Surfactant for fracturing dialysis oil displacement and preparation method thereof

Abstract

The invention provides a surfactant for fracturing dialysis oil displacement and a preparation method thereof, and belongs to the technical field of oilfield chemical engineering, and the preparation method comprises the following steps: step S1, synthesis of a Gemini type surfactant: mixing dodecyl dimethyl tertiary amine with 1, 3-dibromopropane for reaction, then adding a sodium hydrogen sulfite aqueous solution, heating for reaction, then cooling, and then adding a sodium hydroxide aqueous solution for reaction to obtain the Gemini type surfactant; the Gemini surface active agent containing the sulfonic acid group is obtained; step S2, preparing modified beta-sitosterol, namely dissolving beta-sitosterol in absolute ethyl alcohol, heating and dissolving, adding KOH, introducing ethylene oxide, continuously heating, adding normal hexane, ultrasonically dispersing, centrifuging, and freeze-drying to obtain the modified beta-sitosterol; and S3, preparation of the surfactant for fracturing dialysis oil displacement: mixing and stirring the Gemini surfactant containing the sulfonic acid group and the modified beta-sitosterol to prepare the surfactant for fracturing dialysis oil displacement. The surfactant for oil displacement is good in oil displacement performance, good in stability, easy to decompose and free of pollution.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemical industry, and in particular to a surfactant for fracturing and dialysis oil recovery and a preparation method thereof. Background Art

[0002] In the modern oil production process, with the gradual depletion of traditional oil reservoirs, the use of fracturing and dialysis flooding technology has become an important means to improve oil recovery and develop unconventional oil reservoirs. Fracturing and dialysis flooding technology injects high-pressure fluid into the reservoir to promote the expansion of rock cracks and form diversion channels to improve the fluidity of oil and gas, thereby achieving effective exploitation of crude oil in the reservoir. However, traditional water drive and gas drive methods are often difficult to effectively improve oil recovery efficiency, especially in low permeability reservoirs, where there are serious problems such as excessive oil-water interfacial tension, uneven oil-water distribution, and large flow resistance. Therefore, the development of efficient surfactants to improve oil-water interaction, reduce capillary force and improve oil fluidity has become the key to enhancing the effect of fracturing and dialysis flooding.

[0003] Most of the existing surfactants used in fracturing and dialysis oil recovery are based on single functional molecules, and their main function is to reduce the oil-water interfacial tension and stabilize the oil-water emulsion. However, these surfactants have certain limitations in practical applications, such as: poor environmental adaptability: traditional surfactants are prone to failure under high temperature, strong acid or strong alkali conditions, and cannot meet the requirements of complex reservoir environments; weak surface activity: the hydrophilic-lipophilic balance of traditional surfactants is not ideal, and they cannot effectively reduce the oil-water interfacial tension, resulting in unsatisfactory oil recovery effects, especially when the reservoir has low porosity and poor permeability, the oil recovery efficiency is difficult to improve; easy to be adsorbed: some surfactants are easily adsorbed by the rock surface in the reservoir, causing them to lose activity after injection, affecting the oil recovery effect, and may cause pollution to the underground environment and oil and gas pipelines.

[0004] Therefore, it is necessary to provide a method for preparing a surfactant for fracturing and dialysis oil recovery to solve the problems existing in the above-mentioned prior art. Summary of the invention

[0005] In view of this, the present invention provides a surfactant for fracturing and dialysis oil recovery and a preparation method thereof, which can achieve the purpose of good oil recovery performance, good stability and easy decomposition without pollution of the surfactant for oil recovery.

