Horizontal well high-pressure water jet coal and coal bed gas co-mining method

Abstract

The invention discloses a horizontal well high-pressure water jet coal and coal bed gas co-mining method, and belongs to the technical field of coal and coal bed gas mining. A horizontal well with a third-opening well body structure is constructed on the ground, drilling is conducted in the mining coal seam in the third-opening process, and after drilling is completed, a glass fiber reinforced plastic casing pipe is hung for well completion; the coiled tubing conveys a high-pressure water jet tool to the bottom of the well, and jet liquid is used for directionally jetting the exploited coal seam; after the local coal cutting target is achieved, the continuous oil pipe and the injection tool are lifted up, and coal cutting is conducted by moving and injecting towards the landing point in sequence; in the coal cutting process, jet fluid carrying pulverized coal and desorbing coalbed methane is returned to the ground, and gas-water-pulverized coal three-phase separation is carried out in a treatment plant; after coal cutting is finished, three-time casing well drilling is carried out again, after well washing, a jet pump is put in for water drainage and gas production, and high-pressure water jet coal and coal bed gas efficient co-production of the horizontal well is achieved; when the gas production rate of the horizontal well is reduced, the permeability of the coal seam around the horizontal section is improved through pulsating water injection from a wellhead, and the gas production time is prolonged; the method is simple and convenient to operate and has remarkable economic, environmental and safety benefits.

Description

Technical Field

[0001] The present invention relates to a method for co - mining coal and coalbed methane by high - pressure water jet in horizontal wells, especially a method that uses coiled tubing to transport a high - pressure water jet tool string to the horizontal well section for hydraulic cutting and crushing of the coal seam to be mined. At the same time, the high pressure inside the wellbore generated by the high - pressure water jet is used to return the jet fluid carrying coal powder and desorbed coalbed methane to the ground, and three - phase separation of coalbed methane, jet fluid, and coal powder is carried out at the treatment plant to obtain industrial products of coalbed methane and coal powder and realize the recycling of the jet fluid, so as to achieve safe and efficient co - mining of coal and coalbed methane in coal mining areas, belonging to the technical field of coal and coalbed methane mining. Background Art

[0002] In the field of energy development in China, coal resources still occupy an important position. As a clean unconventional natural gas resource, the development and utilization of coalbed methane closely related to it have also attracted much attention. With the continuous development of coal mining technology, a lot of experience has been accumulated in the mining of coal and coalbed methane, and various mining methods and processes have been formed. Traditional mining methods often focus on separately mining coal or ground and underground extraction of coalbed methane. For example, coalbed methane is extracted through underground drilling, or coal is mined according to conventional roadway development. During the mining process, relevant technical means are also continuously improved, such as continuously optimizing the drilling layout and improving the performance of extraction equipment, aiming to improve the mining efficiency and safety. At the same time, in order to better balance the two resources of coal and coalbed methane, some comprehensive mining attempts have been gradually carried out, and people have begun to explore how to achieve the coordinated mining of coal and coalbed methane during the mining process to improve the overall resource development efficiency.

[0003] Existing methods for co - mining coal and coalbed methane have many problems. On the one hand, when coal is mined alone, if a large amount of coalbed methane contained in the coal seam cannot be effectively extracted in advance, it will cause safety hazards such as gas over - limit during coal mining, affecting the normal production order of the coal mine and even possibly triggering serious safety accidents. For traditional coalbed methane extraction methods, whether it is ground extraction or underground extraction, there are often situations of low extraction efficiency, and it is impossible to fully extract the coalbed methane in the coal seam for utilization, resulting in waste of resources. When attempting to carry out coordinated mining of coal and coalbed methane, the current mining technology is difficult to achieve close cooperation between the two during the mining process, and there are problems with poor connection. For example, in some processes, the coal - mining link damages the occurrence conditions of coalbed methane, leading to an increase in the difficulty of subsequent coalbed methane extraction; or the coalbed methane extraction operation affects the coal - mining progress, greatly reducing the overall mining efficiency and affecting the economic benefits and sustainable development of the co - mining of coal and coalbed methane.

[0004] In view of the above existing problems, it is particularly necessary to actively carry out research on new methods for co - mining coal and coalbed methane. From the perspective of safety production, only by achieving efficient co - mining of coal and coalbed methane and reasonably extracting coalbed methane in advance can we effectively eliminate the gas hidden dangers during the coal - mining process and ensure the life safety of coal miners and the normal operation of coal - mine production. From the perspective of resource utilization, as a clean energy, if coalbed methane can be efficiently mined synchronously during the coal - mining process, it can not only avoid resource waste, but also increase energy supply and alleviate the energy - shortage situation, meeting the strategic requirements of China's sustainable energy development. Economically, developing a technology that can overcome the drawbacks of existing mining methods and achieve efficient co - mining can reduce the mining costs of coal and coalbed methane, improve the mining efficiency, and thus enhance the economic benefits and market competitiveness of coal enterprises. Therefore, exploring new technologies and processes such as horizontal - well high - pressure water - jet co - mining of coal and coalbed methane has great and urgent practical significance for promoting the high - quality and sustainable development of the coal industry. Summary of the Invention

