Nano-crosslinking agent for fracturing and preparation method thereof

Abstract

The application relates to the technical field of fracturing aids, and is a kind of nano crosslinking agent for fracturing and a preparation method thereof.The nano crosslinking agent for fracturing is prepared from raw materials including a silane coupling agent, nano silicon dioxide, an amino acid, a polybasic organic compound and a metal zirconium salt.The nano crosslinking agent for fracturing is prepared by modifying nano silicon dioxide to obtain modified nano silicon dioxide containing polycarboxyl groups and polyhydroxy groups, and then introducing the modified nano silicon dioxide into conventional organic zirconium (metal zirconium salt) to obtain the nano crosslinking agent for fracturing.The nano crosslinking agent for fracturing has adjustable crosslinking time and high crosslinking efficiency, and can form a gel fracturing fluid with polyacrylamide thickening agent at a low addition amount, and the gel fracturing fluid has excellent salt resistance, high-temperature resistance and shear resistance.

Description

Technical Field

[0001] This invention relates to the field of fracturing additives, specifically a fracturing nano-crosslinking agent and its preparation method. Background Technology

[0002] Hydraulic fracturing is a crucial technology for improving unconventional resources such as tight oil and shale oil and gas. Fracturing fluid, as the key working fluid in hydraulic fracturing, directly determines the efficiency and effectiveness of fracturing. Thickeners, as important main agents in fracturing fluids, are critical to ensuring the overall performance of the fracturing fluid system. Due to their advantages such as good drag reduction, strong thickening ability, low residue content, and insensitivity to bacteria, synthetic polymers have become one of the mainstream directions for the research and application of fracturing fluid thickeners. However, as the development of unconventional oil and gas resources continues to delve into deeper, more complex formations with high water content, high temperatures, and high salinity, traditional fracturing fluid systems based on synthetic polymers generally face problems such as poor temperature resistance, insufficient proppant carrying capacity, and high construction costs. Crosslinking thickeners with a specific crosslinking agent to form gel fracturing fluids is an important means to improve the temperature resistance, shear strength, and proppant carrying capacity of fracturing fluids, and further reduce construction costs.

[0003] Chinese Patent CN108300451B discloses a nanomaterial composite reinforced gel fracturing fluid and its preparation method. The method involves first dispersing nano-SiO2 particles and nano-cellulose in water, then mixing them separately with a polyacrylamide thickener and a crosslinking agent to form first and second solutions. Finally, the first and second solutions are mixed to obtain the final product. This method can further improve the consistency and viscoelasticity of the fracturing fluid, reduce polymer usage and residue. The gel fracturing fluid formed with 0.8% thickener achieves a viscosity of 80°C. o C, 170s -1 The viscosity was 267 mPa·s after 120 min of shearing.

[0004] Chinese Patent CN114561203B discloses a high-mineralization water-based delayed crosslinking gel fracturing fluid and its preparation method. It consists of a pentagonal copolymer hydrophobic associative thickener, an organozirconium crosslinking agent, a temperature stabilizer (one of vitamin C, triethanolamine, and sodium gluconate), and a fluorinated drainage aid FC-2. The gel formed with 0.3% thickener exhibits good temperature resistance and shear strength at 180°C. o C, 170s -1 After 2 hours of shearing, the viscosity reaches 57 mPa·s or higher.

[0005] Chinese patent CN114410287B discloses a composite nano crosslinking agent and its preparation method and application. It is prepared by reacting glycerol, lactic acid, zirconium oxychloride and trisodium citrate and then adding nano titanium dioxide. Using this crosslinking agent to form a gel fracturing fluid can effectively reduce the amount of emulsion drag reducer, increase the viscosity of the fracturing fluid system under high temperature and high shear, prolong the crosslinking time, and improve viscoelasticity and temperature resistance.

[0006] Chinese patent CN116751576A discloses a delayed crosslinking agent for water-based fracturing fluid, its preparation method and application. It is prepared by reacting zirconium oxychloride, diethanolamine, malic acid, isonicotinic acid and ethanol. The fracturing fluid crosslinked with this crosslinking agent has the characteristics of delayed crosslinking time, temperature resistance and temperature and shear resistance. The delayed crosslinking time reaches more than 400s, and the temperature and shear resistance viscosity at 220℃ can reach more than 180mPa·s.

[0007] Chinese patent CN117024478A discloses a multifunctional delayed fracturing fluid crosslinking agent and its preparation method. It is prepared by reacting tris(3-hydroxypropyl)phosphine, zirconium oxychloride and 2-amino-4,6-dihydroxypyrimidine under certain conditions, and then adjusting the pH value to 6 to 7 with ammonia water. Using this crosslinking agent to form a gel fracturing fluid, the crosslinking time is controllable, and the temperature resistance and shear resistance are strong. The crosslinking time can be controlled between 90s and 650s, and the temperature and shear resistance viscosity at 220℃ can reach more than 220mPa·s.

