A composite salt suppressant, fracturing fluid system, its preparation method and application

Abstract

This invention relates to the field of oil and gas field development, specifically to a composite salt suppressant, a fracturing fluid system, its preparation method, and its application. The fracturing fluid system includes an emulsion thickener, a composite salt suppressant, a clay stabilizer, a fluorocarbon drainage aid, a polyether demulsifier, and a degelatinizer. The composite salt suppressant's raw materials include a salt suppressant A and an auxiliary agent B. The raw materials for the salt suppressant A include acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, a hydrophobic associating monomer, a chain transfer agent, and an initiator. The auxiliary agent B is selected from one or more of sodium cocoate, sodium laurate, sodium palmitate, and disodium EDTA. The salt suppressant of this invention has no effect on the performance of the fracturing fluid system, and the composite salt suppressant can achieve a salt suppression rate of over 90% in the fracturing fluid system. The fracturing fluid system can completely degelatinate in high-salt (alkaline) reservoirs, effectively solving the problem of wellbore salt blockage.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development, specifically to a composite salt suppressant, fracturing fluid system, its preparation method, and its application. Background Technology

[0002] During oilfield development and secondary oil recovery processes, the reservoir's energy is continuously consumed, leading to a decline in reservoir pressure, significant degassing of underground crude oil, increased viscosity, and a substantial reduction in well production. To maintain or increase reservoir pressure and achieve higher recovery rates, water injection is necessary. To conserve water resources, oilfield water reinjection is commonly employed. Furthermore, in oilfield extraction, well fracturing is a production enhancement measure that improves the reservoir's conductivity to increase production and injection capacity.

[0003] During oil and gas field production, changes in pressure, temperature, and other conditions, as well as hydrothermal instability and chemical incompatibility, often lead to salt deposition in formations, gravel-filled layers, casing, gas nozzles, and gathering and transportation pipelines. Salt deposition in oil and gas fields severely impacts normal production, causing significant economic losses to oil and gas field development and gas storage operation, and seriously hindering both processes.

[0004] Currently, scale is classified into two categories: soluble scale (sodium chloride) and insoluble scale (calcium carbonate, calcium sulfate, barium sulfate, etc.), and research on related scale inhibitors or salt suppressants is conducted based on this classification. However, there are no reports on sodium carbonate or sodium bicarbonate scale and their composite scale.

[0005] For special soluble alkaline high-salt reservoirs, fracturing fluids dissolve the salt rock layer upon entering the reservoir, resulting in extremely high salinity of the produced water. The temperature decreases during the flowback process, leading to supersaturation and scaling of the produced water in the wellbore, which blocks oil flow channels, severely impacting normal well production and hindering oilfield exploration and development. The use of liquid salt inhibitors to prevent salt formation has attracted widespread attention due to its simple operation, low cost, and rapid effectiveness. Because alkaline salts and sodium chloride have significantly different physicochemical properties, conventional scale inhibitors are ineffective. Therefore, to address the problem of sodium bicarbonate / sodium carbonate salt formation and scaling after fracturing in salt (alkali) formations, it is necessary to develop highly efficient salt inhibitors to form a highly efficient fracturing fluid system that inhibits salt formation in the wellbore.

[0006] Chinese invention patent application CN202010496006.8 discloses a green, environmentally friendly, multifunctional salt scale inhibitor for oil and gas development and its preparation method. The salt scale inhibitor can increase the solubility of salts such as sodium chloride, calcium carbonate, and calcium sulfate, and simultaneously alter the crystal morphology of these three types of scale, forming dendritic or snowflake-like structures, reducing adhesion to the crystal surface. This effectively prevents the deposition of these scales in formations and wellbores during oil and gas production, improving oil and gas well production efficiency. However, it primarily inhibits sodium chloride, calcium carbonate, and calcium sulfate scale; its effect on alkaline sodium bicarbonate / sodium carbonate scale is unclear.

