CO2 response type alkyl amidine surfactant with clay stabilization and oil displacement functions and application method of CO2 response type alkyl amidine surfactant in clay stabilization and oil displacement

Abstract

The invention provides a CO2 response type alkyl amidine surfactant with clay stabilization and oil displacement functions and a method for applying the CO2 response type alkyl amidine surfactant to clay stabilization and oil displacement. The surfactant is protonated after contacting with CO2 and is converted into cations from a nonionic form in situ, the generated cations can be efficiently adsorbed on the surface of clay, and the clay is stabilized by inhibiting hydration expansion and changing wettability; the protonated product has excellent foaming performance and emulsifying capacity, so that the protonated product shows good oil washing and oil displacement performance. The surfactant provided by the invention is suitable for low-permeability tight reservoirs of CO2 storage and CO2 oil displacement, and can synchronously solve the two problems of clay expansion damage and improvement of the crude oil recovery rate.

Description

Technical Field

[0001] This invention relates to the field of chemical additives for oil and gas field development, specifically providing a CO2-responsive alkylamidine surfactant with both clay stabilizing and oil displacement functions, and a method for its application in clay stabilization and oil displacement. Background Technology

[0002] Ultra-low permeability tight oil reservoirs, characterized by poor reservoir properties and low natural productivity, pose significant challenges to their economical and effective development. CO2 injection technology, due to its ability to significantly improve oil recovery and synergistically achieve CO2 geological sequestration, has become a key green development approach to address this challenge. However, while injecting CO2 to improve driving efficiency, this technology also introduces new technical challenges: the acidic environment created by CO2 in formation fluids and its interaction with reservoir minerals (especially clay) may exacerbate the complexity of the reservoir's microstructure.

[0003] CO2 injection poses a direct challenge to traditional oilfield chemical additive systems. On the one hand, to inhibit the hydration swelling and migration of clay minerals in the reservoir, cationic clay stabilizers, such as quaternary ammonium salt cationic surfactants, are typically used. On the other hand, to achieve effective oil displacement, anionic or nonionic surfactants are needed to reduce oil-water interfacial tension, generate foam, or form emulsions, such as petroleum sulfonate anionic surfactants. In a CO2 environment, the functions of these two types of traditional chemical agents may inhibit each other, or even precipitate, leading to synergistic failure. Furthermore, conventional surfactants used for oil displacement do not have the function of inhibiting clay swelling, while clay stabilizers alone contribute little to improving oil washing efficiency. This functional limitation forces the use of complex multi-agent formulations in the field, which is not only costly but also introduces uncontrollable chemical risks and market application limitations in a CO2 environment.

[0004] CO2-responsive surfactants, as smart chemical agents, can reversibly alter their molecular structure (such as protonation) through CO2 stimulation, thereby regulating interfacial properties and achieving functions such as foaming and emulsification, improving oil displacement efficiency while reducing reservoir damage. Therefore, developing CO2-responsive surfactants with both clay stabilizing and oil displacement properties is of great significance for achieving efficient and environmentally friendly oilfield development, especially suitable for CO2-enhanced oil recovery in low-permeability, tight reservoirs and enhanced oil recovery (EOR) technologies. In recent years, CO2-responsive surfactants (such as amidines and guanidines) have attracted much attention due to their reversible protonation characteristics. J. Petrol. Sci. Eng ., 2021, 206, 108985; J. Petrol. Sci. Eng, 12,2020, 186, 106677; CN 119638599 A, etc.). For example, the carboxamidine surfactant reacts with naphthenic acid, and then the water-oil (model oil of alkanes) emulsification and demulsification effect can be achieved by its reaction with CO2 / N2. However, the existing reports lack the evaluation of the oil washing performance of real crude oil, and there is no report on the clay stabilizing performance of carboxamidine surfactants. SUMMARY

[0005] The present application provides a CO2-responsive alkylcarboxamidine surfactant with clay stabilizing and oil displacement functions and a method for the application of the CO2-responsive alkylcarboxamidine surfactant in clay stabilizing and oil displacement. The surfactant does not need to undergo an exchange reaction with an organic acid, and by protonation with CO2, it realizes the dual function of a single agent with clay stabilizing and oil displacement performance, providing a new idea and an efficient and economical solution for alkylcarboxamidine chemical additives for the development of ultra-low permeability and tight oil reservoirs.

