Soluble blanking plug for well completion operation under pressure and use method of soluble blanking plug

Abstract

The invention discloses a soluble blanking plug for under-pressure well completion operation and a using method thereof, and belongs to the technical field of under-pressure operation, the blanking plug comprises a soluble inner core arranged in a hollow connector, the soluble inner core is in a frustum shape, the inner wall of the connector is provided with a step face matched with the upper end face of the soluble inner core, and the inner wall of the connector is connected with the soluble inner core. The conical surface is matched with the outer circumferential surface of the soluble inner core to realize plugging; the soluble inner core comprises a base body and a composite corrosion-resistant coating arranged on the surface of the base body, and a sealing assembly is arranged on the contact surface of the soluble inner core and the inner wall of the connector. The method comprises the following steps: assembling the soluble blanking plug, and connecting the soluble blanking plug to a well entering pipe string; the pipe column is safely fed into a well; after all the pipe columns enter the well, setting and hanging a tubing hanger; the wellhead gas production tree is installed, and the pressure test is qualified; and the soluble blanking plug is dissolved, the production channel is opened, and the natural gas well enters a normal production process. The soluble blanking plug can bear the ultrahigh-pressure and high-temperature underground environment, and the timing pressure bearing function is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure - operated workover, and particularly to a soluble plugging device for pressure - operated well completion workover and its usage method. Background Art

[0002] When running a completion string under pressure in China, mechanical means are usually used to block the pressure inside the pipe. A common process is to connect a ceramic rupture disk at the bottom of the completion string for plugging and sealing inside the pipe. After the completion string is run in place, hung, the equipment is removed, and the gas production tree is installed, positive pressure is applied to break through the ceramic rupture disk to communicate the tubing - casing annulus and realize the tubing - drainage gas - production process; another common process is to connect a blind plug at the bottom of the completion string for plugging and sealing inside the pipe. After the completion string is run in place, hung, the equipment is removed, and the gas production tree is installed, positive pressure is applied to knock out the blind plug to communicate the tubing - casing annulus and realize the tubing - drainage gas - production process; the third common process is to use a soluble plugging device. After the completion string is run in place, hung, the equipment is removed, and the gas production tree is installed, a solution medium is added through the positive eye of the tubing while positive pressure is applied to shear the limit pin of the plugging core, and the plugging core starts to dissolve to communicate the tubing - casing annulus.

[0003] At present, for pressure - operated well completion workover of gas wells abroad, a ceramic rupture disk is mainly used to block the inside of the tubing. After the completion string is successfully run into the well and the gas production tree is installed, positive pressure is applied inside the pipe to break through the ceramic rupture disk to communicate the tubing - casing annulus; there are constant - pressure plugging devices in China, but there is a risk of foreign objects falling into the well and the foreign objects not dissolving; for using a ceramic rupture disk to block the inside of the tubing in China, all are imported products. Currently, this operation tool has the following disadvantages: the risk of foreign objects falling into the well; high risk in positive - pressure - application construction; restricted by foreign suppliers, with a long supply cycle.

[0004] There is no domestic technical contractor for soluble blind plugs above 70 MPa, which cannot meet the construction requirements of wells with a bottom - hole pressure of 70 MPa and above. Therefore, there is an urgent need to design a 70 - MPa high - temperature - resistant soluble plugging device different from blind plugs or ceramic rupture disks and with more price advantages to lay a foundation for the large - scale application of pressure - operated well completion workover. Summary of the Invention

[0005] In order to solve the above problems existing in the soluble plugging device in the prior art, a soluble plugging device for pressure - operated well completion workover and its usage method are proposed.

[0006] In order to achieve the above - mentioned invention purpose, the technical solution of the present invention is as follows: A soluble plugging device for pressure - operated well completion workover, characterized in that it includes a soluble inner core arranged inside a hollow joint. The soluble inner core is in the shape of a frustum of a cone with a smaller upper diameter and a larger lower diameter. A stepped surface matching the upper end surface of the soluble inner core and a conical surface matching the outer circumferential surface of the soluble inner core to achieve plugging are arranged on the inner wall of the joint; the soluble inner core includes a matrix and a composite corrosion - resistant coating arranged on the surface of the matrix, and a sealing component is arranged on the contact surface between the soluble inner core and the inner wall of the joint.

