Supercritical CO2 thickening agent as well as preparation method and application thereof

Abstract

The invention discloses a supercritical CO2 thickening agent as well as a preparation method and application thereof, and belongs to the technical field of oil-gas field development. The supercritical CO2 thickening agent is prepared from the following raw materials in parts by mass: 1.9 to 4 parts of maleic anhydride, 0.9 to 2.1 parts of monocyclic aromatic hydrocarbon, 0.045 to 0.1 part of an initiator, 0.9 to 2.2 parts of a stabilizer, 1.6 to 3.4 parts of an olefine acid ester compound and 100 to 150 parts of water. The supercritical CO2 thickening agent can still keep stable thickening performance under the condition of medium and high temperature of 80 DEG C.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development, and particularly relates to a supercritical CO 2 thickening agent and its preparation method and application. Background Art

[0002] Low-permeability reservoirs are characterized by small pore throats, complex pore structures, and usually accompanied by the development of natural microfractures. The spatial scale distribution of these fractures and pore throats is extensive, where the fracture scale is often in the micron level, while the pore throat scale is in the nanometer level. This results in a relatively high injection water pressure, making it difficult to effectively implement the water injection plan, and the reservoir pressure cannot be replenished in a timely manner, thus leading to insufficient liquid production. In addition, various complex clays present in low-permeability reservoirs can cause phenomena such as velocity sensitivity and water sensitivity during the water injection development process. The clay minerals swell after absorbing water, blocking the pores between particles and causing serious damage to the reservoir. The heterogeneity of the reservoir also affects the capillary force, causing the displacement front to be uneven, resulting in bypassing and plugging, and a large amount of remaining oil fails to be produced. These characteristics pose many technical challenges to the effective development of low-permeability reservoirs.

[0003] CO 2 The CO 2 flooding technology can not only solve the problem of CO 2 sequestration, but more importantly, it can meet the needs of oilfield development and improve the tertiary oil recovery rate. The advantages of this technology include reducing the viscosity of crude oil, swelling crude oil, reducing the interfacial tension, weakening the displacement resistance, and improving the mobility ratio. However, under formation conditions, due to the very low viscosity of CO 2 itself (about 0.03 - 0.10 mPa·s) and the excessive mobility ratio, the "viscous fingering" phenomenon is likely to occur during the injection process, thus reducing the sweep efficiency of CO

[0004] In medium and high temperature reservoirs, the traditional CO 2 flooding technology faces significant challenges. Existing thickening agent systems such as fluorine-containing, hydrocarbon-containing, silicone-oxygen-containing, and oxygen-containing hydrocarbon thickening agents all have certain limitations in high temperature environments: Although fluorine-containing thickening agents have good solubility and viscosity-increasing properties, due to their instability at high temperatures, they may decompose or be modified, resulting in the failure of the thickening agent. Moreover, their environmental cumulative effect and high cost also limit their application in high temperature reservoirs; Hydrocarbon-containing thickening agents form a network structure in CO 2 to increase the viscosity, but under high temperature conditions, these chain segments are prone to pyrolysis, leading to a significant decrease in the thickening effect. Once the temperature exceeds a certain threshold, its viscosity will rapidly decrease and fail to meet the expected usage standards; Although silicone-oxygen-containing thickening agents are relatively stable at high temperatures, a large amount of co-solvent is required to dissolve them in supercritical CO 2dissolves, which not only increases the processing cost but also complicates the practical application. Moreover, in a high-temperature environment, the interaction between siloxane groups and CO 2 may be weakened, affecting its thickening effect. Therefore, under high-temperature reservoir conditions, the existing thickener systems have obvious deficiencies in terms of the persistence of thickening effect and thermal stability, and these defects limit their effectiveness in practical applications. Therefore, there is an urgent need for a new supercritical CO 2 thickener system that can maintain good performance in a high-temperature environment. SUMMARY OF THE INVENTION

[0005] In view of the above technical problems, the present invention provides a supercritical CO 2 thickener and its preparation method and application.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One object of the present invention is to provide a supercritical CO 2 thickener, which, calculated by mass parts, comprises the following raw materials: maleic anhydride 1.9 - 4 parts, monocyclic aromatic hydrocarbon 0.9 - 2.1 parts, initiator 0.045 - 0.1 part, stabilizer 0.9 - 2.2 parts, acrylic ester compound 1.6 - 3.4 parts, and water 100 - 150 parts.

