Betaine Gemini surfactant, clean fracturing fluid and preparation method thereof

Abstract

The invention discloses a betaine Gemini surfactant, a clean fracturing fluid and a preparation method thereof, and belongs to the technical field of oilfield chemistry. The invention comprises the following steps: an alkylamine propionate is obtained by an addition reaction between a long-chain alkyl dimethyl tertiary amine and an acrylate; the alkylamine propionate is then reacted with a dichloro hydrocarbon and neutralized with an alkali to obtain a carboxylate Gemini tertiary amine compound; and finally the compound is reacted with a monohalogenated hydrocarbon to obtain a betaine sweet Gemini surfactant. The fracturing fluid comprises 3-5 wt% of the betaine Gemini surfactant, 1-3 wt% of a composite anti-swelling agent, and the balance is high-mineralization formation water. The formation water is first added, followed by an inorganic salt anti-swelling agent, the temperature is raised to 40-60°C, an organic anti-swelling agent is added, and finally the betaine Gemini surfactant is added to obtain a clean fracturing fluid. The fracturing fluid is heat-resistant, salt-resistant and shear-resistant, has good elastic sand-carrying and drag-reducing effects, and has low damage to formations. The fracturing fluid can be well applied to large-scale hydraulic development of low-permeability and ultra-low-permeability oil and gas reservoirs, tight oil and gas reservoirs, and shale oil and gas reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield chemistry, in particular to a betaine Gemini surfactant, a clean fracturing fluid and a preparation method thereof. Background Art

[0002] With advances in oil and gas exploration and development technologies, my country's oil and gas development is continuously expanding into unconventional reservoirs. Effective development has been achieved in the Changqing Oilfield and Yanchang tight oil and gas reservoirs in Shaanxi Province, and significant progress has been made in the recovery of shale oil and gas within unconventional reservoirs in Sichuan Province and the shale oil and gas reservoirs in the Shengli Oilfield in Shandong Province. These unconventional reservoirs have low permeability, high clay content, and low porosity, often resulting in no commercial gas flow after drilling. Large-scale fracturing (10,000 tons of fluid per 1,000 tons of sand) is the most effective means of developing unconventional reservoirs. The performance of the fracturing fluid plays a key role in fracturing effectiveness. Currently, guar gum fracturing fluid is widely used in fracturing operations, accounting for 70% to 80% of total usage, due to its advantages such as a wide range of raw materials, high base fluid viscosity, good cross-linking properties, mature operation experience, and well-developed supporting facilities. However, guar gum fracturing fluid also has disadvantages such as high formation damage, poor temperature resistance, and difficulty in handling flowback fluid. With the continuous deepening of oil and gas exploration and development, unconventional oil and gas resources have become a hot spot for development. The development of tight oil and gas reservoirs, shale oil and gas reservoirs, coalbed methane reservoirs, shale oil and gas reservoirs, and low- and ultra-low-permeability oil and gas reservoirs is increasing. Traditional guar gum fracturing fluid systems can no longer fully meet the needs of oil and gas production fracturing fluids. As unconventional oil and gas resources have put forward new requirements for extraction technology, a large number of fracturing fluid systems with more excellent performance have emerged. Based on the different chemical compositions of the formula, new fracturing fluid systems can be divided into viscoelastic surfactant fracturing fluids, polymer fracturing fluids, foam fracturing fluids, CO2 fracturing fluids, and other new fracturing fluids.

[0003] Viscoelastic surfactant fracturing fluid (VES), also known as clean fracturing fluid, refers to a type of fracturing fluid that utilizes a viscoelastic surfactant as its primary agent. Schlumberger pioneered the development and use of VES. Depending on the surfactant, it can be categorized as cationic, anionic, nonionic, and amphoteric. Clean fracturing fluids are characterized by their ability to leave no residue after gel breaking, minimize reservoir core damage (9.9% to 10.3%), and exhibit low friction. They offer superior oil and gas production enhancement performance compared to guar gum fracturing fluids and are suitable for fracturing low-permeability reservoirs in unconventional oil and gas reservoirs.

