A two-stage dehydration device and method for oilfield produced fluid transportation pipelines

Abstract

The application discloses a two-stage dehydration device and method for an oilfield produced liquid conveying pipeline, which comprises a produced liquid buffer section, a cyclone generation section, a separation section and a crude oil outflow section which are sequentially connected and coaxially arranged; a produced liquid inlet is arranged on the produced liquid buffer section, a cyclone generation structure is arranged in the cyclone generation section, the cyclone generation structure performs primary oil-water separation, an oil-water separation inducing structure is arranged in the separation section, the oil-water separation inducing structure performs secondary oil-water separation, a waste water outlet channel is arranged on the separation section, a crude oil outlet is arranged on the crude oil outflow section, and the produced liquid inlet and the crude oil outlet are coaxially arranged; the two-stage dehydration device and method can realize two-stage dehydration of the produced liquid in the oilfield conveying pipeline without changing the pipeline arrangement, so that the water content of the produced liquid entering the joint station is reduced, and the problem of high produced liquid treatment cost in the joint station is solved.

Description

Technical Field

[0001] This invention relates to the technical field of oil-water separation devices for produced oil in oilfields, and specifically to a two-stage dehydration device and method for producing oil in oilfield pipelines. Background Technology

[0002] Currently, as crude oil is continuously extracted from oil fields, formation pressure gradually decreases, and oil well production also declines accordingly. Therefore, to maintain formation pressure and ensure stable and high oil production, high-pressure water needs to be injected into the oil reservoir to compensate for the natural energy continuously lost during oil extraction. This also reduces natural gas emissions from the reservoir, lowering environmental pollution. However, while using water injection to improve oil recovery, it also results in excessively high water content in the produced fluid. Currently, the water content of produced fluid in most oil fields exceeds 90%. High water content in produced fluid places greater demands on subsequent dehydration processes, increasing processing costs. Furthermore, carrying a large amount of water into the wellhead also leads to the loss of injection water resources. Therefore, primary dehydration in the produced fluid delivery pipeline near the oil well is a relatively effective method. This can effectively reduce the water content of the produced fluid entering the wellhead and allow the separated water to be reinjected into the oil well for oil production.

[0003] Currently, compact devices capable of oil-water separation include hydrocyclones, T-tube separators, and three-phase separators. Among these, hydrocyclones are widely used due to their small footprint, low cost, and high efficiency. Hydrocyclones can be classified into tangential and axial flow types based on their inlet structure. Axial flow inlets offer a more compact structure and better flow field stability and symmetry. However, existing axial flow hydrocyclones suffer from overflow pipes that prevent the inlet and oil outlet from being coaxial, necessitating re-layout of pipelines during installation, increasing product costs and engineering complexity. Furthermore, existing devices often rely on moving parts, resulting in high failure rates and limited dehydration efficiency, making them unsuitable for long-term operation under high water content conditions. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a two-stage dehydration device and method for oilfield produced fluid transportation pipelines. The purpose is to achieve primary dehydration of produced fluid in oilfield transportation pipelines without changing the pipeline layout, thereby reducing the water content of produced fluid entering the joint station, alleviating the problem of high produced fluid treatment costs in the joint station, and providing a portion of water source for water injection oil production, thus achieving full recycling and utilization of water resources.

[0005] The technical solution of the present invention is as follows: In a first aspect of the invention, a two-stage dehydration device for an oilfield produced fluid transport pipeline is provided, comprising a produced fluid buffer section, a vortex generating section, a separation section, and a crude oil outflow section connected sequentially and coaxially arranged; a produced fluid inlet is provided on the produced fluid buffer section, a vortex generating structure is provided in the vortex generating section for primary oil-water separation, an oil-water separation induction structure is provided in the separation section for secondary oil-water separation, a wastewater outlet channel is provided on the separation section, and a crude oil outlet is provided on the crude oil outflow section, with the produced fluid inlet and crude oil outlet coaxially arranged.

