CN111088024A - High-temperature high-salt oil reservoir oil-washing agent, preparation method thereof and carbon dioxide oil displacement method - Google Patents

Abstract

The invention relates to a high-temperature high-salt oil reservoir oil washing agent, a preparation method thereof and a carbon dioxide oil displacement method, and mainly solves the problems that a surfactant can reach ultralow interfacial tension in the existing oil field high-temperature high-salt oil reservoir environment, but the stripping capability and the oil washing efficiency on crude oil on rocks are not high, and the high-temperature high-salt oil reservoir oil washing agent comprises a cationic surfactant and an anionic surfactant, wherein the molar ratio of the cationic surfactant to the anionic surfactant is 1: 0.01-1: 100; wherein the cationic surfactant is selected from quaternary ammoniumAt least one of a salt or a quaternary ammonium base; the anionic surfactant is selected from at least one of molecular general formulas shown in formula (I), R₁Is selected from C₈～C₃₀Aliphatic radical of (2), R₂Is selected from H or C₈～C₃₀The fat base technical proposal solves the problem well and can be used for CO in oil fields₂And the recovery efficiency is improved by swallowing and spitting and oil displacement.

Description

High-temperature high-salt oil reservoir oil-washing agent, preparation method thereof and carbon dioxide oil displacement method

Technical Field

The invention relates to a high-temperature high-salinity reservoir oil-washing agent, a preparation method thereof and a carbon dioxide oil-displacing method.

Background

With the increase of world energy demand, the reasonable development and utilization of petroleum have attracted great attention of people, and the requirements on the production quantity and the production efficiency of petroleum are higher and higher. The method realizes the efficient exploitation of oil and gas resources, and has practical significance and important strategic significance for improving the yield of crude oil. Conventional oil recovery methods (primary and secondary methods) generally produce only 1/3 for the geological reserves of crude oil, and also fail to produce about 2/3 of crude oil, and thus enhanced oil recovery has become a major issue for oil recovery research in situations where energy is increasingly scarce. Tertiary oil recovery techniques are effective methods for increasing oil recovery and can be divided into four categories: the first is thermal flooding, including steam flooding, in-situ combustion and the like; second, miscible flooding, comprising CO₂Miscible phase, hydrocarbon miscible phase and other inert gas miscible phase flooding; thirdly, chemical flooding; and fourthly, microbial oil recovery, including biopolymer and microbial surfactant flooding. Chemical flooding is a very important and large-scale technology for tertiary oil recovery, and comprises polymer flooding, surfactant flooding, alkali water flooding and the like, and various combination technologies of polymer, alkali and surfactant. The chemical flooding effect is the result of physical action and chemical action, the physical action is the swept action of the displacement fluid, and the chemical action is the microscopic oil displacement action of the displacement fluid, and the core of the chemical flooding effect is to reduce the interfacial tension of the displacement fluid and crude oil, which is why the surfactant plays a significant role in the chemical flooding technology.

Many scholars at home and abroad use CO for oil reservoir₂The research of improving the recovery ratio of crude oil and the laboratory experiment and the field application prove that CO₂Is high in efficiencyAn oil displacing agent. CO2₂Flooding is an important means for improving the recovery ratio of crude oil in tertiary oil recovery of an oil field. CO injection₂The mechanism of action of the technology can be divided into CO₂Miscible flooding and CO₂And (4) non-miscible flooding. The thin oil reservoir mainly adopts CO₂Miscible flooding, whereas heavy oil reservoirs mainly use CO₂And (4) non-miscible flooding. CO2₂The effect of improving the recovery ratio is mainly to promote the expansion of crude oil, improve the oil-water fluidity ratio, dissolve gas flooding and the like. CO2₂Oil displacement is an important means for improving the recovery ratio of crude oil in tertiary oil recovery of an oil field by injecting CO into a stratum₂Gas, reduce the viscosity of crude oil, and achieve the purpose of improving the recovery ratio of crude oil. The main way is dissolving gas flooding; non-miscible flooding through volume expansion and viscosity reduction of crude oil, namely viscosity reduction effect; the hydrocarbons in the crude oil are extracted in the reservoir by the miscible effect.

