Hydrophobic association type acrylamide copolymer, polymer thickening agent for alcohol-based slickwater and preparation method of polymer thickening agent

Abstract

The invention relates to the technical field of oilfield chemistry, in particular to a hydrophobic association type acrylamide copolymer, a polymer thickening agent for alcohol-based slick water and a preparation method thereof.The hydrophobic association type acrylamide copolymer is prepared through the following steps that under protection of inert gas, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and long-chain alkyl acrylate are dissolved in a solvent; adding a cosolvent, stirring and mixing to obtain a first mixed solution; adding a part of the initiator into the first mixed solution, carrying out a first-stage reaction, then adding the rest of the initiator, and carrying out a second-stage reaction, so as to obtain a second mixed solution; and adding a composite regulator into the second mixed solution, adjusting the pH value of the system, stirring, and drying and crushing the product to obtain the hydrophobic association type acrylamide copolymer. The long-acting stable viscosity of the alcohol-based slick water under the conditions of high salinity and high temperature is realized, the surface tension of the gel breaking liquid and the damage rate of a rock core are low, and the gel breaking liquid is suitable for fracturing operation under the condition of a high-temperature and high-salt reservoir.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield chemistry, and provides a hydrophobically associating acrylamide copolymer and a preparation method thereof, as well as a polymer thickening agent for alcohol-based slickwater using the hydrophobically associating acrylamide copolymer as a raw material and a preparation method thereof. Background Art

[0002] Fracturing is an important technical means for the development of unconventional gas reservoirs. The performance of the fracturing fluid during the fracturing operation is an important technical guarantee for fracturing construction. With the in-depth development of unconventional oil and gas resources, the proportion of reservoirs with high temperature (>120°C) and high salinity (salinity > 15×10 4 mg / L) increases year by year. Traditional water-based fracturing fluids rely on polyacrylamide (HPAM) thickeners, but their molecular chains are prone to hydrolysis and scission at high temperatures, and divalent metal ions (such as Ca 2+ and Mg 2+ ) will compress the electric double layer, resulting in viscosity collapse (viscosity retention rate < 40% at 150°C). Although methanol-based slickwater can partially alleviate the salt sensitivity problem, it has defects such as strong volatility, high biological toxicity (LC50 < 500mg / L), and poor compatibility with formation water. Existing improvement schemes include: Chinese patent document with publication number CN118895115A discloses a modified ethylene glycol salt and sensitivity inhibition fracturing fluid system and its preparation method and application, including the following components in mass fractions: 2-acrylamide-2-methylpropanesulfonic acid 10-15%, acrylic acid 2-5%, acrylamide 5-8%, acryloyloxyethyltrimethylammonium chloride 20-50%, epoxy acrylate resin 5-10%, organic zirconium catalyst 0.1-1.0%, and modified ethylene glycol solution 50-90%, and the sum of the mass fractions of each component is 100%. It adopts an ethylene glycol-based system, which reduces the environmental protection risk, but its thickening efficiency is difficult to meet the high sand-carrying requirements of deep reservoirs, and the residual surfactant after gel breaking will increase the oil-water interfacial tension and exacerbate the blockage of reservoir pore throats.

[0003] In addition, aiming at the lack of a stable network structure with shear resistance / salt resistance in traditional linear polymers, it is necessary to construct a thermodynamically stable three-dimensional thickening system through the synergistic design of hydrophobic association and rigid groups (such as sulfonic groups). At the same time, in the face of the dual pressures of the environment and cost, using methanol-based solvents has potential safety hazards in transportation / operation, while environmentally friendly alcohols (such as isopropyl alcohol) cannot meet the on-site continuous mixing requirements due to insufficient solubility, resulting in a polymer dispersion time exceeding 5 minutes. Therefore, there is an urgent need for a thickening agent system with better high temperature resistance, salt resistance, and stability to meet the fracturing transformation requirements of high temperature and high salinity reservoirs. Summary of the Invention

[0004] The present invention provides a hydrophobic associating acrylamide copolymer, a polymer thickening agent for alcohol-based slickwater, and a preparation method thereof, which overcome the above-mentioned deficiencies of the prior art and can effectively solve the problems that the thickening system for existing fracturing fluids has poor high-temperature resistance, salt resistance and stability, and is difficult to meet the fracturing renovation requirements of high-temperature and high-salt reservoirs.

[0005] One of the technical solutions of the present invention is achieved by the following measures: A hydrophobic associating acrylamide copolymer is prepared by the following method: First step, under the protection of an inert gas, acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and long-chain alkyl acrylate are dissolved in a solvent, a cosolvent is added, and after stirring and mixing, a first mixed solution is obtained; Second step, part of the initiator is added to the first mixed solution for the first-stage reaction, and then the remaining initiator is added for the second-stage reaction to obtain a second mixed solution; Third step, a composite regulator is added to the second mixed solution to adjust the pH value of the system, and after stirring, the product is dried and pulverized to obtain a hydrophobic associating acrylamide copolymer.

