CO2 oil displacement foam composition and application thereof

Abstract

The invention provides a CO2 oil displacement foam composition and application thereof. The composition is prepared from the following components in parts by weight: 0.1 to 1.5 parts of foaming agent, 0.1 to 3 parts of foam stabilizer and 95.5 to 99.8 parts of water, the foaming agent is selected from a mixture of an anionic surfactant and a nonionic surfactant; the foam stabilizer is selected from grafted modified nano cellulose; the grafted modified nano cellulose comprises a grafting group, the grafting group is selected from one or more of amino, ester group, carbonyl and carboxyl, and the content of the grafting group is 1.5-2.0 mmol / g. Compared with a single-component foaming agent, the foam performance of the composition can be improved by adopting a mixture of the anionic surfactant and the nonionic surfactant. The grafted modified nanocellulose is used as a foam stabilizer, so that the tackifying effect of the foam stabilizer can be exerted, the precipitation rate of liquid in foam is reduced, and the formed CO2 oil displacement foam system has the characteristics of high network structure strength and good shear resistance.

Description

Technical Field

[0001] This invention relates to the field of oilfield development technology, and more specifically, to a CO2 flooding foam composition and its application. Background Technology

[0002] As my country's economy enters a period of rapid development, the demand for oil and gas resources is gradually increasing. However, the development of conventional oil and gas resources is no longer sufficient to meet these needs, and unconventional oil and gas resources are playing an increasingly important role in oil and gas development. Low-permeability reservoirs, in particular, are rich in reserves and have enormous exploitation potential. Early development primarily relied on waterflooding, but this approach suffers from difficulties in water injection and low waterflooding utilization, severely impacting reservoir development effectiveness. CO2 exists in a supercritical state under reservoir conditions, exhibiting low viscosity, low density, and easy flow. It can penetrate reservoir pores inaccessible to water molecules, increasing its reach. Furthermore, it readily mixes with crude oil, reducing its viscosity and enhancing its fluidity, thus improving oil recovery and demonstrating significant advantages in low-permeability reservoir development. However, due to reservoir heterogeneity and the inherent properties of CO2, CO2 channeling is prone to occur during oil displacement, resulting in a narrow gas reach and low reservoir utilization, negatively impacting the effectiveness of CO2 oil displacement. Therefore, CO2 channeling control is crucial for achieving efficient CO2 oil displacement.

[0003] Foam exhibits unique characteristics in heterogeneous reservoirs, effectively blocking large-scale water inflows but not small-scale ones, and water inflows but not oil inflows, giving it an advantage over systems like gels in terms of channel blocking performance. However, the channel blocking performance of foam is primarily determined by its stability. The high solubility of CO2 in water leads to poor stability in CO2 foam, severely impacting its channel blocking performance and limiting its widespread application.

[0004] Analysis of the foam stabilization mechanism reveals two main methods to improve CO2 foam stability. One method involves adding thickeners to increase the viscosity of the liquid phase, thereby reducing the rate of liquid separation. For example, existing literature (publication number CN101089117A) discloses a CO2 foam plugging system using modified guar gum as a foam stabilizer, with a foaming volume of 430 mL and a foam half-life of 1602 min. Modified guar gum and other polymers increase the viscosity of the system, enhancing foam stability; however, higher viscosity restricts foaming performance, reducing the system's foaming capacity. Furthermore, the large molecular weight and high residue content of these polymers can cause significant reservoir damage, limiting their application in ultra-low to very low permeability reservoirs. The other foam stabilization method involves increasing the liquid film strength to reduce gas permeation. For example, existing literature (publication number CN105238380A) discloses an inorganic microparticle-reinforced foam system with a foaming volume of 390 mL and a foam half-life of 36 min. The particles are small in size (≤2.5μm) and adsorb onto the liquid film surface, enhancing the interfacial strength. However, due to the limited interaction forces between particles, the foaming and stabilizing effects are generally poor. Furthermore, the non-degradable nature of inorganic particles and other solid materials causes irreversible damage to the reservoir. The foam stabilizers added to the above systems all provide stabilization from a single perspective, with limited functionality. For example, existing literature (publication number CN107573915A) discloses a multiphase CO2-stabilized foam system composed of polymer microspheres and amphiphilic polymers. This foam system has a foaming volume of 290mL and a foam half-life of 35min. Multi-functional foam stabilization is achieved by adding polymers and microspheres (particle size range between 10nm and 10μm), but the foaming and stabilizing effects are generally poor, and the preparation process is complex and relatively expensive.

