A quaternary copolymer type acid retarding agent, its preparation method and application

Abstract

The application discloses a kind of tetrapolymer type acidizing retarder and its preparation method and application, it is related to oil and gas exploitation technical field.The retarder is polymerized by acrylamide, sulfonate monomer, allyl polyoxyethylene ether and octadecyl dimethyl allyl ammonium chloride four monomers, other quaternary ammonium salt monomers except octadecyl dimethyl allyl ammonium chloride are not included in the system.By excluding the second quaternary ammonium salt monomer, electrostatic crosslinking caused by polyvalent cation center is cut off, and the viscosity of acid system is reduced to below 4 mPa·s.At the same time, the single quaternary ammonium salt structure unit produces adsorption isolation effect at rock interface, so that the retardation rate under the condition of 110 DEG C is maintained above 82%.The retarder provided by the application has low viscosity, high temperature resistance and salt resistance, and is suitable for high temperature deep well acidizing and fracturing operation.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas extraction technology, and relates to a quaternary copolymer acidification retarder, its preparation method and application. Background Technology

[0002] Acidizing is an important production enhancement measure for oil and gas reservoirs. It involves injecting acid into the wellbore to dissolve formation rocks and minerals, remove near-wellbore contamination, and restore or improve formation permeability. However, conventional acids react too quickly with carbonate rocks, causing the acid to be rapidly consumed near the wellbore, resulting in a short effective range and making it difficult to achieve deep acidizing stimulation.

[0003] To address these issues, researchers have developed adsorption-type retarders. These retarders adsorb onto the rock surface through functional groups in their molecules, forming a physical barrier that slows down the acid-rock reaction rate while maintaining the low viscosity of the acid system, facilitating pumping and backflow. In recent years, related technical solutions have continued to emerge. Chinese invention patent CN116769107A discloses a non-long-chain hydrophobic acid retarder, which uses a binary copolymer of acrylamide and sodium p-styrene sulfonate. The retarding effect is achieved through the hydrophobic adsorption of the benzene ring, explicitly avoiding the use of long-chain alkyl groups. While this method has a certain retarding effect, the adsorption capacity of the benzene ring is weak, and the adsorption film stability is insufficient under high temperature and high salt conditions. The retarding effect decreases significantly with increasing temperature.

[0004] Chinese invention patent CN118562066A discloses an adsorption-type acidification retarder, which uses a copolymer of multiple monomers including propyl polyoxyethylene ether-2400, acryloylaminomethylpropanesulfonic acid, methacryloyloxyethyltrimethylammonium chloride, acrylamide, and octadecyldimethylallylammonium chloride. This scheme introduces two different types of quaternary ammonium salt monomers (methacryloyloxyethyltrimethylammonium chloride and octadecyldimethylallylammonium chloride), which enhances the adsorption capacity. However, the complex molecular chain structure of the multi-component copolymer makes it prone to molecular chain entanglement in acidic solutions, leading to increased system viscosity (measured viscosity > 8 mPa·s). Furthermore, the preparation process is complex and costly, and the introduction of additional quaternary ammonium salts adversely affects high-temperature stability. Summary of the Invention

[0005] To address the problems in existing acid retarder technologies, such as copolymer molecular chain entanglement due to the introduction of multiple quaternary ammonium salts, high initial viscosity of the acid system, and degradation of retarding performance under high temperature conditions, this invention provides a quaternary copolymer acid retarder, its preparation method, a retarding acid system containing the retarder, and its applications.

[0006] This invention is achieved through the following technical solution: A quaternary copolymer acidification retarder is obtained by polymerizing four monomers: acrylamide, sulfonate monomer, allyl polyoxyethylene ether, and octadecyl dimethyl allyl ammonium chloride. The quaternary ammonium salt cationic structural unit in the retarder system is composed of the octadecyl dimethyl allyl ammonium chloride.

[0007] Preferably, the molar ratio of acrylamide, sulfonate monomer, octadecyl dimethyl allyl ammonium chloride, and allyl polyoxyethylene ether is (88-92): (4-6): (0.8-1.2): (3-5).

[0008] Preferably, the sulfonate monomer is selected from at least one of sodium p-styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and sodium 2-acrylamido-2-methylpropanesulfonate.

[0009] Preferably, the weight-average molecular weight of the allyl polyoxyethylene ether is 2000–3000 g / mol.

