Viscosity-reducing and oil-displacing composition for thickened oil, oil-displacing system and application thereof

Abstract

The invention relates to a thick oil viscosity-reducing and oil-displacing composition, an oil-displacing system and application of the thick oil viscosity-reducing and oil-displacing composition. The thick oil viscosity-reducing and oil-displacing composition comprises an amino acid type surfactant, an anionic sulfate type surfactant and water, the viscosity-reducing and oil-displacing composition for the heavy oil disclosed by the invention can remarkably reduce the oil-water interfacial tension, has a relatively good viscosity-reducing effect on the heavy oil under a weak shearing effect, and is relatively high in salt resistance; the oil-displacing agent is compounded with polyacrylamide to obtain an oil-displacing system, the water-oil fluidity ratio can be improved, the oil-displacing efficiency is effectively improved, and the recovery rate of thickened oil is improved.

Description

Technical Field

[0001] The present disclosure relates to the field of heavy oil viscosity reduction, and in particular to a heavy oil viscosity reduction and oil displacement composition, an oil displacement system, and applications thereof. Background Art

[0002] As oil demand continues to rise, marginal heavy oil and asphalt reservoirs, previously considered untapped, are becoming economically valuable resources. Heavy oil, which contains a high concentration of colloids and asphaltenes, has high viscosity and poor fluidity, making it difficult to mine and resulting in low recovery rates.

[0003] Polymer flooding is a commonly used recovery technology for heavy oil reservoirs. This technique involves dissolving polymers in water to increase the viscosity of the water phase, thereby reducing the mobility ratio and increasing the water flooding sweep coefficient. While polymer flooding has a significant oil-increasing effect on conventional crude oil reservoirs, it is less effective in heavy oil reservoirs with higher viscosities. Surfactants are often combined with polymers to form binary composite flooding. Their mechanism of action is to exploit the surfactant's ability to reduce the oil-water interfacial tension, further improving water flooding efficiency. The key to developing highly effective oil-displacement agents is to develop surfactants with excellent compatibility and interfacial properties with polymers. Currently, anionic surfactants or anionic-nonionic composite surfactants are commonly used for oil flooding, but their use often requires the addition of an alkali additive to achieve ultra-low oil-water interfacial tension. Furthermore, for heavy oils with high viscosity, the interfacial tension reduction achieved by existing systems is often insufficient to generate sufficient momentum to displace the remaining oil from the formation voids. Especially for extra-heavy and super-heavy oil reservoirs, since there is no severe disturbance in the formation, it is very challenging to achieve viscosity reduction and oil displacement in these reservoirs with poor fluidity under weak shear.

[0004] Currently, several polymer / surfactant flooding systems for heavy oil reservoirs are disclosed in existing patents, such as:

[0005] CN116285932B discloses a heavy oil viscosity reducer for polymer flooding, which is composed of a nonionic surfactant, a zwitterionic surfactant, a low-carbon alcohol and water. The nonionic and zwitterionic surfactants are both Gemini surfactants. The nonionic surfactant prepared by methanol, glucose and C12 fatty acids is a sugar derivative and a green surfactant. The heavy oil viscosity reducer has excellent temperature and salt resistance and can reduce the oil-water interfacial tension to 10 -3 mN / m, has good emulsification miscibility, and the viscosity reduction rate can reach more than 90%. The viscosity reducer is used in the polymer simulated oil displacement process, which can significantly improve the recovery rate of heavy oil, which can reach more than 60%.

[0006] CN107365575A discloses a heavy oil viscosity reduction and flooding composition and an oil displacement system suitable for heavy oil reservoirs. The heavy oil viscosity reduction and flooding composition is composed of a nonionic / anionic surfactant, an ester compound, a wetting agent and water. When used in combination with a polyacrylamide polymer, it is suitable for Shengli heavy oil reservoirs with a formation viscosity of more than 200mPa.s, and can effectively increase the heavy oil recovery rate by 17.6%-21.6%.

[0007] These oil recovery systems all use conventional anionic or nonionic surfactants or a combination of the two. In order to achieve ultra-low interfacial tension heavy oil viscosity reduction oil recovery compositions, the amount of surfactant used is often large. In addition, the existing systems have relatively poor resistance to calcium and magnesium ions. The biocompatibility of synthetic surfactants is often poor. When used in the oil recovery process, the surfactants remaining in the formation have poor biodegradability and may contaminate the formation, causing permanent damage to the formation permeability, which limits their application in heavy oil reservoirs. Summary of the Invention

[0008] The present invention aims to provide a heavy oil viscosity reduction and flooding composition, an oil flooding system and applications thereof.

[0009] In order to achieve the above-mentioned object, the present disclosure provides, in a first aspect, a heavy oil viscosity reduction and flooding composition, wherein the heavy oil flooding composition comprises an amino acid surfactant, an anionic sulfate surfactant, and water;

[0010] Relative to the total weight of the heavy oil viscosity reduction and flooding composition, the heavy oil viscosity reduction and flooding composition comprises an amino acid surfactant, an anionic sulfate surfactant and water;

[0011] Relative to the total weight of the heavy oil viscosity reduction and flooding composition, the content of the amino acid surfactant is 6-20 weight %, the content of the anionic sulfate surfactant is 2-10 weight %, and the content of water is 70-92 weight %;

[0012] The anionic sulfate surfactant is a cyclic oligomer comprising structural subunit (i), structural subunit (ii) and structural subunit (iii) represented by the following formula:

[0013]

[0014] Among them, * indicates the connection site;

[0015] R1 is selected from C8-C 22 Alkyl;

[0016] R3 and R4 are each independently selected from H or -SO3M, and at least one of R3 and R4 is -SO3M;

[0017] Each R2 is independently selected from H, 2-hydroxypropyl, C1-C5 alkyl;

[0018] M is selected from Li + 、Na + , K + and NH4 + One or more of the .

[0019] Optionally, in the cyclic oligomer, the molar ratio of the total moles of the structural subunit (ii) and the structural subunit (iii) to the structural subunit (i) is (1-6):1, preferably (2-4):1;

[0020] The average sulfonation degree of the cyclic oligomer is 0.8-1.3 mmol / g, preferably 1.0-1.2 mmol / g.

[0021] Optionally, R1 is selected from C8-C 16 The alkyl group is preferably selected from C 10 -C 14 of alkyl.

[0022] Optionally, M is selected from Na + and / or K + .

[0023] Optionally, the anionic sulfate surfactant is a cyclic oligomer comprising structural subunit (i-1), structural subunit (ii-1) and structural subunit (iii-1) represented by the following formula:

[0024]

[0025] Alternatively, the anionic sulfate surfactant is a cyclic oligomer comprising structural subunit (i-2), structural subunit (ii-2) and structural subunit (iii-2) represented by the following formula:

[0026]

[0027] Among them, * indicates the connection site;

[0028] R1 is selected from C8-C 16 The alkyl group is preferably selected from C 10 -C 14 Alkyl;

[0029] M is selected from Na + and / or K + .

