Separate injection tubular column

Abstract

The utility model relates to the technical field of oil production engineering, in particular to a separate injection tubular column. The separate injection pipe column comprises a single pipe section used for being connected to a wellhead and a composite pipe section located below the single pipe section, a high-pressure pipeline and a low-pressure pipeline are arranged in the composite pipe section, a low-pressure inlet, a high-pressure outlet and a low-pressure outlet are formed in the pipe wall of the composite pipe section, and the single pipe section is communicated with the high-pressure outlet through the high-pressure pipeline. The low-pressure inlet and the low-pressure outlet communicate through a low-pressure pipeline. By arranging the low-pressure inlet, the low-pressure inlet can be conveniently connected to an annulus between the pipe column and the casing pipe; the high-pressure outlet and the low-pressure outlet are sequentially formed in the pipeline from top to bottom, so that high-pressure liquid flows out firstly, and the device is more suitable for the working condition that an upper oil layer needs high-pressure injection; the problem that in the prior art, when the injection pressure needed by a lower oil layer is low and the injection pressure needed by an upper oil layer is high, a high-pressure polymer can only be injected between the sleeve and a pipe column, and consequently the sleeve is prone to being damaged is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of oil production engineering, in particular to an injection pipe column. Background Art

[0002] The pressure inside the oil layer is relatively high. During the oil field exploitation process, the oil will be squeezed upward along the pipe string under the pressure inside the oil layer, which makes it easier to exploit the oil. As the oil in the oil layer is lost, the pressure of the oil layer decreases. Therefore, during the exploitation process, it is necessary to inject supplementary fluid into the oil layer to ensure the pressure inside the oil layer. Usually, operators will lower a water injection pipe string into the injection well to inject water into the oil layer to supplement the pressure. In addition, there are often multiple oil layers distributed in the same oil well, and the oil layers are distributed up and down. During the water injection process, it is necessary to use a packer to separate the multiple oil layers separately, and then operate each oil layer separately.

[0003] For example, a Chinese invention patent application with an application publication date of February 12, 2019 and application publication number CN109322648A discloses a distribution injection string for oil well water injection and a method of use, the distribution injection string includes a first outer tube and a first inner tube, the bottom of the first outer tube is also connected in sequence with a third outer tube, a first dispenser and a fourth outer tube, the first inner tube extends between the first dispenser and the fourth outer tube, a screen tube is also provided at the bottom of the fourth outer tube, during water injection, the space inside the first inner tube and between the first outer tube and the first inner tube are independent of each other. The first inner tube is directly connected to the screen tube, and water is injected into the oil layer where the screen tube is located; the space between the first inner tube and the first outer tube is connected to the first dispenser, and water is injected into the oil layer where the first dispenser is located.

[0004] In the prior art, in order to increase the displacement volume and increase the displacement efficiency in the later stage of water injection, a relatively viscous polymer is also injected. Since the above-mentioned injection string needs to inject water between multiple oil layers, the string is often offset and the diameter of each string is small, especially the diameter of the inner tube is narrower. When the polymer is injected, the polymer will block the injection pipe. Therefore, in the injection of polymer, there is also a scheme of using the string and the annulus between the string and the casing for injection. Specifically, as Figure 1 As shown, during the polymer injection process, the lower packer 9 is first used to seal between the two oil layers to ensure that the upper oil layer 300 and the lower oil layer 400 are independent of each other, and then polymer is injected between the casing 12 and the tubing string 14 and inside the tubing string 14 respectively. The polymer between the casing 12 and the tubing string 14 is injected into the upper oil layer 300, and the polymer inside the tubing string 14 is injected into the lower oil layer 400.

[0005] During the construction of an oil well, cement is filled between the casing and the rock or soil layer, but only in the part close to the oil layer. There is no effective support on the outside of the casing at the wellhead and a long distance below the wellhead. After the casing is installed, it is often not removable and replaceable due to the presence of cement at the bottom. In order to protect the casing, high-pressure polymer is often injected into the tubing string during polymer injection, and low-pressure polymer is injected into the annulus between the casing and the tubing string. However, in the above technical solution, the polymer between the casing and the tubing string will be injected into the upper oil layer and the polymer in the tubing string will be injected into the lower oil layer. When the pressure required by the lower oil layer is low and the pressure required by the upper oil layer is high, high-pressure polymer can only be injected into the annulus between the casing and the tubing string, which makes the casing easy to be damaged. Utility Model Content

[0006] The utility model aims to provide an injection string for solving the problem in the prior art that when the required injection pressure of the lower oil layer is low and the required injection pressure of the upper oil layer is high, only high-pressure polymer can be injected between the casing and the string, resulting in easy damage to the casing.