[0010] A method for preparing the aforementioned quaternary copolymer acidification retarder includes the following steps: Acrylamide, sulfonate monomer, allyl polyoxyethylene ether and octadecyl dimethyl allyl ammonium chloride are dispersed in deionized water in a molar ratio to prepare a mixed solution A with a total mass percentage of 33% to 37% of the four monomers. Adjust the pH of the mixed solution to 7.0–7.8, and then introduce inert gas into the mixed solution for 25–35 minutes to obtain mixed solution B; The mixed solution B was heated to 48–53°C, and an initiator accounting for 0.9%–1.1% of the total monomer mass was added. The reaction was carried out at a constant temperature for 4.5–5.5 hours under inert gas protection to obtain a gel-like copolymer. The gel-like copolymer was washed with an organic solvent, dried, and pulverized to obtain a quaternary copolymer-type acidification retarder.

[0011] Preferably, the initiator is an ammonium persulfate-sodium bisulfite redox initiation system, wherein the mass ratio of ammonium persulfate to sodium bisulfite is 1:0.8 to 1.2; and the organic solvent is anhydrous ethanol.

[0012] A terpolymer-type acid retarder comprises the following components in parts by weight: The acidification retarder: 1.2 to 1.4 parts; Hydrochloric acid, calculated as 100% HCl: 18–22 parts; Corrosion inhibitor: 1.3–1.7 parts; Iron ion stabilizer: 0.8–1.2 parts; Drainage aid: 0.4–0.6 parts; Water: Keep to 100 servings; The octadecyl dimethyl allyl ammonium chloride structural unit in the acidification retarder drives the polymer to be adsorbed onto the carbonate rock interface through electrostatic attraction and van der Waals forces, forming a heterogeneous diffusion barrier.

[0013] Preferably, when the retarder accounts for 1.3% of the total mass concentration of the acid solution, the apparent viscosity of the retarding acid prepared by the retarder at 25°C is 3-4 mPa·s, and the acid solution is a 20% hydrochloric acid aqueous solution.

[0014] Preferably, the corrosion inhibitor is a quinoline corrosion inhibitor or its derivative; the iron ion stabilizer is citric acid or acetic acid; and the discharge aid is a fluorocarbon surfactant or a polyoxyethylene ether surfactant.

[0015] Application of a quaternary copolymer acidizing retarder or the retarding acid in acidizing and fracturing operations in oil and gas wells.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This invention provides a quaternary copolymer acidification retarder. The retarder is a quaternary copolymer formed by the polymerization of acrylamide, sulfonate monomers, allyl polyoxyethylene ether, and octadecyl dimethyl allyl chloride to form a linear main chain structure. The acrylamide provides hydrogen bonding to construct the polymer backbone, the sulfonate monomers provide charge repulsion to maintain the high-temperature conformation and inhibit main chain degradation, the allyl polyoxyethylene ether regulates molecular chain flexibility and provides steric hindrance, and the octadecyl dimethyl allyl chloride provides a long-chain hydrophobic association structure and electrostatic adsorption sites to construct a spatial isolation layer at the rock interface. The quaternary ammonium salt cationic structural unit in the copolymer system consists only of octadecyl dimethyl allyl chloride. Other quaternary ammonium salt monomers besides octadecyl dimethyl allyl chloride are excluded from the copolymer system. The single quaternary ammonium salt structural unit breaks the complex electrostatic crosslinking and polyelectrolyte effect caused by the multi-cation centers, reducing the hydrodynamic volume of the molecular chain. The octadecyldimethylallylammonium chloride structural unit drives the polymer to generate electrostatic attraction through the positively charged quaternary ammonium nitrogen center, while simultaneously generating van der Waals forces through the C18 hydrophobic long chain, both adsorbing onto the carbonate rock interface. This dual effect forms a heterogeneous diffusion barrier on the rock surface, reducing the mass transfer rate of hydrogen ions to the rock surface and thus delaying the acid-rock reaction process. The anionic sulfonic acid groups introduced by the sulfonate monomer provide a charge repulsion effect in spatial conformation. Combined with the polymer basic skeleton constructed by acrylamide, this maintains the extended state of the polymer chain under high-temperature conditions, inhibits main chain breakage and degradation, and ensures the retention rate of the retarding performance under high-temperature conditions. The retarder provided by this invention has low viscosity, high temperature resistance, and salt resistance, making it suitable for high-temperature deep well acid fracturing operations.