[0006] The specific scheme of the present invention is as follows: a method for preparing a surfactant for fracturing and dialysis oil recovery, comprising the following steps: Step S1, synthesis of Gemini surfactant: Dodecyldimethyl tertiary amine and 1,3-dibromopropane are mixed and reacted, and then a sodium bisulfite aqueous solution is added, the temperature is raised to react, and then the temperature is lowered to obtain a Gemini surfactant containing a sulfonic acid group; Step S2, preparation of modified β-sitosterol: Dissolve β-sitosterol in anhydrous ethanol, heat and stir to dissolve, add KOH, and introduce ethylene oxide, continue heating to react, then add n-hexane, ultrasonically disperse, centrifuge, and freeze-dry to obtain modified β-sitosterol; Step S3, preparation of surfactant for fracturing and dialysis oil recovery: The sulfonic acid group-containing Gemini surfactant and modified β-sitosterol are mixed and stirred to prepare a surfactant for fracturing dialysis oil recovery.

[0007] Gemini surfactants have a double-chain amphiphilic head group structure. Compared with traditional single-chain surfactants, they have higher interfacial activity and can significantly reduce the oil-water interfacial tension. The amphiphilic head group structure can enhance stability and adapt to high-mineralization oil reservoirs. In addition, the double-chain structure can reduce the ineffective adsorption of surfactants on the rock surface and improve the utilization rate of surfactants.

[0008] The molecular skeleton of β-sitosterol is composed of a tetracyclic steroid nucleus and a long hydrophobic side chain. It contains a large number of hydrophobic groups and can effectively combine with Gemini surfactants through van der Waals forces to form a synergistic effect and enhance interfacial activity. After β-sitosterol is grafted and modified with ethylene oxide, its hydrophilicity is enhanced, which can effectively reduce the oil-water interfacial tension, thereby improving the wettability and dispersibility of the surfactant at the oil-water interface. At the same time, the rigid steroid nucleus of β-sitosterol can be inserted into the layered structure of crude oil colloid-asphaltene, destroying its π-π stacking effect, which can promote oil desorption and improve the recovery rate of oil reservoirs. β-sitosterol itself has good thermal stability and chemical stability. After modification, β-sitosterol can not only enhance the stability of the surfactant, but also improve its stability in high temperature environment, so that the surfactant can maintain good performance under high temperature conditions and avoid decomposition. As a natural plant sterol, β-sitosterol itself has good biodegradability and is environmentally friendly and pollution-free.

[0009] The introduction of polyoxyethylene chains into modified β-sitosterol improves its hydrophilicity, helps reduce the adsorption of surfactants, prevents surfactants from directly contacting the highly mineralized water phase, and makes it less likely to be adsorbed onto the rock surface in the water phase, thereby reducing damage to oil reservoirs and pipelines.

[0010] Preferably, in step S1, the temperature of the mixed reaction is 60-80°C, and the time is 2-3h; the temperature of the temperature-raising reaction is 90-100°C, the pH is 8-9, and the time is 2-4h; the temperature of the cooling reaction is 70-80°C, and the time is 1-2.5h.

[0011] The sulfonation is carried out in three stages by using a gradient temperature control method, which can reduce the generation of by-products and improve the sulfonation efficiency.

[0012] Preferably, in step S2, the heating temperature is 55-65°C; the heating temperature is continued to be 130-140°C, and the time is 4-5h.

[0013] Preferably, in step S3, a composite synergist is further added for mixing and stirring, wherein the ratio of the sulfonic acid group-containing Gemini surfactant, the modified β-sitosterol and the composite synergist is 6:2:1.

[0014] Preferably, the preparation of the composite synergist includes the following steps: mixing lauric acid and β-sitosterol, introducing nitrogen, adding a catalyst, heating and stirring, adding mesoporous SiO2 for mixing, ultrasonic treatment for 30 minutes, and then dispersing in ionic liquid [BMIM] BF6, ultrasonic treatment for 2 hours, and centrifugally drying to obtain the composite synergist.

