An integrated treatment method and device for produced fluid from offshore oilfield polymer flooding

Abstract

The present invention discloses an integrated treatment method and device for produced fluid from offshore oilfield polymer flooding. The integrated treatment method includes a crude oil treatment step, a sewage treatment step and a dirty oil treatment step; the crude oil treatment step: after demulsification, the polymer flooding produced fluid is subjected to oil-water separation, electrostatic coalescence dehydration and electric dehydration in sequence to obtain crude oil for external transmission; the sewage treatment step: after the sewage obtained by oil-water separation, electrostatic coalescence dehydration and electric dehydration is mixed, it is subjected to online pre-oil removal, inclined plate oil removal, gas flotation, filtration and floc online collection in sequence to achieve sewage purification; the dirty oil treatment step: after the dirty oil obtained by online pre-oil removal, inclined plate oil removal and gas flotation is mixed, it is subjected to separate and efficient water separation treatment of the dirty oil, and the obtained oil phase and water phase are respectively used as crude oil for external transmission and enter the sewage treatment step. The present invention has the characteristics of less use of oil-water treatment agent, less sludge generation, low post-processing cost, etc., which can effectively ensure the normal operation of the ground treatment process on the upper platform.

Description

Technical Field

[0001] The invention relates to an integrated processing method and device for produced fluid from offshore oilfield polymer flooding, belonging to the technical field of petroleum development. Background Art

[0002] Polymer flooding is one of the most effective technical means to stabilize and increase oil production. Offshore oil fields have achieved significant economic benefits since the pilot test and large-scale application of polymer flooding in 2003. Due to the partial output of oil-displacing polymer, the degree of oil-water emulsification in polymer flooding produced fluid is aggravated, and the particle size of the emulsified oil droplets formed is small, and the floating speed is slowed down; on the other hand, the produced polymer is adsorbed at the oil-water interface, which enhances the electronegativity of the oil droplet surface, increases the repulsive force between oil droplets, increases the strength of the interfacial film, and weakens the aggregation and coalescence of oil droplets. The combined factors make the difficulty of oil-water separation in produced fluid much greater than that of water flooding. This is the essential reason for the difficulty of polymer flooding produced fluid treatment. The rapid and efficient treatment of polymer-containing produced fluid has become one of the biggest obstacles to the large-scale application of polymer flooding in offshore oil fields. Summary of the invention

[0003] The purpose of the present invention is to provide an integrated treatment method and device for produced fluid from polymer flooding in offshore oil fields, which is an integrated treatment mode of "enhanced oil system, graded water system, separate treatment of dirty oil and graded combined dosing", and has the characteristics of small amount of oil and water treatment agent, small amount of sludge generation, low post-processing cost, etc., and can effectively ensure the normal operation of the ground treatment process on the upper platform.

[0004] The integrated treatment method for offshore oilfield polymer flooding produced fluid provided by the present invention comprises a crude oil treatment step, a sewage treatment step and a waste oil treatment step;

[0005] The crude oil processing step comprises the following steps: the polymer flooding produced fluid is demulsified and then subjected to oil-water separation, electrostatic coalescence dehydration and high-frequency high-voltage electric field enhanced electric dehydration in sequence to obtain the crude oil for external transmission;

[0006] The conditions for the electrostatic coagulation dehydration are: the electric field frequency is 800-1100 Hz.

[0007] The conditions for the high-frequency and high-voltage electric field-enhanced electric dehydration are: an output voltage of 10 kV to 25 kV, and an electric field frequency of 500 to 5000 Hz;

[0008] The sewage treatment step comprises the following steps: after the sewage obtained by the oil-water separation, the electrostatic coalescence dehydration and the high-frequency high-voltage electric field enhanced electric dehydration is mixed, it is sequentially subjected to online pre-oil removal, inclined plate oil removal, air flotation, filtration and online floc collection to achieve long-term purification treatment of the sewage;

[0009] In the sewage treatment step, the online pre-oil removal is performed after adding a non-ionic water-cleaning agent, and the inclined plate oil removal is performed after adding a composite water-cleaning agent;

[0010] The composite water purifier is a mixture of a nonionic water purifier and a zwitterionic water purifier.

