Self-crosslinking viscosifier and method for its preparation

Abstract

The application relates to the technical field of oil field chemistry, and relates to a self-crosslinking thickening agent and a preparation method thereof. The self-crosslinking thickening agent is obtained by copolymerization of acrylamide, acrylic acid, a physical crosslinking monomer and a chemical crosslinking monomer. The physical crosslinking monomer is N-cinnamyl-N,N-dimethylhexadecyl ammonium chloride. The chemical crosslinking monomer is N-allyl-N,N-dimethyl-p-tolualdehyde bromide. The molar ratio of the acrylamide, the acrylic acid, the physical crosslinking monomer and the chemical crosslinking monomer is 70-80:15-25:0.1-0.5:0.1-0.5. The application provides a self-crosslinking thickening agent and a preparation method thereof. The thickening agent has good temperature resistance and salt resistance, meets the current development needs of oil and gas fields, the method principle is reliable, the operation is simple, the reaction condition is mild, and the application prospect in the market is wide. The thickening agent can be widely applied to the development of high-temperature and ultrahigh-temperature reservoir oil and gas resources.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically a self-crosslinking thickener and its preparation method. Background Technology

[0002] my country possesses abundant oil and gas reserves, but their extraction is challenging, with low-permeability reserves accounting for as much as 66%. Based on my country's reservoir geology, hydraulic fracturing technology has become one of the key measures for increasing oil and gas reservoir production. With advancements in deep and ultra-deep well technology in my country, reservoir temperatures are gradually increasing with drilling depth.

[0003] Hydraulic fracturing fluids mainly consist of plant-based fracturing fluids and polymer-based fracturing fluids. Plant-based fracturing fluids offer advantages such as good thickening effect, strong proppant carrying capacity, and low filtration loss; however, they have disadvantages such as poor temperature resistance and higher friction. Synthetic polymer-based thickeners are primarily modified polyacrylamide polymers of different types and relative molecular masses. They can form chemical crosslinks with metal crosslinking agents such as organotitanium and zirconium, exhibiting advantages such as temperature resistance, salt resistance, and shear resistance. Currently, they are widely used in high-temperature and ultra-high-temperature reservoirs.

[0004] Chinese patent document CN104449643A discloses a high-temperature resistant polymer thickener for oilfield fracturing fluids, its preparation method, and its application. The thickener is synthesized by solution polymerization of acrylamide, other olefin monomers, an initiator, and a chain transfer agent in an aqueous solution. The weight ratio of acrylamide, other olefin monomers, and water is 10-20:6-18:62-84. The other olefin monomers are selected from one or more of anionic, cationic, or nonionic olefin monomers, preferably two or three. The resulting ternary or quaternary anionic polyacrylamide polymer with a molecular weight of 4-8.5 million is formed by solution polymerization. After crosslinking with a crosslinking agent, this thickener forms a gel with good elasticity and can withstand temperatures above 210°C. Chinese patent document CN111019042A discloses a high-temperature resistant thickener for fracturing fluid and its preparation method. This high-temperature resistant thickener comprises acrylamide, a salt-resistant functional monomer, and a temperature-sensitive functional monomer free radical; the molar ratio of acrylamide, salt-resistant functional monomer, and temperature-sensitive functional monomer is 1:(0.01~0.08):(0.05~0.15). The thickener, a polyacrylamide copolymerized from acrylamide, salt-resistant monomer, and temperature-sensitive functional monomer, exhibits good temperature resistance and thickening effect after crosslinking with an organozirconium crosslinking agent at temperatures above 200℃. However, both polymers need to be used in conjunction with a metal crosslinking agent to improve the temperature resistance.

[0005] Chinese patent document CN109705834A discloses a composition for preparing a temperature- and salt-resistant fracturing fluid thickener, the temperature- and salt-resistant fracturing fluid thickener prepared using the composition, and a method for preparing the same. The composition comprises the following components: acrylamide, acrylic acid, a hydrophobic monomer, 2-acrylamido-2-methylpropanesulfonic acid, a rigid monomer, a surfactant, and a shielding agent. It utilizes the synergistic effect of the shielding agent and the rigid monomer to enhance the stability of the network structure; however, at high temperatures, it relies solely on the rigid groups for support and lacks dynamic cross-linking repair capabilities.

