A dry powder drag reducer for fracturing fluid and its preparation method

Abstract

This invention provides a dry powder drag-reducing agent for fracturing fluids and its preparation method, belonging to the technical field of fracturing materials for drilling. The method includes the following steps: dissolving 4-bromobutyryl chloride and N-dodecylmethylamine in acetonitrile, heating and stirring to react; adding polyethylene glycol monomethyl ether acrylate and dichloromethane; stirring under a nitrogen atmosphere; purifying to obtain a double-tailed hydrophobic monomer; mixing core-shell Fe3O4 / SiO2 composite nanoparticles, ethanol aqueous solution, KH570, and ammonia solution; stirring; purifying to obtain modified SiO2 / Fe3O4; adding acrylamide, acrylic acid, sodium 2-acrylamido-2-methylpropanesulfonate, the double-tailed hydrophobic monomer, and modified SiO2 / Fe3O4 to water; adjusting the pH value; mixing and stirring with nitrogen gas; adding an azo initiator; stirring; cooling; purifying; vacuum drying; and pulverizing into powder to obtain the dry powder drag-reducing agent for fracturing fluids. This invention achieves good drag-reducing performance while also possessing certain heat resistance, making it better suited for fracturing operations in drilling processes.

Description

Technical Field

[0001] This invention relates to the field of fracturing materials for drilling, specifically to a dry powder drag reducer for fracturing fluid and its preparation method. Background Technology

[0002] In the drilling process of oil and gas field development, fracturing is generally required to achieve the desired production. Fracturing fluid is the working fluid in the fracturing process. It is pressurized by high-pressure pumping equipment and pumped into the formation at high speed through the tubing string. Currently, slickwater fracturing fluid is the most favored fracturing fluid. It has low viscosity and excellent fluidity, which can effectively reduce the pumping pressure during the fracturing process and reduce energy consumption. Therefore, slickwater fracturing fluid system has become a commonly used fracturing technology in the drilling process of oil and gas field development.

[0003] To facilitate fracture propagation and increase gas well production, oil and gas field fracturing operations require the use of drag-reducing agents. However, in large-scale, high-volume fracturing operations, traditional liquid drag-reducing agents suffer from slow dissolution rates, cumbersome preparation, and inconvenient transportation and storage, making them unsuitable for the high-efficiency and rapid demands of on-site operations. Therefore, developing dry powder drag-reducing agents with rapid dissolution rates, low damage, and excellent drag-reducing performance has become an urgent priority.

[0004] Existing dry powder drag reducers include natural polymers and synthetic polymers. Natural polymers are biodegradable drag reducers, mainly including xanthan gum, guar gum and their derivatives. They are reasonably priced and readily available, making them a commonly used drag reducer for fracturing fluids. However, using natural polymers alone as drag reducers has some drawbacks: the hydration and swelling time during fluid preparation is too long, they are prone to biodegradation downhole, and they cannot be used in high-temperature environments, thus affecting drag reduction performance.

[0005] Most synthetic polymers are polyacrylamide-based polymers, which mainly exist in powder form. Their manufacturing process is mature, and they are easy to transport, making them a commonly used drag-reducing agent in oilfields. This type is mainly produced by adding other functional monomers to acrylamide, using a suitable initiation system to undergo free radical polymerization to form a gel, which is then dried and pulverized into polymer powders of different mesh sizes. Based on the ionization properties of polyacrylamide in aqueous solution, it can be classified into anionic, cationic, nonionic, and amphoteric types. Different monomer types affect the various properties of the drag-reducing agent. For example, sulfonate groups with good hydrophilicity can form stable hydrogen bonds with water molecules, and when copolymerized with acrylamide monomers, they enhance the polymer's resistance to temperature and salt. However, this type of powdered polymer has poor distribution and solubility in water, leading to uneven mixing of fracturing fluid, which can damage the delivery pipeline and formation, hindering secondary extraction.

[0006] Therefore, there is a need to provide a dry powder drag reducer for fracturing fluid and its preparation method to solve the problems existing in the prior art. Summary of the Invention

[0007] In view of this, the present invention provides a dry powder drag reducer for fracturing fluid and its preparation method, which can achieve good drag reduction performance while having certain heat resistance, and can be better applied to fracturing operations in the drilling process.

[0008] To achieve the above objectives, the present invention provides a method for preparing a dry powder drag-reducing agent for fracturing fluid, comprising the following steps:

[0009] S1. After dissolving 4-bromobutyryl chloride and N-dodecylmethylamine in acetonitrile, the mixture was heated and stirred to react. Polyethylene glycol monomethyl ether acrylate and dichloromethane were added, and the mixture was stirred under a nitrogen atmosphere. After washing, separation, and rotary evaporation, a double-tailed hydrophobic monomer was obtained.

[0010] S2. Core-shell Fe3O4 / SiO2 composite nanoparticles were added to an ethanol aqueous solution and ultrasonically dispersed. Then KH570 and ammonia solution were added, and the reaction was continuously stirred. After vacuum distillation and centrifugation, the precipitate was collected, washed, and vacuum dried to obtain modified SiO2 / Fe3O4.

[0011] S3. Acrylamide, acrylic acid, sodium 2-acrylamido-2-methylpropanesulfonate, double-tailed hydrophobic monomer, and modified SiO2 / Fe3O4 are added to deionized water and mixed. After adjusting the pH value, nitrogen gas is introduced and the mixture is stirred. Azo initiator is added and the reaction is continued to be stirred. After cooling to room temperature, the mixture is washed, filtered, vacuum dried, and pulverized into powder to obtain a dry powder drag reducer.