[0007] Chinese invention patent application CN201910079709.8 discloses a long-lasting scale inhibitor and oil displacement fracturing agent, along with its preparation and application method. The agent is composed of acid anhydride, alkylolamide polyoxyethylene ether, a scale inhibitor intermediate, sodium bicarbonate, sodium sulfite, and a catalyst. This scale inhibitor and oil displacement fracturing agent achieves a maximum scale inhibition rate of 53-63% against sparingly soluble salts such as calcium carbonate and calcium sulfate, with an oil displacement and scale inhibition time of approximately 6 months. However, this scale inhibitor primarily inhibits calcium sulfate or calcium carbonate scale; its effectiveness against alkaline sodium bicarbonate / sodium carbonate scale is unclear.

[0008] Chinese invention patent application CN201310443538.5 discloses the application of disodium EDTA as a low-temperature crystallization inhibitor for sodium carbonate solution. However, disodium EDTA only has a good inhibitory effect on 20% sodium carbonate solution at 30℃. In contrast, the Fengcheng Formation reservoir in Mahu Oilfield, Xinjiang has a high temperature (above 90℃), high sodium bicarbonate / sodium carbonate content (mineralization of produced water 300,000 mg / L), and formation water pH between 8 and 9.5. Ordinary salt inhibitors have poor salt inhibition effect in strongly alkaline environments, and their effect on sodium bicarbonate type scale is unclear.

[0009] Based on this, a composite salt suppressant and fracturing fluid system is proposed for application in the field of oil and gas field development, which has great economic benefits. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention provides a composite salt suppressant, a fracturing fluid system, and a method for preparing the same. The composite salt suppressant has no effect on the viscosity of the base fluid in the fracturing fluid system, and the fracturing fluid system can effectively solve the problem of wellbore salt blockage after fracturing in salt (alkali) reservoirs.

[0011] To achieve the above-mentioned objectives of this invention, the specific technical solution adopted by this invention is as follows:

[0012] This invention relates to a composite salt suppressant, the raw materials of which include a salt suppressant A and an excipient B, wherein the raw materials of the salt suppressant A include acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, hydrophobic associating monomer, chain transfer agent and initiator; and the excipient B is selected from one or more of sodium cocoate, sodium laurylate and sodium palmitate and disodium EDTA.

[0013] Preferably, the mass ratio of the salt-suppressing agent A to the excipient B is 1:0.05-0.1.

[0014] Preferably, the viscosity-average molecular weight of the salt-suppressing agent A is 2000-50000.

[0015] Preferably, the hydrophobic associating monomer is hexadecyltrimethylallylammonium chloride.

[0016] Preferably, the chain transfer agent is selected from one or more of sodium formate, thiols, and isopropanol.

[0017] Preferably, the initiator comprises K2S2O8 and Na2SO3, wherein the mass ratio of K2S2O8 to Na2SO3 is 2:1-2, preferably 2:1.

[0018] Preferably, the mass ratio of acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, hydrophobic associating monomer, chain transfer agent solution and initiator is 80-120:15-50:1-10:0.003-0.005:0.01-0.08.

[0019] Preferably, the preparation method of the above-mentioned salt-suppressing agent A includes the following steps:

[0020] (1) Acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid are dissolved in water, and the pH is adjusted to obtain an aqueous solution of the monomers;

[0021] (2) Stir and heat the monomer aqueous solution, add hydrophobic associating monomer solution, chain transfer agent solution and initiator solution, react to obtain copolymer solution;

[0022] (3) The copolymer solution is cooled, purified and dried to obtain the copolymer solution.

[0023] Preferably, the reagent for adjusting pH in step (1) is a NaOH solution with a mass concentration of 20%-40% and a pH of 6.5-7.5; the heating in step (2) is heating to 50-90℃.

[0024] Preferably, the mass concentration of the hydrophobic associating monomer solution in step (2) is 15-25%, more preferably 20%; the mass concentration of the chain transfer agent solution is 5-15%, more preferably 10%; and the total mass concentration of the initiator solution is 5-15%, more preferably 10%.

[0025] Preferably, the time for adding the hydrophobic associating monomer solution in step (2) is 0.5-1 h, and the reaction time is 3-5 h.

[0026] Preferably, the purification reagent in step (3) is anhydrous ethanol, wherein the volume ratio of anhydrous ethanol to copolymer solution is 3:0.5-1.5, preferably 3:1.

