Hard coal seam fracturing tool and method

Abstract

The invention relates to the technical field of mining and discloses a hard coal seam cracking tool and method.The hard coal seam cracking tool comprises a cracking assembly, the cracking assembly comprises a first barrel, a second barrel, an overload component and a plugging component, a through hole is formed in the side wall of the first barrel, the second barrel is arranged in the first barrel, and the overload component is arranged in the second barrel; the second barrel can move along the first barrel and has an initial position and a working position, the second barrel blocks the through hole when located at the initial position, the second barrel opens the through hole when located at the working position, and the overload component is arranged between the first barrel and the second barrel and has overload force for preventing the second barrel from being separated from the initial position. The plugging part is used for plugging one end of the second barrel, and when the first barrel is filled with a medium, the medium can push the second barrel to overcome the overload force so as to open the through hole and enable the medium to flow out of the through hole; according to the gas-liquid mixed fracturing device, gas-liquid mixed fracturing with large displacement, large liquid amount and timely temporary plugging can be achieved, sectional fracturing can be achieved, and the fracturing effect is remarkable.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of mining, and particularly relates to a hard coal seam fracturing tool and method. BACKGROUND

[0002] In the related art, the fracturing of hard coal seams is generally carried out by using carbon dioxide blasting technology, electric pulse technology, microwave radiation technology, etc. Such technologies are often carried out in a borehole in a coal mine, and the fracturing range is limited to the surrounding of the borehole, and it is difficult to generate a large area of weakened regions in the hard coal seam to improve the coal cutting efficiency.

[0003] In addition, in the related art, an underground long borehole hydraulic fracturing technology is used. This technology can form a crack with a certain length and height in the hard coal seam, but is limited by the underground operation space, and the fracturing discharge and liquid volume are small, and the crack propagation direction is controlled by the ground stress, and it is difficult to form a large area of complex crack network and weakened regions.

[0004] In summary, the weakening of the hard coal seam currently has the problems of limited underground operation, and the fracturing effect of the related technology is not good. SUMMARY

[0005] The present application aims to at least partially solve one of the technical problems in the related art. To this end, the embodiments of the present application propose a hard coal seam fracturing tool, which can realize gas-liquid mixed impact fracturing, can achieve high-speed gas flow impact fracturing by pressure accumulation, can improve the gas injection and liquid injection discharge by ground operation, and has obvious fracturing effect.

[0006] The embodiments of the present application also propose a fracturing method, which can realize large discharge, large liquid volume, timely temporary plugging, and mixed fracturing mode of gas-liquid in sequence by ground operation, and can segment fracturing, and has significant fracturing effect.

[0007] The hard coal seam fracturing tool of the embodiments of the present application comprises a fracturing assembly, the fracturing assembly comprises a first cylinder, a second cylinder, an overload component, and a plugging component, a through hole is arranged on the side wall of the first cylinder; the second cylinder is arranged in the interior of the first cylinder, the second cylinder is movable along the first cylinder and has an initial position and a working position, the second cylinder blocks the through hole when being in the initial position, and the second cylinder opens the through hole when being in the working position; the overload component is arranged between the first cylinder and the second cylinder and has an overload force for blocking the second cylinder from moving away from the initial position; the plugging component is used for plugging one end of the second cylinder; When the first cylinder is filled with a medium, and when the plugging component plugs the second cylinder, the medium can push the second cylinder to overcome the overload force and move from the initial position to the working position to open the through hole and make the medium flow out of the through hole.

[0008] The hard coal seam fracturing tool of the embodiment blocks the through hole by the second cylinder to achieve the effect of pressure accumulation, and when the overload force is overcome, the high-pressure medium can quickly flow out through the through hole to achieve strong impact on the hard coal seam. In addition, the hard coal seam fracturing tool can be filled with carbon dioxide or water for mixed fracturing, further improving the fracturing effect, and the embodiment is constructed on the ground, facilitating operation and enabling large displacement and large liquid volume of the medium injection, further improving the fracturing effect.

[0009] In some embodiments, a limiting protrusion is arranged on the inner wall surface of the first cylinder, and the second cylinder is in abutment with and limited by the limiting protrusion when the second cylinder moves to the working position.

[0010] In some embodiments, the overload component includes a pin for connecting the first cylinder and the second cylinder, and the shear resistance of the pin forms the overload force, and the second cylinder cuts off the pin after overcoming the overload force. And / or, the plugging component is a spherical body. And / or, a sealing ring is arranged on the contact surface of the second cylinder connected with the plugging component.

[0011] In some embodiments, the through hole is a plurality of through holes, and at least part of the plurality of through holes have different orientations. And / or, the plurality of through holes are uniformly distributed along the circumference of the first cylinder. And / or, the cross-sectional area of the through hole in the direction in which the inner wall surface of the first cylinder extends along the outer wall surface of the first cylinder gradually decreases, so as to increase the flow rate of the medium flowing from the inside of the first cylinder to the outside of the first cylinder.

[0012] In some embodiments, the fracturing assembly is a plurality of fracturing assemblies, the plurality of fracturing assemblies are arranged at intervals and are in communication with each other, and the second cylinder of the plurality of fracturing assemblies can be sequentially plugged by the plugging component. The inner diameters of the second cylinders of the plurality of fracturing assemblies are arranged in an arithmetic progression, and the diameters of the plugging components of the plurality of fracturing assemblies are arranged in an arithmetic progression, so that plugging components of different diameters can sequentially plug second cylinders of different inner diameters.

