in the longitudinal direction. The first section of the horizontal section 14.2 is arranged in the middle of the fracture zone. The second section of the horizontal section 14.2 is arranged in the lower part of the fracture zone. This will help to improve the gas production of the L-shaped horizontal well 14 in the mining-goaf area during both the mining and goaf stages, and extend the stable production time during the mining stage.

[0042] like Figure 8As shown: To meet the coalbed methane extraction requirements of the preparation area and the mining-active area, the L-shaped horizontal well 14 in the mining-active-goaf area adopts a two-section wellbore structure. The first section uses a 444.5mm drill bit, and the diameter of the surface casing in the first section is 377.7mm, which is cemented. The diameter of the second section wellbore is 325mm, and drilling is completed to the target point. To extend the service life of the L-shaped horizontal well 14 in the mining-active-goaf area and to ensure the stability and gas production effect of the horizontal section 14.2 wellbore, a segmented cementing method is adopted. The segmented cementing position is the position of the largest fracture zone above the roof of the target coal seam 10. The upper part of the second section production casing 17 is connected to the slotted screen pipe 16 using a drillable sliding sleeve 8 and an external compression packer 9. The drainage and gas production tubing is connected to the wellhead using a hanger 12. The diameter of the second section production casing 17 is 244.5mm.

[0043] After the coal seam is mined out, the surface wellhead of the L-shaped horizontal well 14 in the mining-goaf area is sealed, and the mining face is converted from the mining area to the goaf area. Two to three years after the goaf is sealed and stabilized, the sealed surface wellhead is opened, and the L-shaped horizontal well 14 in the mining-goaf area takes over from the mining area coalbed methane well for negative pressure extraction. Since the horizontal section 14.2 of the L-shaped horizontal well 14 has collapsed due to the roof collapse, the screen pipe of horizontal section 14.2 is likely deformed by compression. It is necessary to clear the horizontal section 14.2 of the L-shaped horizontal well 14.2 by using a smaller drill bit to drill and clear the horizontal section 14.2 to 10m below the bottom of the target coal seam 10.

[0044] To ensure normal drainage of the extraction pipeline, a 193.7mm diameter goaf production casing 18 is lowered into the wellhead using the hanger 12 at the wellhead. The horizontal section 14.2 of the mining-goaf L-shaped horizontal well 14 is connected to a 193.7mm screen pipe, and negative pressure extraction is carried out on the surface.

[0045] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for continuous extraction of coalbed methane from a single well in multiple zones or in series in a coal mining area, characterized in that: Based on the temporal and spatial relationships and the order of mining, the coal mining area is divided into the planning area, preparation area, mining-initiated area and goaf area; based on the temporal and spatial succession relationship, the coalbed methane wells are divided into coalbed methane wells in the planning-preparation area, coalbed methane wells in the preparation-mining-initiated area, and coalbed methane wells in the mining-goaf area, with one well in multiple areas and multiple areas in series for continuous extraction. When the well type of the coalbed methane wells in the planning-preparation area is a vertical coalbed methane well; in the planning area, a network of vertical coalbed methane wells (1) in the planning-preparation area is arranged parallel to the central axis of the planned coal mining face, and fracturing extraction is carried out; after the coal mining waiting area of ​​the vertical coalbed methane wells (1) is converted into the preparation area, the vertical coalbed methane wells (1) in the planning area are replaced by the coalbed methane wells in the preparation area. During the tunneling process of the main roadway (4), long boreholes (2) are drilled along the direction of tunneling along the coal seam. The fracturing-affected area of ​​the vertical coalbed methane well (1) in the planning-preparation area is connected and depressurized; before the roadway is excavated, the planned working face is subjected to secondary fracturing. When the roadway is excavated, the underground construction of ordinary boreholes (3) along the coal seam is carried out to connect the fracturing fracture end area of ​​the vertical coalbed methane well (1) in the planning-preparation area and the unconnected affected area. The underground long borehole (2) along the coal seam and ordinary borehole (3) along the coal seam are used to enhance the extraction of gas, so as to realize the pre-extraction of coalbed methane in the planning area and the enhanced underground extraction of surface fracturing in the preparation area. When the well type of the coalbed methane wells in the planning-preparation area is a horizontal coalbed methane well; in the planning area, a network of horizontal coalbed methane wells (5) in the planning-preparation area is arranged parallel to the central axis of the planned coal mining face for fracturing and extraction; the horizontal landing point of the horizontal coalbed methane wells (5) in the planning-preparation area is less than 10m away from the cut-off point of the working face, and the target point of the horizontal coalbed methane wells (5) in the planning-preparation area is less than 10m away from the stop-mining line of the working face; after the extraction area of ​​the horizontal coalbed methane wells (5) in the planning-preparation area is converted into the preparation area, the horizontal coalbed methane wells (5) in the planning-preparation area take over from the coalbed methane wells in the planning area as the preparation area. In the process of tunneling the main roadway (4), a long borehole (2) is drilled along the coal seam in the direction of tunneling to connect and depressurize the fracturing influence area of ​​the coal seam horizontal well (5) in the planning-preparation area. Before tunneling, the planned working face is subjected to secondary fracturing. When tunneling, a common borehole (3) is drilled underground along the coal seam to connect the fracturing fracture end area of ​​the coal seam horizontal well (5) in the planning-preparation area and the unconnected influence area. The long borehole (2) and the common borehole (3) are used to enhance the extraction of gas, so as to realize the pre-extraction of coal seam gas in the planning area and the enhanced underground extraction of surface fracturing in the preparation area.