[0015] Lauric acid is a long-chain fatty acid. Through the esterification reaction with β-sitosterol, it can effectively enhance the lipophilicity of the modified surfactant, making it easier for the final surfactant to interact with the oil phase and form a good adsorption structure at the oil-water interface, which helps to drive and disperse the oil, effectively improve the fluidity of the oil layer, and promote the recovery rate. The long-chain structure and esterification modification of lauric acid help to improve the thermal stability and chemical stability of the surfactant, so that it can still maintain good performance in high temperature and acidic environment, thereby extending the service life of the surfactant used for oil displacement during the oil recovery process.

[0016] Preferably, the catalyst is a SDS-HCL mixed solution, wherein the ratio of SDS (sodium dodecyl sulfate) to HCL (hydrochloric acid) is 1:1.

[0017] Preferably, the temperature of the heating and stirring is 110-130° C., and the time is 2-4 hours.

[0018] Preferably, the pore size of the mesoporous SiO2 is 2-5 nm.

[0019] To achieve the above object, the present invention further provides a surfactant for fracturing and dialysis oil recovery prepared by the above method for preparing a surfactant for fracturing and dialysis oil recovery, characterized in that it comprises the following components in parts by weight: 6-18 parts Gemini surfactant and 2-6 parts modified β-sitosterol.

[0020] Preferably, the following components in parts by weight are also included: 1-3 parts of compound enhancer; The raw materials of the Gemini surfactant include 12-36 parts of dodecyldimethyl tertiary amine, 6-18 parts of 1,3-dibromopropane and 20-60 parts of sodium bisulfite aqueous solution; The raw materials of the modified β-sitosterol include 1.5-4.5 parts of β-sitosterol and 3-9 parts of ethylene oxide; The raw materials of the composite synergist include 1-3 parts of lauric acid, 2-6 parts of beta-sitosterol, 9-28 parts of ionic liquid [BMIM] BF6 and 0.6-2 parts of mesoporous SiO2.

[0021] The above technical solution of the present invention includes at least the following beneficial effects: (1) The present invention introduces modified β-sitosterol. The molecular structure of β-sitosterol contains hydrophobic groups, which can form a synergistic effect with Gemini surfactants to enhance interfacial activity. After being modified by ethylene oxide grafting, its hydrophilicity is enhanced, which can effectively reduce the oil-water interfacial tension, promote oil desorption and improve the recovery rate of oil reservoirs.

[0022] (2) β-sitosterol itself has good thermal and chemical stability. After modification, it can improve the stability of oil displacement surfactants in high temperature environments and avoid decomposition. In addition, as a natural plant sterol, β-sitosterol itself has good biodegradability and is environmentally friendly and pollution-free.

[0023] (3) β-Sitosterol is modified by introducing polyoxyethylene chains to improve its hydrophilicity, which helps to reduce the adsorption of surfactants on rocks and pipelines, making it less likely to be adsorbed on the surface of rocks or pipelines, thereby reducing damage to oil reservoirs and pipelines. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. The described embodiments are part of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0025] Example 1 120 g of dodecyldimethyl tertiary amine was mixed with 60 g of 1,3-dibromopropane, and reacted at 70°C for 2.5 h to promote the initial grafting of sulfonic acid groups. Then 200 mL of a 30 wt% aqueous sodium bisulfite solution was added, the temperature was raised to 95°C, and the sulfonation reaction was carried out at a pH of 8-9 for 3 h. The temperature was then lowered to 80°C and reacted for 1 h to obtain a Gemini surfactant containing a sulfonic acid group.

[0026] Take 15 g of β-sitosterol and dissolve it in 45 g of anhydrous ethanol, heat it to 60°C, stir and dissolve it, add 0.5 g of KOH, and pass 30 g of ethylene oxide, continue to heat to 135°C and react for 4 hours, then add 100 mL of n-hexane, ultrasonically disperse it, centrifuge it, and freeze-dry it to obtain modified β-sitosterol.