[0007] Preferably, in one embodiment, the joint includes an upper joint and a lower joint. The upper joint and the lower joint are detachably and fixedly connected, and the soluble core is located inside the upper joint.

[0008] Preferably, in one embodiment, the composite corrosion-resistant coating covers the lower end face and the outer circumferential surface of the soluble core, and the coating thickness is 10 - 15 μm.

[0009] Preferably, in one embodiment, the matrix of the soluble core is made of magnesium alloy material.

[0010] Preferably, in one embodiment, the composite corrosion-resistant coating includes a transition layer, a corrosion-resistant layer, and a stable layer arranged in sequence from the inside to the outside; the transition layer is a layer of metal ions deposited on the magnesium alloy matrix by using physical vapor deposition and chemical vapor deposition techniques and utilizing ions generated by plasma discharge; the corrosion-resistant layer is a multi-element nano-coating deposited on the surface of the transition layer; the stable layer is a multi-layer functional composite ceramic film deposited on the surface of the corrosion-resistant layer.

[0011] Preferably, in one embodiment, shear pins for limiting are radially arranged on the lower end face of the soluble core.

[0012] Preferably, in one embodiment, positioning grooves for installing shear pins are arranged on the circumferential surface of the joint. The number of shear pins and the positioning grooves corresponds one by one and is evenly distributed around the lower end face of the soluble core.

[0013] Preferably, in one embodiment, the joint is provided with a plurality of strip-shaped through holes for communicating the oil and gas production channels below the soluble core.

[0014] Preferably, in one embodiment, a reduced-diameter area is arranged inside the lower joint. Its maximum inner diameter is equal to the maximum outer diameter of the soluble core, and the minimum inner diameter of the reduced-diameter area is the same as the through diameter of the lower joint.

[0015] A method for using a soluble plug for underbalanced completion operations, characterized by comprising the following steps: Step a, assemble the soluble plug according to technical requirements; After installing the prepared soluble core with the sealing assembly, load it from below into the upper joint. Apply force to make the upper end of the soluble core abut against the step surface inside the joint. Then, put the shear pins into the positioning grooves to make them abut against the lower end face of the soluble core, and then connect the upper joint and the lower joint; Step b, connect the soluble plug to the downhole string according to the requirements of the downhole tool string structure; Step c, safely send the string into the well through the underbalanced operation equipment; Step d, after all the strings are in the well, set the tubing hanger; Step e: Install the wellhead gas production tree and pass the pressure test; Step f: According to the construction period requirements, the soluble inner core is subjected to timed pressure bearing. When the pressure difference between the upper and lower parts of the soluble plugging device exceeds 2 MPa, the backflow fluid is poured into the well to open the soluble plugging device; Step g: After the soluble inner core contacts the backflow fluid in the pipe, it quickly dissolves, and finally full-bore production of the downhole string is achieved.

[0016] In summary, the present invention has the following advantages: (1) In the soluble plugging device of the present invention, the soluble inner core uses magnesium alloy as the matrix, and a coating is applied to its lower end face and outer circumferential surface, greatly improving the downhole pressure-bearing and temperature-resistant properties of the magnesium alloy material, enabling the soluble plugging device to achieve the function of timed pressure bearing; (2) In the soluble plugging device of the present invention, the sealing surface of the soluble inner core is matched with the inner conical surface inside the upper joint. Under the impact of the pressure in the pipe, the soluble inner core continuously presses upward along the wedge surface, achieving the self-sealing effect of the conical surface.