[0006] In some embodiments of the present invention, the swirl generating structure includes a first-stage helical guide vane, a conical inner reference structure, and a crude oil guide cone. The first-stage helical guide vane is helically arranged on the conical inner reference structure, and the conical inner reference structure and the crude oil guide cone are arranged symmetrically above and below each other and their cone bottom surfaces are connected.

[0007] In some embodiments of the present invention, the position of the first-stage spiral guide vane on the conical inner reference structure is located inside the shell of the swirl generation section, the top of the conical inner reference structure extends into the shell of the produced fluid buffer section, and the crude oil guide cone extends into the shell of the separation section.

[0008] In some embodiments of the present invention, the oil-water separation induction structure includes a cylindrical inner reference structure and an inner cone. The cylindrical inner reference structure is located above the inner cone, and the top of the inner cone is located in the arc-shaped groove at the bottom of the cylindrical inner reference structure. An oil collection groove is provided inside the cylindrical inner reference structure, and a crude oil outlet channel is provided inside the inner cone. The crude oil outlet channel is connected to the oil collection groove. In some embodiments of the present invention, a two-stage helical guide vane is spirally arranged on the cylindrical inner reference structure, and a two-stage separated crude oil outlet is provided at the top of the inner cone, and the two-stage separated crude oil outlet is connected to the crude oil outlet channel.

[0009] In some embodiments of the present invention, a wastewater discharge chamber is formed between the inner cone and the shell of the separation section. The wastewater discharge chamber is connected to a wastewater outlet channel. Two wastewater outlet channels are provided, and the two wastewater outlet channels are arranged tangentially and symmetrically at the bottom of the shell of the separation section.

[0010] In some embodiments of the present invention, a small cylindrical channel, a gradually expanding channel, and a large cylindrical channel are arranged sequentially from top to bottom within the crude oil outflow section, and the top of the small cylindrical channel is connected to the bottom of the crude oil outlet channel.

[0011] In some embodiments of the present invention, the produced fluid buffer section, the swirl generation section, the separation section and the crude oil outflow section are connected by flanges; the oil-water separation induction structure is disposed on the flange, and the flange is installed between the flanges of the separation section and the crude oil outflow section.

[0012] In a second aspect of the invention, a method for operating a two-stage dehydration device for an oilfield produced fluid transport pipeline is provided, comprising: Produced fluid from water injection enters the produced fluid buffer section through the produced fluid inlet for buffering, and then enters the vortex generation section. Under the action of the vortex generation structure, a vortex is formed and primary oil-water separation is carried out. Then, under the action of the oil-water separation induction structure in the separation section, secondary oil-water separation is carried out. The separated crude oil is discharged through the crude oil outflow section, and the separated wastewater is discharged through the wastewater outlet channel on the separation section. In some embodiments of the present invention, during primary oil-water separation, the crude oil produced fluid first forms a swirling flow under the action of the primary spiral guide vanes, and then the oil-water mixture flows into the separation section, achieving primary oil-water separation under the dual action of the oil-water density difference and the crude oil guide cone. During the two-stage oil-water separation, the unseparated oil-water mixture is accelerated by passing through the two-stage spiral guide vanes and then enters the conical flow area between the separation section and the inner cone. Under the action of the inner cone, the oil and water are separated into two stages. In this area, the dehydrated crude oil forms an inner vortex along the inner cone and then enters the crude oil outlet channel through the two-stage separated crude oil outlet, and enters the crude oil outflow section together with the crude oil after the first stage separation.

[0013] One or more technical solutions of the present invention have the following beneficial effects: (1) The two-stage dehydration device provided by the present invention, through the coaxial arrangement of the produced fluid buffer section, vortex generation section, separation section and crude oil outflow section, enables the device to be directly embedded in the delivery pipeline, realizing a continuous dehydration process of "immediate delivery and separation", avoiding the pipeline rearrangement problem caused by the overflow pipe of the traditional axial flow hydrocyclone. The two-stage separation of produced fluid is achieved through the vortex generation structure and the oil-water separation induction structure, which improves the oil-water separation effect. In addition, the modular segmented design enhances the flexibility and maintainability of the device. Each segment can be disassembled and replaced independently to adapt to the working conditions of produced fluid with different water content, thus extending the service life of the device.