[0006] The following is a further optimization or / and improvement of one of the above-mentioned invention technical solutions: The molecular weight distribution index PDI of the above-mentioned hydrophobic associating acrylamide copolymer is 1.0 to 1.8.

[0007] In the above first step, the total amount of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and long-chain alkyl acrylate and the mass ratio of the solvent is 3% to 10%; the total amount of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and long-chain alkyl acrylate and the mass ratio of the cosolvent is 1:2 to 2:1.

[0008] In the above first step, the stirring and mixing temperature is 35°C to 45°C.

[0009] In the above first step, the molar ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid to long-chain alkyl acrylate is 65 to 75:20 to 30:2 to 8, and the structural formula of the long-chain alkyl acrylate is: R is a long-chain alkyl of C12 to C18.

[0010] In the above first step, the solvent includes by mass parts: 1 to 3 parts of lower alcohol, 1 to 2 parts of polyhydroxy alcohol and 1 to 3 parts of water; wherein, the lower alcohol is methanol, ethanol or isopropanol, and the polyhydroxy alcohol is glycerol or polyethylene glycol 200.

[0011] In the first step above, the cosolvent is 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6).

[0012] In the second step above, the initiator is a mixture of ammonium persulfate and sodium bisulfite, and the total addition amount of the initiator is 0.02% to 0.05% of the total mass of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and long-chain alkyl acrylate.

[0013] In the second step above, 55% to 70% of the total mass of the initiator is added to the first mixed solution for the first-stage reaction. When the viscosity of the system reaches 80 mPa·s to 120 mPa·s, the remaining initiator is added.

[0014] In the second step above, the reaction temperature of the first-stage reaction is 45°C to 50°C, the reaction temperature of the second-stage reaction is 50°C to 60°C, and the reaction time of the second-stage reaction is 0.5 h to 2 h.

[0015] In the third step above, the composite regulator is a mixture of sodium citrate and triethanolamine, and the mass ratio of sodium citrate to triethanolamine is 1:2 to 1:4, adjusting the pH value of the system between 6.5 and 7.5.

[0016] In the third step above, vacuum low-temperature drying is adopted, the drying temperature is 45°C to 55°C, the vacuum degree is between -0.08 MPa and -0.15 MPa, and the water content of the dried product is <3%.

[0017] The second technical solution of the present invention is achieved by the following measures: A preparation method of a hydrophobically associating acrylamide copolymer is carried out according to the following steps: In the first step, under the protection of an inert gas, acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and long-chain alkyl acrylate are dissolved in a solvent, and a cosolvent is added. After stirring and mixing, a first mixed solution is obtained; In the second step, part of the initiator is added to the first mixed solution for the first-stage reaction, and then the remaining initiator is added for the second-stage reaction to obtain a second mixed solution; In the third step, a composite regulator is added to the second mixed solution to adjust the pH value of the system, and after stirring, the product is dried and pulverized to obtain a hydrophobically associating acrylamide copolymer.

[0018] The third technical solution of the present invention is achieved by the following measures: A polymer thickening agent for alcohol-based slickwater, the raw materials are composed by mass percentage: 0.1% to 5% of hydrophobically associating acrylamide copolymer, 0.1% to 1.0% of nano-silica, 50% to 85% of main alcohol solvent, 0.1% to 5% of ionic liquid cosolvent, and the rest is water.

[0019] The following is a further optimization and / or improvement of the third technical solution of the above invention: The above nano-silica is a hydrophobic nano-silicon material.

[0020] The above main alcohol solvent is a mixed solution of lower alcohols and polyhydric alcohols with a mass ratio of 3:1 to 1:2. The lower alcohol is selected from methanol, ethanol or isopropanol, and the polyhydric alcohol is glycerol or polyethylene glycol 200.

[0021] The above ionic liquid co-solvent is 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6).

[0022] The fourth technical solution of the present invention is achieved by the following measures: A preparation method of a polymer thickening agent for alcohol-based slickwater, comprising the following steps: After uniformly mixing the required amount of hydrophobic associative acrylamide copolymer and nano-silica, the main alcohol solvent, the ionic liquid co-solvent and water are added in sequence, and after stirring and mixing, a polymer thickening agent for alcohol-based slickwater is obtained.

