A branch drilling staged fracturing and permeability enhancement method and integrated pressure-pumping device for underground coal mines

Abstract

The present invention discloses a method for increasing the permeability of branch boreholes in underground coal mines by staged fracturing and a pressure-pumping integrated device. The permeability-increasing method adopts a staged fracturing method by throwing soluble fracturing balls, and a salt solution is used to replace the fracturing fluid after fracturing; wherein the soluble fracturing balls are made of low-density resin material, and their specific gravity is less than that of the fracturing fluid, and can be dissolved by soaking in a salt solution, and the piston of the sliding sleeve in the fracturing tool used for fracturing can maintain its position after being pushed and moved by the fracturing fluid and unloading the pressure. The pressure-pumping integrated device is also used for coal seam gas extraction after being used for fracturing by the aforementioned method. The beneficial effect of the present invention is that the permeability-increasing method can realize multi-stage staged fracturing, and can be conveniently applied to the construction of upward holes in underground coal mines, and after the fracturing balls are dissolved by a salt solution, the fracturing pipe can be used to realize gas extraction; the pressure-pumping integrated device has both fracturing and extraction functions, which can effectively improve the extraction efficiency and reduce the extraction cost.

Description

Technical Field

[0001] The invention belongs to the field of coalbed methane development, and in particular relates to a branch drilling segmented fracturing and permeability enhancement method and a pressure-pumping integrated device in an underground coal mine. Background Art

[0002] Due to the complexity of the geological conditions of coal occurrence in Chongqing, the main coal-bearing strata experienced strong tectonic movements after deposition, and the coal structure was severely damaged. Most of the coal seams are soft coal seams with low hardness, high gas pressure and content, and poor permeability, making it difficult to extract coalbed methane (gas). After years of exploration, hydraulic fracturing is one of the key technical measures for gas extraction in low-permeability coal seams. The core technology of "water-controlled gas" and the working mode of "first compression and then extraction" have been formed, and certain results have been achieved. However, this method has the following limitations: (1) Conventional fracturing drilling mainly adopts bottom plate tunnel through-layer drilling or coal seam along-layer drilling for fracturing, which requires large tunnel and drilling construction work and high cost; (2) Each fracturing drill hole is usually only fractured once at the bottom of the hole. Therefore, the number of fracturing drill holes is large, the cost of sealing and fracturing is high, the impact range of single-hole fracturing is small, the gas extraction volume is small, the drilling utilization rate is low, the extraction efficiency is low, and the time to meet the standards is long, resulting in tight deployment of extraction, mining, and excavation. It is urgent to develop a method that can regionalize hydraulic fracturing to increase permeability and efficiently extract gas over a large area.

[0003] In recent years, with the development of unconventional oil and gas industry, horizontal well drilling technology and multi-stage fracturing technology have developed rapidly, such as the "Method for Long Borehole Segmented Fracturing and Permeability Enhancement and Gas Extraction in Coal Seams in Coal Mines" announced in Chinese patent document CN 108643877A. Horizontal well drilling technology has also been widely used in long borehole drilling in coal mines. However, in terms of segmented fracturing technology, due to the limitation of the narrow space in coal mines, it is impossible to accommodate huge ground fracturing equipment, and the power of underground fracturing pumps is limited, and the construction displacement is much smaller than that of ground fracturing pumps, which cannot meet the needs of overall fracturing and permeability enhancement of long boreholes. Therefore, it is urgent to study the technology that can be used for segmented fracturing and permeability enhancement of long boreholes and branch boreholes in coal mines. Achieve uniform permeability enhancement of regional coal seams, improve gas extraction effect, and reduce the risk of gas dynamic disasters.

[0004] Regarding staged fracturing devices, in the development of oil and gas fields, tools such as open hole packers, soluble fracturing balls, and fracturing sleeves with soluble fracturing ball seats have been used. However, there are certain problems with some of these tools when used for underground construction in coal mines. Therefore, improvements and optimizations are needed on this basis.

