Copolymers, methods of making the same, and fracturing fluids

Abstract

The present application relates to fracturing fluid technical field, disclose a kind of copolymer and its preparation method and fracturing fluid.The copolymer of the present application has the structure shown in formula (1), in formula (1), R1 and R2 are each independently selected from halogen;R3 and R4 are each independently selected from H and the alkyl of 1-6 carbon atoms;R5 is selected from the alkyl of 1-20 carbon atoms;a, b, c and d indicate the mole percentage content of structural unit, a is 55-75%, b is 15-25%, c is 1-10%, d is 0.1-5%;N is selected from the integer in 5-10.The high temperature resistance of the fracturing fluid containing the shear thickening copolymer of the present application is excellent.

Description

Technical Field

[0001] This invention relates to the field of fracturing fluid technology, specifically to a copolymer, its preparation method, and a fracturing fluid; more specifically, to a shear-thickening copolymer for high-temperature fracturing fluid, its preparation method, and a high-temperature fracturing fluid containing the shear-thickening copolymer. Background Technology

[0002] With the continuous deepening of oil and gas exploration and development, the proportion of deep oil and gas resources is gradually increasing. Reservoir stimulation is currently one of the most effective ways to improve the productivity of oil and gas wells. However, deep well reservoir stimulation faces many challenges, one of the most important being the insufficient temperature resistance of fracturing fluids. As reservoir depth increases, temperature gradually rises, with some reservoirs reaching or exceeding 200℃. High temperatures often cause a sharp decrease in the viscoelasticity of fracturing fluids, weakening their proppant-carrying capacity and leading to complex situations such as proppant removal. In addition, the performance of fracturing fluids also decreases under prolonged shearing, making it difficult for existing fracturing fluid systems to effectively adapt to operational requirements. Although traditional guar gum fracturing fluids have a good thickening effect, the glycosidic bonds on the main chain of guar gum molecules break at 177℃, severely limiting their application in high-temperature fracturing fluids. Furthermore, the residue after gum breakdown can damage the formation, affecting the fracturing effect. In contrast, synthetic polymer fracturing fluid systems do not contain water-insoluble substances, and the polymer main chain consists of carbon-carbon single bonds, exhibiting excellent thermal stability. Therefore, with the increasing demand for high-temperature resistant fracturing fluids in oilfield operations, it is necessary to develop high-temperature resistant polymer fracturing fluid systems with a temperature resistance of up to 200℃ for fracturing and increasing production in low-permeability, high-temperature wells. Summary of the Invention

[0003] The purpose of this invention is to overcome the problem of insufficient temperature resistance of fracturing fluids in the prior art, and to provide a shear thickening copolymer for high-temperature fracturing fluid, a method for preparing the same, and a high-temperature fracturing fluid containing the shear thickening copolymer. The fracturing fluid containing the shear thickening copolymer of this invention exhibits excellent high-temperature resistance.

[0004] To achieve the above objectives, the present invention provides a copolymer having the structure shown in formula (1).

[0005]

[0006] In equation (1), R1 and R2 are each independently selected from halogens;

[0007] R3 and R4 are each independently selected from H and alkyl groups having 1-6 carbon atoms;

[0008] R5 is selected from alkyl groups having 1-20 carbon atoms;

[0009] a, b, c, and d represent the molar percentage of structural units, where a is 55-75%, b is 15-25%, c is 1-10%, and d is 0.1-5%.

[0010] n is an integer selected from 5 to 10.

[0011] Preferably, in formula (1), R1 and R2 are each independently selected from F, Cl, Br or I, and more preferably each is independently selected from Cl or Br;

[0012] R3 and R4 are each independently selected from H and alkyl groups having 1-3 carbon atoms, and preferably are each independently selected from H and methyl groups;

[0013] R5 is selected from alkyl groups having 6-10 carbon atoms, preferably octyl;

[0014] a, b, c, and d represent the molar percentage of structural units, where a is 70-75%, b is 15-25%, c is 4-9%, and d is 0.5-2%.

[0015] n is selected from 5, 7, 9, or 10.

[0016] Preferably, the copolymer has the structure shown in formula (2).

[0017]

[0018] In formula (2), a, b, c and d represent the molar percentage content of structural units, where a is 55-75%, b is 15-25%, c is 1-10%, and d is 0.1-5%.