[0008] Maleic anhydride and monocyclic aromatic hydrocarbon can form a copolymer, and hydrophilic and hydrophobic groups on the molecular chain of this copolymer are alternately distributed regularly. The stabilizer can copolymerize with the acrylic ester compound to form a polymer with an amphiphilic structure. Maleic anhydride, stabilizer, and acrylic ester compound all contain oxygen atoms, and these oxygen-containing raw materials can form oxygen-containing polymers in the polymerization reaction, thereby obtaining an oxygen-containing hydrocarbon thickener. The oxygen-containing hydrocarbon supercritical CO 2 thickener provided by the present invention includes a CO 2 -philic group that can fully dissolve the polymer in CO 2 and a CO 2 -phobic group that increases the viscosity of CO 2 . The CO 2 -philic group enables the thickener to have good solubility in CO 2 , and the CO 2 -phobic group can enhance the hydrophobic association between molecules through the stacking effect between aromatic rings to hinder the free movement of CO 2 molecules, thereby achieving a thickening effect. This combination of hydrophilic and hydrophobic CO 2 groups enables the polymer to maintain good solubility in supercritical CO 2 and effectively increase the viscosity.

[0009] Maleic anhydride has a CO 2and a hydrophobic group, which can form a copolymer with vinyl acetate monomers during the polymerization reaction to improve the CO 2 solubility, and can also interact with hydrophobic groups such as styrene, increasing the viscosity through the hydrophobic effect to form a more stable thickening structure.

[0010] Furthermore, the monocyclic aromatic hydrocarbon is selected from one or more of styrene, p-xylene, and vinylbenzene.

[0011] The monocyclic aromatic hydrocarbon provided by the present invention contains a hydrophobic CO 2 group, and the hydrophobic CO 2 group hinders the free flow of CO 2 molecules by increasing the intermolecular hydrophobic interaction, thereby increasing the viscosity.

[0012] Furthermore, the initiator is selected from one or more of benzoyl peroxide (BPO), hydrogen peroxide, dialkyl peroxide, and organic hydroperoxide.

[0013] Furthermore, the stabilizer is selected from one or two of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and quinnol dimethacrylate (AMPSO).

[0014] AMPS can still maintain good stability and thickening performance in high-temperature and high-salt concentration environments, and is suitable for harsh reservoir conditions; in addition, AMPS has a strongly polar sulfonic acid group, endowing it with excellent water solubility and hydrophilicity, which helps to copolymerize with other monomers during the synthesis process to form an efficient thickening agent, enhancing the association between polymer chains and improving chemical stability, so that the finally synthesized thickening agent can maintain an excellent thickening effect even under high-temperature conditions. That is to say, stabilizers containing sulfonic acid groups can all achieve the same effect, but compared with AMPS, other stabilizers containing sulfonic acid groups such as AMPSO have too high costs, so using AMPS can effectively reduce costs.

[0015] Furthermore, the acrylate compound is selected from one or more of methyl vinyl acetate, butenyl acetate, ethyl acrylate, and vinyl acetate (VAc).

[0016] The acrylate compound provided by the present invention has a hydrophilic CO 2 group that can enable the polymer to be fully dissolved in CO 2 The hydrophilic CO 2 group has good CO 2 solubility, which can enable the polymer to be fully dissolved in the CO 2 environment.

[0017] The second object of the present invention is to provide a supercritical CO 2Preparation method of thickener, comprising the following steps: dissolving maleic anhydride in water, adding monocyclic aromatic hydrocarbon and then performing heat treatment, adding initiator and partial stabilizer under heating condition and keeping warm, then adding the remaining stabilizer and acrylic ester compound, continuing the reaction, and performing freeze drying and grinding after the reaction ends to obtain supercritical CO 2 thickener powder.

