A shear-resistant high drag reduction medium-viscosity slickwater drag reducer and its preparation method

Abstract

The present invention discloses a shear-resistant high drag reduction medium-viscosity slickwater drag reducer and a preparation method thereof, belonging to the field of deep well / ultra-deep well volume fracturing; the drag reducer is polymerized from acrylamide, a sulfonate ion-containing hydrophobic monomer, a hydrophobic unit micro-block regulator, a molecular weight grading agent and a composite initiator. Through a special sulfonate ion-containing hydrophobic monomer, a hydrophobic unit micro-block regulator matched with the hydrophobic monomer and the control of the polymer molecular weight, the polymer dissolution performance and viscosity increasing performance can be significantly improved; the anti-shear degradation performance of the drag reducer can be improved; it has excellent sand carrying performance and drag reduction performance; it overcomes the shortcomings of the existing drag reducer such as weak anti-shear ability, rapid decline of drag reduction rate and poor sand carrying performance, meets the special requirements of fracturing fluid rheology and "high drag reduction in wellbore" for deep / ultra-deep oil and gas reservoir fracturing, provides key material support for the development of deep / ultra-deep oil and gas resources, and ensures the efficient development goal of deep / ultra-deep oil and gas resources.

Description

Technical Field

[0001] The present invention relates to the field of deep well / ultra-deep well volume fracturing, and particularly relates to a shear-resistant and highly drag-reducing medium-viscosity slickwater drag reducer and a preparation method thereof. Background Art

[0002] During the volume fracturing process of unconventional oil and gas reservoirs, in order to form a complex fracture network and effectively support the complex fracture network, medium-viscosity slickwater (5-10 mPa·s) is widely used, and high drag reduction and high sand-carrying capacity are required for medium-viscosity slickwater. Therefore, high-molecular-weight polyacrylamide is increasingly used, and the molecular weight of some polyacrylamides reaches more than 30 million. However, under high displacement conditions, the Reynolds number is large, the turbulence is intense, and the Reynolds shear degradation is obvious, and the higher the molecular weight, the more severe the degradation. On the one hand, the degradation of the molecular weight leads to a decrease in the drag reduction performance, and on the other hand, the loss of viscoelasticity leads to a weakening of the sand-carrying performance. For the volume fracturing of deep / ultra-deep oil and gas reservoirs, in addition to high displacement, there is also the challenge of long wellbores, which makes the degradation more obvious and puts forward higher requirements for the shear resistance of the drag reducer. Existing linear high-molecular-weight polyacrylamide is difficult to meet the requirements of "high drag reduction in the wellbore and long sand-carrying distance" for deep / ultra-deep oil and gas reservoir fracturing. This technical bottleneck has significantly hindered the development of deep and ultra-deep oil and gas resources. Therefore, it is urgent to develop a medium-viscosity slickwater drag reducer with shear resistance, high drag reduction, and high sand-carrying capacity. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a shear-resistant and highly drag-reducing medium-viscosity slickwater drag reducer and a preparation method thereof. The drag reducer is polymerized from acrylamide, a sulfonate ion-containing hydrophobic monomer, a hydrophobic unit microblock regulator, a molecular weight modifier, and a composite initiator. Through the special sulfonate ion-containing hydrophobic monomer, the hydrophobic unit microblock regulator matching the hydrophobic monomer, and the control of the polymer molecular weight, the present invention can significantly improve the polymer solubility and viscosity-increasing performance; improve the anti-shear degradation performance of the drag reducer; have excellent sand-carrying performance and drag reduction performance; overcome the shortcomings of existing drag reducers such as weak anti-shear ability, rapid decline in drag reduction rate, and poor sand-carrying performance, and can meet the special requirements of deep / ultra-deep oil and gas reservoir fracturing for the rheology of the fracturing fluid and "high drag reduction in the wellbore". The invention provides key material support for the development of deep / ultra-deep oil and gas resources and ensures the efficient development goal of deep / ultra-deep oil and gas resources.