[0008] Chinese patent CN118126083B, authorized by CN118126083B, also discloses a crosslinking agent for fracturing and its preparation method. It adopts a similar technical approach to CN117024478A, which is prepared by reacting tris(3-hydroxypropyl)phosphine, zirconium tetrachloride and N,N-di(3-aminopropyl)ethyl ethylamine under certain conditions and then adjusting the pH to 7 to 8 with ammonia. The crosslinking time of the obtained crosslinking agent can be controlled between 62s and 605s. The fracturing fluid formed by using the crosslinking agent has strong temperature resistance and shear resistance.

[0009] Wang Siyu et al. from China University of Petroleum (East China) prepared a gel fracturing fluid using nonionic polyacrylamide polymer as a thickener and organozirconium crosslinking agent. The gel fracturing fluid formed by 0.5% thickener and 2.5% crosslinking agent has the characteristics of low filtration loss, easy gel breaking, and good sand suspension performance. It was tested at 90℃ for 170 seconds. -1 The viscosity remained above 50 mPa·s after 2 hours of shearing, and the core damage rate of the fracturing fluid was only 14.88% (Wang Siyu et al., Research on formulation system of organic zirconium gel fracturing fluid, Oilfield Chemistry, 2014, 31(02).

[0010] Jin Lian et al. from Yangtze University first synthesized an organozirconium crosslinking agent using zirconium oxychloride, polyol, organic ligand, complexing crosslinking agent, and high-temperature stabilizer. They then crosslinked this agent with a polyacrylamide thickener to prepare a temperature-resistant, slow-crosslinking gel fracturing fluid system. This system was tested at 150℃ for 170 seconds. -1 After 2 hours of shearing, the viscosity is greater than 50 mPa·s. Its sand-carrying capacity and filtration performance are significantly better than those of conventional guar gum fracturing fluid systems. It can achieve complete gel breaking within 1 to 3 hours, leaving no residue and being easy to backflow (Jin Lian et al., Preparation and performance evaluation of temperature-resistant slow-crosslinking organic zirconium gel fracturing fluid, Daily Chemical Industry, 2023, 53(03)).

[0011] The existing patents and published literature mainly use conventional crosslinking agents to crosslink polymers to form gel fracturing fluid systems. However, due to the limited active sites of thickeners and crosslinking agents, problems such as insufficient crosslinking efficiency, high construction friction, and large dosage still exist. To address these issues, the following existing patents and published literature offer some technical solutions.

[0012] Chinese Patent CN106467734B discloses a crosslinking agent for fracturing and its preparation method. The agent is prepared from boric acid, a polyhydroxy compound (at least one of polyvinyl alcohol, sodium alginate, and chitosan), an alkanolamine compound (monoethanolamine, diethanolamine, and triethanolamine), a peroxide (hydrogen peroxide, ammonium persulfate, and potassium persulfate), and water. This crosslinking agent can form a gel fracturing fluid with 0.6% hydroxypropyl guar gum. The crosslinking time is adjustable between 70s and 165s, and the gel is prepared at 190°C. o C, 170s -1 The viscosity remained above 50 mPa·s after 2 hours of shear stress. However, the patent did not address whether the obtained crosslinking agent was suitable for crosslinking synthetic polymer thickeners or its related properties after forming a gel fracturing fluid.

[0013] Chinese patent CN106566516B discloses a method for preparing a structurally controllable guar gum fracturing fluid nano-crosslinking agent. The method involves first preparing nano-silica of different particle sizes through water glass hydrolysis, then surface-modifying an amine-containing alkoxysilane compound with inorganic boron containing borate groups, and finally loading the boron-modified alkoxysilane compound onto the nano-silica through alkoxy hydrolysis. The crosslinking time and efficiency can be controlled by adjusting the size of the nano-silica and the loading amount of the boron-modified alkoxysilane compound. However, this patent does not address whether the obtained crosslinking agent is suitable for crosslinking polymer-based thickeners or its related properties after forming a gel fracturing fluid.

