A dissolving full-gauge staged cementing device and method

Abstract

The application discloses a kind of dissolved full-gauge staged cementing devices and staged cementing methods, to solve the long construction period, high operation risk, poor well condition adaptability, limited path accuracy and other industry core pain points of traditional staged cementing device, the application includes body, upper and lower end connecting part, closing sleeve, opening sleeve, closing plug, opening plug, closing plug seat, opening plug seat, shear pin, sealing device and matching high-concentration chlorine dissolving solution;A closed liquid storage cavity is formed between the closing sleeve and the body for sealing and storing high-concentration chlorine dissolving solution, preventing leakage of dissolving solution before construction and premature dissolution of components, wherein the opening plug, opening plug seat and closing plug seat are made of soluble aluminum-magnesium alloy material, the closing plug is made of a soluble rubber bowl and a soluble aluminum-magnesium alloy integrated structure, all internal plugging components are made of soluble material, and can accurately match the dissolution characteristics of high-concentration chlorine dissolving solution to achieve controllable and complete dissolution.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas cementing engineering technology, specifically relating to a dissolution-type full-bore staged cementing injector. It also discloses a staged cementing method based on the cementing injector, which is applicable to multi-stage cementing operations of various oil and gas wells such as vertical wells, deviated wells, directional wells, and horizontal wells. Background Technology

[0002] Staged cementing units are core downhole tools for multi-stage cementing operations in oil and gas wells. After completing the staged cementing process, traditional staged cementing units leave components such as sealing plugs, plug seats, and opening / closing sleeves inside the tool. These must be lowered into the drilling string for drilling and milling operations to open the wellbore and create a full bore, meeting the requirements of subsequent downhole operations such as logging, perforation, and fracturing. This operational method is complex, has a long overall construction cycle, and the drilling and milling operations are prone to scratching the casing and damaging the cement sheath structure, significantly increasing operating costs and downhole safety risks.

[0003] Currently available no-drill staged cementing units rely primarily on the weight of their internal components to descend to the bottom of the well and achieve borehole clearance, eliminating the need for drilling and milling. However, they still suffer from several technical drawbacks: First, in non-vertical well conditions such as deviated, directional, and horizontal wells, the downhole components are prone to jamming and failure to descend smoothly due to the wellbore inclination and wellwall friction resistance, ultimately requiring additional well cleaning operations and failing to truly simplify the construction process. Second, existing no-drill structures have poor adaptability to well conditions and can only be stably applied to conventional vertical wells, failing to meet the construction needs of complex well structures. Third, the conventional pressure-driven + weight-based bottom-fall control method lacks precision and has weak sealing structure reliability, making it prone to malfunctions such as slurry leakage through circulation holes and component failure, seriously affecting the quality and safety of cementing operations.

[0004] In summary, existing staged cementing machines cannot simultaneously meet the comprehensive requirements of no drilling and milling, full-bore operation, multi-well condition adaptability, and precise operation with reliable sealing, thus hindering the development of multi-stage cementing technology for complex oil and gas wells. Therefore, developing a staged cementing machine with a reasonable structure, controllable operation, full-bore operation achieved through chemical dissolution, and adaptability to all types of wellbores, along with its supporting construction method, is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies, such as the need for drilling and milling in traditional staged cementing machines, poor well condition adaptability of conventional drill-free staged cementing machines, easy component jamming requiring well cleaning operations, and low control precision. It provides a dissolution-type full-bore staged cementing machine and a staged cementing method. This invention employs a combined design of pressure shear control for opening and closing, soluble components, and built-in dissolving liquid. It relies on chemical dissolution to remove internal functional components from the wellbore, eliminating the need for drilling and milling or secondary well cleaning. It is adaptable to all well conditions, including vertical, deviated, directional, and horizontal wells. The opening and closing action is precise, and the sealing performance is excellent. This invention aims to solve the core pain points of traditional staged cementing machines, such as cumbersome subsequent drilling and milling operations, long construction cycles, high operational risks, poor well condition adaptability, and limited wellbore accuracy.

[0006] The technical solution adopted by this invention to solve its technical problem is: A dissolving full-bore graded cement injector includes a body and connecting parts respectively disposed at the upper and lower ends of the body; the connecting parts at the upper and lower ends of the body are respectively equipped with an upper connector and a lower connector, both of which are machined with connecting threads, and achieve sealed connection with the upper sleeve string and the lower sleeve string respectively through the thread structure.

