Double-layer packer for coal mine hydraulic fracturing and testing method thereof
By designing a double-layer packer for hydraulic fracturing in coal mines, which utilizes fracturing fluid to cause the expansion chamber to expand sequentially in a double-layer structure, the problem of wear on the rubber surface of the packer was solved, achieving efficient sealing and cost reduction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CCTEG COAL MINING RES INST
- Filing Date
- 2025-12-30
- Publication Date
- 2026-05-08
AI Technical Summary
The rubber surface of existing hydraulic fracturing and sealing tools in coal mines is easily worn, resulting in a low success rate of directional long borehole segmented fracturing. Frequent tool replacements lead to low construction efficiency and increased material costs.
A double-layer packer for hydraulic fracturing in coal mines is designed, comprising a central inner tube and first and second elastic cylinders sleeved on its outer side. The expansion chamber is expanded sequentially by fracturing fluid. The first elastic cylinder, as the inner layer, can still maintain pressure when the outer layer wears down. The outer layer passively expands to achieve sealing. The controllability is enhanced by combining it with a metal mesh structure.
It improved the success rate of borehole sealing and pressure maintenance, reduced the material cost of fracturing projects, improved construction efficiency, and ensured the success rate of segmented fracturing of long boreholes.
Smart Images
Figure CN121993082A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of hydraulic fracturing control technology in coal mines, and in particular to a double-layer packer for hydraulic fracturing in coal mines and its testing method. Background Technology
[0002] Hydraulic fracturing technology for controlling severe rock pressure in coal mines, including direct and directional drilling, has been widely applied. Currently, the sealing tools used in coal mine fracturing are based on the single-layer structure of sealing devices used in casing fracturing in the petroleum industry. However, the rubber surface of these sealing tools is easily worn and prone to localized cracking, which cannot guarantee the success rate of segmented fracturing in long directional boreholes. Furthermore, frequent replacement of sealing tools leads to low construction efficiency and increased material costs. Summary of the Invention
[0003] This disclosure aims to at least partially address one of the technical problems in the related art.
[0004] Therefore, the purpose of this disclosure is to provide a double-layer packer for hydraulic fracturing in coal mines and a testing method thereof.
[0005] To achieve the above objectives, the first aspect of this disclosure provides a double-layer packer for hydraulic fracturing in coal mines, comprising: a central inner tube, the central inner tube extending axially and having at least one water passage hole extending radially through the central inner tube; a first elastic cylinder, the first elastic cylinder being sleeved on the central inner tube and forming a first expansion cavity on the outside of the central inner tube, and the water passage hole being located within the first expansion cavity; and a second elastic cylinder, the second elastic cylinder being sleeved on the central inner tube and forming a second expansion cavity on the outside of the central inner tube, and the first expansion cavity being located within the second expansion cavity, the cylinder body of the second elastic cylinder being provided with a metal mesh; wherein, when fracturing fluid is introduced into the central inner tube, the first expansion cavity and the second expansion cavity expand sequentially, and the first elastic cylinder and the second elastic cylinder sequentially press against the inner wall of the rock borehole.
[0006] Optionally, the first end of the first elastic cylinder is fixedly sleeved on the central inner tube, and the second end of the first elastic cylinder is slidably and sealingly sleeved on the central inner tube, wherein the water passage hole is located between the first end and the second end of the first elastic cylinder.
[0007] Optionally, the double-layer packer further includes: a first sealing gasket, which is disposed at the second end of the first elastic cylinder and is slidably sleeved on the central inner tube.
[0008] Optionally, the first end of the second elastic cylinder is fixedly sleeved on the central inner tube, and the second end of the second elastic cylinder is slidably and sealingly sleeved on the central inner tube, wherein the first elastic cylinder is located between the first end and the second end of the second elastic cylinder.
[0009] Optionally, the double-layer packer further includes a second sealing gasket, which is disposed at the second end of the second elastic cylinder and is slidably sleeved on the central inner tube.
[0010] Optionally, the double packer further includes a first connector, which is disposed at the first end of the central inner tube and is used to be threadedly connected to the constant pressure opener.
[0011] Optionally, the double packer further includes a second connector, which is disposed at the second end of the central inner tube and is used for threaded connection with the fracturing string.
