Combination gel fracturing fluid and method of making same

Abstract

The present application relates to the technical field of fracturing fluid, and is a combined gel fracturing fluid and a preparation method thereof.The raw materials of the combined gel fracturing fluid include waterproof lock salt-resistant fracturing thickening agent, emulsifier, mineral oil, suspension stabilizer and dispersion stabilizer.In the combined gel fracturing fluid, the raw material waterproof lock salt-resistant fracturing thickening agent has large stable viscosity and excellent viscosity performance, because the sodium 4-vinylbenzenesulfonate is introduced into the waterproof lock salt-resistant fracturing thickening agent, which gives the waterproof lock salt-resistant fracturing thickening agent the dual function of thickening before gel breaking and waterproof locking after gel breaking.Meanwhile, the raw material multi-site nano crosslinking agent is obtained by introducing modified graphene oxide with two-dimensional planar structure into conventional metal zirconium salt, and has high crosslinking efficiency.Finally, the combined gel fracturing fluid formed by the high-efficiency synergy of the waterproof lock salt-resistant fracturing thickening agent and the multi-site nano crosslinking agent has good salt resistance, temperature resistance, shear resistance and gel breaking performance.

Description

Technical Field

[0001] This invention relates to the field of fracturing fluid technology, specifically a combined gel fracturing fluid and its preparation method. Background Technology

[0002] Hydraulic fracturing is a crucial technology for improving unconventional resources such as tight oil and shale oil and gas. Fracturing fluid, as the key working fluid in hydraulic fracturing, directly determines the efficiency and effectiveness of fracturing. Thickeners, as important main agents in fracturing fluids, are critical to ensuring the overall performance of the fracturing fluid system. Due to their advantages such as good drag reduction, strong thickening ability, low residue content, and insensitivity to bacteria, synthetic polymers have become one of the mainstream directions for the research and application of fracturing fluid thickeners. However, as the development of unconventional oil and gas resources continues to delve into deeper, more complex formations with high water cut, high temperature, and high salinity, traditional fracturing fluid systems based on synthetic polymers face numerous problems that urgently need to be addressed. On the one hand, high water cut conditions lead to significant water-lock damage in actual oil and gas production, poor adaptability of traditional fracturing fluids, and serious problems such as a significant decrease in production well productivity or even shutdown. On the other hand, due to the effects of high temperature and high salinity, traditional fracturing fluid systems generally suffer from poor temperature resistance, insufficient proppant carrying capacity, and high construction costs.

[0003] To address these issues, researchers have focused on two main approaches to improve the overall performance of fracturing fluids. First, they added thickeners to the fracturing fluid to prevent or weaken the water-locking effect on oil and gas by reducing surface tension and oil / water interfacial tension, and altering the wettability of the reservoir rock surface. Second, they crosslinked the thickener with a specific crosslinking agent to form a gel-like fracturing fluid, thereby improving its temperature resistance, shear strength, and proppant carrying capacity, and further reducing construction costs.

[0004] Chinese Patent CN104927830B discloses a waterproof fracturing fluid and its preparation method. This method combines a specific ratio of hydroxypropyl guar gum, soda ash, clay stabilizer, bactericide, waterproofing agent (a mixture of hexadecyl dimethyl ammonium bromide, octylphenol polyoxyethylene ether, and fluorocarbon surfactant), and water to address the water-locking effect caused by the inability of traditional fracturing fluids to effectively reduce the surface tension of the filtrate and the interfacial tension between oil and water, thereby improving the permeability of the oil and gas phases. After reacting with an aqueous solution of borax or an organic boron solution, this waterproof fracturing fluid can achieve a flow-through rate of 90% to 93% and reduce the core damage rate to 17% to 14%. Chinese patent CN107345129A discloses a waterproofing agent and its preparation method. The method uses cyclohexane as a solvent, glyceryl monostearate and hexadecyltriethylammonium bromide as emulsifiers, ammonium persulfate as an initiator, and ammonium metavanadate and neodymium oxide as catalysts to polymerize acrylamide with liquid polybutadiene to form a highly active surfactant. At the same time, β-sitosterol is used as a surfactant additive, and γ-aminopropyltriethoxysilane is used to improve the structural properties and increase the adhesion to the reservoir. The surface tension of a 1% aqueous solution is as low as 18.7 mN / m and the interfacial tension is as low as 0.31 mN / m.

[0005] Chinese patent CN113528099A discloses a waterproofing agent and its preparation method. This agent, by combining a nonionic surfactant, anionic surfactant, amphoteric surfactant, low-carbon alcohol, and water, can reduce surface tension to 22.2 mN / m and oil-water interfacial tension to 5.8 × 10⁻⁶ m / s. -3 mN / m, and the contact angle of clear water on the rock surface was reduced from 52.9 mN / m. o Transformed to 73.9 o Chinese Patent CN114890920B discloses a waterproofing agent and its preparation method. It is prepared by reacting disodium 8-aminonaphthalene-1,3,6-trisulfonic acid with bromododecane in a mixed solvent composed of formic acid, formaldehyde, and methanol. The agent features a wide range of raw material sources, a simple preparation process, no pollution, and no byproducts. At a concentration of 0.5 wt%, the waterproofing agent has a surface tension of less than 27 mN / m and an interfacial tension of less than 0.08 mN / m.

[0006] Chinese Patent CN114958330B discloses a waterproofing sealant for fracturing and its preparation method. It is prepared by a synergistic combination of sodium p-perfluorononenoxybenzenesulfonate, perfluorooctyl sulfonyl polyoxyethylene ether, and sodium dodecylbenzenesulfonate in the presence of formate and chloride salts. It exhibits characteristics such as low surface tension, strong hydrophobicity, strong temperature resistance, strong chemical stability, and strong surface interaction with rocks. Its surface tension is below 27 mN / m, and its hydrophilic contact angle is 108.2°. o Suitable for waterproofing locks in sensitive tight gas reservoirs.

[0007] Gong Hongliang of China Oilfield Services Corporation prepared a waterproofing lock agent FR-101 using methyl isobutyl acrylate, methacrylic acid and butyl 2-acrylate as raw materials. When the dosage is 1.2%, the surface tension can be reduced to 23.8 mN / m, which can change the surface wettability of the core thin section from hydrophilic to neutral wettability, and make the core permeability recovery rate reach more than 90% (Gong Hongliang, Preparation and performance evaluation of high efficiency waterproofing lock agent for drilling in low-permeability offshore oilfields, Chemical and Biological Engineering, 2023, 40(10)).

[0008] He Yiming of Yanchang Oilfield Co., Ltd. also prepared an emulsion waterproofing agent, FRT-2, using methyl isobutylene, acrylic acid, and butyl acrylate as raw materials. At an addition of 1.0%, the surface tension can be reduced to 25 mN / m, and the hydrophilic contact angle of the core surface can be reduced from 39.6°. o It changed to 91.3 o And reduce the core water-locking damage rate to below 20% (He Yiming, Research on novel emulsion waterproofing agents suitable for low-permeability gas reservoirs, Chemical Engineer, 2024, 344 (05)).

[0009] Cao Weijia et al. from Northeast Petroleum University prepared short-chain fluorocarbon quaternary ammonium salt surfactants by reacting perfluorohexylsulfonyl fluoride, N,N-dimethylethylenediamine, and ethyl bromoacetate. These surfactants were then compounded with alkylbenzene sulfonate (ABS), sodium α-alkenyl sulfonate (AOS), and fatty alcohol oxyethylene ether sulfate (AES) to form a waterproofing lock-in agent. At a dosage of 0.5%, the oil-water interfacial tension of the aqueous solution reached 0.299 mN / m, and the surface tension reached 20.23 mN / m. This agent could reduce the contact angle of hydrophilic surfaces from 28.097°. o It changed to 67.225 o (Cao Weijia et al., Performance evaluation of waterproofing interlocking agent formulation for low-permeability tight gas reservoirs, Petrochemical Technology, 2024).

