CO2 thickener for supercritical CO2 flooding and preparation method thereof

Abstract

The invention belongs to the technical field of oil and gas field development, and specifically relates to a method for supercritical CO 2 CO2 for oil recovery 2 Thickener and preparation method thereof. A thickener for supercritical CO 2 CO2 for oil recovery 2 The preparation method of the thickener comprises: (1) mixing a maleic anhydride compound and a styrene compound, dissolving the mixture in water, introducing an inert gas and heating; (2) slowly dropping a mixed solution of a vinyl acetate compound and an initiator, cooling after the reaction is completed; (3) filtering, washing the solid phase with an anhydrous alcohol substance, drying and grinding to obtain a thickener product. The supercritical CO thickened by the thickener prepared by the present invention 2 , which can effectively slow down the viscous fingering phenomenon during displacement and improve CO 2 Sweep efficiency, thereby increasing oil recovery.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and specifically relates to a CO2 thickener used for supercritical CO2 oil recovery and a preparation method thereof. Background Art

[0002] CO2 flooding technology for enhanced oil recovery (abbreviated as "CO2 flooding") can not only be used to solve the problem of CO2 storage, but more importantly, it can meet the needs of oil field development and improve the tertiary oil recovery rate. The advantages of CO2 flooding technology are that it can reduce crude oil viscosity, expand crude oil volume, reduce interfacial tension, weaken displacement resistance and improve mobility ratio. However, under formation conditions, the viscosity of CO2 is too small (about 0.03-0.10 mPa·s) and the viscosity of crude oil is relatively large (about 0.10-50 mPa·s), which leads to a large mobility ratio between the displacement phase and the displaced phase. Viscous fingering is prone to occur during the injection process, resulting in a decrease in CO2 sweep efficiency. At present, the methods for controlling CO2 mobility are: supercritical CO2 system with thickening and viscosity enhancement, gas-soluble surfactants, supercritical CO2 emulsions, water-gas dispersion systems and micron foams (bubbles). At the construction site, adding a thickener to CO2 is the simplest and most effective way to control its mobility. Therefore, increasing the viscosity of CO2 is one of the important methods to improve the effect of CO2 flooding. When studying the issue of improving oil recovery by CO2 flooding, it is necessary to consider it from the perspective of increasing CO2 viscosity and reducing CO2 fluidity.

[0003] At present, supercritical CO2 thickeners mainly include fluorine-containing thickeners, hydrocarbons, oxygen-containing hydrocarbons and siloxanes. Although fluorine-containing thickeners have good solubility and viscosity-increasing properties, they have problems such as environmental pollution and high costs, which limit the widespread use of fluorine-containing thickeners; the thickening effect of hydrocarbons currently does not meet the use standards, and in most cases is less than 1 mPa·s; siloxane thickeners require the addition of a large amount of co-solvents to help them dissolve in supercritical CO2.

[0004] A Chinese invention patent application with publication number CN 112341567A discloses a CO2 thickener for supercritical CO2 oil recovery. The thickener contains monomers of fluorinated acrylate, tertiary amine-containing acrylate and styrene, and has low cloud point pressure and excellent thickening performance. However, the thickener has problems such as environmental pollution and high cost, which limits its on-site application in CO2 oil recovery.

[0005] The Chinese invention patent application with publication number CN105331349A discloses a novel CO2 thickener prepared from phenyl glycidyl ether polymer. Under the condition of pressure between 5-30MPa and temperature, the polymer has good solubility in liquid or supercritical CO2 and can increase the viscosity of CO2 by 1.5-2.5 times. The thickener does not contain fluorine and meets environmental protection requirements. However, the increase in CO2 viscosity is limited and is not suitable for industrial application. Summary of the invention

[0006] In view of the defects of the prior art, the present invention provides a CO2 thickener for supercritical CO2 flooding and a preparation method thereof.

[0007] Specifically, the present invention is achieved through the following technical solutions:

[0008] A method for preparing a CO2 thickener for supercritical CO2 flooding, comprising:

[0009] (1) mixing a maleic anhydride compound and a styrene compound, dissolving the mixture in water, introducing an inert gas and heating the mixture;

[0010] (2) slowly adding a mixed solution of vinyl acetate compound and initiator dropwise, and cooling after the reaction is completed;

[0011] (3) Filtering, washing the solid phase with anhydrous alcohol, and then drying and grinding to obtain a thickener product.