[0019] n is an integer selected from 5 to 10.

[0020] Preferably, in formula (2), a, b, c and d represent the molar percentage content of structural units, where a is 70-75%, b is 15-25%, c is 4-9%, and d is 0.5-2%.

[0021] n is selected from 5, 7, 9, or 10.

[0022] According to a second aspect of the present invention, a method for preparing a copolymer is provided, wherein the method includes the following steps:

[0023] 1) The step of polymerizing a monomer solution containing monomers A, B, C and D in the presence of an initiator to obtain a polymer intermediate;

[0024] 2) The step of subjecting the polymer intermediate to a halogenation reaction with a halogenating agent.

[0025] Wherein, monomer A is acrylamide and / or alkylacrylamide, monomer B is acrylic acid and / or alkylacrylic acid, monomer C is sorbic acid, methyl sorbate or ethyl sorbate, and monomer D is alkylphenol polyoxyethylene ether methacrylate;

[0026] The alkyl groups in the alkyl acrylamide and the alkyl acrylic acid are each independently selected from H and alkyl groups having 1-6 carbon atoms; the alkyl groups in the alkylphenol polyoxyethylene ether methacrylate are selected from alkyl groups having 1-20 carbon atoms.

[0027] Based on the total molar amount of monomers A, B, C, and D, monomer A is 55-75 mol%, monomer B is 15-25 mol%, monomer C is 1-10 mol%, and monomer D is 0.1-5 mol%.

[0028] Preferably, the alkyl groups in the alkylacrylamide and the alkylacrylic acid are each independently selected from H and alkyl groups having 1-3 carbon atoms, preferably H and methyl.

[0029] Preferably, the alkyl group in the alkylphenol polyoxyethylene ether methacrylate is selected from alkyl groups with 6-10 carbon atoms, and is preferably octyl.

[0030] Preferably, based on the total molar amount of monomers A, B, C, and D, monomer A is 70-75 mol%, monomer B is 15-25 mol%, monomer C is 4-9 mol%, and monomer D is 0.5-2 mol%.

[0031] Preferably, monomer A is one or more of acrylamide, methacrylamide, ethylacrylamide, and propylacrylamide.

[0032] Preferably, monomer B is one or more selected from acrylic acid, methacrylic acid, ethylacrylic acid, and propylacrylic acid;

[0033] Preferably, the monomer D is one or more of octylphenol polyoxyethylene ether methacrylate (n=5 in formula (3) below), octylphenol polyoxyethylene ether methacrylate (n=7 in formula (3) below), octylphenol polyoxyethylene ether methacrylate (n=9 in formula (3) below), and octylphenol polyoxyethylene ether methacrylate (n=10 in formula (3) below).

[0034]

[0035] Preferably, the initiator is one or more of azobisisobutyronitrile, azobisisovalerate, and azobisisobutyramidine hydrochloride.

[0036] Preferably, the amount of initiator used is 0.05-0.2% of the total weight of the monomers.

[0037] Preferably, the solvent in the monomer solution is one or more of methanol, ethanol, diethyl ether, acetone, toluene, and xylene, and more preferably one or more of ethanol, diethyl ether, and acetone.

[0038] Preferably, the polymerization reaction conditions include: a polymerization temperature of 60-70°C and a polymerization time of 7-8 hours.

[0039] Preferably, in step 2), the halogenating agent is tribromomethane.

[0040] Preferably, the amount of the halogenating agent is 3-8% of the weight of the polymer intermediate.

[0041] Preferably, the conditions for the halogenation reaction include: a reaction temperature of 5-45°C and a reaction time of 10-80 hours.

[0042] According to a third aspect of the present invention, a fracturing fluid is provided, wherein the fracturing fluid contains the copolymer described in the first aspect of the present invention.

[0043] Preferably, the content of the copolymer in the fracturing fluid is 0.1-1% by weight.