[0018] Further, the temperature of the heat treatment is 70 - 80 °C; and / or

[0019] the time of keeping warm is 50 - 70 min; and / or

[0020] the time of continuing the reaction is 2 - 3 h.

[0021] Further, the mass ratio of the partial stabilizer to the remaining stabilizer is (3 - 7)∶(7 - 3);

[0022] The adding method of the acrylic ester compound is dropwise addition through a separating funnel.

[0023] The third object of the present invention is to provide an application of supercritical CO 2 thickener in the field of medium - high temperature oil reservoirs.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] The oxygen - containing hydrocarbon polymer has strong adaptability to temperature and salinity, small adsorption loss, strong field adaptability, which is beneficial to on - site application. The present invention selects an oxygen - containing hydrocarbon thickener, which is characterized by not damaging the formation. This thickener depends on its CO 2 - philic monomers to directly dissolve into supercritical CO 2 without the need for a large amount of additional cosolvent. The synthesized oxygen - containing hydrocarbon thickener can show excellent thickening effect at a relatively low use concentration. When used at a concentration of only 2% wt under the medium - high temperature condition of 80 °C, the viscosity can reach 1.27 - 1.96 mPa·s, and it can still maintain stable thickening performance under the medium - high temperature condition of 80 °C, thereby improving the sweep efficiency and oil recovery rate of supercritical CO 2 in high - temperature oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0027] Figure 1 is the device for measuring supercritical CO 2 thickener in the embodiment of the present invention;

[0028] Figure 2 The supercritical CO₂ prepared in Example 1 2 Dissolution effect diagram of the thickener; (a) The state of the thickener just added to supercritical CO₂ without stirring 2 The state of the thickener just added to supercritical CO₂ 2 without stirring; (b) The state of the thickener just added to supercritical CO₂ 2 and stirred evenly; (c) The state of the thickener just added to supercritical CO₂ 2 and stirred for 7 minutes; (d) The state of the thickener just added to supercritical CO₂ 2 and stirred for 10 minutes 2 ; (d) The state of the thickener just added to supercritical CO₂ 2 and stirred for 10 minutes 2 ;

[0029] Figure 3 The supercritical CO₂ prepared in Example 1 2 Thickening effect diagram of the thickener

[0030] Figure 4 Curves showing the influence of water flooding and pure supercritical CO₂ flooding on the oil recovery rate in oil displacement technology 2 ;

[0031] Figure 5 Curves showing the influence of water flooding and the supercritical CO₂ thickener prepared in Example 1 on the oil recovery rate in oil displacement technology 2 ;

[0032] Figure 6 Graph showing the influence of temperature on the addition amount of different supercritical CO₂ thickeners 2 ;

[0033] Figure 7 Physical diagram of the thickener prepared in Comparative Example 1

[0034] Figure 8 Physical diagram of the thickener prepared in Comparative Example 2

[0035] Figure 9 Physical diagram of the thickener powder prepared in Comparative Example 3 Detailed implementation manners

[0036] The various exemplary implementation manners of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention

[0037] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0039] Without departing from the scope or spirit of the present invention, various improvements and variations can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0040] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0041] The present invention aims to stably increase the viscosity of the supercritical CO thickener to more than 1 mPa·s at an 80°C reservoir, thereby enhancing the diffusion efficiency of CO. 2 By this method, a large amount of carbon dioxide can be dissolved in crude oil, causing the crude oil volume to expand and reducing the viscosity of the crude oil. Furthermore, it can reduce the interfacial tension between the crude oil and the surrounding medium, playing a role in reducing the viscosity of the crude oil, thereby effectively improving the recovery rate of the supercritical CO thickener enhanced oil recovery technology. 2 2

[0042] An embodiment of the present invention provides a supercritical CO thickener, which, by mass fraction, comprises the following raw materials: maleic anhydride 1.9 - 4 parts, monocyclic aromatic hydrocarbon 0.9 - 2.1 parts, initiator 0.045 - 0.1 part, stabilizer 0.9 - 2.2 parts, acrylic ester compound 1.6 - 3.4 parts, and water 100 - 150 parts. 2

[0043] Exemplarily, in the following preferred embodiments of the present invention, the supercritical CO 2The thickener contains 1.96 parts, 2 parts, 4 parts or any range or sub-range between the aforementioned ratios of maleic anhydride.