[0007] In order to achieve the above purpose, the injection column in the utility model adopts the following technical solutions:

[0008] A distribution injection pipe string comprises a single pipe section for connecting to a wellhead and a composite pipe section located below the single pipe section, wherein a high-pressure pipeline and a low-pressure pipeline which are independent of each other during injection are arranged in the composite pipe section, a low-pressure inlet for allowing liquid between the pipe string and the casing to enter is arranged on the pipe wall of the composite pipe section, a high-pressure outlet and a low-pressure outlet located below the high-pressure outlet are also arranged on the composite pipe section, the single pipe section is connected to the high-pressure outlet through the high-pressure pipeline, the low-pressure inlet and the low-pressure outlet are connected through the low-pressure pipeline, and packers are arranged between the low-pressure inlet and the high-pressure outlet and between the high-pressure outlet and the low-pressure outlet.

[0009] Furthermore, the injection column includes a double pipe joint, which includes a connecting structure arranged on the inner wall for connecting the high-pressure pipeline, and a low-pressure pipeline is formed between the pipe wall below the connecting structure of the double pipe joint and the high-pressure pipeline.

[0010] Furthermore, the composite pipe section also includes a liquid outlet structure, and a high-pressure liquid outlet hole and a low-pressure liquid outlet hole are provided on the liquid outlet structure. The high-pressure liquid outlet hole is used to form a high-pressure pipeline, and the low-pressure liquid outlet hole is used to form a low-pressure pipeline. The axis of the high-pressure liquid outlet hole coincides with the axis of the composite pipe section. The high-pressure liquid outlet hole includes a high-pressure outlet section extending radially along the composite pipe section, and the high-pressure outlet is located on the high-pressure outlet section.

[0011] Furthermore, the low-pressure liquid outlet hole is located outside the high-pressure liquid outlet hole.

[0012] Furthermore, there are at least two low-pressure liquid outlet holes, and the plurality of low-pressure liquid outlet holes are arranged at intervals around the axis of the composite pipe section.

[0013] Furthermore, a screen tube is provided on the composite pipe section to form a low-pressure inlet and a low-pressure outlet respectively.

[0014] Furthermore, a one-way flow structure is provided on the liquid outlet structure between the high-pressure liquid outlet hole and the low-pressure liquid outlet hole, so that it is closed when the pressure in the high-pressure pipeline is greater than the pressure in the low-pressure pipeline, and opened when the pressure in the high-pressure pipeline is less than the pressure in the low-pressure pipeline.

[0015] Furthermore, the one-way flow structure includes a one-way pipe section and a valve ball arranged in the one-way pipe section, the one-way pipe section has a closing section whose inner diameter gradually decreases from the high-pressure pipeline to the low-pressure pipeline, and the minimum inner diameter of the closing section is smaller than the diameter of the valve ball.

[0016] Furthermore, a stop structure is provided in the one-way pipe section and / or the high-pressure pipeline to prevent the valve ball from flowing out.

[0017] Furthermore, the stop structure is a stop rod, and the stop rod is fixedly arranged on the high-pressure outlet.

[0018] The beneficial effects of the injection string in the utility model are as follows: the utility model pioneers a kind of injection string, which is convenient for inputting high-pressure liquid by setting a single pipe section; convenient for setting high-pressure pipeline and low-pressure pipeline by setting a composite pipe section, and convenient for injecting high-pressure liquid and low-pressure liquid; convenient for connecting the low-pressure inlet to the annulus between the pipe string and the casing by setting a low-pressure inlet on the pipe wall of the composite pipe section, and convenient for low-pressure liquid in the annulus to enter; convenient for high-pressure liquid to flow out first by setting high-pressure outlet and low-pressure outlet in sequence from top to bottom on the pipeline, which is more suitable for the working condition that the upper oil layer needs high-pressure injection; convenient for separating different oil layers by setting the packer, and avoiding mixing of high-pressure liquid and low-pressure liquid, thereby solving the problem that the casing is easy to be damaged because only high-pressure polymer can be injected between the casing and the pipe string when the pressure required for injection of the lower oil layer is low and the pressure required for injection of the upper oil layer is high in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the injection column in the prior art;

[0020] Figure 2 It is a structural schematic diagram of an embodiment of the injection column in the utility model;

[0021] Figure 3It is a structural schematic diagram of a double pipe joint of an embodiment of the injection pipe column in the utility model;

[0022] Figure 4 It is a structural schematic diagram of the first insertion section of an embodiment of the injection pipe column in the utility model;

[0023] Figure 5 It is a structural schematic diagram of the second insertion pipe section of an embodiment of the injection pipe column in the utility model;

[0024] Figure 6 It is a structural schematic diagram of a one-way flow structure of an embodiment of the injection column in the utility model;

[0025] Figure 7 for Figure 6 Cross-sectional view along the AA axis.

