Structural unit and machine tool for staged fracturing of coal seam roof and fracturing method of structural unit and machine tool

Abstract

The invention focuses on the problem of potential safety hazards caused by a hard roof during deep coal mining, provides a set of innovative scheme for staged fracturing of a coal seam roof, and covers a structural unit, a machine tool and a method. The structure unit is composed of an upper cylinder body set, a lower cylinder body set, an expandable sleeve body, a fracturing fluid injection pipe and a fracturing work assembly. An expansion cavity is formed between the fracturing fluid injection pipe and the expandable sleeve body, and expansion setting of the expandable sleeve body and opening of the fracturing working valve set are achieved through movement of the valve element under different pressures. Compared with a traditional directional long drill hole staged hydraulic fracturing technology, the packer does not need to be dragged by a continuous pipe, and the problems that the operation process is complex and the packer is prone to failure are solved. By presetting the setting pressure, the fracturing pressure and the specific pressure of the fracturing fluid, the machine tool can automatically complete the fracturing operation of each section, so that the construction efficiency is greatly improved, the labor and time cost is reduced, the safety production of a coal mine is powerfully guaranteed, and a new path is developed for the pressure relief treatment of a coal seam roof area.

Description

Technical Field

[0001] The present invention belongs to the technical field of segmented hydraulic fracturing, and particularly relates to a structural unit, a tool and a fracturing method for segmented fracturing of coal seam roof. Background Art

[0002] With the gradual depletion of shallow coal resources, coal mining has expanded to deeper areas, and the mining depth has been continuously increasing. The in-situ stress in deep strata increases, resulting in a sharp increase in the difficulty of mine disaster control. Among them, the problems of large-area suspended roof in the goaf of the working face and strong mine pressure manifestation caused by thick and hard roof are particularly serious. The hard roof is prone to cause large-area suspended roof in the working face, posing a risk of rock burst and seriously threatening the safe production of coal mines.

[0003] At present, the directional long-hole segmented hydraulic fracturing technology is an important means for pressure relief treatment in the coal seam roof area. Its principle is to construct directional long holes in the coal seam roof rock stratum and implement segmented hydraulic fracturing to increase the degree of rock fracture development and prevent roof disasters. However, this technology uses the method of dragging packers with coiled tubing for isolation and segmentation, and there are many drawbacks. On the one hand, packers are usually used in pairs and need to be dragged to the designed position by a drilling rig to achieve the setting of each fracturing section, and the operation process is complex; on the other hand, packers are prone to malfunction and failure during use. Once a problem occurs, the entire fracturing tool string must be removed from the borehole for repair and then re-lowered. This process consumes a large amount of time and manpower, seriously affecting the construction efficiency and increasing the construction cost. Therefore, it is of great significance to develop a simple, stable and reliable fracturing method and tool for segmented fracturing of coal seam roof to ensure the efficient construction of coal seam roof hydraulic fracturing. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a simple, stable and reliable structural unit, tool and method for segmented fracturing of coal seam roof, so as to solve the related problems caused by thick and hard roof in deep coal mining, overcome the drawbacks of the existing directional long-hole segmented hydraulic fracturing technology using the method of dragging packers with coiled tubing, and ensure the efficient construction of coal seam roof hydraulic fracturing.

[0005] To achieve the above purpose, the technical solution adopted is as follows:

[0006] The first aspect of the present invention discloses a structural unit for staged fracturing of a coal seam roof, comprising: an upper cylinder group; a lower cylinder group; an expandable sleeve, which is arranged and fixed between the upper cylinder group and the lower cylinder group in the axial direction; a fracturing fluid injection pipe, which passes through the interior of the upper cylinder group and the expandable sleeve in turn in the axial direction, and the lower end extends into the interior of the lower cylinder group; a gap is left between the outer wall of the fracturing fluid injection pipe and the expandable sleeve to form an expansion cavity; the expansion cavity is connected to the inner cavity of the fracturing fluid injection pipe, so that the fracturing fluid can enter the expansion cavity from the inner cavity of the fracturing fluid injection pipe; a fracturing working assembly, which comprises: a fracturing working pipe, Axially arranged behind the lower cylinder group; the seat seal valve group and the fracturing working valve group, the two are arranged in sequence in the axial direction in the fracturing working pipe, wherein the low-pressure seat seal valve group and the fracturing working valve group are constructed to be able to share the same valve core; the valve core is constructed so that under the seat seal pressure of the fracturing fluid, the valve core is located in the seat seal valve group, so that the fracturing fluid entering the expansion chamber forces the expandable casing to complete the expansion and form a seat seal; under the fracturing pressure of the fracturing fluid, the valve core can slide from the seat seal valve group into the fracturing working valve group, so that the fracturing working valve group works to open the fracturing channel; wherein the seat seal pressure of the fracturing fluid is less than the fracturing pressure.

[0007] In the present invention, the upper cylinder group, the lower cylinder group and the expandable sleeve are closely matched to build a relatively independent and complete sealing system. The expandable sleeve is axially and firmly placed between the upper and lower cylinder groups, which can not only maintain stability when subjected to the pressure of the fracturing fluid, but also lay a reliable physical foundation for the subsequent sealing and fracturing operations.

[0008] The fracturing fluid injection pipe runs through the upper cylinder group, the expandable sleeve and deep into the lower cylinder group in the axial direction, which cleverly combines the dual functions of fluid transportation and structural support. The reserved gap between its outer wall and the expandable sleeve forms an expansion cavity. By connecting the expansion cavity with the inner cavity of the fracturing fluid injection pipe, the fracturing fluid can smoothly flow into the expansion cavity under pressure and promote the expansion of the expandable sleeve. This design based on the principle of fluid mechanics greatly improves the stability and reliability of the sealing process.

