A time-delay opening toe sleeve

Abstract

The application provides a delay opening toe sleeve, comprising: a hollow pipe, a lower end of which is configured as a lower joint and is provided with a first communication hole; a sealing sleeve and a communication sleeve sleeved on the hollow pipe, a first annular space and a second annular space being respectively formed between the sealing sleeve, the communication sleeve and the hollow pipe, the communication sleeve being provided with a second communication hole aligned with the first communication hole; a pressure transmission sleeve arranged between the sealing sleeve and the communication sleeve, the pressure transmission sleeve being provided with a pressure transmission hole; a delay medium and a sleeve arranged in the second annular space; a rupture disc assembly arranged in a side wall of the lower joint, a radial outer side of the rupture disc assembly being provided with a gap in communication with the second annular space; wherein the sleeve blocks the first communication hole and the second communication hole in an initial state, and the pressure transmission hole is closed, the delay opening toe sleeve is configured to make the rupture disc assembly break when a wellbore pressure rises to a test pressure value, and to open the delay opening toe sleeve through the sleeve and the delay medium.

Description

Technical Field

[0001] This invention belongs to the field of downhole operation technology for oil and gas wells, and specifically relates to a delayed-opening toe sleeve. Background Technology

[0002] In the field of oil and gas extraction, with the increasing development of unconventional oil and gas resources, drilling is becoming deeper and horizontal well sections are becoming longer, making development increasingly difficult. Due to the low porosity and tightness of unconventional oil and gas reservoirs, industrial production capacity can only be achieved through fracturing. For the initial fracturing stage, since there is no flow channel in the entire wellbore, two methods are currently commonly used to establish the fracturing channel: continuous tubing perforation and toe-end sliding sleeve.

[0003] Coiled tubing perforation is a mature and highly successful method; however, it faces certain technical limitations due to the special control of explosives, on-site installation, commissioning, and dismantling of coiled tubing equipment, long construction time, and the increasing limitation on the working depth of coiled tubing as well depth and horizontal section length increase. Conventional toe-sleeve perforation, which utilizes pressure differential to open fracturing channels, offers advantages such as lower construction costs and higher efficiency compared to coiled tubing perforation. However, in practical applications, it often encounters difficulties in opening the fracturing channel and fails to meet the requirements for full-wellbore pressure testing.

[0004] Therefore, there is an urgent need for a delayed-opening toe sleeve that can meet the requirements of full-bore pressure testing and can be used for the first stage of fracturing and modification construction. Summary of the Invention

[0005] To address the technical problems mentioned above, this invention aims to provide a delayed-opening toe sleeve that can meet the requirements of full-wellbore pressure testing and can be used for the first stage of fracturing and modification construction.

[0006] To address this, the present invention provides a delayed-opening toe sleeve, comprising: a hollow tube, the lower end of which is configured as a lower connector, and the hollow tube having a first communicating hole; a sealing sleeve and a communicating sleeve axially spaced apart and sleeved on the hollow tube, a first annular space being formed between the sealing sleeve and the hollow tube, and a second annular space being formed between the communicating sleeve and the hollow tube, and the communicating sleeve having a second communicating hole aligned with the first communicating hole; a pressure-transmitting sleeve disposed between the sealing sleeve and the communicating sleeve, the pressure-transmitting sleeve having an axially extending pressure-transmitting hole; a delay medium and a sleeve disposed in the second annular space; and a rupture disc assembly disposed within the sidewall of the lower connector, the rupture disc assembly having a radial... The outer side is provided with a gap communicating with the second annular space; wherein, in the initial state, the sliding sleeve blocks the first communicating hole and the second communicating hole, and the pressure transmitting hole is closed. The delayed opening toe sliding sleeve is configured to cause the rupture disc assembly to rupture when the wellbore pressure rises to the test pressure value, so that the liquid pressure in the wellbore can act on the lower end face of the sliding sleeve through the gap, thereby axially pushing the sliding sleeve and squeezing the delayed medium until the predetermined pressure is reached, opening the pressure transmitting hole, so that the delayed medium can flow into the first annular space through the pressure transmitting hole, thereby enabling the sliding sleeve to move to form a connection between the first communicating hole and the second communicating hole after the pressure test, so as to open the delayed opening toe sliding sleeve.