[0014] (2) This invention employs a two-stage series separation mechanism, comprehensively improving dehydration efficiency and processing quality. The first-stage separation is achieved in the vortex generation section through helical guide vanes and crude oil guide cones, which can quickly and efficiently separate most of the free water in the produced fluid. Subsequently, the second-stage separation targets the fine oil droplets or slight emulsions remaining after the first-stage separation, which are more difficult to process. In the oil-water separation induction section, fine separation is achieved through acceleration by secondary guide vanes and centrifugal action by the inner cone. This staged processing mode ensures that the water content of the final exported crude oil is reduced to a very low level, effectively reducing the dehydration load of the terminal station and directly lowering its processing energy consumption and cost.

[0015] (3) Based on the axial flow hydrocyclone, this invention can realize the primary dehydration process in the oilfield produced fluid transportation pipeline. While reducing the cost of produced fluid dehydration treatment entering the joint station, it can also be used for water resource recycling. While ensuring its treatment efficiency, the internal structure design is optimized to realize the coaxial design of the inlet and oil outlet. It can be embedded in the pipeline without affecting the pipeline layout, effectively reducing the cost of product application. The whole device has a simple and compact structure, low failure rate, high dehydration efficiency, low initial investment and operation and maintenance costs, and can be used for long-term operation in the field. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the external structure of the two-stage dehydration device for oilfield produced fluid transport pipelines according to the present invention; Figure 2 This is a schematic diagram of the internal structure of the two-stage dehydration device for oilfield produced fluid transport pipelines according to the present invention; Figure 3 This is a schematic diagram of the swirl generation section of the present invention, wherein (a) is a schematic diagram of the external structure of the swirl generation section, (b) is a schematic diagram of the internal structure of the swirl generation section, (c) is a top view of the swirl generation section, and (d) is a schematic diagram of the overall swirl generation structure. Figure 4 This is a schematic diagram of the structure of the separation section of the present invention, wherein (a) is a schematic diagram of the external structure of the separation section, and (b) is a top view of the separation section; Figure 5 This is a schematic diagram of the oil-water separation induction structure of the present invention, wherein (a) is a schematic diagram of the external structure of the oil-water separation induction structure, (b) is a schematic diagram of the internal structure of the oil-water separation induction structure, (c) is a top view of the oil-water separation induction structure, and (d) is a schematic diagram of the secondary separation crude oil outlet; Figure 6 This is a schematic diagram of the crude oil outflow section of the present invention.

[0017] In the diagram: 1. Produced fluid buffer section; 2. Swirl generation section; 3. Separation section; 4. Oil-water separation induction structure; 5. Crude oil outflow section; 6. First flange; 7. Second flange; 8. Third flange; 9. Produced fluid inlet; 10. Buffer chamber; 11. Outer shell; 12. First-stage helical guide vane; 13. Conical internal reference structure; 14. Crude oil guide cone; 15. Swirl generation section inlet; 16. Oil collection tank; 17. Crude oil outlet channel; 18. Conical channel; 19. Cylindrical channel; 20. Second-stage helical guide vane; 21. Cylindrical internal reference structure; 22. Inner cone; 23. First and second-stage crude oil outlets; 24. Second and second-stage crude oil outlets; 25. Small cylindrical channel; 26. Gradually expanding channel; 27. Large cylindrical channel; 28. Crude oil outlet; 29. ​​First wastewater outlet channel; 30. Second wastewater outlet channel; 31. First wastewater outlet; 32. Second wastewater outlet. Detailed Implementation

