Composite viscosity reducers, their preparation methods and applications; a method for responsive demulsification of heavy oil produced fluids.

Abstract

This invention relates to the field of heavy oil emulsification and viscosity reduction technology, and discloses a composite viscosity reducer, its preparation method and application, and a method for responsive demulsification of heavy oil produced fluid. The composite viscosity reducer contains a cyclodextrin-based surfactant, water, and modified graphene oxide; the modified graphene oxide comprises graphene oxide and grafted polyethylene oxide chains, the chemical formula of which is -CH2CH(OH)CH2O(CH2CH2O). n CH2CH2OH, where n is any integer selected from 3 to 20; the cyclodextrin-based surfactant contains -OSO3Na and -OH groups. The modified graphene oxide of this invention possesses excellent salt resistance and interfacial properties. When used in a composite viscosity reducer with a cyclodextrin-based surfactant, it can significantly improve the emulsification and viscosity-reducing effect of the viscosity reducer on heavy oil. Simultaneously, utilizing the pH-responsive sites of the composite viscosity reducer, CO2-responsive demulsification of the oil-water emulsion is achieved.

Description

Technical Field

[0001] This invention relates to the field of heavy oil emulsification and viscosity reduction technology, specifically to composite viscosity reducers and their preparation methods and applications, and a method for responsive demulsification of heavy oil produced fluid. Background Technology

[0002] As crude oil extraction enters its mid-to-late stages, reserves of low-viscosity crude oil are decreasing, while the proportion of high-viscosity heavy oil development is increasing year by year. Compared to low-viscosity crude oil, heavy oil contains more gum and asphaltenes, resulting in higher viscosity and poorer fluidity, which significantly increases the difficulty of its extraction.

[0003] Nanomaterials, as a commonly used oilfield additive, possess properties such as resistance to high temperatures, high pressures, high salts, and shearing, complementing traditional organic chemical agents. However, current spherical inorganic nanomaterials, represented by nano-SiO2 and its modified products, suffer from drawbacks such as large dosage and unsatisfactory oil displacement effects. Recent basic research has discovered that the nanoscale layered structure of graphene oxide endows the material with a higher theoretical specific surface area and specific surface energy, resulting in extremely high adsorption efficiency at the oil / water interface, capable of emulsifying Daqing crude oil at ppm-level dosages (Energy & Fuels, 2017, 31, 13439).

[0004] Furthermore, CN114058342A discloses a modified graphene oxide nanosheet thickener, which, by grafting small molecule surfactants onto graphene oxide, can control the interactions between polymer molecules, thereby improving the thickening efficiency of the polymer. However, the viscosity reduction process for heavy oil requires lowering the viscosity of the crude oil system, and the thickener-modified graphene oxide nanomaterials are clearly not suitable for this field.

[0005] Theoretically, the monolayer structure of graphene oxide enables it to spontaneously and efficiently adsorb at the oil-water interface, forming a "rigid" interfacial film. This "rigid" interfacial film is more stable than the "flexible" interfacial film formed by traditional surfactant adsorption, but it is difficult to meet the interfacial curvature required for the formation of water-in-oil emulsions. Furthermore, although some Janus nanomaterials can form Pickering emulsions after emulsifying oily components, these emulsions are highly stable and extremely difficult to demulsify, making it difficult to reprocess the produced crude oil and hindering its refining and utilization. Additionally, due to the large specific surface area of ​​nanomaterials, their stability in formation water and adsorption loss on rock surfaces also urgently need to be addressed.

[0006] Cyclodextrins (CDs), composed of multiple D-glucopyranose units linked by α-1,4 glycosidic bonds, possess a truncated pyramidal structure and are typical functional host molecules. They can form complexes with various bioactive molecules through cavity inclusion and have the advantages of being green and easily degradable, making them ideal carriers for drug molecules and nanomaterials. However, cyclodextrins themselves have high steric hindrance, which prevents them from achieving emulsification and viscosity reduction effects.

[0007] Therefore, there is an urgent need to develop a novel composite emulsification and viscosity reduction system to improve the carrying capacity of graphene oxide-based nanomaterials, enhance their emulsification and viscosity reduction effect on heavy oil, and simultaneously achieve stimulus-responsive demulsification of oil-water mixed emulsions, making the produced fluid easier to process. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of poor emulsification and viscosity reduction effect and difficulty in demulsification in the existing technology.

[0009] During the research, the inventors discovered that grafting graphene oxide with polyethylene glycol monoglycidyl ether resulted in modified graphene oxide nanomaterials with improved salt resistance and stable dispersion in formation water. Simultaneously, the modified graphene oxide nanomaterials exhibited excellent interfacial activity and enhanced emulsification and viscosity reduction properties. This modified graphene oxide, water, and cyclodextrin-based surfactants were combined to form an active composite viscosity reducer. The cyclodextrin-based surfactants in the composite viscosity reducer could encapsulate and stabilize the modified graphene oxide material, allowing it to selectively release upon contact with oil. Through synergistic interaction and co-adsorption at the oil-water interface with colloids in heavy oil, a stable oil-water interfacial film was formed, ultimately achieving the goal of emulsifying and reducing the viscosity of heavy oil. Furthermore, utilizing the pH-responsive sites of the composite viscosity reducer system, CO2-responsive demulsification of the emulsion system was achieved, facilitating post-processing of the produced fluid.

[0010] To achieve the above objectives, the first aspect of the present invention provides a composite viscosity reducer, which contains the following components, each stored independently or in combination: cyclodextrin-based surfactant, water, and modified graphene oxide.

[0011] The modified graphene oxide comprises graphene oxide and grafted polyethylene oxide chains, the chemical formula of which is -CH2CH(OH)CH2O(CH2CH2O). n CH2CH2OH, where n is any integer selected from 3 to 20;

[0012] The cyclodextrin-based surfactant contains -OSO3Na and -OH groups;

[0013] The mass ratio of the modified graphene oxide to the cyclodextrin-based surfactant is 1:(10-500).

[0014] A second aspect of the present invention provides a method for preparing the composite viscosity reducer described in the first aspect, the method comprising: contacting a cyclodextrin-based surfactant, modified graphene oxide, and water.

[0015] The third aspect of this invention provides the application of the composite viscosity reducer described in the first aspect in the field of heavy oil extraction.

[0016] A fourth aspect of the present invention provides a method for responsive demulsification of heavy oil produced fluid, the method comprising:

[0017] (1) The composite viscosity reducer described in the first aspect is brought into first contact with heavy oil to obtain an oil-water mixed emulsion;

[0018] (2) CO2 is introduced into the oil-water emulsion to cause the oil-water emulsion to demulsify and separate water in response.

[0019] The modified graphene oxide provided by this invention has excellent salt resistance and enhanced emulsification and viscosity reduction properties. When used in combination with cyclodextrin-based surfactants in composite viscosity reducers, it can significantly improve the viscosity reduction effect of the viscosity reducer on heavy oil.

[0020] The composite viscosity reducer provided by this invention combines the properties of two types of active materials: cyclodextrin-based surfactants and modified graphene oxide. Through host-guest interactions and synergistic adsorption among the components, a stable oil-water interface film is formed, achieving emulsification and viscosity reduction for extra-heavy oils. Simultaneously, utilizing the pH-responsive sites of the composite viscosity reducer, the oil-water emulsion can be rapidly demulsified and separated into water upon the introduction of CO2, thus simplifying crude oil post-processing.