[0012] This invention obtains a bi-tailed hydrophobic monomer through a two-step synthesis reaction, further enhancing its salt resistance and shear resistance, while maximizing the polymer's association strength with minimal dosage. The specific reaction formula is as follows:

[0013]

[0014] First, quaternization reaction is carried out using 4-bromobutyryl chloride and N-dodecylmethylamine to obtain quaternary ammonium salt. The quaternary ammonium salt is then acylated with polyethylene glycol monomethyl ether acrylate to obtain a double-tailed hydrophobic monomer, which consists of a combination of a long-chain hydrophilic polyethylene glycol segment (PEO) and two hydrophobic C12 chains on the quaternary ammonium salt ion. The longer PEO segment has high hydrophilicity and flexibility. The long PEO chain increases the distance between hydrophobic groups, which plays a steric role and effectively reduces the possibility of strong intramolecular association or early aggregation of molecular chains between hydrophobic groups. This ensures that the molecular chains can be relatively dispersed in water in the early stage of dissolution. Furthermore, the PEO segment can quickly hydrate with water molecules, which greatly promotes the hydrophilicity and dissolution kinetics of the polymer chain. This can improve the final polymer dissolution rate in water, thereby improving the overall drag reduction performance and making it better suited for fracturing operations in drilling processes.

[0015] This invention introduces a double-tailed hydrophobic monomer and modified SiO2 / Fe3O4 into a free radical polymerization reaction to obtain the final polymer, the specific structural formula of which is as follows:

[0016]

[0017] The longer hydrophilic ethylene oxide chains of the bi-tailed hydrophobic monomers extend the bi-tailed hydrophobic chains to more distant positions, significantly increasing the volume occupied by each repeating unit. This effectively suppresses the formation and development of pulsating eddies and increases the thickness of the buffer zone, thereby reducing fluid resistance. The addition of more bi-tailed hydrophobic side chains to the bi-tailed hydrophobic monomers increases the interaction between molecular chains, forming a robust and stable three-dimensional network structure. Furthermore, based on the unique rigid structure of modified SiO2 / Fe3O4, it is introduced into the polymer structure as a monomer. Utilizing its multiple cross-linking effects achieved through physical adsorption and chemical bonding, the strength of the polymer network structure is enhanced. The bi-tailed hydrophobic monomers and modified SiO2 / Fe3O4 synergistically improve… The high drag-reducing agent exhibits excellent shear resistance; furthermore, the interaction between the polymer structure and the modified SiO2 / Fe3O4 effectively delays structural degradation, enhances the polymer structure's resistance to thermal decomposition, and further improves its heat resistance. The sulfonic acid groups in sodium 2-acrylamido-2-methylpropanesulfonate have extremely strong ionization capabilities, maintaining a negative charge even at high salt concentrations, providing a lasting electrostatic repulsion force, inhibiting excessive chain coiling, and synergistically providing rigid skeletal support through modified SiO2 / Fe3O4. Even when the charge is shielded and the chains undergo some coiling, it can prevent the network from completely collapsing, maintaining its basic structure and viscoelasticity. The synergy of both imparts excellent overall salt resistance, enabling better fracturing performance in high-salt water layers or oil and gas reservoir environments. Optionally, in step S1, after dissolving 4-bromobutyryl chloride and N-dodecylmethylamine in acetonitrile, the mixture is stirred at 500 rpm for 20-40 minutes at a reaction temperature of 70-80°C. Then, polyethylene glycol monomethyl ether acrylate is added, and dichloromethane is added dropwise. The mixture is stirred continuously at 0°C under a nitrogen atmosphere for 45-48 hours. After washing 2-5 times with dichloromethane and 8.2% sodium bicarbonate solution, the mixture is separated in a separation funnel and then rotary evaporated to obtain a double-tailed hydrophobic monomer.

[0018] Optionally, the core-shell Fe3O4 / SiO2 composite nanoparticles are obtained by mixing an aqueous ethanol solution, Fe3O4 colloid, and tetraethyl orthosilicate under continuous stirring, adding ammonia, stirring at 300 rpm for 5-7 hours, centrifuging at 10,000 rpm for 10-15 minutes, taking the precipitate, and washing it 3-5 times with deionized water and anhydrous ethanol, respectively.

[0019] Optionally, the volume concentration of the ethanol aqueous solution is 80% and the volume concentration of the ammonia solution is 25%.

[0020] Optionally, the stirring reaction is carried out under sealed conditions, and after washing with deionized water and anhydrous ethanol 3 to 5 times respectively, magnetic separation is performed to finally obtain core-shell Fe3O4 / SiO2 composite nanoparticles.

[0021] Modified SiO2 / Fe3O4 exhibits magnetic responsiveness, and the drag-reducing agent can be efficiently recovered through an external magnetic field after use, avoiding residual pollution of the system or environment, reducing usage costs, and potentially enabling recycling. In addition, in localized high-turbulence regions, the polymer can be directionally manipulated through an external magnetic field to enrich it in key areas (such as near the pipe wall), precisely enhancing the drag-reduction effect.

[0022] Optionally, the Fe3O4 colloid is obtained by mixing FeCl3·6H2O and Na2SO3 solution under nitrogen protection, stirring for 10 min, quickly adding ammonia water and mixing well, heating to 70℃ and adding sodium citrate solution, stirring continuously at 500 rpm for 1-2 h, centrifuging at 8000 rpm for 10-15 min, taking the precipitate, washing it with deionized water 3-5 times, and finally dispersing it in deionized water.

[0023] Here, ammonia provides an alkaline environment, promoting the hydrolysis of metal ions and the formation of iron oxides. Sodium citrate ensures the dispersibility and stability of the product through complexation.

