Fracturing flow-back fluid treatment agent and fracturing flow-back fluid treatment process

Abstract

The invention discloses a fracturing flow-back fluid treating agent which comprises the following components: a nano zinc oxide modified ammonium persulfate gel breaker, a modified chitosan-sodium alginate composite flocculant and a glutaraldehyde-biquaternary ammonium salt compound bactericide. The fracturing flow-back fluid treatment process comprises the following steps: introducing a fracturing flow-back fluid stock solution into an oil separation tank, standing, carrying out preliminary oil removal, pumping into a reaction tank, adding a nano-zinc oxide modified ammonium persulfate gel breaker, carrying out a stirring reaction, adding a modified chitosan-sodium alginate composite gel flocculant, carrying out stirring to form flocs, carrying out standing precipitation, allowing the supernatant liquid to enter a multi-stage filtration link, and carrying out secondary filtration on the supernatant liquid to obtain the fracturing flow-back fluid. Sequentially entering quartz sand, activated carbon and a security filter for multi-stage filtration, adding a glutaraldehyde-biquaternary ammonium salt compound bactericide, and sterilizing to obtain the fracturing flow-back fluid treatment fluid. According to the fracturing flow-back fluid treating agent and the fracturing flow-back fluid treating process, the fracturing flow-back fluid treating efficiency can be improved, and the quality of fracturing flow-back fluid treating fluid is improved.

Description

Technical Field

[0001] This invention relates to the field of oilfield wastewater treatment technology, and in particular to a fracturing flowback fluid treatment agent and a fracturing flowback fluid treatment process. Background Technology

[0002] Fracturing flowback fluid is a complex liquid mixture that is returned from the wellhead after hydraulic fracturing operations in oil and gas fields. It contains various recalcitrant organic matter, polymers, oils, inorganic salts, nitrogen compounds, sulfides, microorganisms, etc., forming a stubborn oil-water emulsion system. It is characterized by high salt content, high COD, high viscosity, and high suspended solids, and its complex composition makes it difficult to treat. Direct discharge or reinjection into the formation will cause serious harm to the environment, groundwater, and soil, leading to soil compaction, salinization, and groundwater pollution. Therefore, it is necessary to treat fracturing flowback fluid to render it harmless.

[0003] Fracturing flowback fluid treatment is a critical environmental step in oil and gas extraction. Its core objective is to remove contaminants through physical, chemical, or biological methods, ensuring that the treated water meets discharge or reuse standards. Traditional fracturing flowback fluid treatment processes utilize breaker agents that are highly temperature-dependent. In low-temperature environments, oxidation times are prolonged, reaction efficiency is low, and breaker action is incomplete, resulting in persistently high flowback fluid viscosity. Furthermore, excessive oxidant residues after breaker action can increase the COD load in subsequent treatments. Single inorganic flocculants are easily interfered with by salt ions in high-salt flowback fluids, significantly reducing flocculation effectiveness and generating large amounts of sludge that are difficult to dewater, increasing sludge treatment costs and environmental burden. Moreover, traditional fracturing flowback fluid treatment agents are inefficient, and the long reaction times at each stage result in a long overall treatment cycle, making it difficult to meet the needs of rapid treatment of large-scale flowback fluids.

[0004] Therefore, this application provides a fracturing flowback fluid treatment agent and a fracturing flowback fluid treatment process to solve the problems of low gel breaking efficiency, poor flocculation effect, limited suspended solids removal effect, and long treatment cycle of the fracturing flowback fluid treatment agent and flowback fluid treatment process, thereby improving the fracturing flowback fluid treatment efficiency, improving the water quality of the fracturing flowback fluid treatment solution, and reducing secondary pollution. Summary of the Invention

[0005] The purpose of this invention is to provide a fracturing flowback fluid treatment agent and a fracturing flowback fluid treatment process to solve the problems mentioned in the background art, such as low gel breaking efficiency, poor flocculation effect, limited removal effect of suspended solids, and long treatment cycle.

[0006] In a first aspect, the present invention provides a fracturing flowback fluid treatment agent comprising the following components: nano zinc oxide modified ammonium persulfate breaker, modified chitosan-sodium alginate composite flocculant, and glutaraldehyde-bisquaternary ammonium salt compound bactericide.

[0007] As a preferred technical solution of the present invention, the nano zinc oxide modified ammonium persulfate breaker is prepared by the following method: ammonium persulfate powder is passed through a 100-mesh sieve, mixed with nano zinc oxide, and ball-milled in a ball mill at a speed of 300 r / min for 40 to 80 minutes to uniformly load the nano zinc oxide onto the surface of the ammonium persulfate. After drying at 60°C for 2 hours, the mixture is passed through a 200-mesh sieve to obtain the nano zinc oxide modified ammonium persulfate breaker.

[0008] As a preferred technical solution of the present invention, in the preparation process of nano zinc oxide modified ammonium persulfate breaker, the nano zinc oxide has a particle size of 30-50 nm and the mass ratio of ammonium persulfate to nano zinc oxide is 10:1.

