High-temperature-resistant instant fracturing fluid thickening agent and preparation method thereof

Abstract

The invention provides a high-temperature-resistant instant fracturing fluid densifier and a preparation method thereof, and belongs to the technical field of oil and gas well fracturing, and the preparation method comprises the following steps: mixing and stirring acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, octadecyl methacrylate, pAMPS, an ammonium sulfate solution and 4-vinylpyridine propyl sulphobetaine, adding an auxiliary agent, and stirring to obtain the high-temperature-resistant instant fracturing fluid densifier. The pH value is adjusted to 5.0-5.5, azobis (isobutylamidine hydrochloride) is added for continuous reaction, washing, separation and vacuum drying are performed, and high-temperature-resistant and salt-resistant copolymer powder is obtained; and adding the high-temperature-resistant and salt-resistant copolymer powder into deionized water, mechanically stirring, sequentially adding maltodextrin, sodium citrate and a hydrophilic auxiliary agent while continuously stirring, continuously stirring, sieving, spray-drying and granulating to obtain the high-temperature-resistant instant fracturing fluid thickening agent. According to the invention, the dissolution rate can be increased while the high-temperature resistance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas well fracturing, in particular to a high-temperature-resistant and fast-dissolving fracturing fluid thickening agent and a preparation method thereof. BACKGROUND

[0002] With the gradual decrease of conventional oil and gas resources, the effective development and utilization of deep and ultra-deep tight and shale reservoir oil and gas resources is particularly important. In order to improve the percolation capacity of such complex reservoirs and improve the oil and gas release conditions, fracturing technology has become the main means of stimulation and reconstruction. Through fracturing, a high-conductivity fracture system can be formed in the reservoir, thereby significantly improving oil and gas production. Fracturing fluid is the core component of fracturing construction, and its rheological properties, sand-carrying capacity and stability are directly related to the fracturing effect, and the thickening agent is the key component that determines the performance of the fracturing fluid. Deep and ultra-deep tight and shale reservoir oil and gas resources are buried deep, so the fracturing fluid thickening agent is required to have good temperature resistance and good shear resistance to improve the stability and construction adaptability under complex working conditions.

[0003] At present, the commonly used thickening agents mainly include two categories of plant gums and synthetic polymers. Plant gum thickening agents such as guar gum and konjac gum are low in price and widely available, but most of them have poor temperature resistance, high residue content and other defects. For example, the commonly used hydroxypropyl guar gum is prone to glycosidic bond rupture at high temperatures, resulting in rapid viscosity decay of the system, which is difficult to meet the sand-carrying requirements of high-temperature well sections. Although synthetic polymer thickening agents are superior to plant gums in terms of temperature resistance, they are prone to irreversible molecular chain rupture under high temperature and high shear conditions, and the viscosity retention of the system is poor. In recent years, oligomer thickening agents have attracted attention due to their small structure and superior shear degradation resistance, but their temperature resistance limit is usually only 90-120℃, which is difficult to apply to deep and ultra-deep fracturing construction exceeding 120℃.

[0004] The application patent with publication number CN101220263A discloses a water-based fracturing fluid thickening agent and its production method. The thickening agent is copolymerized from four monomers of N,N-dialkyl acrylamide, dimethyl diallyl ammonium chloride, acrylonitrile, methacryloyloxyethyl trimethyl ammonium chloride or acryloyloxyethyl trimethyl ammonium chloride. Although it solves the problems of insufficient temperature resistance and instability under high temperature and high shear of the fracturing fluid thickening agent in the prior art, the prepared polymer powder has insufficient hydrophilicity on the surface, which makes the dissolution slow. In actual field fracturing construction, such thickening agent is difficult to completely dissolve in a short time, which cannot meet the requirements of fast-dissolving for rapid preparation or continuous mixing process of fracturing fluid.

[0005] Therefore, it is necessary to provide a high-temperature-resistant and fast-dissolving fracturing fluid thickening agent and a preparation method thereof to solve the problems existing in the prior art. SUMMARY

[0006] Therefore, the application provides a high-temperature-resistant instant fracturing fluid thickening agent and a preparation method thereof, which can improve the high-temperature resistance and the dissolution rate.

[0007] To achieve the above-mentioned purpose, the application provides a preparation method of a high-temperature-resistant instant fracturing fluid thickening agent, which comprises the following steps: S1, 4-vinylpyridine, toluene and 1,3-propane sulfone lactone are mixed, and after high-temperature reaction, filtration, washing and vacuum drying, 4-vinylpyridine propyl sulfobetaine is obtained; S2, acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, acrylic acid, octadecyl methacrylate, pAMPS, an ammonium sulfate solution, 4-vinylpyridine propyl sulfobetaine are mixed and stirred, an additive is added, the pH value is adjusted to 5.0-5.5, azobisdimethylaminoformamidine hydrochloride is added for continuous reaction, and then washing, separation and vacuum drying are performed to obtain a high-temperature-resistant and salt-resistant copolymer powder; S3, the high-temperature-resistant and salt-resistant copolymer powder is added to deionized water for mechanical stirring, maltodextrin, sodium citrate and a hydrophilic additive are sequentially added under continuous stirring, and then stirring, sieving and spray drying granulation are performed to obtain the high-temperature-resistant instant fracturing fluid thickening agent.

