Modified lignosulfonate surfactant and application thereof

Abstract

The invention discloses a modified lignosulfonate surfactant and application thereof, and belongs to the technical field of surfactant preparation.Dimethylaminopropylamine and lauroyl chloride are acylated to obtain an amide intermediate, then the amide intermediate and 2-bromoethyl acrylate are quaternized, a double-bond structure capable of participating in a free radical reaction is introduced, and the modified lignosulfonate surfactant is obtained. The preparation method comprises the following steps: adding alkyl amide quaternary ammonium salt containing double bonds to form alkyl amide quaternary ammonium salt containing double bonds, introducing the double bonds to subsequently realize free radical grafting with lignosulfonate and improve the structural stability and surface activity, and then grafting the quaternary ammonium salt containing double bonds to a lignosulfonate skeleton under the initiation of potassium persulfate to obtain the modified lignosulfonate surfactant. The obtained modified lignosulfonate surfactant is compounded with amphiphilic nano silicon dioxide and polyacrylamide to construct the oil displacement agent, and the oil displacement agent has better interface stability and higher displacement efficiency in a high-salt environment due to the overall synergistic effect.

Description

Technical Field

[0001] This invention belongs to the field of surfactant preparation technology, specifically a modified lignin sulfonate surfactant and its application. Background Technology

[0002] Lignosulfonates are a major byproduct of lignin processing in the pulp and paper industry. Their molecules contain aromatic rings, hydroxyl groups, carboxyl groups, and sulfonate groups, thus exhibiting certain hydrophobic, hydrophilic, and charge characteristics. Initially used primarily as dispersants, water-reducing agents, and binders, lignin sulfonates have been recognized for their anionic surfactant-like interfacial behavior. They can be adsorbed and diffused at the oil-water interface, demonstrating potential for interfacial regulation. Based on this interfacial activity, their applications have gradually expanded from traditional industrial additives to the petroleum extraction field, particularly showing new development potential in chemical enhanced oil recovery (CEM) technology.

[0003] In oil displacement applications, the interfacial activity, salt tolerance, and structural stability of natural lignin sulfonates remain limited. Therefore, existing research mainly focuses on enhancing their functionality through physical blending or composite methods, including the combined use of lignin sulfonates, alkyl sulfonates, nano-silica, and other controllable components to improve their interfacial adsorption strength, viscoelastic properties, and emulsifying ability. As a result, lignin sulfonate-based composite oil displacement agents have become an important development direction for improving the efficiency of chemical oil displacement agents.

[0004] In the prior art, Chinese patent announcement number CN119505855B discloses an oil displacement agent for petroleum development and its preparation method. It uses petroleum sulfonate and sodium lignosulfonate as a surfactant system, combined with nano-silica, polyacrylamide and hydrophilic and lipophilic nanoparticles to form a highly efficient oil displacement agent.

[0005] The above-mentioned schemes mainly rely on the physical compounding of petroleum sulfonates and sodium lignosulfonate to provide interfacial activity, primarily depending on linear alkyl sulfonates. However, single sulfonate groups are highly susceptible to increased ionic strength in high-salt environments. High-valence ions can also form ion pairs with sulfonate groups, causing partial dehydration and aggregation of the surfactant, leading to salting out and a loose interfacial film. Furthermore, the surfactant systems in these schemes lack orientably arranged grafted segments; the molecular arrangement at the oil-water interface relies more on the electrostatic interactions of single sulfonate groups. In high-salt environments, Na+... + Ca 2+ Mg 2+Plasma compresses the hydration shell on the surface of sulfonate, making it difficult to form a dense and stable interfacial film. In addition, nano-silica is more prone to agglomeration and desorption under high salt conditions. When used together, it reduces the interfacial bonding force. Therefore, this scheme is prone to problems such as interfacial instability and decreased displacement efficiency under high-salt reservoir conditions, which reduces the reservoir recovery rate. Summary of the Invention

