A method for co-mining coal and coalbed methane by high-pressure water jetting in horizontal wells

Abstract

A method for the co-mining of coal and coalbed methane by high-pressure water jetting in horizontal wells belongs to the technical field of coal and coalbed methane mining. A horizontal well with a three-well borehole structure is drilled in the mining coal seam by three-well drilling on the ground. After drilling is completed, a fiberglass casing is hung to complete the well. A continuous oil pipe transports the high-pressure water jet tool to the bottom of the well, and the jet liquid is used to spray the mining coal seam in a directional manner. After the local coal cutting target is reached, the continuous oil pipe and the jet tool are lifted up and moved in sequence toward the landing point to spray and cut the coal. During the coal cutting process, the jet liquid carrying coal powder and desorbed coalbed methane is returned to the ground and subjected to three-phase separation of gas, water and coal powder in a processing plant. After the coal cutting is completed, three-well drilling with pipe drilling is resumed, and after washing the well, a jet pump is lowered to drain water and extract gas, thereby achieving efficient co-mining of coal and coalbed methane by high-pressure water jetting in the horizontal well. When the gas production rate of the horizontal well decreases, pulsating water injection from the wellhead increases the permeability of the coal seam around the horizontal section and prolongs the gas production time. The method is simple to operate and has significant economic, environmental and safety benefits.

Description

Technical Field

[0001] The present invention relates to a method for co-mining coal and coalbed methane by using high-pressure water jets in horizontal wells, and in particular to a method for co-mining coal and coalbed methane in a coal mining area by using a continuous oil pipe to transport a high-pressure water jet tool string to a horizontal well section for hydraulic cutting and crushing of the mined coal seam. At the same time, the high pressure inside the wellbore generated by the high-pressure water jet is used to return the jet liquid carrying coal powder and desorbing coalbed methane to the ground, and the three-phase separation of coalbed methane, jet liquid and coal powder is carried out in a processing plant to obtain coalbed methane and coal powder industrial products and realize the recycling of the jet liquid, thereby realizing the safe and efficient co-mining of coal and coalbed methane in a coal mining area. The method belongs to the technical field of coal and coalbed methane mining. Background Art

[0002] Coal resources still hold a significant position in my country's energy development landscape. The closely related coalbed methane (CBM), a clean, unconventional natural gas resource, is also attracting significant attention for its development and utilization. With the continuous advancement of coal mining technology, extensive experience has been accumulated in coal and CBM extraction, resulting in the development of a variety of mining methods and processes. Traditional mining methods often focus on either extracting coal or extracting CBM through surface or underground drilling, such as extracting CBM through underground drilling or mining through conventional shaft and tunnel development. During the mining process, related technical approaches are continuously being refined, such as optimizing drilling layouts and improving the performance of extraction equipment, aiming to enhance mining efficiency and safety. Furthermore, to better balance the utilization of both coal and CBM resources, integrated mining efforts are gradually being developed, exploring how to achieve synergistic extraction of coal and CBM during the mining process to improve overall resource development efficiency.

[0003] Existing coal and coalbed methane extraction methods present numerous problems. On the one hand, when mining coal alone, if the large amount of coalbed methane contained in the coal seam is not effectively extracted in advance, it will cause safety hazards such as gas exceeding the limit during the mining process, affecting the normal production order of the coal mine and even causing serious safety accidents. Traditional coalbed methane extraction methods, whether surface extraction or underground extraction, often suffer from low extraction efficiency and are unable to fully extract and utilize the coalbed methane in the coal seam, resulting in a waste of resources. When attempting to jointly mine coal and coalbed methane, current mining processes make it difficult to achieve close coordination between the two during the mining process, and there is a problem of poor connection. For example, in some processes, the coal mining process damages the coalbed methane occurrence conditions, making subsequent coalbed methane extraction more difficult; or the coalbed methane extraction operation affects the coal mining progress, which greatly reduces the overall mining efficiency and affects the economic benefits and sustainable development of the co-mining of coal and coalbed methane.