[0005] In addition, at present, the research on long borehole segmented fracturing technology in coal mines has been carried out in China, mainly focusing on directional long borehole casing along the coal seam, and realizing segmented isolation and multi-stage fracturing in the casing. However, the coal seams in the southern region are generally soft, and it is difficult to implement long boreholes in these coal seams. Only long branch boreholes on the roof or floor can be implemented (that is, a long borehole main hole is implemented on the roof or floor of the target coal seam, and then branches are opened from the main hole to enter the coal seam). It is difficult to insert casing into the branch long borehole, and the implementation of cement slurry to fix the hole in the branch borehole will close the branch hole that has been formed, and the coal seam section cannot be effectively fractured during fracturing. Therefore, it is necessary to study technical methods that can be used for open-hole branch long borehole segmented fracturing and efficient gas extraction. At the same time, due to the low power of mining fracturing pumps, most of the construction displacement is less than 1 cubic meter per hour. According to the experience of surface hydraulic fracturing in the oil and gas industry, the construction displacement is generally more than several cubic meters per minute. The construction displacement of underground coal mines is much smaller than that of surface fracturing, and the volume transformation of coal seams cannot be carried out well. Therefore, it is necessary to explore ways to increase the construction displacement of underground hydraulic fracturing in coal mines to maximize the construction displacement and fracturing effect.

[0006] For the soluble fracturing balls in the staged fracturing devices, aluminum-magnesium alloy materials are often used in oil and gas field development. The fracturing balls have a large density and can be used in underground drilling without any problems. However, most of the gas control holes in coal mines are upward holes, and the power of the fracturing pumps used in coal mines is much smaller than that of the fracturing pumps used in ground drilling. The construction displacement is less than 1 cubic meter / minute, making it difficult to deliver the usable fracturing balls made of aluminum-magnesium alloy materials into the predetermined position in the fracturing hole, and corresponding improvements are also needed. Summary of the invention

[0007] The first purpose of the present invention is to address the deficiencies of the prior art and provide a method for increasing the permeability of branch boreholes in coal mines by staged fracturing. This method uses a low-density resin material that can be dissolved in a salt solution to make a fracturing ball, whose density is lower than the density of the fracturing fluid and close to the density of clean water. The fracturing ball can be easily pumped into the fracturing sleeve position in the borehole by using a coal mine fracturing pump to achieve seating and isolation, and the fracturing sleeve is opened to achieve staged fracturing. After the fracturing construction is completed, the salt solution is used as a displacement fluid to dissolve the fracturing ball to achieve full-diameter extraction. The second purpose of the present invention is to provide a pressure-extraction integrated device that realizes the integrated operation of dissolving ball fracturing and gas extraction to reduce extraction costs.

[0008] To achieve the first purpose, the present invention adopts the following technical solution.

[0009] A method for increasing the permeability of branch boreholes in coal mines by staged fracturing, which adopts a soluble fracturing ball throwing staged fracturing method, and uses a salt solution to replace the fracturing fluid after fracturing; wherein the soluble fracturing ball is made of a low-density resin material, the specific gravity of which is less than that of the fracturing fluid, and can be dissolved by soaking in the salt solution, and the piston of the sliding sleeve in the fracturing tool used for fracturing can maintain the same position after being pushed and moved by the fracturing fluid and the pressure is relieved.

[0010] The present invention adopts the above-mentioned scheme. Since the ball-throwing staged fracturing method is adopted, the staged fracturing of multiple branch holes in a long borehole in a coal mine can be easily realized, so that each segment corresponds to a branch hole for staged fracturing; and the soluble fracturing ball is made of a low-density resin material, and its specific gravity is less than that of the fracturing fluid and close to that of clean water, so that the staged fracturing of upward boreholes in the coal mine can be realized; at the same time, since the piston of the sliding sleeve in the fracturing tool can maintain its position unchanged after being pushed and moved by the fracturing fluid and unloading the pressure, the crack and the space inside the fracturing tool tube are unobstructed, and the soluble ball can be dissolved after being fully soaked in the salt solution. Therefore, after fracturing, the salt solution is injected into the borehole by replacing the fracturing fluid with the salt solution, so that the soluble fracturing ball is dissolved in the salt solution, so as to realize full-bore extraction.

[0011] Preferably, the salt solution is injected as a displacement fluid of the fracturing fluid after all staged fracturing is completed. Compared with the staged injection of the replacement fluid, the replacement fluid can prevent the soluble fracturing balls that have a blocking effect from being dissolved during the fracturing process, thereby weakening the blocking effect and reducing the staged fracturing effect.