[0009] The seated valve group and the fracturing working valve group of the fracturing working assembly share the same valve core. This design greatly simplifies the internal structure of the structural unit, reduces the number of components, and thus reduces the possibility of failures. When the fracturing fluid is at the seating pressure, the valve core is located in the seated valve group, and the fracturing fluid entering the expansion chamber pushes the expandable sleeve to expand, making it closely fit with the borehole wall to complete effective seating. When the pressure of the fracturing fluid rises to the fracturing pressure, the valve core slides from the seated valve group into the fracturing working valve group, prompting the fracturing working valve group to start and open the fracturing channel, realizing the orderly connection of the two key steps of seating and fracturing. This way of controlling the movement of the valve core by relying on pressure changes is simple and convenient to operate, and can accurately control the timing and scope of the fracturing operation according to actual needs, significantly improving the efficiency and quality of the fracturing operation, and providing a solid basic unit structure guarantee for staged fracturing.

[0010] According to the structural unit disclosed in the first aspect of the present invention, the upper cylinder body group includes an upper outer cylinder body and an upper inner cylinder body sleeved inside the upper outer cylinder body. The upper end of the expandable sleeve is circumferentially clamped between the upper outer cylinder body and the upper inner cylinder body to form a fixation; there is a first gap between the upper outer cylinder body and the fracturing fluid injection pipe, and a second gap between the upper inner cylinder body and the fracturing fluid injection pipe. The fracturing fluid injection pipe is provided with a fluid through hole communicating with the first gap, the second gap communicates with the first gap, and the expansion chamber communicates with the second gap.

[0011] In the present invention, the structural design of the upper cylinder body group including the upper outer cylinder body and the upper inner cylinder body not only firmly fixes the upper end of the expandable sleeve, but also constructs an effective channel for the fracturing fluid to enter the expansion chamber through the setting of the first gap, the second gap and the fluid through hole, ensuring that the fracturing fluid can smoothly push the expandable sleeve to expand, and enhancing the sealing performance and stability of the structure.

[0012] According to the structural unit disclosed in the first aspect of the present invention, the lower cylinder body group includes a lower outer cylinder body and a lower inner cylinder body sleeved inside the lower outer cylinder body. The lower end of the expandable sleeve is circumferentially clamped between the lower outer cylinder body and the lower inner cylinder body to form a fixation; the lower cylinder body group further includes a limit cylinder sleeve, which is fixedly sleeved inside the lower outer cylinder body; the lower end of the fracturing fluid injection pipe abuts against the limit cylinder sleeve to form an axial limit fit.

[0013] In the present invention, the lower outer cylinder body, the lower inner cylinder body and the limit cylinder sleeve of the lower cylinder body group work together. On the one hand, they fix the lower end of the expandable sleeve, and on the other hand, they play an axial limiting role on the fracturing fluid injection pipe, ensuring the stability and reliability of the entire structural unit during the working process and avoiding unnecessary displacement between components.

[0014] According to the structural unit disclosed in the first aspect of the present invention, the setting valve group includes: a setting valve body, which is statically held in the fracturing working pipe; a setting valve switch, which is arranged on the setting valve body and is configured to be able to limit the valve core under the setting pressure state of the fracturing fluid, and the valve core can overcome the limit of the setting valve switch and disengage from the setting valve body under the fracturing pressure state of the fracturing fluid.

[0015] In the present invention, the setting valve body and the setting valve switch of the setting valve group cooperate with each other to limit the valve core or allow the valve core to disengage under different pressure states, precisely control the action stage of the fracturing fluid, and realize the orderly conversion of setting and subsequent fracturing operations. It is one of the key control components for the smooth progress of the staged fracturing process.

[0016] According to the structural unit disclosed in the first aspect of the present invention, the fracturing working valve group includes: a fracturing working valve body, which is arranged in the fracturing working pipe in a manner that can be driven to slide; a fracturing working valve switch, which is arranged on the fracturing working valve body and is configured to be able to limit the valve core under the fracturing pressure state of the fracturing fluid, and the valve core can overcome the limit of the fracturing working valve switch and disengage from the fracturing working valve body under a specific pressure exceeding the fracturing pressure of the fracturing fluid; a valve body liquid outlet is arranged on the fracturing working valve body, and a fracturing liquid outlet is arranged on the fracturing working pipe. In the initial state, the valve body liquid outlet and the fracturing liquid outlet are misaligned and disconnected. Under the fracturing pressure state of the fracturing fluid, the valve core can drive the fracturing working valve body to slide relative to the fracturing working pipe under the limit of the fracturing working valve switch, so that the valve body liquid outlet is connected to the fracturing liquid outlet.

[0017] In the present invention, the design of the fracturing working valve body, the fracturing working valve switch, the valve body liquid outlet and the fracturing liquid outlet of the fracturing working valve group enables the valve core to drive the fracturing working valve body to slide under the fracturing pressure state, realize the connection of the liquid outlet for fracturing operations, and the valve core can disengage under a specific pressure, creating conditions for subsequent switching of fracturing sections, ensuring the efficient progress of fracturing operations and the smooth conversion of sections.