[0010] The existing patents and published studies mainly involve compounding individual thickeners with other substances to form fracturing fluid systems. However, these systems suffer from problems such as insufficient water-locking effect, low overall drainage rate, and high reservoir damage rate due to chromatographic separation risks, inadequate compatibility and synergy, and poor salt resistance.

[0011] Chinese Patent CN114410287B discloses a composite nano-crosslinking agent, its preparation method, and its application. It is prepared by reacting glycerol, lactic acid, zirconium oxychloride, and trisodium citrate, followed by the addition of nano-titanium oxide. Using this crosslinking agent to form a gel-like fracturing fluid effectively reduces the amount of emulsion drag reducer, increases the viscosity of the fracturing fluid system under high temperature and high shear, prolongs the crosslinking time, and improves viscoelasticity and temperature resistance. Chinese Patent CN116751576A discloses a delayed crosslinking agent for water-based fracturing fluid, its preparation method, and its application. It is prepared by reacting zirconium oxychloride, diethanolamine, malic acid, isonicotinic acid, and ethanol. Fracturing fluid crosslinked using this agent exhibits characteristics of delayed crosslinking time, high temperature resistance, and high temperature and shear resistance. The delayed crosslinking time reaches over 400 seconds, and the high temperature and shear resistance viscosity at 220℃ can reach over 180 mPa·s.

[0012] Chinese patent CN117024478A discloses a multifunctional delayed fracturing fluid crosslinking agent and its preparation method. It is prepared by reacting tris(3-hydroxypropyl)phosphine, zirconium oxychloride and 2-amino-4,6-dihydroxypyrimidine under certain conditions, and then adjusting the pH value to 6-7 with ammonia water. Using this crosslinking agent to form a gel fracturing fluid, the crosslinking time is controllable, and the temperature resistance and shear resistance are strong. The crosslinking time can be controlled between 90s and 650s, and the temperature and shear resistance viscosity at 220℃ can reach more than 220mPa·s.

[0013] Chinese patent CN118126083B, authorized by CN118126083B, also discloses a crosslinking agent for fracturing and its preparation method. It adopts a similar technical approach to CN117024478A, which is prepared by reacting tris(3-hydroxypropyl)phosphine, zirconium tetrachloride and N,N-di(3-aminopropyl)ethyl ethylamine under certain conditions and then adjusting the pH to 7 to 8 with ammonia. The crosslinking time of the obtained crosslinking agent can be controlled between 62s and 605s. The fracturing fluid formed by using the crosslinking agent has strong temperature resistance and shear resistance.

[0014] Wang Siyu et al. from China University of Petroleum (East China) prepared a gel fracturing fluid using nonionic polyacrylamide polymer as a thickener and organozirconium crosslinking agent. The gel fracturing fluid formed by 0.5% thickener and 2.5% crosslinking agent has the characteristics of low filtration loss, easy gel breaking, and good sand suspension performance. It was tested at 90℃ for 170 seconds. -1 The viscosity remained above 50 mPa·s after 2 hours of shearing, and the core damage rate of the fracturing fluid was only 14.88% (Wang Siyu et al., Research on formulation system of organic zirconium gel fracturing fluid, Oilfield Chemistry, 2014, 31(02).

[0015] Jin Lian et al. from Yangtze University first synthesized an organozirconium crosslinking agent using zirconium oxychloride, polyol, organic ligand, complexing crosslinking agent, and high-temperature stabilizer. They then crosslinked this agent with a polyacrylamide thickener to prepare a temperature-resistant, slow-crosslinking gel fracturing fluid system. This system was tested at 150℃ for 170 seconds. -1 After 2 hours of shearing, the viscosity is greater than 50 mPa·s. Its sand-carrying capacity and filtration performance are significantly better than those of conventional guar gum fracturing fluid systems. It can achieve complete gel breaking within 1-3 hours, leaving no residue and being easy to backflow (Jin Lian et al., Preparation and performance evaluation of temperature-resistant slow-crosslinking organic zirconium gel fracturing fluid, Daily Chemical Industry, 2023, 53(03)).

[0016] The existing patents and published literature mainly use conventional crosslinking agents to form gel fracturing fluid systems, which still face problems such as insufficient crosslinking efficiency, high construction friction, and large dosage due to the single active sites of thickeners and crosslinking agents.

[0017] In summary, the gel fracturing fluid formed using existing fracturing thickeners and fracturing crosslinking agents has several drawbacks, including high dosage of fracturing thickeners and crosslinking agents, low crosslinking efficiency, poor temperature and shear resistance, poor gel breaking performance, and the lack of waterproofing and locking function after gel breaking. Summary of the Invention

[0018] This invention provides a combined gel fracturing fluid and its preparation method, which overcomes the shortcomings of the prior art. It can effectively solve the problems of existing gel fracturing fluids, such as large dosage of fracturing thickener and fracturing crosslinking agent, low crosslinking efficiency, poor temperature resistance and shear resistance, poor gel breaking performance, and lack of waterproof locking function after gel breaking.

[0019] One of the technical solutions of the present invention is achieved through the following measures: a combined gel fracturing fluid, the raw materials comprising, by weight, 100 parts of a waterproof and salt-resistant fracturing thickener, 4 to 5 parts of an emulsifier, 130 to 140 parts of mineral oil, 3 to 4 parts of a suspension stabilizer, and 3 to 4 parts of a dispersion stabilizer, and the raw materials further comprising a multi-site nano-crosslinking agent, wherein the mass ratio of the waterproof and salt-resistant fracturing thickener to the multi-site nano-crosslinking agent is 1:(0.4 to 0.6).

[0020] The following are further optimizations and / or improvements to one of the above-mentioned inventive technical solutions: The aforementioned waterproof, salt-resistant, and fracturing-resistant thickener comprises, by mass ratio, acrylamide, sodium acrylate, a salt-resistant monomer containing sulfonic acid groups, and a fluorinated monomer containing unsaturated double bonds, wherein the salt-resistant monomer containing sulfonic acid groups is one of sodium 2-acrylamido-2-methylpropanesulfonate, sodium p-acrylamidobenzenesulfonate, sodium 5-acrylamidonaphthalenesulfonate, sodium p-(methyl)-vinylbenzenesulfonate, and sodium 5-(methyl)-vinylnaphthalenesulfonate; and the fluorinated monomer containing unsaturated double bonds is one of sodium p-acrylamido-perfluorooxybenzenesulfonate, sodium p-acrylamido-perfluoroalkylbenzenesulfonate, sodium p-(methyl)-vinylperfluorooxybenzenesulfonate, sodium p-(methyl)-vinylperfluoroalkylbenzenesulfonate, sodium 2-acrylamido-2-perfluorooxypropanesulfonate, and sodium 2-acrylamido-2-perfluoroalkylpropanesulfonate.

[0021] The above-mentioned waterproof and salt-resistant fracturing thickener is obtained by the following method: The first step is to add the required amount of acrylamide, sodium acrylate and salt-resistant monomer containing sulfonic acid groups to water and mix well to obtain a mixture with a mass concentration of 15% to 30%. Adjust the pH value of the mixture and cool it to -2℃ to 2℃. The second step is to add the required amount of fluorinated monomers containing unsaturated double bonds to water and mix well to obtain an aqueous solution of fluorinated monomers containing unsaturated double bonds with a mass concentration of 0.5% to 1.5%. The aqueous solution of fluorinated monomers containing unsaturated double bonds is then cooled to -2°C to 2°C. The third step involves adding an aqueous initiator solution and an aqueous solution of a fluorinated monomer containing unsaturated double bonds to the mixture to initiate the polymerization reaction for 4 to 6 hours, thereby obtaining a colloidal product. The mass concentration of the aqueous initiator solution is 2.0% to 2.5%, and the volume ratio of the initiator in the aqueous initiator solution to the mixture is 1:250 to 350. The initiator in the aqueous initiator solution is a mixture of sodium bisulfite, sodium persulfate, and cerium ammonium sulfate in a volume ratio of 1:1.0 to 1.4:0.10 to 0.15. The fourth step involves chopping, drying, pulverizing, and sieving the colloidal product to obtain a waterproof, salt-resistant, and fracturing-resistant thickener.