[0006] The purpose of this invention is to provide a modified lignin sulfonate surfactant and its application. By designing an alkyl amide quaternary ammonium salt containing double bonds and modifying the lignin sulfonate by free radical grafting, a modified lignin sulfonate surfactant is obtained. At the same time, using the modified lignin sulfonate as the surfactant, amphiphilic nano-silica as the reinforcing filler, and polyacrylamide as the viscosity modifier, a composite oil displacement agent system with excellent interfacial stability and displacement efficiency is constructed, thereby significantly improving reservoir recovery.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A modified lignin sulfonate surfactant is prepared by the following steps:

[0009] Step 1: Dimethylaminopropylamine and dodecyl chloride are acylated in dichloromethane to generate an alkylamide intermediate. The obtained amide intermediate is then quaternized with 2-bromoethyl acrylate to introduce a double bond structure, yielding an alkylamide quaternary ammonium salt containing a double bond.

[0010] Step 2: Disperse lignin sulfonate and disodium ethylenediaminetetraacetate in deionized water, add potassium persulfate as an initiator and alkyl amide quaternary ammonium salt containing double bonds, and obtain modified lignin sulfonate surfactants through free radical graft polymerization.

[0011] Furthermore, the preparation process of the modified lignin sulfonate surfactant is as follows:

[0012] Lignosulfonate, deionized water, and disodium ethylenediaminetetraacetate were placed in a reaction vessel under a nitrogen atmosphere and stirred at 40-50°C for 20-40 min. Then, potassium persulfate and a double-bonded modified alkyl amide quaternary ammonium salt were added, and the mixture was reacted at 50-60°C for 4-6 h. After filtration and washing, the modified lignin sulfonate surfactant was obtained.

[0013] Furthermore, the mass ratio of lignin sulfonate, double-bond modified alkyl amide quaternary ammonium salt, disodium ethylenediaminetetraacetate, potassium persulfate, and deionized water is 20-30:20-30:1-2:1-2:80-120.

[0014] Furthermore, the preparation process of the double-bond modified alkylamide quaternary ammonium salt is as follows:

[0015] The amide intermediate and isopropanol were placed in a reaction vessel under nitrogen atmosphere and stirred at 50-60℃ for 20-40 min. 2-bromoethyl acrylate was added and reacted at 90-100℃ for 6-8 h. The product was then rotary evaporated, and the product was added to ethyl acetate to precipitate. The product was filtered and dried at low temperature to constant weight to obtain a double-bond modified alkyl amide quaternary ammonium salt.

[0016] Furthermore, the ratio of the amide intermediate, 2-bromoethyl acrylate, and isopropanol is 30-40g: 20-30g: 80-120mL.

[0017] Furthermore, the preparation process of the amide intermediate is as follows:

[0018] Dimethylaminopropylamine and dichloromethane were placed in a reaction vessel, and dodecyl chloride was added. The mixture was reacted at 40-60℃ for 4-6 hours. The mixture was extracted, the lower organic phase was collected, filtered, and rotary evaporated to obtain the amide intermediate.

[0019] Furthermore, the ratio of dimethylaminopropylamine, dodecyl chloride, and dichloromethane is 30-40g: 30-40g: 100-200mL.

[0020] This invention also provides the application of modified lignin sulfonate surfactants in oil displacement agents, and the preparation method of the oil displacement agent is as follows:

[0021] Amphiphilic nano-silica and deionized water are placed in a reaction vessel and stirred at 25-35℃ for 10-20 min. Then, modified lignin sulfonate surfactants are added and stirred for another 20-40 min. Polyacrylamide is then slowly added and stirred for 40-60 min. The mixture is then allowed to stand for 8-12 h to obtain the oil displacement agent.

[0022] Furthermore, the mass ratio of amphiphilic nano-silica, modified lignin sulfonate surfactant, polyacrylamide, and deionized water is 2-4:6-10:2-4:200-400.

[0023] Furthermore, the preparation process of amphiphilic nano-silica is as follows:

[0024] Gas-phase nano-silica, anhydrous ethanol, and deionized water were placed in a reaction vessel, and ammonia water with a concentration of 28%wt was added. After stirring at 25-35℃ for 20-40 min, amphiphilic silane was added, and the reaction was carried out at 70-80℃ for 4-6 h. The mixture was then filtered, washed, and vacuum dried to constant weight to obtain amphiphilic nano-silica.

