An alcohol-based fracturing fluid containing modified nanoparticles and its preparation method

Abstract

This invention relates to the field of petroleum extraction technology, specifically to an alcohol-based fracturing fluid containing modified nanoparticles and its preparation method. The alcohol-based fracturing fluid comprises the following components: an alcohol solvent, modified nanoparticles, an anti-swelling agent, a thickener, a polyamide-amine dendritic polymer, a pH adjuster, an optional suspending agent, and water. The modified nanoparticles are prepared by modifying nanoparticles with an alkenyl silane coupling agent, followed by copolymerization with an alkenyl-containing imidazole salt, with the polyimide salt being in-situ grafted onto the surface of the nanoparticles. This invention modifies nanoparticles with an alkenyl silane coupling agent, then copolymerizes them with an alkenyl-containing imidazole salt, forming polyimide salt in-situ grafted onto the nanoparticle surface, thus forming modified nanoparticles. The combined effect of the modified nanoparticles and the polyamide-amine dendritic polymer significantly improves the anti-swelling properties, crosslinking properties, and proppant carrying capacity of the alcohol-based fracturing fluid, with a gelation and adhesion time of 60-90 seconds. Therefore, the alcohol-based fracturing fluid of this invention is particularly suitable for medium- and high-temperature deep wells.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, specifically relating to an alcohol-based fracturing fluid containing modified nanoparticles and its preparation method. Background Technology

[0002] In the extraction of shale oil, fracturing technology is one of the key means to improve shale oil recovery. As the core of fracturing technology, the performance of fracturing fluid directly affects the fracturing effect and the extraction efficiency of shale oil. Fracturing fluid is a fluid mixture pumped into underground shale reservoirs under extremely high pressure. Its main function is to create and maintain flow channels (fracture network) in the dense shale layer, thereby releasing shale oil (and natural gas) that would otherwise be unable to flow. Its core function is to use high pressure to create fractures in the shale and deliver proppant to maintain fracture opening, thereby improving the effective permeability of the reservoir, unlocking the oil and gas resources hidden in the shale pores, and enabling them to flow continuously and economically to production wells.

[0003] Traditional water-based fracturing fluids suffer from numerous problems in practical applications. For example, clay minerals in shale reservoirs readily swell and disperse upon contact with water, leading to reduced reservoir permeability. This indicates a water-sensitivity issue with water-based fracturing fluids, which cannot suppress clay swelling. Alcohol-based fracturing fluids have attracted considerable attention due to their superior ability to suppress viscosity swelling compared to water-based fluids. However, the difficulty in dissolving thickeners in pure alcohol systems and economic considerations prevent the current use of 100% alcohol-based systems. Therefore, while existing alcohol-based fracturing fluids offer advantages in anti-swelling properties compared to water-based fracturing fluids, further improvements are needed. In addition, the crosslinking performance and proppant carrying capacity of alcohol-based fracturing fluids need to be improved. The fracturing fluid needs to maintain a high-viscosity gel state (forming a three-dimensional network through crosslinking agents) to ensure that the proppant (quartz sand / ceramsite) is suspended and transported to the depth of the fracture. Especially in medium- and high-temperature deep wells (above 120°C), the gelation and hanging time is generally required to be 60-90 seconds. Otherwise, the fracturing fluid cannot form a gel with sufficient strength in a suitable time, and it cannot guarantee that the proppant will be stably suspended in the fracturing fluid for a sufficient time, thus failing to effectively form supporting fractures and affecting the conductivity of shale oil.

