SLIDING SHIRT DEVICE

Abstract

A sliding sleeve device (100), comprising: an outer cylinder (2), a circulation hole (21) provided in the wall of the outer cylinder (2); and an inner cylinder (6) provided in an internal cavity of the outer cylinder (2), wherein, in an initial state, the inner cylinder (6) and the outer cylinder (2) are fixed to each other to seal the circulation hole (21) and, in a first state, the inner cylinder (6) can be moved with respect to the outer cylinder (2), thereby removing the seal from the circulation hole (21); a protective mechanism is provided in the circulation hole (21) and the protective mechanism comprises an inner member located on the radially inner side and an outer member located on the radially outer side.

Description

SLIDING SHIRT DEVICE CROSS REFERENCE TO RELATED APPLICATIONS This application claims the priorities of Chinese patent application No. 202010534864.7 entitled Sliding sleeve device and fracturing string containing the same and filed on June 12, 2020, Chinese patent application No. 202010535615.X entitled Fracturing sub and fracturing string containing the same and filed on June 12, 2020, and Chinese patent application No. 202010534832.7 entitled Fracturing sub and fracturing string containing the same and filed on June 12, 2020, the contents of which are incorporated herein in their entirety by reference. TECHNICAL FIELD OF THE INVENTION The present invention relates to the technical field of oil and natural gas well completion, and in particular to a slip sleeve device. TECHNICAL BACKGROUND OF THE INVENTION With the continuous and profound development of oil and gas exploitation, the slip sleeve became one of the fundamental tools to achieve communication with the oil casing annular space in the cementing, completion and fracturing process to fracture the separated layers. During gas testing in oil and gas well completions, the annular space between the tubing string and the wellbore can be accessed through the opening of the slip sleeve, enabling operations such as circulation, fluid replacement, sand fracturing, and so on. For multi-layered, staged construction, multiple slip sleeves are arranged in series within a tubing string. During construction, the slip sleeves are opened sequentially from bottom to top, and the corresponding layers are then fractured one after the other. In this way, fracturing can be performed successively in layers. With the development of exploration and production of tight gas deposits, horizontal well sections are becoming increasingly longer, and the number of stages in sand fracturing is also increasing. Fracturing processes involving dozens of slip sleeves have already been implemented. However, in actual production, the problem of slip sleeves not opening smoothly often arises, impacting construction progress. BRIEF DESCRIPTION OF THE INVENTION With respect to some or all of the above technical problems existing in the prior art, the present invention proposes a sliding sleeve device, which can ensure that said sleeve can be opened smoothly to perform related subsequent operations. According to the present invention, a sliding sleeve device is provided, comprising: an outer cylinder with a circulation hole located in a wall of the outer cylinder; and an inner cylinder disposed in an internal cavity of the outer cylinder, wherein, in an initial state, the inner and outer cylinders are fixed to each other to close the circulation hole, and, in a first state, the inner cylinder can be moved relative to the outer cylinder to release the closure of the circulation hole. A protective mechanism is provided in the circulation hole and includes an internal member located on a radially internal side and an external member located on a radially external side. In a preferred embodiment, the circulation orifice comprises two stages formed in an outer wall of the outer cylinder and circumferentially opposed to each other, where the outer member is configured to extend over said two stages to block the circulation orifice. In a preferred embodiment, the inner member is lubricating grease filled into the circulation orifice and the outer member is a protective cover. In one specific embodiment, a recess is provided in an outer wall of the inner cylinder and at least partially located in the circulation hole in the initial state to allow lubricating grease to enter the recess. In a preferred embodiment, the protective cover is a heat-shrinkable cover or a resin cover. In a preferred embodiment, the outer member is a breakable element that will break under pressure, and the inner member is a support element to support the breakable element and to fall off under pressure. In a preferred embodiment, at least one protruding ring is provided embedded in the breakable element on the outer wall of the outer cylinder in a region between said two stages. In a preferred embodiment, the breakable element is configured as a cement cover formed by hardening the supplied cement grout. In a preferred embodiment, the support element is configured as a plurality of stacked resin balls or as a plurality of stacked metal balls soluble in working fluid. In a preferred embodiment, the support element comprises multiple layers of balls, where the balls are gradually reduced in layers in a direction from the radially inner side to the radially outer side. In one specific embodiment, a layer of lubricating grease is provided on both the inner and outer radial sides of the support element. In a preferred embodiment, the outer member is configured as a plug made of soluble material. In one specific embodiment, a blind hole is provided on a radial inner surface of the plug. In a preferred embodiment, the