Emulsion-modified fracturing fluid for oil well protection and preparation method thereof

Abstract

The present invention relates to the field of fracturing fluid, and in particular to an emulsion-modified fracturing fluid for oil well protection and a preparation method thereof, which is used to solve the problem that although a conventional fracturing fluid can increase oil well production, it is easily ineffective in a high-temperature and high-pressure oil well environment, which not only affects the fracturing effect, but may also cause damage to the oil well, resulting in a poor oil well protection effect; the fracturing fluid has high temperature resistance and salt resistance, so that it can work stably in a high-temperature oil well, and has excellent viscosity, can effectively carry sand during the fracturing process, form stable cracks, is conducive to the effective exploitation of oil and gas resources, can maximize its advantages in oil well protection and production increase, and its preparation method is simple, the cost is low, it is easy to industrialize production, and has broad application prospects.

Description

Technical Field

[0001] The invention relates to the field of fracturing fluid, and in particular to an emulsion-modified fracturing fluid for oil well protection and a preparation method thereof. Background Art

[0002] In the process of oil extraction, fracturing is an important measure to increase production. Fracturing fluid refers to a heterogeneous and unstable chemical system formed by a certain ratio of multiple additives. It is a working fluid used for fracturing oil and gas layers. Its main function is to transfer the high pressure formed by ground equipment to the formation, so that the formation breaks to form cracks and transport proppants along the cracks. Therefore, fracturing fluid plays an important role in increasing oil well production. However, although traditional fracturing fluid can increase oil well production, it is easy to fail in the high temperature and high pressure oil well environment, which not only affects the fracturing effect, but may also cause damage to the oil well, resulting in poor oil well protection effect. Therefore, it is of great practical significance to develop an emulsion-modified fracturing fluid for oil well protection and its preparation method. Summary of the invention

[0003] In order to overcome the above-mentioned technical problems, the purpose of the present invention is to provide an emulsion-modified fracturing fluid for oil well protection and a preparation method thereof, which solves the problem that although traditional fracturing fluid can increase oil well production, it is easy to fail in the high temperature and high pressure oil well environment, which not only affects the fracturing effect, but may also cause damage to the oil well, resulting in poor oil well protection effect.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] An emulsion-modified fracturing fluid for oil well protection comprises the following components in parts by weight:

[0006] 8-16 parts of emulsion modified polyacrylamide, 0.6-1.8 parts of high-efficiency cross-linking agent, 0.1-0.5 parts of surfactant, 0.1-0.5 parts of potassium chloride, 0.1-0.5 parts of defoaming agent and 85-105 parts of water;

[0007] Wherein, the emulsion modified polyacrylamide is prepared by the following steps:

[0008] Step a1: Add dimethylaminopropyl acrylamide, stearyl bromide, hydroquinone and anhydrous acetone to a three-necked flask equipped with a stirrer and a thermometer, stir and react for 10-15 minutes at a temperature of 25-30° C. and a stirring rate of 300-400 r / min, then heat to 60-65° C. and continue stirring and reacting for 3-5 hours. After the reaction is completed, cool the reaction product to room temperature, then rotary evaporate to remove the solvent, then add it to anhydrous ether, then let it stand and precipitate, then vacuum filter, place the filter cake in a vacuum drying oven, and dry it at a temperature of 50-55° C. for 2-3 hours to obtain a quaternary ammonium salt monomer;

[0009] Step a2: Add m-di(trifluoromethyl)aniline, cesium carbonate and N,N-dimethylformamide to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a reflux condenser and a constant pressure dropping funnel, introduce nitrogen protection, stir and react for 15-25 minutes at a temperature of 25-30°C and a stirring rate of 300-400r / min, then add allyl bromide dropwise while stirring, and control the dropping rate to 1-2 drops / s. After the dropwise addition is completed, the temperature is raised to reflux and the stirring reaction is continued for 6-8 hours. After the reaction is completed, the reaction product is cooled to room temperature, then added to distilled water, and then extracted with dichloromethane 2-3 times, the combined extracts are washed with a saturated sodium carbonate solution 2-3 times, then dried with anhydrous magnesium sulfate, and then vacuum filtered, and the filtrate is rotary evaporated to remove the solvent to obtain a fluorine-containing monomer;

[0010] Step a3: Add acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, quaternary ammonium salt monomer, fluorine-containing monomer, sodium dodecyl sulfate and deionized water to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, introduce nitrogen protection, stir and react for 15-25 minutes at a temperature of 25-30° C. and a stirring rate of 300-400 r / min, then add potassium persulfate solution dropwise while stirring, control the dropping rate to 1-2 drops / s, and continue stirring and reacting for 6-8 hours under the condition of heating to 60-65° C. after the dropwise addition is completed. After the reaction is completed, the reaction product is cooled to room temperature, then added to anhydrous ethanol, then allowed to stand and precipitate, then vacuum filtered, and the filter cake is placed in a vacuum drying oven, and dried for 2-3 hours at a temperature of 50-55° C. to obtain an emulsion-modified polyacrylamide.

[0011] As a further solution of the present invention: the usage ratio of the dimethylaminopropyl acrylamide, stearyl bromide, hydroquinone and anhydrous acetone in step a1 is 10 mmol: 11-13 mmol: 10-15 mg: 30-35 mL.

[0012] As a further embodiment of the present invention: the usage ratio of the m-di(trifluoromethyl)aniline, cesium carbonate, N,N-dimethylformamide and allyl bromide in step a2 is 10 mmol: 13-15 mmol: 50-55 mL: 11-13 mmol.