[0021] In addition, by utilizing the encapsulation effect of cyclodextrin-based surfactants on modified graphene oxide nanomaterials, this invention can also achieve targeted release of modified graphene oxide nanomaterials upon contact with oil, thereby reducing the adsorption loss of nanomaterials on rock surfaces. Attached Figure Description

[0022] Figure 1 This is the mass spectrum of the polyethylene glycol monoglycidyl ether prepared in Example 1 of this invention.

[0023] Figure 2 The infrared spectrum of the modified graphene oxide prepared in Example 1 of this invention.

[0024] Figure 3 The mass spectrum of the cyclodextrin-based surfactant intermediate prepared in Example 2 of this invention is shown.

[0025] Figure 4 The cyclodextrin-based surfactant used in Example 2 of this invention 1 H NMR spectrum.

[0026] Figure 5 The image shows the UV-Vis spectrum of the modified graphene oxide aqueous dispersion prepared in Example 1 of this invention. Detailed Implementation

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] As mentioned above, the first aspect of this application provides a composite viscosity reducer containing the following components, which are stored independently or in combination: cyclodextrin-based surfactant, water, and modified graphene oxide.

[0029] The modified graphene oxide comprises graphene oxide and grafted polyethylene oxide chains, the chemical formula of which is -CH2CH(OH)CH2O(CH2CH2O). n CH2CH2OH, where n is any integer selected from 3 to 20;

[0030] The cyclodextrin-based surfactant contains -OSO3Na and -OH groups;

[0031] The mass ratio of the modified graphene oxide to the cyclodextrin-based surfactant is 1:(10-500).

[0032] In this invention, n in the polyoxyethylene chain is any integer from 3 to 20, for example, n is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or any range between any two values, preferably any integer from 5 to 15. The inventors have found that, under this preferred condition, modified graphene oxide exhibits better salt resistance and interfacial properties, and when used in composite viscosity reducers, it can achieve better viscosity reduction effects.

[0033] In a preferred embodiment, the mass ratio of the modified graphene oxide to the cyclodextrin-based surfactant is 1:(15-200). The inventors have found that, under this preferred embodiment, the resulting composite viscosity reducer exhibits superior viscosity-reducing effects.

[0034] Preferably, the grafting rate of polyoxyethylene chains in the modified graphene oxide is 30-50%, more preferably 35-46%, and even more preferably 40-46%. Under this preferred condition, the inventors of the present invention have found that the obtained modified graphene oxide exhibits superior synergistic emulsification and viscosity-reducing properties as well as salt resistance, and can be stably dispersed in high-salt formation water without agglomeration or precipitation. Its use in viscosity-reducing agents can better improve the stability of the oil-water interface film and the emulsification and viscosity-reducing effect.

[0035] In this invention, the grafting rate of the polyoxyethylene chain is calculated based on the difference in mass loss rate between the two graphene oxide materials before and after grafting modification, after heating at 800℃, that is: grafting rate = {(m[modified material] - m[modified material after heating at 800℃]) / m[modified material] - (m[graphene oxide] - m[graphene oxide after heating at 800℃]) / m[graphene oxide]}*100%.

[0036] In this invention, the linking group between the obtained graphene oxide and polyoxyethylene is an ether bond, which is more stable than an ester bond and can withstand acid / alkali aqueous solutions; at the same time, the modified graphene oxide obtained has hydroxyl groups at the end, and will not participate in the grafting reaction.

[0037] Preferably, the modified graphene oxide described in this invention does not contain organic amines.

[0038] In this invention, the infrared spectrometer is a NICOLET 6700 infrared spectrometer with a testing range of 450-4000 cm⁻¹. -1 The results obtained are data after removing the background air.

[0039] Preferably, the modified graphene oxide is obtained by dialysis of a modified graphene oxide aqueous dispersion.

[0040] Preferably, in the composite viscosity reducer, the modified graphene oxide is added in the form of a modified graphene oxide aqueous dispersion.

[0041] To further improve the salt resistance and enhanced emulsification and viscosity reduction properties of modified graphene oxide, this invention provides a preferred embodiment in which the modified graphene oxide aqueous dispersion is prepared by a method comprising the following steps:

[0042] S1: Under alkaline conditions, the aqueous dispersion of graphene oxide is activated with β-cyclodextrin to obtain an activated solution;

[0043] S2: The activation solution is grafted with polyethylene glycol monoglycidyl ether to obtain the grafted product;

[0044] S3: Adjust the pH of the grafted product to neutral using acid, then add amylase for washing to obtain the modified graphene oxide aqueous dispersion.

[0045] Preferably, the graphene oxide sheet diameter does not exceed 2 μm, and more preferably is 50-500 nm. Under this preferred condition, the inventors of the present invention have discovered that the obtained modified graphene oxide exhibits superior salt resistance.

[0046] Preferably, the raw material for the graphene oxide is microcrystalline graphite and / or flake graphite. In this invention, the microcrystalline graphene oxide prepared using microcrystalline graphite can be stably dispersed in high-salinity formation water. Simultaneously, the material exhibits strong dispersion stability and resistance to acids / alkalis, with interfacial tension reduced by an order of magnitude compared to the unmodified form. Therefore, it is suitable for application in various acid / alkali-based oil displacement systems. Furthermore, the cost of using microcrystalline graphite as a raw material is lower than that of flake graphite, making the modified graphene oxide more economical in application.

[0047] Preferably, in step S1, the activation reaction conditions include: a reaction temperature of 60-100℃, preferably 70-90℃; and a reaction time of 1-4 hours, preferably 2-3 hours. The inventors have found that conducting the activation reaction under these conditions is beneficial for increasing the activity of hydroxyl groups in the activation reaction, thereby further improving the grafting efficiency of the polyoxyethylene chains.

[0048] In this invention, the activation reaction is carried out under stirring conditions, and the stirring rate of the activation reaction is 200-800 rpm, preferably 300-500 rpm.

[0049] In a preferred embodiment, in step S2, the grafting reaction conditions include: a reaction temperature of 60-100℃, preferably 70-90℃; and a reaction time of 4-16h, preferably 6-12h.

[0050] Preferably, in step S3, the washing time is 1-4 hours, more preferably 2-3 hours. In this invention, the washing is performed under stirring conditions. There is no particular limitation on the washing stirring rate; those skilled in the art can make adaptive adjustments as needed. Preferably, the washing stirring rate is 200-800 rpm, more preferably 300-500 rpm.

[0051] Preferably, in step S1, the concentration of graphene oxide in the graphene oxide aqueous dispersion is greater than 20 mg / L, and more preferably 500-2000 mg / L.

[0052] Preferably, based on a total volume of 1 L of the mixed solution of graphene oxide aqueous dispersion and cyclodextrin, the amount of β-cyclodextrin used is 100-800 mg, more preferably 300-500 mg. In this invention, if the mass concentration of cyclodextrin is too low, the grafting effect will be poor and the grafting rate will be low; if the mass concentration of cyclodextrin is too high, it will result in waste of raw materials.

