Carbon dioxide flooding thickening agent as well as preparation method and application thereof

Abstract

The invention provides a carbon dioxide flooding thickening agent as well as a preparation method and application thereof. The carbon dioxide flooding thickening agent has a structure as shown in a formula I, the weight-average molecular weight of the carbon dioxide flooding thickening agent is 8000 to 50000. According to the invention, the compound with the structure as shown in the formula I is used for thickening the carbon dioxide, and meanwhile, the weight-average molecular weight of the compound is within a specific range, so that the compound has good solubility with the carbon dioxide, high solubility in the carbon dioxide and good tackifying performance, the viscosity of the carbon dioxide is effectively improved, and the mining efficiency is improved; the use of fluorine-containing and silicon-containing materials is avoided, and the method is green, environment-friendly and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield exploitation, and in particular relates to a carbon dioxide flooding thickener and a preparation method and application thereof. Background Art

[0002] As a high-quality oil displacement agent, carbon dioxide is mainly in supercritical or liquid phase in oil reservoirs. It is mainly used in low permeability oil fields, and can improve the recovery rate by 15% in immiscible flooding and 25% in miscible flooding, which has good application prospects. However, the main problem facing oil field exploitation at present is how to solve the problems of severe gas channeling, poor expansion of swept volume and low recovery rate caused by strong heterogeneity of continental reservoirs. The existing technology mainly suppresses the early breakthrough and viscous fingering of CO2 flooding by adding surfactants or polymers in water-gas alternation (WAG), but there are problems such as short action time and distance, difficult to control foam generated by formation conditions, poor economy, and reservoir damage caused by pipeline corrosion and water sensitivity.

[0003] The CO2 flooding thickener draws on the technical ideas of polymer flooding. It can be dissolved in CO2 or dissolved in CO2 with the addition of a solvent, improving the mobility ratio of CO2 to crude oil in the formation, thereby effectively expanding the swept volume. Experimental studies have shown that compared with pure high-pressure CO2, the oil recovery effect of thickened CO2 is greatly improved. There have also been cases of using thickened CO2 for oil recovery abroad, and the results also show that the recovery rate of thickened CO2 is higher.

[0004] However, the difficulty in studying CO2 thickeners lies in the fact that the thickeners must have a large solubility and a low dissolution pressure in CO2, while also having a more obvious thickening effect. Since the beginning of the study of CO2 thickeners, the research has mainly gone through the following stages: (1) using polymers with larger molecular weights, but the disadvantage is that high molecular weight polymers have low solubility in CO2, requiring the use of a large amount of cosolvents, which increases costs; (2) using low molecular weight polymers to increase the viscosity of CO2 through the interaction between polymers with specific structures, but because they contain a large number of polar groups, their solubility in CO2 is not high, and a large amount of cosolvents still need to be added; (3) designing and synthesizing new thickeners with higher solubility in CO2.

[0005] For example, CN113480990A discloses a preparation method and application of a supercritical carbon dioxide thickener, which is prepared by polymerization of fluorinated hydrocyanate, acrylate compound and styrene under the action of an initiator and an emulsifier, and has a good thickening effect on supercritical carbon dioxide. However, the supercritical carbon dioxide thickener uses fluorine-containing materials, which is costly, not environmentally friendly and requires the use of more solvents.

[0006] A common defect in the prior art is the use of fluorine-containing and silicon-containing polymers, which are expensive and have certain harm to the environment.

[0007] Therefore, it is an urgent problem to be solved in the art to develop a carbon dioxide thickener that has high solubility in carbon dioxide, good thickening effect, does not require the use of fluorine-containing and silicon-containing materials, is low-cost and environmentally friendly. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention aims to provide a carbon dioxide flooding thickener and its preparation method and application. The carbon dioxide flooding thickener has good solubility in carbon dioxide, high solubility, good thickening effect, is conducive to improving mining efficiency, and does not require the use of fluorine-containing and silicon-containing materials, is low in cost and environmentally friendly.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a carbon dioxide flooding thickener, wherein the carbon dioxide flooding thickener has a structure shown in Formula I:

[0011]

[0012] Wherein, R1 and R2 are each independently selected from substituted or unsubstituted C1-C6 straight chain or branched alkyl groups; the substituted substituents include any one of hydroxyl, carboxyl or ester groups; n is 50-300; and the weight average molecular weight of the carbon dioxide flooding thickener is 8000-50000.

