阅读说明：本技术 β-CD双子粘弹性表面活性剂及制备方法和耐温抗盐清洁压裂液 (beta-CD Gemini viscoelastic surfactant, preparation method thereof and temperature-resistant salt-resistant clean fracturing fluid ) 是由 毛金成 徐涛 毛金桦 张阳 杨小江 林冲 于 2021-08-20 设计创作，主要内容包括：本发明公开了一种β-CD双子粘弹性表面活性剂及制备方法和耐温抗盐清洁压裂液。本发明采用环糊精基团、长链叔胺和环氧氯丙烷制备β-CD双子粘弹性表面活性剂,该表面活性剂的临界胶束浓度比普通表面活性剂低2-3个数量级,将制得的表面活性剂作为稠化剂用于制备清洁压裂液,表面活性剂与反离子盐或无机盐复配制得的清洁压裂液使用量低,在120℃、170s～(-1)下60min后黏度能维持在150mPa·s左右,满足现场施工对清洁压裂液的黏度要求,并且具有优异的耐温耐剪切性、黏弹性和悬浮支撑作用,可用于高温油气藏的压裂增产改造。(The invention discloses a beta-CD Gemini viscoelastic surfactant, a preparation method thereof and a temperature-resistant salt-resistant clean fracturing fluid. The invention adopts cyclodextrin group, long-chain tertiary amine and epichlorohydrin to prepare beta-CD gemini viscoelastic surfactant, the critical micelle concentration of the surfactant is 2-3 orders of magnitude lower than that of common surfactant, the prepared surfactant is used as a thickening agent to prepare clean fracturing fluid, and the surfactant and counter ion salt or inorganic chloropropane are used as the thickening agent to prepare clean fracturing fluidThe clean fracturing fluid prepared by salt compounding has low use amount, and the use amount is 170s at 120 DEG C ‑1 The viscosity can be maintained at about 150mPa & s after 60min, the viscosity requirement of field construction on clean fracturing fluid is met, and the high-temperature-resistant shear-resistant fracturing fluid has excellent temperature resistance, viscoelasticity and suspension supporting effect, and can be used for fracturing yield-increasing transformation of high-temperature oil and gas reservoirs.)

1. A beta-CD gemini viscoelastic surfactant is characterized in that the structural formula is as follows:

wherein R is a saturated hydrocarbon chain or an unsaturated hydrocarbon chain having 17 to 21 carbon atoms.

2. The β -CD gemini viscoelastic surfactant according to claim 1, wherein R is a erucic or oleic acid group.

3. A process for the preparation of a β -CD gemini viscoelastic surfactant according to claim 1 or 2, comprising the steps of:

(1) preparing mono-6-p-toluenesulfonyl-beta-cyclodextrin;

(2) preparation of 6-position ethylenediamine monosubstituted beta-cyclodextrin

Adding mono-6-p-toluenesulfonyl-beta-cyclodextrin and ethylenediamine into a reaction vessel according to the molar ratio of 1:1-2, uniformly mixing, and reacting at 60-90 ℃ for 6-8h under a sealed condition to obtain the product;

(3) dissolving long-chain tertiary amine and epoxy chloropropane in a solvent, and reacting at 70-90 ℃ for 10-14h to obtain an intermediate DNPC, wherein the reaction formula is as follows: wherein the molar ratio of the long-chain tertiary amine to the epoxy chloropropane is 1: 1-1.5; the long-chain tertiary amine is at least one of erucic acid amide propyl dimethylamine and oleic acid amide propyl dimethylamine;

(4) adding 6-EDA-beta-CD ethanol solution into the intermediate DNPC, and then carrying out reflux reaction at 60-80 ℃ for 18-24h to prepare the beta-CD gemini viscoelastic surfactant, wherein the reaction formula is shown as follows: wherein the molar ratio of the intermediate DNPC to the 6-EDA-beta-CD is 2-2.5: 1;

4. the method for preparing a beta-CD gemini viscoelastic surfactant according to claim 3, wherein the reaction temperature in the step (3) is 80 ℃ and the reaction time is 12 hours.

