Foam-assisted carbon dioxide huff and puff oil extraction method

Abstract

The invention provides a foam-assisted carbon dioxide huff and puff oil extraction method, and relates to the technical field of oilfield development. The method comprises the steps of sequentially injecting a foam front slug, a foam rear slug, a carbon dioxide slug and a plugging agent slug into a well, replacing with clear water, soaking the well and opening the well for production. According to the method, the foam slug is injected before the carbon dioxide main slug, a dominant seepage channel in a reservoir can be effectively blocked, carbon dioxide is prevented from forming gas channeling along the dominant seepage channel, crude oil recovery is improved, and the foaming agent has super-strong foaming and foam stabilizing performance, is slightly influenced by temperature, salinity and the like and is good in stratum compatibility.

Description

Technical Field

[0001] This application relates to the technical field of oilfield development, and particularly to a method for foam-assisted carbon dioxide huff and puff oil recovery. Background Art

[0002] The carbon dioxide huff and puff oil recovery technology refers to injecting a certain amount of carbon dioxide into the oil reservoir under a certain pressure. After soaking the well for a period of time to allow the carbon dioxide to diffuse and dissolve in the crude oil in the formation, the well is opened for production. The mechanism by which the carbon dioxide huff and puff oil recovery technology can improve the crude oil recovery rate is as follows: After injecting carbon dioxide into the oil reservoir, the carbon dioxide dissolves in the crude oil and formation water, carbonating the formation water, reducing the viscosity of the crude oil, carbonating the formation water, increasing the mobility ratio of the crude oil to the formation water, expanding the swept volume of carbon dioxide in the formation, and thus increasing the crude oil recovery rate.

[0003] However, due to the influence of reservoir heterogeneity and preferential flow channels, after multiple rounds of carbon dioxide huff and puff, the carbon dioxide injected from the oil well will form gas channeling along the preferential flow channels, reducing the swept range of carbon dioxide. The carbon dioxide cannot fully interact with the crude oil in the remaining oil enrichment area. When the well is opened for production, the carbon dioxide will also return along the original pore channels during injection, resulting in an ineffective cycle of carbon dioxide. Therefore, it is necessary to block the preferential flow channels before carbon dioxide huff and puff to improve the effect of carbon dioxide huff and puff.

[0004] Patent CN106811188A discloses an oil recovery method for foam-assisted carbon dioxide huff and puff, which injects a foam pre-slug, a carbon dioxide main slug, a foam post-slug, a plugging agent slug, and water into the reservoir in sequence to avoid carbon dioxide channeling, improve the utilization rate of carbon dioxide, and increase the crude oil recovery rate. However, the foaming agent used therein is a gemini surfactant and partially hydrolyzed polyacrylamide, but its temperature and salt resistance are limited. Summary of the Invention

[0005] The purpose of this application is to provide a method for foam-assisted carbon dioxide huff and puff oil recovery in view of the deficiencies of the prior art. By injecting a foam slug, it can effectively block the preferential flow channels in the reservoir, prevent carbon dioxide from forming gas channeling along the preferential flow channels, increase the crude oil recovery, and the foaming agent has excellent foaming and foam stability performance, is less affected by temperature, salinity, etc., and has good formation compatibility.

[0006] To achieve the above purpose, the technical solution adopted in this application is as follows: A method for foam-assisted carbon dioxide huff and puff oil recovery includes the following steps: Inject a foam pre-slug, a foam post-slug, a carbon dioxide slug, a plugging agent slug, water displacement, soak the well, and open the well for production into the well; wherein, Both the foam pre-slug and the foam post-slug are composed of a foaming agent and a gas. The foaming agent, by mass percentage, includes: 0.2 - 0.4% of a surfactant, 0.1 - 0.2% of polyvinyl alcohol, and the balance being water; the surfactant is an α-olefin sulfonate, sodium fatty acid methyl ester ethoxylate sulfonate, and cardanol polyoxyethylene ether with a mass ratio of (50 - 60):(25 - 40):(10 - 15).