[0004] CN111574989B discloses a multi-hydroxyl thickener, a high-temperature resistant alcohol-based fracturing fluid system, and their applications. The multi-hydroxyl thickener is formed by copolymerizing three monomers—acrylamide, N-vinylpyrrolidone, and N-acrylamidopropyl-N,N,N-dimethylhydroxyethylammonium chloride—in an aqueous solution. The mass ratio of the three monomers, based on the total mass of the monomers, is 40-85% acrylamide, 5-35% N-vinylpyrrolidone, and 3-25% N-acrylamidopropyl-N,N,N-dimethylhydroxyethylammonium chloride. The raw materials of the high-temperature resistant alcohol-based fracturing fluid system include the multi-hydroxyl thickener, a composite crosslinking agent (obtained by reacting borax, zirconium oxychloride, glycerol, triethanolamine, lactic acid, sodium gluconate, and water), a modifier, a high-flash-point alcohol, and water. The alcohol-based fracturing fluid system of this application, by introducing a multi-hydroxyl thickener, exhibits high temperature resistance and shear resistance, with a temperature resistance exceeding 160℃. The use of high-flash-point alcohols enhances the safety of the fracturing system and allows for an alcohol / water ratio exceeding 60%, resulting in advantages such as high flowback rate, minimal formation damage, and safety and environmental friendliness. However, the gelation time of this fracturing fluid is still relatively long, indicating that its proppant-carrying capacity needs further improvement.

[0005] Therefore, there is a need for a fracturing fluid that can effectively suppress clay swelling while having good cross-linking and sand-carrying properties. Summary of the Invention

[0006] This invention provides an alcohol-based fracturing fluid containing modified nanoparticles and its preparation method, in order to solve the problems of clay swelling, insufficient sand carrying capacity and poor crosslinking performance of traditional fracturing fluids in shale oil extraction.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides an alcohol-based fracturing fluid comprising modified nanoparticles, comprising the following components: an alcohol solvent, modified nanoparticles, an anti-swelling agent, a thickener, a polyamide-amine dendritic polymer, a pH adjuster, an optional suspending agent, and water; wherein the modified nanoparticles are prepared by modifying nanoparticles with an alkenyl silane coupling agent and then copolymerizing them with an alkenyl-containing imidazole salt, wherein the polyimide salt is grafted in situ onto the surface of the nanoparticles.

[0009] Furthermore, the mass ratio of nanoparticles, alkenyl silane coupling agent, and alkenyl-containing imidazole salt is 100:(6~10):(8~15), preferably 100:(6~10):(10~15).

[0010] Further, the alkenylsilane coupling agent is at least one of vinyltriethoxysilane, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyltriethoxysilane; the alkenyl-containing imidazole salt is at least one of 1-vinyl-3-butylimidazolium bromide, 1-vinyl-3-ethylimidazolium bromide, 1-vinyl-3-hexylimidazolium chloride, 1-vinyl-3-hydroxyethylimidazolium tetrafluoroborate, and 1-allyl-3-butylimidazolium bromide.

[0011] Preferably, the alkenyl silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane or γ-methacryloyloxypropyltriethoxysilane, and the alkenyl-containing imidazole salt is 1-vinyl-3-hydroxyethylimidazolium tetrafluoroborate.

[0012] Furthermore, the nanoparticles are at least one of nano-titanium dioxide, nano-silica, and nano-zinc oxide, with a particle size D50 of 60~100nm.

[0013] Furthermore, the preparation method of the modified nanoparticles includes the following steps:

[0014] (L1) The alkenylsilane coupling agent was added to water for hydrolysis to obtain a hydrolysate; the nanoparticles were then placed in the hydrolysate and stirred at 50-70°C, and the modified nanoparticles were obtained after purification.

[0015] (L2) Modified nanoparticles, alkenyl-containing imidazole salts, and initiators were added to water, and then copolymerized at 40-60°C. The modified nanoparticles were obtained after purification.