[0012] The above-mentioned method for preparing the CO2 thickener for supercritical CO2 oil recovery, wherein the maleic anhydride-based compound is at least one of maleic anhydride, polyethylene grafted maleic anhydride, polypropylene grafted maleic anhydride, maleic anhydride, 2,3-dimethylmaleic anhydride, and 2,3-diphenylmaleic anhydride.

[0013] In the above-mentioned method for preparing the CO2 thickener for supercritical CO2 flooding, the styrene-based compound is at least one of styrene and sodium styrene sulfonate.

[0014] In the above-mentioned method for preparing the CO2 thickener for supercritical CO2 flooding, in step (1), the heating temperature is 60-100°C.

[0015] In the above-mentioned method for preparing the CO2 thickener for supercritical CO2 oil recovery, the vinyl acetate-based compound is at least one of trimethyl vinyl acetate, vinyl acetoacetate, and vinyl acetate.

[0016] In the above-mentioned method for preparing the CO2 thickener for supercritical CO2 oil recovery, the initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dibenzoyl peroxide, benzoyl peroxide, potassium persulfate and ammonium persulfate.

[0017] In the above-mentioned method for preparing the CO2 thickener for supercritical CO2 oil recovery, the molar ratio of the maleic anhydride compound, the styrene compound, the vinyl acetate compound and the initiator is (1-3): (1-3): (1-3): (0.007-0.06).

[0018] In the above-mentioned method for preparing the CO2 thickener for supercritical CO2 oil recovery, the molar ratio of the maleic anhydride compound, the styrene compound, the vinyl acetate compound and the initiator is (2-3): (1-2): (2-3): (0.01-0.04).

[0019] In the above-mentioned method for preparing the CO2 thickener for supercritical CO2 oil recovery, the reaction time is 60 min-180 min.

[0020] On the other hand, the present invention also provides a CO2 thickener for supercritical CO2 oil recovery, which is prepared by the above-mentioned preparation method.

[0021] The technical solution of the present invention has the following beneficial effects:

[0022] (1) The CO2 thickener for supercritical CO2 oil recovery of the present invention is an oxygen-containing hydrocarbon supercritical CO2 thickener, which is not only green but also has little damage to the formation.

[0023] (2) The method for preparing a CO2 thickener for supercritical CO2 flooding of the present invention synthesizes a supercritical CO2 thickener with low formation pollution and high solubility through a unique raw material formula, and does not require a large amount of co-solvent during the preparation process;

[0024] (3) The CO2 thickener for supercritical CO2 flooding of the present invention has a low concentration and good thickening effect. During use, even if the concentration is lower than 2wt%, the viscosity of supercritical CO2 can be increased to more than 1 mPa·s within 30 minutes, and the viscosity increasing speed is fast;

[0025] (4) The CO2 thickener for supercritical CO2 flooding of the present invention has a simple synthesis method, a short synthesis time, simple preparation and high yield;

[0026] (5) Supercritical CO2 thickened by the thickener of the present invention can effectively slow down the viscous fingering phenomenon during the displacement process, improve the CO2 sweep efficiency, and thus improve the oil recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the following detailed description of the preferred embodiment.The drawings are only for the purpose of illustrating the preferred embodiments and are not to be construed as limiting the invention.

[0028] Figure 1 It is a supercritical CO2 visual reactor;

[0029] Figure 2 This is a diagram showing the effect of thickener dissolution;

[0030] Figure 3 This is a diagram of the supercritical CO2 thickening effect. DETAILED DESCRIPTION

[0031] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0032] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0033] In order to achieve supercritical CO2 displacement, a CO2 thickener is used to increase the viscosity of supercritical CO2 to more than 1 mPa·s, so as to slow down the viscous fingering phenomenon during the CO2 displacement process, improve the sweep efficiency of CO2, and make CO2 dissolve in crude oil in large quantities, expand the volume of crude oil, reduce the viscosity of crude oil, reduce the interfacial tension of crude oil, and thus improve the recovery rate of crude oil. The present invention provides a CO2 thickener for supercritical CO2 flooding and a preparation method thereof.

