An imidazoline-based quaternary ammonium salt clay stabilizer and its preparation method

Abstract

This invention relates to the field of oilfield chemical technology and discloses an imidazoline-based quaternary ammonium salt clay stabilizer and its preparation method. The clay stabilizer is a quaternary ammonium salt with a specific general formula, wherein the counter anion is Br⁻⁶, and n in the general formula is 7, 8, or 9, preferably n is 9. The preparation method includes a two-step reaction: first, 1-(3-aminopropyl)imidazolium and a haloalkane are heated under reflux in a solvent to obtain an intermediate; then, the intermediate is reacted with the haloalkane in a second reaction to obtain the target product. The product of this invention exhibits excellent performance even at a low concentration of 0.1%: a room temperature anti-swelling rate of 87.9%-91.4%, a water wash resistance rate of 94.8%-96.8%, and minimal damage to formation permeability, with a permeability change rate of only 3.5%-5.1%. The synergistic effect of the quaternary ammonium salt cation center and the moderately long alkyl group achieves a synergistic effect of electrostatic adsorption and hydrophobic film formation, solving the problem of existing technologies' difficulty in simultaneously achieving high efficiency, long-lasting effect, and low damage. This method is simple and suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to an imidazoline-based quaternary ammonium salt clay stabilizer and its preparation method. Background Technology

[0002] In oil and gas field development, heterogeneous sandstone reservoirs are rich in water-sensitive clay minerals such as montmorillonite and illite-montmorillonite mixed layers. During operations such as water injection and fracturing, external fluids can easily induce dual permeability damage: first, clay hydration and expansion lead to a reduction in the effective radius of pore throats, exacerbating reservoir heterogeneity; second, dispersed and transported clay particles can cause bridging at the throat, resulting in an irreversible decrease in permeability. Therefore, using clay stabilizers to suppress clay damage is key to protecting reservoirs and improving recovery rates.

[0003] Currently, there are three main types of commonly used clay stabilizers, each with its own limitations. Inorganic salts rely on high-concentration cations to compress the electric double layer, but their effectiveness is short-lived and they are easily diluted by formation water or lost through ion exchange. Organic cationic polymers achieve strong long-term effectiveness through long-chain multi-point adsorption, but the high molecular size effect makes it difficult for them to enter micro- and nano-sized pores, resulting in poor deep swelling prevention and easy adsorption and retention in near-wellbore areas, causing physical blockage and damaging the reservoir. Small-molecule cationic surfactants have small molecular size and low risk of damage, but they are limited by the single cationic head group and single alkyl chain structure, resulting in fewer binding sites with clay and weak adsorption. They are easily desorbed under high temperature, high salinity, and water scouring, and have problems such as poor temperature and salt resistance and insufficient long-term effectiveness. They usually require a high concentration to be effective.

[0004] Existing technologies struggle to achieve a balance between low concentration, high efficiency, long-lasting erosion resistance, and low damage. Therefore, developing a novel, highly efficient clay stabilizer that achieves strong adsorption, high stability, and low damage at low concentrations is of great significance for the efficient development of oil and gas fields. Summary of the Invention

[0005] To address the problem that existing clay stabilizers, as described in the background art, are difficult to achieve a balance between low concentration, high efficiency, long-lasting erosion resistance, temperature and salt resistance, and minimal damage to the reservoir, this invention provides an imidazoline quaternary ammonium salt clay stabilizer and its preparation method.

[0006] In a first aspect, the present invention provides an imidazoline quaternary ammonium salt clay stabilizer, wherein the imidazoline quaternary ammonium salt clay stabilizer is a bromide salt having the following general formula, wherein the counter anion is Br⁻: n is any integer among 7, 8, or 9.

[0007] By adopting the above technical solution, the imidazoline quaternary ammonium salt clay stabilizer molecule provided by the present invention has a quaternary ammonium salt cation center, which can be firmly bonded to the surface of clay particles through electrostatic adsorption; at the same time, the long-chain alkyl in the molecule can form a hydrophobic protective film on the clay surface, effectively inhibiting clay hydration swelling and dispersion.

[0008] Preferably, n is 9; Under the conditions of the embodiments of this application, when the value of n is 9, the clay stabilizer exhibits better overall performance in terms of anti-swelling properties, adsorption stability and field applicability.