2. The method for continuous extraction of coalbed methane from a single well in multiple zones or in series in a coal mining area according to claim 1, characterized in that: The well type of the coalbed methane well in the preparation-mining zone is a vertical coalbed methane well. In the planning area, a network of vertical coalbed methane wells (6) in the preparation-mining zone is arranged in parallel within a range of 30-40m from the return airway (7) along the working face. The target coal seam (10) section is fracturing on the surface through the vertical coalbed methane wells (6) in the preparation-mining zone. After fracturing, the wellhead of the vertical coalbed methane well (6) in the preparation-mining zone is sealed, and enhanced negative pressure extraction is carried out underground. The extraction equipment is removed before the coal seam is mined. After the coal seam is mined, the working face is transformed into a mining zone. The vertical coalbed methane well (6) in the preparation zone is replaced by the coalbed methane well in the mining zone. The wellhead of the vertical coalbed methane well (6) in the preparation zone is opened, and the surface negative pressure extraction equipment is installed. Negative pressure extraction is carried out on the surface without fracturing. Coalbed methane is extracted by utilizing the disturbance of coal seam mining to relieve pressure.

3. The method for continuous extraction of coalbed methane from a single well in multiple zones or in series in a coal mining area according to claim 2, characterized in that: The prepared-mining area coalbed methane vertical well (6) adopts a two-section well structure. The two sections are drilled to 30m below the bottom plate of the target coal seam (10). The segmented cementing method is adopted. The segmented cementing position is the position of the largest fracture zone above the top plate of the target coal seam (10). The upper part of the second section production casing (13) and the production casing (11) of the target coal seam (10) are connected by a drillable sliding sleeve (8) and an external compression packer (9). The drainage gas production tubing (19) is connected to the wellhead by a wellhead hanger (12).

4. The method for continuous extraction of coalbed methane from a single well in multiple zones or in series in a coal mining area according to claim 2, characterized in that: The well type of the coalbed methane well in the mining-goaf area is a vertical coalbed methane well. After the goaf area is closed for 2-3 years, the vertical coalbed methane well (6) in the preparation-mining-moving area is cleared and changed to a coalbed methane well in the mining-goaf area. Only one well is left in each goaf area for negative pressure extraction.

5. The method for continuous extraction of coalbed methane from a single well in multiple zones or in series in a coal mining area according to claim 1, characterized in that: The well type of the coalbed methane wells in the mining-goaf area is a coalbed methane L-shaped horizontal well; in the mining area, a network of mining-goaf L-shaped horizontal wells (14) is arranged in parallel along the working face within a range of 30~40m from the return airway (7); a surface negative pressure extraction device is installed at the wellhead of the mining-goaf L-shaped horizontal wells (14), and negative pressure extraction is carried out on the surface without fracturing, utilizing the coal seam mining disturbance to relieve pressure and extract coalbed methane; after the coal seam is recovered... The wellhead of the L-shaped horizontal well (14) of the mining-goaf coalbed methane is closed, and the working face is changed from the mining area to the goaf. After the goaf is closed for 2 to 3 years, the wellhead of the L-shaped horizontal well (14) of the mining-goaf coalbed methane is opened, and the L-shaped horizontal well (14) of the mining-goaf coalbed methane is replaced by the coalbed methane well in the mining area. The horizontal section (14.2) of the L-shaped horizontal well (14) of the mining-goaf coalbed methane is cleared.

6. The method for continuous extraction of coalbed methane from a single well in multiple zones or in series in a coal mining area according to claim 5, characterized in that: The total length L of the horizontal well section (14.2) of the L-shaped horizontal well (14) in the mining-goaf coalbed methane area is divided into two parts: the first section is 0.4 L long and the second section is 0.6 L long. The horizontal well section (14.2) is designed to be arranged along the downward dip direction of the monoclinal with an inclination angle of 1° to 2°. The fracture zone is divided into three parts in the longitudinal direction: the upper part, the middle part and the lower part of the fracture zone. The horizontal well section (14.2) of the L-shaped horizontal well is located in the lower middle part of the fracture zone in the longitudinal direction. The first section of the horizontal well section (14.2) is arranged in the middle part of the fracture zone. The second section of the horizontal well section (14.2) is arranged in the lower part of the fracture zone.

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