[0018] According to the structural unit disclosed in the first aspect of the present invention, both the setting valve switch and the fracturing working valve switch are spring pins, and the valve core is provided with a contact limiting portion that forms a stopping contact with the pin of the spring pin. The contact limiting portion at least includes a rear cone section that can compress the pin head by means of its own axial sliding to cause the spring pin to contract.

[0019] In the present invention, the setting valve switch and the fracturing working valve switch adopt spring pins, and the valve core is provided with a cooperating contact limiting portion, especially the rear cone section, which can effectively limit and release the valve core under different pressures. This structural design is simple and reliable, improving the control accuracy and stability of the entire structural unit.

[0020] According to the structural unit disclosed in the first aspect of the present invention, the abutting and limiting part further includes a cylindrical transition section located in front of the rear cone section in the moving direction; the valve core further includes a front cylindrical section and a front cone section located in front of the abutting and limiting part in the moving direction, wherein the front cylindrical section can form a circumferential contact with the inner wall of the fracturing working valve body, and the outer diameter of the cylindrical transition section is smaller than that of the front cylindrical section.

[0021] In the present invention, the design of the cylindrical transition section of the abutting and limiting part and the front cylindrical section and the front cone section of the valve core further optimizes the fit between the valve core and the fracturing working valve body, ensures the smoothness of the valve core during the sliding process, and the sealing performance between the valve core and the fracturing working valve body, and improves the reliability of the fracturing operation.

[0022] According to the structural unit disclosed in the first aspect of the present invention, the structural unit further includes a tail joint axially fixed to the tail end of the fracturing working pipe 8, and a compression spring capable of elastically supporting the fracturing working valve body is arranged on the tail joint; in the initial state, the fracturing working valve body abuts against the inner shoulder of the fracturing working pipe by means of the compression spring.

[0023] In the present invention, the arrangement of the tail joint and the compression spring provides elastic support for the fracturing working valve body, keeps the fracturing working valve body in a specific position in the initial state, and can play a buffering and resetting role during the fracturing process, which helps to improve the durability and working efficiency of the entire structural unit.

[0024] The second aspect of the present invention discloses a coal seam roof segmented fracturing tool, including at least two structural units disclosed in the first aspect of the present invention, and the structural units are sequentially connected axially, and all structural units share the same valve core; under a specific pressure where the fracturing fluid exceeds its fracturing pressure, the valve core can overcome the limit of the fracturing working valve group of the previous structural unit and disengage from it to enter the setting valve group of the next structural unit.

[0025] In the present invention, the coal seam roof segmented fracturing tool is formed by connecting multiple above-mentioned structural units and sharing the same valve core. This design enables the tool to be flexibly combined according to actual needs. Through the movement of the valve core between different structural units under different pressures, multi-stage continuous fracturing operations are realized, greatly improving the efficiency and adaptability of the fracturing operation.

[0026] The third aspect of the present invention discloses an automatic sectional fracturing method for coal seam roof, which uses the sectional fracturing tool for coal seam roof disclosed in the second aspect of the present invention, and includes the following steps: S1, lowering the fracturing tool into the borehole to the target position at one time; S2, injecting fracturing fluid into the fracturing fluid injection pipe under the setting pressure of the fracturing fluid, so that the expandable sleeve of the structural unit at the current position of the valve core expands and seals with the hole wall of the borehole, and the setting of the current fracturing section is completed; S3, after the expandable sleeve is completely set, changing the setting pressure of the fracturing fluid to the fracturing pressure, so that the valve core slides axially towards the fracturing working valve group and moves into the fracturing working valve body, so as to drive the fracturing working valve body to slide in the fracturing working pipe, and further make the liquid outlet of the valve body of the fracturing working valve body communicate with the fracturing liquid outlet of the fracturing working pipe, and carry out the fracturing work of the current fracturing section; S4, after the fracturing work of the current fracturing section is completed, changing the fracturing pressure of the fracturing fluid to a specific pressure, so that the valve core disengages from the fracturing working valve group of the current structural unit under the action of the specific pressure and enters the setting valve group of the next structural unit, and restoring the pressure of the fracturing fluid to the setting pressure; S5, repeating steps S2 - S4 until all sectional fracturing is completed; the setting pressure, fracturing pressure and specific pressure of the fracturing fluid can be preset, wherein the setting pressure is less than the fracturing pressure, and the fracturing pressure is less than the specific pressure.

[0027] In the present invention, the automatic sectional fracturing method for coal seam roof is based on the above-mentioned sectional fracturing tool. By presetting different pressure values and operating according to specific steps, it realizes the automatic setting and fracturing work of multiple fracturing sections after the tool is lowered into the borehole at one time. The whole process has a high degree of automation, reduces manual operation and frequent movement of equipment, reduces construction costs, and improves construction safety and efficiency.

[0028] The beneficial effects of the present invention compared with the prior art are as follows:

[0029] 1) The prior art adopts the method of dragging a packer with a coiled tubing, and it is necessary to rely on a drilling rig to drag a pair of packers to the designed position to realize the setting of each fracturing section, and the operation process is complex. In the present invention, under the setting pressure of the fracturing fluid, the expandable sleeve of the structural unit at the current position of the valve core expands and seals with the hole wall of the borehole, and the setting of the current fracturing section is completed, without complex operations such as dragging a packer with a drilling rig, greatly simplifying the construction process. During the whole automatic sectional fracturing process of the coal seam roof, only by sequentially completing steps such as setting, fracturing, and valve core switching according to the preset pressure change, the sectional fracturing can be automatically realized, significantly improving the construction efficiency.