[0004] Yang Jiang et al. studied the mechanism of surfactant clean fracturing fluid requiring a long time to dissolve and establish viscoelasticity after dilution. The research material used was a zwitterionic surfactant clean fracturing fluid. The basic components are scoparia (C 22) betaine (a zwitterionic surfactant), sodium dodecyl sulfate (SDS), isopropyl alcohol, and water. The results show that during the dissolution process, the fracturing fluid system undergoes a three-phase phase consisting of a liquid crystal gel. The addition of a co-surfactant can increase the dissolution rate and viscosity at high temperatures. This study reveals the mechanism by which viscoelastic surfactant fracturing fluids establish viscoelasticity, providing theoretical guidance for subsequent research.

[0005] Invention patent CN202210602245.6 discloses an anionic gemini sulfate viscoelastic surfactant containing two long nonionic polyether chains and two anionic sulfate hydrophilic head groups, as well as a method for preparing the surfactant and a clean fracturing fluid prepared using the surfactant. The surfactant preparation method according to the present invention is environmentally friendly, free of industrial waste, exhibits high surface activity, excellent viscoelasticity, superior rheological properties, and a simple synthesis method. Furthermore, the clean fracturing fluid obtained by compounding the surfactant with an inorganic salt counterion exhibits good viscoelasticity, shear resistance, and excellent rheological properties at low temperatures, meeting national petroleum and natural gas industry standards. It also exhibits good sand-carrying performance, is residue-free, and exhibits strong temperature resistance.

[0006] Invention patent CN202210445501.5 provides a temperature-resistant dihydroxy cationic viscoelastic surfactant, a preparation method thereof, a fracturing fluid and its application. A "double benzene ring structure", a "double hydroxy structure" and a double-tail structure are designed in the surfactant molecular structure to increase its stability. This viscoelastic surfactant can be directly prepared using formation produced water; the fracturing fluid of the present invention includes 4.3-5wt% of the above-mentioned ultra-high temperature resistant surfactant, 3-8wt% of inorganic salts, and the remainder is water. It can be used to prepare a clean fracturing fluid with formation produced water with a mineralization of 60,000 mg / L or less. This fracturing fluid has good temperature and shear resistance. Under the shear conditions of 220°C and 170s', the viscosity is maintained at above 30mPa·s after 2 hours, and can be well applied to large-scale hydraulic development of shale oil and gas reservoirs.

[0007] It can be seen that existing clean fracturing technologies often have problems such as complex processes, difficult flowback fluid treatment, high friction, and poor elastic sand carrying capacity. They cannot achieve the high sand ratio required in large-scale volume fracturing and are limited in the application of volume fracturing development in oil and gas reservoirs with particularly low permeability. Summary of the Invention

[0008] In view of this, the betaine Gemini surfactant, clean fracturing fluid and preparation method thereof of the present invention are characterized by comprising the following steps:

[0009] Step S1: Add a long-chain R alkyl primary amine to ethanol and stir to completely dissolve it. Transfer it to a condensing reflux apparatus, add acrylate dropwise into a dropping funnel under stirring in a constant temperature water bath at 30°C. The addition is completed over 15 to 30 minutes. Then, react at 60 to 80°C for 4 to 8 hours. After the reaction, cool to 40 to 50°C and rotate to remove the solvent methanol and excess methyl acrylate to obtain a white solid intermediate product, R alkylamine propionate. The reaction equation is shown in Figure 1:

[0010]

[0011] Figure 1 Synthesis of R-alkylamine propionate

[0012] Step S2: Add R alkylamine propionate to a three-necked flask, add N,N-dimethylformamide as a solvent, add a few drops of dimethylamine as an acid binder, and then add dichlorohydrocarbon, and react for 4 to 6 hours under stirring in a water bath at 40-60°C. After the reaction, wash with ice water and separate the liquids. Use a rotary evaporator to evaporate the solvent under reduced pressure at 80-90°C, saponify the remaining material with a prepared 30% mass fraction NaOH solution, then wash with anhydrous ethanol and dry it. Subsequently, add a certain amount of dilute hydrochloric acid and stir to separate the layers. After suction filtration, wash the product with deionized water until it is neutral. Finally, dissolve the product in acetone for recrystallization, and place the obtained product in a freeze dryer for drying to remove moisture to obtain a carboxylate Gemini-type tertiary amine compound bis(NR alkyl-N-sodium propionate)R1 alkyldiamine; the reaction equation is shown in Figure 2:

[0013] Figure 2 Synthesis of bis(NR alkyl-N-sodium propionate) R1 alkyl diamine

[0014] Step S3: Add the bis(NR alkyl-N-sodium propionate) R1 alkyl diamine intermediate and the alkyl halide to anhydrous ethanol dissolved in sodium carbonate, reflux at 80-90° C. for 24-48 hours, filter to remove inorganic salts, and then remove the solvent and unreacted alkyl halide using a rotary evaporator; wash twice with a mixed solution of acetone and anhydrous ethanol in a volume ratio of 16-19:1, and dry in a vacuum oven at 30-40° C. to obtain the target product, bis(NR alkyl-N-sodium propionate-NR” alkyl) R1 alkyl ammonium dihalide betaine Gemini surfactant; the reaction equation is shown in Figure 3.

[0015]

[0016] Figure 3 Synthesis of bis(NR alkyl-N-sodium propionate-NR" alkyl) R1 alkylammonium dihalide

[0017] Furthermore, the number of carbon atoms in the alkyl group of the long-chain alkyl tertiary amine in step S1 is any one of 18, 20, 22 or 24.

[0018] Furthermore, the acrylic acid ester in step S1 is any one of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate or isobutyl acrylate.

[0019] Furthermore, the molar ratio of the long-chain alkyl tertiary amine to the methyl acrylate in step S1 is 1:1.1-1.3.

[0020] Furthermore, the dichlorohydrocarbon in step S1 is any one of dichloromethane, dichloroethane, dichloropropane, dichlorobutane, dichloropentane, dichlorohexane, dichloropentane, o-dichlorobenzyl, m-dichlorobenzyl or p-dichlorobenzyl.

[0021] Furthermore, the molar ratio of the alkylamine propionate to the dichlorohydrocarbon in step S2 is 2.1-2.3:1.

[0022] Furthermore, the halogenated hydrocarbon in step S3 is any one of methyl chloride, ethyl chloride, methyl bromide or ethyl bromide.

[0023] Furthermore, the molar ratio of the bis(NR alkyl-N-sodium propionate) R1 alkyl diamine to the halogenated hydrocarbon in step S3 is 1:2.1-2.3.

[0024] The present invention also discloses a betaine Gemini surfactant prepared based on the above preparation method.

[0025] At the same time, the present invention also discloses a clean fracturing fluid prepared using the above-mentioned betaine Gemini-type surfactant, characterized in that the fracturing fluid comprises the following components (calculated by mass fraction): 3-5% of a bis(NR alkyl-N-sodium propionate-NR" alkyl) R1 alkyl ammonium dihalide betaine Gemini-type surfactant; 1%-3% of a clay anti-swelling agent; and the balance is 50,000-100,000 mg / L of high-mineralized formation water.

[0026] Furthermore, the clay anti-swelling agent used in the clean fracturing fluid is composed of potassium chloride and a cationic surfactant selected from the group consisting of dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, and hexadecyltrimethylammonium chloride, wherein the mass ratio of potassium chloride to the cationic surfactant is 1.0 to 2.0:1.

[0027] Furthermore, the preparation method of the clean fracturing fluid is as follows: first, formation water is added at room temperature, and then potassium chloride, a clay anti-swelling agent, is added. After dissolution, the temperature is raised to 40-60°C, and then a cationic surfactant selected from dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride or hexadecyltrimethylammonium chloride is added. After dissolution, a bis(NR alkyl-N-sodium propionate-NR" alkyl) R1 alkyl ammonium dihalide betaine Gemini surfactant is added to finally obtain a clean fracturing fluid.

[0028] The clean fracturing fluid can be used for fracturing development of low-permeability and extra-low-permeability oil and gas reservoirs, ultra-low-permeability oil and gas reservoirs, tight oil and gas reservoirs, shale oil and gas reservoirs and shale oil and gas reservoirs, wherein the temperature of the oil and gas reservoirs is generally not higher than 220°C.