[0004] To achieve the above technical effects, the following technical solutions are adopted:

[0005] A shear-resistant and highly drag-reducing medium-viscosity slickwater drag reducer is polymerized from acrylamide, a sulfonate ion-containing hydrophobic monomer, a hydrophobic unit microblock regulator, a molecular weight modifier, and a composite initiator;

[0006] The molecular structure of the drag reducer is as follows:

[0007] ;

[0008] where x, y, and z are the numbers of each repeating unit;

[0009] The molar ratio of the acrylamide to the sulfonate group-containing hydrophobic monomer is 1: 0.001 - 0.003;

[0010] The mass ratio of the hydrophobic unit micro-block regulator to the sulfonate group-containing hydrophobic monomer is 6:1 - 4:1;

[0011] The addition amount of the molecular weight modifier to the mass of the reaction system is 0.0025% - 0.0075%;

[0012] The addition amount of the composite initiator to the mass of the reaction system is 0.0115% - 0.0225%;

[0013] After the polymerization reaction is completed, post-hydrolysis is carried out with sodium hydroxide, and the molar ratio of acrylamide monomer to sodium hydroxide is 1:0.2 - 0.4;

[0014] The structural formula of the sulfonate group-containing hydrophobic monomer is:

[0015] ;

[0016] where the R group is an alkyl group with 14 carbon atoms or an alkyl group with 16 carbon atoms;

[0017] The hydrophobic unit micro-block regulator is one or more of AEO-7 and AEO-9;

[0018] The molecular weight modifier is one or more of sodium formate, sodium hypophosphite, and n-butyl mercaptan;

[0019] The composite initiator is a multi-component initiator, which is composed of an inorganic oxidant, an organic oxidant, a reducing agent, and a water-soluble azo initiator. The inorganic oxidant is a persulfate, and the addition amount is 0.002 - 0.004% of the reaction system; the organic oxidant is an organic hydroperoxide, and the addition amount is 0.001 - 0.003% of the reaction system; the reducing agent is a sulfite and a bisulfite, and the addition amount is 0.0075 - 0.0125% of the reaction system; the addition amount of the water-soluble azo initiator is 0.001 - 0.003% of the reaction system.

[0020] Furthermore, the molecular weight range of the drag reducer is 25 million - 30 million.

[0021] Further, the inorganic oxidant is ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide; the organic oxidant is one or more of tert-butyl hydroperoxide and cumene hydroperoxide.

[0022] Further, the reducing agent is one of sodium sulfite, sodium bisulfite, and sodium metabisulfite.

[0023] Further, the water-soluble azo initiator is one of 2,2'-azobis(2-(2-imidazolin-2-yl)propane) dihydrochloride, 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)acrylamide), and 2,2'-azobis(2-methylpropionamidine) dihydrochloride.

[0024] Further, the composite initiator is tert-butyl hydroperoxide, ammonium persulfate, sodium bisulfite, and 2,2'-azobis(2-(2-imidazolin-2-yl)propane) dihydrochloride.

[0025] Further, the preparation method of the sulfonate ion-containing hydrophobic monomer is as follows:

[0026] Step S1: In a three-necked flask equipped with a magnetic stirrer, a reflux condenser, a thermometer, and two constant pressure dropping funnels, add tetradecylamine or hexadecylamine and a catalyst in sequence. Add a solution of 2-bromoethyl sulfonate or 2-chloroethyl sulfonate in one constant pressure funnel, and add a NaOH solution in the other constant pressure dropping funnel. Control the reaction pH to be weakly alkaline (9-12), and react at a temperature of 50-70 °C for 6-9 h. After the reaction is completed, precipitate in ethanol, and filter to obtain the intermediate 2-tetradecylaminoethanesulfonate or 2-hexadecylaminoethanesulfonate.

[0027] Step S2: Dissolve the intermediate prepared in Step S1 in dichloromethane, and add Na 2 CO 3 as an acid-binding agent; dropwise add acryloyl chloride from the constant pressure dropping funnel, control the temperature at 15-20 °C, after reacting for 18-24 h, distill off dichloromethane under reduced pressure, and then perform recrystallization with ethanol to obtain the target monomer, which is the sulfonate ion-containing hydrophobic monomer.

[0028] Further, in Step S1, the molar ratio of tetradecylamine or hexadecylamine to 2-bromoethyl sulfonate or 2-chloroethyl sulfonate is 1:0.8 - 1:0.9; the catalyst is tetrabutylammonium bromide, and its content is 1% of the mass of tetradecylamine or hexadecylamine; during the reaction, adjust the dropping rate of the NaOH solution according to the change of pH, and control the pH at 9-12; in Step S2, the molar ratio of the intermediate, Na 2 CO 3 , and acryloyl chloride is 1:3:3.