[0012] Further preferably, the method is carried out according to the following steps:

[0013] The first step is to determine the rock formation for the main long borehole arrangement. In the roof or floor of the coal seam, a rock formation with stable lithology and not easy to expand when exposed to water is selected as the drilling layer for the main long borehole of the branch.

[0014] In the second step, the long borehole main hole driller arranges a drilling site in the coal mine tunnel, uses a mining kilometer directional drill, drills according to the preset drilling trajectory, controls the main hole in the stable rock layer of the roof or floor, and branches from the main hole into the target coal seam. The main hole drilling length is greater than 100 meters and the hole diameter is not less than 120mm;

[0015] The third step is fracturing preparation. According to the needs of fracturing construction, on-site preparation work is carried out for hydraulic fracturing pumps, sand pump groups, high-pressure manifolds, segmented isolation and fracturing tools, fracturing fluids and fracturing sands.

[0016] The fourth step is to determine the connection scheme of the fracturing tool and the sealing tool. According to the branch length drilling data, the location and depth of the branch hole opening are found to ensure that each branch hole is included in a fracturing section, and each sliding sleeve is placed at the branch hole opening. The connection scheme of the fracturing tool and the sealing tool is determined;

[0017] The fifth step is to dredge the borehole and place the fracturing device. By clearing and washing the well, the sediment in the hole is removed, and the main part of the fracturing device formed by the fracturing tool and the sealing tool is placed into the borehole to the set position, and the fracturing pipe opening of the fracturing tool is exposed outside the borehole;

[0018] Step 6: Connect the fracturing tool to the fracturing pump, and connect the exposed pipe port of the fracturing tool to the fracturing pump through a high-pressure pipeline;

[0019] Step 7: Pressure test verification: start the fracturing pump test pipeline to verify the sealing condition, inject water to pressurize and start the packer, and verify the sealing condition; if qualified, proceed to the next step; if unqualified, after finding and eliminating the fault, execute this step repeatedly;

[0020] The eighth step is fracturing the bottom section of the hole. The fracturing pump is started to perform pressure injection, and the injection pressure is gradually increased to the set value of the fracturing pressure range. The fracturing fluid pushes the piston inside the bottom differential pressure sleeve to move, open the through hole on the differential pressure sleeve wall, and perform fracturing construction at the bottom section of the hole;

[0021] The ninth step is ball-throwing fracturing. After the fracturing construction of the previous fracturing section is completed, the pump is stopped to release the pressure. A soluble fracturing ball matching the fracturing sleeve adjacent to the previous fracturing section is thrown into the fracturing tube of the fracturing tool, and the fracturing pump is started. The soluble fracturing ball is delivered to the ball seat of the fracturing sleeve of the corresponding section by the fracturing fluid at a pressure value lower than the fracturing pressure, so as to achieve the isolation of the inside of the fracturing tube and the fracturing section.

[0022] The tenth step is to increase the pressure of the fracturing fluid by continuous water injection and pressure increase to the fracturing pressure range, and push the piston inside the fracturing sleeve to move through the soluble fracturing ball to open the through hole on the fracturing sleeve wall to carry out the fracturing construction of this section;

[0023] Step 11: Determine whether the fracturing construction is completed, and determine whether there is a fracturing section that has not been fractured in the fracturing section adjacent to the current section; if yes, return to step 9; if no, proceed to the next step;

[0024] Step 12: Add salt solution, inject a set proportion of salt solution to replace the fracturing fluid, and the salt solution is used to dissolve the fracturing balls;

[0025] The thirteenth step is to seal the hole and maintain the pressure. After injecting a set amount of salt solution, the hole is sealed and the pressure is maintained for a set time. After the fracturing ball dissolves, each fracturing section can be connected through the fracturing pipe to prepare for pressure relief and gas extraction.

[0026] When manufacturing differential pressure sleeves and fracturing sleeves, the through hole diameter on the sleeve wall should meet the extraction diameter requirements and be larger than the aperture of the sleeve used only for fracturing, so as to ensure smooth staged fracturing construction and realize extraction using the fracturing device.

