A temperature-sensitive associated fracturing fluid thickening agent, a preparation method and application thereof

Abstract

The application provides a temperature-sensitive associated fracturing fluid thickening agent and a preparation method and application thereof, and belongs to the oil field chemical field, wherein the temperature-sensitive associated fracturing fluid thickening agent is a quaternary copolymer or a ternary copolymer; the quaternary copolymer is obtained by copolymerization of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, N-(omega-sulfonic acid C2-C6 linear alkyl) itaconimide and fatty alkyl dimethyl allyl ammonium chloride; and the ternary copolymer is obtained by copolymerization of acrylamide, N-(omega-sulfonic acid C2-C6 linear alkyl) itaconimide and fatty alkyl dimethyl allyl ammonium chloride. The temperature-sensitive associated fracturing fluid thickening agent can be directly prepared under high-salt conditions with high salinity, and the system can still maintain excellent thickening performance and temperature resistance and shear resistance after preparation.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to a temperature-sensitive associative fracturing fluid thickener, its preparation method, and its application. Background Technology

[0002] As global oil and gas exploration and development continues to extend into deeper and higher-temperature, higher-salinity reservoirs, the consumption of fracturing fluid is increasing exponentially. Against this backdrop, the resource utilization of fracturing flowback fluid is no longer simply an environmental requirement, but a core survival principle for the industry that balances ecological benefits and development costs. This involves utilizing high-salinity fluids (often exceeding 100,000 mg / L and rich in Ca)... 2+ Mg 2+ The flowback fluid containing divalent ions can be directly used to formulate fracturing fluid, enabling an "internal recycling" of water resources, significantly reducing freshwater consumption, and completely eliminating wastewater discharge and treatment costs, which highly aligns with the concept of green and low-carbon energy development. However, current fracturing fluid thickener systems are difficult to adapt to this extreme and complex application scenario.

[0003] Natural polymer thickeners and their derivatives are susceptible to salting out due to the influence of high-valence ions such as calcium and magnesium in high-salt environments. This causes molecular chain coiling and collapse, leading to a sharp drop in viscosity and high residue content, which can damage formations. While conventional synthetic polymer thickeners have improved stability to some extent by introducing temperature- and salt-resistant monomers, the "polyelectrolyte effect" remains fatal in high-salt flowback fluids. High concentrations of inorganic salt ions severely compress the polymer double layer, producing a significant "ion shielding effect," resulting in the loss of electrostatic repulsion between molecular chains and a substantial decrease in rheological stability. Existing hydrophobic associative thickeners, although introducing hydrophobic groups to establish a spatial network, are not specifically designed for direct preparation of high-salt flowback fluids. In high-salt environments at room temperature, hydrophobic groups readily undergo intramolecular association (rather than intermolecular association), making dissolution in flowback fluids extremely difficult, resulting in a "clumped" or "fish-eye" appearance. At high temperatures, intense thermal motion easily tears apart this fragile hydrophobic associative network. This forces the site to undergo costly and complex pretreatment of the backflow solution before preparation, such as reverse osmosis desalination and alkali addition to remove hardness. The cumbersome construction procedures completely negate the economic advantages of reusing the backflow solution.

[0004] Extensive research has been conducted on hydrophobic associative fracturing fluid thickeners. CN120647831A discloses a hydrophobic associative fracturing fluid thickener and its preparation method. This technology uses acrylamide, a carboxylic acid-containing monomer (acrylic acid / itaconic acid), a sulfonic acid monomer, and a hydrophobic associative monomer as copolymers, which can possess certain temperature and shear resistance properties. However, this technology still has significant drawbacks: Firstly, the carboxylic acid monomer used (unmodified itaconic acid / acrylic acid) contains free carboxyl groups, which easily react with Ca in high-salinity flowback fluids. 2+ Mg 2+Firstly, complex salting out occurs, indicating insufficient resistance to salt and divalent ions. Secondly, the molecular chains are prone to decarboxylation and degradation at high temperatures, and cannot form a stable synergistic network with hydrophobic associating monomers. Direct use cannot meet the fracturing requirements of high-temperature and high-salinity oil reservoirs.

