High-efficiency staged fracturing series tool string and method for long drill hole in underground coal mine

Abstract

The invention discloses an efficient staged fracturing series tool string and method for a long drill hole in an underground coal mine, which reduce the traditional working procedures, namely, reduce the arrangement of a group of packer ball seats and pins, and save raw materials. A section of tubular column is reduced, namely the overall length of the tool string is shortened, and field installation is more convenient. The steel wire pitching ball can be taken out at any time after the tool string drains water, so that the use is more scientific, and the influence on the fracturing work caused by the traditional ball outlet mode when the field fracturing work is completed and the water is drained is reasonably solved. After the steel wire pitching ball opens the first packer and the ball seat of the packer, the setting position is reached, and after fracturing is completed, the steel wire pitching ball is taken out of the oil pipe to carry out the next section of fracturing work, due to the existence of the standby tool string, after the fracturing work breaks down, the tedious quitting and re-conveying process does not need to be carried out, and the working efficiency is greatly improved. And the overall working efficiency is improved, meanwhile, potential safety hazards are avoided, and the device is suitable for industrial large-scale use and popularization.

Description

Technical Field

[0001] The invention belongs to the field of underground hydraulic fracturing, and particularly relates to a high-efficiency segmented fracturing series tool string and method for long boreholes in coal mines. Background Art

[0002] In the hard roof fracturing and weakening of the working face in coal mines, a fracturing tool string is usually used for fracturing. There is only one fracturing section in the fracturing tool string. Looking from the borehole mouth to the borehole bottom direction, it consists of a releasing tool, a packer, a constant-pressure throttle, a packer, and a shoe ball seat. Throwing a ball to the shoe ball seat can seal the fracturing section and expand the packer; there is also a ball seat in the releasing tool, and the fracturing section can be discarded.

[0003] During use, first inject high-pressure water into the tool string, throw a low-density ball to the ball seat, seal the tool string, then the packer expands, and then inject high-pressure water into the hard rock layer of the coal seam roof through the constant-pressure throttle to pre-form a three-dimensional fracture system composed of several or multiple fractures in the target rock layer of the roof, thereby weakening the overall strength of the hard roof and making it easy to collapse, reducing the hanging length of the hard roof and thus reducing the weighting intensity, achieving the effect of controlling the hard roof; there is a sliding sleeve ball seat at the releasing tool. When the fracturing section cannot be dragged, only a ball can be thrown to open the releasing tool, discard the fracturing section, take out the tool string, reinstall the second fracturing section, and transport it into the borehole.

[0004] In the process of underground hydraulic fracturing construction, this kind of setting adopts the backward fracturing method. When some projects need to carry out ultra-long borehole hydraulic fracturing, the on-site transportation time of the tool string is too long. For example, when the borehole length is greater than 700m, it takes at least one working shift, that is, eight hours, to connect the tool string and the oil pipe. When there is a problem with the fracturing section, it is necessary to withdraw the tool string and reconnect the tool string for transportation, and the time is more than sixteen hours. On the one hand, there are many abnormal situations underground and the safety problems are more prominent. On the other hand, this existing technology greatly reduces the fracturing efficiency and affects the high-efficiency production of the mine. Summary of the Invention

[0005] The purpose of the invention is to provide a high-efficiency segmented fracturing series tool string and method for long boreholes in coal mines to solve the problems of low efficiency and potential safety hazards during fracturing in the prior art.

[0006] To solve the above technical problems, the invention is implemented by adopting the following technical solutions:

[0007] A high-efficiency segmented fracturing series tool string for long boreholes in coal mines includes an external hydraulic pump and a total fracturing tool string. The total fracturing tool string includes at least two fracturing tool strings connected in series from beginning to end;

[0008] The fracturing tool string includes a first packer, a second packer, and a releasing tool connected in series from front to back;

[0009] The described first packer includes a first central pipe. A first lower joint and a first upper joint are respectively arranged at the front and rear parts of the first central pipe. A first expansion cylinder is sleeved in the middle part of the first central pipe. The rear part of the first expansion cylinder is sealingly sleeved on the front part of the first upper joint, and the front part of the first expansion cylinder is sealingly sleeved on the rear part of the first lower joint.

[0010] The described second packer includes a second central pipe. A second lower joint and a second upper joint are respectively arranged at the front and rear parts of the second central pipe. A second expansion cylinder is sleeved in the middle part of the second central pipe. The rear part of the second expansion cylinder is sealingly sleeved on the front part of the second upper joint, and the front part of the second expansion cylinder is sealingly sleeved on the rear part of the second lower joint.

