Process for the preparation of a viscosifier for fracturing

Abstract

The application belongs to the technical field of thickening agent preparation, and particularly relates to a preparation method of a thickening agent for fracturing. The preparation method of the thickening agent for fracturing comprises the following steps: (1) pre-emulsification treatment of dicyclopentadiene oxyethyl acrylate; (2) preparation of an aqueous phase; (3) preparation of an initiator solution; (4) polymerization reaction; and (5) post-treatment. The preparation method of the thickening agent for fracturing comprises the following steps: acrylamide is used as a main monomer, dicyclopentadiene oxyethyl acrylate, 4-[(3-methacrylamidopropyl)dimethylammonio]butane-1-sulfonate and isobutylene amide propyl trimethyl ammonium methyl sulfate are used as functional monomers to perform random copolymerization reaction, a multi-element random copolymerization structure of "rigid temperature-resistant chain segment-amphoteric ion salt-resistant chain segment-cationic adsorption chain segment" is constructed, and the prepared thickening agent for fracturing has excellent salt resistance, high-temperature resistance and high tackifying performance.

Description

Technical Field

[0001] This invention belongs to the field of thickener preparation technology, specifically relating to a method for preparing a thickener for fracturing. Background Technology

[0002] Acid fracturing is one of the main production enhancement measures for carbonate reservoirs. It can significantly improve reservoir permeability, thereby increasing oil and gas well production. It is well known that conventional acidizing operations generally only eliminate permeability damage around the wellbore, resulting in unsatisfactory oil and gas growth and a short effective time. This is because the acid-rock reaction is too rapid, and the active acid does not fully penetrate the formation. Therefore, it needs to be used in conjunction with a thickener. The main functions of the thickener are: increasing viscosity: Due to the long molecular chain length in the thickened acid solution, they entangle and rub against each other, forming a network structure, thus increasing viscosity. Reducing friction: Because the acid solution containing the thickener has its energy dissipation inhibited by the high molecular weight, it significantly reduces friction with the pipe wall during pumping under the same shear conditions. Slowing down flow and reducing filtration loss: After adding the thickener to the acid solution, the actual viscosity increases, thus slowing down flow and reducing filtration loss. Temperature resistance: Structures such as carbon-carbon double bonds, carbon-carbon triple bonds, or benzene rings can enhance the rigidity of molecular chains, and polymers are rich in such structures. Furthermore, strongly polar groups can strengthen the intermolecular forces. All of these factors contribute to improving the stability of the material, giving it temperature resistance.

[0003] Patent CN 102477112A discloses a synthesis process for an acid thickener, which uses only three monomers: AMPS, acrylic acid, and DMDAAC, without any monomers with rigid groups. This results in excessively flexible polymer molecular chains, which are prone to thermal curling at high temperatures and significant viscosity loss. The salt resistance relies solely on the sulfonic acid groups of AMPS, offering limited resistance. Furthermore, the carboxyl groups of acrylic acid readily react with calcium in the formation. 2 + / Mg 2+ Precipitation forms, further reducing salt resistance.

[0004] Currently used acid thickeners and water-based gel fracturing fluid thickeners share many commonalities. Among them, acrylamide polymers are the most widely used and have become the main acid thickeners. Existing polyacrylamide thickeners have limited performance, poor compatibility with acid systems, and rapid viscosity loss, making them unable to meet the requirements of complex acidizing processes. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a thickener for fracturing, wherein the thickener prepared by this method has excellent salt resistance, high temperature resistance and high viscosity-enhancing properties.

[0006] The preparation method of the fracturing thickener of the present invention comprises the following steps:

[0007] (1) Pre-emulsification treatment of dicyclopentadienoxyethyl acrylate

[0008] Dicyclopentadieneoxyethyl acrylate, octylphenol polyoxyethylene ether OP-6 and deionized water were added to a reaction apparatus for pre-emulsification treatment to prepare an emulsion.

[0009] (2) Preparation of aqueous phase

[0010] Under a nitrogen atmosphere, acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, isopropanol and deionized water were stirred and mixed evenly to prepare an aqueous phase.

[0011] (3) Preparation of initiator solution

[0012] Ammonium persulfate was dissolved in deionized water to prepare an ammonium persulfate solution with a mass concentration of 5.66%, and sodium bisulfite was dissolved in deionized water to prepare a sodium bisulfite solution with a mass concentration of 2.44%.