[0013] In some embodiments, the hard coal seam fracturing tool further includes a first oil pipe, an intermediate oil pipe, a safety joint, a depth calibration sub, and a guide head; one end of the first oil pipe is placed on the ground, the other end of the first oil pipe is connected with the safety joint, the safety joint, the depth calibration sub, the plurality of fracturing assemblies, and the guide head are sequentially connected through the intermediate oil pipe. In some embodiments, the safety joint is used to be detached from the safety joint when the operation is abnormal, so that the first tubing is out of the well, the depth-checking sub is used to measure the position where it is located by using a measuring tool, and the steering head is used to facilitate the orientation of the fracturing assembly when it is lowered into the well.

[0014] In some embodiments, the hard coal seam fracturing tool further comprises a directional device and a packer, at least part of the first cylinder is connected with the intermediate tubing or the first tubing through the directional device, the directional device is used to rotate the first cylinder connected therewith to adjust the orientation of the through hole on the first cylinder; the packer is arranged on the intermediate tubing, and the packer is located between two adjacent fracturing assemblies or between the fracturing assembly and the steering head; the packer is used to seal the annular space between the outer wall surface of the intermediate tubing and the well wall.

[0015] Through the fracturing tool of the above-mentioned embodiments, the segmented fracturing of multiple fracturing assemblies can be realized, and the fracturing assembly can be accurately placed into the target position by cooperating with the safety joint, the directional device, the packer and other accessories. The directional device can accurately align the through hole with the coal seam, and the packer can isolate the space during segmented fracturing, thereby improving the fracturing effect.

[0016] The fracturing method of the embodiments of the present application is realized by using the hard coal seam fracturing tool of any one of the above-mentioned embodiments, and comprises the following steps: S1: at least one fracturing assembly is placed into the horizontal section of the L-shaped well by using the first tubing and the intermediate tubing, so that the fracturing assembly is located at the target fracturing position; S2: the blocking component is placed in the first tubing by using one end of the first tubing placed on the ground, the blocking component can be moved into the fracturing assembly corresponding to the diameter thereof and block the second cylinder in the fracturing assembly; S3: the packer adjacent to the fracturing assembly in S2 and towards the steering head is used to seal the annular space between the outer wall surface of the intermediate tubing and the well wall; S4: carbon dioxide is injected into the first tubing by using one end of the first tubing placed on the ground, and pressure maintenance observation is performed, then carbon dioxide is continuously injected to make the second cylinder of the fracturing assembly in S2 overcome the overload force and move to the working position, and the through hole in the fracturing assembly in S2 is opened, then carbon dioxide flows out along the through hole of the fracturing assembly in S2 and impacts the coal seam to make the coal seam fracture, and the injection is stopped after a preset time or working condition is reached; S5: injecting water into the first oil pipe at one end of the first oil pipe placed on the ground and into the annular space between the first oil pipe and the well wall of the L-shaped well, so that a large amount of water enters the coal seam along the existing cracks to make the coal seam cracks continue to expand, and then mixing temporary plugging particles in the water to make the temporary plugging particles block part of the coal seam cracks and divert the water to crack the coal seam in other areas to expand the range of coal seam cracking, and stopping the injection after a preset time or working condition; S6: using the first oil pipe and the intermediate oil pipe to pull out the cracking assembly from the well; S7: after the well is sealed for 30-60 days, gas extraction is carried out, and after the gas extraction reaches the standard, underground coal cutting operation is carried out.

[0017] The cracking method of the embodiment can first use carbon dioxide for impact cracking, and then use water with large displacement and large liquid volume for hydraulic fracturing, thereby improving the cracking effect.

[0018] In some embodiments, when the cracking assembly in S1 is multiple, S2-S5 are repeated, and in S2, only one of the plugging components is put in each time and is used from small to large in diameter, so that multiple cracking assemblies are used for segmented fracturing operation in turn.

[0019] In S4 and S5, the ground microseismic monitoring system is used to adjust the pressure, displacement and liquid volume of the injected carbon dioxide and water in real time. In S1, according to the position of the coal seam where the horizontal section of the L-shaped well is located, the directional device with a suitable orientation is selected and connected with the cracking assembly, so that after the cracking assembly is lowered into the horizontal section of the L-shaped well, the through hole can face the direction where the coal seam is located.

[0020] The cracking method of the above embodiment realizes segmented cracking, and can be used for fracturing from the toe end to the heel end of the horizontal section of the L-shaped well in turn. The carbon dioxide used for fracturing can also desorb the methane gas in the coal seam, thereby facilitating gas extraction. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is the overall schematic diagram of the present application.

[0022] Figure 2 is the front view of the cracking assembly in the initial position in the present application.

[0023] Figure 3 is the front view of the cracking assembly in the working position in the present application.

[0024] Reference signs: 1, cracking assembly; 11, first cylinder; 12, second cylinder; 111, through hole; 13, overload component; 14, plugging component; 15, limiting protrusion; 2, first oil pipe; 3. intermediate tubing; 4. safety joint; 5. depth-checking sub; 6. pilot head; 7. orienting device; 8. packer; 9. L-type well; 91. surface casing; 92. cement; 93. technical casing; 94. oil-casing annulus; 95. horizontal section. DETAILED DESCRIPTION

[0025] Embodiments of the present application are described in detail below with reference to the attached drawings. The embodiments described below are examples of the present application and are not intended to limit the present application.