[0009] As a preferred technical solution of the present invention, the modified chitosan-sodium alginate composite flocculant is prepared by the following method: chitosan is weighed and added to a 1% acetic acid solution, and stirred until completely dissolved to prepare a chitosan solution; sodium alginate is then weighed and added to deionized water, heated to 60°C and stirred until completely dissolved to prepare a sodium alginate solution; the chitosan solution and sodium alginate solution are mixed in a 1:1 volume ratio to obtain mixed solution A; epichlorohydrin, a crosslinking agent, is added to mixed solution A, and the mixture is stirred and reacted at 50°C for 2 hours, washed with water, dried and ground into powder, and passed through a 100-mesh sieve to obtain the modified chitosan-sodium alginate composite flocculant.

[0010] As a preferred technical solution of the present invention, in the preparation process of the modified chitosan-sodium alginate composite flocculant: The mass ratio of chitosan to acetic acid solution is 1:49; The mass ratio of sodium alginate to deionized water is 1:49; The mass ratio of epichlorohydrin to mixed solution A is 1:49.

[0011] As a preferred embodiment of the present invention, the glutaraldehyde-bisquaternary ammonium salt compound bactericide is prepared by the following method: glutaraldehyde, benzalkonium chloride, and didecyldimethylammonium bromide are mixed in a mass ratio of 6:1.6:2.4 to obtain a mixture. Anhydrous ethanol is added to the mixture, and the mixture is stirred until it is completely dissolved to obtain a mixed solution B. Soluble starch is added to the mixed solution B as a carrier and stirred for 45 minutes. The mass ratio of soluble starch to mixed solution B is 1:5, and the stirring speed is 180 r / min. The mixed solution B is placed in a water bath at 50-60°C to evaporate the ethanol. After the mixed solution B becomes a paste, it is transferred to an oven and dried at 80°C for 5 hours. Then, it is placed in a grinder at a speed of 300 r / min and ground for 1 hour to obtain a powder, thus obtaining the glutaraldehyde-bisquaternary ammonium salt compound bactericide.

[0012] As a preferred technical solution of the present invention, in the preparation process of glutaraldehyde-bisquaternary ammonium salt compound bactericide, the mass ratio of anhydrous ethanol to the mixture is 20:1.

[0013] Secondly, the present invention also provides a process for treating fracturing flowback fluid, comprising the following steps: S1. Preliminary oil removal: The raw fracturing flowback fluid is introduced into the oil separator. The raw flowback fluid is left to stand in the oil separator for 4 to 8 hours. The surface oil is collected through the oil collection pipe, the lower sediment is discharged through the bottom pipe of the oil separator, and the middle liquid phase enters the next treatment stage.

[0014] S2. Oxidative Debonding: The backflow liquid that has undergone preliminary oil removal in S1 is pumped into the reaction tank. Nano zinc oxide modified ammonium persulfate debonding agent is added at a mass ratio of 4-6:1000 of debonding agent to backflow liquid. The reaction is stirred at room temperature for 30-40 minutes, and the stirring speed of the reaction tank is set to 200-300 r / min.

[0015] S3. Flocculation and sedimentation: According to the mass ratio of flocculant to backflow liquid of 3-5:1000, add modified chitosan-sodium alginate composite gel flocculant to the backflow liquid after S2 oxidation and degelation, and stir to promote floc formation; after stirring, introduce the backflow liquid into the sedimentation tank, let it stand for 1-2 hours to allow the flocs to settle to the bottom and be discharged from the bottom pipe of the sedimentation tank, and the upper liquid enters the multi-stage filtration process.

[0016] S4. Multi-stage filtration: The upper liquid in S3 enters the quartz sand filter, activated carbon filter and security filter in sequence to remove coarse suspended solids, organic matter and fine particles from the fracturing flowback fluid.

[0017] S5. Sterilization: The liquid that has undergone multi-stage filtration is introduced into the sterilization tank. Glutaraldehyde-bisquaternary ammonium salt compound sterilizing agent is added at a mass ratio of 2-3:1000 between the sterilizing agent and the multi-stage filtered liquid. The mixture is stirred for 20-30 minutes at a stirring speed of 100-150 r / min. After sterilization, the fracturing flowback fluid treatment solution is obtained.

[0018] As a preferred technical solution of the present invention, when adding the modified chitosan-sodium alginate composite gel flocculant in S3, the mixture is first stirred at a speed of 400 r / min for 5 minutes to fully mix the flocculant with the backflow liquid; then it is stirred at a speed of 50-80 r / min for 25 minutes to promote the formation of flocs.