The carbon dioxide oil displacement mechanism mainly comprises 1, viscosity reduction mechanism and CO₂Dissolving in oil, reducing the viscosity of crude oil, improving the fluidity of oil, being beneficial to improving the sweep coefficient of the oil displacement agent and improving the yield of crude oil. At 40 ℃ CO₂Dissolving in asphalt can greatly reduce the viscosity of asphalt. At higher temperatures (greater than 120 ℃), CO₂① residual oil left in an oil layer after water flooding is in inverse proportion to an expansion coefficient, namely the larger the expansion is, the less the oil quantity remained in the oil layer is, ② oil drops dissolving the carbon dioxide push water out of pore spaces, so that a water-wet system forms a drainage process rather than a water absorption process, the relative permeability curve of oil drainage is higher than the automatic oil absorption relative permeability curve of the oil drainage, an oil flow environment which is favorable under any given saturation condition is formed, on the one hand, elastic energy can be obviously increased after the volume expansion of ③ crude oil, on the other hand, the residual oil after the volume expansion is separated or partially separated from the constraint of formation water, and becomes movable oil.3 dissolved gas flooding mechanism, CO in the oil layer₂The dissolved gas, which is partially free to vaporize as the temperature increases downhole, stores some of the energy in the form of pressure energy. When the reservoir pressure is reduced, a large amount of CO₂The oil is dissociated from the crude oil and is driven into a shaft, so that the effect of dissolving gas drive is achieved. Because the gas has higher migration velocity, the oil layer blockage is spit back out. According to statistics, use CO₂Dissolved gas flooding can produce 18.6% of the underground oil. 4 acidizing unblocking action, CO₂The oil is slightly acidic after being dissolved in water and reacts with stratum matrixes, so that part of impurities are acidolyzed, and the permeability of an oil layer is improved. Under a certain pressure difference, part of the free gas has a strong scouring effect on the blockage of the oil layer, and the formation blockage caused by secondary pollution can be effectively dredged. 5 diffusion of molecules, immiscible CO₂The oil displacement mechanism is mainly established in CO₂The oil solubility causes the change of the oil characteristics. In order to minimize oil viscosity and increase oil volume for optimal displacement efficiency, it is necessary to have sufficient time for the CO to flow under reservoir temperature and pressure conditions₂Saturated crude oil. However, the formation matrix is complex, with injected CO₂It is also difficult to mix well with the crude oil in the reservoir. In most cases, it dissolves in the crude oil by the slow diffusion of molecules.

The carbon dioxide has unique performance, and when the crude oil is dissolved with the carbon dioxide, the fluidity, the rheological property and the oil reservoir property are improved. Many successful experiences have been accumulated at home and abroad, so that the oil displacement efficiency of the oil field can be obviously improved, and the recovery ratio of crude oil can be improved. The carbon dioxide flooding technology is an important technical path for developing carbon sequestration of oil companies, and is one of the best combination points for realizing the utilization and sequestration of carbon dioxide resources. The large-scale carbon dioxide is always used for increasing the production of petroleum and coal bed gas, the popularization and the application of the carbon dioxide flooding technology can change waste into valuable, and the technology has the potential of large-scale carbon dioxide sequestration, and is recognized as the most important sequestration mode of carbon dioxide in the near-middle period. Foreign countries have already demonstrated in the field for many years and have obtained good results. For example, the technology has been demonstrated and popularized in the last 80 th century in the United states to obtain depleted oil wellsStable production for a long time is obtained. Carbon dioxide flooding is a mature oil recovery technology. According to incomplete statistics, nearly 80 carbon dioxide flooding projects are currently implemented all over the world. The United states is the country where the carbon dioxide flooding project is most developed, and the amount of carbon dioxide injected into the reservoir per year is about 2000 x 10⁴～3000×10⁴t, where 300X 10⁴t is from waste gas from coal gasification plants and fertilizer plants. According to the research results of the project of ' second potential evaluation of enhanced recovery ratio of oil field developed on land in China ' and research on development strategy ', the carbon dioxide has huge application potential in petroleum exploitation in China. 63.2X 10 which is proved in China⁸the crude oil reserves of the low permeability reservoirs, particularly the reserves which are not used for about 50 percent of the low permeability reservoirs, have more obvious technical advantages than water flooding by using carbon dioxide flooding. With the development and perfection of the technology and the continuous expansion of the application range, carbon dioxide can be predicted to become an important resource for improving the development effect of oil fields and increasing the recovery ratio of crude oil in China.