[0014] Chinese Patent CN117945953B discloses a multi-site crosslinking agent, a gel fracturing fluid, and their preparation and application. The crosslinking agent is prepared by a multi-site branched ligand (obtained via a nucleophilic substitution reaction of amino alcohol, triphenylmethane triisocyanate, and 1,2-dichloroethane), an inorganic high-valent metal salt (one or more of zirconium oxychloride, sodium tetraborate, or titanium tetrachloride), water, and dilute hydrochloric acid. This crosslinking agent, when crosslinked with 0.8% polyacrylamide polymer at a crosslinking ratio of 1:1.25, can achieve a crosslinking efficiency of 90%. o Crosslinking to form a gel within 3 minutes at C, the resulting gel can be stored at 200°C. o C, 170s -1 The viscosity can reach up to 97 mPa·s after 2 hours of shearing. However, the preparation of the crosslinking agent obtained by this patent is complicated and requires the use of hazardous materials such as hydrochloric acid. At the same time, the amount of crosslinking agent used is still large and the cost is high.

[0015] Researchers at Yangtze University, including Xiong Junjie, first prepared surface-modified nano-silica by hydrolyzing γ-aminopropyltrimethoxysilane with sodium silicate. Then, they reacted titanium tetrachloride with the surface-modified nano-silica to prepare a titanium-modified nano-silica crosslinking agent. A gel fracturing fluid formed from this crosslinking agent and 0.35% to 0.4% hydroxypropyl guar gum was then subjected to fracturing at 150°C. o C, 170s -1 After 2 hours of shearing, the viscosity can reach up to 102 mPa·s (Xiong Junjie et al., Research on titanium-modified nano silica crosslinking agent and guar gum fracturing fluid, Applied Chemical Industry, 2021, 50(10)).

[0016] Zeng Linghao of Chongqing University of Science and Technology modified the surface of nano-silica with 3-aminopropyltriethoxysilane, and then further reacted it with boric acid and tetrabutyl titanate to prepare a nano-silica-based boron-titanium composite crosslinking agent. This crosslinking agent was then used with modified xanthated guar gum to form a gel fracturing fluid, which was then subjected to fracturing at 120℃ for 170 seconds. -1 The shear viscosity at 1 hour is around 50 mPa⋅s (Zeng Linghao, Preparation and Performance Analysis of Salt-Tolerant Modified Guar gum Fracturing Fluid Based on Nano-Crosslinking Agent, Chongqing University of Science and Technology, 2023). However, these published documents do not address whether the obtained crosslinking agent is suitable for crosslinking with synthetic polymer thickeners or its related properties after forming a gel fracturing fluid.

[0017] In summary, no reports have been found in the existing patents and published literature regarding multi-active-site crosslinking agents that can be used to efficiently crosslink synthetic polymer thickeners at low dosages. Existing crosslinking agents for fracturing have problems such as large dosage, low crosslinking efficiency, resulting in insufficient temperature and shear resistance and high cost of the formed gel fracturing fluid. Summary of the Invention

[0018] This invention provides a nano-crosslinking agent for fracturing and its preparation method, which overcomes the shortcomings of the prior art. It can effectively solve the problems of large dosage, low crosslinking efficiency, and thus insufficient temperature and shear resistance and high cost of the resulting gel fracturing fluid.

[0019] One of the technical solutions of the present invention is achieved through the following measures: a fracturing nano-crosslinking agent, the raw materials of which include silane coupling agent, nano-silica, amino acids, multi-component organic compounds and metallic zirconium salt, wherein the mass ratio of silane coupling agent to nano-silica is 1:(0.3 to 0.6).

[0020] The following are further optimizations and / or improvements to one of the above-mentioned inventive technical solutions: The aforementioned silane coupling agent is one or more of γ-glycidyl etheroxypropyltrimethoxysilane and 3-glycidyl etheroxypropyltriethoxysilane.

[0021] The above-mentioned amino acids are one or more of glycine, α-aminopropionic acid and γ-aminobutyric acid.

[0022] The aforementioned metallic zirconium salt is one or more of zirconium oxychloride, zirconium tetrachloride, zirconium sulfate, and zirconium nitrate.

[0023] The aforementioned multi-component organic compounds are one or more of polyols, polyacids, and polyacid salts, wherein the polyols are one or more of glycerol, 1,3-propanediol, sorbitol, and xylitol, the polyacids are one or more of lactic acid, citric acid, and phosphoric acid, and the polyacid salts are one or more of sodium lactate, sodium citrate, and sodium phosphate.

[0024] The above-mentioned fracturing nano-crosslinking agent is obtained by the following method: S1, the required amount of nano-silica is uniformly dispersed in an ethanol aqueous solution, then ammonia is added and mixed, and the required amount of silane coupling agent is added and stirred and refluxed to obtain a mixed solution. S2, after the mixture is successively cooled, washed, filtered and dried, intermediate A is obtained; S3, Disperse intermediate A in deionized water, then add amino acids and stir and reflux to obtain the reaction product. After washing and filtration, the reaction product is used to obtain intermediate B. S4. Metal zirconium salt is stirred in deionized water, and then multi-component organic matter and intermediate B are added sequentially and stirred to obtain a mixture. The pH value of the mixture is adjusted and the reaction is initiated to obtain a nano crosslinking agent for fracturing.