[0024] Optionally, the Na2SO3 solution has a molar concentration of 0.5 mol / L, the sodium citrate solution has a mass concentration of 1%, and the ammonia solution has a volume concentration of 25%.

[0025] Optionally, in step S3, acrylamide, acrylic acid, sodium 2-acrylamido-2-methylpropanesulfonate, a double-tailed hydrophobic monomer, and modified SiO2 / Fe3O4 are added to deionized water and mixed evenly. Sodium hydroxide is added to adjust the pH value to 6.0-6.5. Nitrogen gas is introduced into the solution and the mixture is stirred for 30-40 minutes. Then, an azo initiator is added, and the mixture is stirred continuously at 450 rpm at 40-50°C for 5-8 hours. After cooling to room temperature, the mixture is washed 3-5 times with anhydrous ethanol, filtered to collect the product, and vacuum dried at 40-50°C for 16-24 hours. The product is then pulverized into powder to obtain a dry powder drag reducer.

[0026] Azo initiators initiate free radical polymerization in polymerization reactions. They decompose at 40-50°C to generate free radicals, which then initiate the polymerization of monomers such as acrylamide and acrylic acid. The generation of free radicals promotes the polymerization reaction; the product is then pulverized into a fine powder for convenient subsequent applications.

[0027] Optionally, the azo initiator is azobisisobutyramidine hydrochloride.

[0028] The present invention also provides a dry powder drag reducer for fracturing fluid, comprising the following raw materials in parts by weight: 90-100 parts acrylamide, 8-10 parts acrylic acid, 2-3.5 parts sodium 2-acrylamido-2-methylpropanesulfonate, 0.2-0.3 parts double-tailed hydrophobic monomer, 1.2-1.5 g parts modified SiO2 / Fe3O4, and 0.39-0.43 parts azo initiator.

[0029] The above-described technical solution of the present invention has at least the following beneficial effects:

[0030] 1. The double-tailed hydrophobic monomer ensures the hydrophilicity and dispersibility of the polymer through the flexibility and steric hindrance of the PEO segments. Furthermore, the PEO segments greatly promote the hydrophilicity and dissolution kinetics of the polymer chain, which can improve the final polymer dissolution rate in water.

[0031] 2. This invention utilizes the synergistic effect of a dual-tailed hydrophobic monomer and modified SiO2 / Fe3O4 to form a stable polymer during free radical polymerization. The hydrophilic PEO segments extend the hydrophobic chains, suppressing pulsating eddies and reducing fluid resistance, while increasing the buffer zone thickness. Modified SiO2 / Fe3O4 enhances the polymer's three-dimensional network structure, improving shear resistance and heat resistance. The ionization and salt resistance of the sulfonic acid groups further enhance the polymer's stability, ensuring it maintains structural strength and viscoelasticity even in high-salt environments, exhibiting excellent drag-reduction properties. Detailed Implementation

[0032] 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.

[0033] Example 1

[0034] 1.2 g of 4-bromobutyryl chloride and 1.6 g of N-dodecylmethylamine were dissolved in 35 mL of acetonitrile. The mixture was then poured into a three-necked round-bottom flask equipped with a thermometer, a reflux condenser, and a dropping funnel. The mixture was stirred at 500 rpm for 20 min at a reaction temperature of 70 °C. 3.9 g of polyethylene glycol monomethyl ether acrylate was then added, and 35 mL of dichloromethane was added dropwise using a dropping funnel. The mixture was stirred continuously for 45 h under a nitrogen atmosphere at 0 °C. The crude product was washed twice with dichloromethane and 8.2% sodium bicarbonate solution, respectively. The product was then separated in a separating funnel, and dichloromethane and acetonitrile were removed by rotary evaporation to obtain a double-tailed hydrophobic monomer (a thick, brownish-yellow oily liquid).

[0035] 5.4 g of FeCl3·6H2O was placed in a 500 mL three-necked flask. Under nitrogen protection, 40 mL of 0.5 mol / L Na2SO3 solution was added and stirred for 10 min. Then, 6.7 mL of 25% ammonia solution was quickly added and mixed thoroughly, resulting in the formation of black particles. The temperature was raised to 70℃ in a constant-temperature water bath, and 50 mL of 1% sodium citrate solution was added. The mixture was stirred continuously at 500 rpm for 1 h, then centrifuged at 8000 rpm for 10 min. The precipitate was collected, washed three times with deionized water, and finally dispersed in 50 mL of deionized water to obtain stable Fe3O4 colloid. Under continuous stirring, 100 mL of 80% ethanol aqueous solution and 50 mL of... Fe3O4 colloid and 0.42g of tetraethyl orthosilicate were added, followed by 2.7mL of 25% ammonia water. The mixture was stirred in a sealed container at 300rpm for 5h, then centrifuged at 10000rpm for 10min. The precipitate was collected and washed three times with deionized water and anhydrous ethanol, respectively. Finally, core-shell Fe3O4 / SiO2 composite nanoparticles were obtained by magnetic separation.

[0036] 5g of core-shell Fe3O4 / SiO2 composite nanoparticles were added to 40mL of 80% ethanol aqueous solution and ultrasonically dispersed at 300W for 30min. Then, 0.2g of KH570 (CAS No.: 2530-85-0) and 1mL of 25% ammonia solution were added. The mixture was stirred continuously at 300rpm for 8h in a nitrogen atmosphere at 50℃. After removing excess ethanol by vacuum distillation, the mixture was centrifuged at 10000rpm for 10min, the precipitate was collected, washed three times with anhydrous ethanol, and dried under vacuum at 60℃ for 18h to obtain modified SiO2 / Fe3O4.

