Surfactant system, preparation method and application thereof, and in-situ emulsification assisted CO2 oil displacement method

Abstract

The invention discloses a surfactant system, a preparation method and application thereof, and a method for in-situ emulsification assisted CO2 oil displacement. The system comprises water and a surfactant accounting for 0.1-0.5 wt% of the water, wherein the surface active agent is a mixture of a betaine type surface active agent, an extension type surface active agent and a sulfonate surface active agent in any ratio, and the system further comprises 0.01-5wt% of an additive. According to the surfactant system, starting from the interfacial film strength of a single surfactant, the stability of an emulsion is regulated and controlled by changing the compounding proportion of multiple surfactants, and the developed in-situ emulsification-assisted CO2 oil displacement surfactant system with the controllable emulsification blocking CO2 strength can reduce the oil-water interfacial tension while achieving emulsification blocking CO2, so that the oil displacement efficiency is improved, and the oil displacement efficiency is improved. Wide application prospects are realized. The in-situ emulsification-assisted CO2 oil displacement surfactant system provided by the invention has an excellent effect of improving the recovery rate on CO2-driven oil reservoirs, and the in-situ emulsification-assisted CO2 oil displacement recovery rate of core displacement can be improved by 10% or above compared with CO2-WAG displacement.

Description

Technical Field

[0001] The present invention relates to a surfactant system and a preparation method, application and in-situ emulsification auxiliary CO 2 Oil recovery method. Background Art

[0002] CO 2 It is a relatively low-cost gas that can interact with crude oil to a certain extent and is beneficial to crude oil development. 2 Gas can dissolve in crude oil, causing the volume of crude oil to expand, viscosity to decrease, and oil-water interfacial tension to decrease, thereby improving the fluidity of crude oil. When the reservoir pressure is higher than 9.6MPa and the temperature is lower than 105℃, CO 2 The gas is in contact with the crude oil for many times, and the light components in the crude oil are continuously extracted. 2 The light components of crude oil continue to increase, gradually reaching a near-miscible state or a miscible state. 2 Gas can reduce air pollution, reduce the greenhouse effect, and is beneficial to environmental protection. It is also a technology to improve the recovery rate of resources. 2 There are many factors that affect gas development, such as reservoir heterogeneity, CO 2 Unfavorable mobility ratio with crude oil, etc. These problems will cause CO 2 The gas channel is easy to escape, and after the gas channel is formed, the gas will flow along the channel, which is difficult to affect the matrix with high oil content, resulting in the inability of gas to circulate effectively, seriously affecting the development effect of the reservoir. Therefore, effective blocking of the gas channel is the primary issue of gas injection development (Yuan Shiyi, Petroleum Exploration and Development, 2022, 49(04): 828-834. Peng Hao. China University of Petroleum (Beijing), 2018.).

[0003] Currently, surfactants (abbreviated as “surfactants”) are used as auxiliary CO 2 Common additives for oil recovery enhancement: on the one hand, surfactants and CO 2 Contact can generate foam, which has the function of blocking high permeability channels and expanding the swept volume; on the other hand, surfactants also have the functions of reducing interfacial tension, emulsifying and dispersing crude oil and improving wettability during oil displacement. Based on the above requirements, the performance of surfactant systems focuses on reducing surface / interfacial tension, foaming and foam stability, emulsion stability, wettability, viscosity reduction, miscibility reduction, solubility, etc. However, most studies tend to ignore CO 2 The effect of dissolving in the oil-water phase and no in-situ emulsification assisted CO 2 Consider the system composition and effect analysis from the perspective of oil recovery.

[0004] Secondly, for auxiliary CO 2The surfactant system used to generate foam to enhance oil recovery is adsorbed on the gas-liquid interface to reduce surface tension and make CO 2 The solution produces a certain stability of foam during the flow of porous media, thereby blocking gas channeling. Some articles also believe that supercritical CO 2 The foam formed with water can be called "emulsion" (Song Xinmin, Petroleum Exploration and Development, 2023, 50(01): 206-218.). In order to produce the above effects, the surface tension, foaming height, foam half-life, foam seepage process, foam flooding effect, etc. of the surfactant are usually considered, and surfactants with strong ability to reduce surface tension, high foaming height, long foam half-life, large foam seepage resistance, and good foam flooding effect are preferred. However, this system usually ignores the consideration of the properties of oil-water emulsions. Summary of the invention

[0005] In order to at least partially solve the above technical problems existing in the prior art, further enrich the in-situ emulsification assisted CO 2 The present invention provides an in-situ emulsification-assisted CO2-assisted oil displacement system with high stability and strong pore-throat plugging ability. 2 Oil displacement surfactant combination system to improve CO 2 Oil recovery rate.