[0007] Preferably, the surfactant is an α-olefin sulfonate, sodium fatty acid methyl ester ethoxylate sulfonate, and cardanol polyoxyethylene ether with a mass ratio of 58:30:12.

[0008] In this application, by compounding α-olefin sulfonate, sodium fatty acid methyl ester ethoxylate sulfonate, and cardanol polyoxyethylene ether, it has strong foaming performance and foam stability performance, with a long foam half-life (more than 2 h), and can be applied to high-temperature and high-salinity oil reservoirs at 120°C and a salinity of 20,000 mg / L.

[0009] Further, the α-olefin sulfonate is an α-olefin sulfonate with a carbon chain length of C12 - C16.

[0010] Further, the sodium fatty acid methyl ester ethoxylate sulfonate is prepared by subjecting fatty acid methyl ester to an addition reaction with ethylene oxide and then sulfonating it with a sulfonating agent.

[0011] Optionally, the fatty acid methyl ester is selected from C12 - C16 fatty acid methyl esters, preferably any one of methyl laurate, methyl myristate, and methyl palmitate, that is, the sodium fatty acid methyl ester ethoxylate sulfonate is selected from any one of sodium laurate methyl ester ethoxylate sulfonate, sodium myristate methyl ester ethoxylate sulfonate, and sodium palmitate methyl ester ethoxylate sulfonate.

[0012] Optionally, the sulfonating agent is sodium metabisulfite or sodium bisulfite.

[0013] Specifically, the above-mentioned sodium fatty acid methyl ester ethoxylate sulfonate is prepared by the following method: Mix fatty acid methyl ester, ethylene oxide, and the catalyst p-toluenesulfonic acid, react at 150 - 180°C for 4 - 6 h, after the reaction, cool to 85 - 95°C, add the sulfonating agent and water, heat up to 130 - 140°C and react for 5 - 8 h, then cool to obtain; the weight ratio of fatty acid, ethylene oxide, sulfonating agent, catalyst, and water is 1:(1 - 1.5):(0.2 - 0.3):(0.01 - 0.05):(0.4 - 0.6).

[0014] Further, the structural formula of the cardanol polyoxyethylene ether is: ; n is the addition number of ethylene oxide, i.e., the EO number, and n is 6 - 14; R is a C15 unsaturated alkyl group; that is, the cardanol polyoxyethylene ether is a cardanol polyoxyethylene ether with an EO number of 6 - 14.

[0015] In this application, the foaming agents in the foam pre-slug and the foam post-slug can be exactly the same or different. Preferably, the cardanol polyoxyethylene ether injected in the foam pre-slug is a cardanol polyoxyethylene ether with an EO number of 6 - 8, and the cardanol polyoxyethylene ether with an EO number of 12 - 14 is injected in the foam post-slug. Experiments have found that using different cardanol polyoxyethylene ethers in the front and rear sections, injecting the cardanol polyoxyethylene ether with a low EO number, i.e., a small molecular weight, in the pre-slug first, helps carbon dioxide enter the crude oil and rock pores more easily, improving the dissolution of carbon dioxide and the initial sweep range. Injecting the cardanol polyoxyethylene ether with a large EO number, i.e., a large molecular weight, in the rear section forms a foam film with high strength, which can better block the high-permeability channels, forcing carbon dioxide to turn to the low-permeability areas and improving the overall sweep efficiency and recovery rate.

[0016] Furthermore, the molecular weight of the polyvinyl alcohol is 170,000 - 200,000.

[0017] In a further embodiment, the polyvinyl alcohol is also esterified and modified with a C4 - C8 dibasic acid, and the weight ratio of the C4 - C8 dibasic acid to the polyvinyl alcohol is 100:(1 - 3). Optionally, the C4 - C8 dibasic acid is selected from any one of maleic acid, fumaric acid, glutaric acid, adipic acid, pimelic acid, and terephthalic acid.