[0011] The first upper joint of the first packer and the second lower joint of the second packer are coaxially connected through a connecting pipe.

[0012] A cylindrical first ball seat is coaxially arranged on the inner wall of the first upper joint through a pin. A plurality of radially extending water outlet channels are arranged on the side wall of the first upper joint, and all the water outlet channels are sealed by the first ball seat. A first water inlet channel is further arranged on the side wall of the first upper joint. One end of the first water inlet channel is sealed by the first ball seat, and the other end communicates with the joint between the inner wall of the first expansion cylinder and the outer wall of the first central pipe.

[0013] A cylindrical second ball seat is coaxially arranged on the inner wall of the second upper joint through a pin. A second water inlet channel is further arranged on the side wall of the second upper joint. One end of the second water inlet channel is sealed by the second ball seat, and the other end communicates with the joint between the inner wall of the second expansion cylinder and the outer wall of the second central pipe.

[0014] The first ball seat and the second ball seat have the same shape and specifications. A slope angle structure is arranged on the inner wall of the rear part of the second ball seat.

[0015] A cylindrical third ball seat is coaxially arranged on the inner wall of the releasing joint through a pin. A slope angle structure is arranged on the inner wall of the rear part of the third ball seat. The inner diameter of the third ball seat is larger than that of the first ball seat.

[0016] Among the two fracturing tool strings connected end to end of the total fracturing tool string, the inner diameter of the first ball seat of the fracturing tool string at the rear is larger than the inner diameter of the third ball seat of the fracturing tool string at the front.

[0017] It further includes a packer ball group corresponding to each fracturing tool string. The packer ball group includes a first packer ball and a second packer ball. The first packer ball can pass through the inside of its corresponding third ball seat and match the slope angle structure of its corresponding second ball seat. The second packer ball matches the slope angle structure of its corresponding third ball seat.

[0018] The external hydraulic pump can push the first isolation ball forward through the inside of the third ball seat by delivering high-pressure liquid into the fracturing tool string, and move both the second ball seat and the first ball seat forward by sequentially breaking the pins corresponding to the second ball seat and the first ball seat;

[0019] By delivering high-pressure liquid into the fracturing tool string to push the second isolation ball to break the pin corresponding to the third ball seat, and then separating the releasing joint from the second packer.

[0020] The present invention further has the following features:

[0021] Further, both the first expansion cylinder and the second expansion cylinder are rubber cylinders, and support steel belts are respectively arranged inside them.

[0022] Further, a first floating head is arranged between the first expansion cylinder of the first central pipe and the first lower joint;

[0023] A second floating head is arranged between the second expansion cylinder of the second central pipe and the second lower joint.

[0024] Further, it also includes a plurality of sealing rings; the sealing rings are arranged at the following positions of the fracturing tool string:

[0025] Between the first central pipe and the first lower joint;

[0026] Between the second central pipe and the second lower joint;

[0027] Between the first central pipe and the first floating head;

[0028] Between the second central pipe and the second floating head;

[0029] Between the rear part of the first expansion cylinder and the front part of the first upper joint;

[0030] Between the rear part of the second expansion cylinder and the front part of the second upper joint;

[0031] At each first water inlet channel and each second water inlet channel.

[0032] Further, both the first isolation ball and the second isolation ball are low-density balls.

[0033] Further, wire ropes are respectively connected to the first isolation ball and the second isolation ball.

[0034] Further, when the pressure borne by the first ball seat, the second ball seat, and the third ball seat is greater than 15 MPa, the corresponding pins are disconnected.

[0035] Further, a radially extending water outlet channel is provided on the side wall of the first upper joint;

[0036] The distribution angles of the four water outlet channels are 0°, 90°, 180° and 270° respectively;

[0037] The first upper joint is connected to the first ball seat via four pins, and the distribution angles of the four pins are 45°, 135°, 225° and 315° respectively;

[0038] The second upper joint is connected to the second ball seat through four pins, and the distribution angles of the four pins are 45°, 135°, 225° and 315° respectively;

[0039] The throwing handle is connected to the third ball seat through four pins, and the distribution angles of the four pins are 45°, 135°, 225° and 315° respectively.