[0006] As one aspect of the present invention, a surfactant combination system is provided, which comprises water and a surfactant accounting for 0.1 to 0.5 wt% of the water; the surfactant is a mixture of betaine-type surfactants, extending surfactants and sulfonate surfactants in any ratio.

[0007] In one or some possible embodiments, the mass ratio of the betaine surfactant, the extending surfactant and the sulfonate surfactant is (0-10): (0-10): (0-10).

[0008] In one or some possible embodiments, the betaine-type surfactant is an alkyl sulfonate betaine;

[0009] The alkyl sulfobetaine is shown in formula (I): In formula (I), R is selected from a C12-C18 long-chain alkyl group.

[0010] In one or some possible embodiments, the extending surfactant is alkyl alcohol polyoxypropylene polyoxyethylene sulfonate;

[0011] The alkyl alcohol polyoxypropylene polyoxyethylene sulfonate is as shown in formula (II):

[0012]

[0013] In formula (II), n is one of 2, 4, 6, 8 or 10, and R is selected from a long-chain alkyl group of C12 to C18.

[0014] In one or some possible embodiments, the sulfonate surfactant is a petroleum sulfonate;

[0015] The petroleum sulfonate is a mixture of first-line products, second-line products and third-line products in any ratio.

[0016] In one or some possible embodiments, the mixing ratio of the reduced-line product, the reduced-line product and the reduced-line product is (0-5): (0-10): (0-10).

[0017] In one or some possible embodiments, the combination system further includes 0.01-5 wt % of additives.

[0018] In one or some possible embodiments, the additive is an alkaline substance or a neutral salt.

[0019] In one or some possible embodiments, when the additive is an alkaline substance, the mass fraction of the additive added to the combined system is 0.01 to 0.3%;

[0020] When the additive is a neutral salt, the mass fraction of the additive added to the combined system is 0.1 to 5%;

[0021] When the additive is a mixture of an alkaline substance and a neutral salt, the mass fraction of the additive added to the system is 0.01-5%.

[0022] In one or some possible embodiments, the alkaline substance is selected from one or more of sodium carbonate, sodium bicarbonate or sodium hydroxide;

[0023] The neutral salt is selected from one or more of sodium chloride, potassium chloride, calcium chloride, magnesium chloride or sodium sulfate.

[0024] As another aspect of the present invention, it relates to a method for preparing the above-mentioned surfactant combination system, which comprises: mixing the surfactant, the additive and the water to obtain the surfactant combination system of the emulsion.

[0025] As another aspect of the present invention, it relates to the above surfactant combination system in situ emulsification assisted CO 2 Application in oil recovery.

[0026] As another aspect of the present invention, it relates to an in-situ emulsification-assisted CO 2A method for oil displacement, wherein the method uses the above surfactant combination system to perform in-situ emulsification-assisted CO 2 Oil recovery.

[0027] In one or some possible embodiments, during the in situ emulsification-assisted CO 2 During oil displacement, the reservoir conditions are:

[0028] The total mineralization of water in the reservoir is 3000-80000 mg / L;

[0029] The reservoir temperature is 30-100°C;

[0030] The viscosity of the reservoir crude oil at the reservoir temperature is 1 to 20 cp;

[0031] The permeability of the reservoir is 0.01~50mD.

[0032] The surfactant combination system provided by the present invention adjusts the stability of the emulsion by changing the compounding ratio of multiple surfactants from the perspective of the interfacial film strength of a single surfactant. 2 Intensity-controlled in-situ emulsification-assisted CO 2 The combined system of oil displacement surfactants can achieve emulsification and plugging of CO 2 At the same time, it reduces the oil-water interfacial tension and has broad application prospects.

[0033] The in-situ emulsification-assisted CO 2 Oil displacement surfactant combination system for CO 2 The flooding reservoir has excellent enhanced oil recovery effect, and the in-situ emulsification-assisted CO 2 The recovery rate is comparable to CO 2 - WAG flooding (water-gas flooding) increased by more than 10%.