[0027] The reaction formula for salt-suppressing agent A is shown below:

[0028]

[0029] The present invention also relates to a fracturing fluid system, wherein the raw materials of the fracturing fluid system include an emulsion thickener, the above-mentioned composite salt suppressant, a clay stabilizer, a fluorocarbon drainage aid, a polyether demulsifier, and a degelatinizer.

[0030] Preferably, the raw materials consist of the following components by weight: 0.8%-1.2% emulsion thickener, 0.05%-0.5% composite salt suppressant, 0.1%-0.3% clay stabilizer, 0.1%-0.3% fluorocarbon drainage aid, 0.1%-0.3% polyether demulsifier, and 0.05%-0.08% degumming agent, with the balance being water.

[0031] Preferably, the emulsion thickener is modified polyacrylamide or its derivative; the clay stabilizer is selected from one or more of potassium chloride, ammonium chloride, choline chloride, and quaternary ammonium salt organic clay stabilizers; and the degreasing agent is selected from one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0032] This invention also relates to a method for preparing a fracturing fluid system, comprising the following steps:

[0033] The emulsion thickener, compound salt suppressant, clay stabilizer, fluorocarbon drainage aid, polyether demulsifier, and degumming agent are added to water and stirred to obtain the final product.

[0034] Preferably, the water is stirred before being added at a speed of 400-60000 rad / min, and stirred for 1-5 min after being added.

[0035] This invention also relates to the application of composite salt suppressants or composite salt suppressant fracturing fluid systems or fracturing fluid systems prepared by the above-mentioned fracturing fluid system preparation methods in the oil and gas field development field.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] 1. The composite salt inhibitor of the present invention has no effect on the viscosity of the base fluid in the fracturing fluid system;

[0038] 2. The fracturing fluid system can completely break down the gel in high-salt (alkaline) reservoirs, with a kinematic viscosity of less than 5 mm. 2 / s;

[0039] 3. Add 0.05%-0.5% salt inhibitor to the fracturing fluid. Under the condition that the fracturing fluid rupture solution dissolves the mixed salt (sodium bicarbonate:sodium carbonate:sodium chloride = 4.5:4.5:1 (mass ratio)) to saturation at 90℃ and then cools to 10℃, the salt inhibition rate is greater than 90%.

[0040] 4. Based on the physicochemical properties of sodium carbonate or sodium bicarbonate, this invention achieves efficient salt suppression of soluble alkaline scale by synergistically enhancing the effects of multiple inhibition mechanisms, including electrostatic shielding, large steric hindrance, association, and chelation. It also constructs a salt-suppressing fracturing fluid system that meets both wellbore salt suppression and conventional fracturing fluid technology requirements, greatly improving operational efficiency. Attached Figure Description

[0041] Figure 1 This is a comparison chart of the salt-suppressing effects of salt-suppressing agent A and other salt-suppressing agents. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be further described in detail below. The described embodiments are only a part of the present invention and are used to explain the present invention, but are not intended to limit the present invention. Therefore, other embodiments obtained by other people skilled in the art without creative labor are all within the protection scope of the present invention.

[0043] Hexadecyltrimethylallylammonium chloride, GJM-1, was purchased from Sichuan Guangya Polymer Chemical Co., Ltd.

[0044] Preparation of salt-suppressing agent A:

[0045] Weigh out 972.00g of acrylic acid (AA) and 216.00g of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), dissolve them in 2000g of deionized water, and after the monomers are completely dissolved, add 2868.53g of [amount missing]. Neutralize the monomer aqueous solution to pH 7 with 20% NaOH solution, then add 1881.79g of deionized water and stir until homogeneous. Transfer the monomer aqueous solution to a 10L glass reactor equipped with a stirrer, reflux condenser, thermometer, and circulating water bath. Heat to 90℃ with continuous stirring, and begin dropwise addition of 60.00g of hexadecyltrimethylallylammonium chloride solution (20% mass concentration), 0.48g of chain transfer agent solution (10% thiol), and 1.20g of initiator solution (10% K2S2O8 / Na2SO3 (K2S2O8:Na2SO3 = 2:1 by total monomer mass) using a constant flow pump. The monomer solution, chain transfer agent solution, and initiator solution are added dropwise within 30 minutes. After reacting for 3 hours, a copolymer solution is obtained. After cooling, the copolymer solution is purified and dried with anhydrous ethanol (copolymer solution: ethanol volume ratio of 1:3) to obtain the salt-suppressing agent A1 with a purity of 97%.