[0005] Therefore, developing fracturing fluid thickeners that can be directly applied to the preparation of high-mineralization flowback fluids and possess both good solubility and dispersibility at room temperature and a stable associative network structure at high temperatures has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] In view of the technical problems existing in the background art, the present invention provides a temperature-sensitive associative fracturing fluid thickener, its preparation method and application, aiming to solve the technical problems that existing hydrophobic associative thickeners cannot be directly adapted to the preparation of high-mineralization flowback fluids, have difficulty dissolving at room temperature, have unstable associative networks at high temperatures, and have insufficient resistance to salt and divalent ions.

[0007] In a first aspect, the present invention provides a temperature-sensitive associative fracturing fluid thickener, wherein the temperature-sensitive associative fracturing fluid thickener is a quaternary copolymer or a terpolymer; The quaternary copolymer was obtained by copolymerization of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-(ω-sulfonic C2-C6 linear alkyl)itconimide, and aliphatic alkyl dimethylallyl ammonium chloride. The terpolymer was obtained by copolymerizing acrylamide, N-(ω-sulfonic acid C2-C6 linear alkyl) itaconimid, and fatty alkyl dimethyl allyl ammonium chloride. The structural formula of the temperature-sensitive associative fracturing fluid thickener is shown in Formula I or Formula II: Formula I; Formula II; In Formula I, a, b, c, and d are the mole percentages of structural units, a + b + c + d = 100%, and b + c + d ≤ 50%; where a is 50%~98.8%, b is 1%~45%, c is 0.1%~30%, and d is 0.1%~25%; m is a natural number from 2 to 6, and n is 15 or 17. In Formula II, e, f, and g are the mole percentages of structural units, e + f + g = 100%, and f + g ≤ 50%; where e is 50%~99.8%, f is 0.1%~30%, and g is 0.1%~30%; x is a natural number from 2 to 6, and y is 15 or 17.

[0008] Preferably, the ω-sulfonate C2-C6 straight-chain alkyl group in N-(ω-sulfonate C2-C6 straight-chain alkyl)itconimide is selected from any one of 2-sulfonate ethyl, 3-sulfonate propyl, 4-sulfonate butyl, 5-sulfonate pentyl, and 6-sulfonate hexyl.

[0009] Preferably, the fatty alkyl dimethyl allyl ammonium chloride is octadecyl dimethyl allyl ammonium chloride or hexadecyl dimethyl allyl ammonium chloride.

[0010] Secondly, the present invention provides a method for preparing a temperature-sensitive associative fracturing fluid thickener, comprising the following steps: S1. Dissolve different reactive monomers in water to prepare a mixed monomer solution, and adjust the pH of the mixed monomer solution to 7-8; S2. Adjust the temperature of the mixed monomer solution to 10~70℃, introduce nitrogen to remove oxygen, add redox initiator and stir. Stop stirring when the solution shows the phenomenon of climbing rods. Keep the reaction at the temperature for 8~10h to obtain the gel block product. S3. Cut the rubber block into small pieces, dry it to constant weight, and then crush and sieve it to obtain a temperature-sensitive associative fracturing fluid thickener.

[0011] Preferably, the mass fraction of the mixed monomer solution is 5% to 30%.

[0012] Preferably, the redox initiator includes persulfate and bisulfite; the mass ratio of persulfate to bisulfite is 1:(1.1~1.5).

[0013] Preferably, the amount of redox initiator used is 0.05% to 2% of the total mass of the monomer.

[0014] Preferably, the drying temperature is 50~80℃.

[0015] Thirdly, the present invention provides a fracturing fluid, the raw materials for which include the temperature-sensitive associative fracturing fluid thickener described in the first aspect.

[0016] Preferably, the mass concentration of the thermosensitive associative fracturing fluid thickener in the fracturing fluid is 0.2% to 1%.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The thermosensitive associative fracturing fluid thickener of the present invention contains hydrophobic associative monomers, which can not only improve viscosity at low temperatures, but also have the effect of "increased viscosity with increased temperature" at high temperatures. The hydrophobic association between its molecular chains forms a fracturing fluid system with a three-dimensional network structure, which can maintain the extended state of the molecular chains and a stable associative network in a high salinity environment. In particular, the rigid imide ring improves the temperature resistance and the sulfonic acid group at the end of the straight chain strengthens the salt and calcium and magnesium resistance.

[0018] (2) The synthesis process of the thermosensitive associative fracturing fluid thickener of the present invention is simple, does not require the addition of metal crosslinking agent for crosslinking, has low production cost, good solubility, and can be directly prepared using high-salt flowback fluid that has not been desalted and purified. After preparation, the system can still maintain excellent thickening performance and temperature resistance and shear resistance, which is in line with the concept of environmental protection. It fundamentally solves the problems of difficult treatment and low reuse rate of fracturing flowback fluid, and greatly reduces the water consumption and overall cost of fracturing construction.