[0027] Preferably, after the sealing tool is placed in the fifth step, a temporary sealing section is also performed at the hole mouth, and the length of the temporary sealing section is greater than 10 meters, so as to ensure that the sealing tool is firmly installed and safe to use.

[0028] Preferably, the fracturing pressure is set at 20 MPa to 37 MPa, so that the coal seam can be fully fractured and the permeability enhancement effect can be improved.

[0029] Preferably, the fracturing pump is composed of a single pump, or a double pump or multiple pumps connected in parallel to form a fracturing pump group. It can be selected according to different occasions and fracturing requirements to ensure flexible application. In the fracturing pump group scheme, only one of the fracturing pumps is started when delivering the soluble fracturing ball. This reduces energy consumption and ensures smooth and reliable delivery of the ball.

[0030] To achieve the second purpose, the present invention adopts the following technical solution.

[0031] A pressure-pumping integrated device for branch drilling in underground coal mines comprises a fracturing pipe, a plurality of fracturing sleeves are connected in series on the fracturing pipe, a differential pressure sleeve is connected in series on the pipe section of the fracturing pipe close to the bottom of the borehole, and a guide shoe is provided at the far end of the differential pressure sleeve through the pipe section at the bottom of the hole; from the bottom of the borehole to the hole mouth, the inner hole channel of the ball seat on the fracturing sleeve increases in sequence, and a soluble fracturing ball for fracturing in the adjacent fracturing section facing the bottom of the hole can be passed; the fracturing sleeve and the differential pressure sleeve are both provided with an open hole sealer in the direction of the borehole mouth, and the open hole sealer is fixedly connected to the fracturing pipe; the end of the fracturing pipe exposed from the borehole A pressure relief bypass is provided on the pressure relief bypass, a pressure relief valve is provided on the pressure relief bypass, and an outlet end of the pressure relief bypass has an interface for connecting to an air-water separator; the pressure relief bypass is detachably connected to the air-water separator through the interface; the fracturing sleeve and the pressure differential sleeve are both composed of a piston and a sleeve, and a one-way sliding fitting structure for only one-way movement of the piston is formed between the piston and the sleeve, and the one-way sliding fitting structure is formed by a spring sheet and a one-way tooth; a through hole penetrating the sleeve wall is provided on the sleeve wall, and the piston can move under the push of an external force to open the through hole, and the piston of the fracturing sleeve constitutes a ball seat with the inner hole channel.

[0032] The device adopting the above-mentioned scheme forms a structure suitable for segmented fracturing by ball-dropping fracturing by serially connecting multiple fracturing sleeves on the fracturing pipe and serially connecting a pressure differential sleeve on the pipe section of the fracturing pipe close to the bottom of the borehole. When the fracturing balls are soluble balls, after all the fracturing sections are completed, the fracturing fluid is replaced with a salt solution to dissolve the fracturing balls, so that the inside of the fracturing pipe is unobstructed. At the same time, since a gas-water separator is provided at the mouth of the fracturing pipe, the gas extraction system can be connected through the gas-water separator, thereby achieving the purpose of using the fracturing pipe as a gas extraction pipe, reducing the preparation work for gas extraction, and effectively improving the extraction efficiency and reducing the extraction cost. Among them, the fracturing sleeve refers to the fracturing sleeve structure in the "Fracturing Sleeve and Fracturing Method with Dissolvable Fracturing Ball Seat" announced in CN201410638145. The difference between the pressure differential sleeve and the fracturing sleeve is that the piston of the pressure differential sleeve does not form a ball seat structure, nor is an internal channel set. The piston slides under the high pressure of the fracturing fluid to open the through hole in the sleeve wall; but the difference from the prior art is also the common feature of the pressure differential sleeve and the fracturing sleeve in the present application, that is, a unidirectional sliding matching structure is formed between the piston and the sleeve for only unidirectional movement of the piston, so as to keep the open state after pressure relief, so as to facilitate the extraction of coal seam gas.

[0033] Preferably, the open hole sealer is a bag-type sealer, the interior of which is connected to the interior of the fracturing pipe via a first one-way valve, so that the sealing pressure of the sealer increases with the increase of the fracturing pressure, thereby achieving the purpose of reliable plugging.