[0008] In the application, the 4-vinylpyridine propyl sulfobetaine is prepared by nucleophilic ring-opening quaternization reaction of 4-vinylpyridine and 1,3-propane sulfone lactone, and the structural formula is as follows: The 4-vinylpyridine propyl sulfobetaine is introduced as an amphoteric ion monomer, and the strong hydrated ion pair composed of the pyridine quaternary ammonium cation and the sulfonic acid anion can inhibit the curling and aggregation of chains in high-salinity and Ca 2+ / Mg 2+ brine containing Ca

[0009] In the preparation of the high-temperature-resistant and salt-resistant copolymer powder, octadecyl methacrylate is also introduced, and the structural formula is as follows: The long-chain hydrophobic alkyl side groups form a large number of reversible physical cross-linking points in the aqueous phase through hydrophobic association, so that the polymer chain can still maintain a temporary three-dimensional network structure under high temperature and high shear conditions, further improving the viscosity and shear resistance of the system; meanwhile, the pyridine aromatic ring in the 4-vinyl pyridine propyl sulfobetaine unit is preferentially distributed near the hydrophobic association domain, while the quaternary ammonium cation / sulfonic acid anion zwitterion head group stretches into the aqueous phase, forming a hydration enrichment layer in the interface region around the hydrophobic association domain. In this way, sufficient hydrophobic association strength is maintained, and excessive aggregation of the hydrophobic domain into hard blocks is avoided, so that the hydrophobic association structure can reversibly open and close under high temperature and high shear, and can self-recover after shearing, thereby having both high-temperature shear resistance and system stability.

[0010] In order to further improve the dissolution rate of the fracturing fluid thickening agent, the present application constructs a porous powder system by combining the high-temperature-resistant and salt-resistant copolymer powder with malt dextrin, sodium citrate and other hydrophilic aids after the high-temperature-resistant and salt-resistant copolymer powder is prepared. The malt dextrin forms a porous brittle skeleton during the spray drying process, so that the internal structure of the dried particles has a large number of micropores, improving the water permeation speed, and the sodium citrate plays a micro-foaming and permeation guiding role during the drying and reswelling process, which is beneficial to the rapid entry of water into the internal part of the particles along the pore channel, accelerates the disintegration of the particles to release the polymer chains, and the hydrophilic aid further improves the wettability and dispersibility of the particle surface; the porous particles formed after the spray drying granulation have a large specific surface area, and the prepared fracturing fluid thickening agent can realize rapid wetting-permeation-disintegration after being contacted with water, effectively avoiding the common problems of fish eyes, agglomeration and slow dissolution on site, so as to achieve the effect of instant dissolution.

[0011] Optionally, in the step S1, 10-12 mass parts of 4-vinyl pyridine, 120-150 volume parts of toluene are added into a reaction kettle, mixed and stirred, 13-15 mass parts of 1,3 propane sulfone lactone is added for high-temperature reaction, then filtered, washed with acetone for 3-5 times, and vacuum dried to obtain 4-vinyl pyridine propyl sulfobetaine.

[0012] Optionally, the mixing and stirring time is 5-10 min, the high-temperature reaction temperature is 75-85℃, and the time is 18-20 h, and the vacuum drying temperature is 50-60℃, and the time is 18-24 h.

[0013] Optionally, the pAMPS is obtained by dissolving 8-12 mass parts of 2-acrylamido-2-methylpropane sulfonic acid in 40 volume parts of deionized water, adding 0.1-0.12 mass parts of azobisdimethylaminoformamide hydrochloride, and reacting at 50℃ in a nitrogen environment for 6-8 h.

[0014] The present application can effectively prevent the further agglomeration of particles and the gelation of the whole system by pre-preparing pAMPS and introducing it into the main polymerization system as a component, and the pre-prepared pAMPS is a water-soluble polymer with a large number of sulfonic acid groups, which still has good water solubility and strong hydrophilicity in the subsequent 25% ammonium sulfate salting-out medium, can be adsorbed on the surface of the newly generated polymer particles during the copolymerization reaction, and form a charged and strongly hydrated protective layer, so that the reaction can be stably carried out in the form of dispersion / emulsion polymerization.

[0015] Optionally, in the step S2, 30-35 parts by mass of acrylamide, 6-10 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid, 1.5-3 parts by mass of acrylic acid, 0.3-0.5 parts by mass of stearyl methacrylate and pAMPS are added into 200-220 parts by volume of 25% ammonium sulfate solution, 0.78-1.5 parts by mass of 4-vinylpyridine propyl sulfobetaine is added and stirred at a speed of 500 rpm for 20-50 min, then an additive is added, the pH value is adjusted to 5.0-5.5 by sodium hydroxide, and the system is purged with nitrogen for 20-30 min, 0.2-0.3 g of azobisdimethylaminoformamidine hydrochloride is added, and the reaction is continued at 50-60°C for 6-8 h, then the polymer is separated by washing with anhydrous ethanol for 3-5 times, and vacuum drying for 18-24 h to obtain the high-temperature-resistant and salt-resistant copolymer powder.