[0017] (3) In the soluble plugging device of the present invention, the multi-component composite corrosion-resistant coating actually also serves as a kind of filling seal, closely fitting with the inner wall of the upper joint; combined with the sealing component arranged on the outer circular surface of the soluble inner core to achieve combined sealing, together with the self-sealing of the soluble inner core, a triple sealing effect is achieved, enabling the soluble inner core to withstand the ultra-high pressure and high-temperature downhole environment of 105 MPa and 150 °C; (4) In the soluble plugging device of the present invention, the upper end of the soluble inner core uses stepped pressure bearing, and the step at the reduced diameter of the lower joint holds the soluble inner core that moves downward after cutting the shear pin, enabling the inner core to dissolve in the sleeve and preventing falling objects; (5) In the soluble plugging device of the present invention, a strip-shaped through hole is arranged below the soluble inner core inside the joint to ensure normal production after the soluble inner core dissolves or falls; (6) The use of the soluble plugging device of the present invention can reduce the construction risk of directly applying pressure to open the rupture disc, save the operation cost and construction period. At the same time, the ultra-high pressure-bearing and temperature-resistant properties meet the vast majority of working conditions, filling the technical gap; BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0019] Figure 1 It is a structural diagram of the downhole string; Figure 2 It is a structural diagram of a soluble plugging device; Figure 3 It is a schematic diagram of the soluble and controllable core of a soluble plugging device of the present invention; Figure 4 It is a schematic diagram of the upper end face of the soluble and controllable core of a soluble plugging device according to the present invention; Figure 5 It is a schematic diagram of the structure of the composite corrosion-resistant coating; In the figure: 1. Upper joint, 2. Lower joint, 3. Soluble inner core, 301. Circumferential surface, 302. Upper end face, 303. Lower end face, 4. Sealing assembly, 5. Shearing pin, 6. Substrate, 7. Composite corrosion-resistant coating, 701. Transition layer, 702. Corrosion-resistant layer, 703. Stabilizing layer, 8. Strip-shaped through hole, 9. Reduced-diameter area, 10. Tubing hanger, 11. Tubing, 12. Soluble plugging device, 13. Screen pipe, 14. Guide shoe. Specific embodiments

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and shown in the accompanying drawings here can be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0022] It should be noted that: Similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0023] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "vertical", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the present invention is usually placed during use, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive distinction and cannot be construed as indicating or implying relative importance.

[0024] In the description of the present invention, it should also be noted that, unless otherwise clearly specified and defined, the terms "set", "installed", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0025] Under-pressure operation refers to the construction operation carried out in the wellbore with the help of an under-pressure operation machine under the under-pressure state at the wellhead of a gas well or an oil and gas well. The under-pressure operation machine mainly includes an operation main machine and a wellhead blowout preventer group. The main machine is mainly used to overcome the gravity or upward force of the pipe string in the well, and the blowout preventer combination of the wellhead series and the plugging tool in the pipe string are used to control the well pressure, so as to realize the equipment for pulling and lowering the pipe string or rotating operation under the condition of under-pressure at the wellhead.

[0026] Embodiment 1 The present invention provides a soluble plug 12 for under-pressure completion operation, as Figure 2 shown, its structure includes an upper joint 1, a lower joint 2 and a soluble inner core 3. Among them, both the upper joint 1 and the lower joint 2 are hollow steel structures, and the upper joint 1 and the lower joint 2 are detachably fixedly connected. Preferably, they are connected by screw threads.

[0027] The soluble inner core 3 is located inside the upper joint 1, and its outer surface cooperates with the inner surface of the upper joint 1 to form a seal. Preferably, in this embodiment, the overall shape of the soluble inner core 3 is a frustum of a cone with a smaller diameter at the top and a larger diameter at the bottom, and the angle between the central axis and the generatrix of the frustum is less than 20°. A step surface that cooperates with the upper end surface 302 of the soluble inner core 3 and an inner conical surface that cooperates with the circumferential surface 301 of the soluble inner core 3 are provided inside the upper joint 1. In this embodiment, the upper end surface 302 of the soluble inner core 3 is the dissolving surface, the lower end surface 303 is the pressure-bearing surface, and the circumferential surface 301 is the sealing surface. Here, "upper" and "lower" are consistent with the upper and lower of the pipe string.