[0013] As a further embodiment of the present invention: the usage ratio of the acrylamide, 2-acrylamide-2-methylpropane sulfonic acid, quaternary ammonium salt monomer, fluorine-containing monomer, sodium dodecyl sulfate, deionized water and potassium persulfate solution in step a3 is 50-60 g: 3.5-5.5 g: 1.8-3.6 g: 1.2-3.0 g: 0.1-0.3 g: 80-100 mL: 10-15 mL.

[0014] As a further solution of the present invention: the mass fraction of the potassium persulfate solution in step a3 is 2-3%.

[0015] As a further solution of the present invention: the high-efficiency cross-linking agent is prepared by the following steps:

[0016] Step b1: 1,4-di(bromomethyl)benzene, diethanolamine, anhydrous potassium carbonate and dimethyl sulfoxide are added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a reflux condenser, and nitrogen is introduced for protection. The mixture is stirred for reaction at a temperature of 25-30° C. and a stirring rate of 300-400 r / min for 15-25 min, and then the mixture is heated to reflux and stirred for reaction for 20-30 h. After the reaction is completed, the reaction product is cooled to room temperature, and then vacuum filtered, the filtrate is rotary evaporated to remove the solvent, and then silica gel column chromatography is performed with a developing agent to obtain a polyhydroxy hyperbranched skeleton;

[0017] Step b2: Add a polyhydroxy hyperbranched skeleton, diphenylmethane diisocyanate, dibutyltin dilaurate and methyl ethyl ketone into a three-necked flask equipped with a stirrer and a thermometer, and stir the reaction at a temperature of 25-30°C and a stirring rate of 300-400r / min for 20-30min, then heat the mixture to 70-75°C and continue stirring the reaction for 3-5h, then cool to room temperature, add triethylamine and continue stirring the reaction for 20-30min, and after the reaction is completed, add the reaction product into distilled water, and then rotary evaporate to remove the solvent to obtain a high-efficiency cross-linking agent.

[0018] As a further scheme of the present invention: the usage ratio of the 1,4-di(bromomethyl)benzene, diethanolamine, anhydrous potassium carbonate and dimethyl sulfoxide in step b1 is 10mmol:20mmol:25-30mmol:30-40mL; the developing solvent is a mixture of chloroform and anhydrous ethanol in a volume ratio of 5:1.

[0019] As a further solution of the present invention: the usage ratio of the polyhydroxy hyperbranched skeleton, diphenylmethane diisocyanate, dibutyltin dilaurate, methyl ethyl ketone and triethylamine in step b2 is 10mmol:40mmol:0.01-0.03g:50-60mL:13-15mL.

[0020] As a further solution of the present invention: a method for preparing an emulsion-modified fracturing fluid for oil well protection comprises the following steps:

[0021] Step 1: Weigh 8-16 parts of emulsion-modified polyacrylamide, 0.6-1.8 parts of high-efficiency crosslinking agent, 0.1-0.5 parts of surfactant, 0.1-0.5 parts of potassium chloride, 0.1-0.5 parts of defoaming agent and 85-105 parts of water according to weight parts;

[0022] Step 2: Add emulsion-modified polyacrylamide and water into a mixer and stir and mix. After mixing evenly, add a high-efficiency cross-linking agent, a surfactant, potassium chloride and a defoaming agent in sequence and stir and mix evenly to obtain an emulsion-modified fracturing fluid for oil well protection.

[0023] As a further solution of the present invention: the surfactant is a mixture of Tween 80 and sodium dodecylbenzene sulfonate in a mass ratio of 1:1.

[0024] As a further solution of the present invention: the defoamer is one of LT-130 defoamer and LT-8120 defoamer.

[0025] Beneficial effects of the present invention:

[0026] The invention discloses an emulsion-modified fracturing fluid for oil well protection and a preparation method thereof. The emulsion-modified polyacrylamide and water are added into a mixer and stirred and mixed. After the mixture is uniformly mixed, a high-efficiency cross-linking agent, a surfactant, potassium chloride and a defoaming agent are added in sequence and stirred and mixed. The mixture is uniformly mixed to obtain an emulsion-modified fracturing fluid for oil well protection. The fracturing fluid has high temperature resistance and salt resistance, so that it can work stably in high-temperature oil wells. The fracturing fluid has excellent viscosity, can effectively carry sand during the fracturing process, and forms stable cracks, which is beneficial to the effective exploitation of oil and gas resources. The advantages in oil well protection and production increase can be brought into play to the greatest extent. The preparation method is simple, the cost is low, and it is easy to industrialize and produce. The fracturing fluid has broad application prospects.

[0027] In the process of preparing the fracturing fluid, an emulsion-modified polyacrylamide is first prepared. First, dimethylaminopropyl acrylamide and stearyl bromide are reacted, and the tertiary amine group on the dimethylaminopropyl acrylamide reacts with the bromine atom on the stearyl bromide to form a quaternary ammonium group to obtain a quaternary ammonium salt monomer. Then, m-di(trifluoromethyl)aniline and allyl bromide are reacted, and the amino group on the m-di(trifluoromethyl)aniline reacts with the bromine atom on the allyl bromide to introduce an alkenyl group to obtain a fluorine-containing monomer. Finally, acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, a quaternary ammonium salt monomer, and a fluorine-containing monomer are used as polymerization monomers for emulsion polymerization to obtain an emulsion-modified polyacrylamide. Polyacrylamide; The emulsion-modified polyacrylamide improves the high temperature resistance and salt resistance of the fracturing fluid by introducing sulfonic acid monomers and fluorine-containing monomers into polyacrylamide, greatly improving its stability and significantly improving the heat resistance and shear resistance of the fracturing fluid. The quaternary ammonium salt monomer can effectively improve its antibacterial properties, avoid bacterial growth, reduce the biodegradation ability of bacteria on the fracturing fluid, and enhance the long-term high-performance protection of the fracturing fluid on the oil well. In addition, the modified polyacrylamide has excellent viscosity and can effectively carry sand during the fracturing process to form stable cracks, greatly improving the advantages of the fracturing fluid in protecting the oil well and increasing production.

