Integrated oilfield produced liquid treatment device and method

Abstract

The invention relates to an integrated oilfield produced liquid treatment device and method, and belongs to the technical field of oilfield multiphase separation. The device comprises multiple stages of produced liquid treatment devices which are connected in series from low to high; a cavity in each stage of produced liquid treatment device comprises a bottom desanding section, a water pre-separation section, an electrostatic coalescence section and an outlet section which are sequentially communicated from bottom to top; an inlet is formed between the pre-water-diversion section and the electrostatic coalescence section, and the outlet section of the lower-stage produced liquid treatment device is communicated with the inlet of the higher-stage produced liquid treatment device; the pre-water-diversion section is a pipeline with a set inclination angle, an oily sewage outlet is formed in the bottom of the pre-water-diversion section, and a high-voltage alternating-current insulated electrode is arranged in the electrostatic coalescence section. By adopting a'pre-water-diversion + high-frequency electrostatic coalescence 'process, supplying power through a high-frequency power supply and using a high-voltage electrode protected by an insulating layer, the front-end dehydration effect can be remarkably improved, the phenomenon of'electric field collapse' is avoided, and the device is not easy to break down and is suitable for high-water-content land and ocean platforms in various environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of oilfield multiphase separation, and particularly relates to an integrated oilfield produced fluid treatment device and method. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] As the exploration and development difficulties gradually increase, oilfield exploitation has entered a stage with technical requirements of high water content, high recovery degree, and high oil production rate. Therefore, the water content of the crude oil entering the electro-dehydrator after preliminary separation by the three-phase separator is still relatively high. The traditional electro-dehydration process cannot effectively treat the high-water-content oilfield produced fluid. And since the electrostatic coalescence device usually uses a power frequency power supply and the high-voltage electrodes lack insulation layer protection at the present stage, problems such as "collapse of the electric field" are likely to occur in the equipment, resulting in the unstable operation of the dehydration equipment.

[0004] In the special environment of offshore oilfields, more challenges are faced in treating oilfield produced fluid. The space on the offshore platform is limited. The traditional dehydration process used in oilfields is the "three-phase separator + multi-stage settling tank" process. This process has too long dehydration time and high energy consumption. The dehydration equipment used not only occupies a large area, but is also easily affected by the marine environment, such as problems of high humidity, seawater corrosion, etc., further increasing the difficulty of equipment maintenance and operation. Therefore, the requirements for new crude oil dehydration equipment in offshore oilfields are more urgent, and technical solutions that are compact, efficient, and have a simplified dehydration process are needed. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide an integrated oilfield produced fluid treatment device and method, which adopts an integrated design of multi-stage sand removal - water separation - electrocoalescence; pre-dehydration is carried out on the produced fluid in the pre-water separation section before the crude oil enters the coalescer, and after pre-dehydration, the crude oil with a lower water content is sent to the electrocoalescence section with applied voltage for efficient droplet coalescence, realizing multi-stage continuous treatment, thereby shortening the overall treatment process and significantly reducing energy consumption.

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

[0007] In a 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 sand removal section, a pre-separation section, an electrostatic coalescence section, and an outlet section that are connected in sequence from bottom to top; an inlet is provided between the pre-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, an oily sewage outlet is provided at the bottom of the pre-separation section, and a high-voltage AC insulating electrode is provided in the electrostatic coalescence section.

[0010] Optionally, the inlet of the lowest stage is connected to the crude oil emulsion pipeline, and the outlet of the highest stage is connected to the purified oil pipeline, which can be directly connected to the devices on the oil production platform. Since this device can not only achieve multi-stage continuous treatment of the produced fluid, but also significantly shorten the treatment process, reduce the floor area and greatly reduce the energy consumption, it can effectively cope with various challenges in the treatment of produced fluid in offshore oilfields.

[0011] Optionally, the high-voltage AC insulating electrode is connected to a high-voltage high-frequency power supply; the range of the voltage output by the high-voltage high-frequency power supply to the high-voltage AC insulating electrode is 6 kV to 15 kV, and the range of the output electric field frequency is 500 Hz to 7 kHz; the current generated by the pulsed electric field generated by the high-frequency pulsed power supply adopted in the present invention is small and is not likely to cause electrolysis of the water phase. Therefore, applying a high-frequency high-voltage pulsed electric field is not likely to cause breakdown of the electric field, thereby enhancing the polarization of droplets, and the pulsed electric field can effectively increase the oscillation times of droplets, creating more contact opportunities for droplets, and thus obtaining a better droplet coalescence effect.