[0005] Technical Problem: The object of the present invention is to overcome the problems such as high risk of gas outburst during the underground coal mining process, resource waste caused by the escape of coalbed methane during the ventilation process of coal mining, great difficulty in surface development of coalbed methane and low resource recovery rate. A method for co - mining coal and coalbed methane by horizontal - well high - pressure water - jet is provided. The high - pressure water - jet tool string is conveyed by coiled tubing to the horizontal well section to hydraulically cut and break the coal seam to be mined. At the same time, the high pressure inside the wellbore generated by the high - pressure water - jet returns the jet fluid carrying coal powder and desorbed coalbed methane to the ground, and three - phase separation of coalbed methane, jet fluid and coal powder is carried out in the treatment plant to obtain industrial products of coalbed methane and coal powder and realize the recycling of the jet fluid, achieving a method for safe and efficient co - mining of coal and coalbed methane in coal - mine areas, which can produce significant economic, environmental and safety benefits.

[0006] Technical Solution: To achieve the above object, a method for co - mining coal and coalbed methane by horizontal - well high - pressure water - jet of the present invention includes the following steps: (a) Construct a horizontal well with an L - shaped three - opening wellbore structure on the ground in the coal - mine area, creating a three - dimensional configuration of "L - shaped three - opening wellbore". Through the composite - trajectory design of the vertical section - build - up section - horizontal section, the limitation of the conventional U - shaped well is broken through, and the accurate coverage of the three - dimensional space of the coal seam by a single wellbore is realized: First, drill the first opening of the horizontal well to 15 m below the interface between the loose layer and the bedrock, set the surface casing and cement it. Construct the surface - casing cement layer from bottom to top around the surface casing to the ground; Then, directionally drill the second opening of the horizontal well to 1 m above the roof of the coal seam to be mined, set the technical casing and cement it. Construct the technical - casing cement layer from bottom to top around the technical casing to the ground; After the third section of the horizontal well encounters the coal seam to be mined and reaches the landing point, continue to drill horizontally along the coal seam to be mined for 300 - 500 m. After completion of drilling, hang the production casing made of fiberglass. (b)Place the coiled tubing workover truck on the ground, connect the high-pressure manifold on the coiled tubing workover truck to the high-pressure water jet plunger pump, and install the high-pressure water jet tool string in the coiled tubing and then send it into the horizontal well inlet. Start the hydraulic control system of the coiled tubing workover truck to send the coiled tubing wound on the drum into the horizontal well, and start the high-pressure water jet plunger pump. Inject liquid into the coiled tubing through the coiled tubing injection head, and send the high-pressure water jet tool string to the bottom of the horizontal well, so that the high-pressure water reaches the conical nozzles distributed annularly on the high-pressure water jet tool string and sprays bidirectionally in a conical shape along the inclined direction of the coal seam to be mined, so as to hydraulically cut and crush the coal seam to be mined within the influence range of the high-pressure water jet. (c)When the high-pressure water jet tool string located inside the wellbore and close to the coal seam to be mined completes the cutting and crushing of the current coal seam section through reciprocating spraying in the wellbore, use the drum device of the hydraulic control system to slowly lift the coiled tubing and the high-pressure water jet tool string in steps of the length of one high-pressure water jet tool string. Then, through the intermittent / continuous high-pressure water jet method, realize the full-section extended hydraulic cutting and crushing of the coal seam to be mined near the entire horizontal well section of the horizontal well. (d)After the high-pressure water jet hydraulically cuts and crushes the coal body of the coal seam to be mined, use the high pressure generated by the high-pressure water jet plunger pump to carry the mixture formed after crushing, that is, the jet liquid carrying coal powder and desorbed coal seam gas, out of the wellbore annulus to the surface treatment plant. Based on the density differential separation principle, carry out three-phase separation of coal powder, coal seam gas, and jet liquid through multi-level vibrating screening in the treatment plant to obtain industrial products of coal powder and coal seam gas. The filtered jet liquid enters the jet liquid tank, and after being pressurized by the high-pressure water jet plunger pump, it is re-injected into the coiled tubing and enters the horizontal well, realizing the recycling of the jet liquid during the process of high-pressure water jet hydraulic cutting and crushing of the coal seam to be mined. (e)After the work of high-pressure water jet cutting and crushing the coal body of the coal seam to be mined in the entire horizontal well section is completed, lift and remove the coiled tubing and the high-pressure water jet tool string, and drill again along the third section wellbore of the horizontal well before the high-pressure water jet, connecting the variable-diameter bit and the drill pipe with the slotted screen pipe to form a new third section wellbore of the horizontal well after the high-pressure water jet. Use the slotted screen pipe to support the new third section wellbore of the horizontal well after the high-pressure water jet to meet the requirements of the gas-water flow for the seepage channel during the subsequent drainage and gas production process of the horizontal well. (f)After the new third section wellbore of the horizontal well after the high-pressure water jet is formed and supported by hanging the slotted screen pipe, lower the coiled tubing from the surface to the bottom of the horizontal well at the horizontal well wellhead for positive circulation well flushing. After well flushing, lift out the well flushing tubing and then lower the jet pump for long-term drainage and gas production operation of the horizontal well to realize the surface development of coal seam gas within the well control range of the horizontal well. (g) As the production time of the horizontal well extends, when the gas production rate of the horizontal well drops to ≤ 1000 m 3 / d, high-pressure pulsating water injection is carried out from the annulus between the technical casing and the tubing. By utilizing the stimulating effect of high-pressure pulsating water injection on the coal seam mined in the horizontal well section, the permeability of the coal seam mined around the wellbore in the horizontal well section is increased, thereby improving the gas production effect of the horizontal well and the recovery rate of coalbed methane resources, and realizing the efficient co-production of high-pressure water jet coal and coalbed methane in the horizontal well.

