Salt-tolerant fracturing drag reducer and preparation method thereof

Abstract

The invention discloses a salt-tolerant fracturing drag reducer and a preparation method thereof, and relates to the technical field of oil and gas field fracturing exploitation, and the salt-tolerant fracturing drag reducer is prepared from the following raw materials by weight: 30-40 parts of acrylamide, 10-20 parts of 3-[N, N-dimethyl formamide], and 10-20 parts of a surfactant. 10-20 parts of N-dimethyl-[2-(2-methylpropyl-2-enoyloxy) ethyl] ammonium] propane-1-sulfonic acid inner salt, 5-8 parts of reactive beta-cyclodextrin quaternary ammonium salt, 10-15 parts of N-acryloylmorpholine, 10-15 parts of 3-(1, 2, 4-trimethyl-1, 3, 4-trimethyl-1, 3, 4-trimethyl-1, 3, 4-trimethyl-1, 3, 4-trimethyl-1, 3, 4-trimethyl-1, 3, 4- The invention relates to a graphene oxide quantum dot modified hyperbranched polyamide resin, which is prepared from the following components in parts by weight: 3 to 6 parts of 1, 1-difluoro-2-propylene-1-yl)-2 (1H)-quinoxalinone, 8 to 12 parts of hyperbranched polyamide resin, 0.5 to 2 parts of initiator, 0.2 to 1 part of chain transfer agent, and 0.3 to 0.7 part of graphene oxide quantum dot. The drag reducer is excellent in salt resistance and drag reduction performance and good in stability under the environment conditions of high temperature and high salinity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field fracturing mining, in particular to a salt-tolerant fracturing drag-reducing agent and a preparation method thereof. BACKGROUND

[0002] In the field of oil and gas mining, fracturing technology is one of the key means to improve oil and gas production. As the core additive of fracturing fluid, fracturing drag-reducing agent can significantly reduce the flow resistance of fluid in the pipeline and improve the efficiency of fracturing construction. With the gradual expansion of oil and gas resource development to deep and complex geological conditions, the demand for mining in high salinity formations is increasing, which drives the rapid development of salt-tolerant fracturing drag-reducing agents. It is particularly important to develop salt-tolerant fracturing drag-reducing agents with excellent comprehensive performance and performance stability.

[0003] At present, common fracturing drag-reducing agents include polyacrylamide type, natural macromolecule type and surfactant type. The emulsion type polyacrylamide type has specificity, different emulsions are needed for different water qualities, and the price is high and the amount is large. The natural macromolecule type has high fracturing gel residue content and great damage to low permeability layers, which limits its use. The surfactant type needs to be compatible with many additives, has strong toxicity, and can cause water pollution after long-term use. In addition, these drag-reducing agents generally have poor salt tolerance and are not environmentally friendly. In high salinity produced water, it is difficult for them to play their role in drag reduction. A large amount of metal ions compress the drag-reducing agents together through electrostatic pressure, making it difficult to stretch and hydrate to form linear polymer fluid.

[0004] In order to solve the above problems, a salt-tolerant fracturing drag-reducing agent and a preparation method thereof are disclosed in Chinese patent No. CN115558054B. A new pH-sensitive surfactant is prepared by compounding maleic acid and dimethylamino-octadecyl acetamide, and is used to construct a pH-sensitive polymer emulsion drag-reducing agent. The drag-reducing agent shows good salt tolerance and stability, and can be quickly dissolved by adjusting the pH. It not only balances the storage stability and dissolution speed, but also provides a new idea for the design and production of drag-reducing agents, which helps to improve the efficiency of drag-reducing agents. However, the salt tolerance and drag reduction of the drag-reducing agent under high temperature and high salinity conditions still need to be further improved.

[0005] Therefore, it is necessary to develop a salt-tolerant fracturing drag-reducing agent with excellent salt tolerance and drag reduction under high temperature and high salinity conditions, and a preparation method thereof, which conforms to market demand, has wide market value and application prospect, and is of great significance to promote the development of the field of oil and gas field fracturing mining. SUMMARY

[0006] The present application aims to overcome the deficiencies of the prior art and provide a salt-tolerant fracturing drag reducer with excellent salt tolerance, salt resistance and stability under high temperature and high salinity environmental conditions and a preparation method thereof.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is: a salt-tolerant fracturing drag reducer, which is prepared from the following raw materials in parts by weight: acrylamide 30-40 parts, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt 10-20 parts, reactive beta-cyclodextrin quaternary ammonium salt 5-8 parts, N-acryloyl morpholine 10-15 parts, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxaline ketone 3-6 parts, hyperbranched polyamide resin 8-12 parts, initiator 0.5-2 parts, chain transfer agent 0.2-1 part, and graphene oxide quantum dots 0.3-0.7 part.

