An anionic gemini surfactant, a microfoam oil displacement agent, and its preparation and application

Abstract

This invention provides an anionic gemini surfactant, a microfoam oil displacement agent, its preparation method, and its application. The anionic gemini surfactant is selected from at least one of the structures shown in formula (I), and the microfoam oil displacement agent comprises anionic gemini surfactant, amphoteric surfactant, polymer, and water. Because the spacer group in the anionic gemini surfactant is a hydroxyl-substituted group, it can form hydrogen bonds with both anionic gemini surfactant and amphoteric surfactant molecules, resulting in a tight arrangement at the interface, which improves surface elasticity and foam stability, making it suitable for enhanced oil recovery in oil fields.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical technology, specifically relating to an anionic gemini surfactant, a microfoam oil displacement agent, and their preparation and application. Background Technology

[0002] Foam fluid enhanced oil recovery technology has been used in oilfields for nearly 40 years and has broad application prospects. Compared with conventional foam, microfoam has a smaller size, with bubble diameters generally less than 100 μm, and exhibits better uniformity, stability, and mobility. Microfoam flooding, while ensuring system injectability, relies on the sealing and oil-washing effects of the microfoam system to increase reservoir pressure, improve subsequent fluid flow direction, and increase oil displacement efficiency, thereby enhancing the final recovery rate and demonstrating excellent application potential.

[0003] Gemini surfactants are a class of surfactants formed by chemically linking two monomeric surfactants together at or near their head groups via a spacer group. Compared to traditional monomeric surfactants, they exhibit lower critical micelle concentrations, higher interfacial activity, and better wetting properties, making them highly promising for enhancing oil recovery.

[0004] Most reported surfactants are cationic gemini surfactants. Chinese patents CN114105776A, CN106540631A, CN103406065A, CN104607099A, etc., disclose dialkyl quaternary ammonium salt cationic, diester-based quaternary ammonium salt cationic, imidazole-based cationic, and pyridinyl cationic gemini surfactants. However, cationic surfactants suffer from high adsorption loss in formations, and their compatibility with commonly used foam stabilizers (generally negatively charged) in microfoaming agents is poor. For example, the literature (Journal of Canadian Petroleum Technology. 2008, 47(11):15-21) describes that mixing cationic surfactant HTAB with foam stabilizer XG will produce hair-like precipitates.

[0005] The stability and strength of microbubbles affect the swept volume and oil recovery rate. Poor foam stability limits the ability to control cross-contamination. Therefore, improving foam stability and strength is a key focus in the research and development of microbubble enhanced oil recovery. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a novel microfoam oil displacement agent, its preparation method, and its applications. The microfoam oil displacement agent contains anionic gemini surfactants, amphoteric surfactants, and polymers. By altering the functional groups in the gemini surfactants and through their synergistic effect with the amphoteric surfactants, higher surface activity can be achieved, thus stabilizing the aqueous foam phase.

[0007] One objective of this invention is to provide an anionic gemini surfactant having the structure shown in formula (I):

[0008]

[0009] In formula (I),

[0010] R1 and R2 are independently selected from any one of C2 to C22 hydrocarbon groups or substituted hydrocarbon groups, wherein the substituent in the substituted hydrocarbon group is any one of ester group, amide group, or hydroxyl group;

[0011] R3 is selected from any one of the hydroxyl-substituted hydrocarbon groups from C1 to C10;

[0012] R4 and R5 are independently selected from any one of C1 to C8 alkylene or substituted alkylene groups, wherein the substituent in the substituted alkylene group is any one of ester group, amide group, or hydroxyl group;

[0013] X- represents an anion or an anionic group.

[0014] According to an embodiment of the present invention, in formula (I),

[0015] R1 and R2 are independently selected from one of the hydrocarbon groups from C4 to C20. Preferably, R1 and R2 are independently selected from any one of the alkyl and alkenyl groups from C4 to C20. More preferably, R1 and R2 are independently selected from any one of the alkyl groups from C8 to C18.