[0023] The present invention starts from both the molecular structure and the solvent, and provides a hydrophobic associative acrylamide copolymer and a polymer thickening agent for alcohol-based slickwater. The polymer thickening agent for alcohol-based slickwater of the present invention has the functions of drag reduction, sand carrying and low damage. The alcohol-based slickwater prepared therefrom has long-term viscosity stability (viscosity > 50 mPa·s) under the conditions of 20×10 4 mg / L salinity and 150 °C, and the surface tension of the gel-breaking fluid is ≤ 28.5 mN / m, and the core damage rate is < 15%. It provides a solution with both high performance and environmental adaptability for reservoir stimulation under extreme conditions. At the same time, the alcohol-based monomers after degradation have the function of reducing water lock damage, and are especially suitable for the development of unconventional oil and gas reservoirs. Specific embodiments

[0024] The present invention is not limited by the following embodiments, and the specific implementation manners can be determined according to the technical solutions of the present invention and the actual situation. All chemical reagents and chemical supplies mentioned in the present invention are well-known and commonly used chemical reagents and chemical supplies in the prior art unless otherwise specified; the percentages in the present invention are mass percentages unless otherwise specified; the normal temperature and room temperature in the present invention generally refer to the temperature from 15 °C to 25 °C, and are generally defined as 25 °C.

[0025] The present invention will be further described below in conjunction with embodiments: Example 1: The hydrophobic associative acrylamide copolymer is prepared by the following method: In the first step, under the protection of an inert gas, acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and long-chain alkyl acrylate are dissolved in a solvent, and a co-solvent is added. After stirring and mixing, a first mixed solution is obtained; In the second step, a partial amount of initiator is added to the first mixed solution for the first-stage reaction, and then the remaining initiator is added for the second-stage reaction to obtain a second mixed solution. In the third step, a composite regulator is added to the second mixed solution to adjust the pH value of the system, followed by stirring. The product is dried and pulverized to obtain a hydrophobically associating acrylamide copolymer.

[0026] Example 2: As an optimization of the above example, the molecular weight distribution index PDI of the hydrophobically associating acrylamide copolymer is 1.0 to 1.8.

[0027] Example 3: As an optimization of the above example, in the first step, the mass ratio of the total amount of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and long-chain alkyl acrylate to the solvent is 3% to 10%; the mass ratio of the total amount of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and long-chain alkyl acrylate to the cosolvent is 1:2 to 2:1.

[0028] Example 4: As an optimization of the above example, in the first step, the stirring and mixing temperature is 35°C to 45°C.

[0029] Example 5: As an optimization of the above example, in the first step, the molar ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and long-chain alkyl acrylate is 65 to 75:20 to 30:2 to 8, where the structural formula of the long-chain alkyl acrylate is: R is a long-chain alkyl group with 12 to 18 carbon atoms.

[0030] Example 6: As an optimization of the above example, in the first step, the solvent includes, by mass parts: 1 to 3 parts of lower alcohol, 1 to 2 parts of polyhydric alcohol, and 1 to 3 parts of water; among them, the lower alcohol is methanol, ethanol, or isopropanol, and the polyhydric alcohol is glycerol or polyethylene glycol 200.

[0031] Example 7: As an optimization of the above example, in the first step, the cosolvent is 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6).

[0032] Example 8: As an optimization of the above example, in the second step, the initiator is a mixture of ammonium persulfate and sodium bisulfite, and the total addition amount of the initiator is 0.02% to 0.05% of the total mass of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and long-chain alkyl acrylate.

[0033] Example 9: As an optimization of the above example, in the second step, an initiator with a total mass of 55% to 70% is added to the first mixed solution for the first-stage reaction. When the viscosity of the system reaches 80 mPa·s to 120 mPa·s, the remaining initiator is added.

[0034] Example 10: As an optimization of the above example, in the second step, the reaction temperature of the first-stage reaction is 45°C to 50°C, the reaction temperature of the second-stage reaction is 50°C to 60°C, and the reaction time of the second-stage reaction is 0.5 h to 2 h.

[0035] Example 11: As an optimization of the above example, in the third step, the composite regulator is a mixture of sodium citrate and triethanolamine, and the mass ratio of sodium citrate to triethanolamine is 1:2 to 1:4, adjusting the pH value of the system between 6.5 and 7.5.

[0036] Example 12: As an optimization of the above example, in the third step, vacuum low-temperature drying is adopted, the drying temperature is 45°C to 55°C, the vacuum degree is between -0.08 MPa and -0.15 MPa, and the moisture content of the dried product is <3%.

[0037] Example 13: The polymer thickening agent for alcohol-based slick water, the raw materials are composed by mass percentage: 0.1% to 5% of hydrophobic associative acrylamide copolymer, 0.1% to 1.0% of nano-silica, 50% to 85% of main alcohol solvent, 0.1% to 5% of ionic liquid co-solvent, and the rest is water.

[0038] Example 14: As an optimization of the above example, the nano-silica is a hydrophobic nano-silica material. In the present invention, the nano-silica adopts BASF TS-421 nano-silica.

