An integrated oilfield produced fluid treatment device and method

Abstract

This invention relates to an integrated oilfield produced fluid treatment device and method, belonging to the field of oilfield multiphase separation technology. The device comprises a multi-stage produced fluid treatment unit connected in series from low to high. Each stage of the produced fluid treatment unit has a cavity comprising, from bottom to top, a bottom desanding section, a pre-water separation section, an electrostatic coalescence section, and an outlet section. An inlet is provided between the pre-water separation section and the electrostatic coalescence section, and the outlet section of the lower-stage produced fluid treatment unit is connected to the inlet of the higher-stage produced fluid treatment unit. The pre-water separation section is a pipe with a set inclination angle, and an oily wastewater outlet is provided at the bottom of the pre-water separation section. A high-voltage AC insulated electrode is provided in the electrostatic coalescence section. This invention, by employing a "pre-water separation + high-frequency electrostatic coalescence" process, powered by a high-frequency power supply and using a high-voltage electrode with an insulating layer, can significantly improve the front-end dehydration effect, avoid the "field collapse" phenomenon, and is less prone to breakdown, making it suitable for high-water-content land and offshore platforms in various environments.

Description

Technical Field

[0001] This invention belongs to the field of oilfield multiphase separation technology, specifically relating to an integrated oilfield produced fluid treatment device and method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] As exploration and development become increasingly challenging, oilfield production has entered a stage with high water content, high recovery rates, and high oil extraction speeds. Therefore, the crude oil entering the electrostatic dehydrator after initial separation by a three-phase separator still has a relatively high water content. Traditional electrostatic dehydration processes cannot effectively handle oilfield produced fluids with high water content. Furthermore, because current electrostatic coalescence devices typically use industrial frequency power supplies and lack insulation protection for the high-voltage electrodes, the equipment is prone to problems such as "electric field collapse," leading to unstable operation of the dehydration equipment.

[0004] In the unique environment of offshore oilfields, processing produced fluids presents numerous challenges. Limited space on offshore platforms means that traditional oilfield dehydration processes, such as three-phase separators and multi-stage settling tanks, are time-consuming and energy-intensive. The dehydration equipment used is not only large in size but also susceptible to the effects of the marine environment, such as high humidity and seawater corrosion, further increasing the difficulty of equipment maintenance and operation. Therefore, offshore oilfields urgently require new crude oil dehydration equipment, necessitating compact, efficient, and simplified technical solutions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an integrated oilfield produced fluid treatment device and method, which adopts a multi-stage desanding-water separation-electro-coalescing integrated design. Before crude oil enters the coalescer, it undergoes pre-dehydration in the pre-water separation section. After pre-dehydration, crude oil with lower water content is sent to the electro-coalescing section for efficient droplet coalescence, achieving multi-stage continuous treatment, thereby shortening the overall treatment process and significantly reducing energy consumption.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] In the first aspect, an integrated oilfield produced fluid treatment device includes a multi-stage produced fluid treatment device connected in series from low to high.

[0008] The cavity in each stage of the produced fluid treatment device includes a bottom desanding section, a pre-water separation section, an electrostatic coalescence section, and an outlet section connected sequentially from bottom to top; an inlet is provided between the pre-water separation section and the electrostatic coalescence section, and the outlet section of the lower stage produced fluid treatment device is connected to the inlet of the higher stage produced fluid treatment device;

[0009] The pre-separation section is a pipe with a set inclination angle, and an oily wastewater outlet is provided at the bottom of the pre-separation section. A high-voltage AC insulating electrode is provided in the electrostatic coalescence section.

[0010] Optionally, the lowest-level inlet connects to the crude oil emulsion pipeline, and the highest-level outlet connects to the purified oil pipeline. It can be directly connected to the equipment on the oil production platform. Since this equipment can not only realize multi-stage continuous processing of produced fluids, but also significantly shorten the processing flow, reduce the footprint and greatly reduce energy consumption, it can effectively meet various challenges in the processing of produced fluids in offshore oil fields.