[0034] Preferably, the end of the fracturing pipe exposed from the borehole is also provided with a ball throwing bypass having a ball throwing port, and the ball throwing bypass is provided with a valve capable of closing the ball throwing port, so as to facilitate the ball throwing and achieve reliable sealing after the ball throwing.

[0035] The beneficial effects of the present invention are that the permeability enhancement method can realize multi-stage segmented fracturing and can be conveniently applied to the upward hole construction in coal mines. After the fracturing balls are dissolved by salt solution, the fracturing pipe can be used to realize gas extraction. The integrated fracturing and extraction device has both fracturing and extraction functions, which can effectively improve the extraction efficiency and reduce the extraction cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the structure of the integrated pressure-pumping device of the present invention. This figure is also used to illustrate the staged fracturing method.

[0037] Figure 2 It is a schematic diagram of the structure of the sliding sleeve part in the device of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings, but the present invention is not limited to the scope of the described embodiments.

[0039] Example 1, see Figure 1 A method for increasing the permeability of branch boreholes in coal mines by staged fracturing, which adopts a soluble fracturing ball throwing staged fracturing method, and replaces the fracturing fluid with a salt solution after fracturing; wherein the soluble fracturing ball is made of a low-density resin material, whose specific gravity is less than that of the fracturing fluid, and can be dissolved by soaking in a salt solution.

[0040] The salt solution is injected as a displacement fluid of the fracturing fluid after all staged fracturing is completed. The method is specifically carried out in the following steps:

[0041] The first step is to determine the rock formation for the main long borehole arrangement. In the roof or floor of the coal seam, a rock formation with stable lithology and not easy to expand when exposed to water is selected as the drilling layer for the main long borehole of the branch.

[0042] In the second step, the long borehole main hole driller arranges a drilling site in the coal mine tunnel, uses a mining kilometer directional drill, drills according to the preset drilling trajectory, controls the main hole in the stable rock layer of the roof or floor, and branches from the main hole into the target coal seam. The main hole drilling length is greater than 100 meters and the hole diameter is not less than 120mm;

[0043] The third step is fracturing preparation. According to the needs of fracturing construction, on-site preparation work is carried out for hydraulic fracturing pumps, sand pump groups, high-pressure manifolds, segmented isolation and fracturing tools, fracturing fluids and fracturing sands.

[0044] The fourth step is to determine the connection scheme of the fracturing tool and the sealing tool. According to the branch length drilling data, the location and depth of the branch hole opening are found to ensure that each branch hole is included in a fracturing section, and each sliding sleeve is placed at the branch hole opening. The connection scheme of the fracturing tool and the sealing tool is determined;

[0045] The fifth step is to dredge the borehole and place the fracturing device. The sediment in the hole is removed by clearing and washing the well, and the main part of the fracturing device formed by the fracturing tool and the sealing tool is placed into the borehole to the set position;

[0046] Step 6: Connect the fracturing tool to the fracturing pump, and connect the exposed pipe port of the fracturing tool to the fracturing pump through a high-pressure pipeline;

[0047] Step 7: Pressure test verification: start the fracturing pump test pipeline to verify the sealing condition, inject water to pressurize and start the packer, and verify the sealing condition; if qualified, proceed to the next step; if unqualified, after finding and eliminating the fault, execute this step repeatedly;

[0048] The eighth step is fracturing the bottom section of the hole. The fracturing pump is started to perform pressure injection, and the injection pressure is gradually increased to the set value of the fracturing pressure range. The fracturing fluid pushes the piston inside the bottom differential pressure sleeve to move, open the through hole on the differential pressure sleeve wall, and perform fracturing construction at the bottom section of the hole;

[0049] The ninth step is ball-throwing fracturing. After the fracturing construction of the previous fracturing section is completed, the pump is stopped to release the pressure. A soluble fracturing ball matching the fracturing sleeve adjacent to the previous fracturing section is thrown into the fracturing tube of the fracturing tool, and the fracturing pump is started. The soluble fracturing ball is delivered to the ball seat of the fracturing sleeve of the corresponding section by the fracturing fluid at a pressure value lower than the fracturing pressure, so as to achieve the isolation of the inside of the fracturing tube and the fracturing section.

