CO2 response foam plugging agent based on compounding of attapulgite and alkyl amidine as well as preparation method and application of CO2 response foam plugging agent

Abstract

The invention discloses a CO2 response foam plugging agent based on attapulgite and alkyl amidine compounding and a preparation method thereof.The CO2 response foam plugging agent is prepared from, by mass, 6-12 parts of modified attapulgite, 30-35 parts of alkyl amidine, 15-24 parts of betaine and 9-12 parts of polymer enhancer; wherein the alkyl amidine comprises at least one of long-chain alkyl amidine and aromatic cycloalkyl amidine. The CO2 response foam plugging agent based on the compounding of the attapulgite and the alkyl amidine has the characteristics of high foaming amount, strong foam stability, temperature resistance, salt resistance and the like.

Description

TECHNICAL FIELD

[0001] The present application generally relates to the technical field of oil extraction foam plugging agents, and particularly relates to a CO2-responsive foam plugging agent based on attapulgite and alkyl amidine, and a preparation method and application thereof. BACKGROUND

[0002] At present, under the background of international energy shortage, international society advocating energy saving and emission reduction, and oil extraction difficulty, major oilfields are actively upgrading technologies. CO2 flooding technology is mature and has been applied on a large scale. It can improve the recovery rate by more than 10% in the exploitation process of low permeability reservoirs, which has a positive significance for energy development. However, due to the existence of reservoir fractures, CO2 gas channeling along the fractures is inevitable in the process of CO2 flooding technology in field application, which not only reduces the recovery efficiency of CO2 to crude oil, resulting in unsatisfactory exploitation effect, but also causes environmental pollution due to CO2 emission.

[0003] In the prior art, the solution measure under the premise of environmental protection and no pollution to the formation is usually to plug the fractures with foam plugging agents, but the conventional plugging agents have problems such as low foaming amount and poor foam stability. In addition, it is also worth noting that the reservoir environment of most oilfields has the characteristics of high salinity, and the salinity generally reaches 1x10 5 ~3x10 5 mg / L, and some high-salt blocks even exceed 3x10 5 mg / L. The high-salt environment poses a severe challenge to the performance of foam plugging agents. The hydrophilic groups in the molecules of traditional surfactant-based foam plugging agents are easy to have charge interaction with Na + , Ca 2+ and other salt ions in the reservoir, resulting in shielding of surface charge and significant decrease in surface activity. In a high-salinity environment, not only does the foaming capacity of the foam plugging agent decrease (the foaming volume decreases by more than 30%), but also the mechanical strength of the foam film is weakened, the liquid drainage half-life is shortened by more than 50%, and the foam half-life is even reduced to less than 10 minutes, which cannot maintain the plugging structure for a long time, and CO2 gas channeling occurs again in a short time. At the same time, most surfactants are prone to precipitation under high-salt conditions, which are left in the formation pores, resulting in irreversible decrease in the permeability of the reservoir and causing additional formation damage. The conventional foam plugging agent is not designed to adapt to the high-salt reservoir environment, and it is difficult to meet the needs of actual high-salt reservoir applications.

[0004] Therefore, it is urgent to provide a new CO2-responsive foam plugging agent scheme in order to improve the foam plugging effect, improve the foam stability, avoid oil layer pollution and formation plugging, and at the same time be suitable for high-salt reservoir application environment. SUMMARY

[0005] To solve at least one or more technical problems as mentioned above, the present application proposes, in multiple aspects, a CO2-responsive foam plugging agent based on attapulgite and alkyl amidine and a preparation method thereof.

[0006] In a first aspect, the present application provides a CO2-responsive foam plugging agent based on attapulgite and alkyl amidine, which comprises, in mass parts, 6-12 parts of modified attapulgite, 30-35 parts of alkyl amidine, 15-24 parts of betaine, and 9-12 parts of a polymer reinforcing agent; wherein the alkyl amidine comprises at least one of long-chain alkyl amidine and aromatic ring alkyl amidine.

[0007] In some embodiments, the alkyl amidine comprises at least one of N'-long-chain alkyl-N,N-diethyl ethyl amidine and N'-(4-alkyl benzene)-N,N-dimethyl amidine.

[0008] In other embodiments, the modified attapulgite is attapulgite surface-modified by dodecyltrimethoxysilane and / or hexadecyltrimethoxysilane.

[0009] In yet other embodiments, the modified attapulgite has a water phase contact angle of 70°-90°.

[0010] In some embodiments, the betaine comprises dodecyl dimethyl betaine; and / or the polymer reinforcing agent comprises polyacrylamide with a molecular weight of 5 million to 8 million.

[0011] In a second aspect, the present application provides a preparation method of the CO2-responsive foam plugging agent as described in any one of the first aspect of the present application, comprising: mixing 6-12 parts of modified attapulgite and 30-35 parts of alkyl amidine in mass parts, and reacting at a first temperature to obtain a complex intermediate; mixing the complex intermediate with 15-24 parts of betaine and 9-12 parts of a polymer reinforcing agent in mass parts to obtain the CO2-responsive foam plugging agent.

[0012] In some embodiments, the preparation method further comprises: mixing attapulgite powder with a 2%-4% volume fraction of a silane coupling agent aqueous solution to obtain a mixture; placing the mixture in a constant-temperature water bath at 60°C-65°C, continuously stirring at a speed of 200 rpm-300 rpm for 4-6 hours, and then filtering, washing, and drying to obtain modified attapulgite with a water phase contact angle in the range of 70°-90°.

