Polyether amphoteric viscoelastic surfactant, preparation method and weighted fracturing fluid

Abstract

The application discloses a polyether amphoteric viscoelastic surfactant, a preparation method and a weighted fracturing fluid. The weighted fracturing fluid comprises the following components in percentage by mass: 6-8% of the polyether amphoteric viscoelastic surfactant, 55-70% of calcium chloride, 1-3% of a dispersing agent and 1-2% of a compound surfactant, and the balance is water. The application provides a high-density weighted clean fracturing fluid system with a temperature resistance up to 180 DEG C. The system uses cheap calcium chloride as a weighting agent, can realize efficient weighting with a density of 1.43 g / cm3, and significantly improves the temperature resistance, shear resistance, and static sand suspension capacity while maintaining the low friction and low damage advantages of the clean fracturing fluid, thereby providing a novel and feasible solution for fracturing construction of an ultra-deep well high-temperature and high-pressure reservoir.

Description

Technical Field

[0001] This invention belongs to the technical field of fracturing fluid systems for ultra-deep well high-temperature and high-pressure reservoir stimulation, and particularly relates to a polyether amphoteric viscoelastic surfactant, its preparation method, and a weighted fracturing fluid. Background Technology

[0002] Ultra-deep wells and high-temperature, high-pressure reservoirs typically exhibit characteristics such as dense reservoirs, strong tectonic stress, and high pore pressure. This often leads to abnormally high surface pressure during fracturing operations, potentially exceeding the equipment's bearing capacity and seriously threatening operational safety and continuity. Using weighted fracturing fluid to reduce wellhead operating pressure has become a key technical approach to address this challenge.

[0003] Scholars both domestically and internationally have conducted numerous explorations in this area. For example, barium bromide was used as a weighting agent in deep-sea oilfields in the Gulf of Mexico, increasing the density of fracturing fluid to 1.38 g / cm³ and successfully applying it to multiple wells. The weighting system developed by K. Bartko et al. significantly reduced the required operating pressure from 138 MPa to 103 MPa, but this system still suffers from high friction and significant reservoir damage. In China, commonly used weighted fracturing fluid systems still face a series of key technical bottlenecks when dealing with ultra-deep, high-temperature, and high-pressure fracturing. On the one hand, commonly used weighting agents such as sodium chloride and potassium chloride have limited densities (approximately 1.1~1.2 g / cm³), while bromides and nitrates are expensive or pose corrosion and safety risks. Formates, although used to some extent, easily interfere with cross-linking and corrode the tubing. In contrast, calcium chloride has advantages such as wide availability, low cost, and high solubility; its saturated brine density can reach 1.39 g / cm³ at room temperature, making it an ideal choice for achieving high-density weighting. On the other hand, existing fracturing fluid systems have significant drawbacks: guar gum-based fracturing fluids have high residue content, which further exacerbates reservoir damage after weighting. For example, CN102676148A provides a high-density, low-friction fracturing fluid with high guar gum and temperature stabilizer content, making it difficult to break the gel and increasing the difficulty of flowback. While synthetic polymer fracturing fluids offer low friction, low residue, and good temperature resistance, their thickeners (such as polyacrylamide) are sensitive to salt, and their viscosity tends to drop sharply in high-salinity environments, leading to uneven mixing and unstable performance. Furthermore, both systems rely on multiple additives such as crosslinking agents and breaker agents, resulting in complex processes and high costs. For instance, CN114790386A developed a high-temperature resistant calcium chloride-weighted polymer fracturing fluid, which improves temperature resistance while using calcium chloride for weighting, but still requires multiple additives for synergistic effects, making the process more complicated. VES-type clean fracturing fluids offer the potential to overcome the aforementioned drawbacks due to their advantages such as residue-free operation, low friction, self-breaking properties, and simple formulation. However, their micelle structure is prone to dissociation at high temperatures, and high salt concentrations can disrupt the equilibrium environment for micelle formation, limiting their application under high-temperature and high-density conditions. Specifically, CN109536155A indicates that surfactants at higher salinity levels are highly susceptible to phase separation, causing the solution system to lose viscosity and thus failing to achieve functions such as sand carrying and fracture creation.

[0004] In summary, existing weighted fracturing fluid systems cannot simultaneously meet multiple requirements such as high-density weighting, high-temperature resistance, low damage, and simple construction. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the primary objective of this invention is to provide a polyether amphoteric viscoelastic surfactant, its preparation method, and a weighting fracturing fluid. The weighting fracturing fluid of this invention is simple and convenient to prepare, possesses advantages such as excellent static sand-suspending capacity, good solubility, strong temperature and shear resistance, and low friction, making it suitable for fracturing stimulation of ultra-deep wells, high-temperature, and high-pressure reservoirs.

[0006] The objective of this invention is achieved through the following technical solution: A polyether amphoteric viscoelastic surfactant is prepared from raw materials in one of the following combinations by mass percentage: Combination 1: 4%~15% erucic acid, 1%~6% amination reagent, 2%~10% ethylene oxide, 2%~10% quaternization reagent, 0.03%~0.2% first catalyst, 0.2%~0.4% second catalyst, 0.02%~15% pH adjuster, 0%~8% dehydrating agent, 18.9%~30% first solvent, 24.3%~43.2% second solvent, 0%~1% reducing agent, 0%~6% oxidizing agent, and 0%~0.1% antioxidant; Combination 2: 4%~15% methyl erucic acid, 1%~6% amination reagent, 2%~10% ethylene oxide, 2%~10% quaternary amination reagent, 0%~0.14% third catalyst, 0.02%~0.15% fourth catalyst, 0.05%~0.20% fifth catalyst, 0.02%~15% pH adjuster, 0%~8% dehydrating agent, 18%~20.7% third solvent, 16.3%~22.7% fourth solvent, 14.8%~15.8% fifth solvent, 10.8%~21.9% sixth solvent, 0%~1% reducing agent, 0%~6% oxidizing agent, and 0%~0.1% antioxidant.