plug comprises a connecting segment and a tilting element, which are sequentially positioned in a direction from the radially external side to the radially internal side and connected to each other. The connecting segment is fixedly coupled to the circulation port, while the tilting element is configured to be reduced in size in the direction from the radially external side to the radially internal side. In a preferred embodiment, the outer member is configured as a breakable disc, which includes a main body portion fixedly connected to the circulation hole, and a disc portion that is breakable under pressure. In a preferred embodiment, a free space in communication with the circulation hole is provided between the outer cylinder and the inner cylinder and the outer axial ends of the circulation hole. In a preferred embodiment, the free space is an enlarged hole formed in the inner wall of the outer cylinder, where the enlarged hole comprises an inclined surface, such that the free space narrows in a direction away from the circulation hole. BRIEF DESCRIPTION OF THE DRAWINGS The following preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the drawings: Figure 1 shows a sliding sleeve device according to a first embodiment of the present invention, wherein the sliding sleeve device is in an initial state; Figure 2 shows the sliding sleeve device of Figure 1 in a first state; Figure 3 is an enlarged view of the sliding sleeve device of Figure 1, showing an area where a circulation hole is located; Figure 4 shows a sliding sleeve device according to a second embodiment of the present invention, wherein the sliding sleeve device is in an initial state; Figure 5 is an enlarged view of the sliding sleeve device of Figure 4, showing an area where a circulation hole is located; Figure 6 shows a sliding sleeve device according to a third embodiment of the present invention, wherein the sliding sleeve device is in an initial state; Figure 7 shows an enlarged view of area A of Figure 6 in a shape; Figure 8 shows an enlarged view of area A of Figure 6 in another shape; and Figure 9 shows an enlarged view of area A of Figure 6 in an additional shape. In the drawings, the same reference numbers are used to indicate the same components. The drawings are not drawn to scale. DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in greater detail below with reference to the accompanying drawings. In the context of the present invention, the directional terms "upward," "upstream," "upward," or similar terms refer to a direction toward the wellhead, while the directional terms "downward," "downstream," "downward," or similar terms refer to a direction away from the wellhead. Furthermore, the direction along the length of the slip sleeve device is referred to as the longitudinal or axial direction, and the direction perpendicular to the longitudinal or axial direction is referred to as the radial direction, wherein the orientation of the radial direction toward the formation is referred to as radially outward, while the orientation away from the formation is referred to as radially inward. Figure 1 shows a sliding sleeve device 100 according to a first embodiment of the present invention. As shown in Figure 1, the The sliding sleeve device 100 includes an outer cylinder 2 and an inner cylinder 6. A circulation hole 21 is provided in the wall of the outer cylinder 2, allowing communication between the inside and outside of the device, to provide a channel for the fracturing operation. The circulation hole may also be referred to as the fracturing hole, flow guide hole, or similar names. The inner cylinder 6 is disposed in an internal cavity of the outer cylinder 2. For example, the inner cylinder 6 may be disposed in an inner wall of the outer cylinder 2 via a shear pin 5 and thus be permanently connected to the outer cylinder 2. In an initial state of the sliding sleeve device 100, as shown in Figure 1, the inner cylinder 6 closes the circulation hole 21.After subjecting the inner cylinder 6 to an axially downward force that reaches the shear pressure of the shear pin 5, the shear pin 5 shears, allowing the inner cylinder 6 to move downward relative to the outer cylinder 2, thereby releasing the closure of the circulation port 21 from within. In other words, the circulation port 21 opens. Figure 2 shows the first state of the sliding sleeve device 100. In this state, the circulation port 21 is released by the internal cylinder 6, i.e., the circulation port 21 is opened. After this, the fracturing fluid pumping operation can begin. After the fracturing fluid is pumped, the sliding sleeve device 100 is in a second state (not shown). The person of the mid-level trade knows the structure, operations, and states of the sliding sleeve device as mentioned above, and therefore a detailed description of these is omitted herein. Figure 3 is an enlarged view of the sliding sleeve device 100 as shown in Figure 1, showing an area near the circulation hole 21. According to the present invention, the circulation hole 21 is filled with lubricating grease (not shown). On one hand, the lubricating grease occupies the space of the circulation hole 21, preventing or reducing the entry of impurities into the area between the inner cylinder 6 and the outer cylinder 2. On the other hand, when the inner cylinder 6 moves relative to the outer cylinder 2, the lubricating grease can enter the area between the inner cylinder 6 and the outer cylinder 2 to provide lubrication. In this way, the inner cylinder 6 can move more smoothly relative to the outer cylinder 2, ensuring smooth opening of the inner cylinder 6. According to one embodiment of the present invention, a recess 61 is provided in