[0029] A preparation method of a shear-resistant high drag reduction medium-viscosity slickwater drag reducer, which is a post-hydrolysis process:

[0030] Feed acrylamide monomer and sulfonate ion-containing hydrophobic monomer according to the formula ratio, and use ultrapure water to prepare a mixed solution with a total monomer mass concentration of 20-35%; add a hydrophobic unit micro-block regulator and a molecular weight grading agent to the mixed solution, then adjust the pH value of the solution to 7.0-9.0, lower the system temperature to 0-5°C, and then add a water-soluble azo initiator and a reducing agent; introduce nitrogen and stir for 30-40 minutes, then add an oxidizing agent, and carry out adiabatic polymerization for 3-8 hours. After the adiabatic polymerization is completed, granulate, hydrolyze, dry, and pulverize to obtain the target polymer.

[0031] Furthermore, the pH value of the solution is adjusted with sodium hydroxide and acetic acid; the pH value of the solution is 8.0-8.5; the system temperature is 0°C; the adiabatic polymerization time is 5-7 hours.

[0032] The present invention discloses a shear-resistant high drag reduction medium-viscosity slickwater drag reducer and its preparation method. The drag reducer is polymerized from acrylamide, sulfonate ion-containing hydrophobic monomer, hydrophobic unit micro-block regulator, molecular weight grading agent and composite initiator. The present invention cooperates with a special sulfonate ion-containing hydrophobic monomer, a hydrophobic unit micro-block regulator matching the hydrophobic monomer and the control of the polymer molecular weight, and carries out synergistic polymerization. The combined action of several polymer substances results in a polymer molecular structure different from the prior art. The difference and superiority of the molecular structure can significantly improve the polymer dissolution performance and viscosity-increasing performance; improve the anti-shear degradation performance of the drag reducer; have excellent sand-carrying performance and drag reduction performance; overcome the disadvantages of the existing drag reducer such as weak anti-shear ability, rapid decline of drag reduction rate, and poor sand-carrying performance, and can meet the special requirements of the rheology of fracturing fluid and "high drag reduction in wellbore" for deep / ultra-deep oil and gas reservoir fracturing. The invention provides key material support for the development of deep / ultra-deep oil and gas resources and ensures the efficient development goal of deep / ultra-deep oil and gas resources. Brief Description of the Drawings

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. The drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0034] Figure 1 It is the H 1 -NMR diagram of the sulfonate ion-containing hydrophobic monomer in the embodiment of the present invention;

[0035] Figure 2It is the HPLC-MS diagram of the sulfonate ion-type hydrophobic monomer in the embodiments of the present invention. Detailed implementation manners

[0036] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further descriptions of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0038] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should also be understood that when the terms "include" and / or "comprise" are used in this specification, they indicate the presence of features, steps, operations and / or combinations thereof.

[0039] First, a sulfonate ion-type hydrophobic monomer is synthesized, and its preparation method is as follows:

[0040] Step S1: In a three-necked flask equipped with a magnetic stirrer, a reflux condenser tube, a thermometer, and two constant-pressure dropping funnels, add tetradecylamine or hexadecylamine and a catalyst (tetrabutylammonium bromide) in sequence. Add a solution of sodium 2-bromoethylsulfonate or sodium 2-chloroethylsulfonate to one of the constant-pressure funnels, and add a NaOH solution to the other constant-pressure dropping funnel. By adjusting the dropping rate of the NaOH solution, control the reaction pH value and react at a temperature of 50-70 °C for 6-9 h. After the reaction is completed, precipitate in ethanol and filter to obtain the intermediate sodium 2-tetradecylaminoethanesulfonate or sodium 2-hexadecylaminoethanesulfonate;

[0041] In the step S1, the molar ratio of tetradecylamine or hexadecylamine to the solution of sodium 2-bromoethylsulfonate or sodium 2-chloroethylsulfonate is 1:0.8-1:0.9; the catalyst is tetrabutylammonium bromide, and its content is 1% of the mass of tetradecylamine or hexadecylamine; control the pH value between 9 and 12 by controlling the dropping rate of the sodium hydroxide solution.

