Polymer surfactant, microemulsion for improving recovery ratio, and preparation method therefor

Abstract

A polymer surfactant, a microemulsion for improving the recovery ratio, and a preparation method therefor. The polymer surfactant comprises a structural unit derived from an asymmetric maleate, a structural unit derived from an acrylamide, and a structural unit derived from sodium allyl sulfonate. The microemulsion comprises the polymer surfactant, an oil, an alcohol, a co-surfactant and water. The microemulsion has good resistance to rock adsorption and temperature resistance.

Description

Polymer surfactants and microemulsions for enhanced oil recovery and their preparation methods Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to polymer surfactants and microemulsions for enhancing oil recovery, and methods for their preparation. Background Technology

[0002] The importance of unconventional oil and gas resources, such as shale oil and gas and tight oil and gas, has increased with the decline in conventional oil production. However, the complex rock properties, small pore throat size, inefficient sweep efficiency, heterogeneity, limited permeability, and low fluid flowability of unconventional reservoirs pose challenges to improving their recovery rates. Currently, microemulsions show great potential for enhancing reservoir oil and gas recovery.

[0003] EP3008283A1 discloses a method and composition for stimulating hydrocarbon production from underground formations, and US20210148203A1 discloses an allyl alcohol-based solubility enhancer for an aqueous surfactant used in enhanced oil recovery. Both technologies involve compositions containing water, a solvent, and a surfactant that form an emulsion or microemulsion in the formation. However, the adsorption of the surfactant in the rock can lead to inconsistent component ratios in the emulsion or microemulsion after injection into the formation. Furthermore, the temperature resistance of microemulsions used for enhanced oil recovery needs further improvement.

[0004] Therefore, existing microemulsions used to enhance oil recovery suffer from problems such as poor resistance to rock adsorption and / or poor temperature resistance. Summary of the Invention

[0005] To address at least one of the aforementioned technical problems, the present invention aims to provide a polymer surfactant and a method for preparing the same, as well as a microemulsion for enhancing oil recovery and a method for preparing the same. The microemulsion of the present invention exhibits good resistance to rock adsorption and temperature resistance.

[0006] To achieve the above objectives, a first aspect of the present invention provides a polymeric surfactant comprising: structural units derived from an asymmetric maleate, structural units derived from acrylamide, and structural units derived from sodium allyl sulfonate; wherein the asymmetric maleate comprises structural units derived from maleic anhydride, structural units derived from polyethylene glycol, and structural units derived from alkyl glycosides; and based on 100% of the total mass of the polymeric surfactant, the content of the structural units derived from the asymmetric maleate is 6-34%, the content of the structural units derived from acrylamide is 33-54%, and the content of the structural units derived from sodium allyl sulfonate is 33-40%.

[0007] According to a specific embodiment of the present invention, preferably, based on the total mass of the asymmetric maleic acid ester as 100%, the content of the structural units derived from maleic anhydride is 12-24%, the content of the structural units derived from polyethylene glycol is 34-38%, and the content of the structural units derived from alkyl glycosides is 41-50%.

[0008] According to a specific embodiment of the present invention, preferably, the structural unit derived from the asymmetric maleate has the structure shown in formula (I):

[0009] Where x = 1-10, m = 1.2-1.8, n = 3-10, and R is a C2-C12 alkyl group.

[0010] According to a specific embodiment of the present invention, preferably, the structural unit derived from acrylamide has the structure shown in formula (II):

[0011] Where y = 20 - 60.

[0012] According to a specific embodiment of the present invention, preferably, the structural unit derived from sodium allyl sulfonate has the structure shown in formula (III):

[0013] Where z = 5-15.

[0014] According to a specific embodiment of the present invention, preferably, the molecular weight of the polymer surfactant is 1500-16000.

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned polymeric surfactant, comprising the following steps:

[0016] (1) Maleic anhydride and polyethylene glycol are subjected to a first reaction in an organic solvent and in the presence of a catalyst under a protective gas environment to obtain a first reaction mixture system; the first reaction mixture system is mixed with an alkyl glycoside and subjected to a second reaction under a protective gas environment to obtain a second reaction mixture system; the second reaction mixture system is post-treated to obtain an asymmetric maleic acid ester.

[0017] (2) In a protective gas environment, the asymmetric maleate, acrylamide and sodium allyl sulfonate are subjected to a third reaction in water and in the presence of an initiator to obtain a third reaction post-mixture system; after post-treatment of the third reaction post-mixture system, the polymer surfactant is obtained.

[0018] According to a specific embodiment of the present invention, preferably, the catalyst comprises one or a combination of several of p-toluenesulfonic acid, titanium isopropoxide, and boric acid.

[0019] According to a specific embodiment of the present invention, preferably, the temperature of the first reaction is 95-120°C and the time is 8-12 hours.

[0020] According to a specific embodiment of the present invention, preferably, the temperature of the second reaction is 110-140°C and the time is 5-10 hours.

[0021] According to a specific embodiment of the present invention, preferably, the initiator includes one or a combination of several of the following: peroxide initiators, azo initiators, and redox initiators.

[0022] According to a specific embodiment of the present invention, preferably, the asymmetric maleate, acrylamide and sodium allyl sulfonate are mixed with water to obtain a system; a protective gas is introduced into the system at 0-5°C, then the pH value of the system is adjusted to 5-10, and then the initiator is added to carry out the third reaction.

[0023] According to a specific embodiment of the present invention, preferably, the temperature of the third reaction is 10-50°C and the time is 6-9 hours.

[0024] A third aspect of the present invention provides a microemulsion for enhancing oil recovery, comprising: the aforementioned polymeric surfactant, oil, alcohol, co-surfactant, and water; wherein, based on the total mass of the microemulsion for enhancing oil recovery as 100%, the content of the polymeric surfactant is 5%-15%, the content of the oil is 3%-10%, the content of the alcohol is 1%-8%, the content of the co-surfactant is 3%-15%, and the content of water is 52% or more.

[0025] According to a specific embodiment of the present invention, preferably, the oil includes one or a combination of several of the following: vegetable oil, mineral oil, silicone oil, limonene, and oleic acid.

[0026] According to a specific embodiment of the present invention, preferably, the alcohol includes C2-C10 alcohols.

[0027] According to a specific embodiment of the present invention, preferably, the co-surfactant includes one or a combination of several of alkyl sulfonates, alkylphenol polyoxyethylene ethers, alkenylphenol polyoxyethylene ethers, aryl alkenylphenol polyoxyethylene ethers, fatty alcohol polyoxyethylene ethers, alkylbenzene sulfonates, and alkyl sulfates.

[0028] According to a specific embodiment of the present invention, preferably, the D50 particle size of the microemulsion used to improve oil recovery is 9-100 nm.

[0029] A fourth aspect of the present invention provides a method for preparing the above-mentioned microemulsion for improving oil recovery, comprising the following steps:

[0030] A co-surfactant and water are mixed to form an aqueous phase; an oil, an alcohol, and a polymeric surfactant are mixed to form an oil phase; the aqueous phase and the oil phase are heated separately, and the oil phase is added dropwise to the aqueous phase under stirring conditions to obtain the microemulsion used to improve oil recovery.