the outer wall of the inner cylinder 6, as shown in Figure 3. In the initial state, the recess 61 is located in the outer wall of the inner cylinder 6 in a position corresponding to the circulation hole 21. In this way, the lubricating grease can be filled not only into the circulation hole 21 but also into the recess 61. When the inner cylinder 6 moves downward relative to the outer cylinder 2, the recess 61 facilitates the entry of the lubricating grease into the area between the inner cylinder 6 and the outer cylinder 2, further ensuring the lubricating effect. Preferably, the recess 61 is formed as a stepped groove. As shown in Figure 3, according to a preferred embodiment of the present invention, a free space 8 is formed in communication with the circulation hole 21 between the outer cylinder 2 and the inner cylinder 6, but outside the axial ends of the circulation hole 21. The free space 8 may be formed only in the inner wall of the outer cylinder 2 or only in the outer wall of the inner cylinder 6, or in both. In a specific embodiment, an enlarged hole 62 may be provided in the inner wall of the outer cylinder 2 immediately outside the circulation hole 21. A wall surface of the enlarged hole 62 is preferably configured to have an inclined surface 63, such that the free space 8 narrows in both directions axially away from the circulation hole 21.On one hand, the aforementioned structure allows lubricating grease to easily enter the clearance 8, enabling it to be smoothly delivered to the area between the inner cylinder 6 and the outer cylinder 2, following the movement of the inner cylinder 6. This improves lubrication between the inner cylinder 6 and the outer cylinder 2, ensuring the smooth downward movement of the inner cylinder 6. On the other hand, the inclined surface 63 ensures that the clearance 8 gradually decreases in size, acting as a barrier to prevent impurities from entering the area between the inner cylinder 6 and the outer cylinder 2. In one embodiment, as shown in Figure 3, a protective cover 4 is provided to block the circulation port 21 in the outer wall of the outer cylinder 2. This prevents the lubricating grease in the circulation port 21 from flowing out and also prevents impurities from entering the port 21 and contaminating the lubricating grease. In the initial state and the first state of the sliding sleeve device 100, the protective cover 4 blocks the circulation port 21. In the second state of the sliding sleeve device 100, the protective cover 4 is broken by the action of the fracturing fluid, thus opening the circulation port 21. In one specific embodiment, the protective cover 4 is a heat-shrinkable cover disposed on the outer wall of the outer cylinder 2. Preferably, the heat-shrinkable cover is 0.5–2 mm thick and has two ends that overlap the outer wall of the outer cylinder 2 by a length of at least 5 cm. In this way, the protective cover 4 can not only serve to protect the lubricating grease but can also be ruptured by the action of the fracturing fluid to expose the circulation port 21. That is, no special rupturing tool is required for this protective cover 4. As long as fracturing fluid is supplied, the protective cover 4 will rupture under pressure to expose the circulation port 21, which greatly simplifies operations. In one specific embodiment, the protective cover 4 can also be configured as a vulcanized rubber cover on the outer wall of the outer cylinder 2. In one particular embodiment, as shown in Figure 1, two opposing stage faces 22 are provided on the outer wall of the outer cylinder 2. These two stage faces 22 are positioned opposite each other along the circumferential direction of the circulation hole 21. In this way, the protective cover 4 can extend over the two stage faces 22. With this arrangement, the outer wall of the protective cover 4 does not protrude beyond the outer wall of the outer cylinder 2, thus ensuring the safety of the protective cover 4 and preventing accidental damage to it when lowering the sliding sleeve device 100. Preferably, the heat-shrinkable cover is formed by composite molding of an irradiation-crosslinked polyolefin-based material and a special heat-melt sealing adhesive. During the production and installation process, the heat-shrinkable cover is applied to the outer cylinder 2 by hot baking. For example, prior to installation, the surface of the outer wall of the outer cylinder 2 between the faces of stage 22 is sandblasted and deoxidized to a Sa2.5 level, and then the heat-shrinkable cover is placed around the outer cylinder 2. The heat-shrinkable cover is then heated and baked to ensure it is securely positioned on the outer cylinder 2. The hot baking process can be carried out from the middle to both ends, and the heat-shrinkable cover can be rolled back and forth with a roller to release air. In an alternative embodiment, the protective cover 4 is configured as a resin cover provided in the circulation port 21. For example, the resin cover can be 0.5–2 mm thick. Thus, the protective cover 4 can not only serve to protect the lubricating grease but can also be ruptured by the action of the fracturing fluid to expose the circulation port 21. That is, no special rupturing tool is required for this protective cover 4. As long as fracturing fluid is supplied, the protective cover 4 will rupture under pressure to expose the circulation port 21, which greatly simplifies operations. The resin coating can be formed using two-component epoxy resin or commercially available epoxy resin powder. For example, two-component epoxy resin contains components A and B, where component A includes epoxy resin, leveling agent, thinner, plasticizer, hardener, filler, or similar