[0030] 2) During the use of existing packers, they are prone to malfunction and failure. Once a problem occurs, the entire fracturing tool string must be removed from the borehole for repair and then re-lowered. For the structural unit and tooling for segmented fracturing of coal seam roof in the present invention, its setting and fracturing operations are achieved through the position switching of the valve core under different pressures. Key components such as the expandable sleeve body have relatively simple structures and high reliability. For example, the setting valve group and the fracturing working valve group are configured to share the same valve core. The movement of the valve core under different pressures precisely controls the setting and fracturing processes, reducing the failure points caused by complex components and improving the overall stability.

[0031] 3) Due to the complex operation and frequent failures in the prior art, when repairing, the entire fracturing tool string needs to be removed and then re-lowered, consuming a large amount of time and manpower, resulting in a significant increase in construction costs. After simplifying the operation process and improving the stability in the present invention, the input of time cost and labor cost during the construction process is reduced. After being once lowered into the borehole to the target position, the entire segmented fracturing process can be completed through preset pressure changes, without the need for frequent repairs and re-lowering of the tool string, effectively reducing the construction cost, which is of great significance for ensuring the efficient construction of hydraulic fracturing of coal seam roof.

[0032] The following discloses in detail the structural unit, tooling and its fracturing method for segmented fracturing of coal seam roof in the present invention in combination with the embodiments shown in the accompanying drawings and the reference numerals. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of a single structural unit of the present invention;

[0034] Figure 2 is Figure 1 a partial enlarged view of part A in

[0035] Figure 3 It is a schematic diagram of the overall structure of the fracturing tooling of the present invention, composed of Figure 3 a and Figure 3 b, where Figure 3 a is the upper half of the overall structure of the fracturing tooling; Figure 3 b is the lower half of the overall structure of the fracturing tooling, showing as a whole that the fracturing tooling of the present invention is axially connected by two structural units, Figure 3 a shows the view of the structural unit located in the upper section, Figure 3 b shows the view of the structural unit located in the lower section;

[0036] Figure 4 It is a schematic diagram of the fracturing tooling of the present invention in the set pressure state, composed of Figure 4 a and Figure 4 b, where Figure 4a is the upper half of the overall structure of the fracturing tool; Figure 4 b is the lower half of the overall structure of the fracturing tool;

[0037] Figure 5 This is a schematic diagram of the fracturing tool of the present invention under the fracturing pressure state, which is composed of Figure 5 a and Figure 5 b, where Figure 5 a is the upper half of the fracturing tool; Figure 5 b is the lower half of the fracturing tool;

[0038] Figure 6 This is a schematic diagram of the fracturing tool of the present invention under the pressure state in the next stage, which is composed of Figure 6 a and Figure 6 b, where Figure 6 a is the upper half of the fracturing tool; Figure 6 b is the lower half of the fracturing tool;

[0039] Figure 7 This is a schematic diagram of the fracturing tool of the present invention under the fracturing setting pressure state in the next stage, which is composed of Figure 7 a and Figure 7 b, where Figure 7 a is the upper half of the fracturing tool; Figure 7 b is the lower half of the fracturing tool;

[0040] Figure 8 This is a schematic diagram of different states of the valve core of the present invention, which is composed of Figure 8 a and Figure 8 b, where Figure 8 a shows that the valve core just enters the fracturing working valve group and the fracturing working valve sleeve has not moved yet; Figure 8 b shows the state when the valve core drives the fracturing working valve to move to the liquid outlet to form a connection;

[0041] Figure 9 This is a schematic diagram of the force state of the switch of the present invention.

[0042] Reference numerals

[0043] Fracturing fluid injection pipe 1, expandable sleeve body 2, upper outer cylinder 3, upper inner cylinder 4, lower outer cylinder 5, lower inner cylinder 6, limit cylinder sleeve 7, fracturing working pipe 8, valve core 9, setting valve body 10, setting valve switch 11, fracturing working valve body 12, fracturing working valve switch 13, valve body liquid outlet 14, fracturing liquid outlet 15, pin 16, rear cone section 17, cylindrical transition section 18, front cylindrical section 19, front cone section 20, compression spring 21. Detailed implementation manners

[0044] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other without conflict.

[0045] In the field of deep coal mining, as the mining depth increases, the management of the coal seam roof becomes a key problem. The coal seam roof staged fracturing technology provided by the present invention aims to solve the drawbacks of the traditional directional long-hole staged hydraulic fracturing technology and provide strong support for safe production. The specific implementation method of the invention will be described in detail below with reference to the accompanying drawings.

[0046] like Figure 1 and Figure 2 As shown, the present invention discloses a structural unit for staged fracturing of the coal seam roof, which comprises an upper cylinder group, a lower cylinder group, an expandable sleeve 2, a fracturing fluid injection pipe 1 and a fracturing working assembly. The upper cylinder group, the lower cylinder group and the expandable sleeve 2 are closely matched to construct a relatively independent and complete sealing system. The expandable sleeve 2 is axially and firmly placed between the upper and lower cylinder groups, which can not only maintain stability when subjected to the pressure of the fracturing fluid, but also lay a reliable physical foundation for subsequent sealing and fracturing operations.

[0047] The fracturing fluid injection pipe 1 axially passes through the upper cylinder group, the expandable sleeve 2 and penetrates into the lower cylinder group, ingeniously combining the dual functions of fluid transportation and structural support. The reserved gap between its outer wall and the expandable sleeve 2 forms an expansion cavity. By connecting the expansion cavity with the inner cavity of the fracturing fluid injection pipe 1, the fracturing fluid can smoothly flow into the expansion cavity under pressure, pushing the expandable sleeve 2 to expand. This design greatly improves the stability and reliability of the sealing process.

