阅读说明：本技术 一种页岩气压裂液用多糖改性抗盐降阻剂及其制备方法 (Polysaccharide modified salt-resistant resistance-reducing agent for shale gas fracturing fluid and preparation method thereof ) 是由 王洪庆 龙惊惊 王远 周悦 孙慧 李欣 王加友 于 2019-12-03 设计创作，主要内容包括：本发明涉及降阻剂的制备,具体说是一种页岩气压裂液用多糖改性抗盐降阻剂及其制备方法。抗盐降阻剂为粘均分子量为700万-1800万的共聚物,共聚物结构中单体以重量份数计,丙烯酰胺：水解丙烯酰胺或丙烯酸：改性多糖：单元B＝45～89：5～20：1～5：5～30。本发明通过对几种生物多糖进行结构修饰改性,引入双键基团,成为新型可聚合的抗盐单体,并按一定配比与丙烯酰胺等单体共聚,形成分子量高,更稳定的聚合物,兼具两者的优良性能,形成抗盐、耐高温的新型聚丙烯酰胺共聚物,特别适合高矿化度水压裂工艺。(The invention relates to preparation of a resistance reducing agent, in particular to a polysaccharide modified salt-resistant resistance reducing agent for a shale gas fracturing fluid and a preparation method thereof. The salt-resistant and resistance-reducing agent is a copolymer with the viscosity average molecular weight of 700-1800 ten thousand, and in the copolymer structure, the weight parts of monomers are as follows: hydrolysis of acrylamide or acrylic acid: modified polysaccharide: and the unit B is 45-89: 5-20: 1-5: 5 to 30. According to the invention, several biological polysaccharides are subjected to structural modification, double-bond groups are introduced to form a novel polymerizable salt-resistant monomer, and the novel polymerizable salt-resistant monomer is copolymerized with monomers such as acrylamide and the like according to a certain proportion to form a polymer with high molecular weight and stability, and the polymer has the excellent performances of both, so that a novel salt-resistant and high-temperature-resistant polyacrylamide copolymer is formed, and the novel polyacrylamide copolymer is particularly suitable for a high-salinity water fracturing process.)

1. The polysaccharide modified salt-resistant resistance-reducing agent for the shale gas fracturing fluid is characterized by comprising the following components in parts by weight: the salt-resistant and resistance-reducing agent is a copolymer with the viscosity average molecular weight of 700-1800 ten thousand, and in the copolymer structure, the weight parts of monomers are as follows: hydrolysis of acrylamide or acrylic acid: modified polysaccharide: and the unit B is 45-89: 5-20: 1-5: 5 to 30.

2. The polysaccharide modified anti-salt friction reducer for shale gas fracturing fluid as claimed in claim 1, wherein: the unit B is selected from one or more of 2-acrylamide-2-methylpropanesulfonic Acid (AMPS), sodium vinylsulfonate, sodium propenyl sulfonate, sodium styrene sulfonate and N-vinyl pyrrolidone.

3. The polysaccharide modified anti-salt friction reducer for shale gas fracturing fluid as claimed in claim 1 or 2, wherein:

mixing acrylamide, hydrolyzed acrylamide or acrylic acid, a monomer B and modified polysaccharide according to the proportion, dissolving the mixture in water to serve as a water phase, adding a compound emulsifier and a redox initiator to serve as an oil phase, carrying out polymerization reaction for 4-10 hours by adopting an inverse emulsion polymerization method, and drying and crushing to prepare the powder resistance reducing agent after the quadripolymer gel is obtained through solution polymerization; the initial reaction temperature of the polymerization is 0-40 ℃, the later reaction temperature is 40-80 ℃, the pH value of the system is 4-10, the dosage of the initiator is 0.8-3 percent of the total weight of the monomers, and the final concentration of the emulsifier in the polymerization reaction is 40-80 g/L.

4. The polysaccharide modified anti-salt friction reducer for shale gas fracturing fluid as claimed in claim 3, wherein: the initiator is as follows: ammonium persulfate and sodium bisulfite; VA-044; emulsifier: span-80, Tween-80, isomeric alcohol polyoxyethylene ether 1309, OP-10, fatty acid diethanolamide and polymeric ester high molecular emulsifier.

5. The polysaccharide modified anti-salt friction reducer for shale gas fracturing fluid as claimed in claim 1, wherein: the modified polysaccharide is obtained by carrying out esterification reaction on hydroxyl on polysaccharide and Maleic Acid (MA), Acrylic Acid (AA), methacrylic acid (MAA) or itaconic acid (ITA) in the presence of a catalyst; wherein the polysaccharide is one or more of xanthan gum, scleroglucan, welan gum, butyl glucoside, dodecyl glucoside, alginic acid, propylene glycol alginate and alpha-cyclodextrin.