[0013] In other embodiments, the silane coupling agent in the silane coupling agent aqueous solution comprises dodecyltrimethoxysilane and / or hexadecyltrimethoxysilane.

[0014] In yet some embodiments, the preparation method further comprises: mixing the modified palygorskite with the alkyl amidine, and after ultrasonic dispersion, stirring and reacting at the first temperature for a first time length, wherein the first temperature is 40-45°C, and the first time length is 1-2h.

[0015] In some embodiments, the preparation method further comprises: mixing the compounded intermediate with the betaine and the polymer reinforcing agent, and after stirring and reacting at 40-45°C for 30-35min, obtaining the CO2-responsive foam plugging agent.

[0016] In a third aspect, the application relates to the use of the CO2-responsive foam plugging agent based on the combination of palygorskite and alkyl amidine in CO2 flooding technology.

[0017] By means of the CO2-responsive foam plugging agent based on the combination of palygorskite and alkyl amidine and the preparation method thereof, the present application can improve the foaming capacity of the foam plugging agent by utilizing the good surface performance and stability of the modified palygorskite, and improve the salt resistance of the foam plugging agent by utilizing the structural characteristics of the modified palygorskite; meanwhile, the foam plugging agent can further enhance the adsorption capacity at the gas-liquid interface, improve the foam stability and temperature resistance and salt resistance by combining the low surface tension of betaine and the tackiness of the polymer reinforcing agent. In addition, palygorskite is widely available and low in cost, and the material is biodegradable, which meets the demand of green exploitation, so the prepared CO2-responsive foam plugging agent also has the characteristics of environmental protection and easy degradation. BRIEF DESCRIPTION OF DRAWINGS

[0018] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description read in conjunction with the accompanying drawings, in which several embodiments of the present application are illustrated by way of example and not limitation. In the drawings, like reference numerals refer to like elements throughout, and:

[0019] Figure 1 An exemplary flow chart of the preparation method of the CO2-responsive foam plugging agent of the present application is shown. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0021] It should be understood that the terms "comprises" and "comprising," when used in the specification and claims of this application, indicate the presence of the described features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0022] It should also be understood that the terms used in the specification and the claims are for the purpose of describing specific embodiments and are not intended to limit the application. As used in this specification and the claims, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "and / or," as used herein, refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0023] The specific embodiments of the present application will be described in detail below with reference to the attached drawings.

[0024] In a first aspect, the present application provides a CO2-responsive foam plugging agent based on attapulgite and alkyl amidine, the CO2-responsive foam plugging agent comprising, in mass fraction: modified attapulgite 6-12 parts, alkyl amidine 30-35 parts, betaine 15-24 parts, and polymer reinforcing agent 9-12 parts; wherein the alkyl amidine comprises at least one of long-chain alkyl amidine and aromatic ring alkyl amidine.

[0025] Exemplarily, the modified attapulgite can be, for example, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, or 12 parts, etc. Exemplarily, the betaine can be 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, 21 parts, 22 parts, 23 parts, or 24 parts, etc.

[0026] Attapulgite is a natural clay mineral, and modified attapulgite is obtained after surface modification. In some embodiments, the modified attapulgite can be attapulgite surface-modified by dodecyltrimethoxysilane and / or hexadecyltrimethoxysilane. The dodecyltrimethoxysilane and / or hexadecyltrimethoxysilane undergoes a hydrolysis condensation reaction with the hydroxyl groups on the surface of the attapulgite, successfully introducing long-chain alkyl groups onto the surface of the attapulgite particles, forming a hydrophobic functional layer, and converting the attapulgite particles from strong hydrophilicity to partial neutrality, achieving hydrophobic modification of the surface of the attapulgite particles.

[0027] Attapulgite is a 2:1 type layered magnesium aluminosilicate with a needle-like / fibrous crystal structure and a high density of surface hydroxyl (-OH) groups. Here, "2:1 type layered magnesium aluminosilicate" refers to a "sandwich" structure where each basic structural unit layer consists of two silicon-oxygen tetrahedral sheets (T-sheets) and one magnesium-aluminum-oxygen octahedral sheet (O-sheet) covalently bonded together. After modification with silane coupling agents (DTMS / HDTMS), attapulgite exhibits a high density of long-chain alkyl grafts, resulting in a denser hydrophobic layer. This allows for more robust anchoring of the oil-water interface in high-salt environments, reducing the damage to the interfacial film caused by salt ions. Experiments have shown that when the salinity increases to 2 × 10⁻⁶, the... 5 At a concentration of mg / L (high salt conditions), the modified attapulgite system of the present invention can still maintain a high emulsification index of 88.8%, and the droplets do not coalesce, indicating that the modified attapulgite system of the present invention has excellent salt resistance.

[0028] In other embodiments, the aqueous contact angle of the modified attapulgite is 70° to 90°. Modified attapulgite with this range of aqueous contact angles exhibits enhanced hydrophobicity, allowing for better adsorption at the gas-liquid interface, strengthening the foam film, and thus improving its role in stabilizing the foam structure. Simultaneously, this contact angle range balances hydrophobicity and compatibility with the liquid system, avoiding dispersion problems of the modified attapulgite in the plugging agent compound system due to excessive hydrophobicity.