[0042] Step S2: Dissolve the intermediate obtained in the step S1 in dichloromethane, and simultaneously add Na 2 CO 3As an acid-binding agent; acryloyl chloride was added dropwise from a constant-pressure dropping funnel, the temperature was controlled at 20 °C, and after reacting for 18 h, dichloromethane was removed by distillation under reduced pressure, and then recrystallized with ethanol to obtain the target monomer, which was a sulfonate ion-containing hydrophobic monomer (the R group was an alkyl group with C16 or C14); in the step S2, the intermediate, Na 2 CO 3 , and the molar ratio of acryloyl chloride was 1:3:3.

[0043] The 1H-NMR spectrum of the obtained sulfonate ion-containing hydrophobic monomer (the R group was an alkyl group with C14) was as 1 shown; the HPLC-MS spectrum of the sulfonate ion-containing hydrophobic monomer (the R group was an alkyl group with C14) was as Figure 1 shown. Figure 2 shown.

[0044] Example 1

[0045] Acrylamide monomer and sulfonate ion-containing hydrophobic monomer (the R group was an alkyl group with C16) were fed in a ratio of 1:0.002, and a mixed solution with a total monomer mass concentration of 25% was prepared with ultrapure water; hydrophobic unit micro-block regulator AEO-7 was added to the mixed solution, and the addition amount was such that the mass ratio of the hydrophobic unit micro-block regulator to the hydrophobic monomer was 5:1. Sodium formate as a molecular weight modifier was added at 50 ppm, and then the pH value of the solution was adjusted to 8.0 with sodium hydroxide and acetic acid. After adjusting the system temperature to 0 °C, sodium bisulfite at 100 ppm, ammonium persulfate at 30 ppm, and azo initiator 2,2-azobis(2-(2-imidazolin-2-yl)propane) dihydrochloride at 10 ppm were added. After purging with nitrogen and stirring for 30 minutes, tert-butyl hydroperoxide at 20 ppm was added, and adiabatic polymerization was carried out for 3 - 8 h. After the adiabatic polymerization was completed, granulation, hydrolysis (adding sodium hydroxide with a molar mass of 30% of acrylamide, hydrolyzing in a sealed state at 90 °C for 2 hours), drying, and pulverization were carried out to obtain the target polymer. The viscosity-average molecular weight of the high-temperature resistant, salt-resistant and instant-soluble fracturing fluid thickening agent obtained in Example 1 was measured and calculated to be 27 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0046] Example 2

[0047] The method of Example 1 was followed, with the difference being that the addition amount of sodium hydroxide during hydrolysis was 20% of the molar mass of acrylamide. The viscosity-average molecular weight of the high-temperature resistant, salt-resistant and instant-soluble fracturing fluid thickening agent obtained in Example 2 was measured and calculated to be 26.4 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0048] Example 3

[0049] It was carried out according to the method of Example 1, with the difference that the addition amount of sodium hydroxide during hydrolysis was 40% of the molar mass of acrylamide. The viscosity-average molecular weight of the high-temperature and salt-resistant instant fracturing fluid thickening agent obtained in Example 3 was tested and calculated to be 26.5 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0050] Example 4

[0051] It was carried out according to the method of Example 1, with the difference that the acrylamide monomer and the sulfonate group-containing hydrophobic monomer were fed in a ratio of 1:0.003. The viscosity-average molecular weight of the high-temperature and salt-resistant instant fracturing fluid thickening agent obtained in Example 4 was tested and calculated to be 26.7 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0052] Example 5

[0053] It was carried out according to the method of Example 1, with the difference that the acrylamide monomer and the sulfonate group-containing hydrophobic monomer were fed in a ratio of 1:0.001. The viscosity-average molecular weight of the high-temperature and salt-resistant instant fracturing fluid thickening agent obtained in Example 5 was tested and calculated to be 27.1 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0054] Example 6

[0055] It was carried out according to the method of Example 1, with the difference that the mass ratio of the hydrophobic unit micro-block regulator to the hydrophobic monomer was 6:1. The viscosity-average molecular weight of the high-temperature and salt-resistant instant fracturing fluid thickening agent obtained in Example 6 was tested and calculated to be 26.2 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0056] Example 7

[0057] It was carried out according to the method of Example 1, with the difference that the mass ratio of the hydrophobic unit micro-block regulator to the hydrophobic monomer was 4:1. The viscosity-average molecular weight of the high-temperature and salt-resistant instant fracturing fluid thickening agent obtained in Example 7 was tested and calculated to be 26.8 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0058] Example 8

