A scale-inhibiting polymer viscosifier and a method for preparing the same

Abstract

The application discloses a scale-inhibiting polymer thickening agent and a preparation method thereof. The thickening agent is prepared by copolymerization of four monomers, namely itaconic acid, 2-acrylamide-2-methylpropanesulfonic acid, isopropyl acrylphosphonic acid and acrylamide, through an aqueous solution polymerization reaction. The four-component copolymer has both scale inhibition and fracturing functions. The scale inhibition functional groups are introduced into the molecular chain of the polymer thickening agent, so that the 'one agent with multiple effects' is realized. Technical defects, such as a complex liquid preparation process, low construction efficiency, poor compatibility and high risk of interaction between chemical agents in the prior art are effectively overcome. The application is especially suitable for fracturing stimulation operation of oil and gas wells prone to scaling.

Description

Technical Field

[0001] This invention belongs to the field of oilfield scale-inhibiting fracturing fluid technology, and relates to a scale-inhibiting polymer thickener and its preparation method. Background Technology

[0002] In oil and gas field development, fracturing plays an indispensable role as a key technology for enhancing oil recovery. However, in actual fracturing operations, as fracturing fluid is continuously injected into the formation, the temperature and pressure conditions of the formation change significantly, disrupting the original chemical equilibrium of the formation water. This change causes divalent metal ions such as calcium and barium in the formation water to react with carbonate and sulfate ions, forming insoluble precipitates such as calcium carbonate, calcium sulfate, and barium sulfate. These precipitates gradually accumulate in the pipeline, causing not only pipeline blockage and increased frictional resistance to fluid flow, but also severely hindering the normal movement of fluids. This leads to a series of problems, including decreased oil well production, frequent pump jamming, and difficulties in water injection wells, seriously affecting the efficient development of oil and gas fields.

[0003] To address these challenges, traditionally, scaling problems have relied on a two-stage approach: first, using plant-based adhesives or polyacrylamide-based thickeners to construct a proppant-carrying system to ensure the fracturing fluid can effectively carry proppant into the formation; second, adding scale inhibitors during fracturing fluid flowback to prevent precipitate formation. However, this approach not only involves complex on-site fluid preparation processes and high reagent consumption, but also often results in high residue levels, increasing the difficulty and cost of subsequent treatment.

[0004] Several innovative solutions have been proposed in the existing technology to address the scale inhibition problem in oilfields. For example, Chinese patent application CN115894813A discloses an oilfield fracturing fluid scale inhibitor produced by polymerizing three monomers. This scale inhibitor exhibits excellent calcium carbonate scale inhibition performance and shows no flocculation, precipitation, or stratification after being added to the fracturing fluid, thus meeting the scale inhibition requirements during fracturing operations. Additionally, Chinese patent application CN105949371A discloses a ternary polymerized scale inhibitor synthesized using acrylic acid, acrylamide, and self-made monomers. This process is simple, the raw materials are readily available, and the scale inhibition rate is high, effectively preventing scaling problems in oilfield gathering and transportation pipelines.

[0005] While the aforementioned patents have made significant progress in oilfield scale inhibition, they all have limitations: they are used only as single scale inhibitors and do not possess the thickening and sand-carrying properties required for fracturing fluids. Therefore, developing a fracturing fluid that can achieve both efficient scale inhibition and thickening and sand-carrying functions is of great significance for improving oil and gas field extraction efficiency and reducing production costs, and is also a key problem that urgently needs to be solved in the field of oilfield chemistry. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a scale-inhibiting polymer thickener and its preparation method, thereby solving the technical problem that although existing oilfield scale inhibition solutions can effectively prevent scaling through a single scale inhibitor, they do not possess the thickening and proppant-carrying properties required by fracturing fluids, thus failing to simultaneously solve the dual requirements of sediment blockage and fluid proppant carrying in fracturing operations.