[0053] Preferably, the alkaline conditions in step S1 are provided by an alkaline substance, namely sodium hydroxide and / or potassium hydroxide. In this invention, conducting the activation reaction under alkaline conditions can increase the activity of hydroxyl groups in the activation solution and improve the grafting rate of polyoxyethylene chains in the modified graphene oxide.

[0054] In a preferred embodiment, in step S1, the pH value of the alkaline condition is 9-12, and more preferably 10-11.

[0055] Preferably, the mass ratio of polyethylene glycol monoglycidyl ether to graphene oxide is (5-100):1, for example, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, and any range between any two values, preferably (10-30):1.

[0056] In a preferred embodiment, in step S3, based on a total volume of 1L of graphene oxide aqueous dispersion, the amount of amylase used is 50-800mg, preferably 100-400mg.

[0057] Preferably, in step S3, the acid is selected from at least one of hydrochloric acid and sulfuric acid; the concentration of the acid is preferably 0.1-10 mol / L.

[0058] In step S3 of this invention, amylase is used for washing, which can remove cyclodextrin through enzymatic hydrolysis.

[0059] According to another preferred embodiment, in step S2, the polyethylene glycol monoglycidyl ether is prepared by the following method:

[0060] The polyethylene glycol monoglycidyl ether was prepared by reacting polyethylene glycol with potassium carbonate and epichlorohydrin under stirring conditions.

[0061] The molar ratio of polyethylene glycol, potassium carbonate, and epichlorohydrin is 1:(0.1-1):(1.1-10).

[0062] Preferably, the molar ratio of polyethylene glycol, potassium carbonate, and epichlorohydrin is 1:(0.5-1):(1.5-10). The inventors have found that, under this preferred condition, the polyethylene glycol monoglycidyl ether obtained is used to prepare modified graphene oxide, and the resulting modified graphene oxide exhibits better enhanced emulsification and viscosity-reducing effects.

[0063] In a preferred embodiment, the polyethylene glycol monoglycidyl ether has the following structural formula: n is any integer from 3 to 20, preferably any integer from 5 to 15.

[0064] Preferably, the temperature of the first reaction is 20-50℃, more preferably 25-40℃; the reaction time is 12-36h, more preferably 20-30h.

[0065] In this invention, the first reaction is preferably carried out under stirring conditions. There is no particular limitation on the stirring rate, and those skilled in the art can make adaptive adjustments as needed. Preferably, the stirring rate is 200-800 rpm, and more preferably 300-500 rpm.

[0066] Preferably, the average molecular weight of the polyethylene glycol is 200-600. In this invention, if the average molecular weight of the polyethylene glycol is too high, the polyethylene glycol exists in solid form, resulting in a low reaction yield; if the average molecular weight of the polyethylene glycol is too low, the stability of the obtained polyethylene glycol monoglycidyl ether is not good enough.

[0067] In a preferred embodiment, after the first reaction is completed, solvent extraction and solvent removal are performed sequentially to obtain the polyethylene glycol monoglycidyl ether.

[0068] The present invention does not particularly limit the extraction method. For example, polyethylene glycol monoglycidyl ether can be extracted to the dichloromethane phase using a 1 / 1 volume ratio water / dichloromethane solvent system, the dichloromethane phase can be collected, and the solvent can be removed to obtain polyethylene glycol monoglycidyl ether.

[0069] It should be noted that, in this invention, the method for preparing the modified graphene oxide is preferably carried out under stirring conditions. There are no particular requirements for the stirring speed; parameters known in the art can be used. For example, the stirring speed can be 200-800 rpm, preferably 300-500 rpm.

[0070] The aforementioned preparation method of the present invention may also involve various post-processing operations known in the art, such as rotary evaporation, extraction, washing, filtration, etc. The present invention does not have any particular limitations in this regard, and those skilled in the art should not understand it as a limitation of the present invention.

[0071] The modified graphene oxide preparation method provided by this invention is simple, environmentally friendly, and easy to operate. It utilizes the ring-opening reaction of hydroxyl groups with polyethylene glycol monoglycidyl ether to graft hydrophilic polyoxyethylene groups onto the surface of graphene oxide. Compared with polyethylene glycol diglycidyl ether, the use of polyethylene glycol monoglycidyl ether for modification in this invention effectively avoids bridging between nanosheets, thereby improving the salt resistance of the modified graphene oxide and effectively inhibiting its accumulation and aggregation. Furthermore, the addition of β-cyclodextrin provides hydrophobic reaction sites for the reaction, increasing the success rate of grafting polyoxyethylene groups onto the graphene oxide surface.

[0072] In a preferred embodiment, the cyclodextrin-based surfactant has the structure shown in formula (I):

[0073]

[0074] In the structure of equation (I), x is 2, y is any integer from 1 to 5, z is any integer from 0 to 4, and y + z = 5, -C 12 H 25 The label indicates n-dodecyl. The inventors discovered that, under this preferred condition, the resulting composite viscosity reducer exhibits even better viscosity-reducing effects.

[0075] In a preferred embodiment, the amount of water used is such that the mass concentration of the modified graphene oxide in the composite viscosity reducer is 10 mg / L-50 mg / L, and the mass concentration of the cyclodextrin-based surfactant is 500 mg / L-5000 mg / L.

[0076] It should be noted that the water in the composite viscosity reducer can be deionized water or formation water with a mineralization of less than 50,000 mg / L. Those skilled in the art can choose according to their needs.

[0077] It should be noted that, in this invention, the mass concentration of the modified graphene oxide is calculated based on the mass concentration of graphene oxide.

[0078] More preferably, the amount of water used is such that the mass concentration of the modified graphene oxide in the composite viscosity reducer is 10 mg / L-30 mg / L, and the mass concentration of the cyclodextrin-based surfactant is 1000 mg / L-2000 mg / L. The inventors have found that, under this preferred condition, the composite viscosity reducer exhibits better emulsification and viscosity reduction effects, and superior demulsification and water separation effects.

[0079] This invention does not specify a method for preparing the cyclodextrin-based surfactant; those skilled in the art can use known techniques in the field. However, to obtain a cyclodextrin-based surfactant with superior surface activity, this invention provides a preferred method for preparing the cyclodextrin-based surfactant, the method comprising:

[0080] Sa: In the presence of solvent I and catalyst, β-cyclodextrin and 1,2-epoxytetradecane were subjected to a first contact reaction, filtered, and the intermediate product was obtained.

[0081] Sb: In the presence of solvent II, the intermediate product is sulfonated with a sulfonating agent to obtain mixture IV;

[0082] Sc: The pH of the mixture I was adjusted to 7-9 using sodium hydroxide; the solvent was removed to obtain the cyclodextrin-based surfactant.

[0083] In this invention, the method for preparing the cyclodextrin-based surfactant is preferably carried out under stirring. There are no special requirements for the stirring speed, and parameters known in the art can be used.

[0084] Preferably, in step Sa, the conditions for the first contact reaction include: a temperature of 60-90°C and a time of 3-8 hours.

[0085] Preferably, the sulfonation reaction conditions include: a temperature of 0-90°C and a time of 1-24 hours.

[0086] In a preferred embodiment, in step Sa, the solvent I is water, and the catalyst is an alkali metal hydroxide or 4-dimethylaminopyridine.

[0087] Preferably, the alkali metal hydroxide is selected from at least one of NaOH and KOH.