[0022] The above-mentioned multi-site nano-crosslinking agent raw materials include silane coupling agents, graphene oxide, amino acids, multi-component organic compounds and zirconium salts, wherein the mass ratio of silane coupling agent to graphene oxide is 1:(0.3 to 0.6).

[0023] The aforementioned silane coupling agent is one or more of methyltrimethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, and ethyltriethoxysilane.

[0024] The above-mentioned amino acid is one of glycine, aminoacetic acid, α-aminopropionic acid, and γ-aminobutyric acid.

[0025] The aforementioned multi-component organic compounds are polyols or polyacids. The polyols are one or more of glycerol, 1,3-propylene glycol, sorbitol, and xylitol, and the polyacids are one or more of lactic acid, citric acid, phosphoric acid, sodium lactate, sodium citrate, and sodium phosphate.

[0026] The aforementioned metallic zirconium salt is one or more of zirconium oxychloride, zirconium tetrachloride, zirconium sulfate, and zirconium nitrate.

[0027] The above-mentioned multi-site nano-crosslinking agent is obtained by the following method: S1, graphene oxide is uniformly dispersed in an aqueous ethanol solution with a mass concentration of 90% to 95%, and silane coupling agent is added and stirred. After reflux reaction at 60°C to 70°C for 5 to 7 hours, a mixture is obtained. The mixture is then cooled, washed, filtered and dried to obtain an intermediate. S2, add water to the intermediate and ultrasonically disperse for 1 to 2 hours, then add amino acids and stir. Reflux at 70 to 75°C for 6 to 7 hours to obtain the reaction product. Cool the reaction product to room temperature and let it stand, then centrifuge for 20 to 40 minutes. Take the supernatant, wash and dry it to obtain modified graphene oxide. The mass ratio of the intermediate to the amino acid is 1:(2.5 to 3.5). S3. Add zirconium salt to water and mix well. Then add multi-component organic matter and modified graphene oxide in sequence and stir to obtain a mixed solution. Adjust the pH of the mixed solution to 7.0 to 8.5 with a pH adjuster and react at 60℃ to 70℃ for 5 to 6 hours to obtain a multi-site nano-crosslinking agent. The mass ratio of zirconium salt, water, multi-component organic matter and modified graphene oxide is 1:(4.0 to 5.0):(0.6 to 0.8):(1.2 to 1.5). The pH adjuster is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate and sodium carbonate.

[0028] The emulsifiers mentioned above are one or more of Span 60, Span 80, Tween 20 and Tween 40.

[0029] The aforementioned mineral oil is one or more of No. 5 white oil, No. 10 white oil, and No. 15 white oil.

[0030] The aforementioned suspension stabilizer is one or more of organically modified bentonite, organically modified attapulgite, and organically modified nanocellulose.

[0031] The aforementioned dispersant and stabilizer is one or more of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

[0032] The above-mentioned combined gel fracturing fluid is obtained by the following method: First, mix the required amount of mineral oil and emulsifier evenly, then add the required amount of suspension stabilizer and mix evenly, then add the required amount of dispersant stabilizer and mix evenly, and finally add the required amount of waterproof and salt-resistant fracturing thickener to obtain a suspension emulsion type waterproof and salt-resistant fracturing thickener. Then, the suspension emulsion type waterproof lock salt-resistant fracturing thickener was mixed with water to obtain an aqueous solution of suspension emulsion type waterproof lock salt-resistant fracturing thickener with a mass concentration of 0.6% to 0.8%. Finally, after mixing the aqueous solution of the suspension emulsion-type waterproof and salt-resistant fracturing thickener with a mass concentration of 0.5% to 0.6% and the required amount of multi-site nano-crosslinking agent, a combined gel fracturing fluid is obtained.

[0033] The second technical solution of the present invention is achieved through the following measures: a method for preparing a combined gel fracturing fluid, which is carried out according to the following method: First, mix the required amount of mineral oil and emulsifier evenly, then add the required amount of suspension stabilizer and mix evenly, then add the required amount of dispersant stabilizer and mix evenly, and finally add the required amount of waterproof and salt-resistant fracturing thickener to obtain a suspension emulsion type waterproof and salt-resistant fracturing thickener. Then, after adding water to the suspension emulsion type waterproof lock salt-resistant fracturing thickener and stirring evenly, an aqueous solution with a mass concentration of 0.6% to 0.8% of the suspension emulsion type waterproof lock salt-resistant fracturing thickener is obtained; Finally, after mixing the aqueous solution of the suspension emulsion-type waterproof and salt-resistant fracturing thickener with a mass concentration of 0.5% to 0.6% and the required amount of multi-site nano-crosslinking agent evenly, a combined gel fracturing fluid is obtained.

[0034] In the combined gel fracturing fluid of this invention, the raw material, a waterproof and salt-resistant fracturing thickener, exhibits stable high viscosity and excellent viscosity performance. This is because a fluorine-substituted monomer containing unsaturated double bonds is introduced into the waterproof and salt-resistant fracturing thickener, giving it the dual functions of thickening before gel breaking and waterproofing after gel breaking. Simultaneously, the raw material, a multi-site nano-crosslinking agent, is obtained by introducing modified graphene oxide with a two-dimensional planar structure into conventional zirconium salts, resulting in high crosslinking efficiency. Finally, the combined gel fracturing fluid, formed by the efficient synergy of the waterproof and salt-resistant fracturing thickener and the multi-site nano-crosslinking agent, possesses good salt resistance, temperature resistance, shear resistance, gel breaking performance, and waterproofing after gel breaking. Detailed Implementation

[0035] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0036] The present invention will be further described below with reference to embodiments: Example 1: The combined gel fracturing fluid comprises, by weight, 100 parts of waterproof and salt-resistant fracturing thickener, 4 to 5 parts of emulsifier, 130 to 140 parts of mineral oil, 3 to 4 parts of suspension stabilizer, and 3 to 4 parts of dispersion stabilizer. The raw materials also include a multi-site nano-crosslinking agent. The mass ratio of the waterproof and salt-resistant fracturing thickener to the multi-site nano-crosslinking agent is 1:(0.4 to 0.6).

[0037] Example 2: As an optimization of the above example, the raw materials for the waterproof and salt-resistant fracturing thickener include acrylamide, sodium acrylate, a salt-resistant monomer containing sulfonic acid groups, and a fluorinated monomer containing unsaturated double bonds in a mass ratio of 1:0.18 to 0.32:0.01 to 0.1:0.002 to 0.006. The salt-resistant monomer containing sulfonic acid groups is one of sodium 2-acrylamido-2-methylpropanesulfonate, sodium p-acrylamidobenzenesulfonate, sodium 5-acrylamidonaphthalenesulfonate, sodium p-(methyl)-vinylbenzenesulfonate, and sodium 5-(methyl)-vinylnaphthalenesulfonate. The fluorinated monomer containing unsaturated double bonds is one of sodium p-acrylamido-perfluorooxybenzenesulfonate, sodium p-acrylamido-perfluoroalkylbenzenesulfonate, sodium p-(methyl)-vinylperfluorooxybenzenesulfonate, sodium p-(methyl)-vinylperfluoroalkylbenzenesulfonate, sodium 2-acrylamido-2-perfluorooxypropanesulfonate, and sodium 2-acrylamido-2-perfluoroalkylpropanesulfonate.