[0019] (3) The present invention also provides a ternary copolymer system with qualified performance, which has lower raw material cost than the quaternary system and is suitable for fracturing of medium and high temperature (≤90℃) and high salt reservoirs. It can be flexibly selected according to the on-site working conditions. Attached Figure Description

[0020] Figure 1 The infrared spectrum of N-(3-sulfopropyl)itconimide prepared in Example 1 of this invention. Detailed Implementation

[0021] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0022] To address the technical problems of existing hydrophobic associative thickeners, such as their inability to directly adapt to high-salinity flowback fluid formulations, difficulty in dissolving at room temperature, instability of the associative network at high temperatures, and insufficient resistance to salts and divalent ions, this invention provides a temperature-sensitive associative fracturing fluid thickener, its preparation method, and its application. Specifically, itaconic acid is directionally modified into N-(ω-sulfonic acid C2-C6 straight-chain alkyl)itaconicimide. The rigid imide ring enhances temperature resistance, and the terminal sulfonic acid groups of the straight chain strengthen resistance to salts and calcium / magnesium ions, fundamentally solving the two major defects of itaconic acid. This thickener forms a fracturing fluid system with a three-dimensional network structure through hydrophobic association between molecular chains. It maintains the extended state of the molecular chains and a stable associative network in high-salinity environments, exhibiting superior high-temperature thickening capabilities.

[0023] In a first aspect, embodiments of the present invention provide a temperature-sensitive associative fracturing fluid thickener, wherein the temperature-sensitive associative fracturing fluid thickener is a quaternary copolymer or a terpolymer; The quaternary copolymer was obtained by copolymerization of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-(ω-sulfonic C2-C6 linear alkyl)itconimide, and aliphatic alkyl dimethylallyl ammonium chloride. The terpolymer was obtained by copolymerizing acrylamide, N-(ω-sulfonic acid C2-C6 linear alkyl) itaconimid, and fatty alkyl dimethyl allyl ammonium chloride. The structural formula of the temperature-sensitive associative fracturing fluid thickener is shown in Formula I or Formula II: Formula I; Formula II; In Formula I, a, b, c, and d are the mole percentages of structural units, a + b + c + d = 100%, and b + c + d ≤ 50%; where a is 50%~98.8%, b is 1%~45%, c is 0.1%~30%, and d is 0.1%~25%; m is a natural number from 2 to 6, and n is 15 or 17. In Formula II, e, f, and g are the mole percentages of structural units, e + f + g = 100%, and f + g ≤ 50%; where e is 50%~99.8%, f is 0.1%~30%, and g is 0.1%~30%; x is a natural number from 2 to 6, and y is 15 or 17.

[0024] In the technical solution of this invention embodiment, itaconic acid is directionally modified into N-(ω-sulfonic acid C2-C6 straight-chain alkyl) itaconicimide. This is a core technical means to adapt itaconic fluids for high-temperature and high-salinity oil reservoirs and to achieve direct preparation of flowback fluids. Unmodified itaconic acid cannot meet the requirements of the operating conditions. The specific reasons for modification are as follows: Unmodified itaconic acid has a flexible carboxyl structure, and decarboxylation and chain breakage occur when the formation temperature is above 80°C, resulting in rapid loss of fracturing fluid viscosity. After modification, itaconicimide forms a five-membered rigid ring, which greatly improves thermal stability and ensures that the molecular chain of the copolymer does not break and the association network does not collapse at a formation temperature of 90°C. In addition, the carboxyl group of unmodified itaconic acid readily reacts with Ca. 2+ Mg 2+ Complex salting out directly fails in high-salinity flowback fluids. The modified monomer, by introducing sulfonic acid propyl groups, forms a synergistic bissulfonic acid group with AMPS (2-acrylamido-2-methylpropanesulfonic acid), allowing for direct use in flowback fluid formulations without sedimentation or flocculation. This modified monomer possesses both rigid rings and amphiphilic structures, acting as molecular bridges to improve the copolymerization uniformity of acrylamide, AMPS, and octadecyldimethylallyl ammonium chloride. It avoids intramolecular association at room temperature and network tearing at high temperatures, achieving a temperature-increase viscosity effect, thus meeting the proppant-carrying requirements of fracturing fluids.