[0046] Weigh 1155.00g of acrylic acid (AA) and 315.00g of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), dissolve them in 2000g of deionized water, and after the monomers have dissolved in the aqueous solution, add 3501.51g of [amount missing]. Neutralize the monomer aqueous solution to pH 7 with 20% NaOH solution, and add 875.50g of deionized water. Transfer the solution to a 10L glass reactor equipped with a stirrer, reflux condenser, thermometer, and circulating water bath. Heat to 80℃ with continuous stirring. Begin dropwise addition of 150.00g of hexadecyltrimethylallylammonium chloride solution (20% mass concentration), 0.45g of chain transfer agent solution (10% thiol), and 3.00g of initiator solution (10% K2S2O8 / Na2SO3, K2S2O8:Na2SO3 = 2:1 based on total monomer mass). Control the dropwise addition rate with a constant flow pump. The monomer solution, chain transfer agent solution, and initiator solution are added within 1 hour. After reacting for 3 hours, a copolymer solution is obtained. After cooling, the copolymer solution is purified and dried with anhydrous ethanol (copolymer solution: ethanol volume ratio 1:3) to obtain salt-suppressing agent A2 with a purity of 97.5%.

[0047] Weigh 1296.00g of acrylic acid (AA) and 450g of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), dissolve them in 2000g of deionized water, and after the monomers have dissolved in the aqueous solution, add 2011.73g of [amount missing]. 40% NaOH solution was used to neutralize to pH 7, and then 1966.33g of deionized water was added and stirred until homogeneous. The monomer aqueous solution was transferred to a 10L glass reactor equipped with a stirrer, reflux condenser, thermometer, and circulating water bath. The reactor was heated to 70℃ with continuous stirring. Then, 270g of hexadecyltrimethylallylammonium chloride solution (20% mass concentration), 0.54g of chain transfer agent solution (10% sodium formate), and 5.40g of initiator solution (10% K₂S₂O₈ / Na₂SO₃, K₂S₂O₈:Na₂SO₃ = 2:1 by total monomer mass) were added dropwise. The dropping rate was controlled by a constant flow pump, and the monomer solution, chain transfer agent solution, and initiator solution were added within 1 hour. After reacting for 4 hours, a copolymer solution was obtained. After cooling, the copolymer solution was purified and dried with anhydrous ethanol (copolymer solution: ethanol volume ratio 1:3) to obtain the salt-suppressing agent A3 with a purity of 97.8%.

[0048] Weigh out 1428.00g of acrylic acid (AA) and 567.00g of 2-acrylamide-2-methylpropanesulfonic acid (AMPS), dissolve them in 2000g of deionized water, and after the monomers have dissolved in the aqueous solution, add 2248.65g of [amount missing]. Neutralize the monomer aqueous solution to pH 7 with 40% NaOH solution, then add 1222.53g of deionized water and stir until homogeneous. Transfer the monomer aqueous solution to a 10L glass reactor equipped with a stirrer, reflux condenser, thermometer, and circulating water bath. Heat to 60℃ with continuous stirring, and begin dropwise addition of 525g of hexadecyltrimethylallylammonium chloride solution (20% mass concentration), 0.42g of chain transfer agent solution (10% sodium formate), and 8.40g of initiator solution (10% K2S2O8:Na2SO3 (K2S2O8:Na2SO3 = 2:1 by total monomer mass)). Control the dropping rate with a constant flow pump, and complete the addition of monomer solution, chain transfer agent solution, and initiator solution within 1 hour. After reacting for 5 hours, a copolymer solution is obtained. After cooling, purify and dry the copolymer solution with anhydrous ethanol (copolymer solution:ethanol volume ratio 1:3) to obtain salt-suppressing agent A4 with a purity of 98.3%.