[0028] In the process of preparing the fracturing fluid, a high-efficiency cross-linking agent is also prepared. First, 1,4-di(bromomethyl)benzene and diethanolamine are reacted, and the bromine atoms on the 1,4-di(bromomethyl)benzene react with the secondary amino group NH in the diethanolamine to introduce a large number of hydroxyl groups to obtain a polyhydroxy hyperbranched skeleton. Then, the polyhydroxy hyperbranched skeleton and diphenylmethane diisocyanate are reacted, and the hydroxyl groups on the polyhydroxy hyperbranched skeleton react with an isocyanate group on the diphenylmethane diisocyanate, and a large number of isocyanate groups are introduced to obtain a high-efficiency cross-linking agent. The high-efficiency cross-linking agent can cross-link multiple polyacrylamides using a large number of isocyanate groups contained in its molecular structure, thereby enhancing the mechanical strength and stability of the fracturing fluid, making it have better shear resistance, and can show excellent viscosity stability under high-temperature shearing, and can also improve its viscosity and sand carrying capacity, thereby improving the conductivity of the fracture and the fracturing effect. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Embodiment 1:

[0031] This embodiment is a method for preparing an emulsion-modified fracturing fluid for oil well protection, comprising the following steps:

[0032] Step S1: 10 mmol of dimethylaminopropyl acrylamide, 11 mmol of stearyl bromide, 10 mg of hydroquinone and 30 mL of anhydrous acetone are added to a three-necked flask equipped with a stirrer and a thermometer, and the mixture is stirred at 25° C. and a stirring rate of 300 r / min for 10 min, and then the mixture is heated to 60° C. and the stirring reaction is continued for 3 h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then the reaction product is added to anhydrous ether, and then allowed to stand for precipitation, and then vacuum filtered, and the filter cake is placed in a vacuum drying oven, and dried at 50° C. for 2 h to obtain a quaternary ammonium salt monomer;

[0033] Step S2: 10 mmol of m-di(trifluoromethyl)aniline, 13 mmol of cesium carbonate and 50 mL of N,N-dimethylformamide are added to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a reflux condenser and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred for reaction at a temperature of 25° C. and a stirring rate of 300 r / min for 15 min, and then 11 mmol of allyl bromide is added dropwise while stirring, and the dropping rate is controlled to be 1 drop / s. After the addition is completed, the temperature is raised to reflux and the stirring reaction is continued for 6 h. After the reaction is completed, the reaction product is cooled to room temperature and then added to distilled water, and then extracted with dichloromethane twice, the combined extracts are washed with a saturated sodium carbonate solution twice, and then dried with anhydrous magnesium sulfate, and then vacuum filtered, and the filtrate is rotary evaporated to remove the solvent to obtain a fluorine-containing monomer;

[0034] Step S3: 50g acrylamide, 3.5g 2-acrylamide-2-methylpropane sulfonic acid, 1.8g quaternary ammonium salt monomer, 1.2g fluorine-containing monomer, 0.1g sodium dodecyl sulfate and 80mL deionized water are added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred and reacted for 15min at a temperature of 25°C and a stirring rate of 300r / min. Then, 10mL of a 2% potassium persulfate solution is added dropwise while stirring, and the dropping rate is controlled to be 1 drop / s. After the dropwise addition is completed, the mixture is heated to 60°C and the stirring reaction is continued for 6h. After the reaction is completed, the reaction product is cooled to room temperature, then added to anhydrous ethanol, then allowed to stand and precipitate, then vacuum filtered, and the filter cake is placed in a vacuum drying oven and dried at a temperature of 50°C for 2h to obtain an emulsion-modified polyacrylamide;

[0035] Step S4: 10 mmol 1,4-di(bromomethyl)benzene, 20 mmol diethanolamine, 25 mmol anhydrous potassium carbonate and 30 mL dimethyl sulfoxide are added to a three-necked flask equipped with a stirrer, a thermometer, a gas guide tube and a reflux condenser, and nitrogen is introduced for protection. The mixture is stirred for reaction at a temperature of 25° C. and a stirring rate of 300 r / min for 15 min, and then the mixture is heated to reflux and stirred for reaction for 20 h. After the reaction is completed, the reaction product is cooled to room temperature, and then vacuum filtered, and the filtrate is rotary evaporated to remove the solvent, and then silica gel column chromatography is performed using a mixture of chloroform and anhydrous ethanol in a volume ratio of 5:1 as a developing solvent to obtain a polyhydroxy hyperbranched skeleton;