[0040] A method for using a long borehole high-efficiency staged fracturing series tool string in a coal mine, the method is based on the above-mentioned long borehole high-efficiency staged fracturing series tool string in a coal mine, and comprises the following steps:

[0041] Step 0, determining all the fracturing stages that require fracturing operations within the completed borehole;

[0042] Step 1, lowering the total fracturing tool string into the bottom of the borehole, and dragging the total fracturing tool string backward until the frontmost fracturing tool string reaches the first fracturing stage;

[0043] Step 2: inserting a first spacer ball corresponding to the frontmost fracturing tool string into the total fracturing tool string, using an external hydraulic pump to deliver high-pressure liquid into the total fracturing tool string to push the first spacer ball, so that the first spacer ball destroys the pin of the second ball seat and pushes the second ball seat forward, and the whole of them is pushed forward to destroy the pin corresponding to the first ball seat, and push the first ball seat to move forward;

[0044] Step 3: The external hydraulic pump continues to deliver high-pressure liquid to the interior of the total fracturing tool string, so that the first expansion cylinder and the second expansion cylinder expand to press against the side wall of the borehole, thereby forming an annular fracturing zone between the outer wall of the connecting pipe and the inner wall of the corresponding position of the borehole, and the high-pressure liquid flows out from the water outlet channel to perform fracturing operations until the fracturing of the fracturing section is completed;

[0045] Step 4: the external hydraulic pump stops the high-pressure liquid until the first expansion cylinder and the second expansion cylinder return to their original state, and determines whether the total fracturing tool string can continue to be dragged backward;

[0046] If it can continue to be dragged backward, the entire fracturing tool string is dragged until the frontmost fracturing tool string reaches the next fracturing stage and then proceeds to step 5;

[0047] If it is impossible to continue dragging backward, then insert the second isolation ball corresponding to the frontmost fracturing tool string, and use an external hydraulic pump to deliver high-pressure liquid into the total fracturing tool string to push the second isolation ball, causing the second isolation ball to break the pin corresponding to the third ball seat. Then, after the release in the frontmost fracturing tool string disconnects from the second packer, continue to drag the total fracturing tool string until the next fracturing tool string reaches the next fracturing stage and then enter Step 5;

[0048] Step 5: Repeat Steps 1 - 4 until all the fracturing stages in the borehole are completed.

[0049] Compared with the prior art, the present invention has the following technical effects:

[0050] The high-efficiency sectional fracturing series tool string and method for long boreholes in coal mines of the present invention reduce traditional processes, that is, reduce the arrangement of a set of packer ball seats and pins, saving raw materials. It reduces one section of the pipe string, that is, shortens the overall length of the tool string, making on-site installation more convenient. The wire-launched ball can be taken out at any time after the tool string is drained, making it more scientific in use, and reasonably solving the impact of the traditional ball discharging method on fracturing work during drainage when the on-site fracturing work is completed. After the wire-launched ball opens the ball seat of the first packer and the packer, it reaches the setting position. Until the fracturing is completed, it is then taken out from the oil pipe to carry out the next section of fracturing work, without the need for a long and cumbersome process of withdrawing and re-delivering, improving the overall work efficiency while avoiding potential safety hazards, and being suitable for large-scale industrial use and promotion. Description of the Drawings

[0051] Figure 1 is the overall structural schematic diagram of the high-efficiency sectional fracturing series tool string for long boreholes in coal mines of the present invention;

[0052] Figure 2 is Figure 1 the enlarged view of part A of

[0053] Figure 3 is Figure 1 the enlarged view of part B of

[0054] The meanings of the reference numerals in the figure are as follows:

[0055] 1, first central pipe; 2, first lower joint; 3, first upper joint; 4, first expansion cylinder; 5, second central pipe; 6, second lower joint; 7, second upper joint; 8, second expansion cylinder; 9, connecting pipe; 10, first ball seat; 11, water outlet channel; 12, first water inlet channel; 13, second ball seat; 14, second water inlet channel; 15, third ball seat; 16, first isolation ball; 17, second isolation ball; 18, support steel strip; 19, first floating head; 20, second floating head. Detailed Embodiments

[0056] It should be noted that all components in the present invention, unless otherwise specified, are all components known in the prior art. For example, the floating head adopts a commonly known floating head.

[0057] The connection relationships of all components in the present invention, unless otherwise specified, are all connection relationships known in the prior art. For example, the connections between the central pipe and the upper and lower connectors, and between the central pipe and the floating head are known in the prior art.

[0058] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations made on the basis of the technical solutions of the present application fall within the protection scope of the present invention.