[0018] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0019] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is intended to include the plural form as well. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0020] Example 1 In a typical embodiment of the present invention, a two-stage dehydration device for oilfield produced fluid transport pipelines is proposed, such as... Figure 1 , Figure 2 and Figure 4 As shown, the system includes a produced fluid buffer section 1, a vortex generating section 2, a separation section 3, and a crude oil outflow section 5, which are connected sequentially and coaxially. The produced fluid buffer section 1 has a cylindrical structure with an internal buffer chamber 10. The top of the buffer section 1 is a produced fluid inlet 9, and the bottom is a produced fluid outlet. The produced fluid enters the buffer chamber 10 through the produced fluid inlet 9, where it acts as a buffer. The outer shell 11 of the vortex generating section 2 has a cylindrical structure with an internal vortex generating structure for primary oil-water separation. The separation section 3 has an oil-water separation induction structure 4 for secondary oil-water separation. The separation section 3 has a wastewater outlet channel, and the crude oil outflow section has a crude oil outlet 28. The produced fluid inlet 9 and the crude oil outlet 28 are coaxially arranged.

[0021] The aforementioned two-stage dehydration unit, with its coaxially arranged produced fluid buffer section 1, cyclone generation section 2, separation section 3, and crude oil outflow section 5, allows the unit to be directly embedded in the delivery pipeline, achieving a continuous dehydration process of "immediate delivery and separation." This avoids the pipeline rearrangement problems caused by overflow pipes in traditional axial-flow hydrocyclones. Furthermore, the modular segmented design enhances the unit's flexibility and maintainability; each section can be independently disassembled and replaced to adapt to produced fluid conditions with different water contents, extending the unit's service life. The two-stage separation of the produced fluid is achieved through the cyclone generation structure and the oil-water separation induction structure 4, improving the oil-water separation effect.

[0022] In this embodiment, the produced fluid buffer section 1, the vortex generating section 2, the separation section 3, and the crude oil outflow section 5 are connected by flanges. Specifically, the produced fluid buffer section 1 and the vortex generating section 2 are connected by a first flange 6, and the vortex generating section 2 and the separation section 3 are connected by a second flange 7. The oil-water separation induction structure 4 is mounted on a flange, which is installed between the separation section 3 and the crude oil outflow section 5 by a third flange 8. Therefore, this device adopts a modular design, with each part connected by flanges, enhancing the replaceability of the device parts and facilitating maintenance.

[0023] like Figure 3 As shown, the swirl generating structure includes a first-stage helical guide vane 12, a conical inner reference structure 13, and a crude oil guide cone 14. Both the conical inner reference structure 13 and the crude oil guide cone 14 are conical structures. The first-stage helical guide vane 12 is spirally arranged on the conical inner reference structure 13. The conical inner reference structure 13 and the crude oil guide cone 14 are symmetrically arranged vertically, and their cone bottom surfaces are connected. The conical inner reference structure 13 serves as the inner reference for the first-stage helical guide vane 12 and is used to stabilize the produced fluid entering the swirl generating section 2 through the swirl generating section inlet 15. A swirling cavity is formed between the first-stage spiral guide vane 12, the conical inner reference structure 13, and the outer shell 11 of the swirling section 2. The top of the swirling section 2 is the swirling section inlet 15. The inlet of the swirling section 2 is connected to the produced fluid outlet of the produced fluid buffer section 1. After the produced fluid enters the swirling cavity, it forms a swirling flow under the action of the first-stage spiral guide vane 12. The crude oil guide cone 14 is used to realize the first-stage separation of oil and water and guide the separated crude oil into the oil collection tank 16.

[0024] Furthermore, the top of the first-stage spiral guide vane 12 is separated from the top of the conical inner reference structure 13 by a set distance, that is, the first-stage spiral guide vane 12 is only distributed in the lower middle part of the conical inner reference structure 13. The position where the first-stage spiral guide vane 12 is provided on the conical inner reference structure 13 is located inside the outer shell 11 of the swirl generation section 2. The top of the conical inner reference structure 13 extends into the shell of the produced fluid buffer section 1, and the crude oil guide cone 14 extends into the shell of the separation section 3.

