Environment-friendly oil displacement agent for oil field

Abstract

The invention relates to the technical field of oilfield development, and particularly discloses an environment-friendly oilfield oil displacement agent. The environment-friendly oil displacement agent for the oil field is prepared from the following raw materials in parts by weight: 70 to 90 parts of carboxylated sesbania oil loaded nano silicon dioxide and 10 to 30 parts of a composite surfactant, according to the carboxylated sesbania oil loaded nano silicon dioxide, uniform loading of the sesbania oil to the nano silicon dioxide is realized through a carboxylation-sol-gel two-step method, so that the problem that nano particles are extremely easy to agglomerate and lose nano characteristics during oil displacement is avoided, and the oil displacement effects of the sesbania oil and the nano silicon dioxide are fully exerted; the oil displacement efficiency of the oil displacement agent is improved.

Description

Technical Field

[0001] The present application relates to the technical field of oilfield development, and more specifically, to an environmentally friendly oilfield flooding agent. Background Art

[0002] Oil production and oilfield development can be divided into three stages: primary, secondary, and tertiary. Primary recovery utilizes the reservoir's natural energy, with recovery rates below 15%. Secondary recovery involves externally supplementing formation energy (such as water or gas injection) to maintain formation energy, thereby increasing recovery rates, with rates reaching up to 45%. Tertiary recovery involves injecting other fluids, employing physical, chemical, and biological methods to alter reservoir rock and fluid properties, thereby increasing reservoir recovery after water flooding. Recovery rates range from 50% to 90%. Chemical flooding is categorized as polymer flooding, surfactant flooding, alkaline flooding, and composite flooding. Within tertiary recovery, any method that adds chemical agents to the injected water to alter the properties of the displacing fluid or the interface between the displacing fluid and crude oil, thereby increasing oil recovery, falls under the category of chemical flooding. The corresponding chemical agents are known as polymer flooding agents, surfactant flooding agents, alkaline flooding agents, and composite flooding agents.

[0003] Patent application publication number CN106318359A discloses an oil-displacing agent system. The system is obtained by uniformly mixing partially hydrolyzed polyacrylamide (HPAM), a water-soluble phenolic resin, an activator, a water-soluble carbonate, and a dispersant in the presence of water. Based on 1 part by weight of the partially hydrolyzed polyacrylamide, the water-soluble phenolic resin content is 0.05-0.2 parts by weight, the activator content is 0.1-1 parts by weight, the water-soluble carbonate content is 2-6 parts by weight, and the dispersant content is 2-6 parts by weight. The oil-displacing agent system provided in this patent application exhibits good surface viscosity and excellent temperature and salt resistance. It is suitable for use as an oil-displacing agent in tertiary oil recovery from high-calcium-magnesium reservoirs, potentially improving tertiary oil recovery efficiency. However, with the development of oil, especially the advancement of enhanced oil recovery technology towards low-carbon and environmentally friendly directions, oilfield polymers need to organically integrate economy, effectiveness and green environmental performance, and at the same time have biocompatibility and degradability. However, HPAM has low biocompatibility and poor degradability, resulting in complex post-processing procedures for produced fluids, high costs, high environmental pollution risks, and poor environmental protection. Summary of the Invention

[0004] In order to improve the environmental friendliness of oilfield displacing agents, the present application provides an environmentally friendly oilfield displacing agent.

[0005] The present application provides an environmentally friendly oil-field flooding agent, comprising the following raw materials in parts by weight: 70-90 parts of carboxylated sesbania oil loaded with nano-silica and 10-30 parts of a composite surfactant; The preparation method of carboxylated sesbania oil-loaded nano-silica comprises the following steps: S1, mixing 100 parts by weight of sesbania oil and 100-150 parts by weight of xylene, adding 60-70 parts by weight of maleic anhydride and 0.5-1.0 parts by weight of p-toluenesulfonic acid, heating to 120-140° C. under nitrogen protection, stirring and reacting for 4-6 hours, cooling, washing, and evaporating to obtain carboxylated sesbania oil; S2, 10-20 parts by weight of ethyl orthosilicate and 30-80 parts by weight of ethanol are uniformly mixed, 80-100 parts by weight of carboxylated sesbania oil are added, and the mixture is stirred to form a mixed solution, water and ammonia water are then added dropwise, the pH is adjusted to 8-10, and the mixture is stirred for 1 hour to form a sol, which is reacted at 60-80°C for 12-24 hours, and then solidified, washed, and dried to obtain carboxylated sesbania oil-loaded nano-silica.

[0006] By adopting the above technical scheme, sesbania oil has high thermal stability and oxidation resistance and is easy to degrade in soil and water, is environmentally friendly and has good biodegradability, and has high surface activity, can reduce the oil-water interfacial tension, improve oil recovery efficiency, and is suitable for high-temperature and high-pressure oil production environments; and nano-silica has excellent hydrophobicity, which is conducive to adsorption on the oil-water interface. Its retention in the porous medium of the oil reservoir causes the increase of seepage resistance, injection pressure and suction pressure difference, expands the swept volume and thus improves the oil recovery rate; the present application uses natural sesbania oil as a raw material, and after carboxylation modification, the material formed by compounding with nano-silica has both the environmental friendliness of natural products and the advantages of the present invention. The good properties of the material and the special properties of the nanoparticles can achieve uniform loading of nano-silica, avoid the problem that the nanoparticles are very likely to agglomerate and lose their nano-properties during oil displacement, give full play to the oil displacement effect of the sesbania oil and nano-silica, improve the oil displacement efficiency of the oil displacement agent, and make it have good salt resistance and temperature stability during the oil displacement process, and be suitable for complex oil reservoir environments; at the same time, after the material is compounded with a surfactant, it can form an efficient oil displacement system at low concentration, which has both cost advantages and oil displacement efficiency; in addition, the oil displacement agent of the present application does not use partially hydrolyzed polyacrylamide and the basic material sesbania used has good biodegradability, realizing the organic unity of economy, effectiveness and green environmental protection performance.

