An offshore fracturing flowback fluid in-situ treatment method and treatment device

Abstract

The present application relates to the technical field of sewage treatment, in particular to a kind of offshore fracturing flowback fluid in situ processing method and processing device, processing method is: S1, in the offshore fracturing flowback fluid to be treated composite demulsification destabilizer is added to carry out gel breaking reaction, then by pre-aeration treatment, obtain primary purified water;S2, primary purified water is treated by self-cleaning ozone oxidation;S3, self-cleaning ozone oxidation effluent is filtered by membrane to remove suspended solids and bacteria, obtain membrane concentrated water and membrane production water;S4, membrane concentrated water is backflowed to step S1 after being treated by light irradiation sterilization;Membrane production water is treated by self-circulation deoxygenation, and treated water is obtained.The processing method ensures that fracturing flowback fluid meets the standard for reuse and ensures long-term stable operation of the system without using hazardous chemicals, and the modular compact layout occupies small area, and finally the key indicators of effluent all meet or are better than offshore fracturing fluid compounding reuse standard.

Description

Technical Field

[0001] This invention relates to a method and apparatus for in-situ treatment of marine fracturing flowback fluid, belonging to the field of wastewater treatment technology. Background Technology

[0002] Large quantities of fracturing fluid are used in offshore oil and gas extraction. Fracturing fluid is a liquid formulated with water, chemical additives, and particulate matter. Water is the most abundant component, accounting for over 90% of the total mass. Chemical additives mainly include polymers, cross-linking agents, corrosion inhibitors, and stabilizers, resulting in an extremely complex composition. After fracturing operations are completed, a large amount of fracturing flowback fluid is discharged from the wellhead to the surface. This flowback fluid contains residues from the fracturing fluid reaction, exhibiting a highly complex composition with high salt content, high hardness, and high polymer content. It cannot be directly reused as water for fracturing fluid reconstitution. It must be treated to meet the relevant environmental protection requirements of the offshore oil and gas extraction industry (pH ≥ 5, polymer ≤ 50 mg / L, sulfate-reducing bacteria 0 CFU / mL, iron bacteria ≤ 25 CFU / mL, saprophytic bacteria ≤ 25 CFU / mL, dissolved oxygen ≤ 0.02 mg / L) before it can be used as recycled water for fracturing fluid reconstitution.

[0003] Currently, the conventional treatment methods for fracturing flowback fluid in onshore oil and gas extraction mainly involve oil removal, suspended solids removal, and reduction of median particle size before reprocessing and reuse. However, offshore fracturing flowback fluid is limited by factors such as the limited space on offshore platforms, equipment load-bearing capacity, environmental and climatic conditions, hazardous chemicals, and explosion prevention requirements. There is currently no effective treatment technology, especially for polymers. If polymers are not thoroughly treated, using them as recycled water for fracturing fluid reprocessing will have the following consequences: (1) Damage to fracturing fluid performance: The residual polymers in recycled water will overlap with the thickeners, guar gum, polyacrylamide and other components in the fracturing fluid, causing the system viscosity to exceed the standard; the residual polymers will interfere with the crosslinking reaction between the crosslinking agent and the main agent, resulting in problems such as delayed crosslinking, uneven crosslinking, and insufficient gel strength, which will prevent the formation of a stable gel, thus greatly reducing the sand carrying capacity of the fracturing fluid and easily causing sand blockage; the residual polymers will also enhance the oil-water emulsification effect, forming a stable polymer oil-water emulsion, and the oil content of the compound solution will exceed the standard, affecting the performance of the fracturing fluid.

[0004] (2) Affects the use of chemicals and increases operating costs: The residual polymer molecular chains in the recycled water will adsorb breaker, surfactant, bactericide and other additives, hindering the effectiveness of the chemicals. The breaker will not break the gel completely and will be difficult to return; the surfactant will have a sharp reduction in its oil removal, wetting and drainage effects; the bactericide will be ineffective and will easily breed bacteria and algae, causing the system to deteriorate. On-site, additional thickeners, crosslinking agents, breaker and other raw materials need to be added, which will directly increase the cost of chemicals for offshore fracturing operations. At the same time, the limited storage space on the platform will further exacerbate the pressure on material storage.

[0005] (3) Blockage of pipelines and equipment, increasing the risk of platform operation and maintenance: Polymers and entrained solid impurities in recycled water are prone to adhere, deposit, and gel in mixing tanks, conveying pipelines, high-pressure pumps, wellheads, and the inner walls of downhole screen pipes, leading to frequent malfunctions. Offshore platforms are high-risk explosion-proof areas with limited space for equipment maintenance, high difficulty in operation and cleaning, and abnormal equipment conditions will further increase the risk of safety production.

[0006] Therefore, developing a marine fracturing flowback fluid treatment system that can efficiently remove organic matter, polymers, bacteria, dissolved oxygen, and other substances from fracturing flowback fluid, and that is stable in operation and occupies a small area, so that the treated fracturing flowback fluid can be reconstituted and reused as fracturing fluid, is of great value. Summary of the Invention

[0007] This invention addresses the technical challenge of safely and efficiently treating and reusing polymer fracturing flowback fluid within the confined space of offshore platforms. It provides an in-situ treatment method and apparatus for offshore fracturing flowback fluid. This method does not use any hazardous chemicals. It achieves efficient polymer removal at room temperature using a non-oxidizing composite demulsifier and destabilizer. Combined with a closed-loop design involving membrane filtration, a specific sequence of self-circulating deoxygenation, and UV sterilization and reflux of membrane concentrate, it ensures that the fracturing flowback fluid meets standards for reuse and guarantees long-term stable system operation without the use of hazardous chemicals. Furthermore, its modular and compact layout minimizes the footprint. The final effluent meets or exceeds the standards for the reuse of offshore fracturing fluid, providing a safe, efficient, and compact complete solution for the in-situ resource utilization of fracturing flowback fluid in offshore oil and gas extraction.

[0008] The technical solution of this invention to solve the above-mentioned technical problems is as follows: a method for in-situ treatment of offshore fracturing flowback fluid, wherein the treatment method is as follows: S1. Add a composite demulsifier and destabilizer to the offshore fracturing flowback fluid to be treated to carry out the demulsification reaction, and then proceed with pre-aeration treatment and sedimentation treatment to obtain primary purified water. The composite demulsifier and destabilizer includes polyethylene polyamine polyether, citric acid complexed polysilicon ferric chloride, polydimethyl diallyl ammonium chloride, and dimethylamine epichlorohydrin polymer. S2. The primary purified water is subjected to self-cleaning ozone oxidation treatment; S3. The ozone oxidation effluent is then filtered through a membrane to remove suspended solids and bacteria, yielding membrane concentrate and membrane permeate. S4. The membrane concentrate is sterilized by light irradiation and then returned to step S1 for further treatment. The membrane permeate is subjected to self-circulating deoxygenation treatment to obtain treated water.

[0009] Furthermore, the composite demulsifier and destabilizer consists of: polyethylene polyamine polyether, citric acid complexed polysilicon ferric chloride, polydimethyldiallylammonium chloride, and dimethylamine epichlorohydrin polymer, with the mass ratio of each substance being (20-50):(100-200):(1-2):1. The amount of the composite demulsifier added is 50-300 mg / L.

[0010] Furthermore, the debonding reaction in step S1 is carried out in a pre-aeration debonding tank, which is equipped with an integrated partitioned destabilization reaction zone for the debonding reaction, an aeration zone for pre-aeration treatment, and a sedimentation zone for sedimentation treatment.

[0011] Furthermore, in step S2, the primary purified water is first filtered by an automatic membrane filter and then enters the oxidation reactor for ozone oxidation treatment. The ozone gas generated by the ozone generator is passed through an ozone aerator to form fine bubbles with a diameter of 30-80μm. The ozone concentration in the water during the ozone oxidation reaction is 10-15mg / L, and the temperature is 15-35℃.

[0012] In step S3, the membrane filtration uses an ultrafiltration membrane with a pore size of 0.01-0.03 μm. The ultrafiltration membrane is made of hydrophilic modified polyvinylidene fluoride, the operating pressure is 0.15-0.25 MPa, and the water production rate is ≥92%.

[0013] Furthermore, in S4, the self-circulating deoxygenation treatment is carried out in a self-circulating deoxygenation tank, and the vacuum pressure in the self-circulating deoxygenation tank is -0.095MPa to -0.098MPa; The self-circulating deoxygenator includes at least a primary spiral flow deoxygenation chamber and a secondary atomizing spray deoxygenation chamber; In step S4, during the photo-irradiation sterilization process, ultraviolet light with a wavelength of 185nm or 254nm is used for irradiation, with an irradiation intensity of 30-60mW / cm² and a hydraulic residence time of 10-20s.

[0014] Furthermore, after step S1, the viscosity of the effluent is reduced to ≤2.05 mPa·s, the polymer content is reduced to ≤40 mg / L, the suspended solids content is reduced to ≤100 mg / L, and the COD is reduced to ≤3000 mg / L; The COD of the effluent from step S2 is ≤300 mg / L; The dissolved oxygen in the effluent after self-circulation deoxygenation treatment in step S4 is ≤0.01mg / L.

[0015] The present invention also discloses an in-situ treatment device for offshore fracturing flowback fluid. The treatment device includes a pre-aeration depolymerization tank, a self-cleaning ozone reaction tank, a membrane filter and a self-circulating deoxygenation tank connected in sequence, and a photoirradiation sterilization tank connected between the concentrate outlet of the membrane filter and the inlet of the pre-aeration depolymerization tank. The pre-aeration depolymerization tank is divided into a destabilization reaction zone, an aeration zone, and a sedimentation zone by a partition. The aeration zone is equipped with an aerator, and the sedimentation zone is equipped with a primary purification outlet and a guide plate. The self-circulating deoxygenating tank is equipped with a primary spiral flow deoxygenating chamber located at the top and a secondary atomizing spray deoxygenating chamber located at the bottom.

[0016] Furthermore, the pre-aeration depolymerization box is a closed box, and a partition is provided between the destabilization reaction zone, the aeration zone and the sedimentation zone. The offshore fracturing flowback fluid to be treated is transported between the destabilization reaction zone, the aeration zone and the sedimentation zone by overflow. An overflow slag removal plate is provided at the upper part of the sedimentation zone, and several guide plates are provided on the wall of the sedimentation zone. The angle between the guide plates and the horizontal is 45°-60° or 120°-135°. The arrangement of the guide plates forms an "S" shaped flow channel on the wall.

[0017] Furthermore, the self-cleaning ozone reactor is equipped with multiple baffles. The angle between the baffles and the horizontal is 0°-45°, and the length of the baffles is 1 / 4-1 / 3 of the total diameter of the self-cleaning ozone reactor. The baffles are arranged in a left-right axially symmetrical manner, and the arrangement of the baffles forms a "Z"-shaped flow channel on the reactor wall.

[0018] Furthermore, in the self-circulating deoxygenating tank, the primary spiral flow channel deoxygenating chamber is provided with several spiral flow channels, and the upper inlet of the spiral flow channels is connected to the water inlet pipe at the upper end of the primary spiral flow channel deoxygenating chamber; the upper end of the secondary atomizing spray deoxygenating chamber is provided with several nozzles. When the liquid level in the primary spiral flow deoxygenation chamber reaches 1 / 2 to 2 / 3 of the total height of the primary spiral flow deoxygenation chamber, the nozzle is turned on; when the liquid level in the secondary atomizing spray deoxygenation chamber reaches 1 / 2 to 2 / 3 of the total height of the secondary atomizing spray deoxygenation chamber, the drain outlet of the self-circulating deoxygenation tank is opened.

[0019] Furthermore, the light irradiation sterilization chamber is provided with several light irradiation reaction chambers, and each light irradiation reaction chamber is provided with a light irradiation lamp group and a cooling system. The cooling system includes an inner circulation cooling channel and an outer circulation cooling channel, and the lamp tubes of the light irradiation lamp group are arranged inside the inner circulation cooling channel.

[0020] The beneficial effects of this invention are: (1) In the in-situ treatment method for offshore fracturing flowback fluid described in this invention, the entire treatment process does not use any acids, alkalis, oxidants (such as persulfate, hydrogen peroxide, etc.) or other hazardous chemicals. Instead, it uses a special non-oxidizing composite demulsifier and destabilizer (all agents are not listed in the hazardous chemicals catalog) to react with polyacrylamide polymers, reducing the molecular weight and viscosity to achieve demulsification and flocculation. It is more effective than conventional persulfate-based oxidizing demulsifiers and introduces no byproducts; it is non-corrosive, has no risk of combustion or explosion, and is safe for transportation and storage, reducing the frequency of equipment maintenance. It is especially suitable for offshore platforms with limited space, dense personnel, and limited emergency response capabilities.

