A salt-resistant temperature-resistant polymer fracturing fluid system and a preparation method thereof

Abstract

The present application relates to a kind of anti-salt temperature-resistant polymer fracturing fluid system and its preparation method, belong to petroleum fracturing fluid technical field.The technical problems of poor salt resistance, poor temperature resistance and shear resistance, and low recovery rate of fracturing flowback fluid in the prior art are solved.The anti-salt temperature-resistant polymer fracturing fluid system of the present application includes 1wt%-2wt% thickening agent, 0.3wt%-0.5wt% synergist, 0.01wt%-0.10wt% gel breaker and 97.40wt%-98.69wt% fracturing flowback fluid.The anti-salt temperature-resistant polymer fracturing fluid system has good high-temperature resistance, shear resistance and salt resistance, and has certain reservoir protection function, is suitable for low-displacement, high-sand-ratio, high-viscosity liquid fracturing construction process, and has good sand-carrying property, can be used in the whole process of fracturing (preposition and sand-carrying stage), improves the recycling rate of fracturing flowback fluid.

Description

Technical Field

[0001] This invention belongs to the field of petroleum fracturing fluid technology, specifically relating to a salt-resistant and temperature-resistant polymer fracturing fluid system and its preparation method. Background Technology

[0002] The Sulige Gas Field, located in the Sulige Temple area of ​​Ordos City, Inner Mongolia Autonomous Region, is my country's first large gas field with proven reserves exceeding one trillion cubic meters. The gas-bearing strata of the Sulige Gas Field are composed of multiple horizontally superimposed single sandstone bodies, exhibiting typical characteristics of "low porosity" (average porosity of the He 8 sandstone is 6.74%-9.0%, and that of the Shan 1 sandstone is 2%-9.1%) and "low permeability" (average permeability of the He 8 sandstone is 0.18-0.4×10⁻⁶). -3 μm 2 The average permeability of the sandstone in Mountain 1 is 0.01-0.64×10⁻⁶. -3 μm 2 ), and "low-pressure" gas fields (pressure coefficient between 0.72 and 0.96).

[0003] Currently, the fracturing flowback fluid from the Sulige Gas Field is reused after water treatment using a guar gum fracturing fluid system. However, this system has poor salt resistance and poor temperature and shear resistance, and is generally used as a pre-fracturing fluid, not as a proppant-carrying fluid. The recovery rate of fracturing flowback fluid is low (less than 40%), resulting in a large volume of fracturing flowback fluid generated at the Sulige Gas Field, a large amount of liquid tank equipment required, and high treatment costs, significantly increasing the company's economic burden and environmental pressure. Therefore, fracturing flowback fluid recycling technology is of great significance for achieving sustainable oil and gas resource extraction, ecological protection, and green production.

[0004] Given the characteristics of the Sugeli gas field, and its entry into the mid-to-late stages of development, the reservoirs are thin (3-5m thick in the region, with a minimum mudstone barrier layer of only 1-3m between layers), high in temperature (between 81.1-128.3℃), and highly water-sensitive. Therefore, a "low flow rate, high sand ratio" fracturing technique is commonly used. This technique requires the fracturing fluid to have excellent temperature and shear resistance and sand-carrying capacity. Furthermore, the gas wells are saturated with formation water, with a maximum salinity of 25,000 ppm. The average salinity of the fracturing flowback fluid is greater than 12,000 ppm, with high calcium, magnesium, and iron ion content and numerous impurities. After repeated recycling, the salinity, calcium and magnesium ion content, and impurity content will be even higher. Therefore, to achieve the goal of repeated recycling of the fracturing flowback fluid and improve the recovery rate, the requirements for the salt resistance of the fracturing fluid are even more stringent. Summary of the Invention

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows.

[0006] In view of this, in order to solve the technical problems of poor salt resistance, poor temperature and shear resistance, and low recovery rate of fracturing flowback fluid in the prior art, the present invention provides a salt- and temperature-resistant polymer fracturing fluid system and its preparation method.

[0007] The technical means adopted by the present invention to achieve the above objectives are as follows.

[0008] In a first aspect, the present invention provides a salt-resistant and temperature-resistant polymer fracturing fluid system, comprising 1wt%-2wt% thickener, 0.3wt%-0.5wt% synergist, 0.01wt%-0.10wt% breaker and 97.40wt%-98.69wt% fracturing flowback fluid;

[0009] The thickener comprises 45.3wt%-54.7wt% acrylamide, 39.5wt%-49wt% acrylic acid, 1.2wt%-2.0wt% 2-acrylamido-2-methylpropanesulfonic acid, 0.1wt%-1wt% styrene, and 2.4wt%-5.7wt% modified polyethylene glycol.