[0007] Preferably, the preparation method of the sesbania oil comprises the following steps: (1) Screening sesbania seed waste, crushing it, and drying it to a constant weight to obtain sesbania powder; (2) Extracting the sesbania powder in supercritical CO2, vacuum drying, and filtering to obtain sesbania oil.

[0008] By adopting the above-mentioned technical solution, this application realizes the efficient extraction of sesbania oil under low temperature and high pressure environment through the high diffusivity and selective solubility characteristics of supercritical CO2, retains the unsaturated bonds and polar functional groups of sesbania oil, and provides high-quality raw materials for subsequent carboxylation and nano-silica loading.

[0009] Preferably, in S1, the acid value of the carboxylated sesbania oil is 350-400 mgKOH / g.

[0010] By adopting the above technical solution, optimizing the acid value can directly affect the oil displacement efficiency by regulating the interfacial bonding strength between carboxyl groups and nano-silica, the interfacial activity, and the rheological properties of the oil displacement agent system. When the acid value is too low, the carboxyl groups have insufficient binding sites with silica, resulting in poor nanoparticle dispersion and a small reduction in interfacial tension, which limits the improvement in the oil displacement efficiency and sweep coefficient of the oil displacement agent. When the acid value is too high, the excessive density of carboxyl groups may cause nanoparticle agglomeration. At the same time, excessive carboxyl groups are prone to ion shielding effects in high-salt oil reservoir environments, weakening the salt resistance and viscoelasticity of the oil displacement agent. Studies have shown that when the acid value is controlled at 350-400 mgKOH / g, the oil displacement agent can not only form a stable covalent-electrostatic complex with silica through carboxyl groups, reducing the oil-water interfacial tension, but also use the hydrophilicity of carboxyl groups to regulate the system mobility and expand the sweep volume, thereby improving the oil displacement efficiency in heat-resistant and salt-tolerant oil reservoir environments and achieving an optimal balance between interfacial activity and stability.

[0011] Preferably, the composite surfactant is a mixture of a fatty acid methyl ester sulfonate surfactant and an amphoteric surfactant with an isoelectric point pH=6.5-7.5 in a mass ratio of 1-3:1.

[0012] By adopting the above technical solution, fatty acid methyl ester sulfonate (MES) is a non-toxic, harmless, degradable bio-based surfactant with excellent environmental properties. When it is compounded with amphoteric surfactants, in terms of charge characteristics, the amphoteric agent in the isoelectric point range is electrically neutral or weakly anionic in the common pH environment of oil reservoirs, and has weak electrostatic repulsion with the anionic groups of MES, avoiding precipitation and forming stable mixed micelles, and reducing the critical micelle concentration; in terms of interfacial performance, the synergistic effect of the two reduces interfacial tension, and constructs a dense and fluid interfacial film through hydrophobic interactions and hydrogen bonds, reducing crude oil stripping resistance and reducing residual oil saturation; in terms of environmental adaptability, the charge shielding and micelle reconstruction capabilities of the amphoteric agent improve the salt resistance and stability of the compound system under high salinity, comprehensively achieving improved oil displacement efficiency and optimized recovery rate.

[0013] The present application uses carboxylated sesbania oil loaded with nano-silica and compounded with fatty acid methyl ester sulfonate and amphoteric surfactant with isoelectric point pH=6.5-7.5 as an oil field displacement agent, and multiple synergistic mechanisms significantly improve the oil displacement efficiency; the hydroxyl groups on the surface of the nano-silica form hydrogen bonds and covalent bonds with the carboxyl groups of the carboxylated sesbania oil, constructing a "nanoparticle-polymer" stable network, enhancing the viscosity of the system, and effectively regulating the mobility ratio; the high specific surface area of the nano-silica adsorbs MES and amphoteric surfactant molecules, increasing the interfacial adsorption amount, forming a "nanoparticle-surfactant" composite adsorption layer, and reducing the interfacial tension; the carboxyl groups of the carboxylated sesbania oil and the polar groups of the amphoteric surfactant stabilize the micelle structure through electrostatic interaction, and at the same time, the steric hindrance effect of the nano-silica inhibits micelle aggregation, thereby reducing the critical micelle concentration; ultimately, through the synergistic effect of "viscosity regulation-interface strengthening-micelle stabilization-salt resistance enhancement", the crude oil recovery rate is improved.

[0014] Preferably, the preparation method of the fatty acid methyl ester sulfonate surfactant comprises the following steps: Step 1: Mix fatty acid methyl ester and diethanolamine, add sodium hydroxide, heat to 110-130° C. for reaction for 4-6 hours, and then evaporate to dryness and cool to obtain fatty acid alkanolamide; the molar ratio of fatty acid methyl ester to diethanolamine is 1:1.2-1.3; the amount of sodium hydroxide added is 0.5%-1% of the mass of the fatty acid methyl ester; Step 2: dissolving propane sultone in tetrahydrofuran, adding fatty acid alkanolamide and sodium hydroxide, heating to reflux temperature, stirring and reacting for 12-16 hours, and rotary evaporating to dryness and cooling to obtain a fatty acid methyl ester sulfonate surfactant; the molar ratio of the fatty acid alkanolamide to propane sultone is 1.02-1.05:1.2-1.3; and the amount of sodium hydroxide added is 1%-1.5% of the mass of the fatty acid alkanolamide.

[0015] By adopting the above technical scheme, the surfactant synthesized in the present application is a biomass surfactant, which is non-toxic, harmless, and degradable, and has little damage to the environment and the formation, thereby achieving the goal of comprehensive resource utilization of urban food waste; at the same time, the synthesis reaction conditions are mild, the preparation process is simple, and the process is reasonable, which is suitable for large-scale production.

[0016] Preferably, the structural formula of the fatty acid methyl ester is C n H 2n+1 COOCH3, n=11-18.