[0039] Example 15: As an optimization of the above example, the main alcohol solvent is a mixed solution of lower alcohols and polyhydric alcohols with a mass ratio of 3:1 to 1:2. The lower alcohol is selected from methanol, ethanol or isopropanol, and the polyhydric alcohol is glycerol or polyethylene glycol 200.

[0040] Example 16: As an optimization of the above example, the ionic liquid co-solvent is 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6).

[0041] Example 17: The preparation method of the polymer thickening agent for alcohol-based slick water includes the following steps: After mixing the required amount of hydrophobic associative acrylamide copolymer and nano-silica evenly, the main alcohol solvent, ionic liquid co-solvent and water are added in sequence, and after stirring and mixing, the polymer thickening agent for alcohol-based slick water is obtained.

[0042] Example 18: (1) Preparation of Hydrophobically Associating Acrylamide Copolymer: Under nitrogen protection, 5 parts by mass of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and octadecyl methacrylate (SMA) (the molar ratio of AM, AMPS, and SMA is 70:25:5) were dissolved in 80 parts of a solvent (the mass ratio of isopropanol, glycerol, and water is 1:1:1). The temperature was controlled at 40 °C, and the magnetic stirring speed was 500 r / min. After complete dissolution (about 30 min), 5 parts of a co-solvent (1-butyl-3-methylimidazolium hexafluorophosphate) was added, and the mixture was stirred for 10 min to obtain a first mixed solution.

[0043] Prepare an oxidation-reduction initiation system: Ammonium persulfate (APS) and sodium bisulfite (SHS) were mixed in a mass ratio of 1:1, and the total addition amount was 0.04% of the monomer mass.

[0044] 60% of the initiator (APS + SHS) was added to the first mixed solution, the temperature was raised to 50 °C, and the reaction was carried out for 2 h. The viscosity of the system increased to 100 mPa·s. The remaining 40% of the initiator was added, and the temperature was further raised to 55 °C, and the reaction was maintained for 1 h to promote the formation of a hydrophobic association network, obtaining a second mixed solution.

[0045] Sodium citrate-triethanolamine composite regulator (the mass ratio of sodium citrate to triethanolamine is 1:3) was added to the second mixed solution to adjust the pH value of the system to 7.0 ± 0.2, and the mixture was stirred for 10 min. The product was transferred to a vacuum dryer, the temperature was controlled at 50 °C, and the vacuum degree was -0.09 MPa. After drying until the moisture content < 3%, a hydrophobically associating acrylamide copolymer was obtained.

[0046] The molecular weight distribution index PDI of the hydrophobically associating acrylamide copolymer obtained in this example was 1.5.

[0047] (2) Preparation of a Polymer Thickener for Alcohol-Based Slickwater: The raw materials of the polymer thickener for alcohol-based slickwater were composed by mass percentage as follows: 80% of the main alcohol solvent (isopropanol and glycerol were compounded in a mass ratio of 2:1), 2.5% of the hydrophobically associating acrylamide copolymer, 2% of the ionic liquid co-solvent (1-butyl-3-methylimidazolium hexafluorophosphate), 0.2% of nano-silica, and the rest was deionized water.

[0048] Preparation process: The hydrophobically associating acrylamide copolymer was ground into a 100-mesh powder by a pulverizer. After being mechanically mixed evenly with nano-silica, the main alcohol solvent, the ionic liquid co-solvent, and water were added in sequence, and after stirring and mixing, a polymer thickener for alcohol-based slickwater was obtained.

[0049] Example 19: (1) Preparation of hydrophobically associating acrylamide copolymer: Under nitrogen protection, 5 parts by mass of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and C14 alkyl acrylate (the molar ratio of AM, AMPS, and C14 alkyl acrylate is 65:30:5) were dissolved in 80 parts of solvent (the mass ratio of isopropanol, glycerol, and water is 1:1:1). The temperature was controlled at 45 °C, and the magnetic stirring speed was 500 r / min. After complete dissolution (about 30 min), 5 parts of co-solvent (1-butyl-3-methylimidazolium hexafluorophosphate) was added, and the mixture was stirred for 10 min to obtain the first mixed solution.

[0050] Prepare a redox initiation system: Ammonium persulfate (APS) and sodium bisulfite (SHS) were mixed in a mass ratio of 1:1, and the total addition amount was 0.04% of the monomer mass.

[0051] 60% of the initiator (APS + SHS) was added to the first mixed solution, the temperature was raised to 50 °C, and the reaction was carried out for 2 h. The viscosity of the system increased to 80 mPa·s; the remaining 40% of the initiator was added, and the temperature was further raised to 55 °C, and the reaction was maintained for 2 h to promote the formation of a hydrophobic association network, obtaining the second mixed solution.