[0029] Alkyl amidines are a class of organic compounds with a nitrogen atom bonded to two alkyl or aryl groups. Alkyl amidines exhibit good lipophilicity, reducing surface tension, promoting foam formation, and serving as the main component of foam, thus contributing to increased foam volume. Long-chain alkyl amidines refer to alkyl amidines with a relatively long carbon chain (usually at least 12 carbon atoms) in the alkyl portion; this structure makes them excellent at reducing liquid surface tension and improving foam stability. Aromatic alkyl amidines, on the other hand, introduce an aromatic ring (such as a benzene ring) into the structure of alkyl amidines, making the molecular structure more stable. This is similar to adding protection at the "spearhead" position of long-chain alkyl amidines, enhancing their durability and stability under specific conditions.

[0030] In some embodiments, the long-chain alkyl amidine may include, for example, N'-long-chain alkyl-N,N-diethylacetamidine, which has the following structural formula:

[0031] (Structure 1);

[0032] Where R is C n H 2n+1 n is an integer between 8 and 14.

[0033] In other embodiments, the aromatic alkylamidinium may include, for example, N'-(4-alkylbenzene)-N,N-dimethylamidinium, which has the following structural formula:

[0034] (Structure 2);

[0035] Where R1 is C 12 -C 18 The alkyl group, where R2 is H or -CH3.

[0036] In some embodiments, the alkylamidine includes long-chain alkylamidine and aromatic alkylamidine, such as N'-long-chain alkyl-N,N-diethylacetamidine and N'-(4-alkylbenzene)-N,N-dimethylamidine. Simultaneous use of both long-chain alkylamidine and aromatic alkylamidine allows for increased foaming volume due to the low surface tension of the long-chain alkylamidine, while the rigid structure of the aromatic alkylamidine enhances foam stability. This combination provides complementary advantages in foam formation and maintenance, further improving the foam system's foaming volume, stability, and adaptability to complex environments. In some preferred embodiments, the mass ratio of long-chain alkylamidine to aromatic alkylamidine is 1:1, thereby fully leveraging their synergistic effect.

[0037] Betaine can further reduce the surface tension of foam plugging agents, helping to form a stable foam layer while enhancing the plugging agent's adsorption capacity to fractures. In some embodiments, betaine includes dodecyl dimethyl betaine. Dodecyl dimethyl betaine has a moderate carbon chain length, which, while reducing surface tension, also maintains good solubility and spreadability, allowing the foam plugging agent to perform better in complex reservoir environments. Furthermore, dodecyl dimethyl betaine is environmentally friendly and meets the requirements of sustainable development.

[0038] Furthermore, in the foam plugging agent system of this application, the addition of betaine can further optimize the gas-liquid interface performance and help ensure the salt resistance of the system. Specifically, the anionic and cationic groups of dodecyl dimethyl betaine form a stable "internal salt structure" through intramolecular electrostatic interactions, Na... + Ca 2+ It is difficult for cations to destroy its molecular integrity, even in mineralization > 2 × 10 5Even in high-salt environments (mg / L), no precipitation or deactivation occurs, and surface activity is maintained continuously. The long-chain alkyl group (dodecyl) of betaine can synergistically adsorb with the hydrophobic chains on the modified attapulgite surface, forming a "particle-surfactant" composite interfacial layer on the foam film surface. This layer is dense and hydrophobic, physically blocking salt ions from penetrating into the membrane and preventing salt ions from damaging the double-layer structure of the foam film. The hydrophilic groups of betaine (quaternary ammonium salt + carboxyl group) can anchor the aqueous phase, maintaining stable gas-liquid interfacial tension even under high salt conditions, reducing foam rupture caused by interfacial tension fluctuations.

[0039] Polymer reinforcing agents can increase the viscosity and stability of foam sealing agents, improve the temperature and salt resistance of foam, and prevent premature foam breakage. The amide groups (-CONH2) of polyacrylamide can form hydrogen bonds with the hydroxyl groups (-OH) on the surface of modified attapulgite, constructing a three-dimensional network structure of "polyacrylamide-modified attapulgite" in the foam system. This three-dimensional network structure can physically block salt ions from entering the foam film, preventing salt ions from compressing the double layer and damaging the film structure; simultaneously, the three-dimensional network structure enhances the mechanical strength of the foam film to support its morphology and delay foam breakage. In some embodiments, the polymer reinforcing agent includes polyacrylamide with a molecular weight of 5 million to 8 million. Polyacrylamide with a molecular weight of 5 million to 8 million can achieve a balance between thickening and solubility, providing good reinforcing effects without significantly increasing costs.

[0040] If the molecular weight is below 5 million, the chain segments are too short, resulting in insufficient thickening properties of polyacrylamide. In high-salt environments, chain segment contraction is easily caused by the "salting-out effect," leading to a sharp drop in thickening effect and an inability to inhibit rapid drainage of the foam film, thus affecting the stability, temperature resistance, and salt tolerance of the foam plugging agent. If the molecular weight is above 8 million, the chain segments are too long, making inter-chain aggregation prone to occur in high-salt conditions. This results in excessively high system viscosity, reduced fluidity, and poor solubility, hindering foam formation and affecting foam permeability, which is detrimental to foam sealing of reservoir fractures. Therefore, a molecular weight range of 5 million to 8 million, with moderate chain segment length, is the preferred range for polyacrylamide to achieve ideal thickening effects in foam systems, while avoiding aggregation, ensuring system dispersibility, and meeting the performance requirements of foam plugging agents.