[0017] Furthermore, this invention utilizes allyl polyoxyethylene ether with a weight-average molecular weight of 2000–3000 g / mol, which provides steric hindrance through its long side chains, thereby reducing entanglement between molecular chains. The synergistic effect of this mechanism allows the apparent viscosity of the retarding acid prepared at a mass concentration of 1.3% to be controlled at 3–4 mPa·s at 25°C, which is beneficial for reducing on-site pumping friction. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is a flowchart illustrating the preparation process of the quaternary copolymer acidification retarder of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] This invention discloses a quaternary copolymer acidizing retarder without additional quaternary ammonium salts, its preparation method, and its application, relating to the field of oil and gas extraction technology. The retarder is polymerized from four monomers: acrylamide, sulfonate monomer, allyl polyoxyethylene ether, and octadecyl dimethyl allyl ammonium chloride, and does not contain any quaternary ammonium salt monomers other than DMAAC-18. Compared with existing multi-component copolymer systems that introduce multiple quaternary ammonium salts, this invention finds that omitting the second quaternary ammonium salt monomer significantly reduces the viscosity of the acid system from >8 mPa·s to <4 mPa·s, increases the high-temperature (110℃) retarding rate from 71.2% to over 82%, and simultaneously improves thermal stability, demonstrating an unexpectedly superior effect through simplification. The retarder of this invention has low viscosity, high-temperature resistance, good retarding effect, strong salt resistance, and good compatibility. Its preparation process is simple and low-cost, making it suitable for high-temperature deep well acidizing operations and possessing broad industrial application prospects.

[0022] This invention, through precise design of the monomer composition and ratio of the copolymer, employs a quaternary copolymer system containing only one cationic hydrophobic monomer, omitting other quaternary ammonium salt monomers, and optimizes the polymerization process to obtain an acidification retarder with a simple molecular chain structure, low entanglement, and high thermal stability. This retarder can form a dense adsorption layer in acidic solutions, effectively delaying acid-rock reactions while maintaining extremely low system viscosity, facilitating construction and backfilling.

[0023] This invention provides a quaternary copolymer acidification retarder, obtained by polymerization of four monomers: acrylamide (AM), sulfonate monomer (MS), allyl polyoxyethylene ether (APEG), and octadecyl dimethyl allyl ammonium chloride (DMAAC-18). The quaternary ammonium salt cationic structural unit in this retarder system is composed of the octadecyl dimethyl allyl ammonium chloride.

[0024] Acrylamide provides amide groups, which helps improve the polymer's water solubility and hydrogen bond adsorption capacity on rock surfaces; sulfonate monomers introduce sulfonic acid groups, enhancing the polymer's salt resistance, high-temperature resistance, and stability against high-valence metal ions; allyl polyoxyethylene ether (APEG) contains a large number of ethoxy units, which can bind to polar hydrophilic groups on the rock surface through strong hydrogen bonding, providing the main adsorption driving force; octadecyl dimethyl allyl ammonium chloride (DMAAC-18) provides long-chain hydrophobic alkyl (C18) and quaternary ammonium salt cations, which adsorb onto negatively charged rock surfaces through electrostatic attraction, and the hydrophobic long chains align outwards to form a physical isolation layer, hindering the contact between hydrogen ions and the rock. This invention explicitly excludes other quaternary ammonium salt monomers (such as short-chain quaternary ammonium salts) besides DMAAC-18, avoiding molecular chain entanglement and high-temperature instability caused by the coexistence of multiple quaternary ammonium salts. This results in a simple molecular chain structure and uniform charge distribution of the retarder, making it less prone to entanglement in acidic solutions and thus maintaining low viscosity. At the same time, the adsorption layer of a single hydrophobic long chain is more ordered and denser, improving the isolation effect at high temperatures. Omitting additional quaternary ammonium salts also reduces unstable structures such as ester bonds, enhancing thermal stability.

[0025] Furthermore, the molar ratio of monomers—acrylamide, sulfonate monomer, octadecyl dimethyl allyl ammonium chloride, and allyl polyoxyethylene ether—is (88–92): (4–6): (0.8–1.2): (3–5). Within this ratio range, acrylamide, as the main skeletal monomer, provides sufficient degree of polymerization and water solubility; the proportion of sulfonate monomer is moderate, providing sufficient salt and temperature resistance without causing excessive molecular chain rigidity due to excess; DMAAC-18, as the only hydrophobic cationic monomer, is controlled at a low proportion (approximately 1 part) to avoid intermolecular aggregation caused by excessive hydrophobic groups; the proportion of APEG is relatively high (3–5 parts), ensuring sufficient ethoxy adsorption sites to compensate for potential loss of adsorption capacity due to the reduction of hydrophobic monomers. This achieves an optimal balance between adsorption performance, salt and temperature resistance, and low viscosity. Experiments show that within this ratio range, a retarder at 1.3% concentration can reduce the acid viscosity to below 4 mPa·s, and the retardation rate at 110℃ exceeds 82%.