6. The polysaccharide modified anti-salt friction reducer for shale gas fracturing fluid as claimed in claim 3, wherein: the hydrolysis degree of the hydrolyzed polyacrylamide is 10-30%, the hydrolysis temperature is 50-90 ℃, and the hydrolysis time is 0.5-4 hours; when the Acrylic Acid (AA) is adopted, the monomer is directly polymerized, and the copolymerization mass ratio is 5-20%.

7. The preparation method of the polysaccharide modified anti-salt resistance-reducing agent for the shale gas fracturing fluid as claimed in claim 1, is characterized in that: mixing acrylamide, hydrolyzed acrylamide or acrylic acid, a monomer B and modified polysaccharide according to the proportion, dissolving the mixture in water to serve as a water phase, adding a compound emulsifier and a redox initiator to serve as an oil phase, carrying out polymerization reaction for 4-10 hours by adopting an inverse emulsion polymerization method, and drying and crushing to prepare the powder resistance reducing agent after the quadripolymer gel is obtained through solution polymerization; the initial reaction temperature of the polymerization is 0-40 ℃, the later reaction temperature is 40-80 ℃, the pH value of the system is 4-10, the dosage of the initiator is 0.8-3 percent of the total weight of the monomers, and the final concentration of the emulsifier in the polymerization reaction is 40-80 g/L.

8. The preparation method of the polysaccharide modified anti-salt resistance-reducing agent for the shale gas fracturing fluid as claimed in claim 7, wherein the preparation method comprises the following steps: the modified polysaccharide is a modified polysaccharide monomer obtained by carrying out esterification reaction on hydroxyl groups on polysaccharide and Maleic Acid (MA), Acrylic Acid (AA), methacrylic acid (MAA), acryloyl chloride or itaconic acid (ITA) in the presence of a catalyst; wherein, the molar ratio of the polysaccharide to the unsaturated acid is 1: 2-6, the catalyst is p-toluenesulfonic acid, concentrated sulfuric acid, phosphorous acid, tetrabutyl titanate or solid super acid, and the dosage is 0.1-0.8% of the total reactants.

9. The polysaccharide modified anti-salt friction reducer for shale gas fracturing fluid as claimed in claim 7, wherein: the hydrolysis degree of the hydrolyzed polyacrylamide is 10-30%, the hydrolysis temperature is 50-90 ℃, and the hydrolysis time is 0.5-4 hours; when the Acrylic Acid (AA) is adopted, the monomer is directly polymerized, and the copolymerization mass ratio is 5-20%.

10. The application of the polysaccharide modified anti-salt resistance-reducing agent for the shale gas fracturing fluid as claimed in claim 1, is characterized in that: the resistance reducing agent is applied to a shale gas-water-based fracturing mining process.

Technical Field

The invention relates to preparation of a resistance reducing agent, in particular to a polysaccharide modified salt-resistant resistance reducing agent for a shale gas fracturing fluid and a preparation method thereof.

Background

Currently, with the steady production of global conventional oil and gas, along with the increase of demand, the unconventional oil and gas exploration and development represented by compact oil and shale oil and gas are different military projections, and the world petroleum industry starts to step into a turning point of the repeated conventional and unconventional oil and gas development after going through the conventional oil and gas stage for a half century. Fracturing is an important means for improving the yield of shale gas wells, and the friction reducer plays an important role as an important additive of fracturing fluid.

At present, with the exhaustion of shallow layer oil and gas resources, the exploration and development of oil and gas reservoirs gradually turn to deep strata, and Ca in fracturing flowback fluid of unconventional oil and gas reservoirs²⁺、Mg²⁺、Cl^-And the total mineralization is very high, the performance of a resistance reducing water system is greatly influenced, and higher requirements are provided for the performance of the resistance reducing agent: (1) the resistance reduction rate is higher; (2) higher salt tolerance: at present, 10 ten thousand of saline (1000g of deionized water, 28g of calcium chloride, 72g of sodium chloride) and 511s of drag reducer are generally required^-1Under the shearing condition, the viscosity index meets the requirement; (3) high temperature resistance; (4) low cost, no toxicity and harm, and the emission meets the requirement of environmental protection.