[0006] Chinese patent document CN113880983A discloses a self-associative reinforced integrated waterborne high-temperature resistant thickener and its preparation method. The dispersed high-temperature resistant polymer is prepared by aqueous solution polymerization of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, octadecyl dimethyl allyl ammonium chloride, and a high-temperature resistant monomer. After the dispersant and dispersant stabilizer are mixed evenly, the dispersed phase, dispersant aid, and surfactant are added and stirred at high speed to form the waterborne high-temperature resistant thickener. It adopts hydrophobic association reinforcement technology, which improves the temperature resistance through physical association by introducing hydrophobic monomers (such as octadecyl dimethyl allyl ammonium chloride). However, it lacks chemical crosslinking support, and the dynamic crosslinking is prone to dissociation under high shear conditions. The salt resistance depends on the synergy of surfactants, and its adaptability to high-mineralized salt water is limited.

[0007] Therefore, developing temperature- and salt-resistant polymers to meet the needs of slickwater fracturing in high-temperature and ultra-high-temperature reservoirs has become an urgent problem to be solved. Summary of the Invention

[0008] This invention provides a self-crosslinking thickener and its preparation method, which overcomes the shortcomings of the prior art and can effectively solve the problem that existing temperature-resistant and salt-resistant polymers cannot meet the requirements of slickwater fracturing in high-temperature and ultra-high-temperature reservoirs.

[0009] One of the technical solutions of the present invention is achieved through the following measures: a self-crosslinking thickener, obtained by copolymerization of acrylamide, acrylic acid, physically crosslinking monomers and chemically crosslinking monomers;

[0010] The physical crosslinking monomer is N-cinnamyl-N,N-dimethylhexadecylammonium chloride;

[0011] The chemical crosslinking monomer is N-allyl-N,N-dimethyl-p-benzaldehyde ammonium bromide;

[0012] The molar ratio of acrylamide, acrylic acid, physical crosslinking monomer and chemical crosslinking monomer is (70 to 80): (15 to 25): (0.1 to 0.5): (0.1 to 0.5).

[0013] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions:

[0014] The above-mentioned self-crosslinking thickener has the structure shown in the following formula:

[0015]

[0016] In the formula, m1, m2, m3 and m4 are the number of repeating units in each structural unit, and the ratio of m1, m2, m3 and m4 is (70 to 80): (15 to 25): (0.1 to 0.5): (0.1 to 0.5).

[0017] The molecular weight of the aforementioned self-crosslinking thickener is between 3 million and 9 million.

[0018] The above self-crosslinking thickener was prepared according to the following steps:

[0019] Step 1: Add acrylamide, acrylic acid, physical crosslinking monomer, and chemical crosslinking monomer to water, and adjust the pH to neutral to obtain a monomer mixture.

[0020] Step 2: Remove dissolved oxygen from the monomer mixture;

[0021] Step 3: Add a photoinitiator to the monomer mixture to carry out a photopolymerization reaction. After the reaction product is crushed, soaked, dried, and pulverized, a self-crosslinking thickener is obtained.

[0022] In step one above, the total mass fraction of acrylamide, acrylic acid, physically crosslinked monomers, and chemically crosslinked monomers in the monomer mixture is 20% to 30%.

[0023] In step three above, the photopolymerization reaction lasts for 3 to 6 hours and the reaction temperature is 10°C to 30°C.

[0024] The photoinitiator mentioned above is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; the amount of photoinitiator used is 0.01wt% to 0.1wt% of the total mass of acrylamide, acrylic acid, physical crosslinking monomer, and chemical crosslinking monomer.

[0025] The above-mentioned N-cinnamyl-N,N-dimethylhexadecylammonium chloride (physical crosslinking monomer) was prepared according to the following steps:

[0026] The required amounts of hexadecylamine and cinnamyl chloride were dissolved in a solvent and refluxed. The reaction product was concentrated and recrystallized to obtain N-cinnamyl-N,N-dimethylhexadecylammonium chloride.