[0026] As shown in the drawings, the hard coal seam fracturing tool of the present embodiment includes a fracturing assembly 1, which includes a first cylinder 11, a second cylinder 12, an overload component 13, and a blocking component 14. Figures 1-3 The first cylinder 11 has a through hole 111 in its side wall. The second cylinder 12 is disposed inside the first cylinder 11 and is movable along the first cylinder 11 and has an initial position and a working position. When the second cylinder 12 is in the initial position, it blocks the through hole 111, and when the second cylinder 12 is in the working position, it opens the through hole 111. The overload component 13 is disposed between the first cylinder 11 and the second cylinder 12 and has an overload force that blocks the second cylinder 12 from moving away from the initial position. The blocking component 14 is used to block one end of the second cylinder 12. When the first cylinder 11 is filled with a medium, and when the blocking component 14 blocks the second cylinder 12, the medium can push the second cylinder 12 to move from the initial position toward the working position to overcome the overload force and open the through hole 111, so that the medium flows out of the through hole 111.

[0027] The hard coal seam fracturing tool of the present embodiment achieves the blocking of the through hole 111 in the first cylinder 11 by the second cylinder 12 and the overload component 13, so that when the first cylinder 11 is filled with a medium, the medium cannot be discharged temporarily and the pressure is built up. After the pressure rises, the high-pressure medium pushes the second cylinder 12 to move and overcome the overload force to move away from the initial position, so that the high-pressure medium flows out of the through hole 111 quickly, impacting the hard coal seam and achieving fracturing of the coal seam. Subsequently, different media can be continuously filled into the first cylinder 11 to achieve continuous fracturing of the hard coal seam.

[0028]

[0029] ​In the embodiment, the blocking component 14 and the second cylinder 12 are designed separately, that is, when the blocking component 14 is not installed, the second cylinder 12 can be used as a part of the pipeline for normal medium flow. Only when cracking is needed, the blocking component 14 is put in to achieve pressure build-up cracking and open the through hole 111. Meanwhile, when there are multiple cracking assemblies 1, they can be used in series, and the cracking assembly 1 in front can be put in without the blocking component 14 so that the medium can pass through.

[0030] In some specific embodiments, the medium can be carbon dioxide, liquid carbon dioxide, nitrogen, water and the like to meet the impact demand of hard coal seam. The medium can have a certain pressure to facilitate the increase of the filling speed and the final impact pressure.

[0031] In some specific embodiments, the outer diameter of the first cylinder 11 is smaller than the inner diameter of the L-shaped well 9, so that the entire cracking assembly 1 can be put into the L-shaped well 9. In addition, the first cylinder 11, the second cylinder 12, the overload component 13 and the blocking component 14 are made of high-strength alloy steel to meet the pressure-bearing and corrosion-resistant requirements.

[0032] In some specific embodiments, the initial position of the second cylinder 12 is limited by the overload component 13, and the working position of the second cylinder 12 is achieved by limiting components such as limiting blocks, protrusions, retaining rings, screws and the like to limit the second cylinder 12 and prevent the second cylinder 12 from falling into the well from the working position.

[0033] In some embodiments, the inner wall surface of the first cylinder 11 is provided with a limiting protrusion 15, and the second cylinder 12 is stopped by the limiting protrusion 15 and is limited by the limiting protrusion 15 when moving to the working position. So that the second cylinder 12 is subjected to high pressure impact of the medium and moves to the working position from the initial position.

[0034] In some specific embodiments, a sealing ring is provided on the outer edge surface of the second cylinder 12 to improve the sealing between the second cylinder 12 and the first cylinder 11 when the second cylinder 12 is in the initial position and in the working position.

[0035] In some embodiments, the overload component 13 includes a pin for connecting the first cylinder 11 and the second cylinder 12, the shear resistance of the pin forms an overload force, and the second cylinder 12 cuts off the pin after overcoming the overload force. The blocking component 14 is a spherical body. The contact surface of the second cylinder 12 connected with the blocking component 14 is a conical surface and is provided with a sealing ring to ensure the close fit between the blocking component 14 and the second cylinder 12.

[0036] The pin simultaneously connects the first cylinder 11 and the second cylinder 12, so that the second cylinder 12 is fixed in the initial position. When the second cylinder 12 moves, a shearing force is applied to the pin at the connection between the first cylinder 11 and the second cylinder 12. The shearing resistance of the pin is the overload force. When the pin is broken, the second cylinder 12 can move to the working position. In addition, the blocking component 14 is a spherical body, which can conveniently and accurately block the end of the second cylinder 12, and also facilitates the subsequent rolling of the blocking component 14 when it is lowered along the pipeline. The sealing ring arranged at the end of the second cylinder 12 in contact with the blocking component 14 can ensure good sealing between the blocking component 14 and the second cylinder 12, thereby improving the pressure holding effect and preventing gas leakage.

[0037] In some specific embodiments, the second cylinder 12 is a straight cylinder, and the diameter remains constant along its axial direction. The fracturing assembly 1 is placed in the horizontal section 95 of the L-shaped well 9, and the second cylinder 12 is connected to the blocking component 14 at the end facing the heel end of the horizontal section. In this way, the blocking component 14 seals with the second cylinder 12 and pushes the second cylinder 12 to move.

[0038] In some specific embodiments, the second cylinder 12 can also be a conical cylinder, wherein the diameter of the end facing the heel end of the horizontal section is large, and the diameter of the end facing the toe end of the horizontal section is small and smaller than the diameter of the blocking component 14, so that the blocking component 14 can be placed inside the second cylinder 12 to achieve blocking.

[0039] In some embodiments, the through hole 111 is a plurality of through holes, and at least part of the plurality of through holes 111 have different orientations. Specifically, the plurality of through holes 111 can be arranged in any direction along the circumference of the first cylinder 11. In practice, it can be selected as needed to face a specific direction or to be uniformly distributed along the circumference of the first cylinder 11, etc. so that the through hole 111 can face the position of the coal seam during fracturing, so that the medium can impact the coal seam.