[0007] This invention is achieved through the following technical solution: A method for preparing a scale-inhibiting polymer thickener includes the following steps: S1: Mix the reactants and stir at room temperature until completely dissolved to obtain a monomer solution; the reactants are acrylamide, itaconic acid, 2-acrylamide-2-methylpropanesulfonic acid and isopropenzyme. S2: Add urea and EDTA-2Na to the monomer solution and adjust the pH of the solution to 6.8~7.0 to obtain a prepolymerized monomer solution; S3: Control the temperature of the prepolymerized monomer solution to 0-5 ℃, continuously introduce nitrogen gas to remove oxygen, then add oxidant solution, add reducing agent solution dropwise within 5-10 minutes, stop nitrogen introduction when the viscosity of the reaction solution rises, seal the reaction system, and allow it to heat up naturally. After the reaction is completed, take out the colloid, and after cutting, drying and pulverizing, obtain the scale-inhibiting polymer thickener.

[0008] Preferably, the acrylamide accounts for 55% to 70% of the total mass of the reactants, the itaconic acid accounts for 15% to 25% of the total mass of the reactants, the 2-acrylamido-2-methylpropanesulfonic acid accounts for 10% to 20% of the total mass of the reactants, and the isopropenzyme accounts for 5% to 10% of the total mass of the reactants.

[0009] Preferably, the isopropenphosphonic acid is prepared by the following method: phosphorus trichloride and acetone are mixed, stirred and reacted, glacial acetic acid is added, and the reaction is continued under reflux to obtain the isopropenphosphonic acid.

[0010] Preferably, the reactive monomer accounts for 25% of the total mass of the prepolymerized monomer solution.

[0011] Preferably, in step S2, the pH value is adjusted to 6.8~7.0 using sodium hydroxide solution, and the solution temperature is ≤20 ℃ during the pH adjustment process.

[0012] Preferably, in step S2, the urea and EDTA-2Na account for 0.1%~0.5% and 0.02%~0.08% of the mass of the reaction monomers, respectively.

[0013] Preferably, in step S3, the oxidant is ammonium persulfate, and its mass accounts for 0.2% to 0.5% of the mass of the reactant monomer.

[0014] Preferably, in step S3, the reducing agent is ascorbic acid and sodium formaldehyde sulfoxylate, which account for 0.05%~0.2% and 0.05%~0.15% of the mass of the reactant monomers, respectively.

[0015] A scale-inhibiting polymer thickener is prepared by the method described above.

[0016] A scale-inhibiting polymeric fracturing fluid is prepared by dissolving the above-mentioned scale-inhibiting polymeric thickener in water to prepare an aqueous solution with a mass concentration of 0.1% to 0.4%.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a method for preparing a scale-inhibiting polymer thickener. This method, through innovative molecular structure design and polymerization process, fundamentally solves the problem of the separation between "scale inhibition" and "thickening and sand-carrying" functions in existing technologies. Its core solution lies in abandoning the traditional "single scale inhibitor + thickener in-situ physical mixing" model, instead selecting monomers with different functions for aqueous solution copolymerization. In this formulation, acrylamide serves as the main monomer, providing the polymer backbone to achieve thickening and sand-carrying capabilities; while itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and isopropenzyme are introduced as functional monomers. These functional monomers not only endow the polymer molecular chain with scale-inhibiting properties such as capturing metal ions and inhibiting the formation of calcium carbonate / barium sulfate precipitates, but the strongly polar groups of AMPS also enhance the stability of the polymer under high temperature and high salt environments. These monomers are synthesized into a single molecular chain in a "one-pot" process through steps S1-S3, achieving "multi-effect in one agent." This not only avoids the risks of chemical interactions (such as flocculation and precipitation) during on-site compounding, but also ensures that the fracturing fluid can simultaneously solve the problem of wellbore scaling and blockage while carrying proppant, significantly improving construction efficiency and operational safety.

[0018] Furthermore, the acrylamide accounts for 55% to 70% of the total mass of the reactants, the itaconic acid accounts for 15% to 25%, the 2-acrylamido-2-methylpropanesulfonic acid accounts for 10% to 20%, and the isopropenzyme accounts for 5% to 10%. This ratio precisely controls the hydrophilic / hydrophobic balance of the molecular chains. The acrylamide ratio ensures the base viscosity; the itaconic acid and phosphonic acid monomer ratio controls the scale inhibition capability; and the AMPS ratio maintains temperature and salt resistance. An imbalance in these ratios may lead to insufficient viscosity or a decrease in scale inhibition efficiency. This range ensures optimal synergy between rheological properties and scale inhibition rate.

