An acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding, its preparation method and application

Abstract

The present invention provides an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding, its preparation method and application, belonging to the technical field of CO2 enhanced oil recovery. The preparation method of the acetylated surfactant of the present invention includes the steps of: under the action of catalyst A, reacting an aqueous solution of gluconic acid and n-octanol to obtain n-octyl gluconate; under the action of catalyst B, reacting n-octyl gluconate and acetic anhydride to obtain an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding. The preparation method of the surfactant of the present invention is simple, the raw materials are cheap and widely available, green and low in cost; the obtained surfactant can interact with CO2, has high CO2 affinity, and can effectively reduce the minimum miscibility pressure of CO2 miscible flooding.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 flooding, and particularly relates to an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding, a preparation method thereof, and an application thereof. Background Art

[0002] CO2 flooding technology is divided into miscible flooding, near-miscible flooding, and immiscible flooding. Among them, miscible flooding has a high oil washing efficiency because it can achieve miscibility with crude oil and completely eliminate the interfacial tension. The minimum miscibility pressure (MMP) is an important parameter for evaluating whether miscible flooding can be formed. Crude oil produced from reservoirs with poor continental sedimentation and reservoir formation conditions has the characteristics of high density, high viscosity, and high heavy component content. Such crude oil often has a high miscibility pressure and shows the characteristic that the miscibility pressure is greater than the formation fracture pressure in the actual production process. Therefore, to achieve miscible flooding, the reservoir environment must meet the miscibility conditions, which requires reducing the minimum miscibility pressure.

[0003] Currently, the commonly used methods for reducing the miscibility pressure are mainly divided into three categories: miscible solvent method, supercritical microemulsion method, and surfactant method. Among them, the miscible solvent method is limited due to defects such as the source of gas supply and separation from crude oil under formation conditions; the supercritical microemulsion method is limited due to limited pressure reduction and instability due to the influence of water; the surfactant method is a CO2-philic and oil-philic surfactant developed inspired by hydrophilic-lipophilic surfactants. It can act on the CO2-oil interface and reduce the MMP by eliminating the interfacial tension. This method was first discovered by T. Hoefling in 1991 that perfluorinated alkyl ethers have good solubility in supercritical CO2, and thus the design concept of CO2-philic surfactants was proposed.

[0004] CO2-philic surfactants are mainly divided into three categories: fluorine-containing, siloxane-containing, and hydrocarbon-containing. Among them, fluorine-containing surfactants show excellent performance in the field of CO2-philic. F atoms can generate specific interactions with CO2, so fluorine-containing surfactants can be well dissolved in CO2; however, fluorine-containing surfactants have the problems of being environmentally unfriendly and costly. Siloxane-containing surfactants have high surface activity, and the main chain of siloxane-containing has high chain flexibility and can be closely arranged on the interface, thereby greatly reducing the oil-CO2 interfacial tension and further reducing the minimum miscibility pressure; however, due to the large amount of surfactant used in the oilfield site, and the high cost of siloxane-containing, and siloxane-containing surfactants are easily hydrolyzed in water, resulting in waste of surfactants. Therefore, at present, many scientific researchers are looking for hydrocarbon-containing surfactants that can be well dissolved in CO2, are green, and are inexpensive.

[0005] Hydrocarbon surfactants have the advantages of being green and low-cost. If a CO₂-philic hydrocarbon surfactant with good CO₂ solubility can be studied to greatly reduce the minimum miscibility pressure of CO₂ miscible flooding, it has practical significance for the popularization of CO₂ miscible flooding. Currently, the hydrocarbon surfactants with good CO₂ solubility are mainly non-ionic surfactants, which mainly contain CO₂-philic groups such as carbonyl groups and ether bonds. It has been found that oxygen-containing groups can have a strong Lewis acid-base interaction with CO₂, thereby enhancing their solubility in CO₂ and further reducing the minimum miscibility pressure. Guo Ping (Petroleum Drilling & Production Technology, 2012, 34(2): 81-84.) et al. invented an oil-soluble surfactant CAE, which can reduce the minimum miscibility pressure by 22.3%. Liao (Acta Physico-Chimica Sinica, 2019, 36(10): 1907034.) et al. studied a cetyl octyl acetate, and this surfactant can reduce the miscibility pressure by 16.04%. Currently, the existing hydrocarbon surfactants are limited by their weak CO₂-philic properties, so the reduction of the miscibility pressure is limited. Therefore, there is an urgent need to develop a hydrocarbon surfactant with strong CO₂-philicity, which can effectively reduce the miscibility pressure and is green, low-cost, and has a wide range of raw material sources. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, especially the poor solubility of existing hydrocarbon surfactants in CO₂, resulting in the inability to achieve the effect of reducing MMP, the present invention provides an acetylated surfactant for reducing the minimum miscibility pressure of CO₂ miscible flooding, its preparation method and application. The preparation method of the surfactant of the present invention is simple, the raw materials are cheap, widely sourced, green, and low-cost; the obtained surfactant can interact with CO₂, has high CO₂-philicity, and can effectively reduce the minimum miscibility pressure of CO₂ miscible flooding.