[0012] Optionally, each stage of the oily sewage outlet is connected to the total sewage outlet pipeline, and the total sewage outlet pipeline is connected to the sewage treatment system for sewage treatment.

[0013] Optionally, the high-voltage AC insulating electrode and the cavity are isolated by an insulating cover plate and fixed in the cavity through the insulating cover plate; since the high-voltage AC electrode is protected by an insulating layer, it can significantly improve the oil-water separation effect and avoid the phenomenon of "collapse of the electric field" at the same time. Compared with the traditional electro-dehydration process, it can ensure stable operation of the equipment, reduce the floor area and shorten the treatment process, and can realize energy-saving and integration of crude oil treatment.

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

[0015] Optionally, the inlets of each stage of the produced fluid treatment device are respectively connected to the inlet sampling branch pipes; the outlet sections of each stage of the produced fluid treatment device are respectively connected to the purified oil sampling branch pipes; for calculating the dehydration efficiency through the sampling branch pipes at various positions, and then adjusting the high-voltage high-frequency voltage applied on the high-voltage AC insulating electrode.

[0016] Optionally, the oily sewage outlets of the produced liquid treatment devices at each level are respectively connected to sewage sampling branch pipes, which are used to test the oil content in water through the sampling branch pipes at various positions, so as to measure the pollution degree of water quality and judge the impact on and requirements for the water quality treatment process.

[0017] Optionally, an exhaust pipe is arranged between the electrostatic coalescence section and the outlet section. The exhaust pipe is connected to the external environment. Before the experiment starts, the exhaust valve needs to be opened to fill the whole tubular coalescer with the crude oil emulsion, so as to prevent the gas in the coalescence section from affecting the distribution of the electric field, and the existence of gas will reduce the treatment capacity of the coalescer.

[0018] Optionally, it includes three-level produced liquid treatment devices, which can basically meet the requirements of high-water-cut onshore and offshore platforms, effectively improve the oil-water separation efficiency and reduce the residence time in the settling tank. The purified crude oil after treatment can reach the qualified transportation index. Compared with the traditional electro-dehydration process, it can ensure the stable operation of the equipment, reduce the floor area, shorten the treatment process, effectively reduce the energy consumption, and realize the energy-saving and integrated treatment of crude oil.

[0019] Optionally, an electric heating device and a flow regulating device are arranged in sequence before the inlet of the lowest level. The electric heating device is used for heating and heat preservation of the oil products in the device; an oil-water mixing heat preservation tank including an electric heating device and an oil-water stirring device is arranged before the inlet of the lowest-level pre-separation water area; the flow regulating device includes a precision regulating valve and a mass flowmeter. Before the crude oil emulsion enters the device, a precision regulating valve is arranged before the inlet of the pre-separation water area to control its flow rate, and a mass flowmeter is used for flow measurement. By controlling the flow rate, the flow velocity is controlled to control the flow pattern; after being mixed by the stirrer and heated by the electric heater, the crude oil emulsion passes through the precision regulating valve and the mass flowmeter for measurement, and then is sent into the inlet of the pre-separation water area by a double-screw pump.

[0020] In the second aspect, a method for treating produced liquid in an oilfield based on the above integrated produced liquid treatment device in an oilfield includes the following processes:

[0021] The produced liquid in the oilfield enters the inlet of the lowest level, and oil-water separation is carried out in the pre-separation water section. The water droplets in the crude oil emulsion that are not separated coalesce into large droplets under the action of the electric field force and settle to the pre-separation water section and are discharged from the oily sewage outlet. The solid sand and gravel settle to the bottom sand removal section with the water. The oil fraction after electrostatic coalescence enters the inlet of the upper level along the outlet section, and the purified oil after being treated by multiple devices is discharged from the outlet section of the highest level.

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

[0023] Optionally, the gas in 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 and reducing the treatment efficiency of the coalescer, or from reducing the throughput of the coalescer.

[0024] Optionally, the solid grit passes through the sand filter and is discharged from the sand discharge port.