[0009] Secondly, the present invention provides a method for preparing the above-mentioned imidazoline quaternary ammonium salt clay stabilizer, characterized by comprising the following steps: S1: Imidazole compounds containing primary amino groups and haloalkanes are heated under reflux in an organic solvent to carry out the first quaternization reaction. After the reaction is completed, the monoalkylated imidazole intermediate is obtained by post-treatment. S2: The monoalkylated imidazole intermediate obtained in step S1 and the haloalkane are heated under reflux in an organic solvent to carry out a second reaction. After the reaction is completed, the imidazole-lined quaternary ammonium salt clay stabilizer is obtained by post-treatment.

[0010] By adopting the above technical solution, the synthesis reaction equation of the preparation method of the present invention is as follows: S1: ; S2: .

[0011] This invention, through the above-described synthesis method, can prepare a small-molecule cationic clay stabilizer. This compound, with the synergistic effect of its quaternary ammonium salt cation center and alkyl chain, can achieve efficient electrostatic adsorption and dense hydrophobic film formation on clay minerals even at low concentrations, thus exhibiting excellent anti-swelling effect, water-washing resistance, and reservoir compatibility. The preparation method has a clear process route, mild reaction conditions, simple operation, and readily available raw materials, making it suitable for large-scale production.

[0012] Preferably, in step S1, the imidazole compound containing a primary amino group is 1-(3-aminopropyl)imidazolium; Preferably, in steps S1 and S2, the haloalkane is 1-bromooctane, 1-bromononane, or 1-bromodecane; More preferably, in steps S1 and S2, the haloalkane is 1-bromodecane.

[0013] Preferably, in steps S1 and S2, the organic solvent is an alcohol solvent; More preferably, the alcohol solvent is anhydrous ethanol.

[0014] Preferably, in steps S1 and S2, the reaction is carried out under an inert atmosphere. More preferably, the inert atmosphere is nitrogen.

[0015] Preferably, in step S1, the molar ratio of the 1-(3-aminopropyl)imidazolium to the haloalkane is 1:(1.0-1.2); Preferably, in step S1, the reaction temperature of the heating reflux is 70-80°C; More preferably, in step S1, the reaction temperature of the heating reflux is 78°C.

[0016] Preferably, in step S1, the reaction time of the heating reflux reaction is 8-15 hours; Preferably, in step S2, the molar ratio of the monoalkylated imidazole intermediate to the haloalkane is 1:(1.0-1.2); Preferably, in step S2, the reaction temperature of the heating reflux is 70-80°C; More preferably, in step S2, the reaction temperature of the heating reflux is 78°C.

[0017] Preferably, in step S2, the reaction time of the heating reflux reaction is 20-30 hours; Preferably, in step S1, after the reaction is complete, the solvent is removed by rotary evaporation, the crude product is washed with ethyl acetate, and dried to obtain the monoalkylated imidazole intermediate; Preferably, in step S2, after the reaction is completed, most of the solvent is removed by rotary evaporation, acetone is added to the residue to precipitate solid, and the solid is obtained by filtration, cold acetone washing, and vacuum drying to obtain the imidazoline quaternary ammonium salt clay stabilizer.

[0018] In summary, the present invention has the following beneficial effects; 1. The imidazoline-based quaternary ammonium salt clay stabilizer provided by this invention contains a quaternary ammonium salt cation center in its molecular structure. It can firmly bind to the surface of clay particles through electrostatic adsorption, effectively neutralizing the negative charge of clay and inhibiting hydration swelling even at low concentrations. At the same time, the alkyl chain in the molecule can form a hydrophobic protective layer on the clay surface, preventing water molecule wetting and avoiding clay dispersion. This dual mechanism enables it to exhibit excellent anti-swelling effect even at low concentrations. Furthermore, the synergistic effect of the hydrophobic film and strong electrostatic adsorption improves the resistance to water washing and erosion, providing long-term and stable performance to meet the long-term development needs of oil and gas fields. 2. The preparation method of the present invention adopts a two-step reaction, with a clear process route, mild reaction conditions, and simple operation; the raw materials are readily available, the post-processing steps are simple, the reproducibility is good, and it is suitable for industrial-scale production; in addition, the product has a small molecular structure and small hydrodynamic size, which makes it easy to enter the micro-nano pores of low-permeability reservoirs to achieve deep processing, and has low potential damage to formation permeability. Attached Figure Description

[0019] Figure 1 The infrared spectrum of the clay stabilizer prepared according to the present invention is shown.