[0007] The technical solution of the present invention is as follows:

[0008] An acetylated surfactant for reducing the minimum miscibility pressure of CO₂ miscible flooding has the structure shown in Formula Ⅰ below:

[0009]

[0010] Ⅰ.

[0011] The preparation method of the above-mentioned acetylated surfactant for reducing the minimum miscibility pressure of CO₂ miscible flooding includes the steps:

[0012] (1) Under the action of catalyst A, n-octyl gluconate Ⅱ is obtained by reacting an aqueous solution of gluconic acid and n-octanol.

[0013]

[0014] Ⅱ;

[0015] (2) Under the action of catalyst B, n-octyl gluconate and acetic anhydride react to obtain an acetylated surfactant that reduces the minimum miscibility pressure of CO2 miscible flooding.

[0016] Preferably according to the present invention, in step (1), the mass concentration of the gluconic acid aqueous solution is 45-55%; the molar ratio of gluconic acid to n-octanol is 1-2.2:1, preferably 1:1.

[0017] Preferably according to the present invention, in step (1), catalyst A is selected from one of concentrated sulfuric acid with a mass concentration of 95-98%, concentrated phosphoric acid with a mass concentration of greater than or equal to 85%, potassium hydroxide, or phosphotungstic acid; the molar amount of catalyst A is 0.5-3% of the molar amount of gluconic acid, preferably 3%.

[0018] Preferably, the phosphotungstic acid is phosphotungstic acid supported on SiO2, and the specific preparation steps are as follows: Dissolve phosphotungstic acid (HPW) in an ethanol aqueous solution, add the oxide carrier SiO2, stir at room temperature for 20-30 h, remove the solvent by rotary evaporation, and then calcine in an air atmosphere at 200-400 °C for 2-4 h to obtain; wherein, the volume ratio of ethanol to water is 1:1, the mass ratio of phosphotungstic acid to the volume of the ethanol aqueous solution is 0.005-0.02 g / mL, and the mass ratio of phosphotungstic acid (HPW) to the oxide carrier SiO2 is 1:0.5-2.

[0019] Preferably according to the present invention, in step (1), when catalyst A is a liquid, n-octanol and catalyst A are respectively and simultaneously added dropwise to the gluconic acid aqueous solution, or the gluconic acid aqueous solution and catalyst A are respectively and simultaneously added dropwise to n-octanol; when catalyst A is a solid, catalyst A is fully dispersed in the gluconic acid aqueous solution, and then n-octanol is added dropwise, or catalyst A is fully dispersed in n-octanol, and then the gluconic acid aqueous solution is added dropwise.

[0020] Preferably according to the present invention, in step (1), the reaction temperature is 100-120 °C, the reaction time is 3-5 h, and the reaction is carried out under stirring conditions; preferably, the reaction temperature is 110-115 °C, and the reaction time is 3-4 h.

[0021] Preferably according to the present invention, in step (1), the post-treatment method of the reaction solution obtained by the reaction includes the steps of: washing the reaction solution successively with water, sodium carbonate aqueous solution, and water, and drying the organic phase with magnesium sulfate and distilling under normal pressure to obtain n-octyl gluconate Ⅱ.