[0012] Optionally, at least one of the water passages includes: a first water passage, which is disposed on the central inner tube and arranged radially along the central inner tube, and is located within the first expansion cavity; and a second water passage, which is disposed on the central inner tube and arranged radially along the central inner tube, and is located within the first expansion cavity; wherein the first water passage and the second water passage are spaced apart along the axial direction of the central inner tube.
[0013] The second aspect of this disclosure provides a testing method for a double-layer packer for hydraulic fracturing in coal mines, as provided in the first aspect of this disclosure, comprising: S1: connecting the first end of the central inner tube of the double-layer packer to an oil injection device and sealing the second end of the central inner tube; S2: placing the sealed double-layer packer in a test pipeline, wherein the end of the test pipeline near the second end of the central inner tube is a closed structure, and the end of the test pipeline near the first end of the central inner tube is an open structure; S3: starting the oil injection device and controlling the oil injection device to inject oil with progressively increasing pressure into the central inner tube along a preset time line, wherein each pressure level is maintained for a preset duration; S4: recording the pressure and time curves of the double-layer packer and judging the quality of the double-layer packer based on the recorded pressure and time curves.
[0014] Optionally, the test method further includes: cutting a slit of a preset length on the second elastic cylinder of the double packer; repeating steps S1 to S4.
[0015] The technical solution provided in this disclosure may include the following beneficial effects: When the outer second elastic cylinder experiences wear, tear, and leakage, the inner first elastic cylinder can still maintain pressure and expand. The outer second elastic cylinder passively expands to achieve normal hole sealing, avoiding frequent packer replacements due to packer failure during long-drilled segmented fracturing processes. This not only ensures the success rate of hole sealing and pressure maintenance and improves construction efficiency, but also effectively reduces the material costs of fracturing projects.
[0016] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description
[0017] The above and / or additional aspects and advantages of this disclosure will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, in which: Figure 1 This is a schematic diagram of the structure of a double-layer packer for hydraulic fracturing in coal mines according to an embodiment of this disclosure; Figure 2 This is a schematic diagram of the structure of a double-layer packer for hydraulic fracturing in coal mines during testing, according to an embodiment of this disclosure. As shown in the figure: 1. Central inner tube, 11. First water passage hole, 12. Second water passage hole; 2. First elastic cylinder; 3. Second elastic cylinder; 4. First sealing gasket; 5. Second sealing gasket; 6. First connector; 7. Second connector. 100. Oil injection device; 200. Test pipeline; 300. Plug. Detailed Implementation
[0018] Embodiments of this disclosure are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are used only to explain this disclosure, and should not be construed as limiting this disclosure. Rather, embodiments of this disclosure include all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.
[0019] like Figure 1 and Figure 2As shown in the figure, this disclosure proposes a double-layer packer for hydraulic fracturing in coal mines, comprising: a central inner tube 1, a first elastic cylinder 2, and a second elastic cylinder 3. The central inner tube 1 extends axially and has at least one water passage hole extending radially through it. The first elastic cylinder 2 is sleeved on the central inner tube 1, forming a first expansion cavity on the outside of the central inner tube 1, with the water passage hole located within the first expansion cavity. The second elastic cylinder 3 is sleeved on the central inner tube 1, forming a second expansion cavity on the outside of the central inner tube 1, with the first expansion cavity located within the second expansion cavity. The cylinder body of the second elastic cylinder 3 is provided with a metal mesh. When fracturing fluid is introduced into the central inner tube 1, the first and second expansion cavities expand sequentially, and the first and second elastic cylinders 2 and 3 press against the inner wall of the borehole sequentially.
[0020] It is understandable that, since the first elastic cylinder 2 is sleeved on the central inner tube 1 and forms a first expansion cavity on the outside of the central inner tube 1, and the water passage is located inside the first expansion cavity, when fracturing fluid is introduced into the central inner tube 1, the first expansion cavity can expand outward under the action of the fracturing fluid. Furthermore, since the second elastic cylinder 3 is sleeved on the central inner tube 1 and forms a second expansion cavity on the outside of the central inner tube 1, and the first expansion cavity is located inside the second expansion cavity, when the first expansion cavity expands outward, the second expansion cavity can expand outward under the action of the first expansion cavity. Thus, when the double-layer packer is placed on the inner wall of the borehole and fracturing fluid is introduced, the sequential expansion of the first expansion cavity and the second expansion cavity can be used to press the first elastic cylinder 2 and the second elastic cylinder 3 against the inner wall of the borehole in sequence, thereby achieving the sealing and blocking of the borehole.