[0007] In one embodiment, an upper connector is fitted onto the upper end of the hollow tube, and the first annular space is formed between the upper connector and the pressure-transmitting sleeve in the axial direction and between the hollow tube and the sealing sleeve in the radial direction.

[0008] In one embodiment, the two ends of the sealing sleeve are respectively adapted to the upper connector and the pressure transmission sleeve through stepped joints, a first sealing element is provided between the sealing sleeve and the connection surfaces of the upper connector and the pressure transmission sleeve, and a second sealing element is provided between the hollow tube and the upper connector and the pressure transmission sleeve.

[0009] In one embodiment, a pressure relief sleeve is provided within the first annular space, the pressure relief sleeve being configured to form a receiving cavity within the first annular space.

[0010] In one embodiment, delay valves are fixedly installed at both ends of the pressure transmission orifice, and the inlet end of each delay valve is configured to face the second annular space.

[0011] In one embodiment, the delay valve includes a valve body with an orifice, an elastic element mounted inside the valve body, and a valve core adapted to the elastic element, wherein the orifice diameter of the delay valve is set to be in the range of 0.1 mm to 10 mm.

[0012] In one embodiment, the rupture disc assembly includes a mounting base and a rupture disc mounted within the mounting base, the rupture pressure of the rupture disc being in the range of 20 to 130 MPa.

[0013] In one embodiment, the two ends of the connecting sleeve are respectively adapted to the pressure transmitting sleeve and the lower connector through stepped joints, and a third sealing element is provided between the connecting surfaces of the connecting sleeve and the lower connector and the pressure transmitting sleeve.

[0014] In one embodiment, the inner surface of the sliding sleeve is provided with first dynamic seals that are axially spaced apart. In the initial state, the first dynamic seals are located on both axial sides of the first communicating hole.

[0015] Furthermore, a second dynamic seal is provided on the outer surface of the sliding sleeve, which is axially spaced apart. In the initial state, the second dynamic seal is located on both sides of the second connecting hole.

[0016] In one embodiment, the delay medium is a low-melting-point alloy, which is solid at room temperature and becomes a flowable liquid when it reaches its melting point.

[0017] Compared with the prior art, the advantages of this application are:

[0018] The delayed-opening toe sleeve of the present invention can meet the requirements of full-bore pressure testing, is suitable for the first stage of fracturing and stimulation construction, significantly reduces completion costs, and greatly improves construction efficiency. This delayed-opening toe sleeve enables reliable and accurate pressure testing, and has a high success rate in opening after pressure testing. The fracture disc assembly and delayed valve in the delayed-opening toe sleeve can be adjusted to different specifications according to actual working conditions to adapt to different requirements, thus expanding the application range of the delayed-opening toe sleeve. Furthermore, fracturing and stimulation construction using the delayed-opening toe sleeve is simple in process, highly efficient, low in cost, and safe. Attached Figure Description

[0019] The present invention will now be described with reference to the accompanying drawings.

[0020] Figure 1 The structure of the delayed-opening toe sleeve according to the present invention is shown.

[0021] Figure 2 yes Figure 1 A cross-sectional view along line AA in the middle.

[0022] Figure 3 The structure of another embodiment of the pressure relief sleeve is schematically shown.

[0023] Figure 4 yes Figure 1 A magnified view of region B in the middle.

[0024] Figure 5 The diagram schematically illustrates the state in which the delayed-opening toe sleeve structure according to the present invention is inserted into the target sublayer.

[0025] In this application, all drawings are schematic and are used only to illustrate the principles of the invention, and are not drawn to scale. Detailed Implementation

[0026] The present invention will now be described with reference to the accompanying drawings. It should be noted that these descriptions are provided merely to illustrate the principles of the invention and do not limit the scope of the invention.

[0027] For ease of understanding, in this application, the end closest to the wellhead is defined as the upper end, upstream end, or similar terms, for example... Figure 1 The left end is defined as the end furthest from the wellhead, while the end furthest from the wellhead is defined as the lower end, downstream end, or similar terms, for example... Figure 1 The right end of the middle.