Research by the Scoring military et al (see 2000, 2, 30, volume, 1, university of northwest, university, journal of science, edition, 28-31) suggests that a mixed system of cetyltrimethylammonium bromide (CTAB) and Sodium Dodecyl Sulfate (SDS) has a solubilizing effect. In the process of oil exploitation, oil displacement can be realized by utilizing solubilization, and oil adhered to rock formation sand is washed down, so that the oil recovery rate is improved. The Huanghong Kong et al (No. 4 of volume 29 of 8 month of 2007, 101-104) researches the interfacial tension of a complex system of anionic surfactants such as petroleum sulfonate, petroleum carboxylate, alkylbenzene sulfonate and the like, cetyl trimethyl ammonium bromide and alkali and draws the following conclusion: the addition of cationic surfactant improves the interfacial activity of petroleum carboxylate, alkylbenzene sulfonate and petroleum sulfonate

In the current practice process of improving the recovery ratio by using carbon dioxide, problems also exist, such as gas channeling, high requirements on miscible phase pressure, strong extraction capability of CO2 on light hydrocarbon components in residual crude oil, and relatively poor oil washing efficiency on heavy components deposited on rocks, especially in the oil reservoir environment with high temperature and high salt under the stratum condition. Therefore, the combined process of the carbon dioxide and the high-temperature high-salinity reservoir oil-washing agent is one of the ways for further improving the recovery ratio in the carbon dioxide huff-puff and puff process and the oil displacement process.

Disclosure of Invention

One of the technical problems to be solved by the invention is that the surfactant can achieve ultralow interfacial tension in the high-temperature and high-salinity oil reservoir environment of the existing oil field, but has low capability of stripping crude oil on rocks and low oil washing efficiency, especially CO₂The problem of poor oil washing efficiency in oil displacement and huff and puff is to provide a high-efficiency oil washing agent for high-temperature and high-salinity oil reservoir suitable for carbon dioxide flooding, which is prepared by mixing with CO₂The alternative injection improves the crude oil stripping capability and the oil washing efficiency on the rock, achieves the aim of further improving the recovery ratio of the crude oil, and has the advantages of no alkali, no corrosion and scale damage, low use concentration and high oil washing efficiency.

The second technical problem to be solved by the invention is to provide a preparation method of the high-efficiency oil washing agent for the high-temperature high-salinity oil reservoir, which is suitable for carbon dioxide flooding and corresponds to the first technical problem.

The invention aims to solve the technical problem of providing a carbon dioxide flooding method, and the method is suitable for solving the technical problem of high-temperature high-salinity oil reservoir high-efficiency oil washing agent and CO suitable for carbon dioxide flooding₂The alternate injection improves the crude oil stripping capability and the oil washing efficiency on the rock, and achieves the purpose of further improving the recovery ratio of the crude oil.

In order to solve one of the above technical problems, the technical scheme adopted by the invention is as follows: the high-temperature high-salt oil reservoir oil-washing agent comprises a cationic surfactant and an anionic surfactant, wherein the molar ratio of the cationic surfactant to the anionic surfactant is 1: 0.01-100; wherein the cationic surfactant is selected from at least one of quaternary ammonium salt or quaternary ammonium base; the anionic surfactant is selected from at least one of the molecular formulas shown in the formula (I):

in the formula (I), R₁Is selected from C₈～C₃₀Aliphatic radical of (2), R₂Is selected from H or C₈～C₃₀M, M' is a cation or a cationic group.