[0016] Furthermore, in step (L1), the ratio of the alkenylsilane coupling agent to water is 6-10 g: 1000-1500 mL. The hydrolysis reaction conditions are: hydrolysis at 40-50°C for 30-50 min at pH 4-5; the stirring reaction time is 2-4 h; the purification treatment is: after the reaction, the solid is obtained by filtration, washed with pure water until the filtrate is neutral, and dried at 60-80°C for 8-24 h. After hydrolysis, the alkenylsilane coupling agent generates Si-OH, which undergoes a condensation reaction with the -OH on the surface of the nanoparticles, thereby modifying the surface of the nanoparticles with the alkenylsilane coupling agent in the form of chemical bonds. The modified nanoparticles have improved hydrophobicity, which is beneficial to their dispersion in the system; at the same time, it is beneficial to the uniform polymerization reaction on the surface of the nanoparticles.

[0017] Furthermore, in step (L2), the amount of initiator is 0.4~0.7wt% of the nanoparticles, and the initiator is at least one of hydrogen peroxide, potassium persulfate, and ammonium persulfate; the copolymerization reaction time is 2~5h, preferably 3~4h. The alkenyl groups on the modified nanoparticles copolymerize with the alkenyl-containing imidazole salt under the action of the initiator, forming polyimide salts that are in situ grafted onto the surface of the nanoparticles, thus obtaining the modified nanoparticles.

[0018] The polyamide-amine dendritic polymer (PAMAM) has a second-generation or third-generation structure, specifically selected from G2-PAMAM or G3-PAMAM. PAMAM is a dendritic polymer whose structure radiates outward from a central core, resembling a number shape. It is divided into different generations or sequences; the higher the generation, the more complex the branching structure. Each generation of dendritic structure possesses functional groups such as amine and amide groups; the more generations, the more functional groups. In this invention, PAMAM is used as a crosslinking agent. Compared to traditional organoboron and organozirconium crosslinking agents, PAMAM has the advantages of high crosslinking efficiency and network stability, forming a more homogeneous and high-density three-dimensional network. Furthermore, the amide bonds (-CO-NH-) of PAMAM are stable at high temperatures, and after shearing, the network can be rapidly reconstructed through hydrogen bonding / electrostatic interactions between the amine groups and the polymer, thus exhibiting temperature and shear resistance. In addition, due to its hierarchical structure and abundant functional groups, PAMAM requires a smaller amount of crosslinking agent compared to traditional crosslinking agents.

[0019] Nanoparticles, due to their unique nano-effects, are commonly used in fracturing fluids to improve rheology and reduce filtration loss. This invention utilizes in-situ copolymerization of nanoparticles modified with a silane coupling agent to form polyimide salt polymeric links on the nanoparticle surface, thus creating modified nanoparticles. The inventors discovered that the modified nanoparticles, in conjunction with PAMAM, significantly enhance the anti-swelling and cross-linking properties (sand-carrying capacity) of alcohol-based fracturing fluids. This is likely because, firstly, the modified nanoparticles exhibit increased hydrophobicity, forming an effective hydrophobic protective film on the clay surface, preventing direct contact between water and clay and thus inhibiting clay swelling. Secondly, the polyimide salt grafted onto the modified nanoparticle surface is a polyionic liquid (polycationic), which can efficiently bind to the negative charge on the viscous surface of shale, further significantly enhancing the anti-swelling effect. Thirdly, the PAMAM in this invention has a highly branched structure and a large number of terminal active functional groups (-NH2), which can form hydrogen bonds or covalent crosslinks with the hydroxyl or amide groups of thickeners (such as hydroxyethyl cellulose and polyacrylamide). That is, the special structure of PAMAM enables it to form high-density crosslinking points with the thickener, thereby constructing a dense and stable three-dimensional network structure, thus improving the proppant-carrying capacity of the fracturing fluid. Furthermore, the polyimidezazole salt polymer chains grafted onto the surface of the modified nanoparticles can entangle with PAMAM, forming physical crosslinking points, further enhancing the three-dimensional network structure, thereby further enhancing the proppant-carrying capacity of the fracturing fluid. In addition, the polyimidezazole salt grafted onto the surface of the modified nanoparticles has a large heterocyclic structure, which can provide a steric hindrance effect, thereby improving the dispersibility of the nanoparticles in the fracturing fluid and increasing the stability of the fracturing fluid.