[0008] Preferably, the reactive beta-cyclodextrin quaternary ammonium salt is prepared according to the method of Example 6 of the Chinese invention patent with the authorization announcement No. CN106008755B.

[0009] Preferably, the hyperbranched polyamide resin is hyperbranched polyamide resin Hyper HPN202.

[0010] Preferably, the initiator is at least one of ammonium persulfate and potassium persulfate.

[0011] Preferably, the chain transfer agent is 2-mercaptoethanol.

[0012] Preferably, the graphene oxide quantum dots have 1-5 layers, a thickness of 1-2 nm, and a lateral dimension of 5-15 nm.

[0013] Another object of the present application is to provide a preparation method of the salt-tolerant fracturing drag reducer, which comprises the following steps: mixing the raw materials except the chain transfer agent uniformly in parts by weight to obtain a mixed raw material, adding the mixed raw material into deionized water, and ultrasonically dispersing for 25-35 min; then stirring for 30-40 min under an inert gas atmosphere at 38-42 DEG C, increasing the temperature to 65-75 DEG C at a rate of 1-2 DEG C / min, maintaining the temperature for 2-3 h of polymerization reaction, then adding the chain transfer agent and continuing to stir for 1-2 h; after the reaction is completed, cooling the reaction product to room temperature, adding sodium hydroxide solution to adjust the pH value to 7-8, and then sequentially performing spray drying, crushing and sieving to obtain the salt-tolerant fracturing drag reducer.

[0014] Preferably, the mass ratio of the mixed raw material to deionized water is 1:(3-5).

[0015] Preferably, the inert gas is any one of nitrogen, helium, neon and argon.

[0016] Due to the application of the above technical solution, the present invention has the following beneficial effects:

[0017] (1) The preparation method of the salt-resistant fracturing drag reducer disclosed in this invention does not require special equipment, requires little capital investment, has a simple process flow, is easy to control production conditions, is highly operable, consumes little energy, is suitable for large-scale production, and has high promotion and application value.

[0018] (2) The salt-resistant fracturing drag reducer disclosed in this invention is made from the following raw materials in parts by weight: 30-40 parts acrylamide, 10-20 parts 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt, 5-8 parts reactive β-cyclodextrin quaternary ammonium salt, 10-15 parts N-acryloylmorpholine, 3-6 parts 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxalinone, 8-12 parts hyperbranched polyamide resin, 0.5-2 parts initiator, 0.2-1 parts chain transfer agent, and 0.3-0.7 parts graphene oxide quantum dots. Through the synergistic effect of the raw materials, the drag reducer exhibits excellent salt resistance and drag reduction properties and good stability under high temperature and high salinity conditions.

[0019] (3) The salt-resistant fracturing drag reducer disclosed in this invention contains both sulfonic acid groups and quaternary ammonium salts in the inner salt molecule of 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid, forming an "anion-cation pair" structure. The strong hydrophilicity of the sulfonic acid groups can shield salt ions (such as Ca2+) through hydration. 2+ Mg 2+ The positive charge of quaternary ammonium salts can form electrostatic repulsion with anions in salt water, reducing polymer chain coiling and precipitation, thus maintaining stable viscosity of the solution even at high salt concentrations. The cyclic structure of β-cyclodextrin in reactive β-cyclodextrin quaternary ammonium salts can encapsulate some salt ions, reducing their shielding effect on polymer chains. The quaternary ammonium salt groups further enhance salt resistance through electrostatic interactions, while the rigid structure of cyclodextrin can improve the mechanical strength of polymer chains, reducing chain breakage caused by salt ions. 3-(1,1-difluoro-2-propen-1-yl) The introduction of fluorocarbon bonds by 2(1H)-quinoxalone creates a hydrophobic environment on the molecular surface due to its strong electronegativity, reducing the direct interaction between salt ions and polymer chains. At the same time, the chemical resistance of fluoride can resist corrosive ions in highly mineralized water and maintain the stability of the molecular structure. The highly branched three-dimensional network structure in hyperbranched polyamide resin can prevent salt ions from approaching the polymer backbone through steric hindrance, and the amide groups (-CONH-) on the branches can form multiple hydrogen bonds with water molecules, enhancing the thickness of the hydration layer and further weakening the destructive effect of salt ions.