[0019] Furthermore, the isopropenzyl phosphonic acid is prepared by the following method: phosphorus trichloride and acetone are mixed, stirred, and reacted. Then, glacial acetic acid is added, and the reaction is continued under reflux to obtain the isopropenzyl phosphonic acid, which is a key scale-inhibiting functional monomer. This preparation method describes a specific synthetic route, ensuring the activity of the phosphonic acid groups in the monomer, thereby guaranteeing the smooth progress of the subsequent copolymerization reaction and the high-efficiency scale inhibition performance of the final product. It also solves the problems of the source and unstable activity of specific functional monomers.

[0020] Furthermore, the reactive monomer accounts for 25% of the total mass of the prepolymerization monomer solution. Maintaining this 25% concentration ensures both the polymerization rate and conversion rate while preserving suitable system fluidity. Excessive concentration leads to heat dissipation difficulties and an increased risk of explosive polymerization; insufficient concentration negatively impacts production efficiency. A concentration of 25% is the optimal choice for industrial production, balancing safety and efficiency.

[0021] Furthermore, in step S2, the pH value is adjusted to 6.8-7.0 using sodium hydroxide solution, with the solution temperature ≤20 ℃ during the pH adjustment process. The pH value directly affects the ionization state of the monomer and the initiation efficiency of free radical polymerization. Controlling the pH at near-neutral (6.8-7.0) and low temperature (≤20℃) conditions prevents excessively strong acidity or alkalinity from causing premature side reactions or hydrolysis of the monomers (especially itaconic acid and phosphonic acid), thus ensuring the controllability of the polymerization reaction.

[0022] Furthermore, in step S2, the urea and EDTA-2Na account for 0.1%~0.5% and 0.02%~0.08% of the mass of the reactant monomers, respectively. Urea, as a chain transfer agent, can adjust the molecular weight of the polymer, reduce branching, and improve solubility. EDTA-2Na, as a chelating agent, can complex trace metal ions in the raw materials, prevent them from catalyzing free radical decomposition, thereby improving the stability of the polymerization reaction and the temperature resistance of the final product.

[0023] Furthermore, in step S3, the oxidant is ammonium persulfate, which accounts for 0.2% to 0.5% of the reactant monomer mass. Ammonium persulfate is a commonly used and highly efficient initiator for aqueous solution polymerization. Limiting its dosage to between 0.2% and 0.5% provides an appropriate amount of free radicals, ensuring stable initiation of the polymerization reaction even at low temperatures of 0-5°C, and avoiding excessively rapid reaction (over-progression) due to too much initiator or incomplete reaction due to too little initiator.

[0024] Furthermore, in step S3, the reducing agent is ascorbic acid and sodium formaldehyde sulfoxylate, accounting for 0.05%~0.2% and 0.05%~0.15% of the mass of the reactant monomers, respectively. The use of a composite reducing agent system of ascorbic acid and sodium formaldehyde sulfoxylate, combined with ammonium persulfate to constitute a redox initiation system, significantly reduces the polymerization activation energy, allowing the reaction to proceed smoothly at a low temperature of 0-5℃. This effectively suppresses the "explosive polymerization" phenomenon during the polymerization process, ensuring the uniformity of the product's molecular weight distribution, thereby obtaining a high-performance thickener. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The temperature and shear resistance curves of the scale-inhibiting polymeric fracturing fluid in Example 1 are shown. Figure 2 The temperature and shear resistance curves of the scale-inhibiting polymeric fracturing fluid in Example 2 are shown. Figure 3 The temperature and shear resistance curves of the scale-inhibiting polymeric fracturing fluid in Example 3 are shown. Figure 4 The graph shows the temperature and shear resistance curves of the scale-inhibiting polymeric fracturing fluid in Example 4. Detailed Implementation