At present, the resistance reducing agent used for fracturing at home and abroad mainly takes partially Hydrolyzed Polyacrylamide (HPAM) as a main component and is an emulsion type resistance reducing agent prepared by solid and inverse emulsion polymerization. However, the application of the conventional linear polymer of partially hydrolyzed polyacrylamide is faced with many problems by high-temperature and high-salinity oil reservoirs: with the increase of inorganic salt in high-salinity water, the charge shielding effect among polymer molecular chains is enhanced, the molecular chains are easy to curl, and the apparent viscosity of the solution is greatly reduced; the polymer can be hydrolyzed under the conditions of high temperature and high salt, and the compound action of dissolved oxygen in the solution can also cause the main chain of the polymer to be broken and degraded, so that the viscosity of the solution is greatly reduced, and the performance is weakened or even completely loses efficacy. Aiming at the defects, some sulfonic monomers for improving the salt resistance are adopted: AMPS, sodium vinylsulfonate, sodium propenyl sulfonate, vinylbenzenesulfonic acid; cyclic structure monomer: modifying N-vinyl pyrrolidone, N-allyl imidazole, acryloyl morpholine and the like; modifying by adopting a hydrophobic monomer; a proper amount of cross-linking agent is introduced to synthesize the polymer with low cross-linking degree, but the modified resistance reducing agent still cannot meet the configuration requirement of the high-salinity flowback fluid, so that the novel salt-resistant resistance reducing agent is developed, the repeated utilization of the unconventional fracturing flowback fluid is realized, the recovery ratio is further improved, and the method has urgent practical requirements and good application prospects.

In the prior art, a sulfonic acid group salt-resistant monomer is adopted, because the reactivity ratio of the salt-resistant monomer is low, the molecular weight of the polymer is far lower than that of a polyacrylamide homopolymer after the monomer is copolymerized with an acrylamide monomer, and the polymer serving as a resistance reducing agent can meet the resistance reducing requirement only with higher molecular weight, the reduction of the molecular weight is offset to a certain extent by the improvement of a salt-resistant type, and actually the resistance reducing rate and the salt resistance are not obviously improved.

In recent years, polysaccharide polymers represented by xanthan gum have attracted much attention, and due to their unique helical spatial structure and molecular structure, they are high temperature resistant, high salt resistant and good in shear resistance. The xanthan gum solution has good compatibility and stability in the presence of various salts. It can be prepared by 10 percent of KCl and 10 percent of CaCl in percentage by mass₂、5％Na₂CO₃The viscosity of the solution is almost unchanged after long-term storage (25 ℃, 90 d). The polysaccharide polymer generally has the characteristics of stable physical and chemical properties, acid and alkali resistance, temperature resistance, calcium and magnesium resistance, high mechanical stability and the like. Because the main and side chains of the large molecules of the xanthan gum polysaccharide contain a large number of active groups such as hydroxyl, carboxyl, ketal and the like, the research is mainly focused on generating graft copolymers with some special polymerization monomers under the action of an initiator, high-energy radiation and the like, so that the performance of the xanthan gum is reflected.

However, documents 1 to 5 describe that the polysaccharide component is compounded with polyacrylamide, and only simple mixing or intermolecular association such as hydrogen bond is performed to form a so-called graft copolymer, which exerts a certain synergistic effect, but it is difficult to effectively polymerize the polysaccharide and the acrylamide monomer with special structures, and to exert the functions of salt resistance, temperature resistance and the like to the maximum extent, and most of them are merely physically mixed. Meanwhile, the polysaccharide component has large using amount, high cost and difficult dissolution and processing, and is difficult to be applied to shale gas fracturing.

Document 1, a salt-tolerant shear-resistant deep sea bacteria exopolysaccharide oil displacement system CN101845296B, discloses an oil displacement system prepared from a water solution of bacteria exopolysaccharide, which has stronger salt-tolerant and shear-resistant capabilities than the traditional partially hydrolyzed polyacrylamide system. The mineralization degree of less than 10%, preferably 5% is required, and the requirement of over 10 ten thousand salt water in industry can not be met.

Document 2 an environment-friendly oil field oil recovery compound based on biopolysaccharide and its application CN 108342189 are compounded by biopolysaccharide and polyacrylamide, and have certain effects of high temperature resistance and salt tolerance: the solution with the salinity of 150000ppm is prepared into 3000ppm by adopting the water, compared with the initial viscosity of clear water, the viscosity of polyacrylamide is reduced by 53.42 percent, while the viscosity of the compound is reduced by only 6.79 percent, and the salt-resistant effect is better than that of single polysaccharide and HPAM. But the polysaccharide content is high, the price is high, the solubility of the mixture of the polysaccharide and the polysaccharide is poor, the use process is limited, and the instant emulsion drag reducer is difficult to prepare.