[0044] Exemplarily, in the following preferred embodiments of the present invention, the supercritical CO 2 The thickener contains 1 part, 1.04 parts, 2.1 parts or any range or sub-range between the aforementioned ratios of monocyclic aromatic hydrocarbons.

[0045] Exemplarily, in the following preferred embodiments of the present invention, the supercritical CO 2 The thickener contains 0.048 parts, 0.050 parts, 0.1 part or any range or sub-range between the aforementioned ratios of initiators.

[0046] Exemplarily, in the following preferred embodiments of the present invention, the supercritical CO 2 The thickener contains 1.02 parts, 1.03 parts, 2.11 parts or any range or sub-range between the aforementioned ratios of stabilizers.

[0047] Exemplarily, in the following preferred embodiments of the present invention, the supercritical CO 2 The thickener contains 1.72 parts, 1.74 parts, 3.4 parts or any range or sub-range between the aforementioned ratios of acrylate compounds.

[0048] Exemplarily, in the following preferred embodiments of the present invention, the supercritical CO 2 The thickener contains 100 parts, 150 parts or any range or sub-range between the aforementioned ratios of water.

[0049] In some embodiments of the present invention, the monocyclic aromatic hydrocarbons include one or more of styrene, p-xylene and vinylbenzene. Exemplarily, in the following embodiments of the present invention, styrene can be selected as an example for effect verification of the monocyclic aromatic hydrocarbons.

[0050] In some embodiments of the present invention, the initiators include one or more of benzoyl peroxide, hydrogen peroxide, dialkyl peroxide and organic hydroperoxide. Exemplarily, in the following embodiments of the present invention, benzoyl peroxide can be selected as an example for effect verification of the initiators.

[0051] In some embodiments of the present invention, the stabilizer is one or both of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and quinnol dimethacrylate (AMPSO). Exemplarily, in the following embodiments of the present invention, AMPS can be selected as an example for effect verification of the stabilizer.

[0052] In some embodiments of the present invention, the acrylate compound includes one or more of methyl vinyl acetate, butenyl acetate, ethyl acrylate, and vinyl acetate. Exemplarily, in the following embodiments of the present invention, vinyl acetate may be selected as an example for effect verification of the acrylate compound.

[0053] The above-mentioned supercritical CO 2 The preparation method of the thickener includes the following steps: dissolving maleic anhydride in water, adding a monocyclic aromatic hydrocarbon and then performing heat treatment, adding an initiator and a stabilizer under heating conditions and keeping warm, subsequently adding the remaining stabilizer and the acrylate compound, continuing the reaction, and after the reaction is completed, performing freeze-drying and grinding to obtain the supercritical CO 2 thickener powder.

[0054] In some embodiments of the present invention, the temperature of the heat treatment is 70 - 80 °C. Exemplarily, in the following preferred embodiments of the present invention, the temperature of the heat treatment is 75 °C, 80 °C, or any value between the aforementioned ranges.

[0055] In some embodiments of the present invention, the time for keeping warm is 50 - 70 min. Exemplarily, in the following preferred embodiments of the present invention, the time for keeping warm is 55 min, 60 min, 65 min, or any value between the aforementioned ranges.

[0056] In some embodiments of the present invention, the time for continuing the reaction is 2 - 3 h. Exemplarily, in the following preferred embodiments of the present invention, the time for continuing the reaction is 2 h, 3 h, or any value between the aforementioned ranges.