[0022] According to the preferred embodiment of the present invention, in step (1), the preparation method of gluconic acid n-octyl ester II comprises the following steps: under stirring conditions, n-octanol and catalyst A are added dropwise to a gluconic acid aqueous solution, stirred for reaction, and then washed, dried, and distilled at normal pressure to obtain gluconic acid n-octyl ester II;

[0023] Alternatively, under stirring conditions, the aqueous solution of gluconic acid and the catalyst A are added dropwise to n-octanol simultaneously, stirred for reaction, and then washed, dried, and distilled under normal pressure to obtain n-octyl gluconic acid ester II;

[0024] Alternatively, the catalyst A is fully dispersed in an aqueous solution of gluconic acid, n-octanol is added dropwise under stirring, reacted by stirring, and then washed, dried, and distilled under normal pressure to obtain n-octyl gluconic acid ester II;

[0025] Alternatively, the catalyst A is fully dispersed in n-octanol, and an aqueous solution of gluconic acid is added dropwise under stirring, and the mixture is reacted by stirring, and then washed, dried, and distilled under normal pressure to obtain n-octyl gluconic acid ester II.

[0026] Preferably according to the present invention, in step (2), the molar ratio of acetic anhydride to n-octyl gluconate is 5-10:1, preferably 5-6:1.

[0027] Preferably, in step (2), the catalyst B is selected from one of iodine, concentrated sulfuric acid with a mass concentration of 95-98%, thionyl chloride, p-toluenesulfonic acid or cupric perchlorate; and the molar amount of the catalyst B is 3-5% of the molar amount of n-octyl gluconate, preferably 3%.

[0028] Preferably, according to the present invention, in step (2), the reaction temperature is 0-8°C, the reaction time is 1-3h, and the reaction is carried out under stirring conditions; preferably, the reaction temperature is 0-5°C, and the reaction time is 1-1.5h.

[0029] Preferably, in step (2) of the present invention, the post-treatment method of the reaction solution obtained by the reaction comprises the steps of: adding ice water to the reaction solution, extracting with chloroform, taking the organic phase, adding triethylamine to the organic phase, stirring sufficiently, and then washing with a saturated sodium thiosulfate aqueous solution, drying the organic phase with anhydrous sodium sulfate, and distilling to obtain an acetylated surfactant that reduces the minimum miscible pressure of CO2 miscible drive.

[0030] Preferably, in step (2) of the present invention, the method for preparing an acetylated surfactant for reducing the minimum miscible pressure of CO2 miscible flooding comprises the following steps: uniformly mixing acetic anhydride and n-octyl gluconate, cooling to 0-8°C, adding catalyst B, reacting by stirring, then adding ice water, extracting, washing, drying and distilling the organic phase to obtain the acetylated surfactant for reducing the minimum miscible pressure of CO2 miscible flooding.

[0031] Application of the acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding in CO2 flooding

[0032] Preferably according to the present invention, application of the acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding in CO2 miscible flooding

[0033] The preparation route of the acetylated surfactant of the present invention is as follows:

[0034]

[0035] The technical features and beneficial effects of the present invention are as follows:

[0036] 1. A large number of CO2-philic groups (acetoxy groups) are introduced into the surfactant of the present invention, which improves the solubility of hydrocarbon surfactants in CO2 and has the advantage of low use concentration.

[0037] 2. The surfactant of the present invention has both CO2-philic groups (acetoxy groups) and lipophilic groups (alkyl chains), can act on the interface between CO2 and oil, reduce the CO2-oil interfacial tension, thereby reducing the minimum miscibility pressure, promoting miscibility, and improving the recovery rate of miscible flooding.

[0038] 3. The surfactant of the present invention is a small molecule hydrocarbon surfactant with excellent CO2 solubility. Different from macromolecular CO2-philic surfactants, it does not need to be used with a cosolvent when in use.

[0039] 4. The surfactant of the present invention is a hydrocarbon surfactant, which has the advantages of being green and low-cost compared with fluorocarbon and siloxane aerosoluble surfactants with good solubility.

[0040] 5. Gluconic acid is used as the starting material in the present invention, which is green, inexpensive and widely sourced. After a series of reactions, the acetylated surfactant is prepared. The preparation method is simple, green and low-cost.