[0018] Specifically, the steps for the esterification modification of the polyvinyl alcohol are as follows: Add the polyvinyl alcohol to 20 times its weight of water, heat to 70 - 90°C, add the C4 - C8 dibasic acid and mix evenly, add p-toluenesulfonic acid, heat to 100 - 120°C, react under nitrogen protection for 3 - 5 h, cool to room temperature after the reaction, adjust the pH to neutral, add ethanol for precipitation, filter, and wash to obtain the product.

[0019] Adding the esterified and modified polyvinyl alcohol to the foaming agent in this application has a good balance of hydrophilicity and hydrophobicity, can reduce the surface tension of the foam liquid film, effectively prevent the rupture and coalescence of the foam, extend the foam half-life, enhance the foam stability ability, enabling it to maintain a good plugging effect during the plugging process, and improving the stability of the foam in harsh environments such as high salinity, so that it can still maintain good performance under the salinity condition of 80,000 mg / L. Controlling the ratio of the C4 - C8 dibasic acid to the polyvinyl alcohol during the preparation process of the above esterified and modified polyvinyl alcohol can prevent the excessive amount of the dibasic acid, which not only cannot improve the foam stability but may also lead to a decrease in foam stability and affect the temperature resistance and salt resistance.

[0020] Further, the volume ratio of the foaming agent to the gas is 1:(0.02 - 0.1).

[0021] Further, the plugging agent slug injects a polyacrylamide gel - type plugging agent.

[0022] Optionally, the polyacrylamide gel - type plugging agent, by weight, comprises the following components: 0.3 - 0.5 parts of acrylamide, 0.1 - 0.3 parts of acrylic acid, 0.1 - 0.3 parts of sodium allylsulfonate, 0.01 - 0.03 parts of N,N′ - methylenebisacrylamide, 80 - 100 parts of water, 0.01 - 0.05 parts of sodium hydroxide, and 0.01 - 0.03 parts of initiator.

[0023] Optionally, the polyacrylamide gel - type plugging agent is prepared by the following method: Add acrylamide, acrylic acid, and sodium allylsulfonate into water, add sodium hydroxide, add N,N′ - methylenebisacrylamide and initiator, and react at 100 °C for 2 h to obtain.

[0024] Further, the injection volume and displacement of each stage are adjusted according to the actual situation.

[0025] Preferably, the total injection volume of the foam pre - slug and the foam post - slug is 200 - 700 t; more preferably, the injection volume ratio of the foam pre - slug to the foam post - slug is (50 - 70):(30 - 50); The displacement of the foam pre - slug is 8 t / h - 10 t / h, and the displacement of the foam post - slug is 3 t / h - 5 t / h.

[0026] Preferably, the injection volume of the carbon dioxide slug is 200 - 600 t, and the displacement is 3 t / h - 8 t / h.

[0027] Preferably, the injection volume of the plugging agent slug is 10 - 50 t, and the displacement is 3 t / h - 5 t / h.

[0028] Preferably, the injection volume of the clean - water displacement is 20 - 50 t.

[0029] Further, the soaking time is 20 - 30 days.

[0030] Compared with the prior art, the present application has the following beneficial effects: 1. The foam - assisted carbon dioxide huff - and - puff oil production method provided by the present application can effectively plug the preferential flow channels in the reservoir by injecting two foam slugs before the carbon dioxide main slug, prevent carbon dioxide from channeling along the preferential flow channels, improve the oil recovery, and the foaming agent has excellent foaming and foam - stabilizing properties, is less affected by temperature, salinity, etc., and has good formation compatibility.

[0031] 2. The foaming agent provided by this application, through the synergistic effect of α-olefin sulfonate, sodium fatty acid methyl ester ethoxylate sulfonate and cashew phenol polyoxyethylene ether, greatly enhances the foaming performance and foam stability of the foaming agent, has a long foam half-life, and at the same time improves the tolerance to harsh reservoir conditions, and improves the stability of the foam in harsh environments such as high temperature, high acidity and high salinity, enabling it to achieve a high plugging efficiency under high temperature and high salinity conditions, thereby improving oil recovery; adding esterified modified polyvinyl alcohol to the foaming agent can further enhance the stability of the foaming agent and also improve its salinity tolerance performance, enabling it to be applicable to oil reservoirs with a salinity of 80,000 mg / L. Specific embodiments

[0032] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand this application, but do not limit this application in any way. The following content is only an exemplary illustration of the scope claimed in this application. Those skilled in the art can make various changes and modifications to the invention of this application based on the disclosed content, and it should also fall within the scope claimed in this application.