substances. ML / t / ZUZÓ / UZZ I uo, while component B includes curing agent, promoter, thinner, filler, or similar. In the operation, component A and component B are first mixed together uniformly in a 1:1 ratio, then filled into circulation hole 21 and allowed to dry naturally. When solid epoxy resin powder is used, it can be filled into circulation hole 21 using a powder spraying system and then heat-cured using a drying and curing system. It should be noted that when the resin cover is used, it is only necessary to fill the circulation hole 21 with resin material, regardless of whether the resin material is liquid or solid. The protective cover 4 thus formed does not need to be overlapped on the outer wall of the outer cylinder 2, and therefore the stage faces 22 are not required in this case. Furthermore, as shown in Figure 1, the sliding sleeve device 100 also includes an upper seal 1 and a lower seal 7. The lower end face of the upper seal 1 extends into the inner cavity of the outer cylinder 2 and is fixedly connected to it. For example, internal threads are formed on the inner wall of the upper end of the upper seal 1 for this connection. The lower seal 7 is arranged at the lower end of the outer cylinder 2 and is fixedly connected to it. Simultaneously, the upper end face of the lower seal 7 extends into the inner cavity of the outer cylinder 2 to form a receiving platform for the inner cylinder 6 during its downward movement. For example, internal threads are provided on the outer wall of the lower end of the lower seal 7 for this connection. Furthermore, the sliding sleeve device 100 may also include at least one sealing ring 3. For example, a plurality of sealing rings 3 may be arranged between the inner cylinder 6 and the outer cylinder 2, located in positions adjacent to the axial ends of the circulation hole 21 and those of the shear pin 5. Figure 4 shows a sliding sleeve device 200, which may also be called a fracturing adapter, according to a second embodiment of the present invention. As shown in Figure 4, the sliding sleeve device 200 includes an outer cylinder 202 and an inner cylinder 206. A circulation hole 221 is provided in the wall of the outer cylinder 202, allowing communication between the inside and outside to provide a channel for the fracturing operation. The inner cylinder 206 is disposed in an internal cavity of the outer cylinder 202. For example, the inner cylinder 206 can be disposed in an inner wall of the outer cylinder 202 by means of a shear pin 205 and thus be permanently connected to the outer cylinder 202.In an initial state of the sliding sleeve device 200, as shown in Figure 4, the inner cylinder 206 closes the circulation port 221. After subjecting the inner cylinder 206 to an axially downward force that reaches the shear pressure of the shear pin 205, the shear pin 205 shears, allowing the inner cylinder 206 to move downward relative to the outer cylinder 202, thereby releasing the closure of the circulation port 221 from within. That is, the circulation port 221 opens. Furthermore, as shown in Figure 4, the sliding sleeve device 200 further includes an upper seal 201, a lower seal 207, and multiple sealing rings 203 arranged between the inner cylinder 206 and the outer cylinder 202. Their structures and positions are similar to those described in the first embodiment of the present invention, and therefore detailed descriptions of these are omitted here. Figure 5 is an enlarged view of the sliding sleeve device 200 of Figure 4, showing an area near the circulation port 221. According to the present invention, a breakable element 204 is provided in the circulation port 221 to block the port 221 in the initial state of the sliding sleeve device 200 and thus prevent impurities from entering the port 221 before the fracturing operation. After the inner cylinder 206 moves downward, the breakable element 204 can be broken in response to pressure in the sliding sleeve device 200, exposing the circulation port 221 for the subsequent fracturing operation. With the breakable element 204, impurities and the like can be effectively prevented from entering the circulation port 221 and, therefore, from entering the area between the inner cylinder 206 and the outer cylinder 202, thus ensuring the smooth downward movement of the inner cylinder 206. In particular, when the sliding sleeve device 200 is used in a well cementing operation integrated with well completion, the provision of the breakable element 204 can prevent cement slurry from accumulating in the circulation port 221. Consequently, the cement slurry cannot solidify in the circulation port 221 and block it, thus greatly reducing the risk of the inner cylinder 206 being unable to move downward. In one particular embodiment, the breakable element 204 is configured as a cement coating formed by the curing of the applied cement grout. The cement coating can be 2–8 mm thick, for example, 3 mm. This arrangement is simple to achieve, resulting in a high hardness of the breakable element 204. Therefore, during the lowering of the sliding sleeve device 200 or the cementing process, the breakable element 204 can satisfactorily protect the circulation port 221, preventing impurities from entering it. At the same time, the breakable element 204 is relatively brittle and will break easily under the pressure of the fracturing fluid, so it does not interfere with normal fracturing operations. Furthermore, the breakable element ML / t / ZUZÓ / UZZ I υο Element 204 can be formed using a simple process. For example, the cementitious material can be supplied on-site, allowing the breakable element 204 to be formed after the cement has cured. Therefore, breakable element 204 can