[0025] Optionally, the dehydration efficiency is calculated based on the sampling results of the sampling branch pipes in each section, and the electric field parameters such as the electric field frequency and electric field strength are adjusted. Since the optimal electric field parameters corresponding to different crude oil emulsions are different, the corresponding electric field parameters are adjusted according to the sampling results at different positions. 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 sewage sampling branch pipe is used to measure the oil content index in the water at the sewage outlet, and this index is used to measure the degree of water pollution and to judge the impact on and requirements for the water treatment process.

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

[0028] 1. By adopting the "pre-separation + high-frequency electrostatic coalescence" process, powered by a high-frequency power supply and using a high-voltage AC electrode with an insulating layer protection, the present invention can significantly improve the front-end dehydration effect, avoid the "collapse of the electric field" phenomenon, is not easily punctured, is applicable to high-water-content onshore and offshore platforms in various environments, effectively improves the oil-water separation efficiency and reduces the residence time in the settling tank. The treated purified crude oil can meet the qualified transportation index. Compared with the traditional electro-dehydration process, it can ensure stable operation of the equipment, reduce the floor area, shorten the treatment process, effectively reduce energy consumption, and achieve energy-saving and integrated treatment of crude oil.

[0029] 2. Compared with the current oil-water separation technology of single-stage pre-separation tubular electrostatic coalescers, by adopting the method of connecting multiple tubular electrostatic coalescers in series to continuously reduce the water content of crude oil step by step, the present invention significantly increases the crude oil throughput, more flexibly adapts to the characteristics of different crude oils, reduces equipment failures or efficiency decline problems caused by high-load operation of the single-stage system, and enables the treatment efficiency of each electrostatic coalescer to reach the highest, so as to achieve continuous and efficient treatment of crude oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The schematic diagrams in the specification forming a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments and descriptions thereof are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0031] Figure 1 It is a schematic structural diagram of the integrated oilfield produced fluid treatment device in Embodiment 1.

[0032] Figure 2 It is a schematic structural diagram of the pre-separation section in Embodiment 1.

[0033] Figure 3 It is a schematic structural diagram of the electrostatic coalescence section in Example 1.

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

[0035] Among them, 1. Inlet; 2. Preliminary water separation section; 3. High-voltage AC insulating electrode; 4. Electrostatic coalescence section; 5. Insulating cover plate; 6. Outlet section; 7. Oil-containing sewage outlet; 8. Bottom sand removal section; 9. Exhaust pipe; 10. High-voltage high-frequency power supply; 11. Flange; 12. Inlet sampling branch pipe; 13. Sewage sampling branch pipe; 14. Purified oil sampling branch pipe; 15. Intermediate first-stage preliminary water separation section; 16. Intermediate first-stage outlet section; 17. Topmost preliminary water separation section; 18. Purified oil outlet section; 19. Total sewage outlet pipe; 20. Central slot; 21. Bolt hole; 22. Fan-shaped hole. Detailed implementation manners

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

[0037] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners of the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, 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 liquid treatment device, as Figure 1 shown, includes three stages of produced liquid treatment devices connected in series from low to high;

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

[0041] As Figure 2 shown, the preliminary water separation section 2 is a pipeline with a set inclination angle, and an oil-containing sewage outlet 7 is provided at the bottom of the preliminary water separation section 2. As Figure 3 shown, a high-voltage AC insulating electrode 3 is provided in the electrostatic coalescence section 4.

[0042] In view of the problem that the current single-stage pre-separation water pipe type electrostatic coalescer oil-water separation technology cannot flexibly combine the operating parameters of different coalescence sections and at the same time results in a small throughput of the electrostatic coalescer, three-stage electrostatic coalescers are set up in this embodiment to continuously carry out oil-water separation. By adopting the method of connecting multiple tubular electrostatic coalescers in series, the water content of crude oil can be continuously reduced stage by stage, the throughput of crude oil can be significantly increased, the characteristics of different crude oils can be more flexibly adapted, the equipment failures or efficiency decline problems caused by high-load operation of the single-stage system can be reduced, and the processing efficiency of each stage of electrostatic coalescer can reach the highest, so as to realize the continuity and high efficiency of crude oil processing. On the other hand, in this embodiment, by adopting the "pre-separation of water + high-frequency electrostatic coalescence" process, the front-end dehydration effect is significantly improved. The high-frequency power supply is used and the high-voltage alternating current electrode with an insulating layer protection is used. While improving the oil-water separation effect, the phenomenon of "collapse of the electric field" is avoided (which refers to: during the operation of the electro-dehydrator, due to certain factors, the electric field collapses, the current increases sharply, and even spark discharge is triggered, which may cause the equipment to trip or be damaged in severe cases). Compared with the traditional electro-dehydration process, it can ensure the stable operation of the equipment, reduce the floor area and shorten the processing flow, and can realize the energy saving and integration of crude oil processing.