[0059] It was carried out according to the method of Example 1, with the difference that the hydrophobic unit micro-block regulator was replaced with AEO-9. The viscosity-average molecular weight of the high-temperature and salt-resistant instant fracturing fluid thickening agent obtained in Example 8 was tested and calculated to be 27.1 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0060] Comparative Example 1

[0061] It was carried out according to the method of Example 1, with the difference that the R group of the sulfonate ion-type hydrophobic monomer was an alkyl group with 12 carbon atoms. The viscosity-average molecular weight of the high-temperature resistant, salt-resistant and instant-soluble fracturing fluid thickening agent obtained in Comparative Example 1 was measured and calculated to be 27.4 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0062] Comparative Example 2

[0063] It was carried out according to the method of Example 1, with the difference that the R group of the sulfonate ion-type hydrophobic monomer was an alkyl group with 18 carbon atoms. The viscosity-average molecular weight of the high-temperature resistant, salt-resistant and instant-soluble fracturing fluid thickening agent obtained in Comparative Example 2 was measured and calculated to be 26.9 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0064] Comparative Example 3

[0065] It was carried out according to the method of Example 1, with the difference that the hydrophobic monomer was dimethylhexadecylallylammonium chloride. The viscosity-average molecular weight of the high-temperature resistant, salt-resistant and instant-soluble fracturing fluid thickening agent obtained in Comparative Example 3 was measured and calculated to be 27.2 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0066] Comparative Example 4

[0067] It was carried out according to the method of Example 1, with the difference that the mass ratio of the hydrophobic unit micro-block regulator to the hydrophobic monomer was 7:1. The viscosity-average molecular weight of the high-temperature resistant, salt-resistant and instant-soluble fracturing fluid thickening agent obtained in Comparative Example 4 was measured and calculated to be 27.3 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0068] Comparative Example 5

[0069] It was carried out according to the method of Example 1, with the difference that the mass ratio of the hydrophobic unit micro-block regulator to the hydrophobic monomer was 3:1. The viscosity-average molecular weight of the high-temperature resistant, salt-resistant and instant-soluble fracturing fluid thickening agent obtained in Comparative Example 5 was measured and calculated to be 27.5 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0070] Comparative Example 6

[0071] It was carried out according to the method of Example 1, with the difference that the addition amount of the molecular weight modifier sodium formate was increased to 100 ppm. The viscosity-average molecular weight of the high-temperature resistant, salt-resistant and instant-soluble fracturing fluid thickening agent obtained in Comparative Example 6 was measured and calculated to be 20 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0072] Comparative Example 7

[0073] It was carried out according to the method of Example 1, with the difference that: the addition amount of sodium formate as the molecular weight modifier was reduced to 10 ppm. The viscosity-average molecular weight of the high-temperature and salt-resistant instant fracturing fluid thickener obtained in Comparative Example 7 was measured and calculated to be 33 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0074] Comparative Example 8

[0075] It was carried out according to the method of Example 1, with the difference that: the hydrophobic unit micro-block regulator was replaced with AEO-5. The viscosity-average molecular weight of the high-temperature and salt-resistant instant fracturing fluid thickener obtained in Comparative Example 8 was measured and calculated to be 27.2 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0076] Comparative Example 9

[0077] It was carried out according to the method of Example 1, with the difference that: the hydrophobic unit micro-block regulator was replaced with AEO-15. The viscosity-average molecular weight of the high-temperature and salt-resistant instant fracturing fluid thickener obtained in Comparative Example 9 was measured and calculated to be 27.1 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0078] Comparative Example 10

[0079] It was carried out according to the method of Example 1, with the difference that: the hydrophobic unit micro-block regulator was replaced with OP-10. The viscosity-average molecular weight of the high-temperature and salt-resistant instant fracturing fluid thickener obtained in Comparative Example 10 was measured and calculated to be 27.3 million using an Ubbelohde viscometer (0.55 mm tube diameter) according to GB / T 12005.10-92.