[0040] In some specific embodiments, the number of through holes 111 is preferably 6-8, and the arrangement mode is designed differently according to the relative position of the horizontal wellbore and the hard coal seam.

[0041] Case one: If the horizontal section 95 is located in the middle of the hard coal seam, the through holes 111 can be uniformly distributed, for example, the through holes 111 are designed as two groups, each group contains 3 through holes 111 arranged along the circumference of the first cylinder 11, and the spacing between the through holes 111 of the two groups along the axial direction of the first cylinder 11 is 0.3-0.6m. so that the impact medium can be emitted in all directions.

[0042] Case two: if the horizontal section 95 is located on the upper part of the hard coal seam, the through hole 111 needs to be arranged downward, the through hole 111 is designed as multiple groups along the axial direction of the first cylinder 11, each group contains two through holes 111, both of which are vertically downward or both of which are inclined downward. The interval between the adjacent two groups of through holes 111 along the axial direction of the first cylinder 11 is 0.2-0.4m, which can ensure that the through hole 111 is directed to the lower hard coal seam by using the orientation device 7 during installation and use.

[0043] Case three: if the horizontal section 95 is located on the lower part of the hard coal seam, the through hole 111 needs to be arranged upward, the through hole 111 is designed as multiple groups along the axial direction of the first cylinder 11, each group contains two through holes 111, both of which are vertically upward or both of which are inclined upward. The interval between the adjacent two groups of through holes 111 along the axial direction of the first cylinder 11 is 0.2-0.4m, which can ensure that the through hole 111 is directed to the upper hard coal seam by using the orientation device 7 during installation and use.

[0044] In some embodiments, the cross-sectional area of the through hole 111 in the direction in which the inner wall surface of the first cylinder 11 extends along the outer wall surface of the first cylinder 11 gradually decreases, so as to increase the flow rate when the medium passes through the through hole 111, thereby increasing the impact force on the coal seam.

[0045] In some embodiments, the fracturing assembly 1 is multiple, the multiple fracturing assemblies 1 are arranged at intervals and are connected to each other between the first cylinders 11, and the second cylinders 12 in the multiple fracturing assemblies 1 can be sequentially blocked by the blocking components 14. The inner diameters of the second cylinders 12 in the multiple fracturing assemblies 1 are arranged in an arithmetic progression, and the diameters of the blocking components 14 in the multiple fracturing assemblies 1 are arranged in an arithmetic progression, so that blocking components 14 of different diameters can sequentially block second cylinders 12 of different inner diameters.

[0046] Specifically, the difference between the inner diameters of the multiple second cylinders 12 is 2mm, and the difference between the inner diameters of the corresponding blocking components 14 is also 2mm. In the adjacent two fracturing assemblies 1 arranged in an arithmetic progression, the smaller diameter blocking component 14 can pass through the larger diameter second cylinder 12. In order to sequentially drop the blocking components 14 from small to large on the ground, so that the multiple fracturing assemblies 1 can be sequentially blocked according to the diameters of the second cylinders 12 from small to large.

[0047] In some specific embodiments, the horizontal section 95 includes a heel end and a toe end, and the multiple fracturing assemblies 1 are arranged at intervals along the length of the horizontal section 95, the interval is 15-30m, and the multiple fracturing assemblies 1 are sequentially arranged from small to large according to the diameters of the second cylinders 12 from the toe end to the heel end. In order to achieve the effect of sequentially fracturing from the toe end to the heel end.

[0048] In some embodiments, the coal seam fracturing tool further comprises a first oil pipe 2, an intermediate oil pipe 3, a safety joint 4, a depth correction short section 5 and a guide head 6.

[0049] Wherein, one end of the first tubing 2 is placed on the ground, the other end of the first tubing 2 is connected with the safety joint 4, the safety joint 4, the depth calibration sub 5, the plurality of fracturing assemblies 1 and the guide head 6 are connected in sequence through the intermediate tubing 3. The safety joint 4 is used to be disconnected from the safety joint 4 when the operation is abnormal, so that the first tubing 2 is out of the well. The depth calibration sub 5 is used to measure the position where it is located by using a measuring tool. The guide head 6 is used to facilitate the orientation when the fracturing assembly 1 is lowered into the well. The first cylinder 11 is provided with a standard API thread to connect with the intermediate tubing 3 or other accessories.

[0050] In the hard coal seam fracturing tool of the embodiment, the accessories commonly used in the existing oil and gas exploitation, such as the safety joint 4, the depth calibration sub 5 and the guide head 6, are utilized. The connection and lowering of the plurality of fracturing assemblies 1 are facilitated. The safety joint 4 adopts a modular design. The core components include a male joint, a female joint and a sealing device. The male joint end is provided with a sliding groove structure. The mechanical interlocking is formed by a pin and the female joint. The high pressure sealing is realized by cooperating with an O-shaped sealing ring. The depth calibration sub 5 generally has a depth measuring assembly, a communication assembly and an electronic module, etc. It can feedback its own depth to the controller on the ground. The guide head 6 is generally a conical head. It facilitates pushing away the sundries in the well when it is lowered into the well.

[0051] In some embodiments, the hard coal seam fracturing tool further comprises a directional device 7 and a packer 8. At least part of the first cylinder 11 is connected with the intermediate tubing 3 or the first tubing 2 through the directional device 7. The directional device 7 is used to rotate the first cylinder 11 connected therewith to adjust the orientation of the through hole 111 on the first cylinder 11. The packer 8 is arranged on the intermediate tubing 3. The packer 8 is located between the adjacent two fracturing assemblies 1 and between the fracturing assembly 1 and the guide head 6. The packer 8 is used to seal the annular space between the outer wall surface of the intermediate tubing 3 and the well wall.