[0028] In a certain preferred implementation manner, in order to further improve the sealing effect, the structure of the soluble inner core 3 is designed as Figure 2 shown, a positioning groove is provided on its circumferential surface 301, and a sealing component 4 is placed in the positioning groove. The sealing component 4 is composed of an O-ring and a support seal.

[0029] Furthermore, as Figure 4As shown, the soluble core 3 includes an internal matrix 6 and a multi-component composite corrosion-resistant coating 7 provided outside the matrix 6, and the coating thickness is 10 - 15 μm. The matrix 6, as the main part of the soluble core 3, is made of a magnesium alloy material. The multi-component composite corrosion-resistant coating 7 covers the lower end face 303 and the circumferential face 301 of the soluble core 3 to isolate the contact of the solution medium at the lower end of the soluble plug 12. A partial coating can also be designed on the upper end face 302 of the soluble core 3, leaving only the dissolution surface. To improve the dissolution rate, empty grooves can also be dug on the upper end face 302 of the soluble core 3 according to design requirements, such as Figure 2 shown.

[0030] Furthermore, as Figure 5 shown, the structure of the multi-component composite corrosion-resistant coating 7 includes a transition layer 701, a corrosion-resistant layer 702, and a stable layer 703 arranged in sequence from the inside to the outside. The transition layer 701 is a layer of metal ions deposited on the magnesium alloy matrix 6 by using physical vapor deposition and chemical vapor deposition techniques and utilizing ions generated by plasma discharge; the corrosion-resistant layer 702 is a multi-component nano-coating deposited on the surface of the transition layer 701, with small pores between ions to prevent corrosion from occurring after liquid intrusion and effectively protect the internal magnesium alloy matrix 6; the stable layer 703 is a multi-layer functional composite ceramic film deposited on the surface of the corrosion-resistant layer 702.

[0031] Preferably, the transition layer is an Al x Mg 1-x inner layer, the corrosion-resistant layer is an Al x Mg 1-x / Al y Ti 1-y nano-multilayer, and the stable layer is an A y Ti 1-y 0 amorphous layer. Among them, x is the mass ratio of aluminum element in Al x Mg 1-x , y is the mass ratio of Al element in Al y Ti 1-y or A y Ti 1-y 0, 0.3 ≤ x ≤ 0.7, 0.5 ≤ y ≤ 0.95.

[0032] Preferably, the thickness of the transition layer is 0.15 - 0.5 μm, the thickness of the corrosion-resistant layer is 2 - 10 μm, and the thickness of the stable layer is 0.5 - 3.5 μm.

[0033] Through the above structural design, the sealing surface of the soluble core 3 cooperates with the inner conical surface inside the upper joint 1. Under the impact of the internal pressure of the pipe, the soluble core 3 continuously presses upward along the wedge-shaped surface to achieve pressure bearing, and at the same time achieve the conical surface self-sealing effect. At the same time, the multi-component composite corrosion-resistant coating 7 actually also acts as a filling seal and fits tightly with the inner wall of the upper joint 1; combined with the sealing assembly 4 arranged on the outer cylindrical surface of the soluble core 3 to achieve combined sealing, a triple sealing effect is achieved, enabling the soluble core 3 to withstand the ultra-high pressure and high temperature downhole environment of 105 MPa and 150 °C.

[0034] Embodiment 2 On the basis of Embodiment 1, the present invention proposes a soluble plug 12 for pressure-while-completing operation. Different from Embodiment 1, a shear pin 5 is arranged at the lower end face 303 of the soluble core 3. The shear pin 5 is arranged radially and is used for the limit of the lower end face 303 of the soluble core 3. A positioning groove for installing the shear pin 5 is arranged on the circumferential surface 301 of the upper joint 1. The number of shear pins 5 and the positioning grooves corresponds one by one. Preferably, four shear pins 5 are arranged and are evenly distributed around the lower end face 303 of the soluble core 3.