[0007] Preferably, the amination agent is at least one selected from N,N-dimethylpropanediamine and dimethylamine.

[0008] Preferably, the quaternizing agent is at least one selected from sodium 3-chloro-2-hydroxypropanesulfonate, sodium 2-chloroethylsulfonate, and sodium chlorosulfonate.

[0009] Preferably, the first catalyst is one of sodium methoxide and cesium hydroxide.

[0010] Preferably, the second catalyst is one of methanesulfonic acid and p-toluenesulfonic acid.

[0011] Preferably, the third catalyst is nickel chloride.

[0012] Preferably, the fourth catalyst is sodium methoxide.

[0013] Preferably, the fifth catalyst is one of methanesulfonic acid and p-toluenesulfonic acid.

[0014] Preferably, the pH adjuster is at least one selected from sodium hydroxide solution, potassium hydroxide solution, sodium bicarbonate solution, dilute sulfuric acid, and dilute hydrochloric acid.

[0015] Preferably, the dehydrating agent is at least one of dicyclohexylcarbodiimide and N,N'-diisopropylcarbodiimide.

[0016] Preferably, the first solvent is one of xylene and dimethylformamide (DMF).

[0017] Preferably, the second solvent is one of ethanol and isopropanol.

[0018] Preferably, the third solvent is tetrahydrofuran.

[0019] Preferably, the fourth solvent is an aqueous solution of acetone.

[0020] Preferably, the fifth solvent is one of dimethylformamide and xylene.

[0021] Preferably, the sixth solvent is one of an aqueous ethanol solution and ethanol.

[0022] Preferably, the reducing agent is at least one of sodium borohydride and potassium borohydride.

[0023] Preferably, the oxidant is at least one of potassium permanganate and pyridine chlorochromate.

[0024] Preferably, the antioxidant is at least one of TBHQ and vitamin E.

[0025] The preparation method of the above-mentioned polyether amphoteric viscoelastic surfactant, for combination one, includes the following steps: S1. Weigh erucic acid according to the stated mass percentage, add the first catalyst, heat to 100~130℃ under a protective atmosphere, and vacuum under stirring to remove water and low-boiling-point impurities from the reaction system; then continue heating to 120~160℃, control the system pressure at 0.2~0.6MPa, add ethylene oxide and maintain the aforementioned temperature and pressure conditions for the reaction; after the reaction is complete, cool down and remove unreacted ethylene oxide to obtain ethoxylated erucic acid; S2. The ethoxylated erucic acid is mixed evenly with the amination reagent, the second catalyst, and the first solvent. If the component contains a dehydrating agent, the temperature is first lowered to 0-5°C, the dehydrating agent is added, and the mixture is kept warm and stirred. Then the temperature is raised to 110-160°C for reaction. When the acid value of the reaction solution is ≤5mgKOH / g, the precipitate is filtered, and excess solvent and amination reagent are removed to obtain ethoxylated erucic acid amide tertiary amine. If the component does not contain a dehydrating agent, after the reaction at 110-160°C, water is separated and impurities are removed using a water separator. When the acid value of the reaction solution is ≤5mgKOH / g, the solvent and excess amination reagent are removed to obtain ethoxylated erucic acid amide tertiary amine. S3. The ethoxylated erucamide tertiary amine is mixed evenly with the second solvent and heated to 60-70°C with stirring to dissolve. Then, a quaternizing agent and a pH adjuster are added. If the component does not contain an antioxidant, the reaction is carried out at 70-90°C for 4-8 hours. After the reaction is complete, part of the second solvent is removed, the mixture is cooled to crystallize, filtered, and dried to obtain the solid polyether amphoteric viscoelastic surfactant. If the component contains an antioxidant, the antioxidant is added and the reaction is carried out at 70-90°C for 4-8 hours. When the tertiary amine conversion rate is ≥98%, the solution of the polyether amphoteric viscoelastic surfactant is obtained. Part of the second solvent is recovered under reduced pressure, and the mixture is cooled to crystallize, filtered, and dried to obtain the solid polyether amphoteric viscoelastic surfactant. For combination two, the following steps are included: S1. Weigh methyl erucic acid according to the mass percentage, add the third solvent, the third catalyst and the reducing agent, and carry out the reduction reaction at 25~40℃ for 2~4h. After the reaction is completed, add pH adjuster to neutralize or hydrolyze, separate the liquid and purify by distillation to obtain the corresponding alcohol. S2. Add a fourth catalyst to the alcohol obtained in S1, heat to 100-130°C under a protective atmosphere, and remove water and low-boiling-point impurities from the reaction system under stirring and vacuum conditions. Then continue to heat to 120-160°C, control the system pressure at 0.2-0.6 MPa, add ethylene oxide, and carry out the reaction under the aforementioned temperature and pressure conditions. After the reaction is complete, cool down and remove unreacted ethylene oxide to obtain ethoxylated mustard alcohol. S3. Dissolve ethoxylated mustard in a fourth solvent, add a pH adjuster and an oxidant, and carry out an oxidation reaction at 30~50℃ for 4~6 hours. Filter and remove the solvent to finally obtain ethoxylated erucic acid. S4. Mix the ethoxylated erucic acid with the amination reagent, the fifth catalyst, and the fifth solvent evenly. If the component contains a dehydrating agent, first cool to 0-5°C, add the dehydrating agent, and keep it warm while stirring. Then, raise the temperature to 110-160°C to react. When the acid value of the reaction solution is ≤5mgKOH / g, first filter to remove the generated solid precipitate, and then remove the solvent and excess amination reagent to obtain ethoxylated erucic acid amide tertiary amine. If the component does not contain a dehydrating agent, stir and raise the temperature to 110-160°C to react. During this process, use a water separator to separate water and remove impurities. When the acid value of the reaction solution is ≤5mgKOH / g, remove the solvent and excess amination reagent to obtain ethoxylated erucic acid amide tertiary amine. S5. Mix the ethoxylated erucamide tertiary amine with the sixth solvent evenly, and heat to 60~70℃ while stirring to dissolve. If the component contains an antioxidant, add the antioxidant and quaternizing agent, adjust the pH of the system to 7~8, and react at 70~90℃ for 4~8 hours to obtain the solution of the polyether amphoteric viscoelastic surfactant. If the component does not contain an antioxidant, add the quaternizing agent, adjust the pH of the system to 7~8, and react at 70~90℃ for 4~8 hours. When the tertiary amine conversion rate is ≥98%, the solution of the polyether amphoteric viscoelastic surfactant is obtained.