[0020] (4) The disclosed salt-tolerant fracturing drag-reducing agent is a copolymer of acrylamide and N-acryloylmorpholine. The acrylamide provides the main chain skeleton, and the morpholine ring structure of N-acryloylmorpholine can increase the flexibility and inter-chain entanglement ability of the molecular chain, forming a high-viscosity network structure and improving the drag-reducing efficiency. The molecular weight distribution is adjusted by mercaptoethanol to avoid excessive entanglement caused by excessively long molecular chains or insufficient viscosity caused by excessively short molecular chains, so that the polymer can form effective resistance buffering and maintain good pumpability in flow. The nanoscale size of the graphene oxide quantum dots can be uniformly dispersed in the polymer network, and through π-π stacking and hydrogen bonding with the polymer chain, a "physical crosslinking point" is formed, significantly improving the viscosity and shear resistance of the solution. The surface of the graphene oxide quantum dots is rich in functional groups such as carboxyl and hydroxyl groups, which can capture Ca 2+ , Mg 2+ and other cations in the salt solution through electrostatic adsorption and coordination to form a stable ionic complex layer, reducing the charge shielding effect of salt ions on the polymer main chain. The branched structure of the hyperbranched polyamide resin interpenetrates with the linear polymer chain to form an "interpenetrating network", which can achieve high viscosity at low concentration, and the hydroxyl groups at the end of the branched chain can form hydrogen bonds with the sulfonic acid groups and amide groups to further strengthen the stability of the network structure.

[0021] (5) The disclosed salt-tolerant fracturing drag-reducing agent. The introduction of fluoride and graphene oxide quantum dots improves the thermal stability of the polymer, and the three-dimensional network structure of the hyperbranched polyamide can resist molecular chain rupture under high shear rate, making it suitable for high temperature and high pressure scenes such as deep well fracturing. DETAILED DESCRIPTION

[0022] The following description is provided to disclose the present application so that those skilled in the art can implement the present application. The preferred embodiments in the following description are only examples, and other obvious modifications can be made by those skilled in the art.

[0023] Example 1

[0024] A salt-tolerant fracturing drag-reducing agent is prepared by mixing the following raw materials in parts by weight: acrylamide 30 parts, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt 10 parts, reactive β-cyclodextrin quaternary ammonium salt 5 parts, N-acryloylmorpholine 10 parts, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxaline ketone 3 parts, hyperbranched polyamide resin 8 parts, initiator 0.5 parts, chain transfer agent 0.2 parts, and graphene oxide quantum dots 0.3 parts.

[0025] The reactive β-cyclodextrin quaternary ammonium salt is prepared according to the method of Example 6 of the Chinese invention patent with the authorized announcement No. CN106008755B; the hyperbranched polyamide resin is hyperbranched polyamide resin Hyper HPN202; the initiator is ammonium persulfate; the chain transfer agent is 2-mercaptoethanol; the number of layers of the graphene oxide quantum dot is 1-5, the thickness is 1-2 nm, and the lateral size is 5-15 nm.

[0026] A preparation method of the salt-resistant fracturing drag reducer comprises the following steps: uniformly mixing other raw materials except the chain transfer agent by weight parts to obtain a mixed raw material, adding the mixed raw material into deionized water, and ultrasonic dispersing for 25 min; then stirring for 30 min under an inert gas atmosphere at 38℃, and then increasing the temperature to 65℃ at a rate of 1℃ / min, keeping the temperature for 2 hours of polymerization reaction, then adding the chain transfer agent, and continuing to stir for 1 h; after the reaction is completed, the reaction product is cooled to room temperature, sodium hydroxide solution is added to adjust the pH value to 7, and then spray drying, crushing and sieving are sequentially performed to obtain the salt-resistant fracturing drag reducer; the mass ratio of the mixed raw material to the deionized water is 1:3; and the inert gas is nitrogen.