[0027] The solvent mentioned above is anhydrous ethanol.

[0028] The reflux reaction temperature is 80°C to 85°C, and the reaction time is 12 hours to 36 hours.

[0029] The molar ratio of the above-mentioned hexadecylamine to cinnamyl chloride is 1 to 1.2:1.

[0030] The above-mentioned N-allyl-N,N-dimethyl-p-benzaldehyde ammonium bromide (chemical crosslinking monomer) was prepared according to the following steps:

[0031] The required amount of p-dimethylaminobenzaldehyde and bromopropylene are dissolved in the reaction solvent and refluxed. After the reaction product is concentrated and recrystallized, N-allyl-N,N-dimethylp-benzaldehyde ammonium bromide (chemical crosslinking monomer) is obtained.

[0032] The solvent used in the above reaction is acetonitrile.

[0033] The reflux reaction temperature is 80°C to 85°C, and the reaction time is 6 hours to 24 hours.

[0034] The molar ratio of p-dimethylaminobenzaldehyde to bromopropene is 1:1 to 1.2.

[0035] The second technical solution of the present invention is achieved through the following measures: a method for preparing a self-crosslinking thickener, comprising the following steps:

[0036] Step 1: Add acrylamide, acrylic acid, physical crosslinking monomer, and chemical crosslinking monomer to water, and adjust the pH to neutral to obtain a monomer mixture.

[0037] Step 2: Remove dissolved oxygen from the monomer mixture;

[0038] Step 3: Add a photoinitiator to the monomer mixture to carry out a photopolymerization reaction. After the reaction product is crushed, soaked, dried, and pulverized, a self-crosslinking thickener is obtained.

[0039] This invention provides a self-crosslinking thickener and its preparation method. The thickener has good temperature and salt resistance properties, which meets the current needs of oil and gas field development. The method is reliable in principle, simple to operate, and has mild reaction conditions. It has broad market application prospects and can be widely used in the development of oil and gas resources in high-temperature and ultra-high-temperature reservoirs. Attached Figure Description

[0040] Appendix Figure 1 This is a viscosity-concentration relationship curve of self-crosslinking thickener S1 to S4 and thickener D1 in Test Example 1 of the present invention.

[0041] Appendix Figure 2 This is a graph showing the viscosity-mineralization (NaCl) relationship between self-crosslinking thickeners S1 to S4 and thickener D1 in Test Example 2 of the present invention.

[0042] Appendix Figure 3 This is a graph showing the viscosity-mineralization (CaCl) relationship between self-crosslinking thickeners S1 to S4 and thickener D1 in Test Example 2 of the present invention.

[0043] Appendix Figure 4 This is a viscosity-temperature curve of polymer D1 in test example 3 of the present invention.

[0044] Appendix Figure 5 This is a viscosity-temperature curve of polymer S3 in test example 3 of the present invention. Detailed Implementation

[0045] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0046] The present invention will be further described below with reference to embodiments:

[0047] Example 1: This self-crosslinking thickener is obtained by copolymerization of acrylamide, acrylic acid, physically crosslinking monomers and chemically crosslinking monomers;

[0048] The physical crosslinking monomer is N-cinnamyl-N,N-dimethylhexadecylammonium chloride;

[0049] The chemical crosslinking monomer is N-allyl-N,N-dimethyl-p-benzaldehyde ammonium bromide;

[0050] The molar ratio of acrylamide, acrylic acid, physical crosslinking monomer and chemical crosslinking monomer is (70 to 80): (15 to 25): (0.1 to 0.5): (0.1 to 0.5).

[0051] Example 2: As an optimization of the above embodiment, the self-crosslinking thickener has the structure shown in the following formula:

[0052]

[0053] In the formula, m1, m2, m3 and m4 are the number of repeating units in each structural unit, and the ratio of m1, m2, m3 and m4 is (70 to 80): (15 to 25): (0.1 to 0.5): (0.1 to 0.5).