[0007] In step (a), the thickness of the coal seam to be mined > 2.5 m, the dip angle < 30°, the air-dried basis gas content > 12 m 3 / t, the coal body structure is primary structural coal or fragmented coal, the coal seam structure is a simple structural coal seam, the permeability > 0.1 mD, and the landing point burial depth is 300 - 600 m.

[0008] In step (a), the inner diameter of the production casing made of fiberglass suspension > 80 mm, the wall thickness > 7 mm, the collapse strength > 15 MPa. The inner end of the production casing made of fiberglass is lowered to the bottom of the horizontal well, and the outer end of the production casing is suspended at the lower end of the technical casing by a hanger.

[0009] In the step, the maximum working pressure of the high-pressure water jet piston pump > 45 MPa, the maximum water injection rate > 300 L / min, and the continuous working time > 24 h; the inner diameter of the coiled tubing > 5 cm, and the maximum pressure resistance > 50 MPa.

[0010] In step (b), the high-pressure water jet tool string is composed of 3 - 5 injection pipes with a length of 1 m connected in series. Each injection pipe is distributed with 8 - 10 nozzles. The nozzles are annularly distributed around the injection pipe, forming a gradual transition of the water flow from a cylindrical shape to a conical shape, and the axis of the cone forms an angle with the axis of the coiled tubing; the effective hydraulic cutting radius of a single nozzle is 0.5 - 2.0 m.

[0011] In step (c), the intermittent high-pressure water jet method is as follows: first lift the coiled tubing and the high-pressure water jet tool string. When reaching the set position of the previous injection point, then start the high-pressure water jet piston pump to make the high-pressure water spray out from the nozzles of the high-pressure water jet tool string at the front end of the coiled tubing, and carry out hydraulic cutting and fragmentation on the coal seam mined within the influence range of the high-pressure water jet; the continuous high-pressure water jet method is as follows: during the process of slowly lifting the coiled tubing and the high-pressure water jet tool string, keep the high-pressure water jet piston pump continuously injecting water to make the high-pressure water spray out from the nozzles of the high-pressure water jet tool string at the front end of the coiled tubing, and carry out hydraulic cutting and fragmentation on the coal seam mined within the influence range of the high-pressure water jet.

[0012] In step (d), the jet liquid carrying pulverized coal and desorbing coalbed methane returns to the ground through the annulus space between the production casing and the coiled tubing, and after passing through the spiral pipe or cavitation pressure reduction, it is transported to the treatment plant through a closed pipeline; in the treatment plant, first, the coalbed methane is separated from the jet liquid containing pulverized coal by a gravity gas-liquid separator, and then the pulverized coal is separated from the jet liquid by filtration, cyclone, and step-by-step precipitation methods.

[0013] In step (e), the variable-diameter bit is made of PDC material. After the variable-diameter bit is opened, the diameter > 180 mm, and after it is closed, the diameter is less than 110 mm; the slotted screen pipe is a casing of N80 or P110 steel grade, with an inner diameter of 130 - 170 mm, a wall thickness > 9 mm, the pre-cut strip-shaped slots extend along the direction of the screen pipe, the single slot length is 30 - 40 mm, the slot width is 2 - 3 mm, and the slot density is 8 - 12 slots / m.

[0014] In step (f), the long-term drainage and gas production operation of the horizontal well includes 6 stages: slow drainage, pressure buildup drainage, pressure-controlled gas production, pressure reduction and production increase, gas production attenuation, and pulsating excitation production increase. During the drainage and production process, the drainage and production pipe control system of the horizontal well is formulated in stages according to the gas and water production performance of the horizontal well; the jet pump extracts high-pressure fracturing fluid from the power liquid pool through a power liquid pump installed on the ground, and is driven by the power liquid pump to transport the produced gas and produced water out and discharge them through the gas transmission pipeline and the water transmission pipeline. The jet pump is located 4 - 6 m above the landing point of the horizontal well, and the lower end of the suction port is located 2 - 3 m above the landing point of the horizontal well.

[0015] In step (g), during the high-pressure pulsating water injection, the wellhead pressure of the horizontal well is controlled to vary within the range of 2 - 12 MPa, the pulsating water injection pressure difference is controlled within 6 - 8 MPa, the pulsating water injection excitation cycle times are controlled within 40 - 60 times, and the pulsating water injection operation duration is controlled within 2 - 3 days.