[0011] In the above-mentioned integrated treatment method, the non-ionic water-clearing agent is an ethylene oxide (EO)-propylene oxide (PO) block copolymer with non-ionic polyacrylamide and polyethyleneimine as initiators;

[0012] The zwitterionic water purifier is zwitterionic polyacrylamide or dimethyldiallyl ammonium chloride-sodium allyl sulfonate copolymer;

[0013] The dosage of the non-ionic water purifier is 10 to 150 ppm;

[0014] The dosage of the zwitterionic water purifier is 10 to 150 ppm;

[0015] The non-ionic water purifier and the composite water purifier are added in a swirl mixing and dosing manner;

[0016] The waste oil treatment step comprises the following steps: the waste oil obtained by the online pre-oil removal, the inclined plate oil removal and the air flotation is mixed and then treated separately in a waste oil water separator, wherein the waste oil is separated from the water after adding an aged oil dehydrating agent, and the obtained oil phase and water phase are respectively used as the external crude oil and enter the wastewater treatment step.

[0017] In the above-mentioned integrated treatment method, in the crude oil treatment step, the demulsifier used for demulsification is a multi-branched condensed ring phenol polyether demulsifier or a polyurethane demulsifier;

[0018] The multi-branched condensed ring phenol polyether demulsifier can be a multi-branched condensed ring phenol polyether prepared with hexahydric phenol, formaldehyde, polyamine, ethylene oxide and propylene oxide as raw materials;

[0019] The polyurethane demulsifier can be prepared according to the following method: 1) melamine and glycerol are mixed to obtain a mixture of melamine and glycerol, and the mixture of melamine and glycerol is subjected to an alkoxylation ring-opening polymerization reaction with propylene oxide and ethylene oxide in sequence under base catalysis to obtain a mixture of melamine polyether and glycerol polyether; 2) the mixture of melamine polyether and glycerol polyether is used as a raw material and toluene-2,4-diisocyanate is used as a crosslinking agent to carry out a crosslinking polymerization reaction to obtain a polyurethane type crude oil demulsifier, and the specific method can be referred to the method disclosed in Chinese patent application No. 201610008701.9;

[0020] The dosage of the demulsifier is 10 to 200 ppm.

[0021] In the above-mentioned integrated processing method, in the crude oil processing step, the oil-water separation adopts a primary separator or a secondary separator.

[0022] In the above-mentioned integrated treatment method, in the sewage treatment step, the flotation agent used in the air flotation is a cationic polyacrylamide or a terpolymer prepared with block polyether macromonomer (such as PEP-90), N,N-dimethyldiallylammonium chloride (DM) and acryloyloxyethyltrimethylammonium chloride (DAC) as raw materials;

[0023] The filtering is carried out in a walnut shell filter;

[0024] After the filtration, the method further comprises a step of collecting flocs online.

[0025] In the above-mentioned integrated treatment method, in the waste oil treatment step, the aged oil dehydrating agent is a catechin demulsifier;

[0026] The catechin demulsifier can be prepared according to the following method:

[0027] 1) adding a methanol solution of epigallocatechin gallate to tetraethylenepentamine, removing the methanol to obtain a dark brown viscous liquid; adding a formaldehyde aqueous solution to the dark brown viscous liquid, heating to 50-90° C. to react for 8-12 hours; after the reaction is completed, rotary evaporation and vacuum drying to obtain a product as an initiator (EAPA, a dark brown viscous liquid);