[0020] Furthermore, the alcohol solvent is selected from at least one of isopropanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, n-pentanol, and n-hexanol. As a base solvent for fracturing fluids, alcohol solvents possess low surface tension and good wettability, effectively reducing damage to shale reservoirs while providing a dispersion medium for other components.

[0021] Furthermore, the anti-swelling agent is a polyquaternary ammonium salt, such as polyquaternary ammonium salt-2 or polyquaternary ammonium salt-42. Polyquaternary ammonium salts are cationic polymers that neutralize the surface charge of clay by exchanging cations with the clay surface, effectively inhibiting clay swelling and dispersion, thereby improving the shale anti-swelling rate.

[0022] Furthermore, the thickener is selected from at least one of hydroxyethyl cellulose and nonionic polyacrylamide, preferably nonionic polyacrylamide. The weight-average molecular weight of hydroxyethyl cellulose is 1.2 million Da to 1.5 million Da, and the weight-average molecular weight of nonionic polyacrylamide is 5 million Da to 10 million Da. The thickener can increase the viscosity of the fracturing fluid, thereby improving its sand-carrying capacity and suspension performance.

[0023] Furthermore, the pH adjuster is an aqueous solution of hydrochloric acid, acetic acid, formic acid, sodium bicarbonate, and potassium bicarbonate, and the pH adjuster adjusts the pH of the system to 7-9.

[0024] Furthermore, the suspending agent is selected from at least one of attapulgite and bentonite. The suspending agent can improve the suspension stability of the proppant (quartz sand or ceramsite) in fracturing fluid.

[0025] Furthermore, based on 100% of the total weight of the alcohol-based fracturing fluid, the alcohol-based fracturing fluid containing modified nanoparticles comprises the following components:

[0026] 55-70 wt% of alcohol solvents

[0027] Modified nanoparticles 2~5wt%,

[0028] Anti-swelling agent 3~8wt%,

[0029] Thickener 2~6wt%,

[0030] Polyamide-amine dendritic polymer 0.05~0.15wt%,

[0031] pH adjuster 0.05~0.2wt%,

[0032] 0~1wt% of suspending agent

[0033] Water 15~35wt%.

[0034] Secondly, the present invention provides a method for preparing the above-mentioned alcohol-based fracturing fluid containing modified nanoparticles, comprising the following steps:

[0035] (S1) Add the modified nanoparticles to an alcohol solvent and stir at high speed to disperse the modified nanoparticles evenly to obtain a suspension;

[0036] (S2) Add the anti-swelling agent and thickener to water and stir until they are dissolved evenly to form a viscous liquid;

[0037] (S3) Add the viscous liquid from step (S2) to the suspension from step (S1), then add the suspending agent and stir evenly, and finally add the pH adjuster to adjust the pH of the system to 7~9.

[0038] (S4) Before fracturing, add polyamide-amine dendritic polymer to form alcohol-based fracturing fluid.

[0039] Further, the high-speed stirring in step (S1) is 800~1200 r / min for 60~90 min; the stirring in step (S2) is 300~500 r / min for 40~70 min.

[0040] An alcohol-based fracturing fluid is added as a breaker after the fracturing operation is completed, so that it is backflowed; the breaker is at least one of potassium persulfate, ammonium persulfate, and hydrogen peroxide, preferably ammonium persulfate.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. In this invention, after modifying nanoparticles with an alkenyl silane coupling agent, they are copolymerized with an alkenyl-containing imidazole salt to form polyimide salts grafted in situ onto the surface of the nanoparticles, thus forming modified nanoparticles. The modified nanoparticles and polyamide-amine dendritic polymer (PAMAM) work together to significantly improve the anti-swelling and cross-linking properties (sand carrying capacity) of the alcohol-based fracturing fluid. Its gelation and hanging time is 60~90s. Therefore, the alcohol-based fracturing fluid of this invention is particularly suitable for medium- and high-temperature deep wells.