[0021] (2) The offshore fracturing flowback fluid in-situ treatment device of the present invention consists of a pre-aeration de-galvanizing tank, a self-cleaning ozone reaction tank, a membrane filter, a self-circulating deoxygenation tank, and a photoirradiation sterilization tank. Each module adopts an integrated and compact design, which saves more than 50% of the land area compared with the traditional process, meets the limited space requirements of offshore platforms, is lightweight, and is easy to hoist and transport. The modules can be disassembled and assembled independently, adapting to offshore hoisting, ship transportation and other conditions.

[0022] (3) In the offshore fracturing flowback fluid in-situ treatment device described in this invention, the pre-aeration and de-galvanizing box adopts a closed box structure, which effectively blocks the possibility of combustion or explosion accidents after gas leakage, and significantly improves the safety and long-term operational reliability of the entire water treatment system; abandoning the traditional scraper that relies on continuous operation of mechanical scrapers, the overflow slag removal based on the gravity self-flow principle is adopted, which greatly simplifies the internal structure of the equipment and achieves stable long-term operation; the system has multiple sets of guide plates built in, which are arranged in a regular staggered manner to form an "S"-shaped flow channel with a clear flow direction guidance function, which not only ensures that the water flows along the predetermined trajectory, but also significantly extends the actual hydraulic residence time through multiple reversals, enhances the probability of particle collision and floc aggregation efficiency in turbulent disturbance, and promotes the full settling of fine suspended solids, colloids and other impurities, resulting in excellent and stable effluent quality, with turbidity below 2 NTU and SS concentration less than 10 mg / L.

[0023] (4) An automatic membrane filter is installed at the inlet of the self-cleaning ozone reactor. The automatic membrane filter automatically scrapes off the suspended solids deposited on the membrane surface according to their weight, eliminating the need for manual cleaning and preventing suspended solids in the incoming water from entering the self-cleaning ozone reactor. The self-cleaning ozone reactor has no filler and does not require the addition of any reagents during the reaction process. By setting up "Z"-shaped baffles to extend the residence time of ozone in the water, the ozone oxidation efficiency is increased by 3-5 times compared to the traditional ozone oxidation efficiency, which can reduce COD to ≤300mg / L.

[0024] (5) The self-circulating deoxygenator adopts an innovative multi-stage synergistic deoxygenation structure. The core of the first-stage spiral flow deoxygenation chamber adopts a three-dimensional spiral rising flow channel design, which increases the path length by 2-3 times and expands the gas-liquid contact surface area by 3-5 times, providing sufficient mass transfer interface and reaction time for efficient dissolved oxygen release. Secondly, it is equipped with an intelligent graded liquid level feedback control system. When the liquid level in the first-stage spiral flow deoxygenation chamber rises to the design height, the second-stage atomizing spray deoxygenation chamber can be triggered in real time by the PLC controller, and the high-pressure atomizing nozzle is opened simultaneously to form a "liquid film-droplet" dual-mode deoxygenation mechanism, realizing dynamic matching of deoxygenation load and optimization of energy efficiency. The entire process is carried out under normal temperature conditions for self-circulating deoxygenation operation, completely avoiding the steam heating link required by traditional thermal deoxygenation, and the energy saving effect is extremely outstanding; it completely gets rid of the dependence on traditional chemical deoxygenation agents (such as sodium sulfite, sodium bisulfite, etc.), reducing the cost of agents. The dissolved oxygen concentration in the effluent is consistently maintained at an ultra-low level of ≤0.01 mg / L, which is better than the upper limit of dissolved oxygen (≤0.02 mg / L) required by the standard for compound reclaimed water. This effectively ensures the long-term corrosion protection of the water injection network and the formation. Moreover, the entire process is completely sterilized, and no bacterial sludge is generated, which would cause secondary pollution.

[0025] (6) The present invention adopts a specific process sequence of “pre-aeration and gel breaking → self-cleaning ozone oxidation → membrane filtration → self-circulating deoxygenation (membrane concentrate → photo-irradiation sterilization reflux)”, and the units form a close functional synergy and mutual guarantee relationship: pre-aeration and gel breaking provides low polymer and low suspended solids influent conditions for ozone oxidation, which greatly reduces the oxidative load of ozone; ozone oxidation breaks the ring-chain of large organic molecules into small organic molecules, effectively alleviating the organic pollution of the membrane filtration unit and extending the membrane cleaning cycle to more than 45 days; and the sequential design of “membrane filtration first and self-circulating deoxygenation later” utilizes the ultrafiltration membrane to remove bacteria ≥99%. A 9% retention rate provides sterile influent conditions for the deoxygenation process, completely eliminating the formation of biofilm inside the deoxygenation tank. This ensures that the deoxygenation tank can operate continuously for more than 90 days without cleaning, and the dissolved oxygen in the effluent is stably controlled at ≤0.01mg / L, far exceeding the requirement of ≤0.02mg / L for compound reuse. The design of returning the membrane concentrate to the front end after photo-irradiation sterilization allows the bacterial residues after sterilization to be flocculated and discharged as scum under the action of the front-end composite demulsifier. This forms a closed-loop microbial control system of "concentrate → UV inactivation → return to the front end → flocculation removal", effectively preventing the accumulation of live bacteria and biological contamination within the system. The water treated using the method and apparatus described in this invention exhibits comprehensive performance superior to the requirements for compounding and reuse stipulated by the offshore oil and gas extraction industry (polymer ≤ 50 mg / L, sulfate-reducing bacteria 0 CFU / mL, iron bacteria ≤ 25 CFU / mL, saprophytic bacteria ≤ 25 CFU / mL, dissolved oxygen ≤ 0.02 mg / L). This effectively avoids the damage of residual polymers to the crosslinking performance and proppant carrying capacity of the compounded fracturing fluid, eliminates the adsorption and consumption of polymers by breaker agents, surfactants, and other additives, eliminates the risk of adhesion and blockage on the inner walls of pipelines and equipment, and ensures that the flowback fluid can be stably compounded and reused as fracturing fluid in the long term after treatment. This achieves the safe and efficient resource utilization of offshore fracturing flowback fluid and has broad market application prospects and promotional value. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the offshore fracturing flowback fluid in-situ treatment device described in this invention; Figure 2 This is a schematic diagram of the structure of the pre-aeration and gel breaking box described in this invention; Figure 3 This is a schematic diagram of the structure of the self-cleaning ozone reactor described in this invention; Figure 4 This is a schematic diagram of the structure of the self-circulating deoxygenator described in this invention; Figure 5 This is a schematic diagram of the spiral flow channel described in this invention; Figure 6 This is a schematic diagram of the structure of the light irradiation sterilization box described in this invention; Figure 7This is a schematic diagram of the circulating cooling structure of the light irradiation reaction chamber described in this invention; Figure 8 This is a schematic diagram of the structure of a single light irradiation reaction chamber; Figure 9 for Figure 8 AA section diagram; In the diagram: 1. Pre-aeration and depolymerization chamber; 2. Self-cleaning ozone reactor; 3. Membrane filter; 4. Self-circulating deoxygenation tank; 5. Photoirradiation sterilization chamber. 101. Destabilization reaction zone; 102. Aeration zone; 103. Sedimentation zone; 104. Aerator; 105. Primary purification outlet; 106. Baffle plate; 107. Overflow slag removal plate; 108. Raw water inlet; 109. Chemical dosing port; 110. Vent; 111. Pressure gauge; 112. First partition plate; 113. Second partition plate; 201. Ozone inlet; 202. Ozone aerator; 203. Baffle plate; 204. Separator plate; 205. Ozone outlet; 206. Overflow plate; 207. Ozone exhaust valve; 208. Sewage outlet; 401. Primary spiral flow deoxygenation chamber; 402. Secondary atomizing spray deoxygenation chamber; 403. Spiral flow channel; 404. Water inlet pipe; 405. Nozzle; 406. Safety valve; 407. Gas-liquid separator; 408. Primary exhaust valve; 409. Secondary exhaust valve; 410. Vacuum pump; 411. Drain pump; 412. First level gauge; 413. Second level gauge; 501. Irradiation reaction chamber; 502. Internal circulation cooling channel; 503. External circulation cooling channel; 504. Lamp tube; 505. Lamp holder; 506. Water inlet pipe; 507. Water outlet; 508. Coolant circulation tank. Detailed Implementation

[0027] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0028] Unless otherwise defined, 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. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0029] like Figure 1 As shown, an in-situ treatment method for offshore fracturing flowback fluid is described, wherein the treatment method is as follows: S1. Add a composite demulsifier and destabilizer to the offshore fracturing flowback fluid to be treated to carry out the demulsification reaction, and then proceed with pre-aeration treatment and sedimentation treatment to obtain primary purified water. The composite demulsifier and destabilizer includes polyethylene polyamine polyether, citric acid complexed polysilicon ferric chloride, polydimethyl diallyl ammonium chloride, and dimethylamine epichlorohydrin polymer. S2. The primary purified water is subjected to self-cleaning ozone oxidation treatment; S3. The ozone oxidation effluent is then filtered through a membrane to remove suspended solids and bacteria, yielding membrane concentrate and membrane permeate. S4. The membrane concentrate is sterilized by light irradiation and then returned to step S1 for further treatment. The membrane permeate is subjected to self-circulating deoxygenation treatment to obtain treated water.

[0030] Specifically, the amount of the composite demulsifier added is 50-300 mg / L (i.e., 50-300 mg of composite demulsifier is added to 1 L of fracturing flowback fluid).

[0031] The demulsification reaction does not use hazardous chemicals such as acids, alkalis, and oxidants (hydrogen peroxide, persulfate, sodium hypochlorite, etc.). Instead, it uses a non-oxidizing composite demulsifier and destabilizer with a pH of 5-7. It is non-corrosive, not classified as a hazardous chemical, and can be easily transported and controlled. The reaction is carried out at room temperature for 30-40 minutes, which can destroy the molecular structure of polymers in wastewater, reduce the molecular weight and viscosity of water, reducing viscosity to ≤2.05 mPa·s, polymer concentration from 3000-6000 mg / L to ≤40 mg / L, suspended solids to ≤100 mg / L, and COD from 10000-30000 mg / L to ≤3000 mg / L.

[0032] The composite demulsifier and destabilizer consists of polyethylene polyamine polyether, citric acid complexed polysilicon ferric chloride, polydimethyl diallyl ammonium chloride, and dimethylamine epichlorohydrin polymer (none of these components are hazardous chemicals). It selects a relatively mild method to achieve flocculation of high polymers in fracturing flowback fluid, thereby reducing the molecular weight of the polymer and the viscosity of the wastewater.

[0033] The composite demulsifier and destabilizer first adsorbs onto the surface of oil-in-water or polymer-in-oil emulsion particles in fracturing flowback fluid at multiple points, causing distortion and rupture of the outer interface of the emulsion. This releases the fine oil droplets or suspended matter inside, causes adjacent oil droplets to polymerize, and expands the outer polymer, thus achieving the demulsification effect. Secondly, the iron ions provided by the composite demulsifier and destabilizer will crosslink with carboxyl groups (-COO-) and amino groups (-NH2) on the polymer, causing the polymer to destabilize and reducing the viscosity of the wastewater.

[0034] The characteristics of composite demulsifiers and destabilizers include: high stability, no hydrolysis to generate hydroxide precipitates, long shelf life, and wide pH range; high flocculation performance, the complex morphology carries a higher positive charge, strong charge neutralization ability, and the long organic chains can improve adsorption and bridging ability, producing denser flocs and faster settling speed, achieving good flocculation effect without the need for conventional PAC and PAM flocculants.

[0035] Specifically, the composite demulsifier consists of: polyethylene polyamine polyether, citric acid complexed polysilicon ferric chloride, polydimethyldiallylammonium chloride, and dimethylamine epichlorohydrin polymer, with a corresponding mass ratio of (20-50):(100-200):(1-2):1.