In the above technical solution, preferably R is₁Is selected from C₈～C₂₂Alkyl of R₂Is selected from H or C₈～C₂₂Alkyl group of (1).

In the above technical solution, preferably R is₁At least one selected from dodecyl, hexadecyl and octadecyl; r₂Selected from H or at least one of dodecyl, hexadecyl and octadecyl.

In the above technical solution, preferably M, M' is H⁺、Na⁺、NH₄ ⁺、Ca²⁺、Mg²⁺、Al³⁺At least one of (1).

In the above technical solution, the quaternary ammonium salt is preferably selected from tetraalkylammonium salts; the quaternary ammonium base is preferably selected from tetraalkyl quaternary ammonium bases.

In the above technical solution, the preferable scheme of the anionic surfactant is at least one of sodium dodecyl diphenyl ether disulfonate, tetradecyl diphenyl ether disulfonate, hexadecyl diphenyl ether disulfonate, and octadecyl diphenyl ether disulfonate.

In the technical scheme, the molar ratio of the cationic surfactant to the anionic surfactant is preferably 1 (1-10).

To solve the second technical problem, the invention adopts the following technical scheme: the preparation method of the high-temperature high-salinity reservoir oil-washing agent in any one of the technical schemes for solving the technical problems comprises the following steps:

(a) respectively dissolving the anionic surfactant and the cationic surfactant in water to obtain an anionic surfactant aqueous solution and a cationic surfactant aqueous solution;

(b) and (b) mixing the anionic surfactant aqueous solution and the cationic composite surfactant aqueous solution prepared in the step (a) according to the molar ratio of the cationic surfactant to the anionic surfactant, and uniformly stirring to obtain the required high-temperature high-salt oil reservoir oil-washing agent.

In order to solve the third technical problem, the technical scheme adopted by the invention is as follows: a carbon dioxide oil displacement method comprises the steps of alternately injecting an oil displacement agent containing the high-temperature high-salinity oil reservoir oil displacement agent according to any one of the technical schemes for solving the technical problems and carbon dioxide into an oil reservoir to contact with crude oil, and displacing the crude oil.

In the technical scheme, the oil reservoir temperature of the oil reservoir is preferably 60-120 ℃; further preferably 80 to 100 ℃.

In the technical scheme, the oil displacement agent comprises the following components in percentage by mass:

(1) 0.01-5.0% of the high-temperature high-salinity oil reservoir oil-washing agent by mass of the contained cationic surfactant and anionic surfactant;

(2) 92.0-99.98% of injected water.

In the technical scheme, the preferable range of the dosage of the oil-washing agent for the high-temperature and high-salinity oil reservoir is 0.05-1.0%; the preferable range of the dosage of the injected water is 98.00-99.90%.

In the above technical solution, the carbon dioxide flooding method preferably includes the following steps:

(a) respectively dissolving the needed anionic surfactant and cationic surfactant in water, and then mixing the anionic surfactant and the cationic surfactant according to a proportion to obtain the needed high-temperature high-salinity oil reservoir oil-washing agent;

(b) mixing the required amount of the high-temperature high-salinity oil reservoir oil-washing agent prepared in the step (a) with the required amount of injected water, and stirring for 1-3 hours to obtain the required oil-displacing agent;

(c) under the condition of oil reservoir temperature, stratum water is used for displacement to be oil-free, then the oil displacement agent prepared in the step (b) is injected, and then CO is injected₂Alternately injecting oil displacement agent and CO₂And driving water to 100 percent.

The high-efficiency oil washing agent for the high-temperature high-salinity oil reservoir has the following advantages:

(1) surfactant composition in the groundCan form 10 with underground crude oil under layer conditions^-3～10^-4The milli-Newton/meter ultra-low interfacial tension and the oil washing rate of more than 90 percent simultaneously overcome the defects of carbon dioxide huff and puff and the oil washing efficiency of heavy components in the oil displacement process, meet the requirement of environmental protection, have no harm to equipment and can achieve the optimal oil washing efficiency;

(2) temperature 80-120 ℃, degree of mineralization more than 30000-100000 mg/l, Ca²⁺、Mg²⁺The concentration of the catalyst is 0-4000 mg/L, and the catalyst can still form 10 with underground crude oil^-3～10^-4Ultra-low interfacial tension of milli-newtons per meter, with simple CO₂Compared with foam flooding or pure surfactant flooding, the method can still improve the recovery ratio by more than 10 percent on the basis, and obtains better technical effect.