[0025] In step S1 above, the amount of ethanol aqueous solution added is 6 to 7 times the weight of nano silica, the mass concentration of ethanol aqueous solution is 95% to 98%, and ammonia water accounts for 1 / 100 of the total weight of ethanol aqueous solution, nano silica and silane coupling agent.

[0026] In step S1 above, during the reflux reaction, the reaction temperature is 75°C to 85°C, and the reaction time is 4 to 5 hours.

[0027] In step S2 above, cooling is cooling to room temperature, washing is performed using anhydrous ethanol as the washing solvent, and the washing and filtration are performed 3 to 4 times. Drying is specifically performed under vacuum at 80°C to 85°C for 22 to 26 hours.

[0028] In step S3 above, the mass ratio of intermediate A to amino acid is 1:(2.5 to 4.5).

[0029] In step S3 above, dispersion specifically involves ultrasonic dispersion for 0.5 h to 1.0 h, reflux reaction at a temperature of 55 °C to 60 °C and a reaction time of 4 h to 5 h, and washing and filtration specifically involve washing and filtration of the reaction product with anhydrous ethanol and deionized water 2 to 3 times respectively.

[0030] In step S4 above, the mass ratio of zirconium salt, deionized water, multi-component organic compound and intermediate B is 1:(4 to 5):(0.6 to 0.8):(0.7 to 1.3).

[0031] In step S4 above, the pH value of the mixture is adjusted to 6.5 to 8.0 using a pH adjuster, which is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, and sodium carbonate.

[0032] In step S4 above, the reaction temperature is 55℃ to 65℃ and the reaction time is 4.5h to 5.0h.

[0033] The second technical solution of the present invention is achieved through the following measures: a method for preparing a nano-crosslinking agent for fracturing, obtained by the following method: S1, the required amount of nano-silica is uniformly dispersed in an ethanol aqueous solution, then ammonia is added and mixed, and the required amount of silane coupling agent is added and stirred and refluxed to obtain a mixed solution. S2, after the mixture is successively cooled, washed, filtered and dried, intermediate A is obtained; S3, Disperse intermediate A in deionized water, then add amino acids and stir and reflux to obtain the reaction product. After washing and filtration, the reaction product is used to obtain intermediate B. S4. Metal zirconium salt is stirred in deionized water, and then multi-component organic matter and intermediate B are added sequentially and stirred to obtain a mixture. The pH value of the mixture is adjusted and the reaction is initiated to obtain a nano crosslinking agent for fracturing.

[0034] The fracturing nano-crosslinking agent of this invention is obtained by modifying nano-silica to obtain modified nano-silica containing multiple carboxyl groups and multiple hydroxyl groups. It is obtained by introducing modified nano-silica containing multiple carboxyl groups and multiple hydroxyl groups into conventional organic zirconium (zirconium salt). The fracturing nano-crosslinking agent of this invention has an adjustable crosslinking time and high crosslinking efficiency. It can efficiently and synergistically form a gel fracturing fluid with polyacrylamide thickener at a low addition amount, which has excellent salt resistance, high temperature resistance and shear resistance. Detailed Implementation

[0035] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0036] The present invention will be further described below with reference to embodiments: Example 1: The fracturing nano-crosslinking agent is made of silane coupling agent, nano-silica, amino acids, multi-component organic compounds and zirconium salt, wherein the mass ratio of silane coupling agent to nano-silica is 1:(0.3 to 0.6).

[0037] Example 2: As an optimization of the above example, the silane coupling agent is one or more of γ-glycidoxypropyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane, with the following structural formula: .

[0038] Example 3: As an optimization of the above examples, the amino acid is one or more of glycine, α-aminopropionic acid, and γ-aminobutyric acid, and its structural formula is: .

[0039] Example 4: As an optimization of the above examples, the metallic zirconium salt is one or more of zirconium oxychloride, zirconium tetrachloride, zirconium sulfate, and zirconium nitrate.

[0040] Example 4: As an optimization of the above examples, the multi-component organic compound is one or more of polyols, polyacids, and polyacid salts, wherein the polyol is one or more of glycerol, 1,3-propanediol, sorbitol, and xylitol, the polyacid is one or more of lactic acid, citric acid, and phosphoric acid, and the polyacid salt is one or more of sodium lactate, sodium citrate, and sodium phosphate.