[0088] Preferably, in step Sa, the amount of solvent I used is 1-10 mL relative to 1 mmol of the β-cyclodextrin, and the amount of catalyst used is 0.005-0.1 mmol.

[0089] Preferably, in step Sa, the molar ratio of β-cyclodextrin to 1,2-epoxytetradecane is 1:(1-32). More preferably, the molar ratio of β-cyclodextrin to 1,2-epoxytetradecane is 1:7.

[0090] According to another preferred embodiment, in step Sb, the mass ratio of the intermediate to the sulfur trioxide pyridine complex is 1:1.0-3.0.

[0091] Preferably, the content of active SO3 in the sulfur trioxide pyridine complex is 45-55 wt%.

[0092] Preferably, the amount of solvent II is 5-20 mL relative to 1 g of the intermediate product.

[0093] Preferably, in step Sb, the sulfonation reaction conditions are at least: a temperature of 0-90°C and a time of 1-24 hours.

[0094] In a preferred embodiment, in step Sb, solvent II is selected from at least one of tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0095] In step Sc of the present invention, the sodium hydroxide is preferably added in the form of an aqueous solution, and the concentration of the aqueous solution of sodium hydroxide is 5wt%-15wt%.

[0096] The composite viscosity reducer provided by this invention has excellent emulsification and viscosity reduction effects on heavy oil through the synergistic effect of modified graphene oxide and cyclodextrin-based surfactants.

[0097] As previously stated, a second aspect of the present invention provides a method for preparing the composite viscosity reducer described in the first aspect, the method comprising: contacting a cyclodextrin-based surfactant, modified graphene oxide, and water.

[0098] It should be noted that in this invention, the definitions and amounts of the cyclodextrin-based surfactant, modified graphene oxide, and water are the same as those of the corresponding components described in the first aspect, and will not be repeated here. Those skilled in the art should not understand this as a limitation of the invention.

[0099] Preferably, the contact conditions include: a temperature of 10-35°C, a time of 30-60 min, and a stirring speed of 100-500 rpm.

[0100] As previously stated, the third aspect of this invention provides the application of the composite viscosity reducer described in the first aspect in the field of heavy oil extraction.

[0101] As previously described, a fourth aspect of the present invention provides a method for responsive demulsification of heavy oil produced fluid, the method comprising:

[0102] (1) The composite viscosity reducer described in the first aspect is brought into first contact with heavy oil to obtain an oil-water mixed emulsion;

[0103] (2) CO2 is introduced into the oil-water emulsion to break the emulsion and separate the water.

[0104] In a preferred embodiment, the viscosity of the heavy oil at 50°C is 10,000-30,000 mPa·s.

[0105] Preferably, the method further includes: in step (1), the substance obtained after the first contact is allowed to stand for 1-4 hours to obtain an oil-water mixed emulsion.

[0106] In a preferred embodiment, in step (1), the mass ratio of the composite viscosity reducer to the heavy oil is 3:7 to 7:3. In this preferred embodiment, the inventors have found that the composite viscosity reducer has a better emulsifying and viscosity-reducing effect on the heavy oil, achieving a viscosity reduction rate of not less than 99% for the target heavy oil.

[0107] Preferably, in step (1), the conditions for the first contact include: a temperature of 40-60°C and a time of 10-300 min.

[0108] Preferably, in step (2), the CO2 flow rate is 0.5-5 L / min, and the aeration time is 1-5 min. More preferably, in step (2), the CO2 flow rate is 0.5-2 L / min, and the aeration time is 1-5 min. Under this preferred condition, the inventors found that the composite viscosity reducer has a better demulsifying effect on oil-water emulsions containing heavy oil.

[0109] The present invention provides a method for responsive demulsification of heavy oil produced fluid. It uses a composite viscosity reducer to emulsify and reduce the viscosity of heavy oil. The cyclodextrin-based surfactant in the composite viscosity reducer has a pH-responsive group that is responsive to CO2. After CO2 is introduced, the emulsion can be rapidly demulsified and separated into phases, thereby simplifying crude oil post-processing.

[0110] The present invention will be described in detail below through examples. Unless otherwise specified, all reagents used in the following examples are commercially available chemical reagents, and there are no particular limitations in this regard. The water used in the following preparation examples is distilled water, and the water used in the examples and comparative examples is formation water with a mineralization of 20000 mg / L. Room temperature is expressed as 25 ± 3 °C.

[0111] The main raw materials used in the example are as follows:

[0112] Graphene oxide: a single-layer nanomaterial with a sheet diameter of 50-100 nm and a mass concentration of 0.5 mg / mL, purchased from Pioneer Nanomaterials Technology Co., Ltd.

[0113] Epichlorohydrin: 99% purity, purchased from Beijing Yiyinuokai Technology Co., Ltd.;

[0114] Polyethylene glycol 400: average molecular weight 400, purchased from Beijing Yiyinuokai Technology Co., Ltd.;

[0115] β-Cyclodextrin: 99% purity, purchased from Beijing Yiyinuokai Technology Co., Ltd.;

[0116] 1,2-Epoxytetradecane: 95% purity, purchased from TCI Chemical Industry Development Co., Ltd.;

[0117] Amylase: α-amylase, purity 2000u / g, purchased from Adamas Reagents Ltd.

[0118] Preparation Example 1: Preparation of Modified Graphene Oxide

[0119] (1) Take 100 mL of graphene oxide aqueous dispersion (500 mg / L), add 50 mg of β-cyclodextrin, then add sodium hydroxide to adjust the pH of the system to 10.0, stir at 80℃ and 500 rpm for 2 hours to obtain the activated solution;

[0120] (2) Weigh 16g of polyethylene glycol 400 and 5.5g of potassium carbonate into a single-necked flask. Add 10g of epichlorohydrin under stirring at 25°C and a stirring rate of 500rpm. Continue the reaction for 24 hours, then stop stirring. Extract the polyethylene glycol monoglycidyl ether to the dichloromethane phase using 200mL of a water / dichloromethane (volume ratio 1:1) mixture. Collect the dichloromethane phase, remove the solvent, and obtain the product polyethylene glycol monoglycidyl ether.

[0121] Then, 1.5g of polyethylene glycol monoglycidyl ether was added to the above activation solution, and the reaction was continued at 80℃ and 500rpm for 8 hours. Heating was then stopped, and the mixture was cooled to room temperature to obtain the grafted product.

[0122] (3) Add 1 mol / L hydrochloric acid to the above grafted product to adjust the pH value to 7, then add 10 mg of amylase and stir at 25℃ and 500 rpm for 3 hours to obtain modified graphene oxide aqueous dispersion.

[0123] The polyethylene glycol monoglycidyl ether obtained in step (2) was subjected to mass spectrometry analysis, and the mass spectrum is shown below. Figure 1 As shown, since polyethylene glycol 400 is a mixture, its mass spectrum also shows multiple molecular ion peaks. For example, 449.5 corresponds to the polyethylene glycol monoglycidyl ether product with an n value of 7, 493.5 corresponds to the polyethylene glycol monoglycidyl ether product with an n value of 8, and 537.5 corresponds to the polyethylene glycol monoglycidyl ether product with an n value of 9.