[0030] Optionally, the amino acid surfactant is selected from one or more of sodium lauroyl glycinate, sodium lauroyl glutamate, sodium lauroyl sarcosinate, sodium cocoyl glutamate, sodium cocoyl sarcosinate and sodium cocoyl glycinate.

[0031] Optionally, based on the total weight of the heavy oil viscosity reduction and flooding composition, the content of the amino acid surfactant is 8-15 weight %, the content of the anionic sulfate surfactant is 4-8 weight %, and the content of water is 77-88 weight %.

[0032] A second aspect of the present disclosure provides a method for preparing the heavy oil viscosity reduction and flooding composition according to the first aspect of the present disclosure, the method comprising mixing the amino acid surfactant, the anionic sulfate surfactant, and the water;

[0033] The method for preparing the anionic sulfate surfactant comprises the following steps:

[0034] (1) in the presence of solvent I and a catalyst, contacting a 1,2-epoxy compound represented by formula (I-1) with a cyclodextrin compound represented by formula (I-2) to obtain an intermediate;

[0035]

[0036] (2) contacting the intermediate with a sulfonating agent in the presence of solvent II to carry out a sulfonation reaction to obtain a mixture I;

[0037] (3) contacting the mixture I with an alkaline substance containing M to obtain a mixture II having a pH value of 7 or greater;

[0038] The sum of m, n, and z is any integer between 5 and 11.

[0039] Optionally, the mixing is performed under stirring conditions, which include: temperature of 15-40° C., time of 10-80 min, and stirring speed of 50-600 rpm.

[0040] Optionally, the cyclodextrin compound includes one or more of cyclodextrin, methylcyclodextrin, hydroxyethylcyclodextrin and hydroxypropylcyclodextrin;

[0041] The catalyst includes one or more of alkali metal hydroxide and 4-dimethylaminopyridine;

[0042] The sulfonating agent includes one or more of sulfur trioxide pyridine complex, fuming sulfuric acid, sulfur trioxide, concentrated sulfuric acid, chlorosulfonic acid and aminosulfonic acid;

[0043] The solvent I comprises water;

[0044] The solvent II includes one or more of tetrahydrofuran, 1,4-dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and pyridine;

[0045] The alkaline substance includes one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide and ammonia water.

[0046] Optionally, in step (1), the molar ratio of the cyclodextrin compound to the 1,2-epoxy compound is 1:(1-40), preferably 1:(1-32);

[0047] The contact reaction conditions include: temperature of 30-100°C, time of 1-10 hours; preferably, temperature of 60-90°C, time of 3-8 hours;

[0048] Relative to 1 mmol of the cyclodextrin compound, the amount of the solvent I is 0.1-50 mL, and the amount of the catalyst is 0.001-0.1 mmol;

[0049] Preferably, relative to 1 mmol of the cyclodextrin compound, the amount of the solvent I is 1-10 mL, and the amount of the catalyst is 0.005-0.1 mmol.

[0050] Optionally, in step (2), the weight ratio of the intermediate to the sulfonating agent is 1:(0.5-5.0), preferably 1:(1.0-3.0);

[0051] Relative to 1g of the intermediate, the amount of the solvent II is 5-20mL;

[0052] The conditions of the sulfonation reaction include: temperature of 0-90° C. and time of 1-24 h.

[0053] A third aspect of the present disclosure provides an oil displacement system, the oil displacement system comprising the heavy oil viscosity reduction displacement composition according to the first aspect of the present disclosure, polyacrylamide, and water;

[0054] Relative to the total weight of the oil displacement system, the content of the heavy oil viscosity reduction displacement composition is 0.1-1 weight %, the content of the polyacrylamide is 0.05-0.3 weight %, and the content of water is 98.7-99.85 weight %.

[0055] Optionally, relative to the total weight of the oil displacement system, the content of the heavy oil viscosity reduction displacement composition is 0.3-0.8 wt %, the content of the polyacrylamide is 0.1-0.2 wt %, and the content of water is 99.0-99.6 wt %.

[0056] Optionally, the molecular weight of the polyacrylamide is 8 million to 20 million, preferably 12 million to 20 million.

[0057] The fourth aspect of the present disclosure provides application of the oil displacement system described in the third aspect of the present disclosure in heavy oil production.

[0058] Through the above technical solution, the present invention compounded an anionic sulfate surfactant modified by cyclodextrin with an amino acid surfactant to obtain a heavy oil viscosity reduction and flooding composition, wherein the anionic sulfate surfactant has strong aggregation ability and good oil-water interfacial activity, and the critical micelle concentration is as low as 0.037mM, which can greatly accelerate the penetration and dispersion process of the heavy oil viscosity reduction and flooding composition in the heavy oil, so that the heavy oil viscosity reduction and flooding composition of the present invention can still effectively reduce the viscosity of the heavy oil at a lower surfactant concentration. Compounding the anionic sulfate surfactant with a specific structure of the present invention with an amino acid surfactant can reduce interfacial tension, and can reduce the oil-water interfacial tension to 10 -3 The viscosity of heavy oil is on the order of mN / m, which can significantly reduce the viscosity of heavy oil in rock pores. The oil displacement system obtained by compounding the heavy oil viscosity reduction and flooding composition with polyacrylamide can not only increase the viscosity of the water phase and reduce the mobility ratio, but also adsorb on the surface of oil droplet particles, playing a role in stabilizing the emulsified oil droplets, thereby effectively improving the oil displacement efficiency and the recovery rate of heavy oil. In addition, the heavy oil viscosity reduction and flooding composition has good salt resistance, including good adaptability to heavy oil reservoirs containing formation water with high calcium and magnesium ions. The anionic sulfate-type surfactant modified based on cyclodextrin also has the advantages of good biocompatibility, easy biodegradation, no secondary pollution, and less damage to the formation.

[0059] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0061] Figure 1 This is the MALDI-TOF-MS spectrum of the anionic sulfate surfactant intermediate modified based on β-cyclodextrin prepared in Preparation Example 1 of the present disclosure.

[0062] Figure 2 The anionic sulfate surfactant product based on β-cyclodextrin modification prepared in Preparation Example 1 of the present disclosure is 1 H NMR spectrum.

[0063] Figure 3This is the MALDI-TOF-MS spectrum of the anionic sulfate surfactant intermediate modified based on α-cyclodextrin prepared in Preparation Example 2 of the present disclosure.