[0035] The upper joint 1 is designed with a sleeve structure at the position below the soluble core 3. A plurality of strip-shaped through holes 8 are evenly opened on the surface of the sleeve structure to communicate with the oil and gas production channels. The lower end of the upper joint 1 is provided with an external thread, and the upper end of the lower joint 2 is provided with an internal thread, and the two are screwed and fixed.

[0036] Furthermore, a reduced-diameter area 9 is arranged inside the lower joint 2. The inner diameter of the reduced-diameter area 9 is large at the top and small at the bottom, and its maximum inner diameter is equal to the maximum outer diameter of the soluble core 3. The minimum inner diameter of the reduced-diameter area 9 is the same as the through diameter of the lower joint 2. In the process of the pressure-while-completing string technology, the soluble plug 12 is connected to the bottom of the completion string for internal pipe plugging and sealing. After the pin is cut, the soluble core 3 falls into the upper end of the reduced-diameter area 9 of the lower joint 2, thereby communicating with the oil and gas production channels. At the same time, the plug core gradually dissolves within a specified time to realize gas production inside the tubing 11.

[0037] Embodiment 3 The following combines application examples to illustrate the usage method of a soluble plug 12 for pressure-while-completing operation of the present invention, including the following steps: Step a. Assemble the soluble plug 12 according to technical requirements After installing the prepared soluble core 3 with the sealing assembly 4, it is loaded into the inside of the upper joint 1 from below, and force is applied to make the upper end of the soluble core 3 abut against the step surface inside the joint. Then, the shear pin 5 is placed from the positioning groove to abut against the lower end face 303 of the soluble core 3, and then the upper joint 1 and the lower joint 2 are connected.

[0038] Step b: Connect the soluble plug 12 to the appropriate position in the downhole string according to the requirements of the downhole tool string structure.

[0039] In the manner Figure 1 shown, connect the downhole string in sequence, including the tubing 11, the tubing hanger 10 at the top, the screen pipe 13 at the bottom of the tubing 11, and the guide shoe 14. Connect the soluble plug 12 at a position above the screen pipe 13 according to the requirements of the downhole tool string structure.

[0040] Step c: Safely lower the string into the well through the pressure control operation equipment When the first tubing 11 balances the pressure, use multiple pressure balancing and pressure relief to remove the air in the well; when lowering the last 5 tubings 11 close to the neutral point of the string, conduct a heavy string test for each tubing, and real-time check and adjust the depth of the neutral point of the string. When lowering the last tubing 11, close the slip group and the lower working blowout preventer.

[0041] Step d: After all the strings are lowered into the well, set the tubing hanger 10 Step e: Complete the installation of the wellhead gas production tree and pass the pressure test Disassemble the pressure control operation device and the safety blowout preventer group, and install the gas production tree. Connect the pumping pipeline to the gas production tree and pass the pressure test, and pump the backflow fluid into the tubing 11.

[0042] Step f: Pump or pour the backflow fluid into the well to open the soluble plug 12, or dissolve the soluble plug 12.

[0043] Step g: After the soluble core 3 contacts the backflow fluid in the pipe, it quickly dissolves, and finally the full-bore production of the downhole string is realized.

[0044] According to the construction cycle requirements, after the soluble core 3 is pressurized regularly, when the pressure difference between the upper and lower parts of the soluble plug exceeds 2 MPa, the pin of the soluble plug 12 can also be cut off to make the soluble core 3 move down, the production channel is opened, and the natural gas well enters the normal production process.

[0045] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Any simple modification or equivalent change made to the above embodiments based on the technical essence of the present invention falls within the protection scope of the present invention.

Claims

1. A soluble plugging device for pressure completion operation, characterized in that It includes a soluble inner core (3) arranged inside a hollow joint. The soluble inner core (3) is in the shape of a frustum of a cone with a smaller upper diameter and a larger lower diameter. A step surface is arranged on the inner wall of the joint, which cooperates with the upper end surface (302) of the soluble inner core (3), and a conical surface that cooperates with the outer circumferential surface (301) of the soluble inner core (3) to achieve sealing; the soluble inner core (3) includes a matrix (6) and a composite corrosion-resistant coating (7) arranged on the surface of the matrix (6). A sealing component (4) is arranged on the contact surface between the soluble inner core (3) and the inner wall of the joint.