[0036] Polyethylene polyamine polyether, as the main demulsifier, penetrates and disrupts the emulsion interface film, releasing fine oil droplets or suspended matter inside, causing adjacent oil droplets to polymerize, and expanding the external polymer, thus achieving the demulsification effect. Citric acid-complexed polysilicon ferric chloride, as a flocculant, provides a high positive charge and complex network structure, crosslinking with the carboxyl and amino groups of the polymer. Polydimethyl diallyl ammonium chloride, as a flocculant aid, enhances charge neutralization and adsorption bridging. Dimethylamine epichlorohydrin polymer, as an auxiliary coagulant, promotes floc densification and accelerates sedimentation. The four components of the composite demulsifier and destabilizer perform the functions of "demulsification-crosslinking-binding-compacting" in a synergistic manner to achieve demulsification, flocculation, and sedimentation.

[0037] If the content of polyethylene polyamine polyether exceeds the specified range, although the emulsion interface is fully disrupted, the released oil droplets and suspended solids cannot be effectively "captured" due to insufficient flocculant, resulting in small and loose flocs and increased effluent turbidity. If the content is below the specified range, demulsification is incomplete, and oil droplets remain encased in the polymer network structure, failing to achieve efficient oil removal. Too low a ratio of citric acid-complexed polysilicon ferric chloride leads to insufficient iron ions, weak charge neutralization, and difficulty in floc formation. Too high a ratio causes excessive iron ions to reverse the surface charge of the flocs, causing them to redisperse, while also introducing excessive iron ions that affect effluent color and subsequent water quality. A ratio of polydimethyldiallyl ammonium chloride to dimethylamine epichlorohydrin polymer (1-2):1 is considered a "micro-enhancement." Exceeding this value results in an excessively rapid polymerization reaction rate, leading to gelation and consequently worsening the sedimentation effect.

[0038] If the dosage of the composite demulsifier destabilizer deviates, multiple problems may occur, such as incomplete demulsification (high viscosity, high COD), low oil and impurity removal efficiency, slow settling speed, and waste of reagents. Ultimately, this will lead to deterioration of the effluent quality of the air flotation (increased SS and oil content), and increase the load on the subsequent ozone and membrane filtration units.

[0039] The suspended solids and oily substances mainly treated in the pre-aeration and de-gelling box 1 have particle sizes in the range of tens to hundreds of micrometers. This is exactly the particle size matching relationship with the microbubbles generated by the aerator 104. The bubbles can effectively adhere to and carry these particles to the surface of the liquid, so that the suspended solids and oils can be efficiently captured and removed by the bubbles.

[0040] More specifically, the preparation method of the polyethylene polyamine polyether and citric acid complexed polysilicon ferric chloride is as follows: The preparation method of polyethylene polyamine polyether is as follows: Polyethylene polyamine and potassium hydroxide catalyst are added to a reactor. Under a nitrogen-filled environment and pressure controlled at 0.25-0.3 MPa, the temperature is raised to 110-125℃ and stirred for 30-60 min. Then, propylene oxide is added, and the temperature is further raised to 130-150℃ and stirred for 15-30 min. Ethylene oxide is then added and stirred for 15-30 min. Finally, the same amount of propylene oxide as in the previous step is added, and the reaction is stirred for 45-60 min. After depressurization, the product, polyethylene polyamine polyether, is obtained. The mass fraction ratio of polyethylene polyamine:potassium hydroxide:propylene oxide:ethylene oxide is (2-8):(3.5-5):(300-450):(75-95).

[0041] The specific preparation method of the polyethylene polyamine polyether used in this embodiment of the invention is as follows: Polyethylene polyamine and potassium hydroxide catalyst are added to a reactor. Under a nitrogen-filled environment and with the pressure controlled at 0.3 MPa, the temperature is raised to 120°C and stirred for 40 min. Then, propylene oxide is added, and the temperature is further raised to 140°C and stirred for 20 min. Ethylene oxide is then added and stirred for another 20 min. Finally, the same amount of propylene oxide as in the previous step is added, and the mixture is stirred for 50 min. After depressurization, the product, polyethylene polyamine polyether, is obtained. The mass fraction ratio of polyethylene polyamine:potassium hydroxide:propylene oxide:ethylene oxide is 5:4:400:85.

[0042] The preparation method of citric acid complexed polysilicic ferric chloride is as follows: Sodium silicate is dissolved in water, and 10-20% hydrochloric acid aqueous solution is slowly added at a stirring rate of 200-300 r / min and at room temperature to obtain a polysilicic acid solution; FeCl3 aqueous solution is added dropwise to the polysilicic acid solution at a stirring rate of 200-300 r / min and at room temperature and mixed thoroughly, and stirring is continued for 2-4 h to obtain polysilicic ferric chloride with n(Fe):n(Si) = (1.0-1.2):1. Iron solution; under a stirring speed of 300~500 r / min, citric acid is added to the polysilicon ferric chloride solution, n(citric acid):n(Fe)=(1-1.75):1 (molar ratio), and stirring is continued for 30-60 min to ensure that the citric acid is fully and uniformly dispersed; under a stirring speed of 200~300 r / min, 5% sodium bicarbonate aqueous solution is slowly added dropwise to adjust the pH of the system to a stable level of 2.0-3.0, and the mixture is allowed to stand for 12-18 hours to obtain citric acid-complexed polysilicon ferric chloride. Compared with ordinary polysilicon ferric chloride, citric acid-complexed polysilicon ferric chloride can prevent premature hydrolysis of polysilicon ferric chloride to form ferric hydroxide precipitate, which would weaken the destabilizing effect, extend the service life of the agent, and enhance the flocculation effect.

[0043] The specific preparation method of citric acid complexed polysilicon ferric chloride used in this embodiment of the invention is as follows: Sodium silicate is dissolved in water, and 10% hydrochloric acid solution is slowly added at a stirring rate of 200 r / min and at room temperature to obtain a polysilicic acid solution; FeCl3 solution is added dropwise to the polysilicic acid solution at a stirring rate of 200 r / min and at room temperature and mixed thoroughly, and stirring is continued for 2-4 h to obtain a polysilicon ferric chloride solution with n(Fe):n(Si)=1:1; Citric acid is added to the polysilicon ferric chloride solution at a stirring rate of 350 r / min, with n(citric acid):n(total iron)=1:1 (molar ratio), and stirring is continued for 45 min to ensure that the citric acid is fully and uniformly dispersed; 5% sodium bicarbonate solution is slowly added dropwise at a stirring rate of 200 r / min to adjust the pH of the system to a stable level of 2.4, and the system is allowed to stand for 12 hours to obtain citric acid complexed polysilicon ferric chloride.

[0044] The polydimethyldiallyl ammonium chloride used in this embodiment of the invention is a high-quality domestic product with a solid content of 40% and a molecular weight of 1 million.

[0045] The dimethylamine epichlorohydrin polymer used in the embodiments of the present invention is a high-quality domestic product with a solid content of 50%.

[0046] Specifically, step S1 is carried out in the pre-aeration debonding tank 1, which is equipped with an integrated partitioned destabilization reaction zone for debonding reaction, an aeration zone for pre-aeration treatment, and a sedimentation zone for sedimentation treatment.

[0047] More specifically, the pre-aeration demulsifier tank 1 is a closed system, equipped with an explosion-proof motor to prevent the risk of explosion in the offshore drilling platform area due to gas diffusion. The aeration process, combined with the use of a composite demulsifier and destabilizer, mainly removes polymers, oils, and suspended solids from the backflow fluid, reducing the viscosity of the wastewater.

[0048] Specifically, in step S2, self-cleaning refers to installing an automatic membrane filter at the inlet of the self-cleaning ozone reactor 2 to prevent suspended solids in the incoming water from entering the self-cleaning ozone reactor 2. The automatic membrane filter automatically scrapes off the suspended solids deposited on the filter surface based on their weight, eliminating the need for manual cleaning. The self-cleaning ozone reactor 2 contains no filler, and no reagents are added during the reaction process. The ozone gas generated by the ozone generator is aerated by the ozone aerator 202 to form fine bubbles with a diameter of 30-80μm. The ozone concentration in the water is 10-15mg / L, and the temperature is 15-35℃. By setting up a "Z"-shaped baffle 203 to extend the residence time of ozone in the water, the ozone oxidation efficiency is increased by 3-5 times compared to the traditional ozone oxidation efficiency, which can reduce COD to ≤300mg / L.

[0049] Specifically, in step S3, the membrane filtration uses an ultrafiltration membrane with a pore size of 0.01-0.03 μm. The ultrafiltration membrane is made of hydrophilic modified polyvinylidene fluoride, the operating pressure is 0.15-0.25 MPa, and the water production rate is ≥92%. It can not only filter suspended solids generated during the ozone oxidation process, but also filter bacteria in the water (sulfate-reducing bacteria, iron bacteria, saprophytic bacteria, etc.), ensuring that the bacterial indicators meet the standards, and the final effluent does not require a sterilization device.

[0050] Specifically, in S4, the self-circulating deoxygenation treatment is carried out in the self-circulating deoxygenation tank 4, and the vacuum pressure in the self-circulating deoxygenation tank 4 is -0.095MPa to -0.098MPa; The self-circulating deoxygenator 4 includes at least a primary spiral flow deoxygenation chamber 401 and a secondary atomizing spray deoxygenation chamber 402.

[0051] Dissolved oxygen corrodes metal equipment and provides favorable conditions for the growth and reproduction of microorganisms, so it is essential to remove dissolved oxygen from water. In a closed container, any gas present on the water surface is directly proportional to its partial pressure, and the solubility of a gas is only related to its own partial pressure. Under certain pressure, as water temperature increases, the partial pressure of water vapor increases, while the partial pressures of air and oxygen decrease. At 100℃, the partial pressure of oxygen drops to zero, and the dissolved oxygen in the water also drops to zero. When the pressure on the water surface is less than atmospheric pressure, the solubility of oxygen can also reach zero at lower water temperatures. This allows oxygen molecules above the water surface to be expelled, the oxygen partial pressure to become zero, and oxygen continuously escapes from the water, achieving deoxygenation. Deoxygenation can be achieved at room temperature. Therefore, a multi-stage self-circulating deoxygenating tank 4 is designed. This self-circulating deoxygenating tank 4 requires no heating or energy consumption, does not require the addition of chemicals, and performs multi-stage deoxygenation, reducing the dissolved oxygen in the effluent to ≤0.01mg / L, fully meeting the requirement of ≤0.02mg / L.

[0052] Specifically, in step S4, during the photo-irradiation sterilization process, ultraviolet light with a wavelength of 185nm or 254nm is used for irradiation, with an irradiation intensity of 30-60mW / cm² and a hydraulic residence time of 10-20s.

[0053] Ultraviolet (UV) radiation can cause nucleic acid mutations, inhibit their replication, and hinder protein synthesis. Furthermore, it generates free radicals that can cause photoionization, leading to bacterial death. When microorganisms are irradiated with UV light at wavelengths of 185nm or 254nm, energy transfer and accumulation occur. Once a certain amount is accumulated, the UV radiation damages the molecular structure of deoxyribonucleotides (DNA) or ribonucleotides (RNA) in the microbial cells, preventing bacteria / viruses from replicating and transcribing their genetic material, thus causing cell death and achieving sterilization. Most bacteria / viruses can achieve an inactivation rate of over 99% when the cumulative UV dose reaches 20mJ. When bacteria / viruses absorb 185nm or 254nm UV radiation exceeding 3600~65000uW / cm², the inactivation rate is significantly higher. 2 At the appropriate dosage, its deoxyribonucleotides (DNA) and ribonucleotides (RNA) are severely damaged, losing their viability and reproductive capacity, thereby achieving the effect of eliminating bacteria / viruses.

[0054] Process flow description: such as Figure 1As shown, the offshore fracturing flowback fluid first enters the pre-aeration demulsifier tank 1. In the demulsification and destabilization zone, a composite demulsifier and destabilizer are added to reduce the polymer content of the flowback fluid and disrupt the colloidal structure of the system. The demulsified liquid then enters the aeration zone, where suspended solids and oils float to the surface under the action of fine bubbles and are scraped off. The clear liquid then enters the self-cleaning ozone reactor 2, where the strong oxidizing properties of ozone decompose recalcitrant organic matter. The ozone effluent enters the membrane filtration system, where the membrane's efficient retention separates the product water and concentrate. The concentrate enters the photoirradiation reactor 5, where microorganisms are effectively killed under specific light source irradiation and then enters the front-end treatment for flocculation and sedimentation or removal as scum. The membrane product water enters the self-circulating deoxygenation tank 4, where dissolved oxygen is removed from the water under negative pressure to prevent oxygen corrosion of the injection network and formation. The effluent after self-circulating deoxygenation treatment meets the re-mixing standards and is ultimately used for the re-mixing and reuse of fracturing fluid. This process integrates physical separation, chemical oxidation, and advanced treatment technologies, enabling efficient purification and reuse of fracturing flowback fluid.

