Long-acting double-pipe polymer injection pipe column and construction method

Abstract

The application discloses a long-acting double-pipe injection polymer pipe column and a construction method, and relates to the field of oil exploitation, which can establish an oil-casing annular circulation channel, efficiently and stably realize reliable well flushing at the oil-casing annular and the annular safety valve, effectively remove polymer impurities, improve the maintenance efficiency and operation stability of the double-pipe injection polymer well, and prolong the service life of the pipe column.

Description

Technical Field

[0001] This invention relates to the field of petroleum development technology, specifically to a long-lasting dual-tube polymer injection string and its construction method. Background Technology

[0002] Currently, in order to ensure annular safety, dual-pipe polymer injection tubing in offshore oilfields is equipped with annular safety valves. During long-term polymer injection or when injection is stopped, polymer can accumulate in the flow channels of the annular safety valves, which can easily lead to problems with poor well cleaning.

[0003] Announcement No. CN220828233U discloses a high-temperature deep well dual-pipe water injection string, including an inner water injection string and an outer water injection string. The lower end of the outer water injection string is sealed to the inner water injection string by a primary diversion and distribution unit, and the injected water is diverted by a constant pressure screen pipe. The inner water injection string has an inner pipe safety valve and a sealing plug 1 in the inner water injection pipe. A secondary diversion and distribution unit consisting of a sealing plug 3 and a sealing working cylinder 2 is connected and installed in the inner water injection string between oil layer 1 and oil layer 2. A drillable and millable permanent packer is installed in the inner water injection string below the secondary diversion and distribution unit. The lower end of the inner water injection string is connected to the water injection guide head.

[0004] Announcement No. CN108222853B discloses a dual-pipe water injection string and method for offshore oilfields. In the dual-pipe water injection string, the inner pipe string includes an inner pipe and a polished rod connected vertically, and the outer pipe string includes an outer pipe. The outer pipe is also equipped with a pressure-regulating screen pipe, a two-stage internal sealing tool, and a washable well sealing tool. The pressure-regulating screen pipe is located below a through-type annular safety packer, connecting the annulus of the inner and outer pipes with the upper oil layer. The two-stage internal sealing tool is located below the pressure-regulating screen pipe and cooperates with the polished rod to seal the annulus of the inner and outer pipes. The washable well sealing tool is located at the lower end of the outer pipe and cooperates with a sand-proof casing sealing cylinder located between the sand-proof casing in the upper and lower oil layers to seal. The lower end of the polished rod is connected to the lower oil layer.

[0005] Announcement No. CN205117297U discloses a concentric double-tube gas well production tubing string, including casing, small tubing hanger, small tubing four-way connector, large tubing hanger, outer tubing string, downhole safety valve, inner tubing string, annular downhole safety valve, double-tube packer, small-diameter tubing short section, small working tube, single-tube packer, and large working tube. The outer tubing string is suspended in the casing by the large tubing hanger. The single-tube packer seals the casing. The large working tube is connected to the outer tubing string. The small tubing four-way connector is located on the original four-way connector at the top of the casing. The inner tubing string is fitted inside the outer tubing string and suspended on the small tubing four-way connector by the small tubing hanger. The double-tube packer seals the outer tubing string. The small working tube is connected to the inner tubing string. The small-diameter tubing short section is fixed to the double-tube packer. The annular downhole safety valve is located at the upper end of the small-diameter tubing short section and is connected to the inner tubing string.

[0006] None of the aforementioned existing technologies propose an annular safety valve unblocking structure, and their tubing service life is not as good as that of this invention.