[0037] 100g acrylamide, 10g acrylic acid, 3.5g sodium 2-acrylamido-2-methylpropanesulfonate, 0.3g double-tailed hydrophobic monomer, and 1.5g modified SiO2 / Fe3O4 were added to 600mL of deionized water and mixed thoroughly. Sodium hydroxide was added to adjust the pH to 6.0. Nitrogen gas was bubbled into the solution and the mixture was stirred for 30min. Then, 0.43g azobisisobutyramidine hydrochloride (CAS No.: 2997-92-4) was added. The mixture was stirred continuously at 450rpm at 50℃ for 5h. After cooling to room temperature, the product was washed three times with anhydrous ethanol, filtered, and collected. The product was then vacuum dried at 50℃ for 24h and pulverized into powder to obtain a dry powder drag reducer.

[0038] Example 2

[0039] 1.2 g of 4-bromobutyryl chloride and 1.6 g of N-dodecylmethylamine were dissolved in 35 mL of acetonitrile. The mixture was then poured into a three-necked round-bottom flask equipped with a thermometer, a reflux condenser, and a dropping funnel. The mixture was stirred at 500 rpm for 40 min at a reaction temperature of 80 °C. 3.9 g of polyethylene glycol monomethyl ether acrylate was then added, and 35 mL of dichloromethane was added dropwise using a dropping funnel. The mixture was stirred continuously for 48 h under a nitrogen atmosphere at 0 °C. The crude product was then washed five times with dichloromethane and an 8.2% sodium bicarbonate solution, respectively. The product was then separated in a separating funnel, and the dichloromethane and acetonitrile were removed by rotary evaporation to obtain a double-tailed hydrophobic monomer (a thick, brownish-yellow oily liquid).

[0040] 5.4 g of FeCl3·6H2O was placed in a 500 mL three-necked flask. Under nitrogen protection, 40 mL of 0.5 mol / L Na2SO3 solution was added and stirred for 10 min. Then, 6.7 mL of 25% ammonia solution was quickly added and mixed thoroughly, resulting in the formation of black particles. The temperature was raised to 70℃ in a constant-temperature water bath, and 50 mL of 1% sodium citrate solution was added. The mixture was stirred continuously at 500 rpm for 2 h. After centrifugation at 8000 rpm for 15 min, the precipitate was collected, washed five times with deionized water, and finally dispersed in 50 mL of deionized water to obtain stable Fe3O4 colloid. Under continuous stirring, 100 mL of 80% ethanol aqueous solution and 50 mL of... Fe3O4 colloid and 0.42g of tetraethyl orthosilicate were added, followed by 3mL of 25% ammonia water. The mixture was stirred in a sealed container at 300rpm for 7h, then centrifuged at 10000rpm for 15min. The precipitate was collected and washed five times with deionized water and anhydrous ethanol, respectively. Finally, core-shell Fe3O4 / SiO2 composite nanoparticles were obtained by magnetic separation.

[0041] 5g of core-shell Fe3O4 / SiO2 composite nanoparticles were added to 40mL of 80% ethanol aqueous solution and ultrasonically dispersed at 300W for 30min. Then, 0.25g of KH570 (CAS No.: 2530-85-0) and 1mL of 25% ammonia solution were added. The mixture was stirred continuously at 300rpm for 12h in a nitrogen atmosphere at 65℃. After removing excess ethanol by vacuum distillation, the mixture was centrifuged at 10000rpm for 10min, the precipitate was collected, washed 5 times with anhydrous ethanol, and dried under vacuum at 60℃ for 24h to obtain modified SiO2 / Fe3O4.

[0042] 90g acrylamide, 8g acrylic acid, 2g sodium 2-acrylamido-2-methylpropanesulfonate, 0.2g double-tailed hydrophobic monomer, and 1.2g modified SiO2 / Fe3O4 were added to 550mL of deionized water and mixed thoroughly. Sodium hydroxide was added to adjust the pH to 6.5. Nitrogen gas was bubbled into the solution and the mixture was stirred for 40min. Then, 0.39g azobisisobutyramidine hydrochloride (CAS No.: 2997-92-4) was added. The mixture was stirred continuously at 450rpm at 40℃ for 8h. After cooling to room temperature, the product was washed 5 times with anhydrous ethanol, filtered, and collected. The product was then vacuum dried at 40℃ for 24h and pulverized into powder to obtain a dry powder drag reducer.

[0043] Example 3

[0044] 1.2 g of 4-bromobutyryl chloride and 1.6 g of N-dodecylmethylamine were dissolved in 35 mL of acetonitrile. The mixture was then poured into a three-necked round-bottom flask equipped with a thermometer, a reflux condenser, and a dropping funnel. The mixture was stirred at 500 rpm for 30 min at a reaction temperature of 75 °C. 3.9 g of polyethylene glycol monomethyl ether acrylate was then added, and 35 mL of dichloromethane was added dropwise using a dropping funnel. The mixture was stirred continuously for 47 h under a nitrogen atmosphere at 0 °C. The crude product was washed three times with dichloromethane and an 8.2% sodium bicarbonate solution, respectively. The product was then separated in a separating funnel, and the dichloromethane and acetonitrile were removed by rotary evaporation to obtain a double-tailed hydrophobic monomer (a thick, brownish-yellow oily liquid).