[0064] Figure 4 The anionic sulfate surfactant product based on α-cyclodextrin modification prepared in Preparation Example 2 of the present disclosure is 1 H NMR spectrum.

[0065] Figure 5 This is the MALDI-TOF-MS spectrum of the anionic sulfate surfactant intermediate modified based on γ-cyclodextrin prepared in Preparation Example 3 of the present disclosure.

[0066] Figure 6 The anionic sulfate surfactant product based on γ-cyclodextrin modification prepared in Preparation Example 3 of the present disclosure is 1 H NMR spectrum. DETAILED DESCRIPTION

[0067] The following describes the specific embodiments of the present disclosure in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0068] A first aspect of the present disclosure provides a heavy oil viscosity reduction and displacement composition, the heavy oil displacement composition comprising an amino acid surfactant, an anionic sulfate surfactant, and water;

[0069] Relative to the total weight of the heavy oil viscosity reduction and flooding composition, the heavy oil viscosity reduction and flooding composition comprises an amino acid surfactant, an anionic sulfate surfactant and water;

[0070] Relative to the total weight of the heavy oil viscosity reduction and flooding composition, the content of the amino acid surfactant is 6-20 weight %, the content of the anionic sulfate surfactant is 2-10 weight %, and the content of water is 70-92 weight %;

[0071] The anionic sulfate surfactant is a cyclic oligomer comprising structural subunit (i), structural subunit (ii) and structural subunit (iii) represented by the following formula:

[0072]

[0073] Among them, * indicates the connection site;

[0074] R1 is selected from C8-C 22 Alkyl;

[0075] R3 and R4 are each independently selected from H or -SO3M, and at least one of R3 and R4 is -SO3M;

[0076] Each R2 is independently selected from H, 2-hydroxypropyl, C1-C5 alkyl;

[0077] M is selected from Li + 、Na + , K + and NH4 + One or more of the .

[0078] The disclosed heavy oil viscosity reduction and flooding composition contains a cyclodextrin-modified anionic sulfate surfactant and an amino acid surfactant. The anionic sulfate surfactant has strong aggregation ability and good oil-water interfacial activity, accelerating its penetration and dispersion in heavy oil, enabling good viscosity reduction efficiency at a relatively low content. Furthermore, the composition has advantages such as good biocompatibility, easy biodegradation, no secondary pollution, and minimal damage to formations. When combined with the amino acid surfactant, the composition can reduce the viscosity of heavy oil in rock pores and exhibits good salt resistance, making it suitable for heavy oil reservoirs with formation water containing high calcium and magnesium ion contents.

[0079] The present disclosure does not impose any specific restrictions on the arrangement of the structural subunits.

[0080] In this disclosure, “C8-C 22 "Alkyl" means an alkyl group having a total carbon number of 8 to 22, including C8-C 22 Straight chain alkyl, C8-C 22 The branched alkyl group may be, for example, a straight chain alkyl group or a branched alkyl group having a total carbon number of 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or 22. For example, it may be methyl, ethyl, isopropyl, n-pentyl, n-hexyl, n-dodecyl, n-heptadecyl, etc. 16 Alkyl", "C 10 -C 14 "C1-C5 alkyl" and "C1-C5 alkyl" have similar explanations, except that the number of carbon atoms is different.

[0081] In order to make the anionic sulfate surfactant have stronger surface activity, according to one embodiment of the present disclosure, R1 is selected from C8-C 16 The alkyl group is preferably selected from C 10 -C 14 The alkyl group is more preferably -C 12 H 25 , specifically n-dodecyl. In the above case, the obtained anionic sulfate surfactant has stronger surface activity.

[0082] According to one embodiment of the present disclosure, M is selected from Na + and / or K + .

[0083] According to one embodiment of the present disclosure, in the cyclic oligomer, the molar ratio of the total moles of the structural subunit (ii) and the structural subunit (iii) to the structural subunit (i) is (1-6):1, preferably (2-4):1.

[0084] According to one embodiment of the present disclosure, the average degree of sulfonation of the cyclic oligomer is 0.8-1.3 mmol / g, preferably 1.0-1.2 mmol / g, wherein the average degree of sulfonation of the prepared anionic sulfate surfactant is determined by titration with a NaOH standard solution according to the literature (China Paper Industry, 2006, (11): 38-40).

[0085] According to a preferred embodiment of the present disclosure,

[0086] R1 is selected from C8-C 16 Alkyl;

[0087] R3 and R4 are each independently selected from H or -SO3M, and at least one of R3 and R4 is -SO3M;

[0088] Each R2 is independently selected from H, 2-hydroxypropyl, methyl;

[0089] M is selected from Li + 、Na + , K + and NH4 + One or more of the following;

[0090] In the cyclic oligomer, the molar ratio of the total moles of the structural subunit (ii) and the structural subunit (iii) to the structural subunit (i) is (1-6):1.

[0091] According to another preferred embodiment of the present disclosure, the anionic sulfate surfactant is a cyclic oligomer comprising structural subunit (i-1), structural subunit (ii-1) and structural subunit (iii-1) shown in the following formula:

[0092]

[0093] Alternatively, the anionic sulfate surfactant is a cyclic oligomer comprising structural subunit (i-2), structural subunit (ii-2) and structural subunit (iii-2) represented by the following formula:

[0094]

[0095] Among them, * indicates the connection site;

[0096] R1 is selected from C8-C 16 The alkyl group is preferably selected from C 10 -C 14 Alkyl;

[0097] M is selected from Na + and / or K + .

[0098] According to one embodiment of the present disclosure, the amino acid surfactant is selected from one or more of sodium lauroyl glycinate, sodium lauroyl glutamate, sodium lauroyl sarcosinate, sodium cocoyl glutamate, sodium cocoyl sarcosinate and sodium cocoyl glycinate.

[0099] A second aspect of the present disclosure provides a method for preparing the heavy oil viscosity reduction and flooding composition according to the first aspect of the present disclosure, the method comprising mixing the amino acid surfactant, the anionic sulfate surfactant, and the water;

[0100] The method for preparing the anionic sulfate surfactant comprises the following steps:

[0101] (1) in the presence of solvent I and a catalyst, contacting a 1,2-epoxy compound represented by formula (I-1) with a cyclodextrin compound represented by formula (I-2) to obtain an intermediate;

[0102]

[0103] (2) contacting the intermediate with a sulfonating agent in the presence of solvent II to carry out a sulfonation reaction to obtain a mixture I;

[0104] (3) contacting the mixture I with an alkaline substance containing M to obtain a mixture II having a pH value of 7 or greater;

[0105] The sum of m, n, and z is any integer between 5 and 11.

[0106] In the present disclosure, the definitions of R1, R2, and M in the 1,2-epoxy compound represented by formula (I-1), the cyclodextrin compound represented by formula (I-2), and the alkaline substance are the same as those defined above.