[0028] Specifically: 62g of epigallocatechin gallate (EGCG) was dissolved in methanol, added to 154g of tetraethylenepentamine, and the methanol was removed by rotary evaporation to obtain a dark brown viscous liquid; it was added to a three-necked flask, and 66g of formaldehyde aqueous solution was added to the three-necked flask dropwise, and the temperature was raised to 80°C for reaction for 10h after the addition was completed. After rotary evaporation, vacuum drying was performed at 50°C for 48h to obtain the initiator EAPA (a dark brown viscous liquid);

[0029] 2) adding the initiator, KOH and propylene oxide (PO) into a high-pressure reactor in sequence, with a reaction temperature of 100 to 140° C. and a reaction pressure of 0.2 to 0.4 MPa, and continuing the reaction. The pressure in the high-pressure reactor gradually decreases. When the gauge pressure drops to -0.1 MPa, the reaction is complete, and an EA-PO type lipophilic polyether is obtained;

[0030] Specifically, the initiator EAPA and KOH are added to the autoclave in sequence, and after the autoclave is sealed and leak-checked, the temperature is raised and the pressure is reduced to -0.1MPa. When the temperature is raised to 120°C, propylene oxide (PO) is slowly and continuously introduced according to a certain mass ratio to control the pressure of the autoclave to be lower than 0.4MPa. After the addition is completed, PO continues to react, and the pressure in the autoclave gradually decreases, and the gauge pressure drops to -0.1MPa, indicating that the reaction is complete, and EA-PO type lipophilic polyether is obtained;

[0031] 3) The EA-PO type lipophilic polyether, KOH and ethylene oxide (EO) are sequentially added into a high-pressure reactor, the reaction temperature is 100-120° C., the reaction pressure is 0.15-0.35 MPa, the reaction is continued, and the pressure in the high-pressure reactor gradually decreases. When the gauge pressure drops to -0.1 MPa, it indicates that the reaction is complete, and the catechin demulsifier is obtained;

[0032] Specifically, EA-PO type lipophilic polyether and KOH are sequentially added to the autoclave, and a certain mass of ethylene oxide (EO) is slowly and continuously introduced in the same preparation method; due to the high activity of EO, the pressure is controlled below 0.3 MPa and the temperature is controlled below 120°C; after the addition is completed, the pressure of the reactor drops to -0.1 MPa, indicating that the reaction is complete.

[0033] That is, a catechin demulsifier is obtained;

[0034] The dosage of the aged oil dehydrating agent is 10 to 200 ppm;

[0035] The oil phase obtained by separating the waste oil from water is used as the crude oil for external transmission;

[0036] The water phase obtained by separating the waste oil from water is mixed with the wastewater obtained by the oil-water separation, the electrostatic coagulation dehydration and the electric dehydration and then subjected to wastewater treatment.

[0037] The waste oil obtained in the wastewater treatment step of the present invention is collected and treated separately (aging oil is subjected to independent and efficient dehydration treatment), thereby ensuring the dehydration effect of the crude oil treatment system. Through this treatment step, the effect of electric dehydration is improved, the electric dehydration temperature in the crude oil treatment step can be increased from 81°C to 87°C, and the water content of the oil phase is reduced from 10-12% to 4-7%, laying a solid foundation for further improving the dehydration effect of polymer flooding produced fluid.

[0038] The present invention further provides an integrated processing device for produced fluid from offshore oilfield polymer flooding, comprising a crude oil processing structure, a sewage processing structure and a waste oil processing structure; the characteristics of the device are:

[0039] The crude oil processing structure comprises an oil-water separator, a high-frequency stable electricity three-phase separator and a high-frequency high-voltage electric field enhanced electric dehydrator connected in sequence;

[0040] The sewage treatment structure comprises an online pre-oil removal device, an oil remover, an air flotation device, a filter and an online floc collection device connected in sequence;

[0041] The oil phase outlets of the oil-water separator, the high-frequency stable electricity three-phase separator and the high-frequency high-voltage electric field enhanced electric dehydrator are connected to the inlet of the online pre-oil removal device;

[0042] The waste oil treatment structure includes a waste oil water separator;

[0043] The online pre-oil removal device (the online pre-oil removal device realizes the "tubularization" of water treatment facilities, quickly completes the pre-treatment of a large amount of produced water, and ensures the hydraulic retention time of crude oil treatment), the oil remover and the oil phase outlet of the air flotation device are connected to the inlet of the waste oil water separator;

[0044] The oil phase outlet of the waste oil water separator is connected to the outlet of the high-frequency and high-voltage electric field enhanced electric dehydrator, and the water phase outlet is connected to the inlet of the online pre-oil removal device.