[0059] A high-efficiency staged fracturing series tool string for long boreholes in coal mines includes an external hydraulic pump, and is characterized in that it includes a total fracturing tool string, and the total fracturing tool string includes at least two fracturing tool strings connected in series end to end;

[0060] The fracturing tool string includes a first packer, a second packer and a release joint connected in series in sequence from front to back;

[0061] The first packer includes a first central pipe 1. A first lower joint 2 and a first upper joint 3 are respectively sleeved on the front and rear parts of the first central pipe 1. A first expansion cylinder 4 is sleeved on the middle part of the first central pipe 1. The rear part of the first expansion cylinder 4 is hermetically sleeved on the front part of the first upper joint 3, and the front part of the first expansion cylinder 4 is hermetically sleeved on the rear part of the first upper joint 3;

[0062] The second packer includes a second central pipe 5. A second lower joint 6 and a second upper joint 7 are respectively sleeved on the front and rear parts of the second central pipe 5. A second expansion cylinder 8 is sleeved on the middle part of the second central pipe 5. The rear part of the second expansion cylinder 8 is hermetically sleeved on the front part of the second upper joint 7, and the front part of the second expansion cylinder 8 is hermetically sleeved on the rear part of the second upper joint 7;

[0063] The first packer and the second packer are coaxially connected by a connecting pipe 9 using their respective first upper joint 3 and second lower joint 6;

[0064] A cylindrical first ball seat 10 is coaxially arranged on the inner wall of the first upper joint 3 through a pin; a plurality of radially distributed water outlet channels 11 are opened on the side wall of the first upper joint 3, and all the water outlet channels 11 are sealed by the first ball seat 10; a first water inlet channel 12 is also arranged on the side wall of the first upper joint 3. One end of the first water inlet channel 12 is sealed by the first ball seat 10, and the other end communicates with the joint between the inner wall of the first expansion cylinder 4 and the outer wall of the first central pipe 1;

[0065] A cylindrical second ball seat 13 is coaxially arranged on the inner wall of the second upper joint 7 through a pin; a second water inlet channel 14 is further provided on the side wall of the second upper joint 7; one end of the second water inlet channel 14 is sealed by the second ball seat 13, and the other end communicates with the joint between the inner wall of the second expansion cylinder 8 and the outer wall of the second central tube 5;

[0066] The first ball seat 10 and the second ball seat 13 have the same specifications, and a slope angle structure is provided on the inner wall at the rear of the second ball seat 13;

[0067] A cylindrical third ball seat 15 is coaxially arranged on the inner wall of the release joint through a pin; a slope angle structure is provided on the inner wall at the rear of the third ball seat 15; the inner diameter of the third ball seat 15 is larger than that of the first ball seat 10;

[0068] In two fracturing tool strings connected to each other in the total fracturing tool string, the inner diameter of the first ball seat 10 of the fracturing tool string at the rear is larger than the inner diameter of the first ball seat 10 of the fracturing tool string at the front;

[0069] It further includes a packer ball group corresponding to each fracturing tool string one by one. The packer ball group includes a first packer ball 16 and a second packer ball 17; the first packer ball 16 can pass through the inside of its corresponding third ball seat 15 and match the slope angle structure of its corresponding second ball seat 13, and the second packer ball 17 matches the slope angle structure of its corresponding third ball seat 15; the packer ball just gets stuck at the slope angle, and a part is located in the conical cavity formed by the slope angle;

[0070] The external hydraulic pump can:

[0071] Push the first packer ball 16 through the inside of the third ball seat 15 by means of delivering high-pressure liquid into the fracturing tool string, and make the second ball seat 13 and the first ball seat 10 move backward in sequence by means of sequentially breaking the pins corresponding to the second ball seat 13 and the first ball seat 10;

[0072] Push the second packer ball 17 to break the pin corresponding to the third ball seat 15 by means of delivering high-pressure liquid into the fracturing tool string, so as to separate the release joint from the second packer;

[0073] In this embodiment, for each fracturing stage, two packer ball groups with different ball diameters are respectively matched. Ball seats are provided in both the first packer and the second packer, and the ball seats of the two are of the same size. The ball in the front can open the ball seats in the first packer and the second packer, and the inner diameter of the third ball seat 15 in the release joint is larger than that of the first ball seat 10 and the second ball seat 13. The ball in the rear is used to open the release joint.

[0074] An outer water inlet channel is provided in the second packer. Initially, it is blocked by the second ball seat 13. After being opened by the corresponding packer ball, it can be used to deliver high-pressure water to expand the second expansion cylinder 8.

[0075] The first packer is provided with a water inlet channel and a water outlet channel 11, which is initially blocked by the first ball seat 10. After being opened by the corresponding packing ball, the water inlet channel can be used to transport high-pressure water to expand the first expansion cylinder 4; the water outlet channel can transport high-pressure water into the borehole for rock layer hydraulic fracturing work.