5. The method for preparing beta-CD gemini viscoelastic surfactant according to claim 3, wherein the solvent in the step (3) is a mixture of an organic solvent and water, and the organic solvent is ethanol, isopropanol or n-propanol.

6. The process for preparing a beta-CD gemini viscoelastic surfactant according to claim 3, wherein the reflux temperature in step (4) is 70 ℃.

7. Use of the beta-CD gemini viscoelastic surfactant of claim 1 or 2 in the preparation of a temperature-resistant, salt-resistant clean fracturing fluid.

8. The temperature-resistant salt-resistant clean fracturing fluid is characterized by comprising the following components in percentage by mass: 1-3% of beta-CD gemini viscoelastic surfactant, 3-6.4% of counter ion salt or inorganic salt and the balance of water.

9. The temperature-resistant salt-resistant clean fracturing fluid of claim 8, wherein the counter ion salt or inorganic salt is one or a mixture of potassium chloride, ammonium chloride, sodium salicylate, sodium benzoate, potassium hydrogen benzoate, carboxyl benzene sulfonate and sodium sulfosalicylate.

10. The preparation method of the temperature-resistant salt-resistant clean fracturing fluid of claim 8 or 9, wherein the beta-CD gemini viscoelastic surfactant is added into water, then the counter ion salt or inorganic salt is added, and the mixture is stirred until the mixture is completely dissolved.

Technical Field

The invention relates to the technical field of oilfield chemistry, in particular to a beta-CD gemini viscoelastic surfactant, a preparation method thereof and a temperature-resistant salt-resistant clean fracturing fluid.

Background

In the world, most of large-scale high-permeability oil and gas fields around the world enter the later exploitation stage, the demand of all countries in the world on oil is continuously increased, the teams for oil exploration and development at home and abroad begin to enter low-permeability, ultra-low-permeability and unconventional marginal oil and gas reservoirs, the reservoir fracturing reformation becomes the key for improving the crude oil recovery ratio, the requirements of oil field production on the reservoir exploitation degree and the fracturing reformation efficiency are continuously improved, the conventional reservoir reformation (comprising reformation process and working solution) exposes various defects, and particularly along with the development of unconventional shale gas, compact oil and the like, the conventional reservoir reformation cannot meet the requirements of the conventional fracturing reformation, the working fluid is used as a soul for reservoir transformation, the quality of the working fluid determines the success or failure of transformation measures, and the research and development of the high-performance working fluid become problems to be solved urgently in the current unconventional oil and gas reservoir transformation. Therefore, stable, environmentally friendly alternatives should be developed as soon as possible. Fortunately, when clean fracturing fluid using small molecule Viscoelastic Surfactant (VES for short) as thickening agent meets formation water or oil gas, gel breaking can occur without any insoluble residues. In addition, the advent of clean fracturing fluid systems successfully solved the above problems.

VES is one of water-based fracturing fluids, and has the following action mechanism: in the surfactant solution, the surfactant which initially exists in a monomolecular state is sequentially agglomerated into spherical micelles, rod-shaped micelles or wormlike micelles along with the increase of concentration, and a cross-linked network structure is gradually formed, so that the aims of carrying a propping agent and fracturing and seam making are fulfilled; proper amount of counter ion salt is added into the surfactant solution system to promote the formation of micelle structure. When the micelle solution meets a large amount of water or oil, the gemini surfactant molecules are greatly solubilized due to the characteristics of hydrophilic or lipophilic groups, the micelle structure is unzipped or broken, and the micelle solution automatically breaks the gel. Compared with the traditional water-based vegetable gum fracturing fluid, the clean fracturing fluid has the advantages of simple preparation, low abrasion resistance, no residue, small damage to stratum, high flowback speed after construction, high flowback rate and the like. However, the traditional clean fracturing fluid takes a single-chain surfactant as a thickening agent, and has poor temperature resistance, so the use of the traditional clean fracturing fluid is limited to a certain extent. Gemini surfactants contain one hydrophilic group (ionic head group or polar group) and two hydrophobic groups (fatty chain, carbon silicon chain or fluorocarbon chain) and are linked by a linking group at both polar groups. The special structure determines many unique properties of the gemini surfactant, such as high surface activity, low critical micelle concentration, excellent wettability, unique rheological property and the like. The gemini surfactant is used as a thickening agent to prepare the clean fracturing fluid, so that the defects of the traditional clean fracturing fluid can be overcome. Although the clean fracturing fluid prepared by using the gemini surfactant as a thickening agent can resist temperature, the clean fracturing fluid which can resist salt while improving the temperature resistance has not been reported.