[0041] As described above, the CO2-responsive foam plugging agent of this application achieves the technical effects of increasing foaming volume, enhancing adsorption capacity, and improving foam stability, permeability, and temperature and salt resistance through the synergistic effect of its components, such as utilizing the surface properties and stability of modified attapulgite, the foaming properties of alkyl amidine, the low surface tension and amphoteric structure of betaine to provide physical anchoring for modified attapulgite, constructing a composite interface film with modified attapulgite to achieve anti-salt precipitation, the thickening properties of polymer reinforcing agents, and combining modified attapulgite to enhance the support of the foam film.

[0042] Furthermore, the proportions of the components in the CO2-responsive foam plugging agent of this application have been optimized, resulting in significant beneficial effects. Specifically, the addition of small amounts of modified attapulgite and polymer reinforcing agents enhances adsorption capacity without significantly increasing viscosity; alkyl amidine, as the main component, provides sufficient foaming power; and an appropriate amount of betaine optimizes foaming capacity, preventing the foam film from becoming too thin.

[0043] In a second aspect, this application also provides a method for preparing a CO2-responsive foam plugging agent, to obtain the aforementioned CO2-responsive foam plugging agent. The following will be combined with... Figure 1 Describe it.

[0044] Figure 1 An exemplary flowchart illustrating a method for preparing a CO2-responsive foam plugging agent according to an embodiment of this application is shown. Figure 1 As shown, the preparation method 100 may include: step S102, mixing 6-12 parts by weight of modified attapulgite and 30-35 parts by weight of alkylamidine, and reacting at a first temperature to obtain a compound intermediate; step S104, mixing the compound intermediate with 15-24 parts by weight of betaine and 9-12 parts by weight of polymer reinforcing agent to obtain a CO2-responsive foam plugging agent.

[0045] In some embodiments, in step S102, the modified attapulgite is mixed with alkylamidine and ultrasonically dispersed, then stirred and reacted at a first temperature for a first duration, wherein the first temperature is 40°C to 45°C and the first duration is 1 to 2 hours. In other embodiments, in step S102, ultrasonic dispersion is performed for 20 minutes, and the stirring speed during the reaction is 400 rpm.

[0046] In other embodiments, in step S104, the compound intermediate is mixed with betaine and a polymer reinforcing agent, and the mixture is stirred at 40°C to 45°C for 30 to 35 minutes to obtain a CO2-responsive foam blocker. In some embodiments, the stirring speed in step S104 is 400 rpm.

[0047] In the preparation method of this application, the components used to prepare the CO2-responsive foam plugging agent are mixed in a stepwise manner. Firstly, this ensures that the modified attapulgite and alkylamidine are thoroughly and uniformly mixed to form a stable alkylated layer, enhancing the surface properties of the compound intermediate. Secondly, adding betaine and the polymer reinforcing agent after obtaining the compound intermediate avoids interference with the modified attapulgite and alkylamidine. Furthermore, stepwise mixing allows for better control of the reaction conditions at each step, improving the accuracy of the reaction and the consistency of product performance, facilitating stable control in industrial production.

[0048] Furthermore, in some embodiments, before step S102, the preparation method 100 may further include: mixing attapulgite powder with a 2%~4% volume fraction of silane coupling agent aqueous solution to obtain a mixture; placing the mixture in a constant temperature water bath at 60℃~65℃ and stirring continuously at a speed of 200rpm~300rpm for 4h~6h; and after filtration, washing, and drying, obtaining modified attapulgite with an aqueous phase contact angle of 70°~90°.

[0049] In other embodiments, the silane coupling agent in the aqueous solution of the silane coupling agent includes dodecyltrimethoxysilane and / or hexadecyltrimethoxysilane.

[0050] In the preparation of the modified attapulgite described above, the silane coupling agent reacts with the hydroxyl groups on the surface of attapulgite to form chemical bonds, thereby introducing organic groups onto the surface of the attapulgite. Sufficient contact and reaction between the silane coupling agent and the attapulgite surface can be promoted by continuously stirring the mixture at 200 rpm in a 60°C constant-temperature water bath for 4 hours. The 60°C temperature helps accelerate the hydrolysis and condensation reactions of the silane coupling agent, while continuous stirring ensures the uniformity of the reaction.

[0051] Understandably, factors such as the type and concentration of the silane coupling agent, fluctuations in the water bath temperature, and stirring time can all affect the aqueous contact angle of modified attapulgite. For example, under the same conditions, attapulgite modified with hexadecyltrimethoxysilane (HDTMS) has a higher aqueous contact angle than attapulgite modified with dodecyltrimethoxysilane (DTMS) or a mixture of DTMS and HDTMS, due to its longer carbon chains and denser hydrophobic layer. Furthermore, among the modification process parameters, the amount of silane coupling agent, stirring time (i.e., reaction time), and stirring speed also have a significant impact on the modification of attapulgite. For instance, increasing the amount of silane coupling agent helps to improve the aqueous contact angle of modified attapulgite; ensuring a certain stirring time helps to ensure sufficient grafting of long carbon chain molecules; and a high stirring speed can break up attapulgite powder agglomeration to ensure uniform grafting of the silane coupling agent.