[0038] Example 3: As an optimization of the above examples, a waterproof, salt-resistant fracturing thickener was obtained by the following method: The first step is to add the required amount of acrylamide, sodium acrylate and salt-resistant monomer containing sulfonic acid groups to water and mix well to obtain a mixture with a mass concentration of 15% to 30%. Adjust the pH value of the mixture and cool it to -2℃ to 2℃. The second step is to add the required amount of fluorinated monomers containing unsaturated double bonds to water and mix well to obtain an aqueous solution of fluorinated monomers containing unsaturated double bonds with a mass concentration of 0.5% to 1.5%. The aqueous solution of fluorinated monomers containing unsaturated double bonds is then cooled to -2°C to 2°C. The third step involves adding an aqueous initiator solution and an aqueous solution of a fluorinated monomer containing unsaturated double bonds to the mixture to initiate the polymerization reaction for 4 to 6 hours, thereby obtaining a colloidal product. The mass concentration of the aqueous initiator solution is 2.0% to 2.5%, and the volume ratio of the initiator in the aqueous initiator solution to the mixture is 1:250 to 350. The initiator in the aqueous initiator solution is a mixture of sodium bisulfite, sodium persulfate, and cerium ammonium sulfate in a volume ratio of 1:1.0 to 1.4:0.10 to 0.15. The fourth step involves chopping, drying, pulverizing, and sieving the colloidal product to obtain a waterproof, salt-resistant, and fracturing-resistant thickener. The salt-resistant monomer containing sulfonic acid groups is one or more of acrylamide short-chain alkyl sulfonic acid / sulfonate and unsaturated sulfonic acid / sulfonate monomers containing rigid groups.

[0039] The structural formula of the salt-resistant monomer of acrylamide short-chain alkyl sulfonic acid / sulfonate is: Where n is an integer from 1 to 3; The structural formula of the salt-resistant monomer of unsaturated sulfonic acid / sulfonate containing rigid groups is: Where n is an integer between 0 and 1.

[0040] The structural formula of a fluorine-substituted monomer containing an unsaturated double bond is: Where m is an integer from 0 to 1, and n is an integer from 4 to 9.

[0041] Example 4: As an optimization of the above examples, the raw materials for the multi-site nano-crosslinking agent include silane coupling agent, graphene oxide, amino acids, multi-component organic compounds and zirconium salts, wherein the mass ratio of silane coupling agent to graphene oxide is 1:(0.3 to 0.6).

[0042] Example 5: As an optimization of the above examples, the silane coupling agent is one or more of methyltrimethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, and ethyltriethoxysilane.

[0043] Example 6: As an optimization of the above examples, the amino acid is one of glycine, aminoacetic acid, α-aminopropionic acid and γ-aminobutyric acid.

[0044] Example 7: As an optimization of the above examples, the multi-component organic compound is a polyol or a polyacid. The polyol is one or more of glycerol, 1,3-propanediol, sorbitol and xylitol, and the polyacid is one or more of lactic acid, citric acid, phosphoric acid, sodium lactate, sodium citrate and sodium phosphate.

[0045] Example 8: As an optimization of the above examples, the metallic zirconium salt is one or more of zirconium oxychloride, zirconium tetrachloride, zirconium sulfate, and zirconium nitrate.

[0046] Example 9: As an optimization of the above examples, a multi-site nano-crosslinking agent was obtained according to the following method: S1. Graphene oxide is uniformly dispersed in an aqueous ethanol solution with a mass concentration of 90% to 95%. A silane coupling agent is then added and stirred. The mixture is refluxed at 60°C to 70°C for 5 to 7 hours to obtain a mixture. The mixture is then subjected to cooling, washing, filtration, and drying to obtain an intermediate with the following structural formula: S2, the intermediate was ultrasonically dispersed with water for 1 to 2 hours, then amino acids were added and stirred. The mixture was refluxed at 70 to 75°C for 6 to 7 hours to obtain the reaction product. The reaction product was cooled to room temperature and allowed to stand, then centrifuged for 20 to 40 minutes. The supernatant was collected, washed, and dried to obtain modified graphene oxide. The mass ratio of the intermediate to the amino acids was 1:(2.5 to 3.5). The structural formula of the modified graphene oxide is: The structural formula for R is: ; S3. Add zirconium salt to water and mix well. Then add multi-component organic matter and modified graphene oxide in sequence and stir to obtain a mixed solution. Adjust the pH of the mixed solution to 7.0 to 8.5 with a pH adjuster and react at 60℃ to 70℃ for 5 to 6 hours to obtain a multi-site nano-crosslinking agent. The mass ratio of zirconium salt, water, multi-component organic matter and modified graphene oxide is 1:(4.0 to 5.0):(0.6 to 0.8):(1.2 to 1.5). The pH adjuster is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate and sodium carbonate.

[0047] Example 10: As an optimization of the above examples, the emulsifier is one or more of Span 60, Span 80, Tween 20 and Tween 40.

[0048] Example 11: As an optimization of the above example, the mineral oil is one or more of No. 5 white oil, No. 10 white oil and No. 15 white oil.

[0049] Example 12: As an optimization of the above examples, the suspension stabilizer is one or more of organic modified bentonite, organic modified attapulgite, and organic modified nanocellulose.

[0050] Example 13: As an optimization of the above examples, the dispersant stabilizer is one or more of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

[0051] Example 14: As an optimization of the above examples, a combined gel fracturing fluid was obtained according to the following method: First, mix the required amount of mineral oil and emulsifier evenly, then add the required amount of suspension stabilizer and mix evenly, then add the required amount of dispersant stabilizer and mix evenly, and finally add the required amount of waterproof and salt-resistant fracturing thickener to obtain a suspension emulsion type waterproof and salt-resistant fracturing thickener. Then, the suspension emulsion type waterproof lock salt-resistant fracturing thickener was mixed with water to obtain an aqueous solution of suspension emulsion type waterproof lock salt-resistant fracturing thickener with a mass concentration of 0.6% to 0.8%. Finally, after mixing the aqueous solution of the suspension emulsion-type waterproof and salt-resistant fracturing thickener with a mass concentration of 0.5% to 0.6% and the required amount of multi-site nano-crosslinking agent, a combined gel fracturing fluid is obtained.

[0052] Compared with existing technologies, the composite gel fracturing fluid of this invention features a stable and high viscosity with excellent viscosity performance in its raw material, a waterproof and salt-resistant fracturing thickener. This is because the thickener incorporates fluorine-substituted monomers with unsaturated double bonds, giving it a dual function of thickening before gel breaking and waterproofing after gel breaking. Simultaneously, the raw material multi-site nano-crosslinking agent is obtained by introducing modified graphene oxide with a two-dimensional planar structure into conventional zirconium salts, resulting in high crosslinking efficiency. Finally, the composite gel fracturing fluid, formed by the efficient synergy of the waterproof and salt-resistant fracturing thickener and the multi-site nano-crosslinking agent, exhibits high viscosity performance at 50000 mg / L mineralization (calcium and magnesium ion content 5000 mg / L). The addition of 0.6% to 0.8% of the waterproof and salt-resistant fracturing thickener and 0.24% to 0.48% of the multi-site nano-crosslinking agent creates a gel fracturing fluid that, at 240°C, achieves high viscosity. o C, 170s -1 After shearing for 2 hours under the specified conditions, the viscosity was 65 mPa·s, the surface tension of the gelling liquid was as low as 18.5 mN / m, and the oil / water interfacial tension was as low as 0.4568 mN / m, which reduced the wetting angle of the hydrophilic surface from 55.4°. o Change to 91.3 o Therefore, the combined gel fracturing fluid of the present invention has good salt resistance, temperature resistance, shear resistance and gel breaking performance.