[0007] In summary, the technical solutions, technical problems to be solved, and beneficial effects of the above-disclosed technologies are all different from those of the present invention. Regarding the more technical features, technical problems to be solved, and beneficial effects of the present invention, the above-disclosed technical documents do not provide any technical inspiration. Summary of the Invention

[0008] In view of the above-mentioned defects in the existing technology, the purpose of this invention is to provide a long-lasting dual-tube polymer injection column and its construction method.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] On one hand, the present invention provides a long-lasting dual-tube polymer injection string, including a layered sand control polymer injection string, a safety layered string, and an inner string. The safety layered string is equipped with an annular safety valve and also includes an offset valve well-washing mechanism. The offset valve well-washing mechanism is provided below the annular safety valve on the safety layered string. The offset valve well-washing mechanism is used to unblock the annular safety valve.

[0011] Furthermore, the bias valve well-washing mechanism includes a body, which is tubular, and a bias valve is provided on the side wall of the body;

[0012] Specifically, the bias valve includes a valve body, the valve body is provided with a valve passage with one end open, the side wall of the valve passage is connected to the interior of the body through an injection port, and a ball seat and a spindle are provided in the valve passage;

[0013] Specifically, the mandrel is located at the closed end of the valve passage, the mandrel is connected to the valve body, a spring is sleeved on the mandrel, the ball seat is located at the open end of the valve passage, the ball seat is connected to the valve body, a valve ball is disposed between the spring and the ball seat, and the spring pushes the valve ball against the ball seat.

[0014] Furthermore, the valve channel is connected to a backwash sleeve on the outside of the ball seat, and the backwash sleeve has at least two oblique elongated holes on its side wall.

[0015] Furthermore, the mandrel is threadedly connected to the valve body and extends out of the valve body.

[0016] Furthermore, the sand-control injection string includes a suspended packer, an upper injection screen pipe, a layered packer, a lower injection screen pipe, a hydraulic anchor, and an external plug, which are connected sequentially from top to bottom through a first oil pipe.

[0017] Furthermore, the safety layered tubing includes an outer safety layered tubing and an inner safety layered tubing;

[0018] Specifically, the external safety layered tubing string includes an annular safety valve, an offset valve well-washing mechanism, an annular safety packer, an upper perforated screen pipe, an inner sealing working cylinder, and a positioning joint, which are connected sequentially from top to bottom through a second tubing.

[0019] Specifically, the inner safety layered tubing string includes an interlayer packer, a lower perforated screen tube, and an inner threaded plug, which are connected sequentially from top to bottom via a third tubing.

[0020] Specifically, the outer safety layered tubing and the inner safety layered tubing are connected by a variable-thread connector.

[0021] Furthermore, when the positioning joint is positioned with the suspension packer, the interlayer packer is located between the upper injection screen pipe and the lower injection screen pipe.

[0022] Furthermore, the inner tubing string includes a downhole safety valve, an upper sealing plug, and a lower sealing plug, which are connected sequentially from top to bottom via a fourth tubing.

[0023] Furthermore, the upper sealing plug mates with the annular safety valve, the lower sealing plug mates with the inner sealing working cylinder, and the fourth sealing oil pipe annularly seals the second oil pipe;

[0024] Specifically, the annular safety valve and interlayer packer are controlled via hydraulic lines.

[0025] Secondly, the present invention provides a construction method for a long-lasting dual-tube polymer injection string, comprising the following steps:

[0026] Connect the layered sand control and polymer injection tubing string, lower it into the well, set the layered packers, and release the suspended packers after they are set.

[0027] Then connect the safety layered tubing string and lower it into the well. Position the connector to the top of the dropper of the suspension packer, and set the interlayer packer in the first tubing. Set the annular safety packer.

[0028] Finally, connect the inner tubing string and lower it into the well. Seal the lower plug and seal it with the inner sealing working cylinder. Seal the upper plug and seal it with the annular safety valve.