[0010] Preferably, the raw materials of the thickener include 49.1 wt% acrylamide, 44.6 wt% acrylic acid, 1.3 wt% 2-acrylamido-2-methylpropanesulfonic acid, 0.5 wt% styrene and 4.5 wt% modified polyethylene glycol.

[0011] Preferably, the modified polyethylene glycol is tannic acid-modified polyethylene glycol.

[0012] More preferably, the preparation method of the tannic acid-modified polyethylene glycol includes the following steps:

[0013] A1: Take dried polyethylene glycol and dissolve it in dichloromethane by stirring. Add triethylamine and stir to dissolve to obtain mixed solution one.

[0014] A2: Dissolve p-toluenesulfonyl chloride in dichloromethane, stir and mix well to obtain mixed solution two;

[0015] A3: Under ice-water bath conditions, add mixture two dropwise to mixture one. After the addition is complete, keep the mixture at 20-25℃ for 22-24 hours. After the reaction is complete, wash with hydrochloric acid 2-3 times, concentrate the reaction solution, precipitate with cold diethyl ether at 0-3℃, filter to obtain a solid, dry, and obtain intermediate product one.

[0016] A4: Add intermediate product one and ammonia water to the reaction vessel and keep it at 120-140℃ for 5-8 hours. Cool to room temperature, extract the reaction solution with dichloromethane multiple times, combine the organic phases, add sodium hydroxide aqueous solution to the organic phase, stir, filter, and wash the solid with distilled water until neutral to obtain intermediate product two.

[0017] A5: Dissolve the prepared intermediate product II in distilled water, adjust the pH to 7-8, add tannic acid, and stir the reaction at 50-60℃ for 12-24 hours. After the reaction is complete, evaporate the reaction solution to obtain modified polyethylene glycol.

[0018] More preferably, in step A1, the polyethylene glycol is one or more of PEG-3000 and PEG-4000.

[0019] More preferably, in step A1, the molar ratio of polyethylene glycol to triethylamine is 1:10-12.

[0020] More preferably, in step A1, the mass ratio of polyethylene glycol to dichloromethane is 1:2-2.5.

[0021] More preferably, in step A2, the molar ratio of p-toluenesulfonyl chloride to polyethylene glycol is 8-10:1.

[0022] More preferably, in step A2, the mass ratio of p-toluenesulfonyl chloride to dichloromethane is 1:2.5-3.

[0023] Preferably, in step A2, the concentration method is distillation or rotary evaporation; more preferably, the distillation is vacuum distillation.

[0024] More preferably, in step A3, the dripping rate is 2-3 d / s.

[0025] More preferably, in step A3, the concentration of the hydrochloric acid is 3 mol / L.

[0026] More preferably, in step A3, the volume of the cold ether used is 5-6 times the volume of the reaction liquid.

[0027] More preferably, in step A4, the molar ratio of the ammonia water to the polyethylene glycol in step A1 is 3-4:1.

[0028] More preferably, in step A4, the concentration of the sodium hydroxide aqueous solution is 10 wt%, and the amount of the sodium hydroxide aqueous solution used is equal to the volume of the organic phase.

[0029] More preferably, in step A4, the stirring time is 5-6 hours after adding the sodium hydroxide aqueous solution.

[0030] More preferably, in step A5, the molar ratio of tannic acid to polyethylene glycol in step A1 is 3-5:1.

[0031] More preferably, in step A5, the pH is adjusted using a glycine-sodium hydroxide buffer solution, wherein the concentration of the glycine-sodium hydroxide buffer solution is 0.05 mol / L and the pH is 8.5-9.5.

[0032] Preferably, the preparation method of the thickener includes the following steps:

[0033] According to the proportions of each raw material, add modified polyethylene glycol to water, stir to dissolve, then add acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and styrene, stir to mix well, adjust the pH to 6-9, introduce an inert atmosphere, keep the reaction at an inert atmosphere for 30-60 minutes, then raise the temperature to 35-55℃ and keep it at that temperature for 20-40 minutes, add the initiator, introduce an inert atmosphere for another 10 minutes, and then keep the reaction at a sealed temperature for 12-15 hours to obtain the crude reaction product. The crude reaction product is then refined, dried and pulverized to obtain the anti-salt thickener.

[0034] Preferably, the pH is adjusted using a 25 wt% sodium hydroxide solution.

[0035] Preferably, the inert atmosphere is nitrogen.

[0036] Preferably, the initiator is any one of hydrogen peroxide, ammonium persulfate, potassium persulfate, and cerium ammonium nitrate, and the mass ratio of the initiator to acrylamide is 1:50.