[0044] The copolymer of this invention incorporates mechanoresponsive groups. Under shear stress, these groups open and undergo nucleophilic substitution, forming more stable covalent bonds and thus increasing the copolymer's viscosity. As described later, the fracturing fluid system prepared using the shear-thickening copolymer was tested at 200°C for 100 seconds. -1 Under shearing conditions of 120 min, the viscosity remained above 100 mPa·s. Furthermore, the preparation method of the shear-thickening copolymer of this invention is convenient to operate, uses low-cost raw materials, and has broad market prospects. Attached Figure Description

[0045] Figure 1 The infrared spectrum is that of the shear-thickening copolymer obtained in Example 1.

[0046] Figure 2 The variable shear rheological curve is for the fracturing fluid prepared with 0.3% by weight copolymer in Example 1.

[0047] Figure 3 The shear recovery rheological curve is for the fracturing fluid prepared with 0.3% by weight copolymer in Example 2.

[0048] Figure 4 The temperature and shear rheological curves of the fracturing fluid prepared with 0.3% by weight copolymer in Example 3 are shown.

[0049] Figure 5The temperature and shear rheological curves of the fracturing fluid prepared with 0.4% by weight copolymer in Example 3 are shown.

[0050] Figure 6 Temperature and shear rheological curves of the fracturing fluid prepared with 0.5% by weight copolymer in Example 4.

[0051] Figure 7 Temperature and shear rheological curves of the fracturing fluid prepared with 0.6% by weight copolymer in Example 5. Detailed Implementation

[0052] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0053] In this invention, the "halogen" is F, Cl, Br or I, preferably F, Cl or Br, more preferably Cl or Br, and particularly preferably Br.

[0054] In this invention, "alkyl group having 1-6 carbon atoms" can be a straight-chain alkyl group or a branched-chain alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, etc. Among them, methyl, ethyl or n-propyl is preferred, and methyl is particularly preferred.

[0055] In this invention, the alkyl group having 1-20 carbon atoms can be a straight-chain alkyl group or a branched-chain alkyl group, for example: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, isohexyl. Among them, octyl is preferred.

[0056] According to a first aspect of the present invention, a copolymer is provided, wherein the copolymer has the structure shown in formula (1).

[0057]

[0058] In equation (1), R1 and R2 are each independently selected from halogens;

[0059] R3 and R4 are each independently selected from H and alkyl groups having 1-6 carbon atoms;

[0060] R5 is selected from alkyl groups having 1-20 carbon atoms;

[0061] a, b, c, and d represent the molar percentage of structural units, where a is 55-75%, b is 15-25%, c is 1-10%, and d is 0.1-5%.

[0062] n is an integer selected from 5 to 10.

[0063] In this invention, although the structure of the copolymer is represented by formula (1), it does not mean that the monomer structures are necessarily connected in the order shown in formula (1). It is a copolymer structure in which the monomer structures are arbitrarily connected to each other.

[0064] The copolymer of the present invention is a shear-thickening copolymer. The copolymer of the present invention has excellent shear-thickening properties, which is presumably due to the following: as shown in the following formula (which is the chemical equation for the reaction of the copolymer under shear), dibromocyclopropane undergoes ring-opening under shear force to generate dibromoallyl, which then undergoes a nucleophilic substitution reaction with the amide group in acrylamide, resulting in cross-linking between the copolymers and thus increasing the viscosity.

[0065]

[0066] According to the present invention, preferably, in formula (1), R1 and R2 are each independently selected from F, Cl, Br or I, more preferably each independently selected from F, Cl or Br, even more preferably each independently selected from Cl or Br, and particularly preferably Br.

[0067] According to the present invention, preferably, in formula (1), R3 and R4 are each independently selected from H and alkyl groups having 1-3 carbon atoms, preferably each independently selected from H and methyl groups, and particularly preferably H.

[0068] According to the present invention, preferably, R5 is selected from alkyl groups having 6-10 carbon atoms, more preferably octyl.

[0069] According to the present invention, preferably, a, b, c and d represent the molar percentage content of the structural unit, where a is 70-75%, b is 15-25%, c is 4-9%, and d is 0.5-2%.

[0070] As mentioned above, 'a' represents the molar percentage content of the structural unit, for example: 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, etc., as well as any range formed by any two of the above.

[0071] As mentioned above, 'b' represents the molar percentage of the structural unit, for example, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, etc., as well as any two of the above ranges.

[0072] As mentioned above, 'c' represents the molar percentage of the structural unit, for example: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., as well as any two of the above ranges.