[0027] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0028] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0029] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0030] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0031] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0032] This invention discloses a method for preparing a scale-inhibiting polymeric fracturing fluid, comprising the following steps: S1: Mix the reactants and stir at room temperature until completely dissolved to obtain a monomer solution; the reactants are acrylamide, itaconic acid, 2-acrylamide-2-methylpropanesulfonic acid and isopropenzyme. The acrylamide accounts for 55% to 70% of the total mass of the reactants, the itaconic acid accounts for 15% to 25% of the total mass of the reactants, the 2-acrylamido-2-methylpropanesulfonic acid accounts for 10% to 20% of the total mass of the reactants, and the isopropenzyme accounts for 5% to 10% of the total mass of the reactants. The preparation method of the isopropenphosphonic acid is as follows: Phosphorus trichloride and acetone were added to a three-necked flask equipped with a stirrer and a reflux condenser. The reaction temperature was controlled at 30°C, and the reaction was carried out for 30-60 minutes. Glacial acetic acid was then added, and the reaction was continued for 4.5 hours to obtain a crude product. The crude product was then obtained by vacuum distillation, yielding a golden-yellow viscous liquid, which was the target product. The molar ratio of phosphorus trichloride, acetone, and glacial acetic acid was 1.0:1.2:5.0.

[0033] S2: Add urea and EDTA-2Na to the monomer solution and adjust the pH of the solution to 6.8~7.0 to obtain a prepolymerized monomer solution; The reactant monomer accounts for 25% of the total mass of the prepolymerized monomer solution. At the same time, the pH value is adjusted to 6.8~7.0 using a 30% sodium hydroxide solution. The solution temperature must be ≤20 ℃ during the pH adjustment process.

[0034] The urea and EDTA-2Na account for 0.1%~0.5% and 0.02%~0.08% of the mass of the reactants, respectively. S3: Control the temperature of the prepolymerized monomer solution to 0-5℃, continuously purge with nitrogen for 30 minutes to remove oxygen, then add an oxidant solution, and add a reducing agent solution dropwise over 5-10 minutes. Stop purging with nitrogen when the viscosity of the reaction solution increases, seal the reaction system, and allow it to heat up naturally. After the reaction is complete, remove the colloid, and after cutting, drying, and pulverizing, obtain the scale-inhibiting polymer thickener.

[0035] In one specific embodiment, the oxidant solution is added to the reaction system all at once, and after 5 minutes, the reducing agent solution is added dropwise to the reaction system over 5-10 minutes.

[0036] The oxidant is ammonium persulfate, which accounts for 0.2% to 0.5% of the mass of the reactants. The concentration of the oxidant solution is 1%. The reducing agents are ascorbic acid and sodium formaldehyde sulfoxylate, accounting for 0.05%~0.2% and 0.05%~0.15% of the mass of the reactants, respectively. The concentration of the reducing agent solution is 1%. This invention synthesizes a "one-agent-multiple-effect" polymer through the copolymerization reaction of multiple monomers. This polymer can maintain good viscosity and sand-carrying performance under high temperature and high shear conditions, while also having scale inhibition properties, reducing the use of additives in fracturing operations and lowering costs.

[0037] Furthermore, this invention also discloses a scale-inhibiting polymer thickener prepared by the above method, the structural formula of which is: ; Where x is 7000~21000; y is 1200~3600; z is 600~1800; w is 500~1500; This invention discloses a scale-inhibiting polymer thickener and its preparation method. Addressing the challenges of wellbore scaling during oil and gas field development, such as blockage, pump jamming, and water injection difficulties, this invention proposes an integrated design of scale-inhibiting functional monomers and fracturing fluid main components, overcoming the problems of complex on-site preparation, low construction efficiency, and high compatibility risks associated with traditional "single scale inhibitor + on-site compounding." This invention utilizes an aqueous solution polymerization method to synthesize a polymer with both scale inhibition and fracturing functions by quaternary copolymerization of functional monomers such as itaconic acid, 2-acrylamide-2-methylpropanesulfonic acid, and isopropenzyme with acrylamide. Performance evaluation results show that, in terms of rheological properties, the fracturing fluid exhibits an apparent viscosity >100 mPa·s before shear at a 0.4% mass concentration and 25°C; after 90°C and 170 s… -1After 1 hour of continued shearing, the residual viscosity remained above 50 mPa·s, meeting the requirements for proppant carrying in high-temperature deep wells. Regarding scale inhibition performance, at a concentration of 0.1% and a temperature of 80°C, the fracturing fluid exhibited stable scale inhibition rates of 83%–95% for CaCO3, 81%–93% for CaSO4, and 85%–97% for BaSO4, demonstrating excellent scale inhibition performance. This polymer combines high-temperature, high-shear proppant carrying capacity with efficient scale inhibition, achieving a "multi-effect" fracturing fluid, significantly improving operational efficiency and reducing risks.