[0027] Example 2

[0028] A salt-resistant fracturing drag reducer is prepared from the following raw materials by weight parts: acrylamide 33 parts, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt 12 parts, reactive β-cyclodextrin quaternary ammonium salt 6 parts, N-acryloyl morpholine 11 parts, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxaline ketone 4 parts, hyperbranched polyamide resin 9 parts, initiator 1 part, chain transfer agent 0.3 parts, and graphene oxide quantum dot 0.4 parts.

[0029] The reactive β-cyclodextrin quaternary ammonium salt is prepared according to the method of Example 6 of the Chinese invention patent with the authorized announcement No. CN106008755B; the hyperbranched polyamide resin is hyperbranched polyamide resin Hyper HPN202; the initiator is potassium persulfate; the chain transfer agent is 2-mercaptoethanol; and the number of layers of the graphene oxide quantum dot is 1-5, the thickness is 1-2 nm, and the lateral size is 5-15 nm.

[0030] A preparation method of the salt-tolerant fracturing drag reducer comprises the following steps: uniformly mixing other raw materials except chain transfer agent according to weight parts to obtain mixed raw materials, adding the mixed raw materials into deionized water, and ultrasonic dispersion for 27 min; then stirring for 33 min under inert gas atmosphere at 39℃, and then increasing the temperature to 67℃ at a rate of 1.2℃ / min, keeping the temperature for 2.3 hours of polymerization reaction, then adding chain transfer agent, and continuing to stir for 1.2h; after the reaction is completed, the reaction product is cooled to room temperature, sodium hydroxide solution is added to adjust the pH value to 7.3, and then spray drying, crushing and sieving are sequentially performed to obtain the salt-tolerant fracturing drag reducer; the mass ratio of the mixed raw materials to the deionized water is 1:3.5; and the inert gas is helium.

[0031] Example 3

[0032] A salt-tolerant fracturing drag reducer comprises the following raw materials according to weight parts: acrylamide 35 parts, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium] propane-1-sulfonic acid inner salt 15 parts, reactive β-cyclodextrin quaternary ammonium salt 6.5 parts, N-acryloyl morpholine 13 parts, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxaline ketone 4.5 parts, hyperbranched polyamide resin 10 parts, initiator 1.4 parts, chain transfer agent 0.6 parts, and graphene oxide quantum dot 0.5 parts.

[0033] The reactive β-cyclodextrin quaternary ammonium salt is prepared according to the method of Example 6 of the Chinese patent for invention with the authorized announcement No. CN106008755B; the hyperbranched polyamide resin is hyperbranched polyamide resin Hyper HPN202; the initiator is ammonium persulfate; the chain transfer agent is 2-mercaptoethanol; and the graphene oxide quantum dot has 1-5 layers, a thickness of 1-2nm, and a lateral size of 5-15nm.

[0034] A preparation method of the salt-tolerant fracturing drag reducer comprises the following steps: uniformly mixing other raw materials except chain transfer agent according to weight parts to obtain mixed raw materials, adding the mixed raw materials into deionized water, and ultrasonic dispersion for 30 min; then stirring for 35 min under inert gas atmosphere at 40℃, and then increasing the temperature to 70℃ at a rate of 1.5℃ / min, keeping the temperature for 2.5 hours of polymerization reaction, then adding chain transfer agent, and continuing to stir for 1.5h; after the reaction is completed, the reaction product is cooled to room temperature, sodium hydroxide solution is added to adjust the pH value to 7.5, and then spray drying, crushing and sieving are sequentially performed to obtain the salt-tolerant fracturing drag reducer; the mass ratio of the mixed raw materials to the deionized water is 1:4; and the inert gas is neon.

[0035] Example 4

[0036] A kind of salt-tolerant fracturing drag reducer, including the following by weight parts of each raw material made: acrylamide 38 parts, 3-[N,N-dimethyl-[2-(2-methylprop-2-enyl oxy) ethyl] ammonium] propane-1-sulfonic acid inner salt 18 parts, reactive β-cyclodextrin quaternary ammonium salt 7.5 parts, N-acryloyl morpholine 14 parts, 3-(1,1-difluoro-2-propylene-1-yl)-2(1H)-quinoxaline ketone 5.5 parts, hyperbranched polyamide resin 11 parts, initiator 1.8 parts, chain transfer agent 0.9 parts, graphene oxide quantum dot 0.6 parts.