[0031] The present invention has at least the following beneficial effects:

[0032] The polymer surfactant of this invention contains structural units derived from alkyl glycosides, as well as various groups such as polyoxyethylene, ester, sulfonic acid, and amide groups, which enhances the rock adsorption resistance, temperature resistance, and salt resistance of the microemulsion containing this polymer surfactant. Furthermore, the preparation method of the polymer surfactant of this invention has advantages such as environmental friendliness, easy control of reaction conditions, stable reaction process, and ease of industrialization. Additionally, the microemulsion of this invention is an oil-in-water type and has a spherical (or near-spherical) structure. This spherical structure provides steric hindrance, preventing the polymer surfactant and co-surfactant in the microemulsion from adsorbing onto the rock surface, thus improving the rock adsorption resistance of the microemulsion. Moreover, the interaction between the polymer surfactant in the oil phase and the co-surfactant in the aqueous phase of the microemulsion further enhances the rock adsorption resistance. Furthermore, the microemulsion of this invention has a small particle size, ensuring good injectability. Moreover, the microemulsion of this invention exhibits rapid biodegradation and excellent environmental friendliness. The microemulsion of the present invention can improve oil and gas recovery by changing the wettability of rock surfaces and reducing capillary resistance. It can be used as an oil displacement agent, especially suitable as an oil displacement agent for unconventional reservoirs. Attached Figure Description

[0033] Figure 1 shows the Fourier transform infrared spectrum of the polymer surfactant in Example 1.

[0034] Figure 2 is a transmission electron microscope image of the microemulsion in Example 1.

[0035] Figure 3 is a transmission electron microscope image of the microemulsion in Example 2.

[0036] Figure 4 is a transmission electron microscope image of the microemulsion in Example 3.

[0037] Figure 5 is a transmission electron microscope image of the microemulsion in Example 4.

[0038] Figure 6 is a transmission electron microscope image of the microemulsion in Example 5. Detailed Implementation

[0039] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the present invention will now be described in detail below, but this should not be construed as limiting the scope of the invention.

[0040] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0041] It should be noted that, unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0042] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0043] According to a specific embodiment of the first aspect of the present invention, the present invention provides a polymer surfactant comprising: structural units derived from an asymmetric maleate, structural units derived from acrylamide, and structural units derived from sodium allyl sulfonate; wherein the asymmetric maleate comprises structural units derived from maleic anhydride, structural units derived from polyethylene glycol, and structural units derived from alkyl glycosides; and based on 100% of the total mass of the polymer surfactant, the content of the structural units derived from the asymmetric maleate is 6-34%, the content of the structural units derived from acrylamide is 33-54%, and the content of the structural units derived from sodium allyl sulfonate is 33-40%.

[0044] In some embodiments, based on the total mass of the asymmetric maleic acid ester, the content of the structural units derived from maleic anhydride is 12-24%, the content of the structural units derived from polyethylene glycol is 34-38%, and the content of the structural units derived from alkyl glycosides is 41-50%.

[0045] In some embodiments, the structural unit derived from the asymmetric maleate ester has the structure shown in formula (I):

[0046] Where x = 1-10, m = 1.2-1.8, n = 3-10, and R is a C2-C12 alkyl group.

[0047] In some embodiments, the structural unit derived from acrylamide has the structure shown in formula (II):

[0048] Where y = 20 - 60.

[0049] In some embodiments, the structural unit derived from sodium allyl sulfonate has the structure shown in formula (III):

[0050] Where z = 5-15.

[0051] In some embodiments, the polymeric surfactant has the structure shown in formula (IV):

[0052] Where x = 1-10, y = 20-60, z = 5-15, m = 1.2-1.8, n = 3-10, and R is a C2-C12 alkyl group.

[0053] In some embodiments, the molecular weight of the polymer surfactant is 1500-16000; preferably, the molecular weight of the polymer surfactant is 5000-10000.

[0054] According to a specific embodiment of the second aspect of the present invention, the present invention provides a method for preparing the above-mentioned polymer surfactant, which includes the following steps:

[0055] (1) Maleic anhydride and polyethylene glycol are subjected to a first reaction in an organic solvent and in the presence of a catalyst under a protective gas environment to obtain a first reaction mixture system; the first reaction mixture system is mixed with an alkyl glycoside and subjected to a second reaction under a protective gas environment to obtain a second reaction mixture system; the second reaction mixture system is post-treated to obtain an asymmetric maleic acid ester.

[0056] (2) In a protective gas environment, the asymmetric maleate, acrylamide and sodium allyl sulfonate are subjected to a third reaction in water and in the presence of an initiator to obtain a third reaction post-mixture system; after post-treatment of the third reaction post-mixture system, the polymer surfactant is obtained.

[0057] In some embodiments, the mass ratio of the maleic anhydride, the polyethylene glycol, and the alkyl glycoside can be determined based on the above structural formula. Specifically, the mass ratio of the maleic anhydride, the polyethylene glycol, and the alkyl glycoside is 1:(1.5-3):(1.8-4).

[0058] In some embodiments, the catalyst includes, but is not limited to, one or a combination of several of p-toluenesulfonic acid, titanium isopropoxide, and boric acid.

[0059] In some embodiments, the amount of catalyst used may be 1%-8% of the total mass of the maleic anhydride and the polyethylene glycol.

[0060] In some embodiments, the organic solvent in step (1) includes, but is not limited to, toluene, benzene, and N,N-dimethylformamide.

[0061] In some embodiments, the amount of organic solvent used in step (1) can be 85%-95% of the total mass of the maleic anhydride and the polyethylene glycol.

[0062] In some embodiments, the temperature of the first reaction is 95-120°C and the time is 8-12 hours.

[0063] In some embodiments, the temperature of the second reaction is 110-140°C and the time is 5-10 hours.

[0064] In some embodiments, the post-treatment of the second reaction mixture system may include, but is not limited to, washing with organic solvents and rotary evaporation. The organic solvents used include, but are not limited to, at least one of acetone, methanol, ethanol, and petroleum ether.

[0065] In some embodiments, the mass ratio of the asymmetric maleate, the acrylamide, and the sodium allyl sulfonate can be determined based on the above structural formula. Specifically, the mass ratio of the asymmetric maleate, the acrylamide, and the sodium allyl sulfonate is 1:(1-8):(1-6).

[0066] In some embodiments, the mass ratio of the amount of water used in step (2) to the total amount of the asymmetric maleate, the acrylamide and the sodium allyl sulfonate can be (14-25):(3-15).

[0067] In some embodiments, the initiator includes, but is not limited to, one or more combinations of peroxide initiators, azo initiators, and redox initiators. Specifically, the peroxide initiator includes, but is not limited to, one or more combinations of potassium persulfate, sodium persulfate, and hydrogen peroxide. The azo initiator includes, but is not limited to, one or more combinations of 2,2'-azobis[2-(2-imidazoline-2-yl)propane] dihydrochloride, azobis(2,5-dimethyl-6-carboxy)hexanonitrile, 4,4'-azobis(4-cyanopentanoic acid), azobisisobutamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobisisopropylimidazoline hydrochloride, and azobisisopropylimidazoline. The oxidizing agent in the redox initiator includes, but is not limited to, one or more combinations of potassium persulfate, sodium persulfate, and hydrogen peroxide, and the reducing agent includes, but is not limited to, one or more combinations of sodium bisulfite, sodium thiosulfate, and sodium metabisulfite.

[0068] In some embodiments, the amount of the initiator may be 0.01-0.05% of the total mass of the asymmetric maleate, the acrylamide, and the sodium allyl sulfonate.