[0013] In the present invention, a compound having a structure shown in Formula I is selected for thickening carbon dioxide. At the same time, the weight-average molecular weight of the compound is within a specific range. It not only has good solubility in carbon dioxide and high solubility in carbon dioxide, but also has good viscosity-increasing performance, effectively improves the viscosity of carbon dioxide, solves the problem of reducing the fluidity of carbon dioxide in porous media, improves mining efficiency, avoids the use of fluorine-containing, silicon-containing and other materials, is green, environmentally friendly and low in cost.

[0014] In the present invention, the C1-C6 straight chain or branched alkyl group includes C1, C2, C3, C4, C5, C6 straight chain or branched alkyl groups; exemplary groups include but are not limited to methyl, ethyl, n-propyl, isopropyl, butyl, pentyl or hexyl, etc.

[0015] In the present invention, n is 50 to 300, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, etc.

[0016] In the present invention, the weight average molecular weight of the carbon dioxide flooding thickener is 8000-50000, for example, it can be 8000, 8200, 8500, 8800, 9000, 9200, 9500, 9800, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, 25000, 26000, 28000, 30000, 32000, 34000, 36000, 38000, 40000, 42000, 44000, 46000, 48000, 50000, etc.

[0017] In the present invention, when the weight average molecular weight of the carbon dioxide flooding thickener is within the above-defined range, the thickening effect is better.

[0018] Preferably, R1 and R2 are each independently selected from any one of ethyl, n-propyl and isopropyl.

[0019] In the present invention, the R1 and R2 are selected from specific groups, which have a better thickening effect.

[0020] In a second aspect, the present invention provides a method for preparing the carbon dioxide flooding thickener according to the first aspect, the preparation method comprising the following steps:

[0021] In the presence of an initiator, the monomer is subjected to a free radical polymerization reaction to obtain the carbon dioxide flooding thickener; the monomer contains an ester group and a carbon-carbon double bond.

[0022] Preferably, the monomer includes at least one of dimethyl butenedioate, diethyl butenedioate, di-n-propyl butenedioate, diisopropyl butenedioate, and dibutyl butenedioate.

[0023] Preferably, the initiator includes at least one of an organic peroxide initiator, an inorganic peroxide initiator or an azo initiator.

[0024] Preferably, the initiator comprises dibenzoyl peroxide and / or azobisisobutyronitrile.

[0025] Preferably, the mass ratio of the initiator to the monomer is 1:(40-400), for example, 1:40, 1:42, 1:46, 1:50, 1:52, 1:54, 1:60, 1:62, 1:64, 1:66, 1:68, 1:70, 1:74, 1:78, 1:80, 1:82, 1:86, 1:90, 1:92, 1:96, 1: 1:(60-120).

[0026] Preferably, the temperature of the free radical polymerization reaction is 80-110°C, for example, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C, 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, etc.

[0027] Preferably, the free radical polymerization reaction time is 48 to 96 h, for example, it can be 48 h, 50 h, 52 h, 54 h, 56 h, 58 h, 60 h, 62 h, 64 h, 66 h, 68 h, 70 h, 72 h, 74 h, 76 h, 78 h, 80 h, 82 h, 84 h, 86 h, 88 h, 90 h, 92 h, 94 h, 96 h, etc.

[0028] Preferably, the free radical polymerization reaction is carried out in the presence of a protective atmosphere.

[0029] In the present invention, the protective atmosphere includes but is not limited to nitrogen.

[0030] Preferably, the rotation speed of the free radical polymerization reaction is 200-400 rpm, for example, it can be 200 rpm, 220 rpm, 250 rpm, 280 rpm, 300 rpm, 320 rpm, 350 rpm, 380 rpm, 400 rpm, etc.

[0031] Preferably, after the free radical polymerization reaction is completed, the step of heating to 170-190° C. (for example, 170° C., 175° C., 180° C., 185° C., 190° C.) and vacuum drying is also included.