[0025] Furthermore, the ratio of fumed nano-silica, amphiphilic silane, ammonia, anhydrous ethanol and deionized water is 10-20g: 4-6g: 0.5-1mL: 80-100mL: 8-10mL.

[0026] Furthermore, the preparation process of amphiphilic silanes is as follows:

[0027] A silane containing hydrophobic alkyl segments, sodium chloroethyl sulfonate, and anhydrous ethanol were placed in a reaction vessel and reacted at 70-80°C for 4-6 hours. The mixture was then filtered, washed, and vacuum dried to constant weight to obtain an amphiphilic silane.

[0028] Furthermore, the ratio of hydrophobic alkyl silane, sodium chloroethyl sulfonate, and anhydrous ethanol is 10-20g: 10-20g: 80-100mL.

[0029] Furthermore, the preparation process of silanes containing hydrophobic alkyl segments is as follows:

[0030] 3-Aminopropyltriethoxysilane, 1-bromohexane and anhydrous ethanol were placed in a reaction vessel and reacted at 70-80℃ for 5-6 hours. The mixture was then rotary evaporated to obtain a silane containing hydrophobic alkyl segments.

[0031] Furthermore, the ratio of 3-aminopropyltriethoxysilane, 1-bromohexane, and anhydrous ethanol is 20-30g: 20-30g: 100-120mL.

[0032] The beneficial effects of this invention are:

[0033] 1. The modified lignin sulfonate surfactant prepared in this invention simultaneously introduces long alkyl hydrophobic segments, quaternary ammonium salt cationic groups, and amide structures onto the lignin backbone, thereby forming a typical macromolecular amphiphilic structure. This allows it to be used effectively as a surfactant in oil displacement agents. The hydrophobic segments enhance its affinity in the oil phase, while the sulfonate and quaternary ammonium salt groups improve its solubility and interfacial migration ability in the aqueous phase, which is beneficial for achieving directional and tight adsorption at the oil-water interface. The quaternary ammonium salt cation can electrostatically adsorb acidic components, gums, and resins in crude oil, making the interfacial film more stable. The amide structure improves the toughness of the interfacial film through hydrogen bonding, thereby effectively inhibiting oil droplet aggregation and improving interfacial stability. In addition, the quaternary ammonium salt groups have good salt resistance and are not prone to desolvation or aggregation in high ionic strength environments. They can maintain the full extension of the molecular chain and interfacial activity, thus maintaining the stability of the interfacial film in salt solutions and improving the displacement efficiency of the oil displacement agent in high-salt environments.

[0034] 2. The amphiphilic nano-silica prepared in this invention introduces a structure on the particle surface where hydrophobic segments and hydrophilic silanols coexist through silanol condensation and silane coupling reactions. This gives it both oil-phase affinity and water-phase dispersibility. As a reinforcing filler in oil displacement agents, its hydrophobic segments can interact with hydrocarbons in crude oil, enhancing the anchoring ability of particles at the interface. The hydrophilic silanols form a stable hydration layer with the aqueous phase through hydrogen bonding and electrostatic interactions, inhibiting particle aggregation. Furthermore, in a salt solution environment, the amphiphilic structure avoids the defects of nano-silica that easily agglomerates, settles, and desorbs from the interface under high salt conditions. It maintains long-term stable dispersion under high ionic strength conditions, effectively enhancing the interfacial film strength. Thus, it can continuously maintain low interfacial tension in complex environments, significantly improving the oil displacement effect.

[0035] 3. The modified lignin sulfonate surfactant and amphiphilic nano-silica prepared in this invention can achieve synergistic assembly at the interface through hydrogen bonding and electrostatic interactions. The macromolecule provides a flexible and continuous interfacial film, while the nanoparticles provide a rigid supporting framework. Together, they construct a stable particle-reinforced interfacial film. Furthermore, the quaternary ammonium salt and sulfonate-formed electrolytic groups can maintain strong hydration capacity even in high-salt environments. When they are adsorbed onto the surface of amphiphilic nano-silica, they can form a stable hydration shell on the outer layer of the particles, blocking Ca2+. 2+ Mg 2+ High-valence ions approach the particle surface, ensuring the long-term dispersion of nanoparticles in high-salt solutions. The interfacial anchoring of the particles also prevents the desorption of dielectric groups in the brine, allowing the interfacial film to remain dense and tough under high-salt conditions. Through this synergistic mechanism, the prepared oil displacement agent achieves better interfacial stability and displacement efficiency in high-salt environments, thereby improving reservoir recovery. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1: This example provides a modified lignin sulfonate surfactant, prepared through the following steps:

[0038] S1: Place 30g of dimethylaminopropylamine and 100mL of dichloromethane in a reaction vessel, add 30g of dodecyl chloride, and react at 40℃ for 4h. After the reaction is completed, place the reaction solution in a separatory funnel, extract twice with 5%wt sodium bicarbonate solution and dichloromethane, collect the lower organic phase, filter to remove impurities, and rotary evaporate the filtrate until the solvent is completely removed to obtain the amide intermediate.

[0039] S2: Place 30g of amide intermediate and 80mL of isopropanol in a reaction vessel under nitrogen atmosphere protection, stir at 200r / min for 20min at 50℃, add 20g of 2-bromoethyl acrylate, react at 90℃ for 6h, after the reaction is completed, rotary evaporate until the solvent is completely removed, add the product to ethyl acetate to precipitate, filter, and dry the filter cake at 30℃ to constant weight to obtain double bond modified alkyl amide quaternary ammonium salt.

[0040] S3: Place 20g of lignin sulfonate, 80g of deionized water and 1g of disodium ethylenediaminetetraacetate in a reaction vessel under nitrogen atmosphere protection. Stir at 200r / min for 20min at 40℃. Then add 1g of potassium persulfate and 20g of double-bonded modified alkyl amide quaternary ammonium salt. React at 50℃ for 4h. After the reaction is completed, cool to room temperature, filter, and wash the filter cake twice with deionized water and anhydrous ethanol to obtain modified lignin sulfonate surfactant.

[0041] Example 2: This example provides a modified lignin sulfonate surfactant, prepared through the following steps:

[0042] S1: Place 35g of dimethylaminopropylamine and 150mL of dichloromethane in a reaction vessel, add 35g of dodecyl chloride, and react at 50℃ for 5h. After the reaction is completed, place the reaction solution in a separatory funnel, extract it three times with a 5%wt sodium bicarbonate solution and dichloromethane, collect the lower organic phase, filter to remove impurities, and rotary evaporate the filtrate until the solvent is completely removed to obtain the amide intermediate.

[0043] S2: 35g of amide intermediate and 100mL of isopropanol were placed in a reaction vessel under nitrogen atmosphere protection and stirred at 250r / min for 30min at 55℃. 25g of 2-bromoethyl acrylate was added and reacted at 95℃ for 7h. After the reaction was completed, the solvent was completely removed by rotary evaporation. The product was added to ethyl acetate to precipitate and filtered. The filter cake was dried at 40℃ to constant weight to obtain double bond modified alkyl amide quaternary ammonium salt.

[0044] S3: 25g of lignin sulfonate, 100g of deionized water and 1.5g of disodium ethylenediaminetetraacetate were placed in a reaction vessel under nitrogen atmosphere protection. After stirring at 250r / min for 30min at 45℃, 1.5g of potassium persulfate and 25g of double-bond modified alkyl amide quaternary ammonium salt were added. The reaction was carried out at 55℃ for 5h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with deionized water and anhydrous ethanol to obtain modified lignin sulfonate surfactant.

[0045] Example 3: This example provides a modified lignin sulfonate surfactant, prepared through the following steps:

[0046] S1: Place 40g of dimethylaminopropylamine and 200mL of dichloromethane in a reaction vessel, add 40g of dodecyl chloride, and react at 60℃ for 6h. After the reaction is completed, place the reaction solution in a separatory funnel, extract it 4 times with a 5%wt sodium bicarbonate solution and dichloromethane, collect the lower organic phase, filter to remove impurities, and rotary evaporate the filtrate until the solvent is completely removed to obtain the amide intermediate.