[0073] As mentioned above, d represents the molar percentage of structural units, for example: 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, etc., as well as any two of the above ranges.

[0074] According to the present invention, n is selected from 5, 6, 7, 8, 9 or 10; preferably, n is selected from 5, 7, 9 or 10.

[0075] In a preferred embodiment of the invention, the copolymer has the structure shown in formula (2).

[0076]

[0077] In equation (2), a, b, c and d represent the molar percentage of structural units, where a is 55-75%, b is 15-25%, c is 1-10%, and d is 0.1-5%; n is an integer selected from 5-10.

[0078] Preferably, in formula (2), a, b, c and d represent the molar percentage content of structural units, a is 70-75%, b is 15-25%, c is 4-9% and d is 0.5-2%; n is selected from 5, 7, 9 or 10.

[0079] According to a second aspect of the present invention, a method for preparing a copolymer is provided, wherein the method includes the following steps:

[0080] 1) The step of polymerizing a monomer solution containing monomers A, B, C and D in the presence of an initiator to obtain a polymer intermediate;

[0081] 2) The step of subjecting the polymer intermediate to a halogenation reaction with a halogenating agent.

[0082] Wherein, monomer A is acrylamide and / or alkylacrylamide, monomer B is acrylic acid and / or alkylacrylic acid, monomer C is sorbic acid, methyl sorbate or ethyl sorbate, and monomer D is alkylphenol polyoxyethylene ether methacrylate;

[0083] The alkyl groups in the alkyl acrylamide and the alkyl acrylic acid are each independently selected from H and alkyl groups having 1-6 carbon atoms; the alkyl groups in the alkylphenol polyoxyethylene ether methacrylate are selected from alkyl groups having 1-20 carbon atoms.

[0084] Based on the total molar amount of monomers A, B, C, and D, monomer A is 55-75 mol%, monomer B is 15-25 mol%, monomer C is 1-10 mol%, and monomer D is 0.1-5 mol%.

[0085] According to the present invention, preferably, the alkyl groups in the alkylacrylamide and the alkylacrylic acid are each independently selected from H and alkyl groups having 1-3 carbon atoms, more preferably independently selected from H and methyl, and particularly preferably H.

[0086] According to the present invention, preferably, the alkyl group in the alkylphenol polyoxyethylene ether methacrylate is selected from alkyl groups having 6-10 carbon atoms, and more preferably octyl.

[0087] According to the present invention, preferably, based on the total molar amount of monomers A, B, C and D, monomer A is 70-75 mol%, monomer B is 15-25 mol%, monomer C is 4-9 mol%, and monomer D is 0.5-2 mol%.

[0088] According to the present invention, preferably, monomer A is one or more of acrylamide, methacrylamide, ethylacrylamide and propylacrylamide; more preferably, monomer A is acrylamide and / or methacrylamide; particularly preferably, monomer A is acrylamide.

[0089] According to the present invention, preferably, the monomer B is one or more selected from acrylic acid, methacrylic acid, ethyl acrylic acid and propyl acrylic acid; more preferably, the monomer B is acrylic acid and / or methacrylic acid; particularly preferably, the monomer B is acrylic acid.

[0090] According to the present invention, preferably, the monomer D is one or more selected from octylphenol polyoxyethylene ether methacrylate (n=5), octylphenol polyoxyethylene ether methacrylate (n=7), octylphenol polyoxyethylene ether methacrylate (n=9), and octylphenol polyoxyethylene ether methacrylate (n=10). Here, n refers to the number of repeating units of the polyoxyethylene ether.

[0091] Particularly preferably, the monomer D is selected from one or more of octylphenol polyoxyethylene ether methacrylate (n=5 in formula (3) below), octylphenol polyoxyethylene ether methacrylate (n=7 in formula (3) below), octylphenol polyoxyethylene ether methacrylate (n=9 in formula (3) below) and octylphenol polyoxyethylene ether methacrylate (n=10 in formula (3) below).

[0092]

[0093] In this invention, monomer AD can be obtained commercially or through conventional synthetic methods in the art. For example, monomer D can be obtained by reacting alkylphenol polyoxyethylene ether with methacrylamide chloride.

[0094] According to the present invention, preferably, the initiator is an azo initiator; more preferably, the initiator is one or more selected from azobisisobutyronitrile, azobisisovalerate, and azobisisobutyramidine hydrochloride.