[0107] According to one embodiment of the present disclosure, the sum of m, n, and z is any integer from 6 to 8.

[0108] In the present disclosure, the cyclodextrin compounds, 1,2-epoxy compounds and sulfonating agents can be commercially available chemical reagents, or can be prepared by those skilled in the art according to methods known in the art.

[0109] According to one embodiment of the present disclosure, in step (1), the cyclodextrin compound includes one or more of cyclodextrin, methylcyclodextrin, hydroxyethylcyclodextrin and hydroxypropylcyclodextrin, wherein the cyclodextrin includes one or more of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin.

[0110] According to one embodiment of the present disclosure, the molar ratio of the cyclodextrin compound to the 1,2-epoxy compound is 1:(1-40), preferably 1:(1-32).

[0111] According to one embodiment of the present disclosure, the solvent I may be, for example, water, and the catalyst may include one or more of an alkali metal hydroxide and 4-dimethylaminopyridine, wherein the alkali metal hydroxide may include one or more of NaOH, KOH, and LiOH. The present disclosure does not specifically limit the water, and may include deionized water, tap water, or the like.

[0112] According to one embodiment of the present disclosure, in step (1), the contact reaction conditions include: temperature of 30-100° C., time of 1-10 h; preferably, temperature of 60-90° C., time of 3-8 h.

[0113] According to one embodiment of the present disclosure, in step (1), the amount of the solvent I is 0.1-50 mL, and the amount of the catalyst is 0.001-0.1 mmol, relative to 1 mmol of the cyclodextrin compound. Preferably, the amount of the solvent I is 1-10 mL, and the amount of the catalyst is 0.005-0.1 mmol, relative to 1 mmol of the cyclodextrin compound.

[0114] According to one embodiment of the present disclosure, the method further comprises: in step (1), filtering and drying the product after the contact reaction between the 1,2-epoxy compound and the cyclodextrin compound. The present disclosure does not particularly limit the specific methods of filtering and drying, and those skilled in the art can perform the methods according to known methods; as long as an intermediate can be obtained after the solvent is removed and dried to a constant weight.

[0115] According to one embodiment of the present disclosure, in step (2), the sulfonating agent includes one or more of sulfur trioxide pyridine complex, fuming sulfuric acid, sulfur trioxide, concentrated sulfuric acid, chlorosulfonic acid and aminosulfonic acid, wherein the content of active SO3 in the sulfur trioxide pyridine complex is 45-55 weight %; when the sulfonating agent includes more than two kinds, the present disclosure does not impose any specific limitation on their ratio.

[0116] According to one embodiment of the present disclosure, in step (2), the weight ratio of the intermediate to the sulfonating agent is 1:(0.5-5.0), preferably 1:(1.0-3.0).

[0117] According to one embodiment of the present disclosure, in step (2), the amount of the solvent II used is 5-20 mL relative to 1 g of the intermediate.

[0118] According to one embodiment of the present disclosure, in step (2), the solvent II includes one or more of tetrahydrofuran, 1,4-dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and pyridine.

[0119] According to one embodiment of the present disclosure, in step (2), the conditions of the sulfonation reaction include: temperature of 0-90° C., and time of 1-24 h.

[0120] According to one embodiment of the present disclosure, in step (3), the alkaline substance includes one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide and ammonia water.

[0121] In the present disclosure, the alkaline substance is preferably added in the form of an aqueous solution, and the concentration of the aqueous solution of the alkaline substance is 0.1-50% by weight, preferably 5-15% by weight.

[0122] According to one embodiment of the present disclosure, in step (3), the pH value of the mixture II is 7-9.

[0123] In this disclosure, unless otherwise specified, the pH value refers to the test value at 25°C and normal pressure.

[0124] In the present disclosure, steps (1) to (3) are preferably carried out under stirring conditions, and there is no specific limitation on the stirring speed, and conventional parameters in the art can be used.

[0125] According to one embodiment of the present disclosure, the method further comprises: removing the solvent from the product obtained in step (3) by rotary evaporation, and drying to obtain an anionic sulfate surfactant. The present disclosure does not particularly limit the specific methods of the rotary evaporation and the drying, and they can be carried out using known technical means in the art.

[0126] According to one embodiment of the present disclosure, mixing can be performed under stirring conditions, which include: temperature of 15-40°C, time of 10-80 min, stirring speed of 50-600 rpm, and the stirring method can be magnetic stirring.

[0127] According to a preferred embodiment of the present disclosure, a method for preparing a heavy oil viscosity reduction and flooding composition includes: completely dissolving an amino acid surfactant and an anionic sulfate surfactant in water; there are no special requirements for the specific method of dissolution, and various methods that can be conceived by those skilled in the art can be used.

[0128] A third aspect of the present disclosure provides an oil displacement system, the oil displacement system comprising the heavy oil viscosity reduction displacement composition according to the first aspect of the present disclosure, polyacrylamide, and water;

[0129] Relative to the total weight of the oil displacement system, the content of the heavy oil viscosity reduction displacement composition is 0.1-1 weight %, the content of the polyacrylamide is 0.05-0.3 weight %, and the content of water is 98.7-99.85 weight %.

[0130] The oil displacement system disclosed herein includes a heavy oil viscosity reduction displacement composition containing a cyclodextrin-modified anionic sulfate surfactant and an amino acid surfactant, as well as polyacrylamide. These compositions can increase aqueous phase viscosity, reduce mobility ratio, and adsorb on the surface of oil droplets to stabilize emulsified oil droplets. This effectively improves oil displacement efficiency and enhances heavy oil recovery.

[0131] According to one embodiment of the present disclosure, relative to the total weight of the oil displacement system, the content of the heavy oil viscosity reduction displacement composition is 0.3-0.8 weight%, the content of the polyacrylamide is 0.1-0.2 weight%, and the content of water is 99.0-99.6 weight%; specifically, the content of the heavy oil viscosity reduction displacement composition is 0.4 weight%, the content of the polyacrylamide is 0.2 weight%, and the content of water is 99.4 weight%.

[0132] According to one embodiment of the present disclosure, the molecular weight of the polyacrylamide is 8 million to 20 million, preferably 12 million to 20 million.

[0133] According to one embodiment of the present disclosure, a method for preparing an oil displacement system includes: mixing a heavy oil viscosity reduction displacement composition, polyacrylamide and water. The mixing can be carried out under stirring conditions at a temperature of 20-40°C, a time of 60-180 minutes, and a stirring speed of 200-600 rpm. The stirring method can be magnetic stirring.

[0134] According to a preferred embodiment of the present disclosure, a method for preparing an oil displacement system includes: completely dissolving a heavy oil viscosity reduction displacement composition and polyacrylamide in water; there is no special requirement for the specific method of dissolution, and various methods that can be conceived by those skilled in the art can be used.