[0004] Given the aforementioned issues, actively researching new methods for co-mining coal and coalbed methane is crucial. From a safety production perspective, only by achieving efficient co-mining of coal and coalbed methane and effectively extracting coalbed methane in advance can we effectively eliminate gas hazards during the mining process, safeguard the lives of coal miners, and ensure the normal operation of coal mines. From a resource utilization perspective, as a clean energy source, efficient simultaneous mining of coalbed methane during the mining process not only avoids resource waste but also increases energy supply, alleviates energy shortages, and meets the strategic requirements of my country's sustainable energy development. On an economic level, developing technologies that overcome the drawbacks of existing mining methods and achieve efficient co-mining can reduce coal and coalbed methane mining costs, improve mining efficiency, and ultimately enhance the economic benefits and market competitiveness of coal enterprises. Therefore, exploring new technologies and processes for co-mining coal and coalbed methane, such as horizontal well high-pressure water jetting, is of 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 purpose of the present invention is to overcome the problems of high risk of gas outburst during underground coal mining, waste of resources caused by coalbed methane leakage during coal mining ventilation, difficulty in ground development of coalbed methane and low resource recovery rate, etc., and provide a method for co-mining of coal and coalbed methane by high-pressure water jet in horizontal wells. A continuous oil pipe is used to transport a high-pressure water jet tool string to the horizontal well section to hydraulically cut and crush the mined coal seam. At the same time, the high pressure inside the wellbore generated by the high-pressure water jet is used to return the jet liquid carrying coal powder and desorbing coalbed methane to the ground, and the three-phase separation of coalbed methane, jet liquid and coal powder is carried out in the processing plant to obtain coalbed methane and coal powder industrial products and realize the recycling of jet liquid, thereby realizing a method for safe and efficient co-mining of coal and coalbed methane in coal mining areas, which can produce significant economic, environmental and safety benefits.

[0006] Technical solution: To achieve the above-mentioned purpose, the present invention provides a method for co-mining coal and coalbed methane by high-pressure water jetting in horizontal wells, comprising the following steps:

[0007] (a) An L-shaped horizontal well with a three-wellbore structure was constructed on the ground within the coal mining area. This three-dimensional "L-shaped three-wellbore" configuration was created. The composite trajectory design of the vertical section, the deflection section, and the horizontal section was used to break through the limitations of conventional U-shaped wells and achieve precise three-dimensional coverage of the coal seam with a single wellbore.

[0008] First, the horizontal well was drilled to 15 m below the interface between the loose layer and the bedrock, and the surface casing was lowered for cementing. The surface casing cementing layer was constructed from bottom to top around the surface casing to the surface.

[0009] Then, the horizontal well was directionally drilled to 1 m above the roof of the mined coal seam, and the technical casing was lowered for cementing. A cement layer for the technical casing was constructed from bottom to top around the technical casing to the ground.

[0010] After the horizontal well is drilled three times and reaches the landing point when encountering the mined coal seam, it continues to drill horizontally along the mined coal seam for 300 to 500 meters. After drilling is completed, the production casing made of fiberglass reinforced plastic is hung;

[0011] (b) Placing a coiled tubing vehicle on the ground, connecting the high-pressure manifold on the coiled tubing vehicle to a high-pressure water jet plunger pump, inserting a high-pressure water jet tool string into the coiled tubing, and delivering the tool string to the horizontal well inlet, actuating the hydraulic control system of the coiled tubing vehicle to deliver the coiled tubing wound on a drum into the horizontal well, actuating the high-pressure water jet plunger pump, injecting fluid into the coiled tubing through a coiled tubing injection head, and delivering the high-pressure water jet tool string to the bottom of the horizontal well. High-pressure water passes through the coiled tubing and reaches the annularly distributed conical nozzles on the high-pressure water jet tool string, where it sprays in a bidirectional conical manner along the inclination direction of the mined coal seam, thereby hydraulically cutting and crushing the mined coal seam within the range of influence of the high-pressure water jet;

[0012] (c) After the high-pressure water jet tool string located inside the wellbore and near the mined coal seam completes the cutting and crushing of the currently mined coal seam section through reciprocating jetting within the wellbore, the roller device of the hydraulic control system is used to slowly lift the coiled tubing and the high-pressure water jet tool string in steps of one times the length of the high-pressure water jet tool string. Then, intermittent / continuous high-pressure water jetting is used to achieve full-segment hydraulic cutting and crushing of the mined coal seam near the wellbore throughout the entire horizontal well section;

[0013] (d) After the coal body of the mined coal seam is hydraulically cut and crushed by a high-pressure water jet, the mixture formed after the crushing, i.e., the jet liquid carrying coal powder and desorbed coalbed methane, is carried out through the wellbore annulus to a surface processing plant using the high pressure generated by the high-pressure water jet plunger pump. Based on the principle of density difference sorting, the three-phase separation of coal powder, coalbed methane, and jet liquid is carried out at the processing plant through multi-level vibration screening to obtain coal powder and coalbed methane industrial products. The filtered jet liquid enters the jet liquid tank and is pressurized by the high-pressure water jet plunger pump before being re-injected into the coiled tubing and then into the horizontal well, thus realizing the recycling of the jet liquid during the process of hydraulic cutting and crushing of coal seams by high-pressure water jet;

[0014] (e) After the high-pressure water jet cutting and crushing work of the coal seam and coal body in the entire horizontal well section is completed, the coiled tubing and the high-pressure water jet tool string are lifted and removed, and the horizontal well section three-way wellbore before the high-pressure water jet is drilled again by connecting the reducer drill bit to the drill pipe and the slotted screen pipe to form a new three-way wellbore after the high-pressure water jet. The slotted screen pipe is used to support the new three-way wellbore after the high-pressure water jet to meet the requirements of the gas and water flow on the seepage channel during the subsequent horizontal well drainage and gas production process;