[0026] Furthermore, preferably, the preferred molar ratio of acrylamide, sulfonate monomer, octadecyl dimethyl allyl ammonium chloride, and allyl polyoxyethylene ether is 90:5:1:4. The optimal ratio, determined through extensive experimental screening, is as follows: 90 parts acrylamide ensures the flexibility and water solubility of the polymer backbone; 5 parts sulfonate monomer provide sufficient sulfonic acid groups to stabilize the molecular chain conformation at high temperatures; 1 part DMAAC-18 provides a hydrophobic long chain sufficient to form an effective isolation layer without excessive amount; and 4 parts APEG, whose molar number is exactly four times that of DMAAC-18, provides sufficient hydrogen bonding adsorption.

[0027] Furthermore, the sulfonate monomer is selected from at least one of sodium p-styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and sodium 2-acrylamido-2-methylpropanesulfonate; wherein, the sulfonate monomers all contain strong anionic sulfonic acid groups and have polymerizable double bonds, enabling them to copolymerize well with monomers such as acrylamide. Sodium p-styrene sulfonate contains a benzene ring structure, which can provide additional hydrophobic contribution; AMPS contains amide and sulfonic acid groups, and its structure is similar to that of acrylamide, resulting in good compatibility.

[0028] Furthermore, the weight-average molecular weight of the allyl polyoxyethylene ether (APEG) is 2000–3000 g / mol. The molecular weight of APEG determines the length of its ethoxy chain. If the molecular weight is too low (<2000), the number of ethoxy groups is insufficient, resulting in weak hydrogen bond adsorption; if the molecular weight is too high (>3000), the polymer is too hydrophilic, which may affect its effective adsorption on the rock surface. A molecular weight range of 2000–3000 ensures that APEG contains a sufficient number of ethoxy units (approximately 45–68), enabling it to form a strong and stable hydrogen bond network with the rock surface, thus enhancing the adsorption persistence of the retarder.

[0029] Furthermore, the molar ratio of APEG to DMAAC-18 is (3–5):1. This ratio ensures the quantitative proportion between the adsorption groups (APEG) and the hydrophobic isolation layer forming groups (DMAAC-18). The molar number of APEG is at least 3 times that of DMAAC-18 to ensure sufficient adsorption strength, so that even with a low DMAAC-18 content, the hydrophobic long chains can be anchored to the rock surface through strong hydrogen bonds.

[0030] Furthermore, at a mass concentration of 1.3%, the apparent viscosity of the retarded acid prepared with the retarder at 25°C was 3–4 mPa·s. This viscosity range is close to that of water (approximately 1 mPa·s), indicating that the retarder causes almost no thickening in the acid solution. This is because the molecular chain structure is simple, the charge density is moderate, there are no redundant hydrophobic side chains, and there is no severe intermolecular entanglement.

[0031] Ester bonds (-COO-) are prone to hydrolytic breakage under high-temperature and acidic conditions, leading to polymer degradation and failure. The monomers selected in this invention, including acrylamide (amide bond), APEG (ether bond), sulfonate monomers (sulfonic acid group, amide bond, or benzene ring), and DMAAC-18 (quaternary ammonium salt, carbon-carbon bond), do not contain ester bonds. Therefore, the copolymer's main chain and side chains are composed of hydrolysis-resistant and high-temperature-resistant chemical bonds such as amide bonds, ether bonds, carbon-carbon bonds, and sulfonic acid groups. This molecular design enables the retarder to exhibit excellent thermal and chemical stability under high-temperature (>300℃) and strong acidic environments, with an initial decomposition temperature ≥309℃ and a mass loss rate ≤19% at 350℃, far superior to polymers containing ester bonds.

[0032] This invention provides a method for preparing the above-mentioned quaternary copolymer type acidification retarder, such as... Figure 1 As shown, it includes the following steps: (1) Acrylamide (AM), sulfonate monomer (MS), allyl polyoxyethylene ether (APEG) and octadecyl dimethyl allyl ammonium chloride (DMAAC-18) in a molar ratio n(AM):n(MS):n(DMAAC-18):n(APEG) = (88~92):(4~6):(0.8~1.2):(3~5) are added to a reaction vessel, and deionized water is added to dissolve them to prepare a mixed solution A with a total monomer mass concentration of 33~37%. (2) Adjust the pH of the mixed solution in step (1) to 7.0-7.8, and introduce inert gas into the solution for 25-35 minutes to remove dissolved oxygen, thus obtaining mixed solution B; (3) Heat the solution from step (2) to 48-53°C, add an initiator (ammonium persulfate-sodium bisulfite redox initiation system, mass ratio 1:0.8-1.2) accounting for 0.9%-1.1% of the total monomer mass, and react at a constant temperature for 4.5-5.5 hours under inert gas protection to obtain a gel-like copolymer; (4) The gel-like copolymer obtained in step (3) is washed 2 to 4 times with anhydrous ethanol or other organic solvents, dried under vacuum at 45 to 55°C to constant weight, and then pulverized to obtain the quaternary copolymer type acidification retarder.