[0080] Comparative Example 11

[0081] The difference from Example 1 is that acrylate segments are introduced by a copolymerization process. The specific route is as follows: Acrylamide monomer, sodium acrylate monomer, and a sulfonate ion-containing hydrophobic monomer (with an alkyl group of C16 for the R group) are fed in a ratio of 1:0.3:0.002, and a mixed solution with a total monomer mass concentration of 25% is prepared using ultrapure water. Hydrophobic unit microblock regulator AEO-7 is added to the mixed solution, with the addition amount being a mass ratio of the microblock regulator to the hydrophobic monomer of 5:1. Sodium formate as a molecular weight modifier is added at 50 ppm. Then, the pH value of the solution is adjusted to 8.0 using sodium hydroxide and acetic acid. After adjusting the system temperature to 0 °C, 100 ppm of sodium bisulfite, 30 ppm of ammonium persulfate, and 10 ppm of azo initiator 2,2'-azobis(2-(2-imidazolin-2-yl)propane) dihydrochloride are added. After purging with nitrogen and stirring for 30 minutes, 20 ppm of tert-butyl hydroperoxide is added, and adiabatic polymerization is carried out for 3 - 8 h. After the adiabatic polymerization is completed, granulation, drying, and pulverization are carried out to obtain the target polymer. Using an Ubbelohde viscometer (with a tube diameter of 0.55 mm), the viscosity-average molecular weight of the high-temperature and salt-resistant instant-dissolving fracturing fluid thickener obtained in Comparative Example 11 is tested and calculated according to GB / T 12005.10 - 92 to be 20 million.

[0082] Comparative Example 12

[0083] It is carried out according to the method of Example 1, with the difference that the hydrophobic unit microblock regulator is not added. Using an Ubbelohde viscometer (with a tube diameter of 0.55 mm), the viscosity-average molecular weight of the high-temperature and salt-resistant instant-dissolving fracturing fluid thickener obtained in Example 2 is tested and calculated according to GB / T 12005.10 - 92 to be 27.2 million.

[0084] Comparative Example 13

[0085] It is carried out according to the method of Example 1, with the difference that the azo component is not added to the initiator. The reaction fails, the colloid is very soft, and there is a large amount of unreacted liquid.

[0086] Comparative Example 14

[0087] It is carried out according to the method of Example 1, with the difference that ammonium persulfate is not added to the initiator. The reaction fails, the reaction temperature stops rising after reaching 20 °C, and a large amount of monomers remain unreacted, so the reaction fails.

[0088] Comparative Example 15

[0089] It is carried out according to the method of Example 1, with the difference that tert-butyl hydroperoxide is not added to the initiator. The reaction cannot be initiated, and the polymerization fails.

[0090] Comparative Example 16

[0091] The mainstream high molecular weight drag reducer in the market, partially hydrolyzed polyacrylamide, with a molecular weight of 30 million and a hydrolysis degree of 30%.

[0092] The performance evaluation methods of the polymer solutions in the examples and comparative examples are as follows:

[0093] (1) Measurement of the gelling time

[0094] Add 400 mL of clear water into a 1000 mL beaker respectively. Under the stirring speed of 500 r / min, add samples with a mass fraction of 0.04% respectively, and record the gelling time after adding the thickener (the glass rod can draw filaments). The specific data are shown in Table 1.

[0095] (2) Viscosity increasing performance test

[0096] After stirring in clear water at 25 °C and a rotation speed of 500 r / min for 3 min, use a six-speed viscometer to measure the viscosities at 170 s -1 under the concentrations of 0.04%, 0.05%, 0.06% and 0.07% respectively. The results are shown in Table 1. Then, through fitting and concentration adjustment, find the concentrations corresponding to the viscosities of 5 mPa·s and 10 mPa·s for each sample. The results are shown in Table 2.

[0097] Table 1 Gelling time and viscosity increasing performance of samples

[0098]

[0099] For the comparative polymer that fails to meet the standards in the viscosity increasing test and gelling time test, no other performance evaluations are carried out.

[0100] Table 2 Concentrations corresponding to the viscosities of 5 mPa·s and 10 mPa·s of samples

[0101]

[0102] (3) Drag reduction performance

[0103] Test the drag reduction rates of the examples and comparative examples, and perform according to the regulations for measuring the drag reduction rate in Chapter 7.8 of SY-T 7627-2021. Take the 5-min drag reduction rate data as the drag reduction rate value, as shown in Table 3.

[0104] Table 3 Drag reduction rates corresponding to the viscosities of 5 mPa·s and 10 mPa·s of samples

[0105]

[0106] (4) Sand-carrying performance

[0107] Prepare a target solution of approximately 400 mL with a 1000 mL capacity. During sample preparation, stir at a speed of 500 r / min for 3 min. Pour 100 mL of the test solution into a 100 mL graduated cylinder, and then measure the sedimentation rate of 20 / 40 mesh ceramsite in the graduated cylinder. Repeat the measurement of the sedimentation rate of 20 ceramsites and then take the average value, as shown in Table 4.