[0041] Example 5: As an optimization of the above examples, a fracturing nano-crosslinking agent was obtained by the following method: S1, the required amount of nano-silica is uniformly dispersed in an ethanol aqueous solution, then ammonia is added and mixed, and the required amount of silane coupling agent is added and stirred and refluxed to obtain a mixed solution. S2, after the mixture is successively cooled, washed, filtered and dried, intermediate A is obtained, namely epoxy-modified nano-silica, with the following structural formula: ; S3. Intermediate A is dispersed in deionized water, then amino acids are added and stirred under reflux to obtain the reaction product. After washing and filtration, intermediate B is obtained, which is modified nano-silica containing multiple carboxyl and hydroxyl groups, with the following structural formula: The structural formula for R is: ; S4. Metal zirconium salt is stirred in deionized water, and then multi-component organic matter and intermediate B (modified nano-silica containing multiple carboxyl groups and multiple hydroxyl groups) are added in sequence and stirred to obtain a mixture. The pH value of the mixture is adjusted and the reaction is initiated to obtain a nano-crosslinking agent for fracturing.

[0042] Example 6: As an optimization of the above example, in step S1, the amount of ethanol aqueous solution added is 6 to 7 times the weight of nano silica, the mass concentration of ethanol aqueous solution is 95% to 98%, and ammonia water accounts for 1 / 100 of the total weight of ethanol aqueous solution, nano silica and silane coupling agent.

[0043] Example 7: As an optimization of the above example, in step S1, the reaction temperature during reflux is 75°C to 85°C, and the reaction time is 4h to 5h.

[0044] Example 8: As an optimization of the above example, in step S2, the cooling is to cool to room temperature, the washing solvent is anhydrous ethanol, the washing and filtration are performed 3 to 4 times, and the drying is specifically vacuum drying at 80°C to 85°C for 22 to 26 hours.

[0045] Example 9: As an optimization of the above example, in step S3, the mass ratio of intermediate A to amino acid is 1:(2.5 to 4.5); the dispersion is specifically ultrasonic dispersion for 0.5 h to 1.0 h; during reflux reaction, the reaction temperature is 55 °C to 60 °C and the reaction time is 4 h to 5 h; the washing and filtration are specifically washing and filtration of the reaction product with anhydrous ethanol and deionized water 2 to 3 times respectively.

[0046] Example 10: As an optimization of the above example, in step S4, the mass ratio of zirconium salt, deionized water, multi-component organic compound and intermediate B is 1:(4 to 5):(0.6 to 0.8):(0.7 to 1.3).

[0047] Example 11: As an optimization of the above example, in step S4, the pH value of the mixture is adjusted to 6.5 to 8.0 using a pH adjuster, wherein the pH adjuster is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate and sodium carbonate.

[0048] Example 12: As an optimization of the above example, in step S4, the reaction temperature is 55°C to 65°C and the reaction time is 4.5h to 5.0h.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention first modifies nano-silica with a silane coupling agent to obtain intermediate A (epoxy-containing modified nano-silica). Then, intermediate A (epoxy-containing modified nano-silica) is modified with amino acids to obtain intermediate B (polycarboxyl and polyhydroxy modified nano-silica). Finally, intermediate B (polycarboxyl and polyhydroxy modified nano-silica) is introduced into conventional organozzirconium (zirconium salt) to form a fracturing nano-crosslinking agent, which significantly improves the crosslinking efficiency. The gel fracturing fluid formed by the efficient synergy of the fracturing nano-crosslinking agent and polyacrylamide thickener has excellent salt resistance, high temperature resistance, and shear resistance. It possesses at least the following superior properties: at a mineralization of 100,000 mg / L (calcium and magnesium ion content of 8,000 mg / L), the crosslinking time of the fracturing nano-crosslinking agent is adjustable from 55 s to 300 s; after crosslinking the fracturing nano-crosslinking agent with an addition amount of 0.25% to 0.45% and the polyacrylamide thickener with an addition amount of 0.7% to 0.8%, a gel fracturing fluid is formed at 200℃ for 170 s. -1 After shearing for 2 hours under the specified conditions, the viscosity is greater than 60 mPa·s.