[0055] like Figure 1 As shown, an in-situ treatment device for offshore fracturing flowback fluid is provided. The treatment device includes a pre-aeration depolymerization tank 1, a self-cleaning ozone reaction tank 2, a membrane filter 3 and a self-circulating deoxygenation tank 4 connected in sequence, and a photoirradiation sterilization tank 5 connected between the concentrate outlet of the membrane filter 3 and the inlet of the pre-aeration depolymerization tank 1. The pre-aeration depolymerization tank 1 is divided into a destabilization reaction zone 101, an aeration zone 102 and a sedimentation zone 103 by a partition. The aeration zone 102 is equipped with an aerator 104. The sedimentation zone 103 is equipped with a primary purification outlet 105 and a guide plate 106. The self-cleaning ozone reactor 2 is equipped with an ozone aerator 202, a baffle plate 203, a partition plate 204, an overflow plate 206, and an ozone exhaust valve 207.

[0056] The self-circulating deoxygenating tank 4 is provided with a primary spiral flow deoxygenating chamber 401 located at the top and a secondary atomizing spray deoxygenating chamber 402 located at the bottom.

[0057] Specifically, such as Figure 2 As shown, the pre-aeration depolymerization box 1 is a closed box, and a partition is provided between the destabilization reaction zone 101, the aeration zone 102 and the sedimentation zone 103. The offshore fracturing flowback fluid to be treated overflows sequentially through the destabilization reaction zone 101, the aeration zone 102 and the sedimentation zone 103. An overflow slag removal plate 107 is provided in the upper part of the sedimentation zone 103, and several guide plates 106 are provided on the wall of the sedimentation zone 103. The angle between the guide plates 106 and the horizontal is 45°-60° or 120°-135°. The arrangement of the guide plates 106 forms an "S" shaped flow channel on the wall.

[0058] More specifically, the side of the pre-aeration depolymerization tank 1 is provided with a raw water inlet 108, a chemical dosing port 109, and a primary purification outlet 105. The raw water inlet 108 and the chemical dosing port 109 are both connected to the destabilization reaction zone 101. The chemical dosing port 109 is located at the upper part of the destabilization reaction zone 101, and the raw water inlet 108 is located at the lower part of the destabilization reaction zone 101. The primary purification outlet 105 is located at the lower part of the sedimentation zone 103.

[0059] More specifically, the upper end of the pre-aeration and de-blending box 1 is provided with an exhaust port 110 and a pressure gauge 111, which facilitates the observation and adjustment of the air pressure inside the pre-aeration and de-blending box 1 at any time.

[0060] More specifically, the partition between the destabilization reaction zone 101 and the aeration zone 102 is a first partition plate 112, and the partition between the aeration zone 102 and the sedimentation zone 103 is a second partition plate 113. The height of the first partition plate 112 and the second partition plate 113 is 3 / 5 to 4 / 5 of the total height of the aeration box, and the installation height of the overflow slag removal plate 107 is 1 / 10 to 1 / 5 of the height of the upper end of the second partition plate 113; the primary purification outlet 105 is located at a height of 1 / 5 to 1 / 4 of the bottom of the sedimentation zone 103.

[0061] By precisely defining the key structural dimensions of each zone within the pre-aeration demulsifying tank, the organic integration and efficient synergy of three functions—demulsification reaction, air flotation separation, and gravity sedimentation—are achieved within a limited space. The height of the first partition plate 113 and the second partition plate 114 is set to 3 / 5 to 4 / 5 of the total height of the tank, allowing the offshore fracturing flowback fluid to overflow sequentially through the destabilization reaction zone 101, the aeration zone 102, and the sedimentation zone 103. Simultaneously, sufficient effective water depth is maintained for each functional area—the destabilization reaction zone 101 has sufficient volume to ensure thorough mixing and reaction between the composite demulsifier / destabilizer and the flowback fluid; the microbubbles released by the aerators 104 in the aeration zone 102 have sufficient water depth to adhere to and float suspended solids and oils; more importantly, this height range ensures a reasonable space between the liquid surface of the aeration zone 102 and the top of the tank, allowing scum floating to the surface to stably accumulate towards the overflow scum removal plate 107, achieving continuous overflow scum removal without a scraper. The overflow slag removal plate 107 is installed at a height of 1 / 10 to 1 / 5 of the upper end of the second partition plate 114. This position ensures that the slag layer has sufficient thickness to continuously and stably overflow into the slag discharge area above the sedimentation zone 103, while preventing the upper clear liquid from being carried out by the slag. Thus, automatic separation of slag and clear liquid after air flotation separation is achieved without any moving parts. The primary purification outlet 105 is set at a height of 1 / 5 to 1 / 4 of the bottom of the sedimentation zone 103, ensuring that there is sufficient settling space at the bottom of the sedimentation zone 103 for residual suspended solids to settle fully to the bottom of the tank. The outlet 105 avoids the bottom sedimented sludge layer and the upper slag layer, and the water exits from the middle area where the water quality is most stable. The precise coordination of the above three dimensional parameters enables the entire pre-aeration and depolymerization tank 1 to achieve continuous and stable solid-liquid-gas three-phase separation under sealed conditions, without a scraper or moving parts, relying solely on the reasonable design of its structural dimensions. The effluent turbidity is less than 2 NTU and the SS concentration is less than 10 mg / L, fully meeting the stringent requirements of offshore platforms for equipment simplicity, reliability, and explosion-proof safety.

[0062] More specifically, the purpose of setting the guide plates 106 in the sedimentation zone 103 is to guide suspended solids that cannot float on the surface to gather on the guide plates 106 and settle to the bottom of the tank, which is beneficial to improving the clarity of the effluent. The guide plates 106 are set below the overflow slag removal plate 107. All guide plates 106 are of the same length, and the length of each guide plate 106 is 1 / 12 to 1 / 10 of the length of the second partition plate 113. There are 3-4 horizontal guide plates and 3-5 vertical guide plates. The interval between two adjacent vertical guide plates 106 is 1 / 4 to 1 / 3 of the length of the guide plate 106. The horizontal guide plates 106 have the same inclination angle, and the two adjacent rows of vertical guide plates 106 are axially symmetrical, thus forming parallel "S"-shaped flow channels between the guide plates 106.

[0063] By systematically and precisely defining the number, arrangement, and size ratio of the guide plates 106 in the sedimentation zone 103, a close hydrodynamic cooperative relationship is formed between the guide plates 106, achieving efficient gravity sedimentation of fine suspended matter without the need for external power or moving parts. Specifically, the length of each guide plate 106 is 1 / 12 to 1 / 10 of the length of the second partition plate 114. This ratio ensures that the guide plate 106 has sufficient extension length in the sedimentation zone 103 to guide the water flow direction to deflect significantly, while not encroaching too much on the sedimentation space and causing blockage. 3-4 guide plates 106 are set in the horizontal direction and 3-5 guide plates 106 are set in the vertical direction. The interval between two adjacent guide plates 106 in the vertical direction is controlled to be 1 / 4 to 1 / 3 of the length of the guide plate 106. This multi-level configuration, combined with precise vertical spacing, forces the water flow to repeatedly turn back during horizontal flow, changing the flow path from a straight line to a broken line. The actual hydraulic residence time is extended several times compared to the free flow state without guide plates 106. More importantly, the vertically adjacent rows of guide plates 106 are arranged symmetrically, and the inclination angle of each guide plate 106 in the same horizontal direction is consistent. This structural feature causes the flow direction of water between adjacent rows of guide plates 106 to form a regular alternating reversal. When the water flows into the gap along the guide of the first row of guide plates 106 at a certain inclination angle, the flow direction is forced to turn to the other side when facing the second row of guide plates 106 which is symmetrical to it. This process is carried out in sequence between each layer of guide plates 106, and finally, parallel multi-layer "S"-shaped series flow channels are formed in the entire sedimentation zone 103. This "S"-shaped flow channel not only achieves a forced change in fluid direction but also generates regular turbulent disturbances within the channel. This significantly increases the probability of collisions between suspended particles in the water and the wall of the guide plate 106, causing fine particles to separate from the water under the combined effects of inertial collisions and gravitational settling. The particles then accumulate on the surface of the guide plate 106 and slide to the bottom of the pool. Simultaneously, each "S"-shaped bend is equivalent to a micro-sedimentation unit. The water flow velocity slows down at the bend, the particle settling distance is shortened, and the settling efficiency accumulates step by step. After 3 to 5 stages of multi-stage vertical sedimentation, the effluent water quality is fully purified, and the suspended solids concentration is reduced to an extremely low level. This ensures that the fine flocs and suspended solids remaining after the front-end de-gelling and flotation treatment will not enter the subsequent ozone oxidation and membrane filtration units, providing a reliable water quality guarantee for the long-term stable operation of the entire system.

[0064] Specifically, such as Figure 3As shown, the self-cleaning ozone reactor 2 has a symmetrical structure, with an ozone inlet 201 on the side, an ozone aerator 202 installed inside the reactor, and a drain outlet 208 at the bottom. The ozone generated by the ozone generator is mixed with the primary purified water through the ozone aerator 202 and enters the self-cleaning reactor 2. The baffles 203 are evenly distributed on the wall of the self-cleaning ozone reactor 2. The angle between the baffles 203 and the horizontal is 0°-45°, and the length of the baffles 203 is 1 / 4-1 / 3 of the total diameter of the self-cleaning ozone reactor 2. The baffles 203 are symmetrical about the left and right axis inside the self-cleaning ozone reactor 2. The arrangement of the baffles 203 forms a "Z" shaped flow channel on the reactor wall. The ozone effluent after the reaction flows into the ozone outlet 205 through the overflow plate 206 and is discharged into the next treatment unit. The residual ozone tail gas is discharged into the ozone tail gas destroyer for treatment through the ozone tail gas discharge valve 207.

[0065] By designing the baffle plate 203 inside the self-cleaning ozone reactor 2, the mixture of ozone and primary purified water flows upwards along the "Z"-shaped flow channel, extending the flow path of the water and thus extending the residence time of ozone molecules in the water. This ensures that the organic matter in the water fully contacts and reacts with the ozone, avoiding the problems of insufficient reaction, low efficiency, and low ozone utilization rate caused by the "straight upward" flow of water out of the ozone reactor in conventional ozone oxidation reactors.

[0066] Specifically, such as Figure 4 , Figure 5 As shown, in the self-circulating deoxygenator 4, several spiral channels 403 are vertically installed in the primary spiral flow channel deoxygenation chamber 401, and the upper inlet of the spiral channel 403 is connected to the water inlet pipe 404 at the upper end of the primary spiral flow channel deoxygenation chamber 401; several nozzles 405 are provided at the upper end of the secondary atomizing spray deoxygenation chamber 402; membrane permeate enters the self-circulating deoxygenator 4 through the water inlet pipe 404.

[0067] More specifically, a safety valve 406 is provided at the top of the primary spiral flow deoxygenation chamber 401, and a drain outlet and a drain pump 411 are connected to the bottom of the secondary atomizing spray deoxygenation chamber 402; the upper part of the primary spiral flow deoxygenation chamber 401 is connected to the upper part of the gas-liquid separator 407 through a pipeline and a vacuum pump 410, and a primary exhaust valve 408 is provided on the pipeline; the upper part of the secondary atomizing spray deoxygenation chamber 402 is connected to the upper part of the gas-liquid separator 407 through a pipeline and a vacuum pump 410, and a secondary exhaust valve 409 is provided on the pipeline. The lower part of the gas-liquid separator 407 is connected to the water inlet pipe 404 at the upper end of the primary spiral flow deoxygenation chamber 401 through a pipeline.

[0068] Membrane permeate after membrane filtration enters the self-circulating deaerator 4 through the inlet pipe 404. In the primary spiral flow deaerator chamber 401, the membrane permeate flows continuously down the spiral flow channel 403. At this time, the primary exhaust valve 408 is opened, and the vacuum pump 410 extracts the gas in the tank, which enters the gas-liquid separator 407. When the liquid level in the primary spiral flow deaerator chamber 401 reaches a certain height, the nozzle 405 of the secondary atomizing spray deaerator chamber 402 and the secondary exhaust valve 409 are opened. The vacuum pump 410 continues to run, extracting the gas in the tank and entering the gas-liquid separator 407. When the liquid level in the secondary atomizing spray deaerator chamber 402 reaches a certain height, the drain pump 411 is opened to pump the deoxygenated water in the tank out of the drain outlet. The liquid in the gas-liquid separator 407 flows back to the inlet pipe 404 of the self-circulating deaerator 4, and the gas is discharged. The actual pressure setting value of vacuum pump 410 is -0.095MPa to -0.098MPa.