[0069] In some embodiments, the asymmetric maleate, acrylamide, and sodium allyl sulfonate are mixed with water to obtain a system; a protective gas is introduced into the system at 0-5°C, and then the pH of the system is adjusted to 5-10, followed by the addition of the initiator to carry out the third reaction. The reagents used to adjust the pH can be conventional acids and / or bases, such as hydrochloric acid and / or sodium hydroxide.

[0070] In some embodiments, the temperature of the third reaction is 10-50°C and the time is 6-9 hours.

[0071] In some embodiments, post-treatment of the mixture system following the third reaction includes, but is not limited to, organic solvent precipitation, solid-liquid separation, drying, and pulverization. The organic solvents used include, but are not limited to, at least one of acetone, methanol, ethanol, and petroleum ether.

[0072] According to a specific embodiment of the present invention, the present invention also provides a polymer surfactant prepared by the above-described method for preparing polymer surfactants.

[0073] According to a specific embodiment of a third aspect of the present invention, the present invention provides a microemulsion for enhancing oil recovery, comprising: the aforementioned polymeric surfactant, oil, alcohol, co-surfactant, and water; wherein, based on the total mass of the microemulsion for enhancing oil recovery being 100%, the content of the polymeric surfactant is 5%-15%, the content of the oil is 3%-10%, the content of the alcohol is 1%-8%, the content of the co-surfactant is 3%-15%, and the content of water is 52% or more.

[0074] In some embodiments, the oil includes, but is not limited to, one or a combination of several of vegetable oils, mineral oils, silicone oils, limonene, and oleic acid. Specifically, the oil includes, but is not limited to, one or a combination of several of liquid paraffin, limonene, and oleic acid.

[0075] In some embodiments, the alcohol includes, but is not limited to, C2-C10 alcohols. Specifically, the alcohol includes, but is not limited to, isopropanol and / or n-butanol.

[0076] In some embodiments, the co-surfactant includes, but is not limited to, one or a combination of several of alkyl sulfonates, alkylphenol polyoxyethylene ethers, alkenylphenol polyoxyethylene ethers, aryl alkenylphenol polyoxyethylene ethers, fatty alcohol polyoxyethylene ethers, alkylbenzene sulfonates, and alkyl sulfates. Specifically, the co-surfactant includes, but is not limited to, one or a combination of several of sodium dodecyl sulfonate, styrene-phenol polyoxyethylene ether, sodium dodecylbenzene sulfonate, and sodium dodecyl sulfate.

[0077] In some embodiments, the microemulsion for enhancing oil recovery further comprises salt, wherein the salt content is 0.1-5% based on 100% of the total weight of the microemulsion for enhancing oil recovery.

[0078] In some embodiments, the salt includes, but is not limited to, sodium chloride and / or potassium chloride.

[0079] In some embodiments, the microemulsion used to enhance oil recovery has a D50 particle size of 9-100 nm.

[0080] In some embodiments, the droplets of the microemulsion used to enhance oil recovery are spherical.

[0081] In some embodiments, the microemulsion used to enhance oil recovery is an oil displacement agent.

[0082] According to a specific embodiment of the fourth aspect of the present invention, the present invention provides a method for preparing the above-described microemulsion for improving oil recovery, comprising the following steps:

[0083] A co-surfactant and water are mixed to form an aqueous phase; an oil, an alcohol, and a polymeric surfactant are mixed to form an oil phase; the aqueous phase and the oil phase are heated separately, and the oil phase is added dropwise to the aqueous phase under stirring conditions to obtain the microemulsion used to improve oil recovery.

[0084] In some embodiments, the aqueous phase and the oil phase are heated to a temperature of 40-60°C.

[0085] The technical solutions of the present invention are specifically illustrated below through embodiments, but the present invention is not limited to these embodiments. Of course, various modifications can be made within the scope of the key points of the present invention.

[0086] Test method:

[0087] The content of structural units derived from asymmetric maleate, acrylamide, sodium allyl sulfonate, maleic anhydride, polyethylene glycol, and alkyl glycosides was determined using a Bruker AVANCE 400 superconducting nuclear magnetic resonance spectrometer. 1 The test was performed using 1H-NMR with a sample tube diameter of 5 mm, deuterated water as the solvent, a sample concentration of 15% (W / V), room temperature (23±2℃), and 16 scans. The chemical shift of tetramethylsilane was 0 ppm for calibration.

[0088] The calculation methods for the content of structural units derived from maleic anhydride, polyethylene glycol, and alkyl glycosides are as follows: A peak at approximately 6.49 ppm can be considered the chemical shift of the -CH=CH- hydrogen atom on the maleic anhydride structural unit in the asymmetric maleic ester; a peak at approximately 6.15 ppm can be considered the chemical shift of the CH-O-COO- hydrogen atom on the alkyl glycoside structural unit in the asymmetric maleic ester; and a peak at approximately 4.32 ppm can be considered the chemical shift of the -O-CH2-CH2-O- hydrogen atom on the polyethylene glycol structural unit in the asymmetric maleic ester. The signal peak area integrals corresponding to the structural units derived from maleic anhydride, alkyl glycosides, and polyethylene glycol are S, P, and Q, respectively. The mass ratio of structural units derived from maleic anhydride, structural units derived from alkyl glycosides, and structural units derived from polyethylene glycol is (S / 2 × molar mass of maleic anhydride structural unit): (P × molar mass of alkyl glycoside structural unit): (Q / 2 × molar mass of polyethylene glycol structural unit). The content of structural units derived from maleic anhydride = (S / 2 × molar mass of maleic anhydride structural unit) / [(S / 2 × molar mass of maleic anhydride structural unit) + (P × molar mass of alkyl glycoside structural unit) + (Q / 2 × molar mass of polyethylene glycol structural unit)]; the content of structural units derived from alkyl glycoside = (P × molar mass of alkyl glycoside structural unit) / [(S / 2 × molar mass of maleic anhydride structural unit) + (P × molar mass of alkyl glycoside structural unit) + (Q / 2 × molar mass of polyethylene glycol structural unit)]; the content of structural units derived from polyethylene glycol = (Q / 2 × molar mass of polyethylene glycol structural unit) / [(S / 2 × molar mass of maleic anhydride structural unit) + (P × molar mass of alkyl glycoside structural unit) + (Q / 2 × molar mass of polyethylene glycol structural unit)].