[0052] Sodium citrate-triethanolamine composite regulator (the mass ratio of sodium citrate to triethanolamine is 1:3) was added to the second mixed solution to adjust the pH value of the system to 7.0 ± 0.2, and the mixture was stirred for 10 min; the reaction solution was transferred to a vacuum dryer, the temperature was controlled at 50 °C, and the vacuum degree was -0.09 MPa. After drying until the moisture content was <3%, a hydrophobically associating acrylamide copolymer was obtained.

[0053] The molecular weight distribution index PDI of the hydrophobically associating acrylamide copolymer obtained in this example was 1.7.

[0054] (2) Preparation of a polymer thickener for alcohol-based slickwater: The raw materials were composed by mass percentage as follows: The main alcohol solvent was 75% (isopropanol and polyethylene glycol 200 were compounded in a mass ratio of 1:2), the hydrophobically associating acrylamide copolymer was 2.5%, the ionic liquid co-solvent (1-butyl-3-methylimidazolium hexafluorophosphate) was 1.5%, nano-silica was 0.2%, and the rest was deionized water.

[0055] Preparation process: The hydrophobically associating acrylamide copolymer was ground into 100-mesh powder by a pulverizer. After being mechanically mixed evenly with nano-silica, the main alcohol solvent, ionic liquid co-solvent, and water were added in sequence, and after stirring and mixing, a polymer thickener for alcohol-based slickwater was obtained.

[0056] Example 20: (1) Preparation of hydrophobic associating acrylamide copolymer: Under nitrogen protection, a total of 5 parts by mass of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and octadecyl methacrylate (SMA) (the molar ratio of AM, AMPS, and SMA is 68:24:8) were dissolved in 85 parts of a solvent (the mass ratio of isopropanol, glycerol, and water is 2:1:1). The temperature was controlled at 40 °C, and the magnetic stirring speed was 500 r / min. After complete dissolution (about 30 min), 5 parts of a co-solvent (1-butyl-3-methylimidazolium hexafluorophosphate) was added, and the mixture was stirred for 10 min to obtain a first mixed solution.

[0057] Prepare a redox initiation system: Ammonium persulfate (APS) and sodium bisulfite (SHS) were mixed in a mass ratio of 1:1, and the total addition amount was 0.04% of the monomer mass.

[0058] To the first mixed solution, 70% of the initiator was added, the temperature was raised to 45 °C, and the reaction was carried out for 3 h. The viscosity of the system increased to 110 mPa·s; the remaining 30% of the initiator was added, and the temperature was further raised to 55 °C, and the reaction was maintained for 1.5 h to promote the formation of a hydrophobic association network, obtaining a second mixed solution.

[0059] Sodium citrate-triethanolamine composite regulator (the mass ratio of sodium citrate to triethanolamine is 1:3) was added to the second mixed solution to adjust the pH value of the system to 7.0 ± 0.2, and the mixture was stirred for 10 min; the reaction solution was transferred to a vacuum dryer, the temperature was controlled at 50 °C, and the vacuum degree was -0.09 MPa, and dried until the moisture content < 3% to obtain a hydrophobic associating acrylamide copolymer.

[0060] The molecular weight distribution index PDI of the hydrophobic associating acrylamide copolymer obtained in this example was 1.3.

[0061] (2) Preparation of a polymer thickener for alcohol-based slickwater: The raw materials were composed by mass percentage as follows: 80% of the main alcohol solvent (isopropanol and glycerol were compounded in a mass ratio of 2:1), 2.5% of the hydrophobic associating acrylamide copolymer, 1.0% of the ionic liquid co-solvent (1-butyl-3-methylimidazolium hexafluorophosphate), 0.2% of nano-silica, and the rest was deionized water.

[0062] Preparation process: The hydrophobic associating acrylamide copolymer was ground into a powder of 100 mesh by a pulverizer. After being mechanically mixed evenly with nano-silica, the main alcohol solvent, the ionic liquid co-solvent, and water were added in sequence, and the mixture was stirred to obtain a polymer thickener for alcohol-based slickwater.

[0063] Example 21: (1)Preparation of hydrophobically associating acrylamide copolymer: Under nitrogen protection, 5 parts by mass of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and octadecyl methacrylate (SMA) (molar ratio of AM, AMPS, and SMA is 70:28:2) were dissolved in 70 parts of solvent (mass ratio of ethanol, polyethylene glycol 200, and water is 2:1:2). The temperature was controlled at 40 °C, and the magnetic stirring speed was 500 r / min until completely dissolved (about 30 min). 3 parts of cosolvent (1-butyl-3-methylimidazolium hexafluorophosphate) was added and stirred for 10 min to obtain the first mixed solution.

[0064] Prepare the redox initiation system: Ammonium persulfate (APS) and sodium bisulfite (SHS) were mixed in a mass ratio of 1:1, and the total addition amount was 0.05% of the monomer mass.