[0053] Example 15: This waterproof, salt-resistant fracturing thickener comprises acrylamide, sodium acrylate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-acrylamido-perfluorooxybenzenesulfonate in a mass ratio of 1:0.18:0.01:0.005, and is obtained by the following method: First, add the required amounts of acrylamide, sodium acrylate, and sodium 2-acrylamido-2-methylpropanesulfonate to water and mix well to obtain a mixture with a mass concentration of 24%. Adjust the pH of the mixture to 9 with sodium bicarbonate aqueous solution and cool it to 0℃. The second step is to add the required amount of sodium p-acrylamido-perfluorooxybenzenesulfonate to the water and mix well to obtain an aqueous solution of sodium p-acrylamido-perfluorooxybenzenesulfonate with a mass concentration of 1.0%. The aqueous solution of sodium p-acrylamido-perfluorooxybenzenesulfonate is then cooled to 0°C. The third step involves adding an aqueous initiator solution and an aqueous solution of sodium p-acrylamido-perfluorooxybenzenesulfonate to the mixture to initiate the polymerization reaction for 4 hours, thereby obtaining a colloidal product. The mass concentration of the aqueous initiator solution is 2.0%, and the volume ratio of the initiator in the aqueous initiator solution to the mixture is 1:300. The initiator in the aqueous initiator solution is a mixture of sodium bisulfite, sodium persulfate, and cerium ammonium sulfate in a volume ratio of 1:1.2:0.12. The fourth step involves cutting the colloidal product into particles of approximately 5mm, drying, pulverizing, and sieving through an 80-mesh sieve to obtain a waterproof, salt-resistant fracturing thickener with a mesh size ≥ 80, labeled FSSKY-1. The viscosity-average molecular weight of the waterproof, salt-resistant fracturing thickener FSSKY-1 obtained in Example 15 was determined to be 19.1 million Daltons using an Ubbelohde viscometer (0.55mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0054] Example 16: The procedure was carried out according to Example 15, except that the mass ratio of acrylamide, sodium acrylate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-acrylamido-perfluorooxybenzenesulfonate was 1:0.18:0.1:0.002 to obtain a waterproof, salt-resistant fracturing thickener FSSKY-2 with a mesh size ≥80. The viscosity-average molecular weight of the waterproof, salt-resistant fracturing thickener FSSKY-2 obtained in Example 2 was determined to be 18.65 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0055] Example 17: The procedure was carried out according to Example 15, except that the mass ratio of acrylamide, sodium acrylate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-acrylamido-perfluorooxybenzenesulfonate was 1:0.18:0.01:0.006 to obtain a waterproof, salt-resistant fracturing thickener FSSKY-3 with a mesh size ≥80. The viscosity-average molecular weight of the waterproof, salt-resistant fracturing thickener FSSKY-3 obtained in Example 3 was determined to be 19.13 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0056] Example 18: The procedure was carried out according to Example 15, except that the mass ratio of acrylamide, sodium acrylate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-acrylamido-perfluorooxybenzenesulfonate was 1:0.18:0.1:0.006 to obtain a waterproof, salt-resistant fracturing thickener FSSKY-4 with a mesh size ≥80. The viscosity-average molecular weight of the waterproof, salt-resistant fracturing thickener FSSKY-4 obtained in Example 4 was determined to be 18.14 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0057] Example 19: The procedure was carried out according to Example 15, except that the mass ratio of acrylamide, sodium acrylate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-acrylamido-perfluorooxybenzenesulfonate was 1:0.32:0.01:0.002 to obtain a waterproof, salt-resistant fracturing thickener FSSKY-5 with a mesh size ≥80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant fracturing thickener FSSKY-5 obtained in Example 5 was determined to be 17.68 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0058] Example 20: The procedure was carried out according to Example 15, except that the mass ratio of acrylamide, sodium acrylate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-acrylamido-perfluorooxybenzenesulfonate was 1:0.32:0.01:0.006 to obtain a waterproof, salt-resistant fracturing thickener FSSKY-6 with a mesh size ≥80. The viscosity-average molecular weight of the waterproof, salt-resistant fracturing thickener FSSKY-6 obtained in Example 6 was determined to be 16.83 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0059] Example 21: The procedure was carried out according to Example 15, except that the mass ratio of acrylamide, sodium acrylate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-acrylamido-perfluorooxybenzenesulfonate was 1:0.32:0.1:0.002 to obtain a waterproof, salt-resistant fracturing thickener FSSKY-7 with a mesh size ≥80. The viscosity-average molecular weight of the waterproof, salt-resistant fracturing thickener FSSKY-7 obtained in Example 7 was determined to be 17.21 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0060] Example 22: The procedure was carried out according to Example 15, except that the mass ratio of acrylamide, sodium acrylate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-acrylamido-perfluorooxybenzenesulfonate was 1:0.32:0.1:0.006 to obtain a waterproof, salt-resistant fracturing thickener FSSKY-8 with a mesh size ≥80. The viscosity-average molecular weight of the waterproof, salt-resistant fracturing thickener FSSKY-8 obtained in Example 8 was determined to be 16.45 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0061] Example 23: The procedure was carried out according to Example 15, except that sodium 2-acrylamido-2-methylpropanesulfonate was replaced with sodium p-acrylamidobenzenesulfonate, resulting in a waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-9 with a mesh size ≥ 80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-9 obtained in Example 9 was determined to be 18.79 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0062] Example 24: The procedure was carried out according to Example 15, except that sodium 2-acrylamido-2-methylpropanesulfonate was replaced with sodium 5-acrylamidonaphthalenesulfonate, resulting in a waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-10 with a mesh size ≥ 80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-10 obtained in Example 10 was determined to be 17.84 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0063] Example 25: The procedure was carried out according to Example 15, except that sodium 2-acrylamido-2-methylpropanesulfonate was replaced with sodium p-(methyl)-vinylbenzenesulfonate to obtain a waterproof, salt-resistant, and fracturing thickener FSSKY-11 with a mesh size ≥ 80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant, and fracturing thickener FSSKY-11 obtained in Example 11 was determined to be 18.27 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0064] Example 26: The procedure was carried out according to Example 15, except that sodium 2-acrylamido-2-methylpropanesulfonate was replaced with sodium 5-(methyl)-vinylnaphthalenesulfonate, resulting in a waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-12 with a mesh size ≥ 80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-12 obtained in Example 12 was determined to be 16.78 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0065] Example 27: The procedure was carried out according to Example 15, except that sodium p-acrylamido-perfluorooxybenzenesulfonate was replaced with sodium p-(methyl)-vinylperfluorooxybenzenesulfonate, resulting in a waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-13 with a mesh size ≥ 80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-13 obtained in Example 13 was determined to be 18.36 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0066] Example 28: The procedure was carried out according to Example 15, except that sodium p-acrylamido-perfluorooxybenzenesulfonate was replaced with sodium 2-acrylamido-2-perfluorooxypropanesulfonate, resulting in a waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-14 with a mesh size ≥ 80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-14 obtained in Example 14 was determined to be 19.5 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0067] Example 29: The procedure was carried out according to Example 24, except that sodium p-acrylamido-perfluorooxybenzenesulfonate was replaced with sodium p-(methyl)-vinylperfluorooxybenzenesulfonate, resulting in a waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-15 with a mesh size ≥ 80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-15 obtained in Example 15 was determined to be 16.47 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0068] Example 30: The procedure was carried out according to Example 24, except that sodium p-acrylamido-perfluorooxybenzenesulfonate was replaced with sodium 2-acrylamido-2-perfluorooxypropanesulfonate, resulting in a waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-16 with a mesh size ≥ 80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-16 obtained in Example 16 was determined to be 16.95 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0069] Example 31: The procedure was followed according to Example 22, except that sodium 2-acrylamido-2-methylpropanesulfonate was replaced with sodium p-(methyl)-vinylbenzenesulfonate, and sodium acrylamide-perfluorooxybenzenesulfonate was replaced with sodium p-(methyl)-vinylperfluorooxybenzenesulfonate, resulting in a waterproof, salt-resistant fracturing thickener FSSKY-17 with a mesh size ≥ 80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant fracturing thickener FSSKY-17 obtained in Example 17 was determined to be 15 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0070] Example 32: The procedure was carried out according to Example 22, except that sodium 2-acrylamido-2-methylpropanesulfonate was replaced with sodium p-(methyl)-vinylbenzenesulfonate, and sodium acrylamide-perfluorooxybenzenesulfonate was replaced with sodium 2-acrylamido-2-perfluorooxypropanesulfonate, resulting in a waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-18 with a mesh size ≥ 80 mesh. The viscosity-average molecular weight of the waterproof, salt-resistant, and fracturing-resistant thickener FSSKY-18 obtained in Example 18 was determined to be 15.76 million Daltons using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the standard GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide".