[0048] The seat seal valve group and the fracturing working valve group of the fracturing working assembly share the same valve core 9. Figure 2 The seat seal valve group is composed of a seat seal valve body 10 stationary in the fracturing working pipe 8 and a seat seal valve switch 11 thereon. The seat seal valve body 10 is made of high-strength stainless steel and has good corrosion resistance and mechanical strength. The seat seal valve switch 11 is a spring pin, and the end of its column pin 16 is provided with a hemispherical protrusion. The valve core 9 is provided with a stop limit portion that contacts with the spring pin column pin 16, and the surface of the rear cone section 17 of the portion is an inclined surface. During the fracturing operation, when the fracturing fluid is injected into the fracturing fluid injection pipe 1, as the pressure increases, the fracturing fluid generates a thrust on the valve core 9. Figure 9As shown, assume that the fracturing fluid pressure acting on the valve core 9 is P, the contact area between the pin 16 of the setting valve switch 11 and the valve core 9 is S, and the number of pins 16 is N. The force exerted on a single pin 16 in contact with the inclined plane in the axial direction is: F = P * S / N, where P is the fracturing fluid pressure, S is the contact area between the pin 16 and the valve core 9, and N is the number of pins 16. At this time, the setting valve switch 11 and the pin 16 can be regarded as a whole, and are subjected to the thrust of the valve core 9 and the elastic force of the compression spring 21. At the same time, the thrust exerted on a single pin 16 in the vertical direction is: F1 = F / tanθ, where F is the force exerted on the pin 16 in the axial direction, and θ is the angle between the inclined plane of the rear cone section 17 and the axial direction. At the same time, according to the principle of force action, the force F2 exerted on the valve core 9 by the setting valve switch 11 in the axial direction can be expressed as F2 = P * S. Under the setting pressure, this force keeps the valve core 9 in the current position, ensuring that the fracturing fluid entering the expansion cavity pushes the expandable sleeve 2 to expand and set. When the fracturing fluid pressure rises to the fracturing pressure, the valve core 9 overcomes the limit and disengages from the setting valve body 10, preparing for the subsequent fracturing operation.

[0049] The fracturing working valve group includes a fracturing working valve body 12 that can slide in the fracturing working pipe 8 and a fracturing working valve switch 13 thereon. The fracturing working valve switch 13 is also a spring pin. In a preferred embodiment, the fracturing working valve body 12 and the fracturing working pipe 8 are matched through a guide key and a guide groove to ensure the straightness during the sliding process.

[0050] Reference Figure 8 , Figure 8 Figure a shows the state where the valve core has just entered the fracturing working valve group and the fracturing working valve sleeve has not yet moved, which is an intuitive presentation of the initial stage when the valve core enters the fracturing working valve group. Figure 8 Figure b shows the state where the valve core drives the fracturing working valve to move to the liquid outlet to form a connection, reflecting the key action of the valve core and the fracturing working valve body cooperating with each other during the working process of the fracturing working valve group, and finally realizing the connection between the liquid outlet 14 of the valve body and the fracturing liquid outlet 15 on the fracturing working pipe 8.

[0051] When the pressure of the fracturing fluid rises to the fracturing pressure, the valve core 9 overcomes the limit of the setting valve switch 11 and disengages from the setting valve body 10. After that, the inclined surface of the valve core 9 contacts the fracturing working valve switch 13 under the action of the fracturing fluid. At this time, assuming that the contact area between the valve core 9 and the fracturing working valve switch 13 is S1, the fracturing fluid pressure P (which is the fracturing pressure at this time) acting on the valve core 9 acts on the part in contact with the fracturing working valve switch 13, generating a force F3 = P * S1 that causes the valve core 9 to push the fracturing working valve body 12. Under the fracturing pressure, the hemispherical protrusion of the fracturing working valve switch 13 abuts against the inclined surface of the rear cone section 17 of the valve core 9. This force limits the valve core 9 and drives the fracturing working valve body 12 to slide, so that the liquid outlet 14 of the valve body is changed from being misaligned and disconnected from the fracturing liquid outlet 15 on the fracturing working pipe 8 to being connected, opening the fracturing channel. When the pressure of the fracturing fluid exceeds the fracturing pressure and reaches a specific pressure, the valve core 9 overcomes the limit of the fracturing working valve switch 13 and disengages from the fracturing working valve body 12, facilitating the switching of the fracturing section.

[0052] In the embodiment of the present invention, both the setting valve switch and the fracturing working valve switch adopt spring pins, and the valve core 9 is provided with a corresponding abutting and limiting part, especially the rear cone section 17, which can effectively limit and release the valve core 9 under different pressures. This structural design is simple and reliable, improving the control accuracy and stability of the entire structural unit.

[0053] As Figure 2 shown, in order to further optimize the cooperation between the valve core 9 and the fracturing working valve body 12, the abutting and limiting part further includes a cylindrical transition section 18, and the valve core 9 further includes a front cylindrical section 19 and a front cone section 20. The front cylindrical section 19 is in circumferential contact with the inner wall of the fracturing working valve body 12, and the outer diameter of the cylindrical transition section 18 is smaller than the outer diameter of the front cylindrical section 19. This structural design can ensure the smoothness of the valve core 9 during the sliding process and the sealing performance between the valve core 9 and the fracturing working valve body 12, improving the reliability of the fracturing work.