[0016] R3 is selected from any one of the hydroxy-substituted hydrocarbon groups from C3 to C6. Preferably, R3 is selected from any one of the hydroxy-substituted hydrocarbon groups from C3 to C4. More preferably, R3 is selected from any one of -CH2CH(OH)CH2-, -CH2CH(OH)CH2CH2-, and -CH2CH(OH)CH(OH)CH2-.

[0017] R4 and R5 are independently selected from any one of C1 to C5 alkylene or hydroxy-substituted alkylene, preferably, R4 and R5 are independently selected from any one of C1 to C4 alkylene or hydroxy-substituted alkylene;

[0018] X - COO - or SO3 - .

[0019] The second objective of this invention is to provide a method for preparing the above-mentioned anionic gemini surfactant, comprising: reacting a component including a primary amine or its derivative, a halosulfonate compound or a halocarboxylate compound, and a dihaloalcohol to obtain the anionic gemini surfactant. Preferably, the preparation method specifically includes the following steps:

[0020] (1) Add a primary amine or its derivative, a halosulfonate compound or a halocarboxylate compound to a solvent and heat to react;

[0021] (2) Add a dihalool to the system after the reaction in step (1) and continue the reaction. The product is concentrated, washed and recrystallized to obtain the anionic gemini surfactant.

[0022] According to an embodiment of the present invention, in the above-described method for preparing anionic gemini surfactants:

[0023] The primary amine or its derivative is selected from at least one of primary amines or their derivatives having 2 to 22 carbon atoms, preferably from at least one of aliphatic primary amines having 4 to 20 carbon atoms; more preferably from at least one of n-decylamine, dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine;

[0024] The halosulfonate compound is selected from at least one of haloalkylsulfonates or their derivatives having 1 to 8 carbon atoms, preferably from at least one of haloalkylsulfonates or halohydroxyalkylsulfonates having 1 to 4 carbon atoms, and more preferably from at least one of sodium 2-chloroethylsulfonate, sodium 2-bromoethylsulfonate, sodium 3-chloro-2-hydroxypropanesulfonate, and sodium 4-chloro-1-hydroxy-butanesulfonate.

[0025] The halocarboxylate compounds are selected from at least one of haloalkylcarboxylates or their derivatives having 2 to 9 carbon atoms, preferably from at least one of haloalkylcarboxylates or halohydroxyalkylcarboxylates having 2 to 5 carbon atoms, and more preferably from at least one of sodium chloroacetate, sodium bromoacetate, sodium β-chloropropionate, and sodium β-bromopropionate.

[0026] The dihaloalcohol is selected from dihaloalcohols having 1 to 10 carbon atoms, preferably from dihaloalcohols having 3 to 4 carbon atoms, and more preferably from at least one of 1,3-dichloro-2-propanol, 1,3-dibromo-2-propanol, 1,4-dichloro-2-butanol, 1,4-dibromo-2-butanol, 1,4-dichloro-2,3-butanediol, and 1,4-dibromo-2,3-butanediol.

[0027] The molar ratio of the primary amine or its derivative, halosulfonate compound or halocarboxylate compound, and dihaloalcohol is 1:(1-1.5):(0.5-0.75), preferably 1:(1-1.2):(0.5-0.6);

[0028] The solvent in step (1) is selected from a mixture of water and organic solvent. Preferably, the organic solvent is selected from alcohols, and more preferably from at least one of ethanol, isopropanol, and ethylene glycol. More preferably, the solvent is selected from at least one of ethanol / water, isopropanol / water, and ethylene glycol / water, and the ratio of water to organic solvent in the solvent is 1:(0.8 to 1.2).

[0029] The reaction conditions in step (1) are: pH 8-10, 70-90℃ for 6-16 hours;

[0030] The reaction conditions in step (2) are: 70-90℃ for 6-16 hours;

[0031] The concentration, washing, and recrystallization in step (2) can all be carried out using the commonly used heating concentration, solvent washing, and recrystallization processes in the art. For example, most of the solvent can be removed from the solution after the reaction by rotary evaporation, followed by washing with an organic solvent (e.g., acetone) and recrystallization with a solvent (e.g., acetone / water) to obtain the anionic gemini surfactant.