[0017] By adopting the above technical solution, the molecular structure of the surfactant has a great influence on the interfacial tension of the oil-water mixture, and the length of the base chain in the surfactant molecular structure will also affect its oil displacement effect. The longer the base chain, the smaller the interfacial tension generated after adding it to the oil-water mixture. However, as the base chain length increases, the interfacial tension will increase again. It can be considered that in order for the surfactant to play the role of reducing the interfacial tension of the oil-water mixture to the greatest extent, there is a critical value for the number of carbon atoms on the base chain in its molecular structure. When the number of carbon atoms on the base chain is greater than this critical value, the base chain will interfere with the interaction between the surfactant and water, thereby reducing the degree of reduction in interfacial tension, that is, reducing the deoiling effect of the surfactant. Therefore, when using surfactant flooding technology to improve crude oil recovery, it is generally more important to control the number of carbon atoms on the base chain in the molecular structure of the surfactant added to the oil-water mixture.

[0018] Preferably, the fatty acid methyl ester is methyl laurate, methyl myristate, methyl palmitate or methyl stearate.

[0019] Preferably, the amphoteric surfactant is sulfobetaine.

[0020] By adopting the above technical solution, betaine-type amphoteric surfactants can be dissolved in acidic, neutral and alkaline aqueous solutions, and there is no precipitation even at the isoelectric point; among them, sulfobetaine has the advantages of mild performance, easy biodegradation, strong calcium soap dispersibility, high interfacial activity, and resistance to hard water and high concentrations of acid and alkali. At the same time, sulfobetaine itself has a certain viscoelasticity, which can help reduce the water-oil mobility ratio. At the same time, when it is combined with fatty acid methyl ester sulfonate surfactants, no chromatographic separation occurs.

[0021] Preferably, the synthesis method of the sulfobetaine adopts a two-step method: in the first step, a carbonyl compound and dimethylamine are used to synthesize an intermediate N,N-dimethylalkyl tertiary amine under the action of a reducing agent; in the second step, the intermediate undergoes a quaternization reaction to generate the target product sulfobetaine; the carbonyl compound is a C12-C14 aldehyde or ketone.

[0022] By adopting the above technical solution, N,N-dimethylalkyl tertiary amine is an important intermediate for the synthesis of betaine. The synthesis of N,N-dimethylalkyl tertiary amine by carbonyl reduction method is not only economical and environmentally friendly, but also has relatively mild reaction conditions, does not require heating, and can be reacted at room temperature. It also has a high yield and is a green and non-toxic reaction.

[0023] Preferably, the composite surfactant further includes an alcohol auxiliary, and the alcohol auxiliary is one of isopropyl alcohol, tert-hexanol and n-butanol.

[0024] By adopting the above technical solution, an alcohol additive is added as a co-surfactant to the surfactant. After the alcohol additive is added to the oil-water mixture along with the surfactant, the alcohol molecules in the additive can reduce the surface charge of the oil-water mixture. After the surface charge of the oil-water mixture is reduced, it needs to regain a stable equilibrium state, at which point the surfactant will continue to decompose and release its charge. This continued decomposition of the surfactant improves the efficiency of the surfactant, enhancing its performance and increasing oil recovery efficiency. The alcohol additive can also reduce the viscosity of the oil-water mixture, reduce the abrasive resistance of the rock pores to the oil-water mixture, and reduce the energy loss of the oil-water mixture during migration. Therefore, selecting the right alcohol additive can better utilize the performance of the surfactant and improve the oil recovery efficiency of surfactant flooding technology.

[0025] In summary, this application has the following beneficial effects: 1. The material formed by the present application by using natural sesbania oil as raw material and modifying it by carboxylation and then compounding it with nano-silica has both the environmental friendliness of natural products and the special properties of nanoparticles, which can achieve uniform loading of nano-silica, avoid the problem that nanoparticles easily agglomerate and lose their nano-properties during oil displacement, give full play to the oil displacement effect of sesbania oil and nano-silica, and improve the oil displacement efficiency of the oil displacement agent; at the same time, the basic material sesbania used in the oil displacement agent of the present application has good biodegradability, realizing the organic unity of economy, effectiveness and green environmental protection performance.

[0026] 2. This application uses carboxylated sesbania oil-loaded nano-silica as a compound with fatty acid methyl ester sulfonate and an amphoteric surfactant with an isoelectric point of pH = 6.5-7.5 as an oil field flooding agent, and improves crude oil recovery through the synergistic effect of "viscosity regulation-interface strengthening-micelle stabilization-salt resistance enhancement".

[0027] 3. The composite surfactant of the present application also includes an alcohol adjuvant, which can better exert the performance of the surfactant and improve the oil displacement efficiency of the surfactant flooding technology. DETAILED DESCRIPTION

[0028] The present application is further described in detail below with reference to the embodiments.

[0029] Unless otherwise specified, the raw materials used in the preparation examples, embodiments and comparative examples of this application are all commercially available.