[0135] The fourth aspect of the present disclosure provides use of the heavy oil viscosity reduction and flooding composition-polyacrylamide mixture described in the third aspect of the present disclosure in heavy oil production.

[0136] The present invention will be further described below with reference to the embodiments.

[0137] Unless otherwise specified, the instruments, reagents, and materials used in the following examples are all conventional instruments, reagents, and materials available in the prior art and can be obtained through regular commercial channels. The experimental methods and detection methods used in the following examples are all conventional experimental methods and detection methods available in the prior art, unless otherwise specified.

[0138] The raw materials used in the examples and comparative examples are as follows:

[0139]

[0140]

[0141] Preparation Example 1

[0142] Preparation of anionic sulfate surfactant T1 based on β-cyclodextrin:

[0143] Weigh 10 mmol of β-cyclodextrin and 70 mmol of 1,2-epoxytetradecane into a reaction flask. Then, add 20 mL of water, 0.05 mmol of 4-dimethylaminopyridine, and a magnet. Stir the reaction at 85°C for 7 hours. Stop the reaction, filter, and dry to obtain Intermediate I as a white solid.

[0144] Intermediate I contains the following structural subunits:

[0145] -C 12 H 25 represents n-dodecyl;

[0146] The structure of intermediate I was characterized by MALDI-TOF-MS. Figure 1 As shown, peaks at mass-to-charge ratios of 1369.350, 1581.509, 1793.666, 2005.817, 2217.964, 2430.107, and 2642.248 correspond to the molecular ion peaks of the intermediates obtained after 1-7 primary hydroxyl groups react with 1,2-epoxytetradecane; this result proves that intermediate I has been prepared. Figure 1 The intensity of MALDI-TOF-MS shows that in intermediate I, and The molar ratio is 1:2.5.

[0147] 1 g of intermediate I and 10 mL of N,N-dimethylformamide were added to a three-necked flask. At the same time, 2 g of sulfur trioxide pyridine complex (active SO3 content: 50 wt%) was weighed and dissolved in 5 mL of N,N-dimethylformamide. The mixture was added to the three-necked flask and stirred at 50°C for 2 h. The mixture was cooled to room temperature and a 10 wt% aqueous sodium hydroxide solution was added to adjust the pH to 7. The solvent was removed by rotary evaporation and dried to obtain the product anionic sulfate surfactant T1 with a yield of 81%.

[0148] The anionic sulfate surfactant T1 is a cyclic oligomer composed of the following structural subunits:

[0149]

[0150] According to the calculation of the intermediate structure, the molar ratio of the total moles of structural subunit (ii) and structural subunit (iii) to structural subunit (i) is 2.5:1.

[0151] The anionic sulfate surfactant T1 was 1 H NMR characterization (deuterated solvent used was deuterated water), the results are as follows Figure 2 As shown, 1 H NMR (D2O): δ=0.78(-C 11 H 22 CH3),1.20-1.65(-C 11 H 22 CH3),3.28-3.85(-CH2OH,-CH-CH2-O-CH2-CHOH-C 12 H 25 ,-O-CH-CH-CH2-O-,-CHOH,),4.06(-CH-CH2-OSO3Na),4.18-4.49(-CH-CH2-OSO3Na,-CH-CH2-O-CH2-CHOH-C 12 H 25 ).

[0152] Depend on Figure 2 It can be seen that there are two broad peaks at 4.06 and 4.18-4.49 ppm. Among them, 4.06 ppm corresponds to -CH-CH2OSO3Na, and 4.18-4.49 ppm corresponds to -CH-CH2-OSO3Na and -CH-CH2-O-CH2-CHOH-C 12 H 25 , proving the successful progress of the sulfonation reaction and the existence of the sulfonation product.

[0153] The average degree of sulfonation of the anionic sulfate surfactant T1 in this embodiment is 1.15 mmol / g.

[0154] Preparation Example 2

[0155] Preparation of anionic sulfate surfactant T2 based on α-cyclodextrin:

[0156] Weigh 10 mmol of α-cyclodextrin and 90 mmol of 1,2-epoxytetradecane into a reaction flask. Then, add 10 mL of water, 0.30 mmol of 4-dimethylaminopyridine, and a magnet. Stir the reaction at 60°C for 8 hours. Stop the reaction, filter, and dry to obtain Intermediate II.

[0157] Intermediate II contains the following structural subunits:

[0158] -C 12 H 25 represents n-dodecyl.

[0159] The mass spectrometry characterization of intermediate II was performed, and the results were as follows Figure 3 The product spectrum has peaks at mass-to-charge ratios of 1207.304, 1419.462, 1631.613, 1843.762, 2055.906, and 2268.046, which correspond to the molecular ion peaks of amphiphilic α-cyclodextrin obtained after the contact reaction of 1-6 primary hydroxyl groups with 1,2-epoxytetradecane, proving that the product was successfully prepared. Figure 3 The intensity of MALDI-TOF-MS shows that in intermediate II, and The molar ratio is 1:2.

[0160] 1 g of intermediate II, 10 mL of N,N-dimethylformamide, and 1.4 g of chlorosulfonic acid were added to a three-necked flask, and the mixture was stirred at 0°C for 1 h. 10 wt % sodium hydroxide was added to adjust the pH to 7. The solvent was removed by rotary evaporation and the mixture was dried to obtain anionic sulfate surfactant T2 in a yield of 77%.

[0161] The anionic sulfate surfactant T2 is a cyclic oligomer composed of the following structural subunits:

[0162]

[0163] According to the calculation of the intermediate structure, the molar ratio of the total moles of structural subunit (ii) and structural subunit (iii) to structural subunit (i) is 2:1.

[0164] The anionic sulfate surfactant T2 was 1 H NMR characterization (deuterated solvent used was deuterated DMSO), the results are as follows Figure 4 As shown, 1H NMR (DMSO-d6): δ=0.97(-C 11 H 22 CH3),1.36-1.67(-C 11 H 22 CH3),3.66-3.76(-CH2OH,-CH-CH2-O-CH2-CHOH-C 12 H 25 ,-O-CH-CH-CH2-O-,-CHOH,),3.99(-CH-CH2-OSO3Na),4.22(-CH-CH2-OSO3Na,-CH-CH2-O-CH2-CHOH-C 12 H 25 ),5.22(-O-CH-O-).

[0165] Depend on Figure 4 It can be seen that there are two broad peaks at 3.99-4.22ppm. Among them, 3.99ppm corresponds to -CH-CH2OSO3Na, 4.22ppm corresponds to -CH-CH2-OSO3Na, -CH-CH2-O-CH2-CHOH-C 12 H 25 , proving the success of the sulfonation reaction and the existence of the sulfonation product.