[0032] A third objective of this invention is to provide a microfoam oil displacement agent, comprising the above-mentioned anionic gemini surfactant or anionic gemini surfactant obtained by the above preparation method.

[0033] According to an embodiment of the present invention, the microfoam oil displacement agent comprises the anionic gemini surfactant, the amphoteric surfactant, and the polymer;

[0034] Specifically, the zwitterionic surfactant is a betaine-type zwitterionic surfactant, preferably lauramidopropyl betaine;

[0035] The polymer is selected from at least one of biopolymers and synthetic polymers, wherein the biopolymer is selected from at least one of starch, xanthan gum, guar gum, and carboxymethyl cellulose, preferably xanthan gum; the synthetic polymer is partially hydrolyzed polyacrylamide.

[0036] Based on the total weight of the microfoam oil displacement agent as 100%, the anionic gemini surfactant is 0.03-0.25%, preferably 0.05-0.2%; the amphoteric surfactant is 0.05-0.35%, preferably 0.1-0.3%; the polymer is 0.1-0.5%, preferably 0.1-0.4%; and the balance is water.

[0037] The fourth objective of this invention is to provide a method for preparing the above-mentioned microfoam oil displacement agent, comprising: stirring a component including anionic gemini surfactant, amphoteric surfactant, polymer and water until homogeneous, thereby obtaining the microfoam oil displacement agent.

[0038] According to an embodiment of the present invention, the preparation method specifically includes: first, stirring the polymer to dissolve it evenly in water to obtain a polymer solution; then, adding the anionic gemini surfactant and the amphoteric surfactant to the polymer solution, stirring to dissolve, and finally obtaining the microfoam oil displacement agent. The stirring and dissolving operations described above do not have special requirements, as long as the components are dissolved.

[0039] The fifth objective of this invention is to provide the application of the above-mentioned microfoam oil displacement agent or the microfoam oil displacement agent obtained by the above preparation method in oilfield oil production.

[0040] The microfoam oil displacement agent provided by this invention comprises anionic gemini surfactant, amphoteric surfactant, polymer, and water. The anionic gemini surfactant connects two hydrophilic groups and a hydrophobic chain via spacer groups, fundamentally overcoming the separation tendency caused by the charge repulsion or hydration of ionic head groups in traditional single-ionic surfactants. Simultaneously, the spacer groups are hydroxyl-substituted groups, and intermolecular hydrogen bonding interactions promote the close arrangement of the anionic gemini surfactant on the surface, resulting in higher surface activity. The amphoteric surfactant has good hydrophilicity at its polar end, and the electrostatic attraction between the quaternary ammonium positive charge and the carboxylate negative charge, along with electrostatic and hydrogen bonding interactions with the anionic groups and hydroxyl groups in the anionic gemini surfactant, further weakens the electrostatic repulsion. The two components have a synergistic effect, increasing surface activity and surface elasticity, resulting in better foam stability.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The microfoam oil displacement agent provided by the present invention contains anionic gemini surfactants, which avoids the problem of adsorption loss of cationic gemini surfactants. At the same time, it has good compatibility with commonly used polymer foam stabilizers for microfoams and will not produce precipitation.

[0043] 2. The microfoam oil displacement agent provided by the present invention contains anionic gemini surfactant spacer groups that are hydroxyl-substituted groups, which can form hydrogen bonds with anionic gemini surfactant molecules and amphoteric surfactant molecules, resulting in a tightly packed surface arrangement, which improves surface activity and surface elasticity and is beneficial to the stability of the foam. Detailed Implementation

[0044] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0045] All raw materials used in the examples are readily available for purchase.