[0006] The first aspect of the present application protects a CO2-responsive alkylcarboxamidine surfactant with clay stabilizing and oil displacement functions, wherein the alkylcarboxamidine is a straight-chain alkylcarboxamidine, and the chemical structure of the straight-chain alkylcarboxamidine is as follows:

[0007] The straight-chain alkylcarboxamidine includes one or more of N-dodecyl-N, N-dimethylformamidine, N-tridecyl-N, N-dimethylformamidine, N-tetradecyl-N, N-dimethylformamidine, N-pentadecyl-N, N-dimethylformamidine, N-hexadecyl-N, N-dimethylformamidine, N-heptadecyl-N, N-dimethylformamidine, and N-octadecyl-N, N-dimethylformamidine.

[0008] The second aspect of the present application protects a method for the application of a CO2-responsive alkylcarboxamidine surfactant with clay stabilizing and oil displacement functions in clay stabilizing.

[0009] Preferably, the method comprises the following steps: (a) preparing an aqueous solution of the alkylcarboxamidine surfactant with a concentration of 0.1-1.0 wt.%; (b) passing carbon dioxide gas into the aqueous solution of the alkylcarboxamidine surfactant prepared in step (a) for a certain period of time to completely protonate the alkylcarboxamidine surfactant, thereby obtaining a protonated alkylcarboxamidine surfactant solution; (c) adding the protonated alkylcarboxamidine surfactant solution into clay, and the mass ratio of the clay to the protonated alkylcarboxamidine surfactant is 50:1-5:1.

[0010] The third aspect of the present application protects a method for the application of a CO2-responsive alkylcarboxamidine surfactant with clay stabilizing and oil displacement functions in oil displacement.

[0011] Preferably, the method comprises the following steps: (a) preparing an aqueous solution of alkyl amidine surfactant with a concentration of 0.01-1.0 wt.%; (b) passing carbon dioxide gas into the aqueous solution of alkyl amidine surfactant prepared in step (a) for a certain period of time to completely protonate the alkyl amidine surfactant, thereby obtaining a protonated alkyl amidine surfactant solution; (c) adding the protonated alkyl amidine surfactant solution into oil sand, and the mass ratio of oil sand to protonated alkyl amidine surfactant is 1000:1-10:1. Advantages

[0012] (1) The present application integrates the traditional independent clay stabilizing function and oil displacement function into a single alkyl amidine molecular structure, realizes the characteristics of "one dose and double effect", simplifies the chemical injection process, reduces the total amount of chemicals and operation cost, and avoids the compatibility risk between different chemicals.

[0013] (2) The CO2-responsive switch-type alkyl amidine surfactant provided by the present application can realize "on-demand activation" of the reservoir, can accurately act on the target area, reduces invalid consumption, and is especially suitable for collaborative use with CO2 oil displacement technology. BRIEF DESCRIPTION OF DRAWINGS

[0014] The following drawings only schematically illustrate and explain the present application, and do not serve to limit the scope of the present application, in which: Figure 1 is the synthesis route of the alkyl amidine of the present application; Figure 2 is the nuclear magnetic resonance spectrum of the alkyl amidine molecule of the present application; Figure 3 is the mass spectrum of the alkyl amidine molecule of the present application; Figure 4 is the surface activity parameter of the aqueous solution of the alkyl amidine molecule of the present application; Figure 5 is the HLB value, emulsion interfacial charge and interfacial tension of the alkyl amidine molecule of the present application; Figure 6 is the foaming performance of the aqueous solution of the alkyl amidine of Example 1 of the present application before and after contacting with CO2; Figure 7 is the emulsifying performance of the aqueous solution of the alkyl amidine of Example 1 of the present application before and after contacting with CO2; Figure 8 is the clay stabilizing performance of the aqueous solution of the alkyl amidine of Example 2 of the present application before and after contacting with CO2; Figure 9 is the clay stabilizing implementation case data result of the alkyl amidine molecule of Example 2 of the present application; Figure 10 Example 3 of this application shows the clay washing performance before and after contact between the alkylamidine aqueous solution and CO2; Figure 11 This is the data result of the washing oil performance implementation case of alkyl amidine molecules in Example 3 of this application; Detailed Implementation

[0015] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0016] To facilitate understanding of the present invention, a more complete description of this application will be provided below with reference to relevant embodiments. Preferred embodiments of the present application are given below. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough and complete understanding of the disclosure of this application will be achieved.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0018] As used herein, the terms "and / or," "or / and," and "and / or" encompass any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR."

[0019] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0020] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0021] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0022] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument, such as ±5°C, ±4°C, ±3°C, ±2°C, or ±1°C.