[0016] The present application forms a multi-copolymer network containing long-chain hydrophobic side groups and zwitterionic side groups through free radical dispersion / emulsion copolymerization in a high-salt aqueous medium. During the reaction, pAMPS as a hydrophilic macromolecule with sulfonic acid groups is beneficial to be adsorbed on the surface of the newly generated polymer particles, forming a charged and strongly hydrated protective layer, thereby significantly slowing down the particle agglomeration trend, so that the polymerization process can be stably carried out in the form of dispersion / emulsion polymerization. Finally, the residual salt and unreacted monomers are removed by ethanol washing, and the high-temperature-resistant and salt-resistant copolymer powder with a main chain composed of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and acrylic acid (AA) and side chains introducing C18 long-chain hydrophobic groups and 4-vinylpyridine propyl sulfobetaine zwitterionic groups is obtained after vacuum drying. Under the conditions of aqueous solution and actual fracturing fluid, the sulfonic acid groups and carboxyl groups in the copolymer are partially ionized, and the 4-vinylpyridine propyl sulfobetaine units exist in the form of internal salt type zwitterions, and the ionic structure is as follows: Optionally, the additive is 3.5-4.5 parts by mass of OP-10 and 2-3 parts by mass of dodecyl mercaptan.

[0017] In the present application, OP-10 is used as a non-ionic surfactant, which can improve the dispersion stability of each monomer and the generated polymer particles in a high-salt medium; and dodecyl mercaptan is introduced as a chain transfer agent, which can effectively control the molecular weight and molecular weight distribution of the polymer and prevent excessive crosslinking.

[0018] Optionally, in step S2, 0.3 to 0.8 parts by weight of methacrylamide chitosan are added when adding 4-vinylpyridinylpropyl sulfobetaine.

[0019] Methacrylamide chitosan has a molecular backbone containing polyamine and polyhydroxy structures, which, together with methacryloyl groups, participate in free radical polymerization. This allows chemical crosslinking points to be formed between polymer chain segments. Furthermore, the rigid structure of the chitosan backbone forms a second network reinforcement structure. This dual network structure, which is synergistically constructed with hydrophobically associated octadecyl methacrylate, further improves the polymer's high-temperature resistance and shear resistance, preventing chain breakage and viscosity reduction under shear conditions.

[0020] Optionally, the methacrylamide chitosan is obtained by dissolving 3-5 parts by weight of chitosan powder in 100-120 parts by volume of a 3% acetic acid solution, stirring at room temperature for 8-10 hours, adding 12-15 parts by weight of methacrylic anhydride and stirring magnetically for 4-6 hours, purifying using a cellulose dialysis membrane, washing with deionized water 3-5 times, and freeze-drying under vacuum.

[0021] Preferably, the molecular weight cutoff of the cellulose dialysis membrane is 14 kDa.

[0022] Optionally, in step S3, the high-temperature and salt-resistant copolymer powder is added to deionized water and mechanically stirred at 500-600 rpm for 40-60 minutes at room temperature. Maltodextrin, sodium citrate, and a hydrophilic additive are added sequentially while continuously stirring. The mixture is then mechanically stirred at 500-600 rpm for 30-50 minutes, sieved, spray-dried, and granulated to obtain a high-temperature resistant, fast-dissolving fracturing fluid thickener. The hydrophilic additive is one of PEG-6000, hydroxypropyl starch, and sodium carboxymethyl cellulose.

[0023] This invention uses one of PEG-6000, hydroxypropyl starch, and sodium carboxymethyl cellulose as a hydrophilic agent to distribute it evenly on the particle surface, enhance wettability, and enable the particles to quickly demulsify, wet, and disintegrate into microparticle units upon contact with water, thereby further improving dissolution efficiency and achieving rapid dissolution.

[0024] The present invention also provides a high-temperature resistant, fast-dissolving fracturing fluid thickener, comprising the following raw materials in parts by weight: 80-100 parts of high-temperature resistant and salt-resistant copolymer powder, 300 parts of deionized water, 35-45 parts of maltodextrin, 8-10 parts of sodium citrate, and 4-5 parts of hydrophilic additives.

[0025] This invention, through the compounding of this group ratio, ensures that the thickener still has excellent viscosity retention performance under high temperature and high salt conditions. On the other hand, it uses maltodextrin to construct a porous framework, sodium citrate to form microporous channels, and hydrophilic additives to improve wetting and dispersibility, so that the product is in the form of a fast-dissolving porous powder. After being added to water, it can be quickly wetted, penetrated and disintegrated, significantly shortening the solution preparation time and reducing fish eyes and agglomeration.

[0026] The above-described technical solution of the present invention has at least the following beneficial effects: 1. This invention introduces 4-vinylpyridinylpropylsulfonyl betaine, an amphoteric internal salt structure, which is suitable for high mineralization and Ca content. 2+ / Mg 2+ Salt water helps to inhibit chain curling and aggregation, significantly improving the polymer's salt resistance, resistance to polyvalent cation salting out, and solubility viscosity. At the same time, its pyridine aromatic ring improves the overall thermal stability and high-temperature viscosity retention rate.

[0027] 2. Octadecyl methacrylate provides long-chain hydrophobic association sites to construct a temporary three-dimensional network under high temperature and high shear. 4-Vinylpyridinylpropyl sulfobetaine preferentially accumulates in the interfacial region around the hydrophobic association domain, which maintains the hydrophobic association strength and prevents excessive aggregation. This allows the structure to reversibly open and close under high temperature and high shear, achieving viscosity self-recovery, and combining shear resistance with system stability. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are some embodiments of the present invention, and all other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0029] Example 1 5g of chitosan powder was dissolved in 120mL of 3% acetic acid solution and stirred at room temperature for 10h to obtain a chitosan solution. 15g of methacrylic anhydride was added and magnetically stirred for 6h. After purification using a cellulose dialysis membrane with a molecular weight cutoff of 14kDa, the solution was washed 5 times with deionized water and freeze-dried under vacuum to obtain methacrylamide chitosan. 10.5g of 4-vinylpyridine and 150mL of toluene were added to a reaction vessel and stirred for 10min. 13.5g of 1,3-propanesulfonyl lactone (CAS No. 1120-71-4) was added and reacted at 80℃ for 20h. After filtration, the solution was washed 5 times with acetone and dried under vacuum at 50℃ for 24h to obtain 4-vinylpyridinepropylsulfonate betaine.