[0011] Optionally, the high-voltage AC insulated electrode is connected to a high-voltage high-frequency power supply; the high-voltage high-frequency power supply outputs a voltage ranging from 6kV to 15kV to the high-voltage AC insulated electrode, and the output electric field frequency ranges from 500Hz to 7kHz; the pulse electric field generated by the high-frequency pulse power supply used in this invention produces a small current, which is less likely to cause electrolysis of the aqueous phase. Therefore, applying a high-frequency high-voltage pulse electric field is less likely to cause breakdown of the electric field, thereby enhancing the polarization of the droplets. Furthermore, the pulse electric field can effectively increase the number of droplet oscillations, creating more contact opportunities for the droplets, and thus achieving a better droplet coalescence effect.

[0012] Optionally, the oily wastewater outlet of each stage is connected to the main wastewater outlet pipeline, which in turn is connected to the wastewater treatment system for wastewater treatment.

[0013] Optionally, the high-voltage AC insulated electrode is isolated from the cavity by an insulating cover plate and fixed in the cavity by the insulating cover plate. Since the high-voltage AC electrode is protected by an insulating layer, the oil-water separation effect can be significantly improved while avoiding the "collapse of electric field" phenomenon. Compared with the traditional electric dehydration process, it can ensure stable operation of the equipment, reduce the footprint, shorten the processing flow, and realize energy saving and integration of crude oil processing.

[0014] Optionally, the bottom sand removal section is equipped with a sand filter and a sand discharge port for periodically discharging solid sand and gravel that settle with water.

[0015] Optionally, the inlet of each stage of the produced fluid treatment device is connected to an inlet sampling branch pipe; the outlet section of each stage of the produced fluid treatment device is connected to a purified oil sampling branch pipe; this is used to calculate the dehydration efficiency through the sampling branch pipes at each location, and then adjust the high-voltage high-frequency voltage applied to the high-voltage AC insulating electrode.

[0016] Optionally, the oily wastewater outlets of each stage of the produced fluid treatment device are connected to wastewater sampling branch pipes, which are used to test the oil content in the water through the sampling branch pipes at various locations, thereby measuring the degree of water pollution and judging the impact and requirements on the water treatment process.

[0017] Optionally, an exhaust pipe is provided between the electrostatic coalescence section and the outlet section. The exhaust pipe is connected to the external environment. Before the experiment begins, the exhaust valve needs to be opened to fill the entire pipeline coalescer with crude oil emulsion to prevent the presence of gas in the coalescence section from affecting the distribution of the electric field. The presence of gas will also reduce the coalescer's processing capacity.

[0018] Optional features include a three-stage produced fluid treatment unit, which can basically meet the needs of high water-cut land and offshore platforms, effectively improve oil-water separation efficiency and reduce the residence time in settling tanks. The treated purified crude oil can meet the qualified indicators for transportation. Compared with the traditional electro-dehydration process, it can ensure stable equipment operation, reduce the footprint, shorten the processing flow, effectively reduce energy consumption, and achieve energy-saving and integrated crude oil treatment.

[0019] Optionally, an electric heating device and a flow regulating device are sequentially installed before the lowest-level inlet. The electric heating device is used for heating and maintaining the temperature of the oil in the device. An oil-water mixing and heat preservation tank containing an electric heating device and an oil-water stirring device is installed before the inlet of the lowest-level pre-water separation section. The flow regulating device includes a precision regulating valve and a mass flow meter. Before the crude oil emulsion enters the device, a precision regulating valve is installed before the inlet of the pre-water separation section to control its flow rate, and a mass flow meter is used to measure the flow rate. By controlling the flow rate, the flow velocity is controlled to control the flow state. After being mixed by the stirrer and heated by the electric heater, the crude oil emulsion is then measured by the precision regulating valve and the mass flow meter and then pumped into the inlet of the pre-water separation section by a twin-screw pump.