[0019] As a preferred embodiment of the present invention, the quartz sand filter in S4 has a filtration accuracy of 5-10 μm, removing coarser fine suspended solids from the water; the activated carbon filter has an activated carbon particle size of 0.5-2 mm, further adsorbing organic matter and odors in the liquid; and the security filter has a filtration accuracy of 1 μm.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses nano-zinc oxide-modified ammonium persulfate as a breaker in a fracturing flowback fluid treatment agent. After modification with nano-zinc oxide, the ammonium persulfate's oxidizing activity is enhanced, accelerating its decomposition to generate sulfate free radicals, thereby speeding up the destruction of the molecular structure of thickeners such as guar gum in the flowback fluid. This rapidly reduces the viscosity of the fracturing flowback fluid at room temperature, solving the problems of low breaker efficiency and long reaction time of traditional breaker agents in complex environments. Simultaneously, the modification of ammonium persulfate with nano-zinc oxide improves the environmental friendliness of the fracturing flowback fluid treatment agent, reducing the amount of ammonium persulfate used, minimizing the impact of residual oxidants on subsequent treatment, and reducing secondary pollution to the environment.

[0021] 2. This invention uses a modified chitosan-sodium alginate composite gel as a flocculant in fracturing flowback fluid treatment agents, offering the dual advantages of high-efficiency flocculation and environmental friendliness. The modified chitosan-sodium alginate composite gel flocculant combines the strong charge neutralization ability of inorganic flocculants with the excellent adsorption and bridging properties of organic flocculants. Its optimized molecular structure allows it to maintain good stability and flocculation performance even in high-salt environments. It can rapidly adsorb suspended solids and colloidal particles in water through charge neutralization and adsorption bridging, forming large, dense flocs with rapid sedimentation, effectively improving flocculation and sedimentation efficiency and reducing the residence time of fracturing flowback fluid in the sedimentation tank. Traditional single inorganic flocculants are easily affected by salt ions in high-salt fracturing flowback fluids, resulting in significantly reduced flocculation effects, large amounts of sludge, and difficulties in dewatering. While ordinary organic flocculants have good flocculation effects, their poor biodegradability easily causes secondary pollution. Furthermore, both chitosan and sodium alginate are natural polymer materials with good biodegradability, resulting in sludge that poses little environmental hazard and reduces the risk of secondary pollution.

[0022] 3. This invention utilizes a glutaraldehyde-bisquaternary ammonium salt compound bactericide in fracturing flowback fluid treatment agents, significantly improving the bactericidal effect and extending its duration. With prolonged use of traditional single bactericides, bacteria easily develop resistance, leading to a gradual decline in bactericidal efficacy, particularly against stubborn bacteria such as sulfate-reducing bacteria. Glutaraldehyde has a broad-spectrum bactericidal effect, rapidly penetrating bacterial cell membranes and destroying their proteins and nucleic acids, thus exerting its bactericidal effect. Quaternary ammonium salts adsorb onto the bacterial surface, altering cell membrane permeability and causing leakage of internal substances, leading to bacterial death. The combination of glutaraldehyde and quaternary ammonium salts produces a synergistic effect, broadening the bactericidal spectrum and providing excellent killing effects against a variety of bacteria. Furthermore, the glutaraldehyde-bisquaternary ammonium salt compound bactericide can maintain its bactericidal effect for a certain period, extending the duration of bactericidal action, reducing the frequency of bactericide application, and lowering treatment costs.

[0023] 4. This invention employs multi-stage filtration in the treatment process of fracturing flowback fluid, sequentially using quartz sand, activated carbon, and a security filter. The quartz sand and security filters primarily focus on filtration precision, intercepting particles in the treated fluid. The activated carbon filter, on the other hand, emphasizes adsorption capacity; its particle size selection is matched to the volume and contaminant concentration of the fracturing flowback fluid, adsorbing organic matter, odors, pigments, etc. The design prioritizes adsorption efficiency, ensuring that organic matter is fully adsorbed when the fracturing flowback fluid passes through the activated carbon filter. This multi-stage filtration process, using quartz sand, activated carbon, and a security filter, removes coarse suspended solids, organic matter, and fine particles from the fracturing flowback fluid. The stability of the treated fluid is significantly improved after filtration, with a substantial reduction in suspended solids content, creating favorable conditions for subsequent sterilization. This solves the problems of insufficient targeting and large fluctuations in the quality of fracturing flowback fluid treated by traditional filtration methods. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the fracturing flowback fluid treatment according to the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of the phrase "embodiment" in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0028] like Figure 1 As shown, a fracturing flowback fluid treatment process includes the following steps: S1. Preliminary oil removal: The raw fracturing flowback fluid is introduced into the oil separator and left to stand for 4 to 8 hours. The surface oil is collected through the oil collection pipe, the lower sediment is discharged through the bottom pipe of the oil separator, and the middle liquid phase enters the next treatment stage.

[0029] S2. Oxidative Debonding: The backflow liquid that has undergone preliminary oil removal in S1 is pumped into the reaction tank. Nano zinc oxide modified ammonium persulfate debonding agent is added at a mass ratio of 4-6:1000 of debonding agent to backflow liquid. The reaction is stirred at room temperature for 30-40 minutes, and the stirring speed of the reaction tank is set to 200-300 r / min.