[0007] The inner cavity of the main body is equipped with a closing sleeve and an opening sleeve from top to bottom. The closing sleeve is fixed to the main body by a closing sleeve pin, and the opening sleeve is fixed to the main body by an opening sleeve pin. Both the closing sleeve pin and the opening sleeve pin are pressure shear pins, which can be sheared and destroyed under a preset pressure.

[0008] A shut-off plug seat is fixedly installed on the inner side of the lower end of the shut-off sleeve. The shut-off plug, inserted at the wellhead, can descend along the casing and sit on the shut-off plug seat. The outer wall of the shut-off sleeve and the inner wall of the main body enclose a sealed cavity, which is pre-filled with a high-concentration chloride solution, and the chloride solution is arranged in the area above the shut-off plug. The shut-off sleeve is equipped with sealing devices on the upper and lower sides of the sealed cavity and on the upper and lower sides of the shut-off sleeve pin, so as to achieve sealed storage of chloride solution in the sealed cavity and sealing of the area of ​​the shut-off sleeve pin, which can effectively prevent chloride solution from leaking before construction and prematurely dissolving internal components.

[0009] The main body has circulation holes on its sidewalls, which are initially completely sealed by the outer wall of the opening sleeve. An opening plug seat is fixedly installed on the inner side of the lower end of the opening sleeve. The opening plug inserted at the wellhead can pass through the closing plug seat sequentially and finally sit on the opening plug seat. Sealing devices are installed on both the upper and lower sides of the circulation holes and on both the upper and lower sides of the opening sleeve pins to achieve sealing between the circulation hole area and the periphery of the opening sleeve pins, preventing slurry leakage during cementing.

[0010] This device adopts an equal-diameter design: the final inner diameter of the closing sleeve and the opening sleeve is equal to the inner diameter of the sleeve string, so that the closing plug can pass smoothly inside the sleeve string; the maximum outer diameter of the opening plug is smaller than the inner diameter of the closing plug seat, ensuring that the opening plug can pass through the closing plug seat without obstruction.

[0011] The present invention adopts a differentiated soluble material design for the core functional components: the opening plug, opening plug seat, and closing plug seat are all made of soluble aluminum-magnesium alloy; the closing plug is a composite of soluble rubber cup and soluble aluminum-magnesium alloy; the high-concentration chloride solution built into the device can gradually dissolve the aluminum-magnesium alloy and soluble rubber cup.

[0012] When the opening plug is seated in the opening plug seat, the wellhead pressure is increased to the set value, the opening sleeve pin is sheared off, and the opening sleeve moves downward along the body, releasing the blockage of the circulation hole and opening it. When the closing plug is seated in the closing plug seat, the wellhead pressure continues to increase to the corresponding set value, the closing sleeve pin is sheared off, and the closing sleeve moves downward along the body, sealing the circulation hole and closing it. During the downward movement of the closing sleeve, the sealing structure of the sealed cavity simultaneously fails, and the high concentration of chloride solution inside the sealed cavity automatically overflows, dissolving the internal soluble components.

[0013] A well injection method using the above-mentioned dissolution-type full-bore staged cementing device includes the following steps: Step 1: Lower the tool into the wellbore Connect the dissolution-type full-bore staged cementing device to the designed position of the casing string, and connect it in series with the casing string. Run it into the wellbore to the preset depth along with the casing string; connect a conventional cementing device to the bottom of the casing string.

[0014] Step 2: Complete the first stage of cement injection. Inject cement slurry into the casing string to fill the annulus from the bottom of the well to the position of this dissolving full-bore staged cement injector. The cement slurry is then injected in reverse into the annulus of the wellbore through the ordinary cement injector at the bottom of the casing string until the cement level reaches or approaches the position of this staged cement injector, thus completing the first stage of cement injection. The process is then left to stand and wait for the first stage of cement to solidify.

[0015] Step 3: Dispense the opening plug to open the circulation hole. After the first stage of cement has cured, an opening plug is inserted into the casing string. The opening plug moves down the casing string, passes through the closing plug seat in sequence, and finally sits on the opening plug seat, thus sealing the opening sleeve with the lower casing string. A pressurization operation is performed from the wellhead. When the pressure reaches the preset shear pressure, the opening sleeve pin is sheared off, the opening sleeve moves downward along the body, and the circulation hole on the side wall of the body is exposed, forming a circulation channel that connects the inside of the casing with the annulus of the wellbore outside the casing.