[0028] Figure 1 The structure of the delayed-opening toe sleeve 100 according to the present invention is shown. Figure 1 As shown, the delayed-opening toe sleeve 100 includes an upper connector 1, a hollow tube 2, a sealing sleeve 3, a pressure-transmitting sleeve 4, a connecting sleeve 5, a delay medium 6, a sliding sleeve 7, and a rupture disc assembly 8. The hollow tube 2 has a central flow channel, and the lower end of the hollow tube 2 is configured as a lower connector 21. The hollow tube 2 also has a first connecting hole 22 penetrating the sidewall, which is preferably located near the lower connector 21. The sealing sleeve 3 and the connecting sleeve 5 are axially spaced and sleeved on the hollow tube 2, with the sealing sleeve 3 located at the upper end of the connecting sleeve 5. The pressure-transmitting sleeve 4 is disposed axially between the sealing sleeve 3 and the connecting sleeve 5, and the pressure-transmitting sleeve 4 has an axially extending pressure-transmitting hole 40. A first annular space 30 is formed between the sealing sleeve 3 and the hollow tube 2, and a second annular space 50 is formed between the connecting sleeve 5 and the hollow tube 2. The connecting sleeve 5 has a second connecting hole 51 aligned with the first connecting hole 22. The delay medium 6 and the sliding sleeve 7 are arranged in the second annular space 50, with the delay medium 6 located at the upper end of the sliding sleeve 7. The rupture disc assembly 8 is disposed within the side wall of the lower connector 21, and a slit (not shown) communicating with the second annular space 50 is provided on the radially outer side of the rupture disc assembly 8.

[0029] In the initial state, the sliding sleeve 7 is positioned between the first connecting hole 22 and the second connecting hole 51, with the lower end face of the sliding sleeve 7 abutting against the upper end face of the lower connector 21, thereby sealing the first connecting hole 22 and the second connecting hole 51 so that the delayed opening toe sliding sleeve 100 is in a closed state. Simultaneously, the pressure transmission hole 40 within the pressure transmission sleeve 4 is configured to be closed in the initial state. The delayed opening toe sliding sleeve 100 is configured to cause the rupture disc assembly to rupture when the wellbore pressure rises to the test pressure value, allowing the liquid pressure inside the wellbore to act through the gap on the lower end face of the sliding sleeve 7, axially pushing the sliding sleeve 7 and compressing the delayed medium 6 until a predetermined pressure is reached, opening the pressure transmission hole 40. This allows the delayed medium 6 to flow into the first annular space 30 through the pressure transmission hole 40, thereby enabling the sliding sleeve 7 to move to the upper end of the first connecting hole 22 and the second connecting hole 51 after the pressure test, connecting the first connecting hole 22 and the second connecting hole 51, thus opening the delayed opening toe sliding sleeve 100.

[0030] According to the present invention, such as Figure 1 As shown, the upper connector 1 is fitted onto the upper end of the hollow tube 2. The upper end of the upper connector 1 is constructed as a negative cone-shaped connecting buckle for connecting to the upper tube column 110 (see...). Figure 5 This connection method enables quick connection or disassembly between the delayed-opening toe sleeve 100 and the upper column 110.

[0031] The first annular space 30 is formed between the upper connector 1 and the pressure transmitting sleeve 4 axially and between the hollow tube 2 and the sealing sleeve 3 radially. In one embodiment, the two ends of the sealing sleeve 3 are respectively fitted to the upper connector 1 and the pressure transmitting sleeve 4 via stepped connectors, and a first sealing element 31 is provided between the connecting surfaces of the sealing sleeve 3 and the upper connector 1 and the pressure transmitting sleeve 4. Figure 1 As shown, the lower end of the upper connector 1 is constructed as an outer stepped connector, and both ends of the sealing sleeve 3 are constructed as inner stepped connectors. The upper end of the sealing sleeve 3 is adapted to the outer stepped connector of the upper connector 1 through the corresponding inner stepped connector and is fixedly connected by threads. The first sealing element 31 is installed between the connecting surfaces of the inner stepped connector and the outer stepped connector.

[0032] Similarly, as Figure 1 As shown, both ends of the pressure-transmitting sleeve 4 are constructed as external stepped joints. The upper end of the pressure-transmitting sleeve 4 is fitted with the inner stepped joint at the lower end of the sealing sleeve 3 through the external stepped joint and is fixedly connected by threads. At the same time, a second sealing element 32 is provided between the hollow tube 2, the upper joint 1, and the pressure-transmitting sleeve 4. Thus, the upper joint 1, the hollow tube 2, the sealing sleeve 3, and the pressure-transmitting sleeve 4 together form a closed first annular space 30.