[0026] In the figure: 1, single pipe section; 2, double pipe joint; 21, first threaded section; 22, second threaded section; 23, third threaded section; 3, small oil pipe; 4, upper screen; 5, upper packer; 6, first plugging section; 7, second plugging section; 8, liquid outlet structure; 9, lower packer; 10, lower screen; 11, thread plug; 12, casing; 13, outer pipe section; 14, pipe string; 61, first plugging section body; 62, first sealing assembly; 63, first sealing Sealing ring; 64, first raised section; 65, second sealing assembly; 66, second sealing ring; 67, second raised section; 71, limiting section; 72, fourth threaded section; 81, main body; 82, fifth threaded section; 83, sixth threaded section; 84, center hole; 85, radial perforation; 86, eccentric hole; 87, stop rod; 88, one-way pipe section; 89, valve ball; 810, seventh threaded section; 300, upper oil layer; 400, lower oil layer. DETAILED DESCRIPTION

[0027] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0028] In the utility model, a composite pipe section is provided, and a low-pressure inlet, a high-pressure outlet and a low-pressure outlet are provided on the composite pipe section. A low-pressure pipeline connecting the low-pressure inlet and the low-pressure outlet is provided to allow low-pressure liquid in the annulus between the pipe string and the casing to pass through, and a high-pressure pipeline connecting the single pipe section and the high-pressure outlet is provided to facilitate the passage of high-pressure liquid in the single pipe section, thereby realizing that high-pressure oil flows through the pipe string and enters the upper oil layer.

[0029] In the embodiment 1 of the injection column of the utility model:

[0030] like Figure 2As shown, in this embodiment, the injection string is used to be set in a water injection well or a polymer injection well, and then the oil layer is injected with water or polymer. The injection string includes a single pipe section 1 for connecting to the wellhead and a composite pipe section located below the single pipe section 1. The composite pipe section is provided with a high-pressure pipeline and a low-pressure pipeline that are independent of each other during liquid injection. A packer for separating the oil layers is provided on the outer wall of the composite pipe section. There are two packers, one of which is located above the upper oil layer 300, thereby forming an upper packer; the other packer is located between the upper oil layer 300 and the lower oil layer 400 to form a lower packer. Under the action of the packer, the upper oil layer 300 and the lower oil layer 400 are separated to prevent the liquid from flowing to each other.

[0031] like Figure 2 and Figure 3 As shown, a high-pressure pipeline and a low-pressure pipeline are arranged inside the composite pipe segment at the same time, that is, the part extending downward from the single pipe segment 1 has multiple flow channels. In order to facilitate the arrangement of the high-pressure pipeline and the low-pressure pipeline, a double pipe joint 2 is arranged on the injection column, and the high-pressure pipeline and the low-pressure pipeline located inside the injection column are formed at the double pipe joint 2 at the same time. Specifically, the double pipe joint 2 is tubular, and the diameters of the inner cavity of the double pipe joint 2 are larger at both ends and smaller in the middle. A first threaded section 21 for connecting the single pipe segment 1 and a third threaded section 23 for connecting the composite pipe segment downstream are arranged at both ends of the double pipe joint 2, and a second threaded section 22 for connecting the high-pressure pipeline is also arranged on the inner wall of the middle section of the double pipe joint 2, and the second threaded section 22 also constitutes a connection structure for connecting the high-pressure pipeline. The second threaded section 22 divides the double pipe joint 2 into two sections, the upper section forms the single pipe segment 1, and the lower section forms the composite pipe segment. Of course, the main purpose of the double pipe joint 2 is to form two flow channels in the composite pipe section. Therefore, in other embodiments, the double pipe joint 2 may not be provided, but a double-layer oil pipe may be welded on the injection pipe string, and the double-layer oil pipe may be used as a high-pressure pipeline and a low-pressure pipeline respectively. Alternatively, in other embodiments, the connection structure may also be provided as a quick-insert structure.