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

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

[0045] As Figure 1 shown, a coalescer wiring section is arranged between the electrostatic coalescence section 4 and the outlet section 6. The side of the coalescer wiring section is opened with holes and welded with an electricity connection pipeline, and the wiring pipeline is connected to the high-voltage high-frequency power supply 10 outside the cavity; high-voltage electrical insulation covers 5 are arranged above and below the high-voltage alternating current insulation electrode 3 to play a role of sealing and fixing. The high-voltage electrical insulation covers 5 are installed on Figure 4In the central slot 20, and is connected to the high-voltage high-frequency power supply 10 through the wire extending out of the through-hole of the central slot 20. The connection method between the insulating cover plate 5 and the electrostatic coalescence section 4 is bolt connection; the voltage range output by the high-voltage high-frequency power supply 10 to the high-voltage AC insulating electrode 3 is 6 kV to 15 kV, and the output electric field frequency range is 500 Hz to 7 kHz. The high-voltage high-frequency power supply 10 of each stage of the produced liquid treatment device is controlled separately; the selection of the electric field parameters has a greater impact on the electrostatic coalescence parameters. During the electro-dehydration process, there is often a critical electric field parameter that makes the electro-dehydration effect reach the optimal. The electric field parameters can be specifically expressed as the electric field frequency and the electric field strength. The electric field strength has an extremely important impact on the demulsification efficiency. When the electric field strength is too low, the external electric field cannot provide enough energy for the dispersed-phase droplets to break the droplet interface film, so the droplets are not easy to coalesce; as the electric field strength increases, the speed at which the two droplets approach each other will increase, the time will decrease and show an exponential decline. However, when the electric field strength is too high, the interface film breaks, and secondary droplets are ejected, and the emulsion will instead produce an electric dispersion phenomenon. The formation of secondary droplets will inhibit the coalescence of droplets in the emulsion, thereby reducing the demulsification efficiency; for the electric field frequency, there is also an optimal frequency that makes the electrostatic coalescence effect reach the best. This is because the pulse electric field period is close to the droplet natural period, and the droplet natural frequency resonates with the applied electric field frequency, sharply increasing the droplet collision rate and reducing the droplet interface film strength, making the droplets coalesce. Continuing to increase the electric field frequency, the droplet approach time tends to be stable, and the deformation degree of the droplets will no longer change. At this time, the stretching degree of the droplets mainly depends on the electric field force acting on them and is independent of the frequency; the optimal electric field frequency is mainly jointly affected by the applied electric field strength, the water content of the oil product itself, the conductivity, the natural frequency of the emulsion, etc.; the current generated by the pulse electric field generated by the high-frequency pulse power supply is small and is not easy to cause the electrolysis of the water phase. Therefore, applying a high-frequency high-voltage pulse electric field is not easy to cause the breakdown of the electric field, thereby enhancing the polarization of the droplets, and the pulse electric field can effectively increase the oscillation times of the droplets, creating more contact opportunities for the droplets, and thus obtaining a better droplet coalescence effect; since the water content of the crude oil in the electrostatic coalescer shows a gradually decreasing trend, the electric field parameters that need to be set for each stage of the electrostatic coalescer are also very different.

[0046] The oil-containing sewage outlet 7 of each stage is connected to the sewage total outlet pipe 19; the oil-containing sewage outlet pipe of the highest-stage pre-separation water area is joined into the oil-containing sewage outlet pipe of the middle-stage pre-separation water area through a 90° elbow; the oil-containing sewage outlet pipe of the middle-stage pre-separation water area and the oil-containing sewage outlet pipe of the highest-stage separation water area are joined into the sewage outlet branch pipe through a tee; the oil-containing sewage outlet pipe of the lowest-stage pre-separation water area and the sewage outlet branch pipe are joined into the sewage total outlet pipe 19 through a tee; the sewage total outlet pipe 19 is connected to the sewage treatment system.