[0049] Based on the synthesized salt-suppressing agents A1-A4, saturated brine (sodium carbonate:sodium bicarbonate:sodium chloride = 4.5:4.5:1 (mass ratio)) was prepared under a 90℃ water bath. Different concentrations of salt-suppressing agents A1-A4 and other salt-suppressing agents were added according to the formula in Table 1. After standing in a 10℃ water bath for 24 hours, the weight of the precipitated salt crystals was measured, and the salt suppression rate was calculated. Specific results are shown in Table 1.

[0050] The salt suppression rate is calculated as follows:

[0051] (1) Take 100g of tap water into a wide-mouth bottle, keep it at a constant temperature of 90℃ for 10min, then add compound salt (sodium bicarbonate: sodium carbonate: sodium chloride = 45:45:10 (mass ratio)) until saturated, and stir to dissolve for 30min.

[0052] (2) Take out the saturated solution of the composite salt in (1) and cool it at 10℃ for 24h. Transfer the solution to the vacuum filter funnel and filter for about 5min. Place the filter paper in a vacuum drying oven (0.09MPa, 45℃) to dry. Weigh and calculate the mass of the precipitated salt crystals as w0.

[0053] (3) Add a salt inhibitor to the solution described in (1), and repeat (1)-(2) for the remaining steps to obtain salt crystals with mass w1.

[0054] The formula for calculating the salt suppression rate is as follows:

[0055] Ysj=(w0-w1) / w0×100%

[0056] Ysj — Salt suppression rate, %;

[0057] w0 – Salt mass without added salt suppressant, in g;

[0058] w1 – The mass of salt formation after adding salt inhibitor, in g.

[0059] Note: The salt suppression rate of the fracturing fluid system is achieved by replacing tap water in step (1) of the above method with fracturing fluid breaker.

[0060] Table 1. Comparison of salt inhibition rates of salt-inhibiting agent A at different concentrations with other salt-inhibiting agents.

[0061]

[0062]

[0063] From Table 1 and Figure 1 Test results show that, for high-temperature, high-salinity, and alkaline reservoirs, the low molecular weight (molecular weight between 2000 and 50000) salt-suppressing agent A synthesized in this invention achieves a salt suppression rate between 75% and 85% when added at a dosage of 0.05% to 0.50%. However, for sodium bicarbonate / sodium carbonate type soluble scale, due to its strong alkalinity and significant temperature-dependent solubility variations, other commercially available composite salt-suppressing agents have a significantly reduced salt suppression effect, far lower than the salt suppression rates of the salt-suppressing agents A1-A4 of this invention.

[0064] Example 1: Comparative experiment on the salt suppression rate of composite salt suppressants composed of salt-suppressing agents A1-A4 and excipient B.

[0065] Based on the synthesized salt-suppressing agents A1-A4, they were combined with different salt-suppressing adjuvants B in Table 2. A saturated mixed salt solution (sodium carbonate:sodium bicarbonate:sodium chloride = 4.5:4.5:1 (mass ratio)) was prepared according to the method described in the specific embodiments. Different concentrations of the composite salt-suppressing agent were added according to the formula in Table 2. After standing in a 10℃ water bath for 24 hours, the weight of the precipitated salt crystals was measured, and the salt suppression rate was calculated. The specific results are shown in Table 2.

[0066] Table 2 Comparison of salt inhibition rates of different compound salt inhibitor formulations

[0067]

[0068] As shown in Table 2, the salt inhibition rate of salt inhibitors A1-A4 combined with sodium fatty acids of different carbon chains 12-16 is between 90-95%, which further enhances the salt inhibition rate of salt inhibitor A alone. When a small amount of disodium EDTA is added, a ternary composite salt inhibition system is formed, resulting in a salt inhibition rate of 95% or higher. Disodium EDTA has a synergistic salt inhibition effect on the composite salt inhibitor.

[0069] Example 2: Comparative Experiment of Low-Viscosity Fracturing Fluid Systems and Their Salt Inhibition Rates

[0070] Preparation of fracturing fluid system:

[0071] The fracturing fluid system was prepared according to the formula in Table 3 and the fracturing fluid preparation method in the invention. Before preparation, the water was stirred at a speed of 600 rad / min. After adding the raw materials, the mixture was stirred for 1 min to obtain the fracturing fluid system.