[0020] Figure 2 The image shows the 1H NMR spectrum of the clay stabilizer prepared according to this invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Unless otherwise specified, the reagents used in the following embodiments are all commercially available products, and the methods used are all conventional methods in the art.

[0022] Example 1: Preparation of imidazoline quaternary ammonium salt clay stabilizer (n=7); Step 1: In a 250 mL three-necked flask equipped with a magnetic stirrer, a condenser, and a nitrogen inlet tube, add 12.52 g (0.10 mol) of 1-(3-aminopropyl)imidazolium and 18.07 g (0.10 mol) of 1-bromooctane; add 100 mL of anhydrous ethanol as a solvent, and under nitrogen protection, heat the reaction system to 78°C and stir under reflux for 12 hours; after the reaction is complete, cool the reaction solution to room temperature, remove the solvent by rotary evaporation, and obtain a pale yellow oily crude product; repeatedly wash the crude product with ethyl acetate (3 × 30 mL) to remove unreacted raw materials; finally, dry the obtained product under vacuum at 50°C for 6 hours to obtain a pale yellow oily monoalkylated imidazolium intermediate; Step 2: Dissolve the monoalkylated imidazole intermediate in 150 mL of anhydrous ethanol and transfer it to the three-necked flask mentioned above; under ice-water bath cooling and nitrogen protection, slowly add 18.07 g (0.10 mol) of 1-bromooctane; after the addition is complete, remove the ice-water bath, heat the reaction system to 78°C, and continue stirring for 24 hours; after the reaction is complete, cool to room temperature, and remove most of the solvent by rotary evaporator; add 50 mL of cold acetone to the viscous residue, and a large amount of pale yellow solid immediately precipitates; collect the solid by vacuum filtration and wash thoroughly with cold acetone (3 × 20 mL) to remove residual bromide and solvent; place the obtained solid in a vacuum drying oven and dry at 50°C to constant weight to obtain a pale yellow powder, which is the target product, the imidazole quaternary ammonium salt clay stabilizer, whose structure corresponds to the compound with n=7 in the general formula: .

[0023] Example 2: Preparation of imidazoline quaternary ammonium salt clay stabilizer (n=7); Step 1: In a 250 mL three-necked flask equipped with a magnetic stirrer, a condenser, and a nitrogen inlet tube, add 12.52 g (0.10 mol) of 1-(3-aminopropyl)imidazolium and 21.684 g (0.12 mol) of 1-bromooctane; add 100 mL of anhydrous ethanol as a solvent, and heat the reaction system to 78°C under nitrogen protection, stirring and refluxing for 12 hours; after the reaction is complete, cool the reaction solution to room temperature, remove the solvent by rotary evaporation, and obtain a pale yellow oily crude product; repeatedly wash the crude product with ethyl acetate (3 × 30 mL) to remove unreacted raw materials; finally, dry the obtained product under vacuum at 50°C for 6 hours to obtain a pale yellow oily monoalkylated imidazolium intermediate; Step 2: Dissolve the monoalkylated imidazole intermediate in 150 mL of anhydrous ethanol and transfer it to the three-necked flask mentioned above; under ice-water bath cooling and nitrogen protection, slowly add 21.684 g (0.12 mol) of 1-bromooctane; after the addition is complete, remove the ice-water bath, heat the reaction system to 78°C, and continue stirring for 24 hours; after the reaction is complete, cool to room temperature, and remove most of the solvent by rotary evaporator; add 50 mL of cold acetone to the viscous residue, and a large amount of pale yellow solid immediately precipitates; collect the solid by vacuum filtration and wash thoroughly with cold acetone (3 × 20 mL) to remove residual bromide and solvent; place the obtained solid in a vacuum drying oven and dry at 50°C to constant weight to obtain a pale yellow powder, which is the target product, the imidazole quaternary ammonium salt clay stabilizer, whose structure corresponds to the compound with n=7 in the general formula: .