[0043] 2. The alcohol-based fracturing fluid of the present invention causes little damage to the reservoir and is safe and environmentally friendly. Detailed Implementation

[0044] The present application will be further described in detail below with reference to the embodiments, but the embodiments are only used to explain the relevant invention and not to limit the invention.

[0045] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0046] The particle size D50 of the nano-silica is 72 nm.

[0047] G2-PAMAM and G3-PAMAM were purchased from Chengdu Kele Biotechnology Co., Ltd.

[0048] Polyquaternium-2 and polyquaternium-4 were purchased from Zhongshan Dixin Chemical Co., Ltd.

[0049] The weight-average molecular weight of nonionic polyacrylamide is approximately 8 million to 9 million Da.

[0050] Hydroxyethyl cellulose has a weight-average molecular weight of approximately 1.2 million to 1.3 million Da.

[0051] The organic zirconium crosslinking agent SL-EXP4206 was selected from Qingdao Lide Oilfield Service Co., Ltd.

[0052] Prepare modified silicon nanoparticles.

[0053] Preparation Example 1

[0054] (L1) 8g of γ-methacryloxypropyltriethoxysilane was added to 1200 mL of water, the pH was adjusted to 4.5, and then hydrolyzed at 45℃ for 40 min to obtain a hydrolysate; 100g of nano-silica was then placed in the hydrolysate and stirred at 60℃ for 2.5 h. After the reaction was completed, the solid was obtained by filtration. The solid was washed with pure water until the filtrate was neutral, and then dried at 70℃ for 24 h to obtain modified nano-silica.

[0055] (L2) All the modified nano silica prepared in step (S1), 10g of 1-vinyl-3-hydroxyethylimidazolium tetrafluoroborate, and 0.6g of ammonium persulfate were added to water and reacted at 55°C. After the reaction was completed, the solid was obtained by filtration. The solid was washed with pure water until the filtrate was neutral and then dried at 70°C for 24h to obtain modified nanoparticle-1.

[0056] Preparation Example 2

[0057] The rest is the same as in Preparation Example 1, except that the amount of 1-vinyl-3-hydroxyethylimidazolium tetrafluoroborate used in step (L2) is 8g, and the modified nanoparticles-2 are finally obtained.

[0058] Preparation Example 3

[0059] The rest is the same as in Preparation Example 1, except that the amount of 1-vinyl-3-hydroxyethylimidazolium tetrafluoroborate used in step (L2) is 12g, and the modified nanoparticles-3 are finally obtained.

[0060] Preparation Example 4

[0061] The rest is the same as in Preparation Example 1, except that the amount of 1-vinyl-3-hydroxyethylimidazolium tetrafluoroborate used in step (L2) is 15g, and the modified nanoparticles-4 are finally obtained.

[0062] Preparation Example 5

[0063] The rest is the same as in Preparation Example 1, except that: in step (L1), vinyltriethoxysilane is used to replace γ-methacryloyloxypropyltriethoxysilane in equal molar form, and in step (L2), 1-vinyl-3-butylimidazolium bromide is used to replace 1-vinyl-3-hydroxyethylimidazolium tetrafluoroborate in equal molar form, and finally modified nanoparticles-5 are obtained. Example 1

[0064] An alcohol-based fracturing fluid containing nano-modified particles, comprising the following components:

[0065] 1,2-Propanediol 62wt%,

[0066] Modified nanoparticles - 1 3wt%,

[0067] Polyquaternium salt - 2 5wt%,

[0068] Nonionic polyacrylamide 4wt%,

[0069] G3-PAMAM 0.1wt%,

[0070] pH adjuster sodium bicarbonate 0.1 wt%,

[0071] 0.2 wt% bentonite

[0072] Water 25.6 wt%.

[0073] Prepare an alcohol-based fracturing fluid using the above components according to the following steps:

[0074] (S1) Add the modified nanoparticle-1 to 1,2-propanediol and stir at 1000 r / min for 70 min to disperse the modified nanoparticle-1 evenly and obtain a suspension.