[0016] Step 4: Secondary cementing operation, closing the circulation hole and starting the dissolution process. Secondary cementing operations are carried out through the opened circulation holes; after the secondary cementing operations are completed, a shut-off plug is inserted into the wellbore. The upper part of the shut-off plug contains high-pressure replacement fluid and the lower part contains cement slurry. Under high pressure, the shut-off plug moves down along the tubing string and squeezes the remaining cement slurry in the tubing through the circulation holes into the wellbore annulus. The shut-off plug continues to descend and eventually sits on the shut-off plug seat. Pressure is increased again from the wellhead. Once the pressure reaches the set value, the shut-off sleeve pin is sheared, and the shut-off sleeve moves downward along the body. The circulation hole is completely sealed and closed by the shut-off sleeve and the matching sealing device. As the closing sleeve moves downward, its upper sealing structure shifts, the sealed cavity fails to seal, and the high-concentration chloride solution inside overflows outward, first coming into full contact with the closing plug and closing plug seat and gradually dissolving them, thus forming the full bore in this area.

[0017] Step 5: The entire component is dissolved, and the wellbore is completely formed to full bore. The overflowing high-concentration chloride solution continued to flow downwards, contacting and gradually and completely dissolving the opening plug and opening plug seat, simultaneously forming a full bore in the area where the opening sleeve was located. At this point, all soluble functional components inside the staged cementing unit were completely dissolved and removed, leaving no obstructions or residual parts inside the wellbore. The entire wellbore formed a continuous and complete full bore, and the multi-stage cementing operation was completed.

[0018] This method can be applied to various well conditions such as vertical wells, deviated wells, directional wells, and horizontal wells. No drilling and milling operations or secondary well cleaning operations are required throughout the construction process and after completion.

[0019] Beneficial effects of the invention Compared with existing traditional staged cementing devices and conventional drill-free staged cementing devices, this invention has several outstanding technical advantages: (1) Wide range of well conditions adaptability This invention abandons the traditional method of relying on the weight of components to reach the bottom to achieve the borehole diameter. Instead, it uses the principle of chemical dissolution to remove internal components. It is completely unaffected by wellbore inclination, wellbore friction, and wellbore trajectory changes. It can stably adapt to various complex well conditions such as vertical wells, inclined wells, directional wells, and horizontal wells, breaking through the limitations of existing tools.

[0020] (2) Truly achieve drilling-free and milling-free, and secondary well cleaning-free By relying on the built-in high-concentration chloride solution to dissolve all soluble functional components, the wellbore naturally forms a full diameter after construction, eliminating the need for subsequent operations such as drilling, milling, and well cleaning. This greatly simplifies the multi-stage cementing construction process, effectively shortens the overall construction cycle, and reduces manpower, equipment investment, and overall operating costs.

[0021] (3) Precise motion control and high sealing reliability The structure adopts a graded pressure shear pin combined with a multi-stage independent sealing device. The opening and closing actions of the circulation hole are independent of each other, the opening and closing pressure thresholds are controllable, and the actions are precise. Multiple sealing structures seal the solution storage chamber, the pin area, and the circulation hole area respectively, which can effectively prevent leakage, slurry crossing, opening and closing jamming and other faults, and improve the safety and quality of cementing construction.

[0022] (4) The duct diameter is continuous and complete, and it has strong versatility. The design ensures that the final inner diameter of the closing sleeve and opening sleeve is equal to that of the casing string. After the components are completely dissolved, there are no residual debris. The wellbore flow is smooth and continuous, which can meet the requirements of various conventional downhole operations such as logging, perforation, and fracturing. It has strong versatility.