[0108] Table 4 Sedimentation velocities corresponding to sample viscosities of 5 mPa·s and 10 mPa·s

[0109]

[0110] (5)Shear resistance

[0111] Prepare a target solution of approximately 400 mL in a 1000 mL capacity beaker. During sample preparation, stir at a speed of 500 r / min for 3 min. Take 300 mL of the test solution and measure the viscosity value (mPa·s) at 170 s using a six-speed rotational viscometer. After the test, pour it into a WARING blender and shear it at a speed of 3000 r / min for 5 min, then measure the viscosity after shearing. Finally, calculate the viscosity retention value before and after shearing, as shown in Table 5. -1 The viscosity value (mPa·s) at 170 s is measured, and after the test, it is poured into a WARING blender and sheared at a speed of 3000 r / min for 5 min, then the viscosity after shearing is measured. Finally, calculate the viscosity retention value before and after shearing, as shown in Table 5.

[0112] Table 5 Viscosity shear retention rates corresponding to sample viscosities of 5 mPa·s and 10 mPa·s

[0113]

[0114] In summary, the present invention discloses a shear-resistant high drag reduction medium-viscosity slickwater drag reducer and its preparation method. The drag reducer is polymerized from acrylamide, a sulfonate ion-containing hydrophobic monomer, a hydrophobic unit micro-block regulator, a molecular weight modifier, and a composite initiator. Through the cooperation of a special sulfonate ion-containing hydrophobic monomer, a hydrophobic unit micro-block regulator matching the hydrophobic monomer, and the control of the polymer molecular weight, the present invention achieves synergistic polymerization. The combined action of several polymer substances results in a polymer molecular structure different from the prior art. The difference and superiority of the molecular structure can significantly improve the polymer dissolution performance and viscosity-increasing performance; improve the anti-shear degradation performance of the drag reducer; have excellent sand-carrying performance and drag reduction performance; overcome the shortcomings of existing drag reducers such as weak anti-shear ability, rapid decline of drag reduction rate, and poor sand-carrying performance, and can meet the special requirements of fracturing fluid rheology and "high drag reduction in the wellbore" for deep / ultra-deep oil and gas reservoirs. This invention provides key material support for the development of deep / ultra-deep oil and gas resources and ensures the efficient development goal of deep / ultra-deep oil and gas resources.

[0115] At this point, those skilled in the art will recognize that although the embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived from the disclosed content of the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and construed as covering all such other variations or modifications.

Claims

1. A shear-resistant, high-drag-reducing, medium-viscosity, slippery water drag reducer, characterized in that: The drag reducer is formed by polymerization reaction of acrylamide, sulfonate ion-containing hydrophobic monomer, hydrophobic unit microblock regulator, molecular weight regulator and composite initiator; The molecular structure of the drag reducer is: ； Wherein, x, y, z are the number of each repeating unit; The molar ratio of acrylamide to sulfonate ion-containing hydrophobic monomer is 1: 0.001-0.003; The mass ratio of the hydrophobic unit microblock regulator to the sulfonate ion-containing hydrophobic monomer is 6:1-4:1; The mass ratio of molecular weight regulator to reaction system is 0.0025%-0.0075%; The mass ratio of the composite initiator to the reaction system is 0.0115%-0.0225%; After the polymerization reaction is completed, sodium hydroxide is used for post-hydrolysis, and the molar ratio of acrylamide monomer to sodium hydroxide is 1:0.2-0.4; The structural formula of the sulfonate ion-containing hydrophobic monomer is: ; Wherein, the R group is a C14 alkyl group or a C16 alkyl group; The hydrophobic unit microblock regulator is one or more of AEO-7 and AEO-9; The molecular weight regulator is one or more of sodium formate, sodium hypophosphite, and n-butyl mercaptan; The composite initiator is a multi-element initiator, which is composed of an inorganic oxidant, an organic oxidant, a reducing agent, and a water-soluble azo initiator. The inorganic oxidant is a persulfate, and the amount added is 0.002-0.004% of the reaction system; the organic oxidant is an organic hydrogen peroxide, and the amount added is 0.001-0.003% of the reaction system; the reducing agent is sodium sulfite or sodium bisulfite, and the amount added is 0.0075-0.0125% of the reaction system; the amount of the water-soluble azo initiator added is 0.001-0.003% of the reaction system; The molecular weight of the drag reducer ranges from 26.2 to 30 million.