[0095] Preferably, the initiator is used at 0.05-0.2% of the total weight of the monomers, more preferably 0.05-0.1%, and particularly preferably 0.1%.

[0096] According to the present invention, the monomer solution is obtained by mixing the monomer in a solvent. The solvent in the monomer solution may be one or more of methanol, ethanol, diethyl ether, acetone, toluene and xylene, preferably one or more of ethanol, diethyl ether and acetone, and more preferably ethanol.

[0097] According to the present invention, the monomer content in the monomer solution can be 5-15% by weight, preferably 5-10% by weight, and more preferably 8-10% by weight.

[0098] According to the present invention, the conditions for the polymerization reaction include: a polymerization temperature of 50-80°C and a polymerization time of 5-15 hours; preferably, the conditions for the polymerization reaction include: a polymerization temperature of 60-70°C and a polymerization time of 7-8 hours.

[0099] According to the present invention, in step 2), the halogenating agent is tribromomethane;

[0100] Preferably, the amount of the halogenating agent is 3-8% of the weight of the polymer intermediate, more preferably 4-7%, more preferably 5-6%, and particularly preferably 5%.

[0101] According to the present invention, in step 2), preferably, the halogenation reaction is carried out in the presence of a catalyst (preferably hexadecyltrimethylammonium bromide). The amount of the catalyst is 0.001-0.1% of the weight of the polymer intermediate, preferably 0.005-0.01%.

[0102] According to the present invention, in step 2), the conditions for the halogenation reaction include: a reaction temperature of 5-45°C and a reaction time of 10-80 hours; preferably, the conditions for the halogenation reaction include: a reaction temperature of 20-40°C and a reaction time of 15-30 hours.

[0103] According to a third aspect of the present invention, a fracturing fluid is provided, wherein the fracturing fluid contains the copolymer described in the first aspect of the present invention.

[0104] According to the present invention, the content of the copolymer in the fracturing fluid is 0.1-1 wt%, more preferably 0.2-0.8 wt%, and even more preferably 0.3-0.6 wt%.

[0105] The present invention will be described in detail below through embodiments, but the present invention is not limited to the following embodiments.

[0106] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0107] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0108] Example 1

[0109] 1) Preparation of shear-thickening copolymers

[0110] (1) Dissolve 0.05 mol of methacryloyl chloride and 0.05 mol of (2,4,4-trimethylpentyl-2-yl)phenol polyoxyethylene ether (n=5, purchased from Chengdu Kelong Chemical Co., Ltd. OP-5) in dichloromethane and react for 12 hours under ice bath conditions to obtain monomer octylphenol polyoxyethylene ether methacrylate (n=5);

[0111] (2) Add 70% acrylamide, 20% acrylic acid, 9% sorbic acid and 1% octylphenol polyoxyethylene ether methacrylate (n=5) to ethanol to prepare an ethanol solution with a monomer concentration of 10%. Heat to 60°C and add azobisisobutyronitrile initiator. After polymerization for 7 hours, remove the solvent to obtain the copolymer intermediate.

[0112] (3) Dissolve 5g of copolymer intermediate in 200mL of dichloromethane, and add 0.1g of cetyltrimethylammonium bromide, 4.5g of tribromomethane and 6g of sodium hydroxide. Purge with nitrogen for 1 hour, and then stir at room temperature for 24 hours. Wash the organic phase with ethanol until neutral, and obtain the shear-thickened copolymer after drying and rotary evaporation.

[0113] Figure 1 The infrared spectrum of the shear-thickening copolymer obtained in Example 1 shows that the synthesized shear-thickening copolymer contains amide groups, carboxyl groups, ether bonds, benzene rings and bromohydrocarbons, indicating that the synthesized polymer has the structure shown in formula (1).

[0114] 2) Preparation of high-temperature resistant fracturing fluid

[0115] To prepare a high-temperature resistant fracturing fluid with a mass fraction of 0.3 wt%, 0.3 parts by weight of copolymer thickener were slowly added to 99.7 parts by weight of water under stirring conditions, and the mixture was stirred for 2 hours to obtain the high-temperature resistant fracturing fluid.