[0041] 6. The purpose of acetylation after obtaining n-octyl gluconate in the present invention is to provide more oxygen-containing groups, because the oxygen-containing groups can provide more and stronger Lewis acid-base interactions with C in CO2. At the same time, the ester groups show a relatively loose and extended state, which can increase the chance of contact with CO2, thereby improving the affinity with CO2, enhancing CO2 solubility, and allowing more surfactants to enter the formation. If acetylation is not carried out, the strong hydrogen bond interaction between hydroxyl groups will cause strong intermolecular interactions between surfactant molecules, thereby reducing the interaction between surfactant-CO2, and reducing the solubility. Description of the Drawings

[0042] Figure 1The infrared spectrum of n-octyl acetylgluconate prepared in Example 1.

[0043] Figure 2 The 1H NMR spectrum of n-octyl acetylgluconate prepared in Example 1.

[0044] Figure 3 The solubility experiment diagram of n-octyl acetylgluconate prepared in Example 1 and CO2.

[0045] Figure 4 The relationship diagram of optical power and pressure for the solubility experiment of n-octyl acetylgluconate prepared in Example 1 and CO2.

[0046] Figure 5 The demixing experiment diagram of n-octyl acetylgluconate / CO2 / diesel (bottom) and CO2 / diesel (top) prepared in Example 1. Detailed implementation mode

[0047] The present invention will be further described below in conjunction with specific embodiments.

[0048] The reagents, materials and equipment used in the examples can be obtained from commercial channels without special instructions; the experimental methods are conventional methods without special instructions.

[0049] Example 1

[0050] A preparation method of an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding, comprising the steps:

[0051] (1) Add 31.62 mL (0.1 mol) of 50% aqueous gluconic acid solution to a 500 mL three-necked flask equipped with a reflux device, start stirring and heating. When the temperature reaches 110 °C, use a constant pressure funnel to dropwise add 15.74 mL (0.1 mol) of n-octanol solution (one drop per 4 - 6 s), and at the same time slowly dropwise add 0.16 mL (0.003 mol) of 98% concentrated sulfuric acid from another opening of the three-necked flask, one drop per 3 - 5 s. After the n-octanol solution is added dropwise, keep the temperature in the three-necked flask at 110 °C and stir for 3 h to obtain a brown oily product. Transfer the oily product to a separatory funnel, wash it successively with water, 10 wt% aqueous sodium carbonate solution, and water. The organic phase is dried over magnesium sulfate and then distilled under atmospheric pressure to obtain n-octyl gluconate in the collection flask. The single-step yield is 83.92%.

[0052] (2) 9.6 mL (0.1 mol) of acetic anhydride was charged into a 500 mL single-necked flask, and then 6.41 mL (0.02 mol) of n-octyl gluconate was added and mixed evenly. The single-necked flask was placed in an ice bath to ensure the temperature was between 0 and 5 °C, and 0.03 mL (0.0006 mol) of concentrated sulfuric acid with a mass concentration of 98% was slowly added, followed by stirring for 1 h. After the reaction was completed, the reactants were poured into 100 mL of ice water at 0 to 5 °C, and stirring was continued. Chloroform was added for extraction. After extraction, the organic phase was separated using a separatory funnel, and triethylamine was added to the organic phase and stirred thoroughly to remove acetic anhydride. Then, it was washed with a saturated aqueous solution of sodium thiosulfate. The organic phase was dried over anhydrous sodium sulfate and then distilled to remove chloroform, obtaining the final product, acetylated surfactant, with a single-step yield of 84.4%.

[0053] The infrared spectrum and 1H spectrum of the product synthesized in Example 1 are as Figure 1 and Figure 2 shown. Figure 1 In -1 , the characteristic absorption peak of the -CH2- bond appears at 2950 cm -1 ; the stretching vibration of -CH3 occurs at 2993 cm -1 ; the stretching vibration absorption peak of the C=O (ester) group correspondingly appears at 1731 cm -1 , and the asymmetric stretching vibration peak of -C-O-C- appears at 1269 cm -1 and 1241 cm -1 ; the symmetric stretching vibration peak of -C-O-C- appears at 1193 cm

[0054] Example 2

[0055] A preparation method of an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding is as described in Example 1, except that: in step (1), the 50% aqueous solution of gluconic acid used was slightly in excess (35 mL, 0.22 mol).