[0069] More specifically, the spiral flow channel 403 within the primary spiral flow deoxygenation chamber 401 is as follows: Figure 5 As shown, membrane permeate flows into the primary spiral flow deoxygenation chamber 401 through the inlet pipe 404, flowing down along the rotation direction of the spiral flow. The spiral flow design aims to increase the residence time of the wastewater and the interface area between the liquid and the gas environment inside the tank. This allows dissolved gases such as oxygen in the wastewater to diffuse to the surface more quickly and be extracted by the vacuum pump 410, achieving deoxygenation. The spiral flow 403 is installed vertically, and the wastewater flows down the flow channel in a spiral direction (clockwise or counterclockwise) from top to bottom. The inner diameter of the spiral flow 403 is 1 / 5 to 1 / 3 of the inner diameter of the primary spiral flow deoxygenation chamber 401. The spiral angle (the angle between the spiral blades and the horizontal direction) of the spiral flow 403 is 20° to 35°, and the length of a single spiral flow is 1 / 2 to 3 / 4 of the total height of the primary spiral flow deoxygenation chamber 401. The primary exhaust valve 408 and its pipe are located at the top of the primary spiral flow deoxygenation chamber 401, above the first level gauge 412. The first level gauge 412 measures the liquid level in the primary spiral flow deoxygenation chamber 401 from bottom to top. The upper limit of the liquid level is 3 / 4 of the total height of the primary spiral flow deoxygenation chamber 401. When the liquid level in the primary spiral flow deoxygenation chamber 401 reaches 1 / 2 to 2 / 3 of the total height of the primary spiral flow deoxygenation chamber 401, the nozzle 405 of the secondary atomizing spray deoxygenation chamber 402 and the secondary exhaust valve 409 are opened.

[0070] The secondary exhaust valve 409 and its pipeline are located at the top of the secondary atomizing spray deoxygenation chamber 402, above the second level gauge 413. The second level gauge 413 measures the liquid level in the secondary atomizing spray deoxygenation chamber 402 from bottom to top. The upper limit of the liquid level is 3 / 4 of the total height of the secondary atomizing spray deoxygenation chamber 402. When the liquid level in the secondary atomizing spray deoxygenation chamber 402 reaches 1 / 2 to 2 / 3 of the total height of the secondary atomizing spray deoxygenation chamber 402, the drain outlet and drain pump 411 are opened to pump out the deoxygenated wastewater.

[0071] Through the systematic design of the dimensional parameters of the spiral flow channel inside the self-circulating deoxygenator 4 and the linkage control logic of the exhaust valve and level gauge, the synergistic optimization of gas-liquid mass transfer efficiency and deoxygenation process automation was achieved. The inner diameter of the spiral flow channel is 1 / 5-1 / 3 of the inner diameter of the deoxygenation chamber, the spiral angle is 20°-35°, and the flow channel length is 1 / 2-3 / 4 of the total height of the chamber. The synergistic cooperation of these three dimensional parameters allows the water to form a moderately thick and stable thin water film when it flows down along the spiral flow channel 403, increasing the specific surface area of ​​gas-liquid contact. At the same time, the spiral structure of the flow channel gives the water flow a moderate centrifugal force, prolonging the actual residence time of the water flow under low pressure environment, so that dissolved oxygen can escape and undergo sufficient mass transfer process under vacuum suction. Based on this, the first-stage exhaust valve 408 is located at the top of the first-stage deoxygenation chamber and above the first level gauge 413. The first level gauge 413 measures the liquid level from bottom to top and sets the upper limit of the liquid level to 3 / 4 of the total height of the chamber. This ensures that there is sufficient low-pressure space in the deoxygenation chamber for oxygen to escape during the first-stage spiral deoxygenation process. The exhaust port is always above the liquid surface, which ensures the unobstructed gas passage and prevents the liquid from being accidentally drawn out by the vacuum pump 410. When the liquid level accumulates to 1 / 2 to 2 / 3 of the total height, the second-stage atomizing spray deoxygenation is activated. The timing control ensures that the first-stage spiral flow channel deoxygenation has fully removed most of the dissolved oxygen before the second-stage spray atomizing deoxygenation is activated, avoiding the superposition and redundancy of the two-stage deoxygenation functions and the waste of resources. The second-stage atomizing spray deoxygenation chamber 402 also opens to drain water when the liquid level reaches 1 / 2 to 2 / 3 of its total height. This ensures both the effective residence time of the second-stage spray deoxygenation and that the liquid level in the self-circulating deoxygenation tank 4 is always within a safe and controllable range. The geometric design of the spiral flow channel 403 provides sufficient mass transfer efficiency for the first-stage deoxygenation. The real-time feedback of the level gauge and the sequential linkage of the exhaust valve, nozzle 405 and drain pump 411 upgrade the two-stage deoxygenation from independent physical spaces to a dynamic relay process of "liquid film deoxygenation → droplet deep deoxygenation". Under the premise of ensuring that the dissolved oxygen in the effluent is consistently below 0.02 mg / L, the deoxygenation efficiency and treatment capacity are maximized. At the same time, it achieves fully automated operation without the need for chemical reagents, taking into account both operational stability and economy.

[0072] Specifically, such as Figure 6 , Figure 7 , Figure 8 , Figure 9As shown, the light irradiation sterilization box 5 is provided with several light irradiation reaction chambers 501. The light irradiation reaction chamber 501 is provided with a light irradiation lamp group and a cooling system. The cooling system includes an inner circulation cooling channel 502 and an outer circulation cooling channel 503. The lamp tubes 504 of the light irradiation lamp group are arranged inside the inner circulation cooling channel 502. The lamp tubes 504 are installed in the light irradiation reaction chamber 501 through lamp holders 505.

[0073] More specifically, the photoirradiation sterilization chamber 5 is a horizontal design. Membrane concentrate after membrane filtration enters the chamber through the inlet pipe 506, with water flowing from the center to the two side photoirradiation reaction chambers 501, descending along the "S"-shaped flow channels. Under the irradiation of the ultraviolet lamp (lamp tube 504 is an ultraviolet lamp), sulfate-reducing bacteria, iron bacteria, saprophytic bacteria, and other microorganisms are killed and lose their vitality. Finally, the water flows back to the pre-aeration and depolymerization chamber 1 through the outlet pipe 507. During the photoirradiation sterilization process, the irradiation energy causes the water temperature to rise, resulting in significant heat generation. Therefore, a dual internal and external circulation system is used for cooling. Coolant flows through pipes into the internal circulation channel located on the outer wall of the photoirradiation lamp column and the external circulation channel located on the outer wall of the photoirradiation reaction chamber 501. The circulating flow of the coolant displaces the heat generated by the photoirradiation, achieving a cooling effect.

[0074] Each layer consists of two symmetrical light irradiation reaction chambers 501, with a total number of 2n chambers, n=1,2,3... Each light irradiation reaction chamber 501 contains a light irradiation lamp assembly integrating a lamp holder 505 and a lamp tube 504. Each lamp holder 505 has 1-3 lamp posts arranged centrally symmetrically. The lamp tubes 504 have a power of 80-120W, primarily outputting 185nm or 254nm ultraviolet light, with a light irradiance intensity of 30-60mW / cm². 2 The lamp tube is made of high-purity quartz glass with an ultraviolet transmittance of ≥90%.

[0075] The coolant is mainly clean water cooled by the cooling system, with the water temperature controlled between 5-15℃. The inner circulation cooling channel 502 and the outer circulation cooling channel 503 are both connected to the coolant circulation tank 508. The coolant flows in the inner circulation cooling channel 502 and the outer circulation cooling channel 503 in the same or opposite directions to ensure that the temperature does not exceed 40℃ during the light irradiation reaction.

[0076] Example 1:

[0077] This embodiment uses hydraulic fracturing flowback fluid generated by an offshore oil and gas exploration platform as the treatment target. This platform generates approximately 500m³ of flowback fluid daily. 3The current treatment method for fracturing flowback fluid is to perform only simple pretreatment to remove oil and sand before reuse. However, this incomplete treatment leads to excessive levels of polymers, COD, and bacteria, posing a risk of pipeline corrosion and blockage. The raw fracturing flowback fluid before pretreatment has the following water quality indicators, as shown in Table 1.

[0078] Table 1. Raw water parameters of fracturing flowback fluid in Example 1

[0079] The raw water from the fracturing flowback fluid was treated using the treatment method and device described in this invention. The specifications of some of the equipment in the treatment device are shown in Table 2 below.

[0080] Table 2 Specifications of some equipment in the processing apparatus of Example 1

[0081] The modular equipment of this invention is installed and debugged in a land-based factory, then transported by ship to an offshore platform, where it is stacked and installed in two layers. Each processing unit module is connected by pumps, pipes, electrical wires, and other supporting facilities, with a total footprint of 70m². 2 The total height is 7m, compared to traditional processes with the same processing capacity (which occupy an area of ​​approximately 150-200m²). 2 It saves more than 53%.

[0082] The specific process conditions are as follows: (1) Pre-aeration and depolymerization unit: influent flow rate 25m 3 The compound demulsifier / destabilizer dosage is 180 mg / L, the residence time in the destabilization reaction zone is 35 min, the dissolved air pressure is 0.38 MPa, the dissolved air-water reflux ratio is 30%, and the residence time in the aeration tank zone is 20 min. The fracturing flowback fluid enters the pre-aeration demulsifier / destabilizer tank via a centrifugal pump through the inlet. Simultaneously, the compound demulsifier / destabilizer is added in the destabilization reaction zone, where a stirrer ensures thorough mixing of the flowback fluid and the agent. Under the action of the agent, the polymer molecular structure in the water is destroyed, the colloidal system becomes unstable, and the viscosity rapidly decreases. The mixture overflows to the oil and impurity removal zone, where aerators release a large number of microbubbles. These bubbles adhere to suspended solids and oils, rising to the surface to form a scum layer. The scum continuously flows into the sedimentation zone via overflow. In the sedimentation zone, wastewater flows in an "S"-shaped channel formed by guide plates, and residual suspended solids gradually settle. Finally, the clarified effluent is discharged from the outlet located 1 / 4 of the way from the bottom of the tank. The height of both the first and second partition plates is 2.7m (total height of the box is 3.5m). A composite demulsifier and destabilizer is prepared according to the formula and method described in this invention, with the following mass ratio of components: polyethylene polyamine polyether: citric acid complexed polysilicon ferric chloride: polydimethyldiallyl ammonium chloride: dimethylamine epichlorohydrin polymer = 30:150:1.5:1.

[0083] The effluent (primary purified water) from the pre-aeration and de-gelling unit is shown in Table 3 below.

[0084] Table 3. Effluent test results of the pre-aeration and depolymerization unit in Example 1

[0085] (2) Self-cleaning ozone oxidation unit: inlet water flow rate 25m 3 The ozone concentration in the water was 10 mg / L / h, and the angle between the baffle plate and the horizontal was 45°. Water from the pre-aeration and de-galvanizing tank was piped into the self-cleaning ozone reactor. An automatic membrane filter at the inlet removed any remaining suspended solids. Ozone was generated using air as the gas source. Ozone decomposed recalcitrant organic matter in the water through strong oxidation, breaking down large organic molecules into smaller ones. After ozone oxidation, the COD decreased from 2450 mg / L to 235 mg / L, achieving a total removal rate of 90.4%. The effluent color was significantly reduced, becoming colorless and transparent with no odor. Specific test results are shown in Table 4 below.

[0086] Table 4. Effluent test results of the self-cleaning ozone oxidation unit in Example 1

[0087] (3) Membrane filtration unit: A hollow fiber ultrafiltration membrane module is used, with the membrane material being modified polyvinylidene fluoride (the ultrafiltration membrane used in this embodiment is Beijing Sainuo STM600-P40 membrane), and the membrane pore size is 0.03μm. The influent flow rate is 25m³ / h. 3 / h, operating pressure 0.20MPa (constant pressure operation), filtration cycle 45min (40min operation + 5min air-water backwash), backwash water volume is 8% of the production water volume, and production water rate ≥92%.