[0016] Beneficial effects: Due to the adoption of the above technical solutions, the present invention overcomes the problems of high cost in traditional underground coal mining, high risk of gas outburst during underground coal mining, waste of resources caused by the escape of a large amount of coalbed methane due to underground ventilation in coal mines, aggravation of the greenhouse effect by the air drainage of coalbed methane to the atmosphere, great difficulty in surface development of coalbed methane and low resource recovery rate. The high-pressure water jet tool string is conveyed by coiled tubing to the horizontal well section to hydraulically cut and crush the coal seam to be mined. At the same time, the high pressure inside the wellbore generated by the high-pressure water jet returns the jet fluid carrying coal powder and desorbed coalbed methane to the ground, and the three-phase separation of coalbed methane, jet fluid and coal powder is carried out in the treatment plant to obtain industrial products of coalbed methane and coal powder and realize the recycling of the jet fluid, thus realizing a method for the safe and efficient co-mining of coal and coalbed methane in coal mining areas and improving the economic benefits of coal and coalbed methane development. First of all, the use of horizontal wells significantly increases the contact area of the well for coal seam mining, increases the coal and coalbed methane resources controlled by the well, and reduces the engineering cost of coal and coalbed methane mining; secondly, the high-pressure water jet tool string is used to jet, cut and crush the coal seam to be mined, realizing the fluidized mining of coal resources; thirdly, the surface treatment plant carries out three-phase separation of gas, water and coal powder for the jet fluid, recovers industrial products of coalbed methane and coal powder, and recycles the jet fluid, realizing the co-mining of coal and coalbed methane, reducing the amount of jet fluid used, and protecting the ecological environment of the mining area; finally, the jet pump is used for drainage and pressure reduction and the annulus injection excitation method is adopted to efficiently develop the coalbed methane within the well control range of the horizontal well, significantly improving the gas production effect of the horizontal well and the recovery rate of coalbed methane. The main advantages compared with the prior art are as follows: 1) The co-mining of coal and coalbed methane is carried out on the ground using horizontal wells, there is no risk of casualties caused by underground gas outburst, and the safety is high; 2) The co-mining of coal and coalbed methane is carried out by using horizontal wells and high-pressure water jet methods. The well-controlled resource volume is large, the recovery rates of coal and coalbed methane are high, and the economic benefits of the co-mining of coal and coalbed methane are significant; 3) The three-phase separation of gas, water and coal powder is carried out by using the ground treatment plant, realizing the recovery of industrial products of coalbed methane and coal powder, recycling the jet fluid, having little impact on the ecological environment of the mining area, and saving water resources in the mining area; 4) The jet pump is used for drainage and pressure reduction and the annulus injection excitation method is adopted to fully develop the coalbed methane, improving the gas production effect of the horizontal well and realizing the efficient development of coalbed methane.

[0017] 5) The technical process is simple, the engineering implementation cost is low, and the economic, environmental and social benefits are good. Description of the drawings

[0018] Figure 1 It is a schematic diagram of the high-pressure water jet cutting, crushing coal body and three-phase separation and recycling method of gas, water and coal powder of the present invention.

[0019] Figure 2 It is a schematic diagram of the structure of the horizontal well jet pump high-pressure water jet tool string of the present invention.

[0020] Figure 3 is Figure 2 the schematic cross - sectional view of section Ⅰ - Ⅰ in

[0021] Figure 4 is the schematic diagram of the structure of the variable - diameter bit and slotted screen pipe drilling in the three - opening well section of the present invention.

[0022] Figure 5 is the schematic diagram of the development method of coalbed methane drainage by horizontal well jet pump in the present invention.

[0023] In the figure: 1 - ground; 2 - horizontal well; 3 - interface between loose layer and bedrock; 4 - surface casing; 5 - surface casing cementing layer; 6 - coal seam to be mined; 7 - technical casing; 8 - technical casing cementing layer; 9 - landing point; 10 - production casing; 11 - coiled tubing workover truck; 12 - high - pressure water jet plunger pump; 13 - coiled tubing; 14 - coiled tubing injector head; 15 - high - pressure water jet tool string; 16 - bottom of horizontal well; 17 - nozzle; 18 - coal powder; 19 - coalbed methane; 20 - jet fluid; 21 - treatment plant; 22 - jet fluid tank; 23 - three - opening wellbore; 24 - variable - diameter bit; 25 - slotted screen pipe; 26 - new three - opening wellbore; 27 - drill pipe; 28 - jet pump; 29 - lower end of suction inlet; 30 - hanger; 31 - power fluid pump; 32 - power fluid pool; 33 - gas pipeline; 34 - water pipeline. Detailed implementation manners