[0056] Other steps and conditions are the same as in Example 1.

[0057] The single-step yield of n-octyl gluconate in step (1) was 79.93%; the single-step yield of the product, acetylated surfactant, was 81.12%.

[0058] Example 3

[0059] A preparation method of an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding is as described in Example 1, except that: in step (1), the dropping order in the esterification reaction was changed, and the specific steps are as follows:

[0060] Add 15.74 mL (0.1 mol) of n-octanol solution to a 500 mL three-necked flask equipped with a reflux device. Start stirring and heating. When the temperature reaches 110 °C, use a constant-pressure funnel to dropwise add 31.62 mL (0.1 mol) of a 50% aqueous gluconic acid solution (one drop every 4 - 6 s), and at the same time slowly dropwise add 0.16 mL (0.003 mol) of 98% concentrated sulfuric acid (one drop every 3 - 5 s) from another opening of the three-necked flask. After the dropwise addition of the aqueous gluconic acid solution is completed, keep the temperature in the three-necked flask at 110 °C and stir for 3 h to obtain a brown oily product. Transfer the oily product to a separatory funnel and wash it successively with water, 10 wt% aqueous sodium carbonate solution, and water. The organic phase is dried over magnesium sulfate and then distilled under atmospheric pressure to obtain n-octyl gluconate in the collection flask.

[0061] Other steps and conditions are the same as in Example 1.

[0062] In step (1), the single-step yield of n-octyl gluconate is 82.3%; the single-step yield of the product acetylated surfactant is 83.25%

[0063] Example 4

[0064] A preparation method of an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding, as described in Example 1, except that: in step (1), the reaction temperature of the esterification reaction is changed to 115 °C.

[0065] Other steps and conditions are the same as in Example 1.

[0066] In step (1), the single-step yield of n-octyl gluconate is 77.37%; the single-step yield of the product acetylated surfactant is 78.25%.

[0067] Example 5

[0068] A preparation method of an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding, as described in Example 1, except that: in step (1), the esterification reaction time is changed to 4 h.

[0069] Other steps and conditions are the same as in Example 1.

[0070] In step (1), the single-step yield of n-octyl gluconate is 79.71%; the single-step yield of the product acetylated surfactant is 85%.

[0071] Example 6

[0072] A preparation method of an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding, as described in Example 1, except that: in step (2), the amount of acetic anhydride is changed to 0.12 mol, and the molar ratio of acetic anhydride to n-octyl gluconate is 6:1.

[0073] Other steps and conditions are the same as those in Example 1.

[0074] The single-step yield of the obtained acetylated surfactant is 82.5%.

[0075] Example 7

[0076] A preparation method of an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding, as described in Example 1, except that: in step (2), the acetylation reaction time is changed, and the reaction time is 1.5 h.

[0077] Other steps and conditions are the same as those in Example 1.

[0078] The single-step yield of the obtained acetylated surfactant is 83.56%.

[0079] Example 8

[0080] A preparation method of an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding, as described in Example 1, except that: in step (2), the catalyst in the acetylation reaction is changed, and 0.15 g (0.0006 mol) of elemental iodine is used as the catalyst.

[0081] Other steps and conditions are the same as those in Example 1.

[0082] The single-step yield of the obtained acetylated surfactant is 80.52%.

[0083] Example 9

[0084] A preparation method of an acetylated surfactant for reducing the minimum miscibility pressure of CO2 miscible flooding, as described in Example 1, except that: in step (1), the catalyst used is 2.88 g of SiO2-supported phosphotungstic acid catalyst (50PW / SiO2, where the content of phosphotungstic acid is 50 wt%), and the molar amount of phosphotungstic acid is 0.5% of the molar amount of gluconic acid;

[0085] The specific preparation steps of the SiO2-supported phosphotungstic acid catalyst are as follows: Dissolve phosphotungstic acid (HPW) in an ethanol aqueous solution (the volume ratio of ethanol to water is 1:1), and the mass ratio of phosphotungstic acid to the volume of the ethanol aqueous solution is 0.01 g / mL; Add the oxide support SiO2, and the mass ratio of phosphotungstic acid (HPW) to the oxide support SiO2 is 1:1; Stir at room temperature for 24 h, remove the solvent by rotary evaporation, and then calcine in an air atmosphere at 300 °C for 3 h, and dry for later use.