[0027] 16 g of lauric acid and 32 g of β-sitosterol were mixed, nitrogen was introduced, and 18 mL of catalyst solution (mixed by SDS and HCL in a ratio of 1:1) was added, the temperature was raised to 120°C, and the reaction was stirred for 3 hours. Then 10 g of mesoporous SiO2 was added and mixed, ultrasonically treated for 30 minutes, and then dispersed in 150 mL of ionic liquid [BMIM] BF6, ultrasonically treated for 2 hours, and centrifuged and dried to obtain a composite enhancer.

[0028] The sulfonic acid group-containing Gemini surfactant, modified β-sitosterol and composite synergist were mixed in a ratio of 6:2:1, and stirred at 50° C. for 2 h to obtain a surfactant for fracturing dialysis flooding.

[0029] Example 2 Mix 120 g of dodecyldimethyl tertiary amine and 60 g of 1,3-dibromopropane, react at 60°C for 3 h to promote the initial grafting of sulfonic acid groups, then add 300 mL of 30 wt% sodium bisulfite aqueous solution, heat to 90°C, and carry out sulfonation reaction at pH 8-9 for 4 h, then cool to 70°C and react for 2.5 h to obtain a Gemini surfactant containing sulfonic acid groups.

[0030] Take 15 g of β-sitosterol and dissolve it in 45 g of anhydrous ethanol, heat it to 60°C, stir and dissolve it, add 0.5 g of KOH, and pass 30 g of ethylene oxide, continue to heat to 135°C and react for 4 hours, then add 100 mL of n-hexane, ultrasonically disperse it, centrifuge it, and freeze-dry it to obtain modified β-sitosterol.

[0031] 10 g of lauric acid and 32 g of β-sitosterol were mixed, nitrogen was introduced, and 18 mL of catalyst solution (mixed by SDS and HCL in a ratio of 1:1) was added, the temperature was raised to 110°C, and the reaction was stirred for 4 hours. Then 10 g of mesoporous SiO2 was added and mixed, ultrasonically treated for 30 minutes, and then dispersed in 100 mL of ionic liquid [BMIM] BF6, ultrasonically treated for 2 hours, and centrifuged and dried to obtain a composite enhancer.

[0032] The sulfonic acid group-containing Gemini surfactant, modified β-sitosterol and composite synergist were mixed in a ratio of 6:2:1, and stirred at 50° C. for 2 h to obtain a surfactant for fracturing dialysis flooding.

[0033] Example 3 Mix 360 g of dodecyldimethyl tertiary amine and 180 g of 1,3-dibromopropane, react at 80°C for 2.5 h to promote the initial grafting of sulfonic acid groups, then add 600 mL of 30 wt% sodium bisulfite aqueous solution, heat to 100°C, and carry out sulfonation reaction at pH 8-9 for 2 h, then cool to 80°C for 1 h to obtain a Gemini surfactant containing sulfonic acid groups.

[0034] Take 30 g of β-sitosterol and dissolve it in 90 g of anhydrous ethanol, heat it to 55°C, stir and dissolve it, add 0.5 g of KOH, and pass 60 g of ethylene oxide, continue to heat to 140°C and react for 4 hours, then add 100 mL of n-hexane, ultrasonically disperse it, centrifuge it, and freeze-dry it to obtain modified β-sitosterol.

[0035] 16 g of lauric acid and 32 g of β-sitosterol were mixed, nitrogen was introduced, and 18 mL of catalyst solution (mixed by SDS and HCL in a ratio of 1:1) was added, the temperature was raised to 120°C, and the reaction was stirred for 3 h. Then 10 g of mesoporous SiO2 was added and mixed, ultrasonically treated for 30 min, and then dispersed in 180 mL of ionic liquid [BMIM] BF6, ultrasonically treated for 2 h, and centrifuged and dried to obtain a composite enhancer.

[0036] The sulfonic acid group-containing Gemini surfactant, modified β-sitosterol and composite synergist were mixed in a ratio of 6:2:1, and stirred at 50° C. for 2 h to obtain a surfactant for fracturing dialysis flooding.