[0033] All kinds of chemical reagents used in the embodiments of this application are obtained through conventional commercial channels unless otherwise specified.

[0034] This application provides a method for foam-assisted carbon dioxide huff and puff oil recovery, including the following steps: Inject a foam pre-slug, a foam post-slug, a carbon dioxide slug, a plugging agent slug, displace with clear water, shut in the well, and then open the well for production into the well.

[0035] To verify the effect of the above method for foam-assisted carbon dioxide huff and puff oil recovery, this application verifies the above method through indoor core simulation experiments. Prepare core samples with a length of 30 cm, a diameter of 3 cm, a permeability of 58 mD, and a porosity of 28.6%; saturate the core samples with formation water with a salinity of 6480 mg / L at a displacement rate of 3 mL / min, and then saturate the core samples with crude oil at a displacement rate of 0.5 mL / min, and then age for 48 h; the viscosity of the crude oil used is 10.7 mPa·s at 65 °C; displace the crude oil in the core with clear water with a salinity of 1060 mg / L at a displacement rate of 0.5 mL / min until the water cut reaches 90%.

[0036] Taking the above core samples as an example, the following further illustrates this application in the form of specific embodiments. It should be noted that the indoor core simulation experiments use smaller doses and displacements, and are adjusted according to the actual reservoir conditions during actual production.

[0037] Example 1 This embodiment provides a method for foam-assisted CO₂ huff and puff oil recovery, comprising the following steps: (1) Inject a foam pre-slug of 3 g at a displacement rate of 1 mL / min; (2) Inject a foam post-slug of 2 g at a displacement rate of 0.5 mL / min; (3) Inject 7 g of CO₂ at a displacement rate of 0.5 mL / min; (4) Inject 2 g of a plugging agent at a displacement rate of 0.3 mL / min; the plugging agent is prepared by the following method: Add 0.3 parts of acrylamide, 0.1 part of acrylic acid, and 0.1 part of sodium allylsulfonate to 100 parts of water, add 0.01 part of sodium hydroxide, add 0.01 part of N,N′-methylenebisacrylamide, 0.01 part of an initiator, and react at 100 °C for 2 h to obtain it; it can be understood that the plugging agent can be replaced with conventional polyacrylamide gel plugging agents in the art without special limitations; (5) Inject 2 g of water for displacement, and after standing for 20 days, measure the oil production volume in 30 min and calculate the recovery factor.

[0038] Among them, the foam pre-slug and the foam post-slug are prepared by adding 5 g of CO₂ to a foaming agent; the foaming agent is prepared by the following method: Add 0.2 parts of a surfactant to 99.6 parts of water, add 0.2 parts of polyvinyl alcohol (molecular weight 170,000), and stir evenly to obtain the foaming agent; the surfactant is sodium dodecene sulfonate, sodium lauric acid methyl ester ethoxylate sulfonate, and cardanol polyoxyethylene ether (EO number 14) with a mass ratio of 50:40:10.

[0039] Example 2 The difference from Example 1 is that the foaming agent is prepared by the following method: Add 0.4 parts of a surfactant to 99.5 parts of water, add 0.1 parts of polyvinyl alcohol (molecular weight 200,000), and stir evenly to obtain the foaming agent; the surfactant is sodium hexadecene sulfonate, sodium myristic acid methyl ester ethoxylate sulfonate, and cardanol polyoxyethylene ether (EO number 12) with a mass ratio of 58:30:12.