[0166] The average degree of sulfonation of the anionic sulfate surfactant T2 in this embodiment is 1.16 mmol / g.

[0167] Preparation Example 3

[0168] Preparation of anionic sulfate surfactant T3 based on γ-cyclodextrin:

[0169] Weigh 10 mmol of γ-cyclodextrin and 320 mmol of 1,2-epoxytetradecane into a reaction flask. Then, add 100 mL of water, 0.80 mmol of 4-dimethylaminopyridine, and a magnet. Stir the reaction at 90°C for 3 hours. Stop the reaction, filter, and dry to obtain white intermediate III.

[0170] Intermediate III contains the following structural subunits:

[0171] -C 12 H 25 represents n-dodecyl.

[0172] The mass spectrometry characterization of intermediate III was performed, and the results were as follows Figure 5The product spectrum has peaks at mass-to-charge ratios of 1531.287, 1743.433, 1955.569, 2167.702, 2379.833, 2591.964, 2804.094, and 3016.224, which correspond to the molecular ion peaks of amphiphilic γ-cyclodextrin obtained after 1-8 primary hydroxyl groups react with 1,2-epoxytetradecane, proving that the product was successfully prepared. Figure 5 The intensity of MALDI-TOF-MS shows that in intermediate III, and The molar ratio is 1:3.

[0173] In a three-necked flask at 0°C, 1 g of intermediate III, 10 mL of N,N-dimethylformamide, and 2.35 g of concentrated sulfuric acid were added. The mixture was stirred for 1 h. 10 wt % potassium hydroxide was added to adjust the pH to 7. The solvent was removed by rotary evaporation and the mixture was dried to obtain anionic sulfate surfactant T3 in a yield of 76%.

[0174] The anionic sulfate surfactant T3 is a cyclic oligomer composed of the following structural subunits:

[0175]

[0176] According to the calculation of the intermediate structure, the molar ratio of the total moles of structural subunit (ii) and structural subunit (iii) to structural subunit (i) is 3:1.

[0177] The anionic sulfate surfactant T3 was 1 H NMR characterization (deuterated solvent used was deuterated DMSO), the results are as follows Figure 6 As shown, 1 HNMR (DMSO-d6): δ=0.97(-C 11 H 22 CH3),1.35-1.67 (-C 11 H 22 CH3), 3.73-3.98(-CH2OH,-CH-CH2-O-CH2-CHOH-C 12 H 25 ,-O-CH-CH-CH2-O-,-CHOH,-CH-CH2-OSO3Na),4.16(-CH-CH2-OSO3Na,-CH-CH2-O-CH2-CHOH-C 12 H 25 ),5.26(-O-CH-O-).

[0178] Depend on Figure 6It can be seen that there are two peaks in the proton chemical shift at 3.98-4.16ppm. Among them, 3.98ppm corresponds to -CH-CH2OSO3Na, 4.16ppm corresponds to -CH-CH2-OSO3Na, -CH-CH2-O-CH2-CHOH-C 12 H 25 , proving the successful progress of the sulfonation reaction and the existence of the sulfonation product.

[0179] The average degree of sulfonation of the anionic sulfate surfactant T3 in this example is 1.12 mmol / g.

[0180] The surface tension values ​​of the anionic sulfate surfactants T1-T3 prepared in the examples at different concentrations were measured using a K100 surface tension meter from KRUSS, Germany, using the hanging sheet method. The test temperature was 25°C. As the surfactant concentration increased, the surface tension value continued to decrease. After a certain critical concentration, the surface tension value remained essentially constant. This critical concentration is defined as the critical aggregation concentration (CAC). The critical aggregation concentrations of the anionic sulfate surfactants T1-T3 were 0.048 mM, 0.037 mM, and 0.051 mM, respectively.

[0181] The anionic sulfate surfactants T1-T3 obtained in the above preparation example were used to prepare a heavy oil viscosity reduction and flooding composition. In the following examples and comparative examples, 10 g of the heavy oil viscosity reduction and flooding composition was prepared.

[0182] Example 1

[0183] Under magnetic stirring conditions at 20° C. and 300 rpm, 0.5 g of surfactant T1 prepared in Preparation Example 1 and 1.0 g of sodium cocoyl glutamate were added to 8.5 g of water and stirred for 30 min until completely dissolved, thereby obtaining a heavy oil viscosity reduction and flooding composition, numbered A1.

[0184] Example 2

[0185] Under magnetic stirring conditions at 25° C. and 200 rpm, 0.8 g of surfactant T2 prepared in Preparation Example 2 and 0.8 g of sodium lauroyl sarcosinate were added to 8.4 g of water and stirred for 40 min until completely dissolved, thereby obtaining a heavy oil viscosity reduction and flooding composition, numbered A2.

[0186] Example 3

[0187] Under magnetic stirring conditions at 30° C. and 400 rpm, 0.4 g of surfactant T3 prepared in Preparation Example 3 and 1.2 g of sodium cocoyl glycinate were added to 8.4 g of water and stirred for 20 min until completely dissolved, thereby obtaining a heavy oil viscosity reduction and flooding composition, numbered A3.

[0188] Example 4

[0189] Under magnetic stirring conditions at 30° C. and 300 rpm, 0.5 g of surfactant T1 prepared in Preparation Example 1 and 1.5 g of sodium lauroyl glutamate were added to 8.0 g of water and stirred for 30 min until completely dissolved, thereby obtaining a heavy oil viscosity reduction and flooding composition, numbered A4.

[0190] Example 5

[0191] Under magnetic stirring conditions at 20° C. and 300 rpm, 0.2 g of surfactant T1 prepared in Preparation Example 1 and 2.0 g of sodium cocoyl glutamate were added to 7.8 g of water and stirred for 30 min until completely dissolved to obtain a heavy oil viscosity reduction flooding composition, numbered A5.

[0192] Example 6

[0193] Under magnetic stirring conditions at 20° C. and 300 rpm, 1.0 g of surfactant T1 prepared in Preparation Example 1 and 0.6 g of sodium cocoyl glutamate were added to 8.4 g of water and stirred for 30 min until completely dissolved to obtain a heavy oil viscosity reduction and flooding composition, numbered A6.

[0194] Comparative Example 1

[0195] Under magnetic stirring conditions at 20° C. and 300 rpm, 0.5 g of a conventional anionic surfactant, SDS (sodium dodecyl sulfate), and 1.0 g of sodium cocoyl glutamate were added to 8.5 g of water and stirred for 30 min until completely dissolved, thereby obtaining a heavy oil viscosity reduction flooding composition, numbered D1.