[0005] Given the shortcomings of the above CO2 foam sealing and channeling methods, there is an urgent need to research and develop a CO2 flooding foam system, which is of great significance for oil reservoir development. Summary of the Invention

[0006] The main objective of this invention is to provide a CO2 flooding foam composition and its application, in order to solve the problem that the foaming and foam stabilization effects of existing CO2 flooding foam compositions are generally poor, resulting in low recovery rates during reservoir development.

[0007] To achieve the above objectives, the present invention provides a CO2 oil displacement foam composition, comprising, by weight, 0.1 to 1.5 parts of a foaming agent, 0.1 to 3 parts of a foam stabilizer, and 95.5 to 99.8 parts of water; wherein the foaming agent is selected from a mixture of anionic and nonionic surfactants; the foam stabilizer is selected from grafted modified nanocellulose; the grafted modified nanocellulose includes grafting groups, which are selected from one or more of the group consisting of amino, ester, carbonyl, and carboxyl groups, and the content of grafting groups in the grafted modified nanocellulose is 1.5 to 2.0 mmol / g.

[0008] Furthermore, by weight, the CO2 oil displacement foam composition comprises 0.2 to 1 part foaming agent, 0.1 to 1 part foam stabilizer, and 98 to 99.7 parts water.

[0009] Furthermore, in the foaming agent, the weight ratio of anionic surfactant to nonionic surfactant is (0.1-1):(0.1-0.5).

[0010] Furthermore, the anionic surfactant is selected from one or more of the group consisting of sulfate compounds, sulfonate compounds, sulfate ester compounds, and carboxylate compounds; the nonionic surfactant is selected from one or more of the group consisting of fatty alcohol polyoxyethylene ether, fatty alcohol polyoxypropylene polyoxyethylene ether, fatty alcohol polyoxyethylene polyoxypropylene ether, and alkyl glycoside compounds.

[0011] Furthermore, the anionic surfactant is selected from sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and C. 12 ~C 18 Sodium fatty alcohol hydroxyethyl sulfonate, sodium dodecyl alcohol polyoxyethylene ether sulfate, C 14 ~C 18 One or more of the group consisting of sodium α-olefin sulfonate and sodium oleate.

[0012] Furthermore, the nonionic surfactant is selected from C 12 ~C 18 Fatty alcohol polyoxyethylene ether, C 13 ~C 15 Fatty alcohol polyoxypropylene polyoxyethylene ether, C 10 ~C 16 Fatty alcohol polyoxyethylene polyoxypropylene ether, C8~C 16 One or more of the group consisting of alkyl glycosides.

[0013] Furthermore, the grafted modified nanocellulose includes grafted side chains with a molecular weight of 60.1–302.4 g / mol.

[0014] Furthermore, the nanocellulose is modified using a modifier via Schiff base method, esterification reaction method, or nucleophilic substitution reaction method to obtain grafted modified nanocellulose.

[0015] Furthermore, the modifier is selected from polyurethane, 2,3-epoxypropyltrimethylammonium chloride, 3-hydroxybutyrate, C3-C7 acetate, maleate, C... 15 ~C 20 One or more of the group consisting of alkenyl succinic anhydride, ethylenediamine, and 2,2,6,6-tetramethylpiperidine oxide.

[0016] Furthermore, the weight ratio of nanocellulose to modifier is (1-5):(2-10).

[0017] Furthermore, the grafted modified nanocellulose has a diameter of 10–300 nm and a length of 0.5–20 μm.