[0075] (S2) Add polyquaternium-2 and nonionic polyacrylamide to water and stir at 400 r / min for 50 min until dissolved and uniform to form a viscous liquid;

[0076] (S3) Add the viscous liquid from step (S2) to the suspension from step (S1), then add bentonite and stir evenly, and finally add sodium bicarbonate as a pH adjuster to adjust the pH of the system to 8.0.

[0077] (S4) Before fracturing, add G3-PAMAM to form an alcohol-based fracturing fluid. Example 2

[0078] The rest is the same as in Example 1, except that modified nanoparticles-2 prepared in Preparation Example 2 are used instead of modified nanoparticles-1. Example 3

[0079] The rest is the same as in Example 1, except that modified nanoparticles-3 prepared in Preparation Example 3 are used instead of modified nanoparticles-1. Example 4

[0080] The rest is the same as in Example 1, except that modified nanoparticles-4 prepared in Preparation Example 4 are used instead of modified nanoparticles-1. Example 5

[0081] The rest is the same as in Example 1, except that modified nanoparticle-5 prepared in Preparation Example 5 is used instead of modified nanoparticle-1. Example 6

[0082] The rest of Example 1 is the same, except that the proportions of the components in the alcohol-based fracturing fluid are different, specifically:

[0083] 1,2-Propanediol 70wt%,

[0084] Modified nanoparticles - 1 5wt%,

[0085] Polyquaternium salt - 2 3wt%,

[0086] 6 wt% nonionic polyacrylamide

[0087] G3-PAMAM 0.05wt%,

[0088] pH adjuster sodium bicarbonate 0.1 wt%,

[0089] 0.2 wt% bentonite

[0090] Water 15.65 wt%. Example 7

[0091] The rest of Example 1 is the same, except that the components and proportions of the alcohol-based fracturing fluid are different, specifically:

[0092] 1,2-Butanediol 55wt%,

[0093] Modified nanoparticles - 1 2wt%,

[0094] Polyquaternium-4 8wt%,

[0095] 2 wt% hydroxyethyl cellulose

[0096] G2-PAMAM 0.15wt%,

[0097] pH adjuster sodium bicarbonate 0.1 wt%,

[0098] Water 32.75 wt%.

[0099] Prepare an alcohol-based fracturing fluid using the above components according to the following steps:

[0100] (S1) Add the modified nanoparticle-1 to 1,2-butanediol and stir at 1000 r / min for 70 min to disperse the modified nanoparticle-1 evenly and obtain a suspension.

[0101] (S2) Add polyquaternium-4 and hydroxyethyl cellulose to water and stir at 400 r / min for 50 min until dissolved and a viscous liquid is formed;

[0102] (S3) Add the viscous liquid from step (S2) to the suspension from step (S1), and then add sodium bicarbonate as a pH adjuster to adjust the pH of the system to 7.5.

[0103] (S4) Before fracturing, add G2-PAMAM to form an alcohol-based fracturing fluid.

[0104] Comparative Example 1

[0105] The rest is the same as in Example 1, except that an equal mass of nano-silica is used to replace the modified nanoparticles-1, that is, the nano-silica is not modified.

[0106] Comparative Example 2

[0107] The rest is the same as in Example 1, except that an equal mass of organozirconium crosslinking agent SL-EXP4206 is used instead of G3-PAMAM.