[0030] Preparation Example 1-3 Carboxylated Sesbania oleifera oil loaded with nano-silica Preparation Example 1 This preparation example discloses a method for preparing carboxylated sesbania oil-loaded nano-silica, which specifically comprises the following steps: (1) After removing impurities from the sesbania seed waste, crush it on a grinder and dry it at 55°C to constant weight to obtain particles with an average particle size of 150 μm. Put 30 g of the crushed particles into the extraction kettle and seal the kettle body; open the CO2 cylinder and fill it with CO2 at a rate of 5 MPa / min to a system pressure of 1 MPa. Maintain it for 5 minutes and then empty it. Repeat this three times to exhaust the air in the kettle; start the high-pressure pump to increase the pressure of the liquid CO2 to 28 MPa. At the same time, the preheater is heated to 42°C to make the CO2 reach a supercritical state. Adjust the CO2 flow rate to 12 L / h and maintain it for 30 minutes. The supercritical CO2 flows through the extraction kettle, dissolves the oil and fat, and then enters the separation kettle; collect the oil and fat in the separation kettle every 15 minutes until the extraction time reaches 75 minutes; the extracted oil and fat is treated in a vacuum drying oven at 40°C and a vacuum degree of -0.09 MPa for 1 hour, and filtered through a 0.45 μm filter membrane to obtain sesbania oil and fat; (2) 10 g of sesbania oil and 10 g of xylene were mixed evenly, and then 6 g of maleic anhydride and 0.05 g of p-toluenesulfonic acid were added. The temperature was raised to 120 ° C under nitrogen protection, stirred for reaction for 2 h, and then raised to 140 ° C for reaction for 2 h. After the reaction, the reaction solution was quickly cooled to room temperature in an ice-water bath, washed twice with 5 wt% sodium carbonate solution, and then washed with deionized water until neutral. The water was removed by centrifugation, and the residue was distilled under reduced pressure at a vacuum degree of -0.05 MPa and a temperature of 60 ° C. The residue was washed twice with petroleum ether and dried in vacuum to obtain carboxylated sesbania oil; 1 g of carboxylated sesbania oil was weighed, dissolved in neutral ethanol-ether, and titrated with 0.1 mol / L KOH. The calculated acid value was 335.8 mg KOH / g; (3) 3 g of ethanol was mixed with 1 g of TEOS, and the mixture was stirred magnetically for 10 min. 8 g of molten hydroxylated sesbania oil was added and stirred at 300 r / min for 20 min to form a mixed solution. Water and ammonia water with a volume ratio of 3:1 were mixed and added to the mixed solution at a rate of 1 drop / s, while maintaining a stirring rate of 400 r / min. The pH of the system was adjusted to 8, and the mixture was placed in a water bath and heated to 60 °C. The reaction was carried out for 24 h to form a gel, and the mixture was allowed to stand for aging at 70 °C for 12 h. The mixture was then washed three times with 100 mL of an ethanol-water mixture with a volume ratio of 7:3, and dried at a vacuum degree of -0.09 MPa and 60 °C to constant weight to obtain carboxylated sesbania oil-loaded nanosilica.

[0031] Preparation Example 2 This preparation example discloses a method for preparing carboxylated sesbania oil-loaded nano-silica, which specifically comprises the following steps: (1) After removing impurities from the sesbania seed waste, crush it on a grinder and dry it at 55°C to constant weight to obtain particles with an average particle size of 150 μm. Put 30 g of the crushed particles into the extraction kettle and seal the kettle body; open the CO2 cylinder and fill it with CO2 at a rate of 5 MPa / min to a system pressure of 1 MPa. Maintain it for 5 minutes and then empty it. Repeat this three times to exhaust the air in the kettle; start the high-pressure pump to increase the pressure of the liquid CO2 to 28 MPa. At the same time, the preheater is heated to 42°C to make the CO2 reach a supercritical state. Adjust the CO2 flow rate to 12 L / h and maintain it for 30 minutes. The supercritical CO2 flows through the extraction kettle, dissolves the oil and fat, and then enters the separation kettle; collect the oil and fat in the separation kettle every 15 minutes until the extraction time reaches 75 minutes; the extracted oil and fat is treated in a vacuum drying oven at 40°C and a vacuum degree of -0.09 MPa for 1 hour, and filtered through a 0.45 μm filter membrane to obtain sesbania oil and fat; (2) 10 g of sesbania oil was mixed evenly with 13 g of xylene, and then 6.5 g of maleic anhydride and 0.08 g of p-toluenesulfonic acid were added. The temperature was raised to 120 ° C under nitrogen protection, and the mixture was stirred for reaction for 2 h. The temperature was then raised to 140 ° C for reaction for 3 h. After the reaction, the reaction solution was quickly cooled to room temperature in an ice-water bath, washed twice with 5 wt% sodium carbonate solution, and then washed with deionized water until neutral. The water was removed by centrifugation, and the mixture was distilled under reduced pressure at a vacuum degree of -0.05 MPa and a temperature of 60 ° C. The residue was washed twice with petroleum ether and dried under vacuum to obtain carboxylated sesbania oil. 1 g of carboxylated sesbania oil was weighed, dissolved in neutral ethanol-ether, and titrated with 0.1 mol / L KOH. The calculated acid value was 380.2 mg KOH / g. (3) 6 g of ethanol was mixed with 1.5 g of TEOS, and the mixture was stirred magnetically for 10 min. 9 g of molten hydroxylated sesbania oil was added and stirred at 300 r / min for 20 min to form a mixed solution. Water and ammonia water with a volume ratio of 3:1 were mixed and added to the mixed solution at a rate of 1 drop / s, while maintaining a stirring rate of 400 r / min. The pH of the system was adjusted to 9, and the mixture was placed in a water bath and heated to 70 °C. The reaction was carried out for 18 h to form a gel, and the mixture was allowed to stand for aging at 70 °C for 12 h. The mixture was then washed three times with 100 mL of an ethanol-water mixture with a volume ratio of 7:3, and dried at a vacuum degree of -0.09 MPa and 60 °C to constant weight to obtain carboxylated sesbania oil-loaded nanosilica.