[0037] Preferably, the process of purifying the crude reaction product is as follows: the crude reaction product is added to anhydrous diethyl ether, stirred for 1-2 hours, soaked for 10-12 hours, filtered, evaporated under reduced pressure, and the resulting solid is soaked and washed in anhydrous ethanol 2-3 times, and then filtered.

[0038] Preferably, the raw materials of the synergist include 10wt%-30wt% organozzirconium crosslinking agent, 0.5wt%-1wt% pH adjuster, 3wt%-5wt% clay stabilizer, 2wt%-10wt% sodium dodecylbenzenesulfonate, 1wt%-5wt% benzalkonium chloride, 1wt%-3wt% perfluorocarbon surfactant and 46wt%-82.5wt% water.

[0039] More preferably, the pH adjuster is citric acid.

[0040] Preferably, the synergist is prepared by dissolving sodium dodecylbenzenesulfonate completely in water according to the proportions of each raw material, adding organozirconium crosslinking agent, benzalkonium chloride, clay stabilizer and perfluorocarbon surfactant, stirring for 10-15 minutes, adding pH adjuster, and continuing to stir for 30-45 minutes to obtain the synergist.

[0041] Preferably, the fracturing flowback fluid has a mineralization of 5000-20000ppm, a calcium and magnesium ion content of ≤1000ppm, and an iron ion content of ≤100ppm.

[0042] Preferably, the degreasing agent is ammonium persulfate; more preferably, the ammonium persulfate is added as ammonium persulfate powder or ammonium persulfate capsules.

[0043] Secondly, the present invention provides a method for preparing the above-mentioned salt-resistant and temperature-resistant polymer fracturing fluid system, the steps of which are as follows:

[0044] Under stirring conditions, the thickener, synergist, and breaker were added to the fracturing flowback fluid at a uniform rate according to the specified ratio, and stirred evenly to obtain a salt-resistant and temperature-resistant polymer fracturing fluid system.

[0045] Preferably, the stirring speed is 500-600 r / min.

[0046] The principle of this invention is as follows:

[0047] 1. The salt-resistant thickener of the present invention uses 2-acrylamido-2-methylpropanesulfonic acid, styrene, and modified polyethylene glycol as raw materials. The sulfonic acid groups introduced by 2-acrylamido-2-methylpropanesulfonic acid have strong electrostatic repulsion, which can improve the salt resistance of the thickener. The steric hindrance of the benzene ring of styrene can better maintain the molecular chain without deformation, thus improving the salt resistance of the thickener. The modified polyethylene glycol is interspersed between the molecular chains of polyacrylamide, which is beneficial to maintaining the spatial structure of polyacrylamide.

[0048] Furthermore, the modified polyethylene glycol (PEG) is first aminated to increase the accessibility of potential binding sites, and then modified with tannic acid. On one hand, introducing polyhydroxy tannic acid into the thickener not only increases the polymer's water solubility, but also demonstrates a strong complexing ability for salt ions, especially iron ions. The introduction of tannic acid can complex and fix these salt ions, thereby stabilizing them, reducing their impact on the polymer molecules, and improving the thickener's salt resistance. On the other hand, the presence of tannic acid facilitates the softening of PEG, allowing it to better integrate into the polyacrylamide molecular chain, and also enhances its thickening ability to some extent.

[0049] The synergist of this invention uses organozirconium crosslinking agent, sodium dodecylbenzenesulfonate, and perfluorocarbon surfactant as raw materials. The organozirconium crosslinking agent enhances the temperature and shear resistance of the fracturing fluid, while the synergistic effect of sodium dodecylbenzenesulfonate and benzalkonium chloride can reduce interfacial tension. The perfluorocarbon surfactant can reduce the surface tension of the fracturing fluid.

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0051] The salt- and temperature-resistant polymer fracturing fluid system of this invention possesses excellent high-temperature resistance, shear resistance, and salt resistance, while also exhibiting certain reservoir protection functions. It is suitable for fracturing operations with low flow rates, high sand ratios, and high viscosity, and has good proppant carrying capacity, allowing its use throughout the entire fracturing process (pre-fracturing and proppant carrying stages), thus improving the recycling rate of fracturing flowback fluid. Tests show that the polymer fracturing fluid system of this invention can recycle fracturing flowback fluid with a salinity of 5000-20000 ppm, calcium and magnesium ion content ≤1000 ppm, and iron ion content ≤100 ppm. After temperature and shear resistance tests, the shear viscosity is ≥50 mPa·s, the static suspended proppant (25 wt% sand ratio) is ≥90% after 1 hour, the gel breaking time is ≤240 min, the surface tension is ≤30 mN / m, and the interfacial tension is ≤3 mN / m. It is suitable for low flow rates (<5 m³ / s). 3 / min), high sand ratio (>480kg / m 3 The high-viscosity fracturing flowback fluid reuse fracturing construction technology can be used throughout the entire fracturing process (pre-fracturing and proppant-carrying stages). Detailed Implementation

[0052] The method of the present invention will be described below through embodiments. The embodiments are merely specific descriptions of the claims of the present invention, and the claims include, but are not limited to, the contents of the embodiments.