[0054] Example 3: As an optimization of the above examples, the molecular weight of the self-crosslinking thickener is 3 million to 9 million.

[0055] Example 4: As an optimization of the above examples, the self-crosslinking thickener was prepared according to the following steps:

[0056] Step 1: Add acrylamide, acrylic acid, physical crosslinking monomer, and chemical crosslinking monomer to water, and adjust the pH to neutral to obtain a monomer mixture.

[0057] Step 2: Remove dissolved oxygen from the monomer mixture;

[0058] Step 3: Add a photoinitiator to the monomer mixture to carry out a photopolymerization reaction. After the reaction product is crushed, soaked, dried, and pulverized, a self-crosslinking thickener is obtained.

[0059] Example 5: As an optimization of the above example, in step one, the total mass fraction of acrylamide, acrylic acid, physically crosslinked monomers and chemically crosslinked monomers in the monomer mixture is 20% to 30%.

[0060] Example 6: As an optimization of the above example, in step three, the photopolymerization reaction time is 3h to 6h and the reaction temperature is 10℃ to 30℃.

[0061] Example 7: As an optimization of the above example, the photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; the amount of photoinitiator is 0.01wt% to 0.1wt% of the total mass of acrylamide, acrylic acid, physical crosslinking monomer and chemical crosslinking monomer.

[0062] Example 8: As an optimization of the above examples, N-cinnamyl-N,N-dimethylhexadecylammonium chloride (physical crosslinking monomer) was prepared according to the following steps:

[0063] The required amounts of hexadecylamine and cinnamyl chloride were dissolved in a solvent and refluxed. The reaction product was concentrated and recrystallized to obtain N-cinnamyl-N,N-dimethylhexadecylammonium chloride.

[0064] The reaction process is as follows:

[0065] .

[0066] Example 9: As an optimization of the above examples, the solvent is anhydrous ethanol.

[0067] Example 10: As an optimization of the above example, the reflux reaction temperature is 80°C to 85°C and the reaction time is 12 hours to 36 hours.

[0068] Example 11: As an optimization of the above example, the molar ratio of hexadecylamine to cinnamyl chloride is 1~1.2:1.

[0069] Example 12: As an optimization of the above examples, N-allyl-N,N-dimethyl-p-benzaldehyde ammonium bromide (chemical crosslinking monomer) was prepared according to the following steps:

[0070] The required amount of p-dimethylaminobenzaldehyde and bromopropylene were dissolved in the reaction solvent and refluxed. The reaction product was concentrated and recrystallized to obtain N-allyl-N,N-dimethylp-benzaldehyde ammonium bromide.

[0071] The reaction process is as follows:

[0072] .

[0073] Example 13: As an optimization of the above examples, the reaction solvent is acetonitrile.

[0074] Example 14: As an optimization of the above example, the reflux reaction temperature is 80°C to 85°C and the reaction time is 6 hours to 24 hours.

[0075] Example 15: As an optimization of the above example, the molar ratio of p-dimethylaminobenzaldehyde to bromopropylene is 1:1 to 1.2.

[0076] Example 16:

[0077] (1) Preparation of physically crosslinked monomers:

[0078] 0.12 mol of hexadecylamine and 0.1 mol of cinnamyl chloride were weighed and dissolved in 100 mL of anhydrous ethanol; the mixture was refluxed at 85 °C for 36 hours; the reaction was stopped, and the reaction product was subjected to rotary evaporation, recrystallization with ethyl acetate, and vacuum drying to obtain the physically crosslinked monomer N-cinnamyl-N,N-dimethylhexadecylammonium chloride, with a yield of 98.8%.

[0079] (2) Preparation of chemically cross-linked monomers:

[0080] 0.1 mol of p-dimethylaminobenzaldehyde and 0.12 mol of bromopropene were dissolved in 100 mL of acetonitrile; the mixture was refluxed at 85 °C for 24 hours; the reaction was stopped, and the reaction product was subjected to rotary evaporation, recrystallization with ethyl acetate, and vacuum drying to obtain the chemically crosslinked monomer N-allyl-N,N-dimethylp-benzaldehyde ammonium bromide with a yield of 99.1%.