[0037] Example 4 Mix 240 g of dodecyldimethyl tertiary amine and 120 g of 1,3-dibromopropane, react at 65°C for 3 h to promote the initial grafting of sulfonic acid groups, then add 500 mL of 30 wt% sodium bisulfite aqueous solution, heat to 90°C, and carry out sulfonation reaction at pH 8-9 for 2.5 h, then cool to 75°C and react for 1.5 h to obtain a Gemini surfactant containing sulfonic acid groups.

[0038] Take 15 g of β-sitosterol and dissolve it in 45 g of anhydrous ethanol, heat it to 55°C, stir and dissolve it, add 0.5 g of KOH, and pass 30 g of ethylene oxide, continue to heat to 140°C and react for 4 hours, then add 100 mL of n-hexane, ultrasonically disperse it, centrifuge it, and freeze-dry it to obtain modified β-sitosterol.

[0039] 12 g of lauric acid and 20 g of β-sitosterol were mixed, nitrogen was introduced, and 18 mL of catalyst solution (mixed by SDS and HCL in a ratio of 1:1) was added. The temperature was raised to 115°C and stirred for reaction for 3.5 h. Then 10 g of mesoporous SiO2 was added for mixing. The mixture was ultrasonically treated for 30 min, and then dispersed in 90 mL of ionic liquid [BMIM] BF6. The mixture was ultrasonically treated for 2 h and centrifuged to obtain a composite enhancer.

[0040] The sulfonic acid group-containing Gemini surfactant, modified β-sitosterol and composite synergist were mixed in a ratio of 6:2:1, and stirred at 50° C. for 2 h to obtain a surfactant for fracturing dialysis flooding.

[0041] Example 5 Mix 120 g of dodecyldimethyl tertiary amine and 60 g of 1,3-dibromopropane, react at 75°C for 2 h to promote the initial grafting of sulfonic acid groups, then add 200 mL of 30 wt% sodium bisulfite aqueous solution, heat to 90°C, and carry out sulfonation reaction at pH 8-9 for 3.5 h, then cool to 70°C and react for 1.5 h to obtain a Gemini surfactant containing sulfonic acid groups.

[0042] Take 45 g of β-sitosterol and dissolve it in 90 g of anhydrous ethanol, heat it to 65°C, stir and dissolve it, add 0.5 g of KOH, and pass 90 g of ethylene oxide, continue to heat to 130°C and react for 5 hours, then add 100 mL of n-hexane, ultrasonically disperse it, centrifuge it, and freeze-dry it to obtain modified β-sitosterol.

[0043] 30 g of lauric acid and 45 g of β-sitosterol were mixed, nitrogen was introduced, and 18 mL of catalyst solution (mixed by SDS and HCL in a ratio of 1:1) was added, the temperature was raised to 130 ° C, and the reaction was stirred for 2 h. Then 6 g of mesoporous SiO2 was added for mixing, ultrasonic treatment was performed for 30 min, and then dispersed in 200 mL of ionic liquid [BMIM] BF6, ultrasonic treatment was performed for 2 h, and a composite enhancer was obtained after centrifugal drying.

[0044] The sulfonic acid group-containing Gemini surfactant, modified β-sitosterol and composite synergist were mixed in a ratio of 6:2:1, and stirred at 50° C. for 2 h to obtain a surfactant for fracturing dialysis flooding.

[0045] Example 6 Mix 240 g of dodecyldimethyl tertiary amine and 120 g of 1,3-dibromopropane, react at 70°C for 2 h to promote the initial grafting of sulfonic acid groups, then add 400 mL of 30 wt% sodium bisulfite aqueous solution, heat to 100°C, and carry out sulfonation reaction at pH 8-9 for 2 h, then cool to 75°C and react for 1.5 h to obtain a Gemini surfactant containing sulfonic acid groups.