[0065] 60% of the initiator (APS + SHS) was added to the first mixed solution, the temperature was raised to 50 °C, and the reaction was carried out for 2 h. The viscosity of the system increased to 100 mPa·s; the remaining 40% of the initiator was added and the temperature was further raised to 55 °C, and the reaction was maintained for 1 h to promote the formation of the hydrophobic association network to obtain the second mixed solution.

[0066] Sodium citrate - triethanolamine composite regulator (mass ratio of sodium citrate to triethanolamine is 1:3) was added to the second mixed solution, and the pH value of the system was adjusted to 7.0 ± 0.2 and stirred for 10 min; the reaction solution was transferred to a vacuum dryer, the temperature was controlled at 50 °C, and the vacuum degree was -0.09 MPa, and dried until the moisture content < 3% to obtain the hydrophobically associating acrylamide copolymer.

[0067] The molecular weight distribution index PDI of the hydrophobically associating acrylamide copolymer obtained in this example was 1.5.

[0068] (2)Preparation of high molecular weight thickener for alcohol-based slickwater: The raw materials were composed by mass percentage as follows: Main alcohol solvent 60% (ethanol and polyethylene glycol 200 were compounded in a mass ratio of 1:1), hydrophobically associating acrylamide copolymer 3.5%, ionic liquid cosolvent (1-butyl-3-methylimidazolium hexafluorophosphate) 0.8%, nano-silica 0.5%, and the rest was deionized water.

[0069] Preparation process: The hydrophobically associating acrylamide copolymer was ground to 100-mesh powder by a grinder, mechanically mixed with nano-silica evenly, and then the main alcohol solvent, ionic liquid cosolvent, and water were added in sequence, and stirred and mixed to obtain the high molecular weight thickener for alcohol-based slickwater.

[0070] Example 22: (1) Preparation of hydrophobically associating acrylamide copolymer: Under nitrogen protection, a total of 5 parts by mass of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and octadecyl methacrylate (SMA) (molar ratio of AM, AMPS, and SMA is 70:28:2) were dissolved in 80 parts of a solvent (mass ratio of isopropanol, glycerol, and water is 1:1:1). The temperature was controlled at 40 °C, and the magnetic stirring speed was 500 r / min until completely dissolved (about 30 min). Then 5 parts of a co-solvent (1-butyl-3-methylimidazolium hexafluorophosphate) were added and stirred for 10 min to obtain the first mixed solution.

[0071] Prepare a redox initiation system: ammonium persulfate (APS) and sodium bisulfite (SHS) were mixed in a mass ratio of 1:1, and the total addition amount was 0.05% of the monomer mass.

[0072] 60% of the initiator (APS + SHS) was added to the first mixed solution, and the temperature was raised to 50 °C. The reaction was carried out for 2 h, and the system viscosity increased to 100 mPa·s. The remaining 40% of the initiator was added, and the temperature was further raised to 55 °C and the reaction was maintained for 1 h to promote the formation of a hydrophobic association network, obtaining the second mixed solution.

[0073] Sodium citrate-triethanolamine composite regulator (mass ratio of sodium citrate to triethanolamine is 1:4) was added to the second mixed solution to adjust the system pH value to 7.0 ± 0.2, and stirred for 10 min. The reaction solution was transferred to a vacuum dryer, the temperature was controlled at 50 °C, and the vacuum degree was -0.09 MPa, and dried until the water content < 3% to obtain the hydrophobically associating acrylamide copolymer.

[0074] The molecular weight distribution index PDI of the hydrophobically associating acrylamide copolymer obtained in this example was 1.5.

[0075] (2) Preparation of a polymer thickener for alcohol-based slickwater: The raw materials were composed by mass percentage as follows: The main alcohol solvent was 80% (isopropanol and glycerol were compounded in a mass ratio of 2:1), the hydrophobically associating acrylamide copolymer was 2.5%, the ionic liquid co-solvent (1-butyl-3-methylimidazolium hexafluorophosphate) was 0.8%, nano-silica was 0.5%, and the rest was deionized water.

[0076] Preparation process: The hydrophobically associating acrylamide copolymer was ground into 100-mesh powder by a pulverizer. After being mechanically mixed evenly with nano-silica, the main alcohol solvent, ionic liquid co-solvent, and water were added in sequence, and stirred and mixed to obtain the polymer thickener for alcohol-based slickwater.

[0077] Comparative Example 1: Different from Example 18, in the preparation of the hydrophobic associating acrylamide copolymer, the molar ratio of the three monomers is acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and octadecyl methacrylate (SMA) = 80:20:10, and the polydispersity index PDI of the prepared polymer is 0.9.

[0078] Comparative Example 2: Different from Example 18, in the preparation of the hydrophobic associating acrylamide copolymer, all the initiator was added at once, and the reaction was carried out at 50 °C for 3 hours.