be provided without site restrictions, and the operation can be performed in real time at low cost. According to the present invention, as shown in Figure 5, a support element 209 is further provided in the circulation hole 221 on a radially internal side of the breakable element 204. The support element 209 is used to support the breakable element 204, preventing it from breaking prematurely, thus improving safety. Instead of being fixed in the circulation hole 221, the support element 209 is configured to fall out under pressure, so as not to impede the fracturing operation. In this way, with the support element 209, the breakable element 204 can be held on the radially internal side of the circulation hole 221, to prevent the breakable element 204 from breaking prematurely, thus improving safety. The support element 209 is filled into the circulation hole 221, which, on the one hand, occupies the space of the circulation hole 221 and thus prevents or reduces impurities from entering the area between the inner cylinder 206 and the outer cylinder 202. On the other hand, the support element 209 serves to support the breakable element 204, protecting it from breaking when compressed. In a preferred embodiment, the support element 209 is configured as a plurality of metal or resin balls stacked together. For example, the metal or resin balls can have a diameter of 1-2 mm. In addition to providing support and occupying space, the support element 209 can be easily thrown into the annular space after the breakable element 204 breaks during the fracturing fluid pumping procedure, leaving the circulation orifice 221 fully exposed. Preferably, the support element 209 is made of soluble material, such as soluble magnesium alloy, soluble aluminum alloy, or soluble resin. This way, after being thrown into the annular space, the support element 209 will react with the well fluid and then dissolve. This arrangement can effectively prevent the support element 209 from influencing the formation or from causing blockages due to the support element 209 returning to the wellhead. Ideally, the support element 209 is formed with holes to increase its contact area with the well fluid, ensuring uniform, rapid, and complete dissolution. It should be noted that the support element 209 can be formed from other components or substances. For example, the circulation hole 221 is filled with semi-solid lubricating grease, which can perform not only a lubricating function but also a support function. It should also be noted that the support element 209 can be configured not only in a spherical shape but also in other shapes, such as a square, a conical shape, or similar. Furthermore, the holes in the support element 209 can be through holes or blind holes, or one or more holes. In one particular embodiment, when the support element 209 is configured as a plurality of balls, the diameter of the support element 209 gradually decreases in a direction from the radially inner side to the radially outer side of the sliding sleeve device 200. Specifically, in the radial direction from the inside out, the support elements 209 are arranged in layers, wherein the support elements 209 of the innermost layer have the largest diameter to enhance support strength, while those of the outermost layer have the smallest diameter to reduce the spacing between the support elements 209 and prevent the breakable element 204 formed by the cement grout from being excessively introduced into the space between the support elements 209. Preferably, to prevent cement grout from entering the space of the support element 209 during installation, lubricating grease can be provided on both radial sides of the support element 209, i.e., between the support element 209 and the breakable element 204, and between the support element 209 and the inner cylinder 206. The lubricating grease located between the support element 209 and the breakable element 204 prevents cement grout from entering the space of the support element 209, effectively controlling the design thickness of the cement plug and ensuring that the breakable element 204 can be completely broken. The lubricating grease located between the support element 209 and the inner cylinder 206 provides lubrication, ensuring the smooth downward movement of the inner cylinder 206 relative to the outer cylinder 202. In one particular embodiment, as shown in Figure 4, two opposing stage faces 222 are provided on the outer wall of the outer cylinder 202. These two stage faces 222 are located at opposite ends of the circulation bore 21. This allows the breakable element 204 to extend over the two stage faces 222. With this arrangement, the outer wall of the breakable element 204 does not protrude from the outer wall of the outer cylinder 202, ensuring the safety of the protective cover 204 and preventing accidental damage to the breakable element 204 when the sliding sleeve device 200 is lowered. In a preferred embodiment, a plurality of protruding rings (not shown) are provided on the outer wall of the outer cylinder 202 between the faces of the stage 222. In this way, after the cement grout has cured to form the breakable element 204, the protruding rings will become embedded in the breakable element 204. For example, the protruding ring may be one formed by machining the outer wall of the outer cylinder 202, threads formed on the outer wall of the outer cylinder 202, one formed on the outer wall of the outer cylinder 202 by welding, or a rubber or similar ring arranged around the outer wall of the outer cylinder 202. On one hand, the protruding rings improve the friction between the cement grout and the outer cylinder 202, ensuring that the breakable element 204 can