[0015] (f) After the new three-hole wellbore of the horizontal well is formed after high-pressure water jetting and the slotted screen pipe support is suspended, a coiled tubing is run from the wellhead of the horizontal well to the bottom of the horizontal well for positive circulation flushing. After the well is flushed, the well flushing tubing is pulled out and a jet pump is run to perform long-term drainage and gas production operations in the horizontal well, thereby realizing the surface development of coalbed methane within the well control range of the horizontal well;

[0016] (g) As the horizontal well drainage time increases, when the horizontal well gas production rate drops to ≤1000 m 3 / d later, high-pressure pulsating water is injected from the technical casing and the annulus of the oil pipe. The high-pressure pulsating water injection is used to stimulate the coal seams mined in the horizontal well section, thereby improving the permeability of the coal seams mined around the wellbore of the horizontal well section, thereby improving the gas production effect of the horizontal well and the coalbed methane resource recovery rate, and realizing the efficient co-mining of coal and coalbed methane by high-pressure water jetting in the horizontal well.

[0017] In step (a), the thickness of the mined coal seam is greater than 2.5 m, the inclination angle is less than 30°, and the air-dried gas content is greater than 12 m 3 / t, the coal body structure is primary structure coal or crushed coal, the coal seam structure is simple structure coal seam, the permeability is greater than 0.1 mD, and the landing point is buried at a depth of 300 to 600 m.

[0018] In step (a), the inner diameter of the suspended fiberglass production casing is greater than 80 mm, the wall thickness is greater than 7 mm, and the collapse strength is greater than 15 MPa. The inner end of the fiberglass production casing is lowered to the bottom of the horizontal well, and the outer end of the production casing is suspended on the lower end of the technical casing with a hanger.

[0019] In the steps, the maximum working pressure of the high-pressure water jet plunger pump is greater than 45 MPa, the maximum water injection rate is greater than 300 L / min, and the continuous working time is greater than 24 h; the inner diameter of the coiled tubing is greater than 5 cm, and the maximum pressure resistance is greater than 50 MPa.

[0020] In step (b), the high-pressure water jet tool string consists of 3 to 5 jet pipes with a length of 1 m connected in series, each jet pipe is equipped with 8 to 10 nozzles, which are arranged in a circular pattern around the jet pipe, forming a water flow that gradually transitions 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 to 2.0 m.

[0021] In step (c), the intermittent high-pressure water jet method is as follows: first, the coiled tubing and the high-pressure water jet tool string are lifted up, and when the set last injection point position is reached, the high-pressure water jet plunger pump is started again, so that high-pressure water is ejected from the nozzle of the high-pressure water jet tool string at the front end of the coiled tubing, and the mined coal seam within the range of influence of the high-pressure water jet is hydraulically cut and crushed; the continuous high-pressure water jet method is as follows: while slowly lifting the coiled tubing and the high-pressure water jet tool string, the high-pressure water jet plunger pump is kept continuously pumping water, so that high-pressure water is ejected from the nozzle of the high-pressure water jet tool string at the front end of the coiled tubing, and the mined coal seam within the range of influence of the high-pressure water jet is hydraulically cut and crushed.

[0022] In step (d), the jet liquid carrying coal powder and desorbed coalbed methane is returned to the ground through the annular space between the technical casing and the coiled tubing, and after passing through a spiral tube or cavitation decompression, it is transported to a treatment plant through a closed pipeline; in the treatment plant, the coalbed methane and the jet liquid containing coal powder are first separated by a gravity gas-water separator, and then the coal powder and the jet liquid are separated by filtration, cyclone, and step-by-step sedimentation.

[0023] In step (e), the variable diameter drill bit is made of PDC material, and the diameter of the variable diameter drill bit after opening is greater than 180 mm, and the diameter after closing is less than 110 mm; the slotted screen pipe is an N80 or P110 steel grade casing with an inner diameter of 130-170 mm and a wall thickness greater than 9 mm. The pre-cut strip slots extend along the screen pipe direction, the length of a single slot is 30-40 mm, the slot width is 2-3 mm, and the slot density is 8-12 slots / m.

[0024] In step (f), the long-term drainage and gas production operation of the horizontal well includes six stages: slow drainage, pressure-holding drainage, pressure-controlled gas production, pressure reduction and production increase, gas production attenuation, and pulsation excitation and production increase. During the drainage and production process, a drainage and production control system for the horizontal well is formulated in stages according to the gas and water production performance of the horizontal well; the jet pump draws high-pressure fracturing fluid from the power fluid pool through a power fluid pump installed on the ground, and is driven by the power fluid pump to transport and discharge the produced gas and produced water through the gas pipeline and the water pipeline. The jet pump is located 4 to 6 meters above the landing point of the horizontal well, and the lower end of the suction port is located 2 to 3 meters above the landing point of the horizontal well.