[0045] In the above-mentioned integrated treatment device, the oil-water separator may be a primary oil-water separator or a secondary oil-water separator;

[0046] The high-frequency stable electricity three-phase separator can be a high-frequency high-voltage stable electricity coalescer, a compact electrostatic coalescer, an online electrostatic coalescer, a container-built-in electrostatic coalescer or a low-water content coalescer;

[0047] The high-frequency stable power three-phase separator can enhance the dehydration effect of the oil-water separator, so that the water content of the outlet crude oil is less than 20%, meeting the inlet index of the electric dehydrator, and achieving the final crude oil water content of less than 1%;

[0048] The degreaser is a slanted plate degreaser;

[0049] The filter is a walnut shell filter.

[0050] In the above-mentioned integrated treatment device, the inlet ends of the online pre-oil removal device and the deoiler are both provided with swirl mixing and dosing devices to realize graded composite dosing, remove as much oil as possible through physical technology, and make the oil content at the inlet of the inclined plate deoiler as close as possible to its inlet design index (oil content ≤ 1500 mg / L), thereby reducing the dosage of the reagents and ensuring the deoiling effect;

[0051] The outlet of the filter is connected to an online floc collection device and a water injection buffer tank in sequence.

[0052] The present invention has the following beneficial effects:

[0053] The water content of exported crude oil is significantly reduced, the polymer retention rate is high, the daily sludge production is significantly reduced, the clogging and coking conditions have improved qualitatively, the cost of hazardous waste disposal has been significantly reduced, and the terminal environmental protection emission reduction has been significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a schematic structural diagram of an integrated processing device for produced fluid from offshore oilfield polymer flooding according to the present invention.

[0055] Figure 2 The present invention is a flow chart of the integrated treatment method of offshore oilfield polymer flooding produced fluid.

[0056] Figure 3 are the kinetic parameters of emulsion stability at different frequencies.

[0057] Figure 4 The inlet and outlet moisture contents of the high frequency and stable power three-phase separator were measured in the field test.

[0058] Figure 5 It is the oil removal rate of different dosing methods in the field test.

[0059] Figure 6 This is the floc state obtained by adding different water purifiers in the field test.

[0060] Figure 7 These are actual pictures after each treatment step in the sewage treatment process during the field test.

[0061] Figure 8 This is the effect of adding different agents to the waste oil treatment step in the field test.

[0062] Fig. 9 It is the water content of crude oil exported from the platform after adopting the integrated treatment method of the present invention.

[0063] Fig.10 It is the average daily amount of oily sludge on site (in tons).

[0064] Fig.11 The state of the sludge in the on-site platform buffer tank (the left picture is obtained by the existing treatment method, and the right picture is obtained by the integrated treatment method of the present invention).

[0065] Figure 1 The marks are as follows:

[0066] 1. Oil-water separator, 2. High-frequency stable electricity three-phase separator, 3. High-frequency high-voltage electric field enhanced electric dehydrator, 4. Online pre-oil removal device, 5. Inclined plate oil remover, 6. Air flotation separator, 7. Walnut shell filter, 8. Floc online collection device, 9. Water injection buffer tank, 10. Dirty oil water separator, 11. Cyclone mixing and dosing device. DETAILED DESCRIPTION

[0067] The present invention is further described below in conjunction with the accompanying drawings, but the present invention is not limited to the following embodiments.