[0033] Furthermore, the initiator is an ammonium persulfate-sodium bisulfite redox system (mass ratio 1:0.8–1.2), and the organic solvent is anhydrous ethanol. This redox initiation system generates free radicals at relatively low temperatures (48–53°C), avoiding side reactions and excessively large molecular weights caused by high-temperature initiation. The initiation efficiency is highest when the ratio of ammonium persulfate to sodium bisulfite is close to 1:1. Anhydrous ethanol is a poor solvent for polymers, but it can dissolve unreacted monomers and impurities, facilitating washing and purification. This initiation system can yield copolymers with low number-average molecular weights and narrow molecular weight distributions, thereby reducing acid viscosity; simultaneously, the lower reaction temperature reduces energy consumption and equipment requirements.

[0034] This invention provides a retarding acid comprising the aforementioned acidification retarder, composed of the following components in parts by weight: 1.2-1.4 parts acidification retarder, 18-22 parts hydrochloric acid (calculated as 100% HCl), 1.3-1.7 parts corrosion inhibitor, 0.8-1.2 parts iron ion stabilizer, 0.4-0.6 parts drainage aid, and water to the balance of 100 parts. This formulation is based on approximately 20% hydrochloric acid, with a specific proportion of the retarder of this invention added. The corrosion inhibitor prevents the acid from corroding the tubing; the iron ion stabilizer complexes the iron ions generated by formation dissolution, preventing secondary precipitation; and the drainage aid reduces interfacial tension and promotes the return of residual acid.

[0035] Furthermore, the corrosion inhibitor is a quinoline-based corrosion inhibitor or its derivative, which blocks the electrochemical corrosion microcells through chemical adsorption on the metal surface; the iron ion stabilizer is citric acid, acetic acid or its salt, which masks high-valence metal cations through coordination complexation; the drainage aid is a fluorocarbon surfactant or a polyoxyethylene ether surfactant, which changes the wettability of the rock surface by reducing the interfacial tension of the gas-liquid-solid three-phase system.

[0036] This invention provides a method for reducing the viscosity of an acid retarder system and improving its high-temperature retarding performance by controlling the degree of polymer molecular chain entanglement. In the monomer composition of the copolymer-type acid retarder, only one cationic hydrophobic monomer is used, and other short-chain cationic quaternary ammonium salt monomers are excluded.

[0037] Furthermore, using an ammonium persulfate-sodium bisulfite redox initiation system at a polymerization temperature of 48–53°C, the number-average molecular weight of the resulting retarder was lower than that of the copolymer obtained using an azo initiator at the same monomer concentration. Azo initiators (such as azobisisobutyramidine hydrochloride) typically initiate polymerization at higher temperatures, which can easily lead to excessively large molecular weights; while redox systems can initiate polymerization efficiently at low temperatures, with milder reactions, fewer chain transfer reactions, and resulting in polymers with lower molecular weights and narrower molecular weight distributions.

[0038] This method encapsulates the core idea of ​​this invention from a higher dimension of molecular design—by reducing the number of cationic monomer types (retaining only one long-chain hydrophobic cationic monomer), it avoids the electrostatic interactions between molecular chains and the entanglement caused by hydrophobic aggregation resulting from the coexistence of multiple quaternary ammonium salts, thereby reducing macroscopic viscosity. Simultaneously, the adsorption layer of a single hydrophobic long chain is more ordered and exhibits higher stability at high temperatures. This method provides a universal design approach that can guide the development of more low-viscosity, high-temperature resistant retarders, with protection scope not limited to specific monomer combinations.

[0039] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1 Preparation of acidification retarder RS-1: Weigh acrylamide (AM), sodium p-styrene sulfonate (MS), octadecyl dimethyl allyl ammonium chloride (DMAAC-18), and allyl polyoxyethylene ether (APEG-2400, weight average molecular weight MW≈2400) in a molar ratio n(AM):n(MS):n(DMAAC-18):n(APEG-2400)=90:5:1:4. Add the monomers to a reaction vessel equipped with a stirrer and a thermometer, add deionized water to prepare a mixed solution with a total monomer mass concentration of 35%, and stir to dissolve.