[0024] The present invention will be further described below in combination with the embodiments in the accompanying drawings: As Figure 1 shown, a method for co - mining coal and coalbed methane by high - pressure water jet in horizontal wells of the present invention comprises the following specific steps: (a) Construct a horizontal well 2 with a three - opening wellbore structure in the shape of an L on the ground 1 in the coal mining area, creating a three - dimensional configuration of "L - shaped three - opening wellbore". By designing a composite trajectory of vertical section - build - up section - horizontal section, break through the limitations of conventional U - shaped wells, and achieve precise coverage of the three - dimensional space of the coal seam by a single wellbore: First, drill the first section of the horizontal well 2 to 15 m below the interface 3 between the loose layer and the bedrock, lower the surface casing 4 for cementing, and construct the surface casing cementing layer 5 from bottom to top around the surface casing 4 to the ground 1; Then, directionally drill the second section of the horizontal well 2 to 1 m above the roof of the coal seam 6 to be mined, lower the technical casing 7 for cementing, and construct the technical casing cementing layer 8 from bottom to top around the technical casing 7 to the ground 1; Then, after the third section of the horizontal well 2 drills through the coal seam 6 to reach the landing point 9, continue to horizontally drill 300 - 500 m along the coal seam 6 to be mined. After completion of drilling, hang the production casing 10 made of fiberglass; The thickness of the exploited coal seam 6 is > 2.5 m, the dip angle is < 30°, the air-dried basis gas content is > 12 m 3 / t, the coal body structure is primary structural coal or fragmented coal, the coal seam structure is a simple structural coal seam, the permeability is > 0.1 mD, the burial depth of the landing point 9 is 300 - 600 m; the inner diameter of the production casing 10 made of suspended fiberglass is > 80 mm, the wall thickness is > 7 mm, the collapse strength is > 15 MPa, the inner end of the production casing 10 made of fiberglass is lowered to the bottom 16 of the horizontal well, and the outer end of the production casing 10 is suspended at the lower end of the technical casing 7 by a hanger 30, as Figure 4 shown; (b)Place the coiled tubing workover truck 11 on the ground, connect the high-pressure manifold on the coiled tubing workover truck 11 to the high-pressure water jet plunger pump 12, and after sleeving the high-pressure water jet tool string 15 in the coiled tubing 13, send it into the horizontal well inlet. Start the hydraulic control system of the coiled tubing workover truck 11 to send the coiled tubing 13 wound on the drum into the horizontal well 2, and start the high-pressure water jet plunger pump 12. Inject liquid into the coiled tubing 13 through the coiled tubing injection head 14, and send the high-pressure water jet tool string 15 to the bottom 16 of the horizontal well, so that the high-pressure water reaches the conical nozzles 17 distributed annularly on the high-pressure water jet tool string 15 through the coiled tubing 13 and performs two-way conical spraying along the inclined direction of the exploited coal seam 6, so as to hydraulically cut and break the exploited coal seam 6 within the influence range of the high-pressure water jet; The maximum working pressure of the high-pressure water jet plunger pump 12 is > 45 MPa, the maximum water injection rate is > 300 L / min, and the continuous working time is > 24 h; the inner diameter of the coiled tubing is > 5 cm, and the maximum pressure resistance is > 50 MPa.

[0025] The high-pressure water jet tool string 15 is composed of 3 - 5 injection pipes with a length of 1 m in series. Each injection pipe is distributed with 8 - 10 nozzles 17. The nozzles 17 are distributed annularly around the injection pipe, forming a gradual transition of the water flow from a cylindrical shape to a conical shape, and the axis of the cone forms an angle with the axis of the coiled tubing 13; the effective hydraulic cutting radius of a single nozzle is 0.5 - 2.0 m.

[0026] (c)When the high-pressure water jet tool string 15 located inside the wellbore and close to the exploited coal seam 6 completes the cutting and breaking of the current exploited coal seam 6 section through reciprocating spraying in the wellbore, use the drum device of the hydraulic control system to slowly lift the coiled tubing 13 and the high-pressure water jet tool string 15 in steps of the length of the high-pressure water jet tool string 15, and then through the intermittent / continuous high-pressure water jet method, realize the full-section extended hydraulic cutting and breaking of the exploited coal seam 6 near the entire horizontal well section of the horizontal well 2; The described intermittent high-pressure water jet method is as follows: First, lift the coiled tubing 13 and the high-pressure water jet tool string 15. When reaching the position of the previous set injection point, then start the high-pressure water jet piston pump 12, so that high-pressure water sprays out from the nozzle 17 of the high-pressure water jet tool string 15 at the front end of the coiled tubing 13, and hydraulically cuts and crushes the exploited coal seam 6 within the influence range of the high-pressure water jet. The described continuous high-pressure water jet method is as follows: During the process of slowly lifting the coiled tubing 13 and the high-pressure water jet tool string 15, keep the high-pressure water jet piston pump 12 injecting water continuously, so that high-pressure water sprays out from the nozzle 17 of the high-pressure water jet tool string 15 at the front end of the coiled tubing 13, and hydraulically cuts and crushes the exploited coal seam 6 within the influence range of the high-pressure water jet, as Figure 2 and Figure 3 shown.

[0027] (d) After the high-pressure water jet hydraulically cuts and crushes the coal body of the exploited coal seam 6, use the high pressure generated by the high-pressure water jet piston pump 12 to take the mixture formed after crushing, that is, the jet liquid 20 carrying coal powder 18 and desorbed coalbed methane 19, out to the surface treatment plant 21 through the wellbore annulus. Based on the density differential separation principle, at the treatment plant 21, multi-level vibrating screening is carried out for the three-phase separation of coal powder 18, coalbed methane 19, and jet liquid 20 to obtain industrial products of coal powder 18 and coalbed methane 19. The filtered jet liquid 20 enters the jet liquid tank 22, and then after being pressurized by the high-pressure water jet piston pump 12, it is reinjected into the coiled tubing 13 and enters the horizontal well 2, realizing the recycling of the jet liquid 20 during the process of high-pressure water jet hydraulically cutting and crushing the exploited coal seam 6. The jet liquid 20 carrying coal powder 18 and coalbed methane 19 returns to the ground 1 through the annulus space between the technical casing 7 and the coiled tubing 13, and after passing through a spiral pipe or cavitation pressure reduction, it is transported to the treatment plant 21 through a closed pipeline. At the treatment plant 21, first, the coalbed methane 19 is separated from the jet liquid 20 containing coal powder through a gravity gas-water separator, and then the coal powder 18 is separated from the jet liquid 20 through filtration, cyclone, and step-by-step precipitation methods.