[0032] Preparation Example 3 This preparation example discloses a method for preparing carboxylated sesbania oil-loaded nano-silica, which specifically comprises the following steps: (1) After removing impurities from the sesbania seed waste, crush it on a grinder and dry it at 55°C to constant weight to obtain particles with an average particle size of 150 μm. Put 30 g of the crushed particles into the extraction kettle and seal the kettle body; open the CO2 cylinder and fill it with CO2 at a rate of 5 MPa / min to a system pressure of 1 MPa. Maintain it for 5 minutes and then empty it. Repeat this three times to exhaust the air in the kettle; start the high-pressure pump to increase the pressure of the liquid CO2 to 28 MPa. At the same time, the preheater is heated to 42°C to make the CO2 reach a supercritical state. Adjust the CO2 flow rate to 12 L / h and maintain it for 30 minutes. The supercritical CO2 flows through the extraction kettle, dissolves the oil and fat, and then enters the separation kettle; collect the oil and fat in the separation kettle every 15 minutes until the extraction time reaches 75 minutes; the extracted oil and fat is treated in a vacuum drying oven at 40°C and a vacuum degree of -0.09 MPa for 1 hour, and filtered through a 0.45 μm filter membrane to obtain sesbania oil and fat; (2) 10 g of sesbania oil was mixed with 15 g of xylene, and then 7 g of maleic anhydride and 0.1 g of p-toluenesulfonic acid were added. The mixture was heated to 120 °C under nitrogen protection, stirred for reaction for 3 h, and then heated to 140 °C for reaction for 3 h. After the reaction, the reaction solution was quickly cooled to room temperature in an ice-water bath, washed twice with 5 wt% sodium carbonate solution, and then washed with deionized water until neutral. The water was removed by centrifugation, and the mixture was distilled under reduced pressure at a vacuum degree of -0.05 MPa and a temperature of 60 °C. The residue was washed twice with petroleum ether and dried under vacuum to obtain carboxylated sesbania oil. 1 g of carboxylated sesbania oil was weighed, dissolved in neutral ethanol-ether, and titrated with 0.1 mol / L KOH. The calculated acid value was 420.5 mg KOH / g. (3) 8 mL of ethanol was mixed with 2 g of TEOS, and the mixture was stirred magnetically for 10 min. 10 g of molten hydroxylated sesbania oil was added and stirred at 300 r / min for 20 min to form a mixed solution. Water and ammonia water with a volume ratio of 3:1 were mixed and added to the mixed solution at a rate of 1 drop / s, while maintaining a stirring rate of 400 r / min. The pH of the system was adjusted to 10, and the mixture was placed in a water bath and heated to 80 °C. The reaction was carried out for 12 h to form a gel, and the mixture was allowed to stand for aging at 70 °C for 12 h. The mixture was then washed three times with 100 mL of an ethanol-water mixture with a volume ratio of 7:3, and dried at a vacuum degree of -0.09 MPa and 60 °C to constant weight to obtain carboxylated sesbania oil-loaded nanosilica.

[0033] Preparation Example 4-7 Composite Surfactant Preparation Example 4 This preparation example discloses a method for preparing a composite surfactant, which specifically comprises the following steps: (1) 0.1 mol of methyl myristate and 0.12 mol of diethanolamine were mixed in a three-necked flask equipped with a magnetic rotor, a condenser, and a thermometer. 0.12 g of sodium hydroxide was added to the three-necked flask, and the flask was placed in an oil bath and heated to 110°C. After stirring for 6 hours, the mixture was dried by rotary evaporation and cooled to obtain myristic acid alkanolamide. 0.12 mol of propane sultone was dissolved in 100 mL of tetrahydrofuran, and then 0.102 mol of myristic acid alkanolamide was added. After sufficient dissolution, the mixture was placed in a three-necked flask equipped with a magnetic rotor, a condenser, and a thermometer. 0.32 g of sodium hydroxide was added to the three-necked flask, and the mixture was heated to 66°C. After stirring for 16 hours, the mixture was dried by rotary evaporation and cooled to obtain myristic acid amide sulfonate surfactant. (2) Weigh 5 g of dodecanal into a three-necked flask, add 20 mL of a solution formed by methanol-water with a volume ratio of 3:1, start stirring, and slowly drop 4 mL of 30 wt% dimethylamine solution at 30 ° C using a dropping funnel. Adjust the pH of the system to 6 with acetic acid, then add 1.8 g of sodium cyanoborohydride, heat to 55 ° C and react for 7 h. Adjust the pH of the reaction solution to 10 with sodium hydroxide, separate the liquid and take the organic phase, remove the solvent by rotary evaporation, and obtain N, N-dimethyldodecyl tertiary amine; add 0.1 mol N, N-dimethyl Dodecyl tertiary amine was dissolved in 120 mL of a solution of isopropanol-water in a volume ratio of 2:1, and 0.1 g of calcium carbonate was added. The temperature was raised to 70°C with stirring, and 0.11 mol of propane sultone was added dropwise. During the addition, 1 mol / L HCl was used to maintain the pH of the system at 7. After the addition was completed, the temperature was kept at 70°C for 8 hours. The solvent was removed by rotary evaporation, and the product was dissolved in ethanol-water in a volume ratio of 4:1. The free sulfonate group was removed by a strong basic anion resin, and then recrystallized from acetone and dried in vacuo to obtain sulfobetaine. (3) 10 g of myristic acid amide sulfonate surfactant and 10 g of sulfobetaine were mixed to obtain a composite surfactant.

[0034] Preparation Example 5 This preparation example discloses a method for preparing a composite surfactant, which specifically comprises the following steps: (1) 0.1 mol of methyl laurate and 0.125 mol of diethanolamine were mixed in a three-necked flask equipped with a magnetic rotor, a condenser, and a thermometer. 0.19 g of sodium hydroxide was added to the three-necked flask, and the flask was placed in an oil bath and heated to 120°C. After stirring for 5 hours, the mixture was dried by rotary evaporation and cooled to obtain lauric acid alkanolamide. 0.125 mol of propane sultone was dissolved in 100 mL of tetrahydrofuran, and then 0.104 mol of lauric acid alkanolamide was added. After sufficient dissolution, the mixture was placed in a three-necked flask equipped with a magnetic rotor, a condenser, and a thermometer. 0.39 g of sodium hydroxide was added to the three-necked flask, and the mixture was heated to 66°C. After stirring for 14 hours, the mixture was dried by rotary evaporation and cooled to obtain lauramide sulfonate surfactant. (2) Weigh 5 g of dodecanal into a three-necked flask, add 20 mL of a solution formed by methanol-water with a volume ratio of 3:1, start stirring, and slowly drop 4 mL of 30 wt% dimethylamine solution at 30 ° C using a dropping funnel. Adjust the pH of the system to 6 with acetic acid, then add 1.8 g of sodium cyanoborohydride, heat to 55 ° C and react for 7 h. Adjust the pH of the reaction solution to 10 with sodium hydroxide, separate the liquid and take the organic phase, remove the solvent by rotary evaporation, and obtain N, N-dimethyldodecyl tertiary amine; add 0.1 mol N, N-dimethyl Dodecyl tertiary amine was dissolved in 120 mL of a solution of isopropanol-water in a volume ratio of 2:1, and 0.1 g of calcium carbonate was added. The temperature was raised to 70°C with stirring, and 0.11 mol of propane sultone was added dropwise. During the addition, 1 mol / L HCl was used to maintain the pH of the system at 7. After the addition was completed, the temperature was kept at 70°C for 8 hours. The solvent was removed by rotary evaporation, and the product was dissolved in ethanol-water in a volume ratio of 4:1. The free sulfonate group was removed by a strong basic anion resin, and then recrystallized from acetone and dried in vacuo to obtain sulfobetaine. (3) 10 g of lauramide sulfonate surfactant and 20 g of sulfobetaine were mixed to obtain a composite surfactant.