Document 3 HPAM studies rheological properties and synergistic effects with xanthan gum solutions. Southwest oil university, master's paper, 2014. The HPAM has a large number of carboxyl and amide groups on its side chains, and associates with the polysaccharide through intermolecular interactions such as hydrogen bonding, thereby improving the rheological properties of the polymer.

Document 4 is based on the preparation and performance studies of polysaccharide modified hyperbranched polymers. The southwest university of petroleum, the academic thesis of bachelor, is well known. The effect is as follows: at a concentration of 2000mg/L, a degree of mineralization of 3X 10⁴～20×10⁴mg/L range, the viscosity of the polymer solution can still be maintained at about 60 mpa.s after aging for 90 days at 80 ℃, and the viscosity of the polymer solution can be maintained at 25-50 mpa.s after aging for 90 days at 90 ℃. Shear stress 0.The frequency scanning experiment result under 5Pa shows that the polymer solution is represented as viscoelastic fluid in the frequency range of 0.01-10 Hz, and the polymer has better thickening property and excellent anti-shearing capability under the conditions of high temperature and high salt.

Document 5^[1]Novel microbial polysaccharide property [ J ] suitable for polymer flooding of harsh reservoir]The oil drilling and production process, 2019,41(03):393-398, explores the feasibility of the novel microorganism polysaccharide diutan, welan gum and xanthan gum as the novel oil displacement polymer. Novel microbial polysaccharides are reported to have good water solubility, with solution viscosity increasing with increasing concentration; the solution shows good shear resistance and placement stability; compared with the traditional HPAM solution, the microbial polysaccharide solution has obviously improved temperature resistance, alkali resistance, salt resistance and the like; the microbial polysaccharide oil displacement effect is obviously superior to HPAM, so the microbial polysaccharide oil displacement agent can be used as a novel oil displacement agent suitable for harsh oil reservoirs.

Documents 3, 4, and 5 are only simple mixtures of polymers and polysaccharides, but feasibility studies are only performed from the aspects of association mechanism, rheological property, and the like, and salt resistance of polymer segments is not fundamentally improved, which proves that neither the polysaccharides nor the modified polysaccharides alone can satisfy 1 × 10 salt resistance⁶The requirement of mineralization degree of more than mg/L, the technological requirements of shearing resistance, temperature resistance and the like, and difficult industrial application.

Disclosure of Invention

The invention aims to provide a polysaccharide modified salt-resistant resistance-reducing agent for shale gas fracturing fluid and a preparation method thereof.

In order to achieve the purpose, the invention adopts the technical scheme that:

the polysaccharide modified salt-resistant resistance-reducing agent for the shale gas fracturing fluid is a copolymer with the viscosity-average molecular weight of 700-1800 ten thousand, and in the copolymer structure, the weight parts of monomers are as follows: hydrolysis of acrylamide or acrylic acid: modified polysaccharide: and the unit B is 45-89: 5-20: 1-5: 5 to 30.

The unit B is selected from one or more of AMPS, sodium ethylene sulfonate, sodium propenyl sulfonate, sodium styrene sulfonate and N-vinyl pyrrolidone.

Further, mixing acrylamide, hydrolyzed acrylamide or acrylic acid, a monomer B and modified polysaccharide according to the proportion, dissolving the mixture in water to serve as a water phase, adding a composite emulsifier and a redox initiator to serve as an oil phase, carrying out polymerization reaction for 4-10 hours by adopting an inverse emulsion polymerization method, obtaining a quadripolymer through solution polymerization to form polymer gel, and drying and crushing the polymer gel to prepare the powder resistance reducing agent; the initial reaction temperature of the polymerization is 0-40 ℃, the later reaction temperature is 40-80 ℃, the pH value of the system is 4-10, the dosage of the initiator is 0.8-3 percent of the total weight of the monomers, and the final concentration of the emulsifier in the polymerization reaction is 40-80 g/L.

The initiator is as follows: ammonium persulfate and sodium bisulfite; VA-044; emulsifier: span-80, Tween-80, isomeric alcohol polyoxyethylene ether 1309, OP-10, fatty acid diethanolamide and polymeric ester high molecular emulsifier.