[0025] like Figure 5 As shown, the oil-water separation induction structure 4 includes a cylindrical inner reference structure 21 and an inner cone 22. The cylindrical inner reference structure 21 is located above the inner cone 22, and the top of the inner cone 22 is located within the arc-shaped groove at the bottom of the cylindrical inner reference structure 21. The inner cone 22 is used to achieve secondary oil-water separation. An oil collection groove 16 is provided inside the cylindrical inner reference structure 21, and a crude oil outlet channel 17 is provided inside the inner cone 22. The crude oil outlet channel 17 is connected to the oil collection groove 16. The oil collection groove 16 is an inverted conical cavity structure, located below the crude oil guide cone 14 and at a set distance from the crude oil guide cone 14, to guide the crude oil after the first-stage separation into the crude oil outlet channel 17. The crude oil outlet channel 17 includes a conical channel 18 and a cylindrical channel 19. The conical channel 18 is located above the cylindrical channel 19 and is interconnected to facilitate the rapid discharge of the separated crude oil.

[0026] Furthermore, a secondary spiral guide vane 20 is spirally arranged on the cylindrical inner reference structure 21, and a secondary separation crude oil outlet is provided at the top of the inner cone 22. The cylindrical inner reference structure 21 serves as the inner reference for the secondary spiral guide vane 20. This design not only prevents water from entering the oil collection tank 16 after primary separation but also helps prevent some water from entering the secondary separation crude oil outlet without secondary separation, effectively reducing the occurrence of short-circuit flow. The secondary spiral guide vane 20 is used to accelerate the unseparated oil-water mixture after primary separation. The outlet angle of the secondary spiral guide vane 20 (the angle between the bottom of the guide vane and the horizontal line) is smaller than the outlet angle of the primary spiral guide vane 12, so that the swirling velocity generated by the secondary spiral guide vane 20 is less than the swirling velocity generated by the primary spiral guide vane, thus preventing emulsification caused by high turbulence intensity during secondary separation. The secondary separation crude oil outlet includes a first secondary separation crude oil outlet and a second secondary separation crude oil outlet arranged symmetrically. The secondary separation crude oil outlet is connected to the crude oil outlet channel 17. The narrow outlet space of the secondary separation crude oil outlet can effectively reduce the occurrence of short-circuit flow and prevent water from entering the crude oil outlet channel 17 through this point.

[0027] In this embodiment, the oil-water separation induction structure 4 adopts an integrated molding design, which ensures the stability of the complex structure.

[0028] In this embodiment, a wastewater discharge chamber is formed between the inner cone 22 and the shell of the separation section 3. The wastewater discharge chamber is connected to a wastewater outlet channel, and two wastewater outlet channels are provided, including a first wastewater outlet channel 29 and a second wastewater outlet channel 30. The two wastewater outlet channels are arranged tangentially and symmetrically at the bottom of the shell of the separation section 3. The wastewater outlet channels are designed tangentially and symmetrically on the wall of the separation chamber, and the tangential direction is consistent with the outlet direction of the secondary spiral guide vane 20, which ensures the timely discharge of wastewater after separation and avoids the impact of axial flow on the layout of the oil pipeline.

[0029] like Figure 6 As shown, the crude oil outflow section 5 is provided with a small cylindrical channel 25, a gradually expanding channel 26, and a large cylindrical channel 27 arranged sequentially from top to bottom. The top of the small cylindrical channel 25 is connected to the bottom of the crude oil outlet channel 17, and the bottom of the large cylindrical channel 27 is the crude oil outlet 28. The crude oil flow channel in the crude oil outflow section 5 has an expanding structure, which can improve the outflow capacity of the separated crude oil. The diameter of the large cylindrical channel 27 in the crude oil outflow section 5 is the same as the diameter of the produced fluid inlet 9, thereby enabling the embedded installation of the dehydration device without changing the pipeline layout.