[0025] In step (g), during the high-pressure pulsating water injection, the wellhead pressure of the horizontal well is controlled to vary in the range of 2 to 12 MPa, the pulsating water injection pressure difference is controlled to be 6 to 8 MPa, the number of pulsating water injection excitation cycles is controlled to be 40 to 60 times, and the duration of the pulsating water injection operation is controlled to be 2 to 3 days.

[0026] Beneficial effects: Due to the adoption of the above technical solution, the present invention overcomes the problems of high cost of traditional underground coal mining, high risk of gas outburst during underground mining, waste of resources caused by large amount of coalbed methane escaped due to ventilation in coal mines, exacerbation of greenhouse effect by coalbed methane exhaust into the atmosphere, difficulty in surface development of coalbed methane and low resource recovery rate. A continuous oil pipe is used to transport a string of high-pressure water jet tools to the horizontal well section to hydraulically cut and crush the mined coal seam. At the same time, the high pressure inside the wellbore generated by the high-pressure water jet is used to return the jet liquid carrying coal powder and desorbed coalbed methane to the ground. The three-phase separation of coalbed methane, jet liquid and coal powder is carried out in the processing plant to obtain coalbed methane and coal powder industrial products and realize the recycling of jet liquid, thereby realizing a method for 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, the use of horizontal wells significantly increases the contact area of the well for mining coal seams, increases the amount of well-controlled coal and coalbed methane resources, and reduces the engineering costs of coal and coalbed methane mining; second, high-pressure water jet tool strings are used to spray, cut, and crush the mined coal seams, realizing fluidized mining of coal resources; third, the ground processing plant separates the jet liquid into three phases of gas, water, and coal powder, recovers coalbed methane and coal powder industrial products, and recycles the jet liquid, realizing the co-mining of coal and coalbed methane, and reducing the amount of jet liquid, protecting the ecological environment of the mining area; finally, the jet pump drainage and pressure reduction, and annular water injection stimulation methods are used to efficiently develop coalbed methane within the well control range of the horizontal well, significantly improving the gas production effect of the horizontal well and the coalbed methane recovery rate. The main advantages compared with existing technologies are:

[0027] 1) Horizontal wells are used on the ground to mine coal and coalbed methane together, eliminating the risk of casualties caused by underground gas outbursts and providing high safety.

[0028] 2) Coal and coalbed methane co-mining is carried out by using horizontal wells and high-pressure water jets. The well-controlled resources are large, the coal and coalbed methane recovery rates are high, and the economic benefits of co-mining coal and coalbed methane are significant;

[0029] 3) Using a surface treatment plant to separate the three phases of gas, water and pulverized coal, we can recover coalbed methane and pulverized coal as industrial products and recycle the jet fluid, which has little impact on the ecological environment of the mining area and saves water resources in the mining area;

[0030] 4) The jet pump drainage and pressure reduction and annular water injection stimulation methods are used to fully develop the coalbed methane, which improves the gas production effect of horizontal wells and realizes efficient development of coalbed methane.

[0031] 5) The technology and process are simple, the project implementation cost is low, and the economic, environmental and social benefits are good. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the method for high-pressure water jet cutting, crushing coal body and gas-water-coal powder three-phase separation and recycling of the present invention.

[0033] Figure 2 This is a schematic diagram of the structure of the horizontal well jet pump high-pressure water jet tool string of the present invention.

[0034] Figure 3 for Figure 2 Schematic diagram of the Ⅰ-Ⅰ section.

[0035] Figure 4 It is a schematic diagram of the drilling structure of the three-well section variable diameter drill bit and slotted screen pipe of the present invention.

[0036] Figure 5 This is a schematic diagram of the coalbed methane development method using a horizontal well jet pump according to the present invention.

[0037] In the figure: 1-ground; 2-horizontal well; 3-unconsolidated layer and bedrock interface; 4-surface casing; 5-surface casing cement layer; 6-mined coal seam; 7-technical casing; 8-technical casing cement layer; 9-landing point; 10-production casing; 11-coiled tubing vehicle; 12-high-pressure water jet plunger pump; 13-coiled tubing; 14-coiled tubing injection 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-processing plant; 22-jet fluid tank; 23-three-hole well; 24-reducing drill bit; 25-slotted screen; 26-new three-hole well; 27-drill pipe; 28-jet pump; 29-lower end of suction port; 30-hanger; 31-power fluid pump; 32-power fluid tank; 33-gas pipeline; 34-water pipeline. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the embodiments in the accompanying drawings:

[0039] like Figure 1 As shown, the present invention provides a method for co-mining coal and coalbed methane by using high-pressure water jets in horizontal wells, and the specific steps are as follows:

[0040] (a) An L-shaped horizontal well 2 with a three-wellbore structure was constructed on the ground 1 within the coal mining area. This three-dimensional "L-shaped three-wellbore" configuration was created. The composite trajectory design of the vertical section, the deflection section, and the horizontal section was used to overcome the limitations of conventional U-shaped wells, achieving precise three-dimensional coverage of the coal seam with a single wellbore.