[0057] In some embodiments of the present invention, the mass ratio of the stabilizer to the remaining stabilizer is (0.51 - 1.01)∶(0.51 - 1.1). Exemplarily, in the following preferred embodiments of the present invention, the mass ratio of the stabilizer to the remaining stabilizer is 3∶7, 7∶3, or any value between the aforementioned ratios.

[0058] In some embodiments of the present invention, the acrylate compound is added by dropping through a separatory funnel, and the dropping rate is controlled to finish dropping 1.6 - 3.4 g (parts) of the acrylate compound within 8 - 10 min.

[0059] The supercritical CO 2 The thickener can be applied to the field of medium-high temperature oil reservoirs. The medium-high temperature mentioned in the present invention refers to the range between 50 - 80 °C.

[0060] As an exemplary embodiment, the supercritical CO 2Preparation method of thickener, comprising the following steps: First, dissolve 1.9 - 4 g of maleic anhydride in 100 - 150 mL of water, add 0.9 - 2.1 g of monocyclic aromatic hydrocarbon, and heat to 70 - 80 °C; subsequently, add 0.045 - 0.1 g of initiator and 0.51 - 1.01 g of stabilizer, react for 50 - 70 min, then continue to add 0.51 - 1.1 g of stabilizer, and dropwise add 1.6 - 3.4 g of acrylate compound through a separatory funnel within 10 minutes, and continue to react for 2 - 3 h; after the reaction is completed, freeze-dry the mixed solution for 24 h and grind it to obtain supercritical CO 2 Thickener powder.

[0061] In the present invention, "parts" refers to parts by mass unless otherwise specified.

[0062] All raw materials used in the present invention are obtained by purchasing on the market.

[0063] The technical solution of the present invention will be further described below through examples.

[0064] Figure 1 Device for measuring supercritical CO 2 Thickener of the present invention.

[0065] Example 1

[0066] A preparation method of supercritical CO 2 Thickener, comprising the following steps: First, dissolve 2 g of maleic anhydride in 100 mL of water, add 1 g of styrene, and heat to 75 °C; subsequently, add 0.050 g of benzoyl peroxide and 0.52 g of AMPS, react for 65 min, then continue to add 0.51 g of AMPS, and dropwise add 1.74 g of vinyl acetate through a separatory funnel within 10 minutes, and continue to react for 2 h; after the reaction is completed, freeze-dry the mixed solution for 24 h and grind it to a particle size between 5 - 30 μm to obtain 2.32 g of supercritical CO 2 Thickener powder.

[0067] Synthesized critical CO 2 The molecular formula of the thickener is:

[0068]

[0069] Example 2

[0070] A preparation method of supercritical CO 2Preparation method of thickener, comprising the following steps: First, dissolve 4 g of maleic anhydride in 150 mL of water, add 2.1 g of styrene, and heat to 80 °C; subsequently, add 0.1 g of benzoyl peroxide and 1.01 g of AMPS, react for 55 min, then continue to add 1.1 g of AMPS, and dropwise add 3.4 g of vinyl acetate through a separatory funnel within 8 minutes, and continue to react for 3 h; after the reaction is completed, freeze-dry the mixed solution for 24 h and grind it to a particle size between 5 - 30 μm to obtain 4.81 g of supercritical CO 2 Thickener powder.

[0071] Example 3

[0072] A preparation method of supercritical CO 2 Thickener, comprising the following steps: First, dissolve 1.96 g of maleic anhydride in 100 mL of water, add 1.04 g of styrene, and heat to 80 °C; subsequently, add 0.048 g of benzoyl peroxide and 0.51 g of AMPS, react for 60 min, then continue to add 0.51 g of AMPS, and dropwise add 1.72 g of vinyl acetate through a separatory funnel within 10 minutes, and continue to react for 2 h; after the reaction is completed, freeze-dry the mixed solution for 24 h and grind it to a particle size between 5 - 30 μm to obtain 2.23 g of supercritical CO 2 Thickener powder.