[0045] 5.4 g of FeCl3·6H2O was placed in a 500 mL three-necked flask. Under nitrogen protection, 40 mL of 0.5 mol / L Na2SO3 solution was added and stirred for 10 min. Then, 6.7 mL of 25% ammonia solution was quickly added and mixed thoroughly, resulting in the formation of black particles. The temperature was raised to 70℃ in a constant-temperature water bath, and 50 mL of 1% sodium citrate solution was added. The mixture was stirred continuously at 500 rpm for 1.5 h. After centrifugation at 8000 rpm for 12 min, the precipitate was collected, washed four times with deionized water, and finally dispersed in 50 mL of deionized water to obtain stable Fe3O4 colloid. Under continuous stirring, 100 mL of 80% ethanol aqueous solution and 50 mL of... were added sequentially to a beaker. Fe3O4 colloid and 0.42g of tetraethyl orthosilicate were added, followed by 2.8mL of 25% ammonia solution. The mixture was stirred in a sealed container at 300rpm for 6h, then centrifuged at 10000rpm for 12min. The precipitate was collected and washed four times with deionized water and anhydrous ethanol, respectively. Finally, core-shell Fe3O4 / SiO2 composite nanoparticles were obtained by magnetic separation.

[0046] 5g of core-shell Fe3O4 / SiO2 composite nanoparticles were added to 40mL of 80% ethanol aqueous solution and ultrasonically dispersed at 300W for 30min. Then, 0.22g of KH570 (CAS No.: 2530-85-0) and 1mL of 25% ammonia solution were added. The mixture was stirred continuously at 300rpm for 10h in a nitrogen atmosphere at 55℃. After removing excess ethanol by vacuum distillation, the mixture was centrifuged at 10000rpm for 10min, the precipitate was collected, washed four times with anhydrous ethanol, and dried under vacuum at 60℃ for 20h to obtain modified SiO2 / Fe3O4.

[0047] 95g acrylamide, 9g acrylic acid, 2.5g sodium 2-acrylamido-2-methylpropanesulfonate, 0.25g double-tailed hydrophobic monomer, and 1.3g modified SiO2 / Fe3O4 were added to 570mL of deionized water and mixed thoroughly. Sodium hydroxide was added to adjust the pH to 6.2. Nitrogen gas was bubbled into the solution and the mixture was stirred for 35min. Then, 0.4g azobisisobutyramidine hydrochloride (CAS No.: 2997-92-4) was added. The mixture was stirred continuously at 450rpm at 45℃ for 7h. After cooling to room temperature, the product was washed four times with anhydrous ethanol, filtered, and collected. The product was then vacuum dried at 45℃ for 18h and pulverized into powder to obtain a dry powder drag reducer.

[0048] Example 4

[0049] 1.2 g of 4-bromobutyryl chloride and 1.6 g of N-dodecylmethylamine were dissolved in 35 mL of acetonitrile. The mixture was then poured into a three-necked round-bottom flask equipped with a thermometer, a reflux condenser, and a dropping funnel. The mixture was stirred at 500 rpm for 25 min at a reaction temperature of 75 °C. 3.9 g of polyethylene glycol monomethyl ether acrylate was then added, and 35 mL of dichloromethane was added dropwise using a dropping funnel. The mixture was stirred continuously for 46 h under a nitrogen atmosphere at 0 °C. The crude product was then washed four times with dichloromethane and an 8.2% sodium bicarbonate solution, respectively. The product was then separated in a separating funnel, and dichloromethane and acetonitrile were removed by rotary evaporation to obtain a double-tailed hydrophobic monomer (a thick, brownish-yellow oily liquid).

[0050] 5.4 g of FeCl3·6H2O was placed in a 500 mL three-necked flask. Under nitrogen protection, 40 mL of 0.5 mol / L Na2SO3 solution was added and stirred for 10 min. Then, 6.7 mL of 25% ammonia solution was quickly added and mixed thoroughly, resulting in the formation of black particles. The temperature was raised to 70℃ in a constant-temperature water bath, and 50 mL of 1% sodium citrate solution was added. The mixture was stirred continuously at 500 rpm for 1.5 h. After centrifugation at 8000 rpm for 13 min, the precipitate was collected, washed four times with deionized water, and finally dispersed in 50 mL of deionized water to obtain stable Fe3O4 colloid. Under continuous stirring, 100 mL of 80% ethanol aqueous solution and 50 mL of... Fe3O4 colloid and 0.42g of tetraethyl orthosilicate were added, followed by 2.9mL of 25% ammonia water. The mixture was stirred in a sealed container at 300rpm for 6h, then centrifuged at 10000rpm for 14min. The precipitate was collected and washed four times with deionized water and anhydrous ethanol, respectively. Finally, core-shell Fe3O4 / SiO2 composite nanoparticles were obtained by magnetic separation.

[0051] 5g of core-shell Fe3O4 / SiO2 composite nanoparticles were added to 40mL of 80% ethanol aqueous solution and ultrasonically dispersed at 300W for 30min. Then, 0.22g of KH570 (CAS No.: 2530-85-0) and 1mL of 25% ammonia solution were added. The mixture was stirred continuously at 300rpm for 10h in a nitrogen atmosphere at 60℃. After removing excess ethanol by vacuum distillation, the mixture was centrifuged at 10000rpm for 10min, the precipitate was collected, washed four times with anhydrous ethanol, and dried under vacuum at 60℃ for 20h to obtain modified SiO2 / Fe3O4.

[0052] 95g acrylamide, 9g acrylic acid, 3g sodium 2-acrylamido-2-methylpropanesulfonate, 0.2g double-tailed hydrophobic monomer, and 1.4g modified SiO2 / Fe3O4 were added to 570mL of deionized water and mixed thoroughly. Sodium hydroxide was added to adjust the pH to 6.3. Nitrogen gas was bubbled into the solution and the mixture was stirred for 35min. Then, 0.41g azobisisobutyramidine hydrochloride (CAS No.: 2997-92-4) was added. The mixture was stirred continuously at 450rpm for 6h at 45℃. After cooling to room temperature, the product was washed three times with anhydrous ethanol, filtered, and collected. The product was then vacuum dried at 40℃ for 24h and pulverized into powder to obtain a dry powder drag reducer.