[0071] Example 33: This multi-site nano-crosslinking agent was obtained by the following method: S1, 0.6 g of graphene oxide was ultrasonically dispersed in a 95% ethanol aqueous solution for 2 h, and 2.0 g of silane coupling agent (methyltrimethoxysilane) was added and stirred. After reflux reaction at 65 °C for 6 h, a mixture was obtained. The mixture was cooled to room temperature, washed with acetone and vacuum filtered 3 times, and dried at 70 °C for 15 h to obtain an intermediate. S2, 0.5g of intermediate was ultrasonically dispersed in water for 1h, and then 1.2g of amino acid (glycine) was added dropwise and stirred. The mixture was refluxed at 70℃ for 6h to obtain the reaction product. The reaction product was cooled to room temperature and allowed to stand for 10h. After centrifugation at 1500r / min for 20min, the supernatant was taken. The supernatant was washed twice with 65% ethanol aqueous solution and water and filtered to obtain modified graphene oxide. The mass ratio of intermediate to amino acid was 1:(2.5 to 3.5). S3, add 18g of metallic zirconium salt (zirconium oxychloride) to 90g of water and stir for 5min, then add multi-component organic matter (glycerol) and continue stirring for 5min, then add 24g of modified graphene oxide and stir for 5min to obtain a mixed solution. Adjust the pH of the mixed solution to 7.5 with a pH adjuster (sodium hydroxide) and react at 65℃ for 6h to obtain a multi-site nano-crosslinking agent, labeled as DWDJL-1.

[0072] Example 34: The difference between this multi-site nano-crosslinking agent and Example 33 of the present invention is that the raw material "silane coupling agent (methyltrimethoxysilane)" is modified to "silane coupling agent (ethyltriethoxysilane)". The remaining steps are the same, and the multi-site nano-crosslinking agent is obtained and labeled as DWDJL-2.

[0073] Example 35: The difference between this multi-site nano-crosslinking agent and Example 33 of the present invention is that the raw material "amino acid (glycine)" is changed to "amino acid (γ-aminobutyric acid)", while the other steps are the same, and the multi-site nano-crosslinking agent is obtained and labeled as DWDJL-3.

[0074] Example 36: The difference between this multi-site nano-crosslinking agent and Example 33 of the present invention is that the raw material "multi-organic compound (glycerol)" is changed to "multi-organic compound (lactic acid)", while the rest of the steps are the same, and the multi-site nano-crosslinking agent is obtained and labeled as DWDJL-4.

[0075] Example 37: The difference between this multi-site nano-crosslinking agent and Example 33 of the present invention is that the raw material "multi-component organic compound (glycerol)" is modified to "multi-component organic compound (a mixture of glycerol and lactic acid in a mass ratio of 1:1)". The remaining steps are the same, and the multi-site nano-crosslinking agent is obtained and labeled as DWDJL-5.

[0076] Example 38: This combined gel fracturing fluid is obtained according to the following method: First, 139g of mineral oil (10# white oil) and 4.6g of emulsifier (Span 60) were mixed and stirred under strong stirring for 20 minutes. Then, 3.2g of suspension stabilizer (organic modified bentonite YJT-601, purchased from Korla Tongyi Industry and Trade Co., Ltd.) was added and dispersed and stirred for 25 minutes. Next, 3.2g of dispersion stabilizer (fatty alcohol polyoxyethylene ether) was added and stirred for 40 minutes. Finally, 100g of the waterproof and salt-resistant fracturing thickener (FSSKY-1) prepared in Example 15 of this invention was slowly added and stirred for 1 hour to obtain a suspension emulsion type waterproof and salt-resistant fracturing thickener. Then, the suspension emulsion type waterproof lock salt-resistant fracturing thickener was added to water and stirred for 2 minutes to obtain an aqueous solution with a mass concentration of 0.6% for the suspension emulsion type waterproof lock salt-resistant fracturing thickener. Finally, 100g of an aqueous solution of a suspension emulsion-type waterproof and salt-resistant fracturing thickener with a mass concentration of 0.6% and 0.24g of the multi-site nano-crosslinking agent (DWDJL-1) prepared in Example 33 of this invention were mixed to obtain a combined gel fracturing fluid, labeled as DJYLY-1.

[0077] Example 39: The combined gel fracturing fluid was prepared according to the method of Example 38, except that the multi-active site nano-crosslinking agent was replaced with DWDJL-4 to obtain the combined gel fracturing fluid, labeled as DJYLY-2.

[0078] Example 40: The combined gel fracturing fluid was prepared according to the method of Example 38, except that the multi-active site nano-crosslinking agent was replaced with DWDJL-5 to obtain the combined gel fracturing fluid, labeled as DJYLY-3.

[0079] Example 41: The combined gel fracturing fluid was prepared according to the method of Example 40, except that the effective mass concentration of the waterproof and salt-resistant fracturing thickener was changed to 0.8%, and the amount of the multi-active site nano-crosslinking agent was changed to 0.48g, resulting in the combined gel fracturing fluid labeled DJYLY-4.

[0080] Comparative Example 1: The fracturing thickener differs from that in Example 15 of this invention in that it does not contain fluorine-substituted monomers with unsaturated double bonds in the raw materials, while the other steps are the same, and it is labeled as DKY-1.

[0081] Comparative Example 2: The fracturing thickener differs from that in Example 22 of this invention in that it does not contain fluorine-substituted monomers with unsaturated double bonds in the raw materials, while the other steps are the same, and it is labeled as DKY-2.

[0082] Comparative Example 3: The fracturing thickener differs from that in Example 31 of this invention in that it does not contain fluorine-substituted monomers with unsaturated double bonds in the raw materials, while the other steps are the same, and it is labeled as DKY-3.

[0083] Comparative Example 4: The fracturing thickener differs from that in Example 32 of this invention in that it does not contain fluorine-substituted monomers with unsaturated double bonds in the raw materials, while the other steps are the same, and it is labeled as DKY-4.

[0084] Comparative Example 5: The fracturing crosslinking agent differs from that in Example 37 of this invention in that it does not contain modified graphene oxide. Specifically, 18g of metallic zirconium salt (zirconium oxychloride) is added to 90g of water and stirred for 5min. Then, a multi-component organic compound (glycerol) is added and stirred for another 5min to obtain a mixed solution. The pH of the mixed solution is adjusted to 7.5 using a pH adjuster (sodium hydroxide), and then reacted at 65°C for 6h to obtain the fracturing crosslinking agent. The remaining steps are the same, and it is labeled as DJL-1.

[0085] Comparative Example 6: The difference between this gel fracturing fluid and Example 38 of the present invention is that the raw material "waterproof and salt-resistant fracturing thickener FSSKY-1 prepared in Example 15 of the present invention" is replaced with "fracturing thickener DKY-4 prepared in Comparative Example 1", while the other steps remain unchanged.

[0086] Comparative Example 7: The difference between this gel fracturing fluid and Example 38 of the present invention is that the raw material "multi-site nano-crosslinking agent DWDJL-1 prepared in Example 33 of the present invention" is replaced with "fracturing crosslinking agent DJL-1 prepared in Comparative Example 5", while the other steps remain unchanged.

[0087] Comparative Example 8: The difference between this gel fracturing fluid and Example 41 of the present invention is that the raw material "multi-site nano-crosslinking agent DWDJL-1 prepared in Example 33 of the present invention" is replaced with "fracturing crosslinking agent DJL-1 prepared in Comparative Example 5", while the other steps remain unchanged.

[0088] Experimental Example 1: The performance of the waterproof and salt-resistant fracturing thickener of the present invention was investigated.

[0089] Experimental methods: The performance of the waterproof and salt-resistant fracturing thickeners prepared in Examples 15 to 32 of this invention was investigated. The performance included tackification time, viscosity release rate, and viscosity. Comparative Examples 1 to 4 were used as controls.

