Zwitterionic acid liquid viscosifier, its preparation method and application

Abstract

The present application relates to the technical field of oil field chemicals, and provides a zwitterionic acid liquid gelling agent, a preparation method and application thereof, the zwitterionic acid liquid gelling agent is prepared by copolymerization of 70wt%-80wt% of acrylamide, 10wt%-20wt% of anionic monomer, 1wt%-10wt% of cationic monomer and 0.1wt%-1wt% of functional monomer with an initiator, the zwitterionic acid liquid gelling agent is synergized by the cationic monomer and the functional monomer, and multiple structure protection is combined, so that the problem of insufficient viscosity increase and poor thermal stability of the conventional gelling agent under extreme conditions such as ultrahigh temperature and strong acid is effectively solved, the zwitterionic acid liquid gelling agent has efficient viscosity increase capacity, high viscosity retention rate and stable performance under high temperature, and is suitable for reservoir acidification operation to improve acidification effect.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical reagent technology, and more specifically, to an amphoteric acid thickener, its preparation method, and its application. Background Technology

[0002] In oil and gas field development, acidizing is a key technique for improving reservoir permeability and enhancing oil and gas recovery. This technology involves injecting acid (such as hydrochloric acid, arginine, or organic acids) into the formation to dissolve carbonate rocks or etch fracture walls, creating efficient flow channels and thus increasing formation permeability, ultimately achieving the goal of enhanced production. In this process, the performance of the acid system directly affects the effectiveness of the acidizing operation, and the acid thickener, as a core additive, plays an irreplaceable role. Firstly, by increasing the acid viscosity, it reduces the rate of acid loss in the reservoir, enabling deeper penetration of the acid. Secondly, it hinders the flow of H+ through a high-viscosity film. + The transfer to the rock surface slows down the acid-rock reaction rate and extends the action distance.

[0003] Currently, conventional acid thickeners generally suffer from insufficient thickening capacity, poor thermal stability, and weak acid and shear resistance under extreme conditions such as ultra-high temperature, strong acid, and strong shear, making it difficult to simultaneously meet the comprehensive requirements of efficient thickening and long-term stability. This technological bottleneck severely restricts the application of acidizing technology in the development of deep, ultra-deep, and unconventional oil and gas resources, and is particularly difficult to meet the acidizing operation requirements of ultra-high temperature reservoirs.

[0004] Therefore, there is an urgent need to develop a novel zwitterionic acid thickener that can maintain excellent structural stability and thickening properties in ultra-high temperature environments. The development of such a thickener has significant engineering application value and strategic importance for promoting the development of ultra-high temperature reservoir acidizing technology and expanding the space for efficient development of unconventional oil and gas resources. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides an amphoteric acid thickener, its preparation method, and its application. This amphoteric acid thickener, through the synergistic effect of cationic monomers and functional monomers combined with multiple structural protections, effectively solves the problems of insufficient thickening and poor thermal stability of conventional thickeners under extreme conditions such as ultra-high temperature and strong acid. It has high viscosity thickening capacity, high viscosity retention rate at high temperatures, and stable performance, making it suitable for reservoir acidizing operations to improve the acidizing effect.

[0006] In a first aspect, the present invention provides an amphoteric acid thickener, which is copolymerized by adding an initiator to a mixture of 70wt%-80wt% acrylamide, 10wt%-20wt% anionic monomer, 1wt%-10wt% cationic monomer and 0.1wt%-1wt% functional monomer in a mass percentage.

[0007] The anionic monomer is at least one of 4-acrylamido-4-methyl-1,1-dioxotetrahydrothiophene-3-sulfonic acid, sodium styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and methacrylic acid.