[0029] Furthermore, it also includes the following steps: layered polymer injection, opening the annulus safety valve, injecting liquid through the annulus of the second tubing and the fourth tubing, the liquid exits the second tubing through the annulus safety valve, returns to the second tubing 20 through the offset valve well washing mechanism, exits the second tubing 20 through the upper perforated screen pipe, enters the first tubing through the space between the suspended packer and the positioning joint, and enters the upper oil layer through the upper polymer injection screen pipe;

[0030] Liquid is injected through the fourth tubing, and then passes through the downhole safety valve, the lower perforated screen, and the lower injection screen to enter the lower oil layer.

[0031] Furthermore, it also includes the following steps: during backwashing, the hydraulic control line is pressurized to keep the annulus safety valve open, the surface hydraulic line of the interlayer packer is depressurized, the rubber sleeve is retracted, and the well washing passage is made available;

[0032] Backwash water flows in from the annulus of the second and fourth tubings, flows out from the upper perforated screen, passes through the annulus between the first and third tubings, flows into the third tubing from the lower perforated screen, and finally returns through the fourth tubing.

[0033] Furthermore, the procedure also includes the following steps: when the annular safety valve is blocked, the hydraulic control line is pressurized to keep the annular safety valve open, and fluid is injected into the annulus through the second and fourth oil pipes. The fluid will flow through the backwash sleeve and ball seat, push open the valve ball, and then flow out from the injection port to flush the annular safety valve passage, effectively relieving the blockage.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1. This invention can establish a circulation channel in the annulus of the casing and tubing, and efficiently and stably achieve reliable well cleaning at the annulus and annulus safety valve, effectively remove polymer impurities, improve the maintenance efficiency and operational stability of dual-tube polymer injection wells, and extend the service life of the tubing string;

[0036] 2. This invention has a reasonable structure, high reliability, and is easy to construct and install. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of a long-lasting dual-tube polymer injection column according to the present invention;

[0038] Figure 2 This invention relates to the flow path of the upper and lower layers of the tubing column for dispensing.

[0039] Figure 3 This is the streamline path of the tubing string for backwashing wells in this invention;

[0040] Figure 4 This is the flow path for unblocking the annular safety valve of the present invention;

[0041] Figure 5 This is a schematic diagram of the bias valve well-washing mechanism in this invention.

[0042] In the diagram: 1. Downhole safety valve; 2. Annular safety valve; 3. Sealing plug.

[0043] 4. Offset valve well washing mechanism, 401 body, 402 spindle, 403 gasket, 404 spring, 405 injection port, 406 valve ball, 407 ball seat, 408 backwash sleeve, 409 through hole;

[0044] 5. Annular safety packer; 6. Upper perforated screen tube; 7. Inner sealing working cylinder; 8. Sealing lower plug; 9. Positioning joint; 10. Suspended packer; 11. Upper injection screen tube; 12. Interlayer packer; 13. Layered packer; 14. Lower perforated screen tube; 15. Hydraulic anchor; 16. Internal threaded plug; 17. External threaded plug; 18. Hydraulic control line; 19. Fourth oil pipe; 20. Second oil pipe. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Example 1:

[0047] Please see Figures 1 to 5 The present invention provides a long-lasting dual-tube polymer injection string, comprising a layered sand-proof polymer injection string, a safety layered string, and an inner string.

[0048] Furthermore, the sand-prevention and polymer injection string includes a suspended packer 10, an upper polymer injection screen pipe 11, a layered packer 13, a lower polymer injection screen pipe, a hydraulic anchor 15, and an external threaded plug 17, which are connected sequentially from top to bottom through a first oil pipe.

[0049] Among them, the suspension packer 10 is used to suspend the sand-proof injection pipe column by hand.

[0050] Among them, the layered packer 13 is located between two oil layers and is used for oil layer isolation.

[0051] Among them, the upper injection screen pipe 11 and the lower injection screen pipe connect the upper oil layer and the lower oil layer, respectively.

[0052] Among them, hydraulic anchor 15 is used to anchor the sand-prevention injection pipe column.