[0124] Take 10 mL of the modified graphene oxide aqueous dispersion prepared above, dialyze it through a dialysis membrane in distilled water for one week to remove unreacted raw materials, then freeze-dry the dialyzed graphene oxide aqueous dispersion, and characterize the structure of the modified graphene oxide by infrared spectroscopy. The infrared spectrum is shown below. Figure 2 As shown.

[0125] exist Figure 2 In the middle, the spectrum is at 3432cm -1 The characteristic absorption peak at 1730 cm⁻¹ represents the stretching vibration peak of the remaining unreacted hydroxyl groups in graphene oxide and the newly formed OH groups after ring opening of the epoxy groups. -1 The characteristic absorption peak at 1633 cm⁻¹ corresponds to the carbon-oxygen double bond of the carboxylic acid group on graphene oxide. -1 The characteristic absorption peak at 1101 cm⁻¹ corresponds to the carbon-carbon double bonds in graphene oxide. -1 The peak corresponds to the stretching vibration peak of COC in the polyoxyethylene group, at 845 cm⁻¹. -1 The peak at 1450 cm⁻¹ is the stretching vibration peak of Cc in polyoxyethylene groups. -1 and 2855cm -1The peaks at the ellipse correspond to the CH vibration absorption peaks of the polyoxyethylene groups. These spectral peaks demonstrate that the polyoxyethylene chains are chemically bonded to the graphene oxide surface.

[0126] 0.50 g of freeze-dried modified graphene oxide powder was weighed into a quartz boat and heated to 800 °C for 2 h in a tube furnace at a heating rate of 10 °C / min. The mass loss was measured, and the grafting rate of polyoxyethylene groups on the surface of graphene oxide was calculated to be 45.2% according to the aforementioned grafting rate formula.

[0127] Preparation Example 2: Preparation of Cyclodextrin-based Surfactants

[0128]

[0129] Weigh 10 mmol of β-cyclodextrin and 70 mmol of 1,2-epoxytetradecane into a reaction flask, and then add 20 mL of tap water, 0.05 mmol of 4-dimethylaminopyridine and a magnetic particle, respectively. Subsequently, the reaction system was stirred at 85 °C for 7 h, the reaction was stopped, and the white solid intermediate product (structure shown in formula (1)) was obtained by filtration.

[0130] The intermediate product was characterized by MALDI-TOF-MS, and its structure is as follows: Figure 3 As shown, the spectrum exhibits peaks at mass-to-charge ratios of 1369.350, 1581.509, 1793.666, 2005.817, 2217.964, 2430.107, and 2642.248, corresponding to the molecular ion peaks of the alkyl-modified β-cyclodextrin (Formula 1) obtained after the ring-opening reaction of 1–7 primary hydroxyl groups with 1,2-epoxytetradecane. This result demonstrates the successful grafting of hydrophobic alkyl chains onto the cyclodextrin backbone to obtain the reaction intermediate. Simultaneously, from… Figure 3 According to the intensity of MALDI-TOF-MS, x is 2 and y+z=5 in the product of the structure shown in equation (1).

[0131] Add 1g of intermediate product and 10mL of N,N-dimethylformamide to a three-necked flask. At the same time, weigh 2g of sulfur trioxide pyridine complex (active SO3 content 50wt%) and dissolve it in 5mL of N,N-dimethylformamide. Add it to the three-necked flask containing the intermediate product. Stir the reaction at 50℃ for 2h. Cool to room temperature and add 10wt% sodium hydroxide aqueous solution to adjust the pH to 7. Remove the solvent by rotary evaporation and dry to obtain the product cyclodextrin-based surfactant (structure as shown in formula (2)). The yield is 81%.

[0132] The product cyclodextrin-based surfactant was subjected to... 1 ¹H NMR characterization (using deuterated water as the deuterated solvent) yielded the following results: Figure 4 As shown, 1H 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 ).

[0133] Depend on Figure 4 It can be seen that there are two broad peaks in the proton chemical shift at 4.06 ppm and 4.18-4.49 ppm. Specifically, 4.06 ppm corresponds to -CH-CH2OSO3Na, and the peaks at 4.18-4.49 ppm correspond to -CH-CH2-OSO3Na and -CH-CH2-O-CH2-CHOH-C, respectively. 12 H 25 This proves the successful conduct of the sulfonation reaction and the existence of the sulfonation product.

[0134] In this embodiment, the average sulfonation degree of the cyclodextrin-based surfactant was 1.15 mmol / g, which was determined by titration with NaOH standard solution in the literature (China Paper Industry, 2006, (11): 38-40.).

[0135] Example 1

[0136] Weigh 2g of cyclodextrin-based surfactant, 40mL of 500mg / L modified graphene oxide aqueous dispersion, and 960mL of formation water (mineralization 20000mg / L) and add them to a beaker. Stir at 500rpm for 30min at 25℃ until the mixture is homogeneous to obtain composite viscosity reducer A1.

[0137] In this composite viscosity reducer, the mass concentration of modified graphene oxide is 20 mg / L, and the mass concentration of cyclodextrin-based surfactant is 2000 mg / L.

[0138] Example 2

[0139] Weigh 3g of cyclodextrin-based surfactant, 20mL of 500mg / L modified graphene oxide aqueous dispersion, and 980mL of formation water (mineralization 20000mg / L) and add them to a beaker. Stir at 200rpm for 40min at 35℃ until the mixture is homogeneous to obtain composite viscosity reducer A2.

[0140] In this composite viscosity reducer, the mass concentration of modified graphene oxide is 10 mg / L, and the mass concentration of cyclodextrin-based surfactant is 3000 mg / L.

[0141] Example 3

[0142] Weigh 1g of cyclodextrin-based surfactant, 100mL of 500mg / L modified graphene oxide aqueous dispersion, and 900mL of formation water (mineralization 20000mg / L) and add them to a beaker. Stir at 100rpm for 60min at 25℃ until the mixture is homogeneous to obtain composite viscosity reducer A3.

[0143] In this composite viscosity reducer, the mass concentration of modified graphene oxide is 50 mg / L, and the mass concentration of cyclodextrin-based surfactant is 1000 mg / L.

[0144] Example 4

[0145] Weigh 0.5g of cyclodextrin-based surfactant, 60mL of 500mg / L modified graphene oxide aqueous dispersion, and 940mL of formation water (mineralization 20000mg / L) and add them to a beaker. Stir at 500rpm for 60min at 10℃ until the mixture is homogeneous to obtain composite viscosity reducer A4.

[0146] In this composite viscosity reducer, the mass concentration of modified graphene oxide is 30 mg / L, and the mass concentration of cyclodextrin-based surfactant is 500 mg / L.

[0147] Example 5

[0148] Weigh 5g of cyclodextrin-based surfactant, 20mL of 500mg / L modified graphene oxide aqueous dispersion, and 980mL of formation water (mineralization 20000mg / L) and add them to a beaker. Stir at 500rpm for 40min at 25℃ until the mixture is homogeneous to obtain composite viscosity reducer A5.

[0149] In this composite viscosity reducer, the mass concentration of modified graphene oxide is 10 mg / L, and the mass concentration of cyclodextrin-based surfactant is 5000 mg / L.

[0150] Example 6

[0151] Weigh 0.8g of cyclodextrin-based surfactant, 30mL of 500mg / L modified graphene oxide aqueous dispersion, and 970mL of formation water (mineralization 20000mg / L) and add them to a beaker. Stir at 350rpm for 50min at 25℃ until the mixture is homogeneous to obtain composite viscosity reducer A6.