Disclosure of Invention

In order to solve the defects in the prior art, the invention aims to provide a beta-CD gemini viscoelastic surfactant, a preparation method thereof and a temperature-resistant salt-resistant clean fracturing fluid.

The technical scheme for solving the technical problems is as follows: providing a beta-CD gemini viscoelastic surfactant, wherein the structural formula of the surfactant is as follows:

wherein R is a saturated hydrocarbon chain or an unsaturated hydrocarbon chain with 17-21 carbon atoms, preferably R is a erucic acid group or an oleic acid group, the erucic acid group is the part left after the carboxyl group of the erucic acid is removed, and the oleic acid group is the part left after the carboxyl group of the oleic acid is removed.

The invention has the beneficial effects that: beta-CD (cyclodextrin) is selected as a spacer in the beta-CD gemini viscoelastic surfactant, and the molecular volume of the surfactant is larger, so that the area of a hydrophilic group is relatively increased, and the stacking parameter P of the surfactant is increased.

The preparation method of the beta-CD gemini viscoelastic surfactant comprises the following steps:

(1) preparation of mono-6-p-toluenesulfonyl-beta-cyclodextrin

The structural formula of the mono-6-p-toluenesulfonyl-beta-cyclodextrin is as follows:

(2) preparation of 6-position ethylenediamine monosubstituted beta-cyclodextrin

Adding mono-6-p-toluenesulfonyl-beta-cyclodextrin and ethylenediamine into a reaction vessel according to the molar ratio of 1:1-2, uniformly mixing, and reacting at 60-90 ℃ for 6-8h under a sealed condition to obtain the product;

(3) dissolving long-chain tertiary amine and epoxy chloropropane in a solvent, and reacting at 70-90 ℃ for 10-14h to obtain an intermediate DNPC, wherein the reaction formula is as follows: wherein the molar ratio of the long-chain tertiary amine to the epoxy chloropropane is 1: 1-1.5; the long-chain tertiary amine is at least one of erucic acid amide propyl dimethylamine and oleic acid amide propyl dimethylamine;

(4) adding 6-EDA-beta-CD ethanol solution into the intermediate DNPC, and then carrying out reflux reaction at 60-80 ℃ for 18-24h to prepare the beta-CD gemini viscoelastic surfactant, wherein the reaction formula is shown as follows: wherein the molar ratio of the intermediate DNPC to the 6-EDA-beta-CD is 2-2.5: 1;

on the basis of the technical scheme, the invention can be further improved as follows:

further, the specific process of the step (1) is as follows: dissolving beta-cyclodextrin in a solvent under an alkaline condition in a ice salt bath environment, dropwise adding p-toluenesulfonyl chloride to react for 2-3h, then performing suction filtration, and then performing vacuum drying at 35-45 ℃ to obtain mono-6-p-toluenesulfonyl-beta-cyclodextrin (6-OTs-beta-CD), wherein the reaction formula is shown as follows; wherein, the mol ratio of the beta-cyclodextrin to the p-toluenesulfonyl chloride is 1: 1-1.5; the solvent is preferably a mixture of an organic solvent and water, wherein the organic solvent is ethanol, isopropanol or n-propanol; the specific reaction formula is as follows:

further, in the step (3), the reaction temperature is 80 ℃, and the reaction time is 12 hours.

Further, in the step (3), the solvent is preferably a mixture of an organic solvent and water, and the organic solvent is ethanol, isopropanol or n-propanol.