[0032] As a preferred technical solution of the present invention, the preparation method specifically comprises the following steps:

[0033] In the presence of a protective atmosphere and an initiator, a monomer containing an ester group and a carbon-carbon double bond is subjected to a free radical polymerization reaction at 80 to 110° C. for 48 to 96 hours, then heated to 170 to 190° C. and vacuum-dried to obtain the carbon dioxide flooding thickener; the mass ratio of the initiator to the monomer is 1:(40 to 400).

[0034] In the present invention, the preparation method, by controlling the mass ratio of the monomer to the initiator within a specific range and coordinating the process parameters, can achieve a high conversion rate of the monomer, a small amount of by-products, and obtain a thickener with a moderate weight average molecular weight, so that the thickening effect of the thickener is good.

[0035] In a third aspect, the present invention provides a use of the carbon dioxide flooding thickener according to the first aspect in thickening supercritical carbon dioxide and / or liquid carbon dioxide.

[0036] Preferably, the solubility of the carbon dioxide flooding thickener in supercritical carbon dioxide and / or liquid carbon dioxide is ≥3%, for example, it may be 3%, 4%, 5%, 6%, 7%, 8%, etc.

[0037] In the present invention, the solubility refers to the mass fraction of the carbon dioxide flooding thickener in carbon dioxide.

[0038] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) Compared with existing polymer thickeners, the product does not contain fluorine, silicon and aromatic groups, is environmentally friendly, easily degradable, low cost and simple preparation process.

[0041] (2) The carbon dioxide flooding thickener has good reservoir injectability, good solubility in supercritical carbon dioxide or liquid carbon dioxide, high solubility, and can effectively increase the viscosity of carbon dioxide at 20 MPa and 80° C., with good thickening effect;

[0042] (3) The carbon dioxide flooding thickener can significantly improve the displacement effect of carbon dioxide, delay the gas breakthrough time, and significantly increase the recovery degree; the gas-oil ratio after gas breakthrough is significantly reduced; it is particularly suitable for carbon dioxide flooding in low permeability reservoirs, and has broad application potential, especially for water-sensitive reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The hydrogen nuclear magnetic resonance spectra of diethyl maleate monomer and the carbon dioxide flooding thickener provided in Example 1;

[0044] in, Figure 1 A is the H NMR spectrum of diethyl maleate monomer; Figure 1 B is a hydrogen nuclear magnetic resonance spectrum of the carbon dioxide flooding thickener provided in Example 1 of the present invention;

[0045] Figure 2 is a graph showing the change in viscosity of the carbon dioxide fluid at different concentrations of the carbon dioxide flooding thickener provided in Example 1 of the present invention;

[0046] Figure 3 This is a curve diagram showing the variation of recovery degree and gasoline ratio with the volume of injected carbon dioxide without adding carbon dioxide flooding thickener;

[0047] Figure 4 This is a curve diagram showing the change of the recovery degree and gasoline ratio with the volume of injected carbon dioxide after adding the carbon dioxide flooding thickener provided in Example 1. DETAILED DESCRIPTION

[0048] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0049] Example 1

[0050] This embodiment provides a carbon dioxide flooding thickener, and the carbon dioxide flooding thickener has the following structure:

[0051] The weight average molecular weight of the carbon dioxide flooding thickener is 23,100.

[0052] This embodiment provides a method for preparing the carbon dioxide flooding thickener, which specifically comprises the following steps:

[0053] In a dry three-necked flask equipped with a mechanical stirring device, 140 g of diethyl maleate monomer and 1.2 g of dibenzoyl peroxide initiator were added under nitrogen, sealed and adjusted to 80°C, then stirred and reacted for 72 hours. After the reaction was completed, it was directly heated to 180°C and dried by a vacuum pump to obtain the carbon dioxide flooding thickener.

[0054] The structure of the polymer obtained in Example 1 was characterized by hydrogen nuclear magnetic resonance spectroscopy. Figure 1 As shown, it is shown that the carbon dioxide flooding thickener is synthesized.

[0055] Example 2

[0056] This embodiment provides a carbon dioxide flooding thickener, and the carbon dioxide flooding thickener has the following structure:

[0057] The weight average molecular weight of the carbon dioxide flooding thickener is about 32,000.