[0018] To achieve the above objectives, another aspect of the present invention provides the application of the CO2 flooding foam composition provided in this application in oil reservoir development.

[0019] Applying the technical solution of this invention, the CO2 flooding foam composition provided in this application includes specific types of foaming agents and foam stabilizers. Compared to using a single-component foaming agent, this application uses a mixture of anionic and nonionic surfactants, which can exert a synergistic effect, thereby improving the foam performance of the CO2 flooding foam composition. Using grafted modified nanocellulose as a foam stabilizer can exert its thickening effect and slow down the precipitation rate of liquid inside the foam; simultaneously, because grafted modified nanocellulose has the aforementioned specific chemical groups, it has good affinity with CO2, allowing it to adsorb onto the surface of the bubbles. This results in the CO2 flooding foam system formed by the CO2 flooding foam composition having high network structure strength and good shear resistance, thereby enhancing the strength of the liquid film and maintaining a stable liquid film balance during reservoir development. Moreover, grafted modified nanocellulose is derived from biomaterials and is easily degradable. Compared to using other chemical products or inorganic solid particles as foam stabilizers, grafted modified nanocellulose can significantly reduce the damage to the reservoir when using the flooding foam composition for reservoir development, making it environmentally friendly. In addition, the grafted modified nanocellulose has a diameter at the nanometer level, which can solve the problem of limited application of polymers or large solid particles.

[0020] Compared to other ranges, limiting the content of grafting groups in grafted modified nanocellulose to the range described above in this application is beneficial to improving its thickening effect, slowing down the precipitation rate of liquid inside the foam, improving the strength and shear resistance of the network structure in the CO2 oil displacement foam system, and improving the strength of the liquid film. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 The relationship between the viscosity of the foam solution prepared in Example 1 and Comparative Example 1 of the present invention and the shear rate is shown.

[0023] Figure 2 The viscoelastic properties of the foam solution prepared in Example 1 of the present invention at different shear frequencies are shown. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0025] As described in the background section, existing CO2 flooding foam compositions generally have poor foaming and foam stabilizing effects, leading to low oil recovery rates during reservoir development. To address these technical problems, this application provides a CO2 flooding foam composition comprising, by weight, 0.1–1.5 parts of a foaming agent, 0.1–3 parts of a foam stabilizer, and 95.5–99.8 parts of water; wherein the foaming agent is selected from a mixture of anionic and nonionic surfactants; the foam stabilizer is selected from grafted modified nanocellulose; the grafted modified nanocellulose includes grafting groups selected from one or more of the group consisting of amino, ester, carbonyl, and carboxyl groups, and the content of grafting groups in the grafted modified nanocellulose is 1.5–2.0 mmol / g.

[0026] The CO2 flooding foam composition provided in this application includes specific types of foaming agents and foam stabilizers. Compared to using a single-component foaming agent, this application uses a mixture of anionic and nonionic surfactants, which can exert a synergistic effect to improve the foam performance of the CO2 flooding foam composition. Using grafted modified nanocellulose as a foam stabilizer can exert its thickening effect and slow down the rate of liquid precipitation inside the foam. Simultaneously, because grafted modified nanocellulose possesses the aforementioned specific chemical groups, it has a good affinity for CO2, allowing it to adsorb onto the surface of the bubbles. This results in a CO2 flooding foam system with high network structure strength and good shear resistance, thereby enhancing the strength of the liquid film and maintaining its stable equilibrium during reservoir development. Furthermore, grafted modified nanocellulose is derived from biomaterials and is easily degradable. Compared to using other chemical products or inorganic solid particles as foam stabilizers, grafted modified nanocellulose can significantly reduce reservoir damage during reservoir development using the flooding foam composition, making it environmentally friendly. In addition, the grafted modified nanocellulose has a diameter at the nanometer level, which can solve the problem of limited application of polymers or large solid particles.