[0053] Furthermore, the safety layered tubing string includes an outer safety layered tubing string and an inner safety layered tubing string. The outer safety layered tubing string includes an annular safety valve 2, an offset valve well-washing mechanism 4, an annular safety packer 5, an upper perforated screen 6, an inner sealing working cylinder 7, and a positioning joint 9, which are connected sequentially from top to bottom through a second tubing 20. The inner safety layered tubing string includes an interlayer packer 12, a lower perforated screen 14, and an inner threaded plug 16, which are connected sequentially from top to bottom through a third tubing. The outer safety layered tubing string and the inner safety layered tubing string are connected by a variable thread joint.

[0054] The annular safety valve 22 is used for annular safety control and backwashing, and is controlled via the hydraulic control line 18. This tool opens and closes the annular channel via the hydraulic control line 18. When water injection is required, the surface control cabinet pressurizes and opens the annular safety valve, connecting the water injection channel. In case of emergency, the pressure in the hydraulic control line 18 is released, and the annular safety valve quickly closes, achieving safe control of the annular channel.

[0055] Among them, the bias valve well-washing mechanism 4 is used to extend the life of the annular safety valve 2.

[0056] Among them, the annular safety packer 5 is used to seal the annulus of the oil jacket.

[0057] Among them, the upper perforated screen tube 6 and the lower perforated screen tube 14 are used for flow.

[0058] The inner sealing working cylinder 7 is used for a tight fit and seal with the inner tubing.

[0059] The positioning joint 9 is used for positioning with the suspension packer 10.

[0060] The interlayer packer 12 is used to seal the first oil pipe and the third oil pipe. The interlayer packer 12 is a hydraulic packer controlled by the hydraulic control line 18.

[0061] Specifically, when the positioning joint 9 is positioned with the suspension packer 10, the interlayer packer 12 is located between the upper injection screen pipe 11 and the lower injection screen pipe.

[0062] Furthermore, the inner tubing string includes a downhole safety valve 1, an upper sealing plug 3, and a lower sealing plug 8, which are connected sequentially from top to bottom via a fourth tubing 19.

[0063] Among them, downhole safety valve 1 is used to prevent blowout.

[0064] Among them, the upper sealing plug 3 is used in conjunction with the sealing working cylinder in the annular safety valve 2 to seal the annular space between the fourth oil pipe 19 and the second oil pipe 20; the lower sealing plug 8 is used in conjunction with the inner sealing working cylinder 7 to seal the annular space between the fourth oil pipe 19 and the second oil pipe 20, ensuring effective stratification of the inner and outer pipes, and the inner pipe is equipped with a small-diameter downhole safety valve.

[0065] Among them, the lower sealing plug 8 cooperates with the inner sealing working cylinder to seal the annular space between the fourth oil pipe 19 and the second oil pipe 20.

[0066] Specifically, in one application example, the first oil pipe is a Φ127mm oil pipe, the second oil pipe 20 is a Φ101.6mm oil pipe, the third oil pipe is a Φ73mm oil pipe, and the fourth oil pipe 19 is a Φ60.3mm oil pipe.

[0067] A long-lasting dual-tube polymer injection string has functions such as low-shear sand control polymer injection, safety control, stratified polymer injection, and backwashing.

[0068] The tubing safety valve 1, the annular safety valve 2, and the annular safety packer 5 together form a downhole safety control system, providing comprehensive safety control.

[0069] Interlayer packer 12, upper sealing plug 3, and lower sealing plug 8 form a sealed stratified system. Upper sealing plug 3 is positioned at annular safety valve 2, and lower sealing plug 8 is positioned at inner sealing working cylinder 7. Pressurization via ground hydraulic lines sets annular safety packer 5 and interlayer packer 12, achieving stratified polymer injection. The upper layer solution enters the upper oil layer through the annular space of the fourth oil pipe 19, the second oil pipe 20, annular safety valve 2, upper perforated screen pipe 6, first oil pipe, and upper polymer injection screen pipe 11. The lower layer solution is injected directly into the third oil pipe through the fourth oil pipe 19, and then enters the lower oil layer through the lower perforated screen pipe 14 and lower polymer injection screen pipe. (See attached diagram) Figure 2 .