[0030] The working principle of the two-stage dehydration device provided in this embodiment is as follows: Produced fluid from water injection enters the buffer chamber 10 of the produced fluid buffer section 1 from the produced fluid inlet 9, and then enters the vortex generation section 2 through the inlet of the vortex generation section 2. Under the action of the first-stage spiral guide vane 12, a vortex is formed. Then the oil-water mixture flows into the separation section 3. Due to the density difference between oil and water, the oil after the vortex forms moves centripetally, while the water moves centrifugally. Therefore, under the dual action of the oil-water density difference and the crude oil guide cone 14, primary separation of oil and water can be achieved. A portion of the dehydrated crude oil flows into the oil collection tank 16 along the crude oil guide cone 14, and then flows into the crude oil outflow section 5 through the crude oil outlet channel 17.

[0031] The oil-water mixture that was not separated after the primary separation flows through the secondary spiral guide vanes 20 for acceleration. It then enters the conical flow area between the shell and the inner cone 22 of the separation section 3. Due to centrifugal force, the denser water phase is thrown towards the outer pipe wall, forming an external swirling flow that flows downwards. The less dense crude oil, under centrifugal force, gathers towards the axis and forms an internal swirling flow along the inclined surface of the inner cone 22, moving upwards. The structure of the inner cone 22 effectively guides and gathers these separated crude oils, achieving secondary oil-water separation. After secondary dehydration, the crude oil enters the crude oil outlet channel 17 through the secondary separation crude oil outlet, and together with the crude oil from the primary separation, enters the crude oil outflow section 5, finally being discharged through the crude oil outlet 28. The separated wastewater forms an external swirling flow within the conical flow area between the separation section 3 and the inner cone 22, then enters the first wastewater outlet channel 29 and the second wastewater outlet channel 30, and is discharged from both outlets.

[0032] This two-stage dehydration device utilizes two-stage spiral guide vanes to generate swirling flow and uses crude oil guide cone 14 and inner cone 22 to achieve two-stage separation of oil and water, improving the oil-water separation efficiency. In addition, the crude oil outlet channel 17 is designed in the inner cone 22 of the separation chamber, realizing the coaxial design of the produced fluid inlet 9 and the crude oil outlet 28. It can be embedded in existing pipelines without the need for pipeline redesign, and can achieve immediate input and output.

[0033] Example 2 In a typical embodiment of the present invention, a method for operating a two-stage dehydration device for an oilfield produced fluid transport pipeline is provided, comprising: Produced fluid from water injection enters the produced fluid buffer section 1 from the produced fluid inlet 9 for buffering, and then enters the vortex generation section 2. Under the action of the vortex generation structure, a vortex is formed and primary oil-water separation is carried out. Then, under the action of the oil-water separation induction structure 4 in the separation section 3, secondary oil-water separation is carried out. The separated crude oil is discharged through the crude oil outflow section 5, and the separated wastewater is discharged through the wastewater outlet channel on the separation section 3.

[0034] Furthermore, during the primary separation of oil and water, the crude oil produced fluid first forms a swirling flow under the action of the primary spiral guide vane 12, and then the oil-water mixture flows into the separation section 3, where the primary separation of oil and water is achieved under the dual action of the oil-water density difference and the crude oil guide cone 14. During the two-stage oil-water separation, the unseparated oil-water mixture is accelerated by the two-stage spiral guide vane 20 and then enters the conical flow area between the separation section 3 and the inner cone 22. Under the action of the inner cone 22, the oil and water are separated into two stages. In this area, the dehydrated crude oil forms an internal vortex along the inner cone 22 and then enters the crude oil outlet channel 17 through the two-stage separated crude oil outlet, and enters the crude oil outflow section 5 together with the crude oil after the first stage separation.