[0027] Compared to other ranges, limiting the content of grafting groups in grafted modified nanocellulose to the range described above in this application is beneficial to improving its thickening effect, slowing down the precipitation rate of liquid inside the foam, improving the strength and shear resistance of the network structure in the CO2 oil displacement foam system, and improving the strength of the liquid film.

[0028] In summary, with the vigorous promotion of the national CCUS (Carbonized Oil Flooding) goals, CCUS-EOR technology has become one of the important technologies for CO2 utilization and storage. The CO2 flooding foam composition provided in this application is of great significance for the efficient utilization of CO2 and has a very broad application prospect.

[0029] In a preferred embodiment, the CO2 flooding foam composition comprises, by weight, 0.2 to 1 part foaming agent, 0.1 to 1 part foam stabilizer, and 98 to 99.7 parts water. The weight percentages of the foaming agent, foam stabilizer, and water include, but are not limited to, the ranges described above. Limiting these percentages to the ranges facilitates the synergistic effect of anionic and nonionic surfactants, further improving the foam performance of the CO2 flooding foam composition. Simultaneously, it also facilitates better utilization of the thickening effect of grafted modified nanocellulose, further slows down the rate of liquid precipitation within the foam, further enhances the strength of the network structure in the CO2 flooding foam system, further improves shear resistance, and consequently enhances the strength of the liquid film, maintaining a stable liquid film balance during reservoir exploitation.

[0030] In a preferred embodiment, the weight ratio of anionic surfactant to nonionic surfactant in the foaming agent is (0.1-1):(0.1-0.5). The weight ratio of anionic surfactant to nonionic surfactant includes, but is not limited to, the above range. Limiting it to this range is beneficial for further enhancing the synergistic effect of the two surfactants, thereby further improving the foaming performance of the CO2 flooding foam composition and thus improving the oil recovery rate in reservoir development.

[0031] In a preferred embodiment, the anionic surfactant includes, but is not limited to, one or more of the group consisting of sulfate compounds, sulfonate compounds, sulfate ester compounds, and carboxylate compounds; the nonionic surfactant includes, but is not limited to, one or more of the group consisting of fatty alcohol polyoxyethylene ether, fatty alcohol polyoxypropylene polyoxyethylene ether, fatty alcohol polyoxyethylene polyoxypropylene ether, and alkyl glycoside compounds. Compared to other types, using the above-mentioned anionic and nonionic surfactants is beneficial to further enhance their synergistic effect, thereby further improving the foam performance of the CO2 flooding foam composition, and thus improving the oil recovery rate of reservoir development.

[0032] To further improve the foaming performance of the CO2 flooding foam composition, thereby further improving the oil recovery rate, preferably, the anionic surfactant includes, but is not limited to, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and C... 12 ~C 18 Sodium fatty alcohol hydroxyethyl sulfonate, sodium dodecyl alcohol polyoxyethylene ether sulfate, C 14 ~C 18 One or more of the group consisting of sodium α-olefin sulfonate and sodium oleate.

[0033] To further improve the foaming performance of the CO2 flooding foam composition, thereby further improving the oil recovery rate, preferably, the nonionic surfactant includes, but is not limited to, C 12 ~C 18 Fatty alcohol polyoxyethylene ether, C 13 ~C 15 Fatty alcohol polyoxypropylene polyoxyethylene ether, C 10 ~C 16 Fatty alcohol polyoxyethylene polyoxypropylene ether, C8~C 16 One or more of the group consisting of alkyl glycosides.

[0034] In a preferred embodiment, the grafted modified nanocellulose includes grafted side chains with a molecular weight of 60.1–302.4 g / mol. The molecular weight of the grafted side chains includes, but is not limited to, the above range. Limiting it to this range is beneficial for further improving its thickening effect, for further slowing down the precipitation rate of liquid inside the foam, and for further improving the strength and shear resistance of the network structure in the CO2-driven oil displacement foam system, thereby further improving the strength of the liquid film.

[0035] In a preferred embodiment, nanocellulose is modified using a modifier via Schiff base method, esterification reaction method or nucleophilic substitution reaction method to obtain grafted modified nanocellulose.