[0037] The reactive β-cyclodextrin quaternary ammonium salt is made according to the method of Example 6 of the Chinese invention patent with the authorized announcement number CN106008755B; the hyperbranched polyamide resin is hyperbranched polyamide resin Hyper HPN202; the initiator is ammonium persulfate, potassium persulfate mixed at a mass ratio of 1:3; the chain transfer agent is 2-mercaptoethanol; the number of layers of the graphene oxide quantum dot is 1-5, the thickness is 1-2 nm, and the lateral dimension is 5-15 nm.

[0038] A preparation method of the salt-tolerant fracturing drag reducer includes the following steps: mixing other raw materials except the chain transfer agent uniformly by weight parts to obtain a mixed raw material, adding to deionized water, and ultrasonic dispersion for 33 min; then stirring for 38 min under an inert gas atmosphere at 41℃, and then heating to 73℃ at a rate of 1.8℃ / min, keeping the temperature for 2-3 hours of polymerization reaction, then adding the chain transfer agent, and continuing to stir for 1-2 h; after the reaction is completed, the reaction product is cooled to room temperature, sodium hydroxide solution is added to adjust the pH value to 7.8, and then spray drying, crushing and sieving are sequentially performed to obtain the salt-tolerant fracturing drag reducer; the mass ratio of the mixed raw material to deionized water is 1:4.5; and the inert gas is argon.

[0039] Example 5

[0040] A kind of salt-tolerant fracturing drag reducer, including the following by weight parts of each raw material made: acrylamide 40 parts, 3-[N,N-dimethyl-[2-(2-methylprop-2-enyl oxy) ethyl] ammonium] propane-1-sulfonic acid inner salt 20 parts, reactive β-cyclodextrin quaternary ammonium salt 8 parts, N-acryloyl morpholine 15 parts, 3-(1,1-difluoro-2-propylene-1-yl)-2(1H)-quinoxaline ketone 6 parts, hyperbranched polyamide resin 12 parts, initiator 2 parts, chain transfer agent 1 part, graphene oxide quantum dot 0.7 parts.

[0041] The reactive beta-cyclodextrin quaternary ammonium salt is prepared according to the method of Example 6 of the Chinese invention patent with the authorization announcement No. CN106008755B; the hyperbranched polyamide resin is hyperbranched polyamide resin Hyper HPN202; the initiator is ammonium persulfate; the chain transfer agent is 2-mercaptoethanol; the layer number of the graphene oxide quantum dot is 1-5, the thickness is 1-2 nm, and the lateral size is 5-15 nm.

[0042] A preparation method of the salt-resistant fracturing drag reducer comprises the following steps: uniformly mixing other raw materials except the chain transfer agent by weight parts to obtain a mixed raw material, adding the mixed raw material into deionized water, and ultrasonic dispersing for 35 min; then stirring for 40 min under an inert gas atmosphere at 42℃, and then increasing the temperature to 75℃ at a rate of 2℃ / min, keeping the temperature for 3 hours of polymerization reaction, then adding the chain transfer agent, and continuing to stir for 2h; after the reaction is completed, the reaction product is cooled to room temperature, sodium hydroxide solution is added to adjust the pH value to 8, and then spray drying, crushing and sieving are sequentially performed to obtain the salt-resistant fracturing drag reducer; the mass ratio of the mixed raw material to the deionized water is 1:5; and the inert gas is nitrogen.

[0043] Comparative Example 1

[0044] A salt-resistant fracturing drag reducer and a preparation method thereof are basically the same as those of Example 1, except that the reactive beta-cyclodextrin quaternary ammonium salt and the graphene oxide quantum dot are not added.

[0045] Comparative Example 2

[0046] A salt-resistant fracturing drag reducer and a preparation method thereof are basically the same as those of Example 1, except that the 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxaline ketone and the hyperbranched polyamide resin are not added.