[0088] The ozone-oxidized effluent is pumped into a membrane filter via a booster pump. Water molecules permeate through the membrane wall and enter the inner cavity of the membrane fibers, where they collect as permeate. Suspended solids, colloids, bacteria, and other pollutants are trapped on the outside of the membrane fibers by the membrane pores. The permeate is clear and transparent, with almost complete removal of suspended solids and turbidity, and a bacterial retention rate of ≥99.9%, providing clean influent conditions for subsequent self-circulating deoxygenation. Specific test results are shown in Table 5 below.

[0089] Table 5. Effluent test results of the membrane filtration unit in Example 1

[0090] (4) Self-circulating deoxygenation unit: The self-circulating deoxygenation tank is vertical, divided into two deoxygenation zones. The first-stage spiral flow deoxygenation chamber is located in the upper part, equipped with a spiral flow channel; the second-stage atomizing spray deoxygenation chamber is located in the lower part, equipped with a spray water distribution system. A first-stage exhaust valve and a second-stage exhaust valve are installed on the side of the tank, connected to a vacuum pump via pipeline. A gas-liquid separator is installed at the vacuum pump outlet. The spiral blades have an angle (spiral angle) of 28° with the horizontal direction, an inner diameter of 0.55 m (1 / 4 of the tank's inner diameter), a spiral flow channel length of 2.8 m, a clockwise rotation direction, and a pitch of 0.32 m. The inlet water flow rate is 23 m³ / h, and the vacuum pump pressure is -0.097 MPa.

[0091] Membrane permeate enters the top of the multi-stage vacuum deaerator through the inlet pipe. Initially, the wastewater flows downwards from top to bottom in a rotating manner, guided by the spiral blades. Due to the spiral flow channel design, the wastewater forms a thin, uniform water film that flows along the channel surface, ensuring full contact with the low-pressure gas environment inside the tank. The vacuum pump operates continuously, rapidly releasing dissolved gases such as oxygen and carbon dioxide. The primary exhaust valve opens, and the released gas is drawn into the gas-liquid separator via the vacuum pump. The gas is discharged, and the condensate flows back to the inlet pipe. As wastewater continues to flow in, the liquid level in the primary spiral flow deaerator chamber gradually rises. When the liquid level reaches half the total height of the primary spiral flow deaerator chamber, the control system automatically opens the nozzles of the secondary deaerator layer and the secondary exhaust valve. The wastewater is atomized into fine droplets by the nozzles, creating a large gas-liquid contact surface area within the secondary atomized spray deaerator chamber, further removing residual dissolved oxygen. When the liquid level in the secondary atomizing spray deoxygenation chamber reaches half of the total height of the chamber, the control system activates the drain pump to pump the deoxygenated wastewater out of the drain outlet. The opening sequence of the two-stage exhaust valves is interlocked with the liquid level to ensure stable pressure inside the tank. The liquid collected in the gas-liquid separator is automatically returned to the inlet pipe every 4 hours.

[0092] The dissolved oxygen content in the self-circulating deoxygenated water was reduced to 0.006 mg / L, far below the required 0.02 mg / L, and no heating or chemical deoxygenating agent was required during the process. Specific results are shown in Table 6 below.

[0093] Table 6 Dissolved oxygen content of the self-circulating deoxygenated water in Example 1

[0094] (5) Photoirradiation sterilization unit: Inlet water flow rate: 23m³ 3 / h, hydraulic residence time 15s, UV lamp irradiation intensity 42mW / cm 2The lamps operate continuously for 20 hours per day. The concentrate from the membrane filter enters the photo-irradiation sterilization chamber via pipeline. 185nm or 254nm ultraviolet light penetrates the water layer and irradiates the bacteria in the concentrate, destroying their DNA / RNA structure and achieving inactivation. The sterilized concentrate is then pumped back to the inlet of the pre-aeration and deflocculation tank. After mixing with the original fracturing flowback fluid, the inactivated bacterial residues carried in the concentrate are flocculated and form dense flocs under the action of the deflocculation and destabilizing agent, which are discharged as scum or sediment. The test results of the photo-irradiated sterilized effluent are shown in Table 7 below.

[0095] Table 7. Bacterial content of effluent from light irradiation sterilization in Example 1

[0096] This embodiment verifies the effectiveness of the hazardous chemical-free end-to-end treatment process of the present invention and the feasibility of its modular design. The system operates stably, and all indicators of the effluent exceed the environmental protection standards for compounding and reuse required by offshore oil and gas exploration enterprises. Key results are as follows: (1) The entire process does not use any hazardous chemicals such as acids, alkalis, persulfates, etc., thus eliminating safety risks such as hazardous chemical leakage, corrosion, and explosion.

[0097] (2) Modular installation saves more than 50% of the floor space compared with traditional processes, which is suitable for the limited space requirements of offshore platforms.

[0098] (3) The composite demulsifier and destabilizer achieved a polymer removal rate of 99.16% and a COD removal rate of 86.6% at room temperature, with significant effect.

[0099] (4) The dissolved oxygen in the self-circulating deoxygenated water is ≤0.02mg / L, requiring no heating or reagents, which is energy-saving and environmentally friendly.

[0100] (5) Sterilization throughout the entire process ensures that no bacteria are detected in the effluent.

[0101] The treatment of the fracturing flowback fluid in Example 1 is shown in Table 8 below.

[0102] Table 8. Treatment of fracturing flowback fluid in Example 1

[0103] Example 2:

[0104] This embodiment uses hydraulic fracturing flowback fluid generated by an offshore oil and gas exploration platform as the treatment target. This platform generates approximately 500m³ of flowback fluid daily. 3 The fracturing flowback fluid of this platform is of worse quality than that of Example 1. Its influent water quality indicators are shown in Table 9 below.

[0105] Table 9. Raw water parameters of fracturing flowback fluid in Example 2

[0106] To cope with higher concentrations of pollutants, while maintaining the exact same process flow as in Example 1, this example adjusts key operating parameters as follows: (1) Pre-aeration depolymerization unit: Due to the higher polymer content in the influent, the dosage of composite demulsifier and destabilizer is increased to 260 mg / L, and the reaction residence time is extended to 45 min.

[0107] (2) Self-cleaning ozone oxidation unit: Considering the high COD of the influent, the ozone concentration in the water is increased to 14 mg / L.

[0108] Other process conditions are the same as in Example 1. The fracturing flowback fluid treatment in Example 2 is shown in Table 10 below.

[0109] Table 10. Treatment of fracturing flowback fluid in Example 2

[0110] This embodiment verifies the flexible adaptability of the present invention in the face of different water quality conditions: by increasing the dosage of breaker and ozone and appropriately extending the reaction time, higher concentrations of fracturing flowback fluid were successfully treated, proving the adaptability of the process of the present invention to the influent load.

[0111] Example 3:

[0112] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1, except that the mass ratio of polyethylene polyamine polyether, citric acid complexed polysilicon ferric chloride, polydimethyl diallyl ammonium chloride, and dimethylamine epichlorohydrin polymer in the composite demulsifier of Example 3 was 20:100:1:1.

[0113] The effluent (primary purified water) from the pre-aeration and de-gelling unit is shown in Table 11 below.

[0114] Table 11. Effluent test results of the pre-aeration and depolymerization unit in Example 3

[0115] The treatment of the fracturing flowback fluid in Example 3 is shown in Table 12 below.

[0116] Table 12 Treatment of fracturing flowback fluid in Example 3

[0117] The results show that when the components in the composite demulsifier of Example 3 are in the lower limit of the ratio of 20:100:1:1, the final effluent of the whole system still meets the fracturing fluid compounding standard. This verifies that the composite demulsifier can still achieve the standard treatment when the ratio is in the range of (20-50):(100-200):(1-2):1 at a lower value.

[0118] Example 4:

[0119] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1, except that the mass ratio of polyethylene polyamine polyether, citric acid complexed polysilicon ferric chloride, polydimethyl diallyl ammonium chloride, and dimethylamine epichlorohydrin polymer in the composite demulsifier of Example 4 was 50:200:2:1.

[0120] The effluent (primary purified water) from the pre-aeration and de-gelling unit is shown in Table 13 below.

[0121] Table 13. Effluent test results of the pre-aeration and depolymerization unit in Example 4

[0122] The treatment of the fracturing flowback fluid in Example 4 is shown in Table 14 below.

[0123] Table 14 Treatment of fracturing flowback fluid in Example 4

[0124] The results show that when the components in the composite demulsifier of Example 3 are in the lower limit of the ratio of 20:100:1:1, the front-end degreasing, oil removal and polymer removal effects are better, and the final effluent of the whole system still meets the fracturing fluid compounding standard. This verifies that the composite demulsifier can still achieve the standard treatment when the ratio is higher in the range of (20-50):(100-200):(1-2):1.

[0125] Comparative Example 1:

[0126] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1, except that the effluent from the self-cleaning ozone reaction unit in this Comparative Example 1 process directly enters the self-circulating deoxygenation tank, and the membrane filter is placed after the self-circulating deoxygenation tank.

[0127] That is, the process of Example 1 is as follows: pre-aeration depolymerization tank → self-cleaning ozone reaction tank → membrane filter → self-circulating deoxygenation tank (membrane concentrate → photoirradiation sterilization tank).

[0128] The process of Comparative Example 1 is as follows: pre-aeration and depolymerization tank → self-cleaning ozone reactor → self-circulating deoxygenation tank → membrane filter (membrane concentrate → photoirradiation sterilization tank).

[0129] Other process conditions are the same as in Example 1. The results of Comparative Example 1 and Example 1 are compared in Table 15 below.

[0130] Table 15 Comparison of results between Comparative Example 1 and Example 1

[0131] In Example 1, the membrane filtration unit, placed before the self-circulating deoxygenation unit, effectively removed microorganisms from the wastewater, creating favorable influent conditions for deoxygenation. In contrast, Comparative Example 1 placed the self-circulating deoxygenation unit before the membrane filtration unit, leading to microbial interference and significantly reducing the effectiveness of the self-circulating deoxygenation. Ultimately, the dissolved oxygen in the effluent failed to meet standards, and membrane fouling accelerated dramatically. This demonstrates that the sequence of "membrane filtration first, then self-circulating deoxygenation" is crucial for ensuring stable system operation and achieving compliant effluent.

[0132] Comparative Example 2:

[0133] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1. The difference was that no membrane filtration unit was used in the process of Comparative Example 2. After pretreatment by the ozone oxidation unit in Comparative Example 2, the effluent directly entered the self-circulating deoxygenation tank. The deoxygenated effluent entered the photo-irradiation sterilization box, and the bacteria in the influent were treated solely by ultraviolet sterilization.

[0134] That is, the process of Example 1 is as follows: pre-aeration depolymerization tank → self-cleaning ozone reaction tank → membrane filter → self-circulating deoxygenation tank (membrane concentrate → photoirradiation sterilization tank).

[0135] The process of Comparative Example 2 is as follows: pre-aeration debonding tank → self-cleaning ozone reaction tank → self-circulating deoxygenation tank → photoirradiation sterilization tank.

[0136] Other process conditions were the same as in Example 1. The two process units of Example 1 and Comparative Example 2 were run continuously for 90 days. During this period, the changes in the self-circulating deoxygenation tank were observed and the relevant water quality was recorded. The specific comparison results are shown in Tables 16 and 17 below.

[0137] Table 16 Comparison of self-circulating deoxygenation tanks in Comparative Example 2 and Example 1

[0138] Table 17 Comparison of effluent water quality between Comparative Example 2 and Example 1

[0139] In Example 1, the dissolved oxygen in the effluent remained consistently below 0.01 mg / L, while in Comparative Example 2, it began to consistently exceed the standard (>0.02 mg / L) after 30 days of operation. This was because a biofilm formed in the self-circulating deaerator of Comparative Example 2, hindering the escape and mass transfer of oxygen. SRB was never detected in Example 1, but it began to be detected in Comparative Example 2 after 15 days of operation, rising to 35 CFU / mL after 60 days, exceeding the required levels for the compound. This was because the biofilm in the self-circulating deaerator of Comparative Example 2 became a breeding ground for bacteria. Although subsequent photo-irradiation sterilization could kill some bacteria, the bacteria deep within the biofilm were difficult to reach with ultraviolet light and might multiply again in the pipes, resulting in severely excessive levels of microorganisms in the effluent.