[0053] Example 5

[0054] 1.2 g of 4-bromobutyryl chloride and 1.6 g of N-dodecylmethylamine were dissolved in 35 mL of acetonitrile. The mixture was then poured into a three-necked round-bottom flask equipped with a thermometer, reflux condenser, and dropping funnel. The mixture was stirred at 500 rpm for 30 min at a reaction temperature of 70 °C. 3.9 g of polyethylene glycol monomethyl ether acrylate was then added, and 35 mL of dichloromethane was added dropwise using a dropping funnel. The mixture was stirred continuously for 47 h under a nitrogen atmosphere at 0 °C. The crude product was washed twice with dichloromethane and 8.2% sodium bicarbonate solution, respectively. The product was then separated in a separating funnel, and dichloromethane and acetonitrile were removed by rotary evaporation to obtain a double-tailed hydrophobic monomer (a thick, brownish-yellow oily liquid).

[0055] 5.4 g of FeCl3·6H2O was placed in a 500 mL three-necked flask. Under nitrogen protection, 40 mL of 0.5 mol / L Na2SO3 solution was added and stirred for 10 min. Then, 6.7 mL of 25% ammonia solution was quickly added and mixed thoroughly, resulting in the formation of black particles. The temperature was raised to 70℃ in a constant-temperature water bath, and 50 mL of 1% sodium citrate solution was added. The mixture was stirred continuously at 500 rpm for 2 h. After centrifugation at 8000 rpm for 10 min, the precipitate was collected, washed three times with deionized water, and finally dispersed in 50 mL of deionized water to obtain stable Fe3O4 colloid. Under continuous stirring, 100 mL of 80% ethanol aqueous solution and 50 mL of... Fe3O4 colloid and 0.42g of tetraethyl orthosilicate were added, followed by 2.7mL of 25% ammonia water. The mixture was stirred in a sealed container at 300rpm for 7h, then centrifuged at 10000rpm for 10min. The precipitate was collected and washed five times with deionized water and anhydrous ethanol, respectively. Finally, core-shell Fe3O4 / SiO2 composite nanoparticles were obtained by magnetic separation.

[0056] 5g of core-shell Fe3O4 / SiO2 composite nanoparticles were added to 40mL of 80% ethanol aqueous solution and ultrasonically dispersed at 300W for 30min. Then, 0.26g of KH570 (CAS No.: 2530-85-0) and 1mL of 25% ammonia solution were added. The mixture was stirred continuously at 300rpm for 12h in a nitrogen atmosphere at 50℃. After removing excess ethanol by vacuum distillation, the mixture was centrifuged at 10000rpm for 10min, the precipitate was collected, washed three times with anhydrous ethanol, and dried under vacuum at 60℃ for 22h to obtain modified SiO2 / Fe3O4.

[0057] 97g acrylamide, 9g acrylic acid, 3g sodium 2-acrylamido-2-methylpropanesulfonate, 0.26g double-tailed hydrophobic monomer, and 1.5g modified SiO2 / Fe3O4 were added to 600mL of deionized water and mixed thoroughly. Sodium hydroxide was added to adjust the pH to 6.2. Nitrogen gas was bubbled into the solution and the mixture was stirred for 37min. Then, 0.41g azobisisobutyramidine hydrochloride (CAS No.: 2997-92-4) was added. The mixture was stirred continuously at 450rpm at 45℃ for 8h. After cooling to room temperature, the product was washed three times with anhydrous ethanol, filtered, and collected. The product was then vacuum dried at 50℃ for 16h and pulverized into powder to obtain a dry powder drag reducer.

[0058] Example 6

[0059] 1.2 g of 4-bromobutyryl chloride and 1.6 g of N-dodecylmethylamine were dissolved in 35 mL of acetonitrile. The mixture was then poured into a three-necked round-bottom flask equipped with a thermometer, a reflux condenser, and a dropping funnel. The mixture was stirred at 500 rpm for 40 min at a reaction temperature of 70 °C. 3.9 g of polyethylene glycol monomethyl ether acrylate was then added, and 35 mL of dichloromethane was added dropwise using a dropping funnel. The mixture was stirred continuously for 48 h under a nitrogen atmosphere at 0 °C. The crude product was washed twice with dichloromethane and 8.2% sodium bicarbonate solution, respectively. The product was then separated in a separating funnel, and dichloromethane and acetonitrile were removed by rotary evaporation to obtain a double-tailed hydrophobic monomer (a thick, brownish-yellow oily liquid).

[0060] 5.4 g of FeCl3·6H2O was placed in a 500 mL three-necked flask. Under nitrogen protection, 40 mL of 0.5 mol / L Na2SO3 solution was added and stirred for 10 min. Then, 6.7 mL of 25% ammonia solution was quickly added and mixed thoroughly, resulting in the formation of black particles. The temperature was raised to 70℃ in a constant-temperature water bath, and 50 mL of 1% sodium citrate solution was added. The mixture was stirred continuously at 500 rpm for 1 h, then centrifuged at 8000 rpm for 15 min. The precipitate was collected, washed five times with deionized water, and finally dispersed in 50 mL of deionized water to obtain stable Fe3O4 colloid. Under continuous stirring, 100 mL of 80% ethanol aqueous solution and 50 mL of... Fe3O4 colloid and 0.42g of tetraethyl orthosilicate were added, followed by 2.7mL of 25% ammonia water. The mixture was stirred in a sealed container at 300rpm for 5h, then centrifuged at 10000rpm for 15min. The precipitate was collected and washed three times with deionized water and anhydrous ethanol, respectively. Finally, core-shell Fe3O4 / SiO2 composite nanoparticles were obtained by magnetic separation.