[0089] The calculation methods for the content of structural units derived from asymmetric maleate, acrylamide, and sodium allyl sulfonate are as follows: A peak at approximately 6.15 ppm can be considered the chemical shift of the CH-O-COO- hydrogen atom on the alkyl glycoside structural unit in the polymer surfactant; a peak at approximately 6.00 ppm can be considered the chemical shift of the -NH2 hydrogen atom on the acrylamide structural unit in the polymer surfactant; and a peak at approximately 3.24-3.49 ppm can be considered the chemical shift of the -CH-O-COO- hydrogen atom on the sodium allyl sulfonate structural unit in the polymer surfactant. 2-Chemical shift of the S-hydrogen atom. The signal peak area integrals corresponding to the structural units from alkyl glycosides, acrylamide, and sodium allyl sulfonate are W, X, and Y, respectively. The mass ratio of the structural units from asymmetric maleate, acrylamide, and sodium allyl sulfonate is (W × molar mass of asymmetric maleate): (X / 2 × molar mass of acrylamide): (Y / 2 × molar mass of sodium allyl sulfonate). The content of structural units derived from asymmetric maleate esters = (W × molar mass of asymmetric maleate ester structural unit) / [(W × molar mass of asymmetric maleate ester structural unit) + (X / 2 × molar mass of acrylamide structural unit) + (Y / 2 × molar mass of sodium allyl sulfonate structural unit)]; the content of structural units derived from acrylamide = (X / 2 × molar mass of acrylamide structural unit) / [(W × molar mass of asymmetric maleate ester structural unit) + (X / 2 × molar mass of acrylamide structural unit) + (Y / 2 × molar mass of sodium allyl sulfonate structural unit)]; the content of structural units derived from sodium allyl sulfonate = (Y / 2 × molar mass of sodium allyl sulfonate structural unit) / [(W × molar mass of asymmetric maleate ester structural unit) + (X / 2 × molar mass of acrylamide structural unit) + (Y / 2 × molar mass of sodium allyl sulfonate structural unit)]. Molecular weight of polymer surfactants: Analyzed using a MALDI-TOF MS instrument with α-cyano-4-hydroxycinnamic acid as the matrix and Nd:YAG laser in reflectance mode and negative ion mode. The mass-to-charge ratio (m / z) of the molecular ion peak in the obtained spectrum is [relative molecular weight MH of the polymer]. - The mass-to-charge ratio + 1 represents the molecular weight of the polymer surfactant.

[0090] The structure of the polymer surfactant was determined using a FT-IR2000 leaf Fourier transform infrared spectrometer via the KBr tableting method.

[0091] D50 particle size of microemulsion: After staining the microemulsion with phosphotungstic acid, images of the microemulsion were acquired using transmission electron microscopy, and the D50 particle size of the microemulsion was obtained after data processing.

[0092] The sources of raw materials in the following examples and comparative examples:

[0093] Maleic anhydride, polyethylene glycol, alkyl glycosides, p-toluenesulfonic acid, toluene, sodium allyl sulfonate, acrylamide, azobisisobutylimidazoline hydrochloride, 2,2'-azobis[2-(2-imidazoline-2-yl)propane] dihydrochloride, 4,4'-azobis(4-cyanovaleric acid), azobis(2,5-dimethyl-6-carboxy)hexanolynitrile, azobisisopropylimidazoline hydrochloride: from Shanghai Maclean Biochemical Technology Co., Ltd.;

[0094] Liquid paraffin, limonene, oleic acid, isopropanol, n-butanol, sodium dodecyl sulfonate, styrene-phenol polyoxyethylene ether, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate: from Sinopharm Chemical Reagent Co., Ltd.

[0095] Example 1

[0096] Preparation of polymer surfactants:

[0097] 3.5 g of maleic anhydride, 9 g of toluene, 6 g of polyethylene glycol (n = 8, molecular weight 370 g / mol), and 0.5 g of p-toluenesulfonic acid were placed in a dry round-bottom flask equipped with a reflux condenser and a nitrogen inlet. The mixture was heated to 110 °C under a nitrogen atmosphere and stirred with a magnetic stirrer. After 8 hours of reaction, a first reaction mixture was obtained. 7.5 g of alkyl glycoside (R = C8H17, m = 1.4) was added to the first reaction mixture, and the mixture was heated to 140 °C under a nitrogen atmosphere and stirred with a magnetic stirrer. After 5 hours of reaction, a second reaction mixture was obtained. The second reaction mixture was washed three times with 10 mL of petroleum ether each time, and then rotary evaporated to obtain an asymmetric maleate ester.

[0098] 1.4 g of asymmetric maleate, 7.8 g of sodium allyl sulfonate, and 10.4 g of acrylamide were added to 20 g of deionized water to obtain a monomer mixture system. The monomer mixture system was placed in a constant temperature water bath at 0 °C and stirred while nitrogen gas was introduced into the monomer mixture system. Then, the pH value of the monomer mixture system was adjusted to 7 using sodium hydroxide. 0.005 g of azobisisobutylimidazoline hydrochloride was added, and the mixture was reacted at 50 °C for 6 hours to obtain a third reaction mixture system. The third reaction mixture system was precipitated with acetone, filtered, and the solid product obtained after filtration was dried and pulverized to obtain a polymer surfactant.

[0099] The Fourier transform infrared spectrum of the polymer surfactant in this embodiment is shown in Figure 1. In Figure 1, at 3455 cm⁻¹... - 1 The absorption peak is due to the stretching vibration of the hydroxyl group O—H; 3248 cm⁻¹ -1 The absorption peak is for the stretching vibration of the NH group of the amide group; 2817 cm⁻¹ -1 The absorption peak is due to the stretching vibration of C—H; 1614 cm⁻¹ -1 The absorption peak is for the stretching vibration of C=O; 1117 cm⁻¹ -1 The absorption peak is for the stretching vibration of the ether group C—O—C; 723 cm⁻¹ -1 The alkyl group in the alkyl glycoside is alkyl-(CH2). a-(a>4) plane rocking vibration absorption peak; 510cm -1 This is the absorption peak of the stretching vibration of CS in sulfonic acid groups.

[0100] Based on the above characterization data, it can be determined that the polymer surfactant of this embodiment includes structural units derived from asymmetric maleate, structural units derived from acrylamide, and structural units derived from sodium allyl sulfonate; wherein, the asymmetric maleate includes structural units derived from maleic anhydride, structural units derived from polyethylene glycol, and structural units derived from alkyl glycosides. Based on the total mass of the polymer surfactant as 100%, the content of structural units derived from asymmetric maleate is 7.14%, the content of structural units derived from acrylamide is 53.06%, and the content of structural units derived from sodium allyl sulfonate is 39.8%. Based on the total mass of the asymmetric maleate as 100%, the content of structural units derived from maleic anhydride is 20.6%, the content of structural units derived from polyethylene glycol is 35.3%, and the content of structural units derived from alkyl glycosides is 44.1%.

[0101] The mass-to-charge ratio (m / z) of the mass spectrum peaks of the polymer surfactant in this embodiment is shown in Table 1. The mass-to-charge ratio in Table 1 plus 1 is the molecular weight of the polymer surfactant.

[0102] The structural unit derived from the asymmetric maleate has the structure shown in formula (I):

[0103] Where x = 1 - 3, m = 1.4, n = 8, and R is C8H17.

[0104] The structural unit derived from acrylamide has the structure shown in formula (II):

[0105] Where y = 55 - 60.

[0106] The structural unit derived from sodium allyl sulfonate has the structure shown in formula (III):

[0107] Where z = 12-15.

[0108] Preparation of microemulsions:

[0109] 1.2g sodium dodecyl sulfonate and 10g deionized water were mixed and stirred for 30 min to form an aqueous phase; 1.5g limonene and 1g n-butanol were mixed, and then 1.5g of the polymer surfactant of this embodiment was added and stirred for 30 min to form an oil phase; the aqueous phase and the oil phase were heated to 60°C respectively, and the oil phase was added dropwise to the aqueous phase under stirring conditions. After cooling to room temperature, a microemulsion was obtained.

[0110] Figure 2 shows the transmission electron microscope (TEM) image of the microemulsion from this embodiment after phosphotungstic acid staining. As can be seen from Figure 2, the droplets of the microemulsion in this embodiment are distributed as discrete nanospheres. The D50 particle size of the microemulsion in this embodiment is approximately 20 nm.