[0053] Unless otherwise specified, the reagents and materials described in the following examples are commercially available; and the test methods described are conventional methods unless otherwise specified.

[0054] Example 1

[0055] Step 1: Preparation of Modified Polyethylene Glycol

[0056] A1: Take dried polyethylene glycol (PEG-4000) and stir to dissolve it in dichloromethane with a mass equal to that of polyethylene glycol. Add triethylamine and stir to dissolve to obtain mixed solution one. The molar ratio of polyethylene glycol to triethylamine is 1:10.

[0057] A2: Dissolve p-toluenesulfonyl chloride in 2.5 times the mass of p-toluenesulfonyl chloride in dichloromethane, stir and mix well to obtain mixed solution two, the molar ratio of p-toluenesulfonyl chloride and polyethylene glycol is 10:1.

[0058] A3: Under ice-water bath conditions, add mixed solution 2 dropwise to mixed solution 1 at a rate of 2-3 d / s. After the addition is complete, keep the mixture at 22℃ for 24 h. After the reaction is complete, wash the mixture 2-3 times with 3 mol / L hydrochloric acid, concentrate the reaction solution by vacuum distillation, precipitate the solution with 5 times the volume of cold diethyl ether at 0-3℃, filter the precipitate, and dry the solid to obtain intermediate product 1.

[0059] A4: Add intermediate product one to an autoclave, add ammonia water, the molar ratio of ammonia water to polyethylene glycol is 3:1, keep the reaction at 140℃ for 6h, cool to room temperature, extract the reaction solution multiple times with dichloromethane, combine the organic phases, add an equal volume of 10wt% sodium hydroxide aqueous solution to the organic phase, stir for 6h, filter, wash the solid with distilled water until neutral to obtain intermediate product two.

[0060] A5: Dissolve the prepared intermediate product II in 100 times its mass of distilled water, adjust the pH to 7-8 with 0.05 mol / L glycine-sodium hydroxide buffer solution with pH 8.5-9.5, add tannic acid, and add tannic acid to polyethylene glycol in a molar ratio of 4:1. Stir and react at 50°C for 24 h. After the reaction is complete, evaporate the reaction solution to dryness to obtain modified polyethylene glycol.

[0061] Step 2: Preparation of Thickener

[0062] The thickener's raw materials include 49.1 wt% acrylamide, 44.6 wt% acrylic acid, 1.3 wt% 2-acrylamido-2-methylpropanesulfonic acid, 0.5 wt% styrene, and 4.5 wt% modified polyethylene glycol.

[0063] Modified polyethylene glycol was added to water and stirred until dissolved. Acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and styrene were then added and stirred until well mixed. 25 wt% sodium hydroxide solution was added to adjust the pH to 6-9. Nitrogen gas was introduced and the reaction was kept at a nitrogen atmosphere for 45 min. The temperature was raised to 55℃ and kept at that temperature for 20 min. Ammonium persulfate initiator was added. The mass ratio of ammonium persulfate to acrylamide was 1:50. Nitrogen gas was introduced for another 10 min. The reaction was kept at a sealed temperature for 14 h to obtain the crude product. The crude product was added to anhydrous diethyl ether, stirred for 1-2 h, and soaked for 10 h. After filtration, the product was evaporated under reduced pressure to obtain a solid. The solid was soaked and washed 2-3 times in anhydrous ethanol, filtered, and dried to obtain a thickener.

[0064] Step 3: Preparation of the synergist

[0065] The synergist in this embodiment is composed of 20 wt% organozzirconium crosslinking agent, 0.8 wt% pH adjuster, 3 wt% clay stabilizer, 2 wt% sodium dodecylbenzenesulfonate, 3 wt% benzalkonium chloride, 1 wt% perfluorocarbon surfactant and 70.2 wt% water.

[0066] Pump water into a mixing tank according to the ratio and stir continuously at a rate of 500 r / min. Add sodium dodecylbenzenesulfonate and stir until completely dissolved. Then add organozirconium crosslinking agent, benzalkonium chloride, clay stabilizer and perfluorocarbon surfactant. Stir for 10 min and then add citric acid as a pH adjuster. Continue stirring for 30 min to obtain the synergist.