[0036] In a preferred embodiment, the modification process includes the following steps: ultrasonically treating the nanocellulose dispersion for 5 min; after ultrasonic treatment, mixing it with the modifier dispersion to obtain a reaction system; placing the reaction system at 40°C, continuously introducing nitrogen gas into the reaction system, and continuously stirring at a speed of 400-600 r / min for 0.5-1 h; then adding the reducing agent NaBH4, adjusting the speed to 200-500 r / min, continuously introducing nitrogen gas into the reaction system, and reacting for 5-6 h; after the reaction is completed, placing the entire reaction system into a dialysis bag and dialysis until neutral to obtain grafted modified nanocellulose.

[0037] In a preferred embodiment, the modifier includes, but is not limited to, polyurethane, 2,3-epoxypropyltrimethylammonium chloride, 3-hydroxybutyrate, 1,4-dioxane, C3-C7 acetate, maleate, trimethylsilane, and C... 15 ~C 20 One or more of the following groups are included: alkenyl succinic anhydride, ethylenediamine, and 2,2,6,6-tetramethylpiperidine oxide. Compared to other types, the use of the above-mentioned modifiers is beneficial for obtaining grafted modified nanocellulose with specific chemical groups, thereby further improving its thickening effect, further slowing down the precipitation rate of liquid inside the foam, further improving the strength and shear resistance of the network structure in the CO2 oil displacement foam system, and thus further improving the strength of the liquid film.

[0038] In a preferred embodiment, the weight ratio of nanocellulose to the modifier is (1-5):(2-10). The weight ratio of nanocellulose to the modifier includes, but is not limited to, the above range. Limiting it to the above range is beneficial to further improve its thickening effect, to further slow down the precipitation rate of liquid inside the foam, and to further improve the strength and shear resistance of the network structure in the CO2 oil displacement foam system, thereby further improving the strength of the liquid film.

[0039] In a preferred embodiment, the grafted modified nanocellulose has a diameter of 10–300 nm and a length of 0.5–20 μm. The diameter and length of the grafted modified nanocellulose include, but are not limited to, the above ranges. Limiting them to these ranges is beneficial for better exerting its thickening effect and also for broadening its application scope.

[0040] The second aspect of this application also provides an application of the CO2 flooding foam composition provided in this application in oil reservoir development. The CO2 flooding foam composition provided in this application has excellent foam performance, and the formed flooding foam system has high network structure strength and good shear resistance. Its application in oil reservoir development can improve oil recovery.

[0041] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0042] Example 1

[0043] A CO2-driven oil displacement foam composition comprising: 0.2 wt% SDS, 0.2 wt% C 14 The composition comprises alkyl glycosides (APG), 0.3 wt% grafted modified nanocellulose, and 99.3 wt% water. The grafted modified nanocellulose contains amino groups at a concentration of 1.58 mmol / g, has a molecular weight of 151 g / mol for the grafted branches, and exhibits a diameter of 50 nm and a length of 3 μm.

[0044] In this Example 1, the Schiff base method was used to modify nanocellulose with the modifier 2,3-epoxypropyltrimethylammonium chloride, including the following steps:

[0045] 50 mL of a 2 mg / mL nanocellulose dispersion (using deionized water as solvent) was sonicated for 5 min. After sonication, it was mixed with 40 mL of a 10 mg / mL aqueous solution of 2,3-epoxypropyltrimethylammonium chloride to obtain a reaction system. The reaction system was placed at 40 °C, and nitrogen gas was continuously introduced into the reaction system while stirring continuously at 400 r / min for 0.5 h. Then, 0.51 mol of NaBH4 was added, and the stirring speed was adjusted to 500 r / min. The reaction was carried out for 5 h. After the reaction was completed, the entire reaction system was placed in a dialysis bag and dialyzed until neutral to obtain grafted modified nanocellulose.

[0046] Example 2

[0047] A CO2-driven oil displacement foam composition comprising: 0.2 wt% SDS, 0.2 wt% C 18The ingredients are fatty alcohol polyoxyethylene ether, 0.3 wt% grafted modified nanocellulose, and 99.3 wt% water. The grafted modified nanocellulose is the same as in Example 1.