[0013] (4) Polymerization reaction

[0014] Under nitrogen protection, the emulsion at 50-51℃ is added to the aqueous phase in one go and mixed. The temperature is raised to 68-70℃, and ammonium persulfate solution and sodium bisulfite solution are added dropwise to carry out the polymerization reaction. The temperature is raised to 83-85℃ for aging to prepare the reaction solution.

[0015] (5) Post-processing

[0016] Cool the reaction solution to 43-45℃, add anhydrous ethanol while stirring to precipitate, let stand for 30-35 minutes, then filter, dry and sieve to prepare the thickener for fracturing fluid.

[0017] In step (1), the mass ratio of dicyclopentadieneoxyethyl acrylate, octylphenol polyoxyethylene ether OP-6, and deionized water is 10:2.5-2.7:25.

[0018] In step (1), the pre-emulsification temperature is 50-51℃, the pre-emulsification speed is 3000r / min, and the pre-emulsification time is 12-15min.

[0019] The molar ratio of acrylamide in step (2), 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, and dicyclopentadienoxyethyl acrylate in step (1) is 62-63 : 24-25 : 5-6 : 2-3.

[0020] In step (2), the mass ratio of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, and isobutylamidopropyltrimethylammonium methyl sulfate to deionized water is 0.68-0.70:1.

[0021] In step (2), isopropanol is used as a chain transfer agent, and the mass of isopropanol accounts for 0.23% of the total mass of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate and isobutenamidopropyltrimethylammonium methyl sulfate in step (2).

[0022] In step (2), the mixing temperature is 30℃, the mixing time is 12-15 min, and the mixing speed is 300 r / min.

[0023] The mixing temperature in step (4) is 25℃, the mixing time is 2-3 min, and the heating rate when the temperature is raised to 68-70℃ is 1℃ / min.

[0024] In step (4), the polymerization reaction uses ammonium persulfate solution and sodium bisulfite solution as initiators. The initiators are added in a stepwise dropwise manner: First, ammonium persulfate solution accounting for 70% of the total mass of ammonium persulfate solution and sodium bisulfite solution accounting for 70% of the total mass of sodium bisulfite solution are added within 30 minutes, and the reaction is kept at 68-70℃ for 30 minutes. Then, the remaining ammonium persulfate solution and sodium bisulfite solution are added within 15 minutes.

[0025] The stepwise dropwise addition of the initiator helps to smoothly initiate the polymerization reaction, avoid explosive exothermic reactions, and allow the monomers to participate in chain growth in a uniform and orderly manner. This is conducive to the formation of polymer molecular chains with a more concentrated molecular weight distribution and a more regular structure, ultimately improving the thickening performance and shear stability of the resulting thickener.

[0026] In step (4), the polymerization temperature is 68-70℃ and the polymerization time is 60-65min.

[0027] The maturation time in step (4) is 58-60 min.

[0028] In step (4), the volume ratio of ammonium persulfate solution to sodium bisulfite solution is 1:1.

[0029] In step (4), the molar amount of ammonium persulfate in the ammonium persulfate solution is 0.21-0.23% of the sum of the molar amounts of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, and dicyclopentadienyloxyethyl acrylate in step (2).

[0030] Step (4) Control the stirring speed at 200 r / min throughout the entire reaction process.

[0031] In step (5), the volume of anhydrous ethanol is 2.5 times the volume of the reaction liquid, the stirring speed is 50 r / min, and the precipitation time is 18-20 min.

[0032] In step (5), the drying temperature is 60℃, the drying time is 8h, the drying vacuum degree is -0.09MPa, and it passes through an 80-mesh sieve.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) The preparation method of the thickener for fracturing described in this invention uses acrylamide as the main monomer and dicyclopentadienoxyethyl acrylate, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate and isobutylamidopropyltrimethylammonium methyl sulfate as functional monomers to carry out random copolymerization reaction to construct a multi-component random copolymer structure of "rigid temperature resistant segment - zwitterionic salt resistant segment - cationic adsorption segment", so that the prepared thickener for fracturing has excellent salt resistance, high temperature resistance and high thickening performance.