2. The soluble plugging device for underbalanced completion operation according to claim 1, wherein, The joint includes an upper joint (1) and a lower joint (2). The upper joint (1) and the lower joint (2) are detachably and fixedly connected, and the soluble inner core (3) is located inside the upper joint (1).

3. The soluble plugging device for underbalanced completion operation according to claim 1, wherein The composite corrosion-resistant coating (7) covers the lower end surface (303) and the outer circumferential surface (301) of the soluble inner core (3), and the coating thickness is 10 - 15 μm.

4. The soluble plugging device for underbalanced completion operation according to claim 1, characterized in that, The matrix (6) of the soluble inner core (3) is made of magnesium alloy material.

5. The soluble plugging device for underbalanced completion operation according to claim 1 or 3, characterized in that, The composite corrosion-resistant coating (7) includes a transition layer (701), a corrosion-resistant layer (702), and a stable layer (703) arranged in sequence from the inside to the outside; the transition layer (701) is a layer of metal ions deposited on the magnesium alloy matrix (6) by using physical vapor deposition and chemical vapor deposition techniques and utilizing ions generated by plasma discharge; the corrosion-resistant layer (702) is a multi-element nano-coating deposited on the surface of the transition layer (701); the stable layer (703) is a multi-layer functional composite ceramic film deposited on the surface of the corrosion-resistant layer (702).

6. The soluble plugging device for underbalanced completion operation according to claim 1, wherein Radially arranged shear pins (5) for limiting are arranged on the lower end surface (303) of the soluble inner core (3).

7. The soluble plugging device for underbalanced completion operation according to claim 6, wherein Positioning grooves for installing the shear pins (5) are arranged on the circumferential surface (301) of the joint. The number of shear pins (5) and the positioning grooves corresponds one by one, and they are evenly distributed around the lower end surface (303) of the soluble inner core (3).

8. The soluble plugging device for pressure-keeping well completion operation according to claim 1, characterized in that, A number of strip-shaped through holes (8) for communicating with the oil and gas production channel are arranged below the soluble inner core (3) of the joint.

9. The soluble plugging device for underbalanced completion operation according to claim 2, characterized in that, A reduced-diameter area (9) is arranged inside the lower joint (2). Its maximum inner diameter is equal to the maximum outer diameter of the soluble inner core (3), and the minimum inner diameter of the reduced-diameter area (9) is the same as the through-diameter of the lower joint (2).

10. A method for using a soluble plugging device for underbalanced completion operations, characterized in that, It includes the following steps: Step a: Assemble the soluble plugging device (12) according to technical requirements; After installing the prepared soluble inner core (3) with the sealing component (4), load it into the upper joint (1) from below. Apply force to make the upper end of the soluble inner core (3) abut against the step surface inside the joint. Then, put the shear pins (5) into the positioning grooves to make them abut against the lower end surface (303) of the soluble inner core (3), and then connect the upper joint (1) and the lower joint (2); Step b: Connect the soluble plugging device (12) to the downhole string according to the requirements of the downhole tool string structure; Step c: Use a pressure-operated workover rig to safely lower the string into the well; Step d: After all the strings are lowered into the well, set the tubing hanger (10); Step e: Complete the installation of the wellhead gas production tree and pass the pressure test; Step f: According to the construction period requirements, after the soluble inner core (3) is pressurized regularly, when the pressure difference between the upper and lower parts of the soluble plugging device exceeds 2 MPa, the backflow fluid is poured into the well to open the soluble plugging device (12); Step g: After the soluble inner core (3) contacts the backflow fluid in the pipe, it dissolves rapidly, and finally full-bore production of the downhole string is achieved.

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