be securely fixed to the outer cylinder 202, thus guaranteeing safety.On the other hand, the protruding rings can provide a sealing effect to effectively prevent impurities from entering the circulation hole 221 through the space between the breakable element 204 and the outer cylinder 202, effectively preventing impurities from entering the area between the inner cylinder 206 and the outer cylinder 202. As an additional arrangement, as shown in Figure 4, a clearance 208 is formed in communication with the circulation hole 221 between the outer cylinder 202 and the inner cylinder 206, and is located outside the two axial ends of the circulation hole 221. In a specific embodiment, an enlarged hole 262 may be provided in the inner wall of the outer cylinder 202 immediately outside the circulation hole 221. A wall surface of the enlarged hole 262 is preferably configured to have an inclined surface 263, so that the clearance 208 narrows in both directions axially away from the circulation hole 221. On one hand, the above structure allows lubricating grease to easily enter the clearance 208, so that the lubricating grease can be smoothly driven into the area between the inner cylinder 206 and the outer cylinder 202 and follow the movement of the inner cylinder 206.This improves lubrication between the inner cylinder 206 and the outer cylinder 202, which also ensures the smooth downward movement of the inner cylinder 206. On the other hand, the inclined surface 263 ensures that the clearance 208 gradually decreases in size, acting as a barrier to prevent impurities from entering the area between the inner cylinder 206 and the outer cylinder 202. Figure 6 shows a sliding sleeve device 300, which may also be called a fracturing adapter, according to a third embodiment of the present invention. As shown in Figure 6, the sliding sleeve device 300 includes an outer cylinder 302 and an inner cylinder 306. A circulation hole 321 is provided in the wall of the outer cylinder 302, allowing communication between the inside and outside to provide a channel for the fracturing operation. The inner cylinder 306 is disposed in an internal cavity of the outer cylinder 302. For example, the inner cylinder 306 can be disposed in an inner wall of the outer cylinder 302 by means of a shear pin 305 and can thus be permanently connected to the outer cylinder 302.In an initial state of the sliding sleeve device 300, as shown in Figure 6, the inner cylinder 306 closes the circulation port 321. After subjecting the inner cylinder 306 to an axially downward force that reaches the shear pressure of the shear pin 305, the shear pin 305 shears, allowing the inner cylinder 306 to move downward relative to the outer cylinder 302, thus releasing the closure of the circulation port 321 from the inside. That is, the circulation port 321 is opened. Furthermore, as shown in Figure 6, the sliding sleeve device 300 further includes an upper seal 301, a lower seal 307, and multiple sealing rings 303 arranged between the inner cylinder 306 and the outer cylinder 302. Their structures and positions are similar to those described in the first embodiment of the present invention, and therefore detailed descriptions of these are omitted here. According to the present invention, a protective element 304 is further provided in the circulation port 321, as shown in Figure 6. The protective element 304 is used to block the circulation port 321 in the initial state of the sliding sleeve device 300, to prevent impurities from entering the circulation port 321 before the fracturing operation. According to the present invention, the protective element 304 is configured to leave the circulation port 321 exposed after the internal cylinder 306 moves downward to release the closure of the circulation port 321, so that the fracturing operation can be carried out. With the protective element 304, impurities and the like are effectively prevented from entering the circulation port 321 and, therefore, from entering the area between the inner cylinder 306 and the outer cylinder 302, ensuring the smooth downward movement of the inner cylinder 306. In particular, when the sliding sleeve device 300 is used in a well cementing operation integrated with well completion, the provision of the protective element 304 prevents cement slurry from accumulating in the circulation port 321. Consequently, the cement slurry cannot solidify in the circulation port 321 and block it, thus greatly reducing the risk of the inner cylinder 306 being unable to move downward. The specific structure of the protective element 304 in the sliding sleeve device 300 according to the third embodiment of the present invention will be described in detail below with reference to Figures 7 to 9. In one embodiment, the protective element 304 is configured as a plug, made of a soluble material, which can block the circulation port 321 from the outside. The plug can be partially filled with the circulation port 321, as shown in the Figure 7, or almost completely fill the circulation hole 321, as shown in Figure 8. In one particular example, the inner cylinder 306 is configured to receive a ball. In operation, after dropping the ball into the inner cylinder 306, pressure builds up to shear the shear pin 305, and the inner cylinder 306 moves downward under the pressure, thus clearing the blockage in the circulation hole 321 from within. At this point, dissolving fluid can be pumped into the internal cavity of the slip sleeve device 300, dissolving the plug-like protective element 304, which exposes the circulation hole 321. In this case, the fracturing operation can be performed at the formation level where the slip sleeve device 300 is located. Preferably, the