[0046] Example 1

[0047] (1) Preparation of anionic gemini surfactants

[0048] The anionic gemini surfactant 14-S(OH)-3(OH)-S(OH)-14 has the following molecular structure:

[0049]

[0050] Its preparation method:

[0051] 1 mol of tetradecylamine and 1.1 mol of sodium 3-chloro-2-hydroxypropanesulfonate were added to a reaction vessel, along with 200 mL of an ethanol / water mixture (v:v1:1). The pH was adjusted to 9, and the reaction was carried out at 80°C for 8 hours. Then, 0.55 mol of 1,3-dibromo-2-propanol was added, and the reaction was continued for another 8 hours. Most of the solvent was removed by rotary evaporation, and acetone was added and stirred. The mixture was cooled to 0°C and maintained at that temperature for 2 hours. The solid was purified by recrystallization from acetone / water to obtain the product.

[0052] (2) Preparation of microfoam oil displacement agent

[0053] Xanthan gum was slowly added to 150 mL of water while stirring until it dissolved completely, yielding a polymer solution. Anionic gemini surfactant 14-S(OH)-3(OH)-S(OH)-14 and amphoteric surfactant lauramidopropyl betaine were added to the polymer solution while stirring at low speed and stirred until dissolved. The mixed solution contained 0.2% polymer by mass, 0.08% anionic gemini surfactant by mass, and 0.2% amphoteric surfactant by mass.

[0054] (3) Performance testing of microfoaming agents

[0055] Take 100 mL of microfoaming agent, place it in a Waring stirrer, stir at 3500 r / min for 3 min, and record the foaming volume and half-life of the formed microfoam. The experimental temperature is room temperature.

[0056] Example 2

[0057] (1) Preparation of surfactants

[0058] The anionic gemini surfactant 12-C-4(OH)-C-12 has the following molecular structure:

[0059]

[0060] Its preparation method:

[0061] 1 mol of dodecylamine and 1.1 mol of sodium chloroacetate were added to a reaction vessel, followed by 200 mL of an ethanol / water mixture (v:v1:1). The pH was adjusted to 9, and the reaction was carried out at 80°C for 8 hours. Then, 0.55 mol of 1,4-dibromo-2-butanol was added, and the reaction was continued for another 8 hours. Most of the solvent was removed by rotary evaporation, and acetone was added and stirred. The mixture was cooled to 0°C and maintained at that temperature for 2 hours. The solid was purified by recrystallization from acetone / water to obtain the product.

[0062] (2) Preparation of microfoam oil displacement agent

[0063] Xanthan gum was slowly added to 150 mL of water while stirring until it dissolved completely, yielding a polymer solution. Anionic gemini surfactant 12-C-4(OH)-C-12 and amphoteric surfactant lauramidopropyl betaine were added to the polymer solution while stirring at low speed and stirred until dissolved. The mixed solution contained 0.2% polymer by mass, 0.1% anionic gemini surfactant by mass, and 0.15% amphoteric surfactant by mass.

[0064] (3) Performance testing of microfoaming agents

[0065] Take 100 mL of microfoaming agent, place it in a Waring stirrer, stir at 3500 r / min for 3 min, and record the foaming volume and half-life of the formed microfoam. The experimental temperature is room temperature.

[0066] Example 3

[0067] (1) Preparation of microfoam oil displacement agent

[0068] The anionic gemini surfactant used was 14-S(OH)-3(OH)-S(OH)-14 from Example 1. The preparation was the same as the microfoam oil displacement agent in Example 1, except that the polymer mass fraction was changed to 0.4%.

[0069] (2) Performance testing of microfoaming agents

[0070] Take 100 mL of microfoaming agent, place it in a Waring stirrer, stir at 4000 r / min for 3 min, and record the foaming volume and half-life of the formed microfoam. The experimental temperature is room temperature.