[0111] Example 2

[0112] Preparation of polymer surfactants:

[0113] 3 g of maleic anhydride, 6.38 g of toluene, 4.5 g of polyethylene glycol (n = 6, molecular weight 282 g / mol), and 0.075 g of p-toluenesulfonic acid were placed in a dry round-bottom flask equipped with a reflux condenser and a nitrogen inlet. The mixture was heated to 95 °C under a nitrogen atmosphere and stirred with a magnetic stirrer. After 8 hours of reaction, a first reaction mixture was obtained. 5.4 g of alkyl glycoside (R = C6H13, m = 1.2) was added to the first reaction mixture, and the mixture was heated to 110 °C under a nitrogen atmosphere and stirred with a magnetic stirrer. After 5 hours of reaction, a second reaction mixture was obtained. The second reaction mixture was washed three times with 10 mL of methanol each time, and then rotary evaporated to obtain an asymmetric maleate ester.

[0114] 2g of asymmetric maleate, 2g of sodium allyl sulfonate, and 2g of acrylamide were added to 28g of deionized water to obtain a monomer mixture system. The monomer mixture system was placed in a constant temperature water bath at 2°C and stirred while nitrogen gas was introduced into the monomer mixture system. Then, the pH value of the monomer mixture system was adjusted to 5 using sodium hydroxide, and 0.001g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride was added. The mixture was then reacted at 10°C for 9 hours to obtain a third reaction mixture system. The third reaction mixture system was precipitated with acetone, filtered, and the solid product obtained after filtration was dried and pulverized to obtain a polymer surfactant.

[0115] The absorption peak assignments of the Fourier transform infrared spectra of the polymer surfactant in this embodiment are shown in Table 1 below.

[0116] Based on the characterization data in Table 1, the polymer surfactant of this embodiment can be determined to include: structural units derived from asymmetric maleate, structural units derived from acrylamide, and structural units derived from sodium allyl sulfonate; wherein, the asymmetric maleate includes structural units derived from maleic anhydride, structural units derived from polyethylene glycol, and structural units derived from alkyl glycosides. Based on the total mass of the polymer surfactant as 100%, the content of the structural units derived from asymmetric maleate is 33.4%, the content of the structural units derived from acrylamide is 33.3%, and the content of the structural units derived from sodium allyl sulfonate is 33.3%. Based on the total mass of the asymmetric maleate as 100%, the content of the structural units derived from maleic anhydride is 23.2%, the content of the structural units derived from polyethylene glycol is 34.9%, and the content of the structural units derived from alkyl glycosides is 41.9%. The structural units derived from asymmetric maleate have the structure shown in structural formula (I), wherein x = 4-6, m = 1.2, n = 6, and R is C6H13. The structural unit derived from acrylamide has the structure shown in structural formula (II), wherein y = 40-50. The structural unit derived from sodium allyl sulfonate has the structure shown in structural formula (III), wherein z = 10-12.

[0117] The mass-to-charge ratio (m / z) of the mass spectrum peaks of the polymer surfactant in this embodiment is shown in Table 1. The mass-to-charge ratio in Table 1 plus 1 is the molecular weight of the polymer surfactant.

[0118] Preparation of microemulsions:

[0119] 0.54 g of styrene-based phenol polyoxyethylene ether and 15.84 g of deionized water were mixed and stirred for 30 min to form an aqueous phase. 0.54 g of liquid paraffin and 0.18 g of isopropanol were mixed, and then 0.9 g of the polymer surfactant of this embodiment was added. The mixture was stirred for 30 min to form an oil phase. The aqueous phase and the oil phase were heated to 50 °C respectively. Under stirring conditions, the oil phase was added dropwise to the aqueous phase. After cooling to room temperature, a microemulsion was obtained.

[0120] The transmission electron microscope (TEM) image of the microemulsion of this embodiment after phosphotungstic acid staining is shown in Figure 3. The D50 particle size of the microemulsion of this embodiment is approximately 24.6 nm.

[0121] Example 3

[0122] Preparation of polymer surfactants:

[0123] 3.5 g of maleic anhydride, 9.312 g of toluene, 6.3 g of polyethylene glycol (n = 4, molecular weight 194 g / mol), and 0.294 g of p-toluenesulfonic acid were placed in a dry round-bottom flask equipped with a reflux condenser and a nitrogen inlet. The mixture was heated to 100 °C under a nitrogen atmosphere and stirred with a magnetic stirrer. After reacting for 10 hours, a first reaction mixture was obtained. 7.1 g of alkyl glycoside (R = C4H9, m = 1.2) was added to the first reaction mixture, and the mixture was heated to 120 °C under a nitrogen atmosphere and stirred with a magnetic stirrer. After reacting for 7 hours, a second reaction mixture was obtained. The second reaction mixture was washed three times with 10 mL of ethanol each time, and then rotary evaporated to obtain an asymmetric maleate ester.

[0124] 1.5 g of asymmetric maleate, 4.5 g of sodium allyl sulfonate, and 6 g of acrylamide were added to 30 g of deionized water to obtain a monomer mixture system. The monomer mixture system was placed in a constant temperature water bath at 3 °C and stirred while nitrogen gas was introduced into the monomer mixture system. Then, the pH value of the monomer mixture system was adjusted to 6 using sodium hydroxide, and 0.0012 g of 4,4'-azobis(4-cyanopentanoic acid) was added. The mixture was then reacted at 30 °C for 7 hours to obtain a third reaction mixture system. The third reaction mixture system was precipitated with acetone, filtered, and the solid product obtained after filtration was dried and pulverized to obtain a polymer surfactant.

[0125] The absorption peak assignments of the Fourier transform infrared spectra of the polymer surfactant in this embodiment are shown in Table 1 below.

[0126] Based on the characterization data in Table 1, the polymer surfactant of this embodiment can be determined to include: structural units derived from asymmetric maleate, structural units derived from acrylamide, and structural units derived from sodium allyl sulfonate; wherein, the asymmetric maleate includes structural units derived from maleic anhydride, structural units derived from polyethylene glycol, and structural units derived from alkyl glycosides. Based on the total mass of the polymer surfactant as 100%, the content of the structural units derived from asymmetric maleate is 12.5%, the content of the structural units derived from acrylamide is 50%, and the content of the structural units derived from sodium allyl sulfonate is 37.5%. Based on the total mass of the asymmetric maleate as 100%, the content of the structural units derived from maleic anhydride is 20.7%, the content of the structural units derived from polyethylene glycol is 37.3%, and the content of the structural units derived from alkyl glycosides is 42%. The structural units derived from asymmetric maleate have the structure shown in structural formula (I), wherein x = 3-5, m = 1.2, n = 4, and R is C4H9. The structural unit derived from acrylamide has the structure shown in structural formula (II), wherein y = 50-55. The structural unit derived from sodium allyl sulfonate has the structure shown in structural formula (III), wherein z = 8-10.

[0127] The mass-to-charge ratio (m / z) of the mass spectrum peaks of the polymer surfactant in this embodiment is shown in Table 1. The mass-to-charge ratio in Table 1 plus 1 is the molecular weight of the polymer surfactant.

