Copolymer and preparation method therefor, copolymer fiber composition, fracturing fluid, and use

Abstract

The present invention relates to the technical field of gas reservoir production. Disclosed are a copolymer and a preparation method therefor, a polylactic acid fiber and a preparation method therefor, a copolymer fiber composition, a fracturing fluid, and a use. The copolymer comprises a structural unit A as represented by formula 1, a structural unit B as represented by formula 2, a structural unit C as represented by formula 3 and / or formula 4, and a structural unit D as represented by formula 5 and / or formula 6; based on the total weight of the copolymer, the content of the structural unit A is 40-60 wt%, the content of the structural unit B is 20-30 wt%, the content of the structural unit C is 15-20 wt%, and the content of the structural unit D is 5-25 wt%. The copolymer has excellent salt resistance, high temperature resistance, and stability. A fracturing fluid system comprising the copolymer can be applied to a high-temperature deep well having the highest temperature of 158℃.

Description

Copolymer and preparation method thereof, copolymer fiber composition and fracturing fluid and application thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Chinese patent application No. 202310967300.6, filed on August 2, 2023, entitled “Copolymer and preparation method thereof, polylactic acid fiber and preparation method thereof, copolymer fiber composition and fracturing fluid and application thereof,” the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of gas reservoir exploitation, and in particular to a copolymer and a preparation method thereof, a copolymer fiber composition, a fracturing fluid and applications thereof. Background Art

[0004] With the rapid global demand for oil and natural gas, the focus is shifting from conventional reservoirs to the exploration and development of deep, high-temperature reservoirs. However, as reservoir geology becomes increasingly complex, reservoir transformation becomes increasingly difficult. Fracturing is a key technical measure for reservoir stimulation and transformation, and fracturing fluid is a crucial component of the fracturing process. Selecting the right, high-performance fracturing fluid is crucial for achieving reservoir fracturing transformation.

[0005] Currently, fracturing fluids commonly used both domestically and internationally fall into two categories: natural plant-based guar gum fracturing fluids and synthetic polymer-based fracturing fluid systems. Guar gum fracturing fluids offer high viscosity and excellent sand-carrying properties, but they also suffer from high pipeline friction and high residue content, which can significantly damage reservoir formations. Furthermore, increasing the guar gum dosage to improve the fluid's heat resistance significantly increases material costs. The slickwater system in polymer fracturing fluids is capable of creating large-scale, complex fracture networks and connecting natural fractures in formations, making it the primary fracturing fluid for volumetric fracturing of unconventional oil and gas reservoirs. However, conventional slickwater systems are not heat-resistant and have poor sand-carrying properties, making them ineffective in carrying proppant into fractures to form effective fracture pathways. CN108841370A uses the reverse microemulsion method to prepare a polymer thickener and introduces polyvinyl acetal high-strength fibers to increase the sand-carrying performance of the fracturing fluid. It can be used for fracturing and reconstruction of medium- and low-temperature reservoirs (below 70°C). However, the problem of poor temperature resistance of slick water fracturing fluid still exists. In addition, designated equipment must be configured at the construction site to dissolve and disperse the fibers. The poor fiber dispersion performance seriously reduces the efficiency of the fiber fracturing fluid.

[0006] Summary of the Invention

[0007] The present invention aims to overcome the problem in the prior art that deep-well high-temperature reservoir fracturing fluids have difficulty in achieving high-temperature resistance, easy sand carrying, low friction, easy flowback, and low damage. The present invention provides a copolymer and a preparation method thereof, a polylactic acid fiber and a preparation method thereof, a copolymer fiber composition, a fracturing fluid, and applications thereof. The copolymer has salt-resistant and high-temperature resistant functional groups and a rigid structure. The fracturing fluid system containing the copolymer, on the basis of salt and high-temperature resistance, has the excellent properties of easy sand carrying, high sand carrying capacity, low friction, easy flowback, and low damage. In addition, the fracturing fluid flowback fluid is recyclable, conforming to the green and sustainable development strategy, and has low production costs.

[0008] In order to achieve the above object, the first aspect of the present invention provides a copolymer, wherein the copolymer contains a structural unit A represented by formula 1, a structural unit B represented by formula 2, a structural unit C represented by formula 3 and / or formula 4, and a structural unit D represented by formula 5 and / or formula 6.

[0009] Wherein, in formula 1, R1 is hydrogen or methyl;

[0010] In formula 2, R2 is hydrogen or methyl;

[0011] In formula 3, R3 is hydrogen or methyl; R4 is wherein R5 and R5' are each independently hydrogen or methyl;

[0012] In formula 4, R6 is hydrogen or methyl; R7 is methyl, benzyl or where R 13 is methylene, C2-C6 straight or branched alkylene; n is an integer of 1-4;

[0013] In formula 5, R8 is hydrogen or methyl; R9 is Among them, R 14 C 10 -C 20 A straight or branched chain alkyl group;

[0014] In formula 6, R 10 is hydrogen or methyl, R 11 for

[0015] Based on the total weight of the copolymer, the content of structural unit A is 40-60 wt%, the content of structural unit B is 20-30 wt%, the content of structural unit C is 15-20 wt%, and the content of structural unit D is 5-25 wt%.

[0016] A second aspect of the present invention provides a method for preparing a copolymer, wherein the preparation method comprises:

[0017] (1) first mixing monomer 1, monomer 2, monomer 3, and water to obtain an aqueous solution; wherein monomer 1 has a structure shown in formula I, monomer 2 has a structure shown in formula II, and monomer 3 has a structure shown in formula III and / or formula IV;

[0018] (2) in the presence of a first solvent, performing a second mixing of monomer 4 and an emulsifier to obtain an oil phase solution; wherein the monomer 4 has a structure represented by formula V and / or formula VI;

[0019] (3) in the presence of a protective atmosphere and an initiator, the aqueous phase solution and the oil phase solution are subjected to a third mixing and polymerization to obtain the copolymer;

[0020] Wherein, in formula I, R1 is hydrogen or methyl;

[0021] In formula II, R2 is hydrogen or methyl;

[0022] In formula III, R3 is hydrogen or methyl; R4 is wherein R5 and R5' are each independently hydrogen or methyl;

[0023] In formula IV, R6 is hydrogen or methyl; R7 is methyl, benzyl or where R 13 is methylene, C2-C6 straight or branched alkylene; n is an integer of 1-4;

[0024] In formula V, R8 is hydrogen or methyl; R9 is Among them, R 14 C 10 -C 20 A straight or branched chain alkyl group;

[0025] In formula VI, R 10 is hydrogen or methyl, R 11 for

[0026] Wherein, based on the total mass of monomer 1, monomer 2, monomer 3 and monomer 4, the content of monomer 1 is 40-60wt%, the content of monomer 2 is 20-30wt%, the content of monomer 3 is 15-20wt%, and the content of monomer 4 is 5-25wt%.

[0027] The third aspect of the present invention provides a copolymer prepared by the above preparation method.

[0028] A fourth aspect of the present invention provides a polylactic acid fiber, wherein the polylactic acid fiber comprises polylactic acid nanospheres and polylactic acid microfibers;

[0029] Wherein, the weight ratio of the polylactic acid nanospheres to the polylactic acid microfibers is 1:0.3-3;

[0030] Wherein, the average particle size of the polylactic acid nanospheres is 122-143 nm;

[0031] The average length of the polylactic acid micron fiber is 700-800 μm, and the average diameter is 600-800 nm.