[0021] In addition, by utilizing the metal mesh structure of the second elastic cylinder 3, the outer layer of the double-layer packer can achieve a controllable structure for plastic expansion and pressure maintenance. Furthermore, when the outer second elastic cylinder 3 experiences wear, rupture, and leakage, the inner first elastic cylinder 2 can still maintain pressure and expand. The outer second elastic cylinder 3 passively expands to achieve normal hole sealing, avoiding frequent packer replacements due to packer failure during long-drilled segmented fracturing processes. This not only ensures the success rate of hole sealing and pressure maintenance and improves construction efficiency, but also effectively reduces the material costs of fracturing projects.
[0022] It should be noted that the central inner tube 1 is used for the introduction of external fracturing fluid into the rock borehole, and for the discharge of fracturing fluid from the rock borehole during depressurization. The specific type of the central inner tube 1 can be set according to actual needs and there are no restrictions on it. For example, the central inner tube 1 can be a galvanized thick-walled steel pipe with a wall thickness of 6mm or more, which can prevent corrosion from mine water.
[0023] The water passage of the central inner tube 1 is used for the fracturing fluid to flow into the first expansion chamber when pressurized, and for the fracturing fluid to flow out of the first expansion chamber when depressurized.
[0024] The first elastic cylinder 2 serves as the inner structure of the double-layer packer, used to generate a force that presses against the inner wall of the rock borehole under the action of fracturing fluid. The specific type of the first elastic cylinder 2 can be set according to actual needs and is not limited thereto. For example, the first elastic cylinder 2 can be a cylindrical structure made of wear-resistant rubber.
[0025] The second elastic cylinder 3, as the outer structure of the double-layer packer, is used to contact the inner wall of the rock borehole and mainly bears the friction of the inner wall of the rock borehole. The specific type of the second elastic cylinder 3 can be set according to actual needs and is not limited thereto. For example, the second elastic cylinder 3 can be a cylindrical structure made of wear-resistant rubber, and double-layer steel wires are wound and arranged to form a metal mesh, which is bonded to the rubber, so that the second elastic cylinder 3 forms a cylindrical structure with controllable expansion.
[0026] The plastic expansion rate of the second elastic cylinder 3 is controlled within 1.2 times the outer diameter of the double packer.
[0027] like Figure 1 and Figure 2 As shown, in some embodiments, the first end of the first elastic cylinder 2 is fixedly sleeved on the central inner tube 1, and the second end of the first elastic cylinder 2 is sealed and slidably sleeved on the central inner tube 1, wherein the water passage hole is located between the first end and the second end of the first elastic cylinder 2.
[0028] It is understandable that, since the first end of the first elastic cylinder 2 is fixedly sleeved on the central inner tube 1, and the second end of the first elastic cylinder 2 is sealed and slidably sleeved on the central inner tube 1, the first elastic cylinder 2 can be stably arranged on the central inner tube 1 by means of the fixed setting of the first end, and at the same time, the sliding arrangement of the second end facilitates the expansion action of the first expansion chamber.
[0029] It should be noted that the first end of the first elastic cylinder 2 can be set close to the first end of the central inner tube 1, and conversely, the second end of the first elastic cylinder 2 can be set close to the second end of the central inner tube 1.
[0030] like Figure 1 As shown, in some embodiments, the double packer further includes a first sealing gasket 4, which is disposed at the second end of the first elastic cylinder 2 and is slidably sleeved on the central inner tube 1.
[0031] It is understandable that, since the first sealing gasket 4 is located at the second end of the first elastic cylinder 2 and is slidably sleeved on the central inner tube 1, the second end of the first elastic cylinder 2 can be slidably arranged on the central inner tube 1, while the first sealing gasket 4 can be used to achieve sealing, thereby preventing the leakage of fracturing fluid at the second end of the first elastic cylinder 2, and thus ensuring the stable sealing of the double packer in the rock borehole.
[0032] It should be noted that the first sealing gasket 4 is used for sliding sealing of the second end of the first elastic cylinder 2 on the central inner tube 1. The specific type of the first sealing gasket 4 can be set according to actual needs and there are no restrictions on it.