[0041] The pH of the reaction solution was adjusted to 7.5 using sodium hydroxide solution, and high-purity nitrogen gas was bubbled into the system for 30 minutes to remove dissolved oxygen. The system was then heated to 50°C in a water bath, and 1.0% of the total monomer mass of initiator (ammonium persulfate to sodium bisulfite mass ratio of 1:1) was added. The reaction was carried out at a constant temperature for 5 hours under nitrogen protection to obtain a transparent gel-like copolymer. The obtained gel-like copolymer was washed three times with anhydrous ethanol to remove unreacted monomers. The washed product was dried to constant weight in a vacuum drying oven at 50°C and then pulverized to obtain the acidification retarder RS-1.

[0042] Preparation of slow-release acid RA-1: The weight ratio of each component of the slow-release acid is as follows: 1.3 parts of acidification retardant RS-1, 65 parts of 31% industrial hydrochloric acid (equivalent to 20 parts of 100% pure HCl), 1.5 parts of benzyl chloroquinoline as a corrosion inhibitor, 1.0 part of citric acid as an iron ion stabilizer, 0.5 parts of perfluorooctyl sulfonate as a drainage aid, and water to make up the remainder to 100 parts.

[0043] Add the calculated amount of water to the preparation tank. While stirring, add the corrosion inhibitor, iron ion stabilizer, and drainage aid sequentially. After the system is thoroughly mixed, add hydrochloric acid, and finally add the acidification retarder RS-1. Continue stirring for 30 minutes until the polymer is completely dissolved to obtain the retarded acid RA-1.

[0044] Example 2 The difference from Example 1 is that the monomer molar ratio was adjusted to n(AM):n(MS):n(DMAAC-18):n(APEG-2400) = 89:5.5:0.9:4.6, the sulfonate monomer was 2-acrylamido-2-methylpropanesulfonic acid (AMPS), the reaction temperature was 52°C, and the reaction time was 5 hours. The resulting retarder was designated RS-2, and the retarding acid was designated RA-2. Other conditions were the same as in Example 1.

[0045] Example 3 The difference from Example 1 is that the monomer molar ratio was adjusted to n(AM):n(MS):n(DMAAC-18):n(APEG-2400) = 91:4.5:1.1:3.4, the initiator dosage was 1.0%, the reaction temperature was 49°C, and the reaction time was 5.2 hours. The resulting retarder was designated RS-3, and the retarding acid was designated RA-3. Other conditions were the same as in Example 1.

[0046] Comparative Example 1 (CN116769107A scheme comparison) Referring to the embodiment of Chinese invention patent CN116769107A, acrylamide (AM) and sodium p-styrene sulfonate (SSS) were copolymerized in a molar ratio of n(AM):n(SSS)=90:10, with a total monomer mass concentration of 30%, potassium persulfate (0.8%) as the initiator, a reaction temperature of 60°C, and a reaction time of 6 hours to prepare a comparative retarder RS-D1, and a comparative retarder acid RA-D1 was prepared according to the same retarder acid formulation.

[0047] Comparative Example 2 (CN118562066A scheme comparison) Referring to the embodiment of Chinese invention patent CN118562066A, a six-component copolymer was used: propyl polyoxyethylene ether-2400, acryloamidomethylpropanesulfonic acid, methacryloyloxyethyltrimethylammonium chloride, acrylamide, and octadecyldimethylallylammonium chloride, with a molar ratio of 4:5:1:88:2, a total monomer mass concentration of 35%, and azobisisobutyramidine hydrochloride (0.9%) as the initiator. The reaction temperature was 50°C, and the reaction time was 5.5 hours to prepare a comparative retarder RS-D2. A comparative retarder acid RA-D2 was also prepared according to the same retarder acid formulation.

[0048] Performance testing and data summary: 1. Viscosity test The apparent viscosity of the slow-speed acid systems prepared in Examples 1-3 and Comparative Examples 1-2 was tested at 25°C using a rotational viscometer, and the results are shown in Table 1.

[0049] Table 1. Viscosity comparison of various slow-release acid systems

[0050] Test results show that the viscosity of the slow-release acid system prepared in the embodiments of the present invention is below 4 mPa·s, significantly lower than 8.7 mPa·s of scheme CN118562066A (a reduction of more than 50%), and slightly better than 4.2 mPa·s of scheme CN116769107A. This indicates that the present invention, by optimizing the quaternary copolymer system and omitting the second quaternary ammonium salt monomer, unexpectedly obtained a lower system viscosity, which is beneficial for reducing pumping friction.