[0023] (5) Simple structure and convenient construction With its integrated structural design, it is lowered into the wellbore in one go along with the casing string. The construction process is procedural, with minimal human intervention. The dissolution process is completed automatically, resulting in high operational stability and good value for field promotion and application. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Figure 1 This is a schematic diagram illustrating the operating conditions of this dissolution-type full-bore staged cement injector. Figure 2 This is a schematic diagram of the three-dimensional structure of the dissolution-type full-bore graded cement injector; Figure 3 This is a schematic diagram of the main sectional view of the dissolution-type full-bore staged cement injector. In the diagram, 1 is the upper connector, and 11 is the upper thread. 2. Body; 21. High-concentration chloride solution injection port; 22. Sealed cavity; 23. Closed sleeve pin; 24. Opened sleeve pin; 25. Circulation hole; 3. Closing sleeve; 31. Sealing ring I; 32. Sealing ring II; 33. Sealing ring III; 4. Open the sleeve; 41. Sealing ring IV; 42. Sealing ring V; 5. Lower connector, 51. Lower thread; 6. Close the plug seat; 61. Close the plug; 7. Open the stopper seat; 71. Open the stopper; 8. Formation; 9. Casing string; 91. Bottom cementing device; 10. Well body; 101. Wellbore annulus; 102. Cement slurry. Detailed Implementation

[0026] Those skilled in the art should understand that the present invention is not limited to the specific embodiments described below. Any equivalent modifications, substitutions, and improvements made without departing from the core technical solution of the present invention shall fall within the protection scope of the present invention.

[0027] Example 1: Structural Example of a Dissolution-Type Full-Diameter Staged Cement Injector As shown in Figures 2 and 3, the main body of this device is a cylindrical body 2. The upper end of the body 2 is connected to the sleeve string 9 via an upper connector 1, and the lower end of the body 2 is connected to the lower connector 5. The upper connector 1 is machined with an upper thread 11, and the lower connector 5 is machined with a lower thread 51. The threaded structure achieves a sealed connection. The overall inner diameter of the device is consistent with the inner diameter of the sleeve string 9, ensuring the continuity of the pipe diameter.

[0028] The inner cavity of the main body 2 is arranged with a closing sleeve 3 and an opening sleeve 4 arranged sequentially from top to bottom along the axial direction. The closing sleeve 3 is fixed inside the main body 1 by closing sleeve pin 23, and the opening sleeve 4 is fixed inside the main body by opening sleeve pin 24. Both sets of pins are pressure shearing structures, which can be sheared under the action of preset wellhead pressure.

[0029] The inner side of the closing sleeve 3 is fixedly installed with a closing plug seat 6, which is used to receive the closing plug 61 inserted at the wellhead. The outer wall of the closing sleeve 3 and the inner wall of the main body 2 form a sealed cavity 22. A high-concentration chloride solution injection port 21 is opened on the main body 2. During the assembly stage, the solution is injected into the sealed cavity 22 through the high-concentration chloride solution injection port 21. After the injection is completed, the injection port is sealed. The sealed cavity 22 is located in the area above the closing plug 61. Sealing ring I 31, sealing ring II 32, and sealing ring III 33 are installed on the closing sleeve 3 to provide multiple seals for the sealed cavity 22 and the area of ​​the closing sleeve pin 23, respectively, to prevent premature leakage of the solution and accidental corrosion of internal components.

[0030] A circulation hole 25 is opened on the side wall of the main body 2. During the tool lowering into the wellbore and the first stage of cementing, the circulation hole 25 is completely sealed by the outer wall of the opening sleeve 4. An opening plug seat 7 is fixedly installed on the inner side of the opening sleeve 4 to receive the opening plug 71. Sealing rings IV 41 and V 42 are installed on the outer side of the opening sleeve 4 to seal the circulation hole 25 and the area around the opening sleeve pin 24, preventing slurry leakage during cementing operations.

[0031] In terms of size fit, the maximum outer diameter of the opening plug 71 is smaller than the inner diameter of the closing plug seat 6, allowing it to pass through the closing plug seat 6 without obstruction; the closing plug 61 adopts a soluble rubber cup + soluble aluminum-magnesium alloy composite structure, and its outer diameter, i.e. the outer diameter of the soluble rubber cup, is flexibly interference-matched with the inner diameter of the sleeve string 9, ensuring smooth descent and reliable setting and sealing.

[0032] In terms of material configuration, the opening plug 71, the opening plug seat 7, and the closing plug seat 6 are all made of soluble aluminum-magnesium alloy; the closing plug 61 is a combination of soluble rubber cup and soluble aluminum-magnesium alloy; the high concentration of chloride solution in the sealed cavity 22 can achieve uniform and complete dissolution of all the above soluble components.