[0048] Example 3

[0049] A CO2-driven oil displacement foam composition comprising: 0.2 wt% SDBS, 0.2 wt% C 12 Alkyl glycoside (APG), 0.3 wt% grafted modified nanocellulose, and 99.3 wt% water. The grafted modified nanocellulose was the same as in Example 1.

[0050] Example 4

[0051] A CO2-driven oil displacement foam composition comprising: 0.2 wt% C 14 Sodium α-olefin sulfonate (AOS), 0.2 wt% C 12 Alkyl glycoside (APG) and 99.6 wt% water. The grafted modified nanocellulose was the same as in Example 1.

[0052] Example 5

[0053] A CO2-driven oil displacement foam composition comprising: 0.5 wt% SDS, 0.2 wt% C 14 Alkyl glycoside (APG), 0.3 wt% grafted modified nanocellulose, and 99.0 wt% water. The grafted modified nanocellulose was the same as in Example 1.

[0054] Example 6

[0055] A CO2-driven oil displacement foam composition comprising: 0.2 wt% SDS, 0.4 wt% C 14 Alkyl glycoside (APG), 0.3 wt% grafted modified nanocellulose, and 99.1 wt% water. The grafted modified nanocellulose was the same as in Example 1.

[0056] Example 7

[0057] A CO2-driven oil displacement foam composition comprising: 0.5 wt% SDS, 0.2 wt% C 14 Alkyl glycoside (APG), 0.5 wt% grafted modified nanocellulose, and 98.8 wt% water. The grafted modified nanocellulose was the same as in Example 1.

[0058] Example 8

[0059] The difference from Example 1 is that the total weight percentage of foaming agent in the CO2 oil displacement foam composition is 0.1 wt%, and the weight ratio of SDS to APG is 1:2.

[0060] Example 9

[0061] The difference from Example 1 is that the total weight percentage of foaming agent in the CO2 oil displacement foam composition is 1.5 wt%, and the weight ratio of SDS to APG is 2:1.

[0062] Example 10

[0063] The difference from Example 1 is that the weight percentage of grafted modified nanocellulose in the CO2 flooding foam composition is 0.1 wt%.

[0064] Example 11

[0065] The difference from Example 1 is that the grafted modified nanocellulose content in the CO2 oil displacement foam composition is 3 wt%.

[0066] Example 12

[0067] The difference from Example 1 is that only the amount of modifier is changed, so that the weight ratio of nanocellulose to modifier is 1:5, and the molecular weight of the grafted side chain of the obtained grafted modified nanocellulose is 60.1 g / mol.

[0068] Example 13

[0069] The difference from Example 1 is that only the amount of modifier is changed, so that the weight ratio of nanocellulose to modifier is 1:4, and the molecular weight of the grafted side chains of the obtained grafted modified nanocellulose is 302.4 g / mol.

[0070] Example 14

[0071] The difference from Example 1 is that only the amount of modifier is changed, so that the molar ratio of glucose units to modifier in nanocellulose is 1:1, and the molecular weight of the grafted side chains of the obtained grafted modified nanocellulose is 46.1 g / mol.

[0072] Comparative Example 1

[0073] The difference from Example 1 is that no grafted modified nanocellulose was added.

[0074] A CO2-driven oil displacement foam composition comprising: 0.2 wt% SDS, 0.2 wt% C 14 Alkyl glycosides (APG) and 99.6 wt% water.

[0075] Comparative Example 2

[0076] The difference from Example 2 is that no grafted modified nanocellulose was added.

[0077] A CO2-driven oil displacement foam composition comprising: 0.2 wt% SDS, 0.2 wt% C 18 Fatty alcohol polyoxyethylene ether and 99.6 wt% water.

[0078] Comparative Example 3

[0079] The difference from Example 3 is that no grafted modified nanocellulose was added.