[0090] Specifically, the tack-on time is determined by placing the waterproof and salt-resistant fracturing thickener prepared in Examples 15 to 32 of this invention into a beaker containing brine (total mineralization 100,000 mg / L, of which calcium and magnesium ion content is 8,000 mg / L), and preparing a brine solution of the waterproof and salt-resistant fracturing thickener with a mass concentration of 0.6% and 0.8%. The solution is then stirred and dissolved at room temperature using a high-speed stirrer at a speed of 400 ± 50 r / min. The solution is then picked up with a glass rod and a string is drawn out. The corresponding time is recorded as the tack-on time.

[0091] Viscosity and viscosity release rate are specifically determined by mixing a 0.6% and 0.8% (by mass) water solution of a waterproof, salt-resistant, and fracturing thickener with these concentrations using a six-speed rotary viscometer at 100 r / min (170 s). -1 The viscosity values ​​were tested at different dissolution times to calculate the viscosity release rate.

[0092] Experimental Results: The performance of the waterproof, salt-resistant fracturing thickener of the present invention is shown in Table 1. As can be seen from Table 1, the thickeners (FSSKY-1, FSSKY-3, FSSKY-4, FSSKY-9, FSSKY-11, FSSKY-13, and FSSKY-14) prepared by introducing fluorine-substituted monomers containing unsaturated double bonds in Examples 15, 17, 18, 23, 25, 27, and 28, respectively, showed significantly higher stable viscosities at thickener additions of 0.6% and 0.8% compared to the fracturing thickeners (DKY-1, DKY-2, DKY-3, and DKY-4, without the introduction of fluorine-substituted monomers containing unsaturated double bonds) prepared in Comparative Examples 1 to 4. This indicates that the waterproof, salt-resistant fracturing thickeners prepared in Examples 15 to 32 of the present invention have higher stable viscosities and excellent thickening properties.

[0093] Experimental Example 2: The performance of the multi-site nano-crosslinking agent of the present invention was investigated.

[0094] Experimental Methods: The crosslinking performance of the multi-site nano-crosslinking agents prepared in Examples 33 to 37 of this invention was investigated. Specifically, at 90°C, 100g of saline solutions (total mineralization of the saline solution was 100,000 mg / L, with calcium and magnesium ion content of 8,000 mg / L) containing 0.6% and 0.8% of the waterproof, salt-locking, and anti-fracture thickener prepared in Examples 15 to 32 of this invention, respectively, were mixed with 0.24g to 0.48g of the multi-site nano-crosslinking agents prepared in Examples 33 to 37 of this invention. The gel strength was determined by visually inspecting the gel using a glass rod and observing the gel strength code method to evaluate the crosslinking performance. Comparative Example 5 was used as a control.

[0095] Experimental Results: The crosslinking properties of the multi-site nano-crosslinking agents prepared in Examples 33 to 37 of this invention are shown in Table 2. In Table 2, A is a non-probe gel, B is a high-flow gel, C is a flow gel, D is a medium-flow gel, E is a nearly non-flow gel, F is a high-deformation non-flow gel, G is a medium-deformation non-flow gel, H is a slightly-deformation non-flow gel, and I is a rigid gel. As can be seen from Table 2, the multi-site nano-crosslinking agents (DWDJ) prepared in Examples 33, 36, and 37 after introducing modified graphene oxide... The crosslinked gels formed by the multi-site nano-crosslinking agent (DJL-1, DWDJL-4, DWDJL-5) with 0.6% and 0.8% waterproof and salt-resistant fracturing thickeners showed significantly greater strength than the gels formed by the multi-site nano-crosslinking agent (DJL-1, without modified graphene oxide) prepared in Comparative Example 5. Meanwhile, the crosslinked gels formed by the multi-site nano-crosslinking agent (DWDJL-5) obtained by simultaneously introducing glycerol and lactic acid in Example 37 with 0.6% and 0.8% waterproof and salt-resistant fracturing thickeners showed significantly stronger strength.

[0096] Experimental Example 3: The performance of the combined gel fracturing fluid of the present invention was investigated.

[0097] Experimental methods: The performance of the combined gel fracturing fluids prepared in Examples 38 to 41 of this invention was investigated, including temperature resistance, shear strength, and gel breaking performance. Comparative Examples 6 to 8 were used as controls.

[0098] The temperature resistance and shear strength properties were specifically tested using an RS6000 advanced rheometer PZ38 coaxial cylindrical rotor system at 180℃ (or 240℃) and 170s. -1 The combined gel fracturing fluids prepared in Examples 38 to 41 of this invention were subjected to temperature resistance and shear resistance tests. The viscosity change curve over time was recorded and the final stable viscosity value was recorded. The duration from heating to the end of the test was 2 hours.

[0099] Specifically, the gel breaking performance was tested by weighing 100g of the combined gel fracturing fluid prepared in Examples 38 to 41 of this invention and placing it into a metal sealed container, adding 0.05% ammonium persulfate, sealing and aging at 180°C for different times, and then taking it out. The viscosity, surface tension, oil / water interfacial tension and residue content of the gel breaking fluid were tested according to the industry standard SY / T 5107-2016 "Performance Evaluation Method of Water-based Fracturing Fluid". Among them, the viscosity, surface tension, oil / water interfacial tension and residue content of the gel breaking fluid were all tested at room temperature, and the oil / water interfacial tension test used kerosene as the oil phase.

[0100] Experimental results: The temperature and shear resistance properties of the combined gel fracturing fluid of the present invention are shown in Table 3. As can be seen from Table 3, the combined gel fracturing fluids prepared in Examples 33 to 37 using multi-site nano-crosslinking agents (DWDJL-1, DWDJL-4, and DWDJL-5) after introducing modified graphene oxide, with additions of 0.6% and 0.8% of waterproof and salt-resistant fracturing thickener, exhibit significantly stronger temperature and shear resistance properties than those obtained in Comparative Examples 6 to 8. This indicates that the combined gel fracturing fluid of the present invention possesses excellent temperature and shear resistance properties.

[0101] The gel breaking performance of the combined gel fracturing fluid of the present invention is shown in Table 4. The combined gel fracturing fluids prepared in Examples 33 to 37 using multi-site nano-crosslinking agents (DWDJL-1, DWDJL-4, and DWDJL-5) after introducing modified graphene oxide, with additions of 0.6% and 0.8% of waterproof and salt-resistant fracturing thickener, exhibited good gel breaking performance. The viscosity and residue content after gel breaking were comparable to those of the combined gel fracturing fluids prepared in Comparative Examples 6 to 8, while the surface tension and oil / water interfacial tension of the gel breaking fluid were significantly lower than those in Comparative Examples 6 to 8, and the contact angle was significantly higher. The lowest surface tension reached 18.5 mN / m, and the lowest oil / water interfacial tension was 0.4568 mN / m, which can reduce the wetting angle of hydrophilic surfaces from 55.4°. o Change to 91.3 o Therefore, this indicates that the combined gel fracturing fluid of the present invention has good gel-breaking performance.

[0102] In summary, the composite gel fracturing fluid of this invention features a stable, high-viscosity, and excellent thickening agent for water-locking and salt-resistant fracturing. This is because the water-locking and salt-resistant fracturing thickener incorporates fluorine-substituted monomers with unsaturated double bonds, giving it the dual functions of thickening before gel breaking and water-locking after gel breaking. Simultaneously, the multi-site nano-crosslinking agent is obtained by introducing modified graphene oxide with a two-dimensional planar structure into conventional zirconium salts, resulting in high crosslinking efficiency. Finally, the composite gel fracturing fluid, formed by the efficient synergy of the water-locking and salt-resistant fracturing thickener and the multi-site nano-crosslinking agent, exhibits good salt resistance, temperature resistance, shear resistance, gel breaking performance, and water-locking function after gel breaking.