[0025] Furthermore, in some embodiments, the ω-sulfonate C2-C6 straight-chain alkyl group in N-(ω-sulfonate C2-C6 straight-chain alkyl)itconimide is selected from any one of 2-sulfonate ethyl, 3-sulfonate propyl, 4-sulfonate butyl, 5-sulfonate pentyl, and 6-sulfonate hexyl.

[0026] In the technical solution of this invention embodiment, ω-sulfonic acid C2-C6 straight-chain alkyl means that a sulfonic acid group (-SO3H) is attached to the end (ω position) of the C2-C6 straight-chain alkyl chain.

[0027] In the technical solutions of this invention, N-(ω-sulfonic acid C2-C6 straight-chain alkyl)itconimides all have the same structure and function: the rigid ring of the five-membered imide ensures temperature resistance, the sulfonic acid group at the end of the straight chain achieves strong salt resistance, and the moderate carbon chain of C2-C6 ensures copolymerization uniformity; among them, N-(3-sulfonic acid propyl)itconimide is the optimal choice, and monomers of the same series can achieve the technical effects of temperature-sensitive association and direct high-salt solution preparation of this invention.

[0028] Furthermore, in some embodiments, the fatty alkyl dimethyl allyl ammonium chloride is octadecyl dimethyl allyl ammonium chloride or hexadecyl dimethyl allyl ammonium chloride.

[0029] Secondly, embodiments of the present invention provide a method for preparing a temperature-sensitive associative fracturing fluid thickener, comprising the following steps: S1. Dissolve different reactive monomers in water to prepare a mixed monomer solution, and adjust the pH of the mixed monomer solution to 7-8; S2. Adjust the temperature of the mixed monomer solution to 10~70℃, introduce nitrogen to remove oxygen, add redox initiator and stir. Stop stirring when the solution shows the phenomenon of climbing rods. Keep the reaction at the temperature for 8~10h to obtain the gel block product. S3. Cut the rubber block into small pieces, dry it to constant weight, and then crush and sieve it to obtain a temperature-sensitive associative fracturing fluid thickener.

[0030] Furthermore, in some embodiments, the mass fraction of the mixed monomer solution is 5% to 30%.

[0031] Furthermore, in some embodiments, the redox initiator includes persulfate and bisulfite.

[0032] Furthermore, in some embodiments, the mass ratio of persulfate to bisulfite is 1:(1.1~1.5).

[0033] Furthermore, in some embodiments, the amount of redox initiator is 0.05% to 2% of the total mass of the monomer.

[0034] Furthermore, in some embodiments, the stirring speed is 100~250 r / min.

[0035] Furthermore, in some embodiments, the drying temperature is 50~80°C.

[0036] Thirdly, embodiments of the present invention provide a fracturing fluid, the raw materials for which include the temperature-sensitive associative fracturing fluid thickener described in the first aspect.

[0037] Furthermore, in some embodiments, the mass concentration of the thermosensitive associative fracturing fluid thickener in the fracturing fluid is 0.2% to 1%.

[0038] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0039] Example 1 The preparation method of N-(3-sulfopropyl)itconimide is as follows: (1) Add 250 mL of pre-chilled dimethyl carbonate to a 500 mL three-necked flask, then add 28 g of itaconic anhydride and stir until completely dissolved; use an ice bath to lower the system temperature to 0-5 °C, and under stirring conditions, slowly add 40.3 g of sodium 3-aminopropane sulfonate in batches, maintain the temperature at 0-5 °C and stir for 30 min, then remove the ice bath and continue stirring at room temperature for 3 h to obtain crude N-(sulfonylpropyl)itaconic acid; introduce nitrogen into the system, seal the neck of the three-necked flask, and set aside for later use.

[0040] (2) Transfer the sealed three-necked flask from step 1 to a fume hood, assemble a thermometer, a spherical condenser and a stirring device, and turn on the stirring; add 6.6g of anhydrous sodium carbonate to the system, stir for 10min to disperse it evenly, then add 100g of propionic anhydride and 0.03g of hydroquinone monomethyl ether, slowly raise the temperature to 90℃ (reflux state), and react at a constant temperature for 7h; keep stirring during the reaction to avoid local overheating, stop heating after the reaction is completed, and let it cool naturally to room temperature.