[0029] The technical effects of the present invention are:

[0030] The invention solves the problem that the traditional clean fracturing fluid, which relies mainly on viscous sand carrying and supplemented by elastic sand carrying under acidic and high-salinity conditions, has high friction resistance, low injection volume, and cannot achieve the high sand carrying ratio required for large-scale volume fracturing. The betaine surfactant has two quaternary ammonium groups and two carboxyl groups, which improves the acid and salt resistance. The role of the linking group increases the compactness of the arrangement of surfactant molecules on the surface interface, significantly improves the surface and interface activity of the material, and effectively improves the clean washing ability of the fracturing fluid. In addition, under the hydrophobic association of the ultra-long hydrophobic chain, the betaine surfactant and the inorganic salt are more likely to self-assemble to form a supramolecular structure, greatly improving the elasticity of the liquid. The clean fracturing prepared by the present invention has low viscosity, good injectability, and improved acid and salt resistance. It embodies the characteristics of elastic sand carrying as the main fluid and viscous sand carrying as the auxiliary fluid. The sand carrying volume can reach 15%. The fracturing fluid has low friction resistance and has application prospects in large-scale volume fracturing in oil and gas reservoirs with extremely low permeability. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents, etc. used therein are all commercially available unless otherwise specified.

[0032] Example 1

[0033] (1) Betaine Gemini surfactant and preparation method

[0034] (1) Take 32.1g of octadecyl primary amine, add it to 100ml of ethanol and stir until completely dissolved, transfer it to a condenser reflux device, add 10.32g of methyl acrylate dropwise into a dropping funnel under stirring in a constant temperature water bath at 30°C, complete the addition within 20 minutes, then react at 70°C for 8 hours, cool to 50°C after the reaction is completed, and rotate to remove the solvent methanol and excess methyl acrylate to obtain a white solid intermediate product, N-octadecyl-β-aminopropionic acid methyl ester.

[0035] (2) Weigh 44.77g of the intermediate product and add it to a three-necked flask. Add 100mL of N,N-dimethylformamide as a solvent, then add 4 drops of triethylamine as an acid binder, and then add 8.75g of o-dibenzyl chloride. Stir in a water bath at 80℃ for 4 hours. After the reaction, wash with ice water and separate the liquid. Use a rotary evaporator to evaporate the solvent at 85℃. Saponify the remaining material with 25mL of a prepared 30% NaOH solution, then wash with 100ml of anhydrous ethanol and dry it. Subsequently, add a certain amount of dilute hydrochloric acid to neutralize the excess NaOH, stir and separate the layers, filter and wash the product with deionized water until it is neutral. Finally, dissolve the product in 50mL of acetone for recrystallization, and place the obtained product in a freeze dryer for drying to remove moisture to obtain the refined bis(sodium N-octadecyl-N-propionate) o-phenylenediamine intermediate.

[0036] (3) 18.32 g of bis(N-octadecyl-N-sodium propionate) o-phenylenediamine intermediate and 2.121 g of chloroform were added to 50 L of anhydrous ethanol dissolved with 2 g of sodium carbonate, and the mixture was refluxed at 90° C. for 48 hours. The inorganic salts were removed by filtration, and the solvent and unreacted chloroform were removed by rotary evaporation. The mixture was washed twice with 50 L of a mixed solution of acetone and anhydrous ethanol in a volume ratio of 19:1, and dried in a vacuum oven at 40° C. to obtain the target product, bis(N-octadecyl-N-sodium propionate-N-methyl) o-phenylenediamine dichloride betaine Gemini surfactant.

[0037] (2) The clean fracturing fluid and preparation method

[0038] (1) First, add formation water from a low-permeability or extra-low-permeability oil reservoir in a western oil field at room temperature. The total mineralization is 65315 mg / L (sodium ion 26141 mg / L, chloride ion 34355 mg / L, magnesium ion 3022 mg / L, calcium ion 450 mg / L, carbonate ion 1347 mg / L), and then add 2g of clay anti-swelling agent potassium chloride and dissolve it completely.