[0152] In this composite viscosity reducer, the mass concentration of modified graphene oxide is 15 mg / L, and the mass concentration of cyclodextrin-based surfactant is 800 mg / L.

[0153] Comparative Example 1

[0154] This comparative example prepared the composite viscosity reducer DA1 according to the method of Example 1, except that no modified graphene oxide aqueous dispersion was added in this comparative example.

[0155] Comparative Example 2

[0156] This comparative example prepared the composite viscosity reducer DA2 according to the method of Example 1, except that 40 mL of 500 mg / L modified graphene oxide aqueous dispersion was replaced with 40 mL of 500 mg / L unmodified graphene oxide aqueous dispersion (i.e., graphene oxide aqueous dispersion).

[0157] Comparative Example 3

[0158] This comparative example prepared the composite viscosity reducer DA3 according to the method of Example 1, except that the cyclodextrin-based surfactant was replaced by β-cyclodextrin by mass.

[0159] Comparative Example 4

[0160] This comparative example prepared modified graphene oxide aqueous dispersion H1 according to the method for preparing modified graphene oxide nanosheet dispersion in Example 1 of CN114058342A;

[0161] Then, the composite viscosity reducer DA4 was prepared according to the method of Example 1 of the present invention, except that the 500 mg / L modified graphene oxide aqueous dispersion was replaced with the 500 mg / L modified graphene oxide aqueous dispersion H1.

[0162] Comparative Example 5

[0163] This comparative example prepared modified graphene oxide nanomaterials according to the method of Preparation Example 1, except that 1.5g of polyethylene glycol monoglycidyl ether was replaced with 1.5g of polyethylene glycol diglycidyl ether to obtain modified graphene oxide aqueous dispersion H2.

[0164] Then, the composite viscosity reducer DA5 was prepared according to the method of Example 1 of the present invention, except that the 500 mg / L modified graphene oxide aqueous dispersion was replaced with 500 mg / L modified graphene oxide aqueous dispersion H2.

[0165] Test Example 1: Salt Tolerance Test

[0166] Take 100 mL of each of the composite viscosity reducers obtained in the above examples and comparative examples into glass test tubes, then let them stand for 30 min and observe the state of the system. The results are shown in Table 1 below:

[0167] Table 1. Status of the composite viscosity reducer

[0168] Example state Example 1 homogeneous clear solution Example 2 homogeneous clear solution Example 3 homogeneous clear solution Example 4 homogeneous clear solution Example 5 homogeneous clear solution Example 6 homogeneous clear solution Comparative Example 1 homogeneous clear solution Comparative Example 2 precipitate Comparative Example 3 homogeneous clear solution Comparative Example 4 precipitate Comparative Example 5 precipitate

[0169] As shown in Table 1, the modified graphene oxide materials used in Examples 1-6 exhibited good salt resistance, and the viscosity reducers prepared from formation water were all clear solutions. Comparative Example 2 showed flocculent precipitate, indicating that the unmodified graphene oxide had poor salt resistance; even with the addition of a cyclodextrin-based surfactant as a stabilizer, it still precipitated as a black flocculent precipitate. Furthermore, Comparative Example 3 demonstrated that both the cyclodextrin-based surfactant and cyclodextrin could stabilize the modified graphene oxide and inhibit its precipitation in saline formation water.

[0170] In Comparative Example 4, the composite viscosity reducer precipitated flocculently, indicating that the entanglement between the dodecyl tail chains on the surface of the modified graphene nanomaterial described in CN114058342A acted as a bridge, making the nanomaterial easily aggregate in brine. The addition of the cyclodextrin-based surfactant could not prevent the precipitation. Comparative Example 5 was similar to Comparative Example 4. The polyethylene glycol diglycidyl ether contained an epoxy three-membered ring reaction site at each end, thus bridging multiple nanosheets together, making the material prone to precipitation and unsuitable for saline formation water systems.

[0171] Test Example 2: Surface Activity Test

[0172] The surface tension values ​​of the composite viscosity reducers prepared in the examples and comparative examples were measured using a K100 surface tension meter from KRUSS GmbH, Germany, using the pendant method. The test temperature was 25℃, and the test results are shown in Table 2. For viscosity reducers that produced precipitation, the surface tension of the clarified aqueous solution was measured after filtering the precipitate.

[0173] Table 2 shows the surface tension of the composite viscosity reducer in each embodiment and comparative example.

[0174] Example Surface tension (mPa·s) Example 1 32.1 Example 2 32.8 Example 3 33.3 Example 4 33.7 Example 5 32.6 Example 6 34.0 Comparative Example 1 35.5 Comparative Example 2 36.0 Comparative Example 3 59.8 Comparative Example 4 34.6 Comparative Example 5 35.8

[0175] As shown in the table above, the surface tension of the composite viscosity reducers in Examples 1-6 is reduced by at least 1.5 mN / m compared to the single cyclodextrin-based surfactant (Comparative Example 1). This is because the two components of the composite system form an active complex. Meanwhile, Comparative Example 3 shows that even when unmodified cyclodextrin and modified graphene oxide form a complex, their interfacial activity is still poor. Comparative Example 4 indicates that after the precipitation of modified graphene oxide nanomaterials, some free N-(2-hydroxyethyl)dodecylamide molecules act together with the cyclodextrin-based surfactant at the water-air interface, reducing the surface tension to 34.6 mN / m. In Comparative Examples 2 and 5, after the precipitation of the modified nanomaterials, the residue in the aqueous solution is the cyclodextrin-based surfactant, and its surface tension is close to that of Comparative Example 1.

[0176] Test Example 3: Viscosity Reduction Performance Test

[0177] The viscosity reduction rate of the composite viscosity reducers used in each embodiment and comparative example was determined for heavy oil. The oil used in the test was heavy oil from the Chenzhuang block of Shengli Oilfield, with a viscosity of 13370 mPa·s at 50°C, which is classified as extra-heavy oil.

[0178] The specific test steps for the viscosity reduction rate of heavy oil are as follows:

[0179] (a) Take 20 grams of the heavy oil sample and place it in a distillation flask;

[0180] (b) Add 10 grams of the composite viscosity reducer from the example to the distillation flask;

[0181] (c) After standing at 50°C for 2 hours, the mixture was gently shaken to obtain an oil-water emulsion. Its viscosity at 50°C was then measured using a HaakeVT550 rotational viscometer.

[0182] (d) The viscosity reduction rate of heavy oil is calculated using the following formula: M=[(η1-η2) / η1]×100%,

[0183] In the formula, η1 refers to the viscosity of crude oil (mPa·s); η2 refers to the viscosity of crude oil emulsion (mPa·s);

[0184] M represents the viscosity reduction rate.

[0185] The viscosity reduction rates of the composite viscosity reducers obtained in each embodiment and comparative example are shown in Table 3. For viscosity reducers that precipitate, the precipitate was filtered and tested using a clear aqueous solution.

[0186] Table 3 shows the viscosity reduction rate of the composite viscosity reducer in each embodiment and comparative example.