[0081] (3) Preparation of self-crosslinking thickener:

[0082] Acrylamide, acrylic acid, the physically crosslinking monomer N-cinnamyl-N,N-dimethylhexadecyl ammonium chloride, and the chemically crosslinking monomer N-allyl-N,N-dimethyl-p-benzaldehyde ammonium bromide were weighed out in a molar ratio of 79.8:20:0.1:0.1. An appropriate amount of distilled water was added, and the mixture was stirred and dissolved evenly. The pH was adjusted to 7 with a 10% NaOH solution, and an appropriate amount of distilled water was added to obtain a monomer mixture with a total monomer mass fraction of 20%.

[0083] Nitrogen gas was bubbled into the monomer mixture for 15 minutes to remove dissolved oxygen from the water; 0.01 wt% of the total monomer mass of the initiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone was added; the mixture was placed under a photoinitiator and the photopolymerization reaction temperature was controlled between 10°C and 30°C. After 6 hours of reaction, a white colloid was obtained. The white colloid was cut into small pieces, soaked in ethanol, dried, and pulverized to obtain a self-crosslinking thickener, denoted as S1.

[0084] Example 17:

[0085] (1) Preparation of physically crosslinked monomers:

[0086] 0.12 mol of hexadecylamine and 0.1 mol of cinnamyl chloride were weighed and dissolved in 100 mL of anhydrous ethanol; the mixture was refluxed at 85 °C for 24 hours; the reaction was stopped, and the reaction product was subjected to rotary evaporation, recrystallization with ethyl acetate, and vacuum drying to obtain the physically crosslinked monomer N-cinnamyl-N,N-dimethylhexadecylammonium chloride, with a yield of 98.6%.

[0087] (2) Preparation of chemically cross-linked monomers:

[0088] 0.1 mol of p-dimethylaminobenzaldehyde and 0.12 mol of bromopropene were dissolved in 100 mL of acetonitrile; the mixture was refluxed at 85 °C for 12 hours; the reaction was stopped, and the reaction product was subjected to rotary evaporation, recrystallization with ethyl acetate, and vacuum drying to obtain the chemically crosslinked monomer N-allyl-N,N-dimethylp-benzaldehyde ammonium bromide with a yield of 98.9%.

[0089] (3) Preparation of self-crosslinking thickener:

[0090] Acrylamide, acrylic acid, the physically crosslinking monomer N-cinnamyl-N,N-dimethylhexadecyl ammonium chloride, and the chemically crosslinking monomer N-allyl-N,N-dimethyl-p-benzaldehyde ammonium bromide were weighed out in a molar ratio of 79.8:20:0.1:0.1. An appropriate amount of distilled water was added, and the mixture was stirred and dissolved evenly. The pH was adjusted to 7 with a 10% NaOH solution, and an appropriate amount of distilled water was added to obtain a monomer mixture with a total monomer mass fraction of 25%.

[0091] Nitrogen gas was bubbled into the monomer mixture for 15 minutes to remove dissolved oxygen from the water; 0.01 wt% of the total monomer mass of the initiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone was added; the mixture was placed under a photoinitiator and the photopolymerization reaction temperature was controlled between 10°C and 30°C. After 5 hours of reaction, a white colloid was obtained. The white colloid was cut into small pieces, soaked in ethanol, dried, and pulverized to obtain a self-crosslinking thickener, denoted as S2.

[0092] Example 18:

[0093] (1) Preparation of physically crosslinked monomers:

[0094] 0.11 mol of hexadecylamine and 0.1 mol of cinnamyl chloride were weighed and dissolved in 100 mL of anhydrous ethanol; the mixture was refluxed at 85 °C for 24 hours; the reaction was stopped, and the reaction product was subjected to rotary evaporation, recrystallization with ethyl acetate, and vacuum drying to obtain the physically crosslinked monomer N-cinnamyl-N,N-dimethylhexadecylammonium chloride, with a yield of 98.4%.