[0050] The tenth step is to increase the pressure of the fracturing fluid by continuous water injection and pressure increase to the fracturing pressure range, and push the piston inside the fracturing sleeve to move through the soluble fracturing ball to open the through hole on the fracturing sleeve wall to carry out the fracturing construction of this section;

[0051] Step 11: Determine whether the fracturing construction is completed, and determine whether there is a fracturing section that has not been fractured in the fracturing section adjacent to the current section; if yes, return to step 9; if no, proceed to the next step;

[0052] Step 12: Add salt solution, inject a set proportion of salt solution to replace the fracturing fluid, and the salt solution is used to dissolve the fracturing balls;

[0053] The thirteenth step is to seal the hole and maintain the pressure. After injecting a set amount of salt solution, the hole is sealed and the pressure is maintained for a set time. After the fracturing ball dissolves, each fracturing section can be connected through the fracturing pipe to prepare for pressure relief and gas extraction.

[0054] Among them, when making the differential pressure sleeve and the fracturing sleeve, the diameter of the through hole on the sleeve wall should meet the extraction diameter requirements, and be larger than the sleeve aperture used only for fracturing. After the sealing tool is placed in the fifth step, it also includes a temporary sealing section at the orifice. The length of the temporary sealing section 11 is greater than 10 meters, and the temporary sealing section should meet the sealing requirements of no leakage during extraction. The fracturing pressure setting value is 20MPa~37Mpa; the fracturing pump is composed of a single pump, or a fracturing pump group is formed by two or more pumps in parallel. In the fracturing pump group scheme, only one of the fracturing pumps is started when the soluble fracturing ball is delivered.

[0055] Example 2, see Figure 1 , Figure 2A pressure-pumping integrated device for branch drilling in underground coal mines, comprising a fracturing pipe 1, a plurality of fracturing sleeves 2 are connected in series on the fracturing pipe 1, a differential pressure sleeve 3 is connected in series on the pipe section of the fracturing pipe 1 close to the bottom of the borehole, and a guide shoe 5 is provided at the distal end of the differential pressure sleeve 3 through the pipe section at the bottom of the hole; from the bottom of the borehole to the orifice, the inner hole channel of the ball seat on the fracturing sleeve 2 is enlarged in sequence, and a soluble fracturing ball for fracturing in the adjacent fracturing section facing the bottom of the hole can be passed, so that in the process of staged fracturing from the bottom of the hole to the orifice, the soluble fracturing ball of each fracturing section can be smoothly delivered to the position; the fracturing sleeve 2 and the differential pressure sleeve 3 are both provided with an open hole sealer 4 in the direction of the borehole orifice, and the open hole sealer 4 is fixedly connected to the fracturing pipe 1; the end of the fracturing pipe 1 exposed from the borehole is provided with a pressure relief bypass 10, and the pressure relief bypass 10 is provided to relieve the pressure. A pressure relief valve 6 is provided on the pressure bypass 10, and the outlet end of the pressure relief bypass 10 has an interface for connecting to the gas-water separator 7; the pressure relief bypass 10 is detachably connected to the gas-water separator 7 through the interface, and the gas-water separator 7 is provided with an air outlet 7a and a liquid outlet 7b; the fracturing sleeve 2 and the pressure differential sleeve 3 are both composed of a piston and a sleeve, and a one-way sliding fitting structure for only one-way movement of the piston is formed between the piston and the sleeve, and the one-way sliding fitting structure is formed by the cooperation of a spring sheet 17 and a one-way tooth; the spring sheet 17 is fixed on the sleeve 18, and the one-way tooth is provided on the piston 19, and a through hole 20 penetrating the sleeve wall is provided on the sleeve wall, and the piston can move under the push of an external force to open the through hole, and the piston of the fracturing sleeve 2 constitutes a ball seat with the inner hole channel, and the ball seat is used to seat the soluble fracturing ball 16. Among them, when manufacturing the differential pressure sleeve and the fracturing sleeve, the diameter of the through hole on the sleeve wall should meet the extraction diameter requirements and be larger than the aperture of the sleeve used only for fracturing.