[0041] (3) After the system cools to room temperature, wear a gas mask and perform vacuum filtration to collect the filter cake; prepare an ethanol-water mixed solvent with a volume ratio of 8:2, heat and reflux until the filter cake is completely dissolved, add 1g of activated carbon to the system, continue reflux for 10min, filter while hot to remove activated carbon and insoluble impurities; collect the filtrate, cool it naturally to room temperature, place it in a refrigerator for 4h, filter after the solid precipitates, wash the filter cake 2-3 times with ice-cold anhydrous ethanol, put the filter cake in a vacuum drying oven to dry, and obtain 50g of the target product N-(3-sulfonylpropyl)itconimide.

[0042] The structural formula of N-(3-sulfonopropyl)itconimide is as follows:

[0043] The N-(3-sulfopropyl)itconimide functional monomer prepared in this embodiment was characterized by Fourier transform infrared spectroscopy (FT-IR), and the results are shown in the appendix. Figure 1 As shown. In the infrared spectrum: 1741 cm⁻¹ -1The presence of a characteristic absorption peak for the C=O asymmetric stretching vibration of the five-membered ring imide structure at 1648 cm⁻¹ confirms the successful ring closure between the starting amine and the anhydride, forming the stable imide core structure of the target product; -1 A characteristic absorption peak, superimposed by the C=O symmetric stretching vibration of the imide and the C=C double bond of the terminal group, appears at 880 cm⁻¹. -1 The presence of an out-of-plane rocking vibration characteristic absorption peak at the terminal CH2=C double bond indicates that the carbon-carbon double bond structure capable of participating in free radical copolymerization is well preserved in the target molecule; 1167 cm⁻¹ -1 1047cm -1 A sulfonic acid group (-SO3) appears at the location. - The characteristic absorption peaks of the asymmetric and symmetric stretching vibrations of the sulfonic acid group confirm that the strongly hydrated sulfonic acid group has been successfully incorporated into the molecular structure. These characteristic absorption peaks perfectly match the molecular structure of the target N-(3-sulfopropyl)itconimide, confirming the successful synthesis of the target functional monomer in this embodiment.

[0044] Example 2 The preparation steps of a temperature-sensitive associative fracturing fluid thickener (quaternary copolymer) are as follows: (1) Take acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, N-(3-sulfonylpropyl)itconimide and octadecyldimethylallylammonium chloride with molar percentages of 92.5%, 5%, 1% and 1.5%, respectively, dissolve them in water, and prepare a mixed monomer solution with a total monomer concentration of 25wt%. Adjust the pH value to about 7 with a sodium hydroxide aqueous solution with a mass fraction of 20%.

[0045] (2) Pour the mixed monomer solution into a 500 mL glass reactor, place it in a 60 °C water bath, and purge with N2 to remove oxygen for 30 min. Add ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.2, with a total amount of 0.2% of the total monomer mass. Stir at a speed of 200 r / min until the solution exhibits the phenomenon of climbing rods. Stop stirring and react for 10 h to obtain a gel-like product.

[0046] (3) Take out the rubber block, cut it into pieces with scissors, put it in a 60℃ oven to dry to constant weight, crush it with a pulverizer, sieve it with a sample sieve, and collect the white powder polymer sample, which is the thermosensitive associative fracturing fluid thickener.

[0047] In this embodiment, the structural formula of the temperature-sensitive associative fracturing fluid thickener is as follows: ; Where a:b:c:d=92.5:5:1:1.5.

[0048] Example 3 The preparation steps of a temperature-sensitive associative fracturing fluid thickener (terpolymer) are as follows: (1) Take acrylamide, N-(3-sulfonylpropyl)itconimide and octadecyldimethylallylammonium chloride with molar percentages of 97.5%, 1% and 1.5%, respectively, dissolve them in water, and prepare a mixed monomer solution with a total monomer concentration of 25wt%. Adjust the pH value to about 7 with a sodium hydroxide aqueous solution with a mass fraction of 20%.

[0049] (2) Pour the mixed monomer solution into a 500ml glass reactor and place it in a 60℃ water bath. Pass N2 through to remove oxygen for 30min. Then add ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.2, with a total amount of 0.2% of the total monomer mass. Stir at a speed of 200r / min until the solution shows the phenomenon of climbing the rod. Stop stirring and react for 10h to obtain a gel-like product.

[0050] (3) Take out the rubber block, cut it into pieces with scissors, put it in a 60℃ oven to dry, then crush the block sample with a pulverizer, sieve the sample with a sieve, and collect the white powder polymer sample, which is the temperature-sensitive associative fracturing fluid thickener.