[0116] Using a HAKKE RS600 rheometer, the shear rate was set to 10-1000 s. -1 The shearing time was 10 min, and the viscosity of the fracturing fluid was observed to change with the shear rate. Figure 2 The variable shear rheological curve of the fracturing fluid prepared with 0.3 wt% copolymer in Example 1 at 160°C is shown in the figure. Figure 2 It can be seen that the high-temperature resistant fracturing fluid prepared in this embodiment can withstand shear rates exceeding 100 s⁻¹. -1 Shear thickening occurred at that time.

[0117] Example 2

[0118] 1) Preparation of shear-thickening copolymers

[0119] (1) Dissolve 0.05 mol of methacryloyl chloride and 0.05 mol of (2,4,4-trimethylpentyl-2-yl)phenol polyoxyethylene ether (n=7, purchased from Chengdu Kelong Chemical Co., Ltd. OP-7) in dichloromethane and react for 12 hours under ice bath conditions to obtain monomer octylphenol polyoxyethylene ether methacrylate (n=7);

[0120] (2) Add 70% acrylamide, 20% acrylic acid, 8% sorbic acid and 2% octylphenol polyoxyethylene ether methacrylate (n=7) to ethanol to prepare an ethanol solution with a monomer concentration of 10%. Heat to 65°C and add azobisisobutyronitrile initiator. The copolymer intermediate is obtained after 7 hours of polymerization.

[0121] (3) Dissolve 5g of copolymer intermediate in 200mL of dichloromethane, and add 0.1g of cetyltrimethylammonium bromide, 4.5g of tribromomethane and 6g of sodium hydroxide. Purge with nitrogen for 1 hour, and then stir at room temperature for 24 hours. Wash the organic phase with ethanol until neutral, and obtain the shear-thickened copolymer after drying and rotary evaporation.

[0122] 2) Preparation of high-temperature fracturing fluid

[0123] To prepare a high-temperature resistant fracturing fluid with a mass fraction of 0.3% by weight: Under stirring conditions, slowly add 0.3 parts by weight of copolymer thickener to 99.7 parts by weight of water and stir for 2 hours to obtain the high-temperature resistant fracturing fluid.

[0124] Using a HAKKE RS600 rheometer, the shear rate was set to 10-1000 s. -1 The shearing time was 10 min, and the viscosity of the fracturing fluid was observed to change with the shear rate. Figure 3 The shear recovery rheological profile of the fracturing fluid prepared with 0.3 wt% copolymer in Example 2 is shown in [reference]. Figure 3It can be seen that the high-temperature resistant fracturing fluid prepared in this embodiment undergoes 5 minutes of 1000 seconds of curing. -1 After cutting, in 100 seconds -1 At the shear rate, the viscosity is higher than the initial viscosity. Figure 4 The temperature and shear rheological curves of the fracturing fluid prepared with 0.3 wt% copolymer in Example 3 are shown in the figure. Figure 4 It can be seen that the high-temperature resistant fracturing fluid prepared in this embodiment can withstand 140℃ for 100 seconds. -1 After 120 minutes of shearing, the viscosity remained above 100 mPa·s. When the temperature reached 140℃, the viscosity of the fracturing fluid stabilized with increasing time.

[0125] Example 3

[0126] 1) Preparation of shear-thickening copolymers

[0127] (1) 0.05 mol of methacryloyl chloride and 0.05 mol of (2,4,4-trimethylpentyl-2-yl)phenol polyoxyethylene ether (n=9, purchased from Chengdu Kelong Chemical Co., Ltd. OP-9) were dissolved in dichloromethane and reacted in an ice bath for 12 hours to obtain the monomer octylphenol polyoxyethylene ether methacrylate (n=9);

[0128] (2) Add 72% acrylamide, 23% acrylic acid, 4% sorbic acid and 1% octylphenol polyoxyethylene ether methacrylate (n=9) to ethanol to prepare an ethanol solution with a monomer concentration of 8%. Heat to 65°C and add azobisisobutyramidine hydrochloride initiator. The polymerization reaction is carried out for 8 hours to obtain the copolymer intermediate.