[0034] Specifically, the method for preparing a CO2 thickener for supercritical CO2 flooding provided by the present invention comprises:

[0035] (1) mixing a maleic anhydride compound and a styrene compound, dissolving the mixture in water, introducing an inert gas and heating the mixture;

[0036] (2) slowly adding a mixed solution of vinyl acetate compound and initiator dropwise, and cooling after the reaction is completed;

[0037] (3) Filtering, washing the solid phase with anhydrous alcohol, and then drying and grinding to obtain a thickener product.

[0038] In the present invention, the carbon-carbon double bonds in the maleic anhydride compound, the styrene compound and the vinyl acetate compound are opened, and a polymerization reaction occurs.

[0039] Among them, maleic anhydride compounds have both CO2-philic and hydrophobic groups, which can form Lewis acid-base reactions with CO2, thereby increasing the viscosity of CO2.

[0040] In some preferred embodiments, the maleic anhydride compound is at least one of maleic anhydride, polyethylene grafted maleic anhydride, polypropylene grafted maleic anhydride, maleic anhydride, 2,3-dimethylmaleic anhydride, and 2,3-diphenylmaleic anhydride.

[0041] The polyethylene grafted with maleic anhydride used in the present invention has an average molecular weight of 3000-8000; the polypropylene grafted with maleic anhydride has an average molecular weight of 5000-10000.

[0042] More preferably, the maleic anhydride compound is at least one of maleic anhydride, 2,3-dimethylmaleic anhydride and 2,3-diphenylmaleic anhydride.

[0043] Among them, styrene compounds contain CO2-repelling groups, which can enhance the hydrophobic association between molecules through the stacking effect between aromatic rings, thereby hindering the free movement of CO2 molecules and achieving the effect of thickening CO2.

[0044] In some preferred embodiments, the styrene-based compound is at least one of styrene and sodium styrene sulfonate.

[0045] In some preferred embodiments, the heating temperature in step (1) is 60-100°C.

[0046] Among them, vinyl acetate compounds contain CO2-philic groups, which can increase the solubility of the polymer in CO2, thereby playing a role in increasing the viscosity of CO2.

[0047] In some preferred embodiments, the vinyl acetate-based compound is at least one of trimethylvinyl acetate, vinyl acetoacetate, and vinyl acetate.

[0048] More preferably, the vinyl acetate compound is at least one of trimethylvinyl acetate and vinyl acetate.

[0049] Among them, the initiator can initiate the polymerization reaction in the polymerization reaction of the thickener monomer, accelerate the polymerization rate and control the molecular weight of the polymer product.

[0050] In some preferred embodiments, the initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dibenzoyl peroxide, benzoyl peroxide, potassium persulfate and ammonium persulfate.

[0051] More preferably, the initiator is at least one of dibenzoyl peroxide and benzoyl peroxide.

[0052] In some preferred embodiments, the molar ratio of the maleic anhydride compound, the styrene compound, the vinyl acetate compound and the initiator is (1-3): (1-3): (1-3): (0.007-0.06).

[0053] The molar ratio of each monomer and the amount of the initiator provided by the present invention are optimized. When the ratio of each monomer is not within the protection scope of the present invention, the synthesized thickener is prone to have problems such as poor thickening effect and poor solubility, and cannot meet the requirements of on-site use.

[0054] More preferably, the molar ratio of the maleic anhydride compound, the styrene compound, the vinyl acetate compound and the initiator is (2-3):(1-2):(2-3):(0.01-0.04).

[0055] In some preferred embodiments, the reaction time is 60 min-180 min.

[0056] The oxygen-containing hydrocarbon CO2 thickener provided by the present invention for supercritical CO2 displacement is an oxygen-containing hydrocarbon CO2 thickener, which is green and has little damage to the formation. During use, the CO2-philic monomer of the thickener itself is melted into the supercritical CO2, and a large amount of cosolvent is not required. Moreover, the synthetic high molecular weight oxygen-containing hydrocarbon thickener is used at a low concentration and has a good thickening effect. When the concentration is 2%wt, it can reach more than 1 mPa·s in 30 minutes.

[0057] Example

[0058] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions. The raw materials used in the following examples are all conventionally purchased.