[0030] S3. Flocculation and sedimentation: According to the mass ratio of flocculant to backflow liquid of 3-5:1000, add modified chitosan-sodium alginate composite gel flocculant to the backflow liquid after S2 oxidation and degelation, stir to promote floc formation, introduce into sedimentation tank for settling, and the upper liquid enters multi-stage filtration.

[0031] S4. Multi-stage filtration: The upper liquid in S3 enters the quartz sand filter, activated carbon filter and security filter in sequence to remove coarse suspended solids, organic matter and fine particles from the fracturing flowback fluid.

[0032] S5. Sterilization: The liquid that has undergone multi-stage filtration is introduced into the sterilization tank. Glutaraldehyde-bisquaternary ammonium salt compound sterilizing agent is added at a mass ratio of 2-3:1000 between the sterilizing agent and the multi-stage filtered liquid. The mixture is stirred for 20-30 minutes at a stirring speed of 100-150 r / min. After sterilization, the fracturing flowback fluid treatment solution is obtained.

[0033] All raw materials used in this invention are commercially available.

[0034] Example 1

[0035] A fracturing flowback fluid treatment agent comprises the following components: nano zinc oxide modified ammonium persulfate breaker, modified chitosan-sodium alginate composite flocculant, and glutaraldehyde-bisquaternary ammonium salt compound bactericide.

[0036] The nano-zinc oxide modified ammonium persulfate breaker was prepared by the following method: ammonium persulfate powder was passed through a 100-mesh sieve, mixed with nano-zinc oxide, and ball-milled in a ball mill at 300 r / min for 40 minutes to uniformly load the nano-zinc oxide onto the surface of the ammonium persulfate. After drying at 60℃ for 2 hours, the mixture was passed through a 200-mesh sieve to obtain the nano-zinc oxide modified ammonium persulfate breaker. The nano-zinc oxide particle size was 30-50 nm, and the mass ratio of ammonium persulfate to nano-zinc oxide was 10:1.

[0037] The modified chitosan-sodium alginate composite flocculant was prepared by the following method: chitosan was weighed and added to a 1% (w / w) acetic acid solution, and stirred until completely dissolved to prepare a chitosan solution; sodium alginate was then weighed and added to deionized water, heated to 60°C and stirred until completely dissolved to prepare a sodium alginate solution; the chitosan solution and sodium alginate solution were mixed at a volume ratio of 1:1 to obtain mixed solution A; epichlorohydrin, a crosslinking agent, was added to mixed solution A, and the mixture was stirred and reacted at 50°C for 2 hours, washed with water, dried, and ground into powder, and passed through a 100-mesh sieve to obtain the modified chitosan-sodium alginate composite flocculant; wherein, the mass ratio of chitosan to acetic acid solution was 1:49, the mass ratio of sodium alginate to deionized water was 1:49, and the mass ratio of epichlorohydrin to mixed solution A was 1:49.

[0038] The glutaraldehyde-bisquaternary ammonium salt compound bactericide was prepared by the following method: glutaraldehyde, benzalkonium chloride, and dialcyldimethylammonium bromide were mixed in a mass ratio of 6:1.6:2.4 to obtain a mixture. Anhydrous ethanol was added to the mixture, and the mixture was stirred until it was completely dissolved to obtain mixed solution B. Soluble starch was added to mixed solution B as a carrier and stirred for 45 minutes. The mass ratio of soluble starch to mixed solution B was 1:5, and the stirring speed was 180 r / min. Mixed solution B was placed in a water bath at 50-60℃ to evaporate the ethanol. After mixed solution B became a paste, it was transferred to an oven and dried at 80℃ for 5 hours. Then, it was placed in a grinder at 300 r / min and ground for 1 hour to obtain a powder, thus obtaining the glutaraldehyde-bisquaternary ammonium salt compound bactericide. The mass ratio of anhydrous ethanol to the mixture was 20:1.

[0039] A process for treating fracturing flowback fluid includes the following steps: S1. Preliminary oil removal: The raw fracturing flowback fluid is introduced into the oil separator. The raw flowback fluid is left to stand in the oil separator for 4 hours. The surface oil is collected through the oil collection pipe, the lower sediment is discharged through the bottom pipe of the oil separator, and the middle liquid phase enters the next treatment stage.

[0040] S2. Oxidative Debonding: The backflow liquid that has undergone preliminary oil removal in S1 is pumped into the reaction tank. Nano zinc oxide modified ammonium persulfate debonding agent is added at a mass ratio of 4:1000 to the backflow liquid. The reaction is stirred at room temperature for 40 minutes, and the stirring speed of the reaction tank is set to 200 r / min.

[0041] S3. Flocculation and Sedimentation: Add modified chitosan-sodium alginate composite gel flocculant to the backflow liquid after S2 oxidation and degelatination at a flocculant to backflow liquid mass ratio of 3:1000. First, stir at 400 r / min for 5 minutes to fully mix the flocculant and backflow liquid; then stir at 50 r / min for 25 minutes to promote floc formation; after stirring, introduce the backflow liquid into the sedimentation tank and let it stand for 1 hour to allow the flocs to settle to the bottom and be discharged from the bottom pipe of the sedimentation tank. The upper liquid enters the multi-stage filtration process.