[0030] 10 g of 2-acrylamido-2-methylpropanesulfonic acid was dissolved in 40 mL of deionized water, and then 0.1 g of azobisisobutyramidine hydrochloride was added. The mixture was reacted at 50 °C under nitrogen for 8 h to obtain pAMPS. 30 g of acrylamide, 6.5 g of 2-acrylamido-2-methylpropanesulfonic acid, 1.5 g of acrylic acid, 0.5 g of octadecyl methacrylate, and pAMPS were added to 220 mL of 25% ammonium sulfate solution. 0.85 g of 4-vinylpyridinium propyl sulfobetaine and 0.5 g of methacrylamide chitosan were added, and the mixture was stirred at 500 rpm for 50 min. Then, 4 g of pAMPS was added... OP-10 (CAS No.: 2201101-54-2) and 2.5g dodecyl mercaptan were mixed, the pH was adjusted to 5.0 with sodium hydroxide, and the mixture was purged with nitrogen for 30 min. Then, 0.26g azobisisobutyramidine hydrochloride was added, and the reaction was continued at 50℃ for 8 h. The mixture was then washed 5 times with anhydrous ethanol, the polymer was separated, and the mixture was vacuum dried for 24 h to obtain a high-temperature and salt-resistant copolymer powder.

[0031] 100g of high-temperature and salt-resistant powder was added to 300mL of deionized water and mechanically stirred at 600rpm for 40min at room temperature. Then, 40g of maltodextrin, 8.5g of sodium citrate and 5g of PEG-6000 were added sequentially while stirring continuously. The mixture was then mechanically stirred at 600rpm for another 50min. The mixture was sieved, spray-dried and granulated to obtain a high-temperature resistant, fast-dissolving fracturing fluid thickener.

[0032] Example 2 3g of chitosan powder was dissolved in 100mL of 3% acetic acid solution and stirred at room temperature for 8h to obtain a chitosan solution. 12g of methacrylic anhydride was added and magnetically stirred for 4h. After purification using a cellulose dialysis membrane with a molecular weight cutoff of 14kDa, the solution was washed three times with deionized water and freeze-dried under vacuum to obtain methacrylamide chitosan. 10g of 4-vinylpyridine and 120mL of toluene were added to a reaction vessel and mixed and stirred for 5min. 13g of 1,3-propanesulfonyl lactone (CAS No. 1120-71-4) was added and reacted at 75℃ for 18h. After filtration, the solution was washed three times with acetone and then dried under vacuum at 50℃ for 18h to obtain 4-vinylpyridinepropylsulfonate betaine.

[0033] 8 g of 2-acrylamido-2-methylpropanesulfonic acid was dissolved in 40 mL of deionized water, and then 0.1 g of azobisisobutyramidine hydrochloride was added. The mixture was reacted at 50 °C under nitrogen for 6 h to obtain pAMPS. 30 g of acrylamide, 6 g of 2-acrylamido-2-methylpropanesulfonic acid, 1.5 g of acrylic acid, 0.3 g of octadecyl methacrylate, and pAMPS were added to 200 mL of 25% ammonium sulfate solution. 0.78 g of 4-vinylpyridinylpropyl sulfobetaine and 0.3 g of methacrylamide chitosan were added, and the mixture was stirred at 500 rpm for 20 min. Then, 3.5 g of pAMPS was added. OP-10 (CAS No.: 2201101-54-2) and 2g of dodecyl mercaptan were mixed with sodium hydroxide to adjust the pH to 5.2. The mixture was purged with nitrogen for 20 min, and 0.2g of azobisisobutyramidine hydrochloride was added. The reaction was continued at 50℃ for 6 h. The polymer was washed three times with anhydrous ethanol, separated, and vacuum dried for 18 h to obtain a high-temperature and salt-resistant copolymer powder.

[0034] Add 80g of high-temperature and salt-resistant powder to 300mL of deionized water and mechanically stir at 500rpm for 40min at room temperature. While stirring continuously, add 35g of maltodextrin, 8g of sodium citrate and 4g of hydroxypropyl starch in sequence, and continue mechanically stirring at 500rpm for 30min. Sieve, spray dry and granulate to obtain high-temperature resistant fast-dissolving fracturing fluid thickener.

[0035] Example 3 5g of chitosan powder was dissolved in 120mL of 3% acetic acid solution and stirred at room temperature for 10h to obtain a chitosan solution. 15g of methacrylic anhydride was added and magnetically stirred for 6h. After purification using a cellulose dialysis membrane with a molecular weight cutoff of 14kDa, the solution was washed 5 times with deionized water and freeze-dried under vacuum to obtain methacrylamide chitosan. 12g of 4-vinylpyridine and 150mL of toluene were added to a reaction vessel and mixed and stirred for 10min. 15g of 1,3-propanesulfonyl lactone (CAS No. 1120-71-4) was added and reacted at 85℃ for 20h. After filtration, the solution was washed 5 times with acetone and then dried under vacuum at 60℃ for 24h to obtain 4-vinylpyridinepropylsulfonate betaine.