[0050] Example 13: This fracturing nano-crosslinking agent is obtained by the following method: S1, 80g of nano-silica was uniformly dispersed in 490g of 98% ethanol aqueous solution, and then 7g of ammonia water was added and stirred until uniform. 133g of silane coupling agent (γ-glycidoxypropyltrimethoxysilane) was slowly added. After stirring continuously at 75℃ and undergoing reflux reaction for 4h, a mixed solution was obtained. S2, the mixture was cooled to room temperature, washed and filtered three times with anhydrous ethanol, and then vacuum dried at 80°C for 24 hours to obtain intermediate A, namely epoxy-modified nano-silica. S3, 40g of intermediate A was ultrasonically dispersed in deionized water for 1h to form a uniform dispersion of intermediate A. 180g of amino acid (aminoacetic acid) was slowly added to the dispersion of intermediate A, and the mixture was stirred and mixed evenly. The mixture was then refluxed at 60℃ for 5h to obtain the reaction product. The reaction product was washed and filtered twice with anhydrous ethanol and deionized water to obtain intermediate B, which is modified nano-silica containing multiple carboxyl groups and multiple hydroxyl groups. S4. 20g of metallic zirconium salt (zirconium oxychloride) was stirred in 90g of deionized water for 6min until fully dissolved. Then, 12g of multi-component organic compound (glycerol) was added and stirred for another 5min. Then, 25g of intermediate B was added and stirred for another 6min to obtain a mixture. The pH of the mixture was adjusted to 7.0 with sodium hydroxide and reacted at 55℃ for 5h to obtain a fracturing nano-crosslinking agent.

[0051] Example 14: The difference between this fracturing nano-crosslinking agent and Example 13 of the present invention is that the "silane coupling agent (γ-glycidoxypropyltrimethoxysilane)" is replaced with "silane coupling agent (3-glycidoxypropyltriethoxysilane)," while the other steps are the same.

[0052] Example 15: The fracturing nano-crosslinking agent differs from that in Example 13 of this invention in that "multi-component organic compound (glycerol)" is replaced with "silane coupling agent multi-component organic compound (lactic acid)", while the other steps are the same.

[0053] Example 16: The fracturing nano-crosslinking agent differs from that in Example 13 of this invention in that "amino acid (aminoacetic acid)" is replaced with "amino acid (γ-aminobutyric acid)," while the other steps are the same.

[0054] Example 17: The fracturing nano-crosslinking agent differs from that in Example 13 of this invention in that "multi-component organic compound (glycerol)" is replaced with "multi-component organic compound (a mixture of glycerol and lactic acid in a mass ratio of 2:1)", while the other steps are the same.

[0055] Example 18: The fracturing nano-crosslinking agent differs from that in Example 13 of this invention in that "multi-component organic compound (glycerol)" is replaced with "multi-component organic compound (a mixture of glycerol and lactic acid in a mass ratio of 1:1)", while the other steps are the same.

[0056] Example 19: The fracturing nano-crosslinking agent differs from that in Example 13 of this invention in that "multi-component organic compound (glycerol)" is replaced with "multi-component organic compound (a mixture of glycerol and lactic acid in a mass ratio of 1:2)", while the other steps are the same.

[0057] Comparative Example 1: The crosslinking agent is obtained by stirring 20g of metallic zirconium salt (zirconium oxychloride) in 90g of deionized water for 6 minutes until fully dissolved, then adding 12g of multi-component organic compound (glycerol) and stirring for another 5 minutes to obtain a mixture. The pH of the mixture is adjusted to 7.0 with sodium hydroxide, and the mixture is reacted at 55℃ for 5 hours to obtain the crosslinking agent.

[0058] Comparative Example 2: The crosslinking agent differs from Comparative Example 1 of the present invention in that "multi-component organic compound (glycerol)" is replaced with "silane coupling agent multi-component organic compound (lactic acid)", while the other steps are the same.

[0059] Comparative Example 3: The crosslinking agent differs from Comparative Example 1 of the present invention in that "multi-component organic compound (glycerol)" is replaced with "multi-component organic compound (a mixture of glycerol and lactic acid in a mass ratio of 2:1)", while the other steps are the same.

[0060] Comparative Example 4: The crosslinking agent differs from Comparative Example 1 of the present invention in that "multi-component organic compound (glycerol)" is replaced with "multi-component organic compound (a mixture of glycerol and lactic acid in a mass ratio of 1:1)", while the other steps are the same.

[0061] Comparative Example 5: The crosslinking agent differs from Comparative Example 1 of the present invention in that "multi-component organic compound (glycerol)" is replaced with "multi-component organic compound (a mixture of glycerol and lactic acid in a mass ratio of 1:2)", while the other steps are the same.

[0062] Experimental Example 1: Investigating the performance of the nano-crosslinking agent for fracturing according to the present invention.

[0063] Experimental methods: Solution preparation: Accurately weigh polyacrylamide thickener XZ-CHJ (from the Engineering Technology Research Institute of Western Drilling Engineering Co., Ltd.) and add it to a beaker containing an appropriate amount of brine (total mineralization 100,000 mg / L, of which calcium and magnesium ion content is 8,000 mg / L). Stir and dissolve the solution for 2 minutes at room temperature and a speed of 400±50 r / min using a high-speed stirrer to prepare a polyacrylamide thickener brine solution with a mass concentration of 0.7% to 0.8%.