[0051] Example 4 The preparation steps of a temperature-sensitive associative fracturing fluid thickener (quaternary copolymer) are as follows: (1) Take 65%, 3%, 30%, and 2% of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, N-(3-sulfonylpropyl)itconimide, and octadecyldimethylallylammonium chloride, respectively, dissolve them in water, and prepare a mixed monomer solution with a total monomer concentration of 25wt%. Adjust the pH value to about 7 with a 20% sodium hydroxide aqueous solution.

[0052] (2) Pour the mixed monomer solution into a 500 mL glass reactor, place it in a 60 °C water bath, and purge with N2 to remove oxygen for 30 min. Add ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.2, with a total amount of 0.2% of the total monomer mass. Stir at a speed of 200 r / min until the solution exhibits the phenomenon of climbing rods. Stop stirring and react for 10 h to obtain a gel-like product.

[0053] (3) Take out the rubber block, cut it into pieces with scissors, put it in a 60℃ oven to dry to constant weight, crush it with a pulverizer, sieve it with a sample sieve, and collect the white powder polymer sample, which is the thermosensitive associative fracturing fluid thickener.

[0054] Example 5 The preparation steps of a temperature-sensitive associative fracturing fluid thickener (quaternary copolymer) are as follows: (1) Take 50%, 35%, 5% and 10% of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-(3-sulfonylpropyl)itconimide and octadecyldimethylallylammonium chloride, dissolve them in water, and prepare a mixed monomer solution with a total monomer concentration of 25wt%. Adjust the pH value to about 7 with a 20% sodium hydroxide aqueous solution.

[0055] (2) Pour the mixed monomer solution into a 500 mL glass reactor, place it in a 60 °C water bath, and purge with N2 to remove oxygen for 30 min. Add ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.2, with a total amount of 0.2% of the total monomer mass. Stir at a speed of 200 r / min until the solution exhibits the phenomenon of climbing rods. Stop stirring and react for 10 h to obtain a gel-like product.

[0056] (3) Take out the rubber block, cut it into pieces with scissors, put it in a 60℃ oven to dry to constant weight, crush it with a pulverizer, sieve it with a sample sieve, and collect the white powder polymer sample, which is the thermosensitive associative fracturing fluid thickener.

[0057] Comparative Example 1 The preparation method of fracturing fluid thickener (N-(3-sulfonylpropyl)itconimide terpolymer) is as follows: (1) Take 89%, 10% and 1% of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid and octadecyl dimethylallyl ammonium chloride, dissolve them in water, and prepare a mixed monomer solution with a total monomer concentration of 25wt%. Adjust the pH value to about 7 with a 10% sodium hydroxide aqueous solution.

[0058] (2) Pour the mixed monomer solution into a 500ml glass reactor and place it in a 60℃ water bath. Pass N2 through to remove oxygen for 30min. Then add ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.2, with a total amount of 0.2% of the total monomer mass. Stir at a speed of 200r / min until the solution shows the phenomenon of climbing the rod. Stop stirring and react for 10h to obtain a gel-like product.

[0059] (3) Take out the rubber block, cut it into pieces with scissors, put it in a 60℃ oven to dry to constant weight, crush it with a pulverizer, sieve it with a sample sieve, and collect the white powder polymer sample, which is the fracturing fluid thickener.

[0060] Comparative Example 2 Commercially available partially hydrolyzed polyacrylamide (HPAM) with a weight-average molecular weight of 1.0 × 10⁻⁶ was used. 7 The degree of hydrolysis is 22%.

[0061] Comparative Example 3 The difference between this invention and Example 2 is that N-(3-sulfonopropyl)itconimide is replaced with an equimolar amount of itaconic acid; the specific preparation method is as follows: (1) Take acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, itaconic acid and octadecyl dimethyl allyl ammonium chloride with molar percentages of 92.5%, 5%, 1% and 1.5%, respectively, dissolve them in water, and prepare a mixed monomer solution with a total monomer concentration of 25wt%. Adjust the pH value to about 7 with a sodium hydroxide aqueous solution with a mass fraction of 20%.

[0062] (2) Pour the mixed monomer solution into a 500 mL glass reactor, place it in a 60 °C water bath, and purge with N2 to remove oxygen for 30 min. Add ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.2, with a total amount of 0.2% of the total monomer mass. Stir at a speed of 200 r / min until the solution exhibits the phenomenon of climbing rods. Stop stirring and react for 10 h to obtain a gel-like product.