[0024] Example 3: Preparation of imidazoline quaternary ammonium salt clay stabilizer (n=8); Step 1: In a 250 mL three-necked flask equipped with a magnetic stirrer, a condenser, and a nitrogen inlet tube, add 12.52 g (0.10 mol) of 1-(3-aminopropyl)imidazolium and 19.31 g (0.10 mol) of 1-bromononane; add 100 mL of anhydrous ethanol as a solvent, and heat the reaction system to 78°C under nitrogen protection, stirring and refluxing for 12 hours; after the reaction is complete, cool the reaction solution to room temperature, remove the solvent by rotary evaporation, and obtain a pale yellow oily crude product; repeatedly wash the crude product with ethyl acetate (3 × 30 mL) to remove unreacted raw materials; finally, dry the obtained product under vacuum at 50°C for 6 hours to obtain a pale yellow oily monoalkylated imidazolium intermediate; Step 2: Dissolve the monoalkylated imidazole intermediate in 150 mL of anhydrous ethanol and transfer it to the three-necked flask mentioned above; under ice-water bath cooling and nitrogen protection, slowly add 19.31 g (0.10 mol) of 1-bromononane; after the addition is complete, remove the ice-water bath, heat the reaction system to 78°C, and continue stirring for 24 hours; after the reaction is complete, cool to room temperature, and remove most of the solvent by rotary evaporation; add 50 mL of cold acetone to the viscous residue, and a large amount of pale yellow solid immediately precipitates; collect the solid by vacuum filtration and wash thoroughly with cold acetone (3 × 20 mL) to remove residual bromide and solvent; place the obtained solid in a vacuum drying oven and dry at 50°C to constant weight to obtain a pale yellow powder, which is the target product, the imidazole quaternary ammonium salt clay stabilizer, whose structure corresponds to the compound with n=8 in the general formula: .

[0025] Example 4: Preparation of imidazoline quaternary ammonium salt clay stabilizer (n=8); Step 1: In a 250 mL three-necked flask equipped with a magnetic stirrer, a condenser, and a nitrogen inlet tube, add 12.52 g (0.10 mol) of 1-(3-aminopropyl)imidazolium and 23.172 g (0.12 mol) of 1-bromononane; add 100 mL of anhydrous ethanol as a solvent, and heat the reaction system to 78°C under nitrogen protection, stirring and refluxing for 12 hours; after the reaction is complete, cool the reaction solution to room temperature, remove the solvent by rotary evaporation, and obtain a pale yellow oily crude product; repeatedly wash the crude product with ethyl acetate (3 × 30 mL) to remove unreacted raw materials; finally, dry the obtained product under vacuum at 50°C for 6 hours to obtain a pale yellow oily monoalkylated imidazolium intermediate; Step 2: Dissolve the monoalkylated imidazole intermediate in 150 mL of anhydrous ethanol and transfer it to the three-necked flask mentioned above; under ice-water bath cooling and nitrogen protection, slowly add 23.172 g (0.12 mol) of 1-bromononane; after the addition is complete, remove the ice-water bath, heat the reaction system to 78°C, and continue stirring for 24 hours; after the reaction is complete, cool to room temperature, and remove most of the solvent by rotary evaporator; add 50 mL of cold acetone to the viscous residue, and a large amount of pale yellow solid immediately precipitates; collect the solid by vacuum filtration and wash thoroughly with cold acetone (3 × 20 mL) to remove residual bromide and solvent; place the obtained solid in a vacuum drying oven and dry at 50°C to constant weight to obtain a pale yellow powder, which is the target product, the imidazole quaternary ammonium salt clay stabilizer, whose structure corresponds to the compound with n=8 in the general formula: .

[0026] Example 5: Preparation of imidazoline quaternary ammonium salt clay stabilizer (n=9); Step 1: In a 250 mL three-necked flask equipped with a magnetic stirrer, a condenser, and a nitrogen inlet tube, add 12.52 g (0.10 mol) of 1-(3-aminopropyl)imidazolium and 20.55 g (0.10 mol) of 1-bromodecane; add 100 mL of anhydrous ethanol as a solvent, and heat the reaction system to 78°C under nitrogen protection, stirring and refluxing for 12 hours; after the reaction is complete, cool the reaction solution to room temperature, remove the solvent by rotary evaporation, and obtain a pale yellow oily crude product; repeatedly wash the crude product with ethyl acetate (3 × 30 mL) to remove unreacted raw materials; finally, dry the obtained product under vacuum at 50°C for 6 hours to obtain a pale yellow oily monoalkylated imidazolium intermediate; Step 2: Dissolve the monoalkylated imidazole intermediate in 150 mL of anhydrous ethanol and transfer it to the three-necked flask mentioned above; under ice-water bath cooling and nitrogen protection, slowly add 20.55 g (0.10 mol) of 1-bromodecane; after the addition is complete, remove the ice-water bath, heat the reaction system to 78°C, and continue stirring for 24 hours; after the reaction is complete, cool to room temperature, and remove most of the solvent by rotary evaporator; add 50 mL of cold acetone to the viscous residue, and a large amount of pale yellow solid immediately precipitates; collect the solid by vacuum filtration and wash thoroughly with cold acetone (3 × 20 mL) to remove residual bromide and solvent; place the obtained solid in a vacuum drying oven and dry at 50°C to constant weight to obtain a pale yellow powder, which is the target product, the imidazole quaternary ammonium salt clay stabilizer, whose structure corresponds to the compound with n=9 in the general formula: .