[0036] Step S5: 10 mmol of a polyhydroxy hyperbranched skeleton, 40 mmol of diphenylmethane diisocyanate, 0.01 g of dibutyltin dilaurate and 50 mL of methyl ethyl ketone were added to a three-necked flask equipped with a stirrer and a thermometer, and stirred for reaction at 25° C. and a stirring rate of 300 r / min for 20 min, then heated to 70° C. and continued to stir for reaction for 3 h, then cooled to room temperature, and then added 13 mL of triethylamine and continued to stir for reaction for 20 min. After the reaction was completed, the reaction product was added to distilled water, and then the solvent was removed by rotary evaporation to obtain a high-efficiency crosslinking agent;

[0037] Step S6: weighing 8 parts of emulsion-modified polyacrylamide, 0.6 parts of a high-efficiency crosslinking agent, 0.1 parts of a surfactant, 0.1 parts of potassium chloride, 0.1 parts of a defoaming agent, and 85 parts of water in parts by weight; the surfactant is a mixture of Tween 80 and sodium dodecylbenzene sulfonate in a mass ratio of 1:1; the defoaming agent is LT-130 defoaming agent;

[0038] Step S7: Add emulsion-modified polyacrylamide and water into a mixer and stir and mix. After mixing evenly, add a high-efficiency cross-linking agent, a surfactant, potassium chloride and a defoaming agent in sequence and stir and mix evenly to obtain an emulsion-modified fracturing fluid for oil well protection.

[0039] Embodiment 2:

[0040] This embodiment is a method for preparing an emulsion-modified fracturing fluid for oil well protection, comprising the following steps:

[0041] Step S1: 10 mmol of dimethylaminopropyl acrylamide, 12 mmol of stearyl bromide, 13 mg of hydroquinone and 32 mL of anhydrous acetone are added to a three-necked flask equipped with a stirrer and a thermometer, and the mixture is stirred at 28° C. and a stirring rate of 350 r / min for 12 min, and then the mixture is heated to 62° C. and the stirring reaction is continued for 4 h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then the reaction product is added to anhydrous ether, and then allowed to stand for precipitation, and then vacuum filtered, and the filter cake is placed in a vacuum drying oven, and dried at 52° C. for 2.5 h to obtain a quaternary ammonium salt monomer;

[0042] Step S2: 10 mmol of m-di(trifluoromethyl)aniline, 14 mmol of cesium carbonate and 52 mL of N,N-dimethylformamide were added to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a reflux condenser and a constant pressure dropping funnel, and nitrogen was introduced for protection. The reaction was stirred for 20 min at a temperature of 28° C. and a stirring rate of 350 r / min. Then, 12 mmol of allyl bromide was added dropwise while stirring, and the dropping rate was controlled to be 1 drop / s. After the addition was completed, the temperature was raised to reflux and the stirring reaction was continued for 7 h. After the reaction was completed, the reaction product was cooled to room temperature and then added to distilled water, and then extracted with dichloromethane for 3 times. The combined extracts were washed with a saturated sodium carbonate solution for 2 times, and then dried with anhydrous magnesium sulfate. Then, vacuum filtered, the filtrate was rotary evaporated to remove the solvent, and a fluorine-containing monomer was obtained;

[0043] Step S3: 55g acrylamide, 4.5g 2-acrylamide-2-methylpropane sulfonic acid, 2.7g quaternary ammonium salt monomer, 2.1g fluorine-containing monomer, 0.2g sodium dodecyl sulfate and 90mL deionized water are added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred and reacted for 20min at a temperature of 28°C and a stirring rate of 350r / min. Then, 12mL of a 2.5% potassium persulfate solution is added dropwise while stirring, and the dropping rate is controlled to be 1 drop / s. After the dropwise addition is completed, the mixture is heated to 62°C and the stirring reaction is continued for 7h. After the reaction is completed, the reaction product is cooled to room temperature, then added to anhydrous ethanol, then allowed to stand and precipitate, then vacuum filtered, and the filter cake is placed in a vacuum drying oven and dried at a temperature of 52°C for 2.5h to obtain an emulsion-modified polyacrylamide;

[0044] Step S4: 10 mmol 1,4-di(bromomethyl)benzene, 20 mmol diethanolamine, 28 mmol anhydrous potassium carbonate and 35 mL dimethyl sulfoxide are added to a three-necked flask equipped with a stirrer, a thermometer, a gas guide tube and a reflux condenser, and nitrogen is introduced for protection. The mixture is stirred for reaction at a temperature of 28° C. and a stirring rate of 350 r / min for 20 min, and then the mixture is heated to reflux and stirred for reaction for 25 h. After the reaction is completed, the reaction product is cooled to room temperature, and then vacuum filtered, and the filtrate is rotary evaporated to remove the solvent, and then silica gel column chromatography is performed using a mixture of chloroform and anhydrous ethanol in a volume ratio of 5:1 as a developing solvent to obtain a polyhydroxy hyperbranched skeleton;

[0045] Step S5: 10 mmol of a polyhydroxy hyperbranched skeleton, 40 mmol of diphenylmethane diisocyanate, 0.02 g of dibutyltin dilaurate and 55 mL of methyl ethyl ketone were added to a three-necked flask equipped with a stirrer and a thermometer, and stirred for reaction at a temperature of 28° C. and a stirring rate of 350 r / min for 25 min, then heated to 72° C. and continued to stir for reaction for 4 h, then cooled to room temperature, and then added 14 mL of triethylamine and continued to stir for reaction for 25 min. After the reaction was completed, the reaction product was added to distilled water, and then the solvent was removed by rotary evaporation to obtain a high-efficiency crosslinking agent;

[0046] Step S6: weighing 12 parts of emulsion-modified polyacrylamide, 1.2 parts of a high-efficiency crosslinking agent, 0.3 parts of a surfactant, 0.3 parts of potassium chloride, 0.3 parts of a defoaming agent, and 95 parts of water in parts by weight; the surfactant is a mixture of Tween 80 and sodium dodecylbenzene sulfonate in a mass ratio of 1:1; the defoaming agent is LT-130 defoaming agent;

[0047] Step S7: Add emulsion-modified polyacrylamide and water into a mixer and stir and mix. After mixing evenly, add a high-efficiency cross-linking agent, a surfactant, potassium chloride and a defoaming agent in sequence and stir and mix evenly to obtain an emulsion-modified fracturing fluid for oil well protection.