[0035] (2) The preparation method of the thickener for fracturing described in this invention involves using dicyclopentadienyloxyethyl acrylate, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, and isobutylamidopropyltrimethylammonium methyl sulfate as functional monomers, and reacting them with the main monomer acrylamide via free radical copolymerization to prepare a modified polyacrylamide thickener. Among them, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate is an amphoteric functional monomer, whose molecular structure contains both quaternary ammonium cations and sulfonic acid anions, exhibiting an anti-polyelectrolyte effect. That is, when the salt concentration increases, the salt ions can shield the mutual attraction between positive and negative charges within the molecule, causing the polymer molecular chain to change from a coiled state to a stretched state, significantly increasing the viscosity of the thickener aqueous solution. Simultaneously, this monomer has an internal salt structure, and will not undergo protonation or deprotonation reactions under any acidity conditions, and its sulfonic acid groups can react with Ca in formation water. 2+ / Mg 2+The formation of soluble ion pairs effectively avoids the calcium and magnesium precipitation problem easily caused by carboxylic acid monomers, significantly enhancing the thickener's resistance to salt and calcium and magnesium. Furthermore, the amide group of this monomer can form an intermolecular hydrogen bond network with the amide group of the acrylamide backbone, strengthening the intermolecular forces and further improving the high-temperature stability of the thickener. Isobutylamidopropyltrimethylammonium methyl sulfate is a cationic functional monomer. The quaternary ammonium positive charge on its molecular chain can generate strong electrostatic adsorption with the negatively charged sites on the surface of sandstone and carbonate reservoir rocks, adsorbing onto the rock pore surface to form a dense adsorption film, thereby reducing the acid filtration coefficient. Simultaneously, after copolymerization with acrylamide, this monomer forms a cationic-neutral segmental microblock structure, which can increase the "anchor point" density of the polymer molecular chain in the reservoir pore throat, inhibiting molecular chain breakage and coiling under high shear, thus improving the shear resistance of the thickener. Dicyclopentadiene oxyethyl acrylate is a rigid functional monomer. The rigid dicyclopentadiene ring in its molecular structure significantly enhances the rigidity of polymer chain segments, suppressing the thermal motion and coiling of molecular chains under high-temperature conditions. Simultaneously, after copolymerization with the acrylamide backbone, this monomer forms a microphase separation structure of rigid-flexible segments, further improving the structural stability of the polymer under high-temperature and high-shear conditions, endowing the thickener with excellent high-temperature and shear resistance. The synergistic effect of these three functional monomers and the acrylamide backbone achieves a synergistic improvement in salt resistance, temperature resistance, and shear resistance, solving the problem of large viscosity loss in traditional polyacrylamide thickeners in high-temperature and high-salt reservoirs.

[0036] (3) The preparation method of the thickener for fracturing described in this invention is simple, the parameters are set reasonably, and the performance of the prepared thickener for fracturing is stable. Detailed Implementation

[0037] Example 1

[0038] The preparation method of the fracturing thickener described in Example 1 consists of the following steps:

[0039] (1) Pre-emulsification treatment of dicyclopentadienoxyethyl acrylate

[0040] Dicyclopentadieneoxyethyl acrylate, octylphenol polyoxyethylene ether OP-6 and deionized water were added to a reaction apparatus for pre-emulsification treatment to prepare an emulsion.

[0041] (2) Preparation of aqueous phase

[0042] Under a nitrogen atmosphere, acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, isopropanol and deionized water were stirred and mixed evenly to prepare an aqueous phase.

[0043] (3) Preparation of initiator solution

[0044] Ammonium persulfate was dissolved in deionized water to prepare an ammonium persulfate solution with a mass concentration of 5.66%, and sodium bisulfite was dissolved in deionized water to prepare a sodium bisulfite solution with a mass concentration of 2.44%.

[0045] (4) Polymerization reaction

[0046] Under nitrogen protection, the emulsion at 51°C was added to the aqueous phase in one go and mixed. The temperature was raised to 69°C, and ammonium persulfate solution and sodium bisulfite solution were added dropwise to carry out the polymerization reaction. The temperature was raised to 84°C for aging to prepare the reaction solution.

[0047] (5) Post-processing

[0048] The reaction solution was cooled to 44°C, and anhydrous ethanol was added to it while stirring to precipitate the solution. After standing for 33 minutes, the solution was filtered, dried, and sieved to obtain a thickener for fracturing fluid.