[0064] Crosslinking performance: At 90°C, 0.25g to 0.45g of the fracturing nano-crosslinking agent prepared in Examples 13 to 19 of this invention was added to 100g of a 0.7% to 0.8% polyacrylamide thickener salt solution and mixed. A stopwatch was started, and the mixture was stirred and observed with a glass rod. The time for complete crosslinking was recorded as the crosslinking time. The gel strength was determined by visual gel strength code method (Sydansk Robert et al., Conformance improvement in asubterranean hydrocarbon-bearing formation using a polymer gel, US4683949, 1987) to evaluate the crosslinking performance. After complete crosslinking, the gel fracturing fluid was obtained.

[0065] Temperature and shear resistance: Using the RS6000 advanced rheometer PZ38 coaxial cylindrical rotor system, the temperature and shear resistance were tested at 200℃ and 170s. -1 The crosslinked fracturing fluid was subjected to a 2-hour temperature and shear resistance test (from heating to the end of the test) and the final stable viscosity value was recorded to evaluate its temperature and shear resistance.

[0066] The experimental method was used to test the crosslinking properties of the fracturing nano-crosslinking agents prepared in Examples 13 to 19 of the present invention and the crosslinking agents prepared in Comparative Examples 1 to 5 with the respective polyacrylamide thickeners, as well as the temperature resistance and shear resistance of the resulting gel fracturing fluids.

[0067] Experimental results: The crosslinking properties of the nano-crosslinking agent and polyacrylamide thickener used in fracturing according to the present invention, as well as the temperature resistance and shear resistance of the resulting gel fracturing fluid, are shown in Table 1. In Table 1, the crosslinking gel grades are as follows: A is non-probing gel, B is high-flow gel, C is flow gel, D is medium-flow gel, E is almost non-flow gel, F is high-deformation non-flow gel, G is medium-deformation non-flow gel, H is slightly-deformation non-flow gel, and I is rigid gel.

[0068] As can be seen from Table 1, the fracturing nano-crosslinking agents prepared in Examples 13 to 19 of the present invention with an addition amount of 0.25% to 0.45% and a addition amount of 0.7% to 0.8% of polyacrylamide thickener can all be completely crosslinked, and the crosslinking gel strength is above grade D. Compared with comparative examples 1 to 5, the crosslinking time and temperature resistance and shear stability viscosity of the fracturing nano-crosslinking agents prepared in Examples 13 to 19 of the present invention are significantly increased. Among them, Example 13 showed a crosslinking time that was more than 22% longer and a temperature-resistant shear-stable viscosity that was more than 25% higher than that of Comparative Example 1; Example 15 showed a crosslinking time that was more than 18% longer and a temperature-resistant shear-stable viscosity that was more than 30% higher than that of Comparative Example 2; Example 17 showed a crosslinking time that was more than 25% longer and a temperature-resistant shear-stable viscosity that was more than 20% higher than that of Comparative Example 3; Example 18 showed a crosslinking time that was more than 24% longer and a temperature-resistant shear-stable viscosity that was more than 18.5% higher than that of Comparative Example 4; and Example 19 showed a crosslinking time that was more than 30% longer and a temperature-resistant shear-stable viscosity that was more than 19.6% higher than that of Comparative Example 5.

[0069] Therefore, compared to Comparative Examples 1 to 5, the fracturing nano-crosslinking agent obtained by introducing modified nano-silica containing multiple carboxyl groups and multiple hydroxyl groups into conventional organozzirconium (zirconium metal salt) in this invention has a significantly improved crosslinking efficiency, and the crosslinking time is adjustable between 55 s and 300 s. Simultaneously, the gel fracturing fluid formed by crosslinking 0.25% to 0.45% of the fracturing nano-crosslinking agent of this invention with 0.7% to 0.8% of polyacrylamide thickener exhibits excellent performance at 200°C for 170 s. -1 After shearing for 2 hours under certain conditions, the viscosity is greater than 60 mPa·s, which greatly improves the temperature resistance and shear strength. In gel fracturing fluid, it can significantly reduce the amount of polyacrylamide thickener and fracturing nano crosslinking agent added.

[0070] In summary, the fracturing nano-crosslinking agent of this invention is obtained by modifying nano-silica to obtain modified nano-silica containing multiple carboxyl groups and multiple hydroxyl groups. It is obtained by introducing modified nano-silica containing multiple carboxyl groups and multiple hydroxyl groups into conventional organic zirconium (zirconium salt). The fracturing nano-crosslinking agent of this invention has an adjustable crosslinking time and high crosslinking efficiency. The gel fracturing fluid formed by the fracturing nano-crosslinking agent and polyacrylamide thickener at a low addition amount has excellent salt resistance, high temperature resistance and shear resistance.