[0020] Secondly, a method for treating produced oil from an integrated oilfield fluid treatment device, comprising the following steps:

[0021] Oilfield produced fluid enters the lowest-level inlet and undergoes oil-water separation in the pre-water separation section. Unseparated water droplets in the crude oil emulsion rise with the oil and enter the electrostatic coalescence section. Under the action of the electric field, they coalesce into large droplets and settle into the pre-water separation section, then are discharged from the oily wastewater outlet. Solid gravel settles with the water to the bottom sand removal section. The oil that has undergone electrostatic coalescence enters the next-level inlet along the outlet section. The purified oil, after being treated by multiple stages, is discharged from the highest-level outlet section.

[0022] Optionally, the crude oil emulsion between the high-voltage AC insulating electrode and the cavity wall in the electrostatic coalescence section undergoes coalescence and sedimentation under the action of a high-voltage high-frequency electric field.

[0023] Optionally, the gas inside the coalescer is discharged from the exhaust pipe; this prevents the gas present in the coalescing section from affecting the distribution of the electric field, reducing the coalescer's processing efficiency, or reducing the coalescer's processing capacity.

[0024] Optionally, solid gravel is filtered through a sand filter and discharged from the sand outlet.

[0025] Optionally, the dehydration efficiency can be calculated based on the sampling results of each sampling branch pipe, and electric field parameters such as electric field frequency and electric field strength can be adjusted. Since the optimal electric field parameters are different for different crude oil emulsions, the corresponding electric field parameters can be adjusted according to the sampling results at different locations. Under the optimal electric field parameters, the water content of the treated crude oil can be minimized and the dehydration efficiency of the process can be maximized.

[0026] Optionally, the wastewater sampling branch pipe is used to measure the oil content index in the water at the wastewater outlet. This index is used to measure the degree of water pollution and to determine the impact and requirements on the water treatment process.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. This invention employs a "pre-water separation + high-frequency electrostatic coalescence" process, powered by a high-frequency power supply and using high-voltage AC electrodes with insulation protection. This significantly improves the front-end dehydration effect, avoids the "electric field collapse" phenomenon, and is less prone to breakdown. It is suitable for high-water-content land and marine platforms in various environments, effectively improving oil-water separation efficiency and reducing sedimentation tank residence time. The purified crude oil after treatment meets the qualified standards for transportation. Compared with traditional electrostatic dehydration processes, it can ensure stable equipment operation, reduce the footprint, shorten the processing flow, effectively reduce energy consumption, and achieve energy-saving and integrated crude oil treatment.

[0029] 2. Compared with the current single-stage pre-separated water pipe electrostatic coalescer oil-water separation technology, this invention uses a multi-stage tubular electrostatic coalescer connected in series to continuously reduce the water content of crude oil, significantly increasing the crude oil processing capacity, more flexibly adapting to the characteristics of different crude oils, reducing equipment failures or efficiency declines caused by high-load operation of single-stage systems, and maximizing the processing efficiency of each stage of electrostatic coalescer to achieve continuous and efficient crude oil processing. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0031] Figure 1 This is a schematic diagram of the integrated oilfield produced fluid treatment device in Example 1.

[0032] Figure 2 This is a schematic diagram of the pre-water separation section in Example 1.

[0033] Figure 3 This is a schematic diagram of the electrostatic coalescence segment in Example 1.

[0034] Figure 4 This is a schematic diagram of the insulating cover plate in Example 1.

[0035] The components are as follows: 1. Inlet; 2. Pre-separation section; 3. High-voltage AC insulating electrode; 4. Electrostatic coalescence section; 5. Insulating cover plate; 6. Outlet section; 7. Oily wastewater outlet; 8. Bottom sand removal section; 9. Exhaust pipe; 10. High-voltage high-frequency power supply; 11. Flange; 12. Inlet sampling branch pipe; 13. Wastewater sampling branch pipe; 14. Purified oil sampling branch pipe; 15. Intermediate first-stage pre-separation section; 16. Intermediate first-stage outlet section; 17. Uppermost pre-separation section; 18. Purified oil outlet section; 19. Main wastewater outlet pipe; 20. Central slot; 21. Bolt hole; 22. Fan-shaped annular hole. Detailed Implementation

[0036] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0037] 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, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. 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.

[0038] Example 1

[0039] An integrated oilfield produced fluid treatment device, such as Figure 1 As shown, it includes a three-stage produced fluid treatment unit connected in series from low to high.