[0086] 31.62 mL (0.1 mol) of 50% aqueous gluconic acid solution was added to a 500 mL three-necked flask equipped with a reflux device, and 2.88 g of SiO2-supported phosphotungstic acid catalyst was added. Stirring was started and the temperature was raised. When the temperature reached 110 °C, 15.74 mL (0.1 mol) of n-octanol solution (one drop was added every 4 - 6 s) was added dropwise using a constant pressure funnel. After the addition of the n-octanol solution was completed, the temperature in the three-necked flask was maintained at 110 °C and stirred for 3 h to obtain a brown oily product. The oily product was filtered to remove the catalyst, then transferred to a separatory funnel and washed successively with water, 10 wt% aqueous sodium carbonate solution, and water. The organic phase was dried over magnesium sulfate and then distilled under atmospheric pressure to obtain n-octyl gluconate in the collection flask.

[0087] Other steps and conditions were the same as in Example 1.

[0088] (1) The single-step yield of n-octyl gluconate was 80.13%; the single-step yield of the product acetylated surfactant was 82.36%.

[0089] Comparative Example 1

[0090] The product used in Comparative Example 1 was a commercially available oil-soluble surfactant AEO-3.

[0091] Comparative Example 2

[0092] The product used in Comparative Example 2 was the n-octyl gluconate synthesized in step (1) of Example 1.

[0093] Test Example:

[0094] I. Solubility experiment

[0095] The surfactant obtained in Example 1 was placed in a high-pressure visible autoclave, and a certain amount of CO2 (the mass of the surfactant was 0.2 wt.% of the mass of CO2) was added to the visible autoclave using an ISCO pump. The experiment was carried out at a temperature of 45 °C. When the pressure reached 20 MPa, the inside of the visible autoclave reached a clear state. The pressure inside the visible autoclave was gradually reduced, and it was observed whether turbidity occurred inside the visible autoclave. The pressure at which turbidity occurred was the cloud point pressure. The CO2 solubility of the product was judged by the size of the cloud point pressure. The smaller the cloud point pressure, the better the CO2 solubility.

[0096] Figure 3The dissolution in the visible autoclave under different pressures is shown. When the pressure is 20 MPa, the inside of the visible autoclave is a clear and transparent single phase, indicating that n-octyl acetylgluconate can dissolve well in CO2. When the pressure reaches 15 MPa, the inside of the visible autoclave is still a clear and transparent single phase. However, when the pressure reaches 10.85 MPa, turbidity suddenly appears inside the visible autoclave, indicating that under this pressure, n-octyl acetylgluconate gradually precipitates from CO2. Therefore, 10.85 MPa is the cloud point pressure under the corresponding experimental conditions.

[0097] The error of observing the cloud point by the naked eye is too large. Therefore, the cloud point is judged by measuring the optical power, and the results are as Figure 4 shown. Figure 4 It is a graph showing the relationship between the pressure and the optical power recorded during the experiment. It can be found that as the pressure decreases, an inflection point appears in the optical power. By taking the first derivative of the optical power-pressure curve, the cloud point can be obtained more accurately. Figure 4 It shows that the inflection point appears at 10.63 MPa. This indicates that at pressures higher than 10.63 MPa, n-octyl acetylgluconate can dissolve in CO2 and has good solubility. Compared with the CO2 miscibility pressure of 30 MPa, it can be used to reduce the minimum miscibility pressure of CO2 miscible flooding.

[0098] II. Evaluation of the ability to reduce MMP

[0099] n-Octyl acetylgluconate can dissolve well in CO2 and has good CO2 solubility. Therefore, it can be applied to reduce the minimum miscibility pressure of CO2 miscible flooding. 60 mL of diesel and the surfactant obtained in Example 1 are loaded into the visible autoclave, and CO2 is injected into the visible autoclave using an ISCO pump (the mass of the surfactant is 0.2 wt.% of the mass of CO2) until the inside of the visible autoclave reaches a clear and transparent single phase. Then, the pressure inside the visible autoclave is gradually reduced, and the pressure point corresponding to the appearance of the cloud point, i.e., the minimum miscibility pressure, is observed. By comparing with the cloud point pressure, i.e., the minimum miscibility pressure, of the sample without the surfactant, the ability of n-octyl acetylgluconate to reduce miscibility is judged.