[0067] Step 4: Preparation of Salt-Resistant and Temperature-Resistant Polymer Fracturing Fluid System

[0068] The polymer fracturing fluid system in this embodiment consists of 1 wt% thickener, 0.3 wt% synergist, 0.01 wt% breaker and 98.69 wt% fracturing flowback fluid.

[0069] Under continuous stirring at a rate of 500 r / min, the breaker, thickener, and synergist were added to the fracturing flowback fluid at a uniform rate according to the ratio, and stirred for 2 minutes. The simulated fracturing flowback fluid had a mineralization of 5000 ppm (the mass concentration ratio of calcium magnesium ions: iron ions: total mineralization was 10:1:200).

[0070] Example 2

[0071] Step 1: Preparation of Modified Polyethylene Glycol

[0072] A1: Take dried polyethylene glycol (PEG-3000) and stir to dissolve it in 2.5 times the mass of polyethylene glycol in dichloromethane. Add triethylamine and stir to dissolve to obtain mixed solution one. The molar ratio of polyethylene glycol to triethylamine is 1:11.

[0073] A2: Dissolve p-toluenesulfonyl chloride in dichloromethane at a mass equal to 3 times that of p-toluenesulfonyl chloride, stir and mix well to obtain mixed solution two, with a molar ratio of p-toluenesulfonyl chloride to polyethylene glycol of 8:1.

[0074] A3: Under ice-water bath conditions, add mixed solution 2 dropwise to mixed solution 1 at a rate of 2-3 d / s. After the addition is complete, keep the mixture at 25℃ for 24 h. After the reaction is complete, wash the mixture 2-3 times with 3 mol / L hydrochloric acid, concentrate the reaction solution under reduced pressure, precipitate the solution with 5 times the volume of the reaction solution in cold diethyl ether at 0-3℃, filter the precipitate, and dry the solid to obtain intermediate product 1.

[0075] A4: Add intermediate product one to an autoclave, add ammonia water, the molar ratio of ammonia water to polyethylene glycol is 4:1, keep the reaction at 120℃ for 8 hours, cool to room temperature, extract the reaction solution multiple times with dichloromethane, combine the organic phases, add an equal volume of 10wt% sodium hydroxide aqueous solution to the organic phase, stir for 6 hours, filter, wash the solid with distilled water until neutral to obtain intermediate product two.

[0076] A5: Dissolve the prepared intermediate product II in 100 times its mass of distilled water, adjust the pH to 7-8 with 0.05 mol / L glycine-sodium hydroxide buffer solution with pH 8.5-9.5, add tannic acid, and add tannic acid to polyethylene glycol in a molar ratio of 3:1. Stir and react at 55℃ for 16 h. After the reaction is complete, evaporate the reaction solution to dryness to obtain modified polyethylene glycol.

[0077] Step 2: Preparation of Thickener

[0078] The thickener in this embodiment comprises 49.6 wt% acrylamide, 45.5 wt% acrylic acid, 1.6 wt% 2-acrylamido-2-methylpropanesulfonic acid, 0.8 wt% styrene and 2.5 wt% modified polyethylene glycol.

[0079] Modified polyethylene glycol was added to water and stirred until dissolved. Acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and styrene were then added and stirred until well mixed. 25 wt% sodium hydroxide solution was added to adjust the pH to 6-9. Nitrogen gas was introduced and the reaction was kept at a nitrogen atmosphere for 30 min. The temperature was raised to 35°C and kept at that temperature for 40 min. Cerium ammonium nitrate initiator was added. The mass ratio of cerium ammonium nitrate to acrylamide was 1:50. Nitrogen gas was introduced for another 10 min. The reaction was kept at a sealed temperature for 12 h to obtain the crude product. The crude product was added to anhydrous diethyl ether, stirred for 1-2 h, and soaked for 12 h. After filtration, the product was evaporated under reduced pressure to obtain a solid. The solid was soaked and washed 2-3 times in anhydrous ethanol, filtered, and dried to obtain the anti-salt thickener.

[0080] Step 3: Preparation of the synergist

[0081] The synergist in this embodiment is composed of 30 wt% organozirconium crosslinking agent, 1 wt% pH adjuster, 5 wt% clay stabilizer, 10 wt% sodium dodecylbenzenesulfonate, 5 wt% benzalkonium chloride, 2 wt% perfluorocarbon surfactant and 47 wt% water.

[0082] Pump water into a mixing tank according to the ratio and stir continuously at a rate of 500 r / min. Add sodium dodecylbenzenesulfonate and stir until completely dissolved. Then add organozirconium crosslinking agent, benzalkonium chloride, clay stabilizer and perfluorocarbon surfactant. Stir for 10 min and then add citric acid as a pH adjuster. Continue stirring for 30 min to obtain the synergist.