[0071] Example 4

[0072] (1) Preparation of microfoam oil displacement agent

[0073] The anionic gemini surfactant used was 14-S(OH)-3(OH)-S(OH)-14 from Example 1. Xanthan gum was slowly added to 150 mL of water under stirring until it dissolved completely, obtaining a polymer solution. The anionic gemini surfactant 14-S(OH)-3(OH)-S(OH)-14 and the amphoteric surfactant lauramidopropyl betaine were added to the polymer solution under low-speed stirring and stirred until dissolved. The mixed solution contained 0.2% polymer by mass, 0.2% anionic gemini surfactant by mass, and 0.1% amphoteric surfactant by mass.

[0074] (2) Performance testing of microfoaming agents

[0075] Take 100 mL of microfoaming agent, place it in a Waring stirrer, stir at 3500 r / min for 3 min, and record the foaming volume and half-life of the formed microfoam. The experimental temperature is room temperature.

[0076] Example 5

[0077] (1) Preparation of surfactants

[0078] The anionic gemini surfactant 12-C-4(OH)2-C-12 has the following molecular structure:

[0079]

[0080] Its preparation method:

[0081] The preparation of the surfactant was the same as in Example 2, except that 1,4-dibromo-2-butanol was replaced with 1,4-dibromo-2,3-butanediol.

[0082] (2) Preparation of microfoam oil displacement agent

[0083] The preparation of the microfoam oil displacement agent is the same as in Example 2, except that the anionic gemini surfactant is replaced with 12-C-4(OH)2-C-12.

[0084] (3) Performance testing of microfoaming agents

[0085] Take 100 mL of microfoaming agent, place it in a Waring stirrer, stir at 3500 r / min for 3 min, and record the foaming volume and half-life of the formed microfoam. The experimental temperature is room temperature.

[0086] Comparative Example 1

[0087] (1) Preparation of surfactants

[0088] The anionic gemini surfactant 12-C-4-C-12 has the following molecular structure:

[0089]

[0090] Its preparation method:

[0091] The preparation of the surfactant was the same as in Example 2, except that 1,4-dibromo-2-butanol was replaced with 1,4-dibromobutane.

[0092] (2) Preparation of microfoam oil displacement agent

[0093] The preparation of the microfoam oil displacement agent is the same as in Example 2, except that the anionic gemini surfactant is replaced with 12-C-4-C-12.

[0094] (3) Performance testing of microfoaming agents

[0095] Same as Example 2.

[0096] Comparative Example 2

[0097] (1) Preparation of microfoam oil displacement agent

[0098] The anionic gemini surfactant used was 14-S(OH)-3(OH)-S(OH)-14 from Example 1. The anionic gemini surfactant 14-S(OH)-3(OH)-S(OH)-14 and the amphoteric surfactant lauramidopropyl betaine were added to water and stirred until dissolved. The mixed solution contained 0.08% anionic gemini surfactant and 0.2% amphoteric surfactant by mass.

[0099] (2) Performance testing of microfoaming agents

[0100] Take 100 mL of microfoaming agent, place it in a Waring stirrer, stir at 3500 r / min for 3 min, and record the foaming volume and half-life of the formed microfoam. The experimental temperature is room temperature.

[0101] Comparative Example 3

[0102] (1) Preparation of surfactants

[0103] Gemini surfactants were prepared according to the method described in the *Acta Physico-Chimica Sinica*, Vol. 20, No. 10, 2004, pp. 1245-1248. The structural formula of the prepared surfactant is as follows:

[0104]

[0105] (2) Preparation of microfoam oil displacement agent

[0106] Xanthan gum was slowly added to 150 mL of water under stirring until it dissolved evenly, yielding a polymer solution. The aforementioned gemini surfactant and zwitterionic surfactant lauramidopropyl betaine were added to the polymer solution under low-speed stirring and stirred until dissolved. The mixed solution contained 0.2% polymer by mass, 0.06% gemini surfactant by mass, and 0.2% zwitterionic surfactant by mass.

[0107] (3) Performance testing of microfoaming agents

[0108] Take 100 mL of microfoaming agent, place it in a Waring stirrer, stir at 3500 r / min for 3 min, and record the foaming volume and half-life of the formed microfoam. The experimental temperature is room temperature.