Further, the reflux temperature in step (4) was 70 ℃.

The beta-CD gemini viscoelastic surfactant is used as a thickening agent to prepare a temperature-resistant and salt-resistant clean fracturing fluid, and the temperature-resistant and salt-resistant clean fracturing fluid comprises the following components in percentage by mass: 1-3% of beta-CD gemini viscoelastic surfactant, 3-6.4% of counter ion salt or inorganic salt and the balance of water.

Further, the counter ion or inorganic salt is one or more of potassium chloride, ammonium chloride, sodium salicylate, sodium benzoate, potassium hydrogen benzoate, carboxyl benzene sulfonate and sodium sulfosalicylate.

The preparation method of the temperature-resistant salt-resistant clean fracturing fluid comprises the following steps: adding the beta-CD gemini viscoelastic surfactant into water, then adding the counter ion salt or inorganic salt, and stirring until the beta-CD gemini viscoelastic surfactant is completely dissolved.

The invention has the following beneficial effects:

the beta-CD gemini viscoelastic surfactant is prepared by adopting a cyclodextrin group, long-chain tertiary amine and epichlorohydrin, the critical micelle concentration of the surfactant is 2-3 orders of magnitude lower than that of a common surfactant, the prepared surfactant is used as a thickening agent for preparing clean fracturing fluid, the use amount of the clean fracturing fluid prepared by compounding the surfactant and a counter ion salt or an inorganic salt is low, and the clean fracturing fluid is prepared at 120 ℃ for 170s^-1The viscosity can be maintained at about 150mPa & s after 60min, the viscosity requirement of field construction on clean fracturing fluid is met, and the high-temperature-resistant shear-resistant fracturing fluid has excellent temperature resistance, viscoelasticity and suspension supporting effect, and can be used for fracturing yield-increasing transformation of high-temperature oil and gas reservoirs.

Drawings

Figure 1 is a rheological profile of a clean fracturing fluid formulated with 3% viscosifier + 6.4% NaSal in example 1.

Figure 2 is a rheological profile of a clean fracturing fluid formulated with 1% viscosifier plus 3% NaSal in example 2.

Figure 3 is a rheological profile of a clean fracturing fluid formulated with 3% viscosifier plus 3% NaSal in example 3.

Figure 4 is a rheological profile of a clean fracturing fluid formulated with 1% viscosifier plus 6.4% NaSal in example 4.

FIG. 5 shows nuclear magnetic spectrum of beta-CD gemini viscoelastic surfactant prepared from erucamidopropyl dimethyl tertiary amine.

FIG. 6 shows nuclear magnetic spectrum of beta-CD gemini viscoelastic surfactant prepared from oleic acid amide propyl dimethyl tertiary amine.

FIG. 7 is a graph of the viscosity change in NaCl solution with 1% -3% thickener in example 4.

FIG. 8 is a plot of the viscosity change in KCl solution with 1% -3% thickener in example 4.

FIG. 9 shows that 1% -3% of thickening agent is added in CaCl in example 4₂Viscosity profile in solution.

FIG. 10 is a graphical representation of the results of example 4 using 1% -3% thickeners in MgCl₂Viscosity profile in solution.

Detailed Description

The following examples are given for the purpose of illustration only and are not intended to limit the scope of the invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Example 1:

a beta-CD gemini viscoelastic surfactant has a structural formula as follows:

the preparation method of the beta-CD gemini viscoelastic surfactant comprises the following steps:

(1) preparation of mono-6-p-toluenesulfonyl-beta-cyclodextrin (6-OTs-beta-CD)