[0033] like Figure 1 and Figure 2 As shown, in some embodiments, the first end of the second elastic cylinder 3 is fixedly sleeved on the central inner tube 1, and the second end of the second elastic cylinder 3 is sealed and slidably sleeved on the central inner tube 1, wherein the first elastic cylinder 2 is located between the first end and the second end of the second elastic cylinder 3.
[0034] It is understandable that, since the first end of the second elastic cylinder 3 is fixedly sleeved on the central inner tube 1, and the second end of the second elastic cylinder 3 is sealed and slidably sleeved on the central inner tube 1, the second elastic cylinder 3 can be stably arranged on the central inner tube 1 by means of the fixed setting of the first end, and at the same time, the sliding arrangement of the second end facilitates the expansion action of the second expansion chamber.
[0035] It should be noted that the first end of the second elastic cylinder 3 can be set close to the first end of the central inner tube 1, and conversely, the second end of the second elastic cylinder 3 can be set close to the second end of the central inner tube 1.
[0036] like Figure 1 As shown, in some embodiments, the double packer further includes a second sealing gasket 5, which is disposed at the second end of the second elastic cylinder 3 and is slidably sleeved on the central inner tube 1.
[0037] It is understandable that, since the second sealing gasket 5 is located at the second end of the second elastic cylinder 3 and is slidably sleeved on the central inner tube 1, the second end of the second elastic cylinder 3 can be slidably arranged on the central inner tube 1, while the second sealing gasket 5 can be used to achieve sealing, thereby preventing the leakage of fracturing fluid at the second end of the second elastic cylinder 3, and thus ensuring the stable sealing of the double packer in the rock borehole.
[0038] It should be noted that the second sealing gasket 5 is used for sliding sealing of the second end of the second elastic cylinder 3 on the central inner tube 1. The specific type of the second sealing gasket 5 can be set according to actual needs, and there are no restrictions on it.
[0039] like Figure 1 and Figure 2 As shown, in some embodiments, the double packer further includes a first connector 6, which is disposed at the first end of the central inner tube 1 and is used to be threadedly connected to the constant pressure opener.
[0040] It is understandable that, based on the first connector 6 at the first end of the central inner tube 1, the double packer can be threadedly connected to the constant pressure opener using the first connector 6, thereby facilitating the use of the constant pressure opener for fracturing operations in the rock borehole.
[0041] It should be noted that the first connector 6 is located at the first end of the central inner tube 1 and is used to connect the constant pressure opener. The specific type of the first connector 6 can be set according to actual needs and there is no restriction on it. For example, the first connector 6 can be set as an internal thread to adapt to the external thread of the constant pressure opener.
[0042] A constant pressure opener, also known as a constant pressure slide valve, can be used for the on / off control of fracturing channels. The specific type of constant pressure opener can be set according to actual needs, and there are no restrictions on it.
[0043] like Figure 1 and Figure 2 As shown, in some embodiments, the double packer further includes a second connector 7, which is disposed at the second end of the central inner tube 1 and is used to be threadedly connected to the fracturing tubing.
[0044] It is understandable that, based on the second connector 7 at the second end of the central inner tube 1, the double packer can be connected to the fracturing string via the second connector 7, thereby facilitating fracturing operations in the borehole in conjunction with the fracturing string.
[0045] It should be noted that the second connector 7 is located at the second end of the central inner tube 1 and is used to connect the fracturing string. The specific type of the second connector 7 can be set according to actual needs and there is no restriction on it. For example, the second connector 7 can be set as an external thread to adapt to the internal thread of the fracturing string.
[0046] The fracturing string, as the core tool string for fracturing operations, connects various functional components and is lowered into the well to a predetermined position to form a fracturing fluid channel. The specific type of fracturing string can be set according to actual needs and there are no restrictions on it.
[0047] like Figure 1 As shown, in some embodiments, at least one water passage includes: a first water passage 11 and a second water passage 12. The first water passage 11 is disposed on the central inner tube 1 and arranged radially along the central inner tube 1, and is located within the first expansion cavity. The second water passage 12 is disposed on the central inner tube 1 and arranged radially along the central inner tube 1, and is located within the first expansion cavity. The first water passage 11 and the second water passage 12 are spaced apart along the axial direction of the central inner tube 1.