[0052] In addition, the 2% volume fraction silane concentration selected in this application is an optimized value that balances grafting efficiency and avoids self-polymerization, ensuring sufficient grafting of hydrophobic groups; the 60℃ constant temperature water bath used is the optimal temperature window for silane hydrolysis and condensation, avoiding insufficient reaction due to excessively low temperature or self-polymerization due to excessively high temperature.

[0053] The combined effect of these factors ensures that the aqueous contact angle of the modified attapulgite remains stable at 70°~90°, satisfying the hydrophobicity requirement to stabilize the foam while also guaranteeing its dispersibility in the plugging agent system.

[0054] Example 1:

[0055] Step 1) Preparation of modified attapulgite: Take 10.000g of attapulgite powder and add an aqueous solution (total volume 100mL) containing 2% volume fraction of silane coupling agent (HDTMS). Stir at 200rpm for 4h in a constant temperature water bath at 60℃. After the reaction is complete, filter the product, wash it three times with deionized water, dry it at 60℃ for 1h, and grind it to obtain modified attapulgite with an aqueous phase contact angle of 70.6°.

[0056] Step 2) Modified attapulgite and alkylamidine compound: Take 0.6g of the modified attapulgite prepared in step 1) and mix it with 3g of N'-octyl-N,N-diethyl acetamidine. After ultrasonic dispersion for 20min, heat to 40℃ and stir at 400rpm for 1h. After cooling, the compound intermediate is obtained.

[0057] Step 3) Preparation of CO2-responsive foam blocker: Add 0.9g of polyacrylamide (molecular weight 5 million) and 1.5g of dodecyl dimethyl betaine to the compound intermediate, and stir at 400rpm for 30min at 40℃ to obtain CO2-responsive foam blocker.

[0058] Example 2:

[0059] Step 1) Preparation of modified attapulgite: Take 10.000g of attapulgite powder and add it to an aqueous solution containing 3% (v / v) HDTMS (total volume 100mL). Stir at 220rpm for 4.5h in a constant temperature water bath at 62℃. After the reaction is complete, filter the product, wash it three times with deionized water, dry it at 60℃ for 1h, and grind it to obtain modified attapulgite with an aqueous phase contact angle of 79.2°.

[0060] Step 2) Modified attapulgite and alkylamidine compound: Take 0.8g of the modified attapulgite prepared in step 1) and mix it with 3.1g of N'-decyl-N,N-diethyl acetamidine. After ultrasonic dispersion for 20min, heat to 41℃ and stir at 400rpm for 1h. After cooling, the compound intermediate is obtained.

[0061] Step 3) Preparation of CO2-responsive foam blocker: Add 1.0g polyacrylamide (molecular weight 6 million) and 1.8g dodecyl dimethyl betaine to the compound intermediate, and stir at 400rpm for 31min at 41℃ to obtain CO2-responsive foam blocker.

[0062] Example 3:

[0063] Step 1) Preparation of modified attapulgite: Take 10.000g of attapulgite powder and add it to an aqueous solution containing 3% HDTMS (total volume 100mL). Stir at 240rpm for 4h in a constant temperature water bath at 63℃. After the reaction is complete, filter the product, wash it three times with deionized water, dry it at 60℃ for 1h, and grind it to obtain modified attapulgite with an aqueous phase contact angle of 83.6°.

[0064] Step 2) Modified attapulgite and alkylamidine compound: Take 1.0g of the modified attapulgite prepared in step 1) and mix it with 3.2g of N'-dodecyl-N,N-diethyl acetamidine. After ultrasonic dispersion for 20min, heat to 42℃ and stir at 400rpm for 1.5h. After cooling, the compound intermediate is obtained.

[0065] Step 3) Preparation of CO2-responsive foam blocker: Add 1.0g polyacrylamide (molecular weight 7 million) and 2.0g dodecyl dimethyl betaine to the compound intermediate, and stir at 400rpm for 32min at 42℃ to obtain CO2-responsive foam blocker.

[0066] Example 4:

[0067] Step 1) Preparation of modified attapulgite: Take 10.000g of attapulgite powder and add it to an aqueous solution containing 3% (v / v) HDTMS (total volume 100mL). Stir at 260rpm for 5h in a constant temperature water bath at 64℃. After the reaction is complete, filter the product, wash it three times with deionized water, dry it at 60℃ for 1h, and grind it to obtain modified attapulgite with an aqueous phase contact angle of 85.1°.

[0068] Step 2) Modified attapulgite and alkylamidine compound: Take 1.0g of the modified attapulgite prepared in step 1) and mix it with 3.3g of N'-tetradecyl-N,N-diethyl acetamidine. After ultrasonic dispersion for 20min, heat to 43℃ and stir at 400rpm for 1.5h. After cooling, the compound intermediate is obtained.

[0069] Step 3) Preparation of CO2-responsive foam blocker: Add 1.1g of polyacrylamide (molecular weight 8 million) and 2.2g of dodecyl dimethyl betaine to the compound intermediate, and stir at 400rpm for 33min at 43℃ to obtain CO2-responsive foam blocker.