[0048] Embodiment 3:

[0049] This embodiment is a method for preparing an emulsion-modified fracturing fluid for oil well protection, comprising the following steps:

[0050] Step S1: 10 mmol of dimethylaminopropyl acrylamide, 13 mmol of stearyl bromide, 15 mg of hydroquinone and 35 mL of anhydrous acetone are added to a three-necked flask equipped with a stirrer and a thermometer, and the mixture is stirred at 30° C. and a stirring rate of 400 r / min for 15 min, and then the mixture is heated to 65° C. and the stirring reaction is continued for 5 h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then the reaction product is added to anhydrous ether, and then allowed to stand for precipitation, and then vacuum filtered, and the filter cake is placed in a vacuum drying oven, and dried at 55° C. for 3 h to obtain a quaternary ammonium salt monomer;

[0051] Step S2: 10 mmol of m-di(trifluoromethyl)aniline, 15 mmol of cesium carbonate and 55 mL of N,N-dimethylformamide are added to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a reflux condenser and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred for reaction for 25 min at a temperature of 30° C. and a stirring rate of 400 r / min. Then, 13 mmol of allyl bromide is added dropwise while stirring, and the dropping rate is controlled to be 2 drops / s. After the addition is completed, the temperature is raised to reflux and the stirring reaction is continued for 8 h. After the reaction is completed, the reaction product is cooled to room temperature and then added to distilled water, and then extracted with dichloromethane for 3 times. The combined extracts are washed with a saturated sodium carbonate solution for 3 times, and then dried with anhydrous magnesium sulfate. Then, vacuum filtered, the filtrate is rotary evaporated to remove the solvent to obtain a fluorine-containing monomer;

[0052] Step S3: 60g acrylamide, 5.5g 2-acrylamide-2-methylpropane sulfonic acid, 3.6g quaternary ammonium salt monomer, 3.0g fluorine-containing monomer, 0.3g sodium dodecyl sulfate and 100mL deionized water are added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred and reacted for 25min at a temperature of 30°C and a stirring rate of 400r / min. Then, 15mL of a 3% potassium persulfate solution is added dropwise while stirring, and the dropping rate is controlled to be 2 drops / s. After the dropwise addition is completed, the mixture is heated to 65°C and the stirring reaction is continued for 8h. After the reaction is completed, the reaction product is cooled to room temperature, then added to anhydrous ethanol, then allowed to stand and precipitate, then vacuum filtered, and the filter cake is placed in a vacuum drying oven and dried at a temperature of 55°C for 3h to obtain an emulsion-modified polyacrylamide;

[0053] Step S4: 10 mmol 1,4-di(bromomethyl)benzene, 20 mmol diethanolamine, 30 mmol anhydrous potassium carbonate and 40 mL dimethyl sulfoxide are added to a three-necked flask equipped with a stirrer, a thermometer, a gas guide tube and a reflux condenser, and nitrogen is introduced for protection. The mixture is stirred for reaction at a temperature of 30° C. and a stirring rate of 400 r / min for 25 min, and then the mixture is heated to reflux and stirred for reaction for 30 h. After the reaction is completed, the reaction product is cooled to room temperature, and then vacuum filtered, and the filtrate is rotary evaporated to remove the solvent, and then silica gel column chromatography is performed using a mixture of chloroform and anhydrous ethanol in a volume ratio of 5:1 as a developing solvent to obtain a polyhydroxy hyperbranched skeleton;

[0054] Step S5: 10 mmol of a polyhydroxy hyperbranched skeleton, 40 mmol of diphenylmethane diisocyanate, 0.03 g of dibutyltin dilaurate and 60 mL of methyl ethyl ketone were added to a three-necked flask equipped with a stirrer and a thermometer, and stirred for reaction at a temperature of 30° C. and a stirring rate of 400 r / min for 30 min, then heated to 75° C. and continued to stir for reaction for 5 h, then cooled to room temperature, and then added 15 mL of triethylamine and continued to stir for reaction for 30 min. After the reaction was completed, the reaction product was added to distilled water, and then the solvent was removed by rotary evaporation to obtain a high-efficiency crosslinking agent;

[0055] Step S6: weighing 16 parts of emulsion-modified polyacrylamide, 1.8 parts of a high-efficiency crosslinking agent, 0.5 parts of a surfactant, 0.5 parts of potassium chloride, 0.5 parts of a defoaming agent, and 105 parts of water in parts by weight; the surfactant is a mixture of Tween 80 and sodium dodecylbenzene sulfonate in a mass ratio of 1:1; the defoaming agent is LT-8120 defoaming agent;

[0056] Step S7: Add emulsion-modified polyacrylamide and water into a mixer and stir and mix. After mixing evenly, add a high-efficiency cross-linking agent, a surfactant, potassium chloride and a defoaming agent in sequence and stir and mix evenly to obtain an emulsion-modified fracturing fluid for oil well protection.