[0095] (2) Preparation of chemically cross-linked monomers:

[0096] 0.1 mol of p-dimethylaminobenzaldehyde and 0.12 mol of bromopropene were dissolved in 100 mL of acetonitrile; the mixture was refluxed at 85 °C for 24 hours; the reaction was stopped, and the reaction product was subjected to rotary evaporation, recrystallization with ethyl acetate, and vacuum drying to obtain the chemically crosslinked monomer N-allyl-N,N-dimethylp-benzaldehyde ammonium bromide with a yield of 99.1%.

[0097] (3) Preparation of self-crosslinking thickener:

[0098] Acrylamide, acrylic acid, the physically crosslinking monomer N-cinnamyl-N,N-dimethylhexadecyl ammonium chloride, and the chemically crosslinking monomer N-allyl-N,N-dimethyl-p-benzaldehyde ammonium bromide were weighed out in a molar ratio of 74.5:25:0.25:0.25. An appropriate amount of distilled water was added, and the mixture was stirred and dissolved evenly. The pH was adjusted to 7 with a 10% NaOH solution, and an appropriate amount of distilled water was added to obtain a monomer mixture with a total monomer mass fraction of 30%.

[0099] Nitrogen gas was bubbled into the monomer mixture for 15 minutes to remove dissolved oxygen from the water; 0.025 wt% of the total monomer mass of the initiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone was added; the mixture was placed under a photoinitiator and the photopolymerization reaction temperature was controlled between 10°C and 30°C. The reaction was carried out for 4 hours to obtain a white colloid; the white colloid was cut into small pieces, soaked in ethanol, dried, and pulverized to obtain a self-crosslinking thickener, denoted as S3.

[0100] Example 19:

[0101] (1) Preparation of physically crosslinked monomers:

[0102] 0.11 mol of hexadecylamine and 0.1 mol of cinnamyl chloride were weighed and dissolved in 100 mL of anhydrous ethanol; the mixture was refluxed at 80 °C for 12 hours; the reaction was stopped, and the reaction product was subjected to rotary evaporation, recrystallization with ethyl acetate, and vacuum drying to obtain the physically crosslinked monomer N-cinnamyl-N,N-dimethylhexadecylammonium chloride, with a yield of 97.6%.

[0103] (2) Preparation of chemically cross-linked monomers:

[0104] 0.1 mol of p-dimethylaminobenzaldehyde and 0.11 mol of bromopropene were dissolved in 100 mL of acetonitrile; the mixture was refluxed at 80 °C for 12 hours; the reaction was stopped, and the reaction product was subjected to rotary evaporation, recrystallization with ethyl acetate, and vacuum drying to obtain the chemically crosslinked monomer N-allyl-N,N-dimethylp-benzaldehyde ammonium bromide with a yield of 98.2%.

[0105] (3) Preparation of self-crosslinking thickener:

[0106] Weigh acrylamide, acrylic acid, the physically crosslinking monomer N-cinnamyl-N,N-dimethylhexadecyl ammonium chloride, and the chemically crosslinking monomer N-allyl-N,N-dimethyl-p-benzaldehyde ammonium bromide in a molar ratio of 79:20:0.5:0.5. Add an appropriate amount of distilled water, stir to dissolve evenly, adjust the pH to 7 with a 10% NaOH solution, and add an appropriate amount of distilled water to obtain a mixture with a total monomer mass fraction of 25%.

[0107] Nitrogen gas was bubbled into the monomer mixture for 15 minutes to remove dissolved oxygen from the water; 0.025 wt% of the total monomer mass of the initiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone was added; the mixture was placed under a photoinitiator and the photopolymerization reaction temperature was controlled between 10°C and 30°C. The reaction was carried out for 4 hours to obtain a white colloid; the white colloid was cut into small pieces, soaked in ethanol, dried, and pulverized to obtain a self-crosslinking thickener, denoted as S4.

[0108] Comparative example:

[0109] Weigh acrylamide and acrylic acid in a molar ratio of 80:20, add an appropriate amount of distilled water, stir to dissolve evenly, adjust the pH to 7 with a 10% NaOH solution, and add an appropriate amount of distilled water to obtain a mixture with a total monomer mass fraction of 25%.