[0008] The cationic monomer is synthesized from (1-chloromethyl-2-chloroethyl) methacrylate and erucic acid / oleamide propyl dimethyl tertiary amine or (1-chloromethyl-2-chloroethyl) methacrylate and alkyl tertiary amine, and its structural formula is as follows:

[0009]

[0010] or ;

[0011] In the formula, R1 is an alkyl chain with 3-16 carbon atoms; R2 is an erucic acid-type C 21 H 41 Or oleic acid type C 17 H 33 ;

[0012] The functional monomer is synthesized from alkylphenol polyoxyethylene ether and acyl chloride, and its structural formula is:

[0013] ;

[0014] In the formula, R is an EO chain of 4-30.

[0015] Furthermore, the zwitterionic acid thickener has a zwitterionic structure, and its structural formula is as follows:

[0016]

[0017] or ;

[0018] Wherein, R1 is an alkyl chain with 3-16 carbon atoms; R2 is an erucic acid type C 21 H 41 Or oleic acid type C 17 H 33 ; R is 4-30 EO chain; a is 70-80 wt%, b is 10-20 wt%, c is 1-10 wt%, d is 0.1-1 wt%.

[0019] Furthermore, the initiator is at least one selected from 2,2'-azobisisobutylamidine dihydrochloride, azobisisobutylimidazoline hydrochloride, ammonium persulfate, potassium persulfate, sodium bisulfite, and sodium sulfite.

[0020] Furthermore, the initiator mass is 0.01wt%-0.06wt% of the total monomer mass.

[0021] Furthermore, the functional monomer can also be replaced by one or more of alkylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and isomeric alcohol polyoxyethylene ether through autonomous synthesis.

[0022] Secondly, based on the same inventive concept, the present invention provides a method for preparing the zwitterionic acid thickener according to any one of the first aspects, comprising the following steps:

[0023] Acrylamide, anionic monomer, cationic monomer and functional monomer are dissolved in deionized water to obtain a mixed solution. The pH of the mixed solution is adjusted, and an initiator is added under nitrogen protection to carry out a copolymerization reaction. After the reaction is completed, the mixture is cut, dried and pulverized and sieved to obtain a zwitterionic acid thickener. The solid content of the mixed solution is 35 wt%.

[0024] Furthermore, the pH adjustment of the mixture is specifically carried out by placing the mixture in an ice-water bath and adjusting the pH of the mixture to 6.0-7.0.

[0025] Furthermore, the copolymerization reaction under nitrogen protection involves introducing nitrogen for 40-60 minutes, adding the initiator, and reacting at an initiation temperature of 3-9°C for 4-7 hours.

[0026] Thirdly, based on the same inventive concept, the present invention provides the application of the zwitterionic acid thickener of any one of the first aspects or the zwitterionic acid thickener prepared by any one of the preparation methods of the second aspect in reservoir acidizing operations.

[0027] Furthermore, the zwitterionic acid thickener is mixed with the acid at a mass ratio of 0.6 wt% to prepare a thickened acid solution, which is then injected into the reservoir for acidification operations; the acid solution includes at least one of hydrochloric acid, oxalic acid, and organic acid.

[0028] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0029] 1. This invention designs and synthesizes a novel dual-cationic-dual-long-chain monomer. This monomer possesses both dual cation centers and a dual hydrophobic chain structure, which not only significantly improves the charge density and bonding strength of the polymer under acidic conditions, making its acid resistance far exceed that of conventional monomers, but also greatly enhances the strength and stability of the intermolecular association network through the dual hydrophobic chain structure, providing a solid guarantee for maintaining viscosity under high temperature and high shear conditions.

[0030] 2. This invention grafts long polyoxyethylene ether chains, as functional monomers, onto the polymer backbone via covalent bonding. These hydrophilic, flexible long chains fully extend in aqueous solution, forming a large hydration layer and a strong steric hindrance effect, which effectively inhibits the coiling and degradation of polymer molecules at high temperatures and significantly improves solution viscosity, rheology, and long-term stability.

[0031] 3. The combination of cationic monomers and functional monomers in this invention produces a significant synergistic effect. The hydrophobic long chains provide viscosity by forming physical crosslinking points through association, while the polyoxyethylene ether long chains encapsulate and stabilize these crosslinking points through a large hydration layer, preventing them from dissociating or collapsing under high thermal kinetic energy, thereby ensuring the high strength and durability of the thickening network under ultra-high temperature conditions.