[0068] like Figure 1 As shown, the integrated processing device for produced fluid of offshore oilfield polymer flooding provided by the present invention is an integrated processing system of "enhanced oil system, enhanced water system, and single treatment of waste oil", which is realized by crude oil processing structure, sewage treatment structure and waste oil treatment structure respectively.

[0069] Among them, the crude oil processing structure includes an oil-water separator 1, a high-frequency stable electricity three-phase separator 2 and a high-frequency high-voltage electric field enhanced electric dehydrator 3 connected in sequence, and the oil phase outlet of the high-frequency high-voltage electric field enhanced electric dehydrator 3 is connected to the crude oil export pipeline.

[0070] Among them, the sewage treatment structure includes an online pre-oil removal device 4, an inclined plate oil remover 5, an air flotation separator 6, a walnut shell filter 7, an online floc collection device 8 and a water injection buffer tank 9 connected in sequence, and the oil phase outlets of the oil-water separator 1, the high-frequency stable electricity three-phase separator 2 and the high-frequency high-voltage electric field enhanced electric dehydrator 3 are connected to the inlet of the online pre-oil removal device 4 to treat the sewage obtained from the crude oil treatment. In addition, the inlet ends of the online pre-oil removal device 4 and the inclined plate oil remover 5 are both provided with a cyclone mixing dosing device 11 to achieve graded composite dosing, remove as much oil as possible through physical technology, and make the inlet oil content of the inclined plate oil remover 5 as close to its inlet design index (oil content ≤ 1500 mg / L) as possible, thereby reducing the dosage of the reagent and ensuring the deoiling effect.

[0071] The oil treatment structure includes a waste oil water separator 10, and an aged oil dehydrating agent adding port is provided at the inlet end of the waste oil water separator 10. The oil phase outlet of the waste oil water separator 10 is connected to the outlet of the high-frequency high-voltage electric field enhanced electric dehydrator 3 to treat the waste oil, and the water phase outlet of the waste oil water separator 10 is connected to the inlet of the online pre-oil removal device 4 to treat the sewage.

[0072] In the integrated processing device of the present invention, the oil-water separator 1 can be a primary oil-water separator or a secondary oil-water separator; the high-frequency stable electricity three-phase separator 2 can be a high-frequency high-voltage stable electricity coalescer, a compact electrostatic coalescer, an online electrostatic coalescer, a container-built-in electrostatic coalescer or a low-water content coalescer. The high-frequency stable electricity three-phase separator can enhance the dehydration effect of the oil-water separator, so that the water content of its outlet crude oil is less than 20%, meeting the inlet index of the electric dehydrator, and achieving a final crude oil water content of less than 1%.

[0073] Based on the integrated processing device for producing fluid from offshore oilfield polymer flooding, the integrated processing method provided by the present invention comprises the following steps:

[0074] like Figure 2As shown, it includes a crude oil treatment step (enhanced oil system), a sewage treatment step (enhanced water system) and a waste oil treatment step (separate treatment of waste oil).

[0075] Among them, the crude oil processing step includes the following steps: after the polymer drive produced liquid is demulsified, it is successively subjected to oil-water separation, electrostatic coagulation dehydration and electric dehydration to obtain the crude oil for external transmission; the sewage treatment step includes the following steps: after the sewage obtained by oil-water separation, electrostatic coagulation dehydration and high-frequency high-voltage electric field enhanced electric dehydration is mixed, it is successively subjected to online pre-oil removal, inclined plate oil removal, air flotation, filtration and floc online collection to achieve sewage purification treatment; the waste oil treatment step includes the following steps: after the waste oil obtained by online pre-oil removal, inclined plate oil removal and air flotation is mixed, it is subjected to separate water from the waste oil, the obtained oil phase is used as the crude oil for external transmission, and the water phase enters the sewage treatment step.

[0076] In the crude oil processing step, the demulsifier used for demulsification is a multi-branched polycyclic phenol polyether demulsifier or a polyurethane demulsifier, and the dosage thereof is 10 to 200 ppm.