[0046] Take 15 g of β-sitosterol and dissolve it in 45 g of anhydrous ethanol, heat it to 55°C, stir and dissolve it, add 0.5 g of KOH, and pass 30 g of ethylene oxide, continue to heat to 140°C and react for 4 hours, then add 100 mL of n-hexane, ultrasonically disperse it, centrifuge it, and freeze-dry it to obtain modified β-sitosterol.

[0047] 16 g of lauric acid and 60 g of β-sitosterol were mixed, nitrogen was introduced, and 18 mL of catalyst solution (mixed by SDS and HCL in a ratio of 1:1) was added. The temperature was raised to 125°C and stirred for reaction for 2.5 h. Then 20 g of mesoporous SiO2 was added for mixing. The mixture was ultrasonically treated for 30 min, and then dispersed in 280 mL of ionic liquid [BMIM] BF6. The mixture was ultrasonically treated for 2 h and centrifuged to obtain a composite enhancer.

[0048] The sulfonic acid group-containing Gemini surfactant, modified β-sitosterol and composite synergist were mixed in a ratio of 6:2:1, and stirred at 50° C. for 2 h to obtain a surfactant for fracturing dialysis flooding.

[0049] Example 7 120 g of dodecyldimethyl tertiary amine was mixed with 60 g of 1,3-dibromopropane, and reacted at 75°C for 2 h to promote the initial grafting of sulfonic acid groups. Then 200 mL of a 30 wt% aqueous sodium bisulfite solution was added, the temperature was raised to 90°C, and the sulfonation reaction was carried out at a pH of 8-9 for 3 h. The temperature was then lowered to 80°C and reacted for 1.5 h to obtain a Gemini surfactant containing a sulfonic acid group.

[0050] Take 20 g of β-sitosterol and dissolve it in 80 g of anhydrous ethanol, heat it to 65°C, stir and dissolve it, add 0.5 g of KOH, and pass 40 g of ethylene oxide, continue to heat to 130°C and react for 5 hours, then add 100 mL of n-hexane, ultrasonically disperse it, centrifuge it, and freeze-dry it to obtain modified β-sitosterol.

[0051] 16 g of lauric acid and 32 g of β-sitosterol were mixed, nitrogen was introduced, and 18 mL of catalyst solution (mixed by SDS and HCL in a ratio of 1:1) was added, the temperature was raised to 120°C, and the reaction was stirred for 3 h. Then 15 g of mesoporous SiO2 was added and mixed, ultrasonically treated for 30 min, and then dispersed in 180 mL of ionic liquid [BMIM] BF6, ultrasonically treated for 2 h, and centrifuged and dried to obtain a composite enhancer.

[0052] The sulfonic acid group-containing Gemini surfactant, modified β-sitosterol and composite synergist were mixed in a ratio of 6:2:1, and stirred at 50° C. for 2 h to obtain a surfactant for fracturing dialysis flooding.

[0053] Example 8 120 g of dodecyldimethyl tertiary amine was mixed with 60 g of 1,3-dibromopropane, and reacted at 75°C for 2 h to promote the initial grafting of sulfonic acid groups. Then 200 mL of a 30 wt% aqueous sodium bisulfite solution was added, the temperature was raised to 90°C, and the sulfonation reaction was carried out at a pH of 8-9 for 3 h. The temperature was then lowered to 80°C and reacted for 1.5 h to obtain a Gemini surfactant containing a sulfonic acid group.

[0054] Take 15 g of β-sitosterol and dissolve it in 45 g of anhydrous ethanol, heat it to 65°C, stir and dissolve it, add 0.5 g of KOH, and pass 30 g of ethylene oxide, continue to heat to 130°C and react for 5 hours, then add 100 mL of n-hexane, ultrasonically disperse it, centrifuge it, and freeze-dry it to obtain modified β-sitosterol.

[0055] The sulfonic acid group-containing Gemini surfactant and modified β-sitosterol were mixed in a ratio of 6:2, and stirred at 50° C. for 2 h to obtain a surfactant for fracturing dialysis flooding.