[0187] Viscosity of the system after adding viscosity reducer / (mPa·s) Viscosity reduction rate / % Example 1 42 99.7 Example 2 57 99.6 Example 3 66 99.5 Example 4 103 99.2 Example 5 56 99.6 Example 6 132 99.0 Comparative Example 1 2105 84.3 Comparative Example 2 2886 78.4 Comparative Example 3 12243 8.4 Comparative Example 4 1008 92.5 Comparative Example 5 2337 82.5

[0188] In Table 3, the viscosity reducers used in Examples 1-6 were all able to form oil-in-water emulsions with heavy oil, with viscosity reduction rates all exceeding 99%. This is because the cyclodextrin-based surfactants formed a complex with the modified graphene oxide, resulting in two effects: firstly, the complex enriches at the interface, forming a flexible oil-water interfacial film with excellent emulsification; secondly, the modified graphene oxide in the complex can attract amphiphilic colloidal substances from the heavy oil to enrich at the interface through π-π interactions, ultimately exhibiting a higher viscosity reduction rate.

[0189] Comparative Example 1 shows that, without modified graphene oxide, the cyclodextrin-based surfactant itself has a relatively low viscosity reduction rate for heavy oil, at 84.3%. This indicates that the stabilizing effect of modified graphene oxide on the interface plays a crucial role in achieving the ultra-high viscosity reduction rate. In Comparative Examples 2 and 5, the nanomaterials precipitate, and the viscosity reduction performance of the systems is similar to that of Comparative Example 1. In Comparative Example 3, the interfacial activity of the β-cyclodextrin and modified graphene oxide mixture is poor, and its viscosity reduction rate is only 8.4%. In Comparative Example 4, after the nanomaterials precipitate, some free N-(2-hydroxyethyl)dodecylamide molecules act together with the cyclodextrin-based surfactant at the oil-water interface, resulting in a viscosity reduction rate of 92.5%.

[0190] Test Example 4: Determination of the Adsorption Properties of Modified Graphene Oxide on Rock Surfaces

[0191] The adsorption properties of modified graphene oxide nanomaterials on rock surfaces were measured according to the method described in the literature (Rui Liu, Shi Gao, Qin Peng, et al. Experimental and molecular dynamic studies of amphiphilic graphene oxide for promising nanofluid flooding, Fuel, 2022, 330, 125567). Figure 5 To prepare the UV-Vis spectrum of the modified graphene oxide aqueous dispersion obtained in Example 1, the spectrum showed a peak at 231 nm. By changing the mass concentration of modified graphene oxide (1 mg / L, 2 mg / L, 6 mg / L, 10 mg / L), the UV absorbance of the system at 231 nm was measured, and a standard curve of mass concentration versus absorbance of modified graphene oxide was plotted.

[0192] Take 15g of heavy oil from the Chenzhuang block of Shengli Oilfield and disperse it evenly with 85g of petroleum ether at 60℃ to obtain a heavy oil dispersion. Then, place artificial sandstone slices with a diameter of 2.5cm, a height of 0.1cm, and a thickness of 1cm into the heavy oil dispersion and soak them for 24h. Remove them and dry them to constant weight to obtain oil-wet surface rock slices.

[0193] Untreated rock slices and oil-wet rock slices were respectively immersed in 30 mL of the composite viscosity reducer prepared in the example for 4 hours. The ultraviolet absorption curve of the upper liquid was measured. Then, the concentration of modified graphene oxide in the upper liquid could be obtained according to the standard curve. The measurement results are shown in Table 4.

[0194] Table 4 shows the adsorption amount of modified graphene oxide on rock surfaces in each example and comparative example.

[0195]

[0196] As shown in Table 4, the modified graphene oxide contained in the composite viscosity reducers prepared in Examples 1-6 exhibited low adsorption on the surface of untreated rock sheets, and the concentration of modified graphene oxide in the aqueous phase did not change significantly. However, the modified graphene oxide nanomaterials showed high adsorption on the surface of oil-wet rock sheets, with a very low residual concentration in the dispersion after adsorption. These results indicate that, under the encapsulation effect of cyclodextrin-based surfactants, the modified graphene oxide nanomaterials contained in the composite viscosity reducers in Examples 1-6 can be targeted and released onto oil-containing surfaces with minimal loss on oil-free rock surfaces. This targeted release performance is beneficial for improving the efficiency of modified graphene oxide and reducing the cost of material application.

[0197] In Comparative Examples 2, 4, and 5, the precipitation of graphene oxide nanomaterials in the composite viscosity reducers failed to demonstrate their targeted release effect. Comparative Example 3 showed that β-cyclodextrin itself could also enable the nanomaterials to have a certain oil-reactive targeted release effect, but the adsorption loss of the nanomaterials on the untreated rock surface was higher than in Example 1. This indicates that the cyclodextrin-based surfactant used in these examples could enable the modified graphene oxide nanomaterials to have a better targeted release effect.

[0198] Test Example 5: CO2-responsive demulsification test

[0199] The oil-water emulsions formed in Examples 1-3 and Comparative Example 4 of Test Example 3 were selected. CO2 was introduced into the oil-water emulsion at a gas flow rate of 1 L / min. After 3 minutes of aeration, the mixture was allowed to stand. The time required for the emulsion to break down was recorded. The time required for the emulsion to break down without CO2 introduction was also recorded. The results are shown in Table 5.

[0200] Table 5. Time required for emulsion demulsification in each example and comparative example.

[0201] <![CDATA[Time required for demulsification after introducing CO2]]> <![CDATA[Time required for demulsification without CO2 injection]]> Example 1 15.2min 28.5h Example 2 13.3min 18.6h Example 3 15.5min 29.5h Example 4 14.8min 28.0h Example 5 12.5min 18.0h Example 6 13.5min 19.0h Comparative Example 1 2.0h 1.2h Comparative Example 2 2.0h 1.0h Comparative Example 3 -(Non-emulsifying) -(Non-emulsifying) Comparative Example 4 72.0h 96.0h Comparative Example 5 2.0h 1.0h

[0202] Therefore, it can be seen that in Examples 1-6, the demulsification rate of the system was very fast after CO2 was introduced, and the time required for the emulsion to demulsify was no more than 20 minutes. However, without the introduction of CO2, the demulsification time exceeded 18 hours.

[0203] Comparative Example 1, lacking modified graphene oxide, showed little difference in the time required for emulsion demulsification before and after CO2 introduction, both falling within the range of 1.0-2.0 hours. Comparative Examples 2 and 5, due to the precipitation of nanomaterials in the brine, exhibited similar demulsification performance to Comparative Example 1. The composite viscosity reducer used in Comparative Example 3 had a very low viscosity reduction rate, resulting in minimal emulsification of the heavy oil; therefore, the demulsification time could not be measured. Comparative Example 4, containing free, unreacted single-chain small-molecule surfactants, exhibited a demulsification time as long as 96 hours. Even after carbon dioxide introduction, the small-molecule surfactants remained concentrated at the oil-water interface, resulting in a demulsification time still as long as 72 hours.

[0204] In summary, the modified graphene oxide nanomaterial contained in the composite viscosity reducer of this invention has the effect of targeted release upon contact with oil, which can effectively emulsify heavy oil, achieve efficient viscosity reduction, and reduce material adsorption loss. At the same time, the mixed emulsion formed by the viscosity reducer and heavy oil has the characteristic of CO2-responsive demulsification, which simplifies the post-processing of heavy oil produced fluid, overcomes the technical difficulty of demulsification in nano viscosity reducer systems, and has good practical application value.