[0047] Such as Figure 3As shown, the high-voltage AC insulating electrode 3 is isolated from the cavity by an insulating cover plate 5 and fixed in the cavity through the insulating cover plate 5; the high-voltage AC insulating electrode 3 is inserted into Figure 4 the central slot 20 in it. The connection method between the insulating cover plate 5 and the high-voltage AC insulating electrode 3 is bolt connection; the exposed electrode may cause an electric field short circuit, thus weakening the entire electric field and significantly reducing the dehydration efficiency of the coalescer. By using a high-voltage insulating electrode, not only can the safety and reliability be improved, but also the insulating layer only affects the electric field strength in a local area and does not significantly affect the overall effect; the high-voltage AC insulating electrode 3 adopted in this example is characterized by an uneven electric field, which increases the coalescence 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, which easily makes the coalescer unstable, and the thickness of the insulating layer has a certain influence on the degree of field strength weakening; appropriately selecting an insulating electrode with a moderate thickness can effectively prevent short-circuit events from occurring and keep the coalescence effect unaffected.

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

[0049] The connection method between the pre-separation section 2 and the bottom sand removal section 8 is flange connection, Figure 1 marked as flange 11 in it. The bottom sand removal section 8 is provided 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 regularly discharge solid sand and gravel.

[0050] The inlets 1 of each produced liquid treatment device are respectively connected to the inlet sampling branch pipes 12; the outlet sections 6 of each produced liquid treatment device are respectively connected to the purified oil sampling branch pipes 14.

[0051] As Figure 2 shown, the oily sewage outlets 7 of each produced liquid treatment device are respectively connected to the sewage 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 in the pipe.

[0053] The inclination angle of the pipelines of each pre-separation section 2 is 30 - 60°, and the longitudinal height does not exceed 600 mm; since the angle of the outlet section 6 is relatively gentle, the inlet angles of the inlets 1 of the middle pre-separation section 15 and the top pre-separation section 17 are 120 - 150°.

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

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

[0056] The oilfield produced liquid enters the inlet 1 of the lowest level, and oil-water separation is carried out in the pre-separation water section 2. The unseparated water droplets in the crude oil emulsion enter the electrostatic coalescence section 4 upward with the oil. The crude oil emulsion between the high-voltage AC insulating electrode 3 and the cavity wall in the electrostatic coalescence section 4 coalesces and settles under the action of the high-voltage high-frequency electric field, coalesces into large droplets under the action of the electric field force and settles to the pre-separation water section 2 and is discharged from the oil-containing sewage outlet 7. The solid sand and gravel settle to the bottom sand removal section 8 and are regularly discharged from the sand discharge port. The oil after electrostatic coalescence enters the inlet 1 of the upper level along the outlet section 6, and the purified oil after multi-stage treatment is discharged from the outlet of the highest level.

[0057] The presence of gas will reduce the treatment capacity and the efficiency of the coalescer. Before the device is officially put into operation, the exhaust pipe 9 needs to be opened to discharge the gas in the pipe from the exhaust pipe 9.

[0058] In this example, ball valves are installed on each sampling branch pipe. By controlling the ball valves, oil samples at various positions of the pipeline can be conveniently taken, so as to calculate the dehydration efficiency of each stage of the electrostatic coalescer. The calculation formula for the dehydration efficiency of the electrostatic coalescer is is the water content of the crude oil before passing through the electrostatic coalescence section 4 at the inlet, is the water content of the crude oil after passing through the electrostatic coalescence section 4 at the outlet. According to the crude oil emulsion taken from the sampling branch pipe, the water content of the crude oil can be measured by distillation to judge whether the crude oil after electro-dehydration meets the qualified requirements. According to the calculation formula, the dehydration efficiency of each stage of the electrostatic coalescer can be calculated.

[0059] The sewage sampling branch pipe 13 is used to test the oil content in the water at various positions, so as to measure the degree of water pollution and judge the impact and requirements on the water treatment process.