[0056] The present invention also carries out comparative examples and related tests.

[0057] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that modified β-sitosterol is not prepared in Comparative Example 1, and other compositions and preparation methods are the same as those in Example 1, and a surfactant for fracturing dialysis oil recovery is prepared.

[0058] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that in the preparation of the Gemini surfactant in Comparative Example 2, the gradient temperature control method is not used, but the temperature is directly increased and then the reaction is carried out at a constant temperature. The other compositions and preparation methods are the same as those in Example 1, and a surfactant for fracturing dialysis oil recovery is prepared.

[0059] Comparative Example 3 Comparative Example 3 uses a surfactant sold by Zibo Huizhong Chemical Co., Ltd., model HZ-114.

[0060] Performance testing The reduction of oil-water interfacial tension and oil recovery efficiency of the surfactants for fracturing dialysis oil recovery prepared in Examples 1-8 and Comparative Examples 1-3 were tested by using a physical simulation dialysis oil recovery method; salt resistance was tested using a CaCl2 solution; and thermal stability was tested at 150°C. The test results are shown in Table 1 below.

[0061] Table 1

[0062] It can be seen from the results in Table 1 above that the overall oil recovery performance of the fracturing and dialysis oil recovery surfactant prepared in Comparative Example 1 is reduced compared with that prepared in Examples 1-8, especially in terms of oil recovery efficiency, which is significantly reduced, indicating that the modified β-sitosterol can effectively reduce the oil-water interfacial tension and promote the improvement of recovery rate; the oil recovery performance of Comparative Example 2 is slightly reduced compared with Examples 1-8, and its oil recovery performance is better than that of Comparative Example 1, indicating that in the preparation of Gemini surfactant, the gradient temperature control method can effectively improve the sulfonation efficiency, so that the performance of Gemini surfactant is improved, thereby enhancing the oil recovery performance of the fracturing and dialysis oil recovery surfactant; the surfactant used in Comparative Example 3 has an oil recovery performance much lower than that of the fracturing and dialysis oil recovery surfactant prepared in the embodiment of the present invention, indicating that the fracturing and dialysis oil recovery surfactant prepared by the present invention can effectively improve the recovery rate of the oil reservoir.

[0063] Compared with Example 7, Example 8 did not prepare the composite synergist, resulting in a small decrease in the oil recovery performance, indicating that the composite synergist can promote the improvement of the oil recovery performance of the surfactant used in fracturing and dialysis oil recovery.

[0064] At a temperature of 130°C and a mineralization of 15×10 4 mg / L(Ca 2+ =5000 mg / L) and adsorption time of 24h, 10g of standard sandstone core particles were used to test the static adsorption performance of 100mL of surfactant for fracturing dialysis oil recovery prepared in Example 1, Example 7, Example 8 and Comparative Examples 1-3, and the results are shown in Table 2.

[0065] Table 2

[0066] It can be seen from the results in Table 2 above that compared with Example 1, the adsorption amount of Comparative Example 1 is significantly increased, indicating that modified β-sitosterol can reduce the adsorption of the surfactant for fracturing and dialysis oil recovery on the rock surface and reduce the loss; compared with the test results of Comparative Example 3, the adsorption amount of the surfactant for fracturing and dialysis oil recovery prepared by the embodiment of the present invention is lower, indicating that the surfactant for fracturing and dialysis oil recovery prepared by the present invention is better than the surfactant; compared with Example 7, the test result of the adsorption amount of Example 8 is also increased to a small extent, indicating that the preparation of the composite synergist has a certain promoting effect on reducing the adsorption of the surfactant for fracturing and dialysis oil recovery, which helps to improve the oil recovery utilization rate of the surfactant.

[0067] The above are preferred embodiments of the present invention. A person skilled in the art may make several improvements and modifications without departing from the principles of the present invention. Such improvements and modifications shall also be deemed as the protection scope of the present invention.