[0076] Among them, the releasing function is a disconnecting device, which is provided with a third ball seat 15. The third ball seat 15 is fixed with a pin. When a fault occurs in the fracturing section and it gets stuck in the borehole, the corresponding packing ball is put into the releasing device. After breaking the pin in the releasing device, the core moves backward, and the connection between the releasing device and the second packer will be disconnected, further driving the rear part to fall off and be discarded in the borehole, ensuring that the tool string behind can be dragged.

[0077] The functions of the first packer are as follows: First, expand the front of the fracturing section; Second, the water outlet channel part fractures the hard rock layer. When high-pressure water is injected from the outer first water inlet channel 12, the first expansion cylinder 4 is compressed and expanded, and the first packer begins to contract. The first floating head 19 will move backward, promoting more complete expansion, better sealing effect of the borehole, and also having a certain buffering effect.

[0078] The function of the second packer is to expand the rear of the fracturing section. It should be noted that the expansion principle is similar to the function in the above-mentioned first packer and will not be elaborated here.

[0079] Among them, the releasing device, the second packer, and the front end of the first packer are all internal spiral structures, and the rear ends are all external spiral structures, which are convenient for connecting the front and the back.

[0080] In this embodiment, the first packer is provided with one water outlet channel and two water inlet channels. One water outlet channel is used to output high-pressure water from the first packer into the borehole for hard rock layer hydraulic fracturing work; there are two water inlet channels. One is the water inlet channel inside the central pipe, which transports the high-pressure water required for the front fracturing section, and the other is the water inlet channel outside the central pipe, which is used to expand the first packer during fracturing. In a certain fracturing section, the inner diameters of the ball seats of the second packer and the first packer are the same. Therefore, only one low-density ball needs to be dropped to open the two ball seats in the second packer and the first packer in this fracturing section.

[0081] Designed in this way, first, it saves the cumbersome steps of withdrawing the tool string, re-checking, and then transporting it into the borehole again, greatly saving the time of fracturing operation; second, it makes up for the influence on the fracturing work caused by the easy loss of low-density balls on site, resulting in the inability to accurately judge the position of the low-density balls on site.

[0082] During use, since the cross-sectional area of the inner diameter of the tubing or drill pipe is much larger than the cross-sectional area of the fracturing water outlet orifice, a large throttling pressure difference will be generated during on-site construction, and the throttling pressure difference is sufficient to expand the expansion cylinder of the packer.

[0083] As a preferred solution, both the first expansion cylinder 4 and the second expansion cylinder 8 are rubber cylinders, and support steel belts 18 are respectively arranged inside the two cylinders.

[0084] Such as Figure 2 、 3 As shown, the sparse shaded parts on both sides in the rubber cylinder are the support steel belts 18, which are rigid structures and function to connect and fix the surrounding components. The dense part in the middle is made of rubber material and can expand together with the support steel belt 18. After expansion, it clings to the borehole wall to achieve a sealing effect.

[0085] As a preferred solution, a first floating head 19 is arranged between the first expansion cylinder 4 of the first central tube 1 and the first lower joint 2;

[0086] A second floating head 20 is arranged between the second expansion cylinder 8 of the second central tube 5 and the second lower joint 6.

[0087] As a preferred solution, it further includes a plurality of sealing rings; sealing rings are arranged at the following positions of the fracturing tool string:

[0088] Between the first central tube 1 and the first lower joint 2;

[0089] Between the second central tube 5 and the second lower joint 6;

[0090] Between the first central tube 1 and the first floating head 19;

[0091] Between the second central tube 5 and the second floating head 20;

[0092] Between the rear part of the first expansion cylinder 4 and the front part of the first upper joint 3;

[0093] Between the rear part of the second expansion cylinder 8 and the front part of the second upper joint 7;

[0094] At each first water inlet channel 11 and each second water inlet channel 14.

[0095] As a preferred solution, both the first isolation ball 16 and the second isolation ball 17 are low-density balls.

[0096] Further preferably, the first isolation ball 16 and the second isolation ball 17 are respectively connected with wire ropes. The wire ropes can be connected with materials such as steel wires to prevent the situation of losing the balls.

[0097] In this embodiment, taking the nth fracturing stage as an example, the two low-density balls from the rear to the front are respectively denoted as ball B (secondary low-density ball) and ball A (primary low-density ball), then rB > rA.

[0098] Furthermore, when multiple fracturing stages are set, from the rear fracturing stage to the front fracturing stage, each fracturing stage has two low-density balls with different ball diameters, and the diameter of the low-density balls in the rear fracturing stage is greater than that of the low-density balls in the front fracturing stage. Denote the low-density balls in the nth fracturing stage as ball B and ball A, and the low-density balls in the (n - 1)th fracturing stage as ball D (quadruple low-density ball) and ball C (triple low-density ball),......, then rD > rC > rB > rA >...