[0057] Comparative Example 1:

[0058] This comparative example is a method for preparing an emulsion-modified fracturing fluid for oil well protection, comprising the following steps:

[0059] Step S1: 60g acrylamide, 0.3g sodium dodecyl sulfate and 100mL deionized water are added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred and reacted for 25min at a temperature of 30°C and a stirring rate of 400r / min. Then, 15mL of a 3% potassium persulfate solution is added dropwise while stirring, and the dropping rate is controlled to be 2 drops / s. After the dropwise addition is completed, the mixture is heated to 65°C and stirred for 8h. After the reaction is completed, the reaction product is cooled to room temperature, added to anhydrous ethanol, allowed to stand and precipitate, and then vacuum filtered. The filter cake is placed in a vacuum drying oven and dried at a temperature of 55°C for 3h to obtain an emulsion-modified polyacrylamide;

[0060] Step S2: weighing 16 parts of emulsion-modified polyacrylamide, 0.5 parts of surfactant, 0.5 parts of potassium chloride, 0.5 parts of defoaming agent and 105 parts of water according to weight; the surfactant is a mixture of Tween 80 and sodium dodecylbenzene sulfonate in a mass ratio of 1:1; the defoaming agent is LT-8120 defoaming agent;

[0061] Step S3: Add emulsion-modified polyacrylamide and water into a mixer and stir and mix. After mixing evenly, add surfactant, potassium chloride and defoamer in sequence and stir and mix evenly to obtain emulsion-modified fracturing fluid for oil well protection.

[0062] Comparative Example 2:

[0063] This comparative example is a method for preparing an emulsion-modified fracturing fluid for oil well protection, comprising the following steps:

[0064] Step S1: 60g acrylamide, 5.5g 2-acrylamide-2-methylpropanesulfonic acid, 0.3g sodium dodecyl sulfate and 100mL deionized water are added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred and reacted for 25min at a temperature of 30°C and a stirring rate of 400r / min. Then, 15mL of a 3% potassium persulfate solution is added dropwise while stirring, and the dropping rate is controlled to be 2 drops / s. After the dropwise addition is completed, the mixture is heated to 65°C and stirred for 8h. After the reaction is completed, the reaction product is cooled to room temperature, added to anhydrous ethanol, allowed to stand and precipitate, and then vacuum filtered. The filter cake is placed in a vacuum drying oven and dried at a temperature of 55°C for 3h to obtain an emulsion-modified polyacrylamide;

[0065] Step S2: weighing 16 parts of emulsion-modified polyacrylamide, 0.5 parts of surfactant, 0.5 parts of potassium chloride, 0.5 parts of defoaming agent and 105 parts of water according to weight; the surfactant is a mixture of Tween 80 and sodium dodecylbenzene sulfonate in a mass ratio of 1:1; the defoaming agent is LT-8120 defoaming agent;

[0066] Step S3: Add emulsion-modified polyacrylamide and water into a mixer and stir and mix. After mixing evenly, add surfactant, potassium chloride and defoamer in sequence and stir and mix evenly to obtain emulsion-modified fracturing fluid for oil well protection.

[0067] Comparative Example 3:

[0068] This comparative example is a method for preparing an emulsion-modified fracturing fluid for oil well protection, comprising the following steps:

[0069] Step S1: 10 mmol of dimethylaminopropyl acrylamide, 13 mmol of stearyl bromide, 15 mg of hydroquinone and 35 mL of anhydrous acetone are added to a three-necked flask equipped with a stirrer and a thermometer, and the mixture is stirred at 30° C. and a stirring rate of 400 r / min for 15 min, and then the mixture is heated to 65° C. and the stirring reaction is continued for 5 h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then the reaction product is added to anhydrous ether, and then allowed to stand for precipitation, and then vacuum filtered, and the filter cake is placed in a vacuum drying oven, and dried at 55° C. for 3 h to obtain a quaternary ammonium salt monomer;

[0070] Step S2: 10 mmol of m-di(trifluoromethyl)aniline, 15 mmol of cesium carbonate and 55 mL of N,N-dimethylformamide are added to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a reflux condenser and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred for reaction for 25 min at a temperature of 30° C. and a stirring rate of 400 r / min. Then, 13 mmol of allyl bromide is added dropwise while stirring, and the dropping rate is controlled to be 2 drops / s. After the addition is completed, the temperature is raised to reflux and the stirring reaction is continued for 8 h. After the reaction is completed, the reaction product is cooled to room temperature and then added to distilled water, and then extracted with dichloromethane for 3 times. The combined extracts are washed with a saturated sodium carbonate solution for 3 times, and then dried with anhydrous magnesium sulfate. Then, vacuum filtered, the filtrate is rotary evaporated to remove the solvent to obtain a fluorine-containing monomer;

[0071] Step S3: 60g acrylamide, 5.5g 2-acrylamide-2-methylpropane sulfonic acid, 3.6g quaternary ammonium salt monomer, 3.0g fluorine-containing monomer, 0.3g sodium dodecyl sulfate and 100mL deionized water are added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred and reacted for 25min at a temperature of 30°C and a stirring rate of 400r / min. Then, 15mL of a 3% potassium persulfate solution is added dropwise while stirring, and the dropping rate is controlled to be 2 drops / s. After the dropwise addition is completed, the mixture is heated to 65°C and the stirring reaction is continued for 8h. After the reaction is completed, the reaction product is cooled to room temperature, then added to anhydrous ethanol, then allowed to stand and precipitate, then vacuum filtered, and the filter cake is placed in a vacuum drying oven and dried at a temperature of 55°C for 3h to obtain an emulsion-modified polyacrylamide;