[0047] In order to further illustrate the beneficial technical effects of the salt-resistant fracturing drag reducer involved in the embodiments of the present application, the salt-resistant fracturing drag reducers involved in Examples 1-5 and Comparative Examples 1-2 are subjected to relevant performance tests; the test method is as follows: each drag reducer is respectively mixed with 150,000 mg / L standard salt water (in which the total of calcium and magnesium ions is greater than 1500 mg / L) to prepare a 0.06% high salinity salt water solution, and the performance is evaluated according to SY / T 7627-2021 “Technical Requirements for Water-based Fracturing Fluid”. Among them, the temperature-resistant and shear-resistant ability is the viscosity after shearing for 120 min at a temperature of 150℃ and a shear rate of 170s -1

[0048] Table 1 Salt-resistant fracturing drag reducer

[0049] Item Resistance reduction rate (%) Compatibility with formation fluid Temperature and shear resistance ability (mPa-s) Example 1 85.3 No precipitation No flocculation 95 Example 2 86.1 No precipitation No flocculation 98 Example 3 86.6 No precipitation No flocculation 100 Example 4 87.6 No precipitation No flocculation 102 Example 5 88.0 No precipitation No flocculation 106 Comparative Example 1 74.8 Precipitation Flocculation 82 Comparative Example 2 73.1 Precipitation Flocculation 86

[0050] ​As can be seen from Table 1, the salt-tolerant fracturing drag-reducing agents involved in the embodiments of the application have higher salt-tolerant drag-reducing rates, more excellent compatibility with formation fluids and temperature-resistant and shear-resistant capabilities compared with the products of the comparative examples; the combination use of reactive beta-cyclodextrin quaternary ammonium salt, graphene quantum dots, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxalinone and hyperbranched polyamide resin is beneficial to improving the above-mentioned performances.

[0051] The above examples are only for illustrating the technical concept and characteristics of the application, and the purpose is to enable those skilled in the art to understand the content of the application and implement it, and cannot limit the protection scope of the application. Any equivalent changes or modifications made according to the spirit and essence of the application should be covered within the protection scope of the application.

Claims

1. A salt-tolerant fracturing drag-reducing agent, characterized in that, The raw materials include the following components by weight parts: acrylamide 30-40 parts, 3-[N,N-dimethyl-[2-(2-methylprop-2-enyl oxy) ethyl] ammonium] propane-1-sulfonic acid inner salt 10-20 parts, reactive beta-cyclodextrin quaternary ammonium salt 5-8 parts, N-acryloyl morpholine 10-15 parts, 3-(1,1-difluoro-2-propen-1-yl)-2(1H)-quinoxaline ketone 3-6 parts, hyperbranched polyamide resin 8-12 parts, initiator 0.5-2 parts, chain transfer agent 0.2-1 part, graphene oxide quantum dot 0.3-0.7 parts.

2. The salt-tolerant friction reducer of claim 1, wherein, The hyperbranched polyamide resin is hyperbranched polyamide resin Hyper HPN202.

3. The salt-tolerant friction reducer of claim 1, wherein, The initiator is at least one of ammonium persulfate and potassium persulfate.

4. The salt-tolerant friction reducer of claim 1, wherein, The chain transfer agent is 2-mercaptoethanol.

5. The salt-tolerant friction reducer of claim 1, wherein, The graphene oxide quantum dot has 1-5 layers, a thickness of 1-2 nm, and a lateral dimension of 5-15 nm.

6. A process for the preparation of the salt-tolerant friction reducer according to any one of claims 1 to 5, characterized in that, The method includes the following steps: mixing the other raw materials except the chain transfer agent to obtain a mixed raw material, adding the mixed raw material to deionized water, and ultrasonically dispersing for 25-35 min; then stirring at 38-42°C under an inert gas atmosphere for 30-40 min, heating at a rate of 1-2°C / min to 65-75°C, maintaining the temperature for 2-3 hours of polymerization reaction, then adding the chain transfer agent, and continuing to stir for 1-2 hours; after the reaction is completed, the reaction product is cooled to room temperature, sodium hydroxide solution is added to adjust the pH value to 7-8, and then spray drying, crushing, and sieving are sequentially performed to obtain the salt-resistant fracturing drag reducer.

7. The method of claim 6, wherein the method is characterized by, The mass ratio of the mixed raw material to the deionized water is 1:(3-5).

8. The method of claim 6, wherein the method is characterized by, The inert gas is any one of nitrogen, helium, neon, and argon.