[0032] A fifth aspect of the present invention provides a method for preparing the above-mentioned polylactic acid fiber, wherein the method for preparing the polylactic acid nanospheres comprises:

[0033] (1) dissolving polylactic acid in an organic solvent 1 under ultrasonic conditions to obtain an organic phase 1;

[0034] (2) adding the organic phase 1 of step (1) into water and mixing to obtain the polylactic acid nanospheres;

[0035] The ultrasonic conditions in step (1) include: ultrasonic time of 10-30 min, ultrasonic power of 500-900 W, and temperature of 20-30° C.

[0036] A sixth aspect of the present invention provides a copolymer fiber composition, wherein the copolymer fiber composition comprises the above copolymer, the above polylactic acid fiber or the polylactic acid fiber prepared by the above preparation method, a surfactant and a polymerization inhibitor;

[0037] Wherein, the copolymer fiber composition comprises:

[0038] 85-95 parts by weight of the copolymer;

[0039] 0.5-1.5 parts by weight of the polylactic acid fiber;

[0040] 5-10 parts by weight of the surfactant;

[0041] The polymerization inhibitor is 0.05-0.1 parts by weight.

[0042] A seventh aspect of the present invention provides a fracturing fluid, wherein the fracturing fluid comprises the above-mentioned copolymer fiber composition, a breaker and water;

[0043] Wherein, the fracturing fluid comprises:

[0044] 0.5-1.5 parts by weight of the copolymer fiber composition;

[0045] The gel breaker is 0.1-0.5 parts by weight.

[0046] An eighth aspect of the present invention provides a use of the above-mentioned fracturing fluid in reservoir exploration and development.

[0047] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0048] (1) The copolymer prepared by the present invention has salt-resistant and high-temperature-resistant functional groups and a rigid structure, so that the copolymer has excellent salt resistance, high-temperature resistance and stability.

[0049] (2) The polylactic acid fiber provided by the present invention uses polylactic acid nanospheres and polylactic acid micron fibers in a specific weight ratio. When applied to a fracturing fluid system, it can ensure the sand-carrying performance of the solution and the uniform dispersion of the solute.

[0050] (3) The fracturing fluid provided by the present invention is easy to flow back, which can reduce the damage of the fracturing fluid to the reservoir, and can quickly dissolve and thicken without the need for pre-mixing of the fluid. It meets the technical requirements of large-volume and large-scale fracturing construction and can be applied to high-temperature deep wells with a maximum temperature of 158°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG1 is a graph showing the temperature and shear resistance of the fracturing fluid in Application Example 1. DETAILED DESCRIPTION

[0052] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0053] The first aspect of the present invention provides a copolymer, wherein the copolymer contains a structural unit A represented by formula 1, a structural unit B represented by formula 2, a structural unit C represented by formula 3 and / or formula 4, and a structural unit D represented by formula 5 and / or formula 6.

[0054] Wherein, in Formula 1, R1 is hydrogen or methyl;

[0055] In formula 2, R2 is hydrogen or methyl;

[0056] In formula 3, R3 is hydrogen or methyl; R4 is wherein R5 and R5' are each independently hydrogen or methyl;

[0057] In formula 4, R6 is hydrogen or methyl; R7 is methyl, benzyl or where R 13 is methylene, C2-C6 straight or branched alkylene; n is an integer of 1-4;

[0058] In formula 5, R8 is hydrogen or methyl; R9 is Among them, R 14 C 10 -C 20 A straight or branched chain alkyl group;

[0059] In formula 6, R 10 is hydrogen or methyl, R 11 for

[0060] Based on the total weight of the copolymer, the content of structural unit A is 40-60 wt%, the content of structural unit B is 20-30 wt%, the content of structural unit C is 15-20 wt%, and the content of structural unit D is 5-25 wt%.

[0061] The content of each structural unit in the copolymer provided by the present invention can be obtained by nuclear magnetic resonance, infrared and other detection methods, or determined by the monomers and the monomer feed amount during preparation.

[0062] In the present invention, structural unit A and structural unit B are water-soluble and can improve the solubility and thickening properties of the copolymer. Structural unit C having salt-resistant and high-temperature-resistant functional groups provides the copolymer with salt-resistant and high-temperature-resistant properties. Structural unit D having a rigid structure brings structural stability to the copolymer. The specific content of structural unit A, structural unit B, structural unit C and structural unit D makes the copolymer have both salt-resistant and high-temperature-resistant properties and structural stability.

[0063] Further, according to the present invention, based on the total weight of the copolymer, the content of structural unit A is 45-55wt%, the content of structural unit B is 20-25wt%, the content of structural unit C is 15-18wt%, and the content of structural unit D is 5-17wt%.

[0064] In the present invention, the contents of structural unit A, structural unit B, structural unit C and structural unit D in the copolymer are within the above ranges, and the copolymer has better salt and high temperature resistance and structural stability.

[0065] According to the present invention, in Formula 1, R1 is hydrogen.

[0066] According to the present invention, in Formula 2, R2 is hydrogen.

[0067] According to the present invention, in Formula 3, R3 is hydrogen; R4 is

[0068] Further, according to the present invention, R5 and R5' are methyl groups.

[0069] According to the present invention, in Formula 4, R6 is hydrogen or methyl; R7 is methyl or benzyl, and n is 2 or 3.

[0070] Further, according to the present invention, R6 is a methyl group, R7 is a methyl group, and n is 2 or 3.

[0071] According to the present invention, in Formula 5, R8 is hydrogen; R9 is Among them, R 14 C 15 -C 20 A straight chain or branched chain alkyl group.

[0072] Further, according to the present invention, R 14 for

[0073] According to the present invention, in Formula 6, R 10 is hydrogen, R 11 for

[0074] In one embodiment of the present invention, preferably, the copolymer is selected from one of the following copolymer combinations:

[0075] Copolymer-1: The structural unit A is derived from acrylamide (the structural formula is shown in Formula 1, R1 is hydrogen), the structural unit B is derived from acrylic acid (the structural formula is shown in Formula 2, R2 is hydrogen), and the structural unit C is derived from N,N-dimethylacrylamide (the structural formula is shown in Formula 3, R3 is hydrogen, R4 is R5 and R5' are methyl), the structural unit D is derived from octadecyldimethylpropyleneammonium chloride (the structural formula is shown in Formula 5, R8 is hydrogen, R9 is Among them, R 14 for );

[0076] Copolymer-2: The structural unit A is derived from acrylamide (the structural formula is shown in Formula 1, R1 is hydrogen), the structural unit B is derived from acrylic acid (the structural formula is shown in Formula 2, R2 is hydrogen), the structural unit C is derived from methacryloyloxyethyl trimethylammonium chloride (the structural formula is shown in Formula 4, R6 is methyl, R7 is methyl, and n is 2), and the structural unit D is derived from sodium 4-acrylamidobenzenesulfonate (the structural formula is shown in Formula 6, R 10 is hydrogen, R 11 for );

[0077] According to the present invention, the weight average molecular weight of the copolymer is 8 million g / mol to 10 million g / mol, preferably 8.5 million g / mol to 9 million g / mol.