[0128] Preparation of microemulsions:

[0129] 0.8 g of sodium dodecylbenzenesulfonate and 12.8 g of deionized water were mixed and stirred for 30 min to form an aqueous phase; 0.8 g of oleic acid and 0.32 g of isopropanol were mixed, and then 1.28 g of the polymer surfactant of this embodiment was added and stirred for 30 min to form an oil phase; the aqueous phase and the oil phase were heated to 40 °C respectively, and the oil phase was added dropwise to the aqueous phase under stirring conditions. After cooling to room temperature, a microemulsion was obtained.

[0130] The transmission electron microscope (TEM) image of the microemulsion of this embodiment after phosphotungstic acid staining is shown in Figure 4. The D50 particle size of the microemulsion of this embodiment is approximately 22.3 nm.

[0131] Example 4

[0132] Preparation of polymer surfactants:

[0133] 3 g of maleic anhydride, 8.1 g of toluene, 6.5 g of polyethylene glycol (n = 10, molecular weight 458 g / mol), and 0.54 g of p-toluenesulfonic acid were placed in a dry round-bottom flask equipped with a reflux condenser and a nitrogen inlet. The mixture was heated to 115 °C under a nitrogen atmosphere and stirred with a magnetic stirrer. After reacting for 11 hours, a first reaction mixture was obtained. 9 g of alkyl glycoside (R = C3H7, m = 1.6) was added to the first reaction mixture, and the mixture was heated to 130 °C under a nitrogen atmosphere and stirred with a magnetic stirrer. After reacting for 9 hours, a second reaction mixture was obtained. The second reaction mixture was washed three times with 10 mL of methanol each time, and then rotary evaporated to obtain an asymmetric maleate ester.

[0134] 1.5 g of asymmetric maleate, 7.5 g of sodium allyl sulfonate, and 10.5 g of acrylamide were added to 33 g of deionized water to obtain a monomer mixture system. The monomer mixture system was placed in a constant temperature water bath at 4 °C and stirred while nitrogen gas was introduced into the monomer mixture system. Then, the pH value of the monomer mixture system was adjusted to 8 using sodium hydroxide. 0.007 g of azobis(2,5-dimethyl-6-carboxy)hexanonitrile was added, and the mixture was reacted at 40 °C for 8 hours to obtain a third reaction mixture system. The third reaction mixture system was precipitated with acetone, filtered, and the solid product obtained after filtration was dried and pulverized to obtain a polymer surfactant.

[0135] The absorption peak assignments of the Fourier transform infrared spectra of the polymer surfactant in this embodiment are shown in Table 1 below.

[0136] Based on the characterization data in Table 1, the polymer surfactant of this embodiment can be determined to include: structural units derived from asymmetric maleate, structural units derived from acrylamide, and structural units derived from sodium allyl sulfonate; wherein, the asymmetric maleate includes structural units derived from maleic anhydride, structural units derived from polyethylene glycol, and structural units derived from alkyl glycosides. Based on the total mass of the polymer surfactant as 100%, the content of the structural units derived from asymmetric maleate is 7.7%, the content of the structural units derived from acrylamide is 53.8%, and the content of the structural units derived from sodium allyl sulfonate is 38.5%. Based on the total mass of the asymmetric maleate as 100%, the content of the structural units derived from maleic anhydride is 16.2%, the content of the structural units derived from polyethylene glycol is 35.1%, and the content of the structural units derived from alkyl glycosides is 48.7%. The structural units derived from asymmetric maleate have the structure shown in structural formula (I), wherein x = 1-2, m = 1.6, n = 10, and R is C3H7. The structural unit derived from acrylamide has the structure shown in structural formula (II), wherein y = 45-50. The structural unit derived from sodium allyl sulfonate has the structure shown in structural formula (III), wherein z = 8-10.

[0137] The mass-to-charge ratio (m / z) of the mass spectrum peaks of the polymer surfactant in this embodiment is shown in Table 1. The mass-to-charge ratio in Table 1 plus 1 is the molecular weight of the polymer surfactant.

[0138] Preparation of microemulsions:

[0139] 2.4 g of sodium dodecyl sulfate and 12.6 g of deionized water were mixed and stirred for 30 min to form an aqueous phase. 1.6 g of liquid paraffin and 1 g of n-butanol were mixed, and then 2.4 g of the polymer surfactant of this embodiment was added. The mixture was stirred for 30 min to form an oil phase. The aqueous phase and the oil phase were heated to 45 °C respectively. The oil phase was then added dropwise to the aqueous phase under stirring. After cooling to room temperature, a microemulsion was obtained.

[0140] The transmission electron microscope (TEM) image of the microemulsion of this embodiment after phosphotungstic acid staining is shown in Figure 5. The D50 particle size of the microemulsion of this embodiment is approximately 23.6 nm.

[0141] Example 5

[0142] Preparation of polymer surfactants:

[0143] 3.5 g of maleic anhydride, 13.3 g of toluene, 10.5 g of polyethylene glycol (n = 3, molecular weight 150 g / mol), and 1.12 g of p-toluenesulfonic acid were placed in a dry round-bottom flask equipped with a reflux condenser and a nitrogen inlet. The mixture was heated to 120 °C under a nitrogen atmosphere and stirred with a magnetic stirrer. After reacting for 12 hours, a first reaction mixture was obtained. 14 g of alkyl glycoside (R = C5H11, m = 1.8) was added to the first reaction mixture, and the mixture was heated to 140 °C under a nitrogen atmosphere and stirred with a magnetic stirrer. After reacting for 10 hours, a second reaction mixture was obtained. The second reaction mixture was washed three times with 10 mL of methanol each time, and then rotary evaporated to obtain an asymmetric maleate ester.

[0144] 1.5 g of asymmetric maleate, 9 g of sodium allyl sulfonate, and 12 g of acrylamide were added to 30 g of deionized water to obtain a monomer mixture system. The monomer mixture system was placed in a constant temperature water bath at 5 °C and stirred while nitrogen gas was introduced into the monomer mixture system. Then, the pH value of the monomer mixture system was adjusted to 10 using sodium hydroxide. 0.011 g of azobisisopropylimidazoline hydrochloride was added, and the mixture was reacted at 20 °C for 8 hours to obtain a third reaction mixture system. The third reaction mixture system was precipitated with acetone, filtered, and the solid product obtained after filtration was dried and pulverized to obtain a polymer surfactant.

[0145] The absorption peak assignments of the Fourier transform infrared spectra of the polymer surfactant in this embodiment are shown in Table 1 below.

[0146] Based on the characterization data in Table 1, the polymer surfactant of this embodiment can be determined to include: structural units derived from asymmetric maleate, structural units derived from acrylamide, and structural units derived from sodium allyl sulfonate; wherein, the asymmetric maleate includes structural units derived from maleic anhydride, structural units derived from polyethylene glycol, and structural units derived from alkyl glycosides. Based on the total mass of the polymer surfactant as 100%, the content of the structural units derived from asymmetric maleate is 6.67%, the content of the structural units derived from acrylamide is 53.33%, and the content of the structural units derived from sodium allyl sulfonate is 40%. Based on the total mass of the asymmetric maleate as 100%, the content of the structural units derived from maleic anhydride is 12.5%, the content of the structural units derived from polyethylene glycol is 37.5%, and the content of the structural units derived from alkyl glycosides is 50%. The structural units derived from asymmetric maleate have the structure shown in structural formula (I), wherein x = 1-2, m = 1.8, n = 3, and R is C5H11. The structural unit derived from acrylamide has the structure shown in structural formula (II), wherein y = 25-35. The structural unit derived from sodium allyl sulfonate has the structure shown in structural formula (III), wherein z = 13-15.