[0196] Comparative Example 2

[0197] Under magnetic stirring conditions at 20° C. and 300 rpm, 1.5 g of surfactant T1 prepared in Preparation Example 1 was added to 8.5 g of water and stirred for 30 min until completely dissolved, thereby obtaining a heavy oil viscosity reduction and flooding composition, numbered D2.

[0198] Comparative Example 3

[0199] Under magnetic stirring conditions at 20° C. and 300 rpm, 1.5 g of sodium cocoyl glutamate was added to 8.5 g of water and stirred for 30 min until completely dissolved, thereby obtaining a heavy oil viscosity reduction and flooding composition, numbered D3.

[0200] The heavy oil viscosity reducing flooding composition, polyacrylamide and water in the examples and comparative examples were mixed in a certain proportion to prepare an oil displacement system, i.e., a displacement fluid in the oil displacement test. The displacement fluid ratio is shown in Table 1.

[0201] In order to test the salt resistance of the displacement fluid, high-mineralization water was selected in the preparation of 2# and 4# displacement fluids, with a salinity of 100,000 mg / L, of which Ca 2+ Concentration: 5000mg / L, Mg 2+ Concentration: 5000 mg / L; while the water used in the preparation process of other embodiments and comparative examples was selected from formation water of the corresponding block, and the salinity of the formation water was 12000 mg / L.

[0202] Table 1

[0203]

[0204]

[0205] Test example: Heavy oil viscosity reduction test

[0206] The test used Shengli Oilfield heavy oil (viscosity 20,900 mPa.s at 50°C) to determine its viscosity reduction. The heavy oil viscosity reduction and flooding composition was diluted with formation water from the corresponding block. The formation water had a salinity of 12,000 mg / L and the concentration of the composition was 0.4% by weight. In the viscosity reduction test, the diluted composition was used at a uniform concentration of 50% by weight of the heavy oil.

[0207] The viscosity reduction process is as follows: 25 g of the heavy oil viscosity reduction and displacement composition of the above embodiment or comparative example, which accounts for 50% by weight of the heavy oil, is taken into a beaker and added to 50 g of the test oil. The beaker is placed in a 50°C water bath and kept at constant temperature for 1 hour. A biological shaker is used to simulate the weak shear condition of the formation, with the shaking level being level 1 and the shaking time being 30 minutes. The emulsified morphology of the heavy oil is observed, and then a Brookfield DV-II viscometer is used at 50°C at a shear rate of 7.34s -1 The viscosity was measured and the results are listed in Table 2.

[0208] Calculate the viscosity reduction rate: viscosity reduction rate = (viscosity of heavy oil before viscosity reduction - viscosity of heavy oil after viscosity reduction) / viscosity of heavy oil before viscosity reduction × 100%.

[0209] Table 2

[0210]

[0211] The results of Table 2 show that the heavy oil viscosity reduction flooding composition prepared by compounding anionic sulfate surfactants and amino acid surfactants with a specific structure can achieve efficient viscosity reduction of Shengli heavy oil under simulated weak shear action, with the viscosity after viscosity reduction as low as 38.3mPa.s or less, and the viscosity reduction rate reaches more than 99.82%. In contrast, the heavy oil viscosity reduction flooding composition prepared by replacing the anionic sulfate surfactant based on cyclodextrin modification with the conventional anionic surfactant SDS and compounding it with the amino acid surfactant cannot achieve uniform dispersion of the heavy oil, and the viscosity reduction rate is 70.53%, which is a poor viscosity reduction effect. Comparing Example 1 with Comparative Example 2 and Comparative Example 3, it is impossible to achieve uniform dispersion of the heavy oil by using anionic sulfate surfactants based on cyclodextrin modification or using amino acid surfactants alone, with the viscosity reduction rates of 59.23% and 65.53% respectively, which is a poor viscosity reduction effect.

[0212] Test example: Oil-water interfacial tension evaluation test

[0213] The oil-water interfacial tension of the heavy oil viscosity reduction and flooding compositions prepared in the Examples and Comparative Examples was measured using the spinning drop method using a TX-500C interfacial tension meter. The test oil used was Shengli heavy oil (viscosity 20,900 mPa·s at 50°C), the test temperature was 50°C, and the rotation speed was 5000 rpm. The heavy oil viscosity reduction and flooding compositions were diluted with formation water from the corresponding block to a concentration of 0.4% by weight. The formation water salinity was 12,000 mg / L. The results are listed in Table 3.

[0214] Table 3

[0215] Heavy oil viscosity reduction and flooding composition Interfacial tension / (mN / m) A1 0.00263 A2 0.00323 A3 0.00392 A4 0.00425 A5 0.00749 A6 0.00823 D1 0.02639 D2 0.04574 D3 0.03716

[0216] The results in Table 3 show that the heavy oil viscosity reduction flooding composition provided by the present disclosure can achieve ultra-low oil-water interfacial tension, which can reduce the oil-water interfacial tension to 10 -3 mN / m order of magnitude, which can significantly reduce the viscosity of heavy oil in rock voids.

[0217] Test case simulated oil displacement test

[0218] The oil used in the test is Shengli Oilfield heavy oil, whose viscosity at 50℃ is 20900mPa.s and the viscosity at 80℃ is 1652mPa.s.

[0219] The steps of the oil displacement test are:

[0220] (1) Dry the artificial core to constant weight and measure the core dimensions and gas permeability. Saturate the core with water and determine its pore volume. Saturate the core with Shengli Oilfield heavy oil and record the saturated crude oil volume.

[0221] (2) At 80°C, water was injected to displace the oil until the water content of the produced fluid exceeded 95%, meaning that the heavy oil trapped in the pores could no longer be displaced. 0.5 PV of the prepared displacement fluid was then injected, and water was injected again to displace the oil until the water content of the produced fluid exceeded 95%. The percentage of oil recovery increased compared to water flooding was calculated. Core gas permeability was measured using a permeability meter produced by Dongda Stone Instrument Co., Ltd., and oil displacement tests were conducted using a simulated oil displacement evaluation device produced by Dongda Stone Instrument Co., Ltd. The test results for different displacement fluid compositions are listed in Table 4.

[0222] Table 4

[0223] Displacement fluid number Improved oil recovery / % 1# 30.3 2# 28.5 3# 26.3 4# 25.7 5# 20.8 6# 19.4 7# 24.6 8# 14.2 9# 10.5 10# 11.6

[0224] According to Table 4, the displacement fluid disclosed herein can effectively increase the recovery factor by 19.4%-30.3%, which is significantly better than the comparative example.