[0054] In the present invention, the structural unit further includes a tail joint. The tail joint is axially fixed at the tail end of the fracturing working pipe 8 by threaded connection, and a sealing ring, preferably a rubber O-ring, is provided at the threaded connection to prevent the fracturing fluid from leaking from the connection part between the tail joint and the fracturing working pipe 8, ensuring the pressure stability and transmission efficiency of the fracturing fluid and avoiding the problem of poor fracturing effect caused by leakage. In addition, a compression spring 21 is arranged on the tail joint. In the initial state, the fracturing working valve body 12 abuts against the inner shoulder of the fracturing working pipe 8 by the elastic force of the compression spring 21. The compression spring 21 is made of high-strength spring steel and undergoes a special heat treatment process to improve its elasticity and fatigue life. During the fracturing process, the compression spring 21 provides elastic support, playing a buffering and resetting role, which helps to improve the durability and working efficiency of the entire structural unit.

[0055] As Figure 3As shown in the figure, the present invention also discloses a coal seam roof segmented fracturing tool, which includes at least two structural units disclosed in the present invention. The structural units are sequentially connected axially, and all structural units share the same valve core 9. From Figure 3 It can be clearly seen the connection method of each structural unit and the penetration effect of the valve core 9 therein. During the fracturing process, when the fracturing fluid pressure exceeds the fracturing pressure and reaches a specific pressure, the valve core 9 can overcome the limit of the fracturing working valve group of the previous structural unit, disengage and enter the setting valve group of the next structural unit, thereby realizing multi-stage continuous fracturing operations.

[0056] In the embodiment of the present invention, during the connection process of the structural units, special connection joints are adopted, for example, a combination of threaded connection and clamp connection is used to ensure firm connection between the structural units, and a sealing gasket is provided at the connection to prevent fracturing fluid leakage.

[0057] This design of the present invention enables the tool to flexibly combine the number of structural units according to the actual situation of the coal seam roof and adapt to different fracturing requirements. Through the movement of the valve core 9 between different structural units, the orderly progress of each segmented fracturing operation is realized, greatly improving the efficiency and adaptability of the fracturing operation.

[0058] The specific working principle of the present invention is as follows: The valve core 9 contacts the setting valve switch 11 under the action of the fracturing fluid. The setting valve switch 11 is a spring pin, and the hemispherical protrusion at the end of its pin 16 abuts against the inclined surface of the rear cone section 17 of the limit part of the valve core 9 to form a limit for the valve core 9. As the fracturing fluid enters the expansion cavity, the expandable sleeve body 2 begins to expand and fits tightly with the borehole wall to complete the setting of the first fracturing section.

[0059] Refer to Figures 4 - 7 , Figure 4 shows the situation of the fracturing tool under the setting pressure state. At this time, the valve core 9 is located in the setting valve group, and the expandable sleeve body 2 begins to expand under the action of the fracturing fluid; when the fracturing pressure is reached, the valve core 9 overcomes the limit of the setting valve switch 11 and disengages from the setting valve body 10, and the setting valve switch 11 opens. At this time, because the cross-sectional area of the fracturing fluid acting on the left side of the valve core 9 is larger than that on the right side, the axial pressure pushes the valve core 9 to move to the right.

[0060] The inclined surface of the valve core 9 contacts the fracturing working valve switch 13 under the action of the fracturing fluid. The fracturing working valve switch 13 is also a spring pin, and the hemispherical protrusion at the end of its pin 16 abuts against the inclined surface of the rear cone section 17 of the valve core 9 to limit the valve core 9 and drive the fracturing working valve body 12 to move to the right. Figure 5It shows that under the fracturing pressure condition, the valve core 9 drives the fracturing working valve body 12 to slide, the liquid outlet 14 of the valve body is communicated with the fracturing liquid outlet 15 of the fracturing working pipe 8, and the high-pressure fracturing fluid is injected into the roof rock formation from the fracturing liquid outlet 15 to start the hydraulic fracturing of the first stage. As the fracturing fluid is continuously injected, the water pressure of the rock formation rises. After it is greater than the fracture pressure of the rock formation, the elastic residual energy of the rock formation is released, generating a new fracture network.

[0061] When the pressure of the high-pressure fracturing fluid reaches the set value, the fracturing working valve switch 13 is opened, the valve core 9 overcomes the limit and disengages from the fracturing working valve body 12, and the fracturing working valve body 12 returns to the initial position under the action of the compression spring 21, and the first-stage fracturing construction is completed. Figure 6 It shows that the next stage enters the pressure state, and the valve core 9 is ready to disengage from the fracturing working valve group of the current structural unit; Figure 7 It shows the next-stage fracturing setting pressure state, and the valve core 9 enters the setting valve group of the next structural unit and is ready to start the operation of a new fracturing stage.

[0062] After the first-stage fracturing is completed, the pressure of the fracturing fluid is changed to a specific pressure. Under the action of this pressure, the valve core 9 disengages from the fracturing working valve group of the current structural unit and enters the setting valve group of the next structural unit. Subsequently, the pressure of the fracturing fluid is restored to the setting pressure, and the next stage starts to enter the setting pressure state. Repeat the above processes of setting, fracturing, and switching to realize the staged hydraulic fracturing of the coal seam roof.