[0147] The mass-to-charge ratio (m / z) of the mass spectrum peaks of the polymer surfactant in this embodiment is shown in Table 1. The mass-to-charge ratio in Table 1 plus 1 is the molecular weight of the polymer surfactant.

[0148] Preparation of microemulsions:

[0149] 2.25g of styrene-based phenol polyoxyethylene ether and 7.8g of deionized water were mixed and stirred for 30 minutes to form an aqueous phase. 1.5g of limonene and 1.2g of n-butanol were mixed, and then 2.25g of the polymer surfactant of this embodiment was added and stirred for 30 minutes to form an oil phase. The aqueous phase and the oil phase were heated to 55°C respectively, and the oil phase was added dropwise to the aqueous phase under stirring. After cooling to room temperature, a microemulsion was obtained.

[0150] The transmission electron microscope (TEM) image of the microemulsion of this embodiment after phosphotungstic acid staining is shown in Figure 6. The D50 particle size of the microemulsion of this embodiment is approximately 77.2 nm.

[0151] Table 1

[0152] Comparative Example 1

[0153] This comparative example prepared a microemulsion, which differs from Example 1 in that no polymer surfactant was added to the microemulsion.

[0154] Comparative Example 2

[0155] This comparative example prepared a microemulsion, which differs from Example 1 in that 4g of polymer surfactant was added during the preparation of the microemulsion, while the other components and their amounts remained unchanged.

[0156] Comparative Example 3

[0157] This comparative example prepared a polymer surfactant, which differs from Example 1 in that polyethylene glycol is replaced with 1,4-butanediol, while the amount remains the same.

[0158] This comparative example also prepared a microemulsion, which differs from Example 1 in that the polymer surfactant in the microemulsion is replaced with the polymer surfactant prepared in this comparative example, while the amount remains the same.

[0159] Comparative Example 4

[0160] This comparative example prepared a polymer surfactant, which differs from Example 1 in that: no alkyl glycosides were added, and the mixture after the first reaction was washed and rotary evaporated to obtain maleic ester, which was used in subsequent reactions.

[0161] This comparative example also prepared a microemulsion, which differs from Example 1 in that the polymer surfactant in the microemulsion is replaced with the polymer surfactant prepared in this comparative example, while the amount remains the same.

[0162] Comparative Example 5

[0163] This comparative example prepared a polymer surfactant, which differs from Example 1 in that no acrylamide was added.

[0164] This comparative example also prepared a microemulsion, which differs from Example 1 in that the polymer surfactant in the microemulsion is replaced with the polymer surfactant prepared in this comparative example, while the amount remains the same.

[0165] Comparative Example 6

[0166] This comparative example prepared a polymer surfactant, which differs from Example 1 in that sodium allyl sulfonate was not added.

[0167] This comparative example also prepared a microemulsion, which differs from Example 1 in that the polymer surfactant in the microemulsion is replaced with the polymer surfactant prepared in this comparative example, while the amount remains the same.

[0168] The temperature resistance, salt resistance, stability, rock adsorption resistance, oil displacement performance, and time required for complete degradation of the microemulsions of Examples 1-5 and Comparative Examples 1-6 were evaluated.

[0169] 1. Temperature resistance

[0170] The microemulsion was prepared into an aqueous dispersion with a mass concentration of 0.01% using water. A rotating drop interfacial tensiometer was used to test the interfacial tension of the microemulsion with crude oil (the viscosity of the crude oil used was...) at a rotation speed of 3000 r / min and a temperature of 120℃.

[0171] 1.23 mPa·s, density 0.858 g / cm³ 3 Interfacial tension between (unit: mN / m).

[0172] The test results are shown in Table 2.

[0173] Table 2. Interfacial tension of microemulsions at 120℃

[0174] As shown in Table 2, the interfacial tension between the microemulsion of the present invention and crude oil can reach 10 at 120°C. -3 The extremely low interfacial tension indicates that these microemulsions have good temperature resistance.

[0175] 2. Salt resistance and stability

[0176] The microemulsion was tested with water and brine with a salinity of 400,000 ppm (simulating the ionic composition and content of formation water in ppm): Na + 83006, K + 83710, Ca 2+ 1768, Mg 2+ 387, Cl - 230000, SO4 2- 471, HCO3 - 658) An aqueous dispersion with a mass concentration of 0.01% was prepared, and the interfacial tension between the microemulsion and crude oil was measured using a rotating drop interfacial tension meter at a rotation speed of 3000 r / min and a temperature of 25°C.

[0177] After the aqueous dispersion of the microemulsion prepared with saline was allowed to stand at 25°C for 90 days, the interfacial tension between it and crude oil was tested using the same method.

[0178] The test results are shown in Table 3.

[0179] Table 3. Interfacial tension of microemulsions in water and saline.

[0180] As shown in Table 3, after the microemulsion of the present invention was left to stand in brine at 25°C for 90 days, the interfacial tension between it and crude oil could still reach 10. -3 The magnitude indicates that these microemulsions have good salt resistance and stability.

[0181] 3. Resistance to rock adsorption

[0182] Take 10.00 g of 50 / 60 mesh rock powder and add it to a 150 mL stoppered ground glass conical flask. Then add 90 g of a 0.01% aqueous dispersion of the microemulsion (prepared with water). Place the conical flask in a water bath with constant temperature shaking and shake for 24 h at a shaking frequency of 90 times / min. Filter the system in the conical flask, take the supernatant, and use a UV-Vis spectrophotometer to measure the absorbance of the supernatant at a wavelength of 207 nm. Also measure the absorbance of the 0.01% aqueous dispersion of the microemulsion. Calculate the adsorption amount (unit: mg / g) using the following formula: In the formula, q t Ct represents the adsorption amount at time t, in mg / g; C0 represents the initial concentration of the aqueous dispersion of the microemulsion, in mg / L; Ct represents the initial concentration of the aqueous dispersion of the microemulsion. t Let be the concentration of the microemulsion in the supernatant at time t, in mg / L; V be the volume of the aqueous dispersion of the microemulsion, in L; and m be the weight of the adsorbent (i.e., rock powder) used in the adsorption experiment, in g. Before calculating the adsorption capacity, a calibration curve for the microemulsion needs to be established by relating the aqueous dispersions of the microemulsion at different concentrations to the absorbance, thereby obtaining the concentration of the aqueous dispersion of the microemulsion at time t for calculating the adsorption capacity.

[0183] The test results are shown in Table 4.

[0184] Table 4 Adsorption capacity of microemulsions on rock powder

[0185] As can be seen from Table 4, the adsorption amount of the microemulsions in the embodiments of the present invention on rock powder is less than 0.4 mg / g, indicating good resistance to rock adsorption.

[0186] 4. Oil displacement performance

[0187] The oil displacement performance of the microemulsion was tested according to the methods described in "SY / T 6424-2014 Performance Test Method for Composite Oil Displacement Systems" (9.1-9.4 Evaluation of Oil Displacement Performance of Composite Oil Displacement Systems). Core samples with permeability between 0.07 mD and 0.55 mD were selected. The crude oil used had a viscosity of 1.23 mPa·s and a density of 0.858 g / cm³. 3 The displacement pressure differential is 2 MPa, and the confining pressure is 5 MPa. The composite oil displacement system is an aqueous dispersion of a microemulsion with a mass concentration of 0.3% prepared with water.