[0027] Example 6: Preparation of imidazoline quaternary ammonium salt clay stabilizer (n=9); Step 1: In a 250 mL three-necked flask equipped with a magnetic stirrer, a condenser, and a nitrogen inlet tube, add 12.52 g (0.10 mol) of 1-(3-aminopropyl)imidazolium and 24.66 g (0.12 mol) of 1-bromodecane; add 100 mL of anhydrous ethanol as a solvent, and heat the reaction system to 78°C under nitrogen protection, stirring and refluxing for 12 hours; after the reaction is complete, cool the reaction solution to room temperature, remove the solvent by rotary evaporation, and obtain a pale yellow oily crude product; repeatedly wash the crude product with ethyl acetate (3 × 30 mL) to remove unreacted raw materials; finally, dry the obtained product under vacuum at 50°C for 6 hours to obtain a pale yellow oily monoalkylated imidazolium intermediate; Step 2: Dissolve the monoalkylated imidazole intermediate in 150 mL of anhydrous ethanol and transfer it to the three-necked flask mentioned above; under ice-water bath cooling and nitrogen protection, slowly add 24.66 g (0.12 mol) of 1-bromodecane; after the addition is complete, remove the ice-water bath, heat the reaction system to 78°C, and continue stirring for 24 hours; after the reaction is complete, cool to room temperature, and remove most of the solvent by rotary evaporator; add 50 mL of cold acetone to the viscous residue, and a large amount of pale yellow solid immediately precipitates; collect the solid by vacuum filtration and wash thoroughly with cold acetone (3 × 20 mL) to remove residual bromide and solvent; place the obtained solid in a vacuum drying oven and dry at 50°C to constant weight to obtain a pale yellow powder, which is the target product, the imidazole quaternary ammonium salt clay stabilizer, whose structure corresponds to the compound with n=9 in the general formula: .

[0028] Comparative Example 1: Monoalkyl chain quaternary ammonium salt type clay stabilizer; In a 250 mL three-necked flask equipped with a magnetic stirrer, condenser, and nitrogen inlet tube, 12.52 g (0.10 mol) of 1-(3-aminopropyl)imidazolium and 18.07 g (0.10 mol) of 1-bromooctane were added; 100 mL of anhydrous ethanol was added as a solvent, and the reaction system was heated to 78°C and stirred under reflux for 12 hours under nitrogen protection; after the reaction was completed, the reaction solution was cooled to room temperature, and the solvent was removed by rotary evaporator; 50 mL of cold acetone was added to the residue, stirred, filtered, and the solid was washed with cold acetone (3 × 20 mL); the obtained solid was placed in a vacuum drying oven and dried at 50°C to constant weight to obtain a pale yellow solid; the product is a monoalkyl chain quaternary ammonium salt compound, which contains only one quaternary ammonium salt cation center and one octyl chain in its molecule, and its structure corresponds to the compound with n=7 in the general formula: .