[0032] 4. This invention integrates the thermodynamic stability of rigid groups, the electrochemical stability of zwitterions, and the steric stability of polyoxyethylene ether segments, forming a multi-protection mechanism that enables polymer molecular chains to synergistically resist degradation pathways caused by high temperature, acid, salt, and shear, ultimately achieving a balance between "highly efficient thickening and long-term stability" under harsh ultra-high temperature conditions. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0034] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0035] The mechanism of action of the zwitterionic acid thickener provided by this invention is as follows:

[0036] This invention introduces four major groups into the polymer backbone simultaneously: a rigid benzene ring as a backbone structure to improve temperature resistance; sulfonate anions to provide strong hydration and electrostatic repulsion to enhance salt resistance; quaternary ammonium salt positively charged groups to ensure permanent cationization and adsorption stability in strong acid environments, thus imparting excellent acid resistance; and the introduction of hydrophobic long chains to construct a physical cross-linking network through controllable hydrophobic association effects to achieve efficient thickening.

[0037] When the cationic monomer in the zwitterionic acid thickener is synthesized from (1-chloromethyl-2-chloroethyl) methacrylate and erucic acid / oleic acid propyl dimethyl tertiary amine, the reaction formula is as follows:

[0038] ;

[0039] In the formula, R2 is erucic acid type C 21 H 41 Or oleic acid type C 17 H 33 .

[0040] When the cationic monomer in the zwitterionic acid thickener is synthesized from (1-chloromethyl-2-chloroethyl) methacrylate and an alkyl tertiary amine, the reaction formula is as follows:

[0041] ;

[0042] In the formula, R1 is an alkyl chain with 3-16 carbon atoms.

[0043] The functional monomer in the zwitterionic acid thickener is synthesized from alkylphenol polyoxyethylene ether and methacrylamide chloride, and the reaction formula is shown below:

[0044] .

[0045] The zwitterionic acid thickener is copolymerized from acrylamide, 4-acrylamido-4-methyl-1,1-dioxotetrahydrothiophene-3-sulfonic acid, cationic monomers (two long-chain structures), and functional monomers, as shown in the following reaction formula:

[0046]

[0047] or

[0048] ,

[0049] Wherein, R1 is an alkyl chain with 3-16 carbon atoms; R2 is an erucic acid type C 21 H 41 Or oleic acid type C 17 H 33 a is 70~80wt%, b is 10~20wt%, c is 1~10wt%, and d is 0.1~1wt%.

[0050] 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. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0051] Example 1

[0052] This embodiment provides a zwitterionic acid thickener, the preparation method of which includes the following process:

[0053] 80% acrylamide, 15% 4-acrylamido-4-methyl-1,1-dioxotetrahydrothiophene-3-sulfonic acid, 4.7% cationic monomer synthesized from (1-chloromethyl-2-chloroethyl) methacrylate and erucamide propyl dimethyl tertiary amine, and 0.3% functional monomer synthesized from alkylphenol polyoxyethylene ether and acyl chloride were sequentially added to deionized water (solid content 30%) to prepare a homogeneous solution. The pH of the solution was adjusted to 6.0-7.0 under ice bath conditions, and nitrogen gas was purged for 50 min to remove oxygen. After deoxygenation, 0.03 wt% of 2,2'-azobisisobutylamidine dihydrochloride was added to the solution, and the reaction was carried out at 6°C for 6 h. The polymer was dried and granulated to obtain a zwitterionic acid thickener.

[0054] Example 2

[0055] This embodiment provides an amphoteric acid thickener, which differs from Embodiment 1 only in that:

[0056] The cationic monomer has a mass percentage of 4.5% and is synthesized from (1-chloromethyl-2-chloroethyl) methacrylate and oleamide propyl dimethyl tertiary amine; the functional monomer has a mass percentage of 0.5%; 0.03 wt% of the initiator 2,2'-azobisisobutylamidine dihydrochloride was replaced with 0.06 wt% of azobisisobutylimidazoline hydrochloride, and the reaction was carried out at 3 °C for 7 h.