[0188] The test results are shown in Table 5.

[0189] Table 5 Oil displacement efficiency of microemulsions

[0190] As can be seen from Table 5, the microemulsion of the present invention can further improve the oil displacement efficiency by more than 27% on the basis of water flooding, and has good oil displacement performance.

[0191] 5. Time required for complete degradation of microemulsions

[0192] The biodegradability of the microemulsion was tested according to the method described in GB / T 15818-2018 Test Method for Biodegradability of Surfactants. The test interval was 1 day, and the number of days required for the biodegradability of the sample to reach 100% was recorded as T.

[0193] Table 6 shows the time required for the complete degradation of the microemulsions prepared in Examples 1-5. It can be seen that the complete degradation time of the microemulsions in the embodiments of the present invention is 21-30 days, which has a fast biodegradation rate and excellent environmental friendliness.

[0194] Table 6. Time required for complete degradation of microemulsions

[0195] In summary, the polymer surfactant of this invention contains structural units derived from alkyl glycosides, as well as various groups such as polyoxyethylene, ester, sulfonic acid, and amide groups, which enhances the rock adsorption resistance, temperature resistance, and salt resistance of the microemulsion containing this polymer surfactant. Furthermore, the preparation method of the polymer surfactant of this invention has advantages such as environmental friendliness, easy control of reaction conditions, stable reaction process, and ease of industrialization. Additionally, the microemulsion of this invention is an oil-in-water type and has a spherical (or near-spherical) structure. This spherical structure provides steric hindrance, preventing the polymer surfactant and co-surfactant in the microemulsion from adsorbing onto the rock surface, thus improving the rock adsorption resistance of the microemulsion. Moreover, the interaction between the polymer surfactant in the oil phase and the co-surfactant in the aqueous phase of the microemulsion further enhances the rock adsorption resistance. The microemulsion of this invention has a temperature resistance of up to 120°C and a salt resistance of up to 400,000 ppm. Furthermore, the D50 particle size of the microemulsion of this invention is approximately 20-80 nm, ensuring good injectability. The microemulsions of this invention can improve oil and gas recovery by altering the wettability of rock surfaces and reducing capillary resistance. They can be used as oil displacement agents, increasing oil recovery (i.e., oil displacement efficiency) by more than 27% on top of waterflooding, and are particularly suitable as oil displacement agents for unconventional reservoirs. Furthermore, the microemulsions of this invention exhibit rapid biodegradation and excellent environmental friendliness.

[0196] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A polymeric surfactant comprising: a structural unit from an unsymmetrical maleate, a structural unit from an acrylamide, and a structural unit from sodium allyl sulfonate; wherein the unsymmetrical maleate comprises a structural unit from maleic anhydride, a structural unit from polyethylene glycol, and a structural unit from alkyl glycoside; the content of the structural unit from the unsymmetrical maleate is 6-34%, the content of the structural unit from the acrylamide is 33-54%, and the content of the structural unit from the sodium allyl sulfonate is 33-40%, based on the total mass of the polymer surfactant being 100%.

2. The polymeric surfactant of claim 1, wherein, the content of the structural unit from the maleic anhydride is 12-24%, the content of the structural unit from the polyethylene glycol is 34-38%, and the content of the structural unit from the alkyl glycoside is 41-50%, based on the total mass of the unsymmetrical maleate being 100%.

3. The polymeric surfactant of claim 1, wherein, The structural units derived from the asymmetric maleate have the following formula (I) wherein x = 1-10, m = 1.2-1.8, n = 3-10, and R is a C2-C12 alkyl group.

4. The polymeric surfactant of claim 1, wherein, The structural units derived from acrylamide have the following formula (II) wherein y = 20-60.

5. The polymeric surfactant of claim 1, wherein, The structural unit derived from sodium allylsulfonate has the following formula (III): wherein z = 5-15.

6. The polymeric surfactant of claim 1, wherein, the relative molecular weight of the polymer surfactant is 1500-16000.

7. A method for preparing the polymer surfactant of any one of claims 1-6, comprising the following steps: (1) in a protective gas environment, subjecting maleic anhydride and polyethylene glycol to a first reaction in an organic solvent in the presence of a catalyst to obtain a first post-reaction mixture system; mixing the first post-reaction mixture system with alkyl glycoside, and performing a second reaction in a protective gas environment to obtain a second post-reaction mixture system; and after post-treatment of the second post-reaction mixture system, obtaining an unsymmetrical maleate; (2) in a protective gas environment, subjecting the unsymmetrical maleate, acrylamide, and sodium allyl sulfonate to a third reaction in water in the presence of an initiator to obtain a third post-reaction mixture system; and after post-treatment of the third post-reaction mixture system, obtaining the polymer surfactant.

8. The method of making a polymeric surfactant according to claim 7, wherein, the catalyst comprises one or a combination of several of p-toluenesulfonic acid, titanium isopropoxide, and boric acid.

9. The method of making a polymeric surfactant according to claim 7, wherein, the temperature of the first reaction is 95-120°C, and the time is 8-12 hours.

10. The method of making a polymeric surfactant according to claim 7, wherein, the temperature of the second reaction is 110-140°C, and the time is 5-10 hours.

11. The method of making a polymeric surfactant according to claim 7, wherein, the initiator comprises one or a combination of several of a peroxide initiator, an azo initiator, and an oxidation-reduction initiator.

12. The method of making a polymeric surfactant according to claim 7, wherein, after mixing the unsymmetrical maleate, acrylamide, and sodium allyl sulfonate with water, a system is obtained; protective gas is introduced into the system at 0-5°C, and then the pH value of the system is adjusted to 5-10, and the initiator is added to perform the third reaction.

13. The method of making a polymeric surfactant according to claim 7, wherein, the temperature of the third reaction is 10-50°C, and the time is 6-9 hours.

14. A microemulsion for enhanced oil recovery comprising: The polymer surfactant, oil, alcohol, co-surfactant and water of any one of claims 1-6; wherein the content of the polymer surfactant is 5%-15%, the content of the oil is 3%-10%, the content of the alcohol is 1%-8%, the content of the co-surfactant is 3%-15%, and the content of the water is 52% or more, based on the total mass of the microemulsion for enhanced oil recovery being 100%.

15. The microemulsion for enhanced oil recovery of claim 14, wherein, The oil comprises one or a combination of several of plant oil, mineral oil, silicone oil, limonene and oleic acid.

16. The microemulsion for enhanced oil recovery of claim 14, wherein, The alcohol comprises C2-C10 alcohol.

17. The microemulsion for enhanced oil recovery of claim 14, wherein, The co-surfactant comprises one or a combination of several of alkyl sulfonate, alkyl phenol polyoxyethylene ether, alkenyl phenol polyoxyethylene ether, aryl alkenyl phenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, alkyl benzene sulfonate and alkyl sulfate.

18. The microemulsion for enhanced oil recovery of claim 14, wherein, The D50 particle size of the microemulsion for enhanced oil recovery is 9-100 nm.

19. A preparation method of the microemulsion for enhanced oil recovery of any one of claims 14-18, comprising the following steps: mixing the co-surfactant and water to form an aqueous phase; mixing the oil, alcohol and polymer surfactant to form an oil phase; heating the aqueous phase and the oil phase respectively, and then adding the oil phase into the aqueous phase under stirring to obtain the microemulsion for enhanced oil recovery.

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