[0083] Step 4: Preparation of Salt-Resistant and Temperature-Resistant Polymer Fracturing Fluid System

[0084] The polymer fracturing fluid system in this embodiment consists of 1.5 wt% thickener, 0.4 wt% synergist, 0.03 wt% breaker and 98.07 wt% fracturing flowback fluid.

[0085] Under continuous stirring at a rate of 500 r / min, the breaker, thickener and synergist are added to the fracturing flowback fluid at a uniform rate according to the ratio, and stirred for 2 min. The simulated fracturing flowback fluid has a mineralization of 10000 ppm (the mass concentration ratio of calcium magnesium ions: iron ions: total mineralization is 10:1:200).

[0086] Example 3

[0087] Step 1: Preparation of Modified Polyethylene Glycol

[0088] A1: Take dried polyethylene glycol (PEG-4000) and stir to dissolve it in dichloromethane with a mass equal to that of polyethylene glycol. Add triethylamine and stir to dissolve to obtain mixed solution one. The molar ratio of polyethylene glycol to triethylamine is 1:12.

[0089] A2: Dissolve p-toluenesulfonyl chloride in 2.8 times the mass of p-toluenesulfonyl chloride in dichloromethane, stir and mix well to obtain mixed solution two, with a molar ratio of p-toluenesulfonyl chloride to polyethylene glycol of 9:1.

[0090] A3: Under ice-water bath conditions, add mixed solution 2 dropwise to mixed solution 1 at a rate of 2-3 d / s. After the addition is complete, keep the mixture at 20℃ for 24 h. After the reaction is complete, wash the mixture 2-3 times with 3 mol / L hydrochloric acid, concentrate the reaction solution under reduced pressure, precipitate the solution with 5 times the volume of the reaction solution in cold diethyl ether at 0-3℃, filter the precipitate, and dry the solid to obtain intermediate product 1.

[0091] A4: Add intermediate product one to an autoclave, add ammonia water, the molar ratio of ammonia water to polyethylene glycol is 3:1, keep the reaction at 130℃ for 5h, cool to room temperature, extract the reaction solution multiple times with dichloromethane, combine the organic phases, add an equal volume of 10wt% sodium hydroxide aqueous solution to the organic phase, stir for 6h, filter, wash the solid with distilled water until neutral to obtain intermediate product two.

[0092] A5: Dissolve the prepared intermediate product II in 100 times its mass of distilled water, adjust the pH to 7-8 with 0.05 mol / L glycine-sodium hydroxide buffer solution with pH 8.5-9.5, add tannic acid, and add tannic acid to polyethylene glycol in a molar ratio of 5:1. Stir and react at 60℃ for 12 h. After the reaction is complete, evaporate the reaction solution to dryness to obtain modified polyethylene glycol.

[0093] Step 2: Preparation of Thickener

[0094] The thickener in this embodiment comprises 51.0 wt% acrylamide, 43.3 wt% acrylic acid, 1.7 wt% 2-acrylamido-2-methylpropanesulfonic acid, 0.1 wt% styrene and 3.9 wt% modified polyethylene glycol.

[0095] Modified polyethylene glycol was added to water and stirred until dissolved. Acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and styrene were then added and stirred until well mixed. 25 wt% sodium hydroxide solution was added to adjust the pH to 6-9. Nitrogen gas was introduced and the reaction was kept at a nitrogen atmosphere for 60 min. The temperature was raised to 40℃ and kept at that temperature for 30 min. Potassium persulfate was added as an initiator. The mass ratio of potassium persulfate to acrylamide was 1:50. Nitrogen gas was introduced for another 10 min. The reaction was kept at a sealed temperature for 15 h to obtain the crude product. The crude product was added to anhydrous diethyl ether, stirred for 1-2 h, and soaked for 11 h. After filtration, the product was evaporated under reduced pressure to obtain a solid. The solid was soaked and washed 2-3 times in anhydrous ethanol, filtered, and dried to obtain the thickener.

[0096] Step 3: Preparation of the synergist

[0097] The synergist in this embodiment is composed of 10 wt% organozzirconium crosslinking agent, 0.5 wt% pH adjuster, 4 wt% clay stabilizer, 8 wt% sodium dodecylbenzenesulfonate, 1 wt% benzalkonium chloride, 3 wt% perfluorocarbon surfactant and 73.5 wt% water.