[0078] A second aspect of the present invention provides a method for preparing a copolymer, wherein the preparation method comprises:

[0079] (1) first mixing monomer 1, monomer 2, monomer 3, and water to obtain an aqueous solution; wherein monomer 1 has a structure shown in formula I, monomer 2 has a structure shown in formula II, and monomer 3 has a structure shown in formula III and / or formula IV;

[0080] (2) in the presence of a first solvent, performing a second mixing of monomer 4 and an emulsifier to obtain an oil phase solution; wherein the monomer 4 has a structure represented by formula V and / or formula VI;

[0081] (3) in the presence of a protective atmosphere and an initiator, the aqueous phase solution and the oil phase solution are subjected to a third mixing and polymerization to obtain the copolymer;

[0082] Wherein, in formula I, R1 is hydrogen or methyl;

[0083] In formula II, R2 is hydrogen or methyl;

[0084] In formula III, R3 is hydrogen or methyl; R4 is wherein R5 and R5' are each independently hydrogen or methyl;

[0085] In formula IV, R6 is hydrogen or methyl; R7 is methyl, benzyl or where R 13 is methylene, C2-C6 straight or branched alkylene; n is an integer of 1-4;

[0086] In formula V, R8 is hydrogen or methyl; R9 is Among them, R 14 C 10 -C 20 A straight or branched chain alkyl group;

[0087] In formula VI, R 10 is hydrogen or methyl, R 11 for

[0088] Wherein, based on the total mass of monomer 1, monomer 2, monomer 3 and monomer 4, the content of monomer 1 is 40-60wt%, the content of monomer 2 is 20-30wt%, the content of monomer 3 is 15-20wt%, and the content of monomer 4 is 5-25wt%.

[0089] Further, according to the present invention, based on the total mass of monomer 1, monomer 2, monomer 3 and monomer 4, the content of monomer 1 is 45-55wt%, the content of monomer 2 is 20-25wt%, the content of monomer 3 is 15-18wt%, and the content of monomer 4 is 5-17wt%.

[0090] According to the present invention, in formula I, R1 is hydrogen.

[0091] According to the present invention, in formula II, R2 is hydrogen.

[0092] According to the present invention, in formula III, R3 is hydrogen; R4 is R5 and R5' are methyl groups.

[0093] According to the present invention, in formula IV, R6 is hydrogen or methyl; R7 is methyl or benzyl, and n is 2 or 3.

[0094] According to the present invention, in formula V, R8 is hydrogen; R9 is Among them, R 14 C 15 -C 20 A straight chain or branched chain alkyl group.

[0095] According to the present invention, in formula VI, R 10 is hydrogen, R 11 for

[0096] In one embodiment of the present invention, the monomer 1 is acrylamide (structural formula is shown in Formula I, R1 is hydrogen).

[0097] In a specific embodiment of the present invention, the monomer 2 is acrylic acid (structural formula is shown in Formula II, R2 is hydrogen).

[0098] In one embodiment of the present invention, the monomer 3 is selected from N,N-dimethylacrylamide (the structural formula is shown in Formula III, R3 is hydrogen, R4 is At least one of 2-(acryloyloxy)-N-benzyl-N,N-dimethylethane-1-ammonium chloride (the structural formula is shown in Formula IV, R6 is a methyl group, R7 is a methyl group, and n is 2), methacryloyloxypropyltrimethylammonium chloride (the structural formula is shown in Formula IV, R6 is a methyl group, R7 is a methyl group, and n is 3), acryloyloxyethyltrimethylammonium chloride (the structural formula is shown in Formula IV, R6 is a hydrogen group, R7 is a methyl group, and n is 2), and 2-(acryloyloxy)-N-benzyl-N,N-dimethylethane-1-ammonium chloride (the structural formula is shown in Formula IV, R6 is a hydrogen group, R7 is a benzyl group, and n is 2).

[0099] In one embodiment of the present invention, the monomer 4 is selected from octadecyldimethylpropyleneammonium chloride (structural formula as shown in formula V, R8 is hydrogen, R9 is Among them, R 14 for ) and / or sodium 4-acrylamide benzenesulfonate (structural formula as shown in formula VI, R 10 is hydrogen, R 11 for ).

[0100] According to the present invention, the first mixing condition in step (1) includes: adjusting the pH to 6-7, the temperature to 20-30° C., and the time to 0.5-2 h.

[0101] According to the present invention, the second mixing conditions in step (2) include: a stirring rate of 1000-1500 r / min, a stirring temperature of 20-30° C., and a stirring time of 10-30 min.

[0102] According to the present invention, the third mixing condition in step (3) includes: a stirring rate of 1000-1600 r / min, a stirring temperature of 20-30° C., and a stirring time of 5-30 min.

[0103] According to the present invention, the polymerization reaction conditions in step (3) include: temperature of 36-45° C. and time of 2-3 h.

[0104] According to the present invention, the polymerization in step (3) further comprises: adding a second solvent or an initiator so that the polymerization reaction temperature is 36-45°C.

[0105] According to the present invention, the concentration of monomer 1 in the aqueous solution is 30-40 wt%.

[0106] According to the present invention, there is no particular limitation on the concentration of the monomer 4 in the oil phase solution, as long as the monomer 4 and the emulsifier can be fully mixed.

[0107] According to the present invention, based on the total mass of monomers, emulsifier and initiator, the content of monomer 1, monomer 2, monomer 3 and monomer 4 is 90-98.2wt%, the content of initiator is 0.2-1.2wt%, and the content of emulsifier is 1.6-9wt%.

[0108] In the present invention, the total mass of monomers is the sum of the masses of monomer 1, monomer 2, monomer 3 and monomer 4.

[0109] In the present invention, the content of the initiator is the total mass of the initiator in step (3).

[0110] According to the present invention, the initiator is at least one of an azo initiator, a peroxide initiator and a redox initiator, preferably at least one of azobisisobutyronitrile, benzoyl peroxide, potassium persulfate, tert-butyl hydroperoxide, sodium sulfite and sodium bisulfite.

[0111] According to the present invention, the initiator is at least one of azobisisobutyronitrile, benzoyl peroxide, tert-butyl hydroperoxide-sodium bisulfite composite system and potassium persulfate-sodium sulfite composite system.

[0112] In one embodiment of the present invention, the weight ratio of tert-butyl hydroperoxide to sodium bisulfite is 1:0.3-0.5.

[0113] In one embodiment of the present invention, the weight ratio of potassium persulfate to sodium sulfite is 1:1-2.

[0114] According to the present invention, the first solvent is at least one of kerosene, diesel, white oil, cyclohexane, benzene, toluene and petroleum ether.

[0115] According to the present invention, the emulsifier is a nonionic surfactant, preferably at least one of sorbitan monostearate (Span 60), sorbitan oleate (Span 80), polyoxyethylene sorbitan monostearate (Tween 60), polysorbate 80 (Tween 80) and dodecylphenol polyoxyethylene ether (OP-10).

[0116] According to the present invention, the emulsifier is selected from one of Span 60 / Span 80 compound emulsifier, Tween 60 / Tween 80 compound emulsifier, Span80 / OP-10 compound emulsifier or Tween80 / OP-10 compound emulsifier.

[0117] In a specific embodiment of the present invention, the mass ratio of Span 60 to Span 80 is 1:1-2, the mass ratio of Tween 60 to Tween 80 is 1:0.6-1, the mass ratio of Span 80 to OP-10 is 1:1-2, and the mass ratio of Tween 80 to OP-10 is 1:1-2.

[0118] In the present invention, a compound emulsifier is selected to achieve better emulsification effect and more excellent dispersibility.

[0119] According to the present invention, the second solvent is water.

[0120] The third aspect of the present invention provides a copolymer prepared by the above preparation method.

[0121] In the present invention, the copolymer prepared by the above preparation method can be applied to a reservoir fracturing fluid system, and can improve the high temperature resistance, salt resistance and shear resistance of the fracturing fluid system.