[0058] This embodiment provides a method for preparing the carbon dioxide flooding thickener, which specifically comprises the following steps:

[0059] In a dry three-necked flask equipped with a mechanical stirring device, 140 g of diethyl maleate monomer and 1.3 g of dibenzoyl peroxide initiator were added under nitrogen, sealed and adjusted to 90°C, then stirred and reacted for 96 hours. After the reaction was completed, it was directly heated to 180°C and dried by a vacuum pump to obtain the carbon dioxide flooding thickener.

[0060] Example 3

[0061] This embodiment provides a carbon dioxide flooding thickener, and the carbon dioxide flooding thickener has the following structure:

[0062] The weight average molecular weight of the carbon dioxide flooding thickener is about 28,000.

[0063] This embodiment provides a method for preparing the carbon dioxide flooding thickener, which specifically comprises the following steps:

[0064] In a dry three-necked flask equipped with a mechanical stirring device, 140 g of diethyl maleate monomer and 1.25 g of dibenzoyl peroxide initiator were added under nitrogen, sealed and adjusted to 85°C, then stirred and reacted for 90 hours. After the reaction was completed, it was directly heated to 180°C and dried by a vacuum pump to obtain the carbon dioxide flooding thickener.

[0065] Example 4

[0066] This embodiment provides a carbon dioxide flooding thickener, and the carbon dioxide flooding thickener has the following structure:

[0067] The weight average molecular weight of the carbon dioxide flooding thickener is 9,900.

[0068] This embodiment provides a method for preparing the carbon dioxide flooding thickener, which specifically comprises the following steps:

[0069] In a dry three-necked flask equipped with a mechanical stirring device, 50 g of diethyl maleate monomer and 0.8 g of dibenzoyl peroxide initiator were added under nitrogen, sealed and adjusted to 100°C, then stirred and reacted for 96 hours. After the reaction was completed, it was directly heated to 180°C and vacuum pumped to obtain the carbon dioxide flooding thickener.

[0070] Example 5

[0071] This embodiment provides a carbon dioxide flooding thickener, and the carbon dioxide flooding thickener has the following structure:

[0072] The weight average molecular weight of the carbon dioxide flooding thickener is 8500.

[0073] This embodiment provides a method for preparing the carbon dioxide flooding thickener, which specifically comprises the following steps:

[0074] In a dry three-necked flask equipped with a mechanical stirring device, 50 g of diethyl maleate monomer and 0.4 g of dibenzoyl peroxide initiator were added under nitrogen, sealed and adjusted to 80°C, then stirred and reacted for 96 hours. After the reaction was completed, it was directly heated to 180°C and dried by a vacuum pump to obtain the carbon dioxide flooding thickener.

[0075] Example 6

[0076] This embodiment provides a carbon dioxide flooding thickener, and the carbon dioxide flooding thickener has the following structure:

[0077] The weight average molecular weight of the carbon dioxide flooding thickener is 14,300.

[0078] This embodiment provides a method for preparing the carbon dioxide flooding thickener, which specifically comprises the following steps:

[0079] In a dry three-necked flask equipped with a mechanical stirring device, 84 g of diethyl maleate monomer and 0.56 g of dibenzoyl peroxide initiator were added under nitrogen, sealed and adjusted to 80°C, then stirred and reacted for 48 hours. After the reaction was completed, it was directly heated to 180°C and dried by a vacuum pump to obtain the carbon dioxide flooding thickener.

[0080] Example 7

[0081] This embodiment provides a carbon dioxide flooding thickener, and the carbon dioxide flooding thickener has the following structure:

[0082] The weight average molecular weight of the carbon dioxide flooding thickener is 15,200.

[0083] This embodiment provides a method for preparing the carbon dioxide flooding thickener, which specifically comprises the following steps:

[0084] In a dry three-necked flask equipped with a mechanical stirring device, 40 g of diethyl maleate monomer and 100 mg of dibenzoyl peroxide initiator were added under nitrogen, sealed and adjusted to 80°C, then stirred and reacted for 48 hours. After the reaction was completed, it was directly heated to 180°C and dried by a vacuum pump to obtain the carbon dioxide flooding thickener.