[0098] Pump water into a mixing tank according to the ratio and stir continuously at a rate of 500 r / min. Add sodium dodecylbenzenesulfonate and stir until completely dissolved. Then add organozirconium crosslinking agent, benzalkonium chloride, clay stabilizer and perfluorocarbon surfactant. Stir for 10 min and then add citric acid as a pH adjuster. Continue stirring for 30 min to obtain the synergist.

[0099] Step 4: Preparation of Salt-Resistant and Temperature-Resistant Polymer Fracturing Fluid System

[0100] The polymer fracturing fluid system in this embodiment consists of 2 wt% thickener, 0.5 wt% synergist, 0.06 wt% breaker and 97.44 wt% fracturing flowback fluid.

[0101] Under continuous stirring at a rate of 500 r / min, the breaker, thickener and synergist are added to the fracturing flowback fluid at a uniform rate according to the ratio, and stirred for 2 min. The simulated fracturing flowback fluid has a mineralization of 20000 ppm (the mass concentration ratio of calcium magnesium ions: iron ions: total mineralization is 10:1:200).

[0102] The polymer fracturing fluid systems prepared in Examples 1-3 were subjected to the following performance tests, with conventional fracturing fluid systems used as comparative examples. The performance testing methods are as follows:

[0103] 1. Temperature and shear resistance: tested by a high-temperature, high-pressure rheometer at 170 seconds. -1 Shear rate, isothermal shearing at 110℃ for 60 min, and temperature and shear viscosity were measured.

[0104] 2. Salt resistance: The apparent viscosity of the solution after stirring and mixing the prepared fracturing fluid system is the salt resistance viscosity.

[0105] 3.1h Static suspended sand (25wt% sand ratio): Take the prepared fracturing fluid system, add 25wt% quartz sand (particle size of 40-70 mesh), stir evenly, pour into a measuring cylinder, and let stand for 1h.

[0106] 4. Break-out time: After the fracturing fluid system is stirred evenly, it is placed in a 90℃ constant temperature water bath for breaking-out. The apparent viscosity is measured every 30 minutes. According to Part 3 of Shale Gas Fracturing Fluid: Performance Indicators and Evaluation Methods of Continuously Mixed Fracturing Fluids, it is determined whether the fracturing fluid system has been completely broken-out, and the breaking-out time is calculated.

[0107] The surface tension and interfacial tension of the prepared fracturing fluid system were also tested. All of the above performance tests were conducted on-site.

[0108] The test results are shown in Table 1:

[0109] Table 1

[0110]

[0111] As shown in Table 1, the polymer fracturing fluid system of this invention can recycle fracturing flowback fluid with a salinity of 20,000 ppm. After temperature and shear resistance tests, the shear viscosity is ≥50 mPa·s, the static suspended sand (25 wt% sand ratio) is ≥90% after 1 hour, the gel breaking time is ≤240 min, the surface tension is ≤30 mN / m, and the interfacial tension is ≤3 mN / m. It is suitable for low flow rates (<5 m³ / s). 3 / min), high sand ratio (>480kg / m 3 The high-viscosity fracturing flowback fluid reuse fracturing construction technology can be used throughout the entire fracturing process (pre-fracturing and proppant-carrying stages).

[0112] Obviously, the above embodiments are merely examples for clear illustration and are not intended to limit the embodiments. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all embodiments here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A polymer fracturing fluid system, characterized in that, It includes 1wt%-2wt% thickener, 0.3wt%-0.5wt% synergist, 0.01wt%-0.10wt% breaker and 97.40wt%-98.69wt% fracturing flowback fluid; The raw materials for the thickener include 45.3wt%-54.7wt% acrylamide, 39.5wt%-49wt% acrylic acid, 1.2wt%-2.0wt% 2-acrylamido-2-methylpropanesulfonic acid, 0.1wt%-1wt% styrene, and 2.4wt%-5.7wt% modified polyethylene glycol.

2. The polymer fracturing fluid system according to claim 1, characterized in that, The thickener comprises 49.1 wt% acrylamide, 44.6 wt% acrylic acid, 1.3 wt% 2-acrylamido-2-methylpropanesulfonic acid, 0.5 wt% styrene and 4.5 wt% modified polyethylene glycol.

3. The polymer fracturing fluid system according to claim 1, characterized in that, The modified polyethylene glycol is tannic acid-modified polyethylene glycol.