[0033] like Figure 1As shown, both ends of the connecting sleeve 5 are also constructed as inner stepped joints. In one embodiment, the lower joint 21 is integrally formed with the hollow tube 2, and the lower joint 21 is provided with an outer stepped connecting buckle facing upward. The upper end face of the lower joint 21 is axially spaced from the lower end face of the pressure transmitting sleeve 4. The upper end of the connecting sleeve 5 is adapted to the outer stepped joint of the lower end of the pressure transmitting sleeve 4 through the inner stepped joint and is fixedly connected by threads. At the same time, the lower end of the connecting sleeve 5 is adapted to the outer stepped connecting buckle of the lower joint 21 through the inner stepped joint and is fixedly connected by threads. Thus, the pressure transmitting sleeve 4, the hollow tube 2, the lower joint 21, and the connecting sleeve 5 together form a second annular space 50. In order to ensure the sealing of the connection between the connecting sleeve 5 and the pressure transmitting sleeve 4 and the lower joint 21, a third sealing element 33 is provided between the connecting surfaces of the connecting sleeve 5 and the lower joint and the pressure transmitting sleeve 4, respectively.

[0034] According to the present invention, the hollow tube 2 has multiple first connecting holes 22 evenly distributed circumferentially, and the connecting sleeve 5 has multiple second connecting holes 51 evenly distributed circumferentially. The first connecting holes 22 and the second connecting holes 51 are located in the same axial position and are aligned with each other circumferentially.

[0035] According to one embodiment of the present invention, such as Figure 1 As shown, a pressure relief sleeve 9 may be provided within the first annular space 30. The pressure relief sleeve 9 is configured to form a receiving cavity within the first annular space 30 for accommodating the delay medium 6. In one embodiment, as... Figure 2 As shown, the outer surface of the pressure relief sleeve 9 has multiple axially extending grooves. These grooves are evenly distributed circumferentially and interconnected, forming a receiving cavity around the sealing sleeve 3. In practical applications, the pressure relief sleeve 9 can provide support for the central tube 2, preventing damage to the central tube 2 due to high pressure, thereby effectively protecting the central tube 2.

[0036] like Figure 3 As shown, alternatively, the pressure relief sleeve 9 can also be constructed as a cylinder with an axial length smaller than the axial distance between the lower end face of the upper connector 1 and the upper end face of the pressure transmission sleeve 4, so that the pressure relief sleeve 9 can move axially within the first annular space 30 to form a receiving cavity.

[0037] According to the present invention, delay valves 10 are fixedly installed at both ends of the pressure transmission hole 40, and the inlet end of each delay valve 10 is configured to face the second annular space 50. In one embodiment, the delay valve 10 is fixedly installed in the pressure transmission hole 40 by threads. Figure 4 As shown, the delay valve 10 includes a valve body 101 with an orifice, an elastic element 102 installed within the valve body 101, and a valve core 103 adapted to the elastic element 102. In the initial state, the valve core 103 closes the orifice under the action of the elastic element 102. When the valve core 103 is compressed and reaches a predetermined pressure, the valve core 103 compresses the elastic element 102 and opens the orifice.

[0038] The orifice diameter of the delay valve 10 is set within the range of 0.1mm to 10mm. In actual use, different sizes of delay valve 10 can be selected according to actual needs.

[0039] In one embodiment, such as Figure 4 As shown, the elastic element 102 is a spring, and the valve core 103 is a sealing ball.

[0040] Alternatively, valve core 103 can also be a sliding sealing plug.

[0041] According to the present invention, the rupture disc assembly 8 includes a mounting base 81 and a rupture disc 82 mounted within the mounting base 81. The rupture pressure of the rupture disc 82 is in the range of 20 to 130 MPa. In actual use, rupture discs 82 with different rupture pressures can be selected according to actual needs.

[0042] In this embodiment, an annular space is left between the lower connector 21 and the connecting sleeve 5 to form a gap, and the radial outer side of the rupture disc assembly 8 communicates with the second annular space 50 through this gap.

[0043] According to the present invention, such as Figure 1 As shown, a first dynamic seal 71 is provided on the inner surface of the sliding sleeve 7, axially spaced apart. In the initial state, the first dynamic seal 71 is located on both axial sides of the first connecting hole 22 to ensure the sealing of the first connecting hole 22 in the initial state. Simultaneously, a second dynamic seal 72 is provided on the outer surface of the sliding sleeve 7, axially spaced apart. In the initial state, the second dynamic seal 72 is located on both axial sides of the second connecting hole 51 to ensure the sealing of the second connecting hole 51 in the initial state. Thus, the second annular space 50 remains sealed in the initial state.