[0026] Preferably, for combination two, the solution of the polyether amphoteric viscoelastic surfactant in step S5 is further subjected to partial solvent removal, cooling crystallization, filtration, and drying to obtain the solid polyether amphoteric viscoelastic surfactant.

[0027] Preferably, for combination one, the protective atmosphere in step S1 is nitrogen.

[0028] Preferably, for combination two, the protective atmosphere in step S2 is nitrogen.

[0029] A weighted fracturing fluid comprises the following components in weight percentages: 6% to 8% of the above-mentioned polyether amphoteric viscoelastic surfactant, 55% to 70% of calcium chloride, 1% to 3% of dispersant and 1% to 2% of compound surfactant, with the balance being water.

[0030] Preferably, the weighted fracturing fluid comprises the following components by mass percentage: 8% of the polyether amphoteric viscoelastic surfactant, 55%~70% of calcium chloride, 1% of dispersant and 1% of compound surfactant, with the balance being water.

[0031] Preferably, the dispersant is at least one of isopropanol and ethanol.

[0032] Preferably, the compound surfactant is at least one of octyldecyl glucoside and fatty alcohol polyoxyethylene ether (AEO-20).

[0033] Preferably, the water is at least one of deionized water and formation water.

[0034] Compared with the prior art, the beneficial effects of the present invention include: (1) This invention provides a polyether amphoteric viscoelastic surfactant, which, when used as a thickener, significantly improves the salt resistance and solubility stability of clean fracturing fluid, enabling it to form a homogeneous system in high-salinity brine, and successfully endows the clean fracturing fluid with the ability to "weight up," achieving a density of 1.43 g / cm³. 3 This technology achieves the same or even higher liquid column pressure at extremely low cost, breaking down the technical barriers to applying clean fracturing fluids to deep high-pressure reservoirs.

[0035] (2) The fracturing fluid system prepared by this invention exhibits excellent temperature and shear rheological properties, and can withstand temperatures of 180℃ and 170s. -1 After shearing for 150 minutes under the specified conditions, the viscosity of the system remained at 130 mPa·s. Moreover, it maintained static sand suspension for a long time in a water bath at 50℃, demonstrating excellent and long-lasting sand suspension capacity and structural stability. In addition, in the field construction friction test, its resistance reduction rate remained above 75%, successfully reducing the pipeline friction to about 45 MPa, demonstrating excellent resistance reduction effect.

[0036] (3) The fracturing fluid system prepared by this invention has low raw material cost and simple preparation process. The thickener is prepared by renewable fatty acids and their derivatives and conventional chemical raw materials, and the weighting agent is inexpensive calcium chloride, which is significantly cheaper than traditional systems such as bromide salts. The preparation of clean fracturing fluid only requires dissolving the weighting salt, dispersant, thickener and compound surfactant in water in their respective proportions and stirring. No crosslinking agent, breaker and other additives are required. The process is simple and easy to implement. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the synthesis method of the polyether amphoteric viscoelastic surfactant structure prepared in Example 1.

[0038] Figure 2 The weighted cleaning fracturing fluid prepared for Example 1 was subjected to fracturing at 120°C and 170s. -1 Temperature and shear resistance test curves under the specified conditions.

[0039] Figure 3 The weighted cleaning fracturing fluid prepared for Example 2 was subjected to fracturing at 180°C and for 170 seconds. -1 Temperature and shear resistance test curves under the specified conditions.

[0040] Figure 4 For Example 3, a weighted cleaning fracturing fluid was prepared at 180°C and 170s. -1 Temperature and shear resistance test curves under the specified conditions.

[0041] Figure 5 The weighted cleaning fracturing fluid prepared for Example 4 was subjected to fracturing at 180°C and 170s. -1 Temperature and shear resistance test curves under the specified conditions.

[0042] Figure 6 The figure shows the solubility of the weighted fracturing fluid prepared in Comparative Example 1 in 70% calcium chloride high-salt water (unmodified system).

[0043] Figure 7 The image shows the solubility of the weighted cleaning fracturing fluid prepared in Example 4 in 70% calcium chloride high-salt water (ethoxylated modified system).