[0033] Example 2: Graded Cementing Method Example As shown in Figure 1, a wellbore 10 is drilled in formation 8, and a casing string 9 is installed inside the wellbore, forming a wellbore annulus 101 between the outer wall of the casing string and the wellbore wall; a conventional bottom cementing device 91 is installed at the bottom end of the casing string 9, and the staged cementing devices are installed in series at designated positions on the casing string 9. The specific construction process is as follows: Step 1: Lower the tool into the wellbore Connect this dissolving full-bore staged cementing device to the designed position of the casing string 9, and lower it into the well body 10 to the preset depth along with the entire casing string 9; connect the bottom of the casing string 9 to a conventional ordinary cementing device, i.e., the bottom cementing device. Step 2: Complete the first stage of cement injection. First-stage cementing operation: Cement slurry 102 is injected into the casing string 9, and the cement slurry is injected in reverse into the annulus 101 of the wellbore through the bottom cement injector 91. Grouting continues until the cement level is close to the position of the cement injector for this stage, then the operation is stopped. The amount of cement slurry injected is determined by the annulus volume. The area is then left to cure, awaiting the solidification of the first-stage cement.

[0034] Step 3: Dispense the opening plug to open the circulation hole. Deploying the opening plug to open the circulation hole: After the first stage of cement has solidified, the opening plug 71 is inserted from the wellhead. The opening plug 71 descends along the casing, passes through the closing plug seat 6, and settles into the opening plug seat 7, forming a sealing structure. The wellhead pressure is gradually increased. When the pressure reaches the set value, the opening sleeve pin 24 is sheared, the opening sleeve 4 moves downward, and the circulation hole 25 on the side wall of the main body is fully exposed, establishing a circulation channel between the inside of the casing and the annulus 101 of the wellbore.

[0035] Step 4: Secondary cementing operation, closing the circulation hole and starting the dissolution process. Secondary cementing and circulation hole closure: Secondary cementing operations are carried out using the opened circulation hole 25. After the designed amount of cement is injected, the closure plug 61 is inserted into the wellhead. Under the action of the high-pressure replacement fluid in the upper part, the closure plug 61 moves downward, squeezing the cement slurry in the pipe into the wellbore annulus 101. After the closure plug 61 is seated in the closure plug seat 6, the wellhead is pressurized again, shearing off the closure sleeve pin 23. The closure sleeve 3 moves down as a whole, and in conjunction with the sealing device, completely seals and closes the circulation hole 25. During the downward movement of the closing sleeve 3, the sealing structure at the upper end of the sealed cavity 22 fails, and the high concentration of chloride solution inside overflows outward, starting to erode the closing plug 61 and the closing plug seat 6. This area is the first to form a full-bore. Step 5: The entire component is dissolved, and the wellbore is completely formed to full bore. The components are completely dissolved, and the wellbore forms a full bore: the overflowing high-concentration chloride solution continues to flow downwards, gradually dissolving the opening plug 71 and the opening plug seat 7; after all soluble components have been completely dissolved, there are no obstructing parts inside the staged cementing device, and the wellbore forms a continuous and complete full bore.

[0036] This invention's construction process strictly follows oil and gas well cementing specifications. The two-stage shear pins correspond to independent pressure thresholds, and the sequence of actions is controllable. Component dissolution is automatically completed through chemical reactions, requiring no manual intervention or additional drilling tools, ensuring safe and efficient construction. This device and its supporting methods are adaptable to various well conditions, including vertical, deviated, directional, and horizontal wells. No drilling, milling, or well cleaning operations are required after construction, resulting in low overall construction costs and high application value.

Claims

1. A dissolution-type full-bore staged cement injector, characterized in that: It includes a main body and connecting parts respectively disposed at the upper and lower ends of the main body; the inner cavity of the main body is equipped with a closing sleeve and an opening sleeve from top to bottom. The closing sleeve is fixed to the main body by a closing sleeve pin, and the opening sleeve is fixed to the main body by an opening sleeve pin. Both the closing sleeve pin and the opening sleeve pin can be sheared and destroyed under a set pressure. A shut-off plug seat is provided on the inner side of the lower end of the shut-off sleeve. The shut-off plug dropped into the wellhead can descend along the tubing string and sit on the shut-off plug seat. The outer wall of the shut-off sleeve and the inner wall of the main body enclose a sealed cavity. The sealed cavity is filled with a high concentration of chloride solution, and the solution is arranged above the shut-off plug. The main body has a circulation hole on its side wall, which is initially closed by the outer wall of the opening sleeve; an opening plug seat is provided on the inner side of the lower end of the opening sleeve, and the opening plug inserted at the wellhead can pass through the closing plug seat in sequence and finally sit on the opening plug seat. The inner diameters of the closing sleeve and opening sleeve are designed to be the same as the inner diameter of the sleeve string, allowing the closing plug to pass smoothly inside the sleeve string; the maximum outer diameter of the opening plug is smaller than the inner diameter of the closing plug seat, allowing the opening plug to pass through the closing plug seat without obstruction. The opening plug, opening plug seat, and closing plug seat are all made of soluble aluminum-magnesium alloy; the closing plug is a combination of soluble rubber cup and soluble aluminum-magnesium alloy; the high-concentration chloride solution can dissolve the above-mentioned aluminum-magnesium alloy components and rubber cup components.