[0122] A fourth aspect of the present invention provides a polylactic acid fiber, wherein the polylactic acid fiber comprises polylactic acid nanospheres and polylactic acid microfibers;

[0123] Wherein, the weight ratio of the polylactic acid nanospheres to the polylactic acid microfibers is 1:0.3-3;

[0124] Wherein, the average particle size of the polylactic acid nanospheres is 122-143 nm;

[0125] The average length of the polylactic acid micron fiber is 700-800 μm, and the average diameter is 600-800 nm.

[0126] In the present invention, the content of the L-isomer of the polylactic acid used as the raw material of the polylactic acid nanospheres and the polylactic acid microfibers is 90-99 wt %.

[0127] In the present invention, the polylactic acid fiber comprising polylactic acid nanospheres and polylactic acid micron fibers in a specific weight ratio is applied to a fracturing system to ensure uniform dispersion of the solution and improve sand carrying performance.

[0128] A fifth aspect of the present invention provides a method for preparing the above-mentioned polylactic acid fiber, the method comprising: mixing polylactic acid nanospheres and polylactic acid microfibers; wherein the method for preparing the polylactic acid nanospheres comprises:

[0129] (1) dissolving polylactic acid in an organic solvent 1 under ultrasonic conditions to obtain an organic phase 1;

[0130] (2) adding the organic phase 1 of step (1) into water and mixing to obtain the polylactic acid nanospheres;

[0131] The ultrasonic conditions in step (1) include: ultrasonic time of 10-30 min, ultrasonic power of 500-900 W, and temperature of 20-30° C.

[0132] In the present invention, the polylactic acid nanospheres obtained under specific ultrasonic and mixing conditions have different sizes, and the polylactic acid fibers composed of the polylactic acid nanospheres are applied to the fracturing fluid system, so that the fracturing fluid system is evenly dispersed.

[0133] According to the present invention, the mixing conditions in step (2) include: a stirring speed of 500-700 r / min and a stirring temperature of 20-30°C.

[0134] According to the present invention, the organic solvent 1 is a mixed solution of ethanol and acetone.

[0135] According to the present invention, the volume ratio of ethanol to acetone is 1:1-3.

[0136] According to the present invention, the polylactic acid fiber has a L-isomer content of 90-99 wt%.

[0137] In the preparation method of the polylactic acid nanospheres of the present invention, the polylactic acid can be prepared by the following method:

[0138] (1) Lactic acid and stannous chloride are mixed under anhydrous and oxygen-free conditions, and reacted at 120-150° C. for 5-10 hours to obtain a mixture 1;

[0139] (2) dissolving the mixture in chloroform, adding methanol, mixing, and drying to obtain the polylactic acid.

[0140] According to the present invention, in the method for preparing polylactic acid, the weight ratio of stannous chloride to lactic acid is 1:3000-5000.

[0141] According to the present invention, in the preparation method of polylactic acid, in step (1), stannous chloride is prepared into a 0.05-0.2 wt% solution and then mixed with lactic acid, wherein the solvent of the solution is chloroform.

[0142] According to the present invention, in the method for preparing polylactic acid, there is no particular limitation on the amount of chloroform used, as long as the mixture 1 is fully dissolved.

[0143] According to the present invention, in the method for preparing polylactic acid, in step (2), the mixing conditions include: until a large amount of white fibrous matter appears.

[0144] According to the present invention, in the method for preparing polylactic acid, the drying conditions include: a temperature of 80-100° C. and a time of 5-10 hours, until the polylactic acid reaches a constant weight.

[0145] In the present invention, the polylactic acid micron fiber can be prepared by the following method:

[0146] Pour 5-10wt% polylactic acid dichloromethane solution into the spinning tube, spin at a spinning distance of 15-20cm between the receiving screen and the spinneret, a spinning flow of 0.1-0.3mL / h and a spinning voltage of 7-15kV, and dry at 20-30℃ to obtain polylactic acid micron fibers.

[0147] The sixth aspect of the present invention provides a copolymer fiber composition, wherein the copolymer fiber composition comprises the copolymer described in the first or third aspect, polylactic acid fiber, a surfactant, and a polymerization inhibitor;

[0148] Wherein, the copolymer fiber composition comprises:

[0149] 85-95 parts by weight of the copolymer;

[0150] 0.5-1.5 parts by weight of the polylactic acid fiber;

[0151] 5-10 parts by weight of the surfactant;

[0152] The polymerization inhibitor is 0.05-0.1 parts by weight.

[0153] According to the present invention, in the copolymer fiber composition, the surfactant is selected from at least one of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether and dodecylphenol polyoxyethylene ether.

[0154] According to the present invention, in the copolymer fiber composition, the polymerization inhibitor is selected from at least one of polyvinyl alcohol, sodium polyacrylate and sodium alginate.

[0155] According to the present invention, in the copolymer fiber composition, the polylactic acid fiber preferably comprises polylactic acid nanospheres and polylactic acid microfibers in a specific weight ratio. The polylactic acid nanospheres ensure uniform dispersion of the solution, while the polylactic acid microfibers improve the solution's sand-carrying capacity. When used in a fracturing system, the polylactic acid fiber having this composition can ensure uniform dispersion of the solution and improve sand-carrying capacity.

[0156] According to the present invention, preferably, in the polylactic acid fiber, the weight ratio of the polylactic acid nanospheres to the polylactic acid microfibers is 1:0.3-3;

[0157] According to the present invention, preferably, the average particle size of the polylactic acid nanospheres is 122-143 nm.

[0158] According to the present invention, preferably, the average length of the polylactic acid micron fiber is 700-800 μm, and the average diameter is 600-800 nm.

[0159] In the present invention, preferably, the method for preparing the polylactic acid nanospheres comprises:

[0160] (1) dissolving polylactic acid in an organic solvent 1 under ultrasonic conditions to obtain an organic phase 1;

[0161] (2) adding the organic phase 1 of step (1) into water and mixing to obtain the polylactic acid nanospheres;

[0162] The ultrasonic conditions in step (1) include: ultrasonic time of 10-30 min, ultrasonic power of 500-900 W, and temperature of 20-30° C.

[0163] According to the present invention, the polylactic acid nanospheres obtained under specific ultrasonic and mixing conditions have different sizes, and the polylactic acid fibers composed of the polylactic acid nanospheres are applied to the fracturing fluid system, so that the fracturing fluid system is evenly dispersed.

[0164] According to the present invention, the organic solvent 1 is a mixed solution of ethanol and acetone. Preferably, in the organic solvent 1, the volume ratio of ethanol to acetone is 1:1-3.

[0165] According to the present invention, in the method for preparing polylactic acid nanospheres, the mixing conditions in step (2) include: a stirring speed of 500-700 r / min, a stirring temperature of 20-30° C., and a stirring time of 10-30 min.

[0166] According to the present invention, in the method for preparing the polylactic acid nanospheres, the content of the L-isomer of the polylactic acid is 90-99 wt %.

[0167] In the preparation method of the polylactic acid nanospheres of the present invention, the polylactic acid can be prepared by the following method:

[0168] (1) Lactic acid and stannous chloride are mixed under anhydrous and oxygen-free conditions, and reacted at 120-150° C. for 5-10 hours to obtain a mixture 1;

[0169] (2) dissolving the mixture in chloroform, adding methanol, mixing, and drying to obtain the polylactic acid.

[0170] According to the present invention, in the method for preparing polylactic acid, the weight ratio of stannous chloride to lactic acid is 1:3000-5000.