[0042] S4. Multi-stage filtration: The upper layer of liquid in S3 enters the quartz sand filter with a filtration accuracy of 10μm to remove coarser fine suspended solids in the water; the liquid after filtration by the quartz sand filter enters the activated carbon filter with activated carbon particle size of 0.5-2mm to further adsorb organic matter and odors in the liquid; the liquid after filtration by the activated carbon filter enters the security filter with a filtration accuracy of 1μm.

[0043] S5. Sterilization: The liquid that has undergone multi-stage filtration is introduced into the sterilization tank. Glutaraldehyde-bisquaternary ammonium salt compound sterilizing agent is added at a mass ratio of 2:1000 between the sterilizing agent and the multi-stage filtered liquid. The mixture is stirred for 30 minutes at a stirring speed of 100 r / min. After sterilization, the fracturing flowback fluid treatment solution is obtained.

[0044] Example 2

[0045] A fracturing flowback fluid treatment agent comprises the following components: nano zinc oxide modified ammonium persulfate breaker, modified chitosan-sodium alginate composite flocculant, and glutaraldehyde-bisquaternary ammonium salt compound bactericide.

[0046] The nano-zinc oxide modified ammonium persulfate breaker was prepared by the following method: ammonium persulfate powder was passed through a 100-mesh sieve and mixed with nano-zinc oxide. The mixture was then ball-milled for 60 minutes at a speed of 300 r / min to ensure that the nano-zinc oxide was uniformly loaded onto the surface of the ammonium persulfate. After drying at 60°C for 2 hours, the mixture was passed through a 200-mesh sieve to obtain the nano-zinc oxide modified ammonium persulfate breaker. The nano-zinc oxide particle size was 30–50 nm, and the mass ratio of ammonium persulfate to nano-zinc oxide was 10:1.

[0047] The modified chitosan-sodium alginate composite flocculant was prepared by the following method: chitosan was weighed and added to a 1% (w / w) acetic acid solution, and stirred until completely dissolved to prepare a chitosan solution; sodium alginate was then weighed and added to deionized water, heated to 60°C and stirred until completely dissolved to prepare a sodium alginate solution; the chitosan solution and sodium alginate solution were mixed at a volume ratio of 1:1 to obtain mixed solution A; epichlorohydrin, a crosslinking agent, was added to mixed solution A, and the mixture was stirred and reacted at 50°C for 2 hours, washed with water, dried, and ground into powder, and passed through a 100-mesh sieve to obtain the modified chitosan-sodium alginate composite flocculant; wherein, the mass ratio of chitosan to acetic acid solution was 1:49, the mass ratio of sodium alginate to deionized water was 1:49, and the mass ratio of epichlorohydrin to mixed solution A was 1:49.

[0048] The glutaraldehyde-bisquaternary ammonium salt compound bactericide was prepared by the following method: glutaraldehyde, benzalkonium chloride, and dialcyldimethylammonium bromide were mixed in a mass ratio of 6:1.6:2.4 to obtain a mixture. Anhydrous ethanol was added to the mixture, and the mixture was stirred until it was completely dissolved to obtain mixed solution B. Soluble starch was added to mixed solution B as a carrier and stirred for 45 minutes. The mass ratio of soluble starch to mixed solution B was 1:5, and the stirring speed was 180 r / min. Mixed solution B was placed in a water bath at 50-60℃ to evaporate the ethanol. After mixed solution B became a paste, it was transferred to an oven and dried at 80℃ for 5 hours. Then, it was placed in a grinder at 300 r / min and ground for 1 hour to obtain a powder, thus obtaining the glutaraldehyde-bisquaternary ammonium salt compound bactericide. The mass ratio of anhydrous ethanol to the mixture was 20:1.

[0049] A process for treating fracturing flowback fluid includes the following steps: S1. Preliminary oil removal: The raw fracturing flowback fluid is introduced into the oil separator. The raw flowback fluid is left to stand in the oil separator for 6 hours. The surface oil is collected through the oil collection pipe, the lower sediment is discharged through the bottom pipe of the oil separator, and the middle liquid phase enters the next treatment stage.

[0050] S2. Oxidative Debonding: The backflow liquid that has undergone preliminary oil removal in S1 is pumped into the reaction tank. Nano zinc oxide modified ammonium persulfate debonding agent is added at a mass ratio of 5:1000 to the backflow liquid. The reaction is stirred at room temperature for 35 minutes, and the stirring speed of the reaction tank is set to 250 r / min.

[0051] S3. Flocculation and Sedimentation: Add modified chitosan-sodium alginate composite gel flocculant to the backflow liquid after S2 oxidation and degelatination at a flocculant to backflow liquid mass ratio of 4:1000. First, stir at 400 r / min for 5 minutes to fully mix the flocculant and backflow liquid; then stir at 65 r / min for 25 minutes to promote floc formation; after stirring, introduce the backflow liquid into the sedimentation tank and let it stand for 1.5 hours to allow the flocs to settle to the bottom and be discharged from the bottom pipe of the sedimentation tank. The upper liquid enters the multi-stage filtration process.