[0049] In step (1), the mass ratio of dicyclopentadieneoxyethyl acrylate, octylphenol polyoxyethylene ether OP-6, and deionized water is 10:2.6:25.

[0050] In step (1), the pre-emulsification temperature is 51℃, the pre-emulsification speed is 3000r / min, and the pre-emulsification time is 14min.

[0051] The molar ratio of acrylamide in step (2), 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, and dicyclopentadienoxyethyl acrylate in step (1) is 62.5 : 24.5 : 5.5 : 2.5.

[0052] The mass ratio of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, and isobutylamidopropyltrimethylammonium methyl sulfate in step (2) to deionized water is 0.69:1.

[0053] In step (2), isopropanol is used as a chain transfer agent, and the mass of isopropanol accounts for 0.23% of the total mass of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate and isobutenamidopropyltrimethylammonium methyl sulfate in step (2).

[0054] In step (2), the mixing temperature is 30℃, the mixing time is 13min, and the mixing speed is 300r / min.

[0055] The mixing temperature in step (4) is 25°C, the mixing time is 3 min, and the heating rate when the temperature rises to 69°C is 1°C / min.

[0056] In step (4), the polymerization reaction uses ammonium persulfate solution and sodium bisulfite solution as initiators. The initiators are added in a stepwise dropwise manner: First, ammonium persulfate solution accounting for 70% of the total mass of ammonium persulfate solution and sodium bisulfite solution accounting for 70% of the total mass of sodium bisulfite solution are added within 30 minutes, and the reaction is kept at 69°C for 30 minutes. Then, the remaining ammonium persulfate solution and sodium bisulfite solution are added within 15 minutes.

[0057] The stepwise dropwise addition of the initiator helps to smoothly initiate the polymerization reaction, avoid explosive exothermic reactions, and allow the monomers to participate in chain growth in a uniform and orderly manner. This is conducive to the formation of polymer molecular chains with a more concentrated molecular weight distribution and a more regular structure, ultimately improving the thickening performance and shear stability of the resulting thickener.

[0058] In step (4), the polymerization temperature is 69°C and the polymerization time is 63 min.

[0059] The maturation time in step (4) is 59 min.

[0060] In step (4), the volume ratio of ammonium persulfate solution to sodium bisulfite solution is 1:1.

[0061] The molar amount of ammonium persulfate in the ammonium persulfate solution in step (4) is 0.22% of the sum of the molar amounts of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate and dicyclopentadienoxyethyl acrylate in step (2).

[0062] Step (4) Control the stirring speed at 200 r / min throughout the entire reaction process.

[0063] In step (5), the volume of anhydrous ethanol is 2.5 times the volume of the reaction liquid, the stirring speed is 50 r / min, and the precipitation time is 20 min.

[0064] In step (5), the drying temperature is 60℃, the drying time is 8h, the drying vacuum degree is -0.09MPa, and it passes through an 80-mesh sieve.

[0065] Example 2

[0066] The preparation method of the fracturing thickener described in Example 2 consists of the following steps:

[0067] (1) Pre-emulsification treatment of dicyclopentadienoxyethyl acrylate

[0068] Dicyclopentadieneoxyethyl acrylate, octylphenol polyoxyethylene ether OP-6 and deionized water were added to a reaction apparatus for pre-emulsification treatment to prepare an emulsion.

[0069] (2) Preparation of aqueous phase

[0070] Under a nitrogen atmosphere, acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, isopropanol and deionized water were stirred and mixed evenly to prepare an aqueous phase.

[0071] (3) Preparation of initiator solution

[0072] Ammonium persulfate was dissolved in deionized water to prepare an ammonium persulfate solution with a mass concentration of 5.66%, and sodium bisulfite was dissolved in deionized water to prepare a sodium bisulfite solution with a mass concentration of 2.44%.

[0073] (4) Polymerization reaction

[0074] Under nitrogen protection, the emulsion at 50°C was added to the aqueous phase in one go and mixed. The temperature was raised to 68°C, and ammonium persulfate solution and sodium bisulfite solution were added dropwise to carry out the polymerization reaction. The temperature was raised to 83°C for aging to prepare the reaction solution.