[0035] Preparation Example 6 This preparation example discloses a method for preparing a composite surfactant, which specifically comprises the following steps: (1) 0.1 mol of methyl stearate and 0.13 mol of diethanolamine were mixed in a three-necked flask equipped with a magnetic rotor, a condenser, and a thermometer. 0.24 g of sodium hydroxide was added to the three-necked flask, and the flask was placed in an oil bath and heated to 130°C. After stirring for 4 hours, the mixture was dried by rotary evaporation and cooled to obtain stearic acid alkanolamide. 0.105 mol of propane sultone was dissolved in 100 mL of tetrahydrofuran, and then 0.13 mol of stearic acid alkanolamide was added. After sufficient dissolution, the mixture was placed in a three-necked flask equipped with a magnetic rotor, a condenser, and a thermometer. 0.73 g of sodium hydroxide was added to the three-necked flask, and the mixture was heated to 66°C. After stirring for 12 hours, the mixture was dried by rotary evaporation and cooled to obtain stearic acid amine sulfonate surfactant. (2) Weigh 5 g of dodecanone in a three-necked flask, add 20 mL of a solution formed by methanol-water with a volume ratio of 3:1, start stirring, and slowly drop 6 mL of 30 wt% dimethylamine solution at 30 ° C using a dropping funnel. Adjust the pH of the system to 4 with acetic acid, then add 3.0 g of sodium cyanoborohydride, heat to 55 ° C and react for 7 h. Adjust the pH of the reaction solution to 10 with sodium hydroxide, separate the liquid and take the organic phase, remove the solvent by rotary evaporation, and obtain N, N-dimethyldodecyl tertiary amine; add 0.1 mol N, N-dimethyl Dodecyl tertiary amine was dissolved in 120 mL of a solution of isopropanol-water in a volume ratio of 2:1, and 0.1 g of calcium carbonate was added. The temperature was raised to 70°C with stirring, and 0.11 mol of propane sultone was added dropwise. During the addition, 1 mol / L HCl was used to maintain the pH of the system at 7. After the addition was completed, the temperature was kept at 70°C for 8 hours. The solvent was removed by rotary evaporation, and the product was dissolved in ethanol-water in a volume ratio of 4:1. The free sulfonate group was removed by a strong basic anion resin, and then recrystallized from acetone and dried in vacuo to obtain sulfobetaine. (3) 10 g of stearylamide sulfonate surfactant and 30 g of sulfobetaine were mixed to obtain a composite surfactant.

[0036] Preparation Example 7 This preparation example discloses a method for preparing a composite surfactant, which specifically comprises the following steps: (1) 0.1 mol of methyl laurate and 0.125 mol of diethanolamine were mixed in a three-necked flask equipped with a magnetic rotor, a condenser, and a thermometer. 0.19 g of sodium hydroxide was added to the three-necked flask, and the flask was placed in an oil bath and heated to 120°C. After stirring for 5 hours, the mixture was dried by rotary evaporation and cooled to obtain lauric acid alkanolamide. 0.125 mol of propane sultone was dissolved in 100 mL of tetrahydrofuran, and then 0.104 mol of lauric acid alkanolamide was added. After sufficient dissolution, the mixture was placed in a three-necked flask equipped with a magnetic rotor, a condenser, and a thermometer. 0.39 g of sodium hydroxide was added to the three-necked flask, and the mixture was heated to 66°C. After stirring for 14 hours, the mixture was dried by rotary evaporation and cooled to obtain lauramide sulfonate surfactant. (2) Weigh 5 g of dodecanal into a three-necked flask, add 20 mL of a solution formed by methanol-water with a volume ratio of 3:1, start stirring, and slowly drop 4 mL of 30 wt% dimethylamine solution at 30 ° C using a dropping funnel. Adjust the pH of the system to 6 with acetic acid, then add 1.8 g of sodium cyanoborohydride, heat to 55 ° C and react for 7 h. Adjust the pH of the reaction solution to 10 with sodium hydroxide, separate the liquid and take the organic phase, remove the solvent by rotary evaporation, and obtain N, N-dimethyldodecyl tertiary amine; add 0.1 mol N, N-dimethyl Dodecyl tertiary amine was dissolved in 120 mL of a solution of isopropanol-water in a volume ratio of 2:1, and 0.1 g of calcium carbonate was added. The temperature was raised to 70°C with stirring, and 0.11 mol of propane sultone was added dropwise. During the addition, 1 mol / L HCl was used to maintain the pH of the system at 7. After the addition was completed, the temperature was kept at 70°C for 8 hours. The solvent was removed by rotary evaporation, and the product was dissolved in ethanol-water in a volume ratio of 4:1. The free sulfonate group was removed by a strong basic anion resin, and then recrystallized from acetone and dried in vacuo to obtain sulfobetaine. (3) 10 g of lauramide sulfonate surfactant, 20 g of sulfobetaine and 3 g of isopropyl alcohol were mixed to obtain a composite surfactant.