[0079] Comparative Example 3: Different from Example 18, 1-butyl-3-methylimidazolium hexafluorophosphate was not added in the preparation of the hydrophobic associating acrylamide copolymer.

[0080] Comparative Example 4: Different from Example 18, in the preparation of the polymer thickener for alcohol-based slickwater, 1-butyl-3-methylimidazolium hexafluorophosphate was replaced with an equal amount of sodium metaphosphate solution.

[0081] System performance test According to the shale oil and gas industry standard, a friction reducer and a Hake Marrs-III rheometer were used to carry out the drag reduction performance and temperature and shear resistance performance tests.

[0082] Using mineralized water with a salinity of 15×10 4 mg / L, the polymer thickeners for alcohol-based slickwater prepared in Examples 18 to 22 and the thickeners prepared in Comparative Examples 1 to 4 were formulated into 1.0 wt% thickener solutions, and 0.05 wt% of a breaker (ammonium persulfate) was added. The thickener solutions were placed in an aging tank, and after aging for 120 min at the reservoir temperature (150 °C), their viscosities were tested, and after aging for 12 h, the viscosities of the broken gel liquids after liquid degradation were tested. At the same time, the polymer broken gel liquids were collected, and according to the industry standard, the reservoir damage performance was tested. The test results are shown in Table 1.

[0083] Table 1 。

[0084] The test results show that the fracturing fluid system prepared with the polymer thickener for alcohol-based slickwater of the present invention meets the fracturing fluid industry standard (in the industry standard, the fracturing fluid system needs to simultaneously meet: viscosity > 50 mPa·s, drag reduction rate > 70%, core damage rate < 30%). The temperature and salt tolerance stability performance is higher than the industry standard, and the reservoir damage of the broken gel liquid is much lower than the industry standard.

[0085] The present invention has the following advantages: ① "Synergistic Solubilization of Hydrophobic Association and Ionic Liquid": The present invention innovatively combines a hydrophobic associating acrylamide copolymer with an ionic liquid co-solvent. Through hydrophobic association, a thermodynamically stable three-dimensional network structure is constructed. At the same time, the strong solubility and salt resistance of the ionic liquid are utilized to synergistically improve the viscosity stability of the fracturing fluid in high-temperature (≥150 °C) and high-salt (≥15×10 4 mg / L) environments (viscosity retention rate > 70%), solving the problems of easy hydrolysis and viscosity collapse of traditional water-based systems.

[0086] ② Precise Design of the Molecular Structure of Salt-Tolerant Polymers and Control of Polymerization Narrow Distribution: The present invention copolymerizes acrylamide (AM), sulfonic acid group monomers (AMPS), and long-chain alkyl acrylates in a specific molar ratio, and introduces a molecular weight distribution index control technology to enhance the shear resistance and thermal stability of the polymer. Combined with a segmented initiation polymerization process, it ensures the efficient formation of a hydrophobic association network, achieving long-term viscosity stability (≥50 mPa·s) of the fracturing fluid at a high shear rate of 170 s -1 .

[0087] ③ The organic outer phase uses a compound of low-carbon alcohol and polyhydroxy alcohol as the main alcohol solvent: By optimizing the compound ratio of low-carbon alcohol and polyhydroxy alcohol, the present invention significantly improves the dissolution ability and environmental adaptability of the solvent system, shortens the polymer dispersion time to within 5 minutes, and simultaneously reduces volatility and biological toxicity, meeting the safety and continuous mixing requirements under extreme reservoir conditions.

[0088] ④ Introduction of Nano-Silica to Enhance Viscoelastic Sand-Carrying Performance: The present invention innovatively enhances the viscoelasticity of the system by introducing nano-silica, taking into account sand-carrying performance and resource recycling under extreme conditions, reducing operation costs and reservoir damage.

[0089] In summary, the present invention provides a hydrophobic associating acrylamide copolymer and a polymer thickening agent for alcohol-based slickwater and its preparation method. Adopting the technical concept of "synergistic solubilization of hydrophobic association and ionic liquid", it realizes the long-term viscosity stability of alcohol-based slickwater under the conditions of 15×10 4 mg / L salinity and 150 °C, with a core damage rate < 15%, providing a solution with both high performance and environmental adaptability for reservoir stimulation under extreme conditions.

[0090] The above technical features respectively constitute the embodiments of the present invention, which have strong adaptability and implementation effects. Non-essential technical features can be added or subtracted according to actual needs to meet the requirements of different situations.

Claims

1. A hydrophobic associating acrylamide copolymer, characterized in that It is prepared by the following method: In the first step, under the protection of an inert gas, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and long-chain alkyl acrylate are dissolved in a solvent, a cosolvent is added, and after stirring and mixing, a first mixed solution is obtained; In the second step, a part of the initiator is added to the first mixed solution to carry out the first-stage reaction, and then the remaining initiator is added to carry out the second-stage reaction to obtain a second mixed solution; In the third step, a composite regulator is added to the second mixed solution to adjust the pH value of the system, and after stirring, the product is dried and pulverized to obtain a hydrophobically associating acrylamide copolymer.