[0052] S4. Multi-stage filtration: The upper layer of liquid in S3 enters the quartz sand filter with a filtration accuracy of 7μm to remove coarser fine suspended solids in the water; the liquid after filtration by the quartz sand filter enters the activated carbon filter with activated carbon particle size of 0.5-2mm to further adsorb organic matter and odors in the liquid; the liquid after filtration by the activated carbon filter enters the security filter with a filtration accuracy of 1μm.

[0053] S5. Sterilization: The liquid that has undergone multi-stage filtration is introduced into the sterilization tank. Glutaraldehyde-bisquaternary ammonium salt compound sterilizing agent is added at a mass ratio of 2.5:1000 (sterilizing agent to multi-stage filtered liquid). The mixture is stirred for 25 minutes at a stirring speed of 125 r / min. After sterilization, the fracturing flowback fluid treatment solution is obtained.

[0054] Example 3

[0055] A fracturing flowback fluid treatment agent comprises the following components: nano zinc oxide modified ammonium persulfate breaker, modified chitosan-sodium alginate composite flocculant, and glutaraldehyde-bisquaternary ammonium salt compound bactericide.

[0056] The nano-zinc oxide modified ammonium persulfate breaker was prepared by the following method: ammonium persulfate powder was passed through a 100-mesh sieve, mixed with nano-zinc oxide, and ball-milled in a ball mill at 300 r / min for 80 minutes to uniformly load the nano-zinc oxide onto the surface of the ammonium persulfate. After drying at 60℃ for 2 hours, the mixture was passed through a 200-mesh sieve to obtain the nano-zinc oxide modified ammonium persulfate breaker. The nano-zinc oxide particle size was 30-50 nm, and the mass ratio of ammonium persulfate to nano-zinc oxide was 10:1.

[0057] The modified chitosan-sodium alginate composite flocculant was prepared by the following method: chitosan was weighed and added to a 1% (w / w) acetic acid solution, and stirred until completely dissolved to prepare a chitosan solution; sodium alginate was then weighed and added to deionized water, heated to 60°C and stirred until completely dissolved to prepare a sodium alginate solution; the chitosan solution and sodium alginate solution were mixed at a volume ratio of 1:1 to obtain mixed solution A; epichlorohydrin, a crosslinking agent, was added to mixed solution A, and the mixture was stirred and reacted at 50°C for 2 hours, washed with water, dried, and ground into powder, and passed through a 100-mesh sieve to obtain the modified chitosan-sodium alginate composite flocculant; wherein, the mass ratio of chitosan to acetic acid solution was 1:49, the mass ratio of sodium alginate to deionized water was 1:49, and the mass ratio of epichlorohydrin to mixed solution A was 1:49.

[0058] The glutaraldehyde-bisquaternary ammonium salt compound bactericide was prepared by the following method: glutaraldehyde, benzalkonium chloride, and dialcyldimethylammonium bromide were mixed in a mass ratio of 6:1.6:2.4 to obtain a mixture. Anhydrous ethanol was added to the mixture, and the mixture was stirred until it was completely dissolved to obtain mixed solution B. Soluble starch was added to mixed solution B as a carrier and stirred for 45 minutes. The mass ratio of soluble starch to mixed solution B was 1:5, and the stirring speed was 180 r / min. Mixed solution B was placed in a water bath at 50-60℃ to evaporate the ethanol. After mixed solution B became a paste, it was transferred to an oven and dried at 80℃ for 5 hours. Then, it was placed in a grinder at 300 r / min and ground for 1 hour to obtain a powder, thus obtaining the glutaraldehyde-bisquaternary ammonium salt compound bactericide. The mass ratio of anhydrous ethanol to the mixture was 20:1.

[0059] A process for treating fracturing flowback fluid includes the following steps: S1. Preliminary oil removal: The raw fracturing flowback fluid is introduced into the oil separator. The raw flowback fluid is left to stand in the oil separator for 8 hours. The surface oil is collected through the oil collection pipe, the lower sediment is discharged through the bottom pipe of the oil separator, and the middle liquid phase enters the next treatment stage.

[0060] S2. Oxidative Debonding: The backflow liquid that has undergone preliminary oil removal in S1 is pumped into the reaction tank. Nano zinc oxide modified ammonium persulfate debonding agent is added at a mass ratio of 6:1000 to the backflow liquid. The mixture is stirred and reacted at room temperature for 30 minutes, with the stirring speed of the reaction tank set to 300 r / min.

[0061] S3. Flocculation and Sedimentation: Add modified chitosan-sodium alginate composite gel flocculant to the backflow liquid after S2 oxidation and degelation at a flocculant to backflow liquid mass ratio of 5:1000. First, stir at 400 r / min for 5 minutes to fully mix the flocculant and backflow liquid; then stir at 80 r / min for 25 minutes to promote floc formation; after stirring, introduce the backflow liquid into the sedimentation tank and let it stand for 2 hours to allow the flocs to settle to the bottom and be discharged from the bottom pipe of the sedimentation tank. The upper liquid enters the multi-stage filtration process.