By adopting the technical scheme of the invention, the obtained high-temperature high-salinity reservoir oil-washing agent and carbon dioxide carry out alternate synergistic oil displacement, and the oil displacement is performed with simple CO₂Compared with foam flooding or pure surfactant flooding, the method can still improve the recovery ratio by more than 10 percent on the basis, and obtains better technical effect.

The invention is further illustrated by the following examples.

Detailed Description

[ example 1 ]

Adding about 680 g of diphenyl ether into a reaction kettle, adding about 336 g of alpha-olefin with 12 carbon atoms, adding about 16 g of sulfonated styrene-divinylbenzene copolymer, gradually controlling the temperature to be 80-180 ℃, keeping the temperature for 1-5 hours until the reaction end point, filtering the sulfonated styrene-divinylbenzene copolymer, heating and distilling under reduced pressure, taking 270-350-fold fraction, sending the distilled liquid into a sulfonation kettle, adding 100 g of dichloromethane into the distilled liquid, beginning to dropwise add 235 g of chlorosulfonic acid, controlling the temperature to be 0-80 ℃, simultaneously extracting HCl gas, reacting for 1 hour after finishing the reaction, heating to 50 ℃, measuring the end point, reducing the pressure and extracting dichloromethane after the end point is reached, adding water, adding alkali and a small amount of lime to neutralize the solution to a pH value of 6.5-7.5, filtering, replenishing water to a finished product content of about 45 percent to obtain about 1580 g of sodium didodecyl diphenyl ether disulfonate, the yield based on alpha-olefin reaches more than 99 percent

[ example 2 ]

Adding about 300 g of diphenyl ether into a reaction kettle, adding about 253 g of alpha-olefin with 18C number, adding about 14 g of sulfonated styrene-divinylbenzene copolymer, gradually controlling the temperature to be 80-180 ℃, keeping the temperature for 1-5 hours until the reaction end point, filtering the sulfonated styrene-divinylbenzene copolymer, heating, carrying out reduced pressure distillation, taking 270-350 fraction, sending the distillate into a sulfonation kettle, adding 200 g of petroleum ether into the distillate, beginning to dropwise add 400 g of 120 fuming sulfuric acid, controlling the temperature to be 0-80 ℃, reacting for 1-5 hours, adding about 30 percent of water, stirring for 0.5 hour, standing, carrying out acid precipitation, removing waste acid after layering (the waste acid can be used with high-concentration fuming sulfuric acid in the next sulfonation to reduce the discharge of waste water), distilling off the petroleum ether, adding water, adding alkali and a small amount of lime to neutralize the pH value to be 6.5-7.5, filtering, replenishing water to the filtrate until the content of the finished product is about 45 percent, obtaining about 1390 g of the finished product of the octadecyl diphenyl ether disulfonic acid sodium, and the yield reaches more than 99 percent according to the alpha-olefin

[ example 3 ]

Respectively dissolving phenyl trimethyl ammonium chloride and the sodium didodecyl diphenyl ether disulfonate synthesized in the embodiment 1 into water, and then uniformly mixing the two solutions according to the molar ratio of 1: 0.1 of the phenyl trimethyl ammonium chloride to the sodium didodecyl diphenyl ether disulfonate to obtain the anion and cation compound surfactant. And then mixing the anionic and cationic compound surfactants with the injected water of the original oilfield and stirring for 2 hours to obtain a uniform and transparent high-efficiency oil displacement agent with the concentration of 0.1-0.5 wt%. Table 1 raw field site water properties. And respectively measuring the interfacial tension of the high-efficiency oil displacement agent and the crude oil in the original oilfield by using a TX-500C rotary drop interfacial tension meter. The results are shown in Table 2