[0051] 2. Retarding performance test The acid-rock reaction rates of various slow-rate acid systems at different temperatures were tested using a rotating rock disc apparatus. Test conditions: marble rock disc (diameter 2.5 cm), rotation speed 500 rpm, reaction pressure 7 MPa, reaction time 15 min. The slow-rate was calculated based on the reaction rate of blank hydrochloric acid (15% HCl) under the same conditions; the results are shown in Table 2.

[0052] Table 2 shows the retarding rates of various slow-reacting acid systems at different temperatures.

[0053] Test results show that: (1) At 60°C, the slow rate of the present invention (84.8%~86.1%) is slightly better than that of the CN118562066A scheme (83.5%), and significantly better than that of the CN116769107A scheme (79.8%). (2) Under high temperature conditions of 110℃, the slowing rate of the present invention remains above 82%, while that of the CN118562066A scheme drops to 71.2%, and that of the comparative example CN116769107A scheme drops to 71.5%; (3) It is worth noting that although the comparative example CN118562066A introduced two quaternary ammonium salt monomers, the retardation effect at high temperatures decreased significantly, indicating that the introduction of the second quaternary ammonium salt monomer did not bring the expected synergistic enhancement effect, but may have led to a decrease in thermal stability due to the complexity of the molecular chain. The simplified quaternary system of this invention exhibits better performance retention at high temperatures.

[0054] 3. Thermal stability test The thermal stability of the retarder was tested using a thermogravimetric analyzer (TGA) at a heating rate of 10 °C / min under a nitrogen atmosphere. The results are shown in Table 3.

[0055] Table 3 shows the thermogravimetric analysis results of each retarder.

[0056] Test results show that the thermal stability of the retarder of this invention is significantly better than that of the two comparative examples, with an initial decomposition temperature >309℃ and a mass loss rate of <19% at 350℃, meeting the requirements for high-temperature acidizing operations in deep wells. In particular, compared with the CN118562066A scheme, the thermal stability of this invention is actually improved by omitting the second quaternary ammonium salt.

[0057] 4. Salt resistance test The slow-restriction performance of RA-1 was tested in acid solutions containing different concentrations of CaCl2 (90℃), and the results are shown in Table 4.

[0058] Table 4 shows the slowing rate of RA-1 at different CaCl2 concentrations (90℃).

[0059] Test results show that the retarder of the present invention can still maintain a good retarding effect under high salt conditions. When the CaCl2 content is as high as 70,000 mg / L, the retarding rate is still higher than 80%, which shows good salt resistance.

[0060] 5. Compatibility test RA-1 was mixed with commonly used field additives (corrosion inhibitors, iron ion stabilizers, drainage aids, demulsifiers, etc.) in different proportions, and the presence of precipitation, turbidity, or stratification was observed within 24 hours. The results showed that RA-1 had good compatibility with all kinds of additives and no obvious adverse reactions.

[0061] Conclusion: Extensive experimental research revealed that, while maintaining adsorption performance, excellent adsorption retardation effects can be achieved through a specific combination of four monomers—acrylamide, sulfonate monomer, allyl polyoxyethylene ether, and octadecyl dimethyl allyl ammonium chloride—without introducing a second quaternary ammonium salt monomer. Unexpectedly, omitting the second quaternary ammonium salt monomer significantly reduced the viscosity of the acid system, and the retardation effect was maintained at higher temperatures, demonstrating unexpected technical benefits. This invention's retarder exhibits low viscosity, high temperature resistance, excellent retardation effect, strong salt resistance, good compatibility, simple preparation process, and low cost, proving the superiority of this invention.

[0062] This invention employs a linear quaternary copolymer system, excluding a second quaternary ammonium salt monomer (such as methacryloyloxyethyltrimethylammonium chloride), thereby reducing electrostatic crosslinking and macromolecular entanglement of molecular chains in acidic solutions. Compared to existing technologies using multi-component copolymer systems, the viscosity of the acidic system is reduced from >8 mPa·s to <4 mPa·s, while the apparent viscosity measured in this invention falls within the range of 3–4 mPa·s. The simplified quaternary system improves monomer conversion during polymerization, reducing production costs by 20%–30%.

[0063] The sulfonate monomer (MS) introduced into the molecular chain provides a high-temperature resistant conformation, inhibiting chain breakage under thermodynamic conditions. Thermogravimetric analysis shows that the polymer's initial decomposition temperature is >310℃, and the mass loss rate at 350℃ is 17%~19%. After excluding the second quaternary ammonium salt, the rate retention rate at 110℃ is increased from 71.2% (compared to existing pentagonal copolymer systems) to over 82%.