[0070] The hydraulic anchor 15, upper injection screen pipe 11, lower injection screen pipe, layered packer 13, and suspended packer 10 constitute a sand control and polymer injection system. During backwashing, the annular safety valve 2 is kept open, the surface hydraulic lines are depressurized, and the interlayer packer 12 retracts to create a well-washing passage. Backwash water flows into the annulus between the fourth tubing 19 and the second tubing 20, flows out through the upper perforated screen pipe 6, passes through the annulus between the first and third tubings, flows into the third tubing through the lower perforated screen pipe 14, and finally returns through the fourth tubing 19. (See attached diagram) Figure 3 .

[0071] Furthermore, such as Figure 2 As shown, the bias valve well-washing mechanism 4 includes a body 401, which is tubular. A bias valve is provided on the side wall of the body 401. The bias valve includes a valve body and a valve passage with one open end. The side wall of the valve passage is connected to the interior of the body 401 through an injection port 405. A ball seat 407 and a spindle 402 are provided in the valve passage. The spindle 402 is located at the closed end of the valve passage and is connected to the valve body. A spring 404 is sleeved on the spindle 402. The ball seat 407 is located at the open end of the valve passage and is connected to the valve body. A valve ball 406 is provided between the spring 404 and the ball seat 407. The spring 404 pushes the valve ball 406 against the ball seat 407. A backwash sleeve 408 is connected to the outside of the ball seat 407 of the valve passage.

[0072] The working principle is as follows: The bias valve well-washing mechanism 4 is placed below the annular safety valve 2. During positive injection, fluid enters the annulus between the second tubing 20 and the fourth tubing 19 through the annular safety valve 2, and then enters the central channel of the bias valve well-washing mechanism 4. It flows through the injection port 405 on the body 401, where the valve ball 406 blocks the valve passage, preventing fluid from leaking into the annulus. Once the annular safety valve 2 becomes blocked, the hydraulic control line 18 pressurizes to keep the annular safety valve 2 open, injecting fluid through the annulus between the fourth tubing 19 and the second tubing 20. The fluid flows through the backwash sleeve 408 and the ball seat 407, pushing open the valve ball 406, and then flows out from the injection port 405 on the body 401, flushing the annular safety valve 2 channel, effectively relieving the blockage, stopping the injection, and the valve ball 406 returns to the ball seat 407 under the action of the spring force, achieving a seal. (See attached diagram) Figure 4 , 5 .

[0073] Specifically, the mandrel 402 is threadedly connected to the valve body and extends out of the valve body. The mandrel 402 can be screwed in to make it contact the valve ball 406, thereby closing the function of the bias valve well-washing mechanism 4. The mandrel 402 and the valve body are sealed by threaded engagement.

[0074] Specifically, a gasket 403 is provided between the spring 404 and the valve body.

[0075] Specifically, the ball seat 407 is connected to the valve passage via a thread.

[0076] Specifically, the backwash sleeve 408 is connected to the valve passage via threads, and the side wall of the backwash sleeve 408 is provided with at least two oblique elongated holes to facilitate large-volume backwashing wells.

[0077] Specifically, the side wall of the main body 401 is provided with a wire clamping block, and the wire clamping block is provided with a through hole 409 for fixing cables and pipelines.

[0078] Example 2:

[0079] Based on Example 1, this example provides a construction method for a long-lasting dual-tube polymer injection string, including the following steps:

[0080] S1. When running in, connect the layered sand control and polymer injection tubing according to the scheme described in Example 1, run it into the well, set the layered packer 13, and release the suspended packer 10 after setting it.