[0071] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A nano-crosslinking agent for fracturing, characterized in that... The raw materials include silane coupling agent, nano silica, amino acids, multi-component organic compounds and zirconium salts, wherein the mass ratio of silane coupling agent to nano silica is 1:0.3 to 0.

6.

2. The fracturing nano-crosslinking agent according to claim 1, characterized in that... The silane coupling agent is one or more of γ-glycidoxypropyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane.

3. The fracturing nano-crosslinking agent according to claim 1 or 2, characterized in that... The amino acid is one or more of glycine, α-aminopropionic acid, and γ-aminobutyric acid.

4. The fracturing nano-crosslinking agent according to claim 1, 2, or 3, characterized in that... The metallic zirconium salt is one or more of zirconium oxychloride, zirconium tetrachloride, zirconium sulfate, and zirconium nitrate.

5. The fracturing nano-crosslinking agent according to any one of claims 1 to 4, characterized in that... The multi-component organic compound is one or more of polyols, polyacids, and polyacid salts, wherein the polyol is one or more of glycerol, 1,3-propanediol, sorbitol, and xylitol, the polyacid is one or more of lactic acid, citric acid, and phosphoric acid, and the polyacid salt is one or more of sodium lactate, sodium citrate, and sodium phosphate.

6. The fracturing nano-crosslinking agent according to any one of claims 1 to 5, characterized in that... Obtained using the following method: S1, the required amount of nano-silica is uniformly dispersed in an ethanol aqueous solution, then ammonia is added and mixed, and the required amount of silane coupling agent is added and stirred and refluxed to obtain a mixed solution. S2, after the mixture is successively cooled, washed, filtered and dried, intermediate A is obtained; S3, Disperse intermediate A in deionized water, then add amino acids and stir and reflux to obtain the reaction product. After washing and filtration, the reaction product is used to obtain intermediate B. S4. Metal zirconium salt is stirred in deionized water, and then multi-component organic matter and intermediate B are added sequentially and stirred to obtain a mixture. The pH value of the mixture is adjusted and the reaction is initiated to obtain a nano crosslinking agent for fracturing.

7. The fracturing nano-crosslinking agent according to claim 6, characterized in that... In step S1, the amount of ethanol aqueous solution added is 6 to 7 times the weight of nano silica, the mass concentration of ethanol aqueous solution is 95% to 98%, and ammonia water accounts for 1 / 100 of the total weight of ethanol aqueous solution, nano silica and silane coupling agent; or / and, in step S1, during the reflux reaction, the reaction temperature is 75°C to 85°C, and the reaction time is 4h to 5h.

8. The fracturing nano-crosslinking agent according to claim 6 or 7, characterized in that... In step S2, cooling is performed to room temperature; during washing, anhydrous ethanol is used as the washing solvent; the washing and filtration are performed 3 to 4 times; and drying is specifically performed under vacuum at 80°C to 85°C for 22 to 26 hours. Or / and in step S3, the mass ratio of intermediate A to amino acid is 1:2.5 to 4.

5. Or / and in step S3, dispersion is specifically performed by ultrasonic dispersion for 0.5 to 1.0 hours; during reflux reaction, the reaction temperature is 55°C to 60°C, the reaction time is 4 to 5 hours, and washing and filtration are specifically performed by washing and filtration of the reaction product with anhydrous ethanol and deionized water 2 to 3 times respectively.

9. The fracturing nano-crosslinking agent according to claim 6, 7, or 8, characterized in that... In step S4, the mass ratio of the zirconium salt, deionized water, multi-component organic compound, and intermediate B is 1:4 to 5:0.6 to 0.8:0.7 to 1.3; or / and, in step S4, the pH of the mixture is adjusted to 6.5 to 8.0 using a pH adjuster, which is one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, and sodium carbonate; or / and, in step S4, the reaction temperature is 55°C to 65°C, and the reaction time is 4.5 h to 5.0 h.

10. A method for preparing a fracturing nano-crosslinking agent according to any one of claims 1 to 5, 7 to 9, characterized in that... Perform it as follows: S1, the required amount of nano-silica is uniformly dispersed in an ethanol aqueous solution, then ammonia is added and mixed, and the required amount of silane coupling agent is added and stirred and refluxed to obtain a mixed solution. S2, after the mixture is successively cooled, washed, filtered and dried, intermediate A is obtained; S3, Disperse intermediate A in deionized water, then add amino acids and stir and reflux to obtain the reaction product. After washing and filtration, the reaction product is used to obtain intermediate B. S4. Metal zirconium salt is stirred in deionized water, and then multi-component organic matter and intermediate B are added sequentially and stirred to obtain a mixture. The pH value of the mixture is adjusted and the reaction is initiated to obtain a nano crosslinking agent for fracturing.

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