[0047] S2: 40g of amide intermediate and 120mL of isopropanol were placed in a reaction vessel under nitrogen atmosphere protection and stirred at 300r / min for 40min at 60℃. 30g of 2-bromoethyl acrylate was added and reacted at 100℃ for 8h. After the reaction was completed, the solvent was completely removed by rotary evaporation. The product was added to ethyl acetate to precipitate and filtered. The filter cake was dried at 50℃ to constant weight to obtain double bond modified alkyl amide quaternary ammonium salt.

[0048] S3: 30g of lignin sulfonate, 120g of deionized water and 2g of disodium ethylenediaminetetraacetate were placed in a reaction vessel under nitrogen atmosphere protection. After stirring at 300r / min for 40min at 50℃, 2g of potassium persulfate and 30g of double-bond modified alkylamide quaternary ammonium salt were added. The reaction was carried out at 60℃ for 6h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed 4 times with deionized water and anhydrous ethanol to obtain modified lignin sulfonate surfactant.

[0049] The modified lignin sulfonate surfactants prepared in Examples 1-3 above were obtained by reacting dimethylaminopropylamine with fatty acyl chloride to produce an amide intermediate with a long-chain alkyl and tertiary amine structure. Subsequently, the tertiary amine group in the amide underwent a quaternization substitution reaction with 2-bromoethyl acrylate to introduce an acrylate group with a carbon-carbon double bond, forming a quaternary ammonium salt monomer with a double bond. Finally, under the action of a free radical initiator, the double bond of the quaternary ammonium salt monomer was activated and underwent free radical grafting with the aromatic ring or side chain of the lignin sulfonate, thereby introducing a cationic amide quaternary ammonium side chain onto the lignin skeleton to obtain the modified lignin sulfonate.

[0050] Example 4: This example provides a modified lignin sulfonate surfactant and its application, prepared through the following steps:

[0051] Step 1: Place 20g of 3-aminopropyltriethoxysilane, 20g of 1-bromohexane and 100mL of anhydrous ethanol in a reaction vessel and react at 70℃ for 5h. After the reaction is completed, cool to room temperature and rotary evaporate until the solvent is completely removed to obtain a silane containing hydrophobic alkyl segments.

[0052] Step 2: Place 10g of silane containing hydrophobic alkyl segments, 10g of sodium chloroethyl sulfonate and 80mL of anhydrous ethanol in a reaction vessel and react at 70℃ for 4h. After the reaction is completed, cool to room temperature, filter, wash the filter cake twice with anhydrous ethanol, and dry under vacuum to constant weight to obtain amphiphilic silane.

[0053] Step 3: Place 10g of fumed nano silica, 80mL of anhydrous ethanol and 8mL of deionized water in a reaction vessel, add 0.5mL of 28%wt ammonia water, stir at 200r / min for 20min at 25℃, add amphiphilic silane, react at 70℃ for 4h, cool to room temperature after the reaction is completed, filter, wash the filter cake twice with deionized water and anhydrous ethanol, and vacuum dry to constant weight to obtain amphiphilic nano silica.

[0054] Step 4: Place 2g of amphiphilic nano-silica and 200g of deionized water in a reaction vessel, stir at 120r / min for 10min at 25℃, add 6g of the modified lignin sulfonate surfactant prepared in Example 1, continue stirring for 20min, then slowly add 2g of polyacrylamide, stir for 40min, and let stand for 8h to obtain the oil displacement agent.

[0055] Example 5: This example provides a modified lignin sulfonate surfactant and its application, prepared through the following steps:

[0056] Step 1: Place 25g of 3-aminopropyltriethoxysilane, 25g of 1-bromohexane and 110mL of anhydrous ethanol in a reaction vessel and react at 75℃ for 5.5h. After the reaction is completed, cool to room temperature and rotary evaporate until the solvent is completely removed to obtain a silane containing hydrophobic alkyl segments.

[0057] Step 2: Place 15g of hydrophobic alkyl chain silane, 15g of sodium chloroethyl sulfonate and 90mL of anhydrous ethanol in a reaction vessel and react at 75℃ for 5h. After the reaction is completed, cool to room temperature, filter, wash the filter cake three times with anhydrous ethanol, and vacuum dry to constant weight to obtain amphiphilic silane.