plug can be made of magnesium or aluminum alloy, and the dissolving liquid can be an acidic solution or a solution containing chloride ions. It is worth noting that the duration of plug dissolution can be adjusted by appropriately selecting the plug material, the components, and the concentration of the solution, or similar factors, thus controlling the fracturing time. In one embodiment, a blind hole (not shown) extending radially outward (i.e., in the direction of arrow B in Figure 7) is provided on a radially internal surface of the plug. For example, several blind holes may be provided evenly distributed on the radially internal surface of the plug. Alternatively, only one blind hole may be provided in the center of the plug. This increases the contact area between the dissolving fluid and the plug, allowing the plug to dissolve uniformly, quickly, and completely, thus preventing incomplete dissolution that could hinder the fracturing operation in subsequent stages. Alternatively or additionally, a groove 348 may also be provided extending radially from the sliding sleeve device to the circumferential side of the plug itself. This allows the dissolving fluid to enclose an outer wall of at least one end of the plug, ensuring that the plug is in contact with the dissolving fluid in all directions, from the radially outer side to the radially inner side, during the dissolving process. Consequently, the plug can be dissolved uniformly, rapidly, and completely. Preferably, the plug comprises a connecting segment 342 and a beveling segment 343, which are arranged sequentially from the radially external side to the radially internal side and connected to each other, as shown in Figures 7 and 8. The connecting segment 342 is fixedly coupled to the circulation orifice 321, while the beveling segment 343 is configured to be reduced in size in the radial direction from the outside in, thus forming an intermediate space with the wall of the circulation orifice 321 to facilitate the entry of the dissolving liquid. For example, the ratio of the length of the connecting segment 342 to that of the beveling segment 343 is 0.5:1 to 1:1.Preferably, the connection between the connecting segment 342 and the circulation port 321 is formed as a screw fit or interference fit, with the outer surface of the plug and the outer surface of the outer cylinder 302 on the same arc surface. With this structure, during the lowering of the sliding sleeve device 300, the plug will not interfere with the wellbore and, at the same time, can completely block the circulation port 321 from the outside to prevent impurities, such as cement or similar materials, from entering it. It is easily understood that the outer surface of the plug can be further recessed relative to the outer surface of the outer cylinder 302 in the radial direction, which also prevents sand and cement from entering the area between the inner cylinder 306 and the outer cylinder 302 through the circulation port 321.It will also be easily understood that the cross-section of the protective element 304 can be in different structural shapes, for example, an oval, a square or a polygonal, according to different shapes of the circulation holes 321. In another embodiment, the protective element 304 can also be configured as a breakable disc 304A disposed in the circulation port 321, as shown in Figure 9. The breakable disc 304A includes a main body portion 344A fixedly connected to the circulation port 321 and a disc portion 345A that can be broken off so that the inside and outside of the circulation port 321 communicate with each other. In operation, after the inner cylinder 306 moves downward, pressure builds up to force the disc portion 345A of the breakable disc 304A to break off, exposing the circulation port 321 for subsequent fracturing. According to the present invention, the circulation orifice 321 can be filled with lubricating grease between the protective element 304 and the inner cylinder 306. For example, in the structure shown in Figure 7, a space in the circulation orifice 321 radially inward toward the plug (i.e., the lower portion of the circulation orifice 321 in Figure 7) can be filled with lubricating grease. The lubricating grease can be, for example, lubricating gel. As an additional provision, according to the present invention, a free space (not shown) may be provided in communication with the circulation hole 321 between the outer cylinder 302 and the inner cylinder 306 and outside the axial ends of the circulation hole 321. The free space is similar to the free space 8 mentioned in the first embodiment of the present invention in terms of structure and function, which will not be repeated here. According to another aspect of the present invention, a fracturing string (not shown) is provided, comprising a plurality of slip sleeve devices 100 according to the first embodiment of the present invention, a plurality of slip sleeve devices 200 according to the second embodiment of the present invention, or a plurality of slip sleeve devices 300 according to the third embodiment of the present invention. During the fracturing operation, these slip sleeve devices are opened stage by stage for the fracturing of separate layers. Although the present invention has been described above with reference to exemplary embodiments, various modifications may be made and components may be replaced with equivalents thereof without departing from the scope of the present invention. In particular, provided there is no structural conflict, each technical feature mentioned in each embodiment may be combined in any manner. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that are within the scope of the claims.