[0073] Application Example 1

[0074] Dissolution effect test: Put 2 wt% of the supercritical CO 2 Thickener prepared in Example 1 into the supercritical CO 2 Visible reaction kettle (i.e., the addition amount of the supercritical CO 2 Thickener is 2% of the mass of supercritical CO 2 ), control the pressure of the reaction kettle to 15 MPa and the temperature to 80 °C, specifically refer to Figure 2 , it can be seen that there are no obvious insoluble substances or impurities at the bottom after stirring for 10 min under this condition, indicating that the supercritical CO 2 Thickener prepared in the present invention has very good dissolution effect.

[0075] Application Example 2

[0076] Thickening effect test: Put 2 wt% of the supercritical CO 2 Thickener prepared in Example 1 into the supercritical CO 2 Visible reaction kettle (i.e., the addition amount of the supercritical CO 2 Thickener is 2% of the mass of supercritical CO 2 ), control the pressure of the reaction kettle to 15 MPa and the temperature to 80 °C, after stirring for 30 min under this condition, slip bands are generated on the surface of the viewing window, indicating that supercritical CO2 The thickener already has a certain viscosity. For details, see Figure 3 . From Figure 3 it can be seen that in the high-temperature reservoir at 80 °C, the viscosity of the supercritical CO 2 thickener can be stabilized above 1 mPa·s. In the range of 65 - 73 min of reaction, the viscosity range is 1.27 - 1.96 mPa·s.

[0077] Application Example 3

[0078] Test the influence of the supercritical CO 2 thickener prepared in Detection Example 1 on the oil recovery rate in the oil displacement technology. The specific method is as follows: After thickening in the reaction kettle, the reaction kettle can be connected to the core holder. The core holder is provided with a reflux valve. The thin-integral gas is also supercritical during the process, and the addition amount is 2 wt%. The core permeability is 100 mD, 80 °C, 18 MPa. Pure supercritical CO 2 is used as the control group. 2 As the control group.

[0079] The results are shown in Figure 4 and Figure 5 . From Figure 4 , Figure 5 it can be seen that for the core with a permeability of 100 mD, the water flooding oil recovery rate is 51.85 - 52.72%. The oil displacement extraction amplitude of pure supercritical CO 2 is 14.55%, and the oil displacement extraction amplitude of the supercritical CO 2 after viscosity increase is 18.52%. This shows that the supercritical CO 2 thickener prepared in Example 1 of the present invention can improve the oil recovery rate.

[0080] Comparative Application Example 1

[0081] Thickening effect test: Respectively put 1.5 wt% and 2 wt% of the supercritical CO 2 thickener prepared in Example 1 into the supercritical CO 2 visible reaction kettle (that is, the addition amount of the supercritical CO 2 thickener is 1.5% and 2% of the mass of supercritical CO 2 ), and observe the thickening effect. The results are shown in Figure 6 .

[0082] From Figure 6 it can be seen that when the addition amount of the supercritical CO 2 thickener is 1.5 wt%, its viscosity increase effect decreases significantly with the increase of temperature. When the temperature ≥ 60 °C, the viscosity of the supercritical CO 2 mixed system < 1 mPa·s; when the supercritical CO 2When the addition amount of the thickener is 2 wt%, its viscosity increasing effect changes little with the increase of temperature. When the temperature is ≤ 90 °C, the viscosity of the supercritical CO 2 of the mixed system is > 1 mPa·s.

[0083] Comparative Example 1

[0084] A preparation method of a thickener includes the following steps: First, dissolve 2 g of maleic anhydride in 100 mL of water, add 1 g of styrene, and heat to 75 °C; then, add 0.050 g of benzoyl peroxide and 1.02 g of AMPS, react for 65 min, then continue to add 1.02 g of AMPS, and dropwise add 1.74 g of vinyl acetate through a separatory funnel within 10 minutes, and continue to react for 2 h; after the reaction is completed, freeze-dry the mixed solution for 24 h and grind it to a particle size between 5 - 30 μm to obtain the thickener powder.

[0085] Figure 7 is the physical picture of the thickener prepared in Comparative Example 1. It is found that when the addition amount of sulfonic acid is too much, a jelly-like substance will be formed and it is insoluble in CO 2 .