2. A shear-resistant, high-drag-reducing, medium-viscosity, slippery water drag reducer as claimed in claim 1, characterized in that: The inorganic oxidant is one of ammonium persulfate, sodium persulfate and potassium persulfate; the organic oxidant is one or more of tert-butyl hydroperoxide and isopropylbenzene hydroperoxide.

3. A shear-resistant, high-drag-reducing, medium-viscosity, slippery water drag reducer as claimed in claim 1, characterized in that: The water-soluble azo initiator is one of 2,2-azo(2-(2-imidazoline-2-yl)propane) dihydrochloride, 2,2-azo(2-methyl-N-(2-hydroxyethyl)acrylamide), and 2,2-azobis(2-methylpropane) hydrochloride.

4. A shear-resistant, high-drag-reducing, medium-viscosity, slippery water drag reducer as claimed in claim 1, characterized in that: The composite initiator is tert-butyl hydroperoxide, ammonium persulfate, sodium bisulfite, and 2,2-azo(2-(2-imidazoline-2-yl)propane) dihydrochloride.

5. A shear-resistant, high-drag-reducing, medium-viscosity, slippery water drag reducer as claimed in claim 1, characterized in that: The preparation method of the sulfonate ion-containing hydrophobic monomer is as follows: Step S1: in a three-necked flask equipped with a magnetic stirrer, a reflux cold flow tube, a thermometer, and two constant pressure dropping funnels, tetradecylamine or hexadecylamine and a catalyst are added in sequence, 2-sodium bromoethylsulfonate or 2-sodium chloroethylsulfonate solution is added to one of the constant pressure dropping funnels, and NaOH solution is added to the other constant pressure dropping funnel; by adjusting the dropping speed of the NaOH solution, the pH value of the reaction is controlled, and the reaction is carried out at a temperature of 50-70° C. for 6-9 hours; after the reaction is completed, a precipitate is precipitated in ethanol, and filtered to obtain an intermediate sodium 2-tetradecylaminoethanesulfonate or sodium 2-hexadecylaminoethanesulfonate; Step S2: dissolving the intermediate obtained in step S1 in dichloromethane, and adding Na2CO3 as an acid binding agent; dropping acryloyl chloride from a constant pressure dropping funnel, controlling the temperature at 15-20°C, reacting for 18-24 hours, removing dichloromethane by reduced pressure distillation, and then recrystallizing with ethanol to obtain the target monomer, which is a sulfonate ion-containing hydrophobic monomer.

6. A shear-resistant, high-drag-reducing, medium-viscosity, slippery water drag reducer as claimed in claim 5, characterized in that: In the step S1, the molar ratio of tetradecylamine or hexadecylamine to sodium 2-bromoethylsulfonate or sodium 2-chloroethylsulfonate is 1:0.8-1:0.9; the catalyst is tetrabutylammonium bromide, and its content is 1% of the mass of tetradecylamine or hexadecylamine; during the reaction, the dropping speed of the NaOH solution is adjusted according to the pH change to control the pH value at 9-12; in the step S2, the molar ratio of the intermediate, Na2CO3, and acryloyl chloride is 1:3:

3.

7. The method for preparing a shear-resistant, high-drag-reducing, medium-viscosity and slippery water drag reducer according to any one of claims 1 to 6, characterized in that: The preparation method is: The acrylamide monomer and the sulfonate ion-containing hydrophobic monomer are added according to the formula ratio, and ultrapure water is used to prepare a mixed solution with a total monomer mass concentration of 20-35%; the hydrophobic unit microblock regulator and the molecular weight regulator are added to the mixed solution, and then the pH value of the solution is adjusted to 7.0-9.0, and the system temperature is lowered to 0-5°C and then a water-soluble azo initiator and a reducing agent are added; nitrogen is introduced and stirred for 30-40 minutes, and then an oxidant is added, and adiabatic polymerization is carried out for 3-8 hours. After the adiabatic polymerization is completed, granulation, hydrolysis, drying, and crushing are carried out to obtain a target polymer.

8. The preparation method as claimed in claim 7, characterized in that The pH value of the solution is adjusted by sodium hydroxide and acetic acid; the pH value of the solution is 8.0-8.5; the system temperature is 0° C.; and the adiabatic polymerization time is 5-7 hours.

Images