[0028] (e) After the work of high-pressure water jet cutting and crushing the coal body of the exploited coal seam 6 in the entire horizontal well section is completed, lift and remove the coiled tubing 13 and the high-pressure water jet tool string 15, and then carry out drilling again along the three-opening wellbore 23 of the horizontal well 2 before the high-pressure water jet, connecting the variable-diameter bit 24 of the three-opening section of the horizontal well 2 with the drill pipe 27 and the slotted screen pipe 25 to form a new three-opening wellbore 26 of the horizontal well 2 after the high-pressure water jet. Use the slotted screen pipe 25 to support the new three-opening wellbore 26 of the horizontal well 2 after the high-pressure water jet to meet the requirements of the gas-water flow for the seepage channel during the subsequent drainage and gas production process of the horizontal well 2, as Figure 4As shown; the variable-diameter drill bit 24 is made of PDC material. After the variable-diameter drill bit 24 is opened, the diameter > 180 mm, and after it is closed, the diameter is less than 110 mm; the drill pipe 27 is a common steel drill pipe with a diameter of 89 mm; the slotted screen pipe 25 is a casing of N80 or P110 steel grade, with an inner diameter of 130 - 170 mm, a wall thickness > 9 mm. The pre-cut strip-shaped slots extend along the direction of the screen pipe. The single slot length is 30 - 40 mm, the slot width is 2 - 3 mm, and the slot density is 8 - 12 slots / m.

[0029] (f)After the new triple-opening wellbore 26 of the horizontal well 2 is formed by high-pressure water jet and supported by hanging the slotted screen pipe 25, the coiled tubing 13 is lowered from the wellhead of the horizontal well 2 on the ground 1 to the bottom 16 of the horizontal well for positive circulation well flushing. After well flushing, the well flushing tubing is retrieved, and then the jet pump 28 is lowered to conduct long-term drainage and gas production operations for the horizontal well 2, realizing the surface development of coalbed methane within the well control range of the horizontal well; the long-term drainage and gas production operations of the horizontal well 2 include six stages: slow drainage, pressure buildup drainage, pressure-controlled gas production, pressure reduction and production increase, gas production attenuation, and pulsating excitation for production increase. During the drainage and production process, the drainage and production pipe control system of the horizontal well 2 is formulated in stages according to the gas and water production performance of the horizontal well 2; the jet pump 28 extracts high-pressure fracturing fluid from the power fluid pool 32 through the power fluid pump 31 installed on the ground, and is driven by the power fluid pump 31 to transport the produced gas and produced water out and discharge them through the gas pipeline 33 and the water pipeline 34, as Figure 5 shown; the jet pump 28 is located 4 - 6 m above the landing point 9 of the horizontal well 2, and the lower end 29 of the suction port is located 2 - 3 m above the landing point 9 of the horizontal well 2; (g)As the drainage and production time of the horizontal well extends, when the gas production rate of the horizontal well drops to ≤ 1000 m 3 / d, high-pressure pulsating water injection is carried out from the annulus between the technical casing 7 and the tubing. By using the excitation effect of high-pressure pulsating water injection on the coal seam 6 in the horizontal well section, the permeability of the coal seam 6 around the wellbore in the horizontal well section is improved, thereby improving the gas production effect of the horizontal well 2 and the recovery rate of coalbed methane resources, realizing the efficient co-production of coal and coalbed methane by high-pressure water jet in the horizontal well. When carrying out high-pressure pulsating water injection, the wellhead pressure of the horizontal well 2 is controlled to vary within the range of 2 - 12 MPa, the pulsating water injection pressure difference is controlled within the range of 6 - 8 MPa, the pulsating water injection excitation cycle times are controlled within the range of 40 - 60 times, and the pulsating water injection operation duration is controlled within the range of 2 - 3 days.