[0061] 5g of core-shell Fe3O4 / SiO2 composite nanoparticles were added to 40mL of 80% ethanol aqueous solution and ultrasonically dispersed at 300W for 30min. Then, 0.2g of KH570 (CAS No.: 2530-85-0) and 1mL of 25% ammonia solution were added. The mixture was stirred continuously at 300rpm for 12h in a nitrogen atmosphere at 65℃. After removing excess ethanol by vacuum distillation, the mixture was centrifuged at 10000rpm for 10min, the precipitate was collected, washed three times with anhydrous ethanol, and dried under vacuum at 60℃ for 24h to obtain modified SiO2 / Fe3O4.

[0062] 90g acrylamide, 10g acrylic acid, 2g sodium 2-acrylamido-2-methylpropanesulfonate, 0.3g double-tailed hydrophobic monomer, and 1.2g modified SiO2 / Fe3O4 were added to 600mL of deionized water and mixed thoroughly. Sodium hydroxide was added to adjust the pH to 6.0. Nitrogen gas was bubbled into the solution and the mixture was stirred for 40min. Then, 0.43g azobisisobutyramidine hydrochloride (CAS No.: 2997-92-4) was added. The mixture was stirred continuously at 450rpm at 40℃ for 5h. After cooling to room temperature, the product was washed 5 times with anhydrous ethanol, filtered, and collected. The product was then vacuum dried at 50℃ for 16h and pulverized into powder to obtain a dry powder drag reducer.

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

[0064] Comparative Example 1

[0065] Compared with Example 2, the only difference is that no double-tailed hydrophobic monomer was added. The other preparation methods and components are completely the same, and the dry powder drag reducer is finally obtained.

[0066] Comparative Example 2

[0067] Compared with Example 2, the only difference is that modified SiO2 / Fe3O4 was not added. The other preparation methods and components are completely consistent, and the dry powder drag reducer is finally obtained.

[0068] Comparative Example 3

[0069] Compared with Example 2, the only difference is that nano-silica is used directly to replace modified SiO2 / Fe3O4, while the other preparation methods and components are completely consistent, and the dry powder drag reducer is finally obtained.

[0070] Performance testing

[0071] The performance indicators of the dry powder drag reducers prepared in Examples 1-6 and Comparative Examples 1-3 were tested. The specific test procedures are as follows:

[0072] Preparation:

[0073] Preparation of brine (100,000 mineralization): This 100,000 mineralization brine is prepared from sodium chloride, calcium chloride and deionized water, with a sodium chloride content of 80,000 ppm and a calcium chloride content of 20,000 ppm.

[0074] (1) Drag reduction rate detection

[0075] The dry powder drag-reducing agents prepared in Examples 1-6 and Comparative Examples 1-3 were dissolved in tap water to prepare samples with a mass concentration of 0.5%. After stirring evenly, the drag reduction rate of the samples was determined using a flow loop friction test device according to SY / T6376-2008 "General Technical Conditions for Fracturing Fluids". The drag reduction rate of the samples was calculated using the following formula. ;

[0076]

[0077] In the formula: The stable pressure difference, expressed in Pa, is the pressure difference when clean water flows through the pipeline. The pressure difference, in Pa, represents the stable pressure difference as the drag-reducing agent flows through the pipeline. For drag reduction rate of clear water.

[0078] The drag reduction rate of the dry powder drag-reducing agents prepared in Examples 1-6 and Comparative Examples 1-3 was tested by dissolving them in a brine solution with a mineralization of 100,000, with reference to the drag reduction rate of the above-mentioned water solution. Finally, the drag reduction rate of the brine solution was calculated.

[0079] (2) Kinematic viscosity test

[0080] 0.3g of each of the dry powder drag-reducing agent samples prepared in Examples 1-6 and Comparative Examples 1-3 were weighed and dissolved in 300g of the above-prepared brine. The mixture was stirred at 3000rpm for 3min using a high-frequency stirrer, and its kinematic viscosity (mm) was measured using a Polkidus viscometer (0.8mm inner diameter). 2 / s).

[0081] The specific test results are shown in Table 1.

[0082]

[0083] As shown in Table 1, the dry powder drag-reducing agents prepared in Examples 1-6 of this invention maintain good drag-reducing performance in both clean water and brine with a salinity of 100,000 N·m, showing a significant improvement compared to Comparative Examples 1-3. They still maintain a drag reduction rate of over 80% in brine with a salinity of 100,000 N·m, and after high-speed shearing in brine with a salinity of 100,000 N·m, the kinematic viscosity reaches 3.0 mm. 2 At speeds above a certain threshold, it maintains high viscoelasticity, further demonstrating its good shear resistance and significant salt resistance. The absence of key components in Comparative Examples 1-3 significantly impacts both drag reduction and kinematic viscosity.

[0084] The dry powder drag-reducing agents prepared in Examples 1-6 and Comparative Examples 1-3 were placed in an environment of 120°C for 90 days. Then, the drag reduction rate of water and the drag reduction rate of salt water were tested again. The drag reduction retention rate of water and the drag reduction retention rate of salt water after the samples were placed in an environment of 120°C for 90 days were calculated. The results are shown in Table 2.

[0085]

[0086] As shown in Table 2, the dry powder drag reducing agents prepared in Examples 1-6 of the present invention have a higher drag reduction retention rate than those in Comparative Examples 1-3, indicating that the drag reducing agents have superior performance. After being placed at high temperature for a long time, the drag reduction retention rate of the dry powder drag reducing agents prepared in Examples 1-6 is significantly better than that in Comparative Examples 1-3. This shows that the dry powder drag reducing agents prepared by the technical solution of the present invention not only have excellent drag reduction performance, but also have high temperature resistance and good stability, and can be better applied to fracturing operations in the drilling process.