[0044] Figure 8 The image shows the sand suspension effect of the weighted cleaning fracturing fluid prepared in Example 4. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0046] To better illustrate the technical solution of the present invention, the following detailed description is provided in conjunction with specific embodiments. Specifically, Examples 1 and 2 employ the preparation method of Combination One described above (using erucic acid as the starting material); Examples 3 and 4 employ the preparation method of Combination Two described above (using methyl erucate as the starting material).

[0047] Example 1 A polyether amphoteric viscoelastic surfactant comprises the following components in weight percentage: 10.68% erucic acid, 4.50% amination agent (N,N-dimethylpropylenediamine), 8.33% ethylene oxide, 6.48% quaternization agent (sodium 3-chloro-2-hydroxypropanesulfonate), 0.03% first catalyst (sodium methoxide), 0.28% second catalyst (methanesulfonic acid), 7.58% pH adjuster (20% potassium hydroxide solution), 0% dehydrating agent, 18.94% first solvent (xylene), 43.18% second solvent (ethanol), 0% reducing agent, 0% oxidizing agent, and 0% antioxidant.

[0048] The preparation method of the polyether amphoteric viscoelastic surfactant is as follows: S1. Add 282g of erucic acid and 0.846g of sodium methoxide to a 5L high-pressure reactor. After sealing, purge with nitrogen four times. Heat to 105℃ and dehydrate under vacuum for 45min. Heat to 140℃, control the pressure inside the reactor at 0.4MPa, and slowly introduce 220g of ethylene oxide over 3h. Maintain the reaction temperature for 4h until the pressure stabilizes. Cool to 65℃ and remove unreacted ethylene oxide under vacuum to obtain 495g of ethoxylated erucic acid. S2. Add 495g of ethoxylated erucic acid, 118.8g of N,N-dimethylpropanediamine, 7.4g of methanesulfonic acid, and 500g of xylene to a 2L four-necked flask; reflux at 150℃ for 5 hours, collect 17.8g of water using a water separator, and determine the acid value to be 3.8mg KOH / g; recover xylene by distillation, remove excess amine under reduced pressure, and obtain 570g of tertiary amine; S3. Add 570g of tertiary amine and 1140g of ethanol to a 1L three-necked flask, heat to 70℃ and stir to dissolve; add 171.1g of sodium 3-chloro-2-hydroxypropanesulfonate, add 200g of 20% potassium hydroxide solution dropwise to adjust the pH to 7.5, control the system temperature at 80~85℃, keep the reaction at this temperature for 5h, after the reaction is complete, remove some of the ethanol by vacuum distillation, cool to crystallize, filter and dry to obtain 680g of polyether amphoteric viscoelastic surfactant (thickening agent).

[0049] A weighted fracturing fluid comprises the following components in weight percentages: 8% of the polyether amphoteric viscoelastic surfactant, 55% calcium chloride, 1% isopropanol and 1% octyldecyl glucoside, with the balance being water.

[0050] The density of the weighted fracturing fluid was tested to be 1.26 g / cm³. 3 Rheological testing, such as Figure 2 As shown, from Figure 2 We can see that: at 120℃ and 170s -1 After shearing for 120 minutes under the specified conditions, the viscosity of the system remained at around 480 mPa·s, which is far greater than the minimum viscosity requirement of 25 mPa·s for clean fracturing fluid.

[0051] Example 2 A polyether amphoteric viscoelastic surfactant comprises the following components in weight percentages: 11.25% erucic acid, 4.50% amination agent (N,N-dimethylpropylenediamine), 5.62% ethylene oxide, 5.81% quaternization agent (sodium 2-chloroethylsulfonate), 0.03% first catalyst (cesium hydroxide), 0.37% second catalyst (p-toluenesulfonic acid), 10.50% pH adjuster (15% sodium hydroxide solution), 7.50% dehydrating agent (DCC), 29.99% first solvent (DMF), 24.37% second solvent (isopropanol), 0% reducing agent, 0% oxidizing agent, and 0.06% antioxidant (TBHQ).

[0052] The preparation method of the polyether amphoteric viscoelastic surfactant is as follows: S1. Add 300g of erucic acid and 0.8g of cesium hydroxide to a 5L high-pressure reactor, seal, and purge with nitrogen four times. Heat to 105℃ and evacuate for 40 minutes to remove moisture; heat to 135℃, control the pressure inside the reactor at 0.35MPa, and slowly introduce 150g of ethylene oxide (introducing time 2.5 hours), maintaining the reaction temperature for 3.5 hours until the pressure stabilizes. Cool to 75℃ and evacuate to remove unreacted ethylene oxide, yielding 450g of ethoxylated erucic acid. S2. Add 450g of ethoxylated erucic acid, 120g of N,N-dimethylpropanediamine, 800g of dimethylformamide, and 10g of p-toluenesulfonic acid to a 2L four-necked flask. After stirring evenly, cool to 0-5℃, slowly add 200g of DCC, maintain the temperature and stir for 1 hour, then raise the temperature to 110℃ and react for 5 hours. The acid value of the reaction solution is 4.2mgKOH / g. Filter to remove the generated dicyclohexylurea precipitate, and remove DMF and excess amine by vacuum distillation to obtain 520g of ethoxylated erucic acid amide propyl dimethyl tertiary amine.

[0053] S3. Add 520g of tertiary amine, 650g of isopropanol and 1.5g of TBHQ to a 1L three-necked flask. Heat to 70℃ and stir to dissolve. Slowly add 155g of sodium 2-chloroethylsulfonate and add 280g of 15% sodium hydroxide solution dropwise to maintain pH=7.5-8.0. Control the system temperature to not exceed 90℃. After the addition is complete, heat to 85℃ and keep the reaction at this temperature for 7 hours. The conversion rate of tertiary amine is 99.2%. Recover part of the isopropanol by vacuum distillation. Cool to crystallize, filter and dry to obtain 620g of polyether amphoteric viscoelastic surfactant.