[0062] S4. Multi-stage filtration: The upper layer of liquid in S3 enters the quartz sand filter with a filtration accuracy of 5μm to remove coarser fine suspended solids in the water; the liquid after filtration by the quartz sand filter enters the activated carbon filter with activated carbon particle size of 0.5-2mm to further adsorb organic matter and odors in the liquid; the liquid after filtration by the activated carbon filter enters the security filter with a filtration accuracy of 1μm.

[0063] S5. Sterilization: The liquid that has undergone multi-stage filtration is introduced into the sterilization tank. Glutaraldehyde-bisquaternary ammonium salt compound sterilizing agent is added at a mass ratio of 3:1000 between the sterilizing agent and the multi-stage filtered liquid. The mixture is stirred for 20 minutes at a stirring speed of 150 r / min. After sterilization, the fracturing flowback fluid treatment solution is obtained.

[0064] Comparative Example 1: The difference from Example 3 is that ammonium persulfate was added directly without modification.

[0065] Comparative Example 2: The difference from Example 3 is that aluminum sulfate is used as a flocculant.

[0066] Comparative Example 3: The difference from Example 3 is that glutaraldehyde is used as a bactericide.

[0067] The fracturing flowback fluid treatment fluids using the fracturing flowback fluid treatment agents and fracturing flowback fluid treatment processes described in Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 were tested.

[0068] The fracturing flowback fluids treated in Examples 1, 2, and 3, and Comparative Examples 1, 2, and 3 were analyzed. The COD was determined using HJ 828-2017 "Determination of Chemical Oxygen Demand in Water - Dichromate Method", the total nitrogen concentration was determined using HJ 636-2012 "Determination of Total Nitrogen in Water - Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometric Method", and the ammonia nitrogen concentration was determined using HJ 535-2009 "Determination of Ammonia Nitrogen in Water - Nessler's Reagent Spectrophotometric Method". The results are shown in Table 1.

[0069] Table 1: COD, Total Nitrogen Concentration, and Ammonia Nitrogen Concentration in Fracturing Flowback Fluid

[0070] As shown in Table 1, the fracturing flowback fluid treated with the fracturing flowback fluid treatment agents and treatment processes of Examples 1, 2, and 3 had lower COD, total nitrogen concentration, and ammonia nitrogen concentration; while the fracturing flowback fluid treated with the fracturing flowback fluid treatment agents and treatment processes of Comparative Examples 1, 2, and 3 had higher COD, total nitrogen concentration, and ammonia nitrogen concentration.

[0071] The fracturing flowback fluids treated in Examples 1, 2, and 3, and Comparative Examples 1, 2, and 3 were tested for viscosity using GB / T22314-2008 "Method for Determination of Viscosity of Epoxy Resins in Plastics", suspended solids concentration using GB / T 11901-89 "Determination of Suspended Solids in Water - Gravimetric Method", and petroleum concentration using HJ 637-2018 "Determination of Petroleum and Animal / Vegetable Oils in Water - Infrared Spectrophotometry". The results are shown in Table 2.

[0072] Table 2: Viscosity, Suspended Solids Concentration, and Petroleum Concentration in Fracturing Flowback Fluid

[0073] As shown in Table 2, the fracturing flowback fluid treated with the fracturing flowback fluid treatment agents and treatment processes of Examples 1, 2, and 3 has lower viscosity, suspended solids concentration, and petroleum concentration; while the fracturing flowback fluid treated with the fracturing flowback fluid treatment agents and treatment processes of Comparative Examples 1, 2, and 3 has higher viscosity, suspended solids concentration, and petroleum concentration.

[0074] In summary, the fracturing flowback fluid treatment agent and fracturing flowback fluid treatment process of the present invention can solve the problems of low gel breaking efficiency, poor flocculation effect, limited suspended solids removal effect, and long treatment cycle of traditional fracturing flowback fluid treatment agents and processes, improve the treatment efficiency of fracturing flowback fluid, improve the water quality of fracturing flowback fluid, and meet the needs of high-quality and efficient treatment of large-scale flowback fluid.

[0075] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A fracturing flowback fluid treatment agent, characterized in that, It includes the following components: nano zinc oxide modified ammonium persulfate deflocculator, modified chitosan-sodium alginate composite flocculant, and glutaraldehyde-bisquaternary ammonium salt compound bactericide.

2. The fracturing flowback fluid treatment agent according to claim 1, characterized in that, The nano-zinc oxide modified ammonium persulfate breaker is prepared by the following method: ammonium persulfate powder is passed through a 100-mesh sieve, mixed with nano-zinc oxide, and ball-milled in a ball mill at a speed of 300 r / min for 40 to 80 minutes to uniformly load the nano-zinc oxide onto the surface of the ammonium persulfate. After drying at 60°C for 2 hours, it is passed through a 200-mesh sieve to obtain the nano-zinc oxide modified ammonium persulfate breaker.