[0040] Example 3 The difference from Example 2 is that the foaming agent is prepared by the following method: Add 0.4 g of a surfactant to 99.5 g of water, add 0.1 g of polyvinyl alcohol (molecular weight 200,000), and stir evenly to obtain the foaming agent; the surfactant is sodium hexadecene sulfonate, sodium palmitic acid methyl ester ethoxylate sulfonate, and cardanol polyoxyethylene ether (EO number 6) with a mass ratio of 60:25:15.

[0041] Example 4 The difference from Example 2 is that in the preparation process of the foaming agent, sodium methyl ester ethoxylate sulfonate is replaced with an equal amount of sodium stearate methyl ester ethoxylate sulfonate.

[0042] Example 5 The difference from Example 2 is that in the preparation process of the foaming agent, the EO number of cardanol polyoxyethylene ether is 15.

[0043] Example 6 The difference from Example 2 is that in the preparation process of the foaming agent, the polyvinyl alcohol is maleic acid-modified polyvinyl alcohol, and the maleic acid-modified polyvinyl alcohol is prepared by the following method: Add polyvinyl alcohol (molecular weight 170,000) to 20 times its weight of water, heat to 90 °C, add maleic acid and mix evenly, add p-toluenesulfonic acid accounting for 1% of the mass of polyvinyl alcohol, heat to 120 °C, react for 5 h under nitrogen protection, cool to room temperature after the reaction, adjust the pH to neutral, add ethanol for precipitation, filter, and wash to obtain; the weight ratio of polyvinyl alcohol to maleic acid is 100:1.

[0044] Example 7 The difference from Example 2 is that in the preparation process of the foaming agent, the polyvinyl alcohol is terephthalic acid-modified polyvinyl alcohol, and the terephthalic acid-modified polyvinyl alcohol is prepared by the following method: Add polyvinyl alcohol (molecular weight 200,000) to 20 times its weight of water, heat to 90 °C, add terephthalic acid and mix evenly, add p-toluenesulfonic acid accounting for 1% of the mass of polyvinyl alcohol, heat to 120 °C, react for 5 h under nitrogen protection, cool to room temperature after the reaction, adjust the pH to neutral, add ethanol for precipitation, filter, and wash to obtain; the weight ratio of polyvinyl alcohol to terephthalic acid is 100:3.

[0045] Example 8 The difference from Example 6 is that in the preparation process of the foaming agent, the adipic acid in the adipic acid-modified polyvinyl alcohol is replaced with an equal amount of sebacic acid.

[0046] Example 9 The difference from Example 6 is that in the preparation process of the foaming agent, the weight ratio of polyvinyl alcohol to adipic acid is 100:5.

[0047] Example 10 The difference from Example 2 is that only the foam pre-slug is injected, the injection volume is 5 g, the displacement is 1 mL / min, and the foam post-slug is not injected.

[0048] Example 11 The difference from Example 2 is that the foam pre-slug is 2 g, the foam post-slug is 3 g, and the displacement remains unchanged.

[0049] Example 12 This embodiment provides a method for foam-assisted CO₂ huff and puff oil recovery, comprising the following steps: (1) Inject a foam pre-slug of 3 g at a displacement rate of 1 mL / min; (2) Inject a foam post-slug of 2 g at a displacement rate of 0.5 mL / min; (3) Inject 7 g of CO₂ at a displacement rate of 0.5 mL / min; (4) Inject 2 g of a plugging agent at a displacement rate of 0.3 mL / min; The plugging agent is prepared by the following method: Add 0.3 parts of acrylamide, 0.1 part of acrylic acid, and 0.1 part of sodium allylsulfonate to 100 parts of water, add 0.01 part of sodium hydroxide, add 0.05 part of N,N′-methylenebisacrylamide and 0.01 part of initiator, and react at 100 °C for 2 h to obtain it; It can be understood that the plugging agent can be replaced with conventional polyacrylamide gel plugging agents in the art without special limitation; (5) Inject 2 g of water for displacement, and after standing for 20 days, measure the oil production in 30 min and calculate the recovery factor.