[0075] (5) Post-processing

[0076] The reaction solution was cooled to 43°C, and anhydrous ethanol was added to it while stirring to precipitate the solution. After standing for 30 minutes, the solution was filtered, dried, and sieved to prepare a thickener for fracturing fluid.

[0077] In step (1), the mass ratio of dicyclopentadieneoxyethyl acrylate, octylphenol polyoxyethylene ether OP-6, and deionized water is 10:2.5:25.

[0078] In step (1), the pre-emulsification temperature is 50℃, the pre-emulsification speed is 3000r / min, and the pre-emulsification time is 15min.

[0079] The molar ratio of acrylamide in step (2), 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, and dicyclopentadienoxyethyl acrylate in step (1) is 62:25:5:2.

[0080] The mass ratio of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, and isobutylamidopropyltrimethylammonium methyl sulfate in step (2) to deionized water is 0.68:1.

[0081] In step (2), isopropanol is used as a chain transfer agent, and the mass of isopropanol accounts for 0.23% of the total mass of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate and isobutenamidopropyltrimethylammonium methyl sulfate in step (2).

[0082] In step (2), the mixing temperature is 30℃, the mixing time is 12min, and the mixing speed is 300r / min.

[0083] The mixing temperature in step (4) is 25°C, the mixing time is 3 min, and the heating rate when the temperature rises to 68°C is 1°C / min.

[0084] In step (4), the polymerization reaction uses ammonium persulfate solution and sodium bisulfite solution as initiators. The initiators are added in a stepwise dropwise manner: First, ammonium persulfate solution accounting for 70% of the total mass of ammonium persulfate solution and sodium bisulfite solution accounting for 70% of the total mass of sodium bisulfite solution are added within 30 minutes, and the reaction is kept at 68°C for 30 minutes. Then, the remaining ammonium persulfate solution and sodium bisulfite solution are added within 15 minutes.

[0085] The stepwise dropwise addition of the initiator helps to smoothly initiate the polymerization reaction, avoid explosive exothermic reactions, and allow the monomers to participate in chain growth in a uniform and orderly manner. This is conducive to the formation of polymer molecular chains with a more concentrated molecular weight distribution and a more regular structure, ultimately improving the thickening performance and shear stability of the resulting thickener.

[0086] In step (4), the polymerization temperature is 68℃ and the polymerization time is 65min.

[0087] The maturation time in step (4) is 58 minutes.

[0088] In step (4), the volume ratio of ammonium persulfate solution to sodium bisulfite solution is 1:1.

[0089] The molar amount of ammonium persulfate in the ammonium persulfate solution in step (4) is 0.23% of the sum of the molar amounts of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate and dicyclopentadienoxyethyl acrylate in step (2).

[0090] Step (4) Control the stirring speed at 200 r / min throughout the entire reaction process.

[0091] In step (5), the volume of anhydrous ethanol is 2.5 times the volume of the reaction liquid, the stirring speed is 50 r / min, and the precipitation time is 18 min.

[0092] In step (5), the drying temperature is 60℃, the drying time is 8h, the drying vacuum degree is -0.09MPa, and it passes through an 80-mesh sieve.

[0093] Example 3

[0094] The preparation method of the fracturing thickener described in Example 3 consists of the following steps:

[0095] (1) Pre-emulsification treatment of dicyclopentadienoxyethyl acrylate

[0096] Dicyclopentadieneoxyethyl acrylate, octylphenol polyoxyethylene ether OP-6 and deionized water were added to a reaction apparatus for pre-emulsification treatment to prepare an emulsion.

[0097] (2) Preparation of aqueous phase

[0098] Under a nitrogen atmosphere, acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, isopropanol and deionized water were stirred and mixed evenly to prepare an aqueous phase.

[0099] (3) Preparation of initiator solution

[0100] Ammonium persulfate was dissolved in deionized water to prepare an ammonium persulfate solution with a mass concentration of 5.66%, and sodium bisulfite was dissolved in deionized water to prepare a sodium bisulfite solution with a mass concentration of 2.44%.

[0101] (4) Polymerization reaction

[0102] Under nitrogen protection, the emulsion at 51°C was added to the aqueous phase in one go and mixed. The temperature was raised to 70°C, and ammonium persulfate solution and sodium bisulfite solution were added dropwise to carry out the polymerization reaction. The temperature was raised to 85°C for aging to prepare the reaction solution.