TABLE 1

TABLE 2

Surfactant (% by weight)	0.10	0.2	0.3	0.5
					Interfacial tension (milli-cow/meter)	0.0055	0.0039	0.00176	0.00053

[ example 4 ]

Dodecyl trimethyl ammonium chloride and the sodium stearyl diphenyl ether disulfonate synthesized in the example 2 are respectively dissolved in water, and then the two solutions are uniformly mixed according to the molar ratio of the dodecyl trimethyl ammonium chloride to the sodium stearyl diphenyl ether disulfonate of 1: 5.5, so as to obtain the anion and cation compound surfactant. And then mixing the above-mentioned anion and cation compound surfactant with injected water of Jianghan oilfield, and stirring them for 2 hr so as to obtain a uniform and transparent high-effective oil-displacing agent whose concentration is 0.05-0.5 wt%. Table 3 field water properties of the Jianghan oil field. And respectively measuring the interfacial tension of the high-efficiency oil displacement agent and the crude oil in the Jianghan oil field by using a TX-500C rotary drop interfacial tension meter. The results are shown in Table 4

TABLE 3

TABLE 4

Surfactant (% by weight)	0.05	0.1	0.2	0.5
					Interfacial tension (milli-cow/meter)	0.0083	0.00518	0.0032	0.0028

[ example 5 ]

Octadecyl dimethyl benzyl ammonium chloride and the sodium didodecyl diphenyl ether disulfonate synthesized in the example 1 are respectively dissolved in water, and then the two solutions are uniformly mixed according to the molar ratio of the octadecyl dimethyl benzyl ammonium chloride to the sodium didodecyl diphenyl ether disulfonate of 1: 4.0, so as to obtain the anion and cation compound surfactant. And then mixing the anionic and cationic compound surfactants with injection water of the Shengli oilfield and stirring for 2 hours to obtain a uniform and transparent high-efficiency oil displacement agent with the concentration of 0.1-0.5 wt%. Table 5 victory field water properties. And respectively measuring the interfacial tension of the high-efficiency oil displacement agent and the crude oil of the Shengli oil field by using a TX-500C rotary drop interfacial tension meter. The results are shown in Table 6

TABLE 5

Item

Cl-

SO4 2-

HCO3 -

Na++K+

Ca2+

Mg2+

TDS of water mineralization

Water type

Mg/l

25237

186

634

2540

849

731

30177

CaCl2

TABLE 6

Surfactant (% by weight)	0.10	0.2	0.3	0.5
					Interfacial tension (milli-cow/meter)	0.0060	0.0077	0.0034	0.0025

[ example 6 ]

The prepared high-efficiency oil displacement agent (example 3) is taken, the crude oil on the site of the original oilfield is measured by a visible spectrophotometry method in the oil and gas industry standard SY/T5329-94, the measurement wavelength is 430nm, and the result is shown in Table 7.

TABLE 7

Concentration of oil-washing agent%	0.1	0.2	0.3	0.4	0.5
						Traits	Clarification	Clarification	Clarification	Clarification	Clarification
Efficiency of oil washing (%)	88.32	92.5	94.63	94.08	96.79

[ example 7 ]

The prepared high-efficiency oil displacement agent (example 4) and the crude oil in the field of oil fields in Jianghan are taken, the visible spectrophotometry method which is the method in the standard SY/T5329-94 in the oil and gas industry is adopted, the testing wavelength is 430nm, and the oil washing efficiency is measured, and the result is shown in Table 8.

TABLE 8

Concentration of oil-washing agent%	0.1	0.2	0.3	0.4	0.5
						Traits	Slight turbidity	Clarification	Clarification	Clarification	Clarification
Efficiency of oil washing (%)	91.5	93.2	92.0	95.1	97.6

[ examples 8 to 10 ]

The core displacement experiment was performed on a core having a length of 30 cm, a diameter of 2.5cm and a permeability of 1.5 μm 2, at a displacement experiment temperature of 80 ℃. Firstly, using the formation water of the original oilfield to drive the formation water to 93% water content, and transferring 0.2pv (core pore volume) CO₂After the oil-displacing agent of example 3 (use concentration: 0.4%) was further injected at 0.3pv, 0.2pv CO was further injected₂，CO₂The injection speed is 1, 1.5 and 2.5cm respectively³Min, finally driving water to 100% water content by adopting CO₂The recovery ratio can be improved by being alternatively driven by the oil displacement agent by more than 15.53 percent, 17.65 percent and 17.72 percent.