[0109] Table 1. Performance test results of the microfoam oil displacement agents in the examples and comparative examples.

[0110]

[0111] Table 1 lists the performance test results of the microfoam oil displacement agents obtained from the examples and comparative examples. It can be seen that the microfoam oil displacement agents used in the examples of this invention can all produce micron-sized foam. Compared with Example 1, the oil displacement agent prepared in Comparative Example 2 does not contain polymers, and the resulting foam system has a larger foam diameter, does not belong to microfoam, and has poor stability. Comparing Examples 2, 5, and Comparative Example 1, the spacer groups of the anionic gemini surfactants in the examples contain hydroxyl groups, which can form hydrogen bonds with anionic gemini surfactant molecules and zwitterionic surfactant molecules. Compared with anionic gemini surfactants whose spacer groups do not contain hydrogen bond donors or acceptors, their surfaces are more tightly packed, resulting in significantly improved foam stability. Furthermore, the oil displacement agent with two hydroxyl groups in the spacer group of the anionic gemini surfactant has superior foam stability.

[0112] Test Example 1

[0113] The microfoam oil displacement agent prepared in Example 2 was subjected to a physical simulation displacement experiment. The core used for displacement had a diameter of 2.5 cm, a length of 20 cm, and a permeability of 2.1 μm. 2 The microfoam displacement agent was stirred at 3500 r / min for 3 min to form microfoam. Water flooding was first performed to a water cut of 98%. After water flooding, 1 pv (core pore volume) of the above microfoam was injected, followed by water flooding to a water cut of 98%. The results showed that oil recovery could be increased by 15% based on water flooding.

[0114] Test Example 2

[0115] The microfoam oil displacement agent prepared in Comparative Example 1 was subjected to a physical simulation displacement experiment. The core used for displacement had a diameter of 2.5 cm, a length of 20 cm, and a permeability of 2.0 μm. 2The microfoam displacement agent was stirred at 3500 r / min for 3 min to form microfoam. Water flooding was first performed to a water cut of 98%. After water flooding, 1 pv (core pore volume) of the above microfoam was injected, followed by water flooding to a water cut of 98%. The results showed that the oil recovery rate could be increased by 9.4% based on water flooding.

