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

Abstract

The application provides a high-temperature-resistant and quick-dissolving fracturing fluid thickening agent and a preparation method thereof, and belongs to the technical field of oil and gas well fracturing, and 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 sulfobetaine, adding an additive, adjusting the pH value to 5.0-5.5, adding azobisdimethylaminoformamide hydrochloride to continue the reaction, washing, separating, vacuum drying to obtain a high-temperature-resistant and salt-resistant copolymer powder; adding the high-temperature-resistant and salt-resistant copolymer powder into deionized water and mechanically stirring, adding malt dextrin, sodium citrate and a hydrophilic additive into the deionized water in sequence under continuous stirring, continuing to stir, sieving, spray drying and granulating to obtain the high-temperature-resistant and quick-dissolving fracturing fluid thickening agent. The application can improve the high-temperature-resistant performance and the dissolution rate.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well fracturing technology, specifically to a high-temperature resistant, fast-dissolving fracturing fluid thickener and its preparation method. Background Technology

[0002] With the gradual depletion of conventional oil and gas resources, the effective development and utilization of oil and gas resources in deep and ultra-deep tight reservoirs and shale reservoirs has become particularly important. To improve the permeability of these complex reservoirs and enhance oil and gas release conditions, fracturing technology has become a major production enhancement method. Fracturing can create a highly conductive fracture system within the reservoir, thereby significantly increasing oil and gas production. Fracturing fluid is the core component of fracturing operations; its rheological properties, proppant carrying capacity, and stability directly affect the fracturing effect, while thickeners are key components determining the performance of fracturing fluids. Due to the deep burial of oil and gas resources in deep and ultra-deep tight reservoirs and shale reservoirs, fracturing fluid thickeners are required to possess good temperature resistance and shear strength to improve stability and operational adaptability under complex conditions.

[0003] Currently, the most commonly used thickeners mainly fall into two categories: plant-based gums and synthetic polymers. Plant-based gum thickeners, such as guar gum and konjac gum, are inexpensive and widely available, but most suffer from poor temperature resistance and high residue levels. For example, commonly used hydroxypropyl guar gum is prone to glycosidic bond breakage at high temperatures, leading to a rapid decrease in system viscosity and making it difficult to meet the sand-carrying requirements of high-temperature well sections. Although synthetic polymer thickeners are superior to plant-based gums in terms of temperature resistance, they are prone to irreversible molecular chain breakage under high-temperature and high-shear conditions, resulting in poor viscosity retention. In recent years, oligomer thickeners have attracted attention due to their small structure and superior resistance to shear degradation; however, their temperature resistance limit is typically only 90-120℃, making them unsuitable for deep and ultra-deep fracturing operations exceeding 120℃.

[0004] Patent application CN101220263A discloses a water-based fracturing fluid thickener and its production method. This thickener is copolymerized from four monomers: N,N-dialkylacrylamide, dimethyl diallyl ammonium chloride, acrylonitrile, methacryloyloxyethyltrimethylammonium chloride, or acryloyloxyethyltrimethylammonium chloride. While it solves the problems of insufficient temperature resistance and instability under high temperature and high shear in existing fracturing fluid thickeners, the insufficient hydrophilicity of the polymer powder surface results in slow dissolution. In actual field fracturing operations, this type of thickener is difficult to completely dissolve in a short time, failing to meet the rapid solubility requirements of fracturing fluid rapid preparation or continuous mixing processes.

[0005] Therefore, there is a need to provide a high-temperature resistant, fast-dissolving fracturing fluid thickener and its preparation method to solve the problems existing in the prior art. Summary of the Invention

[0006] In view of this, the present invention provides a high-temperature resistant, fast-dissolving fracturing fluid thickener and its preparation method, which can improve high-temperature resistance while increasing the dissolution rate.

[0007] To achieve the above objectives, the present invention provides a method for preparing a high-temperature resistant, fast-dissolving fracturing fluid thickener, comprising the following steps:

[0008] 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.

[0009] 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.

[0010] 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.

[0011] In this invention, 4-vinylpyridinepropylsulfonobetaine is prepared by a nucleophilic ring-opening quaternization reaction of 4-vinylpyridine with 1,3-propanesulfonate lactone, and its structural formula is as follows:

[0012]

[0013] Introducing 4-vinylpyridinylpropylsulfobetaine as an amphoteric monomer, its strong hydration ion pair, consisting of a pyridine quaternary ammonium cation and a sulfonic acid anion, can be used in high-mineralization, Ca-containing environments. 2+ / Mg 2+ Inhibiting chain coiling and aggregation in brine can impart overall salt resistance, resistance to polyvalent cation salting out, as well as good solubility and viscosity. In addition, the high rigidity of the pyridine aromatic ring in its structure further improves the overall high-temperature stability.