[0171] According to the present invention, in the preparation method of polylactic acid, in step (1), stannous chloride is prepared into a 0.05-0.2 wt% solution and then mixed with lactic acid, wherein the solvent of the solution is chloroform.

[0172] According to the present invention, in the method for preparing polylactic acid, there is no particular limitation on the amount of chloroform used, as long as the mixture 1 can be fully dissolved.

[0173] According to the present invention, in the method for preparing polylactic acid, in step (2), the mixing conditions include: until a large amount of white fibrous matter appears.

[0174] According to the present invention, in the method for preparing polylactic acid, the drying conditions include: a temperature of 80-100° C. and a time of 5-10 hours, until the polylactic acid reaches a constant weight.

[0175] In the present invention, the polylactic acid micron fiber can be prepared by the following method:

[0176] Pour 5-10wt% polylactic acid dichloromethane solution into a spinning tube, spin at a spinning distance of 15-20cm between the receiving screen and the spinneret, a spinning flow of 0.1-0.3mL / h and a spinning voltage of 7-15kV, and dry at 20-30°C to obtain the polylactic acid micron fiber.

[0177] In the present invention, the polylactic acid fiber can be prepared by mixing the polylactic acid nanospheres and polylactic acid micron fibers.

[0178] A seventh aspect of the present invention provides a fracturing fluid, wherein the fracturing fluid comprises the above-mentioned copolymer fiber composition, a breaker and water;

[0179] Wherein, the fracturing fluid comprises:

[0180] 0.5-1.5 parts by weight of the copolymer fiber composition;

[0181] The gel breaker is 0.1-0.5 parts by weight.

[0182] According to the present invention, the gel breaker is at least one of potassium persulfate, sodium persulfate and ammonium persulfate.

[0183] In the present invention, compared with the fracturing fluid system composed of copolymers and polyvinyl acetal high-strength fibers not described in the present invention, the fracturing fluid prepared by the present invention can be applied to deep wells with a maximum temperature of 158°C, and can be quickly dissolved and thickened without the need for advance fluid preparation, thereby meeting the technical requirements of large-volume and large-scale fracturing construction.

[0184] An eighth aspect of the present invention provides a use of the fracturing fluid described in the seventh aspect in reservoir exploration and development.

[0185] The present invention will be described in detail below through examples.

[0186] In the following examples and comparative examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents and instruments used, if no manufacturer is specified, are commercially available conventional products.

[0187] The content of each structural unit in the copolymers prepared in the following examples and comparative examples is determined by the monomers used in the preparation and the monomer feed amount. In the present invention, the monomer feeds are all completely reacted during the preparation.

[0188] The weight average molecular weight of the copolymer was measured by GPC.

[0189] The apparent viscosity of the fracturing fluid was tested in accordance with SY / T 6376-2008 General Technical Specifications for Fracturing Fluids. 350 mL of the fluid was placed in a constant temperature water bath at 30°C for 4 hours. The viscosity was measured using a Fann-35 rotary viscometer or similar product at a speed of 100 r / min (shear rate of 170s -1 ) when the apparent viscosity.

[0190] The fracturing fluid was tested for its temperature resistance according to SY / T 5107-2005 "Method for Evaluating the Performance of Water-Based Fracturing Fluids". The specific conditions were as follows: After the viscometer sample cup was filled with fracturing fluid, the sample was heated. The heating rate was controlled at 3°C / min±0.2°C / min, and the test was started at 30°C. At the same time, the rotor was heated at a shear rate of 170s.-1 The fracturing fluid is rotated and subjected to continuous shear under heating conditions. The temperature corresponding to the apparent viscosity dropping to 50 mPa·s is used to characterize the temperature resistance of the sample.

[0191] The surface tension of the fracturing fluid was tested according to SY / T 5370-1999 “Determination of surface and interfacial tension”.

[0192] The drag reduction performance of the copolymer fiber composition was tested using an indoor pipe friction tester.

[0193] Preparation Example

[0194] Under anhydrous and oxygen-free conditions, 500g of racemic lactide was mixed with 0.05wt% stannous chloride and dehydrated under reduced pressure for 2h. The ampoule was sealed by high-temperature melting. Dehydration and condensation reaction was carried out at 130°C for 5h. The polylactic acid product was collected and dissolved in chloroform. The solution was poured into methanol and stirred until a large amount of white fibers was produced. The product was then dried under vacuum at 80°C for 5h to constant weight to obtain 400g of polylactic acid. The L-isomer content of the polylactic acid was 95wt%.

[0195] Preparation of copolymers

[0196] Example A-1

[0197] (1) 55 g of acrylamide (monomer 1, structural formula as shown in formula I, R1 is hydrogen), 25 g of acrylic acid (monomer 2, structural formula as shown in formula II, R2 is hydrogen) and 15 g of N,N-dimethylacrylamide (monomer 3, structural formula as shown in formula III, R3 is hydrogen, R4 is R5 and R5' are methyl groups) and water were mixed at 25° C. for 1 h, and KOH was added to adjust the pH value of the solution to 6 to obtain an aqueous phase solution with an acrylamide concentration of 30 wt %.

[0198] (2) 5 g of octadecyldimethylallylammonium chloride (monomer 4, structural formula as shown in formula V, R8 is hydrogen, R9 is Among them, R 14 for ), 5g of emulsifier, and white oil were stirred at 1000 rpm for 10 minutes at 25°C until uniformly dispersed to obtain an oil phase solution. The emulsifier was a Span 60 / Span 80 composite emulsifier system with a Span 60:Span 80 mass ratio of 1:2.

[0199] (3) In a nitrogen atmosphere, at 25°C and 1000 r / min, the aqueous phase solution and the oil phase solution were mixed, 0.2 g of initiator azobisisobutyronitrile was added dropwise, and polymerization was carried out at 40°C for 10 min to obtain copolymer A1.

[0200] Based on the total mass of the monomer, the emulsifier and the initiator, the total mass of the monomer is 98.2 wt %, the initiator is 0.2 wt % and the emulsifier is 1.6 wt %.

[0201] The weight average molecular weight is 9×10 6 g / mol, based on the total weight of the copolymer, the content of structural unit A is 55wt%, the content of structural unit B is 25wt%, the content of structural unit C is 15wt%, and the content of structural unit D is 5wt%.

[0202] Example A-2

[0203] A copolymer was prepared according to Example A-1, except that

[0204] In step (1), monomer 3 is methacryloyloxyethyltrimethylammonium chloride (structural formula is shown in Formula IV, R6 is methyl, R7 is methyl, and n is 2).

[0205] In step (2), monomer 4 is sodium 4-acrylamide benzenesulfonate (structural formula is shown in formula VI, R 10 is hydrogen, R 11 for ).

[0206] Copolymer A2 was obtained.

[0207] Based on the total mass of the monomer, the emulsifier and the initiator, the total mass of the monomer is 98.2 wt %, the initiator is 0.2 wt % and the emulsifier is 1.6 wt %.

[0208] The weight average molecular weight is 8.9×10 6 g / mol, the concentration of acrylamide is 35wt%, based on the total weight of the copolymer, the content of structural unit A is 55wt%, the content of structural unit B is 25wt%, the content of structural unit C is 15wt%, and the content of structural unit D is 5wt%.

[0209] Example A-3

[0210] A copolymer was prepared according to Example A-1, except that

[0211] In step (1), 45 g acrylamide, 20 g acrylic acid, and 18 g N,N-dimethylacrylamide.

[0212] In step (2), 17g octadecyldimethylpropyleneammonium chloride and 10g emulsifier.