3. The fracturing flowback fluid treatment agent according to claim 2, characterized in that, The nano zinc oxide particles have a diameter of 30–50 nm, and the mass ratio of ammonium persulfate to nano zinc oxide is 10:

1.

4. The fracturing flowback fluid treatment agent according to claim 1, characterized in that, The modified chitosan-sodium alginate composite flocculant is prepared by the following method: chitosan is weighed and added to a 1% acetic acid solution, and stirred until completely dissolved to prepare a chitosan solution; sodium alginate is then weighed and added to deionized water, heated to 60°C and stirred until completely dissolved to prepare a sodium alginate solution; the chitosan solution and sodium alginate solution are mixed at a volume ratio of 1:1 to obtain mixed solution A; epichlorohydrin, a crosslinking agent, is added to mixed solution A, and the mixture is stirred and reacted at 50°C for 2 hours, washed with water, dried, and ground into powder, and passed through a 100-mesh sieve to obtain the modified chitosan-sodium alginate composite flocculant.

5. The fracturing flowback fluid treatment agent according to claim 4, characterized in that: The mass ratio of chitosan to acetic acid solution is 1:49; The mass ratio of sodium alginate to deionized water is 1:49; The mass ratio of epichlorohydrin to mixed solution A is 1:

49.

6. The fracturing flowback fluid treatment agent according to claim 1, characterized in that, The glutaraldehyde-bisquaternary ammonium salt compound bactericide is prepared by the following method: glutaraldehyde, benzalkonium chloride, and dialcyldimethylammonium bromide are mixed in a mass ratio of 6:1.6:2.4 to obtain a mixture. Anhydrous ethanol is added to the mixture and stirred until the mixture is completely dissolved to obtain mixed solution B. Soluble starch is added to mixed solution B as a carrier and stirred for 45 minutes. The mass ratio of soluble starch to mixed solution B is 1:5, and the stirring speed is 180 r / min. Mixed solution B is placed in a water bath at 50-60℃ to evaporate the ethanol. After mixed solution B becomes a paste, it is transferred to an oven and dried at 80℃ for 5 hours. Then, it is placed in a grinder at a speed of 300 r / min and ground for 1 hour to obtain a powder, thus obtaining the glutaraldehyde-bisquaternary ammonium salt compound bactericide.

7. The fracturing flowback fluid treatment agent according to claim 6, characterized in that, The mass ratio of anhydrous ethanol to the mixture is 20:

1.

8. A fracturing flowback fluid treatment process according to any one of claims 1 to 7, comprising the following steps: S1. Preliminary oil removal: The raw fracturing flowback fluid is introduced into the oil separator. The raw flowback fluid is left to stand in the oil separator for 4 to 8 hours. The surface oil is collected through the oil collection pipe, the lower sediment is discharged through the bottom pipe of the oil separator, and the middle liquid phase enters the next treatment stage. S2. Oxidative degreasing: The backflow liquid that has undergone preliminary oil removal in S1 is pumped into the reaction tank. Nano zinc oxide modified ammonium persulfate degreasing agent is added at a mass ratio of 4-6:1000 of degreasing agent to backflow liquid. The reaction is stirred at room temperature for 30-40 minutes, and the stirring speed of the reaction tank is set to 200-300 r / min. S3. Flocculation and sedimentation: According to the mass ratio of flocculant to backflow liquid of 3-5:1000, add modified chitosan-sodium alginate composite gel flocculant to the backflow liquid after S2 oxidation and degellation, and stir to promote floc formation; after stirring, introduce the backflow liquid into the sedimentation tank, let it stand for 1-2 hours to allow the flocs to settle to the bottom and be discharged from the bottom pipe of the sedimentation tank, and the upper liquid enters the multi-stage filtration stage; S4. Multi-stage filtration: The upper liquid in S3 enters the quartz sand filter, activated carbon filter and security filter in sequence to remove coarse suspended solids, organic matter and fine particles from the fracturing flowback fluid, respectively. S5. Sterilization: The liquid that has undergone multi-stage filtration is introduced into the sterilization tank. Glutaraldehyde-bisquaternary ammonium salt compound sterilizing agent is added at a mass ratio of 2-3:1000 between the sterilizing agent and the multi-stage filtered liquid. The mixture is stirred for 20-30 minutes at a stirring speed of 100-150 r / min. After sterilization, the fracturing flowback fluid treatment solution is obtained.

9. The fracturing flowback fluid treatment process according to claim 8, characterized in that, When adding the modified chitosan-sodium alginate composite gel flocculant to S3, first stir at 400 r / min for 5 minutes to fully mix the flocculant with the backflow liquid; then stir at 50-80 r / min for 25 minutes to promote floc formation.

10. The fracturing flowback fluid treatment process according to claim 8, characterized in that: The quartz sand filter described in S4 has a filtration accuracy of 5-10 μm. The activated carbon filter described in S4 has an activated carbon particle size of 0.5–2 mm; The security filter described in S4 has a filtration accuracy of 1μm.

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