[0077] In the crude oil processing step, the present invention optimizes the optimal electric field frequency to 800-1100 Hz by using the stable kinetic parameter method (TSI). Figure 3 As shown, a stable high-intensity electric field is provided between the electrodes, and the micro-water droplets are instantly polarized, deformed, and aggregated, which accelerates the increase of particle size and speeds up the dehydration of crude oil.

[0078] The present invention conducts field tests at the above-determined optimal electric field frequency (800-1100 Hz), and the inlet water content and outlet water content of the high-frequency stable electric three-phase separator 2 are as follows: Figure 4 As shown, it can be seen that for the polymer-containing produced liquid with a water content of up to 90%, the water content at the outlet of the high-frequency stable power three-phase separator 2 can be reduced to 5%.

[0079] The present invention conducts field tests, and the conditions for controlling the high-frequency high-voltage electric field to strengthen the electric dehydration are: the output voltage is 10kV-25kV, and the electric field frequency is 500-5000Hz. Under this condition, a stable high-intensity electric field can be provided, and micro-water droplets are instantaneously polarized and aggregated, thereby accelerating the dehydration of crude oil. Among them, when the output voltage is 20kV and the electric field frequency is 3000Hz, the inlet water content is 5-30%, and the outlet water content can be reduced to about 2%.

[0080] In the sewage treatment step, online pre-oiling is carried out after adding a non-ionic water-cleaning agent, and inclined plate oiling is carried out after adding a composite water-cleaning agent. The composite water-cleaning agent is a mixture of a non-ionic water-cleaning agent and a zwitterionic water-cleaning agent, wherein the non-ionic water-cleaning agent is non-ionic polyacrylamide, and the zwitterionic water-cleaning agent is zwitterionic polyacrylamide, and the total dosage is 300ppm.

[0081] The present invention investigates the water purifying effects of different water purifiers and the effects of combining different water purifiers: zwitterionic water purifier (zwitterionic polyacrylamide), nonionic water purifier (nonionic polyacrylamide), cationic water purifier (cationic polyacrylamide), and a mixture of zwitterionic water purifier and nonionic water purifier, with a total dosage of 300ppm.

[0082] The above different dosing methods were used to conduct field tests (the crude oil was treated under the above-determined optimal conditions: the demulsifier was a polyurethane demulsifier, the dosage was 100ppm, the electric field frequency of electrostatic coagulation was 1000Hz, and the water phase obtained from the crude oil treatment was treated with water). The oil removal effect was as follows: Figure 5 As shown, it can be seen that the combination of amphoteric and non-ionic water-cleaning agents can increase the oil removal rate by 10% compared with the use of cationic water-cleaning agents alone at the same dosage, and no sticky flocs are produced. Figure 6 As shown (the left picture shows the floc state obtained by using a cationic water purifier, and the right picture shows the floc state obtained by using a composite water purifier); and the effective utilization rate of the graded dosing method (the proportion of the reduction in the amount of the agent when the effect is achieved) is increased by 35% compared with the first method (i.e. the tubular dosing method of adding non-ionic water purifiers and composite water purifiers at the same time).

[0083] The present invention adopts a swirl mixing and dosing method to add non-ionic water purifier and composite water purifier to improve the mixing effect.

[0084] In the sewage treatment step, the flotation agent used in air flotation is a quaternary ammonium salt type small molecule surfactant, a polyamine salt type surfactant or a cationic polyacrylamide;

[0085] The above sewage treatment steps were used for field tests, and the oil removal effect was as follows: Figure 7 As shown, from left to right are sewage inlet liquid, inclined plate outlet liquid, flotation outlet liquid and filtration outlet liquid, which proves the sewage treatment effect of the present invention.