[0044] It is easy to understand that since the delay valve 10 installed in the pressure transmission hole 40 is closed at the beginning, in the initial state, the sliding sleeve 7 forms a sealed cavity in the area of ​​the second annular space 50 corresponding to the upper end of the sliding sleeve 7 through the first dynamic seal 71 and the second dynamic seal 72, and the delay medium 6 is filled in the sealed cavity.

[0045] According to the present invention, the delay medium 6 can be a low-melting-point alloy, such as a tin-bismuth alloy. The delay medium 6 is solid at room temperature and becomes a flowable liquid when it reaches its melting point. This facilitates the arrangement of the delay medium 6 within the second annular space 50 during assembly. When the delay-opening toe sleeve 100 is subjected to a high-temperature environment in the formation, causing the delay medium 6 to reach its melting point, the delay medium 6 transforms into a flowable liquid. Thus, the delay-opening toe sleeve 100 achieves a certain degree of delayed opening effect through the delay medium 6.

[0046] Alternatively, the delay medium 6 can also be water, or a flowable liquid substance such as sealing grease, silicone oil, or paraffin that has high temperature and high viscosity resistance, or a low melting point solid or semi-solid substance.

[0047] The working principle of the delayed-opening toe sleeve 100 according to the present invention is briefly described below. First, the delayed-opening toe sleeve 100 is connected to the completion tubing, such as... Figure 5 As shown, the upper connector 1 is connected to the upper tubing string 110, and the lower connector 21 is connected to the lower tubing string 120. Then, the completion tubing string is lowered into the wellhead, and the toe sleeve 100 is opened after a delay and lowered into the formation 300 to a predetermined depth along with the completion tubing string for cementing. After the cement sets, a cement sheath 200 is formed between the completion tubing and the wellbore. Then, a full wellbore pressure test is performed. When the wellbore pressure rises to the test pressure value, the rupture disc 82 in the rupture disc assembly 8 ruptures. Under pressure, the wellbore fluid passes through the gap between the rupture disc 82, the connecting sleeve 5 and the central tube 2 in sequence, thereby transmitting the wellbore fluid pressure to the lower end face of the sliding sleeve 7, which axially pushes the sliding sleeve 7 and squeezes the delay medium 6 until the predetermined pressure is reached. Then, the delay valve 10 in the pressure transmission hole 40 near the second annular space 50 is opened. The sliding sleeve 7 squeezes the delay medium 6 and slowly flows into the pressure transmission hole 40 through the delay valve 10 near the second annular space 50, and then enters the delay valve 10 near the first annular space 30 through the pressure transmission hole 10, and finally flows into the pressure relief chamber of the first annular space 30. During this process, the sliding sleeve 7 moves upward along the axial direction under the action of wellbore pressure until the sliding sleeve 7 moves to be axially offset from the first connecting hole 22 and the second connecting hole 51, so that the first connecting hole 22 and the second connecting hole 51 are aligned and connected, thereby opening the delayed opening toe sliding sleeve 100.

[0048] Based on the required wellbore pressure testing time, precise calculations ensure that the sliding sleeve 7 does not slide open from the first connecting hole 22 and the second connecting hole 51 during the pressure test, thus guaranteeing that the delayed-opening toe sliding sleeve 100 remains closed throughout the pressure test. After the pressure test, the sliding sleeve 7 slides open, connecting the first connecting hole 22 on the central tube 2 with the second connecting hole 51 on the connecting sleeve 5, thereby opening the delayed-opening toe sliding sleeve 100 and transitioning to the first stage of fracturing construction.

[0049] The delayed-opening toe sleeve 100 of the present invention can meet the requirements of full-bore pressure testing, is suitable for first-stage fracturing and stimulation operations, significantly reduces well completion costs, and greatly improves operational efficiency. This delayed-opening toe sleeve 100 can achieve reliable and accurate pressure testing, and has a high success rate in opening after pressure testing. The fracture disk assembly 8 and the delayed-opening valve 100 in the delayed-opening toe sleeve 100 can be adjusted to different specifications according to actual working conditions to adapt to different requirements, thus expanding the application range of the delayed-opening toe sleeve 100. Furthermore, fracturing and stimulation operations using the delayed-opening toe sleeve 100 are characterized by simple construction technology, high timeliness, low construction cost, and high safety.