[0140] SRB (sulfate-reducing bacteria) are bacteria that can reduce sulfate, sulfite, and thiosulfate to hydrogen sulfide under anaerobic conditions. In Comparative Example 2, the effluent from the fracturing flowback fluid, after passing through the pre-aeration and degelatinization unit and the self-cleaning ozone oxidation unit, still contained a large number of microorganisms. This effluent directly entered the self-circulating deaeration tank. Under the conditions of low dissolved oxygen, high humidity, and residual organic matter in the self-circulating deaeration tank, SRB and other anaerobic bacteria found an ideal growth environment, attaching to the inner wall of the self-cleaning ozone oxidation unit and the surface of the spiral flow channel, forming a biofilm. This biofilm hinders gas-liquid mass transfer, reducing the efficiency of the self-circulating deaeration; microbial respiration produces CO2 and H2S, corroding the tank; and biofilm shedding leads to an increase in suspended solids and bacteria in the effluent.

[0141] Example 1 places the membrane filter before the self-circulating deaerator. The ultrafiltration membrane has a bacterial rejection rate of ≥99%, resulting in an extremely low concentration of microorganisms in the water entering the deaerator. This extremely low bacterial concentration prevents biofilm formation within the deaerator. Simultaneously, some residual organic matter in the membrane permeate is also removed, further limiting the nutrient source for microorganisms. Photoirradiation sterilization serves as the final safeguard, ensuring the inactivation of any missed bacteria and guaranteeing the sterility of the final effluent. This achieves long-term stable system operation and guarantees the quality of the effluent.

[0142] Comparative Example 3:

[0143] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1, except that ozone oxidation was not performed in the process of Comparative Example 3.

[0144] That is, the process of Example 1 is as follows: pre-aeration depolymerization tank → self-cleaning ozone reaction tank → membrane filter → self-circulating deoxygenation tank (membrane concentrate → photoirradiation sterilization tank).

[0145] The process of Comparative Example 3 is as follows: pre-aeration and depolymerization tank → membrane filter → self-circulating deoxygenation tank (membrane concentrate → photoirradiation sterilization tank).

[0146] Other process conditions are the same as in Example 1. The results of Comparative Example 3 and Example 1 are compared in Table 18 below.

[0147] Table 18 Comparison of results between Comparative Example 3 and Example 1

[0148] Example 1, employing the ozone oxidation unit of this invention, effectively breaks down and mineralizes organic matter, reducing the membrane burden and ensuring the quality of the final effluent. In contrast, Comparative Example 3, omitting the ozone oxidation unit, results in a large amount of dissolved organic matter directly impacting the membrane system, causing the system to bear extremely high organic loads, leading to uncontrolled membrane fouling. Furthermore, the ultrafiltration membrane has low organic matter interception efficiency, resulting in severely excessive levels of high-concentration, high-molecular-weight organic matter remaining in the effluent, ultimately failing to meet the COD requirements for reuse. Therefore, the ozone oxidation unit is an indispensable core component for achieving COD compliance and long-term operation of the membrane system.

[0149] Comparative Example 4:

[0150] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1, except that the membrane concentrate was not treated with a photo-irradiation sterilization unit during the process of Comparative Example 4.

[0151] That is, the process of Example 1 is as follows: pre-aeration depolymerization tank → self-cleaning ozone reaction tank → membrane filter → self-circulating deoxygenation tank (membrane concentrate → photoirradiation sterilization tank).

[0152] The process of Comparative Example 4 is as follows: pre-aeration and depolymerization tank → self-cleaning ozone reactor → membrane filter → chemical deoxygenation tank (membrane concentrate → directly returned to the pre-aeration and depolymerization tank), the membrane concentrate is directly returned to the front end without undergoing photo-irradiation sterilization.

[0153] Other process conditions were the same as in Example 1. The process units of Comparative Example 4 and Example 1 were run continuously for 90 days, during which the changes in the unit and the effluent were observed, as detailed in Table 19 below.

[0154] Table 19 Comparison of results between Comparative Example 4 and Example 1

[0155] Example 1 uses the "photoirradiation sterilization box" of this invention. Bacteria enriched in the membrane concentrate are completely killed by ultraviolet light and then returned to the front end. The returned bacteria are "dead bacteria," having no impact on the system. In contrast, Comparative Example 4 directly returns membrane concentrate rich in live bacteria without sterilization treatment. Under suitable conditions (nutrients and packing surface), bacteria multiply rapidly, forming a biofilm, causing severe biofouling, disrupting the stability of the entire treatment device, and ultimately leading to biofouling and deterioration of the effluent quality. Therefore, the "photoirradiation sterilization box" of this invention is a crucial step in preventing biofilm formation and ensuring long-term stable operation of the system.

[0156] Comparative Example 5:

[0157] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1, except that the composite demulsifier and destabilizer described in this invention was not used in the process of Comparative Example 5, but instead a traditional oxidizing demulsifier (ammonium persulfate) was used.

[0158] Other process conditions are the same as in Example 1. The results of Comparative Example 5 and Example 1 are compared in Tables 20 and 21 below.

[0159] Table 20 Comparison of the breaking agents in Comparative Example 5 and Example 1

[0160] The storage and transportation of hazardous chemicals in the unique environment of offshore platforms presents significant challenges. Most offshore platforms lack the facilities for dedicated hazardous chemical storage. Example 1 completely avoids this technical difficulty by not using any hazardous chemicals.

[0161] Table 21 Comparison of effluent from the pre-aeration and depolymerization tanks of Comparative Example 5 and Example 1

[0162] The viscosity, polymer, and suspended solids content in the effluent from the pre-aeration depolymerization unit of Comparative Example 5 were all higher than those in Example 1. The degradation effect of persulfate on polymers was significantly inferior to that of the composite demulsifier and destabilizer described in this invention. The main reasons are: persulfate requires a certain temperature (usually >50℃) and a specific pH (alkaline) to exhibit high oxidative activity; for flowback fluids at room temperature and near neutrality, its initial reaction rate is slow; the high concentration of chloride ions in fracturing flowback fluids quenches persulfate free radicals, severely inhibiting oxidation efficiency; the stable CC backbone structure of polymers makes it difficult for persulfate to fully break down the chains within a limited residence time, resulting in a large amount of medium molecular weight polymer residue, manifested as still high effluent viscosity. Simultaneously, a large amount of sulfate ions are introduced, which sulfate-reducing bacteria can utilize to produce H2S, negatively impacting the equipment. The poor treatment effect of the pre-aeration depolymerization unit places a heavy load on subsequent processes (ozone, membrane filtration), leading to multiple indicators of the final effluent failing to meet standards.

[0163] For typical marine fracturing flowback fluids with high polymer and high chloride ion content, the traditional persulfate oxidation process is significantly inferior to the present invention in terms of treatment effect and overall economic efficiency due to the inhibition of free radicals by chloride ions, harsh reaction conditions, poor treatment effect, and prominent energy consumption and corrosion problems.

[0164] Comparative Example 6:

[0165] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1, except that chemical deoxygenation was used instead of the self-circulating deoxygenation unit in the process of Comparative Example 6.

[0166] That is, the process of Example 1 is as follows: pre-aeration depolymerization tank → self-cleaning ozone reaction tank → membrane filter → self-circulating deoxygenation tank (membrane concentrate → photoirradiation sterilization tank).

[0167] The process of Comparative Example 6 is as follows: pre-aeration de-gelling tank → self-cleaning ozone reactor → membrane filter → chemical deoxygenation tank (membrane concentrate → photoirradiation sterilization tank). The self-circulating deoxygenation is replaced with conventional sodium sulfite chemical deoxygenation, while other units remain unchanged.

[0168] The results of Comparative Example 6 and Example 1 are compared in Table 22 below.

[0169] Table 22 Comparison of results between Comparative Example 6 and Example 1

[0170] Example 1 utilizes the self-circulating deoxygenation tank of this invention, employing a purely physical process with no chemical consumption. The deoxygenation effect is stable and meets standards, with the final effluent dissolved oxygen level far below the 0.02 mg / L requirement for reuse in compound treatment. In contrast, Comparative Example 6 uses chemical deoxygenation agents, whose process is greatly affected by pH, water temperature, and agent activity. To ensure effectiveness, excessive dosage is often required; this not only significantly increases operating costs and the risk of secondary water pollution, but also results in far less stable performance compared to the vacuum deoxygenation of this invention. Therefore, the "self-circulating deoxygenation unit" of this invention is the optimal solution, balancing economy, stability, and water quality safety.

[0171] Comparative Example 7:

[0172] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus, except that the mass ratio of polyethylene polyamine polyether, citric acid-complexed polysilicon ferric chloride, polydimethyldiallyl ammonium chloride, and dimethylamine epichlorohydrin polymer in the composite demulsifier and destabilizer used in Comparative Example 7 was 60:150:1.5:1 (i.e., the proportion of polyethylene polyamine polyether used was higher than the proportion specified in this invention). Other process conditions were the same as in Example 1. The results of Comparative Example 7 and Example 1 are compared in Table 23 below.

[0173] Table 23 Comparison of results between Comparative Example 7 and Example 1

[0174] When the dosage ratio of polyethylene polyamine polyether in the composite demulsifier and destabilizer of Comparative Example 7 exceeded the upper limit of 50%, compared with Example 1, the content of pollutants such as oil, polymer, suspended solids, and COD in the effluent of the pre-aeration de-gelling unit increased significantly. Moreover, the flocs in Comparative Example 7 were in a fine, suspended state in water, and the settling performance decreased.

[0175] Comparative Example 8:

[0176] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus, except that the mass ratio of polyethylene polyamine polyether, citric acid-complexed polysilicon ferric chloride, polydimethyldiallyl ammonium chloride, and dimethylamine epichlorohydrin polymer in the composite demulsifier and destabilizer used in Comparative Example 8 was 30:220:1.5:1 (i.e., the citric acid-complexed polysilicon ferric chloride was used in a higher proportion than specified in this invention). Other process conditions were the same as in Example 1. The results of Comparative Example 8 and Example 1 are compared in Table 24 below.

[0177] Table 24 Comparison of results between Comparative Example 8 and Example 1

[0178] When the dosage ratio of citric acid complexed polysilicon ferric chloride in the composite demulsifier and destabilizer of Comparative Example 8 exceeded the upper limit of 200, the color of the effluent from the pre-aeration degelatination unit was darker and the content of polymers and suspended solids increased compared with Example 1.

[0179] A comparison of the results from Comparative Examples 7, 8, and 1 shows that a reasonable ratio of polyethylene polyamine polyether, citric acid-complexed polysilicon ferric chloride, polydimethyldiallylammonium chloride, and dimethylamine epichlorohydrin polymer in the composite demulsifier and destabilizer is more conducive to the treatment of fracturing flowback fluid. If the proportion of polyethylene polyamine polyether exceeds the acceptable range and is too high, although the emulsion interface is sufficiently disrupted, the released oil droplets and suspended solids cannot be effectively "captured" due to a lack of sufficient flocculant, resulting in increased effluent turbidity and fine, loose flocs. If the proportion of citric acid-complexed polysilicon ferric chloride is too high, excessive iron ions will reverse the surface charge of the flocs, causing them to redisperse, and will also introduce excessive iron ions, affecting the effluent color and subsequent water quality.

[0180] Comparative Example 9:

[0181] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus, except that no first partition was installed between the destabilization reaction zone and the aeration zone in Comparative Example 9; that is, the destabilization reaction zone and the aeration zone were interconnected. Other process conditions were the same as in Example 1. The results of Comparative Example 9 and Example 1 are compared in Table 25 below.

[0182] Table 25 Comparison of results between Comparative Example 9 and Example 1

[0183] A comparison of the results from Comparative Example 9 and Example 1 shows that when no first partition plate is installed between the destabilization reaction zone and the aeration zone, the content of oil, polymers, and suspended solids in the effluent from the pre-aeration deflocculation unit increases. This is because, when the first partition plate is removed, the fracturing flowback fluid and chemicals entering the pre-aeration deflocculation tank gradually come into contact with the microbubbles released by the aerator. Unreacted composite demulsifiers and unreacted polymers enter the aeration zone, causing the microbubbles generated by the aerator to merge, forming large and unevenly sized bubbles. This reduces the collision and adhesion efficiency between the bubbles and suspended solids and oil droplets. The actual effective reaction time between the added composite demulsifier and pollutants in the influent is greatly reduced, resulting in insufficient deflocculation reaction and failure to form dense flocs, leading to increased SS and oil content in the effluent. This verifies that a partition plate must be installed between the destabilization reaction zone and the aeration zone in the pre-aeration deflocculation tank to ensure that the deflocculation reaction obtains sufficient reaction time under stable hydraulic conditions and to provide good floc conditions and a stable bubble environment for air flotation separation.