[0014] In preparing the high-temperature and salt-resistant copolymer powder, this invention also introduces octadecyl methacrylate, the structural formula of which is as follows:

[0015]

[0016] Its long-chain hydrophobic alkyl side groups form numerous reversible physical crosslinking points in the aqueous phase through hydrophobic association, enabling the polymer chains to maintain a temporary three-dimensional network structure under high temperature and high shear conditions, further improving the system's viscosity and shear resistance. Simultaneously, the pyridine aromatic ring in the 4-vinylpyridinylpropylsulfobetaine unit is preferentially distributed near the hydrophobic association domain, while its zwitterionic head group (quaternary ammonium cation / sulfonic acid anion inner salt) extends into the aqueous phase, forming a hydration enrichment layer in the interfacial region surrounding the hydrophobic association domain. This maintains sufficient hydrophobic association strength while preventing excessive aggregation of hydrophobic areas into hard masses, allowing the hydrophobic association structure to reversibly open and close under high temperature and high shear, and to self-recover after shearing, thus combining high-temperature shear resistance with system stability.

[0017] To further improve the dissolution rate of fracturing fluid thickener, this invention, after obtaining a high-temperature and salt-resistant copolymer powder, combines it with maltodextrin, sodium citrate, and other hydrophilic additives to construct a porous powder system. Maltodextrin forms a porous, brittle framework during spray drying, resulting in a large number of micropores inside the dried particles, thus increasing the water phase penetration rate. Sodium citrate plays a role in micro-foaming and penetration guidance during drying and reswelling, facilitating the rapid entry of water into the particle interior along the pores and accelerating particle disintegration and release of polymer chains. The hydrophilic additives further enhance the wettability and dispersibility of the particle surface. The porous particles formed after spray drying and granulation have a large specific surface area, allowing the resulting fracturing fluid thickener to achieve rapid wetting, penetration, and disintegration upon contact with water, effectively avoiding common field problems such as fisheye, agglomeration, and slow dissolution, thereby achieving a rapid dissolution effect.

[0018] Optionally, in step S1, 10-12 parts by weight 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 weight 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.

[0019] 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.

[0020] Optionally, 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.

[0021] This invention introduces pAMPS as a component into the main polymerization system by pre-preparing pAMPS. The pre-prepared pAMPS is a water-soluble polymer with a large number of sulfonic acid groups. It still has good water solubility and strong hydrophilicity in the subsequent 25% ammonium sulfate salting-out medium. During the copolymerization reaction, it can be adsorbed on the surface of newly generated polymer particles to form a charged and strongly hydrated protective layer, which effectively prevents further particle agglomeration and overall gelation of the system, so that the reaction can proceed stably in the form of dispersion / emulsion polymerization.

[0022] Optionally, 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 continues 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.

[0023] This invention utilizes free radical dispersion / emulsion copolymerization in a high-salt water medium to form a multi-component copolymer network containing long-chain hydrophobic side groups and zwitterionic side groups. During the reaction, pAMPS, as a hydrophilic macromolecule with sulfonic acid groups, is readily adsorbed onto the surface of newly generated polymer particles, forming a charged, strongly hydrated protective layer. This significantly slows down particle aggregation, allowing the polymerization process to proceed stably in a dispersion / emulsion polymerization manner. Finally, residual salts and unreacted monomers are removed by ethanol washing, and after vacuum drying, a high-temperature and salt-resistant copolymer powder is obtained. The main chain consists of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and acrylic acid (AA), with C18 long-chain hydrophobic groups and 4-vinylpyridinylpropylsulfobetaine zwitterionic groups introduced into the side chains. Under aqueous solution and actual fracturing fluid conditions, the sulfonic acid and carboxyl groups in the copolymer partially ionize, and the 4-vinylpyridinylpropylsulfobetaine units exist in an internal salt zwitterionic form. Its ionic structure is as follows:

[0024]

[0025] Optionally, the additive is 3.5 to 4.5 parts by weight of OP-10 and 2 to 3 parts by weight of dodecyl mercaptan.

[0026] This invention uses OP-10 as a nonionic surfactant, which can improve the dispersion stability of each monomer and the generated polymer particles in a high-salt medium; at the same time, it introduces dodecyl mercaptan as a chain transfer agent to effectively regulate the polymer molecular weight and molecular weight distribution and prevent excessive cross-linking.

[0027] Optionally, in step S2, 0.3 to 0.8 parts by weight of methacrylamide chitosan are added when adding 4-vinylpyridinylpropyl sulfobetaine.

[0028] 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.

[0029] 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.

[0030] Preferably, the molecular weight cutoff of the cellulose dialysis membrane is 14 kDa.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The above-described technical solution of the present invention has at least the following beneficial effects:

[0036] 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.

[0037] 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

[0038] 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.

[0039] Example 1

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Example 2

[0044] 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.

[0045] 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.