Claims

1. A sliding sleeve device, comprising: an external cylinder, with a circulation hole provided in a wall of the external cylinder; and an internal cylinder disposed in an internal cavity of the external cylinder, wherein, in an initial state, the internal cylinder and the external cylinder are fixed to each other to close the circulation hole and, in a first state, the internal cylinder moves with respect to the external cylinder to release the closure of the circulation hole, wherein a protective mechanism is provided in the circulation hole and includes an internal member located on a radially internal side and an external member located on a radially external side.

2. The sliding sleeve device according to claim 1, wherein the circulation hole comprises two stages formed in an outer wall of the outer cylinder and circumferentially opposed to each other, wherein the outer member is configured to extend over said two stages to block the circulation hole. 3 - The sliding sleeve device according to claim 1 or 2, wherein the inner member is lubricating grease filled into the circulation hole and the outer member is a protective cover.

4. The sliding sleeve device according to claim 3, wherein a recess is provided in an outer wall of the inner cylinder and at least partially located in the circulation hole in the initial state to allow lubricating grease to enter the recess. 5.- The sliding sleeve device according to claim 4, wherein the protective cover is a heat-shrinkable cover that overlaps on the outer cylinder wall, or a rubber sleeve vulcanized on the outer cylinder wall.

6. The sliding sleeve device according to claim 4, wherein the protective cover is a resin cover disposed in the circulation hole.

7. The sliding sleeve device according to claim 2, wherein the outer member is a breakable element that will break under pressure and the inner member is a support element to support the breakable element and to fall off thereunder pressure.

8. The sliding sleeve device according to claim 7, wherein at least one protruding ring is provided embedded in the breakable element on the outer wall of the outer cylinder in a region between said two stages.

9. The sliding sleeve device according to claim 7 or 8, wherein the breakable element is configured as a cement cover formed by hardening the supplied cement grout.

10. The sliding sleeve device according to claim 7, wherein the support element is configured as a plurality of stacked resin balls or as a plurality of stacked metal balls soluble in working fluid.

11. The sliding sleeve device according to claim 10, wherein the support element comprises multiple layers of balls, wherein the balls are gradually reduced in layers in a direction from the radially inner side to the radially outer side.

12. The sliding sleeve device according to any of claims 7 to 11, wherein a lubricating grease layer is provided on both the radially internal and external sides of the support element.

13. The sliding sleeve device according to claim 1 or 2, wherein the external member is configured as a plug made of soluble material. 14.- The sliding sleeve device according to claim 13, wherein a blind hole is provided on a radial inner surface of the plug.

15. The sliding sleeve device according to claim 13 or 14, wherein the plug comprises a connecting segment and a tilting segment, which are arranged sequentially in a direction from the radially external side to the radially internal side and connected to each other, and wherein the connecting segment is fixedly coupled to the circulation hole, while the tilting segment is configured to have a reduced size in the direction from the radially external side to the radially internal side.

16. The sliding sleeve device according to claim 1 or 2, wherein the outer member is configured as a breakable disc, including a main body portion fixedly connected to the circulation hole and a disc portion that is breakable under pressure.

17. The sliding sleeve device according to any of claims 1 to 16, wherein a free space is provided in communication with the circulation hole between the outer cylinder and the inner cylinder and the outer axial ends of the circulation hole.

18. The sliding sleeve device according to claim 17, wherein the clearance is an enlarged hole formed in the inner wall of the outer cylinder, wherein the enlarged hole comprises an inclined surface, such that the clearance narrows in a direction away from the circulation hole.

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