[0129] (3) Dissolve 5g of copolymer intermediate in 200mL of dichloromethane, and add 0.08g of cetyltrimethylammonium bromide, 4g of tribromomethane and 5g of sodium hydroxide. Purge with nitrogen for 1 hour, and then stir at room temperature for 24 hours. Wash the organic phase with ethanol until neutral, and obtain the shear-thickened copolymer after drying and rotary evaporation.

[0130] 2) Preparation of high-temperature resistant fracturing fluid

[0131] To prepare a high-temperature resistant fracturing fluid with a mass fraction of 0.4 wt%, 0.4 parts by weight of copolymer thickener were slowly added to 99.6 parts by weight of water under stirring conditions, and the mixture was stirred for 2 hours to obtain the high-temperature resistant fracturing fluid.

[0132] Using a HAKKE RS600 rheometer, the shear rate was set to 10-1000 s. -1 The shearing time was 10 min, and the viscosity of the fracturing fluid was observed to change with the shear rate. Figure 5The temperature and shear rheological curves of the fracturing fluid prepared with 0.4 wt% copolymer in Example 3 are shown in the figure. Figure 5 It can be seen that the high-temperature resistant fracturing fluid prepared in this embodiment can withstand 160℃ for 100 seconds. -1 After 120 minutes of shearing, the viscosity remained above 80 mPa·s. When the temperature reached 160℃, the viscosity of the fracturing fluid slowly increased over time, exhibiting shear thickening.

[0133] Example 4

[0134] 1) Preparation of shear-thickening copolymers

[0135] (1) Dissolve 0.05 mol of methacryloyl chloride and 0.05 mol of (2,4,4-trimethylpentyl-2-yl)phenol polyoxyethylene ether (n=10, purchased from Chengdu Kelong Chemical Co., Ltd. OP-10) in dichloromethane and react for 12 hours under ice bath conditions to obtain monomer octylphenol polyoxyethylene ether methacrylate (n=10);

[0136] (2) Add 70% acrylamide, 25% acrylic acid, 4.5% sorbic acid and 0.5% octylphenol polyoxyethylene ether methacrylate (n=10) to ethanol to prepare an ethanol solution with a monomer concentration of 8%. Heat to 65°C and add azobisisobutyramidine hydrochloride initiator. The polymerization reaction is carried out for 8 hours to obtain the copolymer intermediate.

[0137] (3) Dissolve 5g of copolymer intermediate in 200mL of dichloromethane, and add 0.05g of cetyltrimethylammonium bromide, 4g of tribromomethane and 5g of sodium hydroxide. Purge with nitrogen for 1 hour, and then stir at room temperature for 24 hours. Wash the organic phase with ethanol until neutral, and obtain the shear-thickened copolymer after drying and rotary evaporation.

[0138] 2) Preparation of high-temperature resistant fracturing fluid

[0139] To prepare a high-temperature resistant fracturing fluid with a mass fraction of 0.5 wt%, 0.5 parts by weight of copolymer thickener were slowly added to 99.5 parts by weight of water under stirring conditions, and the mixture was stirred for 2 hours to obtain the high-temperature resistant fracturing fluid.

[0140] Using a HAKKE RS600 rheometer, the shear rate was set to 10-1000 s. -1 The shearing time was 10 min, and the viscosity of the fracturing fluid was observed to change with the shear rate. Figure 6 The temperature and shear rheological curves of the fracturing fluid prepared with 0.5% by weight copolymer in Example 4 are shown in the attached figure. Figure 6 It can be seen that the high-temperature resistant fracturing fluid prepared in this embodiment can withstand 180°C for 100 seconds. -1After 120 minutes of shearing, the viscosity remained above 100 mPa·s. When the temperature reached 180℃, the viscosity of the fracturing fluid slowly increased over time, exhibiting a shear thickening phenomenon.

[0141] Example 5

[0142] 1) Preparation of shear-thickening copolymers

[0143] (1) Dissolve 0.05 mol of methacryloyl chloride and 0.05 mol of (2,4,4-trimethylpentyl-2-yl)phenol polyoxyethylene ether (n=10, same as above) in dichloromethane and react for 12 hours under ice bath conditions to obtain monomer octylphenol polyoxyethylene ether methacrylate (n=10);

[0144] (2) Add 75% acrylamide, 15% acrylic acid, 9% sorbic acid and 1% octylphenol polyoxyethylene ether methacrylate (n=10) to ethanol to prepare an ethanol solution with a monomer concentration of 10%. Heat to 70°C and add azobisisobutyramidine hydrochloride initiator. After 8 hours of polymerization, the copolymer intermediate is obtained.