[0037] Example 1 This embodiment provides an environmentally friendly oil-field flooding agent, comprising 70 g of carboxylated sesbania oil-loaded nano-silica and 30 g of a composite surfactant; Among them, the carboxylated sesbania oil-loaded nano-silica comes from Preparation Example 1, and the composite surfactant comes from Preparation Example 4.

[0038] Example 2 This embodiment provides an environmentally friendly oil-field flooding agent, comprising 80 g of carboxylated sesbania oil-loaded nano-silica and 20 g of a composite surfactant; Among them, the carboxylated sesbania oil-loaded nano-silica comes from Preparation Example 1, and the composite surfactant comes from Preparation Example 4.

[0039] Example 3 This embodiment provides an environmentally friendly oil-field flooding agent, comprising 90 g of carboxylated sesbania oil-loaded nano-silica and 10 g of a composite surfactant; Among them, the carboxylated sesbania oil-loaded nano-silica comes from Preparation Example 1, and the composite surfactant comes from Preparation Example 4.

[0040] Example 4 This embodiment provides an environmentally friendly oil-field flooding agent, comprising 80 g of carboxylated sesbania oil-loaded nano-silica and 20 g of a composite surfactant; Among them, the carboxylated sesbania oil-loaded nano-silica comes from Preparation Example 2, and the composite surfactant comes from Preparation Example 4.

[0041] Example 5 This embodiment provides an environmentally friendly oil-field flooding agent, comprising 80 g of carboxylated sesbania oil-loaded nano-silica and 20 g of a composite surfactant; Among them, the carboxylated sesbania oil-loaded nano-silica comes from Preparation Example 3, and the composite surfactant comes from Preparation Example 4.

[0042] Example 6 This embodiment provides an environmentally friendly oil-field flooding agent, comprising 80 g of carboxylated sesbania oil-loaded nano-silica and 20 g of a composite surfactant; Among them, the carboxylated sesbania oil-loaded nano-silica comes from Preparation Example 2, and the composite surfactant comes from Preparation Example 5.

[0043] Example 7 This embodiment provides an environmentally friendly oil-field flooding agent, comprising 80 g of carboxylated sesbania oil-loaded nano-silica and 20 g of a composite surfactant; Among them, the carboxylated sesbania oil-loaded nano-silica comes from Preparation Example 2, and the composite surfactant comes from Preparation Example 6.

[0044] Example 8 This embodiment provides an environmentally friendly oil-field flooding agent, comprising 80 g of carboxylated sesbania oil-loaded nano-silica and 20 g of a composite surfactant; Among them, the carboxylated sesbania oil-loaded nano-silica comes from Preparation Example 2, and the composite surfactant comes from Preparation Example 7.

[0045] Comparative Example 1 This comparative example provides an environmentally friendly oilfield flooding agent, comprising 70 g of partially hydrolyzed polyacrylamide and 30 g of a composite surfactant; Among them, the composite surfactant comes from Preparation Example 4.

[0046] Comparative Example 2 This comparative example provides an environmentally friendly oil-field flooding agent, comprising 70 g of sesbania oil, 10 g of nano-silica, and 20 g of a composite surfactant; Among them, the sesbania oil comes from Preparation Example 1, and the composite surfactant comes from Preparation Example 4.

[0047] Comparative Example 3 This comparative example provides an environmentally friendly oil-field flooding agent, comprising 70 g of carboxylated sesbania oil-loaded nano-silica and 30 g of myristic acid amide sulfonate surfactant; Among them, the carboxylated sesbania oil-loaded nano-silica comes from Preparation Example 1, and the myristic amide sulfonate surfactant comes from Preparation Example 4.

[0048] Comparative Example 4 This comparative example provides an environmentally friendly oil-field flooding agent, comprising 70 g of carboxylated sesbania oil loaded with nano-silica and 30 g of sulfobetaine; Among them, the carboxylated sesbania oil-loaded nano-silica comes from Preparation Example 1, and the sulfobetaine comes from Preparation Example 4.

[0049] Performance testing Testing standards: Degradability: The oil-displacing agents of each embodiment and comparative example were prepared with deionized water to prepare 500 mL of an oil-displacing agent solution with a mass concentration of 0.2 wt%, and 0.02 g of active enzyme was added to each solution. The solution was allowed to stand for 45 hours. The apparent viscosity of the solution under the action of the enzyme was measured. The test results are shown in Table 1.

[0050] Determination of interfacial tension: The oil-displacing agents of the examples and comparative examples were diluted with reinjection water to 0.3 wt %. The interfacial tension between the oil-displacing agents and the simulated oil at the same temperature was measured using a spinning drop interface. The measurement results are shown in Table 1.

[0051] Table 1 Performance test data of environmentally friendly oilfield displacement agents in Examples 1-8 and Comparative Examples 1-4

[0052] Combining Example 1 and Comparative Example 1 with reference to Table 1, it can be seen that the oil-displacing agent of the present application uses carboxylated sesbania oil loaded with nano-silica and a composite surfactant. Compared with the binary oil-displacing system composed of partially hydrolyzed polyacrylamide and a composite surfactant, it can better reduce the surface viscosity of the solution and has good biodegradability.

[0053] In combination with Example 1 and Comparative Example 2 and with reference to Table 1, it can be seen that the present application loads nano-silica into modified sesbania oil. On the one hand, sesbania oil has high thermal stability and antioxidant properties and is easily degraded in soil and water bodies, is environmentally friendly, and has good biodegradability. On the other hand, it has high surface activity, can reduce the oil-water interfacial tension, improve oil displacement efficiency, and is suitable for high temperature and high pressure oil extraction environments; and nano-silica has excellent hydrophobicity, which is conducive to adsorption at the oil-water interface. It is retained in the porous medium of the reservoir, causing an increase in seepage resistance, injection pressure and suction pressure differential, expanding the swept volume, and improving the oil displacement rate; the present application combines sesbania oil with nano-silica, uses modified oil as a dispersing carrier, introduces nano-silica into the gaps of the oil to achieve organic-inorganic hybridization, avoids the problem that nanoparticles are very likely to agglomerate and lose their nano characteristics during oil displacement, gives full play to the oil displacement effect of sesbania oil and nano-silica, and at the same time reduces the oil-water interfacial tension and improves the oil displacement efficiency of the oil displacement agent.