[0038] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0039] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0040] Example 1 This embodiment provides a method for preparing a scale-inhibiting thickener, the preparation process of which includes the following steps: Step 1: Add 60% acrylamide, 18% itaconic acid, 16% 2-acrylamide-2-methylpropanesulfonic acid, and 6% isopropenzyme to a 1L beaker by mass percentage, and stir magnetically at room temperature until completely dissolved to obtain a monomer solution.

[0041] Step two: Add 0.25% urea and 0.05% EDTA-2Na to the monomer solution to prepare a solution with a total solids content of 25%. Add an appropriate amount of 30% sodium hydroxide solution to the solution to adjust the pH of the reaction system to 7.0.

[0042] Step 3: Dispense the pH-adjusted monomer solution into reaction flasks and freeze them in a refrigerator until the temperature drops to 0°C. Place the reaction flasks into the reactor and purge them with N2 for 30 minutes to remove oxygen from the reaction flasks.

[0043] Step 4: Add 0.3% ammonium persulfate solution to the reaction flask all at once. After 5 minutes, add 0.1% ascorbic acid solution and 0.08% sodium formaldehyde sulfoxylate solution dropwise to the reaction flask over 10 minutes.

[0044] Step 5: Once the reaction solution becomes viscous, stop the nitrogen flow, seal the reactor, and allow the system to heat up naturally; record the temperature rise curve. After the reaction temperature naturally decreases, remove the reaction product colloid, cut it into small pieces, dry it, and pulverize it into powder.

[0045] Example 2 This embodiment provides a method for preparing a scale-inhibiting thickener, the preparation process of which includes the following steps: Step 1: In a 1L beaker, add 68% acrylamide, 15% itaconic acid, 12% 2-acrylamide-2-methylpropanesulfonic acid, and 5% isopropenzyme in sequence, and stir magnetically at room temperature until completely dissolved to obtain a monomer solution.

[0046] Step two: Add 0.15% urea and 0.05% EDTA-2Na to the monomer solution to prepare a solution with a total solids content of 25%. Add an appropriate amount of 30% sodium hydroxide solution to the solution to adjust the pH of the reaction system to 7.0.

[0047] Step 3: Dispense the pH-adjusted monomer solution into reaction flasks and freeze them in a refrigerator until the temperature drops to 2°C. Place the reaction flasks into the reactor and purge them with N2 for 30 minutes to remove oxygen from the reaction flasks.

[0048] Step 4: Add 0.2% ammonium persulfate solution to the reaction flask all at once. After 10 minutes, add 0.08% ascorbic acid solution and 0.06% sodium formaldehyde sulfoxylate solution dropwise to the reaction flask within 10 minutes.

[0049] Step 5: Once the reaction solution becomes viscous, stop the nitrogen flow, seal the reactor, and allow the system to heat up naturally; record the temperature rise curve. After the reaction temperature naturally decreases, remove the reaction product colloid, cut it into small pieces, dry it, and pulverize it into powder.

[0050] Example 3 This embodiment provides a method for preparing a scale-inhibiting thickener, the preparation process of which includes the following steps: Step 1: In a 1L beaker, add 55% acrylamide, 22% itaconic acid, 15% 2-acrylamide-2-methylpropanesulfonic acid, and 8% isopropenzyme in sequence, and stir magnetically at room temperature until completely dissolved to obtain a monomer solution.

[0051] Step two: Add 0.3% urea and 0.05% EDTA-2Na to the monomer solution to prepare a solution with a total solids content of 25%. Add an appropriate amount of 30% sodium hydroxide solution to the solution to adjust the pH of the reaction system to 7.0.

[0052] Step 3: Dispense the pH-adjusted monomer solution into reaction flasks and freeze them in a refrigerator until the temperature drops to approximately 5°C. Place the reaction flasks into the reactor and purge them with N2 for 30 minutes to remove oxygen from the reaction flasks.