[0050] Among them, the foam pre-slug is prepared by adding 5 g of CO₂ to foaming agent I; Foaming agent I is prepared by the following method: Add 5 parts of surfactant to 94.7 parts of water, add 0.3 part of polyvinyl alcohol (molecular weight 200,000), and stir evenly to obtain the foaming agent; The surfactant is sodium hexadecene sulfonate, sodium methyl palmitate ethoxylate sulfonate, and cardanol polyoxyethylene ether (EO number 6) with a mass ratio of 60:25:15.

[0051] The foam post-slug is prepared by adding 5 g of CO₂ to foaming agent II, 18.1%. Foaming agent II is prepared by the following method: Add 5 parts of surfactant to 94.7 parts of water, add 0.3 part of polyvinyl alcohol (molecular weight 200,000), and stir evenly to obtain the foaming agent; The surfactant is sodium hexadecene sulfonate, sodium methyl myristate ethoxylate sulfonate, and cardanol polyoxyethylene ether (EO number 12) with a mass ratio of 48:40:12.

[0052] Example 13 The difference from Example 12 is that the EO number of cardanol polyoxyethylene ether in foaming agent I used for the foam pre-slug is 8, and the EO number of cardanol polyoxyethylene ether in foaming agent II used for the foam post-slug is 14.

[0053] Example 14 The difference from Example 12 is that the EO number of cardanol polyoxyethylene ether in foaming agent I used for the foam pre-slug is 6, and the EO number of cardanol polyoxyethylene ether in foaming agent II used for the foam post-slug is 16.

[0054] Comparative Example 1 The difference from Example 2 is that in the preparation process of the foaming agent, the surfactants are sodium hexadecene sulfonate, sodium methyl myristate ethoxylate sulfonate and cardanol polyoxyethylene ether (EO12) in a ratio of 40:45:15.

[0055] Comparative Example 2 The difference from Example 2 is that in the preparation process of the foaming agent, the surfactants are sodium hexadecene sulfonate, sodium methyl myristate ethoxylate sulfonate and cardanol polyoxyethylene ether (EO12) in a ratio of 70:20:10.

[0056] Comparative Example 3 The difference from Example 2 is that in the preparation process of the foaming agent, the surfactants are sodium hexadecene sulfonate and sodium methyl myristate ethoxylate sulfonate in a ratio of 60:40, that is, cardanol polyoxyethylene ether is not added.

[0057] Comparative Example 4 The difference from Example 2 is that in the preparation process of the foaming agent, the surfactants are sodium hexadecene sulfonate and cardanol polyoxyethylene ether (EO12) in a ratio of 88:12, that is, sodium methyl myristate ethoxylate sulfonate is not added.

[0058] Test Example 1 In this test, the foaming volume and foam half-life of the foaming agents in the examples and comparative examples were evaluated with reference to the stirring method (Waring-Blender method), and the volume of the foaming agent was 100 mL.

[0059] The measured results are shown in Table 1 below.

[0060] Table 1

[0061] The results show that the foaming agent provided by the present application has excellent foam properties, with a large foaming volume and good foam stability. It can be seen from comparing with Examples 1-3 and Comparative Examples 1-4 that when sodium hexadecene sulfonate, sodium methyl myristate ethoxylate sulfonate and cardanol polyoxyethylene ether in the surfactant are used in a specific ratio combination, the foaming agent has excellent foaming properties, and the foaming performance will decrease if any one of them is missing.

[0062] Test Example 2 The temperature resistance and salinity resistance properties of the foaming agents in the examples and comparative examples were tested. Specifically, After the foaming agent was placed at 120 °C for 24 h, the foaming volume and half-life were tested by the stirring method (Waring-Blender method) and compared with the foam properties in Test Example 1 to evaluate the temperature resistance; Replace the water in the foaming agents in the examples and comparative examples with simulated formation water with a salinity of 20,000 mg / L and 80,000 mg / L respectively, test the foaming volume and half-life, and compare with the foam performance in Test Example 1 to evaluate its salinity tolerance performance.

[0063] The results are shown in Table 2 below.