[0050] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0051] Furthermore, 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 the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0052] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A delayed-opening toe slip sleeve, comprising: A hollow tube (2) has a lower end configured as a lower connector (21), and the hollow tube is provided with a first connecting hole (22); A sealing sleeve (3) and a connecting sleeve (5) are axially spaced apart on the hollow tube. A first annular space (30) is formed between the sealing sleeve and the hollow tube. A pressure relief sleeve (9) is provided in the first annular space. The pressure relief sleeve is configured to form a receiving cavity in the first annular space. A second annular space (50) is formed between the connecting sleeve and the hollow tube. The connecting sleeve is provided with a second connecting hole (51) aligned with the first connecting hole. The pressure-transmitting sleeve (4) is disposed between the sealing sleeve and the connecting sleeve, and the pressure-transmitting sleeve is provided with an axially extending pressure-transmitting hole (40). The delay medium (6) and the sliding sleeve (7) arranged in the second annular space; and A rupture disc assembly (8) is provided in the side wall of the lower connector. The radial outer side of the rupture disc assembly is provided with a gap communicating with the second annular space. The rupture disc assembly includes a mounting base (81) and a rupture disc (82) installed in the mounting base. In its initial state, the sliding sleeve blocks the first and second connecting holes, and the pressure transmitting hole is closed. The delayed-opening toe sleeve is configured to rupture the rupture disc assembly when the wellbore pressure rises to the test pressure value. This allows the liquid pressure inside the wellbore to act on the lower end face of the sleeve through the gap, axially pushing the sleeve and squeezing the delayed medium until a predetermined pressure is reached, at which point the pressure transmission hole is opened. This allows the delayed medium to flow into the first annular space through the pressure transmission hole. After the pressure test, the sleeve can move to connect the first connecting hole and the second connecting hole to open the delayed-opening toe sleeve.

2. The delayed-opening toe sleeve according to claim 1, characterized in that, An upper connector (1) is fitted onto the upper end of the hollow tube, and the first annular space is formed between the upper connector and the pressure transmission sleeve in the axial direction and between the hollow tube and the sealing sleeve in the radial direction.

3. The delayed-opening toe sleeve according to claim 2, characterized in that, The two ends of the sealing sleeve are respectively adapted to the upper connector and the pressure transmission sleeve through stepped joints. A first sealing element (31) is provided between the sealing sleeve and the connection surfaces of the upper connector and the pressure transmission sleeve, and a second sealing element (32) is provided between the hollow tube and the upper connector and the pressure transmission sleeve.

4. The delayed-opening toe sleeve according to claim 1, characterized in that, Delay valves (10) are fixedly installed at both ends of the pressure transmission hole, and the inlet end of each delay valve is arranged to face the second annular space.

5. The delayed-opening toe sleeve according to claim 4, characterized in that, The delay valve includes a valve body (101) with an orifice, an elastic element (102) mounted in the valve body, and a valve core (103) adapted to the elastic element. The orifice diameter of the delay valve is set to be in the range of 0.1 mm to 10 mm.

6. The delayed-opening toe sleeve according to claim 1, characterized in that, The rupture pressure of the rupture disc is in the range of 20 to 130 MPa.

7. The delayed-opening toe sleeve according to claim 1, characterized in that, The two ends of the connecting sleeve are respectively adapted to the pressure transmitting sleeve and the lower connector through stepped joints, and a third sealing element (33) is provided between the connecting surfaces of the connecting sleeve, the lower connector and the pressure transmitting sleeve.

8. The delayed-opening toe sleeve according to claim 1, characterized in that, The inner surface of the sliding sleeve is provided with first dynamic seals (71) that are axially spaced apart. In the initial state, the first dynamic seals are located on both sides of the first communicating hole. Furthermore, a second dynamic seal (72) is provided on the outer surface of the sliding sleeve, which is axially spaced apart. In the initial state, the second dynamic seal is located on both sides of the second connecting hole.

9. The delayed-opening toe sleeve according to claim 1, characterized in that, The delay medium is a low-melting-point alloy, which is solid at room temperature and becomes a flowable liquid when it reaches its melting point.

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