50g (44.1mmol) of beta-cyclodextrin was suspended in 100mL of a mixture of ethanol and water (volume ratio 5:1) by magnetic stirring in a 250mL beaker under ice salt bath conditions, and 16.7mL of sodium hydroxide solution (8.5mol/L) was slowly added dropwise to the beta-cyclodextrin suspension, and the suspension became clear. Then, 25.22g (132.3mmol) of p-toluenesulfonyl chloride (p-TsCl) was dissolved in acetonitrile and added dropwise to a sodium hydroxide solution of cyclodextrin, and the reaction was continued at 22 ℃ for 2 hours after the addition. And (3) after the reaction is finished, filtering unreacted p-TsCl, neutralizing the filtrate by using dilute hydrochloric acid (2.6mol/L) until the pH value of the solution is 8.0, standing overnight at 4 ℃, and filtering to obtain a crude mono-6-p-toluenesulfonyl-beta-cyclodextrin product. And cleaning the crude product with acetone for three times, adding about 150mL of distilled water, recrystallizing for 3 times at 80 ℃, and drying in a vacuum oven at 40 ℃ for 24 hours in vacuum to obtain white crystalline powder, namely the pure mono-6-p-toluenesulfonyl-beta-cyclodextrin.

(2) Preparation of 6-position ethylenediamine monosubstituted beta-cyclodextrin (6-EDA-beta-CD)

Taking 16.0g of pure product 6-OTs-beta-CD, adding 40mL of ethylenediamine and 0.032g of catalyst 4-dimethylaminopyridine under the protection of dry nitrogen, stirring and reacting at 70 ℃ for 7h, removing EDA by rotary evaporation, cooling the obtained light yellow liquid to room temperature, slowly dropwise adding the light yellow liquid into excessive cold acetone, stirring and crystallizing at 4 ℃ to separate out light yellow sticky substances, dissolving a filter cake by using a proper amount of deionized water-methanol mixed solvent (volume ratio is 1: 3) after filtering, dropwise adding the mixture into cold acetone for precipitation, washing by using acetone, and repeatedly purifying for 3 times to obtain 6-position ethylenediamine monosubstituted beta-cyclodextrin (6-EDA-beta-CD).

(3) Preparation of intermediate DNPC

100mmol (42.273g) of long-chain tertiary amine (oleamidopropyl dimethyl tertiary amine) was first dissolved in a 500mL single-neck round-bottom flask containing 150mL of isopropanol, then 110mmol (10.18g) of epichlorohydrin was added to the round-bottom flask, and after stirring at 80 ℃ for 12h, the intermediate DNPC was obtained.

(4) Preparation of beta-CD Gemini viscoelastic surfactant

A500 ml single-neck flask was charged with intermediate DNPC (100mmol, 51.52g) and 6-EDA-. beta. -cd (50mmol, 58.84g), 100ml ethanol was added and the reaction was refluxed at 70 ℃ for 18 h. After the reaction is finished, the solvent ethanol is removed by a rotary evaporator at 45 ℃, so that light yellow grease which is the beta-CD gemini viscoelastic surfactant is obtained, the nuclear magnetism characterization is shown in figure 5, and the yield is 66.57%.

The beta-CD gemini viscoelastic surfactant is used as a thickening agent to prepare clean fracturing fluid, and the clean fracturing fluid comprises the following components in percentage by mass: 3% of beta-CD gemini viscoelastic surfactant, 6.4% of NaSal and the balance of water.

Clean fracturing fluid prepared from 3% of thickening agent and 6.4% of NaSal at 120 ℃ for 170s^-1The rheological property of the suspension sand is shown in figure 1, no obvious sedimentation occurs after 2 hours of static suspension sand, and the viscosity of a gel breaking liquid is less than 5 mPa.s after the gel is broken by 30 percent kerosene.

Example 2:

a beta-CD gemini viscoelastic surfactant has a structural formula as follows:

the preparation method of the beta-CD gemini viscoelastic surfactant comprises the following steps:

(1) preparation of mono-6-p-toluenesulfonyl-beta-cyclodextrin (6-OTs-beta-CD)