[0100] Figure 5To visualize the turbidity of the autoclave, it can be seen that in the system without n-octyl acetylgluconate, the diesel + CO2 system becomes turbid at 19.2 MPa, indicating that the minimum miscibility pressure of this system is 19.2 MPa. While the system with 0.2 wt.% n-octyl acetylgluconate becomes turbid at 14 MPa. Compared with the system without n-octyl acetylgluconate, the minimum miscibility pressure has decreased by 27.08%. Relative to the commercial product (Comparative Example 1), since this product provides more CO2-philic groups (oxygen-containing ester groups), its spatial structure is fluffier than that of ether bonds and can provide more opportunities to contact with CO2. Therefore, it has stronger CO2-philicity than ether bonds. And Comparative Example 2 is n-octyl gluconate without acetylation. Because n-octyl gluconate without acetylation contains more hydroxyl groups, although it also contains oxygen-containing groups, there is a strong hydrogen bond interaction between hydroxyl groups, resulting in poor CO2 solubility, which is also verified by the experimental results. N-octyl acetylgluconate is a green hydrocarbon demixing agent with good demixing performance.

[0101] The miscibility effect and demixing ability of the products obtained in the examples and comparative examples are shown in Table 1 below.

[0102] Table 1 Evaluation results of miscibility effect and demixing ability

[0103]

[0104] Among them, the cloud point pressure in Table 1 refers to the cloud point pressure measured in the solubility experiment, and the minimum miscibility pressure is the cloud point pressure measured in the MMP reduction ability evaluation experiment.

Claims

1. An application of an acetylated surfactant for reducing the minimum miscible pressure of CO2 miscible flooding in CO2 miscible flooding, characterized in that: The mass of the surfactant is 0.2wt.% of the mass of CO2; The acetylated surfactant for reducing the minimum miscible pressure of CO2 miscible flooding has a structure as shown in the following formula I: Ⅰ； The method for preparing the acetylated surfactant for reducing the minimum miscible phase pressure of CO2 miscible phase flooding comprises the steps of: (1) Under the action of catalyst A, aqueous gluconic acid solution and n-octanol react to obtain n-octyl gluconic acid ester II; Catalyst A is selected from concentrated sulfuric acid with a mass concentration of 95-98%; the mass concentration of the gluconic acid aqueous solution is 50%; the molar ratio of gluconic acid to n-octanol is 1:1; the reaction temperature is 110° C., the reaction time is 3 hours, and the reaction is carried out under stirring conditions; the molar amount of catalyst A is 3% of the molar amount of gluconic acid; n-octanol and catalyst A are added to the gluconic acid aqueous solution in a dropwise manner at the same time, or the gluconic acid aqueous solution and catalyst A are added to n-octanol in a dropwise manner at the same time; The post-treatment method of the reaction liquid obtained by the reaction comprises the following steps: washing the reaction liquid with water, sodium carbonate aqueous solution and water in sequence, drying the organic phase with magnesium sulfate and distilling at normal pressure to obtain gluconate n-octyl ester II; Ⅱ； (2) Under the action of catalyst B, n-octyl gluconate and acetic anhydride react to obtain an acetylated surfactant that reduces the minimum miscible pressure of CO2 miscible flooding; Catalyst B is selected from concentrated sulfuric acid with a mass concentration of 95-98%; the molar ratio of acetic anhydride to n-octyl gluconate is 5-6:1; the molar amount of catalyst B is 3% of the molar amount of n-octyl gluconate; the reaction temperature is 0-5°C, the reaction time is 1-1.5h, and the reaction is carried out under stirring conditions; The post-treatment method of the reaction liquid obtained by the reaction comprises the steps of: adding ice water to the reaction liquid, extracting with chloroform, taking the organic phase, adding triethylamine to the organic phase, fully stirring, then washing with a saturated sodium thiosulfate aqueous solution, drying the organic phase with anhydrous sodium sulfate, and distilling to obtain an acetylated surfactant that reduces the minimum miscible phase pressure of CO2 miscible phase drive.

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