[0039] (2) Raise the temperature to 50°C and add 1g of dodecyltrimethylammonium chloride anti-swelling agent until it dissolves completely.

[0040] (3) Maintaining 50° C., 4 g of bis(N-octadecyl-N-propionate sodium-N-methyl)-o-phenylenedimethylammonium dichloride betaine Gemini surfactant was added to obtain a clean fracturing fluid.

[0041] (3) Clean fracturing fluid performance

[0042] The clean fracturing fluid prepared above was sheared for 2 hours at 82°C for 170 seconds, and its apparent viscosity was 62.2 mPa.s. The vibration frequency varied in the range of 1-100 rad / s. The elastic modulus of the clean fracturing fluid was ≥3.0 Pa, and the viscous modulus was ≥0.5 Pa, reflecting that the clean fracturing fluid is mainly elastic with a secondary viscosity. The particle size of the proppant quartz sand was 20-40 mesh, and the bulk density was 1.55-1.6 g / cm 3 , apparent density is 2.45g / cm 3 The fracturing fluid has a sphericity of 0.65-0.75, a settling velocity of 0.082 mm / s for fine sand particles in the fracturing fluid, a maximum sand carrying capacity of 15 wt%, a drag reduction rate of 83.7%, and a core damage rate of 3.56%. This indicates that the fracturing fluid is resistant to heat, salt, and shear, exhibits excellent elastic sand carrying and drag reduction, and exhibits minimal formation damage. These performance characteristics surpass those of the industry standard SY / T6376-2008. Other performance characteristics, such as thickening time, gel breaking time, gel breaking apparent viscosity, residue content, and anti-swelling rate, also meet the industry standard SY / T6376-2008.

[0043] Example 2

[0044] (1) Betaine Gemini surfactant and preparation method

[0045] (1) 37.7 g of dioctyl primary amine was added to 100 ml of ethanol and stirred to completely dissolve. The mixture was transferred to a condenser reflux apparatus, and 14.82 g of n-propyl acrylate was added dropwise to a dropping funnel under stirring in a constant temperature water bath at 30° C. The addition was completed within 15 minutes. The mixture was then reacted at 70° C. for 6 hours. After the reaction was completed, the mixture was cooled to 40° C. and the solvent methanol and excess methyl acrylate were removed by rotation to obtain a white solid intermediate product, N-docosyl-β-aminopropionic acid n-propyl ester.

[0046] (2) Weigh 53.245g of the intermediate product and add it to a three-necked flask. Add 100mL of N,N-dimethylformamide as a solvent, then add 5 drops of triethylamine as an acid binder, and then add 4.95g of 1,2-dichloroethane. React in a water bath at 60℃ with stirring for 5 hours. After the reaction, wash with ice water and separate the liquid. Use a rotary evaporator to evaporate the solvent at 80℃. Saponify the remaining material with 25mL of a prepared 30% NaOH solution, then wash with 100ml of anhydrous ethanol and dry it. Subsequently, add a certain amount of dilute hydrochloric acid to neutralize the excess NaOH, stir and separate the layers, filter and wash the product with deionized water until it is neutral. Finally, dissolve the product in 50mL of acetone for recrystallization, and place the obtained product in a freeze dryer for drying to remove moisture to obtain the refined bis(sodium N-docosyl-N-propionate)ethylenediamine intermediate.

[0047] (3) 19.0 g of the bis(N-docosyl-N-propionic acid sodium)ethylenediamine intermediate and 2.967 g of ethyl chloride were added to 50 L of anhydrous ethanol dissolved with 2.5 g of sodium carbonate, and the mixture was refluxed at 80° C. for 36 hours. The inorganic salts were removed by filtration, and the solvent and unreacted ethyl chloride were removed by rotary evaporation. The mixture was washed twice with 50 L of a mixed solution of acetone and anhydrous ethanol in a volume ratio of 18:1, and dried in a vacuum oven at 40° C. to obtain the target product, bis(N-docosyl-N-propionic acid sodium-N-ethyl)ethylenediamine chloride betaine Gemini surfactant.