[0029] Comparative Example 2: Preparation of imidazoline quaternary ammonium salt clay stabilizer (n=5); Step 1: In a 250 mL three-necked flask equipped with a magnetic stirrer, a condenser, and a nitrogen inlet tube, add 12.52 g (0.10 mol) of 1-(3-aminopropyl)imidazolium and 16.41 g (0.10 mol) of 1-bromohexane; add 100 mL of anhydrous ethanol as a solvent, and heat the reaction system to 78°C under nitrogen protection, stirring and refluxing for 12 hours; after the reaction is complete, cool the reaction solution to room temperature, remove the solvent by rotary evaporation, and obtain a pale yellow oily crude product; repeatedly wash the crude product with ethyl acetate (3 × 30 mL) to remove unreacted raw materials; finally, dry the obtained product under vacuum at 50°C for 6 hours to obtain a pale yellow oily monoalkylated imidazolium intermediate; Step 2: Dissolve the monoalkylated imidazole intermediate in 150 mL of anhydrous ethanol and transfer it to the three-necked flask mentioned above; under ice-water bath cooling and nitrogen protection, slowly add 16.41 g (0.10 mol) of 1-bromohexane; after the addition is complete, remove the ice-water bath, heat the reaction system to 78°C, and continue stirring for 24 hours; after the reaction is complete, cool to room temperature, and remove most of the solvent by rotary evaporator; add 50 mL of cold acetone to the viscous residue, and a large amount of pale yellow solid immediately precipitates; collect the solid by vacuum filtration and wash thoroughly with cold acetone (3 × 20 mL) to remove residual bromide and solvent; place the obtained solid in a vacuum drying oven and dry at 50°C to constant weight to obtain a pale yellow powder solid, which is the target product, the imidazole quaternary ammonium salt clay stabilizer, whose structure corresponds to the compound with n=5 in the general formula: .

[0030] Comparative Example 3: Preparation of imidazoline quaternary ammonium salt clay stabilizer (n=15); Step 1: In a 250 mL three-necked flask equipped with a magnetic stirrer, a condenser, and a nitrogen inlet tube, add 12.52 g (0.10 mol) of 1-(3-aminopropyl)imidazolium and 30.65 g (0.10 mol) of 1-bromohexadecane; add 100 mL of anhydrous ethanol as a solvent, and heat the reaction system to 78°C under nitrogen protection, stirring and refluxing for 12 hours; after the reaction is completed, cool the reaction solution to room temperature, remove the solvent by rotary evaporation, and obtain a pale yellow oily crude product; repeatedly wash the crude product with ethyl acetate (3 × 30 mL) to remove unreacted raw materials; finally, dry the obtained product under vacuum at 50°C for 6 hours to obtain a pale yellow oily monoalkylated imidazolium intermediate; Step 2: Dissolve the monoalkylated imidazole intermediate in 150 mL of anhydrous ethanol and transfer it to the three-necked flask mentioned above; under ice-water bath cooling and nitrogen protection, slowly add 30.65 g (0.10 mol) of 1-bromohexadecane; after the addition is complete, remove the ice-water bath, heat the reaction system to 78°C, and continue stirring for 24 hours; after the reaction is complete, cool to room temperature, and remove most of the solvent by rotary evaporator; add 50 mL of cold acetone to the viscous residue, and a large amount of pale yellow solid immediately precipitates; collect the solid by vacuum filtration and wash thoroughly with cold acetone (3 × 20 mL) to remove residual bromide and solvent; place the obtained solid in a vacuum drying oven and dry at 50°C to constant weight to obtain a pale yellow powder, which is the target product, the imidazole quaternary ammonium salt clay stabilizer, whose structure corresponds to the compound with n=15 in the general formula: .

[0031] Performance testing experiments; Each clay stabilizer sample prepared in each example and comparative example was weighed 0.3g and dissolved in 300mL of deionized water to prepare a clay stabilizer solution with a concentration of 0.1%, and then tested as follows.

[0032] Test 1: The anti-swelling rate test was conducted according to the "SY / T5971-2016 Performance Evaluation Method for Clay Stabilizers Used in Fracturing, Acidizing, and Water Injection in Oil and Gas Fields". The steps are as follows: Weigh 0.50g of sodium bentonite, add it to a 10mL centrifuge tube, add deionized water to the 10mL mark, shake thoroughly, let stand at room temperature for 2 hours, then place it in a centrifuge and centrifuge at 1500r / min for 15 minutes. Read the volume of sodium bentonite in water. Using the same procedure, but instead of deionized water, a clay stabilizer solution of a certain concentration was used to measure the volume of sodium bentonite after centrifugation. The volume of sodium bentonite was measured using kerosene instead of water. The formula for calculating the anti-swelling rate is as follows: In the formula: η is the anti-swelling rate, % The volume of sodium bentonite in kerosene is in mL; The volume of sodium bentonite in the clay stabilizer is in mL; The volume of sodium bentonite in deionized water is expressed in mL.