[0023] In this application, unless otherwise specified, the terms "size," "particle size," and "diameter" generally refer to average values. In this application, "particle size" and "particle diameter" have the same definition, both representing the average particle size of spheres or spheroids.

[0024] In this document, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0025] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0026] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0027] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0028] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0029] The first aspect of this application protects a CO2-responsive alkylamidine surfactant that combines clay stabilization and oil displacement functions, wherein the alkylamidine is a straight-chain alkylamidine, and the chemical structural formula of the straight-chain alkylamidine is as follows: .

[0030] The straight-chain alkylamidines include one or more of N-dodecyl-N,N-dimethylformamidine, N-tridecyl-N,N-dimethylformamidine, N-tetradecyl-N,N-dimethylformamidine, N-pentadecanyl-N,N-dimethylformamidine, N-hexadecyl-N,N-dimethylformamidine, N-heptadecyl-N,N-dimethylformamidine, and N-octadecyl-N,N-dimethylformamidine.

[0031] When the carbon chain length is less than 12, alkylamidines achieve an equilibrium in terms of hydrophilicity and lipophilicity to emulsify the oil phase. However, alkylamidines with a carbon chain length greater than 12 are too hydrophobic and too lipophilic to emulsify crude oil, requiring protonation to adjust their hydrophilicity and lipophilicity to achieve emulsifying ability. Alkylamidines with more than 18 carbon atoms have poor self-solubility.

[0032] The alkylamidinium surfactant of this application was synthesized according to the Scoggins method, the synthetic route of which is attached. Figure 1 As shown. The molar ratio of N,N-dimethylformamide dimethyl acetal (DDA) to alkylamine is 1.2:1. The specific synthesis conditions are as follows (linear alkylamines with an odd number of carbon atoms between 12 and 18 are expensive; this experiment uses alkylamines with an even number of carbon atoms as an example).

[0033] N-Dodecyl-N,N-Dimethylformamidinium (hereinafter referred to as dodecamidinium in the examples): Dodecylamine (0.05 mol, 9.27 g), DDA (0.06 mol, 7.15 g).

[0034] N-Tetradecyl-N,N-Dimethylformamidinium (hereinafter referred to as tetradecamidinium in the examples): tetradecylamine (0.05 mol, 10.67 g), DDA (0.06 mol, 7.15 g).

[0035] N-Hexadecyl-N,N-Dimethylformamidin (hereinafter referred to as hexadecamidin): hexadecylamine (0.05 mol, 12.07 g), DDA (0.06 mol, 7.15 g).

[0036] N-Octadecyl-N,N-Dimethylformamidin (hereinafter referred to as octadecamidin): Octadecylamine (0.05 mol, 13.48 g), DDA (0.06 mol, 7.15 g).

[0037] In the experiment, the condensation reaction temperature was controlled at 65 °C, and the reaction was carried out for 30 minutes under nitrogen protection. The resulting reaction mixture was then rotary evaporated at 50 °C for 20 minutes to remove volatile byproducts and unreacted raw materials. The alkylamidine surfactant of this application was finally collected and stored for later use.

[0038] The molecular structures of the obtained alkylformamidin surfactants were characterized by ¹H NMR and mass spectrometry. (See attached image.) Figure 2 and attached Figure 3 As shown, its chemical structure is completely consistent with the design of the target molecule.

[0039] The second aspect of this application protects a method for applying a CO2-responsive alkylamidine surfactant with both clay stabilizing and oil displacement functions in clay stabilization.

[0040] In some embodiments, the method includes the following steps: (a) Prepare an aqueous solution of alkylamidine surfactant with a concentration of 0.1~1.0 wt.%; (b) Carbon dioxide gas is introduced into the aqueous solution of alkylamidine surfactant prepared in step (a) and maintained for a certain period of time to obtain a protonated alkylamidine surfactant solution; In some embodiments, the CO2 gas is introduced and held for 5-60 minutes to allow the alkylamidine surfactant to be fully protonated.

[0041] (c) Add a protonated alkylamidine surfactant solution to clay, wherein the mass ratio of clay to protonated alkylamidine surfactant is 50:1 to 5:1.

[0042] The synthesized series of alkylamidine surfactants are nonionic surfactants that can stabilize clay through hydrogen bonding. When CO2 is introduced, the surfactants are converted into cationic surfactants. The cationic groups are firmly adsorbed onto the negatively charged clay surface through strong electrostatic attraction, providing a more effective stabilizing effect.