[0072] Step S4: weighing 16 parts of emulsion-modified polyacrylamide, 0.5 parts of surfactant, 0.5 parts of potassium chloride, 0.5 parts of defoaming agent and 105 parts of water according to weight; the surfactant is a mixture of Tween 80 and sodium dodecylbenzene sulfonate in a mass ratio of 1:1; the defoaming agent is LT-8120 defoaming agent;

[0073] Step S5: Add emulsion-modified polyacrylamide and water into a mixer and stir and mix. After mixing evenly, add surfactant, potassium chloride and defoamer in sequence and stir and mix evenly to obtain emulsion-modified fracturing fluid for oil well protection.

[0074] Comparative Example 4:

[0075] This comparative example is a method for preparing an emulsion-modified fracturing fluid for oil well protection, comprising the following steps:

[0076] Step S1: 10 mmol of dimethylaminopropyl acrylamide, 13 mmol of stearyl bromide, 15 mg of hydroquinone and 35 mL of anhydrous acetone are added to a three-necked flask equipped with a stirrer and a thermometer, and the mixture is stirred at 30° C. and a stirring rate of 400 r / min for 15 min, and then the mixture is heated to 65° C. and the stirring reaction is continued for 5 h. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation, and then the reaction product is added to anhydrous ether, and then allowed to stand for precipitation, and then vacuum filtered, and the filter cake is placed in a vacuum drying oven, and dried at 55° C. for 3 h to obtain a quaternary ammonium salt monomer;

[0077] Step S2: 10 mmol of m-di(trifluoromethyl)aniline, 15 mmol of cesium carbonate and 55 mL of N,N-dimethylformamide are added to a four-necked flask equipped with a stirrer, a thermometer, an air guide tube, a reflux condenser and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred for reaction for 25 min at a temperature of 30° C. and a stirring rate of 400 r / min. Then, 13 mmol of allyl bromide is added dropwise while stirring, and the dropping rate is controlled to be 2 drops / s. After the addition is completed, the temperature is raised to reflux and the stirring reaction is continued for 8 h. After the reaction is completed, the reaction product is cooled to room temperature and then added to distilled water, and then extracted with dichloromethane for 3 times. The combined extracts are washed with a saturated sodium carbonate solution for 3 times, and then dried with anhydrous magnesium sulfate. Then, vacuum filtered, the filtrate is rotary evaporated to remove the solvent to obtain a fluorine-containing monomer;

[0078] Step S3: 60g acrylamide, 5.5g 2-acrylamide-2-methylpropane sulfonic acid, 3.6g quaternary ammonium salt monomer, 3.0g fluorine-containing monomer, 0.3g sodium dodecyl sulfate and 100mL deionized water are added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen is introduced for protection. The mixture is stirred and reacted for 25min at a temperature of 30°C and a stirring rate of 400r / min. Then, 15mL of a 3% potassium persulfate solution is added dropwise while stirring, and the dropping rate is controlled to be 2 drops / s. After the dropwise addition is completed, the mixture is heated to 65°C and the stirring reaction is continued for 8h. After the reaction is completed, the reaction product is cooled to room temperature, then added to anhydrous ethanol, then allowed to stand and precipitate, then vacuum filtered, and the filter cake is placed in a vacuum drying oven and dried at a temperature of 55°C for 3h to obtain an emulsion-modified polyacrylamide;

[0079] Step S4: 16 parts of emulsion-modified polyacrylamide, 1.8 parts of diphenylmethane diisocyanate, 0.5 parts of surfactant, 0.5 parts of potassium chloride, 0.5 parts of defoamer and 105 parts of water are weighed in parts by weight; the surfactant is a mixture of Tween 80 and sodium dodecylbenzene sulfonate in a mass ratio of 1:1; the defoamer is LT-8120 defoamer;

[0080] Step S5: Add emulsion-modified polyacrylamide and water into a mixer and stir and mix. After mixing evenly, add diphenylmethane diisocyanate, surfactant, potassium chloride and defoamer in sequence and stir and mix evenly to obtain emulsion-modified fracturing fluid for oil well protection.

[0081] The performance of the fracturing fluid modified by the emulsion for oil well protection of Examples 1-3 and Comparative Examples 1-4 was tested. The test method is as follows: According to SY / T 5107-2005 "Performance Evaluation Method of Water-Based Fracturing Fluid", the heat and shear resistance of the fracturing fluid was tested by using the MARS3 rheometer coaxial sleeve test system (rotor model PZ38) of HAKKE Company, and the shear rate of the rheometer was set to 170s -1 The temperature was raised linearly from 30°C to 200°C within 20 min.

[0082] The test results are shown in the following table:

[0083]

[0084] Referring to the data in the above table, according to the comparison between Examples 1-3 and Comparative Examples 1-4, it can be seen that the emulsion-modified fracturing fluid for oil well protection prepared by using emulsion-modified polyacrylamide containing quaternary ammonium salt monomers, fluorine-containing monomers and high-efficiency cross-linking agents still has excellent performance under high temperature conditions, and has excellent high temperature resistance.

[0085] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0086] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined in this application, they shall all fall within the protection scope of the present invention.