[0087] 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 dry powder drag-reducing agent for fracturing fluid, characterized in that, Includes the following steps: S1. After dissolving 4-bromobutyryl chloride and N-dodecylmethylamine in acetonitrile, the mixture was heated and stirred to react. Polyethylene glycol monomethyl ether acrylate and dichloromethane were added, and the mixture was stirred under a nitrogen atmosphere. After washing, separation, and rotary evaporation, a double-tailed hydrophobic monomer was obtained. S2. Core-shell Fe3O4 / SiO2 composite nanoparticles were added to an ethanol aqueous solution and ultrasonically dispersed. Then KH570 and ammonia solution were added, and the reaction was continuously stirred. After vacuum distillation and centrifugation, the precipitate was collected, washed, and vacuum dried to obtain modified SiO2 / Fe3O4. S3. Acrylamide, acrylic acid, sodium 2-acrylamido-2-methylpropanesulfonate, double-tailed hydrophobic monomer, and modified SiO2 / Fe3O4 are added to deionized water and mixed. After adjusting the pH value, nitrogen gas is introduced and the mixture is stirred. Azo initiator is added and the reaction is continued to be stirred. After cooling to room temperature, the mixture is washed, filtered, vacuum dried, and pulverized into powder to obtain a dry powder drag reducer.

2. The method for preparing a dry powder drag-reducing agent for fracturing fluid according to claim 1, characterized in that, In step S1, 4-bromobutyryl chloride and N-dodecylmethylamine are dissolved in acetonitrile and stirred at 500 rpm for 20-40 minutes at a reaction temperature of 70-80°C. Polyethylene glycol monomethyl ether acrylate is then added, and dichloromethane is added dropwise. The mixture is stirred continuously at 0°C under a nitrogen atmosphere for 45-48 hours. After washing 2-5 times with dichloromethane and an 8.2% sodium bicarbonate solution, the mixture is separated in a separation funnel and then rotary evaporated to obtain a double-tailed hydrophobic monomer.

3. The method for preparing a dry powder drag-reducing agent for fracturing fluid according to claim 1, characterized in that, The core-shell Fe3O4 / SiO2 composite nanoparticles were obtained by mixing an aqueous ethanol solution, Fe3O4 colloid, and tetraethyl orthosilicate under continuous stirring, adding ammonia, stirring at 300 rpm for 5-7 hours, centrifuging at 10,000 rpm for 10-15 minutes, taking the precipitate, and washing it 3-5 times with deionized water and anhydrous ethanol, respectively.

4. The method for preparing a dry powder drag-reducing agent for fracturing fluid according to claim 3, characterized in that, The volume concentration of the ethanol aqueous solution is 80%, and the volume concentration of the ammonia solution is 25%.

5. The method for preparing a dry powder drag-reducing agent for fracturing fluid according to claim 3, characterized in that, The stirring reaction was carried out under sealed conditions. After washing with deionized water and anhydrous ethanol 3 to 5 times respectively, magnetic separation was performed to finally obtain core-shell Fe3O4 / SiO2 composite nanoparticles.

6. The method for preparing a dry powder drag-reducing agent for fracturing fluid according to claim 3, characterized in that, The Fe3O4 colloid was obtained by mixing FeCl3·6H2O and Na2SO3 solution under nitrogen protection, stirring for 10 min, then quickly adding ammonia water and mixing well. The mixture was heated to 70℃ and sodium citrate solution was added. The mixture was stirred continuously at 500 rpm for 1-2 h, then centrifuged at 8000 rpm for 10-15 min. The precipitate was collected, washed 3-5 times with deionized water, and finally dispersed in deionized water.

7. The method for preparing a dry powder drag-reducing agent for fracturing fluid according to claim 6, characterized in that, The Na2SO3 solution has a molar concentration of 0.5 mol / L, the sodium citrate solution has a mass concentration of 1%, and the ammonia solution has a volume concentration of 25%.

8. The method for preparing a dry powder drag-reducing agent for fracturing fluid according to claim 1, characterized in that, In step S3, acrylamide, acrylic acid, sodium 2-acrylamido-2-methylpropanesulfonate, a double-tailed hydrophobic monomer, and modified SiO2 / Fe3O4 are added to deionized water and mixed evenly. Sodium hydroxide is added to adjust the pH value to 6.0-6.

5. Nitrogen gas is introduced into the solution and the mixture is stirred for 30-40 minutes. Then, an azo initiator is added, and the mixture is stirred continuously at 450 rpm at 40-50°C for 5-8 hours. After cooling to room temperature, the mixture is washed 3-5 times with anhydrous ethanol, filtered, and the product is collected. The product is then vacuum dried at 40-50°C for 16-24 hours and pulverized into powder to obtain a dry powder drag reducer.

9. The method for preparing a dry powder drag-reducing agent for fracturing fluid according to claim 1, characterized in that, The azo initiator is azobisisobutyramidine hydrochloride.

10. A dry powder drag-reducing agent for fracturing fluid, characterized in that, The product is prepared by the preparation method according to any one of claims 1 to 9, comprising the following raw materials in parts by weight: 90 to 100 parts of acrylamide, 8 to 10 parts of acrylic acid, 2 to 3.5 parts of sodium 2-acrylamido-2-methylpropanesulfonate, 0.2 to 0.3 parts of a bi-tailed hydrophobic monomer, 1.2 to 1.5 g of modified SiO2 / Fe3O4, and 0.39 to 0.43 parts of azo initiator.

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