[0205] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite viscosity reducer, characterized in that, This composite viscosity reducer contains the following components: cyclodextrin-based surfactant, water, and modified graphene oxide; The modified graphene oxide comprises graphene oxide and grafted polyethylene oxide chains, the chemical formula of which is -CH2CH(OH)CH2O(CH2CH2O). n CH2CH2OH, where n is any integer selected from 3 to 20; The cyclodextrin-based surfactant contains -OSO3Na groups and -OH groups; The mass ratio of the modified graphene oxide to the cyclodextrin-based surfactant is 1:(10-500). The cyclodextrin-based surfactant has the structure shown in formula (I): Formula (I), In the structure of equation (I), x is 2, y is any integer from 1 to 5, z is any integer from 0 to 4, and y + z = 5, -C 12 H 25 Indicates dodecyl; The modified graphene oxide is added in the form of a modified graphene oxide aqueous dispersion; the modified graphene oxide aqueous dispersion is prepared by a method including the following steps: S1: Under alkaline conditions, the aqueous dispersion of graphene oxide is activated with β-cyclodextrin to obtain an activated solution; S2: The activation solution is grafted with polyethylene glycol monoglycidyl ether to obtain the grafted product; S3: Adjust the pH of the grafted product to neutral using acid, then add amylase for washing to obtain the modified graphene oxide aqueous dispersion.

2. The composite viscosity reducer according to claim 1, wherein, The grafting rate of polyoxyethylene chains in the modified graphene oxide is 30-50%.

3. The composite viscosity reducer according to claim 2, wherein, The grafting rate of polyoxyethylene chains in the modified graphene oxide is 35-46%.

4. The composite viscosity reducer according to any one of claims 1-3, wherein, In the polyoxyethylene chain, n is any integer from 5 to 15.

5. The composite viscosity reducer according to any one of claims 1-3, wherein, The mass ratio of the modified graphene oxide to the cyclodextrin-based surfactant is 1:(15-200).

6. The composite viscosity reducer according to claim 1, wherein, In step S1, the conditions for the activation reaction include: a reaction temperature of 60-100℃ and a reaction time of 1-4h.

7. The composite viscosity reducer according to claim 6, wherein, In step S1, the activation reaction conditions include: a reaction temperature of 70-90℃ and a reaction time of 2-3 hours.

8. The composite viscosity reducer according to claim 1, wherein, In step S2, the grafting reaction conditions include: a reaction temperature of 60-100℃ and a reaction time of 4-16h.

9. The composite viscosity reducer according to claim 8, wherein, In step S2, the grafting reaction conditions include: a reaction temperature of 70-90℃ and a reaction time of 6-12h.

10. The composite viscosity reducer according to claim 1, wherein, In step S3, the washing time is 1-4 hours.

11. The composite viscosity reducer according to claim 10, wherein, In step S3, the washing time is 2-3 hours.

12. The composite viscosity reducer according to claim 1, wherein, In step S1, the concentration of graphene oxide in the graphene oxide aqueous dispersion is greater than 20 mg / L.

13. The composite viscosity reducer according to claim 12, wherein, In step S1, the concentration of graphene oxide in the graphene oxide aqueous dispersion is 500-2000 mg / L.

14. The composite viscosity reducer according to claim 1, wherein, Based on a total volume of 1L for the mixed solution of graphene oxide aqueous dispersion and β-cyclodextrin, the amount of β-cyclodextrin used is 100-800 mg.

15. The composite viscosity reducer according to claim 14, wherein, Based on a total volume of 1L for the mixed solution of graphene oxide aqueous dispersion and β-cyclodextrin, the amount of β-cyclodextrin used is 300-500mg.

16. The composite viscosity reducer according to claim 1, wherein, The mass ratio of polyethylene glycol monoglycidyl ether to graphene oxide is (5-100):

1.

17. The composite viscosity reducer according to claim 16, wherein, The mass ratio of polyethylene glycol monoglycidyl ether to graphene oxide is (10-30):

1.

18. The composite viscosity reducer according to claim 1, wherein, In step S3, the amount of amylase used is 50-800 mg, based on a total volume of 1 L of graphene oxide aqueous dispersion.

19. The composite viscosity reducer according to claim 18, wherein, In step S3, the amount of amylase used is 100-400 mg, based on a total volume of 1 L of graphene oxide aqueous dispersion.

20. The composite viscosity reducer according to any one of claims 1-3, wherein, In step S2, the polyethylene glycol monoglycidyl ether is prepared by the following method: The polyethylene glycol monoglycidyl ether was prepared by reacting polyethylene glycol with potassium carbonate and epichlorohydrin under stirring conditions. The molar ratio of polyethylene glycol, potassium carbonate, and epichlorohydrin is 1:(0.1-1):(1.1-10).

21. The composite viscosity reducer according to claim 20, wherein, The molar ratio of polyethylene glycol, potassium carbonate, and epichlorohydrin is 1:(0.5-1):(1.5-10).

22. The composite viscosity reducer according to claim 20, wherein, The temperature of the first reaction is 20-50℃; the reaction time is 12-36h.

23. The composite viscosity reducer according to claim 22, wherein, The temperature of the first reaction is 25-40℃; the reaction time is 20-30h.

24. The composite viscosity reducer according to any one of claims 1-3, wherein, The amount of water used is such that the mass concentration of the modified graphene oxide in the composite viscosity reducer is 10 mg / L-50 mg / L, and the mass concentration of the cyclodextrin-based surfactant is 500 mg / L-5000 mg / L.

25. The composite viscosity reducer according to claim 24, wherein, The amount of water used is such that the mass concentration of the modified graphene oxide in the composite viscosity reducer is 10 mg / L-30 mg / L, and the mass concentration of the cyclodextrin-based surfactant is 1000 mg / L-2000 mg / L.

26. A method for preparing the composite viscosity reducer according to any one of claims 1-25, characterized in that, The method includes contacting a cyclodextrin-based surfactant, modified graphene oxide, and water.

27. The method according to claim 26, wherein, The contact conditions include: a temperature of 10-35℃, a time of 30-60 min, and a stirring speed of 100-500 rpm.

28. The application of the composite viscosity reducer according to any one of claims 1-25 in the field of heavy oil extraction.

29. A method for responsive demulsification of heavy oil produced fluid, characterized in that, The method includes: (1) The composite viscosity reducer described in any one of claims 1-25 is brought into first contact with heavy oil to obtain an oil-water mixed emulsion; (2) CO2 is introduced into the oil-water emulsion to cause the oil-water emulsion to demulsify and separate water in response.

30. The method according to claim 29, wherein, In step (1), the mass ratio of the composite viscosity reducer to the heavy oil is 3:7 to 7:

3.

31. The method according to claim 29 or 30, wherein, In step (1), the conditions for the first contact include: a temperature of 40-60°C and a time of 10-300 min.

32. The method according to claim 29 or 30, wherein, In step (2), the CO2 flow rate is 0.5-5 L / min and the ventilation time is 1-5 min.

33. The method according to claim 29 or 30, wherein, In step (2), the CO2 flow rate is 0.5-2 L / min and the ventilation time is 1-5 min.

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