[0040] The cavity in each stage of produced fluid treatment device is a pipeline type, including a bottom desanding section 8, a pre-water separation section 2, an electrostatic coalescence section 4 and an outlet section 6 connected from bottom to top; an inlet 1 is provided between the pre-water separation section 2 and the electrostatic coalescence section 4, and the outlet section 6 of the lower stage produced fluid treatment device is connected to the inlet 1 of the higher stage produced fluid treatment device.

[0041] like Figure 2 As shown, the pre-separation section 2 is a pipe with a set inclination angle, and the bottom of the pre-separation section 2 is equipped with an oily wastewater outlet 7, as shown. Figure 3 As shown, a high-voltage AC insulating electrode 3 is installed in the electrostatic coalescence section 4.

[0042] To address the limitations of current single-stage pre-separated tubular electrostatic coalescer oil-water separation technology, which cannot flexibly combine operating parameters for different coalescing stages and results in low processing capacity, this embodiment employs a three-stage electrostatic coalescer for continuous oil-water separation. By using a multi-stage tubular electrostatic coalescer connected in series, the water content of crude oil can be continuously reduced stage by stage, significantly increasing crude oil processing capacity. This approach allows for more flexible adaptation to the characteristics of different crude oils, reducing equipment failures or efficiency declines caused by high-load operation in single-stage systems. It maximizes the processing efficiency of each stage of the electrostatic coalescer, thereby achieving continuous and efficient crude oil processing. On the other hand, this embodiment significantly improves the front-end dehydration effect by adopting the "pre-water separation + high-frequency electrostatic coalescence" process. It uses a high-frequency power supply and high-voltage AC electrodes with insulation layer protection, which improves the oil-water separation effect while avoiding the "electric field collapse" phenomenon (referring to the phenomenon that the electric field collapses due to certain factors during the operation of the electrostatic dehydrator, the current increases sharply, and even sparks and discharges, which may cause the equipment to trip or be damaged in severe cases). Compared with the traditional electrostatic dehydration process, it can ensure stable equipment operation, reduce the footprint, shorten the processing flow, and achieve energy saving and integration of crude oil processing.

[0043] like Figure 1 As shown, the lowest level inlet 1 is connected to the crude oil emulsion pipeline, and the highest level outlet is the purified oil outlet section 18, which is connected to the purified oil pipeline.

[0044] like Figure 1 As shown, the lower inlet of the electrostatic coalescence section 4 is connected to the upper outlet pipe of the pre-water separation section 2 via a flange, and the upper outlet of the electrostatic coalescence section 4 is connected to the coalescer wiring section via a flange.