[0053] Step 4: Add 0.35% ammonium persulfate solution to the reaction flask all at once. After 6 minutes, add 0.12% ascorbic acid solution and 0.1% sodium formaldehyde sulfoxylate solution dropwise to the reaction flask over 10 minutes.

[0054] Step 5: Once the reaction solution becomes viscous, stop the nitrogen flow, seal the reactor, and allow the system to heat up naturally; record the temperature rise curve. After the reaction temperature naturally decreases, remove the reaction product colloid, cut it into small pieces, dry it, and pulverize it into powder.

[0055] Example 4 This embodiment provides a method for preparing a scale-inhibiting thickener, the preparation process of which includes the following steps: Step 1: In a 1L beaker, add 55% acrylamide, 25% itaconic acid, 14% 2-acrylamide-2-methylpropanesulfonic acid, and 6% isopropenzyme in sequence, and stir magnetically at room temperature until completely dissolved to obtain a monomer solution.

[0056] Step two: Add 0.40% urea and 0.05% EDTA-2Na to the monomer solution to prepare a solution with a total solids content of 25%. Add an appropriate amount of 30% sodium hydroxide solution to the solution to adjust the pH of the reaction system to 7.0.

[0057] Step 3: Dispense the pH-adjusted monomer solution into reaction flasks and freeze them in a refrigerator until the temperature drops to 0°C. Place the reaction flasks into the reactor and purge them with N2 for 30 minutes to remove oxygen from the reaction flasks.

[0058] Step 4: Add 0.45% ammonium persulfate solution to the reaction flask all at once. After 5 minutes, add 0.18% ascorbic acid solution and 0.15% sodium formaldehyde sulfoxylate solution dropwise to the reaction flask over 10 minutes.

[0059] Step 5: Once the reaction solution becomes viscous, stop the nitrogen flow, seal the reactor, and allow the system to heat up naturally; record the temperature rise curve. After the reaction temperature naturally decreases, remove the reaction product colloid, cut it into small pieces, dry it, and pulverize it into powder.

[0060] Apparent viscosity properties test In this invention, the thickeners obtained in Examples 1-4 were prepared into a polymer fracturing fluid with a mass concentration of 0.4% using deionized water. The viscosity was measured using a six-speed rotational viscometer, and the reading was taken when the viscometer pointer stabilized at a rotation speed of 100 r / min. The test results are shown in Table 1.

[0061] Temperature and shear resistance test In this invention, the thickeners obtained in Examples 1-4 are prepared into a polymer fracturing fluid with a mass concentration of 0.4% using deionized water. The fracturing fluid is then tested using a rheometer at a temperature of 90 °C and a shear rate of 170 s⁻¹. -1 The sample was sheared for 1 hour. The test results are shown in Table 1 and... Figures 1-4 .

[0062] Table 1. Evaluation results of the temperature and shear resistance of the thickeners prepared in Examples 1-4 of this invention.

[0063] Scale inhibition performance test In this invention, the thickeners obtained in Examples 1-4 are prepared into a polymer fracturing fluid with a mass concentration of 0.1% using deionized water. A certain amount of ammonium persulfate breaker is added to this fluid, and it is placed in a water bath at 80°C for breaker preparation until the viscosity is below 5 mPa·s. The resulting breaker solution is stirred evenly, and its scale inhibition efficiency against CaCO3, CaSO4, and BaSO4 is tested according to the Q / SY 17126-2019 standard. The test results are shown in Table 2.

[0064] Table 2. Evaluation results of the scale inhibition performance of the thickeners prepared in Examples 1-4 of this invention.

[0065] From Tables 1-2 and Figures 1-4 It can be seen that when the polymer mass concentration of the present invention is 0.4%, the apparent viscosity of each formulation before shearing at 25°C is greater than 100 mPa·s; after shearing at 90°C, the shear rate is 170 s. -1 After continuous shearing for 1 hour, the remaining viscosity is still greater than 50 mPa·s, meeting the sand-carrying requirements of high-temperature and high-shear operations. Comparing the four examples: Although Example 2 has the highest initial viscosity (158 mPa·s), its inhibition rates for CaCO3, CaSO4, and BaSO4 are only 83%, 81%, and 85%, respectively; while Example 4, although having the lowest initial viscosity (116 mPa·s), achieves a shear viscosity retention rate of 73.5%, meeting the industry requirement of a viscosity retention rate greater than 70% after shearing. Due to its lower initial viscosity, it is beneficial to reduce pump pressure and save energy consumption, and the viscosity meets the basic sand-carrying requirements. Furthermore, it has the best scale inhibition rates for CaCO3, CaSO4, and BaSO4, reaching 95%, 93%, and 97%, respectively. Considering both rheological stability and scale inhibition efficiency, Example 4 is the best technical solution.