[0085] Comparative Example 1

[0086] This comparative example provides a carbon dioxide flooding thickener, which is different from Example 1 only in that the weight average molecular weight of the carbon dioxide flooding thickener is 7000, and the preparation method comprises adding 50 g of diethyl maleate monomer and 0.8 mg of dibenzoyl peroxide initiator under nitrogen conditions; other conditions are the same as those in Example 1.

[0087] Comparative Example 2

[0088] This comparative example provides a carbon dioxide flooding thickener, which differs from Example 1 only in that the diethyl maleate is replaced by dioctyl maleate of equal mass, and other conditions are the same as those of Example 1.

[0089] Performance Testing

[0090] (1) Solubility: When the thickener content is 8%, it is completely dissolved by visual observation, and there is no precipitation after standing for 2 hours, which is qualified;

[0091] (2) Thickening performance: A 1% concentration of carbon dioxide flooding thickener (calculated according to the mass fraction of the thickener in carbon dioxide) was mixed with ethanol in a ratio of 1:1 and poured into an intermediate container, followed by injection of high-pressure CO2, and the mixture was shaken to mix evenly, and allowed to stand for 5 hours to further dissolve and equilibrate; before the experiment, the intermediate container containing the thickener was turned over and shaken again, and then placed in a water bath for heating, and the system pressure was controlled by an ISCO pump; after the temperature and pressure reached 80°C and 20MPa, respectively, the CO2 thickener system was controlled by an ISCO pump to enter the capillary rheometer at a flow rate of 8mL / min, and the pressure data at both ends of the rheometer were obtained by a differential pressure sensor; the data were processed by a rheological method to obtain the viscosity of the CO2 thickener system, i.e., the viscosity of carbon dioxide after thickening; wherein, taking the carbon dioxide flooding thickener provided in Example 1 as an example, the viscosity of carbon dioxide under different concentrations of thickener is shown in the following figure: Figure 2 As shown;

[0092] (3) Mining efficiency: Before the long core displacement experiment began, a 30 cm long and 1.5 cm diameter core was first

[0093] Three cores with a diameter of 3.8 cm and a permeability of 20 mD were spliced ​​and assembled, and multiple layers of filter paper were added between the cores to minimize the impact of fluid accumulation or uneven distribution between the cores on the seepage. After the cores were assembled, the experimental process was connected, the pressure was tested at 50 MPa, and the temperature was tested at 140 °C to confirm that the model had no leakage. On this basis, the experiment was carried out according to the plan. The specific steps are: ① Use methanol and petroleum ether to clean the water and oil in the cores successively until the output fluid is clear and transparent, blow dry with nitrogen, and evacuate; ② At a temperature of 70 °C and a pressure of 15 MPa, first saturate with water and then saturate with oil. After saturation, let it stand for aging for 1 month; ③ Maintain the outlet pressure at 15 MPa and implement pure CO2 gas drive with a displacement rate of 0.05 cm 3 / min, and end the displacement when the gas content reaches 100% (no more oil production); ④ Record key injection and production parameters such as the amount of injected CO2, time, pressure, and the amount of oil, gas, and water produced. Then replace the displacement medium from CO2 to a thickener / CO2 mixed system, and repeat steps ①-④ to carry out the experiment. Record the degree of recovery, the volume of carbon dioxide injected when the gas breaks through (gas breakthrough time), and the gasoline ratio; taking Example 1 as an example, before and after the addition of the CO2 flooding thickener, the curves of the change in the degree of recovery and the gasoline ratio with the volume of injected carbon dioxide are as shown below. Figure 3 (No thickener added), Figure 4 (adding the thickener provided in Example 1); the experimental results show that after adding the CO2 flooding thickener, the CO2 displacement effect is significantly improved, the gas breakthrough time is delayed (from 0.39HCPV to 0.47HCPV), and the recovery rate is greatly increased from 60.38%

[0094] (without adding carbon dioxide thickener) increased to 83.45%, the gas-oil ratio after gas breakthrough changed from rapid increase to slow increase, and the absolute value of the gas-oil ratio decreased significantly after gas breakthrough.