[0054] Combining Examples 6 and 8 with reference to Table 1, it can be seen that the present application improves the oil displacement effect of the oil displacement agent and reduces the oil-water interfacial tension by adding an alcohol adjuvant to the composite surfactant. Specifically, the alcohol molecules in the alcohol adjuvant can reduce the surface charge of the oil-water mixture. When the charge decreases, the system needs to return to a stable equilibrium state, which promotes the continued decomposition of the surfactant and the release of charge. The continued decomposition of the surfactant fully exposes its active sites, thereby improving the interfacial adsorption efficiency and enhancing the oil displacement performance. At the same time, the alcohol adjuvant can also reduce the viscosity of the oil-water mixture, reduce the abrasive resistance of the rock pores to the oil-water mixture, and reduce the energy loss of the oil-water mixture during migration.

[0055] Combining Example 1 and Comparative Examples 3-4 with reference to Table 1, it can be seen that the composite surfactant of the present application is formed by compounding a fatty acid methyl ester sulfonate surfactant and an amphoteric surfactant. This composite system can significantly improve the compatibility with the sesbania oil-modified nano-silica, enhance the interfacial film stability of the oil-displacing agent system, and thereby effectively reduce the oil-water interfacial tension.

[0056] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An environmentally friendly oil-field flooding agent, characterized in that: The method comprises the following raw materials in parts by weight: 70-90 parts of carboxylated sesbania oil-loaded nano-silica and 10-30 parts of a composite surfactant; The preparation method of carboxylated sesbania oil-loaded nano-silica comprises the following steps: S1, mixing 100 parts by weight of sesbania oil and 100-150 parts by weight of xylene, adding 60-70 parts by weight of maleic anhydride and 0.5-1.0 parts by weight of p-toluenesulfonic acid, heating to 120-140° C. under nitrogen protection, stirring and reacting for 4-6 hours, cooling, washing, and evaporating to obtain carboxylated sesbania oil; S2, 10-20 parts by weight of ethyl orthosilicate and 30-80 parts by weight of ethanol are uniformly mixed, 80-100 parts by weight of carboxylated sesbania oil are added, and the mixture is stirred to form a mixed solution, water and ammonia water are then added dropwise, the pH is adjusted to 8-10, and the mixture is stirred for 1 hour to form a sol, which is reacted at 60-80°C for 12-24 hours, and then solidified, washed, and dried to obtain carboxylated sesbania oil-loaded nano-silica.

2. The environmentally friendly oil-field displacing agent according to claim 1, characterized in that: The preparation method of the sesbania oil comprises the following steps: (1) Screening sesbania seed waste, crushing it, and drying it to a constant weight to obtain sesbania powder; (2) Extracting the sesbania powder in supercritical CO2, vacuum drying, and filtering to obtain sesbania oil.

3. The environmentally friendly oil-field displacing agent according to claim 1, characterized in that: In S1, the acid value of the carboxylated sesbania oil is 350-400 mgKOH / g.

4. The environmentally friendly oil-field displacing agent according to claim 1, characterized in that: The composite surfactant is a mixture of a fatty acid methyl ester sulfonate surfactant and an amphoteric surfactant with an isoelectric point pH of 6.5-7.5 in a mass ratio of 1-3:

1.

5. The environmentally friendly oil-field displacing agent according to claim 4, characterized in that: The preparation method of the fatty acid methyl ester sulfonate surfactant comprises the following steps: Step 1: Mix fatty acid methyl ester and diethanolamine, add sodium hydroxide, heat to 110-130° C. for reaction for 4-6 hours, and then evaporate to dryness and cool to obtain fatty acid alkanolamide; the molar ratio of fatty acid methyl ester to diethanolamine is 1:1.2-1.3; the amount of sodium hydroxide added is 0.5%-1% of the mass of the fatty acid methyl ester; Step 2: dissolving propane sultone in tetrahydrofuran, adding fatty acid alkanolamide and sodium hydroxide, heating to reflux temperature, stirring and reacting for 12-16 hours, and rotary evaporating to dryness and cooling to obtain a fatty acid methyl ester sulfonate surfactant; the molar ratio of the fatty acid alkanolamide to propane sultone is 1.02-1.05:1.2-1.3; and the amount of sodium hydroxide added is 1%-1.5% of the mass of the fatty acid alkanolamide.

6. The environmentally friendly oil-field displacing agent according to claim 5, characterized in that: The structural formula of the fatty acid methyl ester is C n H 2n+1 COOCH3, n=11-18.

7. The environmentally friendly oil-field displacing agent according to claim 6, characterized in that: The fatty acid methyl ester is methyl laurate, methyl myristate, methyl palmitate or methyl stearate.

8. The environmentally friendly oil-field displacing agent according to claim 4, characterized in that: The amphoteric surfactant is sulfobetaine.

9. The environmentally friendly oil-field displacing agent according to claim 8, characterized in that: The synthesis method of sulfobetaine adopts a two-step process: in the first step, a carbonyl compound and dimethylamine are used to synthesize an intermediate N,N-dimethylalkyl tertiary amine under the action of a reducing agent; in the second step, the intermediate undergoes a quaternization reaction to generate the target product sulfobetaine; the carbonyl compound is a C12-C14 aldehyde or ketone.

10. The environmentally friendly oil-field displacing agent according to claim 4, characterized in that: The composite surfactant further comprises an alcohol auxiliary agent, and the alcohol auxiliary agent is one of isopropyl alcohol, tert-hexyl alcohol and n-butanol.

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