[0063] Based on the above structure, such a technical effect can be achieved: The staged fracturing tool designed by the present invention is composed of multiple independent structural units, and its characteristic is that it can flexibly adjust the number of connected structural units according to the actual number of fracturing stages required to adapt to different fracturing operation requirements. And the design of the setting valve switch 11, the fracturing working valve switch 13, the fracturing working valve body 12 and the valve core 9 is adopted to realize the automatic control of the fracturing position. The entire fracturing tool string is lowered once, without the need to be dragged by a drilling rig, which simplifies the operation process, reduces the dependence on the drilling rig, reduces the repeated operations caused by packer failures, greatly saves time and labor costs, can effectively improve the construction efficiency and reduce the risk of frequent operations, and has broad application prospects.

[0064] As Figures 4 - 7 shown, the present invention also discloses a method for automatically staged fracturing of a coal seam roof, which uses the above-disclosed staged fracturing tool for a coal seam roof and includes the following steps:

[0065] S1, Lower the fracturing tool into the borehole to the target position in one go: In actual operation, use a dedicated downhole drilling rig to accurately send the fracturing tool into the borehole. During the sending process, it is necessary to precisely measure and control the depth, angle, and verticality of the borehole to ensure that the fracturing tool can reach the predetermined target position. At the same time, to prevent the fracturing tool from being damaged during the downward movement, a protective device is installed on its surface, for example, using a rubber sheath to wrap the key components.

[0066] S2, Inject fracturing fluid into the fracturing fluid injection pipe 1 under the setting pressure of the fracturing fluid: At this time, the expandable sleeve body 2 of the structural unit at the current position of the valve core 9 expands and seals with the borehole wall, completing the setting of the current fracturing section. During the injection of the fracturing fluid, it is necessary to precisely control the pressure and flow rate of the fracturing fluid, and monitor and adjust them in real time through a pressure sensor and a flow control valve to ensure that the expandable sleeve body 2 can expand evenly and stably and form a good seal with the borehole wall.

[0067] S3, After the expandable sleeve body 2 is fully set, change the setting pressure of the fracturing fluid to the fracturing pressure: At this time, the valve core 9 slides axially towards the fracturing working valve group and moves into the fracturing working valve body 12, driving the fracturing working valve body 12 to slide in the fracturing working pipe 8, and then enabling the valve body liquid outlet 14 of the fracturing working valve body 12 to communicate with the fracturing liquid outlet 15 of the fracturing working pipe 8 to carry out the fracturing work of the current fracturing section. During this process, closely monitor the change of the fracturing pressure and adjust it according to the actual situation of the coal seam roof to ensure that the fracturing effect meets the expectations.

[0068] S4, After the fracturing work of the current fracturing section is completed, change the fracturing pressure of the fracturing fluid to a specific pressure: Under the action of the specific pressure, the valve core 9 disengages from the fracturing working valve group of the current structural unit, enters the setting valve group of the next structural unit, and restores the pressure of the fracturing fluid to the setting pressure. This process realizes the automatic switching of staged fracturing, reduces manual intervention, and improves the automation level and efficiency of the construction. During the switching process, ensure that the valve core 9 can disengage and enter smoothly to avoid jamming or misoperation.

[0069] S5, Repeat steps S2 - S4 until all staged fracturing is completed: The setting pressure, fracturing pressure, and specific pressure of the fracturing fluid can be preset, where the setting pressure is less than the fracturing pressure, and the fracturing pressure is less than the specific pressure. The entire process has a high degree of automation, reduces manual operation and frequent movement of equipment, reduces construction costs, and improves construction safety and efficiency. During the entire fracturing process, all links should be monitored and recorded in real time, including pressure changes, flow data, fracturing effects, etc., so as to promptly discover problems and make adjustments.

[0070] The present invention effectively solves the problem of segmented fracturing of the coal seam roof in deep coal mining through unique structural unit design, reasonable machine combination, and automated fracturing method, overcomes the drawbacks of traditional technologies, and provides reliable technical support for the efficient construction of hydraulic fracturing of the coal seam roof.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A structural unit for staged fracturing of coal seam roof, characterized in that Comprising: Upper cylinder block group; Lower cylinder block group; An expandable sleeve body, which is arranged and fixed between the upper cylinder block group and the lower cylinder block group in the axial direction; A fracturing fluid injection pipe, which axially passes through the inside of the upper cylinder block group and the expandable sleeve body in sequence, and its lower end extends into the inside of the lower cylinder block group; there is a gap between the outer wall of the fracturing fluid injection pipe and the expandable sleeve body to form an expansion cavity; the expansion cavity is communicated with the inner cavity of the fracturing fluid injection pipe so that the fracturing fluid can enter the expansion cavity from the inner cavity of the fracturing fluid injection pipe; A fracturing working assembly, which includes: A fracturing working pipe, which is axially arranged behind the lower cylinder block group; A setting valve group and a fracturing working valve group, which are sequentially arranged in the fracturing working pipe in the axial direction, and the low-pressure setting valve group and the fracturing working valve group are configured to share the same valve core; The valve core is configured such that, under the setting pressure of the fracturing fluid, the valve core is located in the setting valve group, so that the fracturing fluid entering the expansion cavity forces the expandable sleeve body to complete expansion to form a seal; under the fracturing pressure of the fracturing fluid, the valve core can slide from the setting valve group into the fracturing working valve group, enabling the fracturing working valve group to work to open the fracturing channel; wherein, the setting pressure of the fracturing fluid is less than the fracturing pressure.