[0052] Specifically, one end of the directional device 7 is rotationally connected, and one end is fixedly connected. The end fixedly connected is connected with the fracturing assembly 1, and the rotationally connected end is connected with the tubing. The directional device 7 is generally designed with eccentric weight. The eccentric arrangement of the directional device 7 is lowered by repeatedly pulling the tubing to achieve the purpose of orientation. The electronic sensor or the electronic pointer can be arranged on the directional device 7 to feedback the orientation of the directional device 7 to the controller on the ground in real time. By connecting the directional device 7 with the first cylinder 11 in advance and determining the pre-connected orientation of the through hole 111, the orientation of the through hole 111 to the coal seam can be realized by pulling the tubing after being lowered into the L-shaped well 9.

[0053] Specifically, the packer 8 has multiple types, and the core principle is that after applying external force, such as water injection, air inflation, etc., the expansion components such as slips, air bags, etc. can be radially expanded to achieve the sealing of the oil-casing annular space. Each fracturing assembly 1 corresponds to a packer 8, and the packer 8 is located on the side of the fracturing assembly 1 towards the toe end. When the fracturing assembly 1 is operated, the packer 8 is first opened to seal the space on the side of the fracturing assembly 1 towards the toe end, so that the medium can be fractured in the area where the fracturing assembly 1 is located, preventing the medium from leaking to the toe end crack, and improving the fracturing effect.

[0054] The fracturing method of the present embodiment is described below, including the following steps: S1: Using the first tubing 2 and the intermediate tubing 3 to place at least one fracturing assembly 1 into the horizontal section 95 of the L-shaped well 9, so that the fracturing assembly 1 is in the target fracturing position.

[0055] S2: Using the first tubing 2 placed on the ground at one end, and placing the sealing component 14 inside the first tubing 2, which can be moved into the fracturing assembly 1 corresponding to its diameter and seal the second cylinder 12 in the fracturing assembly 1.

[0056] S3: Using the packer 8 adjacent to the fracturing assembly 1 in S2 and towards the guide head 6 at one end, so that the packer 8 seals the annular space between the outer wall surface of the intermediate tubing 3 and the well wall.

[0057] S4: Using the first tubing 2 placed on the ground at one end to inject carbon dioxide along the first tubing 2, and observe the pressure holding, then continue to inject carbon dioxide to make the second cylinder 12 of the fracturing assembly 1 in S2 overcome the overloading force and move to the working position and make the through hole 111 in the fracturing assembly 1 in S2 open, then the carbon dioxide flows out along the through hole 111 of the fracturing assembly 1 in S2 and impacts the coal seam to make the coal seam fracture, and stop injecting after reaching the preset time or working condition.

[0058] S5: Using the first tubing 2 placed on the ground at one end and injecting water along the first tubing 2, and injecting water through the annular space between the first tubing 2 and the well wall of the L-shaped well 9, so that a large amount of water enters the coal seam along the existing cracks to make the coal seam cracks continue to expand, then mix temporary plugging particles in the water to make the temporary plugging particles seal part of the coal seam cracks and make the water divert to impact the coal seam in other areas to expand the coal seam fracturing range, and stop injecting after reaching the preset time or working condition.

[0059] S6: Using the first tubing 2 and the intermediate tubing 3 to pull out the fracturing assembly 1 from the well.

[0060] S7: After the well is sealed for 30-60 days, gas extraction is carried out, and after the gas extraction reaches the standard, underground coal cutting operation is carried out.

[0061] In this embodiment, before the fracturing, the exploration and completion of the L-type well 9 are needed first, as follows: 1. Geological evaluation and well trajectory design.

[0062] 1.1. Integrate seismic exploration data, downhole roadway exploration data, logging data, coring data, and drilling exploration data, etc., to analyze the formation sequence and structural characteristics, and obtain the thickness distribution and fluctuation of the hard coal seam.

[0063] 1.2. Obtain the ground stress size, direction and rock mechanics parameters of the formation by using small aperture hydraulic fracturing method, acoustic logging interpretation method, and indoor rock mechanics test, etc., to calculate the fracturing pressure of the hard coal seam.

[0064] 1.3. Use the large water vertical ratio directional drilling machine and the matching drilling equipment on the ground to drill the L-type well 9 to the target coal seam, and the horizontal wellbore direction is along the minimum horizontal principal stress direction of the hard coal seam. The length of the horizontal section 95 is 2000-3000m.

[0065] 1.4. The L-type well 9 uses the while-drilling geosteering technology to adjust the well trajectory in real time, to ensure that the build-up point is located in the coal seam roof rock, and the landing point and the horizontal section 95 are located in the coal seam.

[0066] 2. Completion of the L-type well 9 on the ground.

[0067] 2.1. The L-type well 9 uses two-opening casing completion, and the first opening surface casing 91 is used to block the shallow water layer on the ground, and the casing shoe of the second opening technical casing 93 is located at 30-50m of the horizontal section 95.

[0068] 2.2. The L-type well 9 uses special cementing, and the cement is reversed to the ground. The horizontal section 95 of the wellbore in the hard coal seam uses open hole completion method.

[0069] 2.3. The diameter of the horizontal section 95 of the L-type well 9 is not less than 127mm.

[0070] 2.4. The microseismic monitoring instrument is arranged in the roadway below the horizontal section 95 of the L-type well 9 and on the ground, and the interval of the microseismic monitoring instrument is not more than 80m.