[0086] In the waste oil treatment step, the aged oil dehydrating agent used for dehydrating aged oil is catechin demulsifier, the dosage of which is 10-200ppm, and it is prepared according to the following method: 1) Take 62g of epigallocatechin gallate (EGCG) and dissolve it in methanol, add it to 154g of tetraethylenepentamine, and remove methanol by rotary evaporation to obtain a dark brown viscous liquid; add it to a three-necked flask, add 66g of formaldehyde aqueous solution to the three-necked flask, and heat it to 80℃ for 10h after the addition is completed. After rotary evaporation, vacuum dry it at 50℃ for 48h to obtain the initiator EAPA (dark brown viscous liquid); 2) Add the initiator EAPA and KOH to the high-pressure reactor in sequence, close it for leak detection, heat it up, and reduce the pressure to -0.1MPa. When the temperature rises to 70℃, start vacuuming and continue to 100℃. When the temperature is close to 120℃, propylene oxide (PO) is slowly and continuously introduced according to a certain mass ratio, and the pressure of the reactor is controlled to be lower than 0.4MPa. After the addition is completed, PO continues to react, and the pressure in the autoclave gradually decreases, and the gauge pressure drops to -0.1MPa, indicating that the reaction is complete, and EA-PO type lipophilic polyether is obtained; 3) EA-PO type lipophilic polyether and KOH are added to the autoclave in sequence, and a certain mass of ethylene oxide (EO) is slowly and continuously introduced in the same preparation method; due to the high activity of EO, the pressure is controlled to be lower than 0.3MPa and the temperature is lower than 120℃; after the addition is completed, the pressure of the reactor drops to -0.1MPa, indicating that the reaction is complete.

[0087] The existing oil-water treatment is a closed-loop cycle, and the waste oil is transferred back to the crude oil treatment system, which seriously reduces the treatment efficiency and causes the water content of the exported crude oil to be high and fluctuating. The present invention provides a process for separate treatment of waste oil.

[0088] The results of the on-site demulsification test (SZ36-1 oil field in Bohai Sea) are as follows: Figure 8 As shown, the demulsifier used is catechin demulsifier, and the normal crude oil demulsifier (BH123) used on site is selected as the control, and the demulsifier concentration is 100 mg / L. The results show that the dehydration rate is 80% within 10 minutes and 95% within 40 minutes. The aged oil in the waste oil system contains more than 36% water, 800 to 1,000 cubic meters per day. Using the waste oil separate treatment process, the overall water content of the platform crude oil can be reduced from 10% to 4%.

[0089] The waste oil obtained in the wastewater treatment step of the present invention is collected and subjected to separate high-efficiency dehydration treatment before being transported outward.

[0090] The electric dehydration temperature in the crude oil processing step can be increased from 81°C to 87°C, which improves the equipment processing efficiency and lays a solid foundation for further improving the dehydration effect of polymer flooding produced fluid.

[0091] After the integrated treatment of produced fluid by the present invention, the water content of the oil phase is reduced from 10-12% to 3% ( Fig. 9), the amount of oily sludge at the Suizhong 36-1 terminal treatment plant was reduced from about 120 tons / day to about 30 tons / day (e.g. Fig.10 The platform buffer tank sludge changes from a viscoelastic quilt state to a flowable state, from a large amount to a small amount, and can be pumped (as shown in Fig.11 As shown in the figure, the problem of sludge treatment has been fundamentally reversed.