[0058] Step 3: Place 15g of fumed nano-silica, 90mL of anhydrous ethanol and 9mL of deionized water in a reaction vessel, add 0.8mL of 28%wt ammonia water, stir at 250r / min for 30min at 30℃, add amphiphilic silane, react at 75℃ for 5h, cool to room temperature after the reaction is completed, filter, wash the filter cake three times with deionized water and anhydrous ethanol, and vacuum dry to constant weight to obtain amphiphilic nano-silica.

[0059] Step 4: Place 3g of amphiphilic nano-silica and 300g of deionized water in a reaction vessel, stir at 130r / min for 15min at 30℃, add 8g of the modified lignin sulfonate surfactant prepared in Example 2, continue stirring for 30min, then slowly add 3g of polyacrylamide, stir for 50min, and let stand for 10h to obtain the oil displacement agent.

[0060] Example 6: This example provides a modified lignin sulfonate surfactant and its application, prepared through the following steps:

[0061] Step 1: Place 30g of 3-aminopropyltriethoxysilane, 30g of 1-bromohexane and 120mL of anhydrous ethanol in a reaction vessel and react at 80℃ for 6h. After the reaction is completed, cool to room temperature and rotary evaporate until the solvent is completely removed to obtain a silane containing hydrophobic alkyl segments.

[0062] Step 2: Place 20g of hydrophobic alkyl chain silane, 20g of sodium chloroethyl sulfonate and 100mL of anhydrous ethanol in a reaction vessel and react at 80℃ for 6h. After the reaction is completed, cool to room temperature, filter, wash the filter cake 4 times with anhydrous ethanol, and vacuum dry to constant weight to obtain amphiphilic silane.

[0063] Step 3: Place 20g of fumed nano-silica, 100mL of anhydrous ethanol and 10mL of deionized water in a reaction vessel, add 0.5-1mL of 28%wt ammonia water, stir at 300r / min for 40min at 35℃, then add amphiphilic silane, react at 80℃ for 6h, cool to room temperature after the reaction is completed, filter, wash the filter cake 4 times with deionized water and anhydrous ethanol, and vacuum dry to constant weight to obtain amphiphilic nano-silica.

[0064] Step 4: Place 4g of amphiphilic nano-silica and 400g of deionized water in a reaction vessel, stir at 150r / min for 20min at 35℃, add 10g of the modified lignin sulfonate surfactant prepared in Example 3, continue stirring for 40min, then slowly add 4g of polyacrylamide, stir for 60min, and let stand for 12h to obtain the oil displacement agent.

[0065] The oil displacement agents prepared in Examples 4-6 above were obtained by alkylating 3-aminopropyltriethoxysilane with bromohexane to obtain a silane intermediate with a distinct hydrophobic end structure. Subsequently, this intermediate was further substituted with sodium chloroethyl sulfonate containing sulfonate, so that one end of the molecule maintained a hydrophobic alkyl chain and the other end was introduced with a sulfonate group, thereby forming an amphiphilic silane monomer with both hydrophilic and hydrophobic structures. Then, in a system of nano-silica, water, alcohol and alkaline, the amphiphilic silane was introduced to undergo a hydrolysis-condensation reaction, so that the nano-silica acquired amphiphilic surface characteristics. Finally, using modified lignin sulfonate as a surfactant, amphiphilic nano-silica as an interface reinforcing filler, and polyacrylamide as a viscosity modifier, an oil displacement agent system was constructed by compounding.

[0066] Comparative Example 1: Based on Example 5, commercially available lignin sulfonate was used as the surfactant instead of the modified lignin sulfonate surfactant prepared in Example 2 in step four, while the other steps remained unchanged.

[0067] Comparative Example 2: Based on Example 5, commercially available fumed silica nanoparticles were used instead of the amphiphilic silica nanoparticles in step four, while the other steps remained unchanged.

[0068] Comparative Example 3: Based on Example 5, the amphiphilic nano-silica in step four was removed, while the remaining steps remained unchanged.