[0060] Specifically, in this embodiment, after the oilfield produced liquid enters the first-stage pre-separation water section, pre-separation is carried out in the first-stage pre-separation water section due to the oil-water density difference. Since the density of the crude oil is relatively small, it will enter the electrostatic coalescence section 4 from the upper part of the pre-separation water section after pre-separation; according to Stokes formula it can be known that the droplet diameter has a direct influence on the sedimentation velocity. The larger the droplet diameter, the faster the sedimentation velocity, and the oil-water density difference (ρ w -ρ o) And the viscosity μ of the oil phase also has an important influence on the sedimentation effect. The sedimentation velocity of water droplets is directly proportional to the density difference between oil and water, and inversely proportional to the viscosity of the oil phase. Thus, it can be seen that the preliminary separation effects of crude oil emulsions with different oil properties in the preliminary separation area are very different. Crude oil with low viscosity, low density, and large droplet diameter has a better separation effect in the preliminary separation area, which can reduce the difficulty of oil-water separation in the subsequent electrostatic coalescence section 4. The pre-separated sewage will be discharged from the system through the side sewage outlet pipe; the solid sand and gravel will enter the bottom sand removal section 8 under the action of gravity. After the crude oil enters the electrostatic coalescence section 4, the high-voltage AC insulation electrode 3 at the center position of the coalescer is energized. The coalescence of the oil-water emulsion under the action of the electric field is mainly as follows: after power-on, the droplets are arranged into multiple water chains, and adjacent droplets in each chain merge. When the droplets approach each other, they need to continuously contact and collide, and the interfacial film begins to thin. Until the thickness of the interfacial film reaches the critical thickness, the flow of the emulsion in the electric field causes the rupture of the interfacial film. At this time, the coalescence process between droplets is completed; due to the existence of the interfacial film, the thinning rate of the film is also affected by the capillary pressure and the separation pressure, and can be blocked because the Marangoni effect is significant enough; that is, small water droplets will be coalesced into large water droplets under the action of the non-uniform electric field distributed radially and settle under the action of gravity, and are discharged from the side sewage pipe together with the water after preliminary separation. The crude oil after electrocoalescence treatment enters the intermediate primary preliminary water separation section 15 from the outlet section of the coalescer wiring section for the second preliminary water separation.

[0061] In the intermediate primary preliminary water separation section 15, a very small amount of free water settles, and most of the crude oil emulsion further coalesces and settles in the electrostatic coalescence section at the intermediate primary level. The non-uniform electric field generated by the high-voltage insulation electrode can not only further enhance the coalescence effect of droplets, but also improve the safety and reliability. After power-on, adjacent droplets merge. When the droplets approach each other, they continuously contact and collide, and the interfacial film begins to thin until the interfacial film ruptures at the critical thickness, and the coalescence process between droplets is completed; the crude oil after secondary electrocoalescence enters the top-level preliminary water separation section 17 from the intermediate primary outlet section 16 through the coalescer wiring section for the third preliminary water separation.

[0062] After being treated by the first two levels of electrostatic coalescers, the water content of the crude oil has decreased significantly. Therefore, almost no oily sewage will be produced by sedimentation after the crude oil enters the top-level preliminary water separation section 17. The crude oil can reach the external transportation standard after being treated by the electrostatic coalescence section 4 at the last level.

[0063] In this example, in addition to the electric field parameters having a greater impact on droplet coalescence, the heating temperature and the flow state of the emulsion also affect the oil-water separation efficiency. According to Stokes' formula, temperature also has an impact on the sedimentation velocity, mainly reflected in that as the temperature of the emulsion increases, its viscosity decreases, and the sedimentation velocity between droplets increases accordingly; and after the temperature increases, the collision frequency between droplets also increases, and it is easier for droplets to come into contact and coalesce. However, it still needs to be considered that as the temperature of the emulsion increases, the energy consumption also increases, which may cause the sedimentation of residues in the emulsion and damage the processing equipment. Therefore, when using a coalescer, the temperature of the emulsion should be reasonably controlled to avoid dangerous situations; in addition, the flow state of the emulsion in the flow channel of the coalescer also affects the droplet coalescence process inside the coalescer; when the emulsion is in a laminar flow state under the electric field, the collision between water droplets is not intense enough, the coalescence of small droplets is relatively less, and the sedimentation effect is also unsatisfactory; while in a turbulent flow state of a certain intensity, the droplet collision frequency will increase, resulting in a better coalescence effect.