[0070] Example 5:

[0071] Step 1) Preparation of modified attapulgite: Take 10.000g of attapulgite powder and add it to an aqueous solution containing 4% HDTMS (total volume 100mL). Stir at 280rpm for 5h in a constant temperature water bath at 64℃. After the reaction is complete, filter the product, wash it three times with deionized water, dry it at 60℃ for 1h, and grind it to obtain modified attapulgite with an aqueous phase contact angle of 87.8°.

[0072] Step 2) Modified attapulgite and alkylamidine compound: Take 1.2g of the modified attapulgite prepared in step 1) and mix it with 3.4g of N'-(4-dodecylbenzene)-N,N-dimethylamidine. After ultrasonic dispersion for 20min, heat to 44℃ and stir at 400rpm for 2h. After cooling, the compound intermediate is obtained.

[0073] Step 3) Preparation of CO2-responsive foam blocker: Add 1.1g of polyacrylamide (molecular weight 8 million) and 2.4g of dodecyl dimethyl betaine to the compound intermediate, and stir at 400rpm for 34min at 44℃ to obtain CO2-responsive foam blocker.

[0074] Example 6:

[0075] Step 1) Preparation of modified attapulgite: Take 10.000g of attapulgite powder and add it to an aqueous solution containing 4% HDTMS (total volume 100mL). Stir at 300rpm for 6h in a constant temperature water bath at 65℃. After the reaction is complete, filter the product, wash it three times with deionized water, dry it at 60℃ for 1h, and grind it to obtain modified attapulgite with an aqueous phase contact angle of 89.9°.

[0076] Step 2) Modified attapulgite and alkylamidine compound: Take 1.2g of the modified attapulgite prepared in step 1) and mix it with 3.5g of N'-(4-octadecylbenzene)-N,N-dimethylamidine. After ultrasonic dispersion for 20min, heat to 45℃ and stir at 400rpm for 2h. After cooling, the compound intermediate is obtained.

[0077] Step 3) Preparation of CO2-responsive foam blocker: Add 1.2g of polyacrylamide (molecular weight 8 million) and 2.4g of dodecyl dimethyl betaine to the compound intermediate, and stir at 400rpm for 35min at 45℃ to obtain CO2-responsive foam blocker.

[0078] Comparative Example 1:

[0079] Step 1) Unmodified attapulgite: Take 10.000g of attapulgite powder, add it to 100mL of pure water, and stir at 200rpm for 4h in a constant temperature water bath at 60℃. Filter, dry at 60℃ for 1h, and grind to obtain attapulgite with an aqueous contact angle of 23.2°.

[0080] Step 2) Attachment stone and alkylamidine compound: Take 0.6g of unmodified attapulgite from Step 1) and mix it with 3g of N'-octyl-N,N-diethyl acetamidine. After ultrasonic dispersion for 20min, heat to 40℃ and stir at 400rpm for 1h. After cooling, the compound intermediate is obtained.

[0081] Step 3) Preparation of CO2-responsive foam blocker: Add 0.9g of polyacrylamide (molecular weight 5 million) and 1.5g of dodecyl dimethyl betaine to the compound intermediate, and stir at 400rpm for 30min at 40℃ to obtain CO2-responsive foam blocker.

[0082] Comparative Example 2:

[0083] Step 1) Preparation of modified attapulgite: Take 10.000g of attapulgite powder and add it to an aqueous solution containing 3% (v / v) HDTMS (total volume 100mL). Stir at 220rpm for 4.5h in a constant temperature water bath at 62℃. After the reaction is complete, filter the product, wash it three times with deionized water, dry it at 60℃ for 1h, and grind it to obtain modified attapulgite with an aqueous phase contact angle of 79.2°.

[0084] Step 2) Modified attapulgite and alkylamidine compound: Take 0.8g of the modified attapulgite prepared in step 1) and mix it with 3.1g of N'-decanealkyl-N,N-diethyl acetamidine. After ultrasonic dispersion for 20min, heat to 40℃ and stir at 400rpm for 1h. After cooling, the compound intermediate is obtained.

[0085] Step 3) Preparation of CO2-responsive foam blocker: Add 1.8g of dodecyl dimethyl betaine to the compound intermediate and stir at 400rpm for 30min at 40℃ to obtain CO2-responsive foam blocker.

[0086] Comparative Example 3:

[0087] Step 1) Preparation of modified attapulgite: Take 10.000g of attapulgite powder and add it to an aqueous solution containing 3% (v / v) HDTMS (total volume 100mL). Stir at 240rpm for 4.5h in a constant temperature water bath at 63℃. After the reaction is complete, filter the product, wash it three times with deionized water, dry it at 60℃ for 1h, and grind it to obtain modified attapulgite with an aqueous phase contact angle of 83.6°.

[0088] Step 2) Modified attapulgite and alkylamidine compound: Take 1.0g of the modified attapulgite prepared in step 1) and mix it with 3.2g of N'-dodecyl-N,N-diethyl acetamidine. After ultrasonic dispersion for 20min, heat to 42℃ and stir at 400rpm for 1.5h. After cooling, the compound intermediate is obtained.

[0089] Step 3) Preparation of CO2-responsive foam plugging agent: Add 1.0g of polyacrylamide (molecular weight 7 million) to the compound intermediate and stir at 400rpm for 30min at 40℃ to obtain CO2-responsive foam plugging agent.