[0095] The specific test results are shown in Table 1 (reaction monomer conversion rate):

[0096] Table 1

[0097] Monomer conversion rate (%) Example 1 71 Example 2 75 Example 3 70 Example 4 90 Example 5 40 Example 6 52 Example 7 13 Comparative Example 1 38 Comparative Example 2 60

[0098] As can be seen from Table 1 and Table 2, the carbon dioxide flooding thickener provided by the present invention has a weight average molecular weight within a specific range and adopts a specific preparation method, so that the carbon dioxide flooding thickener has good solubility in carbon dioxide, high solubility, good thickening effect, and is conducive to improving mining efficiency, and does not need to use fluorine-containing and silicon-containing materials, has low cost, is environmentally friendly, and has a simple process, few by-products, and a high monomer conversion rate. As can be seen from Examples 1 to 4.

[0099] It can be seen from Examples 1 to 4 and Examples 5 to 7 and Comparative Examples 1 and 2 that the carbon dioxide flooding thickener is not a specific process parameter and the monomer conversion rate is reduced.

[0100] In summary, the carbon dioxide flooding thickener provided by the present invention not only has high solubility and good thickening effect, but also does not require the use of a large amount of co-solvent, effectively improves the displacement effect of carbon dioxide, delays the gas breakthrough time, and improves the recovery degree. In addition, the preparation process is simple and the cost is low. It does not require the use of fluorine-containing, silicon-containing and aromatic group-containing materials, and has good environmental protection. It is especially suitable for carbon dioxide flooding in low permeability reservoirs, and has broad application potential, especially for water-sensitive reservoirs.

[0101] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A carbon dioxide flooding thickener, characterized in that: The carbon dioxide flooding thickener has a structure shown in Formula I: Wherein, R1 and R2 are each independently selected from substituted or unsubstituted C1-C6 straight chain or branched alkyl groups; the substituted substituents include any one of hydroxyl, carboxyl or ester groups; n is 50 to 300; The weight average molecular weight of the carbon dioxide flooding thickener is 8,000 to 50,000.

2. The carbon dioxide flooding thickener according to claim 1, characterized in that The R1 and R2 are each independently selected from any one of ethyl, n-propyl and isopropyl.

3. A method for preparing a carbon dioxide flooding thickener according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: In the presence of an initiator, the monomer is subjected to a free radical polymerization reaction to obtain the carbon dioxide flooding thickener; the monomer contains an ester group and a carbon-carbon double bond.

4. The preparation method according to claim 3, characterized in that: The monomer comprises at least one of dimethyl butenedioate, diethyl butenedioate, di-n-propyl butenedioate, diisopropyl butenedioate, and dibutyl butenedioate; Preferably, the initiator comprises at least one of an organic peroxide initiator, an inorganic peroxide initiator or an azo initiator; Preferably, the initiator comprises dibenzoyl peroxide and / or azobisisobutyronitrile.

5. The preparation method according to claim 3 or 4, characterized in that: The mass ratio of the initiator to the monomer is 1:(40-400), and more preferably 1:(60-120).

6. The preparation method according to any one of claims 3 to 5, characterized in that: The temperature of the free radical polymerization reaction is 80 to 110°C; Preferably, the free radical polymerization reaction time is 48 to 96 hours.

7. The preparation method according to any one of claims 3 to 6, characterized in that: The free radical polymerization reaction is carried out in the presence of a protective atmosphere; Preferably, the rotation speed of the free radical polymerization reaction is 200 to 400 rpm; Preferably, after the free radical polymerization reaction is completed, the method further comprises heating to 170-190° C. and vacuum drying.

8. The preparation method according to any one of claims 3 to 7, characterized in that: The preparation method specifically comprises the following steps: In the presence of a protective atmosphere and an initiator, a monomer containing an ester group and a carbon-carbon double bond is subjected to a free radical polymerization reaction at 80 to 110° C. for 48 to 96 hours, then heated to 170 to 190° C. and vacuum-dried to obtain the carbon dioxide flooding thickener; the mass ratio of the initiator to the monomer is 1:(40 to 400).

9. Use of the carbon dioxide flooding thickener according to claim 1 or 2 in thickening supercritical carbon dioxide and / or liquid carbon dioxide.

10. The use according to claim 9, characterized in that The solubility of the carbon dioxide flooding thickener in supercritical carbon dioxide and / or liquid carbon dioxide is ≥3%; Preferably, the solubility of the carbon dioxide flooding thickener in supercritical carbon dioxide and / or liquid carbon dioxide is 3% to 8%.

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