[0066] The scale-inhibiting polymeric fracturing fluid of this invention is a quaternary copolymer synthesized from four monomers—acrylamide, itaconic acid, 2-acrylamide-2-methylpropanesulfonic acid, and isopropenzyme—through optimized monomer ratios and polymerization processes. This polymer can simultaneously achieve thickening and proppant carrying while efficiently inhibiting scale under high temperature and high shear conditions, realizing a "one-formula multi-effect" fracturing fluid and solving problems such as complex on-site preparation, low construction efficiency, and high compatibility risks.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a scale-inhibiting polymer thickener, characterized in that, Includes the following steps: S1: Mix the reactants and stir at room temperature until completely dissolved to obtain a monomer solution; the reactants are acrylamide, itaconic acid, 2-acrylamide-2-methylpropanesulfonic acid and isopropenzyme. S2: Add urea and EDTA-2Na to the monomer solution and adjust the pH of the solution to 6.8~7.0 to obtain a prepolymerized monomer solution; S3: Control the temperature of the prepolymerized monomer solution to 0-5 ℃, continuously introduce nitrogen gas to remove oxygen, then add oxidant solution, add reducing agent solution dropwise within 5-10 minutes, stop nitrogen introduction when the viscosity of the reaction solution rises, seal the reaction system, and allow it to heat up naturally. After the reaction is completed, take out the colloid, and after cutting, drying and pulverizing, obtain the scale-inhibiting polymer thickener.

2. The method for preparing a scale-inhibiting polymer thickener according to claim 1, characterized in that, The acrylamide accounts for 55% to 70% of the total mass of the reactants, the itaconic acid accounts for 15% to 25% of the total mass of the reactants, the 2-acrylamido-2-methylpropanesulfonic acid accounts for 10% to 20% of the total mass of the reactants, and the isopropenzyme accounts for 5% to 10% of the total mass of the reactants.

3. The method for preparing a scale-inhibiting polymer thickener according to claim 1, characterized in that, The isopropenphosphonic acid is prepared by the following method: phosphorus trichloride and acetone are mixed, stirred and reacted, glacial acetic acid is added, and the reaction is continued under reflux to obtain the isopropenphosphonic acid.

4. The method for preparing a scale-inhibiting polymer thickener according to claim 1, characterized in that, The reactive monomer accounts for 25% of the total mass of the prepolymerized monomer solution.

5. A method for preparing a scale-inhibiting polymer thickener according to claim 1, characterized in that, In step S2, the pH value is adjusted to 6.8~7.0 using sodium hydroxide solution, and the solution temperature is ≤20 ℃ during the pH adjustment process.

6. The method for preparing a scale-inhibiting polymer thickener according to claim 1, characterized in that, In step S2, the urea and EDTA-2Na account for 0.1%~0.5% and 0.02%~0.08% of the mass of the reactant monomers, respectively.

7. The method for preparing a scale-inhibiting polymer thickener according to claim 1, characterized in that, In step S3, the oxidant is ammonium persulfate, and its mass accounts for 0.2% to 0.5% of the mass of the reactant monomer.

8. The method for preparing a scale-inhibiting polymer thickener according to claim 1, characterized in that, In step S3, the reducing agent is ascorbic acid and sodium formaldehyde sulfoxylate, which account for 0.05%~0.2% and 0.05%~0.15% of the mass of the reactant monomers, respectively.

9. A scale-inhibiting polymer thickener, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. A scale-inhibiting polymeric fracturing fluid, characterized in that, The scale-inhibiting polymer thickener described in claim 9 is dissolved in water to prepare an aqueous solution with a mass concentration of 0.1% to 0.4%, thereby obtaining the scale-inhibiting polymeric fracturing fluid.

Images