[0035] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A two-stage dehydration device for oilfield produced fluid transport pipelines, characterized in that, It includes a produced fluid buffer section, a vortex generating section, a separation section, and a crude oil outflow section that are connected sequentially and coaxially. The produced fluid buffer section is provided with a produced fluid inlet. The vortex generating section is provided with a vortex generating structure for primary oil-water separation. The separation section is provided with an oil-water separation induction structure for secondary oil-water separation. The separation section is provided with a wastewater outlet channel. The crude oil outflow section is provided with a crude oil outlet. The produced fluid inlet and the crude oil outlet are coaxially arranged. The swirl generating structure includes a first-stage helical guide vane, a conical inner reference structure, and a crude oil guide cone. The first-stage helical guide vane is spirally arranged on the conical inner reference structure. The conical inner reference structure and the crude oil guide cone are arranged symmetrically from top to bottom and their bottom surfaces are connected. The oil-water separation induction structure includes a cylindrical inner reference structure and an inner cone. The cylindrical inner reference structure is located above the inner cone, and the top of the inner cone is located in the arc-shaped groove at the bottom of the cylindrical inner reference structure. Two-stage spiral guide vanes are spirally arranged on the cylindrical inner reference structure. An oil collection groove is provided inside the cylindrical inner reference structure, and the oil collection groove is an inverted conical cavity structure. The outlet angle of the two-stage spiral guide vanes is smaller than the outlet angle of the one-stage spiral guide vanes. The outlet angle is the angle between the bottom of the guide vane and the horizontal line.

2. The two-stage dehydration device for oilfield produced fluid transport pipelines as described in claim 1, characterized in that, The conical inner reference structure has a first-stage spiral guide vane located inside the shell of the swirl generation section. The top of the conical inner reference structure extends into the shell of the produced fluid buffer section, and the crude oil guide cone extends into the shell of the separation section.

3. The two-stage dehydration device for oilfield produced fluid transport pipelines as described in claim 1, characterized in that, The inner cone is provided with a crude oil outlet channel, which is connected to the oil receiving tank.

4. The two-stage dehydration device for oilfield produced fluid transport pipelines as described in claim 3, characterized in that, The top of the inner cone is provided with a secondary separation crude oil outlet, which is connected to the crude oil outlet channel.

5. The two-stage dehydration device for oilfield produced fluid transport pipelines as described in claim 3, characterized in that, A wastewater discharge chamber is formed between the inner cone and the shell of the separation section. The wastewater discharge chamber is connected to the wastewater outlet channel. There are two wastewater outlet channels, which are arranged tangentially and symmetrically at the bottom of the shell of the separation section.

6. The two-stage dehydration device for oilfield produced fluid transport pipelines as described in claim 3, characterized in that, The crude oil outflow section is provided with a small cylindrical channel, a gradually expanding channel and a large cylindrical channel in sequence from top to bottom, and the top of the small cylindrical channel is connected to the bottom of the crude oil outlet channel.

7. The two-stage dehydration device for oilfield produced fluid transport pipelines as described in claim 1, characterized in that, The produced fluid buffer section, swirl generation section, separation section, and crude oil outflow section are connected by flanges; the oil-water separation induction structure is mounted on the flange, and the flange is installed between the flanges of the separation section and the crude oil outflow section.

8. A method for operating a two-stage dehydration device for an oilfield produced fluid transport pipeline as described in any one of claims 1-7, characterized in that, include: The produced fluid obtained from water injection enters the produced fluid buffer section from the produced fluid inlet for buffering, and then enters the vortex generation section. Under the action of the vortex generation structure, a vortex is formed and oil-water primary separation is carried out. Then, under the action of the oil-water separation induction structure in the separation section, oil-water secondary separation is carried out. The separated crude oil is discharged through the crude oil outflow section, and the separated wastewater is discharged through the wastewater outlet channel on the separation section. During primary oil-water separation, the crude oil produced fluid first forms a swirling flow under the action of the primary spiral guide vanes, and then the oil-water mixture flows into the separation section. Under the dual action of the oil-water density difference and the crude oil guide cone, primary oil-water separation is achieved. During the two-stage oil-water separation, the unseparated oil-water mixture is accelerated by passing through the two-stage spiral guide vanes and then enters the conical flow area between the separation section and the inner cone. Under the action of the inner cone, the oil and water are separated into two stages. In this area, the dehydrated crude oil forms an inner vortex along the inner cone and then enters the crude oil outlet channel through the two-stage separated crude oil outlet, and enters the crude oil outflow section together with the crude oil after the first stage separation.

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