[0048] (2) Clean fracturing fluid and preparation method

[0049] (1) At room temperature, first add formation water from an oil well in a tight oil reservoir in the western oil field, with a total mineralization of 86721 mg / L (sodium ion 35671 mg / L, chloride ion 44569 mg / L, magnesium ion 3522 mg / L, calcium ion 612 mg / L, carbonate ion 2347 mg / L), and then add 1.75g ​​of clay anti-swelling agent potassium chloride and dissolve it completely.

[0050] (2) Raise the temperature to 55°C and add 1.25g of tetradecyltrimethylammonium chloride anti-swelling agent until it dissolves completely.

[0051] (3) Maintaining 55° C., 4.5 g of bis(N-docosyl-N-propionate sodium-N-ethyl)ethylenediamine chloride betaine Gemini surfactant was added to obtain a clean fracturing fluid.

[0052] (3) Clean fracturing fluid performance

[0053] The prepared clean fracturing fluid was sheared for 2 hours at 121°C for 170 seconds, and its apparent viscosity was 53.6 mPa.s. The viscoelasticity test showed that the elastic modulus of the clean fracturing fluid was ≥2.5 Pa and the viscous modulus was ≥0.4 Pa at a vibration frequency rate range of 1-100 rad / s, reflecting the characteristics of the clean fracturing fluid with elasticity as the main property and viscosity as the auxiliary property. The particle size of the proppant quartz sand was 20-40 mesh, and the bulk density was 1.55-1.6 g / cm 3 , apparent density is 2.45g / cm 3 The sphericity is 0.65-0.75. The settling velocity of the sand particles in the fracturing fluid is 0.063 mm / s, the maximum sand carrying capacity can reach 12%, the drag reduction rate reaches 84.1%, and the core damage rate is 4.76%. This shows that the fracturing fluid is resistant to temperature, salt, and shear, has good elastic sand carrying and drag reduction effects, and has low formation damage. These properties exceed the industry standard SY / T6376-2008. Other properties such as thickening time, gel breaking time, gel breaking apparent viscosity, residue content, and anti-swelling rate meet the industry standard SY / T6376-2008.

[0054] Example 3

[0055] (1) Betaine Gemini surfactant and preparation method

[0056] (1) Take 40.5 g of tetracosyl primary amine, add it to 100 ml of ethanol and stir until completely dissolved, transfer it to a condenser reflux apparatus, add 14.08 g of n-butyl acrylate dropwise into a dropping funnel under stirring in a constant temperature water bath at 30°C, complete the addition within 25 minutes, then react at 60°C for 4 hours. After the reaction is completed, cool it to 45°C and rotate to remove the solvent methanol and excess methyl acrylate to obtain a white solid intermediate product, N-tetracosyl-β-aminopropionic acid n-butyl ester.

[0057] (2) Weigh 51.555g of the intermediate product and add it to a three-necked flask. Add 100mL of N,N-dimethylformamide as a solvent, add 6 drops of triethylamine as an acid binder, and then add 7.05g of 1,5-dichloropentane. Stir in a water bath at 70℃ for 5 hours. After the reaction, wash with ice water and separate the liquid. Use a rotary evaporator to evaporate the solvent at 90℃. Saponify the remaining material with 25mL of a prepared 30% NaOH solution, wash it with 100ml of anhydrous ethanol, and dry it. Subsequently, add a certain amount of dilute hydrochloric acid to neutralize the excess NaOH, stir and separate the layers, filter and wash the product with deionized water until it is neutral. Finally, dissolve the product in 50mL of acetone for recrystallization, and place the obtained product in a freeze dryer for drying to remove moisture to obtain the refined bis(sodium N-tetradecyl-N-propionate)pentanediamine intermediate.

[0058] (3) 19.56 g of the bis(N-tetracosyl-N-sodium propionate)pentanediamine intermediate and 27.09 g of ethyl chloride were added to 50 L of anhydrous ethanol dissolved with 2.5 g of sodium carbonate, and the mixture was refluxed at 85° C. for 24 hours. The inorganic salts were removed by filtration, and the solvent and unreacted ethyl chloride were removed by rotary evaporation. The mixture was washed twice with 50 L of a mixed solution of acetone and anhydrous ethanol in a volume ratio of 16:1, and dried in a vacuum oven at 40° C. to obtain the target product, bis(N-tetracosyl-N-sodium propionate-N-ethyl)pentanediamine chloride betaine Gemini surfactant.