[0099] The working process of using low-density balls in this embodiment is as follows:

[0100] The first case: After a failure occurs in the nth fracturing stage, the equipment cannot be dragged backward in the borehole.

[0101] 1. Lower ball B into the hole with a wire. After releasing the latch, retrieve the downhole tool string to the next fracturing position.

[0102] 2. Retrieve ball B with a wire, lower ball C into the (n - 1)th fracturing stage, and continue to inject high-pressure water to expand the corresponding packer and seal the borehole.

[0103] 3. After the packer expands to seal the borehole, the constant-pressure choke continues to discharge water. Under the action of high water pressure in the sealed section, hydraulic fracturing of the rock formation in the (n - 1)th fracturing stage is carried out.

[0104] The second case: After a problem occurs in the nth fracturing stage, the equipment can be dragged backward in the borehole.

[0105] 1. Deliver the tool string to the fracturing position, lower ball C into the hole with a wire, activate the (n - 1)th fracturing stage, and continuously inject high-pressure water to expand the packer and seal the borehole.

[0106] 2. The same as step 3 in the first case.

[0107] It should be noted that after a problem occurs in the nth fracturing stage, stop injecting high-pressure water, retrieve ball A, and restore the second packer and the first packer to their original sizes to facilitate dragging backward.

[0108] If a failure occurs in the (n - 1)th fracturing stage and fracturing cannot be carried out, then activate the (n - 2)th fracturing stage for fracturing according to the above steps.

[0109] With such a setting, the cumbersome steps of retrieving the tool string for inspection and repair and re-delivering the tool string when a failure occurs in a fracturing stage and fracturing cannot be carried out during the conventional directional long borehole hydraulic fracturing process are omitted, which can greatly save the overall fracturing time, improve the efficiency of directional long borehole hydraulic fracturing, and further ensure the safe and efficient production of the mining party.

[0110] Specifically, when the pressures borne by the first ball seat 10, the second ball seat 13, and the third ball seat 15 are greater than 15 MPa, the corresponding pins are disconnected.

[0111] Four water outlet channels 11 extending radially are provided in the side wall of the first upper joint 3;

[0112] The distribution angles of the four water outlet channels 11 are 0°, 90°, 180° and 270° respectively;

[0113] The first upper joint 3 is connected to the first ball seat 10 by four pins, and the distribution angles of the four pins are 45°, 135°, 225° and 315° respectively;

[0114] The second upper joint 7 is connected to the second ball seat 13 by four pins, and the distribution angles of the four pins are 45°, 135°, 225° and 315° respectively;

[0115] The releasing tool is connected to the third ball seat 15 by four pins, and the distribution angles of the four pins are 45°, 135°, 225° and 315° respectively.

[0116] A method for using a high-efficiency staged fracturing series tool string for long boreholes in coal mines. This method is based on the above-mentioned high-efficiency staged fracturing series tool string for long boreholes in coal mines and includes the following steps:

[0117] Step 0, determine all the fracturing sections that need fracturing operations inside the completed borehole;

[0118] Step 1, lower the total fracturing tool string to the bottom of the borehole, and pull out the total fracturing tool string from the back to the front until the frontmost fracturing tool string reaches the first fracturing section;

[0119] Step 2, put the first packer ball 16 corresponding to the frontmost fracturing tool string into the total fracturing tool string, and use an external hydraulic pump to transport high-pressure liquid into the total fracturing tool string to push the first packer ball 16, thereby sequentially breaking the pins corresponding to the second ball seat 13 and the first ball seat 10, and making the second ball seat 13 and the first ball seat 10 move backward in sequence;

[0120] Step 3, the external hydraulic pump continues to transport high-pressure liquid into the total fracturing tool string, causing the first expansion cylinder 4 and the second expansion cylinder 8 to expand, thereby forming an annular fracturing zone between the outer wall of the connecting pipe 9 and the corresponding position of the borehole, and the high-pressure liquid flows out from the water outlet channel 11 for fracturing operations until the fracturing of this fracturing section is completed;

[0121] Step 4, the external hydraulic pump stops the high-pressure liquid until the first expansion cylinder 4 and the second expansion cylinder 8 return to their original states, and judge whether the total fracturing tool string can be dragged backward continuously;

[0122] If it can be dragged backward continuously, then drag the total fracturing tool string until the frontmost fracturing tool string reaches the next fracturing section and then enter Step 5;

[0123] If it is impossible to continue dragging backward, the second packer 17 corresponding to the frontmost fracturing tool string is deployed, and high-pressure liquid is pumped into the interior of the total fracturing tool string using an external hydraulic pump to push the second packer ball 17, causing the pin corresponding to the third ball seat 15 to be damaged by the second packer ball 17. Subsequently, after the release connection in the frontmost fracturing tool string is disconnected from the second packer, the total fracturing tool string is dragged continuously until the next fracturing tool string reaches the next fracturing stage, and then step 5 is entered;

[0124] Step 5: Repeat steps 1 - 4 until all the fracturing stages in the borehole are completed.