[0034] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention are realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0036] Figure 1 The figure is a trend diagram of the interfacial dilation modulus of the surfactant system according to the embodiment of the present invention as a function of periodic oscillation;

[0037] Figure 2The present invention shows an embodiment of the present invention, the surfactant system, and the water separation rate of the surfactant system varies with the shaking time;

[0038] Figure 3 This is a diagram of the local phenomena of the visualized microscopic oil displacement experiment in Example 2 of the present invention; wherein, the blank part simulates the rock skeleton, the dark shaded part is the oil phase (internal phase), and the light shaded part is the water-in-oil emulsion droplets generated in situ by the external phase. DETAILED DESCRIPTION

[0039] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0040] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0041] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0042] In the description of the present invention, it should be noted that the terms "include", "including", "have", "contain" and the like are open terms, meaning including but not limited to.

[0043] The betaine surfactant used in the embodiment is an industrial grade product, and its effective content is generally 40%. The substance is selected from C12-C18 long-chain alkyl sulfobetaine, wherein the long-chain alkyl can be dodecyl, hexadecyl or octadecyl, etc.;

[0044] The extended surfactant used in the embodiment is an industrial grade product, and its effective content is generally 50%. The substance is selected from C12-C18 long-chain alkyl alcohol polyoxypropylene sulfonate, wherein the long-chain alkyl can be dodecyl, hexadecyl or octadecyl, etc., and the addition number of the embedded segment of the polyoxypropylene group can be any one of 2, 4, 6, 8 or 10;

[0045] The petroleum sulfonate surfactant used in the embodiment is an industrial grade product, and its effective content is generally 50%. The substance is composed of first-line products, second-line products and third-line products, and the mixing ratio is (0-5): (0-10): (0-10), including but not limited to 1:4:7, 2:5:3, 2:3:6, etc.

[0046] The surfactant system prepared in the embodiment is subjected to the CO 2 During oil displacement, the reservoir conditions are: the total mineralization of water in the reservoir is 3000-80000 mg / L; the reservoir temperature is 30-100°C; the viscosity of the crude oil in the reservoir at the reservoir temperature is 1-20 cp; the permeability of the reservoir is 0.01-50 mD. In any embodiment, including but not limited to the total mineralization of water in the reservoir is 20000 mg / L, the reservoir temperature is 70°C, the viscosity of the crude oil in the reservoir at the reservoir temperature is 3.1 cp, and the permeability of the reservoir is 50 mD for high permeability and 5 mD for low permeability.

[0047] The present invention is further described below in conjunction with specific embodiments, and the protection scope of the present invention is not limited by the following embodiments. The materials mainly involved in the embodiments are conventional commercial products, and the water source used in the embodiments is injection water of the target oil field.

[0048] Example 1

[0049] The surfactant system of this embodiment includes 1.2% of the additive (sodium chloride) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0050] Among them, the surfactant is betaine surfactant, and the experimental water is the water injected on-site in a certain test area.

[0051] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0052] Example 2

[0053] The surfactant system of this embodiment includes 1.2% of an additive (potassium chloride) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3 wt % of the water;

[0054] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0055] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0056] Example 3

[0057] The surfactant system of this embodiment includes 1.2% of the additive (sodium sulfate) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0058] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 2:6:2, and the experimental water is the same as that in Example 1.

[0059] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0060] Example 4

[0061] The surfactant system of this embodiment includes 1.2% additive (sodium chloride and sodium sulfate mixed at a mass ratio of 2:1) by weight percentage, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0062] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 2:2:6, and the experimental water is the same as that in Example 1.

[0063] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0064] Example 5

[0065] The surfactant system of this embodiment includes 1.2% additives (sodium chloride, calcium chloride and sodium sulfate mixed in a mass ratio of 1:1:3) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0066] The surfactant is composed of a sulfonate surfactant, and the experimental water is the same as that in Example 1.

[0067] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0068] Example 6

[0069] The surfactant system of this embodiment includes 1.2% of the additive (sodium chloride) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.5wt% of the water;

[0070] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0071] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0072] Example 7

[0073] The surfactant system of this embodiment includes 1.2% of an additive (sodium hydroxide) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3 wt % of the water;

[0074] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0075] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0076] Example 8

[0077] The surfactant system of this embodiment includes 2.4% of the additive (sodium chloride) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0078] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0079] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0080] Example 9

[0081] The surfactant system of this embodiment includes 1.2% of an additive (sodium chloride) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.1 wt% of the water;

[0082] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0083] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0084] Example 10

[0085] The surfactant system of this embodiment includes 1.2% of the additive (sodium chloride) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0086] The surfactant composition is: a betaine surfactant, an extending surfactant and a sulfonate surfactant in a mass ratio of 1:1:1, and the experimental water is the same as that in Example 1.