[0059] (2) Clean fracturing fluid and preparation method

[0060] (1) First, add formation water from a shale oil well in a western oil field at room temperature. The total mineralization is 53947 mg / L (sodium ion 24034 mg / L, chloride ion 27856 mg / L, magnesium ion 927 mg / L, calcium ion 347 mg / L, carbonate ion 783 mg / L), and then add 1.5 g of clay anti-swelling agent potassium chloride and dissolve it completely.

[0061] (2) Raise the temperature to 60°C and add 1.5g of hexadecyltrimethylammonium chloride anti-swelling agent until it dissolves completely.

[0062] (3) Maintaining 60° C., 5 g of bis(N-tetracosyl-N-propionate sodium-N-ethyl)pentanediammonium chloride betaine Gemini surfactant was added to obtain a clean fracturing fluid.

[0063] (3) Clean fracturing fluid performance

[0064] The prepared clean fracturing fluid was sheared for 2 hours at 215°C for 170 seconds, and its apparent viscosity was 38.2 mPa.s. The viscoelasticity test showed that the elastic modulus of the clean fracturing fluid was ≥2.2 Pa and the viscous modulus was ≥0.4 Pa at a vibration frequency rate range of 1-100 rad / s, reflecting the characteristics of the clean fracturing fluid with elasticity as the main property and viscosity as the secondary property. The particle size of the proppant quartz sand was 20-40 mesh, and the bulk density was 1.55-1.6 g / cm 3 , apparent density is 2.45g / cm 3 The sphericity is 0.65-0.75. The sand particles have a settling velocity of 0.043 mm / s in the fracturing fluid, and the maximum sand carrying capacity can reach 10%. The drag reduction rate of this clean fracturing fluid reaches 87.2%, and the core damage rate is 3.95%. This fracturing fluid is resistant to temperature, salt, and shear, and has excellent elastic sand carrying and drag reduction effects, while causing minimal formation damage. These properties exceed the industry standard SY / T6376-2008. Other properties, such as thickening time, gel breaking time, gel breaking apparent viscosity, residue content, and anti-swelling rate, also meet the industry standard SY / T6376-2008.

[0065] The above description does not limit the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with this profession can use the technical content disclosed above to make some changes or modifications to equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a betaine Gemini surfactant, characterized in that: The following steps are involved: Step S1: Add a long-chain R alkyl primary amine to ethanol and stir to completely dissolve it. Transfer it to a condensing reflux apparatus, add acrylate dropwise into a dropping funnel under stirring in a constant temperature water bath at 30°C. The addition is completed over 15 to 30 minutes. Then, react at 60 to 80°C for 4 to 8 hours. After the reaction, cool to 40 to 50°C and rotate to remove the solvent methanol and excess methyl acrylate to obtain a white solid intermediate product R alkylamine propionate. The reaction equation is as follows: (R=C 18 H 37 、C 20 H 41 、C 22 H 45 、C 24 H 49 ;R’=CH3、C2H5、C3H7、C4H8) Step S2: Add R alkylamine propionate to a three-necked flask, add N,N-dimethylformamide as a solvent, add a few drops of dimethylamine as an acid binder, and then add dichlorohydrocarbon. React for 4 to 6 hours under stirring in a water bath at 40-60°C. After the reaction, wash with ice water and separate the liquids. Use a rotary evaporator to evaporate the solvent under reduced pressure at 80-90°C. Saponify the remaining material with a prepared 30% mass fraction NaOH solution, then wash with anhydrous ethanol and dry it. Subsequently, add a certain amount of dilute hydrochloric acid and stir to separate the layers. After suction filtration, wash the product with deionized water until neutral. Finally, dissolve the product in acetone for recrystallization, and place the obtained product in a freeze dryer for drying to remove moisture to obtain a carboxylate Gemini-type tertiary amine compound bis(NR alkyl-N-sodium propionate)R1 alkyldiamine; the reaction equation is as follows: (R1=CH2、C2H4、C3H6、C4H8、C5H 10 、C6H 12 、 R=C 18 H 37 、C 20 H 41 、C 22 H 45 、C 24 H 49 ) Step S3: Add the bis(NR alkyl-N-sodium propionate) R1 alkyl diamine intermediate and alkyl halide to anhydrous ethanol dissolved in sodium carbonate, reflux at 80-90° C. for 24-48 hours, filter to remove inorganic salts, and then remove the solvent and unreacted alkyl halide using a rotary evaporator; wash twice with a mixed solution of acetone and anhydrous ethanol in a volume ratio of 16-19:1, and dry in a vacuum oven at 30-40° C. to obtain the target product, bis(NR alkyl-N-sodium propionate-NR” alkyl) R1 alkyl ammonium dihalide betaine Gemini surfactant; the reaction equation is shown below: (R1=CH2、C2H4、C3H6、C4H8、C5H 10 、C6H 12 、 R=C 18 H 37 、C 20 H 41 、C 22 H 45 、C 24 H 49 ;R”=CH3、C2H5;X=Cl、Br)。 2. The method for preparing a betaine Gemini surfactant according to claim 1, wherein: The number of carbon atoms in the alkyl group of the long-chain alkyl tertiary amine in step S1 is any one of 18, 20, 22 or 24; the acrylate in step S1 is any one of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate or isobutyl acrylate.