[0090] Comparative Example 1 is compared with Example 1; Comparative Example 2 is compared with Example 2; and Comparative Example 3 is compared with Example 3. The CO2-responsive foam plugging agents prepared in Examples 1-4 and Comparative Examples 1-3 were tested, and the test results are shown in Table 2. The testing procedures involved include:

[0091] (1) Concentration of 100mL foaming agent solution: Weigh 1.2g of CO2-responsive foaming agent into 198.8g of high-salt simulated water (mineralization of 160000ppm), stir mechanically at 400r / min to form a foaming agent solution with a mass concentration of 0.6%, and then take 100mL with a graduated cylinder for later use.

[0092] (2) Foaming volume: Pour 100 mL of foaming agent solution into a 500 mL beaker, then blow the foaming agent with CO2 at a gas flow rate of 0.5 L / min for 1 min, then insert the propeller of the mechanical stirrer into the liquid surface, 5 mm away from the bottom of the beaker, and stir mechanically at 2200 r / min for 2 min to form foam.

[0093] (3) Half-life of liquid precipitation: Immediately pour the formed foam into a 1000mL graduated cylinder and read the foam volume V and the time t when half of the liquid has precipitated. 析液半衰期 .

[0094] (4) Foam half-life: Immediately pour the formed foam into a 1000mL graduated cylinder and read the time t when half of the foam has burst. 泡沫半衰期 .

[0095] (5) Simulated water salt ion formula: as shown in Table 1: Simulated salt water ion formula table

[0096] Table 1: Simulated Salt Water Ion Formulation Table

[0097]

[0098] The liquid separation half-life refers to the time required for a foam system to go from its initial formation state to the point where the volume of precipitated liquid reaches half of the total liquid volume of the system. In a foam system, a liquid film exists between the bubbles. Under the influence of gravity and surface tension, the liquid film gradually drains and separates from the foam (i.e., "liquid separation"). The rate of liquid separation directly reflects the foam film's resistance to leakage and its structural stability. The longer this value is, the stronger the foam film's ability to retain liquid and delay liquid film rupture, and the better its short-term stability. This is crucial for foam plugging agents in CO2 flooding of oil fields, which need to maintain the interfacial structure for a long time to seal cracks.

[0099] The foam half-life refers to the time required for a foam system to decay to half its initial volume from its initial formation. During storage or application, the overall volume of foam gradually decreases due to factors such as bubble fusion and film rupture. The foam half-life directly reflects the foam's long-term ability to resist rupture and maintain its overall structural integrity. The longer this value, the stronger the foam's ability to survive in complex environments (such as reservoir temperature and pressure conditions), and the more persistent it can play a role in blocking CO2 gas channeling. It is one of the key indicators for evaluating the core performance of foam plugging agents.

[0100] Table 2:

[0101]

[0102] The test results in Table 1 show that:

[0103] (1) As can be seen from the test data of Examples 1 to 4 in Table 1, under the condition that the concentration of the foaming agent solution in 100 mL is 0.6%, as the amount of modified attapulgite added increases from 6 parts to 12 parts, the amount of betaine added increases from 15 parts to 24 parts, and the molecular weight of polyacrylamide increases from 5 million to 8 million, the foaming volume gradually increases from 453 mL to 489 mL, the half-life of the liquid separation increases from 312 s to 349 s, and the foam half-life increases from 22.5 min to 35.2 min. This trend shows that within the formulation range described in this application, the increase in the amount of modified attapulgite, the increase in the amount of betaine, and the increase in the molecular weight of polyacrylamide can all significantly improve the foaming performance and stability of the CO2-responsive foam plugging agent. Among them, modified attapulgite can enhance the strength of the foam film by optimizing the adsorption capacity at the gas-liquid interface, betaine can further reduce the surface tension to increase the foaming volume, and high molecular weight polyacrylamide can delay foam exudation and rupture through thickening. The synergistic effect of the three makes the performance of the plugging agent gradually improve with the optimization of the formulation parameters. At the same time, the data of Examples 1 to 6 also show that the CO2-responsive foam plugging agent of the present application has excellent salt resistance.

[0104] (2) Example 1 used attapulgite modified with hexadecyltrimethoxysilane and an aqueous phase contact angle of 70.6°, while Comparative Example 1 used unmodified attapulgite with an aqueous phase contact angle of only 23.2°. The other formulation components (30 parts alkylamidine, 15 parts betaine, and 9 parts polyacrylamide) and test conditions were completely identical for both. The data showed that the liquid half-life (312 s) of Example 1 was much longer than that of Comparative Example 1 (187 s), and the foam half-life (22.5 min) was also significantly higher than that of Comparative Example 1 (13.2 min). Only the foaming volume was similar (453 mL vs 450 mL). This indicates that unmodified attapulgite, due to its strong hydrophilicity (too small contact angle), is unable to form a stable adsorption layer at the gas-liquid interface and cannot effectively delay the foam separation and rupture process. However, attapulgite modified with a silane coupling agent has a surface wettability that becomes neutral (water phase contact angle 70°~90°), which allows it to firmly anchor at the gas-liquid interface, significantly enhancing the stability of the foam. This verifies the key role of modified attapulgite in improving the stability of foam plugging agents.