[0108] Testing and Analysis

[0109] The alcohol-based fracturing fluids prepared in Examples 1-7 and Comparative Examples 1-2 were subjected to the following tests:

[0110] Anti-swelling test: Standard core powder (quartz sand:kaolin:montmorillonite = 8:1:1, passed through a 200-mesh sieve) was dried in an oven at 105℃ for 24 hours, and then pressed (under 20MPa for 10 minutes) into several core slices with a diameter of 2.5cm and a thickness of 0.5cm. The core slices were placed in the alcohol-based fracturing fluids prepared in Examples 6-12 and Comparative Examples 1-2, and immersed at 120℃ and 1.5MPa for 12 hours. After immersion, the core slices were removed, the surface residual fluid was washed off and dried, and the thickness difference before and after immersion was measured. The linear expansion rate was calculated using the following formula. The anti-swelling performance of the fracturing fluid was evaluated by the linear expansion rate; the lower the linear expansion rate, the better the anti-swelling performance of the fracturing fluid.

[0111] Linear expansion rate (%) =

[0112] Where H1 is the thickness of the core after impregnation, and H0 is the initial thickness of the core.

[0113] Gel formation and hanging time test: Using an RH-30 rheometer, according to SY / T 6376-2008, the test temperature was 120℃, and the viscosity reaching 200 mPa·s was used as the endpoint to test the gel formation and hanging time. The results are shown in Table 1. Then, 0.05wt% ammonium persulfate was added, and the gel was broken up after 2 hours at 120℃. The viscosity of the gel after breaking up was tested, and the results are shown in Table 1.

[0114] Table 1 Performance Tests of Alcohol-Based Fracturing Fluids

[0115] Alcohol-based fracturing fluid Linear expansion rate of core section (%) Time for gelling and hanging (s) Viscosity of the breaking solution (mPa·s) Example 1 13.5 78 3.5 Example 2 14.9 85 3.1 Example 3 12.8 72 3.6 Example 4 12.3 69 3.8 Example 5 13.7 82 4.2 Example 6 14.3 74 3.8 Example 7 14.4 82 4.0 Comparative Example 1 28.6 89 3.3 Comparative Example 2 18.2 150 4.5

[0116] As shown in Table 1, the linear expansion rate of the core samples does not exceed 15%, indicating that the alcohol-based fracturing fluid prepared in this invention has good anti-swelling performance and can effectively inhibit clay expansion. Furthermore, the gelation and hanging time of the alcohol-based fracturing fluid of this invention is 60-90 seconds, indicating good cross-linking performance and thus good proppant carrying capacity. In addition, conventional breaker can break the gel after gelation, and the viscosity after breaking the gel does not exceed 5 mPa·s, indicating easy flowback and minimal damage to the reservoir. In contrast, the nanoparticles in Comparative Example 1 were unmodified, resulting in poor anti-swelling performance of the corresponding alcohol-based fracturing fluid, with a linear expansion rate of nearly 30%. The conventional cross-linking agent used in Comparative Example 2 resulted in a longer gelation and hanging time for the corresponding alcohol-based fracturing fluid, leading to a correspondingly lower proppant carrying capacity.

Claims

1. An alcohol-based fracturing fluid comprising modified nanoparticles, characterized in that, The product comprises the following components: alcohol solvent, modified nanoparticles, anti-swelling agent, thickener, polyamide-amine dendritic polymer, pH adjuster, optional suspending agent, and water; the modified nanoparticles are prepared by modifying nanoparticles with an alkenyl silane coupling agent and then copolymerizing them with an alkenyl-containing imidazole salt, wherein the polyimidazole salt is grafted in situ onto the surface of the nanoparticles, and the mass ratio of nanoparticles, alkenyl silane coupling agent, and alkenyl-containing imidazole salt is 100:(6~10):(8~15); the alkenyl-containing imidazole salt is at least one of 1-vinyl-3-butylimidazole bromide, 1-vinyl-3-ethylimidazole bromide, 1-vinyl-3-hexylimidazole chloride, 1-vinyl-3-hydroxyethylimidazole tetrafluoroborate, and 1-allyl-3-butylimidazole bromide; Based on 100% of the total weight of the alcohol-based fracturing fluid, the alcohol-based fracturing fluid containing modified nanoparticles comprises the following components: 55-70 wt% of alcohol solvents Modified nanoparticles 2~5wt%, Anti-swelling agent 3~8wt%, Thickener 2~6wt%, Polyamide-amine dendritic polymer 0.05~0.15wt%, pH adjuster 0.05~0.2wt%, 0~1wt% of suspending agent Water 15~35wt%.