[0110] Nitrogen gas was bubbled into the monomer mixture for 15 minutes to remove dissolved oxygen from the water; 0.025 wt% of the total monomer mass of the initiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone was added; the mixture was placed under a photoinitiator and the photopolymerization reaction temperature was controlled between 10°C and 30°C. The reaction was carried out for 4 hours to obtain a white colloid; the white colloid was cut into small pieces, soaked in ethanol, vacuum dried, and pulverized to obtain a thickener, denoted as D1.

[0111] Test Example 1: Analysis of Thickening Performance

[0112] Self-crosslinking thickeners S1 to S4 and thickener D1 were prepared into solutions of a series of concentrations, and the viscosity-concentration relationship curves of each polymer were measured at room temperature using a six-speed viscometer (see...). Figure 1 ).

[0113] from Figure 1As can be seen, when the polymer concentration is low (0.04%), the polymer viscosity is similar; as the polymer concentration increases, the thickening effect of self-crosslinking thickeners S1 to S4 becomes more significant, and the viscosity of the self-crosslinking thickener at a concentration of 0.6% is nearly twice that of the partially hydrolyzed polyacrylamide.

[0114] Test Example 2: Salt Resistance Performance Analysis

[0115] Self-crosslinking thickeners S1 to S4 and thickener D1 were prepared into 0.6% polymer solutions at different salinities. The viscosity-salinity relationship curves of the polymers were measured at room temperature using a six-speed viscometer (see...). Figure 2 and Figure 3 ).

[0116] from Figure 2 and Figure 3 As can be seen, with the increase of mineralization, the apparent viscosity of crosslinking thickeners S1 to S4 and thickener D1 gradually decreases; at 12×10 4 The viscosity retention rate of the self-crosslinking thickener remains above 40% under high salinity conditions of mg / L NaCl; under high divalent ion conditions of 5000 mg / L CaCl2, the viscosity retention rate of self-crosslinking thickeners S1 to S4 remains above 35%, and the viscosity retention rate of D1 is approximately 12%. This indicates that the self-crosslinking thickener of the present invention exhibits excellent salt resistance.

[0117] Test Example 3: Temperature Resistance Performance Analysis

[0118] Thickener D1 and self-crosslinking thickener S3 were formulated into a polymer solution with a concentration of 6000 mg / L. The solution was then tested using a Hacker RS600 high-temperature, high-pressure rheometer at a shear rate of 100 s⁻¹. -1 Under a heating rate of 3℃ / min, the viscosity-temperature relationship curve of the polymer solution was measured (see...). Figure 4 , Figure 5 ).

[0119] from Figure 4 and Figure 5 As can be seen from this, with increasing temperature, thickener D1 (see...) Figure 4 Polymer D1) and self-crosslinking thickener S3 (see Figure 5 The viscosity of polymer S3 decreased. Thickener D1 had a viscosity below 50 mPa·s after the temperature exceeded 155℃; self-crosslinking thickener S3 maintained a viscosity of around 100 mPa·s after the temperature exceeded 180℃, showing better temperature resistance.

[0120] In summary, the self-crosslinking thickener of this invention exhibits excellent temperature and salt resistance, maintaining high viscosity even in high-temperature and high-salinity brine, making it suitable for high-temperature ultra-deep well mining. It also demonstrates outstanding thickening effect, achieving a viscosity nearly twice that of traditional polyacrylamide at the same concentration. Furthermore, it requires no external metal crosslinking agent and exhibits good structural stability. Moreover, the preparation process of this self-crosslinking thickener is mild and simple, with easily controllable conditions, making it suitable for large-scale production and showing promising application prospects.

[0121] The above technical features constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A self-crosslinking viscosifier characterized in that It is obtained by copolymerization of acrylamide, acrylic acid, physically crosslinking monomers and chemically crosslinking monomers under neutral pH conditions; The physical crosslinking monomer is N-cinnamyl-N,N-dimethylhexadecylammonium chloride; The chemical crosslinking monomer is N-allyl-N,N-dimethyl-p-benzaldehyde ammonium bromide; The molar ratio of acrylamide, acrylic acid, physical crosslinking monomer and chemical crosslinking monomer is 70 to 80: 15 to 25: 0.1 to 0.5: 0.1 to 0.