[0045] like Figure 1 As shown, a coalescer wiring section is provided between the electrostatic coalescence section 4 and the outlet section 6. An opening is made on the side of the coalescer wiring section to weld an electrical connection pipe, which connects to the high-voltage high-frequency power supply 10 outside the cavity. A high-voltage electrical insulation cover plate 5 is installed above and below the high-voltage AC insulating electrode 3 to provide sealing and fixation. The high-voltage electrical insulation cover plate 5 is installed on... Figure 4The high-voltage high-frequency power supply 10 is connected to the central slot 20 through the through hole of the central slot 20. The connection between the insulating cover plate 5 and the electrostatic coalescence section 4 is a bolt connection. The high-voltage high-frequency power supply 10 outputs a voltage range of 6kV to 15kV to the high-voltage AC insulating electrode 3, and the output electric field frequency range is 500Hz to 7kHz. The high-voltage high-frequency power supply 10 of each stage of the produced fluid treatment device is controlled independently. The selection of electric field parameters has a significant impact on the electrostatic coalescence parameters. In the process of electrostatic dehydration, there is often a critical electric field parameter that makes the electrostatic dehydration effect optimal. The electric field parameters can be specifically expressed as electric field frequency and electric field strength. Electric field strength has a crucial impact on demulsification efficiency. When the electric field strength is too low, the external electric field cannot provide sufficient energy to disrupt the droplet interface film, thus preventing droplet aggregation. As the electric field strength increases, the velocity at which two droplets approach each other increases, while the time to reach each other decreases exponentially. However, when the electric field strength is too high, the interface film breaks down, secondary droplets are ejected, and the emulsion exhibits electrostatic dispersion. The formation of these secondary droplets inhibits droplet aggregation in the emulsion, thereby reducing demulsification efficiency. Similarly, there exists an optimal frequency for electrostatic aggregation. This is because when the pulsed electric field period is close to the droplet's natural period, the droplet's natural frequency resonates with the applied electric field frequency, dramatically increasing the droplet collision rate, reducing the droplet interface film strength, and causing droplet aggregation. As the electric field frequency continues to increase, the droplet approach time tends to stabilize, and the droplet deformation no longer changes. At this point, the degree of droplet stretching mainly depends on the electric field force and is independent of the frequency. The optimal electric field frequency is mainly affected by the applied electric field strength, the water content of the oil itself, the conductivity, and the natural frequency of the emulsion. The pulse electric field generated by the high-frequency pulse power supply produces a small current, which is not likely to cause electrolysis of the aqueous phase. Therefore, applying a high-frequency, high-voltage pulse electric field is unlikely to cause electric field breakdown, thereby enhancing the polarization of the droplets. Furthermore, the pulse electric field can effectively increase the number of droplet oscillations, creating more contact opportunities for the droplets and thus achieving better droplet coalescence. Since the water content of crude oil in the electrostatic coalescer shows a gradual decreasing trend, the electric field parameters required for each stage of the electrostatic coalescer are also quite different.

[0046] Each level of oily wastewater outlet 7 connects to the main wastewater outlet pipe 19; the oily wastewater outlet pipe of the highest level pre-separation section merges into the oily wastewater outlet pipe of the intermediate level pre-separation section through a 90° elbow; the oily wastewater outlet pipes of the intermediate level pre-separation section and the oily wastewater outlet pipe of the highest level separation zone merge into the wastewater outlet branch pipe through a tee; the oily wastewater outlet pipe of the lowest level pre-separation section and the wastewater outlet branch pipe merge into the main wastewater outlet pipe 19 through a tee; the main wastewater outlet pipe 19 connects to the wastewater treatment system.

[0047] like Figure 3As shown, the high-voltage AC insulated electrode 3 is isolated from the cavity by an insulating cover plate 5, and is fixed in the cavity by the insulating cover plate 5; the high-voltage AC insulated electrode 3 is inserted into... Figure 4 In the central slot 20, the insulating cover 5 is connected to the high-voltage AC insulating electrode 3 by bolts. Exposed electrodes may cause short circuits in the electric field, weakening the overall electric field and significantly reducing the dehydration efficiency of the coalescer. Using high-voltage insulating electrodes not only improves safety and reliability, but also ensures that the insulating layer only affects the electric field strength in a localized area, without significantly impacting the overall effect. The high-voltage AC insulating electrode 3 used in this example features a non-uniform electric field, increasing the coalescing effect of the coalescer. However, its disadvantage is that due to the difficulty of the insulating coating process, the insulating layer is easily broken down, making the coalescer unstable. The thickness of the insulating layer has a certain impact on the degree of field strength weakening. Appropriately selecting an insulating electrode of suitable thickness can effectively prevent short-circuit events and maintain the coalescing effect unaffected.

[0048] like Figure 4 As shown, the insulating cover 5 includes a flange with bolt holes 21, and as... Figure 3 As shown, the flange is fixedly connected to the flange of the electrostatic coalescence section 4. A fan-shaped annular hole 22 is provided between the flange of the insulating cover plate 5 and the central slot 20. The fan-shaped annular hole 22 serves as the fluid inlet and fluid outlet of the electrostatic coalescence section 4.

[0049] The pre-water separation section 2 and the bottom sand removal section 8 are connected by flanges. Figure 1 The flange 11 is marked in the middle. The bottom sand removal section 8 is equipped with a sand filter and a sand discharge port. The function of the sand filter is to filter and separate sand and gravel. Heavy sand and gravel particles are squeezed into the sand discharge port while light sand and gravel are adsorbed on the surface of the sand filter. The sand discharge port is used to periodically discharge solid sand and gravel.