[0213] In step (3), 1.1 g of initiator azobisisobutyronitrile.

[0214] The copolymer A3 was obtained. Based on the total mass of the monomers, the emulsifier and the initiator, the total mass of the monomers was 90 wt %, the initiator was 1 wt %, and the emulsifier was 9 wt %.

[0215] The weight average molecular weight is 8.8×10 6 g / mol, the concentration of acrylamide is 40wt%. Based on the total weight of the copolymer, the content of structural unit A is 45wt%, the content of structural unit B is 20wt%, the content of structural unit C is 18wt%, and the content of structural unit D is 17wt%.

[0216] Example A-4

[0217] A copolymer was prepared according to Example A-1, except that the emulsifier in step (2) was a compound emulsifier system of Tween 60 / Tween 80, and the mass ratio of Tween 60 to Tween 80 was 1:0.6.

[0218] Copolymer A4 was obtained.

[0219] Based on the total mass of the monomers, the emulsifier and the initiator, the total amount of the monomers used was 98.2 wt %, the initiator was 0.2 wt %, and the emulsifier was 1.6 wt %.

[0220] The weight average molecular weight is 8.7×10 6 g / mol, the concentration of acrylamide is 30wt%. Based on the total weight of the copolymer, the content of structural unit A is 55wt%, the content of structural unit B is 25wt%, the content of structural unit C is 15wt%, and the content of structural unit D is 5wt%.

[0221] Example A-5

[0222] The copolymer was prepared according to Example A-1, except that the emulsifier in step (2) was a composite emulsifier system of Span80 / OP-10, and the mass ratio of Span80 to OP-10 was 1:1.

[0223] Copolymer A5 was obtained.

[0224] Based on the total mass of the monomer, the emulsifier and the initiator, the total mass of the monomer is 98.2 wt %, the initiator is 0.2 wt % and the emulsifier is 1.6 wt %.

[0225] The weight average molecular weight is 8.7×10 6g / mol, the concentration of acrylamide is 30wt%. Based on the total weight of the copolymer, the content of structural unit A is 55wt%, the content of structural unit B is 25wt%, the content of structural unit C is 15wt%, and the content of structural unit D is 5wt%.

[0226] Example A-6

[0227] The copolymer was prepared according to Example A-1, except that the emulsifier in step (2) was a compound emulsifier system of Tween 80 / OP-10, and the mass ratio of Tween 80 to OP-10 was 1:1.

[0228] Copolymer A6 was obtained.

[0229] Based on the total mass of the monomer, the emulsifier and the initiator, the total mass of the monomer is 98.2 wt %, the initiator is 0.2 wt % and the emulsifier is 1.6 wt %.

[0230] The weight average molecular weight is 8.5×10 6 g / mol, the concentration of acrylamide is 30wt%. Based on the total weight of the copolymer, the content of structural unit A is 55wt%, the content of structural unit B is 25wt%, the content of structural unit C is 15wt%, and the content of structural unit D is 5wt%.

[0231] Example A-7

[0232] The copolymer was prepared according to Example A-1, except that the initiator in step (3) was benzoyl peroxide.

[0233] Copolymer A7 was obtained.

[0234] Based on the total mass of the monomer, the emulsifier and the initiator, the total mass of the monomer is 98.2 wt %, the initiator is 0.2 wt % and the emulsifier is 1.6 wt %.

[0235] The weight average molecular weight is 8.6×10 6 g / mol, the concentration of acrylamide is 30wt%, based on the total weight of the copolymer, the content of structural unit A is 55wt%, the content of structural unit B is 25wt%, the content of structural unit C is 15wt%, and the content of structural unit D is 5wt%.

[0236] Example A-8

[0237] A copolymer was prepared according to Example A-1, except that the initiator in step (3) was a tert-butyl hydroperoxide-sodium bisulfite composite system, and the weight ratio of tert-butyl hydroperoxide to sodium bisulfite was 1:0.5.

[0238] Copolymer A8 was obtained.

[0239] Based on the total mass of the monomer, the emulsifier and the initiator, the total mass of the monomer is 98.2 wt %, the initiator is 0.2 wt % and the emulsifier is 1.6 wt %.

[0240] The weight average molecular weight is 8.6×10 6 g / mol, the concentration of acrylamide is 30wt%. Based on the total weight of the copolymer, the content of structural unit A is 55wt%, the content of structural unit B is 25wt%, the content of structural unit C is 15wt%, and the content of structural unit D is 5wt%.

[0241] Example A-9

[0242] A copolymer was prepared according to Example A-1, except that the initiator in step (3) was a potassium persulfate-sodium sulfite composite system, and the weight ratio of potassium persulfate to sodium sulfite was 1:2.

[0243] The copolymer A9 was obtained. Based on the total mass of the monomers, the emulsifier and the initiator, the total mass of the monomers was 98.2 wt %, the initiator was 0.2 wt %, and the emulsifier was 1.6 wt %.

[0244] The weight average molecular weight is 8.6×10 6 g / mol, the concentration of acrylamide is 30wt%. Based on the total weight of the copolymer, the content of structural unit A is 55wt%, the content of structural unit B is 25wt%, the content of structural unit C is 15wt%, and the content of structural unit D is 5wt%.

[0245] Example A-10

[0246] A copolymer was prepared according to Example A-1, except that

[0247] In step (1), 40 g acrylamide, 30 g acrylic acid, and 20 g N,N-dimethylacrylamide were added.

[0248] 5g of octadecyldimethylpropyleneammonium chloride in step (2).

[0249] The copolymer A10 was obtained. Based on the total mass of the monomers, the emulsifier and the initiator, the total mass of the monomers was 98.2 wt %, the initiator was 0.2 wt %, and the emulsifier was 1.6 wt %.

[0250] The weight average molecular weight is 8.5×10 6g / mol, the concentration of acrylamide is 30wt%. Based on the total weight of the copolymer, the content of structural unit A is 40wt%, the content of structural unit B is 30wt%, the content of structural unit C is 20wt%, and the content of structural unit D is 5wt%.

[0251] Comparative Example DA-1

[0252] A copolymer was prepared according to Example A-1, except that

[0253] In step (1), 33 g acrylamide, 18 g acrylic acid, and 22 g N,N-dimethylacrylamide were used.

[0254] 27g of octadecyldimethylpropyleneammonium chloride in step (2).

[0255] The copolymer DA1 was obtained. Based on the total mass of the monomers, the emulsifier and the initiator, the total mass of the monomers was 98.2 wt %, the initiator was 0.2 wt %, and the emulsifier was 1.6 wt %.

[0256] The weight average molecular weight is 3.3×10 5 g / mol, the concentration of acrylamide is 30wt%. Based on the total weight of the copolymer, the content of structural unit A is 33wt%, the content of structural unit B is 18wt%, the content of structural unit C is 22wt%, and the content of structural unit D is 27wt%.

[0257] Comparative Example DA-2

[0258] A copolymer was prepared according to Example A-1, except that

[0259] In step (1), monomer 3 is 2-methyl-2-acrylamidopropanesulfonic acid.

[0260] In step (2), monomer 4 is N-vinyl pyrrolidone.

[0261] The copolymer DA2 was obtained. Based on the total mass of the monomers, the emulsifier and the initiator, the total mass of the monomers was 98.2 wt %, the initiator was 0.2 wt %, and the emulsifier was 1.6 wt %.