[0054] A weighted fracturing fluid comprises the following components in weight percentages: 8% of the polyether amphoteric viscoelastic surfactant, 60% calcium chloride, 1% isopropanol and 1% octyldecyl glucoside, with the balance being water.

[0055] The density of the weighted fracturing fluid was tested to be 1.32 g / cm³. 3 Rheological testing, such as Figure 3 As shown, from Figure 3 We can see that: at 180℃ and 170s -1 After shearing for 150 minutes under the specified conditions, the viscosity of the system remained at around 140 mPa·s, which is far greater than the minimum viscosity requirement of 25 mPa·s for clean fracturing fluid.

[0056] Example 3 A polyether amphoteric viscoelastic surfactant comprises the following components in weight percentages: 6.12% methyl erucic acid, 2.37% amination agent (N,N-dimethylpropylenediamine), 3.45% ethylene oxide, 3.65% quaternizing agent (sodium 3-chloro-2-hydroxypropanesulfonate), 0.04% fourth catalyst (sodium methoxide), 0.20% fifth catalyst (p-toluenesulfonic acid), 3.16% pH adjuster (dilute hydrochloric acid, dilute sulfuric acid), 3.95% dehydrating agent (DCC), 20.72% third solvent (tetrahydrofuran), 22.69% fourth solvent (aqueous acetone), 15.79% fifth solvent (DMF), 12.14% sixth solvent (aqueous ethanol), 0.39% reducing agent (sodium borohydride), 5.29% oxidizing agent (potassium permanganate solution), and 0.06% antioxidant (TBHQ).

[0057] The preparation method of the polyether amphoteric viscoelastic surfactant is as follows: S1. Add 310g of methyl erucic acid and 1050g of tetrahydrofuran to a three-necked flask. Add 20g of sodium borohydride in batches while stirring. React at 25-40℃ for 2-4 hours. Add 100g of 10% dilute hydrochloric acid to hydrolyze the excess sodium borohydride. Separate the organic phase and distill to recover the solvent, yielding 285g of mustard alcohol.

[0058] S2. Add mustard and 2g sodium methoxide to the autoclave and purge with nitrogen three times. Dehydrate under vacuum at 110-130℃ for 30 minutes, raise the temperature to 130-160℃, control the pressure at 0.3-0.6MPa, and introduce 175g of EO (added over 2-4 hours). Maintain the reaction temperature for 3-5 hours until the pressure stabilizes. Remove unreacted EO to obtain 461g of ethoxylated mustard.

[0059] S3. Add ethoxylated mustard alcohol, 1150g of solvent (acetone:water = 1:1) and 60g of 10% dilute sulfuric acid to a four-necked flask. Add 268g of 10% potassium permanganate solution dropwise while stirring. React at 30-50℃ for 4-6 hours. Filter to remove catalyst / residue, and distill to recover the solvent to obtain 440g of ethoxylated erucic acid.

[0060] S4. Add ethoxylated erucic acid, 120g of N,N-dimethylpropanediamine, 800g of dimethylformamide, and 10g of p-toluenesulfonic acid to a 2L four-necked flask. After stirring evenly, cool to 0-5℃, slowly add 200g of DCC, maintain the temperature and stir for 1 hour, then raise the temperature to 110℃ and react for 5 hours. The acid value of the reaction solution is 4.5mg KOH / g. Filter to remove the generated dicyclohexylurea precipitate, and remove DMF and excess amine by vacuum distillation to obtain 520g of ethoxylated erucic acid amide propyl dimethyl tertiary amine.

[0061] S5. Add tertiary amine and 615g of mixed solvent (ethanol-water = 1:1) to a 2L three-necked flask, heat to 65℃ and stir to dissolve. Add 3g of TBHQ and mix well. Slowly add 185g of sodium 3-chloro-2-hydroxypropanesulfonate, and add 600g of potassium hydroxide solution dropwise to maintain pH = 7-8, controlling the temperature at 80-85℃. Maintain the reaction temperature for 6 hours to obtain a target product solution with a solid content of 45%.

[0062] A weighted fracturing fluid comprises the following components in weight percentages: 8% of the polyether amphoteric viscoelastic surfactant, 65% calcium chloride, 1% isopropanol and 1% fatty alcohol polyoxyethylene ether (AEO-20), with the balance being water.

[0063] The density of the weighted fracturing fluid was tested to be 1.38 g / cm³. 3 Rheological testing, such as Figure 4 As shown, from Figure 4 We can see that: at 180℃ and 170s -1 After shearing for 150 minutes under the specified conditions, the viscosity of the system remained at around 130 mPa·s, which is far greater than the minimum viscosity requirement of 25 mPa·s for clean fracturing fluid.

[0064] Example 4 A polyether amphoteric viscoelastic surfactant comprises the following components in weight percentage: 6.61% methyl erucic acid, 2.17% amination agent (N,N-dimethylpropylenediamine), 3.55% ethylene oxide, 3.45% quaternary amination agent (sodium 3-chloro-2-hydroxypropanesulfonate), 0.13% third catalyst (nickel chloride), 0.02% fourth catalyst (sodium methoxide), 0.15% fifth catalyst (methanesulfonic acid), 3.20% pH adjuster (dilute hydrochloric acid), 0% dehydrating agent, 19.82% third solvent (tetrahydrofuran), 19.18% fourth solvent (aqueous acetone), 14.81% fifth solvent (xylene), 21.61% sixth solvent (ethanol), 0.39% reducing agent (sodium borohydride), 4.90% oxidizing agent (potassium permanganate solution), and 0% antioxidant.