[0086] Comparative Example 2

[0087] A preparation method of a thickener includes the following steps: First, dissolve 2 g of maleic anhydride in 100 mL of water, add 1 g of styrene, and heat to 75 °C; then, add 0.050 g of benzoyl peroxide and 1.03 g of AMPS, react for 65 min, then dropwise add 1.74 g of vinyl acetate through a separatory funnel within 10 minutes, and continue to react for 2 h; after the reaction is completed, freeze-dry the mixed solution for 24 h and grind it to a particle size between 5 - 30 μm to obtain the thickener powder.

[0088] Figure 8 is the physical picture of the thickener prepared in Comparative Example 2. It can be seen that when AMPS is not added to the system in batches, large granular gelatinous products will be formed, which is not conducive to subsequent reactions.

[0089] Comparative Example 3

[0090] A preparation method of a thickener includes the following steps: First, dissolve 2 g of maleic anhydride in 100 mL of water, add 1 g of styrene, and heat to 90 °C; then, add 0.050 g of benzoyl peroxide and 0.52 g of AMPS, react for 65 min, then continue to add 0.51 g of AMPS, and dropwise add 1.74 g of vinyl acetate through a separatory funnel within 10 minutes, and continue to react for 2 h; after the reaction is completed, freeze-dry the mixed solution for 24 h and grind it to a particle size between 5 - 30 μm to obtain the thickener powder.

[0091] Figure 9It is a physical picture of the thickener powder prepared in Comparative Example 3. It can be found that when the synthesis temperature is higher than 80 °C, the synthesis of maleic anhydride and vinyl acetate is carried out first, which will promote the prior and intensified reaction of these two substances, and a white solid product will be formed, resulting in the prepared thickener being insoluble in CO 2 .

[0092] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A supercritical CO2 thickener, characterized in that: The raw materials include, by weight: 1.9-4 parts of maleic anhydride, 0.9-2.1 parts of monocyclic aromatic hydrocarbons, 0.045-0.1 parts of initiators, 0.9-2.2 parts of stabilizers, 1.6-3.4 parts of olefinic acid ester compounds and 100-150 parts of water.

2. The supercritical CO2 thickener according to claim 1, characterized in that The monocyclic aromatic hydrocarbon is selected from one or more of styrene, p-xylene and vinylbenzene.

3. The supercritical CO2 thickener according to claim 1, characterized in that: The initiator is selected from one or more of dibenzoyl oxide, hydrogen peroxide, dialkyl peroxide and organic hydrogen peroxide.

4. The supercritical CO2 thickener according to claim 1, characterized in that The stabilizer is selected from one or both of 2-acrylamido-2-methyl-1-propane sulfonic acid and quinoline dimethyl acrylate.

5. The supercritical CO2 thickener according to claim 1, characterized in that: The acrylate compound is selected from one or more of methyl acetate, butyl acetate, ethyl acrylate and vinyl acetate.

6. A method for preparing a supercritical CO2 thickener as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: Maleic anhydride is dissolved in water, and monocyclic aromatic hydrocarbons are added and heated. Initiators and part of stabilizers are added in the heated state and kept warm. Then, the remaining stabilizers and olefinic acid ester compounds are added and the reaction is continued. After the reaction is completed, the mixture is freeze-dried and ground to obtain supercritical CO2 thickener powder.

7. The method for preparing a supercritical CO2 thickener according to claim 6, characterized in that: The temperature of the heating treatment is 70-80°C; and / or The insulation time is 50-70 minutes; and / or The reaction time is 2-3 hours.

8. The method for preparing a supercritical CO2 thickener according to claim 6, characterized in that: The mass ratio of the partial stabilizer to the remaining stabilizer is (3-7): (7-3).

9. The method for preparing a supercritical CO2 thickener according to claim 6, characterized in that: The olefinic acid ester compound is added dropwise through a separatory funnel.

10. Use of the supercritical CO2 thickener according to any one of claims 1 to 5 in the field of medium and high temperature oil reservoirs.

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