Claims

1. An integrated treatment method for produced fluid from offshore oilfield polymer flooding, comprising a crude oil treatment step, a sewage treatment step and a waste oil treatment step; The crude oil processing step comprises the following steps: the polymer flooding produced fluid is demulsified and then subjected to oil-water separation, electrostatic coalescence dehydration and high-frequency high-voltage electric field enhanced electric dehydration in sequence to obtain the crude oil for external transmission; The electrostatic coalescence dehydration adopts a high-frequency stable electricity three-phase separator; In the crude oil processing step, the demulsifier used for demulsification is a multi-branched condensed ring phenol polyether demulsifier or a polyurethane demulsifier; The dosage of the demulsifier is 10-200 ppm; The conditions for the electrostatic agglomeration dehydration are: the electric field frequency is 800-1100 Hz; The conditions for the high-frequency and high-voltage electric field-enhanced electric dehydration are: an output voltage of 10 kV to 25 kV, and an electric field frequency of 500 to 5000 Hz; In the crude oil processing step, the oil-water separation adopts a primary separator or a secondary separator; The sewage treatment step comprises the following steps: the sewage obtained by the oil-water separation, the electrostatic coalescence dehydration and the high-frequency high-voltage electric field enhanced electric dehydration is mixed, and then sequentially subjected to online pre-oil removal, inclined plate oil removal, air flotation and filtration to achieve sewage purification; wherein, After adding a non-ionic water-cleaning agent, the online pre-degreasing is performed, and after adding a composite water-cleaning agent, the inclined plate degreasing is performed; The composite water purifier is a mixture of a nonionic water purifier and a zwitterionic water purifier; The nonionic water purifier is an ethylene oxide-propylene oxide block copolymer or a nonionic polyacrylamide with polyethyleneimine as an initiator; The zwitterionic water purifier is dimethyldiallyl ammonium chloride-sodium allyl sulfonate copolymer or zwitterionic polyacrylamide; The dosage of the non-ionic water purifier is 10-150ppm; The dosage of the zwitterionic water purifier is 10-150ppm; The non-ionic water-cleaning agent is added in a swirl mixing and dosing manner for online pre-oil removal and the composite water-cleaning agent is added for inclined plate oil removal; In the sewage treatment step, the flotation agent used in the air flotation is a terpolymer or cationic polyacrylamide prepared from block polyether macromonomer, N,N-dimethyldiallylammonium chloride and acryloyloxyethyltrimethylammonium chloride as raw materials; The filtering is carried out in a walnut shell filter; After the filtration, the step of collecting flocs online is also included; The waste oil treatment step comprises the following steps: the waste oil obtained by the online pre-oil removal, the inclined plate oil removal and the air flotation is mixed, and then subjected to aging oil dehydration and waste oil water separation in sequence, and the obtained oil phase and water phase are respectively used as the external crude oil and enter the wastewater treatment step; The aged oil dehydrating agent used in the aged oil dehydration is a catechin demulsifier; The catechin demulsifier is prepared according to the following method: 1) adding a methanol solution of epigallocatechin gallate to tetraethylenepentamine, removing the methanol to obtain a dark brown viscous liquid; adding a formaldehyde aqueous solution to the dark brown viscous liquid, heating to 50-90°C to react for 8-12 hours; after the reaction is completed, rotary evaporation and vacuum drying to obtain a product as an initiator; 2) The initiator, KOH and propylene oxide are sequentially added into a high-pressure reactor, the reaction temperature is 100-140° C., the reaction pressure is 0.2-0.4 MPa, the reaction is continued, and the pressure in the high-pressure reactor gradually decreases. When the gauge pressure drops to -0.1 MPa, it indicates that the reaction is complete, and an EA-PO type lipophilic polyether is obtained; 3) The EA-PO type lipophilic polyether, KOH and ethylene oxide are sequentially added into a high-pressure reactor, the reaction temperature is 100-120°C, the reaction pressure is 0.15-0.35Mpa, the reaction is continued, and the pressure in the high-pressure reactor gradually decreases. When the gauge pressure drops to -0.1 MPa, it indicates that the reaction is complete, and the catechin demulsifier is obtained; The oil phase obtained by separating the waste oil from the water is mixed with the oil phase obtained by the high-frequency and high-voltage electric field enhanced electric dehydration and then transported out; The water phase obtained by separating the waste oil from water is mixed with the wastewater obtained by oil-water separation, electrostatic coagulation dehydration and high-frequency and high-voltage electric field enhanced electric dehydration, and then subjected to wastewater treatment.

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