[0087] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0088] Embodiment 11

[0089] The surfactant system of this embodiment includes 1.2% of the additive (sodium chloride) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0090] The surfactant is composed of an extending surfactant, and the experimental water is the same as that in Example 1.

[0091] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0092] Example 12

[0093] The surfactant system of this embodiment includes 1.2% additive (sodium hydroxide and sodium bicarbonate mixed at a mass ratio of 1:1) by weight percentage, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0094] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 2:6:2, and the experimental water is the same as that in Example 1.

[0095] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0096] Embodiment 13

[0097] The surfactant system of this embodiment includes 0.01% of an additive (sodium hydroxide) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3 wt % of the water;

[0098] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0099] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0100] Embodiment 14

[0101] The surfactant system of this embodiment includes 0.15% of an additive (sodium hydroxide) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3 wt % of the water;

[0102] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0103] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0104] Embodiment 15

[0105] The surfactant system of this embodiment includes 0.3% of an additive (sodium hydroxide) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3 wt % of the water;

[0106] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0107] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0108] Example 16

[0109] The surfactant system of this embodiment includes 0.1% of an additive (sodium chloride) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3 wt % of the water;

[0110] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0111] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0112] Embodiment 17

[0113] The surfactant system of this embodiment includes 0.25% of the additive (sodium chloride) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0114] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0115] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0116] Embodiment 18

[0117] The surfactant system of this embodiment includes 5% of the additive (sodium chloride) by weight, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0118] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0119] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0120] Embodiment 19

[0121] The surfactant system of this embodiment includes 1.2% additive (sodium chloride and sodium hydroxide mixed in a mass ratio of 1:1) by weight percentage, and the surfactant combination system of this embodiment also includes water and a surfactant accounting for 0.3wt% of the water;

[0122] The surfactant composition is: a betaine surfactant, an extended surfactant and a sulfonate surfactant in a mass ratio of 6:2:2, and the experimental water is the same as that in Example 1.

[0123] The surfactant system of this embodiment is prepared by the following steps: surfactants and additives are prepared according to the above mass percentages and injected into the water on site in the test area to obtain an emulsion surfactant system.

[0124] The surfactant systems prepared in the above Examples 1 to 18 were subjected to the following performance tests.

[0125] Test-Interface Dilation Modulus Test

[0126] When the interface is subjected to periodic compression and expansion, the interfacial tension also changes periodically. The expansion modulus is defined as the ratio of the change in interfacial tension to the change in relative interfacial area, that is:

[0127]

[0128] In formula (III), ε is the expansion modulus, γ is the interfacial tension, and A is the interfacial area.

[0129] The experiment used an interfacial dilational rheology and dynamic contact angle measuring instrument to conduct interfacial tension and dilational rheology experiments. 2 The suspended droplet in a high-pressure environment oscillates periodically, and the instantaneous change of the liquid area is captured by a camera. The dynamic interfacial tension and dynamic interfacial expansion properties are determined by the droplet shape analysis method, and the interfacial expansion rheological properties are measured. The results are shown in Table 1.

[0130] Test 2: Stability test

[0131] For the surfactant systems prepared in Examples 1 to 19, 2 Under the reservoir conditions when the solubility equilibrium is reached, the emulsion stability is determined by the bottle test method. The test temperature is set to 70°C, the experimental water is the water injected on site in a certain test area, and the experimental oil is the simulated oil prepared by dehydrated crude oil in a certain test area. The oil-water volume ratio is 1:1. The emulsion is generated by shaking 100 times at a constant frequency, and the time consumed for 20% of the water to separate is observed. The results are shown in Table 1 and Figure 2 shown.