4. The polymer fracturing fluid system according to claim 3, characterized in that, The preparation method of the tannic acid-modified polyethylene glycol includes the following steps: A1: Take dried polyethylene glycol and dissolve it in dichloromethane by stirring. Add triethylamine and stir to dissolve to obtain mixed solution one. A2: Dissolve p-toluenesulfonyl chloride in dichloromethane, stir and mix well to obtain mixed solution two; A3: Under ice-water bath conditions, add mixture two dropwise to mixture one. After the addition is complete, keep the mixture at 20-25℃ for 22-24 hours. After the reaction is complete, wash with hydrochloric acid 2-3 times, concentrate the reaction solution, precipitate with cold diethyl ether at 0-3℃, filter to obtain a solid, dry, and obtain intermediate product one. A4: Add intermediate product one and ammonia water to the reaction vessel and keep it at 120-140℃ for 5-8 hours. Cool to room temperature, extract the reaction solution with dichloromethane multiple times, combine the organic phases, add sodium hydroxide aqueous solution to the organic phase, stir, filter, and wash the solid with distilled water until neutral to obtain intermediate product two. A5: Dissolve the prepared intermediate product II in distilled water, adjust the pH to 7-8, add tannic acid, and stir the reaction at 50-60℃ for 12-24 hours. After the reaction is complete, evaporate the reaction solution to obtain modified polyethylene glycol.

5. The polymer fracturing fluid system according to claim 4, characterized in that, The molar ratio of polyethylene glycol, triethylamine, p-toluenesulfonyl chloride, ammonia, and tannic acid is 1:10-12:8-10:3-4:3-5; And / or, in step A3, the concentration of the hydrochloric acid is 3 mol / L; And / or, in step A4, the concentration of the sodium hydroxide aqueous solution is 10 wt%, the amount of the sodium hydroxide aqueous solution is equal to the volume of the organic material, and the stirring time is 5-6 hours after adding the sodium hydroxide aqueous solution; And / or, in step A5, the pH is adjusted using a glycine-sodium hydroxide buffer solution, wherein the concentration of the glycine-sodium hydroxide buffer solution is 0.05 mol / L and the pH is 8.5-9.

5.

6. The polymer fracturing fluid system according to claim 1, characterized in that, The preparation method of the thickener includes the following steps: According to the proportions of each raw material, add modified polyethylene glycol to water, stir to dissolve, then add acrylamide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and styrene, stir to mix well, adjust the pH to 6-9, introduce an inert atmosphere, keep the reaction at an inert atmosphere for 30-60 minutes, then raise the temperature to 35-55℃ and keep it at that temperature for 20-40 minutes, add the initiator, introduce an inert atmosphere for another 10 minutes, and then keep the reaction at a sealed temperature for 12-15 hours to obtain the crude reaction product. The crude reaction product is then refined, dried and pulverized to obtain the anti-salt thickener.

7. The polymer fracturing fluid system according to claim 6, characterized in that, The initiator is any one of hydrogen peroxide, ammonium persulfate, potassium persulfate, and cerium ammonium nitrate, and the mass ratio of the initiator to acrylamide is 1:

50. And / or, the inert atmosphere is nitrogen; And / or, the process of purifying the crude reaction product is as follows: the crude reaction product is added to anhydrous diethyl ether, stirred for 1-2 hours, soaked for 10-12 hours, filtered, evaporated under reduced pressure, and the resulting solid is soaked and washed in anhydrous ethanol 2-3 times, and then filtered.

8. The polymer fracturing fluid system according to claim 1, characterized in that, The synergist comprises 10wt%-30wt% organozirconium crosslinking agent, 0.5wt%-1wt% pH adjuster, 3wt%-5wt% clay stabilizer, 2wt%-10wt% sodium dodecylbenzenesulfonate, 1wt%-5wt% benzalkonium chloride, 1wt%-3wt% perfluorocarbon surfactant, and 46wt%-82.5wt% water; The preparation method of the synergist is as follows: Sodium dodecylbenzenesulfonate is completely dissolved in water according to the ratio of each raw material, organozzirconium crosslinking agent, benzalkonium chloride, clay stabilizer and perfluorocarbon surfactant are added, and after stirring for 10-15 minutes, pH adjuster is added, and stirring is continued for 30-45 minutes to obtain the synergist.

9. The polymer fracturing fluid system according to claim 1, characterized in that, The fracturing flowback fluid has a mineralization of 5000-20000ppm, a calcium and magnesium ion content of ≤1000ppm, and an iron ion content of ≤100ppm. The de-gelling agent is ammonium persulfate, which is added in the form of ammonium persulfate powder or ammonium persulfate capsules.

10. The method for preparing the salt-resistant and temperature-resistant polymer fracturing fluid system according to any one of claims 1-9, characterized in that, The steps are as follows: Under stirring conditions, the thickener, synergist, and breaker were added to the fracturing flowback fluid at a uniform rate according to the specified ratio, and stirred evenly to obtain a salt-resistant and temperature-resistant polymer fracturing fluid system.

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