2. The dissolution-type full-bore staged cement injector according to claim 1, characterized in that: The two ends of the main body are connected to an upper connector and a lower connector, respectively. Both the upper connector and the lower connector are machined with threads for connecting the sleeve string. The main body is sealed and connected to the upper sleeve string and the lower sleeve string through the threaded connection.

3. The dissolution-type full-bore staged cement injector according to claim 1, characterized in that: The opening sleeve is equipped with sealing devices on both the upper and lower sides of the circulation hole and the opening sleeve pin to achieve sealing between the circulation hole area and the periphery of the opening sleeve pin. When the opening plug falls from the wellhead and sits on the opening plug seat, the wellhead pressure increases, and the opening sleeve pin is sheared under the set pressure. Then, the opening sleeve moves downward along the body to release the blockage of the circulation hole and open the circulation hole.

4. The dissolution-type full-bore staged cement injector according to claim 1, characterized in that: The closing sleeve is equipped with sealing devices on both the upper and lower sides of the sealed cavity and on both the upper and lower sides of the closing sleeve pin, so as to achieve sealing of the dissolving liquid and sealing of the periphery of the closing sleeve pin; when the closing plug falls from the wellhead and sits on the closing plug seat, the wellhead pressure is increased, and the closing sleeve pin is sheared under the set pressure. Then, the closing sleeve moves downward along the body to block the circulation hole and realize the closure of the circulation hole.

5. A method for graded cementing using a dissolution-type full-bore graded cement injector as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Inside the well, connect the dissolution full-bore staged cement injector to the designed position of the casing string and lower it into the wellbore to the preset depth along with the casing string. Connect the ordinary cement injector to the bottom of the casing string. Step 2: Inject cement slurry into the casing string to fill the annulus from the bottom of the well to the position of the cement injector in this stage. The cement slurry is injected in reverse into the annulus of the wellbore through the ordinary cement injector at the bottom of the casing string until the cement level reaches or approaches the position of the cement injector in this stage. The first stage of cement injection is completed. Let it stand and wait for the first stage of cement to solidify. Step 3: After the first stage of cement has cured, the opening plug is inserted into the casing. The opening plug moves down along the casing and sits on the opening plug seat, thus sealing the opening sleeve with the lower casing string. The wellhead is pressurized. After the pressure reaches the set value, the opening sleeve pin is sheared, the opening sleeve moves downward, and the circulation hole on the body is exposed, forming a circulation channel between the inside and outside of the casing. Step 4: Conduct secondary cementing operations through the circulation hole; after the operation is completed, insert a shut-off plug into the wellbore. The upper part of the shut-off plug contains high-pressure replacement fluid, and the lower part contains cement. The shut-off plug descends under high pressure, squeezing the cement in the pipe through the circulation hole into the wellbore annulus; after the shut-off plug continues to descend and sits in the shut-off plug seat, the wellhead continues to pressurize, the shut-off sleeve pin is sheared off, the shut-off sleeve moves downward, and the circulation hole is sealed closed by the shut-off sleeve and matching seals; as the shut-off sleeve descends, its upper sealing structure moves synchronously, causing the sealed cavity to fail, the dissolving fluid overflows and fully contacts the shut-off plug and shut-off plug seat, and fully erodes the shut-off plug and shut-off plug seat, forming a full-bore at this position; Step 5: The high-concentration chloride solution continues to fall to the position of the open plug and the open plug seat, completely dissolving the open plug and the open plug seat, and simultaneously forming the full bore at the position of the open sleeve.

6. The graded cement injection method according to claim 5, characterized in that: This method can be used for vertical wells, angled wells, directional wells, and horizontal wells. No drilling, milling, or well cleaning operations are required after the construction is completed.

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