[0069] In the above examples and comparative examples, the purchased lignin sulfonate was produced by Shenyang Xingzhenghe Chemical Co., Ltd., named sodium lignin sulfonate, with CAS number 8061-51-6; the fumed silica nanoparticles were produced by Jinan Longcheng Organosilicon Co., Ltd., with a density of 2.2 g / cm³. 3 The polyacrylamide was produced by Zibo Lanerqing Polymer Materials Co., Ltd. It is an anionic type with an average molecular weight of 10 million.

[0070] The modified lignin sulfonate surfactants prepared in Examples 4-6 and Comparative Examples 1-3 and their applications were tested for performance. The test results are shown in Table 1.

[0071] Sample preparation: Referring to standard SY / T 5370-1999, oil displacement agent solutions with a mass fraction of 0.3% were prepared using distilled water and standard salt solution as base solutions. The salt solution was prepared according to the standard brine formula: NaCl:CaCl. 2： A standard salt solution with equal salinity was prepared by mixing MgCl2·6H2O in a ratio of 70:6:4. The oil used in the experiment was a simulated oil prepared by mixing crude oil from the same layer of the rock sample with neutral kerosene in a volume ratio of 1:1. The rock core used in the experiment was a natural rock core with a diameter of 25 mm and a length of 50-75 mm. After drying, vacuum saturation, replacement with simulated oil, and aging at reservoir temperature, it was used for oil displacement experiments.

[0072] Interfacial tension: Referring to standard SY / T 5370-1999, the interfacial tension between the oil displacement agent and the test oil in the two systems was determined by the rotating drop method. The smaller the interfacial tension, the better the interfacial stability.

[0073] Oil recovery rate: Referring to standard GB / T 28912-2012, an unsteady constant rate core displacement experiment was conducted. At 45℃, the core saturated with experimental oil and aged was displaced at a flow rate of 0.5 mL / min. The volume of experimental oil produced during the displacement process was recorded and statistically analyzed, and the oil recovery rate was calculated. The higher the oil recovery rate, the better the effect of the oil displacement agent.

[0074] Table 1. Test results of modified lignin sulfonate surfactants and their applications.

[0075]

[0076] As shown in Table 1, the interfacial stability and oil recovery rate of Examples 4-6 were superior to those of Comparative Examples 1-3. Furthermore, in the salt solution environment, the interfacial tension and oil recovery rate of Comparative Examples 1-3 were significantly reduced, indicating that using modified lignin sulfonate surfactants as surfactants can significantly reduce interfacial tension and improve interfacial stability. The introduced quaternary ammonium salt cationic groups can interact electrostatically with negatively charged acidic components, resins, and colloids in crude oil, making the interfacial film more compact and stable. The amide groups enhance the toughness of the interfacial film, making oil droplets easier to peel off and maintain dispersion. In the brine system, quaternary ammonium salts have good salt resistance, which can maintain molecular solubility and interfacial activity. At the same time, the amphiphilic nano-silica as filler can prevent particle aggregation caused by the salt system through its organic segments, thus maintaining high dispersibility and interfacial stability. Therefore, the synergistic effect of the two not only significantly reduces interfacial tension but also maintains structural stability under high salinity conditions, thereby achieving a sustained high oil recovery rate.

[0077] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A modified lignin sulfonate surfactant, characterized in that, It is prepared through the following steps: Step 1: Dimethylaminopropylamine and dodecyl chloride are acylated in dichloromethane to generate an alkylamide intermediate. The obtained amide intermediate is then quaternized with 2-bromoethyl acrylate to introduce a double bond structure, yielding an alkylamide quaternary ammonium salt containing a double bond. Step 2: Disperse lignin sulfonate and disodium ethylenediaminetetraacetate in deionized water, add potassium persulfate as an initiator and alkyl amide quaternary ammonium salt containing double bonds, and obtain modified lignin sulfonate surfactants through free radical graft polymerization.

2. The modified lignin sulfonate surfactant according to claim 1, characterized in that, The modified lignin sulfonate surfactant described in step two is prepared through the following steps: Lignosulfonate, deionized water and disodium ethylenediaminetetraacetate were placed in a reaction vessel under nitrogen atmosphere and stirred at 40-50℃ for 20-40 min. Then, potassium persulfate and double-bonded modified alkyl amide quaternary ammonium salt were added and reacted at 50-60℃ for 4-6 h. After filtration and washing, modified lignin sulfonate surfactants were obtained. The mass ratio of the lignin sulfonate, the double-bond modified alkylamide quaternary ammonium salt, the disodium ethylenediaminetetraacetate, the potassium persulfate, and the deionized water is 20-30:20-30:1-2:1-2:80-120.