[0036] 12 g of 2-acrylamido-2-methylpropanesulfonic acid was dissolved in 40 mL of deionized water, and then 0.12 g of azobisisobutyramidine hydrochloride was added. The mixture was reacted at 50 °C under nitrogen for 8 h to obtain pAMPS. 35 g of acrylamide, 10 g of 2-acrylamido-2-methylpropanesulfonic acid, 3 g of acrylic acid, 0.4 g of octadecyl methacrylate, and pAMPS were added to 220 mL of 25% ammonium sulfate solution. 1.5 g of 4-vinylpyridinylpropyl sulfobetaine and 0.4 g of methacrylamide chitosan were added, and the mixture was stirred at 500 rpm for 40 min. Then, 4.5 g of... OP-10 (CAS No.: 2201101-54-2) and 3g of dodecyl mercaptan were mixed with sodium hydroxide to adjust the pH to 5.5, purged with nitrogen for 25 min, and 0.3g of azobisisobutyramidine hydrochloride was added. The reaction was continued at 60℃ for 8 h. The polymer was washed 4 times with anhydrous ethanol, separated, and vacuum dried for 24 h to obtain a high-temperature and salt-resistant copolymer powder.

[0037] Add 100g of high-temperature and salt-resistant powder to 300mL of deionized water and mechanically stir at 600rpm for 60min at room temperature. While stirring continuously, add 45g of maltodextrin, 10g of sodium citrate and 5g of sodium carboxymethyl cellulose in sequence, and continue mechanically stirring at 600rpm for 50min. Sieve, spray dry and granulate to obtain a high-temperature resistant, fast-dissolving fracturing fluid thickener.

[0038] Example 4 3.5 g of chitosan powder was dissolved in 110 mL of 3% acetic acid solution and stirred at room temperature for 8.5 h to obtain a chitosan solution. 14 g of methacrylic anhydride was added and magnetically stirred for 5 h. After purification using a cellulose dialysis membrane with a molecular weight cutoff of 14 kDa, the solution was washed four times with deionized water and freeze-dried under vacuum to obtain methacrylamide chitosan. 11 g of 4-vinylpyridine and 140 mL of toluene were added to a reaction vessel and mixed and stirred for 6 min. 14.5 g of 1,3-propanesulfonyl lactone (CAS No. 1120-71-4) was added and reacted at 80 °C for 19 h. After filtration, the solution was washed four times with acetone and then dried under vacuum at 55 °C for 20 h to obtain 4-vinylpyridinepropylsulfonate betaine.

[0039] 10 g of 2-acrylamido-2-methylpropanesulfonic acid was dissolved in 40 mL of deionized water, and then 0.11 g of azobisisobutyramidine hydrochloride was added. The mixture was reacted at 50 °C under nitrogen for 7 h to obtain pAMPS. 32 g of acrylamide, 8 g of 2-acrylamido-2-methylpropanesulfonic acid, 2.5 g of acrylic acid, 0.4 g of octadecyl methacrylate, and pAMPS were added to 210 mL of 25% ammonium sulfate solution. 1.2 g of 4-vinylpyridinium propyl sulfobetaine and 0.6 g of methacrylamide chitosan were added, and the mixture was stirred at 500 rpm for 40 min. Then, 4 g of pAMPS was added. OP-10 (CAS No.: 2201101-54-2) and 2.8 g of dodecyl mercaptan were added, the pH was adjusted to 5.4 with sodium hydroxide, the mixture was purged with nitrogen for 28 min, 0.26 g of azobisisobutyramidine hydrochloride was added, and the reaction was continued at 55 °C for 7.5 h. The mixture was then washed four times with anhydrous ethanol, the polymer was separated, and the mixture was vacuum dried for 22 h to obtain a high-temperature and salt-resistant copolymer powder.

[0040] Add 85g of high-temperature and salt-resistant powder to 300mL of deionized water and mechanically stir at 550rpm for 50min at room temperature. While stirring continuously, add 42g of maltodextrin, 8.5g of sodium citrate and 4.2g of PEG-6000 in sequence, and continue to mechanically stir at 550rpm for 45min. Sieve, spray dry and granulate to obtain a high-temperature resistant, fast-dissolving fracturing fluid thickener.

[0041] Example 5 4.5 g of chitosan powder was dissolved in 115 mL of 3% acetic acid solution and stirred at room temperature for 9 h to obtain a chitosan solution. 13 g of methacrylic anhydride was added and magnetically stirred for 5.5 h. After purification using a cellulose dialysis membrane with a molecular weight cutoff of 14 kDa, the solution was washed three times with deionized water and freeze-dried under vacuum to obtain methacrylamide chitosan. 11.5 g of 4-vinylpyridine and 130 mL of toluene were added to a reaction vessel and stirred for 8 min. 14 g of 1,3-propanesulfonyl lactone (CAS No. 1120-71-4) was added and reacted at 80 °C for 18.5 h. After filtration, the solution was washed five times with acetone and then dried under vacuum at 58 °C for 20 h to obtain 4-vinylpyridinepropylsulfonate betaine.