Claims (10)

1. The high-temperature high-salt oil reservoir oil-washing agent comprises a cationic surfactant and an anionic surfactant, wherein the molar ratio of the cationic surfactant to the anionic surfactant is 1: 0.01-1: 100; wherein the cationic surfactant is selected from at least one of quaternary ammonium salt or quaternary ammonium base; the anionic surfactant is selected from at least one of the molecular formulas shown in the formula (I):

in the formula (I), R₁Is selected from C₈～C₃₀Of (2)Aliphatic radical, R₂Is selected from H or C₈～C₃₀M, M' is a cation or a cationic group.

2. The high temperature high salt reservoir oil-washing agent according to claim 1, wherein R is₁Is selected from C₈～C₂₂Alkyl of R₂Is selected from H or C₈～C₂₂Alkyl group of (1).

3. The high temperature high salt reservoir oil-washing agent according to claim 1, wherein R is₁At least one selected from dodecyl, hexadecyl and octadecyl; r₂Selected from H or at least one of dodecyl, hexadecyl and octadecyl.

4. The high temperature high salt reservoir oil-washing agent according to claim 1, characterized in that M, M' is Na⁺、NH₄ ⁺、Ca²⁺、Mg²⁺、Al³⁺At least one of (1).

5. The high temperature high salt reservoir oil-washing agent according to claim 1, characterized in that the quaternary ammonium salt is selected from tetraalkylammonium salts; the quaternary ammonium base is selected from tetraalkyl quaternary ammonium bases.

6. The preparation method of the high-temperature and high-salinity oil reservoir oil-washing agent as claimed in any one of claims 1 to 5, comprising the following steps:

(a) respectively dissolving needed anionic surfactant and cationic surfactant in water, and then mixing according to a proportion;

(b) and (b) uniformly stirring the anion and cation composite surfactant mixed solution prepared in the step (a) to obtain the required high-temperature high-salinity oil reservoir oil-washing agent.

7. A carbon dioxide oil displacement method, which comprises the steps of alternately injecting an oil displacement agent containing the high-temperature high-salinity oil reservoir oil displacement agent as claimed in any one of claims 1 to 5 and carbon dioxide into an oil reservoir to contact with crude oil, and displacing the crude oil.

8. The carbon dioxide flooding method according to claim 7, characterized in that the oil-displacing agent comprises the following components in percentage by mass based on the total mass of the oil-displacing agent:

(1) the high-temperature high-salt reservoir oil-washing agent according to any one of claims 1 to 5, wherein the amount of the cationic surfactant and the anionic surfactant is 0.01 to 5.0% by mass;

(2) 92.0-99.98% of injected water.

9. The carbon dioxide flooding method according to claim 7 or 8, characterized by comprising the following steps:

(a) respectively dissolving the needed anionic surfactant and cationic surfactant in water, and then mixing the anionic surfactant and the cationic surfactant according to a proportion to obtain the needed high-temperature high-salinity oil reservoir oil-washing agent;

(b) mixing the required amount of the high-temperature high-salinity oil reservoir oil-washing agent prepared in the step (a) with the required amount of injected water, and stirring for 1-3 hours to obtain the required oil-displacing agent;

(c) under the condition of oil reservoir temperature, stratum water is used for displacement to be oil-free, then the oil displacement agent prepared in the step (b) is injected, and then CO is injected₂Alternately injecting oil displacement agent and CO₂And driving water to 100 percent.

10. The carbon dioxide flooding method according to claim 7 or 8, characterized in that the flooding temperature is 60-120 ℃.