The modified polysaccharide is obtained by carrying out esterification reaction on hydroxyl on polysaccharide and Maleic Acid (MA), Acrylic Acid (AA), methacrylic acid (MAA) or itaconic acid (ITA) in the presence of a catalyst; wherein the polysaccharide is one or more of xanthan gum, scleroglucan, welan gum, butyl glucoside, dodecyl glucoside, alginic acid, propylene glycol alginate and alpha-cyclodextrin.

The hydrolysis degree of the hydrolyzed polyacrylamide is 10-30%, the hydrolysis temperature is 50-90 ℃, and the hydrolysis time is 0.5-4 hours; when the Acrylic Acid (AA) is adopted, the monomer is directly polymerized, and the copolymerization mass ratio is 5-20%.

A preparation method of polysaccharide modified salt-resistant resistance-reducing agent for shale gas fracturing fluid comprises the steps of mixing acrylamide, hydrolyzed acrylamide or acrylic acid, monomer B and modified polysaccharide according to the proportion, dissolving the mixture in water to serve as a water phase, using solvent oil as an oil phase, adding a composite emulsifier and a redox initiator, carrying out polymerization reaction for 4-10 hours by adopting an inverse emulsion polymerization method, carrying out solution polymerization to obtain a quadripolymer, forming polymer gel, drying and crushing to prepare the powder resistance-reducing agent; the initial reaction temperature of the polymerization is 0-40 ℃, the later reaction temperature is 40-80 ℃, the pH value of the system is 4-10, the dosage of the initiator is 0.8-3 percent of the total weight of the monomers, and the final concentration of the emulsifier in the polymerization reaction is 40-80 g/L.

The modified polysaccharide is a modified polysaccharide monomer obtained by carrying out esterification reaction on hydroxyl groups on polysaccharide and Maleic Acid (MA), Acrylic Acid (AA), methacrylic acid (MAA), acryloyl chloride or itaconic acid (ITA) in the presence of a catalyst; wherein, the molar ratio of the polysaccharide to the unsaturated acid is 1: 2-6, the catalyst is p-toluenesulfonic acid, concentrated sulfuric acid, phosphorous acid, tetrabutyl titanate or solid super acid, and the dosage is 0.1-0.8% of the total reactants. .

The hydrolysis degree of the hydrolyzed polyacrylamide is 10-30%, the hydrolysis temperature is 50-90 ℃, and the hydrolysis time is 0.5-4 hours; when the Acrylic Acid (AA) is adopted, the monomer is directly polymerized, and the copolymerization mass ratio is 5-20%.

The application of the polysaccharide modified salt-resistant resistance-reducing agent for the shale gas fracturing fluid is to apply the resistance-reducing agent to a shale gas water-based fracturing mining process.

The invention has the advantages that:

aiming at the problems that a single polysaccharide is used as a resistance reducing agent, the price is high, the dissolution time is long in the using process, the agglomeration is easy, the application is difficult and the like, the polysaccharide modified salt-resistant resistance reducing agent for the shale gas fracturing fluid is prepared by introducing polymerizable polysaccharide with salt resistance activity to a macromolecular chain of polyacrylamide, the solution viscosity is obviously improved, and the comprehensive performance of the polymer in temperature resistance and salt resistance is effectively improved.

According to the invention, several biological polysaccharides are subjected to structural modification, double-bond groups are introduced to form a novel polymerizable salt-resistant monomer, and the novel polymerizable salt-resistant monomer is copolymerized with monomers such as acrylamide and the like according to a certain proportion to form a polymer with high molecular weight and stability, and the polymer has the excellent performances of both, so that a novel salt-resistant and high-temperature-resistant polyacrylamide copolymer is formed, and the novel polyacrylamide copolymer is particularly suitable for a high-salinity water fracturing process.

The polysaccharide substance has a stable structure, is not easy to generate chemical reaction, and hydroxyl in the structure is difficult to generate esterification modification reaction. The polysaccharide component has high viscosity after being dissolved in water, and has certain difficulty in reaction if the addition amount is too large in the chemical modification and polymerization reaction processes. The preparation method comprises the steps of preparing a polysaccharide monomer and copolymerizing the polysaccharide monomer with an acrylamide monomer to form a high-molecular-weight and high-salt-resistance polymer; the polymer with more excellent tackifying property is further formed, the grafted side chain has polyhydroxy rigid groups through introducing a neutral polymeric polysaccharide structural unit, the polyhydroxy rigid groups are associated through hydrogen bonds, a better elastic energy storage effect is shown in an aqueous solution, the curling phenomenon is not easy to occur in saline water, the viscosity of the solution is slightly influenced by salinity, and the resistance reducing property is improved. Meanwhile, the amide group and the carboxyl group are well protected from the influence of electrolyte in high-salinity water, and the chemical stability of the polymer is improved; through the combined action of the polymer and the traditional sulfonic acid group salt-tolerant monomer, the salt-resistant stability of the polymer is obviously improved, and the requirement of high-salinity flowback fluid preparation in the prior art is met.