[0043] The third aspect of this application protects a method for applying a CO2-responsive alkylamidine surfactant with both clay stabilizing and oil displacement functions in oil displacement.

[0044] In some embodiments, the method includes the following steps: (a) Prepare an aqueous solution of alkylamidine surfactant with a concentration of 0.01~1.0 wt.%; (b) Carbon dioxide gas is introduced into the aqueous solution of alkylamidine surfactant prepared in step (a) and maintained for a certain period of time to obtain a protonated alkylamidine surfactant solution; In some embodiments, the CO2 gas is introduced and held for 5-60 minutes to allow the alkylamidine surfactant to be fully protonated.

[0045] (c) Add the protonated alkylamidine surfactant solution to the oil sand, wherein the mass ratio of oil sand to protonated alkylamidine surfactant is 1000:1 to 10:1. Example

[0046] 1.1 Interfacial Activity of Alkylamidinium Surfactants Figure 4 and Figure 5 Key physicochemical parameters of the alkylamidine surfactant aqueous solution before and after CO2 contact were summarized and compared, including its surface activity (such as critical micelle concentration (CMC) and surface tension), hydrophilic-lipophilic balance (HLB), emulsion zeta potential, and oil-water interfacial tension. The results show that the alkylamidine surfactant exhibits excellent interfacial activity, significantly reducing the surface tension of the aqueous phase and the oil-water interfacial tension. After CO2 contact, it forms positively charged emulsion droplets at the interface. These characteristics provide crucial data support for its combined clay stabilization and oil displacement functions.

[0047] 1.2 Foaming and Emulsifying Properties 1.2.1 Foaming performance Foaming performance was tested using a stoppered graduated cylinder (100 mL) and distilled water as the solvent. First, a series of aqueous solutions of alkylamidine surfactants with different concentrations (0.01~10 wt.%) were prepared.

[0048] Take 10 mL of sample solution and place it in a stoppered graduated cylinder, then manually shake it up and down 30 times. For CO2-responsive alkylamidine samples, CO2 should be bubbled into the above surfactant solution for 10 minutes, and the resulting foam volume should be recorded and photographed. The foam volume in the system without CO2 bubbling is denoted as _____. V 0, the volume of foam in the CO2 system is denoted as V 1. The change in solution foam volume before and after protonation (Δ) V = V 1- V 0) was used to evaluate the CO2-responsive foaming performance, and the results are as follows: Figure 6As shown, dodecaamidine, tetradecaamidine, hexadecamidine, and octadecamidine all produce good foaming properties upon contact with CO2. Furthermore, in the comparative experiment, decaamidine and octamidine also produced foaming properties upon contact with CO2, but butamidine and hexaamidine did not.

[0049] 1.2.2 Emulsifying properties Prepare a series of aqueous solutions of alkylamidine surfactants with different concentrations (0.01~1.0 wt.%). For each sample, take 10 mL of the solution and transfer it to a stoppered graduated cylinder.

[0050] Then add 10 mL of anhydrous kerosene containing trace amounts of Sudan IV (an oil-soluble dye used for visual comparison of the oil-water interface).

[0051] In an ambient atmosphere (air), CO2 was introduced into the mixture for 30 minutes, and then the mixture was emulsified using a homogenizer at 4000 rpm for 30 seconds each time, repeated 3 times.

[0052] The time required for 5 mL of aqueous phase to separate out during static observation was used as a quantitative evaluation index of emulsion stability. The results are as follows: Figure 7 As shown, dodecaamidine, tetradecaamidine, hexadecaneamidine, and octadecaneamidine all exhibit good emulsifying ability upon contact with CO2. However, in the comparative experiment, butamidine, hexadecaneamidine, decaamidine, and octaneamidine, while possessing emulsifying ability, exhibited demulsification upon contact with CO2, making them unsuitable for oil displacement applications in CO2 reservoirs. Example

[0053] Sodium bentonite was dried at 60 °C for 24 hours to remove moisture. Then, 0.5 g of the dried sodium bentonite was placed in a 10 mL centrifuge tube.

[0054] Add anhydrous kerosene, deionized water, and a 1 wt.% aqueous solution of alkylamidine surfactant to the centrifuge tubes to the mark. Vigorously shake the centrifuge tubes to thoroughly mix the bentonite with the liquid, then let them stand for 2 hours.