[0041] First, the horizontal well 2 is drilled to 15 m below the interface 3 between the loose layer and the bedrock, and the surface casing 4 is lowered for cementing. Then, a surface casing cementing layer 5 is constructed from bottom to top around the surface casing 4 to the ground surface 1.

[0042] Then, the horizontal well 2 is directionally drilled to 1 m above the roof of the mined coal seam 6, and a technical casing 7 is lowered for cementing. A technical casing cementing layer 8 is constructed from bottom to top around the technical casing 7 to the ground surface 1.

[0043] After drilling the horizontal well 2 three times and encountering the mined coal seam 6 and reaching the landing point 9, continue drilling horizontally along the mined coal seam 6 for 300 to 500 m. After drilling is completed, hang the fiberglass-reinforced plastic production casing 10.

[0044] The thickness of the mined coal seam 6 is greater than 2.5 m, the inclination is less than 30°, and the air-dried gas content is greater than 12 m 3 / t, the coal body structure is primary structure coal or crushed coal, the coal seam structure is simple structure coal seam, the permeability is greater than 0.1 mD, and the landing point 9 is buried at a depth of 300 to 600 m; the inner diameter of the suspended fiberglass reinforced plastic production casing 10 is greater than 80 mm, the wall thickness is greater than 7 mm, and the collapse strength is greater than 15 MPa. The inner end of the fiberglass reinforced plastic production casing 10 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, such as Figure 4 As shown;

[0045] (b) placing a coiled tubing vehicle 11 on the ground, connecting the high-pressure manifold on the coiled tubing vehicle 11 to the high-pressure water jet plunger pump 12, inserting a high-pressure water jet tool string 15 into the coiled tubing 13 and delivering it to the horizontal well inlet, actuating the hydraulic control system of the coiled tubing vehicle 11 to deliver the coiled tubing 13 wound on the drum into the horizontal well 2, actuating the high-pressure water jet plunger pump 12, injecting liquid into the coiled tubing 13 through the coiled tubing injection head 14, delivering the high-pressure water jet tool string 15 to the bottom 16 of the horizontal well, causing high-pressure water to pass through the coiled tubing 13 and reach the annularly distributed conical nozzles 17 on the high-pressure water jet tool string 15, where it is bidirectionally sprayed in a conical manner along the inclination direction of the mined coal seam 6, thereby hydraulically cutting and crushing the mined coal seam 6 within the range of influence of the high-pressure water jet;

[0046] The maximum working pressure of the high-pressure water jet plunger pump 12 is greater than 45 MPa, the maximum water injection rate is greater than 300 L / min, and the continuous working time is greater than 24 hours; the inner diameter of the coiled tubing is greater than 5 cm, and the maximum pressure resistance is greater than 50 MPa.

[0047] The high-pressure water jet tool string 15 is composed of 3 to 5 jet pipes with a length of 1 meter connected in series. Each jet pipe is distributed with 8 to 10 nozzles 17. The nozzles 17 are distributed in a ring around the jet pipe, forming a water flow that gradually transitions 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 to 2.0 meters.

[0048] (c) After the high-pressure water jet tool string 15 located inside the wellbore and near the mined coal seam 6 completes the cutting and crushing of the currently mined coal seam 6 section through reciprocating jetting within the wellbore, the roller device of the hydraulic control system is used to slowly lift the coiled tubing 13 and the high-pressure water jet tool string 15 in steps of one times the length of the high-pressure water jet tool string 15. Then, intermittent / continuous high-pressure water jetting is used to achieve extended hydraulic cutting and crushing of the entire horizontal well section of the horizontal well 2 near the mined coal seam 6;

[0049] The intermittent high-pressure water jet method is as follows: first, the coiled tubing 13 and the high-pressure water jet tool string 15 are lifted up, and when the set last injection point position is reached, the high-pressure water jet plunger pump 12 is started to make high-pressure water ejected from the nozzle 17 of the high-pressure water jet tool string 15 at the front end of the coiled tubing 13, and the mined coal seam 6 within the range of influence of the high-pressure water jet is hydraulically cut and crushed; the continuous high-pressure water jet method is as follows: in the process of slowly lifting the coiled tubing 13 and the high-pressure water jet tool string 15, the high-pressure water jet plunger pump 12 is kept continuously pumping water, so that high-pressure water ejected from the nozzle 17 of the high-pressure water jet tool string 15 at the front end of the coiled tubing 13, and the mined coal seam 6 within the range of influence of the high-pressure water jet is hydraulically cut and crushed, as shown in FIG. Figure 2 and Figure 3 shown.