[0065] The preparation method of the polyether amphoteric viscoelastic surfactant is as follows: S1. Add 310g of methyl erucic acid and 930g of tetrahydrofuran to a 1L flask, and add 18.5g of sodium borohydride and 6.2g of nickel chloride while stirring. React at 30℃ for 3 hours. Add 100g of 10% dilute hydrochloric acid to neutralize to pH=7, separate the organic phase, and distill to obtain 285g of mustard alcohol.

[0066] Add 285g of mustard alcohol and 0.86g of sodium methoxide to a 5L high-pressure reactor, purge with nitrogen three times; dehydrate at 120℃ for 30 minutes, raise the temperature to 140℃, and introduce 166.5g of ethylene oxide at 0.4MPa over 2.5 hours. Maintain the reaction temperature for 4 hours to obtain 450g of ethoxylated mustard alcohol.

[0067] Add 450g of ethoxylated mustard, 900g of acetone-water (1:1), and 50g of 10% dilute hydrochloric acid to a 2L flask to adjust the pH to 2.5. Add 230g of 10% potassium permanganate solution dropwise while stirring. React at 40℃ for 5 hours. Filter and distill to obtain 440g of ethoxylated erucic acid.

[0068] S4. Add 440g of the above-mentioned ethoxylated erucic acid and 102g of N,N-dimethylpropanediamine to a 2L four-necked flask, further add 6.9g of methanesulfonic acid as a catalyst and 695g of xylene as a reaction solvent; after stirring evenly, heat to 150℃ and reflux for 5 hours, during which water is separated and impurities are removed using a water separator, and the acid value is measured to be 3.8mg KOH / g; first, distill to recover the xylene solvent, then remove excess amination reagent under reduced pressure, and after cooling, 505g of ethoxylated erucic acid amantadine dimethyl tertiary amine is obtained.

[0069] S5. Add 505g of the above-mentioned tertiary amine and 1014g of ethanol as reaction solvent to a 2L three-necked flask, heat to 65℃ and stir to completely dissolve it; then add 162g of sodium 3-chloro-2-hydroxypropanesulfonate to the system, and add 178g of 10% sodium hydroxide solution dropwise under stirring to maintain the pH value of the system between 7.5 and 8.0; control the system temperature at 80-85℃ and keep the reaction at that temperature for 6 hours; the conversion rate of the tertiary amine is detected to be 98.9%, that is, the target product aqueous solution of the polyether amphoteric viscoelastic surfactant is obtained.

[0070] A weighted fracturing fluid comprises the following components in weight percentages: 8% of the polyether amphoteric viscoelastic surfactant, 70% calcium chloride, 1% isopropanol and 1% fatty alcohol polyoxyethylene ether, with the balance being water.

[0071] The density of the weighted fracturing fluid was tested to be 1.43 g / cm³. 3 Rheological testing, such as Figure 5 As shown, from Figure 5 We can see that: at 180℃ and 170s -1 After shearing for 150 minutes under the specified conditions, the viscosity of the system remained at around 130 mPa·s, which is far greater than the minimum viscosity requirement of 25 mPa·s for clean fracturing fluid.

[0072] Comparative Example 1 A method for preparing a thickener without ethoxylation modification, the specific steps of which are as follows: S1. Add 338.6 g of erucic acid, 107.3 g of N,N-dimethylpropanediamine, 500 g of dimethylformamide, 2.7 g of p-toluenesulfonic acid (0.8% of the mass of erucic acid), and 227 g of dicyclohexylcarbodiimide to a 2 L four-necked flask. After purging with nitrogen three times, heat to 100 °C under nitrogen protection and stir for 7 hours. After the reaction is complete, cool to room temperature, filter to remove the generated dicyclohexylurea, and recover DMF by vacuum distillation of the filtrate to obtain 420 g of crude erucic acid-amylpropyl dimethyl tertiary amine.

[0073] S2. Add 420g of the above-mentioned tertiary amine, 300g of deionized water, and 300g of isopropanol to a 1L three-necked flask, and heat to 70℃ while stirring to dissolve. Add 205g of sodium 3-chloro-2-hydroxypropanesulfonate and 1g of antioxidant TBHQ, and adjust the pH to 8-9 in batches with sodium bicarbonate solid (approximately 80g required). Control the system temperature between 75-80℃ and maintain the reaction temperature for 9 hours.

[0074] S3. After the reaction is complete, the solvent is removed by vacuum distillation. The residue is washed twice with acetone (200 mL each time), filtered, and dried to obtain a white solid, which is 550 g of the thickener without ethoxylation modification.

[0075] A weighted fracturing fluid comprises the following components in weight percentages: 8% of the unethoxylated thickener, 70% calcium chloride, and 1% ethanol, with the balance being water.

[0076] Solubility and static suspension capacity test 1. Solubility test: Test conditions: Under normal temperature (25℃) conditions, the unmodified weighted fracturing fluid base prepared in Comparative Example 1 and the modified weighted fracturing fluid base prepared in Example 4 were stirred at a rate of 800 r / min for 30 minutes to ensure thorough mixing. The mixture was then poured into a 250 mL beaker and allowed to stand at room temperature for 24 hours. The system was observed for phase separation, turbidity precipitation, or salting out. Test results are as follows: Figure 6 and 7 As shown.