[0103] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A combined gel fracturing fluid, characterized in that... The raw materials, by weight, include 100 parts of waterproof and salt-resistant fracturing thickener, 4 to 5 parts of emulsifier, 130 to 140 parts of mineral oil, 3 to 4 parts of suspension stabilizer, and 3 to 4 parts of dispersion stabilizer. The raw materials also include a multi-site nano-crosslinking agent. The mass ratio of the waterproof and salt-resistant fracturing thickener to the multi-site nano-crosslinking agent is 1:0.4 to 0.

6.

2. The combined gel fracturing fluid according to claim 1, characterized in that... The raw materials for the waterproof, salt-resistant, and fracturing-resistant thickener include acrylamide, sodium acrylate, a salt-resistant monomer containing sulfonic acid groups, and a fluorinated monomer containing unsaturated double bonds in a mass ratio of 1:0.18 to 0.32:0.01 to 0.1:0.002 to 0.

006. The salt-resistant monomer containing sulfonic acid groups is one of sodium 2-acrylamido-2-methylpropanesulfonate, sodium p-acrylamidobenzenesulfonate, sodium 5-acrylamidonaphthalenesulfonate, sodium p-(methyl)-vinylbenzenesulfonate, and sodium 5-(methyl)-vinylnaphthalenesulfonate. The fluorinated monomer containing unsaturated double bonds is one of sodium p-acrylamido-perfluorooxybenzenesulfonate, sodium p-acrylamido-perfluoroalkylbenzenesulfonate, sodium p-(methyl)-vinylperfluorooxybenzenesulfonate, sodium p-(methyl)-vinylperfluoroalkylbenzenesulfonate, sodium 2-acrylamido-2-perfluorooxypropanesulfonate, and sodium 2-acrylamido-2-perfluoroalkylpropanesulfonate.

3. The combined gel fracturing fluid according to claim 2, characterized in that... Waterproof and salt-resistant fracturing thickener, obtained by the following method: The first step is to add the required amount of acrylamide, sodium acrylate and salt-resistant monomer containing sulfonic acid groups to water and mix well to obtain a mixture with a mass concentration of 15% to 30%. Adjust the pH value of the mixture and cool it to -2℃ to 2℃. The second step is to add the required amount of fluorinated monomers containing unsaturated double bonds to water and mix well to obtain an aqueous solution of fluorinated monomers containing unsaturated double bonds with a mass concentration of 0.5% to 1.5%. The aqueous solution of fluorinated monomers containing unsaturated double bonds is then cooled to -2°C to 2°C. The third step involves adding an aqueous initiator solution and an aqueous solution of a fluorinated monomer containing unsaturated double bonds to the mixture to initiate the polymerization reaction for 4 to 6 hours, thereby obtaining a colloidal product. The mass concentration of the aqueous initiator solution is 2.0% to 2.5%, and the volume ratio of the initiator in the aqueous initiator solution to the mixture is 1:250 to 350. The initiator in the aqueous initiator solution is a mixture of sodium bisulfite, sodium persulfate, and cerium ammonium sulfate in a volume ratio of 1:1.0 to 1.4:0.10 to 0.

15. The fourth step involves chopping, drying, pulverizing, and sieving the colloidal product to obtain the salt-resistant fracturing thickener.

4. The combined gel fracturing fluid according to claim 1, 2, or 3, characterized in that... The raw materials for the multi-site nano-crosslinking agent include silane coupling agents, graphene oxide, amino acids, multi-component organic compounds, and zirconium salts, wherein the mass ratio of silane coupling agent to graphene oxide is 1:0.3 to 0.

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5. The combined gel fracturing fluid according to claim 4, characterized in that... The silane coupling agent is one or more of methyltrimethoxysilane, ethyltrimethoxysilane, methyltriethoxysilane, and ethyltriethoxysilane; or / and, the amino acid is one of glycine, aminoacetic acid, α-aminopropionic acid, and γ-aminobutyric acid; or / and, the polybasic organic compound is a polyol or a polyacid, the polyol is one or more of glycerol, 1,3-propanediol, sorbitol, and xylitol, and the polyacid is one or more of lactic acid, citric acid, phosphoric acid, sodium lactate, sodium citrate, and sodium phosphate; or / and, the zirconium salt is one or more of zirconium oxychloride, zirconium tetrachloride, zirconium sulfate, and zirconium nitrate.

6. The combined gel fracturing fluid according to claim 4 or 5, characterized in that... The multi-site nano-crosslinking agent was obtained by the following method: S1, graphene oxide is uniformly dispersed in an aqueous ethanol solution with a mass concentration of 90% to 95%, and silane coupling agent is added and stirred. After reflux reaction at 60°C to 70°C for 5 to 7 hours, a mixture is obtained. The mixture is then cooled, washed, filtered and dried to obtain an intermediate. S2, add water to the intermediate and ultrasonically disperse for 1 to 2 hours, then add amino acids and stir. Reflux at 70 to 75°C for 6 to 7 hours to obtain the reaction product. Cool the reaction product to room temperature and let it stand, then centrifuge for 20 to 40 minutes. Take the supernatant, wash and dry it to obtain modified graphene oxide. The mass ratio of the intermediate to the amino acid is 1:2.5 to 3.

5. S3. Add zirconium salt to water and mix well. Then add multi-component organic matter and modified graphene oxide in sequence and stir to obtain a mixed solution. Adjust the pH of the mixed solution to 7.0 to 8.5 with a pH adjuster and react at 60℃ to 70℃ for 5 to 6 hours to obtain a multi-site nano-crosslinking agent. The mass ratio of zirconium salt, water, multi-component organic matter and modified graphene oxide is 1:4.0 to 5.0:0.6 to 0.8:1.2 to 1.

5. The pH adjuster is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate and sodium carbonate.

7. The combined gel fracturing fluid according to any one of claims 1 to 6, characterized in that... The emulsifier is one or more of Span 60, Span 80, Tween 20 and Tween 40; and / or the mineral oil is one or more of No. 5 white oil, No. 10 white oil and No. 15 white oil.

8. The combined gel fracturing fluid according to any one of claims 1 to 7, characterized in that... The suspension stabilizer is one or more of organically modified bentonite, organically modified attapulgite, and organically modified nanocellulose; and / or the dispersing stabilizer is one or more of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

9. The combined gel fracturing fluid according to any one of claims 1 to 8, characterized in that... Obtained using the following method: First, mix the required amount of mineral oil and emulsifier evenly, then add the required amount of suspension stabilizer and mix evenly, then add the required amount of dispersant stabilizer and mix evenly, and finally add the required amount of waterproof and salt-resistant fracturing thickener to obtain a suspension emulsion type waterproof and salt-resistant fracturing thickener. Then, after adding water to the suspension emulsion type waterproof lock salt-resistant fracturing thickener and stirring evenly, an aqueous solution with a mass concentration of 0.6% to 0.8% of the suspension emulsion type waterproof lock salt-resistant fracturing thickener is obtained; Finally, after mixing the aqueous solution of the suspension emulsion-type waterproof and salt-resistant fracturing thickener with a mass concentration of 0.5% to 0.6% and the required amount of multi-site nano-crosslinking agent evenly, a combined gel fracturing fluid is obtained.

10. A method for preparing a combined gel fracturing fluid according to any one of claims 1 to 8, characterized in that... Perform it as follows: First, mix the required amount of mineral oil and emulsifier evenly, then add the required amount of suspension stabilizer and mix evenly, then add the required amount of dispersant stabilizer and mix evenly, and finally add the required amount of waterproof and salt-resistant fracturing thickener to obtain a suspension emulsion type waterproof and salt-resistant fracturing thickener. Then, the suspension emulsion type waterproof lock salt-resistant fracturing thickener was mixed with water to obtain an aqueous solution of suspension emulsion type waterproof lock salt-resistant fracturing thickener with a mass concentration of 0.6% to 0.8%. Finally, after mixing the aqueous solution of the suspension emulsion-type waterproof and salt-resistant fracturing thickener with a mass concentration of 0.5% to 0.6% and the required amount of multi-site nano-crosslinking agent, a combined gel fracturing fluid is obtained.

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