[0081] Then connect the safety layered tubing string and lower it into the well. Positioning connector 9 is lowered to the top of the dropper of the suspension packer 10. The interlayer packer 12 is set in the first tubing, and the annular safety packer 5 is set.

[0082] Finally, connect the inner tubing string and lower it into the well. Seal the lower plug 8 and seal it with the inner sealing working cylinder 7. Seal the upper plug and seal it with the annular safety valve 2.

[0083] S2, Layered polymer injection, open the annular safety valve 2, inject liquid through the annulus of the second tubing 20 and the fourth tubing 19, the liquid exits the second tubing 20 through the annular safety valve 2, returns to the second tubing 20 through the offset valve well washing mechanism 4, exits the second tubing 20 through the upper perforated screen pipe 6, enters the first tubing through the space between the suspended packer 10 and the positioning joint 9, and enters the upper oil layer through the upper polymer injection screen pipe 11;

[0084] Liquid is injected through the fourth tubing 19, and the liquid passes through the downhole safety valve 1, the lower perforated screen pipe 14, and the lower injection screen pipe into the lower oil layer.

[0085] S3. During backwashing, the hydraulic control line 18 is pressurized to keep the annular safety valve 2 open, and the surface hydraulic line 18 of the control packer 12 is depressurized, the rubber sleeve is retracted, and the well washing channel is opened.

[0086] Backwash water flows in through the annulus of the second tubing 20 and the fourth tubing 19, flows out through the upper perforated screen pipe 6, passes through the annulus between the first tubing and the third tubing, flows into the third tubing through the lower perforated screen pipe 14, and finally returns through the fourth tubing 19.

[0087] S4. When the annular safety valve 2 is blocked, the hydraulic control line 18 pressurizes to keep the annular safety valve 2 open, and injects fluid into the annular space through the second oil pipe 20 and the fourth oil pipe 19. The fluid will flow through the backwash sleeve 408 and the ball seat 407, push open the valve ball 406, and then flow out from the injection port 405 to flush the passage of the annular safety valve 2, effectively relieving the blockage.

[0088] All components not discussed in detail in this application, as well as the connection methods of these components, are well-known technologies in this field. They can be directly applied and will not be elaborated further.

[0089] In this invention, the term "multiple" refers to two or more unless otherwise explicitly defined. The terms "install," "connect," "link," and "fix" should be interpreted broadly. For example, "connect" can be a fixed connection, a detachable connection, or an integral connection; "link" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0090] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," "front," "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or unit referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0091] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0092] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A long-lasting dual-tube polymer injection string, comprising a layered sand-control polymer injection string, a safety layered string, and an inner string, wherein the safety layered string is equipped with an annular safety valve, characterized in that, It also includes a bias valve well-washing mechanism; The safety stratified tubing string is equipped with an offset valve well-washing mechanism below the annular safety valve; the offset valve well-washing mechanism is used to unblock the annular safety valve.

2. The long-lasting dual-tube polymer injection string according to claim 1, characterized in that, The bias valve well-washing mechanism includes a body, which is tubular, and a bias valve is provided on the side wall of the body; The bias valve includes a valve body, the valve body is provided with a valve passage with one end open, the side wall of the valve passage is connected to the interior of the body through an injection port, and a ball seat and a spindle are provided in the valve passage; The mandrel is located at the closed end of the valve passage and is connected to the valve body. A spring is sleeved on the mandrel. The ball seat is located at the open end of the valve passage and is connected to the valve body. A valve ball is placed between the spring and the ball seat, and the spring pushes the valve ball against the ball seat.

3. The long-lasting dual-tube polymer injection string according to claim 2, characterized in that, The valve channel is connected to a backwash sleeve on the outside of the ball seat, and the backwash sleeve has at least two oblique elongated holes on its side wall.

4. The long-lasting dual-tube polymer injection string according to claim 2, characterized in that, The mandrel is threaded to the valve body and extends out of the valve body.