[0059] Example 1

[0060] Take 0.02mol of maleic anhydride and dissolve it in 100ml of water and add 0.01mol of styrene. Put the prepared aqueous solution into a three-necked flask and continue to introduce N2 to exclude air. When heated and stirred to 80°C, add 0.0002mol of benzoyl peroxide. Put 0.02mol of vinyl acetate into a separatory funnel and control its flow rate so that it continues to drip into the three-necked flask. After reacting for 2 hours, the reaction is terminated, the reacted material is suction filtered, mixed with room temperature anhydrous ethanol, and then placed in an oven for 24 hours. After drying, the product is ground to obtain a yellow-white powder.

[0061] Example 2

[0062] Take 0.03 mol of 2,3-dimethylmaleic anhydride and dissolve it in 100 ml of water and add 0.02 mol of styrene. Put the prepared aqueous solution into a three-necked flask and continue to introduce N2 to exclude air. When heated and stirred to 100°C, add 0.0004 mol of azobisisobutyronitrile. Put 0.03 mol of trimethylacetic acid vinyl ester into a separatory funnel and control its flow rate so that it continues to drip into the three-necked flask. After 3 hours of reaction, the reaction was terminated, the reacted material was suction filtered, mixed with room temperature anhydrous ethanol, and then placed in an oven for 24 hours. After drying, the product was ground to obtain a yellow-white powder.

[0063] Example 3

[0064] Take 0.02 mol of 2,3-diphenylmaleic anhydride and dissolve it in 100 ml of water and add 0.02 mol of sodium styrene sulfonate. Put the prepared aqueous solution into a three-necked flask and continue to introduce N2 to exclude air. When heated and stirred to 100°C, add 0.0003 mol of dibenzoyl peroxide. Put 0.01 mol of vinyl acetate into a separatory funnel and control its flow rate so that it continues to drip into the three-necked flask. After 3 hours of reaction, the reaction is terminated, the reacted material is suction filtered, mixed with room temperature anhydrous ethanol, and then placed in an oven for 24 hours. After drying, grind to obtain the product, which is mostly a yellow-white powder.

[0065] Test Example 1

[0066] Take 6g of the product of Example 1 and put it into a reactor. Figure 1 As shown, CO2 was continuously introduced for 3 minutes to expel air, and then the reactor temperature was raised to 50°C, and CO2 was introduced to pressurize to 15 MPa. After continuous stirring for 30 minutes, there was no obvious precipitation at the bottom of the reactor, which confirmed that the thickener had good solubility in CO2, such as Figure 2 In addition, after continuous stirring for 30 min, the visible window surface has obvious slip bands, such as Figure 3As shown, it means that supercritical CO2 has a certain viscosity, which is above 1 mPa·s. At the same time, the viscosity of CO2 at 50°C, 15 MPa, and 2 wt% thickener addition was measured by capillary method, and the viscosity reached 1.07 mPa·s, confirming that the thickener has a good thickening effect.

[0067] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A method for preparing a CO2 thickener for supercritical CO2 flooding, characterized in that: include: (1) mixing a maleic anhydride compound and a styrene compound, dissolving the mixture in water, introducing an inert gas and heating the mixture; (2) slowly adding a mixed solution of vinyl acetate compound and initiator dropwise, and cooling after the reaction is completed; (3) filtering, washing the solid phase with anhydrous alcohol, and then drying and grinding to obtain a thickener product; Wherein, the molar ratio of the maleic anhydride compound, the styrene compound, the vinyl acetate compound and the initiator is (1-3): (1-3): (1-3): (0.007-0.06); Among them, the maleic anhydride compound is at least one of maleic anhydride, 2,3-dimethylmaleic anhydride, and 2,3-diphenylmaleic anhydride; the styrene compound is at least one of styrene and sodium styrene sulfonate; and the vinyl acetate compound is at least one of trimethylvinyl acetate, vinyl acetoacetate, and vinyl acetate.

2. The preparation method according to claim 1, characterized in that: In step (1), the heating temperature is 60-100°C.

3. The preparation method according to claim 1, characterized in that: The initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, potassium persulfate and ammonium persulfate.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the maleic anhydride compound, the styrene compound, the vinyl acetate compound and the initiator is (2-3): (1-2): (2-3): (0.01-0.04).

5. The preparation method according to claim 1, characterized in that The reaction time is 60 min-180 min.

6. A CO2 thickener for supercritical CO2 flooding, characterized in that: The preparation method is described in any one of claims 1 to 5.

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