[0057] Example 3

[0058] This embodiment provides an amphoteric acid thickener, which differs from Embodiment 1 only in that:

[0059] The cationic monomer has a mass percentage of 4.2% and is synthesized from (1-chloromethyl-2-chloroethyl) methacrylate and alkyl tertiary amine; the functional monomer has a mass percentage of 0.8%; 0.03 wt% of the initiator 2,2'-azobisisobutylamidine dihydrochloride was replaced with 0.01 wt% of ammonium persulfate, and the reaction was carried out at 9 °C for 4 h.

[0060] Comparative Example 1

[0061] This comparative example provides a zwitterionic acid thickener, which differs from Example 1 only in that:

[0062] No cationic monomers or functional monomers were added to verify the effect of the synergistic effect of cationic monomers and functional monomers on the thickener.

[0063] Comparative Example 2

[0064] This comparative example provides a zwitterionic acid thickener, which differs from Example 1 only in that:

[0065] No functional monomers were added; only 4% cationic monomers were added to verify the effect of single cationic monomers on the thickener.

[0066] Comparative Example 3

[0067] This comparative example provides a zwitterionic acid thickener, which differs from Example 1 only in that:

[0068] No cationic monomers were added; only 0.5% of functional monomers were added to verify the effect of functional monomers alone on the thickener.

[0069] To better understand the present invention, the following tests were performed on the products obtained in the embodiments and comparative examples.

[0070] The types and technical parameters of each raw material in the examples and comparative examples are shown in Table 1:

[0071]

[0072] Test Example 1

[0073] This test example examines the thickening properties of the products obtained in the above embodiments and comparative examples. The test results are as follows:

[0074] The detection method is as follows: First, the zwitterionic thickeners obtained in Comparative Examples 1-3 and Examples 1-3 are prepared into 0.6 wt% polymer solutions using a 15 wt% hydrochloric acid solution. Then, the solutions are tested using a Hacker rheometer at 30°C for 170 seconds. -1 The viscosity of the acid solution was tested, and the results are shown in Table 2.

[0075]

[0076] As shown in Table 2, the apparent viscosity of the acid solutions in Comparative Examples 2 and 3 was higher than that in Comparative Example 1, indicating that both the cationic monomer and the zwitterionic monomer have a positive effect on increasing the acid viscosity. More importantly, among all the comparative groups, the acid viscosities corresponding to Examples 1-3 were significantly higher than those in Comparative Examples 1-3. This result fully demonstrates a significant synergistic thickening effect between the cationic monomer and the zwitterionic monomer, rather than a simple functional additive effect. Among them, the zwitterionic thickener prepared in Example 2 exhibited the best thickening performance, with the highest apparent viscosity value. Therefore, this sample was selected for subsequent temperature resistance tests.

[0077] Test Example 2

[0078] This test example examines the temperature resistance performance of the products obtained in the above embodiments and comparative examples. The test results are as follows:

[0079] The cationic polymer obtained in Example 2 was prepared into 0.6 wt% polymer solutions using a 15 wt% hydrochloric acid solution. The polymer solutions were then tested at 30°C for 170 seconds. -1 The apparent viscosity, η1, was obtained by shearing at the specified shear rate for 120 min; then the polymer solution was heated to 150 °C and subjected to shearing at the specified shear rate for 170 s. -1 The apparent viscosity after 240 min of shearing, denoted as η2, was used to evaluate the temperature resistance of the polymer solution. The results are shown in Table 3.

[0080]

[0081] Among them, viscosity retention rate ,%.

[0082] The data in Table 3 show that Comparative Example 1 exhibits poor thermal stability; Comparative Examples 2 and 3 show improved viscosity retention, indicating that the introduction of cationic or zwitterionic monomers can enhance the polymer's temperature resistance to some extent. However, the retention rates of both are still below 65%, suggesting that the effect of single-structure improvement is limited.