[0033] Test 2: Water Washability Test: Pour out the supernatant from the centrifuge tube after centrifugation in Test 1, add deionized water to 10 mL, stir thoroughly, let stand for 2 hours, and then centrifuge at 1500 r / min for 15 min. Finally, read the final volume of sodium bentonite in the centrifuge tube. The formula for calculating the washability (N) is as follows: In the formula: The volume of sodium bentonite swelling in the clay stabilizer solution is expressed in mL. The volume of sodium bentonite after washing with water is the swelling volume, in mL; The volume of sodium bentonite in deionized water is expressed in mL.

[0034] Test 3: Core Flow Experiment: Under conditions below the critical flow rate, deionized water was first passed through in the forward direction. After the pressure stabilized, the initial permeability of the core was measured. The core was treated with 5PV solution in the reverse direction and allowed to stand for 6 hours. Then, deionized water was passed through in the forward direction. After the pressure stabilized, the permeability of the treated core was measured. The formula for the change rate of clay stabilizer permeability is as follows: In the formula, Permeability change rate, % The initial core permeability is given in mD. denoted as permeability after core processing, in mD.

[0035] The results are summarized in Table 1; Table 1. Performance Test Results .

[0036] Based on Examples 1-6, Comparative Examples 1-3, and Table 1, it can be seen that the imidazoline quaternary ammonium salt clay stabilizer of the present invention exhibits superior comprehensive performance when the alkyl chain length n=7-9. At a low concentration of 0.1%, its room temperature anti-swelling rate is as high as 87.9%-91.4%, and its water-wash resistance rate is as high as 94.8%-96.8%, with low damage to formation permeability, a change rate of only 3.5%-5.1%. Simultaneously, the product has good solubility in water systems, facilitating on-site preparation. Its quaternary ammonium salt cation center can generate electrostatic adsorption with the surface of clay particles, and the alkyl chain can form a hydrophobic protective layer on the clay surface after adsorption, thereby synergistically achieving anti-swelling and water-wash resistance effects. This hydrophobic protective layer helps inhibit the dispersion and migration of clay particles, reducing the risk of pore throat blockage; therefore, the permeability change rate is lower than that of the comparative examples, demonstrating a protective effect on the formation's conductivity.

[0037] Comparative Example 1, containing only one alkyl chain, exhibited significantly reduced anti-swelling and water-washing resistance. Comparative Example 2, with its excessively short alkyl chain (n=5), showed poor anti-swelling and water-washing effects. Comparative Example 3, with its excessively long alkyl chain (n=15), suffered from excessive hydrophobicity leading to reduced solubility, and the steric hindrance of the long chain affected adsorption efficiency, resulting in overall performance inferior to the preferred embodiment of this invention. This fully demonstrates that the quaternary ammonium salt structure and the alkyl chain length range of n=7-9 are key to achieving excellent technical results.

[0038] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. An imidazoline-based quaternary ammonium salt clay stabilizer, characterized in that, It is a quaternary ammonium salt with the following general formula, wherein the counter anion is Br⁻: n is any integer among 7, 8, or 9.

2. The imidazoline quaternary ammonium salt clay stabilizer according to claim 1, characterized in that, n is 9.

3. A method for preparing an imidazoline quaternary ammonium salt clay stabilizer as described in claim 1 or 2, characterized in that, Includes the following steps: S1: Synthesis of monoalkylated intermediate: Imidazole compound containing primary amino group and haloalkane are heated under reflux in an organic solvent to carry out the first quaternization reaction. After the reaction is completed, the solvent is removed, washed and dried to obtain monoalkylated imidazole intermediate. S2: Synthesis of imidazoline quaternary ammonium salt clay stabilizer: The monoalkylated imidazoline intermediate obtained in step S1 and the haloalkane are heated under reflux in an organic solvent to carry out a second reaction. After the reaction is completed, the solvent is removed, the solid is precipitated, filtered, washed and dried to obtain the imidazoline quaternary ammonium salt clay stabilizer.

4. The method according to claim 3, characterized in that, In step S1, the imidazole compound containing a primary amino group is 1-(3-aminopropyl)imidazolium.

5. The method according to claim 3, characterized in that, The haloalkane described in steps S1 and S2 is the same.

6. The method according to claim 5, characterized in that, The haloalkane is 1-bromooctane, 1-bromononane, or 1-bromodecane.

7. The method according to claim 6, characterized in that, The haloalkane is 1-bromodecane.

8. The method according to claim 3, characterized in that, In steps S1 and S2, the organic solvent is an alcohol solvent.

9. The method according to claim 8, characterized in that, The alcohol solvent is anhydrous ethanol.

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