[0103] (5) Post-processing

[0104] The reaction solution was cooled to 45°C, and anhydrous ethanol was added to it while stirring to precipitate the solution. After standing for 35 minutes, the solution was filtered, dried, and sieved to obtain a thickener for fracturing fluid.

[0105] In step (1), the mass ratio of dicyclopentadieneoxyethyl acrylate, octylphenol polyoxyethylene ether OP-6, and deionized water is 10:2.7:25.

[0106] In step (1), the pre-emulsification temperature is 51℃, the pre-emulsification speed is 3000r / min, and the pre-emulsification time is 12min.

[0107] The molar ratio of acrylamide in step (2), 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, and dicyclopentadienoxyethyl acrylate in step (1) is 63:24:6:3.

[0108] The mass ratio of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, and isobutylamidopropyltrimethylammonium methyl sulfate in step (2) to deionized water is 0.70:1.

[0109] In step (2), isopropanol is used as a chain transfer agent, and the mass of isopropanol accounts for 0.23% of the total mass of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate and isobutenamidopropyltrimethylammonium methyl sulfate in step (2).

[0110] In step (2), the mixing temperature is 30℃, the mixing time is 15min, and the mixing speed is 300r / min.

[0111] The mixing temperature in step (4) is 25°C, the mixing time is 2 min, and the heating rate when the temperature is raised to 70°C is 1°C / min.

[0112] In step (4), the polymerization reaction uses ammonium persulfate solution and sodium bisulfite solution as initiators. The initiators are added in a stepwise dropwise manner: First, ammonium persulfate solution accounting for 70% of the total mass of ammonium persulfate solution and sodium bisulfite solution accounting for 70% of the total mass of sodium bisulfite solution are added within 30 minutes, and the reaction is kept at 70°C for 30 minutes. Then, the remaining ammonium persulfate solution and sodium bisulfite solution are added within 15 minutes.

[0113] The stepwise dropwise addition of the initiator helps to smoothly initiate the polymerization reaction, avoid explosive exothermic reactions, and allow the monomers to participate in chain growth in a uniform and orderly manner. This is conducive to the formation of polymer molecular chains with a more concentrated molecular weight distribution and a more regular structure, ultimately improving the thickening performance and shear stability of the resulting thickener.

[0114] In step (4), the polymerization temperature is 70℃ and the polymerization time is 60min.

[0115] The maturation time in step (4) is 60 minutes.

[0116] In step (4), the volume ratio of ammonium persulfate solution to sodium bisulfite solution is 1:1.

[0117] The molar amount of ammonium persulfate in the ammonium persulfate solution in step (4) is 0.21% of the sum of the molar amounts of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate and dicyclopentadienoxyethyl acrylate in step (2).

[0118] Step (4) Control the stirring speed at 200 r / min throughout the entire reaction process.

[0119] In step (5), the volume of anhydrous ethanol is 2.5 times the volume of the reaction liquid, the stirring speed is 50 r / min, and the precipitation time is 20 min.

[0120] In step (5), the drying temperature is 60℃, the drying time is 8h, the drying vacuum degree is -0.09MPa, and it passes through an 80-mesh sieve.

[0121] Comparative Example 1

[0122] The preparation method of the fracturing thickener described in Comparative Example 1 is the same as that in Example 1, except that 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate is not added to the aqueous phase in step (2). The molar ratio of acrylamide in step (2), isobutylamidopropyltrimethylammonium methyl sulfate, and dicyclopentadienyloxyethyl acrylate in step (1) is 62.5: 5.5: 2.5.

[0123] Comparative Example 2

[0124] The preparation method of the fracturing thickener described in Comparative Example 2 is the same as that in Example 1, except that isobutylamidopropyltrimethylammonium methyl sulfate is not added to the aqueous phase in step (2). The molar ratio of acrylamide in step (2), 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, and dicyclopentadienyloxyethyl acrylate in step (1) is 62.5: 24.5: 2.5.

[0125] Comparative Example 3

[0126] The preparation method of the thickener for fracturing described in Comparative Example 3 is the same as that in Example 1, except that step (1) is omitted, no emulsion is added in the polymerization reaction, and the molar ratio of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, and isobutylamidopropyltrimethylammonium methyl sulfate in step (2) is 62.5: 24.5: 5.5.