[0072] The viscosity of the fracturing fluid system after the addition of the salt suppressant and its effect on gel breaking were tested. The testing methods for the viscosity of the fracturing fluid system and the gel breaking fluid were in accordance with "GB / T 10247-2008 Viscosity Measurement Method". The gel breaking agent was added, and gel breaking was performed at 90℃ for 2 hours. After gel breaking, the viscosity of the gel breaking fluid was measured using an Ubbelohde viscometer. Following the method described in the specific implementation method, a saturated mixed salt solution (sodium carbonate:sodium bicarbonate:sodium chloride = 4.5:4.5:1 (mass ratio)) was prepared at 90℃ using the above-mentioned gel breaking fluid. Different concentrations of composite salt suppressant were added according to the formula in Table 3. After standing in a 10℃ water bath for 24 hours, the weight of the precipitated salt crystals was measured, and the salt suppression rate was calculated. The low-viscosity polymer fracturing fluid system was tested using an Ubbelohde viscometer.

[0073] The emulsion thickener is modified polyacrylamide GAF-TE (produced by Sichuan Guangya Polymer Chemical Co., Ltd.);

[0074] The clay stabilizer is a quaternary ammonium salt organic clay stabilizer, specifically ethylenediamine chloride (EDD);

[0075] The discharge aid is a fluorocarbon surfactant, GAF-6 (produced by Sichuan Guangya Polymer Chemical Co., Ltd.);

[0076] The demulsifier is a polyether-based demulsifier GAF-7 (produced by Sichuan Guangya Polymer Chemical Co., Ltd.);

[0077] Table 3 Compatibility of Composite Salt Suppressant with Low-Viscosity Emulsion Fracturing Fluid

[0078]

[0079]

[0080] Example 3: Comparative Experiment of High-Viscosity Fracturing Fluid Systems and Their Salt Suppression Rates

[0081] Preparation of fracturing fluid system:

[0082] The fracturing fluid system was prepared according to the formula in Table 4 and the fracturing fluid preparation method in the invention. Before preparation, the water was stirred at a speed of 400 rad / min. After adding the raw materials, the mixture was stirred for 5 minutes to obtain the fracturing fluid system.

[0083] The high-viscosity polymer fracturing fluid system was tested using a six-speed rotational viscometer for 170 seconds. -1Viscosity at shear rate.

[0084] The emulsion thickener is modified polyacrylamide GAF-TE (produced by Sichuan Guangya Polymer Chemical Co., Ltd.);

[0085] The clay stabilizer is ammonium chloride;

[0086] The discharge aid is a fluorocarbon surfactant, GAF-6 (produced by Sichuan Guangya Polymer Chemical Co., Ltd.);

[0087] The demulsifier is a polyether-based demulsifier GAF-7 (produced by Sichuan Guangya Polymer Chemical Co., Ltd.);

[0088] Table 4 Compatibility of Composite Salt Suppressant with High-Viscosity Emulsion Fracturing Fluid System

[0089]

[0090]

[0091] As shown in Tables 3 and 4, after adding salt inhibitor to the emulsion fracturing fluid system, the viscosity of the fracturing fluid system remained basically unchanged, the fracturing fluid system was able to break the gel normally, and the surface and interfacial tension of the broken gel fluid met the fracturing fluid index.

[0092] In summary, the present invention provides a composite salt suppressant, a fracturing fluid system, and a preparation method thereof. The salt suppressant has no effect on the performance of the fracturing fluid system, and the composite salt suppressant can achieve a salt suppression rate of over 90% in the fracturing fluid system, demonstrating excellent salt suppression effect. It can be industrialized and has good application prospects and profound research significance in the field of oil and gas field development.

[0093] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A composite salt rejection agent, characterized by, The raw material of the composite salt inhibitor comprises a salt inhibitor main agent A and an auxiliary agent B, wherein the raw material of the salt inhibitor main agent A comprises acrylic acid, 2-acrylamide-2-methylpropane sulfonic acid, a hydrophobic associating monomer, a chain transfer agent and an initiator; the auxiliary agent B is selected from one or more of sodium cocoate, sodium laurate, sodium palmitate and disodium EDTA; The viscosity average molecular weight of the salt inhibitor main agent A is 2000-50000.