[0032] Specifically, in this embodiment, a small oil pipe 3 is threadedly assembled on the second threaded section 22, and the small oil pipe 3 constitutes a high-pressure pipeline. After the small oil pipe 3 and the double pipe joint 2 are threadedly assembled, when liquid is injected into the distribution pipe string, the liquid above the second threaded section 22 of the distribution pipe string will all flow into the small oil pipe 3. The small oil pipe 3 and the pipe wall below the second threaded section 22 form an annulus for low-pressure liquid to enter, which constitutes a part of the low-pressure pipeline. It is worth noting that the distribution pipe string needs to extend a long distance in actual working conditions. In order to facilitate processing and manufacturing, the pipe section may not be a complete section but may be spliced ​​from multiple pipe sections, and the multiple pipe sections are connected by threads.

[0033] like Figure 1 , Figure 4 and Figure 5 The bottom of the small oil pipe 3 is also provided with a first inserting pipe section 6 and a second inserting pipe section 7, wherein the upper end of the first inserting pipe section 6 is provided with a threaded connection structure for connecting with the third threaded section 23 of the small oil pipe 3, the first inserting pipe section 6 includes a first plug-in section body 61, and a raised section protruding from the first plug-in section body 61 is also provided on the first plug-in section body 61. In order to achieve a sealing effect, two groups of sealing components are provided, namely, a first sealing component 62 and a second sealing component 65, and each sealing component is provided with a raised section at both ends. In order to facilitate sealing, the raised section is used to squeeze the first sealing component 62 and the second sealing component 65, so that the first sealing component 62 and the second sealing component 65 expand outward to achieve better sealing. A small diameter section is provided on the first plug-in section body 61, and the small diameter section also forms a stage on the first plug-in section body 61, and the stage forms the third raised section. A first sealing component 62 is sleeved on the small diameter section, and then a first protruding section 64 is threadedly assembled on the small diameter section. The first sealing component 62 is expanded outward by the extrusion of the first protruding section 64 and the third protruding section. A small diameter section is also provided at the end of the first protruding section 64 away from the first sealing component 62. The second sealing component 65 is provided on the small diameter section of the first protruding section 64. In order to achieve the extrusion seal of the second sealing component 65, a second protruding section 67 is also provided on the small diameter section of the first protruding section 64. An inclined guide surface is provided at the end of the second protruding section 67 away from the second sealing component 65, thereby facilitating the installation of the first inserting tube section 6. In addition, a first sealing ring 63 is provided between the first protruding section 64 and the first plug-in section body 61, and a second sealing ring 66 is provided between the first protruding section 64 and the second protruding section 67.

[0034] The second inserting pipe section 7 is used to accommodate the first inserting pipe section 6. In order to facilitate the cooperation between the first inserting pipe section 6 and the second inserting pipe section 7, a limiting section 71 that cooperates with the guide surface stopper is also provided on the second inserting pipe section 7. A step structure that cooperates with the guide surface stopper is formed on the limiting section 71. A fourth threaded section 72 that is used to connect with the composite pipe section at the bottom is also provided at the end of the second inserting pipe section 7. The first inserting pipe section 6 is fixedly connected to the small oil pipe 3, and the first inserting pipe section 6 and the second inserting pipe section 7 are plugged and matched, so that the first inserting pipe section 6 and the second inserting pipe section 7 can rotate relative to each other during the installation process, which is convenient for screwing.

[0035] like Figure 2As shown, an outer pipe section 13 is also arranged outside the small oil pipe 3, the first inserting pipe section 6 and the second inserting pipe section 7. The annulus between the small oil pipe 3, the first inserting pipe section 6 and the second inserting pipe section 7 and the outer pipe section 13 constitutes a part of the low-pressure pipeline. At this time, the high-pressure pipeline is located in the middle of the low-pressure pipeline. If the high-pressure pipeline is to be injected into the upper oil layer 300, a structure that can allow the high-pressure pipeline to cross the low-pressure pipeline is also required. Specifically, a liquid outlet structure 8 is also arranged on the composite pipe section for discharging high-pressure liquid and low-pressure liquid. At this time, a low-pressure inlet is also arranged on the outer pipe section 13. Specifically, an upper screen pipe 4 is arranged on the outer pipe section as a low-pressure inlet.