[0132] Table 1 Performance test results

[0133]

[0134] Combination Figure 1 From the performance test data results in Table 2, it can be seen that the interfacial expansion modulus of the surfactant system prepared by the present invention is generally higher from low frequency to high frequency, indicating that the corresponding emulsion liquid film generally has anti-instability properties in the low-frequency to high-frequency oscillation range; among them, the interfacial expansion modulus of Example 2, Example 6, and Example 7 is higher than that of other embodiments, and the anti-instability property is more significant; combined with Examples 12 to 19, the inventor speculates that: when the amount of surfactant added is controlled to 0.3 to 0.5% of the water mass, and the ratio of betaine surfactant, extended surfactant and sulfonate surfactant is further controlled to 3:1:1, and then 1.2% of additives are compounded, the surfactant system of the present invention can achieve a better interfacial expansion modulus. Therefore, the surfactant system prepared by the present invention has an excellent interfacial expansion modulus, indicating that this series of systems can be used in CO 2 Under the existence of certain conditions, it can effectively resist liquid film disturbance and stabilize the oil-water liquid film.

[0135] Combination Figure 2 From the performance test data results of Table 2, it can be seen that the time consumed by the surfactant system prepared by the present invention to separate 20% of the water is generally higher, indicating that the emulsion stability is higher; among them, the emulsion stability of Example 2 is higher than that of other examples, and the emulsion stability is the highest; according to the time consumed by the surfactant system prepared by the present invention to separate 20% of the water, the inventor believes that: this series of systems can be used in CO 2 It can effectively stabilize the oil-water liquid film and emulsion under the condition of existence, thus playing a role in long-term plugging of pore throats and preventing CO 2 The expected effect of gas channeling.

[0136] The inventors conducted a visualized oil displacement experiment on the surfactant system prepared in the above Examples 1 to 19. The specific operation includes:

[0137] Reference Figure 3 As shown in the figure, the experimental temperature was set at 70°C, the experimental water was the on-site injection water of a certain test area, and the experimental oil was the simulated oil prepared by dehydrating crude oil of a certain test area. Before the experiment, the simulated oil was injected into the heterogeneous glass model at a rate of 20 μL / min until the simulated oil filled the entire glass model and there were no bubbles in the pore throats. In the experiment, different types of surfactant solutions and CO were injected at a constant injection rate of 0.1 μL / min. 2 The oil was injected into the glass model in an alternating manner, and the oil displacement results in the glass model were recorded by a microscope. The area ratio of the clustered remaining oil was measured, and the swept volume was calculated as 1-the area ratio of the clustered remaining oil. The results are shown in Table 2, and the visualized microscopic local phenomenon of oil displacement in Example 2 is also given. Figure 3 .

[0138] The inventors conducted actual oil displacement tests on the surfactant systems prepared in Examples 1 to 18 above. The specific operations included:

[0139] Simulating the target reservoir conditions, the in-situ emulsified surfactant system prepared in Examples 1 to 19 was tested for oil displacement using a saturated oil double-tube parallel core. The core gas permeability was: high permeability 50mD, low permeability 5mD, the experimental temperature was 70°C, the experimental water was the on-site injection water of a certain test area, the core outlet back pressure was 10MPa, the injection system was the surfactant system prepared in Examples 1 to 18, the injection rate was 0.1ml / min, and the injection method was water flooding to 98% water content + CO 2 Drive to gas-liquid ratio>2000+0.1PV gas-liquid (CO 2 + surfactant system) alternating 4 times + subsequent CO 2 Drive until the gas-liquid ratio is > 2000. The results of the enhanced oil recovery test of different in-situ emulsified surfactant systems are shown in Table 2;

[0140] Table 2 Swept volume and enhanced recovery of surfactant systems prepared in Examples 1 to 18

[0141]

[0142]

[0143] 1.2% NaCl (aq) was selected as the comparative example of the present invention. When the oil displacement test was performed, the comparative example 1 had no emulsification, resulting in insufficient pressure gradient to make CO 2 Entering the low permeability, the oil recovery rate was measured to be 10.29%.

[0144] From the data results in Table 2, it can be seen that the swept volume of this series of systems is generally larger than that of the comparative example, and has the advantages of expanding CO 2 Correspondingly, the recovery rate of this series of systems is generally greater than that of the comparative example, indicating that the surfactant system prepared by the present invention can expand the CO 2 Impact and enhance oil recovery.

[0145] In addition, in combination with Example 2 and the attached Figure 3 Microscopic visualization of local phenomena of oil displacement, where the white part is the simulated rock skeleton. It can be clearly seen that in the lower half of the image, there are in-situ generated water-in-oil emulsion droplets with oil phase (black) as the inner phase and brown as the outer phase, which are retained on the displacement route, effectively blocking the CO 2 The air bubbles flow with other fluids, thus expanding the swept volume.