Claims

1. A method for co - mining coal and coalbed methane by high - pressure water jet in horizontal wells, characterized in that It includes the following steps: (a)Construct a horizontal well (2) with a three-opening wellbore structure in an L shape on the ground (1) within a coal mining area, creating a three-opening wellbore in an "L shape" three-dimensional configuration. Through the composite trajectory design of the vertical section - build-up section - horizontal section, break through the limitations of conventional U-shaped wells and achieve precise coverage of the three-dimensional space of the coal seam by a single wellbore: First, drill the first opening of the horizontal well (2) to 15 m below the interface (3) between the loose layer and the bedrock, set the surface casing (4) and cement it. Construct a surface casing cement layer (5) around the surface casing (4) from bottom to top to the ground (1); Then, drill the second opening of the horizontal well (2) directionally to 1 m above the roof of the coal seam to be mined (6), set the technical casing (7) and cement it. Construct a technical casing cement layer (8) around the technical casing (7) from bottom to top to the ground (1); After the third opening of the horizontal well (2) encounters the coal seam to be mined (6) and reaches the landing point (9), continue to drill horizontally along the coal seam to be mined (6) for 300 - 500 m. After completion of drilling, hang a production casing (10) made of fiberglass; (b)Place a coiled tubing workover truck (11) on the ground, connect the high-pressure manifold on the coiled tubing workover truck to the high-pressure water jet piston pump (12), and install the high-pressure water jet tool string (15) in the coiled tubing (13) and then send it into the horizontal well inlet. Start the hydraulic control system of the coiled tubing workover truck (11) to send the coiled tubing (13) wound on the drum into the horizontal well (2), and start the high-pressure water jet piston pump (12). Inject liquid into the coiled tubing (13) through the coiled tubing injection head (14), send the high-pressure water jet tool string (15) to the bottom of the horizontal well (16), and make the high-pressure water reach the conical nozzles (17) distributed annularly on the high-pressure water jet tool string (15) through the coiled tubing (13) and spray bidirectionally in a conical shape along the inclined direction of the coal seam to be mined (6), so as to hydraulically cut and break the coal seam to be mined (6) within the influence range of the high-pressure water jet; (c)When the high-pressure water jet tool string (15) located inside the wellbore and close to the coal seam to be mined completes the cutting and breaking of the current section of the coal seam to be mined (6) through reciprocating spraying in the wellbore, use the drum device of the hydraulic control system to slowly lift the coiled tubing (13) and the high-pressure water jet tool string (15) in steps of the length of the high-pressure water jet tool string (15). Then, through intermittent / continuous high-pressure water jet mode, realize the full-section extended hydraulic cutting and breaking of the coal seam to be mined (6) near the entire horizontal well section of the horizontal well (2); (d)After the coal body of the coal seam (6) to be mined is cut and broken by the high-pressure water jet hydraulic force, the high-pressure generated by the high-pressure water jet piston pump (12) is used to carry the mixture formed after crushing, that is, the jet liquid (20) carrying coal powder (18) and desorbed coalbed methane (19), through the wellbore annulus to the surface treatment plant (21). Based on the density differential separation principle, the three-phase separation of coal powder (18), coalbed methane (19), and jet liquid (20) is carried out through multi-level vibrating screening in the treatment plant (21) to obtain industrial products of coal powder (18) and coalbed methane (19). The filtered jet liquid (20) enters the jet liquid tank (22), and then is pressurized by the high-pressure water jet piston pump (12) and reinjected into the coiled tubing (13) and enters the horizontal well (2) to realize the recycling of the jet liquid (20) in the process of high-pressure water jet hydraulic cutting and breaking of the coal seam (6); (e)After the work of cutting and breaking the coal body of the coal seam (6) by high-pressure water jet in the whole horizontal well section is completed, the coiled tubing (13) and the high-pressure water jet tool string (15) are lifted and taken out, and the variable-diameter bit (24) of the third open hole section of the horizontal well (2) is connected to the drill pipe (27) and drilled with the slotted screen pipe (25) along the third open hole (23) of the horizontal well (2) before the high-pressure water jet to form a new third open hole (26) of the horizontal well (2) after the high-pressure water jet. The slotted screen pipe (25) is used to support the new third open hole (26) of the horizontal well (2) after the high-pressure water jet to meet the requirements of the gas-water flow for the seepage channel in the subsequent drainage gas production process of the horizontal well (2); (f)After the new third open hole (26) of the horizontal well (2) after the high-pressure water jet is formed and supported by hanging the slotted screen pipe (25), the coiled tubing (13) is lowered from the wellhead of the horizontal well (2) to the bottom of the horizontal well (16) on the ground (1) for positive circulation well flushing. After well flushing, the well flushing tubing is lifted out and the jet pump (28) is lowered for long-term drainage gas production operation of the horizontal well (2) to realize the surface development of coalbed methane within the well control range of the horizontal well; (g) As the production time of the horizontal well extends, when the gas production rate of the horizontal well drops to ≤ 1000 m 3 / d, high-pressure pulsating water injection is carried out from the annulus between the technical casing (7) and the tubing. By utilizing the stimulating effect of high-pressure pulsating water injection on the coal seam (6) in the horizontal well section, the permeability of the coal seam (6) around the wellbore in the horizontal well section is increased, thereby improving the gas production effect of the horizontal well (2) and the recovery rate of coalbed methane resources, and realizing the efficient co-production of high-pressure water jet coal and coalbed methane in the horizontal well.

2. The method for co - mining coal and coalbed methane by high - pressure water jet in horizontal wells according to claim 1, wherein: In step (a), the thickness of the exploited coal seam (6) > 2.5 m, dip angle < 30°, air-dried basis gas content > 12 m 3 / t, the coal body structure is primary structural coal or fragmented coal, the coal seam structure is a simple structural coal seam, permeability > 0.1 mD, and the burial depth of the landing point (9) is 300 - 600 m.