[0050] The inlet 1 of each level of produced fluid treatment device is connected to the inlet sampling branch pipe 12; the outlet section 6 of each level of produced fluid treatment device is connected to the purified oil sampling branch pipe 14.

[0051] like Figure 2 As shown, the oily wastewater outlets 7 of each produced fluid treatment unit are connected to the wastewater sampling branch pipes 13.

[0052] An exhaust pipe 9 is provided between the electrostatic coalescence section 4 and the outlet section 6. The exhaust pipe 9 is connected to the external environment to discharge the gas inside the pipe.

[0053] The inclination angle of each pre-separation section 2 pipeline is 30-60°, and the longitudinal height does not exceed 600mm; since the angle of the outlet section 6 is relatively gentle, the inlet angle of the inlet 1 of the intermediate first-level pre-separation section 15 and the uppermost pre-separation section 17 is 120-150°.

[0054] The entry angle of the electrostatic coalescence section 4 is 120-150°, which is the angle between the electrostatic coalescence section and the inlet of the pre-water separation section. The longitudinal height does not exceed 630mm. The overall height of the continuous pre-water separation pipe electrostatic coalescer does not exceed 3500mm, and the overall length (length of the floor area) of the continuous pre-water separation pipe electrostatic coalescer does not exceed 3000mm.

[0055] The oilfield produced fluid treatment method based on the above-mentioned integrated oilfield produced fluid treatment device includes the following processes:

[0056] Oilfield produced fluid enters the lowest-level inlet 1 and undergoes oil-water separation in the pre-water separation section 2. Unseparated water droplets in the crude oil emulsion rise with the oil and enter the electrostatic coalescence section 4. In the electrostatic coalescence section 4, the crude oil emulsion between the high-voltage AC insulating electrode 3 and the cavity wall coalesces and settles under the action of a high-voltage high-frequency electric field. Under the action of the electric field force, it coalesces into large droplets and settles into the pre-water separation section 2 and is discharged from the oily wastewater outlet 7. Solid gravel settles with the water to the bottom sand removal section 8 and is periodically discharged from the sand discharge port. The oil after electrostatic coalescence enters the next-level inlet 1 along the outlet section 6. The purified oil after multi-stage treatment is discharged from the top-level outlet.

[0057] The presence of gas will reduce the throughput and decrease the efficiency of the coalescer. Before the device is put into operation, the exhaust pipe 9 needs to be opened to discharge the gas inside the pipe.

[0058] In this example, ball valves are installed on each sampling branch pipe. By controlling these ball valves, oil samples can be easily taken from various points in the pipeline, allowing for the calculation of the dehydration efficiency of each stage of the electrostatic coalescer. The formula for calculating the dehydration efficiency of the electrostatic coalescer is as follows: The water content of crude oil before it passes through electrostatic coalescence section 4 is the water content of the crude oil entering the port. The water content of the crude oil after passing through electrostatic coalescence section 4 at the outlet is given. The water content of the crude oil emulsion taken from the sampling branch pipe can be determined by distillation to judge whether the crude oil after electrostatic dehydration meets the qualification requirements. The dehydration efficiency of each stage of the electrostatic coalescence unit can be calculated using the formula.

[0059] Wastewater sampling branch pipe 13 is used to test the oil content in the water at various locations, thereby measuring the degree of water pollution and determining the impact and requirements on water treatment processes.