2. The structural unit for staged fracturing of coal seam roof according to claim 1, wherein The upper cylinder block group includes an upper outer cylinder block and an upper inner cylinder block sleeved inside the upper outer cylinder block, and the upper end of the expandable sleeve body is circumferentially clamped between the upper outer cylinder block and the upper inner cylinder block to form a fixation; There is a first gap between the upper outer cylinder block and the fracturing fluid injection pipe, and a second gap between the upper inner cylinder block and the fracturing fluid injection pipe. A fluid through hole communicated with the first gap is provided on the fracturing fluid injection pipe, the second gap is communicated with the first gap, and the expansion cavity is communicated with the second gap.

3. The structural unit for staged fracturing of coal seam roof according to claim 1, characterized in that, The lower cylinder block group includes a lower outer cylinder block and a lower inner cylinder block sleeved inside the lower outer cylinder block, and the lower end of the expandable sleeve body is circumferentially clamped between the lower outer cylinder block and the lower inner cylinder block to form a fixation; The lower cylinder block group further includes a limiting cylinder sleeve, which is sleeved and fixed inside the lower outer cylinder block; the lower end of the fracturing fluid injection pipe abuts against the limiting cylinder sleeve to form an axial limiting fit.

4. The structural unit for staged fracturing of coal seam roof according to any one of claims 1-3, characterized in that, The setting valve group includes: A setting valve body, which remains stationary in the fracturing working pipe; A setting valve switch, which is arranged on the setting valve body and is configured to be able to limit the valve core under the setting pressure state of the fracturing fluid, and the valve core can overcome the limit of the setting valve switch and disengage from the setting valve body under the fracturing pressure state of the fracturing fluid.

5. The structural unit for staged fracturing of coal seam roof according to claim 4, characterized in that, The fracturing working valve group includes: A fracturing working valve body, which is arranged in the fracturing working pipe in a manner that can be driven to slide; A fracturing working valve switch, which is arranged on the fracturing working valve body and is configured to be able to limit the valve core under the fracturing pressure state of the fracturing fluid, and the valve core can overcome the limit of the fracturing working valve switch and disengage from the fracturing working valve body under a specific pressure of the fracturing fluid exceeding the fracturing pressure; The fracturing working valve body is provided with a valve body liquid outlet, and the fracturing working pipe is provided with a fracturing liquid outlet. In the initial state, the valve body liquid outlet and the fracturing liquid outlet are misaligned and disconnected. Under the fracturing pressure of the fracturing fluid, the valve core can drive the fracturing working valve body to slide relative to the fracturing working pipe under the limit of the fracturing working valve switch, so that the valve body liquid outlet is communicated with the fracturing liquid outlet.

6. The structural unit for staged fracturing of coal seam roof according to claim 5, characterized in that, Both the setting valve switch and the fracturing working valve switch are spring pins. The valve core is provided with an abutting limit portion that forms an abutting contact with the pin of the spring pin. The abutting limit portion at least includes a rear cone section that can compress the pin head by means of its own axial sliding to make the spring pin contract.

7. The structural unit for staged fracturing of coal seam roof according to claim 6, characterized in that, The abutting limit portion further includes a cylindrical transition section located in front of the rear cone section in the moving direction; The valve core further includes a front cylindrical section and a front cone section located in front of the abutting limit portion in the moving direction. Among them, the front cylindrical section can form a circumferential contact with the inner wall of the fracturing working valve body, and the outer diameter of the cylindrical transition section is smaller than the outer diameter of the front cylindrical section.

8. The structural unit for staged fracturing of coal seam roof according to claim 5, characterized in that, The structural unit further includes a tail joint axially fixed to the tail end of the fracturing working pipe, and a compression spring capable of elastically supporting the fracturing working valve body is arranged on the tail joint; In the initial state, the fracturing working valve body abuts against the inner shoulder of the fracturing working pipe by means of the compression spring.

9. A sectional fracturing tool for coal seam roof, characterized in that, It includes at least two structural units according to any one of claims 1-8. The structural units are sequentially connected axially, and all structural units share the same valve core; Under a specific pressure where the fracturing fluid exceeds its fracturing pressure, the valve core can overcome the limit of the fracturing working valve group of the previous structural unit and disengage from it to enter the setting valve group of the next structural unit.

10. An automatic sectional fracturing method for coal seam roof, characterized in that, The use of the coal seam roof sectional fracturing tool according to claim 9 includes the following steps: S1, Lower the fracturing tool into the borehole to the target position at one time; S2, Inject fracturing fluid into the fracturing fluid injection pipe under the setting pressure of the fracturing fluid, so that the expandable sleeve body of the structural unit where the valve core is currently located expands and seals with the borehole wall to complete the setting of the current fracturing section; S3, After the expandable sleeve body is completely set, change the setting pressure of the fracturing fluid to the fracturing pressure, so that the valve core slides axially towards the fracturing working valve group and moves into the fracturing working valve body, so as to drive the fracturing working valve body to slide in the fracturing working pipe, and then make the valve body liquid outlet of the fracturing working valve body communicate with the fracturing liquid outlet of the fracturing working pipe to perform the fracturing work of the current fracturing section; S4, After the fracturing work of the current fracturing section is completed, change the fracturing pressure of the fracturing fluid to a specific pressure, so that the valve core disengages from the fracturing working valve group of the current structural unit under the action of the specific pressure and enters the setting valve group of the next structural unit, and restore the pressure of the fracturing fluid to the setting pressure; S5, Repeat steps S2-S4 until all sectional fracturing is completed; The setting pressure, fracturing pressure and specific pressure of the fracturing fluid can be preset, where the setting pressure is less than the fracturing pressure, and the fracturing pressure is less than the specific pressure.

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