[0055] Centrifuge the tubes at 1500 rpm for 15 minutes. Record the volume of bentonite, with the volumes of anhydrous kerosene, deionized water, and the aqueous solution of the alkyl amidine surfactant recorded as follows: V 0、 V 1 and V 2. Because kerosene is a non-polar solvent, sodium-based bentonite does not swell in it. V 0 represents the initial volume of the clay used. V 1 and V 2 represents the expanded volume of clay in water with and without alkylamidine surfactant, respectively.

[0056] Calculate the anti-swelling rate according to the following formula ( ),in V 1- V 0 represents the actual expansion volume of clay in water. V 1- V 2 represents the swelling volume measured in the presence of a surfactant.

[0057]

[0058] CO2 gas was bubbled through the prepared aqueous solution of alkylamidine surfactant and maintained for 5-60 min to obtain the protonated alkylamidine surfactant. The above steps were repeated. The surfactant's effect on clay stabilization results are as follows: Figure 8 As shown.

[0059] When the concentration of the alkylamidine aqueous solution is 1 wt.%, the anti-swelling rate of sodium bentonite in the above comparative system (butamidine, hexamidine, octamidine, decanamidine, dodecylamidine, tetradecylamidine, hexadecylamidine, octadecylamidine) is calculated as follows: Figure 9 As shown in the figure. Experiments show that although C4~C18 alkylamidines all exhibit good clay anti-swelling properties, their foaming and emulsification behaviors vary depending on the carbon chain length: butamidine and hexamidine did not exhibit any foaming ability, and could not emulsify after contact with CO2, instead exhibiting demulsification; octamidine and decanamidine, although possessing foaming ability, could not emulsify after contact with CO2, and also exhibited demulsification. Example

[0060] Oil-contaminated sand (hereinafter referred to as oil sand) samples were prepared using crude oil from Changqing Oilfield and in accordance with standard methods.

[0061] 2.0 g of oil sand was dispensed into 50 mL centrifuge tubes, and 20 mL of the corresponding CO2-responsive alkylamidine surfactant aqueous solution was added to each centrifuge tube, with a concentration range of 0.01~1% wt.%.

[0062] After vigorously shaking the centrifuge tubes to fully mix the oil sand and alkylamidine surfactant solution, place them in a 50 ℃ oven and let them stand for 24 h.

[0063] Centrifuge the centrifuge tubes to achieve solid-liquid separation. After removing the upper oil phase, briefly wash the remaining solid with deionized water, dry it at 50 °C, and weigh it.

[0064] Calculate the oil washing efficiency using the following formula ( ):in m 0 represents the initial oil sand mass. m 1 represents the quality of the oil sand after washing and drying. m oilThe crude oil loading on the surface of quartz sand is measured by repeated washing with toluene until the oil sand regains its initial white appearance, as shown in the attached figure. Figure 10 As shown.

[0065]

[0066] Among them, when the concentration of the alkylamidine aqueous solution is 0.05 wt.%, the washing efficiency of dodecylamidine, tetradecylamidine, hexadecylamidine, and octadecylamidine is shown in the attached figure. Figure 11 As shown.

[0067] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0068] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A CO2-responsive alkylamidine surfactant with both clay stabilizing and oil displacement functions, characterized in that, The alkylamidinium is a straight-chain alkylamidinium, and the chemical structural formula of the straight-chain alkylamidinium is as follows: .

2. A method for applying the CO2-responsive alkylamidine surfactant with both clay stabilizing and oil displacement functions as described in claim 1 in clay stabilization.

3. The method according to claim 2, characterized in that, Includes the following steps: (a) Prepare an aqueous solution of alkylamidine surfactant with a concentration of 0.1~1.0 wt.%; (b) CO2 gas is introduced into the aqueous solution of alkylamidine surfactant prepared in step (a) and maintained for a certain time to obtain a protonated alkylamidine surfactant solution; (c) Add a protonated alkylamidine surfactant solution to clay, wherein the mass ratio of clay to protonated alkylamidine surfactant is 50:1 to 5:

1.

4. A method for applying the CO2-responsive alkylamidine surfactant of claim 1, which has both clay stabilizing and oil displacement functions, to oil displacement.

5. The method according to claim 4, characterized in that, Includes the following steps: (a) Prepare an aqueous solution of alkylamidine surfactant with a concentration of 0.01~1.0 wt.%; (b) Carbon dioxide gas is introduced into the aqueous solution of alkylamidine surfactant prepared in step (a) and maintained for a certain period of time to obtain a protonated alkylamidine surfactant solution; (c) Add the protonated alkylamidine surfactant solution to the oil sand, wherein the mass ratio of oil sand to protonated alkylamidine surfactant is 1000:1 to 10:1.

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