3. The method for co-mining coal and coalbed methane by high-pressure water jet in horizontal wells according to claim 1, wherein: In step (a), the inner diameter of the production casing (10) made of suspended fiberglass is > 80 mm, the wall thickness is > 7 mm, and the collapse strength is > 15 MPa. The inner end of the production casing (10) made of fiberglass is lowered to the bottom of the horizontal well (16), and the outer end of the production casing (10) is suspended at the lower end of the technical casing (7) by a hanger (30).

4. The method for co-mining coal and coalbed methane by high-pressure water jet in horizontal wells according to claim 1, characterized in that: In step (b), the maximum working pressure of the high-pressure water jet piston pump (12) is > 45 MPa, the maximum water injection rate is > 300 L / min, and the continuous working time is > 24 h; the inner diameter of the coiled tubing is > 5 cm, and the maximum pressure resistance is > 50 MPa.

5. The method for co-mining coal and coalbed methane by high-pressure water jet in horizontal wells according to claim 1, characterized in that: In step (b), the high-pressure water jet tool string (15) is composed of 3 - 5 injection pipes with a length of 1 m in series. Each injection pipe is distributed with 8 - 10 nozzles (17). The nozzles (17) are annularly distributed around the injection pipe, forming a gradual transition of the water flow from a cylindrical shape to a conical shape, and the axis of the cone forms an angle with the axis of the coiled tubing (13); the effective hydraulic cutting radius of a single nozzle is 0.5 - 2.0 m.

6. The method for co-mining coal and coalbed methane by high-pressure water jet in horizontal wells according to claim 1, characterized in that: In step (c), the intermittent high-pressure water jet method is as follows: First, lift the coiled tubing (13) and the high-pressure water jet tool string (15). When reaching the set position of the previous jetting point, then start the high-pressure water jet piston pump (12) to make the high-pressure water spray out from the nozzle (17) of the high-pressure water jet tool string (15) at the front end of the coiled tubing (13), and perform hydraulic cutting and fragmentation on the exploited coal seam (6) within the influence range of the high-pressure water jet; the continuous high-pressure water jet method is as follows: During the process of slowly lifting the coiled tubing (13) and the high-pressure water jet tool string (15), keep the high-pressure water jet piston pump (12) injecting water continuously to make the high-pressure water spray out from the nozzle (17) of the high-pressure water jet tool string (15) at the front end of the coiled tubing (13), and perform hydraulic cutting and fragmentation on the exploited coal seam (6) within the influence range of the high-pressure water jet.

7. The method for co - mining coal and coalbed methane by high - pressure water jet in horizontal wells according to claim 1, characterized in that: In step (d), the jet fluid (20) carrying coal powder (18) and desorbed coalbed methane (19) returns to the ground (1) through the annulus between the technical casing (7) and the coiled tubing (13), and after passing through the spiral tube or cavitation pressure reduction, it is transported to the treatment plant (21) through a closed pipeline; in the treatment plant (21), first, the coalbed methane (19) is separated from the jet fluid (20) containing coal powder through a gravity gas-liquid separator, and then the coal powder (18) is separated from the jet fluid (20) through filtration, cyclone, and step-by-step precipitation methods.

8. The method for co-mining coal and coalbed methane by high-pressure water jet in horizontal wells according to claim 1, characterized in that: In step (e), the variable-diameter bit (24) is made of PDC material. After the variable-diameter bit (24) expands, the diameter > 180 mm, and after closing, the diameter is less than 110 mm; the drill pipe (27) is a common steel drill pipe with a diameter of 89 mm; the slotted screen pipe (25) is an N80 or P110 steel grade casing with an inner diameter of 130 - 170 mm, a wall thickness > 9 mm, the pre-cut strip-shaped slots extend along the direction of the screen pipe, the single slot length is 30 - 40 mm, the slot width is 2 - 3 mm, and the slot density is 8 - 12 slots / m.

9. The method for co-mining coal and coalbed methane by high-pressure water jet in horizontal wells according to claim 1, characterized in that: In step (f), the long-term drainage and gas production operation of the horizontal well (2) includes 6 stages: slow drainage, pressure buildup drainage, pressure-controlled gas production, pressure reduction and production increase, gas production decline, and pulsating excitation production increase. During the drainage and production process, the drainage and production pipe control system of the horizontal well (2) is formulated in stages according to the gas and water production performance of the horizontal well (2); the jet pump (28) extracts high-pressure fracturing fluid from the power fluid pool (32) through the power fluid pump (31) installed on the ground. Driven by the power fluid pump (31), the produced gas and produced water are transported and discharged through the gas transmission pipeline (33) and the water transmission pipeline (34). The jet pump (28) is located 4 - 6 m above the landing point (9) of the horizontal well (2), and the lower end (29) of the suction port is located 2 - 3 m above the landing point (9) of the horizontal well (2).

10. The method for co-mining coal and coalbed methane by high-pressure water jet in horizontal wells according to claim 1, characterized in that: In step (g), when performing high-pressure pulsating water injection, the wellhead pressure of the horizontal well (2) is controlled to vary within the range of 2 - 12 MPa, the pulsating water injection pressure difference is controlled within the range of 6 - 8 MPa, the pulsating water injection excitation cycle times are controlled within the range of 40 - 60 times, and the pulsating water injection operation duration is controlled within the range of 2 - 3 days.

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