[0042] 9 g of 2-acrylamido-2-methylpropanesulfonic acid was dissolved in 40 mL of deionized water, and then 0.11 g of azobisisobutyramidine hydrochloride was added. The mixture was reacted at 50 °C under nitrogen for 6.5 h to obtain pAMPS. 32 g of acrylamide, 7 g of 2-acrylamido-2-methylpropanesulfonic acid, 2.8 g of acrylic acid, 0.32 g of octadecyl methacrylate, and pAMPS were added to 215 mL of 25% ammonium sulfate solution. 1.2 g of 4-vinylpyridinylpropyl sulfobetaine and 0.7 g of methacrylamide chitosan were added, and the mixture was stirred at 500 rpm for 40 min. Then, 3.6 g of... OP-10 (CAS No.: 2201101-54-2) and 2.2g of dodecyl mercaptan were added, the pH was adjusted to 5.1 with sodium hydroxide, the mixture was purged with nitrogen for 28 min, 0.22g of azobisisobutyramidine hydrochloride was added, and the reaction was continued at 58℃ for 6.5 h. The mixture was then washed three times with anhydrous ethanol, the polymer was separated, and the mixture was vacuum dried for 23 h to obtain a high-temperature and salt-resistant copolymer powder.

[0043] Add 92g of high-temperature and salt-resistant powder to 300mL of deionized water and mechanically stir at 520rpm for 50min at room temperature. While stirring continuously, add 39g of maltodextrin, 9.5g of sodium citrate and 4.8g of sodium carboxymethyl cellulose in sequence, and continue mechanically stirring at 520rpm for 40min. Sieve, spray dry and granulate to obtain a high-temperature resistant, fast-dissolving fracturing fluid thickener.

[0044] Example 6 10.5 g of 4-vinylpyridine and 125 mL of toluene were added to a reaction vessel and stirred for 8 min. Then, 13.5 g of 1,3-propanesulfonyl lactone (CAS No. 1120-71-4) was added and the mixture was reacted at 80 °C for 19 h. After filtration, the mixture was washed four times with acetone and dried under vacuum at 55 °C for 20 h to obtain 4-vinylpyridinepropylsulfonate.

[0045] 11.5 g of 2-acrylamido-2-methylpropanesulfonic acid was dissolved in 40 mL of deionized water, and then 0.1 g of azobisisobutyramidine hydrochloride was added. The mixture was reacted at 50 °C under nitrogen for 7 h to obtain pAMPS. 32 g of acrylamide, 8 g of 2-acrylamido-2-methylpropanesulfonic acid, 2.5 g of acrylic acid, 0.46 g of octadecyl methacrylate, and pAMPS were added to 210 mL of 25% ammonium sulfate solution. 0.85 g of 4-vinylpyridinium propyl sulfobetaine was added, and the mixture was stirred at 500 rpm for 40 min. Then, 4 g of pAMPS was added. OP-10 (CAS No.: 2201101-54-2) and 2.8 g of dodecyl mercaptan were mixed with sodium hydroxide to adjust the pH to 5.0, purged with nitrogen for 30 min, and 0.3 g of azobisisobutyramidine hydrochloride was added. The reaction was continued at 60 °C for 6 h. The polymer was then washed 5 times with anhydrous ethanol, separated, and vacuum dried for 18 h to obtain a high-temperature and salt-resistant copolymer powder.

[0046] Add 100g of high-temperature and salt-resistant powder to 300mL of deionized water and mechanically stir at 600rpm for 40min at room temperature. While stirring continuously, add 35g of maltodextrin, 10g of sodium citrate and 5g of hydroxypropyl starch in sequence, and continue mechanically stirring at 600rpm for 30min. Sieve, spray dry and granulate to obtain a high-temperature resistant, fast-dissolving fracturing fluid thickener.

[0047] The present invention also includes comparative examples and related experiments.

[0048] Comparative Example 1 Compared with Example 1, the only difference is that 4-vinylpyridinepropylsulfonate was not added. The other preparation methods and components are completely consistent, and a high-temperature resistant, fast-dissolving fracturing fluid thickener is finally obtained.

[0049] Comparative Example 2 Compared with Example 1, the only difference is that octadecyl methacrylate was not added. The other preparation methods and components are completely the same, and a high-temperature resistant, fast-dissolving fracturing fluid thickener is finally obtained.

[0050] Comparative Example 3 Compared with Example 1, the only difference is that high-temperature and salt-resistant copolymer powder is directly used as the thickener for high-temperature fast-dissolving fracturing fluid.

[0051] Performance testing To further illustrate the rapid dissolution performance of the high-temperature resistant, fast-dissolving fracturing fluid thickener provided by this invention, the dissolution time of the high-temperature resistant, fast-dissolving fracturing fluid thickeners prepared in Examples 1-6 and Comparative Examples 1-3 of this invention was measured. The specific procedures are as follows: At room temperature, 3g of the high-temperature resistant, fast-dissolving fracturing fluid thickeners prepared in Examples 1-6 and Comparative Examples 1-3 were weighed out and added to 100mL of deionized water under a stirring rate of 150rpm. Timing was started and stopped when the powder completely disappeared. The time taken from the addition of the sample to the disappearance of the powder is the dissolution time of the thickener. The dissolution time results of the high-temperature resistant, fast-dissolving fracturing fluid thickeners prepared in Examples 1-6 and Comparative Examples 1-3 are shown in Table 1.

[0052] As shown in Table 1, the dissolution time of the high-temperature resistant, fast-dissolving fracturing fluid thickeners prepared in Examples 1-6 is less than 50s, which is significantly improved compared to Comparative Example 3. This indicates that the porous fast-dissolving powder system constructed by maltodextrin, sodium citrate, and hydrophilic additives can significantly improve the wetting, disintegration, and swelling speed of the powder, thereby achieving a fast dissolution effect. In contrast, Comparative Example 3 directly uses copolymer powder, and the dissolution time is as high as 425s, which is difficult to meet the requirements for rapid on-site liquid preparation.