[0071] 2.5. The downhole roadway and the ground microseismic monitoring instrument are connected with the ground microseismic analysis system, which is used to monitor the microseismic signal in the fracturing process, to adjust the fracturing construction parameters in real time.

[0072] After the completion of the above L-type well 9, please refer to the attached Figure 1 , which is mainly composed of surface casing 91, cementing cement 92, technical casing 93, oil casing annulus 94, and horizontal section 95. In this embodiment, the fracturing is mainly carried out on the horizontal section 95.

[0073] In step S1, a long connection whole is formed by the first tubing 2, the safety joint 4, the depth calibration nipple 5, the intermediate tubing 3, the guide head 6 and one or more fracturing assemblies 1, facilitating the lowering of a block into the L-shaped well 9. If the fracturing assemblies 1 are multiple, the multiple fracturing assemblies 1 are arranged from the toe end to the heel end in order of the diameters of the second barrels 12 from small to large. And when fracturing, the fracturing assemblies 1 need to be used in sequence from the toe end to the heel end for segmented fracturing.

[0074] In step S2, when the fracturing assemblies 1 in S1 are multiple, only one blocking part 14 is launched each time and used in order of the diameters of the blocking parts 14 from small to large, so that the multiple fracturing assemblies 1 are sequentially subjected to segmented fracturing operation.

[0075] In step S3, when the fracturing assembly 1 to be worked needs to be blocked by the packer at the toe end to isolate the oil jacket annular area at the toe end, so as to avoid the loss of the medium participating in the fracturing from the cracks of the already fractured area during the current fracturing. And the blocking part at the heel end in the current fracturing assembly 1 is in a non-set state, that is, the medium can also be injected from the oil jacket annular area, so as to improve the injection amount and realize subsequent large displacement and large liquid injection.

[0076] In step S4, carbon dioxide fracturing is performed. The carbon dioxide can be liquid carbon dioxide. When injected, first, pressure test is needed to ensure that there is no obvious leakage between the first tubing 2 and the target fracturing assembly 1. After the carbon dioxide pressure reaches the pressure test pressure value, the injection of carbon dioxide is stopped. The pressure test pressure value is preferably 10-20 MPa. At the same time, the pressure value change in the fracturing string is recorded. If the pressure loss within 10 minutes does not exceed 5%, it meets the pressure test requirement, and the injection of carbon dioxide into the fracturing string continues. Until the opening pressure (overload force) is reached, wherein the opening pressure is 3.0-5.0 times the breaking pressure of hard coal seam, to avoid high pressure crushing coal and affecting the subsequent movement of the whole device. The opening pressure is set according to the overload force. The carbon dioxide pressure value corresponding to the shear resistance of a single pin is between 20-30 MPa. The pins are set in multiple and the number can be set as needed to realize different settings of the opening pressure.

[0077] When the pressure of carbon dioxide in the fracturing assembly 1 reaches the opening pressure, the pin is cut off, the second barrel 12 moves to the working position and no longer blocks the through hole 111, and the high-pressure carbon dioxide is shot out along the through hole 111 at high speed and impacts the fractured coal seam.

[0078] The direction of the through hole 111 is set according to the position of the horizontal section 95 in the coal seam. If the horizontal section 95 is in the middle of the coal seam, the through hole 111 is uniformly distributed around the circumference. If the horizontal section 95 is in the upper part of the coal seam, the through hole 111 is downward. If the horizontal section 95 is in the lower part of the coal seam, the through hole 111 is upward. With the inflation of high-speed carbon dioxide gas, the coal seam can be impact fractured. Then, the injection of carbon dioxide is continued, and the fracturing is continued to expand the fracturing range and degree. When it is monitored by the ground microseismic monitoring equipment that the crack no longer expands, that is, the preset working condition is reached, the injection of carbon dioxide can be stopped.

[0079] In step S5, a large displacement fracturing fluid is injected. After the carbon dioxide fracturing in S4, the fracturing fluid is simultaneously injected at random in the annular space between the first tubing 2 and the well wall of the L-shaped well 9 (in the oil jacket annulus). The fracturing fluid uses clean water, and a resistance reducing agent is added to reduce the pipe string friction. The injection displacement is 12-16 m 3 / min, and the water volume for single fracturing is preferably 1200-1600 m 3 . A large amount of water enters the area where the target fracturing assembly 1 in S2 is located, and high-pressure water is continuously used to fracture the coal seam to further expand the fractured area.

[0080] The water flow through the through hole 111 forms a high-speed jet, and continues to expand along the previously fractured crack. At the same time, a negative pressure zone is formed near the through hole 111, and the water in the oil jacket annulus is simultaneously fractured to make the fracturing crack expand to a larger range.

[0081] After fracturing for a period of time, if the water pressure drops rapidly or the fracturing has no effect, temporary plugging particles such as ceramic particles, chemical materials, and organic materials are added to the water. The particle size is single or mixed type, and one or more of 10-20 mesh, 20-40 mesh, and 30-50 mesh is used. The temporary plugging particles fill the formed cracks to divert the water flow to other areas for fracturing, avoiding the water flow flowing into the deep cracks, and expanding the fracturing range. When it is monitored by the ground microseismic monitoring equipment that the crack no longer expands, that is, the preset working condition is reached, the injection of water can be stopped.

[0082] In step S6, after the segmented fracturing is completed, the well is extracted through the first tubing 2 and the fractured fracturing assembly 1. If an abnormal working condition occurs, the first tubing 2 is extracted by opening the safety joint 4.