[0080] A CO2-driven oil displacement foam composition comprising: 0.2 wt% SDBS, 0.2 wt% C 12 Alkyl glycosides (APG) and 99.6 wt% water.

[0081] Comparative Example 4

[0082] The difference from Example 4 is that no grafted modified nanocellulose was added.

[0083] A CO2-driven oil displacement foam composition comprising: 0.2 wt% C 14 Sodium α-olefin sulfonate (AOS), 0.2 wt% C 12 Alkyl glycosides (APG) and 99.6 wt% water.

[0084] Comparative Example 5

[0085] The difference from Example 1 is that C was not added. 18 Fatty alcohol polyoxyethylene ether uses SDS as a single foaming agent.

[0086] A CO2-driven oil displacement foam composition comprising: 0.4 wt% SDS and 99.6 wt% water.

[0087] (1) Foam preparation:

[0088] The common Waring Blender method was used for foam preparation. First, all components of the CO2 flooding foam compositions in the above-mentioned embodiments and comparative examples of this application were added to water according to the above-mentioned dosages, stirred evenly, and prepared into a 100 mL foam system mixture solution. Then, the foam system mixture solution was poured into a Wu Yin stirrer, and CO2 gas was continuously introduced. The mixture was sealed, and the stirring speed was set to 7000 r / min for 3 min. Under normal temperature and pressure, the foam in the Wu Yin stirrer was quickly poured into a 1000 mL graduated cylinder, and a stopwatch was started to record the foam volume V (mL). The time taken for half of the foam to disappear was recorded, i.e., the foam half-life T. 1 / 2 (min), and calculate the comprehensive foam index F by the relationship between foam volume and foaming time. c It is used to evaluate the overall performance of foam.

[0089] (2) Viscosity measurement:

[0090] The viscosity of a foam solution as a function of shear rate was measured at 25°C. Measurements were taken using an Anton Paar rheometer from 0.1 s⁻¹. -1 up to 1000s -1 The effect of shear rate on the viscosity of foam solution was investigated, and the performance of foam systems with and without modified nanocellulose was evaluated.

[0091] (3) Measurement of foam viscoelastic properties:

[0092] At 25°C, the viscoelastic properties of the foam solution at different shear frequencies were measured using an Anton Paar rheometer to evaluate the viscoelasticity of the foam system after the addition of grafted modified nanocellulose.

[0093] The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096] Figure 1 The viscosity of the foam solutions prepared in Example 1 and Comparative Example 1 as a function of shear rate is shown. Figure 1 It can be seen that the viscosity of the foam solution in both Example 1 and Comparative Example 1 gradually decreases with increasing shear rate. Comparing Example 1 and Comparative Example 1 in conjunction with... Figure 1 It can be seen that the viscosity of the system increases after introducing 0.3 wt% grafted modified nanocellulose into the system.

[0097] from Figure 2 It can be seen that the elastic modulus (G”) of the foam solutions prepared in Example 1 is higher than that of the viscous modulus (G’), indicating that the foam has better stability. Moreover, the elasticity of the foam solutions prepared in Example 1 is better than that of Comparative Example 1.

[0098] From the above description, it can be seen that the embodiments of the present invention achieve the following technical effects: Comparing Example 1 with Comparative Example 1, Example 2 with Comparative Example 2, Example 3 with Comparative Example 3, and Example 4 with Comparative Example 4, it is evident that the foam half-life is significantly increased after adding 0.3 wt% grafted modified nanocellulose, indicating that the introduction of grafted modified nanocellulose can exert its foam-stabilizing effect. The foaming performance of the foam system is slightly affected because the addition of the foam stabilizer increases the system viscosity, thus restricting foam formation.

[0099] The inventors discovered in their research that the composite system of anionic surfactant SDS and nonionic surfactant APG exhibits superior overall foam performance. Therefore, Examples 5 to 7 adjusted the dosage of each component in the CO2 flooding foam composition to optimize foam performance. The foam systems obtained in Examples 5 to 7 all have an overall foam index of approximately 20,000, indicating strong foam performance. Furthermore, the foam stability of the system is significantly improved by the grafted modified nanocellulose.