[0053] To further illustrate the shear resistance of the high-temperature resistant, fast-dissolving fracturing fluid thickener provided by this invention, the shear resistance of the high-temperature resistant, fast-dissolving fracturing fluid thickeners prepared in Examples 1-6 and Comparative Examples 1-3 of this invention was measured. The specific procedures are as follows: The high-temperature resistant, fast-dissolving fracturing fluid thickeners prepared in Examples 1-6 and Comparative Examples 1-3 of this invention were added to deionized water to obtain thickener solutions. Organic zirconium crosslinking agents were then added and thoroughly mixed to obtain uniformly dispersed samples. The apparent viscosity of the samples was tested according to SY / T5107-2016 "Performance Evaluation Method for Water-Based Fracturing Fluids" at a temperature of 20°C, a shear time of 3-60 min, and a shear rate of 170 s. -1 The mass fraction of the thickener solution is 1%, and the amount of organozirconium crosslinking agent added is 0.1% of the mass of the thickener solution. Finally, its shear resistance is evaluated based on the viscosity retention rate before and after long-term shearing. The viscosity retention rate is calculated using the following formula (Ⅰ): Wherein, ŋ1 is the apparent viscosity (mPa·s) after shearing for 3 min, and ŋ2 is the apparent viscosity (mPa·s) after shearing for 60 min; the specific shear resistance test results are shown in Table 2.

[0054] As shown in Table 2, the viscosity retention rate of the samples prepared in Examples 1-5 after shearing for 60 minutes was above 90%. In Example 6, the viscosity retention rate decreased to some extent due to the absence of methacrylamide chitosan, which also indicates that methacrylamide chitosan plays a certain role in network support and viscosity maintenance under long-term shearing. The viscosity retention rate in Comparative Example 3 reached 88%, which also indicates that the copolymer powder itself has certain shear resistance. However, the absence of 4-vinylpyridinylpropyl sulfobetaine or octadecyl methacrylate in Comparative Examples 1 and 2 significantly reduced the viscosity retention rate.

[0055] To further illustrate the high-temperature resistance of the high-temperature resistant, fast-dissolving fracturing fluid thickener provided by this invention, the above-mentioned sample was added to a hydrothermal reactor, kept at 200°C for 72 hours, cooled to 30°C, sheared for 3 minutes, and at a shear rate of 170 s. -1 The apparent viscosity was tested, and the viscosity retention rate before and after heat treatment was further calculated according to the above formula (Ⅰ) to evaluate its high temperature resistance performance; the specific high temperature resistance performance test results are shown in Table 3.

[0056] As shown in Table 3, after high-temperature aging at 200℃ for 72 hours, the apparent viscosity of Examples 1-6 of the present invention remained at 228.2-243.5 mPa·s, with a viscosity retention rate of 88.6%-92%. In Example 6, the viscosity retention rate decreased somewhat due to the absence of methacrylamide chitosan, indicating that the introduction of methacrylamide chitosan can further improve the overall strength and viscosity retention of the network at high temperatures. However, the absence of 4-vinylpyridinylpropyl sulfobetaine or octadecyl methacrylate in Comparative Examples 1 and 2 resulted in a significant decrease in viscosity retention, indicating that 4-vinylpyridinylpropyl sulfobetaine and octadecyl methacrylate play an important role in improving the high-temperature resistance of the system.

[0057] To further illustrate the salt resistance of the high-temperature resistant, fast-dissolving fracturing fluid thickener provided by this invention, when preparing the above-mentioned samples, the deionized water in the samples was replaced with saline solution with a salinity of 120,000 mg / L and a total calcium and magnesium ion concentration of 24,000 mg / L. The specific operation is as follows: The high-temperature resistant, fast-dissolving fracturing fluid thickeners prepared in Examples 1-6 and Comparative Examples 1-3 of this invention were added to brine to obtain a thickener solution. Then, an organozirconium crosslinking agent was added and thoroughly mixed to obtain a uniformly dispersed sample. The temperature was 20°C, the shearing time was 3 min, and the shear rate was 170 s. -1 The mass fraction of the thickener solution was 1%, and the amount of organic zirconium crosslinking agent added was 0.1% of the mass of the thickener solution. The apparent viscosity of the sample was measured, and the viscosity retention rate was further calculated according to the above formula (Ⅰ) to evaluate its salt resistance performance. The specific salt resistance performance test results are shown in Table 4.

[0058] As shown in Table 4, in brine with high mineralization and high calcium and magnesium ion content, the apparent viscosity of Examples 1-6 of this invention remained at 222.3-245.3 mPa·s, with a viscosity retention rate of 86.4%-92.7%. The absence of 4-vinylpyridinepropyl sulfobetaine in Comparative Example 1 significantly reduced the viscosity retention rate, indicating that the system in Comparative Example 1 lacking 4-vinylpyridinepropyl sulfobetaine had no viscosity retention ability in high-mineralization brine. The absence of octadecyl methacrylate in Comparative Example 2 also resulted in a certain decrease in viscosity retention rate.

[0059] In summary, by analyzing the data in Tables 1 to 4, it can be concluded that the embodiments of the present invention exhibit significant advantages in four aspects: rapid solubility, shear resistance, high temperature resistance, and salt resistance. Especially under harsh environments such as high temperature and brine, the performance of the embodiments maintains high stability, significantly superior to the comparative samples, and is suitable for demanding oil and gas well fracturing fluid operations.