Claims

1. A micro-foam flooding agent, comprising an anionic gemini surfactant, a zwitterionic surfactant and a polymer, wherein the anionic gemini surfactant has the following formula (I) : wherein R 1 and R 2 are independently selected from any one of C 4-C 20 alkyl groups; R 3 is selected from any one of -CH 2CH(OH)CH 2-, -CH 2CH(OH)CH 2CH 2-, -CH 2CH(OH)CH(OH)CH 2-; R 4 and R 5 are independently selected from any one of C 1-C 5 alkylene or hydroxyl-substituted alkylene; the zwitterionic surfactant is lauryl amidopropyl betaine; the polymer is xanthan gum; the anionic gemini surfactant is 0.03-0.25%, the zwitterionic surfactant is 0.05-0.35%, the polymer is 0.1-0.5%, and the rest is water, based on the total weight of the micro-foam flooding agent. 2.The micro-foam flooding agent according to claim 1, wherein R 4 and R 5 are independently selected from any one of C 1-C 4 alkylene or hydroxyl-substituted alkylene. 3.The preparation method of the anionic gemini surfactant, comprising: reacting components including primary amine or its derivative, halogenated sulfonate compound or halogenated carboxylate compound, and dihalogenated alcohol to obtain the anionic gemini surfactant; the primary amine or its derivative is selected from at least one of C 4-C 20 fatty primary amine; the halogenated sulfonate compound is selected from at least one of C 1-C 4 halogenated alkyl sulfonate or halogenated hydroxyalkyl sulfonate; the halogenated carboxylate compound is selected from at least one of C 2-C 5 halogenated alkyl carboxylate or halogenated hydroxyalkyl carboxylate; and the dihalogenated alcohol is selected from C 3-C 4 dihalogenated alcohol. 4.The preparation method of the anionic gemini surfactant according to claim 3, comprising the following steps: (1) adding the primary amine or its derivative, the halogenated sulfonate compound or the halogenated carboxylate compound into a solvent and heating to react; (2) adding the dihalogenated alcohol into the system after the reaction in step (1) and continuing to react, and then concentrating, washing and recrystallizing the product to obtain the anionic gemini surfactant. 5.The micro-foam flooding agent according to claim 4, wherein the molar ratio of the primary amine or its derivative, the halogenated sulfonate compound or the halogenated carboxylate compound, and the dihalogenated alcohol is 1: (1-1.5) : (0.5-0.75). 6.The micro-foam flooding agent according to claim 5, wherein the molar ratio of the primary amine or its derivative, the halogenated sulfonate compound or the halogenated carboxylate compound, and the dihalogenated alcohol is 1: (1-1.2) : (0.5-0.6). X - is COO - or SO3 - ; 7.The micro-foam flooding agent according to claim 6, wherein the primary amine or its derivative is selected from at least one of n-decylamine, dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine; and / or, ​ ​ ​ ​ 3. The micro-foamed flooding agent according to any one of claims 1 to 2, wherein, ​ 4. The micro-foam flooding agent of claim 3, wherein, ​ ​ ​ ​ ​ ​ ​ ​ ​ The halogenated sulfonate compound is at least one selected from the group consisting of sodium 2-chloroethyl sulfonate, sodium 2-bromoethyl sulfonate, sodium 3-chloro-2-hydroxypropane sulfonate, and sodium 4-chloro-1-hydroxy-butane sulfonate; and / or, The halogenated carboxylate compound is at least one selected from the group consisting of sodium chloroacetate, sodium bromoacetate, sodium β-chloropropionate, and sodium β-bromopropionate; and / or, The dihalogenated alcohol is at least one selected from the group consisting of 1,3-dichloro-2-propanol, 1,3-dibromo-2-propanol, 1,4-dichloro-2-butanol, 1,4-dibromo-2-butanol, 1,4-dichloro-2,3-butanediol, and 1,4-dibromo-2,3-butanediol.

8. The micro-foam oil displacement agent according to claim 4, wherein, The solvent in step (1) is a mixed solvent of water and an organic solvent; and / or, The reaction condition in step (1) is that the pH is 8-10, the reaction is carried out at 70-90°C for 6-16h; and / or, The reaction condition in step (2) is that the reaction is carried out at 70-90°C for 6-16h.

9. The micro-foam oil displacement agent according to claim 8, wherein, The organic solvent is selected from alcohols.

10. The micro-foam oil displacement agent according to claim 9, wherein, The organic solvent is at least one selected from the group consisting of ethanol, isopropanol, and ethylene glycol.

11. The micro-foam oil displacement agent according to claim 1, wherein, based on the total weight of the micro-foam oil displacement agent being 100%, the anionic gemini surfactant is 0.05-0.2%, the zwitterionic surfactant is 0.1-0.3%, the polymer is 0.1-0.4%, and the balance is water. The components including the anionic gemini surfactant, the zwitterionic surfactant, the polymer, and water are stirred uniformly to obtain the micro-foam oil displacement agent.

12. A method of preparing the micro-foamed oil displacement agent of any one of claims 1 to 11, comprising: The preparation method specifically comprises: first, dissolving the polymer uniformly in water to obtain a polymer solution; then, adding the anionic gemini surfactant and the zwitterionic surfactant to the polymer solution, and stirring and dissolving to obtain the micro-foam oil displacement agent.

13. The method of claim 12, wherein the microfoam flooding agent is prepared by the steps of:

14. Use of the micro-foam oil displacement agent according to any one of claims 1-11 or obtained by the preparation method according to claim 12 or 13 in oil field production. ​

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