[0056] Among them, the open hole sealer 4 is a bag-type sealer, the interior of which is connected to the interior of the fracturing pipe 1 through a first one-way valve 8. The end of the fracturing pipe 1 exposed from the borehole is also provided with a ball-dropping bypass 9 with a ball-dropping port and a pressure gauge 15, and the ball-dropping bypass is provided with a valve 12 capable of closing the ball-dropping port; the pipe mouth of the fracturing pipe 1 is provided with a second one-way valve 13, which is used for fracturing pressure maintenance; the pipe mouth of the fracturing pipe 1 is provided with a pipeline interface 14, and the fracturing pipe 1 is connected to the fracturing pump or fracturing pump group by a high-pressure pipeline through the pipeline interface 14.

[0057] In this embodiment, three fracturing sleeves 2 are provided, and one differential pressure sleeve 3 is provided near the bottom of the long borehole. From the hole mouth to the hole bottom, the inner hole channels of the pistons on the three fracturing sleeves 2 gradually increase. The soluble fracturing balls seated on the fracturing sleeve 2 near the differential pressure sleeve 3 can pass through the inner hole channels of the other two fracturing sleeves 2 in the direction of the hole mouth; the soluble fracturing balls seated on the fracturing sleeve 2 in the middle position can pass through the inner hole channel of the fracturing sleeve 2 near the hole mouth.

[0058] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A pressure-extraction integrated device for branch drilling in coal mines, characterized in that: The invention comprises a fracturing pipe (1), wherein a plurality of fracturing sleeves (2) are connected in series to the fracturing pipe (1), a differential pressure sleeve (3) is connected in series to a pipe section of the fracturing pipe (1) close to the bottom of a borehole, and a guide shoe (5) is provided at the far end of the differential pressure sleeve (3) through the pipe section at the bottom of the borehole; from the bottom of the borehole to the borehole mouth, the inner hole channel of the ball seat on the fracturing sleeve (2) increases in size in sequence, and a soluble fracturing ball for fracturing in the adjacent fracturing section in the direction of the bottom of the borehole can be passed; the fracturing sleeve (2) and the differential pressure sleeve (3) are both provided with an open hole sealer (4) in the direction of the borehole mouth, and the open hole sealer (4) is fixedly connected to the fracturing pipe (1); the end of the fracturing pipe (1) exposed from the borehole is provided with a pressure relief device; Bypass (10), a pressure relief valve (6) is provided on the pressure relief bypass (10), and the outlet end of the pressure relief bypass (10) has an interface for connecting to a gas-water separator (7); the pressure relief bypass (10) is detachably connected to the gas-water separator (7) via the interface; the fracturing sleeve (2) and the differential pressure sleeve (3) are both composed of a piston and a sleeve, and a one-way sliding matching structure for only one-way movement of the piston is formed between the piston and the sleeve, and the one-way sliding matching structure is formed by the cooperation of a spring sheet and a one-way tooth; a through hole penetrating the sleeve wall is provided on the sleeve wall, and the piston can move under the push of an external force to open the through hole, and the piston of the fracturing sleeve (2) constitutes a ball seat having the inner hole channel; The open hole sealer (4) is a bag-type sealer, the interior of which is connected to the interior of the fracturing pipe (1) via a first one-way valve (8); The end of the fracturing pipe (1) exposed from the borehole is also provided with a ball-dropping bypass having a ball-dropping opening, and the ball-dropping bypass is provided with a valve capable of closing the ball-dropping opening.

2. A method for increasing permeability of branch holes in underground coal mines by staged fracturing using the integrated pressure-pumping device of claim 1, characterized in that: The method adopts a staged fracturing method of throwing soluble fracturing balls, and uses a salt solution to replace the fracturing fluid after fracturing; wherein the soluble fracturing balls are made of low-density resin material, whose specific gravity is less than that of the fracturing fluid, and can be dissolved by soaking in the salt solution, and the piston of the sliding sleeve in the fracturing tool used for fracturing can maintain its position unchanged after being pushed and moved by the fracturing fluid and the pressure is relieved.

3. The method according to claim 2, characterized in that The salt solution is injected as a displacement fluid of the fracturing fluid after all staged fracturing is completed.