[0064] Table 2

[0065] The results show that the foaming agent provided in this application has a high foaming volume and half-life at 120 °C and a salinity of 20,000 - 80,000 mg / L, indicating excellent temperature tolerance and salinity tolerance.

[0066] Test Example 3 The comparison results of the above Example 2, Examples 10 - 14, Comparative Example 3 and the simple carbon dioxide huff and puff oil production method for improving the recovery factor are shown in Table 3 below. Among them, the steps of the simple carbon dioxide huff and puff oil production method are as follows: (1) Inject 7 g of carbon dioxide at a displacement of 0.5 mL / min; (2) Inject 2 g of plugging agent at a displacement of 0.5 mL / min; (3) Inject 2 g of clear water for displacement. After standing for 20 days, measure the oil production volume in 30 min and calculate the improvement in recovery factor.

[0067] Table 3

[0068] The results show that compared with the simple carbon dioxide huff and puff oil production method, the improvement in recovery factor of the foam-assisted carbon dioxide huff and puff oil production method provided in this application is significantly improved.

[0069] The above description of the embodiments is for those of ordinary skill in the art in this technical field to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, this application is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of this application should be within the protection scope of this application.

Claims

1. A method for foam-assisted CO₂ huff and puff oil recovery, characterized in that, It includes the following steps: Inject a foam pre-slug, a foam post-slug, a carbon dioxide slug, a plugging agent slug, displace with clear water, shut in the well, and start production; Among them, both the foam pre-slug and the foam post-slug are composed of a foaming agent and a gas. The foaming agent, calculated by mass percentage, includes: 0.2 - 0.4% of a surfactant, 0.1 - 0.2% of polyvinyl alcohol, and the balance is water; the surfactant is an α-olefin sulfonate, sodium fatty acid methyl ester ethoxylate sulfonate, and cardanol polyoxyethylene ether with a mass ratio of (50 - 60):(25 - 40):(10 - 15).

2. The method for foam-assisted CO₂ huff and puff oil recovery according to claim 1, wherein, The surfactant is an α-olefin sulfonate, sodium fatty acid methyl ester ethoxylate sulfonate, and cardanol polyoxyethylene ether with a mass ratio of 58:30:

12.

3. The method for foam-assisted CO₂ huff and puff oil recovery according to claim 1, wherein, The α-olefin sulfonate is an α-olefin sulfonate with a carbon chain length of C12 - C16.

4. The method for foam-assisted carbon dioxide huff and puff oil recovery according to claim 1, characterized in that The sodium fatty acid methyl ester ethoxylate sulfonate is prepared by adding ethylene oxide to fatty acid methyl ester and then sulfonating with a sulfonating agent; The fatty acid methyl ester is selected from fatty acid methyl esters of C12 - C16.

5. The method for foam-assisted CO₂ huff and puff oil recovery according to claim 1, characterized in that, The cardanol polyoxyethylene ether is a cardanol polyoxyethylene ether with an EO number of 6 - 14.

6. The method for foam-assisted CO₂ huff and puff oil recovery according to claim 5, wherein, The cardanol polyoxyethylene ether injected in the foam pre-slug is a cardanol polyoxyethylene ether with an EO number of 6 - 8, and the cardanol polyoxyethylene ether injected in the foam post-slug has an EO number of 12 - 14.

7. The method for foam-assisted CO₂ huff and puff oil recovery according to claim 1, characterized in that, The molecular weight of the polyvinyl alcohol is 170,000 - 200,000.

8. The method for foam-assisted CO₂ huff and puff oil production according to claim 7, characterized in that, The polyvinyl alcohol is also esterified and modified with a C4 - C8 dibasic acid, and the weight ratio of the C4 - C8 dibasic acid to polyvinyl alcohol is 100:(1 - 3).

9. The method for foam-assisted CO₂ huff and puff oil recovery according to claim 1, wherein The plugging agent slug injects a polyacrylamide gel type plugging agent.

10. The method for foam-assisted CO₂ huff and puff oil recovery according to claim 1, wherein The injection volume ratio of the foam pre-slug to the foam post-slug is (50 - 70):(30 - 50).

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