2. The hydrophobic associating acrylamide copolymer according to claim 1, characterized in that The molecular weight distribution index PDI of the hydrophobically associating acrylamide copolymer is 1.0 to 1.

8.

3. The hydrophobic associating acrylamide copolymer according to claim 1 or 2, characterized in that In the first step, the mass ratio of the total amount of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and long-chain alkyl acrylate to the solvent is 3% to 10%; the mass ratio of the total amount of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and long-chain alkyl acrylate to the cosolvent is 1:2 to 2:1; Or / and, the stirring and mixing temperature is 35°C to 45°C.

4. The hydrophobic associating acrylamide copolymer according to claim 1, wherein In the first step, the molar ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid to long-chain alkyl acrylate is 65 to 75:20 to 30:2 to 8, where the structural formula of the long-chain alkyl acrylate is: R is a long-chain alkyl with C12 to C18; Or / and, the solvent includes by mass: 1 to 3 parts of lower alcohol, 1 to 2 parts of polyhydroxy alcohol, and 1 to 3 parts of water, where the lower alcohol is methanol, ethanol, or isopropanol, and the polyhydroxy alcohol is glycerol or polyethylene glycol 200; Or / and, the cosolvent is 1-butyl-3-methylimidazolium hexafluorophosphate.

5. The hydrophobic association type acrylamide copolymer according to claim 1, characterized in that In the second step, the initiator is a mixture of ammonium persulfate and sodium bisulfite, and the total addition amount of the initiator is 0.02% to 0.05% of the total mass of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and long-chain alkyl acrylate; Or / and, 55% to 70% of the total mass of the initiator is added to the first mixed solution to carry out the first-stage reaction, and when the viscosity of the system reaches 80 mPa·s to 120 mPa·s, the remaining initiator is added; Or / and, the reaction temperature of the first-stage reaction is 45°C to 50°C, the reaction temperature of the second-stage reaction is 50°C to 60°C, and the reaction time of the second-stage reaction is 0.5 h to 2 h.

6. The hydrophobic associating acrylamide copolymer according to claim 1, characterized in that In the third step, the composite regulator is a mixture of sodium citrate and triethanolamine, the mass ratio of sodium citrate to triethanolamine is 1:2 to 1:4, and the pH value of the system is adjusted between 6.5 and 7.5; Or / and, drying is carried out by vacuum low-temperature drying, the drying temperature is 45°C to 55°C, the vacuum degree is between -0.08 MPa and -0.15 MPa, and the moisture content of the dried product is <3%.

7. A method for preparing a hydrophobically associating acrylamide copolymer according to any one of claims 2 to 6, characterized in that It is carried out according to the following steps: In the first step, under the protection of an inert gas, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and long-chain alkyl acrylate are dissolved in a solvent, a cosolvent is added, and after stirring and mixing, a first mixed solution is obtained; In the second step, a part of the initiator is added to the first mixed solution to carry out the first-stage reaction, and then the remaining initiator is added to carry out the second-stage reaction to obtain a second mixed solution; In the third step, a composite regulator is added to the second mixture to adjust the pH value of the system, followed by stirring. The product is obtained as a hydrophobic associating acrylamide copolymer after drying and pulverization.

8. A polymer thickening agent for alcohol-based slickwater, which uses the hydrophobically associating acrylamide copolymer described in any one of claims 1 to 6 as a raw material, is characterized in that The raw materials are composed by mass percentage as follows: 0.1% to 5% of hydrophobic associating acrylamide copolymer, 0.1% to 1.0% of nano-silica, 50% to 85% of main alcohol solvent, 0.1% to 5% of ionic liquid co-solvent, and the balance is water.

9. The polymeric thickener for alcohol-based slippery water according to claim 8, wherein The nano-silica is a hydrophobic nano-silicon material; Or / and, the main alcohol solvent is a mixed solution of lower alcohols and polyhydric alcohols with a mass ratio of 3:1 to 1:

2. The lower alcohol is selected from methanol, ethanol or isopropanol, and the polyhydric alcohol is glycerol or polyethylene glycol 200; Or / and, the ionic liquid co-solvent is 1-butyl-3-methylimidazolium hexafluorophosphate.

10. A preparation method of the polymer thickening agent for alcohol-based slick water according to claim 8 or 9, characterized in that It includes the following steps: After mixing the required amounts of hydrophobic associating acrylamide copolymer and nano-silica evenly, the main alcohol solvent, ionic liquid co-solvent and water are added in sequence, and a polymer thickener for alcohol-based slickwater is obtained after stirring and mixing.

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