50g (44.1mmol) of beta-cyclodextrin was suspended in 100mL of a mixture of ethanol and water (volume ratio 5:1) by magnetic stirring in a 250mL beaker under ice salt bath conditions, and 16.7mL of sodium hydroxide solution (8.5mol/L) was slowly added dropwise to the beta-cyclodextrin suspension, and the suspension became clear. Then, 25.22g (132.3mmol) of p-toluenesulfonyl chloride (p-TsCl) was dissolved in acetonitrile and added dropwise to a sodium hydroxide solution of cyclodextrin, and the reaction was continued at 22 ℃ for 2 hours after the addition. And (3) after the reaction is finished, filtering unreacted p-TsCl, neutralizing the filtrate by using dilute hydrochloric acid (2.6mol/L) until the pH value of the solution is 8.0, standing overnight at 4 ℃, and filtering to obtain a crude mono-6-p-toluenesulfonyl-beta-cyclodextrin product. And cleaning the crude product with acetone for three times, adding about 150mL of distilled water, recrystallizing for 3 times at 80 ℃, and drying in a vacuum oven at 40 ℃ for 24 hours in vacuum to obtain white crystalline powder, namely the pure mono-6-p-toluenesulfonyl-beta-cyclodextrin.

(2) Preparation of 6-position ethylenediamine monosubstituted beta-cyclodextrin (6-EDA-beta-CD)

Taking 16.0g of pure product 6-OTs-beta-CD, adding 40mL of ethylenediamine and 0.032g of catalyst 4-dimethylaminopyridine, stirring and reacting at 60 ℃ for 7h under the protection of dry nitrogen, removing EDA by rotary evaporation, cooling the obtained light yellow liquid to room temperature, slowly dropwise adding the light yellow liquid into excessive cold acetone, stirring, crystallizing at 4 ℃, and precipitating light yellow sticky substances. And dissolving a filter cake after filtering by using a proper amount of deionized water-methanol mixed solvent (the volume ratio is 1: 3), dropwise adding the mixture into cold acetone for precipitation, washing by using acetone, and repeatedly purifying for 3 times to obtain the 6-position ethylenediamine monosubstituted beta-cyclodextrin (6-EDA-beta-CD).

(3) Preparation of intermediate DNPC

100mmol (42.273g) of long-chain tertiary amine (oleamidopropyl dimethyl tertiary amine) was first dissolved in a 500mL single neck round bottom flask containing 150mL of ethanol, then 110mmol of epichlorohydrin was added to the round bottom flask (10.18g), and the reaction was stirred at 80 ℃ for 12h to obtain intermediate DNPC.

(4) Preparation of beta-CD Gemini viscoelastic surfactant

A500 ml single-neck flask was charged with intermediate DNPC (100mmol 51.52g) and 6-EDA-. beta. -cd (50mmol 58.84g), 100ml ethanol was added and the reaction was refluxed at 70 ℃ for 18 hours. After the reaction is finished, the solvent ethanol is removed by a rotary evaporator at 45 ℃, so that the light yellow grease which is the beta-CD gemini surfactant is obtained, and the nuclear magnetic characterization of the light yellow grease is shown in figure 6.

The beta-CD gemini viscoelastic surfactant is used as a thickening agent to prepare clean fracturing fluid, and the clean fracturing fluid comprises the following components in percentage by mass: 1% of beta-CD gemini viscoelastic surfactant, 3% of NaSal and the balance of water.

Clean fracturing fluid prepared from 1% thickening agent and 3% NaSal at 120 ℃ for 170s^-1The rheological property of the suspension sand is shown in figure 2, no obvious sedimentation occurs after 2 hours of static suspension sand, and the viscosity of a gel breaking liquid is less than 5 mPa.s after the gel is broken by 30 percent kerosene.