4. The method according to claim 2 or 3, characterized in that: Follow these steps: The first step is to determine the rock formation for the main long borehole arrangement. In the roof or floor of the coal seam, a rock formation with stable lithology and not easy to expand when exposed to water is selected as the drilling layer for the main long borehole of the branch. In the second step, the long borehole main hole driller arranges a drilling site in the coal mine tunnel, uses a mining kilometer directional drill, drills according to the preset drilling trajectory, controls the main hole in the stable rock layer of the roof or floor, and branches from the main hole into the target coal seam. The main hole drilling length is greater than 100 meters and the hole diameter is not less than 120mm; The third step is fracturing preparation. According to the needs of fracturing construction, on-site preparation work is carried out for hydraulic fracturing pumps, sand pump groups, high-pressure manifolds, segmented isolation and fracturing tools, fracturing fluids and fracturing sands. The fourth step is to determine the connection scheme of the fracturing tool and the sealing tool. According to the branch length drilling data, the location and depth of the branch hole opening are found to ensure that each branch hole is included in a fracturing section, and each sliding sleeve is placed at the branch hole opening. The connection scheme of the fracturing tool and the sealing tool is determined; The fifth step is to dredge the borehole and place the fracturing device. By clearing and washing the well, the sediment in the hole is removed, and the main part of the fracturing device formed by the fracturing tool and the sealing tool is placed into the borehole to the set position, and the fracturing pipe opening of the fracturing tool is exposed outside the borehole; Step 6: Connect the fracturing tool to the fracturing pump, and connect the exposed pipe port of the fracturing tool to the fracturing pump through a high-pressure pipeline; Step 7: Pressure test verification: start the fracturing pump test pipeline to verify the sealing condition, inject water to pressurize and start the packer, and verify the sealing condition; if qualified, proceed to the next step; if unqualified, after finding and eliminating the fault, execute this step repeatedly; The eighth step is fracturing the bottom section of the hole. The fracturing pump is started to perform pressure injection, and the injection pressure is gradually increased to the set value of the fracturing pressure range. The fracturing fluid pushes the piston inside the bottom differential pressure sleeve to move, open the through hole on the differential pressure sleeve wall, and perform fracturing construction at the bottom section of the hole; The ninth step is ball-throwing fracturing. After the fracturing construction of the previous fracturing section is completed, the pump is stopped to release the pressure. A soluble fracturing ball matching the fracturing sleeve adjacent to the previous fracturing section is thrown into the fracturing tube of the fracturing tool, and the fracturing pump is started. The soluble fracturing ball is delivered to the ball seat of the fracturing sleeve of the corresponding section by the fracturing fluid at a pressure value lower than the fracturing pressure, so as to achieve the isolation of the inside of the fracturing tube and the fracturing section. The tenth step is to increase the pressure of the fracturing fluid by continuous water injection and pressure increase to the fracturing pressure range, and push the piston inside the fracturing sleeve to move through the soluble fracturing ball to open the through hole on the fracturing sleeve wall to carry out the fracturing construction of this section; Step 11: Determine whether the fracturing construction is completed, and determine whether there is a fracturing section that has not been fractured in the fracturing section adjacent to the current section; if yes, return to step 9; if no, proceed to the next step; Step 12: Add salt solution, inject a set proportion of salt solution to replace the fracturing fluid, and the salt solution is used to dissolve the fracturing balls; The thirteenth step is to seal the hole and maintain the pressure. After injecting a set amount of salt solution, the hole is sealed and the pressure is maintained for a set time. After the fracturing ball dissolves, each fracturing section can be connected through the fracturing pipe to prepare for pressure relief and gas extraction.

5. The method according to claim 4, characterized in that After the sealing tool is placed in the fifth step, a temporary sealing section is also included at the hole mouth, and the length of the temporary sealing section is greater than 10 meters.

6. The method according to claim 4, characterized in that The fracturing pressure setting value is 20 MPa~37Mpa.

7. The method according to claim 4, characterized in that The fracturing pump is composed of a single pump, or multiple pumps are connected in parallel to form a fracturing pump group.

8. The method according to claim 7, characterized in that In the fracturing pump group scheme, only one of the fracturing pumps is started when the soluble fracturing balls are delivered.

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