Claims

1. A high-efficiency segmented fracturing series tool string for long boreholes in coal mines, including an external hydraulic pump, characterized in that, Comprising a total fracturing tool string, the total fracturing tool string comprising at least two fracturing tool strings connected in series end to end; The fracturing tool string comprises a first packer, a second packer and a releasing tool connected in series from front to back; The first packer comprises a first central tube (1), a first lower joint (2) and a first upper joint (3) are respectively arranged at the front and rear parts of the first central tube (1), and a first expansion cylinder (4) is sleeved in the middle of the first central tube (1); the rear part of the first expansion cylinder (4) is hermetically sleeved on the front part of the first upper joint (3), and the front part of the first expansion cylinder (4) is hermetically sleeved on the rear part of the first lower joint (2); The second packer comprises a second central tube (5), a second lower joint (6) and a second upper joint (7) are respectively arranged at the front and rear parts of the second central tube (5), and a second expansion cylinder (8) is sleeved in the middle of the second central tube (5); the rear part of the second expansion cylinder (8) is hermetically sleeved on the front part of the second upper joint (7), and the front part of the second expansion cylinder (8) is hermetically sleeved on the rear part of the second lower joint (6); The first upper joint (3) of the first packer and the second lower joint (6) of the second packer are coaxially connected through a connecting pipe (9); A cylindrical first ball seat (10) is coaxially arranged on the inner wall of the first upper joint (3) through a pin; a plurality of radially extending water outlet channels (11) are arranged on the side wall of the first upper joint (3), and all the water outlet channels (11) are sealed by the first ball seat (10); a first water inlet channel (12) is further arranged on the side wall of the first upper joint (3), one end of the first water inlet channel (12) is sealed by the first ball seat (10), and the other end is communicated to the joint between the inner wall of the first expansion cylinder (4) and the outer wall of the first central tube (1); A cylindrical second ball seat (13) is coaxially arranged on the inner wall of the second upper joint (7) through a pin; a second water inlet channel (14) is further arranged on the side wall of the second upper joint (7); one end of the second water inlet channel (14) is sealed by the second ball seat (13), and the other end is communicated to the joint between the inner wall of the second expansion cylinder (8) and the outer wall of the second central tube (5); The first ball seat (10) and the second ball seat (13) have the same shape and specifications, and a slope angle structure is arranged on the inner wall of the rear part of the second ball seat (13); A cylindrical third ball seat (15) is coaxially arranged on the inner wall of the releasing tool through a pin; a slope angle structure is arranged on the inner wall of the rear part of the third ball seat (15); the inner diameter of the third ball seat (15) is larger than that of the first ball seat (10); In the two fracturing tool strings connected end to end of the total fracturing tool string, the inner diameter of the first ball seat (10) of the fracturing tool string at the rear is larger than the inner diameter of the third ball seat (15) of the fracturing tool string at the front; It also includes a sealing ball group corresponding to each fracturing tool string, the sealing ball group including a first sealing ball (16) and a second sealing ball (17); the first sealing ball (16) can pass through the interior of the corresponding third ball seat (15) and match the slope angle structure of the corresponding second ball seat (13), and the second sealing ball (17) matches the slope angle structure of the corresponding third ball seat (15); The external hydraulic pump can push the first isolation ball (16) forward through the interior of the third ball seat (15) by delivering high-pressure liquid into the fracturing tool string, and can move the second ball seat (13) and the first ball seat (10) forward by successively destroying the pins corresponding to the second ball seat (13) and the first ball seat (10); The second packer ball (17) is pushed by delivering high-pressure liquid into the fracturing tool string to destroy the pin corresponding to the third ball seat (15), thereby separating the release tool from the second packer.

2. The high-efficiency sectional fracturing series tool string for long boreholes in underground coal mines according to claim 1, characterized in that, The first expansion cylinder (4) and the second expansion cylinder (8) are both rubber cylinders, and support steel belts (18) are respectively arranged inside the two cylinders.