[0050] (d) After the coal body of the mined coal seam 6 is cut and crushed by the high-pressure water jet, the mixture formed after the crushing, i.e., the jet liquid 20 carrying the coal powder 18 and the desorbed coalbed methane 19, is brought out through the wellbore annulus to the surface processing plant 21 by the high pressure generated by the high-pressure water jet plunger pump 12. Based on the density difference sorting principle, the three-phase separation of the coal powder 18, the coalbed methane 19, and the jet liquid 20 is carried out in the processing plant 21 through multi-level vibration screening to obtain the industrial products of the coal powder 18 and the coalbed methane 19. The filtered jet liquid 20 enters the jet liquid tank 22 and is pressurized by the high-pressure water jet plunger pump 12 and then re-extracted. It is injected into the coiled tubing 13 and enters the horizontal well 2, realizing the recycling of the jet liquid 20 in the process of hydraulic cutting and crushing of the coal seam 6 by high-pressure water jet; the jet liquid 20 carrying coal powder 18 and coalbed methane 19 returns to the ground 1 through the annular space between the technical casing 7 and the coiled tubing 13, and is transported to the treatment plant 21 through a closed pipeline after being reduced in pressure by a spiral tube or cavitation; in the treatment plant 21, the coalbed methane 19 is first separated from the jet liquid 20 containing coal powder by a gravity gas-water separator, and then the coal powder 18 is separated from the jet liquid 20 by filtration, cyclone, and step-by-step sedimentation.

[0051] (e) After the high-pressure water jet cutting and crushing work of the coal seam 6 is completed in the entire horizontal well section, the continuous oil pipe 13 and the high-pressure water jet tool string 15 are lifted and taken out, and the horizontal well 2 three-way wellbore 23 before the high-pressure water jet is drilled again with the variable diameter drill bit 24 connected to the drill pipe 27 and the slotted screen pipe 25 to form a new three-way wellbore 26 of the horizontal well 2 after the high-pressure water jet. The slotted screen pipe 25 is used to support the new three-way wellbore 26 of the horizontal well 2 after the high-pressure water jet, so as to meet the requirements of the gas and water flow on the seepage channel during the subsequent drainage and gas production process of the horizontal well 2, such as Figure 4 As shown; the variable diameter drill bit 24 is made of PDC material, and the diameter of the variable diameter drill bit 24 after opening is greater than 180 mm, and the diameter after closing is less than 110 mm; the drill rod 27 is an ordinary steel drill rod 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 and a wall thickness of greater than 9 mm. The pre-cut strip slots extend along the screen pipe direction, the single slot length is 30-40 mm, the slot width is 2-3 mm, and the slot density is 8-12 slots / m.

[0052] (f) After the high-pressure water jet, the new three-hole well 26 of the horizontal well 2 is formed and the slotted screen pipe 25 is suspended for support. On the ground 1, a continuous oil pipe 13 is lowered from the wellhead of the horizontal well 2 to the bottom 16 of the horizontal well to perform positive circulation flushing. After flushing, the well-washing oil pipe is extracted and then lowered into the jet pump 28 to perform long-term drainage and gas production operations of the horizontal well 2, so as to realize 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-holding drainage, pressure-controlled gas production, pressure reduction and production increase, gas production attenuation, and pulsation stimulation and production increase. During the drainage and production process, the drainage and production 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 and discharge the produced gas and produced water through the gas pipeline 33 and the water pipeline 34. Figure 5 As shown; the jet pump 28 is located 4 to 6 m above the landing point 9 of the horizontal well 2, and the lower end 29 of the suction port is located 2 to 3 m above the landing point 9 of the horizontal well 2;

[0053] (g) As the horizontal well drainage time increases, when the horizontal well gas production rate drops to ≤1000 m 3After 1 day, high-pressure pulsating water is injected from the technical casing 7 and the tubing annulus. This high-pressure pulsating water injection stimulates the coal seam 6 being mined in the horizontal well section, increasing the permeability of the mined coal seam 6 around the wellbore in the horizontal well section. This in turn improves the gas production efficiency and coalbed methane resource recovery rate of horizontal well 2, achieving efficient co-production of coal and coalbed methane by high-pressure water jetting in the horizontal well. During this high-pressure pulsating water injection, the wellhead pressure of horizontal well 2 is controlled within a range of 2 to 12 MPa, the pulsating water injection pressure difference is controlled at 6 to 8 MPa, the number of pulsating water injection stimulation cycles is controlled at 40 to 60, and the duration of the pulsating water injection operation is controlled at 2 to 3 days.