[0048] It is understandable that, since the first water passage 11 and the second water passage 12 are respectively arranged on the central inner tube 1 and arranged radially along the central inner tube 1, and the first water passage 11 and the second water passage 12 are respectively located in the first expansion cavity and distributed axially along the central inner tube 1, the fracturing fluid can flow into the first expansion cavity through the first water passage 11 and the second water passage 12 when pressurized, thereby achieving the sealing and blocking of the rock hole, and when the fracturing fluid is depressurized, it can flow out of the first expansion cavity through the first water passage 11 and the second water passage 12, thereby achieving the release and unloading of the double packer.
[0049] It should be noted that, in specific fracturing operations, the double-layer packer in this embodiment is used as follows: Before sending the double packer into the rock borehole, measure the inner diameter of the fracturing borehole to ensure that the difference between the diameter of the double packer and the diameter of the rock borehole is within the range of 10mm-20mm. When the double packer is sent into the borehole, the two ends are connected to the fracturing string and the constant pressure opener respectively using the first connector 6 and the second connector 7 to form a fracturing tool string. When the double packer is working, high-pressure water flows into the central inner tube 1, enters the first expansion chamber through the first water passage 11 and the second water passage 12, and the first elastic cylinder 2 expands rapidly, pushing the second elastic cylinder 3 to expand until it contacts the inner wall of the rock hole and then squeezes and seals it. When fracturing in a borehole segment, two double-layer packers are used, with a constant pressure switch connected between the two double-layer packers. The front and rear double-layer packers expand simultaneously to form a sealed space, continuously increasing the pressure to cause the rock strata to crack.
[0050] After the pump is stopped during fracturing, the high-pressure water in the first expansion chamber of the double packer flows back into the central inner tube 1 through the first water inlet 11 and the second water inlet 12, and then flows into the fracturing tubing and pipeline.
[0051] In summary, the double-layer packer in this embodiment can ensure the success rate of borehole sealing in rock formations and the effect of hydraulic fracturing in rock formations, improve the efficiency of borehole segmented fracturing construction, and reduce the cost of materials consumed in the project.
[0052] like Figure 2 As shown in the embodiments of this disclosure, a test method for a double-layer packer for hydraulic fracturing in coal mines, as described in the embodiments of this disclosure, is also proposed, including: S1: Connect the first end of the central inner tube 1 of the double packer to the oil injection device 100, and seal the second end of the central inner tube 1; S2: The sealed double packer is placed in the test pipe 200, wherein the end of the test pipe 200 near the second end of the central inner tube 1 is a closed structure, and the end of the test pipe 200 near the first end of the central inner tube 1 is an open structure. S3: Start the oil injection device 100 and control the oil injection device 100 to inject oil with increasing pressure in stages into the central inner tube 1 along a preset time line, and maintain each pressure for a preset duration. S4: Record the pressure and time curves of the double packer, and judge the quality of the double packer based on the recorded pressure and time curves.
[0053] Understandably, the sealed double packer is placed in the test pipeline 200 and oil is injected using the oil injection device 100 to simulate the actual operating state of the double packer. During the simulation, the pressure and time curves of the double packer are generated, and the quality of the double packer is judged based on the recorded pressure and time curves, thus realizing the pressure resistance and sealing test of the double packer.
[0054] It should be noted that the test pipeline 200 is used to simulate the rock borehole environment, while the oil injection device 100 is used to simulate the fracturing fluid injection during the operation of the double packer.
[0055] For example, the second connector 7 at the second end of the central inner tube 1 is sealed with a plug 300 to prevent the central inner tube 1 of the double packer from depressurizing. In addition, the first end of the central inner tube 1 is connected to the high-pressure oil pipe of the oil injection device 100 through an adapter, wherein the high-pressure oil pipe is connected to the high-pressure oil pump of the oil injection device 100.
[0056] The test pipe 200 is made of galvanized steel pipe, with the first end open and the second end sealed by welding steel discs. The inner diameter of the steel pipe is 20mm larger than the outer diameter of the double packer, and the wall thickness of the steel pipe is not less than 8mm.
[0057] During the oil injection process of the oil injection device 100, seven pressure levels can be set, with each level increasing the oil pressure by 10 MPa, holding the pressure for 10 minutes (preset duration), and the maximum test pressure being 70 MPa.
[0058] In some embodiments, the testing method further includes: A slit of a predetermined length is cut into the second elastic cylinder 3 of the double packer; Repeat steps S1 to S4.