Example 3:

a beta-CD gemini viscoelastic surfactant has a structural formula as follows:

the preparation method of the beta-CD gemini viscoelastic surfactant comprises the following steps:

(1) preparation of mono-6-p-toluenesulfonyl-beta-cyclodextrin (6-OTs-beta-CD)

50g (44.1mmol) of beta-cyclodextrin was suspended in 100mL of a mixture of ethanol and water (volume ratio 5:1) by magnetic stirring in a 250mL beaker under ice salt bath conditions, and 16.7mL of sodium hydroxide solution (8.5mol/L) was slowly added dropwise to the beta-cyclodextrin suspension, and the suspension became clear. Then, 25.22g (132.3mmol) of p-toluenesulfonyl chloride (p-TsCl) was dissolved in acetonitrile and added dropwise to a sodium hydroxide solution of cyclodextrin, and the reaction was continued at 22 ℃ for 2 hours after the addition. And (3) after the reaction is finished, filtering unreacted p-TsCl, neutralizing the filtrate by using dilute hydrochloric acid (2.6mol/L) until the pH value of the solution is 8.0, standing overnight at 4 ℃, and filtering to obtain a crude mono-6-p-toluenesulfonyl-beta-cyclodextrin product. And cleaning the crude product with acetone for three times, adding about 150mL of distilled water, recrystallizing for 3 times at 80 ℃, and drying in a vacuum oven at 40 ℃ for 24 hours in vacuum to obtain white crystalline powder, namely the pure mono-6-p-toluenesulfonyl-beta-cyclodextrin.

(2) Preparation of 6-position ethylenediamine monosubstituted beta-cyclodextrin (6-EDA-beta-CD)

Taking 16.0g of pure product 6-OTs-beta-CD, adding 40mL of ethylenediamine and 0.032g of catalyst 4-dimethylaminopyridine under the protection of dry nitrogen, stirring and reacting at 80 ℃ for 7h, removing EDA by rotary evaporation, cooling the obtained light yellow liquid to room temperature, slowly dropwise adding the light yellow liquid into excessive cold acetone, stirring and crystallizing at 4 ℃ to separate out a light yellow sticky substance, dissolving a filter cake by using a proper amount of deionized water-methanol mixed solvent (volume ratio is 1: 3) after filtering, dropwise adding the dissolved filter cake into the cold acetone to precipitate, washing by using acetone, and repeatedly purifying for 3 times to obtain 6-position ethylenediamine monosubstituted beta-cyclodextrin (6-EDA-beta-CD).

(3) Preparation of intermediate DNPC

100mmol (42.273g) of long-chain tertiary amine (erucamidopropyldimethyl tertiary amine) was first dissolved in a 500mL single-neck round-bottom flask containing 150mL of isopropanol, then 110mmol (10.18g) of epichlorohydrin was added to the round-bottom flask, and after stirring at 80 ℃ for 12h, the intermediate DNPC was obtained.

(4) Preparation of beta-CD Gemini viscoelastic surfactant

A500 ml single-neck flask was charged with intermediate DNPC (100mmol 51.52g) and 6-EDA-. beta. -cd (50mmol 58.84g), 100ml isopropanol was added and the reaction was refluxed at 70 ℃ for 18 h. After the reaction is finished, the solvent ethanol is removed by a rotary evaporator at 45 ℃ to obtain a light yellow liquid, so that the obtained light yellow grease is the beta-CD gemini surfactant, and the nuclear magnetism representation of the light yellow grease is shown in figure 5.

The beta-CD gemini viscoelastic surfactant is used as a thickening agent to prepare clean fracturing fluid, and the clean fracturing fluid comprises the following components in percentage by mass: 3% of beta-CD gemini viscoelastic surfactant, 3% of NaSal and the balance of water.

Clean fracturing fluid prepared from 3% of thickening agent and 3% of NaSal at 150 ℃ for 170s^-1The rheological property of the suspension sand is shown in figure 3, no obvious sedimentation occurs after 2 hours of static suspension sand, and the viscosity of a gel breaking liquid is less than 5 mPa.s after the gel is broken by 30 percent kerosene.