[0060] Specifically, in this embodiment, after the oilfield produced fluid enters the primary pre-separation section, it undergoes pre-separation due to the density difference between oil and water. Because the crude oil has a lower density, it enters the electrostatic coalescence section 4 from above the pre-separation section after pre-separation; according to the Stokes equation... It can be seen that the diameter of the water droplet has a direct impact on the settling velocity; the larger the droplet diameter, the faster the settling velocity and the greater the density difference between oil and water (ρ). w -ρ oThe viscosity (μ) of the oil phase also significantly affects the settling effect. The settling velocity of water droplets is directly proportional to the density difference between oil and water, but inversely proportional to the oil phase viscosity. Therefore, the pre-separation effect of crude oil emulsions with different oil properties varies greatly in the pre-separation stage. Low-viscosity, low-density crude oil and crude oil with large droplet diameters show better separation results in the pre-separation stage, reducing the difficulty of subsequent oil-water separation in the electrostatic coalescence stage 4. The pre-separated wastewater is discharged from the system through a side wastewater outlet pipe; solid sand and gravel enter the bottom sand removal stage 8 under gravity. After crude oil enters the electrostatic coalescence section 4, the high-voltage AC insulated electrode 3 at the center of the coalescer is energized. The coalescence of the oil-water emulsion under the action of the electric field is mainly as follows: after energization, the droplets arrange into multiple water chains. Adjacent droplets in each chain merge. When the droplets approach each other, they need to continuously contact and collide, and the interface film begins to thin. When the thickness of the interface film reaches the critical thickness, the emulsion flows in the electric field, causing the interface film to rupture. At this time, the coalescence process between the droplets is completed. Due to the presence of the interface film, the rate of film thinning is also affected by capillary pressure and separation pressure, and can be prevented by the sufficiently significant Marangoni effect. That is, small water droplets will be coalesced into large water droplets by the radially distributed non-uniform electric field, and settle under the action of gravity. They are discharged from the side sewage pipe together with the pre-separated water. The crude oil after electrostatic coalescence treatment enters the intermediate first-stage pre-water separation section 15 from the outlet section of the coalescer wiring section for the second pre-water separation.

[0061] Within the intermediate pre-separation section 15, a very small portion of the free water settles, while most of the crude oil emulsion further coalesces and settles within the intermediate electrostatic coalescence section. The non-uniform electric field generated by the high-voltage insulated electrode not only further enhances the droplet coalescence effect but also improves safety and reliability. After energization, adjacent droplets merge, and as they approach each other, they continuously contact and collide, causing the interfacial film to thin until it reaches a critical thickness and ruptures, completing the coalescence process between the droplets. The crude oil, after secondary energization and coalescence, passes through the coalescer connection section and enters the uppermost pre-separation section 17 from the intermediate stage outlet section 16 for a third pre-separation.

[0062] After being processed by the first two stages of electrostatic coalescing, the water content of the crude oil has been greatly reduced. Therefore, the crude oil will hardly settle and produce oily wastewater after entering the uppermost pre-water separation section 17. After being processed by the last stage of electrostatic coalescing section 4, the crude oil can meet the export standards.

[0063] In this example, besides the significant impact of electric field parameters on droplet coalescence, heating temperature and emulsion flow regime also affect oil-water separation efficiency. According to Stokes' equation, temperature also affects settling velocity, primarily because as emulsion temperature increases, viscosity decreases, leading to increased droplet settling velocity. Furthermore, higher temperature increases the collision frequency between droplets, making them more likely to contact and coalesce. However, it's important to consider that increased emulsion temperature also increases energy consumption, potentially causing residue settling and damaging the processing equipment. Therefore, when using a coalescer, the emulsion temperature should be carefully controlled to avoid dangerous situations. Additionally, the flow regime of the emulsion within the coalescer channel also affects the droplet coalescence process. When the emulsion is in a laminar flow state under an electric field, the collisions between droplets are not intense enough, resulting in less droplet coalescence and less effective settling. Under turbulent conditions of a certain intensity, the droplet collision frequency increases, leading to better coalescence.

[0064] In this example, a precision regulating valve is installed before the inlet of the pre-separation section to control its flow rate, and a mass flow meter is used for flow measurement. By controlling the flow rate, the flow velocity is controlled to control the flow state. The heating and insulation of the oil in the unit are accomplished by an electric heating device. An oil-water mixing and insulation tank containing an electric heater and an oil-water agitator needs to be installed before the inlet of the pre-separation section. After being mixed by the agitator and heated by the electric heater, the crude oil emulsion is pumped into the inlet of the pre-separation section by a twin-screw pump after being measured by the mass flow meter.