[0127] The performance of the fracturing thickeners prepared in Examples 1-3 and Comparative Examples 1-3 was tested, wherein:

[0128] (1) Acid dissolution time: According to industry standard SY / T-6214-1996, the acid dissolution time of the thickener was determined by the powder thickener method. At 30°C, the thickeners prepared in Examples 1-3 and Comparative Examples 1-3 were added to a 25wt% hydrochloric acid solution to make the mass fraction of the thickener 0.5wt%, and stirred to form a uniform mixed solution; the solution was then dissolved in 170s. -1 The mixture was stirred continuously at a shear rate, and the viscosity was measured every 20 minutes. After the viscosity stabilized, the acid dissolution time of the thickener was determined.

[0129] (2) Thickening properties: According to industry standard SY / T-6214-1996, thickeners prepared in Examples 1-3 and Comparative Examples 1-3 were added to a 25wt% hydrochloric acid solution to achieve a thickener mass fraction of 0.5wt%. The thickener was then tested at 30℃ for 170 seconds. -1 The viscosity of each thickened acid solution was measured at different shear rates; the acid dissolution time was also measured at 30℃ and 170s. -1 The viscosity measurement results are shown in Table 1.

[0130] Table 1. Results of acid dissolution time and viscosity test

[0131]

[0132] (3) Temperature resistance: Thickening agents prepared in Examples 1-3 and Comparative Examples 1-3 were added to a 25 wt% hydrochloric acid solution to prepare a thickened acid with a thickening agent mass fraction of 0.5 wt%. The thickened acid was heated from 30°C to 150°C or 170°C and held at that temperature for 4 hours. After naturally cooling to 30°C, the temperature resistance of the acid solution was measured at 170 s. -1 The apparent viscosity at the shear rate is given by the formula ω = μ1. ′ / μ1×100 (μ1 is the initial apparent viscosity at 30℃, μ1 ′ The viscosity retention rate was calculated for the apparent viscosity after aging at 150℃ or 170℃. The test results are shown in Table 2.

[0133] Table 2 Temperature resistance test results

[0134]

[0135] (4) Shear resistance: Thickening agents prepared in Examples 1-3 and Comparative Examples 1-3 were added to a 25 wt% hydrochloric acid solution to prepare a thickened acid with a thickening agent mass fraction of 0.5 wt%. The thickened acid was then tested at 30°C for 511 s. -1 1024s -1 Viscosity at the shear rate, with a continuous shear time of 120 min, is calculated using the following formula: ω′ = μ 120′′ / μ0 ′′ ×100% (middle: μ0) ′′ It is the apparent viscosity under initial shear after isothermal treatment, in μ. 120 ′′ The apparent viscosity is measured after shearing for 120 minutes; the test results are shown in Table 3.

[0136] Table 3 Shear resistance test results

[0137]

[0138] (5) Salt tolerance: 0.5 wt% of the thickener prepared in Examples 1-3 and Comparative Examples 1-3 was added to a 25 wt% hydrochloric acid solution to prepare a thickened acid with a thickening agent mass fraction of 0.5 wt%. 10 wt% and 12 wt% of inorganic salts (CaCl2 to NaCl mass ratio of 1:1) were added and stirred to dissolve the solution. The solution was then subjected to a 170s test. -1 After shearing at the shear rate for 30 minutes, the viscosity retention rate is calculated using the following formula: ω ′′ = μ 30 ′′′ / μ0 ′′′ ×100% (middle: μ0) ′′′ It is the initial apparent viscosity, μ 30 ′′′ The apparent viscosity is measured after shearing for 30 minutes. The viscosity of acid solutions in different systems was measured, and the test results are shown in Table 4.

[0139] Table 4 Salt resistance test results

[0140]

[0141] As shown in Tables 1-4, the fracturing thickeners prepared in Examples 1-3 exhibit significantly better salt resistance, temperature resistance, shear resistance, and high viscosity-enhancing properties than those in Comparative Examples 1-3. In Comparative Examples 1-3, the absence of any one of the functional monomers dicyclopentadienoxyethyl acrylate, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, and isobutylamidopropyltrimethylammonium methyl sulfate leads to a significant decrease in the overall performance of the fracturing thickeners prepared.