[0036] like Figure 6 and Figure 7 As shown, the liquid outlet structure 8 is in the shape of a pipe section, and the liquid outlet structure 8 includes a body 81, and the two ends of the body 81 are respectively provided with a sixth threaded section 83 for connecting the second inserting pipe section 7, a fifth threaded section 82 for connecting the outer pipe section 13, and a seventh threaded section 810 for connecting the lower composite pipe section. The liquid outlet structure 8 needs to allow high-pressure liquid and low-pressure liquid to pass through at the same time, so the liquid outlet structure 8 is provided with high-pressure liquid outlet holes and low-pressure liquid outlet holes arranged at intervals. Specifically, the high-pressure liquid outlet hole includes a central hole located at the axis and radial perforations 85 extending outwardly on both sides of the central hole 84, wherein the axis of the high-pressure liquid outlet hole coincides with the axis of the composite pipe section to facilitate the high-pressure liquid outlet hole to communicate with the small oil pipe 3 and the second inserting pipe section 7. There are multiple low-pressure liquid outlet holes, and the multiple low-pressure liquid outlet holes are arranged at intervals around the axis of the composite pipe section. Specifically, the eccentric hole 86 constitutes the low-pressure liquid outlet hole. In order to better discharge the high-pressure liquid in the high-pressure liquid outlet hole, a high-pressure outlet section extending radially along the composite pipe section is also provided at the end of the high-pressure liquid outlet hole, and the high-pressure outlet section extends to the pipe wall of the composite pipe section, and naturally the high-pressure outlet is located on the high-pressure outlet section. Of course, in other embodiments, the high-pressure liquid outlet hole and the low-pressure liquid outlet hole can also be arranged at intervals around the axis of the composite pipe section, respectively, and at this time, both liquid outlet holes are not located in the middle part. Of course, in other embodiments, the low-pressure liquid outlet hole can no longer be arranged in multiple, but a low-pressure liquid outlet annular groove is provided, and at this time, the high-pressure liquid outlet hole is located in the low-pressure liquid outlet annular groove. In addition, a lower screen tube 10 is also provided below the liquid outlet structure 8, and the lower screen tube 10 constitutes a low-pressure outlet. A wire plug 11 is also provided below the lower screen tube 10.

[0037] like Figure 6As shown, during the injection, the high-pressure pipeline and the low-pressure pipeline need to be kept independent of each other. However, with the use of the injection column, there will be accumulated slag inside the high-pressure pipeline and the low-pressure pipeline of the injection column, which need to be cleaned. Therefore, a one-way flow structure is also provided on the liquid outlet structure 8. Specifically, the one-way flow structure includes a one-way pipe section 88 for connecting the high-pressure liquid outlet hole and the low-pressure liquid outlet hole. The one-way pipe section 88 has a closing section whose inner diameter gradually decreases from the high-pressure pipeline to the low-pressure pipeline. A valve ball 89 is also provided in the one-way pipe section 88. The diameter of the valve ball 89 is larger than the minimum inner diameter of the closing section, and then the valve ball 89 can be pressed against the inner wall of the closing section under the action of the high-pressure liquid in the high-pressure liquid outlet hole. When liquid is passed into the low-pressure pipeline and no liquid is passed into the high-pressure pipeline, the liquid in the low-pressure oil pipe will push the valve ball 89 to move toward the high-pressure pipeline, thereby connecting the one-way flow structure and facilitating the well washing operation. Of course, in other embodiments, the one-way flow structure may also be configured as a one-way valve that connects the high-pressure liquid outlet hole and the low-pressure liquid outlet hole.

[0038] During the well washing operation, it is also necessary to prevent the valve ball 89 from flowing out. Therefore, a stop structure is also provided in the high-pressure pipeline to prevent the valve ball 89 from flowing out. Specifically, the stop structure is a stop rod 87, and the stop rod 87 is fixedly provided on the high-pressure liquid outlet of the liquid outlet structure 8. Of course, in other embodiments, the stop structure can also be a stop plate, and the stop plate can also be installed on the composite pipe section through threaded fasteners to stop the valve ball 89. In this case, the stop plate can also be provided on the high-pressure pipeline. Alternatively, in other embodiments, the stop structure may no longer be provided. When the well washing is required, the valve ball 89 is also recovered. When the next injection operation is performed, a new valve ball 89 is first injected, and the injection operation is performed after the valve ball 89 moves into place.