[0184] Comparative Example 10:

[0185] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1, except that the self-cleaning ozone reactor in Comparative Example 10 was not equipped with baffles. Other process conditions were the same as in Example 1.

[0186] In Example 1, the COD of the effluent from ozone oxidation was 235 mg / L, while in Comparative Example 10, the COD was 886 mg / L. Example 1's self-cleaning ozone reactor featured uniformly arranged baffles, forming a "Z"-shaped flow channel. This extended the residence time by reversing the water flow, thus prolonging the reaction time between ozone and wastewater, improving ozone utilization and organic matter oxidation efficiency, and consistently controlling the effluent COD below 300 mg / L, reducing organic pollution in subsequent membrane units. In contrast, Comparative Example 12 eliminated the baffle design, causing the gas-water mixture to rise along a short, straight path. This resulted in insufficient residence time, leading to a large amount of undissolved ozone escaping and a significant reduction in ozone dissolution and utilization efficiency. Furthermore, the oxidation of macromolecular polymers and organic colloids in the water was incomplete, resulting in ozone effluent severely exceeding standards and failing to meet process control requirements, directly increasing the organic load on subsequent treatment units.

[0187] It has been verified that the "Z"-shaped deflection channel formed by the baffle plate inside the self-cleaning ozone reactor is a necessary structure to extend the gas-liquid contact time, improve ozone utilization efficiency, ensure sufficient ozone oxidation, and control the effluent COD ≤ 300 mg / L. The same oxidation and degradation effect cannot be achieved by relying solely on ozone aerators.

[0188] Comparative Example 11:

[0189] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1, except that both stages of the self-circulating deoxygenation tank in Comparative Example 11 were spiral flow channel deoxygenation chambers. Specifically, the secondary atomizing spray deoxygenation chamber in Example 1 was replaced with a structure identical to the primary spiral flow channel deoxygenation chamber (the nozzle was replaced with a spiral flow channel). Other process conditions were the same as in Example 1.

[0190] In Example 1, the final effluent dissolved oxygen content was 0.006 mg / L, while in Comparative Example 11, the final effluent dissolved oxygen content was 0.058 mg / L, failing to meet the standard of ≤0.02 mg / L for reuse. This is because the primary deoxygenation uses a spiral flow channel, which allows wastewater to form a thin water film on the channel. Dissolved oxygen is then drawn out from the surface of the water film by vacuum suction, reducing the dissolved oxygen concentration in the water from high to low. However, if the spiral flow channel is used to further reduce the dissolved oxygen concentration, the contact is only on one side of the water film, resulting in a limited total surface area and high mass transfer resistance. This only removes most of the easily escaped free dissolved oxygen. For the remaining trace amounts of bound oxygen, mass transfer through the liquid film alone cannot remove them, leading to the effluent dissolved oxygen content failing to meet the standard.

[0191] Comparative Example 12:

[0192] The same fracturing flowback fluid as in Example 1 was treated using the same method and apparatus as in Example 1, except that both stages of the self-circulating deoxygenation tank in Comparative Example 12 were atomizing spray deoxygenation chambers. Specifically, the primary spiral flow channel deoxygenation chamber in Example 1 was replaced with a structure identical to the secondary atomizing spray deoxygenation chamber (the spiral flow channel was replaced with a nozzle). Other process conditions were the same as in Example 1. The results of Comparative Example 12 and Example 1 are compared in Table 26 below.

[0193] Table 26 Comparison of results between Comparative Example 12 and Example 1

[0194] A comparison of the results of Comparative Example 12 and Example 1 shows that the droplet mass transfer efficiency of atomized spraying is better than that of water film mass transfer. The final dissolved oxygen in the effluent of Comparative Example 12 with two-stage atomized spraying is 0.009 mg / L, while that in Example 1 is 0.006 mg / L. The deoxygenation capacity of the two is comparable. However, under the same treatment scale, the operating energy consumption of two-stage atomized spraying is higher, and the liquid level fluctuation in the equipment is more severe, which increases the difficulty of the operator's work.

[0195] Atomized spraying forms a large number of tiny droplets, some of which are carried out by the vacuum pump's airflow in a vacuum environment. To maintain the same vacuum level, the vacuum pump needs to overcome the resistance caused by droplet entrainment. In Comparative Example 12, both stages are atomized spraying, and the vacuum pump inevitably entrains tiny droplets during pumping, resulting in a doubling of the actual pumping volume and a significant increase in the unit power consumption of the deoxygenation unit.

[0196] In Comparative Example 12, the primary atomizing spray reduced the dissolved oxygen concentration to a low level, but it still did not reach the 0.02 mg / L requirement for reuse in compounding. The secondary spray essentially continued "fine deoxygenation" on top of the already low concentration. When the dissolved oxygen concentration in the liquid phase is very low, the oxygen concentration difference across the liquid-gas interface decreases, and the rate of oxygen molecule mass transfer from the liquid phase to the gas phase decreases. To overcome the mass transfer driving force, the vacuum pump must maintain a higher pumping rate and a more stringent vacuum level, resulting in a sharp increase in energy consumption. In contrast, the primary spiral flow channel in Example 1 moderately reduced the dissolved oxygen to a medium concentration, retaining sufficient mass transfer driving force for the secondary atomizing spray, allowing the secondary spray to complete deep deoxygenation within a concentration difference that still has high mass transfer efficiency. This verifies that the self-circulating deoxygenator must adopt a combined structure of "primary spiral flow channel deoxygenation chamber + secondary atomizing spray deoxygenation chamber." The two are not simply superimposed, but rather leverage their respective mass transfer advantages in two different concentration ranges, forming a "liquid film-droplet" dual-modal deoxygenation mechanism to achieve dynamic matching of deoxygenation load and optimization of energy efficiency.

[0197] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0198] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for in-situ treatment of offshore fracturing flowback fluid, characterized in that, The processing method is as follows: S1. Add a composite demulsifier and destabilizer to the offshore fracturing flowback fluid to be treated to carry out the demulsification reaction, and then proceed with pre-aeration treatment and sedimentation treatment to obtain primary purified water. The composite demulsifier and destabilizer includes polyethylene polyamine polyether, citric acid complexed polysilicon ferric chloride, polydimethyldiallyl ammonium chloride, and dimethylamine epichlorohydrin polymer. S2. The primary purified water is subjected to self-cleaning ozone oxidation treatment. S3. The ozone oxidation effluent is then filtered through a membrane to remove suspended solids and bacteria, yielding membrane concentrate and membrane permeate. S4. The membrane concentrate is sterilized by light irradiation and then returned to step S1 for further treatment. The membrane permeate is subjected to self-circulating deoxygenation treatment to obtain treated water.

2. The method for in-situ treatment of offshore fracturing flowback fluid according to claim 1, characterized in that, The composite demulsifier and destabilizer consists of: polyethylene polyamine polyether, citric acid complexed polysilicon ferric chloride, polydimethyldiallylammonium chloride, and dimethylamine epichlorohydrin polymer, with the mass ratio of each substance being (20-50):(100-200):(1-2):

1. The amount of the composite demulsifier added is 50-300 mg / L.

3. The method for in-situ treatment of offshore fracturing flowback fluid according to claim 1, characterized in that, The debonding reaction in step S1 is carried out in a pre-aeration debonding tank, which is provided with a destabilization reaction zone for the debonding reaction, an aeration zone for pre-aeration treatment, and a sedimentation zone for sedimentation treatment.

4. The method for in-situ treatment of offshore fracturing flowback fluid according to claim 1, characterized in that, In step S2, the primary purified water is first filtered by an automatic membrane filter and then enters the oxidation reactor for ozone oxidation treatment. The ozone gas generated by the ozone generator is formed into fine bubbles with a diameter of 30-80μm by the ozone aerator. The ozone concentration in the water during the ozone oxidation reaction is 10-15mg / L and the temperature is 15-35℃. In step S3, the membrane filtration uses an ultrafiltration membrane with a pore size of 0.01-0.03 μm. The ultrafiltration membrane is made of hydrophilic modified polyvinylidene fluoride, the operating pressure is 0.15-0.25 MPa, and the water production rate is ≥92%.

5. The method for in-situ treatment of offshore fracturing flowback fluid according to claim 1, characterized in that, In step S4, the self-circulating deoxygenation process is carried out in a self-circulating deoxygenation tank, and the vacuum pressure in the self-circulating deoxygenation tank is -0.095MPa to -0.098MPa. The self-circulating deoxygenator includes at least a primary spiral flow deoxygenation chamber and a secondary atomizing spray deoxygenation chamber; In step S4, during the photo-irradiation sterilization process, ultraviolet light with a wavelength of 185nm or 254nm is used for irradiation, with an irradiation intensity of 30-60mW / cm² and a hydraulic residence time of 10-20s.

6. The method for in-situ treatment of offshore fracturing flowback fluid according to claim 1, characterized in that, After step S1, the viscosity of the effluent is reduced to ≤2.05 mPa·s, the polymer content is reduced to ≤40 mg / L, the suspended solids content is reduced to ≤100 mg / L, and the COD content is reduced to ≤3000 mg / L. The COD of the effluent from step S2 is ≤300 mg / L; The dissolved oxygen in the effluent after self-circulation deoxygenation treatment in step S4 is ≤0.01mg / L.

7. An in-situ treatment device for offshore fracturing flowback fluid, characterized in that, The treatment device includes a pre-aeration debonding tank, a self-cleaning ozone reaction tank, a membrane filter, and a self-circulating deoxygenation tank connected in sequence, as well as a photoirradiation sterilization tank connected between the concentrate outlet of the membrane filter and the inlet of the pre-aeration debonding tank. The pre-aeration depolymerization tank is divided into a destabilization reaction zone, an aeration zone, and a sedimentation zone by a partition. The aeration zone is equipped with an aerator, and the sedimentation zone is equipped with a primary purification outlet and a guide plate. The self-circulating deoxygenating tank is equipped with a primary spiral flow deoxygenating chamber located at the top and a secondary atomizing spray deoxygenating chamber located at the bottom.

8. The in-situ treatment device for offshore fracturing flowback fluid according to claim 7, characterized in that, The pre-aeration depolymerization box is a closed box, and a partition is provided between the destabilization reaction zone, the aeration zone and the sedimentation zone. The offshore fracturing flowback fluid to be treated overflows through the destabilization reaction zone, the aeration zone and the sedimentation zone in sequence. An overflow slag removal plate is provided at the upper part of the sedimentation zone, and several guide plates are provided on the wall of the sedimentation zone. The angle between the guide plates and the horizontal is 45°-60° or 120°-135°. The arrangement of the guide plates forms an "S" shaped flow channel on the wall.

9. The in-situ treatment device for offshore fracturing flowback fluid according to claim 7, characterized in that, The self-cleaning ozone reactor is equipped with multiple baffles. The angle between the baffles and the horizontal is 0°-45°. The length of the baffles is 1 / 4-1 / 3 of the total diameter of the self-cleaning ozone reactor. They are arranged in a left-right axially symmetrical manner. The arrangement of the baffles forms a "Z" shaped flow channel on the reactor wall. In the self-circulating deoxygenation tank, the first-stage spiral flow channel deoxygenation chamber is provided with several spiral flow channels, and the upper inlet of the spiral flow channels is connected to the water inlet pipe at the upper end of the first-stage spiral flow channel deoxygenation chamber; the upper end of the second-stage atomizing spray deoxygenation chamber is provided with several nozzles. When the liquid level in the primary spiral flow deoxygenation chamber reaches 1 / 2 to 2 / 3 of the total height of the primary spiral flow deoxygenation chamber, the nozzle is turned on; when the liquid level in the secondary atomizing spray deoxygenation chamber reaches 1 / 2 to 2 / 3 of the total height of the secondary atomizing spray deoxygenation chamber, the drain outlet of the self-circulating deoxygenation tank is opened.

10. The in-situ treatment device for offshore fracturing flowback fluid according to claim 7, characterized in that, The light irradiation sterilization chamber is equipped with several light irradiation reaction chambers. Each light irradiation reaction chamber is equipped with a light irradiation lamp group and a cooling system. The cooling system includes an inner circulation cooling channel and an outer circulation cooling channel. The lamp tubes of the light irradiation lamp group are arranged inside the inner circulation cooling channel.

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