3. The modified lignin sulfonate surfactant according to claim 2, characterized in that, The double-bond modified alkylamide quaternary ammonium salt is prepared by the following steps: The amide intermediate and isopropanol were placed in a reaction vessel under nitrogen atmosphere and stirred at 50-60℃ for 20-40 min. 2-bromoethyl acrylate was added and reacted at 90-100℃ for 6-8 h. The product was then rotary evaporated and added to ethyl acetate to precipitate the product. The product was filtered and dried at low temperature to constant weight to obtain a double-bond modified alkyl amide quaternary ammonium salt. The ratio of the amide intermediate, 2-bromoethyl acrylate, and isopropanol is 30-40g: 20-30g: 80-120mL.

4. The modified lignin sulfonate surfactant according to claim 3, characterized in that, The amide intermediate is prepared by the following steps: Dimethylaminopropylamine and dichloromethane were placed in a reaction vessel, dodecyl chloride was added, and the reaction was carried out at 40-60℃ for 4-6 hours. The mixture was extracted, the lower organic phase was collected, filtered, and rotary evaporated to obtain the amide intermediate. The ratio of dimethylaminopropylamine, dodecyl chloride, and dichloromethane is 30-40g: 30-40g: 100-200mL.

5. The application of the modified lignin sulfonate surfactant as described in any one of claims 1-4 in an oil displacement agent, characterized in that, The oil displacement agent is prepared by the following steps: Amphiphilic nano-silica and deionized water are placed in a reaction vessel and stirred at 25-35℃ for 10-20 min. Then, modified lignin sulfonate surfactants are added and stirred for another 20-40 min. Polyacrylamide is then slowly added and stirred for 40-60 min. The mixture is then allowed to stand for 8-12 h to obtain the oil displacement agent.

6. The application according to claim 5, characterized in that, The mass ratio of the amphiphilic nano-silica, modified lignin sulfonate surfactant, polyacrylamide, and deionized water is 2-4:6-10:2-4:200-400.

7. The application according to claim 6, characterized in that, The amphiphilic nano-silica is prepared by the following steps: Gas-phase nano-silica, anhydrous ethanol and deionized water were placed in a reaction vessel, and ammonia water with a concentration of 28%wt was added. After stirring at 25-35℃ for 20-40 min, amphiphilic silane was added, and the reaction was carried out at 70-80℃ for 4-6 h. The mixture was filtered, washed, and vacuum dried to constant weight to obtain amphiphilic nano-silica. The ratio of the amount of fumed nano-silica, amphiphilic silane, ammonia, anhydrous ethanol and deionized water is 10-20g: 4-6g: 0.5-1mL: 80-100mL: 8-10mL.

8. The application according to claim 7, characterized in that, The amphiphilic silane is prepared by the following steps: A silane containing hydrophobic alkyl segments, sodium chloroethyl sulfonate, and anhydrous ethanol were placed in a reaction vessel and reacted at 70-80℃ for 4-6 hours. The mixture was then filtered, washed, and vacuum dried to constant weight to obtain an amphiphilic silane. The ratio of the hydrophobic alkyl segment silane, sodium chloroethyl sulfonate, and anhydrous ethanol is 10-20g: 10-20g: 80-100mL.

9. The application according to claim 8, characterized in that, The hydrophobic alkyl segment silane is prepared by the following steps: 3-Aminopropyltriethoxysilane, 1-bromohexane and anhydrous ethanol were placed in a reaction vessel and reacted at 70-80℃ for 5-6 hours. The mixture was then rotary evaporated to obtain a silane containing hydrophobic alkyl segments.

10. The application according to claim 9, characterized in that, The ratio of 3-aminopropyltriethoxysilane, 1-bromohexane and anhydrous ethanol is 20-30g: 20-30g: 100-120mL.

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