Drawings

Fig. 1 is a typical structure of a polysaccharide modified salt-resistant friction reducer polymer according to an embodiment of the present invention.

Detailed Description

The following examples are presented to further illustrate embodiments of the present invention, and it should be understood that the embodiments described herein are for purposes of illustration and explanation only and are not intended to limit the invention.

According to the invention, several biological polysaccharides are modified, and double bond groups are introduced, so that the biological polysaccharides can be copolymerized with acrylamide. The novel polysaccharide has a double-bond structure, can be polymerized with acrylamide to form a polymer with higher molecular weight and more stability. Has both excellent performances of the two, and forms a novel polyacrylamide copolymer with salt resistance and high temperature resistance.

Example 1

1) Typical polymerizable modified polysaccharide synthesis methods:

chemically modifying and synthesizing xanthan gum: a large number of active hydroxyl groups positioned at the outer side in the xanthan gum molecule react with maleic anhydride, and the high activity of the anhydride is utilized to perform esterification reaction with the hydroxyl groups, so that polymerizable double bonds are introduced, and the modified xanthan gum MX (namely xanthan gum Maleate (MA)) is synthesized.

The specific synthesis conditions are as follows: dissolving 10.5g (0.11mol) of maleic anhydride in 100mL of tetrahydrofuran, adding 20g (0.0214mol) of xanthan gum and swelling for 1 h; wherein the molar ratio of xanthan gum to maleic acid is 1: 5. Adding 0.35g of p-toluenesulfonic acid catalyst and 0.002g of hydroquinone polymerization inhibitor, heating the system to 60 ℃, reacting for 24 hours at constant temperature, cooling the reaction liquid to room temperature, and filtering. The filter cake was washed with tetrahydrofuran (20 mL. times.1), 80% ethanol (10 mL. times.4), and absolute ethanol (20 mL. times.1), respectively, in that order, and dried under vacuum at room temperature for 2h to give the modified polysaccharide monomeric compound, pale white maleic acid monoesterified product (i.e., Unit A), in 61.6% yield.

2) Preparing a salt-resistant and resistance-reducing agent:

adding 120g D20 solvent oil and 12g (Span 80/fatty acid diethanolamide) into a three-neck flask provided with a thermometer, a stirrer and a nitrogen pipe, mixing the solvent oil and the fatty acid diethanolamide according to the mass ratio of 2:1, and quickly stirring to disperse the mixture into a uniform oil phase; accurately weighing 80g of AM, 8g of AMPS and 4g of xanthan gum maleate (unit A), placing in a beaker, adding 96g of distilled water, and completely dissolving to prepare an aqueous phase solution; adding the aqueous phase solution into the oil phase, quickly stirring and emulsifying for 30min to form a water-in-oil emulsion, introducing nitrogen for 30min, controlling the reaction temperature to 35 ℃, adding 0.036g of an initiator (m (ammonium persulfate): m (sodium bisulfite): 1, w (ammonium persulfate-sodium bisulfite): 0.04% (based on the total mass of the monomers)) to initiate polymerization, adding a VA-044 initiator (0.02% of the total mass of the monomers) after the temperature rises, closing N2 when the temperature of the system rises to 60 ℃, continuing heat preservation reaction for 4h, cooling to room temperature, and adding a TX-10 phase transfer agent to obtain the stable emulsion resistance reducer.

Example 2

1) Synthesis of butyl glucoside maleate: adding 102.85g of n-butanol into a three-neck flask provided with a thermometer, a stirrer and a nitrogen pipe, dropwise adding 0.092g of concentrated sulfuric acid under stirring, adding 27.825g of glucose 5 times in 10min, reacting for 4.5h at 105 ℃, detecting the reaction end point by a Fehling reagent, adding 1mL of 2mol/L NaOH solution to neutralize excessive concentrated sulfuric acid after the reaction is finished, and distilling under reduced pressure to remove the n-butanol to obtain the butyl glucoside. Mixing the obtained 0.15mol of butyl glucoside with 29.4g (0.3mol) of maleic anhydride, adding 0.11g of concentrated sulfuric acid, and stirring and reacting at the temperature of 60 ℃ for 3 hours to obtain Butyl Glucoside Maleate (BGMAH).