[0083] Example 2 exhibited an extremely high high-temperature viscosity retention rate, far superior to all comparative examples. This result fully verifies the synergistic effect designed between the cationic monomer and the zwitterionic monomer in this invention: the two are not simply functionally superimposed, but rather, through the overall molecular design of rigid groups, dual cationic centers, hydrophobic long chains, and sterically hindered chain segments, the thermodynamic stability of the polymer molecular chain is significantly enhanced, effectively inhibiting chain degradation and network structure destruction caused by high temperatures, thereby enabling the thickener to maintain excellent and stable thickening ability under extreme high-temperature conditions.

[0084] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0085] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A zwitterionic acid thickener, characterized in that, The zwitterionic acid thickener is copolymerized by adding an initiator to 70wt%-80wt% acrylamide, 10wt%-20wt% anionic monomer, 1wt%-10wt% cationic monomer and 0.1wt%-1wt% functional monomer in a mass percentage. The anionic monomer is at least one of 4-acrylamido-4-methyl-1,1-dioxotetrahydrothiophene-3-sulfonic acid, sodium styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and methacrylic acid. The cationic monomer is synthesized from (1-chloromethyl-2-chloroethyl) methacrylate and erucic acid / oleamide propyl dimethyl tertiary amine or (1-chloromethyl-2-chloroethyl) methacrylate and alkyl tertiary amine, and its structural formula is as follows: or ; In the formula, R1 is an alkyl chain with 3-16 carbon atoms; R2 is an erucic acid-type C 21 H 41 Or oleic acid type C 17 H 33 ; The functional monomer is synthesized from alkylphenol polyoxyethylene ether and acyl chloride, and its structural formula is: ； In the formula, R is an EO chain of 4-30.

2. The thickener according to claim 1, characterized in that, The zwitterionic acid thickener has a zwitterionic structure, and its structural formula is as follows: or ; Wherein, R1 is an alkyl chain with 3-16 carbon atoms; R2 is an erucic acid type C 21 H 41 Or oleic acid type C 17 H 33 ; R is 4-30 EO chain; a is 70-80 wt%, b is 10-20 wt%, c is 1-10 wt%, d is 0.1-1 wt%.

3. The thickener according to claim 1, characterized in that, The initiator is at least one selected from 2,2'-azobisisobutylamidine dihydrochloride, azobisisobutylimidazoline hydrochloride, ammonium persulfate, potassium persulfate, sodium bisulfite, and sodium sulfite.

4. The thickener according to claim 1, characterized in that, The initiator mass is 0.01wt%-0.06wt% of the total monomer mass.

5. A method for preparing an amphoteric acid thickener according to any one of claims 1-4, characterized in that, The preparation method of the zwitterionic acid thickener includes the following steps: Acrylamide, anionic monomer, cationic monomer and functional monomer are dissolved in deionized water to obtain a mixed solution. The pH of the mixed solution is adjusted, and an initiator is added under nitrogen protection to carry out a copolymerization reaction. After the reaction is completed, the mixture is cut, dried and pulverized and sieved to obtain a zwitterionic acid thickener. The solid content of the mixed solution is 35 wt%.

6. The method according to claim 5, characterized in that, The pH adjustment of the mixture is specifically performed by placing the mixture in an ice-water bath and adjusting the pH of the mixture to 6.0-7.

0.

7. The method according to claim 5, characterized in that, The copolymerization reaction under nitrogen protection involves introducing nitrogen for 40-60 minutes, adding the initiator, and reacting at an initiation temperature of 3-9°C for 4-7 hours.

8. The application of any one of the zwitterionic acid thickeners according to claims 1-4 in reservoir acidizing operations.

9. The application according to claim 8, characterized in that, The zwitterionic acid thickener is mixed with the acid at a mass ratio of 0.6 wt% to prepare a thickened acid solution, which is then injected into the reservoir for acidification operations. The acid solution includes at least one of hydrochloric acid, oxalic acid, and organic acid.

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