Claims

1. An emulsion-modified fracturing fluid for oil well protection, characterized in that: It includes the following components by weight: 8-16 parts of emulsion modified polyacrylamide, 0.6-1.8 parts of high-efficiency cross-linking agent, 0.1-0.5 parts of surfactant, 0.1-0.5 parts of potassium chloride, 0.1-0.5 parts of defoaming agent and 85-105 parts of water; Wherein, the emulsion modified polyacrylamide is prepared by the following steps: Step a1: dimethylaminopropyl acrylamide, stearyl bromide, hydroquinone and anhydrous acetone are stirred for reaction. After the reaction is completed, the reaction product is cooled, then rotary evaporated, then added to anhydrous ether, then allowed to stand for precipitation, then vacuum filtered, and the filter cake is dried to obtain a quaternary ammonium salt monomer; Step a2: stirring m-di(trifluoromethyl)aniline, cesium carbonate and N,N-dimethylformamide for reaction, then adding allyl bromide dropwise while stirring, continuing to stir the reaction after the addition is complete, cooling the reaction product after the reaction is complete, then adding it to distilled water, then extracting, washing and drying the extract, then vacuum filtering, and rotary evaporating the filtrate to obtain a fluorine-containing monomer; Step a3: acrylamide, 2-acrylamide-2-methylpropane sulfonic acid, quaternary ammonium salt monomer, fluorine-containing monomer, sodium dodecyl sulfate and deionized water are stirred for reaction, and then potassium persulfate solution is added dropwise while stirring. After the addition is completed, stirring and reacting are continued. After the reaction is completed, the reaction product is cooled, and then added to anhydrous ethanol, and then allowed to stand and precipitate, and then vacuum filtered, and the filter cake is dried to obtain emulsion modified polyacrylamide.

2. The emulsion-modified fracturing fluid for oil well protection according to claim 1, characterized in that: The usage ratio of the dimethylaminopropyl acrylamide, stearyl bromide, hydroquinone and anhydrous acetone in step a1 is 10 mmol: 11-13 mmol: 10-15 mg: 30-35 mL.

3. The emulsion-modified fracturing fluid for oil well protection according to claim 1, characterized in that: The usage ratio of the m-di(trifluoromethyl)aniline, cesium carbonate, N,N-dimethylformamide and allyl bromide in step a2 is 10 mmol:13-15 mmol:50-55 mL:11-13 mmol.

4. The emulsion-modified fracturing fluid for oil well protection according to claim 1, characterized in that: The usage ratio of the acrylamide, 2-acrylamide-2-methylpropane sulfonic acid, quaternary ammonium salt monomer, fluorine-containing monomer, sodium dodecyl sulfate, deionized water and potassium persulfate solution in step a3 is 50-60g: 3.5-5.5g: 1.8-3.6g: 1.2-3.0g: 0.1-0.3g: 80-100mL: 10-15mL; the mass fraction of the potassium persulfate solution is 2-3%.

5. The emulsion-modified fracturing fluid for oil well protection according to claim 1, characterized in that: The highly efficient cross-linking agent is prepared by the following steps: Step b1: 1,4-di(bromomethyl)benzene, diethanolamine, anhydrous potassium carbonate and dimethyl sulfoxide are stirred for reaction. After the reaction is completed, the reaction product is cooled, then vacuum filtered, the filtrate is rotary evaporated, and then silica gel column chromatography is performed with a developing solvent to obtain a polyhydroxy hyperbranched skeleton; Step b2: Stirring the polyhydroxy hyperbranched skeleton, diphenylmethane diisocyanate, dibutyltin dilaurate and methyl ethyl ketone to react, then adding triethylamine and continuing the stirring reaction, after the reaction is completed, adding the reaction product to distilled water, and then rotary evaporation to obtain a high-efficiency crosslinking agent.

6. The emulsion-modified fracturing fluid for oil well protection according to claim 5, characterized in that: The amount ratio of 1,4-di(bromomethyl)benzene, diethanolamine, anhydrous potassium carbonate and dimethyl sulfoxide in step b1 is 10mmol:20mmol:25-30mmol:30-40mL; the developing solvent is a mixture of chloroform and anhydrous ethanol in a volume ratio of 5:

1.

7. The emulsion-modified fracturing fluid for oil well protection according to claim 5, characterized in that: The usage ratio of the polyhydroxy hyperbranched skeleton, diphenylmethane diisocyanate, dibutyltin dilaurate, methyl ethyl ketone and triethylamine in step b2 is 10mmol:40mmol:0.01-0.03g:50-60mL:13-15mL.

8. A method for preparing an emulsion-modified fracturing fluid for oil well protection according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: Weigh 8-16 parts of emulsion-modified polyacrylamide, 0.6-1.8 parts of high-efficiency crosslinking agent, 0.1-0.5 parts of surfactant, 0.1-0.5 parts of potassium chloride, 0.1-0.5 parts of defoaming agent and 85-105 parts of water according to weight parts; Step 2: Add emulsion-modified polyacrylamide and water into a mixer and stir and mix. After mixing evenly, add a high-efficiency cross-linking agent, a surfactant, potassium chloride and a defoaming agent in sequence and stir and mix evenly to obtain an emulsion-modified fracturing fluid for oil well protection.

9. The method for preparing an emulsion-modified fracturing fluid for oil well protection according to claim 8, characterized in that: The surfactant is a mixture of Tween 80 and sodium dodecylbenzene sulfonate in a mass ratio of 1:

1.

10. The method for preparing an emulsion-modified fracturing fluid for oil well protection according to claim 8, characterized in that: The defoamer is one of LT-130 defoamer and LT-8120 defoamer.

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