2) Preparing a salt-resistant and resistance-reducing agent:

adding 60g of solvent oil and 10.4g of SPAN-80 and 1.6gOP-10 into another three-neck flask, and rapidly stirring to disperse the solvent oil into a uniform oil phase; accurately weighing 49g of AM, 20g of acrylic acid, 3.5g of butyl glucoside maleate and 18g of sodium propenyl sulfonate, placing the materials in a beaker, adding 120g of distilled water, and completely dissolving to prepare an aqueous phase solution; adding the aqueous phase solution into the oil phase, rapidly stirring and emulsifying for 30min, introducing nitrogen for 40min, controlling the reaction temperature to 35 ℃, adding an initiator ammonium persulfate to 0.03 percent (based on the total mass of the monomers), dropwise adding a sodium bisulfite reducing agent to initiate polymerization, adding a VA-044 initiator (0.015 percent of the total mass of the monomers) after the temperature rises, and closing N when the temperature of the system rises to 60 DEG C₂And continuing to perform heat preservation reaction for 2 hours, cooling to room temperature, and then adding a proper amount of OP-15 emulsifier to perform phase inversion to obtain the stable emulsion resistance reducer.

Example 3

1) Modified Cyclodextrin (. beta. -CD-A A) Synthesis: weighing a certain amount of beta-CD and 1, 3-Dicyclohexylcarbodiimide (DCC) condensing agent, dissolving the condensing agent in DMF, dropwise adding acrylic acid with the same molar ratio as the DCC at room temperature, dropwise adding for 30min, continuing to react at 80 ℃ for 3h, after the reaction is finished, carrying out vacuum filtration to remove separated solid, precipitating a crude product from filtrate by using acetone, treating the crude product by using acetic acid and potassium carbonate aqueous solution, dissolving the crude product in distilled water and methanol, precipitating and purifying the acetone, and carrying out vacuum drying to obtain the acrylic acid beta-cyclodextrin esterified substance.

2) Preparing a salt-resistant and resistance-reducing agent: according to AM: AMPS: AA: the modified cyclodextrin is synthesized according to the mass ratio of 10:1:2:0.6, the total mass fraction of the monomers is 30%, the emulsifier is compounded by SPAN-80 and SMO-5, the using amount of the emulsifier is 4.5% of the total mass, the kerosene is an inverse solvent, the adding amount of the kerosene is 20% of the total mass, after high-speed emulsification, high-purity nitrogen is introduced for bubbling and deoxygenation for 30min, ammonium persulfate, sodium bisulfite and V50 are sequentially added for initiating polymerization, the polymerization reaction temperature is controlled, and the heat preservation reaction is carried out for about 6 h. Adding an isomeric alcohol polyoxyethylene ether 1309 phase inversion agent for phase inversion to obtain the stable emulsion resistance reducer.

Comparative example 1

Synthesizing a conventional salt-resistant drag reducer: adopting an inverse emulsion polymerization method, taking AA, AMPS and AM as polymerization monomers, wherein the AA accounts for 30% of the total mass of the monomers, the salt-tolerant monomer AMPS accounts for 10% of the total mass of the monomers, the AM monomer accounts for 60%, an emulsifier is a compound of SPAN-80 and TWEEN-80, the using amount is 5.4%, D20 solvent oil is an oil phase solvent, and the volume ratio of the oil to the water is 0.9: 1.1, initiating polymerization by adopting ammonium persulfate/sodium bisulfite and VA-044 composite initiator, wherein the addition amount of the fixed initiator is 0.03 percent, the solid content is 30 percent, the reaction temperature is 30-50 ℃, and 2.5 percent of TX-10 emulsifier is subjected to phase inversion to obtain the emulsion drag reducer.

Comparative example 2

The emulsion resistance reducer in the prior art, which is described in the comparative example, is prepared from the following raw materials in parts by weight: 17 parts of acrylamide, 13 parts of sodium acrylate, 25 parts of 7# white oil solvent, span-802 parts, 0.04 part of ammonium persulfate/sodium bisulfite composite initiator, 01 parts of azodiisobutyronium hydrochloride VA-0440, 3.5 parts of fatty alcohol polyoxyethylene ether (AEO-9) phase transfer agent and 39 parts of water, and the emulsion type resistance reducer is obtained under the same polymerization reaction conditions as those in the above examples.