[0105] (3) The formulation of Example 2 contained 9 parts of polyacrylamide with a molecular weight of 6 million, while Comparative Example 2 excluded polyacrylamide. The remaining components (8 parts of modified attapulgite, 30 parts of alkylamidine, and 18 parts of betaine) and test conditions were the same. The test results showed that the liquid half-life (331s) and foam half-life (29.1min) of Example 2 were much higher than those of Comparative Example 2 (195s and 15.9min, respectively), and the foaming volume of Example 2 (466mL) was slightly higher than that of Comparative Example 2 (455mL). This difference indicates that polyacrylamide, as a polymer reinforcing agent, can effectively increase the viscosity of the foam system, slow down the liquid drainage rate in the foam film (prolonging the liquid half-life), enhance the mechanical strength of the foam film to resist rupture (prolonging the foam half-life), and has a slight promoting effect on the foaming volume. It can be concluded that polyacrylamide is an important component for improving the stability of CO2-responsive foam plugging agents, and the absence of this component will lead to a significant decrease in foam stability.

[0106] (4) The formulation of Example 3 contained 20 parts of dodecyl dimethyl betaine, while Comparative Example 3 did not contain betaine. The other components (10 parts of modified attapulgite, 30 parts of alkylamidine, and 9 parts of polyacrylamide with a molecular weight of 7 million) and test conditions were kept consistent in both. From the data comparison, the foaming volume of Example 3 (478 mL) was significantly higher than that of Comparative Example 3 (400 mL), and the liquid half-life (337 s) and foam half-life (33.5 min) were also higher than those of Comparative Example 3 (232 s and 18.5 min, respectively). This indicates that betaine, as a surface-active component, can effectively reduce the gas-liquid interfacial tension, providing sufficient impetus for foam formation, thereby increasing the foaming volume; at the same time, its adsorption at the gas-liquid interface can synergistically work with modified attapulgite and polyacrylamide to further optimize the foam film structure and delay the liquid separation and rupture process. Therefore, it can be concluded that betaine plays a key role in promoting the foaming performance of CO2-responsive foam plugging agents and can help improve foam stability. The absence of this component will lead to a significant reduction in foaming volume and a significant decline in stability.

[0107] While numerous embodiments of this application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A CO2-responsive foam plugging agent based on a combination of attapulgite and alkyl amidine, characterized in that, The CO2-responsive foam plugging agent comprises, in parts by mass, 6-12 parts of modified palygorskite, 30-35 parts of alkyl amidine, 15-24 parts of betaine, and 9-12 parts of polymer reinforcing agent; wherein the alkyl amidine comprises at least one of long-chain alkyl amidine and aromatic ring alkyl amidine.

2. The CO2-responsive foam plug of claim 1, wherein, The alkyl amidine comprises at least one of N'-long-chain alkyl-N,N-diethylacetamidine and N'-(4-alkylbenzene)-N,N-dimethylamidine.

3. The CO2-responsive foam plug of claim 1, wherein, The modified palygorskite is palygorskite surface-modified by dodecyltrimethoxysilane and / or hexadecyltrimethoxysilane.

4. The CO2-responsive foam plug of claim 1 or 3, wherein, The water phase contact angle of the modified palygorskite is 70-90°.

5. The CO2-responsive foam plug of claim 1, wherein, The betaine comprises dodecyl dimethyl betaine; and / or the polymer reinforcing agent comprises polyacrylamide with a molecular weight of 5-8 million.

6. A method of preparing a CO2-responsive foam plug according to any one of claims 1-5, characterized in that, Comprise: 6-12 parts of modified palygorskite and 30-35 parts of alkyl amidine are mixed and reacted at a first temperature to obtain a compounded intermediate; The compounded intermediate is mixed with 15-24 parts of betaine and 9-12 parts of polymer reinforcing agent in parts by mass to obtain the CO2-responsive foam plugging agent.

7. The production method according to claim 6, wherein The preparation method further comprises: mixing palygorskite powder with a 2%-4% volume fraction of a silane coupling agent aqueous solution to obtain a mixture; placing the mixture in a 60-65°C constant-temperature water bath, continuously stirring at a speed of 200-300 rpm for 4-6 hours, and then filtering, washing, and drying to obtain modified palygorskite with a water phase contact angle in the range of 70-90°.

8. The preparation method according to claim 7, characterized in that, The silane coupling agent in the silane coupling agent aqueous solution comprises dodecyltrimethoxysilane and / or hexadecyltrimethoxysilane.

9. The preparation method according to claim 6, characterized in that, The preparation method further comprises: mixing the modified palygorskite with the alkyl amidine, and after ultrasonic dispersion, stirring and reacting at the first temperature for a first duration, wherein the first temperature is 40-45°C, and the first duration is 1-2 hours.

10. The method of claim 6, wherein, The preparation method further comprises: mixing the compounded intermediate with the betaine and the polymer reinforcing agent, and after stirring and reacting at 40-45°C for 30-35 minutes, obtaining the CO2-responsive foam plugging agent.

11. Use of a CO2-responsive foam plugging agent based on a combination of attapulgite and an alkyl amidine in CO2 flooding technology, characterized in that, The CO2-responsive foam plugging agent based on the compounding of palygorskite and alkyl amidine is the CO2-responsive foam plugging agent of any one of claims 1-5 or the CO2-responsive foam plugging agent prepared by the method of any one of claims 6-10.

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