[0059] It is understandable that the second elastic cylinder 3 of the double packer is cut to simulate the failure condition of the double packer in the rock borehole, so as to ensure the comprehensiveness and accuracy of the test.
[0060] For example, the gap length is no more than 20mm.
[0061] It should be noted that in the description of this disclosure, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this disclosure, unless otherwise stated, "a plurality of" means two or more.
[0062] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of preferred embodiments of this disclosure includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the function involved, as will be understood by those skilled in the art to which embodiments of this disclosure pertain.
[0063] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0064] Although embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.
Claims
1. A double-layer packer for hydraulic fracturing in coal mines, characterized in that, include: A central inner tube, which extends axially and is provided with at least one water passage hole extending radially through the central inner tube. A first elastic cylinder is sleeved on the central inner tube and forms a first expansion cavity on the outside of the central inner tube, and the water passage is located inside the first expansion cavity. The second elastic cylinder is sleeved on the central inner tube and forms a second expansion cavity on the outside of the central inner tube, and the first expansion cavity is located inside the second expansion cavity. The cylinder body of the second elastic cylinder is provided with a metal mesh. When fracturing fluid is introduced into the central inner tube, the first expansion chamber and the second expansion chamber expand in sequence, and the first elastic cylinder and the second elastic cylinder press against the inner wall of the rock borehole in sequence.
2. The double-layer packer for hydraulic fracturing in coal mines according to claim 1, characterized in that, The first end of the first elastic cylinder is fixedly sleeved on the central inner tube, and the second end of the first elastic cylinder is sealed and slidably sleeved on the central inner tube, wherein the water passage hole is located between the first end and the second end of the first elastic cylinder.
3. The double-layer packer for hydraulic fracturing in coal mines according to claim 2, characterized in that, The double packer also includes: A first sealing gasket is disposed at the second end of the first elastic cylinder and is slidably sleeved on the central inner tube.
4. The double-layer packer for hydraulic fracturing in coal mines according to claim 1, characterized in that, The first end of the second elastic cylinder is fixedly sleeved on the central inner tube, and the second end of the second elastic cylinder is sealed and slidably sleeved on the central inner tube, wherein the first elastic cylinder is located between the first end and the second end of the second elastic cylinder.
5. The double-layer packer for hydraulic fracturing in coal mines according to claim 4, characterized in that, The double packer also includes: The second sealing gasket is disposed at the second end of the second elastic cylinder and is slidably sleeved on the central inner tube.
6. The double-layer packer for hydraulic fracturing in coal mines according to claim 1, characterized in that, The double packer also includes: The first connector is located at the first end of the central inner tube and is used to be threadedly connected to the constant pressure opener.
7. The double-layer packer for hydraulic fracturing in coal mines according to claim 1, characterized in that, The double packer also includes: The second connector is located at the second end of the central inner tube and is used for threaded connection with the fracturing tubing string.
8. The double-layer packer for hydraulic fracturing in coal mines according to claim 1, characterized in that, At least one of the water passages includes: The first water passage is provided on the central inner tube and arranged radially along the central inner tube, and the first water passage is located inside the first expansion cavity; The second water passage is provided on the central inner tube and arranged radially along the central inner tube, and the second water passage is located inside the first expansion cavity; The first water passage and the second water passage are distributed at intervals along the axial direction of the central inner tube.
9. A test method for a double-layer packer for hydraulic fracturing in coal mines as described in any one of claims 1-8, characterized in that, include: S1: Connect the first end of the central inner tube of the double packer to the oil injection device, and seal the second end of the central inner tube; S2: The sealed double packer is placed in the test pipe, wherein the end of the test pipe near the second end of the central inner tube is a closed structure, and the end of the test pipe near the first end of the central inner tube is an open structure. S3: Start the oil injection device and control the oil injection device to inject oil with progressively increasing pressure into the central inner tube along a preset time line, and maintain each pressure level for a preset duration; S4: Record the pressure and time curves of the double packer, and determine the quality of the double packer based on the recorded pressure and time curves.
10. The test method for the double-layer packer for hydraulic fracturing in coal mines according to claim 9, characterized in that, The testing method also includes: A slit of a predetermined length is cut into the second elastic cylinder of the double-layer packer; Repeat steps S1 to S4.