[0063] (3) Take out the rubber block, cut it into pieces with scissors, put it in a 60℃ oven to dry to constant weight, crush it with a pulverizer, sieve it with a sample sieve, and collect the white powder polymer sample, which is the fracturing fluid thickener.

[0064] Performance testing Test 1 Viscosity-Temperature Characteristics Experiment The fracturing fluid thickeners prepared in each embodiment and comparative example were directly mixed with 0.5% solutions of simulated formation water at a salinity of 150,000. The stirrer speed was 200 r / min, the temperature was gradually increased from 25℃ to 90℃, and the shear rate was 170 s. -1 Its apparent viscosity was measured under the specified conditions. The evaluation results are shown in Table 1 below.

[0065] Table 1

[0066] Table 1 shows that the temperature-sensitive associative fracturing fluid thickener provided in this embodiment exhibits a continuous increase in viscosity with increasing temperature within the range of 25℃ to 90℃, demonstrating significant high-temperature thickening characteristics. This indicates that this type of polymer possesses both temperature-sensitive associative properties and salt resistance. (At 90℃ and 170s...) -1Under shear conditions, the viscosity remained around 200 mPa·s, far superior to the comparative samples, meeting the viscosity requirements for fracturing fluid in high-temperature, high-salt reservoir fracturing operations. Compared to Example 2, the overall viscosity of Example 3 was significantly lower, with a lower base viscosity and weaker salt resistance than the quaternary system. This indicates that adding AMPS monomer, with its steric hindrance and salt resistance, effectively enhanced the polymer's base viscosity and salt resistance. Example 4 incorporated a large amount of N-(3-sulfonylpropyl)itconimide. Due to the allyl and five-membered ring structure, polymerization was more difficult, resulting in a reduced polymer molecular weight. Macroscopically, this manifested as an initial viscosity lower than Examples 1 and 2. However, the large number of five-membered ring structures and sulfonic acid groups made the polymer viscosity more stable, as clearly shown in the performance tests in Table 2. Example 5, due to the addition of a large amount of octadecyldimethylallylammonium chloride, had increased polymerization difficulty, resulting in an initial viscosity lower than Examples 1 and 2. However, due to the influence of hydrophobic associating groups, the viscosity increased with temperature, exhibiting a significant temperature-sensitive effect.

[0067] The thickener solution in Comparative Example 1 exhibits slight viscosity increase at low temperatures due to weak hydrophobic association. However, at medium to high temperatures, the viscosity rapidly decreases due to network breakdown and chain contraction, exhibiting an overall characteristic of "low base viscosity + weak temperature-sensitive association + rapid viscosity decay at high temperatures." Compared to Examples 2 and 3, Comparative Example 1 shows a significant weakness in temperature and salt resistance, indicating that N-(3-sulfonopropyl)itconimide can synergistically interact with 2-acrylamido-2-methylpropanesulfonic acid and fatty alkyl dimethylallyl ammonium chloride, making it a key functional monomer that can significantly enhance the polymer's high-salt-condition thickening ability and high-temperature stability.

[0068] The thickener in Comparative Example 2 has a high degree of molecular chain curling due to the carboxyl group on its molecular chain being shielded by a large number of cations, making it unable to form an effective spatial network structure. At the same time, the molecular chain undergoes intense thermal motion at high temperatures, resulting in extremely poor temperature and salt resistance under high salinity, which cannot meet the thickening requirements of high-temperature and high-salt oil reservoirs.

[0069] Comparative Example 3 is a thickener prepared using unmodified itaconic acid. Its molecular chain contains free carboxyl groups, and it is significantly affected by the ion shielding effect under high salinity. Its viscosity continues to decrease with increasing temperature, and it has no temperature-sensitive thickening effect. Its viscosity at 90℃ is only 42 mPa·s, which is lower than the requirements of the SY / T6376-2008 standard and cannot meet the fracturing requirements of high-temperature and high-salinity oil reservoirs.

[0070] Test 2 Evaluation of fracturing fluid shear stability The fracturing fluid thickeners prepared in each embodiment and comparative example were directly mixed with water of 150,000 salinity to prepare a 0.5% solution by mass. The solution was then subjected to an environment of 90°C and a shear rate of 170 s⁻¹. -1 The apparent viscosity was measured at different shear times after 120 min of shearing, and the test results are shown in Table 2 below.