[0039] like Figure 2As shown, when liquid injection is required, high-pressure liquid is introduced into the distribution pipe column, and low-pressure liquid is injected between the distribution pipe column and the casing 12. The high-pressure liquid flows into the small oil pipe 3 after passing through the double pipe joint 2, and then flows into the high-pressure liquid outlet hole of the liquid outlet structure 8 through two inserting pipe sections, and finally discharged at the high-pressure outlet. The low-pressure liquid enters the annulus between the small oil pipe 3, the first inserting pipe section 6, the second inserting pipe section 7 and the outer pipe section 13 through the upper screen pipe 4, and then enters the low-pressure liquid outlet hole of the liquid outlet structure 8, and flows out at the lower screen pipe 10. At this time, the high-pressure liquid and the low-pressure liquid will contact the two sides of the valve ball 89 respectively. Under the push of the high-pressure liquid, the valve ball 89 will be squeezed on the closing section to complete the closure of the one-way flow structure. During use, well washing operations are required. At this time, well washing fluid is injected between the distribution pipe string and the casing 12. The well washing fluid enters the low-pressure outlet hole along the low-pressure pipeline, and then acts on the valve ball 89. Since the valve ball 89 is only subjected to force on one side at this time, the valve ball 89 will move upward under the action of the well washing fluid and be restricted by the stop rod 87. The well washing fluid can flow upward along the inside of the distribution pipe string through the two inserting pipe sections and the small oil pipe 3 along the high-pressure outlet hole, thereby completing the well washing operation of the distribution pipe string.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The patent protection scope of the present invention shall be based on the claims. All equivalent structural changes made using the description and drawings of the present invention shall be included in the protection scope of the present invention.

Claims

1. A dispensing column, characterized in that: The invention comprises a single pipe section for connecting to a wellhead and a composite pipe section below the single pipe section, wherein a high-pressure pipeline and a low-pressure pipeline which are independent of each other during injection are arranged in the composite pipe section, a low-pressure inlet for allowing liquid between the pipe string and the casing to enter is arranged on the pipe wall of the composite pipe section, a high-pressure outlet and a low-pressure outlet below the high-pressure outlet are also arranged on the composite pipe section, the single pipe section is connected with the high-pressure outlet through the high-pressure pipeline, the low-pressure inlet and the low-pressure outlet are connected through the low-pressure pipeline, and packers are arranged between the low-pressure inlet and the high-pressure outlet and between the high-pressure outlet and the low-pressure outlet.

2. The injection column according to claim 1, characterized in that: The injection pipe column includes a double pipe joint, which includes a connecting structure arranged on the inner wall for connecting the high-pressure pipeline. A low-pressure pipeline is formed between the pipe wall below the connecting structure of the double pipe joint and the high-pressure pipeline.

3. The injection column according to claim 2, characterized in that: The composite pipe section also includes a liquid outlet structure, on which a high-pressure liquid outlet hole and a low-pressure liquid outlet hole are provided. The high-pressure liquid outlet hole is used to form a high-pressure pipeline, and the low-pressure liquid outlet hole is used to form a low-pressure pipeline. The axis of the high-pressure liquid outlet hole coincides with the axis of the composite pipe section. The high-pressure liquid outlet hole includes a high-pressure outlet section extending radially along the composite pipe section, and the high-pressure outlet is located on the high-pressure outlet section.

4. The injection column according to claim 3, characterized in that: The low-pressure liquid outlet hole is located outside the high-pressure liquid outlet hole.

5. The injection column according to claim 4, characterized in that: There are at least two low-pressure liquid outlet holes, and the plurality of low-pressure liquid outlet holes are arranged at intervals around the axis of the composite pipe section.

6. The injection string according to any one of claims 1 to 5, characterized in that: The composite pipe section is provided with a screen pipe to form a low-pressure inlet and a low-pressure outlet respectively.

7. The injection string according to any one of claims 3 to 5, characterized in that: A one-way flow structure is provided on the liquid outlet structure between the high-pressure liquid outlet hole and the low-pressure liquid outlet hole, so that the liquid outlet hole is closed when the pressure in the high-pressure pipeline is greater than the pressure in the low-pressure pipeline, and is opened when the pressure in the high-pressure pipeline is less than the pressure in the low-pressure pipeline.

8. The injection column according to claim 7, characterized in that: The one-way flow structure includes a one-way pipe section and a valve ball arranged in the one-way pipe section. The one-way pipe section has a closing section whose inner diameter gradually decreases from the high-pressure pipeline to the low-pressure pipeline. The minimum inner diameter of the closing section is smaller than the diameter of the valve ball.

9. The injection column according to claim 8, characterized in that: A stop structure is arranged in the one-way pipe section and / or the high-pressure pipeline to prevent the valve ball from flowing out.

10. The injection column according to claim 9, characterized in that: The stop structure is a stop rod, and the stop rod is fixedly arranged on the high-pressure outlet.

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