Claims

1. A method for co-mining coal and coalbed methane by high-pressure water jetting in a horizontal well, comprising constructing a horizontal well (2) with an L-shaped three-well structure on the ground (1) in a coal mining area, creating an "L-shaped three-well structure" three-dimensional configuration, breaking through the limitations of conventional U-shaped wells through a composite trajectory design of a vertical section-inclination section-horizontal section, and achieving precise three-dimensional coverage of the coal seam by a single wellbore, characterized in that: The following steps are also included: (a) Achieving precise coverage of the three-dimensional space of the coal seam by a single wellbore: First, the horizontal well (2) is drilled to 15 m below the interface (3) between the loose layer and the bedrock, and the surface casing (4) is lowered for cementing. A surface casing cementing layer (5) is constructed from bottom to top around the surface casing (4) to the ground (1); Then, the horizontal well (2) is secondarily directionally drilled to 1 m above the roof of the mining coal seam (6), and a technical casing (7) is lowered for cementing. A technical casing cementing layer (8) is constructed from bottom to top around the technical casing (7) to the ground (1); After the horizontal well (2) is drilled three times and encounters the mining coal seam (6) and reaches the landing point (9), it continues to drill horizontally along the mining coal seam (6) for 300 to 500 meters. After the drilling is completed, a production casing (10) made of glass fiber reinforced plastic is hung; (b) placing a continuous tubing operation vehicle (11) on the ground, connecting the high-pressure manifold on the continuous tubing operation vehicle to the high-pressure water jet plunger pump (12), and inserting the high-pressure water jet tool string (15) into the continuous tubing (13) and then sending it into the horizontal well inlet, starting the hydraulic control system of the continuous tubing operation vehicle (11) to send the continuous tubing (13) wound on the drum into the horizontal well (2), and starting the high-pressure water jet plunger pump (12), injecting liquid into the continuous tubing (13) through the continuous tubing injection head (14), and sending the high-pressure water jet tool string (15) to the bottom (16) of the horizontal well, so that high-pressure water passes through the continuous tubing (13) and reaches the annularly distributed conical nozzles (17) on the high-pressure water jet tool string (15) and sprays in a bidirectional conical manner along the inclined direction of the mined coal seam (6), thereby causing the mined coal seam (6) within the influence range of the high-pressure water jet to be hydraulically cut and crushed; (c) After the high-pressure water jet tool string (15) located inside the wellbore and close to the mined coal seam completes the cutting and crushing of the currently mined coal seam (6) section by reciprocating jetting in the wellbore, the roller device of the hydraulic control system is used to slowly lift the continuous oil pipe (13) and the high-pressure water jet tool string (15) in steps of one time the length of the high-pressure water jet tool string (15), and then the intermittent / continuous high-pressure water jet method is used to achieve the full-section extended hydraulic cutting and crushing of the mined coal seam (6) near the wellbore of the entire horizontal well section of the horizontal well (2); (d) After the coal body of the mined coal seam (6) is cut and crushed by high-pressure water jet hydraulics, the mixture formed after crushing, i.e., the jet liquid (20) carrying coal powder (18) and desorbed coalbed methane (19), is brought out through the wellbore annulus to the ground processing plant (21) by the high pressure generated by the high-pressure water jet plunger pump (12). Based on the density difference sorting principle, the three-phase separation of coal powder (18), coalbed methane (19) and jet liquid (20) is carried out in the processing plant (21) through multi-level vibration screening to obtain industrial products of coal powder (18) and coalbed methane (19). After filtration, The jet liquid (20) enters the jet liquid tank (22), is pressurized by the high-pressure water jet plunger pump (12), and is re-injected into the continuous oil pipe (13) and enters the horizontal well (2), thereby realizing the recycling of the jet liquid (20) in the process of hydraulic cutting and crushing the coal seam (6) by the high-pressure water jet; the jet liquid (20) carrying the coal powder (18) and the desorbed coalbed methane (19) returns to the ground (1) through the annular space between the technical casing (7) and the continuous oil pipe (13), and is transported to the treatment plant (21) through a closed pipeline after being depressurized by a spiral pipe or cavitation; (e) After the high-pressure water jet cutting and crushing work of the coal seam (6) is completed in the entire horizontal well section, the continuous oil pipe (13) and the high-pressure water jet tool string (15) are lifted and taken out, and the horizontal well (2) three-opening wellbore (23) before the high-pressure water jet is drilled again by connecting the variable diameter drill bit (24) to the drill pipe (27) and the slotted screen (25) to form the horizontal well (2) three-opening wellbore (26) after the high-pressure water jet. The slotted screen (25) is used to support the horizontal well (2) three-opening wellbore (26) after the high-pressure water jet, so as to meet the requirements of the gas-water flow on the seepage channel during the subsequent drainage and gas production process of the horizontal well (2); (f) After the high-pressure water jet, the new three-hole well (26) of the horizontal well (2) is formed and the slotted screen pipe (25) is suspended for support. On the ground (1), a continuous oil pipe (13) is lowered from the wellhead of the horizontal well (2) to the bottom of the horizontal well (16) for positive circulation flushing. After the well is flushed, the well-washing oil pipe is extracted and then lowered into the jet pump (28) for long-term drainage and gas production of the horizontal well (2), so as to realize the surface development of coalbed methane within the well control range of the horizontal well. The long-term drainage and gas production operation of the horizontal well (2) includes six stages: slow drainage, pressure-holding drainage, pressure-controlled gas production, pressure reduction and production increase, gas production attenuation, and pulsation excitation and production increase. During the drainage and production process, the drainage and production control system of the horizontal well (2) is formulated in stages according to the gas and water production performance of the horizontal well (2); (g) As the horizontal well drainage time increases, when the horizontal well gas production rate drops to ≤1000 m 3 / d later, high-pressure pulsating water is injected from the technical casing (7) and the annulus of the oil pipe, and the high-pressure pulsating water injection is used to stimulate the mining of the coal seam (6) in the horizontal well section, thereby improving the permeability of the mining coal seam (6) around the wellbore of the horizontal well section, thereby improving the gas production effect of the horizontal well (2) and the recovery rate of coalbed methane resources, and realizing the efficient co-mining of coal and coalbed methane by high-pressure water jet in the horizontal well.