For the drag reduction rate of each obtained drag reduction agent, the indoor evaluation drag reduction rate of the drag reduction agent is 67 percent in the comparative example, while the indoor evaluation drag reduction rate of the drag reduction agent is 78 percent in the invention, the drag reduction agent of the invention is improved in comparison with the drag reduction rate of the comparative example, and is more suitable for the requirement of high-salinity shale gas fracturing construction.

The obtained resistance reducing agent was evaluated:

1) performance characterization, determination of viscosity average molecular weight of the copolymer: taking a certain amount of the synthesized emulsion resistance reducing agent, settling with a large amount of acetone, washing precipitated solids with acetone, petroleum ether and methanol in sequence, and drying to obtain solid polymers, and measuring the molecular weight of the solids in sequence, or measuring the solid content of the emulsion to directly measure the molecular weight of a certain amount of the emulsion. The molecular weight determination method comprises the following steps: the molecular weight of the copolymer was determined by measuring the viscosity of the aqueous solution of the copolymer using a Ubbelohde viscometer in a constant temperature water bath at 30. + -. 0.05 ℃ using 1mol/L and 2mol/L sodium chloride solutions as a solvent, and determining the intrinsic viscosity coefficient of the copolymer by dilution extrapolation (see Table 1).

TABLE 1 molecular weight comparison of copolymers of the examples

	Example 1	Example 2	Example 3	Comparative example 1	Comparative example 2
						Molecular weight	1080 ten thousand	960 ten thousand	1110 ten thousand	720 ten thousand	1250 ten thousand

Through molecular weight data analysis, because the introduced sulfonic acid group salt-resistant monomer has a copolymerization rate lower than AM and AA monomers, the molecular weight is slightly reduced, and the introduced polymer prepared from the polysaccharide monomer has relatively less reduction of the molecular weight, thereby meeting the requirements of the fracturing resistance reducer.

2) Comparison of salt resistance: for emulsions with different solid contents, a certain amount of the resistance reducing agent samples obtained in the above embodiments are weighed according to the concentration of 0.32 per thousand of pure copolymer, and are sequentially dissolved in clear water, 2 ten thousand of saline (6g of calcium chloride +1.6g of magnesium chloride +3g of sodium sulfate +9.4g of sodium chloride in 1L of distilled water), 5 ten thousand of saline and 10 ten thousand of saline, stirred and dissolved by a stirring machine with the rotating speed of 2000rpm for 3min, and the viscosity is measured by an Ubbelohde viscometer (the inner diameter of a capillary is 0.8mm, and the viscometer constant is 0.0293) (see table 2).

TABLE 2 comparison of salt resistance of the resistance-reducing agent in each example

Viscosity retention of the copolymers bonded to the polysaccharide monomer was demonstrated to be much higher than that of unmodified PAM by differential mineralization viscosity measurements. The salt resistance of the modified polymer is obviously improved, and the requirement of high-salinity flowback fluid fracturing workers can be met.

3. And (3) resistance reduction rate testing: the drag reduction was measured using a HAMZ-IV fracturing fluid friction drag tester (see Table 3). The test was carried out according to the following set of 2 formulas:

(1) the formula of the salt-resistant slickwater (clear water) comprises the following components: 0.1 percent of resistance reducing agent, 0.2 percent of high-efficiency anti-swelling agent, 0.1 percent of demulsification cleanup additive and clear water

(2) And the formula of the salt-resistant slickwater (5 ten thousand saline water): 0.1 percent of resistance reducing agent, 0.2 percent of high-efficiency anti-swelling agent, 0.1 percent of demulsifying and cleanup additive and 5 ten thousand salt water

TABLE 3 comparison of drag reduction ratio (%)

Index (I)	Example 1	Example 2	Example 3	Comparative example 1	Comparative example 2
						Formulation 1	76.23	73.54	74.48	70.20	68.25
Formulation 2	73.50	70.36	71.58	67.78	62.65

Note: the high-efficiency anti-swelling agent is ammonium chloride, potassium chloride and the like; the demulsifying and cleanup additive is a fluorine-containing surfactant.

The determination of the resistance reducing rate proves that the resistance reducing rate of the copolymer bonded with the polysaccharide monomer is higher than that of an unmodified polymer, meets the national standard of the resistance reducing rate, has good salt resistance and equivalent dissolving speed, and meets the requirements of high-salinity water fracturing and instant preparation and use.

The above examples only express the specific embodiments of the present application, and the description is more specific and detailed, but not construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present invention, which falls within the protection scope of the present application.