[0060] The above are preferred embodiments of the present invention. Those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant, fast-dissolving fracturing fluid thickener, characterized in that, Includes the following steps: S1. Mix 4-vinylpyridine, toluene, and 1,3-propanesulfonate lactone, react at high temperature, filter, wash, and dry under vacuum to obtain 4-vinylpyridinepropylsulfonate betaine. S2. Acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, octadecyl methacrylate, pAMPS, ammonium sulfate solution, and 4-vinylpyridinylpropyl sulfobetaine are mixed and stirred. Addition agents are added, the pH value is adjusted to 5.0~5.5, azobisisobutyramidine hydrochloride is added and the reaction continues. After washing, separation, and vacuum drying, a high-temperature and salt-resistant copolymer powder is obtained. S3. Add the high-temperature and salt-resistant copolymer powder to deionized water and stir mechanically. While stirring continuously, add maltodextrin, sodium citrate and hydrophilic additives in sequence, continue stirring, sieve, spray dry and granulate to obtain a high-temperature resistant fast-dissolving fracturing fluid thickener.

2. The preparation method of a high-temperature resistant, fast-dissolving fracturing fluid thickener according to claim 1, characterized in that, In step S1, 10-12 parts by mass of 4-vinylpyridine and 120-150 parts by volume of toluene are added to a reaction vessel, mixed and stirred, and 13-15 parts by mass of 1,3-propanesulfonate lactone are added. After high-temperature reaction, the mixture is filtered, washed with acetone 3-5 times, and then dried under vacuum to obtain 4-vinylpyridinepropylsulfonate betaine.

3. The preparation method of a high-temperature resistant, fast-dissolving fracturing fluid thickener according to claim 2, characterized in that, The mixing and stirring time is 5-10 minutes, the high-temperature reaction temperature is 75-85℃ and the time is 18-20 hours, and the vacuum drying temperature is 50-60℃ and the time is 18-24 hours.

4. The preparation method of a high-temperature resistant, fast-dissolving fracturing fluid thickener according to claim 1, characterized in that, The pAMPS is obtained by dissolving 8-12 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid in 40 parts by volume of deionized water, adding 0.1-0.12 parts by weight of azobisisobutyramidine hydrochloride, and reacting at 50°C under nitrogen atmosphere for 6-8 hours.

5. The preparation method of a high-temperature resistant, fast-dissolving fracturing fluid thickener according to claim 1, characterized in that, In step S2, 30-35 parts by weight of acrylamide, 6-10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 1.5-3 parts by weight of acrylic acid, 0.3-0.5 parts by weight of octadecyl methacrylate and pAMPS are added to 200-220 parts by volume of ammonium sulfate solution with a mass concentration of 25%. 0.78-1.5 parts by weight of 4-vinylpyridinylpropyl sulfobetaine are added and the mixture is stirred at 500 rpm for 20-50 min. Then, additives are added, the pH is adjusted to 5.0-5.5 with sodium hydroxide, and the mixture is purged with nitrogen for 20-30 min. 0.2-0.3 g of azobisisobutyramidine hydrochloride is added, and the reaction is continued at 50-60°C for 6-8 h. The mixture is then washed 3-5 times with anhydrous ethanol, the polymer is separated, and vacuum dried for 18-24 h to obtain a high-temperature and salt-resistant copolymer powder.

6. The preparation method of a high-temperature resistant, fast-dissolving fracturing fluid thickener according to claim 1, characterized in that, The additives are 3.5 to 4.5 parts by weight of OP-10 and 2 to 3 parts by weight of dodecyl mercaptan.

7. The preparation method of a high-temperature resistant, fast-dissolving fracturing fluid thickener according to claim 1, characterized in that, In step S2, 0.3 to 0.8 parts by weight of methacrylamide chitosan were added along with 4-vinylpyridinepropyl sulfobetaine.

8. The preparation method of a high-temperature resistant, fast-dissolving fracturing fluid thickener according to claim 7, characterized in that, The methacrylamide chitosan was obtained by dissolving 3-5 parts by weight of chitosan powder in 100-120 parts by volume of 3% acetic acid solution, stirring at room temperature for 8-10 hours, adding 12-15 parts by weight of methacrylic anhydride and stirring magnetically for 4-6 hours, purifying with a cellulose dialysis membrane, washing with deionized water 3-5 times, and freeze-drying under vacuum.

9. The preparation method of a high-temperature resistant, fast-dissolving fracturing fluid thickener according to claim 1, characterized in that, In step S3, the high-temperature and salt-resistant copolymer powder is added to deionized water and mechanically stirred at 500-600 rpm for 40-60 minutes at room temperature. Maltodextrin, sodium citrate, and a hydrophilic additive are added sequentially while stirring continuously. The mixture is then mechanically stirred at 500-600 rpm for 30-50 minutes. After sieving, the mixture is spray-dried and granulated to obtain a high-temperature resistant, fast-dissolving fracturing fluid thickener. The hydrophilic additive is one of PEG-6000, hydroxypropyl starch, and sodium carboxymethyl cellulose.

10. A high-temperature resistant, fast-dissolving fracturing fluid thickener, characterized in that, The thickener is prepared by the method of any one of claims 1 to 9, comprising the following raw materials in parts by weight: 80 to 100 parts of high-temperature and salt-resistant copolymer powder, 300 parts of deionized water, 35 to 45 parts of maltodextrin, 8 to 10 parts of sodium citrate and 4 to 5 parts of hydrophilic additives.

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