[0077] from Figure 6 and Figure 7The comparison shows that the thickener modified by ethoxylation significantly improves the solubility and stability of the fracturing fluid in high salinity brine, and avoids system instability caused by salting out or phase separation.

[0078] 2. Static sand suspension capacity test conditions: 30-40 mesh quartz sand was added to the high-density weighted cleaning fracturing fluid prepared in Example 4 at a sand addition concentration of 20%. The mixture was stirred at a rate of 800 r / min for 20 minutes to ensure uniform mixing. The mixture was then poured into a 250 ml graduated cylinder. The graduated cylinder was placed in a 50°C open water bath and allowed to stand for 1 hour to observe the sand and gravel settling.

[0079] The test results are shown in Figure 8. The system exhibits excellent and long-lasting proppant suspension capacity and structural stability at 50℃, which fully demonstrates that the system has reliable static proppant suspension performance and can meet the core requirements for proppant suspension and delivery in actual fracturing operations.

[0080] 3. On-site construction friction test During fracturing operations in a deep well (6500 m deep) in an oilfield, the reservoir temperature was 130℃. Before on-site friction testing, brine (1.43 g / cm³ KCl brine) with the same density as the fracturing fluid base fluid was first pumped in to obtain a baseline friction curve for subsequent drag reduction calculations. The test string used a 139.7 mm casing for full-bore injection, with a vertical wellbore trajectory, and the inner wall of the string was free of scale and residue.

[0081] The drag reduction performance of the weighted fracturing fluid described in Example 4 was compared with that of traditional polymer drag reducers. The comparison results are shown in Table 1.

[0082] Table 1. Comparison of drag reduction performance

[0083] As shown in Table 1, within a displacement range of 3792.4~3856.4 kg / h, this fracturing fluid exhibits excellent and stable drag reduction performance, with the drag reduction rate consistently maintained at a high level of 76.8%~77.5%, successfully reducing pipeline friction to approximately 45 MPa. This not only proves that the fracturing fluid can significantly reduce energy loss under external shear forces, achieving drag reduction effects comparable to or even better than traditional polymer drag reducers, but also possesses the unique advantages of being residue-free and easy to backflow.

[0084] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A polyether amphoteric viscoelastic surfactant, characterized in that, Prepared from raw materials in one of the following combinations by mass percentage: Combination 1: 4%~15% erucic acid, 1%~6% amination reagent, 2%~10% ethylene oxide, 2%~10% quaternization reagent, 0.03%~0.2% first catalyst, 0.2%~0.4% second catalyst, 0.02%~15% pH adjuster, 0%~8% dehydrating agent, 18.9%~30% first solvent, 24.3%~43.2% second solvent, 0%~1% reducing agent, 0%~6% oxidizing agent, and 0%~0.1% antioxidant; Combination 2: 4%~15% methyl erucic acid, 1%~6% amination reagent, 2%~10% ethylene oxide, 2%~10% quaternary amination reagent, 0%~0.14% third catalyst, 0.02%~0.15% fourth catalyst, 0.05%~0.20% fifth catalyst, 0.02%~15% pH adjuster, 0%~8% dehydrating agent, 18%~20.7% third solvent, 16.3%~22.7% fourth solvent, 14.8%~15.8% fifth solvent, 10.8%~21.9% sixth solvent, 0%~1% reducing agent, 0%~6% oxidizing agent, and 0%~0.1% antioxidant.

2. The polyether amphoteric viscoelastic surfactant according to claim 1, characterized in that, The amination agent is at least one selected from N,N-dimethylpropanediamine and dimethylamine; and / or The quaternizing agent is at least one of sodium 3-chloro-2-hydroxypropanesulfonate, sodium 2-chloroethylsulfonate, and sodium chlorosulfonate; and / or The first catalyst is one of sodium methoxide and cesium hydroxide; and / or The second catalyst is one of methanesulfonic acid and p-toluenesulfonic acid; and / or The third catalyst is nickel chloride; and / or The fourth catalyst is sodium methoxide; and / or The fifth catalyst is one of methanesulfonic acid and p-toluenesulfonic acid; and / or The pH adjuster is at least one of sodium hydroxide solution, potassium hydroxide solution, sodium bicarbonate solution, dilute sulfuric acid, and dilute hydrochloric acid; and / or The dehydrating agent is at least one of dicyclohexylcarbodiimide and N,N'-diisopropylcarbodiimide.

3. The polyether amphoteric viscoelastic surfactant according to claim 1, characterized in that, The first solvent is one of xylene and dimethylformamide (DMF); The second solvent is one of ethanol and isopropanol; and / or The third solvent is tetrahydrofuran; and / or The fourth solvent is an aqueous solution of acetone; and / or The fifth solvent is one of dimethylformamide and xylene; and / or The sixth solvent is one of an aqueous ethanol solution and ethanol; and / or The reducing agent is at least one of sodium borohydride and potassium borohydride; and / or The oxidant is at least one of potassium permanganate and pyridine chlorochromate; and / or The antioxidant is at least one of TBHQ and vitamin E.