[0262] The weight average molecular weight is 3.9×10 5 g / mol, the concentration of acrylamide is 30wt%. Based on the total weight of the copolymer, the content of structural unit A is 55wt%, the content of structural unit B is 25wt%, the content of structural unit C is 15wt%, and the content of structural unit D is 5wt%.

[0263] Comparative Example DA-3

[0264] A copolymer was prepared according to Example A-1, except that

[0265] In step (1), 69 g acrylamide, 15 g acrylic acid, and 15 g N,N-dimethylacrylamide were added.

[0266] 1g of octadecyldimethylpropyleneammonium chloride in step (2).

[0267] The copolymer DA3 was obtained. Based on the total mass of the monomers, the emulsifier and the initiator, the total mass of the monomers was 90 wt %, the initiator was 1 wt %, and the emulsifier was 9 wt %.

[0268] The weight average molecular weight is 2.8×10 5 g / mol, the concentration of acrylamide is 30wt%. Based on the total weight of the copolymer, the content of structural unit A is 69wt%, the content of structural unit B is 15wt%, the content of structural unit C is 15wt%, and the content of structural unit D is 1wt%.

[0269] Preparation of polylactic acid fiber

[0270] Example B-1

[0271] (1) Preparation of polylactic acid nanospheres: 20 g of the polylactic acid prepared in the preparation example, 400 mL of ethanol, and 600 mL of acetone were mixed and ultrasonicated at 25°C and 500 W for 30 min to obtain a 2 wt% polylactic acid solution. The solution was then added to distilled water and stirred at 25°C and 500 rpm for 10 min to obtain 17.5 g of polylactic acid nanospheres. The average particle size of the polylactic acid nanospheres was 131 nm.

[0272] (2) Preparation of polylactic acid micron fibers: 200 mL of a 10 wt% polylactic acid solution in dichloromethane was poured into a spinning tube. The spinning distance between the receiving screen and the spinneret was 15 cm, the spinning flow rate was 0.1 mL / h, and the spinning voltage was 12 kV. The fibers were then dried to produce 19.2 g of polylactic acid micron fibers. The average length of the polylactic acid micron fibers was 743 μm, and the average diameter was 758 nm.

[0273] 10 g of polylactic acid nanospheres and 10 g of polylactic acid microfibers were mixed, with the weight ratio of the polylactic acid nanospheres to the polylactic acid microfibers being 1:1, to obtain polylactic acid fibers B1.

[0274] Example B-2

[0275] Polylactic acid fibers were prepared according to Example B-1, except that 9 g of polylactic acid nanospheres and 3 g of polylactic acid microfibers were mixed, and the weight ratio of polylactic acid nanospheres to polylactic acid microfibers was 3:1, to obtain polylactic acid fibers B2.

[0276] Example B-3

[0277] Polylactic acid fibers were prepared according to Example B-1, except that 3 g of polylactic acid nanospheres and 9 g of polylactic acid microfibers were mixed, and the weight ratio of polylactic acid nanospheres to polylactic acid microfibers was 1:3, to obtain polylactic acid fibers B3.

[0278] Example B-4

[0279] Polylactic acid fiber was prepared according to Example B-1, except that in the preparation of polylactic acid nanospheres (1), ultrasound was applied at 30°C and 900W for 10 minutes to obtain polylactic acid fiber B4.

[0280] Example B-5

[0281] Polylactic acid fiber was prepared according to Example B-1, except that in the preparation of polylactic acid nanospheres (1), the mixture was stirred at 700 r / min at 30° C. for 30 min to obtain polylactic acid fiber B5.

[0282] Comparative Example DB-1

[0283] Polylactic acid fiber was prepared according to Example B-1, except that 3 g of polylactic acid nanospheres and 12 g of polylactic acid microfibers were mixed, and the weight ratio of polylactic acid nanospheres to polylactic acid microfibers was 1:4, to obtain polylactic acid fiber DB1.

[0284] Comparative Example DB-2

[0285] Polylactic acid fiber was prepared according to Example B-1, except that 12 g of polylactic acid nanospheres and 3 g of polylactic acid microfibers were mixed, and the weight ratio of polylactic acid nanospheres to polylactic acid microfibers was 4:1, to obtain polylactic acid fiber DB2.

[0286] Comparative Example DB-3

[0287] Polylactic acid fiber was prepared according to Example B-1, except that in the preparation of polylactic acid nanospheres (1), ultrasound was applied at 25° C. and 1000 W for 30 min to obtain polylactic acid fiber DB3.

[0288] Preparation of copolymer fiber compositions

[0289] The formulations of the copolymer fiber compositions C1-C10 and DC1-DC8 are shown in Table 1.

[0290] Table 1

[0291] At 30°C and a 10mm tubing diameter, the drag reduction of copolymer fiber compositions C1-C10 and DC1-DC8 at varying concentrations (0.05wt%, 0.1wt%, 0.2wt%, 0.3wt%, and 0.4wt%) was studied in clean water and a 10-fold diluted standard brine solution. The standard brine solution was prepared according to SY / T 5107-2005, "Methods for Evaluating the Performance of Water-Based Fracturing Fluids." Specifically, the undiluted standard brine solution consisted of: 2.0wt% KCl + 5.5wt% NaCl + 0.45wt% MgCl2 + 0.55wt% CaCl2. The results are shown in Table 2.

[0292] Table 2

[0293] It can be seen from the results in Table 2 that the indoor drag reduction rate of the copolymer fiber composition of Examples 1 to 10 of the present invention is maintained at above 70%, which shows an excellent drag reduction rate.

[0294] Application Examples

[0295] Application Example 1

[0296] 1.5 parts by weight of the copolymer fiber composition C1, 0.1 parts by weight of potassium persulfate, and 100 parts by weight of water were mixed to obtain a fracturing fluid E1.

[0297] Application Example 2

[0298] 1 part by weight of the copolymer fiber composition C2, 0.3 parts by weight of sodium persulfate, and 100 parts by weight of water were mixed to obtain a fracturing fluid E2.

[0299] Application Example 3

[0300] 0.5 parts by weight of the copolymer fiber composition C2, 0.1 parts by weight of ammonium persulfate, and 100 parts by weight of water were mixed to obtain a fracturing fluid E3.

[0301] Application Example 4-10

[0302] Fracturing fluid was prepared according to Application Example 1, except that the copolymer fiber compositions were C4-C10, respectively, to obtain fracturing fluids E4-E10.

[0303] Comparative Application Examples 1-8

[0304] Fracturing fluids were prepared according to Application Example 1, except that the copolymer fiber compositions were DC1-DC8, respectively, to obtain fracturing fluids DE1-DE8.

[0305] Comparative Application Example 9

[0306] 2 parts by weight of the copolymer fiber composition C1, 0.6 parts by weight of potassium persulfate, and water were mixed to obtain fracturing fluid DE9.

[0307] Test Case

[0308] The performance parameters of fracturing fluids E1-E10 and DE1-DE9 are shown in Table 3. The appearance of the fluid was observed by standing the fracturing fluid at 25°C for 10 minutes.

[0309] Table 3

[0310] It can be seen from the results in Table 3 that the fracturing fluids prepared using the copolymers provided in Examples 1-10 of the present invention have excellent high temperature resistance, easy sand carrying and low friction resistance.

[0311] FIG1 is a graph showing the heat and shear resistance of the fracturing fluid prepared in Application Example 1. As can be seen from the graph, the fracturing fluid provided by the present invention can still maintain a high apparent viscosity at 158° C. and has excellent heat and shear resistance.