[0146] In summary, the surfactant combination system provided by the present invention, starting from the perspective of the interfacial film strength of a single surfactant, controls the stability of the emulsion by changing the compounding ratio of multiple surfactants. 2 Intensity-controlled in-situ emulsification-assisted CO 2 The combined system of oil displacement surfactants can achieve emulsification and plugging of CO 2 At the same time, the oil-water interfacial tension is reduced, and the in-situ emulsification-assisted CO 2 Oil displacement surfactant combination system for CO 2 The flooding reservoir has excellent enhanced oil recovery effect, and the in-situ emulsification-assisted CO 2 The recovery rate is comparable to CO 2 -WAG repellent increased by more than 10%.

[0147] Although the description of the present invention has been quite detailed and has been described in particular with respect to several described embodiments, it is not intended to be limited to any of these details or embodiments or any particular embodiment, so as to effectively cover the intended scope of the present invention. In addition, the present invention is described above with the embodiments foreseeable by the inventors, and its purpose is to provide a useful description, and those non-substantial changes to the present invention that are not currently foreseen may still represent equivalent changes of the present invention.

[0148] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0149] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A surfactant system, characterized in that: The system comprises water and a surfactant accounting for 0.1-0.5 wt% of the water; the surfactant is a mixture of betaine surfactant, extended surfactant and sulfonate surfactant in any ratio.

2. The surfactant system according to claim 1, characterized in that The mass ratio of the betaine-type surfactant, the extending surfactant and the sulfonate-type surfactant is (0-10):(0-10):(0-10).

3. The surfactant system according to claim 1 or 2, characterized in that: The betaine-type surfactant is an alkyl sulfobetaine; The alkyl sulfobetaine is as shown in formula (I): In formula (I), R is selected from a C12-C18 long-chain alkyl group.

4. The surfactant system according to claim 1 or 2, characterized in that: The extending surfactant is alkyl alcohol polyoxypropylene polyoxyethylene sulfonate; The alkyl alcohol polyoxypropylene polyoxyethylene sulfonate is as shown in formula (II): In formula (II), n is one of 2, 4, 6, 8 or 10, and R is selected from a long-chain alkyl group of C12 to C18.

5. The surfactant system according to claim 1 or 2, characterized in that: The sulfonate surfactant is petroleum sulfonate; The petroleum sulfonate is a mixture of first-line products, second-line products and third-line products in any ratio.

6. The surfactant system according to claim 5, characterized in that The mixing ratio of the reduced first-line product, the reduced second-line product and the reduced third-line product is (0-5): (0-10): (0-10).

7. The surfactant system according to claim 1, characterized in that The system also includes 0.01 to 5 wt% of additives.

8. The surfactant system according to claim 7, characterized in that The additive is an alkaline substance and / or a neutral salt.

9. The surfactant system according to claim 8, characterized in that When the additive is an alkaline substance, the mass fraction of the additive added to the system is 0.01 to 0.3%; When the additive is a neutral salt, the mass fraction of the additive added to the system is 0.1 to 5%; When the additive is a mixture of an alkaline substance and a neutral salt, the mass fraction of the additive added to the system is 0.01-5%.

10. The surfactant system according to claim 8 or 9, characterized in that The alkaline substance is selected from one or more of sodium carbonate, sodium bicarbonate or sodium hydroxide; The neutral salt is selected from one or more of sodium chloride, potassium chloride, calcium chloride, magnesium chloride or sodium sulfate.

11. A method for preparing a surfactant system according to any one of claims 1 to 10, characterized in that: The method comprises: mixing the surfactant, the additive and the water to obtain the surfactant system of the emulsion.

12. Use of the surfactant system according to claim 11 in in-situ emulsification-assisted CO2 flooding.

13. A method for in-situ emulsification-assisted CO2 flooding, characterized in that: The method uses the surfactant system as described in any one of claims 1 to 10 to perform in-situ emulsification-assisted CO2 flooding.

14. The method for in-situ emulsification-assisted CO2 flooding according to claim 13, characterized in that: When the in-situ emulsification-assisted CO2 flooding is performed, the reservoir conditions are: The total mineralization of water in the reservoir is 3000-80000 mg / L; The reservoir temperature is 30-100°C; The viscosity of the reservoir crude oil at the reservoir temperature is 1 to 20 cp; The permeability of the reservoir is 0.01~50mD.

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