2. The method for co-mining coal and coalbed methane by high-pressure water jetting in horizontal wells according to claim 1, characterized in that: In step (a), the thickness of the mined coal seam (6) is greater than 2.5 m, the inclination angle is less than 30°, and the air-dried gas content is greater than 12 m 3 / t, the coal body structure is primary structure coal or crushed coal, the coal seam structure is simple structure coal seam, the permeability is greater than 0.1 mD, and the landing point (9) is buried at a depth of 300 to 600 m.

3. The method for co-mining coal and coalbed methane by high-pressure water jetting in horizontal wells according to claim 1, characterized in that: In step (a), the inner diameter of the suspended fiberglass production casing (10) is greater than 80 mm, the wall thickness is greater than 7 mm, and the collapse strength is greater than 15 MPa. The inner end of the fiberglass production casing (10) is lowered to the bottom of the horizontal well (16), and the outer end of the production casing (10) is suspended on 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 jetting in horizontal wells according to claim 1, characterized in that: In step (b), the maximum working pressure of the high-pressure water jet plunger pump (12) is greater than 45 MPa, the maximum water injection rate is greater than 300 L / min, and the continuous working time is greater than 24 h; the inner diameter of the coiled tubing is greater than 5 cm, and the maximum pressure resistance is greater than 50 MPa.

5. The method for co-mining coal and coalbed methane by high-pressure water jetting in horizontal wells according to claim 1 is characterized in that: In step (b), the high-pressure water jet tool string (15) is composed of 3 to 5 jet pipes with a length of 1 m connected in series, and each jet pipe is distributed with 8 to 10 nozzles (17). The nozzles (17) are distributed in a ring around the jet pipe, forming a water flow that gradually transitions 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 to 2.0 m.

6. The method for co-mining coal and coalbed methane by high-pressure water jetting in horizontal wells according to claim 1, characterized in that: In step (c), the intermittent high-pressure water jet method is as follows: first, the continuous tubing (13) and the high-pressure water jet tool string (15) are lifted up, and when the set last injection point position is reached, the high-pressure water jet plunger pump (12) is started again, so that high-pressure water is ejected from the nozzle (17) of the high-pressure water jet tool string (15) at the front end of the continuous tubing (13), and the mined coal seam (6) within the range of influence of the high-pressure water jet is hydraulically cut and crushed; the continuous high-pressure water jet method is as follows: in the process of slowly lifting the continuous tubing (13) and the high-pressure water jet tool string (15), the high-pressure water jet plunger pump (12) is kept continuously injected with water, so that high-pressure water is ejected from the nozzle (17) of the high-pressure water jet tool string (15) at the front end of the continuous tubing (13), and the mined coal seam (6) within the range of influence of the high-pressure water jet is hydraulically cut and crushed.

7. The method for co-mining coal and coalbed methane by high-pressure water jetting in horizontal wells according to claim 1, characterized in that: In step (d), the closed pipeline is transported to the treatment plant (21) for treatment, and the coalbed methane (19) and the jet liquid (20) containing coal powder are first separated by a gravity gas-water separator, and then the coal powder (18) and the jet liquid (20) are separated by filtration, cyclone, and step-by-step sedimentation.

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

9. The method for co-mining coal and coalbed methane by high-pressure water jetting in horizontal wells according to claim 1, characterized in that: In step (f), the jet pump (28) extracts high-pressure fracturing fluid from the power fluid pool (32) through the power fluid pump (31) located on the ground, and is driven by the power fluid pump (31) to transport and discharge the produced gas and produced water through the gas pipeline (33) and the water pipeline (34). The jet pump (28) is located 4 to 6 m above the landing point (9) of the horizontal well (2), and the lower end (29) of the suction port is located 2 to 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 jetting in horizontal wells according to claim 1, characterized in that: In step (g), during the high-pressure pulsating water injection, the wellhead pressure of the horizontal well (2) is controlled to vary within the range of 2 to 12 MPa, the pulsating water injection pressure difference is controlled to be 6 to 8 MPa, the number of pulsating water injection excitation cycles is controlled to be 40 to 60 times, and the duration of the pulsating water injection operation is controlled to be 2 to 3 days.

Images