5. A long-lasting dual-tube polymer injection string according to claim 2, characterized in that, The sand control and polymer injection string includes a suspended packer, an upper polymer injection screen pipe, a layered packer, a lower polymer injection screen pipe, a hydraulic anchor, and an external threaded plug, which are connected sequentially from top to bottom through a first oil pipe.

6. The long-lasting dual-tube polymer injection string according to claim 5, characterized in that, The safety layered tubing includes an outer safety layered tubing and an inner safety layered tubing; The external safety layered tubing string includes, from top to bottom, an annular safety valve, an offset valve well-washing mechanism, an annular safety packer, an upper perforated screen, an inner sealing working cylinder, and a positioning joint, which are connected sequentially from top to bottom via a second tubing. The internal safety layered tubing string includes an interlayer packer, a lower perforated screen tube, and an internal threaded plug, which are connected sequentially from top to bottom via a third tubing. The outer safety layered tubing and the inner safety layered tubing are connected by a variable coupling.

7. A long-lasting dual-tube polymer injection string according to claim 6, characterized in that, When the positioning joint is positioned with the suspension packer, the interlayer packer is located between the upper injection screen pipe and the lower injection screen pipe.

8. A long-lasting dual-tube polymer injection string according to claim 6, characterized in that, The inner tubing string includes a downhole safety valve, a sealing upper plug, and a sealing lower plug, which are connected sequentially from top to bottom via a fourth tubing.

9. A long-lasting dual-tube polymer injection string according to claim 8, characterized in that, The upper sealing plug is engaged with the annular safety valve, and the lower sealing plug is engaged with the inner sealing working cylinder, sealing the fourth oil pipe and the second oil pipe annularly; The annular safety valve and interlayer packer are controlled via hydraulic lines.

10. A construction method for a long-lasting dual-tube polymer injection string, characterized in that, Includes the following steps: Connect the layered sand control and polymer injection tubing string, lower it into the well, set the layered packers, and release the suspended packers after they are set. Then connect the safety layered tubing string and lower it into the well. Position the connector to the top of the dropper of the suspension packer, and set the interlayer packer in the first tubing. Set the annular safety packer. Finally, connect the inner tubing string and lower it into the well. Seal the lower plug and seal it with the inner sealing working cylinder. Seal the upper plug and seal it with the annular safety valve.

11. The construction method of a long-lasting dual-tube polymer injection string according to claim 10, characterized in that, It also includes the following steps: Layered polymer injection: Open the annular safety valve, inject liquid through the annulus of the second and fourth tubings, the liquid exits the second tubing through the annular safety valve, returns to the second tubing 20 through the offset valve well washing mechanism, exits the second tubing 20 through the upper perforated screen, enters the first tubing through the space between the suspended packer and the positioning joint, and enters the upper oil layer through the upper polymer injection screen. Liquid is injected through the fourth tubing, and then passes through the downhole safety valve, the lower perforated screen, and the lower injection screen to enter the lower oil layer.

12. The construction method of a long-lasting dual-tube polymer injection string according to claim 10, characterized in that, It also includes the following steps: During backwashing, the hydraulic control line is pressurized to keep the annulus safety valve open, and the surface hydraulic line of the control packer is depressurized, causing the rubber sleeve to retract and clear the well washing passage. Backwash water flows in from the annulus of the second and fourth tubings, flows out from the upper perforated screen, passes through the annulus between the first and third tubings, flows into the third tubing from the lower perforated screen, and finally returns through the fourth tubing.

13. The construction method of a long-lasting dual-tube polymer injection string according to claim 10, characterized in that, It also includes the following steps: When the annular safety valve becomes blocked, the hydraulic control line is pressurized to keep the annular safety valve open. Fluid is injected into the annulus through the second and fourth oil pipes. The fluid flows through the backwash sleeve and ball seat, pushes open the valve ball, and then flows out from the injection port to flush the annular safety valve passage, effectively relieving the blockage.

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