[0071] Table 2

[0072] Table 2 shows that the fracturing fluid prepared by directly mixing the thermosensitive associative fracturing fluid thickener provided in this embodiment with high-salinity water maintains a viscosity >50 mPa·s after shearing at 90℃ for 120 min, meeting the 50 mPa·s requirement in the "General Technical Conditions for Fracturing Fluids SY / T6376-2008" and conforming to industry requirements. The fracturing fluids prepared by directly mixing the thickeners provided in Comparative Examples 1, 2, and 3 with high-salinity water do not meet the 50 mPa·s requirement in the "General Technical Conditions for Fracturing Fluids SY / T6376-2008" after shearing at 90℃ for 120 min, and therefore do not conform to industry requirements.

[0073] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A temperature-sensitive associative fracturing fluid thickener, characterized in that, The temperature-sensitive associative fracturing fluid thickener is a quaternary copolymer or a ternary copolymer; The quaternary copolymer is obtained by copolymerization of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-(ω-sulfonic acid C2-C6 linear alkyl)itconimide, and fatty alkyl dimethylallyl ammonium chloride; The terpolymer was obtained by copolymerizing acrylamide, N-(ω-sulfonic acid C2-C6 linear alkyl) itaconimid, and fatty alkyl dimethyl allyl ammonium chloride. The structural formula of the temperature-sensitive associative fracturing fluid thickener is shown in Formula I or Formula II: Formula I; Formula II; In Formula I, a, b, c, and d are the mole percentages of structural units, a + b + c + d = 100%, and b + c + d ≤ 50%; where a is 50%~98.8%, b is 1%~45%, c is 0.1%~30%, and d is 0.1%~25%; m is a natural number from 2 to 6, and n is 15 or 17. In Formula II, e, f, and g are the mole percentages of structural units, e + f + g = 100%, and f + g ≤ 50%; where e is 50%~99.8%, f is 0.1%~30%, and g is 0.1%~30%; x is a natural number from 2 to 6, and y is 15 or 17.

2. The thermosensitive associative fracturing fluid thickener according to claim 1, characterized in that, The ω-sulfonyl C2-C6 straight-chain alkyl group in the N-(ω-sulfonic acid C2-C6 linear alkyl)itconimide is selected from any one of 2-sulfonic acid ethyl, 3-sulfonic acid propyl, 4-sulfonic acid butyl, 5-sulfonic acid pentyl, and 6-sulfonic acid hexyl.

3. The thermosensitive associative fracturing fluid thickener according to claim 1, characterized in that, The fatty alkyl dimethyl allyl ammonium chloride is octadecyl dimethyl allyl ammonium chloride or hexadecyl dimethyl allyl ammonium chloride.

4. The preparation method of the temperature-sensitive associative fracturing fluid thickener as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Dissolve different reactive monomers in water to prepare a mixed monomer solution, and adjust the pH of the mixed monomer solution to 7-8; S2. Adjust the temperature of the mixed monomer solution to 10~70℃, introduce nitrogen to remove oxygen, add redox initiator and stir. Stop stirring when the solution shows the phenomenon of climbing rods. Keep the reaction at the temperature for 8~10h to obtain the gel block product. S3. The rubber block is cut into small pieces, dried to constant weight, and then crushed and sieved to obtain a temperature-sensitive associative fracturing fluid thickener.

5. The method for preparing the thermosensitive associative fracturing fluid thickener according to claim 4, characterized in that, The mass fraction of the mixed monomer solution is 5% to 30%.

6. The method for preparing the thermosensitive associative fracturing fluid thickener according to claim 4, characterized in that, The redox initiator includes persulfate and bisulfite; the mass ratio of persulfate to bisulfite is 1:(1.1~1.5).

7. The method for preparing the thermosensitive associative fracturing fluid thickener according to claim 4, characterized in that, The amount of the redox initiator is 0.05% to 2% of the total mass of the monomer.

8. The method for preparing the thermosensitive associative fracturing fluid thickener according to claim 4, characterized in that, The drying temperature is 50~80℃.

9. A fracturing fluid, characterized in that, The raw materials for preparing the fracturing fluid include the thermosensitive associative fracturing fluid thickener as described in any one of claims 1 to 3.

10. The fracturing fluid according to claim 9, characterized in that, The mass concentration of the thermosensitive associative fracturing fluid thickener in the fracturing fluid is 0.2% to 1%.

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