[0064] In this example, a precision regulating valve is set before the inlet of the pre-separation water area to control its flow rate, and a mass flowmeter is used for flow measurement. The flow state is controlled by controlling the flow rate and thus the flow velocity; the heating and heat preservation of the oil product in the device are completed by an electric heating device, and an oil-water mixing heat preservation tank containing an electric heater and an oil-water stirrer needs to be set before the inlet of the pre-separation water area; the crude oil emulsion after being mixed by the stirrer and heated by the electric heater is sent into the inlet of the pre-separation water area by a twin-screw pump after being measured by the mass flowmeter.

[0065] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An integrated oilfield produced fluid processing device, characterized in that: It comprises a multi-stage produced liquid treatment device connected in series from low to high; the cavity in each stage of the produced liquid treatment device comprises a bottom desanding section, a pre-water separation section, an electrostatic agglomeration section and an outlet section which are sequentially connected from bottom to top; an inlet is arranged between the pre-water separation section and the electrostatic agglomeration section, and the outlet section of the produced liquid treatment device of the lower stage is connected to the inlet of the produced liquid treatment device of the higher stage; The pre-water separation section is a pipeline with a set inclination angle, an oily sewage outlet is arranged at the bottom of the pre-water separation section, and a high-voltage AC insulating electrode is arranged in the electrostatic agglomeration section.

2. The integrated oilfield produced fluid processing device according to claim 1, characterized in that: The lowest level inlet is connected to the crude oil pipeline, and the highest level outlet is connected to the purified oil pipeline.

3. The integrated oilfield produced fluid processing device according to claim 1, characterized in that: The high-voltage AC insulated electrode is connected to a high-voltage high-frequency power supply; or, the high-voltage high-frequency power supply outputs a voltage in the range of 6kV to 15kV to the high-voltage AC insulated electrode, and an output electric field frequency in the range of 500Hz to 7kHz.

4. The integrated oilfield produced fluid processing device according to claim 1, characterized in that: The oily wastewater outlet at each level is connected to a main wastewater outlet pipe, and the main wastewater outlet pipe is connected to a wastewater treatment system for wastewater treatment.

5. The integrated oilfield produced fluid processing device according to claim 1, characterized in that: 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.

6. The integrated oilfield produced fluid processing device according to claim 1, characterized in that: The bottom sand removal section is provided with a sand filter and a sand discharge port.

7. The integrated oilfield produced fluid processing device according to claim 1, characterized in that: The inlets of the produced liquid treatment devices at each stage are connected to the inlet sampling branch pipe respectively; the outlet sections of the produced liquid treatment devices at each stage are connected to the purified oil sampling branch pipe respectively; or, the oily wastewater outlets of the produced liquid treatment devices at each stage are connected to the wastewater sampling branch pipe respectively; or, an exhaust pipe is provided between the electrostatic aggregation section and the outlet section.

8. The integrated oilfield produced fluid processing device according to claim 1, characterized in that: An electric heating device and a flow regulating device are sequentially arranged before the lowest level inlet, and the electric heating device is used for heating and keeping the oil in the device warm; an oil-water mixing insulation tank including an electric heating device and an oil-water stirring device is arranged before the lowest level pre-water separation area inlet; the flow regulating device includes a precision regulating valve and a mass flow meter.

9. A method for treating oilfield produced fluid according to any one of claims 1 to 8, characterized in that: The process includes: The produced fluid from the oil field enters the lowest level inlet, and oil and water are separated in the pre-water separation section. The unseparated water droplets in the crude oil emulsion enter the electrostatic agglomeration section with the oil, and are agglomerated into large droplets under the action of the electric field force and settle in the pre-water separation section and are discharged from the oily wastewater outlet. The solid sand and gravel settle with the water to the bottom sand removal section. The oil after electrostatic agglomeration enters the upper level inlet along the outlet section, and the purified oil after treatment by the multi-stage device is discharged from the highest level outlet section.

10. The method for treating oilfield produced fluid according to claim 9, characterized in that: The crude oil emulsion between the high-voltage AC insulating electrode and the cavity wall of the electrostatic agglomeration section agglomerates and settles under the action of the high-voltage and high-frequency electric field; Or, the gas in the pipe is discharged from the exhaust pipe; Or, the solid sand and gravel pass through the sand filter and are discharged from the sand outlet; Or, the dehydration efficiency is calculated through the sampling results of the sampling branch pipes in each section and the electric field frequency and electric field intensity are adjusted.

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