[0312] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A copolymer, characterized in that The copolymer contains a structural unit A represented by Formula 1, a structural unit B represented by Formula 2, a structural unit C represented by Formula 3 and / or Formula 4, and a structural unit D represented by Formula 5 and / or Formula 6. Wherein, in Formula 1, R1 is hydrogen or methyl; In formula 2, R2 is hydrogen or methyl; In formula 3, R3 is hydrogen or methyl; R4 is wherein R5 and R5' are each independently hydrogen or methyl; In formula 4, R6 is hydrogen or methyl; R7 is methyl, benzyl or Where R 13 is methylene, C2-C6 straight chain or branched alkylene; n is an integer of 1-4; In Formula 5, R8 is hydrogen or methyl; R9 is Among them, R 14 C 10 -C 20 A straight chain or branched alkyl group; In formula 6, R 10 is hydrogen or methyl, R 11 for Wherein, based on the total weight of the copolymer, the content of the structural unit A is 40-60wt%, the content of the structural unit B is 20-30wt%, the content of the structural unit C is 15-20wt%, and the content of the structural unit D is 5-25wt%.

2. The copolymer according to claim 1, wherein Based on the total weight of the copolymer, the content of structural unit A is 45-55wt%, the content of structural unit B is 20-25wt%, the content of structural unit C is 15-18wt%, and the content of structural unit D is 5-17wt%; And / or, in Formula 1, R1 is hydrogen; And / or, in Formula 2, R2 is hydrogen; And / or, in Formula 3, R3 is hydrogen; R4 is R5 and R5' are methyl groups; And / or, in Formula 4, R6 is hydrogen or methyl; R7 is methyl or benzyl, and n is 2 or 3; And / or, in Formula 5, R8 is hydrogen; R9 is Among them, R 14 C 15 -C 20 A straight chain or branched alkyl group; And / or, in Formula 6, R 10 For hydrogen.

3. The copolymer according to claim 1 or 2, wherein The weight average molecular weight of the copolymer is 8 million g / mol-10 million g / mol.

4. A method for preparing a copolymer, characterized in that: The preparation method comprises: (1) first mixing monomer 1, monomer 2, monomer 3 and water to obtain an aqueous solution; wherein the monomer 1 has a structure shown in formula I, the monomer 2 has a structure shown in formula II, and the monomer 3 has a structure shown in formula III and / or formula IV; (2) in the presence of a first solvent, performing a second mixing of monomer 4 and an emulsifier to obtain an oil phase solution; wherein the monomer 4 has a structure represented by formula V and / or formula VI; (3) in the presence of a protective atmosphere and an initiator, subjecting the aqueous phase solution and the oil phase solution to a third mixing and polymerization reaction to obtain the copolymer; Wherein, in formula I, R1 is hydrogen or methyl; In formula II, R2 is hydrogen or methyl; In formula III, R3 is hydrogen or methyl; R4 is wherein R5 and R5' are each independently hydrogen or methyl; In formula IV, R6 is hydrogen or methyl; R7 is methyl, benzyl or Where R 13 is a C1-C6 straight chain or branched alkylene group; n is an integer of 1-4; In formula V, R8 is hydrogen or methyl; R9 is Among them, R 14 C 10 -C 20 A straight chain or branched alkyl group; In Formula VI, R 10 is hydrogen or methyl, R 11 for Wherein, based on the total mass of monomer 1, monomer 2, monomer 3 and monomer 4, the content of monomer 1 is 40-60wt%, the content of monomer 2 is 20-30wt%, the content of monomer 3 is 15-20wt%, and the content of monomer 4 is 5-25wt%.

5. The preparation method according to claim 4, wherein The first mixing condition in step (1) includes: adjusting the pH to 6-7, the temperature to 20-30° C., and the time to 0.5-2 h; And / or, the second mixing conditions in step (2) include: a stirring rate of 1000-1500 r / min, a stirring temperature of 20-30° C., and a stirring time of 10-30 min; And / or, the third mixing condition in step (3) includes: a stirring rate of 1000-1600 r / min, a stirring temperature of 20-30° C., and a stirring time of 5-30 min; And / or, the polymerization reaction conditions in step (3) include: temperature of 36-45° C., time of 2-3 h; And / or, the polymerization reaction in step (3) further comprises: adding a second solvent or an initiator so that the polymerization reaction temperature is 36-45° C.; and / or, the concentration of monomer 1 in the aqueous phase solution is 30-40 wt %; And / or, based on the total mass of monomers, emulsifiers and initiators, the content of monomer 1, monomer 2, monomer 3 and monomer 4 is 90-98.2wt%, the content of initiator is 0.2-1.2wt%, and the content of emulsifier is 1.6-9wt%; and / or, the initiator is selected from at least one of an azo initiator, a peroxide initiator and a redox initiator; and / or, the first solvent is selected from at least one of kerosene, diesel, white oil, cyclohexane, benzene, toluene and petroleum ether; And / or, the emulsifier is a nonionic surfactant, preferably at least one selected from sorbitan monostearate, sorbitan oleate, polyoxyethylene sorbitan monostearate, polysorbate 80 and dodecylphenol polyoxyethylene ether; And / or, the second solvent is water.

6. A copolymer obtained by the preparation method according to claim 4 or 5.

7. A copolymer fiber composition, characterized in that The copolymer fiber composition comprises the copolymer according to any one of claims 1 to 3 and 6, polylactic acid fiber, a surfactant and an inhibitor; Wherein, the copolymer fiber composition comprises: 85-95 parts by weight of the copolymer; 0.5-1.5 parts by weight of the polylactic acid fiber; 5-10 parts by weight of the surfactant; The polymerization inhibitor is 0.05-0.1 parts by weight.

8. The copolymer fiber composition according to claim 7, wherein The surfactant is selected from at least one of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether and dodecylphenol polyoxyethylene ether; And / or, the polymerization inhibitor is selected from at least one of polyvinyl alcohol, sodium polyacrylate and sodium alginate.

9. The copolymer fiber composition according to claim 7 or 8, wherein The polylactic acid fibers include polylactic acid nanospheres and polylactic acid micron fibers.

10. The copolymer fiber composition according to claim 9, wherein The weight ratio of the polylactic acid nanospheres to the polylactic acid microfibers is 1:0.3-3; And / or, the average particle size of the polylactic acid nanospheres is 122-143 nm; And / or, the average length of the polylactic acid micron fibers is 700-800 μm, and the average diameter is 600-800 nm.

11. The copolymer fiber composition according to claim 7 or 8, wherein The preparation method of the polylactic acid nanospheres comprises: (1) dissolving polylactic acid in an organic solvent 1 under ultrasonic conditions to obtain an organic phase 1; (2) adding the organic phase 1 of step (1) into water and mixing to obtain the polylactic acid nanospheres; The ultrasonic conditions in step (1) include: ultrasonic time of 10-30 min, ultrasonic power of 500-900 W, and temperature of 20-30° C. And / or, the mixing conditions in step (2) include: stirring speed of 500-700 r / min, stirring temperature of 20-30° C., and time of 10-30 min; And / or, the organic solvent 1 is a mixed solution of ethanol and acetone; And / or, the content of L-isomer of the polylactic acid is 90-99wt%.

12. A fracturing fluid, characterized in that: The fracturing fluid comprises the copolymer fiber composition according to any one of claims 7 to 11, a breaker and water; Wherein, the fracturing fluid comprises: 0.5-1.5 parts by weight of the copolymer fiber composition; The debonding agent is 0.1-0.5 parts by weight.

13. Use of the fracturing fluid according to claim 12 in reservoir exploration and development.

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