3. The preparation method of the betaine Gemini surfactant according to claim 1, wherein: The molar ratio of the long-chain alkyl tertiary amine to the methyl acrylate in step S1 is 1:1.1-1.

3.

4. The method for preparing the betaine Gemini surfactant according to claim 1, wherein: The dichlorohydrocarbon in step S2 is any one of dichloromethane, dichloroethane, dichloropropane, dichlorobutane, dichloropentane, dichlorohexane, dichloropentane, o-dichlorobenzyl, m-dichlorobenzyl or p-dichlorobenzyl.

5. The method for preparing the betaine Gemini surfactant according to claim 1, wherein: The molar ratio of the alkylamine propionate to the dichlorohydrocarbon in step S2 is 2.1-2.3:

1.

6. The method for preparing the betaine Gemini surfactant according to claim 1, wherein: The halogenated hydrocarbon in step S3 is any one of methyl chloride, ethyl chloride, methyl bromide or ethyl bromide.

7. The method for preparing the betaine Gemini surfactant according to claim 1, wherein: The molar ratio of the bis(NR alkyl-N-sodium propionate) R1 alkyl diamine to the halogenated hydrocarbon in step S3 is 1:2.1-2.

3.

8. A betaine Gemini surfactant, characterized in that Prepared by the method according to any one of claims 1 to 7.

9. The clean fracturing fluid prepared from the betaine Gemini surfactant according to claim 8, characterized in that: The fracturing fluid comprises the following components (by mass fraction): 3-5% of a bis(NR-alkyl-sodium-N-propionate-NR"-alkyl)R1-alkyl ammonium dihalide betaine Gemini surfactant; 1-3% of a clay anti-swelling agent; and the balance is formation water with a salinity of 50,000-100,000 mg / L. The clay anti-swelling agent is composed of potassium chloride and a cationic surfactant selected from the group consisting of dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, or hexadecyltrimethylammonium chloride, and the mass ratio of potassium chloride to the cationic surfactant is 1.0-2.0:

1.

10. The method for preparing the clean fracturing fluid according to claim 9, characterized in that: The method comprises the following steps: firstly adding formation water at room temperature, then adding potassium chloride as a clay anti-swelling agent, and after the clay anti-swelling agent is completely dissolved, heating to 40-60° C., then adding a cationic surfactant anti-swelling agent selected from dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride or hexadecyltrimethylammonium chloride, and after the cationic surfactant is completely dissolved, adding bis(NR alkyl-N-sodium propionate-NR” alkyl) R1 alkyl ammonium dihalide betaine Gemini surfactant, and finally obtaining a clean fracturing fluid.

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