[0064] The long-chain alkyl groups carried by the DMAAC-18 structural unit in the retarder adsorb onto the positively charged carbonate rock surface through electrostatic attraction and van der Waals forces, forming a barrier membrane that delays hydrogen ion mass transfer. At a retarder concentration of 1.3%, the retarding rate of the system was measured to be 82–86%. In formation water environments with high divalent metal cation content (CaCl2 concentration reaching 70,000 mg / L), the retarding rate remained above 79%. When this retarder was mixed with conventional acid additives, no precipitation or flocculation was observed in the fluid.

[0065] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0066] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0067] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0068] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0069] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation of these numerical combinations.

[0070] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0071] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0072] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0073] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0074] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0075] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A quaternary copolymer type acidification retarder, characterized in that, The quaternary copolymer acidification retarder is obtained by polymerization of four monomers: acrylamide, sulfonate monomer, allyl polyoxyethylene ether, and octadecyl dimethyl allyl ammonium chloride. The quaternary ammonium salt cationic structural unit in the retarder system is composed of the octadecyl dimethyl allyl ammonium chloride.

2. The quaternary copolymer acidification retarder according to claim 1, characterized in that, The molar ratio of acrylamide, sulfonate monomer, octadecyl dimethyl allyl ammonium chloride, and allyl polyoxyethylene ether is (88-92): (4-6): (0.8-1.2): (3-5).

3. The quaternary copolymer acidification retarder according to claim 1, characterized in that, The sulfonate monomer is selected from at least one of sodium p-styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and sodium 2-acrylamido-2-methylpropanesulfonate.

4. The quaternary copolymer acidification retarder according to claim 1, characterized in that, The weight-average molecular weight of the allyl polyoxyethylene ether is 2000–3000 g / mol.

5. A method for preparing a quaternary copolymer-type acid retarder based on any one of claims 1 to 4, characterized in that, Includes the following steps: Acrylamide, sulfonate monomer, allyl polyoxyethylene ether and octadecyl dimethyl allyl ammonium chloride are dispersed in deionized water in a molar ratio to prepare a mixed solution A with a total mass percentage of 33% to 37% of the four monomers. Adjust the pH of the mixed solution to 7.0–7.8, and then introduce inert gas into the mixed solution for 25–35 minutes to obtain mixed solution B; The mixed solution B was heated to 48–53°C, and an initiator accounting for 0.9%–1.1% of the total monomer mass was added. The reaction was carried out at a constant temperature for 4.5–5.5 hours under inert gas protection to obtain a gel-like copolymer. The gel-like copolymer was washed with an organic solvent, dried, and pulverized to obtain a quaternary copolymer-type acidification retarder.

6. The method for preparing the quaternary copolymer acidification retarder according to claim 5, characterized in that, The initiator is an ammonium persulfate-sodium bisulfite redox initiation system, wherein the mass ratio of ammonium persulfate to sodium bisulfite is 1:0.8-1.2; the organic solvent is anhydrous ethanol.

7. A retarding acid comprising the quaternary copolymer type acidification retarder according to any one of claims 1 to 4, characterized in that, It consists of the following components in parts by weight: The acidification retarder: 1.2 to 1.4 parts; Hydrochloric acid, calculated as 100% HCl: 18–22 parts; Corrosion inhibitor: 1.3–1.7 parts; Iron ion stabilizer: 0.8–1.2 parts; Drainage aid: 0.4–0.6 parts; Water: Keep to 100 servings; The octadecyl dimethyl allyl ammonium chloride structural unit in the acidification retarder drives the polymer to be adsorbed onto the carbonate rock interface through electrostatic attraction and van der Waals forces, forming a heterogeneous diffusion barrier.

8. The slow-release acid according to claim 7, characterized in that, When the retarder accounts for 1.3% of the total mass concentration of the acid solution, the apparent viscosity of the retarded acid prepared with the retarder at 25°C is 3-4 mPa·s, and the acid solution is a 20% hydrochloric acid aqueous solution.

9. The slow-release acid according to claim 7, characterized in that, The corrosion inhibitor is a quinoline corrosion inhibitor or its derivative; the iron ion stabilizer is citric acid or acetic acid; and the discharge aid is a fluorocarbon surfactant or a polyoxyethylene ether surfactant.

10. The application of the quaternary copolymer acidizing retarder according to any one of claims 1 to 4 or the retarding acid according to any one of claims 7 to 9 in acidizing and fracturing operations in oil and gas wells.

Images