[0142] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a thickener for fracturing, characterized in that: It consists of the following steps: (1) Pre-emulsification treatment of dicyclopentadienoxyethyl acrylate Dicyclopentadieneoxyethyl acrylate, octylphenol polyoxyethylene ether OP-6 and deionized water were added to a reaction apparatus for pre-emulsification treatment to prepare an emulsion. (2) Preparation of aqueous phase Under a nitrogen atmosphere, acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, isopropanol and deionized water were stirred and mixed evenly to prepare an aqueous phase. (3) Preparation of initiator solution Ammonium persulfate was dissolved in deionized water to prepare an ammonium persulfate solution with a mass concentration of 5.66%, and sodium bisulfite was dissolved in deionized water to prepare a sodium bisulfite solution with a mass concentration of 2.44%. (4) Polymerization reaction Under nitrogen protection, the emulsion at 50-51℃ is added to the aqueous phase in one go and mixed. The temperature is raised to 68-70℃, and ammonium persulfate solution and sodium bisulfite solution are added dropwise to carry out the polymerization reaction. The temperature is raised to 83-85℃ for aging to prepare the reaction solution. (5) Post-processing Cool the reaction solution to 43-45℃, add anhydrous ethanol to it while stirring to precipitate, let it stand for 30-35 minutes, and then filter, dry and sieve to prepare the thickener for fracturing fluid. Wherein: the molar ratio of acrylamide in step (2), 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, and dicyclopentadienoxyethyl acrylate in step (1) is 62-63 : 24-25 : 5-6 : 2-3; In step (1), the mass ratio of dicyclopentadienyloxyethyl acrylate, octylphenol polyoxyethylene ether OP-6, and deionized water is 10:2.5-2.7:

25. In step (1), the pre-emulsification temperature is 50-51℃, the pre-emulsification speed is 3000r / min, and the pre-emulsification time is 12-15min.

2. The method for preparing the thickener for fracturing according to claim 1, characterized in that: In step (2), the mass ratio of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, and isobutylamidopropyltrimethylammonium methyl sulfate to deionized water is 0.68-0.70:

1.

3. The method for preparing the thickener for fracturing according to claim 1, characterized in that: In step (2), isopropanol is used as a chain transfer agent, and its mass accounts for 0.23% of the total mass of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, and isobutenamidopropyltrimethylammonium methyl sulfate in step (2). In step (2), the mixing temperature is 30℃, the mixing time is 12-15 min, and the mixing speed is 300 r / min.

4. The method for preparing the thickener for fracturing according to claim 1, characterized in that: The mixing temperature in step (4) is 25℃, the mixing time is 2-3 min, and the heating rate when the temperature is raised to 68-70℃ is 1℃ / min; In step (4), the polymerization reaction uses ammonium persulfate solution and sodium bisulfite solution as initiators. The initiators are added in a stepwise dropwise manner: First, ammonium persulfate solution accounting for 70% of the total mass of ammonium persulfate solution and sodium bisulfite solution accounting for 70% of the total mass of sodium bisulfite solution are added within 30 minutes, and the reaction is kept at 68-70℃ for 30 minutes. Then, the remaining ammonium persulfate solution and sodium bisulfite solution are added within 15 minutes.

5. The method for preparing the thickener for fracturing according to claim 1, characterized in that: In step (4), the polymerization temperature is 68-70℃ and the polymerization time is 60-65 min; The maturation time in step (4) is 58-60 min.

6. The method for preparing the thickener for fracturing according to claim 1, characterized in that: In step (4), the volume ratio of ammonium persulfate solution to sodium bisulfite solution is 1:1; In step (4), the molar amount of ammonium persulfate in the ammonium persulfate solution is 0.21-0.23% of the sum of the molar amounts of acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonium]butane-1-sulfonate, isobutylamidopropyltrimethylammonium methyl sulfate, and dicyclopentadienoxyethyl acrylate in step (1). Step (4) Control the stirring speed at 200 r / min throughout the entire reaction process.

7. The method for preparing the thickener for fracturing according to claim 1, characterized in that: In step (5), the volume of anhydrous ethanol is 2.5 times the volume of the reaction liquid, the stirring speed is 50 r / min, and the precipitation time is 18-20 min. In step (5), the drying temperature is 60℃, the drying time is 8h, the drying vacuum degree is -0.09MPa, and it passes through an 80-mesh sieve.

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