[0083] In step S7, after the carbon dioxide impact fracturing and water pressure fracturing weaken the hard coal seam, the well is closed for huff and puff operation. Preferably, the huff and puff time is 30-60 days.

[0084] During the well sealing, the carbon dioxide competes with the methane for adsorption in the hard coal seam, promoting the desorption of the methane. Meanwhile, the carbon dioxide dissolves in the formation water to form an acidic medium, which reacts with the carbonate rock minerals in the hard coal seam, further weakening the hard coal seam.

[0085] After the well sealing, the gas and the fracturing fluid are pumped out using the surface equipment, improving the gas extraction efficiency and reducing the carbon dioxide concentration.

[0086] After the gas extraction reaches the standard, the coal cutting operation is performed in the well.

[0087] In some embodiments, in S4 and S5, the pressure, flow rate and liquid volume of the injected carbon dioxide and water are adjusted in real time using the surface microseismic monitoring system. Meanwhile, a differential design is made according to the surface microseismic monitoring system and the pump pressure curve. When the surface microseismic analysis system monitors that there is a large range of no microseismic signal in the to-be-fractured area, or the pump pressure curve construction pressure rapidly decreases (the decrease is more than 15%), the temporary plugging particles with combined particle sizes are timely added in the oil-casing annulus to promote the diversion and expansion of the hydraulic fractures, and finally a large range of complex network and weakened area is formed.

[0088] The coal seam fracturing tool and method of the embodiment have the following effects: 1. Small influence by the ground stress: The high-pressure carbon dioxide energy-accumulating impact fracturing of the hard coal seam forms a radial fracture network with a certain range that is not affected by the ground stress.

[0089] 2. Large coal seam weakened area: The radial fractures formed by the carbon dioxide impact fracturing after the “large displacement, large liquid volume and timely temporary plugging” water pressure fracturing of the long horizontal section of the surface L-shaped horizontal well expand, and the coal seam cleat fissures are activated, forming a large area of deteriorated hard coal seam, significantly improving the coal cutting efficiency.

[0090] 3. High intelligent degree and strong controllability: The fracture expansion is monitored in real time through the downhole roadway and the surface microseismic, realizing the “visualization” dynamic regulation and control of the fracturing process, and ensuring the uniformity and reliability of the weakening effect.

[0091] 4. One well with multiple uses to reduce costs: After the fracturing and weakening of the hard coal seam, the well is sealed, the carbon dioxide competes with the methane for adsorption, and the desorption of the coal seam methane is promoted. The same wellbore can be used to weaken the coal seam and improve the coal cutting efficiency, and also to efficiently extract the gas, achieving the effect of one well with multiple uses to reduce costs.

[0092] 5. Safer surface operation: The carbon dioxide impact fracturing and the water pressure fracturing are performed on the surface, and there is no operation in the well. The injected carbon dioxide is dissolved in the formation water or discharged during the gas extraction, and the safety of the personnel operation during the subsequent coal cutting and mining is high.

[0093] In the description of the application, it is to be understood that the orientations or positional relationships indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the devices or elements indicated thereby must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the application.

[0094] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated thereby. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise explicitly specified and limited.

[0095] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected or in communication with each other; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication or interaction relationship of two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0096] In the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature, which can be direct contact between the first and second features, or indirect contact between the first and second features through an intermediate medium. Moreover, the first feature "above", "above" and "above" the second feature can be directly above or obliquely above the first feature, or only indicate that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature can be directly below or obliquely below the first feature, or only indicate that the horizontal height of the first feature is less than that of the second feature.

[0097] In this disclosure, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" mean that a particular feature, structure, material, or characteristic is included in at least one embodiment or example of the present disclosure. The illustrative appearances of the above-mentioned terms in various places in the specification are not necessarily referred to the same embodiment or example. Moreover, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. Furthermore, the terminology "comprising" is used in the disclosure as comprising, but not limited to, any indicated features, integers, steps or components. It is also to be understood that the terminology "comprising" can be replaced by the terminology "consisting of" or "consisting essentially of" in some embodiments or examples.

[0098] Although the above-mentioned embodiments have been shown and described, it is to be understood that the above-mentioned embodiments are exemplary, and should not be understood as limiting the present disclosure, and the changes, modifications, replacements and variations of the above-mentioned embodiments made by those skilled in the art are within the protection scope of the present disclosure.

Claims

1. A hard seam fracturing tool characterized by, The cracking assembly (1) comprises: a first cylinder (11) having a through hole (111) on its side wall; a second cylinder (12) placed inside the first cylinder (11), which is movable along the first cylinder (11) and has an initial position and a working position, wherein the second cylinder (12) blocks the through hole (111) when it is in the initial position and opens the through hole (111) when it is in the working position; an overload component (13) arranged between the first cylinder (11) and the second cylinder (12) and having an overload force to prevent the second cylinder (12) from moving away from the initial position; a blocking component (14) for blocking one end of the second cylinder (12); wherein when the first cylinder (11) is filled with medium and the blocking component (14) blocks the second cylinder (12), the medium can push the second cylinder (12) to overcome the overload force and move from the initial position to the working position to open the through hole (111) and make the medium flow out of the through hole (111).

2. The hard seam fracturing tool of claim 1, wherein, A limiting protrusion (15) is arranged on the inner wall of the first cylinder (11), and the second cylinder (12) abuts against and is limited by the limiting protrusion (15) when it moves to the working position.