4. The method for preparing the polyether amphoteric viscoelastic surfactant according to any one of claims 1 to 3, characterized in that, For combination one, the following steps are included: S1. Weigh erucic acid according to the stated mass percentage, add the first catalyst, heat to 100~130℃ under a protective atmosphere, and vacuum under stirring to remove water and low-boiling-point impurities from the reaction system; then continue heating to 120~160℃, control the system pressure at 0.2~0.6MPa, add ethylene oxide and maintain the aforementioned temperature and pressure conditions for the reaction; after the reaction is complete, cool down and remove unreacted ethylene oxide to obtain ethoxylated erucic acid; S2. The ethoxylated erucic acid is mixed evenly with the amination reagent, the second catalyst, and the first solvent. If the component contains a dehydrating agent, the temperature is first lowered to 0-5°C, the dehydrating agent is added, and the mixture is kept warm and stirred. Then the temperature is raised to 110-160°C for reaction. When the acid value of the reaction solution is ≤5mgKOH / g, the precipitate is filtered, and excess solvent and amination reagent are removed to obtain ethoxylated erucic acid amide tertiary amine. If the component does not contain a dehydrating agent, after the reaction at 110-160°C, water is separated and impurities are removed using a water separator. When the acid value of the reaction solution is ≤5mgKOH / g, the solvent and excess amination reagent are removed to obtain ethoxylated erucic acid amide tertiary amine. S3. The ethoxylated erucamide tertiary amine is mixed evenly with the second solvent and heated to 60-70°C with stirring to dissolve. Then, a quaternizing agent and a pH adjuster are added. If the component does not contain an antioxidant, the reaction is carried out at 70-90°C for 4-8 hours. After the reaction is complete, part of the second solvent is removed, the mixture is cooled to crystallize, filtered, and dried to obtain the solid polyether amphoteric viscoelastic surfactant. If the component contains an antioxidant, the antioxidant is added and the reaction is carried out at 70-90°C for 4-8 hours. When the tertiary amine conversion rate is ≥98%, the solution of the polyether amphoteric viscoelastic surfactant is obtained. Part of the second solvent is recovered under reduced pressure, and the mixture is cooled to crystallize, filtered, and dried to obtain the solid polyether amphoteric viscoelastic surfactant. For combination two, the following steps are included: S1. Weigh methyl erucic acid according to the mass percentage, add the third solvent, the third catalyst and the reducing agent, and carry out the reduction reaction at 25~40℃ for 2~4h. After the reaction is completed, add pH adjuster to neutralize or hydrolyze, separate the liquid and purify by distillation to obtain the corresponding alcohol. S2. Add a fourth catalyst to the alcohol obtained in S1, heat to 100-130°C under a protective atmosphere, and remove water and low-boiling-point impurities from the reaction system under stirring and vacuum conditions. Then continue to heat to 120-160°C, control the system pressure at 0.2-0.6 MPa, add ethylene oxide, and carry out the reaction under the aforementioned temperature and pressure conditions. After the reaction is complete, cool down and remove unreacted ethylene oxide to obtain ethoxylated mustard alcohol. S3. Dissolve ethoxylated mustard in a fourth solvent, add a pH adjuster and an oxidant, and carry out an oxidation reaction at 30~50℃ for 4~6 hours. Filter and remove the solvent to finally obtain ethoxylated erucic acid. S4. Mix the ethoxylated erucic acid with the amination reagent, the fifth catalyst, and the fifth solvent evenly. If the component contains a dehydrating agent, first cool to 0-5°C, add the dehydrating agent, and keep it warm while stirring. Then, raise the temperature to 110-160°C to react. When the acid value of the reaction solution is ≤5mgKOH / g, first filter to remove the generated solid precipitate, and then remove the solvent and excess amination reagent to obtain ethoxylated erucic acid amide tertiary amine. If the component does not contain a dehydrating agent, stir and raise the temperature to 110-160°C to react. During this process, use a water separator to separate water and remove impurities. When the acid value of the reaction solution is ≤5mgKOH / g, remove the solvent and excess amination reagent to obtain ethoxylated erucic acid amide tertiary amine. S5. Mix the ethoxylated erucamide tertiary amine with the sixth solvent evenly, and heat to 60~70℃ while stirring to dissolve. If the component contains an antioxidant, add the antioxidant and quaternizing agent, adjust the pH of the system to 7~8, and react at 70~90℃ for 4~8 hours to obtain the solution of the polyether amphoteric viscoelastic surfactant. If the component does not contain an antioxidant, add the quaternizing agent, adjust the pH of the system to 7~8, and react at 70~90℃ for 4~8 hours. When the tertiary amine conversion rate is ≥98%, the solution of the polyether amphoteric viscoelastic surfactant is obtained.

5. The method for preparing the polyether amphoteric viscoelastic surfactant according to claim 4, characterized in that, For combination two, the solution of the polyether amphoteric viscoelastic surfactant in step S5 is further subjected to partial solvent removal, cooling crystallization, filtration, and drying to obtain the solid polyether amphoteric viscoelastic surfactant.

6. The method for preparing the polyether amphoteric viscoelastic surfactant according to claim 4, characterized in that, For combination one, the protective atmosphere in step S1 is nitrogen; and / or For combination two, the protective atmosphere described in step S2 is nitrogen.

7. A weighted fracturing fluid, characterized in that, It comprises the following components by weight percentage: 6% to 8% of the polyether amphoteric viscoelastic surfactant as described in any one of claims 1 to 3, 55% to 70% of calcium chloride, 1% to 3% of dispersant and 1% to 2% of compound surfactant, with the balance being water.

8. The weighted fracturing fluid according to claim 7, characterized in that, It comprises the following components by weight percentage: 8% of the polyether amphoteric viscoelastic surfactant, 55% to 70% of calcium chloride, 1% of dispersant and 1% of compound surfactant, with the balance being water.

9. The weighted fracturing fluid according to claim 7 or 8, characterized in that, The dispersant is at least one of isopropanol and ethanol.

10. The weighted fracturing fluid according to claim 7 or 8, characterized in that, The compound surfactant is at least one of octyldecyl glucoside and fatty alcohol polyoxyethylene ether; and / or The water is at least one of deionized water and formation water.

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