Example 4:

a beta-CD gemini viscoelastic surfactant has a structural formula as follows:

the preparation method of the beta-CD gemini viscoelastic surfactant comprises the following steps:

(1) preparation of mono-6-p-toluenesulfonyl-beta-cyclodextrin (6-OTs-beta-CD)

50g (44.1mmol) of beta-cyclodextrin was suspended in 100mL of a mixture of ethanol and water (volume ratio 5:1) by magnetic stirring in a 250mL beaker under ice salt bath conditions, and 16.7mL of sodium hydroxide solution (8.5mol/L) was slowly added dropwise to the beta-cyclodextrin suspension, and the suspension became clear. Then, 25.22g (132.3mmol) of p-toluenesulfonyl chloride (p-TsCl) was dissolved in acetonitrile and added dropwise to a sodium hydroxide solution of cyclodextrin, and the reaction was continued at 22 ℃ for 2 hours after the addition. And (3) after the reaction is finished, filtering unreacted p-TsCl, neutralizing the filtrate by using dilute hydrochloric acid (2.6mol/L) until the pH value of the solution is 8.0, standing overnight at 4 ℃, and filtering to obtain a crude mono-6-p-toluenesulfonyl-beta-cyclodextrin product. And cleaning the crude product with acetone for three times, adding about 150mL of distilled water, recrystallizing for 3 times at 80 ℃, and drying in a vacuum oven at 40 ℃ for 24 hours in vacuum to obtain white crystalline powder, namely the pure mono-6-p-toluenesulfonyl-beta-cyclodextrin.

(2) Preparation of 6-position ethylenediamine monosubstituted beta-cyclodextrin (6-EDA-beta-CD)

Taking 16.0g of pure product 6-OTs-beta-CD, adding 40mL of ethylenediamine and 0.032g of catalyst 4-dimethylaminopyridine, stirring and reacting at 90 ℃ under the protection of dry nitrogen for 7h, removing EDA by rotary evaporation, cooling the obtained light yellow liquid to room temperature, slowly dropwise adding the light yellow liquid into excessive cold acetone, stirring, crystallizing at 4 ℃, and precipitating light yellow sticky substances. And dissolving a filter cake after filtering by using a proper amount of deionized water-methanol mixed solvent (the volume ratio is 1: 3), dropwise adding the mixture into cold acetone for precipitation, washing by using acetone, and repeatedly purifying for 3 times to obtain the 6-position ethylenediamine monosubstituted beta-cyclodextrin (6-EDA-beta-CD).

(3) Preparation of intermediate DNPC

100mmol (42.273g) of long-chain tertiary amine (erucamidopropyldimethyl tertiary amine) was first dissolved in a 500mL single-neck round-bottom flask containing 150mL of isopropanol, then 110mmol (10.18g) of epichlorohydrin was added to the round-bottom flask, and after stirring at 80 ℃ for 12h, the intermediate DNPC was obtained.

(4) Preparation of beta-CD Gemini viscoelastic surfactant

A500 ml single-neck flask was charged with intermediate DNPC (100mmol 51.52g) and 6-EDA- β -cd (50mmol 58.84g) (6-EDA- β -cd was dissolved with a small amount of water), 100ml isopropanol was added and the reaction was refluxed at 70 ℃ for 18 h. After the reaction is finished, the solvent ethanol is removed by a rotary evaporator at 45 ℃, so that the light yellow grease which is the beta-CD gemini surfactant is obtained, and the nuclear magnetism representation of the light yellow grease is shown in figure 5.

The beta-CD gemini viscoelastic surfactant is used as a thickening agent to prepare clean fracturing fluid, and the clean fracturing fluid comprises the following components in percentage by mass: 1% of beta-CD gemini viscoelastic surfactant, 6.4% of NaSal and the balance of water.

Clean fracturing fluid prepared from 1% thickening agent and 6.4% NaSal at 150 ℃ for 170s^-1The rheological property of the suspension sand is shown in figure 4, no obvious sedimentation occurs after 2 hours of static suspension sand, and the viscosity of a gel breaking liquid is less than 5 mPa.s after the gel is broken by 30 percent kerosene.

The beta-CD gemini viscoelastic surfactant is used as a thickening agent, and 1-3% of the thickening agent (mass fraction of the thickening agent in a salt solution) is respectively added in NaCl, KCl and CaCl₂、MgCl₂The viscosity change in the solution is shown in FIGS. 6-9, thus demonstrating the excellent salt resistance of the beta-CD gemini viscoelastic surfactant.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.