[0065] 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. An integrated oilfield produced fluid treatment device, characterized in that, It includes a multi-stage produced fluid treatment device connected in series from low to high; the cavity in each stage of the produced fluid treatment device includes a bottom sand removal section, a pre-water separation section, an electrostatic coalescence section and an outlet section connected sequentially from bottom to top; an inlet is provided between the pre-water separation section and the electrostatic coalescence section, and the outlet section of the lower stage produced fluid treatment device is connected to the inlet of the higher stage produced fluid treatment device; The pre-separation section is a pipe with a set inclination angle, and the bottom of the pre-separation section is provided with an oily wastewater outlet. The electrostatic coalescence section is provided with a high-voltage AC insulating electrode. The high-voltage AC insulated electrode is connected to a high-voltage high-frequency power supply; the high-voltage high-frequency power supply outputs a voltage of 6 kV to 15 kV to the high-voltage AC insulated electrode, and the output electric field frequency ranges from 500 Hz to 7 kHz. Each level of the produced fluid treatment device has its own independently controlled high-voltage, high-frequency power supply. The high-voltage AC insulating electrode is isolated from the cavity by an insulating cover plate, and is fixed in the cavity by the insulating cover plate; The insulating cover plate includes a flange with bolt holes and is fixedly connected to the flange of the electrostatic coalescing section. A fan-shaped annular hole is provided between the flange of the insulating cover plate and the central slot, which serves as the fluid inlet and fluid outlet of the electrostatic coalescing section.

2. The integrated oilfield produced fluid treatment device as described in claim 1, characterized in that, The lowest level of the pipeline connects to the crude oil pipeline, and the highest level of the pipeline connects to the purified oil pipeline.

3. The integrated oilfield produced fluid treatment device as described in claim 1, characterized in that, The oily wastewater outlet at each stage is connected to the main wastewater outlet pipeline, which in turn is connected to the wastewater treatment system for wastewater treatment.

4. The integrated oilfield produced fluid treatment device as described in claim 1, characterized in that, The bottom sand removal section is equipped with a sand filter and a sand discharge port.

5. The integrated oilfield produced fluid treatment device as described in claim 1, characterized in that, The inlets of each stage of the produced fluid treatment device are connected to inlet sampling branch pipes; the outlets of each stage of the produced fluid treatment device are connected to purified oil sampling branch pipes; the oily wastewater outlets of each stage of the produced fluid treatment device are connected to wastewater sampling branch pipes; and an exhaust pipe is provided between the electrostatic coalescence section and the outlet section.

6. The integrated oilfield produced fluid treatment device as described in claim 1, characterized in that, An electric heating device and a flow regulating device are installed sequentially before the lowest-level inlet. The electric heating device is used to heat and keep the oil in the device warm. An oil-water mixing and heat preservation tank containing an electric heating device and an oil-water stirring device is installed before the inlet of the lowest-level pre-separation water section. The flow regulating device includes a precision regulating valve and a mass flow meter.

7. A method for treating oilfield produced fluid using the apparatus described in claim 5, characterized in that, Includes the following processes: Oilfield produced fluid enters the lowest-level inlet and undergoes oil-water separation in the pre-water separation section. Unseparated water droplets in the crude oil emulsion rise with the oil and enter the electrostatic coalescence section. Under the action of the electric field, they coalesce into large droplets and settle into the pre-water separation section, then are discharged from the oily wastewater outlet. Solid gravel settles with the water to the bottom sand removal section. The oil that has undergone electrostatic coalescence enters the next-level inlet along the outlet section. The purified oil, after being treated by multiple stages, is discharged from the highest-level outlet section.

8. The method for treating produced fluids from oilfields as described in claim 7, characterized in that, In the electrostatic coalescence section, the crude oil emulsion between the high-voltage AC insulating electrode and the cavity wall coalesces and settles under the action of a high-voltage high-frequency electric field. The gas inside the pipe is discharged from the exhaust pipe; Solid sand and gravel are filtered through the sand filter and discharged from the sand outlet; The dehydration efficiency is calculated based on the sampling results of each sampling branch pipe, and the electric field frequency and electric field strength are adjusted accordingly.

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