[0225] In summary, the present invention adopts a compound of a cyclodextrin-modified anionic sulfate surfactant and an amino acid surfactant with a specific structure to prepare a heavy oil viscosity reduction and flooding composition, which can effectively reduce the viscosity of heavy oil at a low surfactant concentration. At the same time, the above composition can form an ultra-low interfacial tension, which can reduce the oil-water interfacial tension to 10 -3 mN / m, significantly reducing the viscosity of heavy oil in rock pores; when combined with polyacrylamide, it can increase water-phase viscosity, reduce mobility ratio, and enhance recovery. Furthermore, the above combination has the advantage of good salt resistance.

[0226] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0227] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0228] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A heavy oil viscosity reduction and flooding composition, characterized in that: The heavy oil viscosity reduction and flooding composition comprises an amino acid surfactant, an anionic sulfate surfactant and water; Relative to the total weight of the heavy oil viscosity reduction and flooding composition, the content of the amino acid surfactant is 6-20 weight %, the content of the anionic sulfate surfactant is 2-10 weight %, and the content of water is 70-92 weight %; The anionic sulfate surfactant is a cyclic oligomer comprising structural subunit (i), structural subunit (ii) and structural subunit (iii) represented by the following formula: Among them, * indicates the connection site; R1 is selected from C8-C 22 Alkyl; R3 and R4 are each independently selected from H or -SO3M, and at least one of R3 and R4 is -SO3M; Each R2 is independently selected from H, 2-hydroxypropyl, C1-C5 alkyl; M is selected from Li + 、Na + , K + and NH4 + One or more of the .

2. The heavy oil viscosity reduction flooding composition according to claim 1, wherein In the cyclic oligomer, the molar ratio of the total moles of the structural subunit (ii) and the structural subunit (iii) to the structural subunit (i) is (1-6):1, preferably (2-4):1; The average sulfonation degree of the cyclic oligomer is 0.8-1.3 mmol / g, preferably 1.0-1.2 mmol / g.

3. The heavy oil viscosity reduction flooding composition according to claim 1, wherein R1 is selected from C8-C 16 The alkyl group is preferably selected from C 10 -C 14 of alkyl.

4. The heavy oil viscosity reduction and flooding composition according to claim 1, wherein M is selected from Na + and / or K + .

5. The heavy oil viscosity reduction and flooding composition according to claim 1, wherein The anionic sulfate surfactant is a cyclic oligomer comprising structural subunit (i-1), structural subunit (ii-1) and structural subunit (iii-1) represented by the following formula: Alternatively, the anionic sulfate surfactant is a cyclic oligomer comprising structural subunit (i-2), structural subunit (ii-2) and structural subunit (iii-2) represented by the following formula: Among them, * indicates the connection site; R1 is selected from C8-C 16 The alkyl group is preferably selected from C 10 -C 14 Alkyl; M is selected from Na + and / or K + .

6. The heavy oil viscosity reduction and flooding composition according to claim 1, wherein: The amino acid surfactant is selected from one or more of sodium lauroyl glycinate, sodium lauroyl glutamate, sodium lauroyl sarcosinate, sodium cocoyl glutamate, sodium cocoyl sarcosinate and sodium cocoyl glycinate.

7. The heavy oil viscosity reduction and flooding composition according to claim 1, wherein: Based on the total weight of the heavy oil viscosity reduction and flooding composition, the content of the amino acid surfactant is 8-15 weight %, the content of the anionic sulfate surfactant is 4-8 weight %, and the content of water is 77-88 weight %.

8. A method for preparing the heavy oil viscosity reduction and flooding composition according to any one of claims 1 to 7, characterized in that: The method comprises mixing the amino acid surfactant, the anionic sulfate surfactant and the water; The method for preparing the anionic sulfate surfactant comprises the following steps: (1) in the presence of solvent I and a catalyst, contacting a 1,2-epoxy compound represented by formula (I-1) with a cyclodextrin compound represented by formula (I-2) to obtain an intermediate; (2) contacting the intermediate with a sulfonating agent in the presence of solvent II to carry out a sulfonation reaction to obtain a mixture I; (3) contacting the mixture I with an alkaline substance containing M to obtain a mixture II having a pH value of 7 or greater; The sum of m, n, and z is any integer between 5 and 11.

9. The method according to claim 8, wherein The mixing is carried out under stirring conditions, which include: temperature of 15-40° C., time of 10-80 min, and stirring speed of 50-600 rpm.

10. The method according to claim 8, wherein The cyclodextrin compound includes one or more of cyclodextrin, methylcyclodextrin, hydroxyethylcyclodextrin and hydroxypropylcyclodextrin; The catalyst includes one or more of alkali metal hydroxide and 4-dimethylaminopyridine; The sulfonating agent includes one or more of sulfur trioxide pyridine complex, fuming sulfuric acid, sulfur trioxide, concentrated sulfuric acid, chlorosulfonic acid and aminosulfonic acid; The solvent I comprises water; The solvent II includes one or more of tetrahydrofuran, 1,4-dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and pyridine; The alkaline substance includes one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide and ammonia water.

11. The method according to claim 8, wherein In step (1), the molar ratio of the cyclodextrin compound to the 1,2-epoxy compound is 1:(1-40), preferably 1:(1-32); The contact reaction conditions include: temperature of 30-100°C, time of 1-10 hours; preferably, temperature of 60-90°C, time of 3-8 hours; Relative to 1 mmol of the cyclodextrin compound, the amount of the solvent I is 0.1-50 mL, and the amount of the catalyst is 0.001-0.1 mmol; Preferably, relative to 1 mmol of the cyclodextrin compound, the amount of the solvent I is 1-10 mL, and the amount of the catalyst is 0.005-0.1 mmol.

12. The method according to claim 8, wherein In step (2), the weight ratio of the intermediate to the sulfonating agent is 1:(0.5-5.0), preferably 1:(1.0-3.0); Relative to 1g of the intermediate, the amount of the solvent II is 5-20mL; The conditions of the sulfonation reaction include: temperature of 0-90° C. and time of 1-24 h.

13. An oil displacement system, characterized in that: The oil displacement system comprises the heavy oil viscosity reduction displacement composition according to any one of claims 1 to 7, polyacrylamide and water; Relative to the total weight of the oil displacement system, the content of the heavy oil viscosity reduction displacement composition is 0.1-1 weight %, the content of the polyacrylamide is 0.05-0.3 weight %, and the content of water is 98.7-99.85 weight %.

14. The oil displacement system according to claim 13, wherein: Relative to the total weight of the oil displacement system, the content of the heavy oil viscosity reduction displacement composition is 0.3-0.8 weight %, the content of the polyacrylamide is 0.1-0.2 weight %, and the content of water is 99.0-99.6 weight %.

15. The oil displacement system according to claim 13, wherein: The molecular weight of the polyacrylamide is 8 million to 20 million, preferably 12 million to 20 million.

16. Use of the oil displacement system according to any one of claims 13 to 15 in heavy oil production.

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