2. The alcohol-based fracturing fluid containing modified nanoparticles according to claim 1, characterized in that, The alkenylsilane coupling agent is at least one of vinyltriethoxysilane and γ-methacryloyloxypropyltriethoxysilane; the nanoparticles are nano-silica with a particle size D50 of 60~100nm.

3. The alcohol-based fracturing fluid containing modified nanoparticles according to claim 1, characterized in that, The alkenyl silane coupling agent is γ-methacryloyloxypropyltriethoxysilane; the alkenyl-containing imidazole salt is 1-vinyl-3-hydroxyethylimidazolium tetrafluoroborate.

4. The alcohol-based fracturing fluid containing modified nanoparticles according to claim 1, characterized in that, The method for preparing the modified nanoparticles includes the following steps: (L1) The alkenylsilane coupling agent was added to water for hydrolysis to obtain a hydrolysate; the nanoparticles were then placed in the hydrolysate and stirred at 50-70°C, and the modified nanoparticles were obtained after purification. (L2) Modified nanoparticles, alkenyl-containing imidazole salts, and initiators were added to water, and then copolymerized at 40-60°C. The modified nanoparticles were obtained after purification.

5. The alcohol-based fracturing fluid containing modified nanoparticles according to claim 4, characterized in that, In step (L1), the ratio of alkenylsilane coupling agent to water is 6-10g:1000-1500mL; the hydrolysis reaction conditions are: hydrolysis at 40-50℃ for 30-50min at pH 4-5; the stirring reaction time is 2-4h; the purification treatment is: after the reaction, the solid is obtained by filtration, the solid is washed with pure water until the filtrate is neutral, and dried at 60-80℃ for 8-24h; and / or in step (L2), the amount of initiator is 0.4-0.7wt% of the mass ratio of nanoparticles, and the initiator is at least one of hydrogen peroxide, potassium persulfate, and ammonium persulfate; the copolymerization reaction time is 2-5h.

6. The alcohol-based fracturing fluid containing modified nanoparticles according to claim 1, characterized in that, The polyamide-amine dendritic polymer has a second-generation or third-generation structure, namely selected from G2-PAMAM or G3-PAMAM.

7. The alcohol-based fracturing fluid containing modified nanoparticles according to claim 1, characterized in that, The alcohol solvent is selected from at least one of isopropanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, n-pentanol, and n-hexanol; and / or the anti-swelling agent is a polyquaternary ammonium salt; and / or the thickener is selected from at least one of hydroxyethyl cellulose and nonionic polyacrylamide, wherein the weight-average molecular weight of hydroxyethyl cellulose is 1.2 million Da to 1.5 million Da, and the weight-average molecular weight of nonionic polyacrylamide is 5 million Da to 10 million Da; and / or the pH adjuster is an aqueous solution of hydrochloric acid, acetic acid, formic acid, sodium bicarbonate, and potassium bicarbonate, wherein the pH adjuster adjusts the pH of the system to 7 to 9; and / or the suspending agent is selected from at least one of attapulgite and bentonite.

8. The method for preparing the alcohol-based fracturing fluid containing modified nanoparticles according to any one of claims 1-7, characterized in that, Includes the following steps: (S1) Add the modified nanoparticles to an alcohol solvent and stir at high speed to disperse the modified nanoparticles evenly to obtain a suspension; (S2) Add the anti-swelling agent and thickener to water and stir until they are dissolved evenly to form a viscous liquid; (S3) Add the viscous liquid from step (S2) to the suspension from step (S1), then add the suspending agent and stir evenly, and finally add the pH adjuster to adjust the pH of the system to 7~9. (S4) Before fracturing, add polyamide-amine dendritic polymer to form alcohol-based fracturing fluid.