2. The composite salt rejection agent of claim 1, wherein The mass ratio of the salt inhibitor main agent A to the auxiliary agent B is 1:0.05-0.

1.

3. The composite salt rejection agent of claim 1, wherein The hydrophobic associating monomer is hexadecyl trimethyl ammonium chloride.

4. The composite salt rejection agent of claim 1, wherein The chain transfer agent is selected from one or more of sodium formate, mercaptan and isopropyl alcohol.

5. The composite salt rejection agent of claim 1, wherein The initiator comprises K2S2O8 and Na2SO3, wherein the mass ratio of K2S2O8 to Na2SO3 is 2:1-2.

6. The composite salt rejection agent of claim 1, wherein The mass ratio of the acrylic acid, 2-acrylamide-2-methylpropane sulfonic acid, hydrophobic associating monomer, chain transfer agent solution and initiator is 80-120:15-50:1-10:0.003-0.005:0.01-0.

08.

7. The composite salt rejection agent of any one of claims 1-6, wherein, The preparation method of the salt inhibitor main agent A comprises the following steps: (1) dissolving acrylic acid and 2-acrylamide-2-methylpropane sulfonic acid in water, adjusting pH to obtain a monomer aqueous solution; (2) stirring and heating the monomer aqueous solution, adding a hydrophobic associating monomer solution, a chain transfer agent solution and an initiator solution, reacting to obtain a copolymer solution; (3) cooling, purifying and drying the copolymer solution to obtain the salt inhibitor main agent A.

8. The composite salt rejection agent of claim 7, wherein, In step (1), the pH adjusting agent is a NaOH solution with a mass concentration of 20%-40% and a pH of 6.5-7.5; in step (2), the heating is to 50-90°C.

9. The composite salt rejection agent of claim 7, wherein, In step (2), the mass concentration of the hydrophobic associating monomer solution is 15-25%, the mass concentration of the chain transfer agent solution is 5-15% and the total mass concentration of the initiator solution is 5-15%.

10. The composite salt rejection agent of claim 7, wherein In step (2), the hydrophobic associating monomer solution is added for 0.5-1h and the reaction is carried out for 3-5h.

11. The composite salt rejection agent of claim 7, wherein In step (3), the purifying agent is anhydrous ethanol, wherein the volume ratio of anhydrous ethanol to the copolymer solution is 3:0.5-1.

5.

12. A fracturing fluid system characterized by, The raw material of the fracturing fluid system comprises, by weight percentage, 0.8%-1.2% of an emulsion thickening agent, 0.05%-0.5% of the composite salt inhibitor according to any one of claims 1-11, 0.1%-0.3% of a clay stabilizer, 0.1%-0.3% of a fluorocarbon type cleanup aid, 0.1%-0.3% of a polyether type demulsifier and 0.05%-0.08% of a gel breaker, with the balance being water; the emulsion thickening agent is modified polyacrylamide GAF-TE.

13. The fracturing fluid system of claim 12, wherein, The clay stabilizer is selected from one or more of potassium chloride, ammonium chloride, choline chloride and quaternary ammonium salt type organic clay stabilizers; the gel breaker is selected from one or more of ammonium persulfate, sodium persulfate and potassium persulfate.

14. A method of preparing the fracturing fluid system of any one of claims 12-13, characterized in that, The method comprises adding the emulsion thickening agent, the composite salt inhibitor, the clay stabilizer, the fluorocarbon type cleanup aid, the polyether type demulsifier and the gel breaker into water and stirring to obtain the fracturing fluid system.

15. The preparation method according to claim 14, characterized in that, The water is stirred at a speed of 400-600 rad / min before the addition, and the stirring time is 1-5 min after the addition.

16. Use of the composite salt inhibitor according to any one of claims 1-11 or the fracturing fluid system according to any one of claims 12-13 or the fracturing fluid system prepared by the preparation method according to any one of claims 14-15 in the field of oil and gas field development.

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