3. The high-efficiency staged fracturing series tool string for long boreholes in coal mines as described in claim 1, characterized in that, A first floating head (19) is provided between the first expansion tube (4) of the first central tube (1) and the first lower joint (2); A second floating head (20) is provided between the second expansion tube (8) and the second lower joint (6) of the second central tube (5).

4. The high-efficiency segmented fracturing series tool string for long boreholes in coal mines as described in claim 1, characterized in that It also includes a plurality of sealing rings; the following positions of the fracturing tool string are all provided with sealing rings: between the first central tube (1) and the first lower joint (2); between the second central tube (5) and the second lower joint (6); between the first central tube (1) and the first floating head (19); between the second center tube (5) and the second floating head (20); Between the rear portion of the first expansion cylinder (4) and the front portion of the first upper joint (3); Between the rear portion of the second expansion cylinder (8) and the front portion of the second upper joint (7); At each first water inlet channel (11) and each second water inlet channel (14).

5. The high-efficiency segmented fracturing series tool string for long boreholes in coal mines as described in claim 1, wherein The first sealing ball (16) and the second sealing ball (17) are both low-density balls.

6. The high-efficiency staged fracturing series tool string for long boreholes in underground coal mines according to claim 5, characterized in that, The first spacer ball (16) and the second spacer ball (17) are respectively connected with wire ropes.

7. The high-efficiency sectional fracturing series tool string for long boreholes in coal mines as described in claim 1, characterized in that, When the pressure borne by the first ball seat (10), the second ball seat (13) and the third ball seat (15) is greater than 15 MPa, the corresponding pins are disconnected.

8. The high-efficiency sectional fracturing series tool string for long boreholes in coal mines as described in claim 7, wherein The side wall of the first upper joint (3) is provided with four radially extending water outlet channels (11); The distribution angles of the four water outlet channels (11) are respectively 0°, 90°, 180° and 270°; The first upper joint (3) is connected to the first ball seat (10) via four pins, and the distribution angles of the four pins are 45°, 135°, 225° and 315° respectively; The second upper joint (7) is connected to the second ball seat (13) via four pins, and the distribution angles of the four pins are 45°, 135°, 225° and 315° respectively; The throwing handle is connected to the third ball seat (15) via four pins, and the distribution angles of the four pins are 45°, 135°, 225° and 315° respectively.

9. A method for using a high-efficiency staged fracturing series tool string for long boreholes in underground coal mines. This method is based on the high-efficiency staged fracturing series tool string for long boreholes in underground coal mines described in claim 6, and is characterized in that, The following steps are involved: Step 0, determining all the fracturing stages that require fracturing operations within the completed borehole; Step 1, lowering the total fracturing tool string into the bottom of the borehole, and dragging the total fracturing tool string backward until the frontmost fracturing tool string reaches the first fracturing stage; Step 2, inserting a first spacer ball (16) corresponding to the frontmost fracturing tool string into the total fracturing tool string, using an external hydraulic pump to deliver high-pressure liquid into the total fracturing tool string to push the first spacer ball (16), so that the first spacer ball (16) destroys the pin of the second ball seat (13) and pushes the second ball seat (13) forward, and the whole is pushed forward to destroy the pin corresponding to the first ball seat (10), and push the first ball seat (10) to move forward; Step 3, the external hydraulic pump continues to deliver high-pressure liquid to the interior of the total fracturing tool string, so that the first expansion cylinder (4) and the second expansion cylinder (8) expand to press against the side wall of the borehole, thereby forming an annular fracturing zone between the outer wall of the connecting pipe (9) and the inner wall of the corresponding position of the borehole, and the high-pressure liquid flows out from the water outlet channel (11) to perform fracturing operations until the fracturing of the fracturing section is completed; Step 4, the external hydraulic pump stops the high-pressure liquid until the first expansion cylinder (4) and the second expansion cylinder (8) return to their original state, and determines whether the total fracturing tool string can continue to be dragged backward; If it is possible to continue dragging backward, the entire fracturing tool string is dragged until the frontmost fracturing tool string reaches the next fracturing stage and then proceeds to step 5; If it cannot be dragged backwards, the second isolation ball (17) corresponding to the frontmost fracturing tool string is put in, and a high-pressure liquid is delivered to the interior of the total fracturing tool string using an external hydraulic pump to push the second isolation ball (17), so that the second isolation ball (17) destroys the pin corresponding to the third ball seat (15), and then the frontmost fracturing tool string is disconnected from the second isolation device, and the total fracturing tool string is continued to be dragged until the next fracturing tool string reaches the next fracturing stage and then enters step 5; Step 5, repeat steps 1-4 until all the fracturing sections in the borehole are fractured.

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