5.

2. The self-crosslinking viscosifier of claim 1, wherein It is prepared according to the following steps: Step 1: Add acrylamide, acrylic acid, physical crosslinking monomer, and chemical crosslinking monomer to water, and adjust the pH to neutral to obtain a monomer mixture. Step 2: Remove dissolved oxygen from the monomer mixture; Step 3: Add a photoinitiator to the monomer mixture to carry out a photopolymerization reaction. After the reaction product is crushed, soaked, dried, and pulverized, a self-crosslinking thickener is obtained.

3. The self-crosslinking thickener according to claim 2, characterized in that... It has the structure shown in the following formula: In the formula, m1, m2, m3 and m4 are the number of repeating units in each structural unit, and the ratio of m1 to m2, m3 and m4 is 70 to 80: 15 to 25: 0.1 to 0.5: 0.1 to 0.

5.

4. The self-crosslinking thickener according to claim 3, characterized in that... The molecular weight ranges from 3 million to 9 million.

5. The self-crosslinking thickener according to claim 2, characterized in that... In step one, the total mass fraction of acrylamide, acrylic acid, physically crosslinked monomers, and chemically crosslinked monomers in the monomer mixture is 20% to 30%.

6. The self-crosslinking thickener according to claim 2 or 5, characterized in that... In step three, the photopolymerization reaction lasts for 3 to 6 hours, and the reaction temperature is 10°C to 30°C. Or / and, the photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; the amount of photoinitiator is 0.01wt% to 0.1wt% of the total mass of acrylamide, acrylic acid, physical crosslinking monomer, and chemical crosslinking monomer.

7. The self-crosslinking thickener according to claim 1, characterized in that... N-Cinnamyl-N,N-Dimethylhexadecylammonium chloride was prepared according to the following steps: The required amounts of hexadecylamine and cinnamyl chloride were dissolved in a solvent and refluxed. The reaction product was concentrated and recrystallized to obtain N-cinnamyl-N,N-dimethylhexadecylammonium chloride.

8. The self-crosslinking thickener according to claim 7, characterized in that... The solvent is anhydrous ethanol.

9. The self-crosslinking thickener according to claim 7 or 8, characterized in that... The reflux reaction temperature is 80°C to 85°C, and the reaction time is 12 to 36 hours.

10. The self-crosslinking thickener according to claim 7 or 8, characterized in that... The molar ratio of hexadecylamine to cinnamyl chloride is 1 to 1.2:

1.

11. The self-crosslinking thickener according to claim 1, characterized in that... N-Allyl-N,N-Dimethyl-p-benzaldehyde ammonium bromide was prepared according to the following steps: The required amount of p-dimethylaminobenzaldehyde and bromopropylene were dissolved in the reaction solvent and refluxed. The reaction product was concentrated and recrystallized to obtain N-allyl-N,N-dimethylp-benzaldehyde ammonium bromide.

12. The self-crosslinking thickener according to claim 11, characterized in that... The reaction solvent is acetonitrile.

13. The self-crosslinking thickener according to claim 11 or 12, characterized in that... The reflux reaction temperature is 80°C to 85°C, and the reaction time is 6 hours to 24 hours.

14. The self-crosslinking thickener according to claim 11 or 12, characterized in that... The molar ratio of p-dimethylaminobenzaldehyde to bromopropene is 1:1 to 1.

2.

15. A method for preparing a self-crosslinking thickener according to any one of claims 1 to 14, comprising the following steps: Step 1: Add acrylamide, acrylic acid, physical crosslinking monomer, and chemical crosslinking monomer to water, and adjust the pH to neutral to obtain a monomer mixture. Step 2: Remove dissolved oxygen from the monomer mixture; Step 3: Add a photoinitiator to the monomer mixture to carry out a photopolymerization reaction. After the reaction product is crushed, soaked, dried, and pulverized, a self-crosslinking thickener is obtained.

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