3. The hard seam fracturing tool of claim 1, wherein, The overload component (13) comprises a pin for connecting the first cylinder (11) and the second cylinder (12), and the shear resistance of the pin forms the overload force, and the second cylinder (12) will cut off the pin after overcoming the overload force; and / or, the blocking component (14) is a spherical body; and / or, a sealing ring is arranged on the contact surface of the second cylinder (12) connected with the blocking component (14).

4. The hard seam fracturing tool of claim 1, wherein, The through hole (111) is a plurality of through holes, and at least part of the plurality of through holes (111) have different orientations; and / or, the plurality of through holes (111) are uniformly distributed along the circumference of the first cylinder (11); and / or, the cross-sectional area of the through hole (111) on the inner wall of the first cylinder (11) gradually decreases in the direction of the outer wall of the first cylinder (11), so as to increase the flow rate of the medium flowing out of the first cylinder (11).

5. The hard seam fracturing tool of claim 1, wherein, The cracking assembly (1) is a plurality of cracking assemblies (1) arranged at intervals and interconnected between the first cylinders (11), and the second cylinders (12) in the plurality of cracking assemblies (1) can be sequentially blocked by the blocking components (14); The inner diameters of the second cylinders in the plurality of cracking assemblies are arranged in an arithmetic progression, and the diameters of the blocking components in the plurality of cracking assemblies are arranged in an arithmetic progression, so that blocking components (14) of different diameters can sequentially block second cylinders (12) of different inner diameters.

6. The hard seam fracturing tool of any one of claims 1-5, wherein, Further comprising: A first oil pipe (2), an intermediate oil pipe (3), a safety joint (4), a depth calibration nipple (5), a guide head (6); one end of the first oil pipe (2) is placed on the ground, the other end of the first oil pipe (2) is connected with the safety joint (4), the safety joint (4), the depth calibration nipple (5), a plurality of the cracking assemblies (1), and the guide head (6) are sequentially connected through the intermediate oil pipe (3); The safety joint (4) is used for being disconnected from the safety joint (4) when an operation is abnormal, so that the first oil pipe (2) is taken out of the well, the depth calibration nipple (5) is used for measuring the position thereof by using a measuring tool, and the guide head (6) is used for facilitating the orientation when the cracking assembly (1) is lowered into the well.

7. The hard seam fracturing tool of claim 6, wherein, Further comprising: A directional device (7), at least part of the first cylinder (11) is connected with the intermediate oil pipe (3) or the first oil pipe (2) through the directional device (7), and the directional device (7) is used for rotating the first cylinder (11) connected therewith to adjust the orientation of the through hole (111) on the first cylinder (11); A packer (8) is arranged on the intermediate oil pipe (3), and the packer (8) is located between two adjacent cracking assemblies (1) and between the cracking assembly (1) and the guide head (6); the packer (8) is used for sealing the annular space between the outer wall surface of the intermediate oil pipe (3) and the well wall.

8. A fracturing method characterized by, The hard coal seam cracking tool of claim 7 is used to realize the cracking method, and the cracking method comprises the following steps: S1: at least one cracking assembly (1) is placed into the horizontal section of the L-shaped well (9) by using the first oil pipe (2) and the intermediate oil pipe (3), so that the cracking assembly (1) is located at a target cracking position; S2: the blocking component (14) is placed in the first oil pipe (2) by using one end of the first oil pipe (2) placed on the ground, the blocking component (14) can be moved into the cracking assembly (1) corresponding to the diameter thereof and block the second cylinder (12) in the cracking assembly (1); S3: the packer (8) adjacent to the cracking assembly (1) in S2 and towards the guide head is used to seal the annular space between the outer wall surface of the intermediate oil pipe (3) and the well wall; S4: carbon dioxide is injected into the first oil pipe (2) by using one end of the first oil pipe (2) placed on the ground, pressure is maintained and observed, then carbon dioxide is continuously injected, so that the second cylinder (12) of the cracking assembly (1) in S2 overcomes the overload force and moves to the working position, the through hole (111) in the cracking assembly (1) in S2 is opened, then carbon dioxide flows out along the through hole (111) of the cracking assembly (1) in S2 and impacts the coal seam, so that the coal seam is cracked, and the injection is stopped after a preset time or working condition. S5: using one end of the first oil pipe (2) placed on the ground and injecting water along the first oil pipe (2) and using the annular space between the first oil pipe (2) and the well wall of the L-shaped well (9) to inject water, so that a large amount of water enters the coal seam along the existing cracks to make the coal seam cracks continue to expand, then mix temporary plugging particles in the water, so that the temporary plugging particles plug part of the coal seam cracks and divert the water to crack other areas of the coal seam, to expand the coal seam cracking range, stop injecting after a predetermined time or working condition is reached; S6: using the first oil pipe (2) and the intermediate oil pipe (3) to pull out the cracking assembly (1) from the well; S7: After the well is sealed for 30-60 days, gas extraction is carried out, and after the gas extraction reaches the standard, underground coal cutting operation is carried out.

9. The cracking method according to claim 8, characterized in that, when the cracking assembly (1) in S1 is multiple, S2-S5 are repeated, and in S2, only one plugging part (14) is put in each time and is used from small to large in diameter, so that multiple cracking assemblies (1) perform segmented fracturing operation in turn.

10. The cracking method according to claim 9, characterized in that, in S4 and S5, the pressure, displacement and liquid volume of injected carbon dioxide and water are adjusted in real time using a ground microseismic monitoring system; in S1, according to the position of the coal seam where the horizontal section of the L-shaped well (9) is located, the directional device (7) with the appropriate orientation is selected and connected with the cracking assembly (1) to make the through hole (111) face the direction of the coal seam after the cracking assembly (1) is lowered into the horizontal section of the L-shaped well (9).

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