[0046] 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 to mechanically stir at 500rpm for 30min. Sieve, spray dry and granulate to obtain high-temperature resistant fast-dissolving fracturing fluid thickener.

[0047] Example 3

[0048] 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.

[0049] 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.

[0050] 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.

[0051] Example 4

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Example 5

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Example 6

[0060] 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.

[0061] 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.

[0062] 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.

[0063] The present invention also includes comparative examples and related experiments.

[0064] Comparative Example 1

[0065] 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.

[0066] Comparative Example 2

[0067] 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.

[0068] Comparative Example 3

[0069] 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.

[0070] Performance testing

[0071] 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:

[0072] 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.

[0073]

[0074] 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.

[0075] 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:

[0076] 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):

[0077]

[0078] 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.

[0079]

[0080] 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.

[0081] 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.

[0082]

[0083] 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.

[0084] 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:

[0085] 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. -1The 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.

[0086]

[0087] 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.

[0088] 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.

[0089] 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, instant fracturing fluid viscosifier, characterized in that, It comprises the following steps: S1, 4-vinylpyridine, toluene, 1, 3 propane sulfone lactone is mixed, after high temperature reaction, filtration, washing, vacuum drying to get 4-vinylpyridine propyl sulfobetaine; S2, 30~35 mass parts of acrylamide, 6~10 mass parts of 2-acrylamido-2-methyl propane sulfonic acid, 1.5~3 mass parts of acrylic acid, 0.3~0.5 mass parts of methacrylic acid octadecyl ester and pAMPS are added to 200~220 volume parts of 25% mass concentration of ammonium sulfate solution, 0.78~1.5 mass parts of 4-vinylpyridine propyl sulfobetaine is added to stir at 500 rpm for 20~50 min, then an additive is added, the pH value is adjusted to 5.0~5.5 with sodium hydroxide, it is purged with nitrogen for 20~30 min, 0.2~0.3 g of azobisdimethylaminoformamide hydrochloride is added, and it is continuously reacted at 50~60 DEG C for 6~8 h, then it is washed with anhydrous ethanol for 3~5 times, the polymer is separated, and vacuum drying is carried out for 18~24 h 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 and mechanically stirred, maltodextrin, sodium citrate and a hydrophilic additive are added in sequence under continuous stirring, stirring is continued, sieving is carried out, and spray drying is carried out to obtain a high temperature resistant and instant fracturing fluid thickening agent; The pAMPS is obtained by dissolving 8~12 mass parts of 2-acrylamido-2-methyl propane sulfonic acid in 40 volume parts of deionized water, adding 0.1~0.12 mass parts of azobisdimethylaminoformamide hydrochloride, and reacting at 50 DEG C under a nitrogen atmosphere for 6~8 h; The additive is 3.5~4.5 mass parts of OP-10 and 2~3 mass parts of dodecyl mercaptan; the hydrophilic additive is one of PEG-6000, hydroxypropyl starch and sodium carboxymethyl cellulose; The high temperature resistant and instant fracturing fluid thickening agent comprises the following raw materials in parts by mass: 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 additive.

2. The preparation method of the high-temperature-resistant instant fracturing fluid thickening agent according to claim 1, characterized in that, In the step S1, 10~12 mass parts of 4-vinylpyridine and 120~150 volume parts of toluene are added to a reaction kettle, mixing and stirring are carried out, 13~15 mass parts of 1, 3 propane sulfone lactone is added, high temperature reaction is carried out, then filtration is carried out, washing is carried out with acetone for 3~5 times, and vacuum drying is carried out to obtain 4-vinylpyridine propyl sulfobetaine.

3. The method according to claim 2, wherein the method is characterized by, The mixing and stirring time is 5~10 min, the high temperature reaction temperature is 75~85 DEG C, the time is 18~20 h, the vacuum drying temperature is 50~60 DEG C, and the time is 18~24 h.

4. The method according to claim 1, wherein the method is characterized by, In the step S2, 0.3~0.8 mass parts of methacrylamide chitosan is also added when 4-vinylpyridine propyl sulfobetaine is added.

5. The method according to claim 4, wherein the method is characterized by, The methyl acrylamide chitosan is prepared by dissolving 3-5 parts by mass 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 mass of methacrylic anhydride, magnetically stirring for 4-6 hours, purifying by using a cellulose dialysis membrane, washing 3-5 times with deionized water, and freeze-drying under vacuum.

6. The method according to claim 1, wherein the method is characterized by, In the step S3, the high-temperature-resistant and salt-resistant copolymer powder is added into deionized water, mechanically stirred at a speed of 500-600 rpm for 40-60 min at room temperature, and then malt dextrin, sodium citrate and a hydrophilic aid are added in sequence under continuous stirring, and the mechanical stirring is continuously performed at a speed of 500-600 rpm for 30-50 min, sieved, and spray-dried to obtain the high-temperature-resistant and instant fracturing fluid thickening agent.

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