[0100] Comparing Example 1 and Comparative Example 5, it can be seen that, compared with the use of a single-component foaming agent, the present application uses a mixture of anionic and nonionic surfactants, which can exert the synergistic effect of the two, thereby improving the foam performance of the CO2 flooding foam composition.

[0101] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A CO2-driven oil displacement foam composition, characterized in that, The CO2 oil displacement foam composition comprises, by weight, 0.1 to 1.5 parts of foaming agent, 0.1 to 3 parts of foam stabilizer, and 95.5 to 99.8 parts of water; wherein the foaming agent is selected from a mixture of anionic and nonionic surfactants; the foam stabilizer is selected from grafted modified nanocellulose; the grafted modified nanocellulose includes grafting groups, which are selected from one or more of the group consisting of amino, ester, carbonyl, and carboxyl groups, and the content of the grafting groups in the grafted modified nanocellulose is 1.5 to 2.0 mmol / g.

2. The CO2 oil displacement foam composition according to claim 1, characterized in that, The CO2 oil displacement foam composition comprises, by weight, 0.2 to 1 part of the foaming agent, 0.1 to 1 part of the foam stabilizer, and 98 to 99.7 parts of the water.

3. The CO2 oil displacement foam composition according to claim 1 or 2, characterized in that, In the foaming agent, the weight ratio of the anionic surfactant to the nonionic surfactant is (0.1-1):(0.1-0.5).

4. The CO2 flooding foam composition according to any one of claims 1 to 3, characterized in that, The anionic surfactant is selected from one or more of the group consisting of sulfate compounds, sulfonate compounds, sulfate ester compounds, and carboxylate compounds; the nonionic surfactant is selected from one or more of the group consisting of fatty alcohol polyoxyethylene ether, fatty alcohol polyoxypropylene polyoxyethylene ether, fatty alcohol polyoxyethylene polyoxypropylene ether, and alkyl glycoside compounds. Preferably, the anionic surfactant is selected from sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and C. 12 ~C 18 Sodium fatty alcohol hydroxyethyl sulfonate, sodium dodecyl alcohol polyoxyethylene ether sulfate, C 14 ~C 18 One or more of the group consisting of sodium α-olefin sulfonate and sodium oleate; Preferably, the nonionic surfactant is selected from C 12 ~C 18 Fatty alcohol polyoxyethylene ether, C 13 ~C 15 Fatty alcohol polyoxypropylene polyoxyethylene ether, C 10 ~C 16 Fatty alcohol polyoxyethylene polyoxypropylene ether, C8~C 16 One or more of the group consisting of alkyl glycosides.

5. The CO2 oil displacement foam composition according to claim 4, characterized in that, The grafted modified nanocellulose includes grafted side chains, the molecular weight of which is 60.1–302.4 g / mol.

6. The CO2 oil displacement foam composition according to claim 5, characterized in that, The grafted modified nanocellulose is obtained by modifying nanocellulose with a modifier using the Schiff base method, esterification reaction method or nucleophilic substitution reaction method.

7. The CO2 oil displacement foam composition according to claim 6, characterized in that, The modifier is selected from polyurethane, 2,3-epoxypropyltrimethylammonium chloride, 3-hydroxybutyrate, 1,4-dioxane, C3-C7 acetate, maleate, trimethylsilane, C 15 ~C 20 One or more of the group consisting of alkenyl succinic anhydride, ethylenediamine, and 2,2,6,6-tetramethylpiperidine oxide.

8. The CO2 oil displacement foam composition according to claim 6, characterized in that, The weight ratio of the nanocellulose to the modifier is (1-5):(2-10).

9. The CO2 flooding foam composition according to any one of claims 1 to 8, characterized in that, The grafted modified nanocellulose has a diameter of 10–300 nm and a length of 0.5–20 μm.

10. The application of the CO2 flooding foam composition according to any one of claims 1 to 9 in oil reservoir development.

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