Claims

1. A method for preparing a surfactant for fracturing and dialysis oil recovery, characterized in that: The following steps are involved: Step S1, synthesis of Gemini surfactant: Dodecyldimethyl tertiary amine and 1,3-dibromopropane are mixed for reaction, and then a sodium bisulfite aqueous solution is added, the temperature is raised for reaction, and then the temperature is lowered to obtain a Gemini surfactant containing a sulfonic acid group; Step S2, preparation of modified β-sitosterol: Dissolve β-sitosterol in anhydrous ethanol, heat and stir to dissolve, add KOH, and introduce ethylene oxide, continue heating to react, then add n-hexane, ultrasonically disperse, centrifuge, and freeze-dry to obtain modified β-sitosterol; Step S3, preparation of surfactant for fracturing and dialysis oil recovery: The sulfonic acid group-containing Gemini surfactant and modified β-sitosterol are mixed and stirred to prepare a surfactant for fracturing dialysis oil recovery.

2. The method for preparing a surfactant for fracturing and dialysis oil recovery according to claim 1, characterized in that: In step S1, the temperature of the mixed reaction is 60-80°C, and the time is 2-3h; the temperature of the temperature-raising reaction is 90-100°C, the pH is 8-9, and the time is 2-4h; the temperature of the cooling reaction is 70-80°C, and the time is 1-2.5h.

3. The method for preparing a surfactant for fracturing and dialysis oil recovery according to claim 1, characterized in that: In step S2, the heating temperature is 55-65°C; the heating temperature is continued to be 130-140°C for 4-5 hours.

4. The method for preparing a surfactant for fracturing and dialysis oil recovery according to claim 1, characterized in that: In the step S3, a composite synergist is further added for mixing and stirring, wherein the ratio of the sulfonic acid group-containing Gemini surfactant, the modified β-sitosterol and the composite synergist is 6:2:

1.

5. The method for preparing a surfactant for fracturing and dialysis oil recovery according to claim 4, characterized in that: The preparation of the composite synergist comprises the following steps: mixing lauric acid and beta-sitosterol, introducing nitrogen, adding a catalyst, heating and stirring, adding mesoporous SiO2 for mixing, ultrasonic treatment for 30 minutes, dispersing in ionic liquid [BMIM] BF6, ultrasonic treatment for 2 hours, and centrifugally drying to obtain the composite synergist.

6. The method for preparing a surfactant for fracturing and dialysis oil recovery according to claim 5, characterized in that: The catalyst is a SDS-HCL mixed solution, wherein the ratio of SDS to HCL is 1:

1.

7. The method for preparing a surfactant for fracturing and dialysis oil recovery according to claim 5, characterized in that: The temperature of heating and stirring is 110-130°C and the time is 2-4h.

8. The method for preparing a surfactant for fracturing and dialysis oil recovery according to claim 5, characterized in that: The pore size of the mesoporous SiO2 is 2-5 nm.

9. A surfactant for fracturing and dialysis oil recovery, characterized in that: The surfactant is prepared by the method for preparing a surfactant for fracturing and dialysis oil recovery according to any one of claims 1 to 8, characterized in that it comprises the following components in parts by weight: 6-18 parts Gemini surfactant and 2-6 parts modified β-sitosterol.

10. A surfactant for fracturing and dialysis oil recovery according to claim 9, characterized in that: Also includes the following components in parts by weight: 1-3 parts of compound enhancer; The raw materials of the Gemini surfactant include 12-36 parts of dodecyldimethyl tertiary amine, 6-18 parts of 1,3-dibromopropane and 20-60 parts of sodium bisulfite aqueous solution; The raw materials of the modified β-sitosterol include 1.5-4.5 parts of β-sitosterol and 3-9 parts of ethylene oxide; The raw materials of the composite synergist include 1-3 parts of lauric acid, 2-6 parts of beta-sitosterol, 9-28 parts of ionic liquid [BMIM] BF6 and 0.6-2 parts of mesoporous SiO2.

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