[0145] (3) Dissolve 5g of copolymer intermediate in 200mL of dichloromethane, and add 0.1g of cetyltrimethylammonium bromide, 5g of tribromomethane and 8g of sodium hydroxide. Purge with nitrogen for 1 hour, and then stir at room temperature for 24 hours. Wash the organic phase with ethanol until neutral, and obtain the shear-thickened copolymer after drying and rotary evaporation.

[0146] 2) Preparation of high-temperature resistant fracturing fluid

[0147] To prepare a high-temperature resistant fracturing fluid with a mass fraction of 0.6 wt%, 0.6 parts by weight of copolymer thickener were slowly added to 99.4 parts by weight of water under stirring conditions, and the mixture was stirred for 2 hours to obtain the high-temperature resistant fracturing fluid.

[0148] Using a HAKKE RS600 rheometer, the shear rate was set to 10-1000 s. -1 The shearing time was 10 min, and the viscosity of the fracturing fluid was observed to change with the shear rate. Figure 7 The temperature and shear rheological curves of the fracturing fluid prepared with 0.6 wt% copolymer in Example 5 are shown in the figure. Figure 7 It can be seen that the high-temperature resistant fracturing fluid prepared in this embodiment can withstand 200℃ for 100 seconds. -1 After 120 minutes of shearing, the viscosity remained above 100 mPa·s. When the temperature reached 200℃, the viscosity of the fracturing fluid slowly increased over time, exhibiting shear thickening.

[0149] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A copolymer, characterized in that, The copolymer has the structure shown in formula (1). Equation (1) In equation (1), R1 and R2 are each independently selected from halogens; R3 and R4 are each independently selected from H and alkyl groups having 1-6 carbon atoms; R5 is selected from alkyl groups having 1-20 carbon atoms; a, b, c, and d represent the molar percentage of structural units, where a is 55-75%, b is 15-25%, c is 1-10%, and d is 0.1-5%. n is an integer selected from 5 to 10.

2. The copolymer according to claim 1, wherein, In equation (1), R1 and R2 are each independently selected from F, Cl, Br or I; R3 and R4 are each independently selected from H and alkyl groups having 1-3 carbon atoms; R5 is selected from alkyl groups having 6-10 carbon atoms; a, b, c, and d represent the molar percentage of structural units, where a is 70-75%, b is 15-25%, c is 4-9%, and d is 0.5-2%. n is selected from 5, 7, 9, or 10.

3. The copolymer according to claim 2, wherein, In equation (1), R1 and R2 are each independently selected from Cl or Br; R3 and R4 are each independently selected from H and methyl groups; R5 stands for octyl.

4. The copolymer according to claim 1, wherein, The copolymer has the structure shown in formula (2). Equation (2) In formula (2), a, b, c and d represent the molar percentage content of structural units, where a is 55-75%, b is 15-25%, c is 1-10%, and d is 0.1-5%. n is an integer selected from 5 to 10.

5. The copolymer according to claim 4, wherein, In formula (2), a, b, c and d represent the molar percentage content of structural units, where a is 70-75%, b is 15-25%, c is 4-9%, and d is 0.5-2%. n is selected from 5, 7, 9, or 10.

6. A method for preparing the copolymer according to any one of claims 1-5, characterized in that, This method Includes the following steps, 1) The step of polymerizing a monomer solution containing monomers A, B, C and D in the presence of an initiator to obtain a polymer intermediate; 2) The step of halogenating the polymer intermediate with a halogenating agent. Wherein, monomer A is acrylamide and / or alkylacrylamide, monomer B is acrylic acid and / or alkylacrylic acid, monomer C is sorbic acid, and monomer D is alkylphenol polyoxyethylene ether methacrylate; The alkyl groups in the alkyl acrylamide and the alkyl acrylic acid are each independently selected from H and alkyl groups having 1-6 carbon atoms; the alkyl groups in the alkylphenol polyoxyethylene ether methacrylate are selected from alkyl groups having 1-20 carbon atoms. Based on the total molar amount of monomers A, B, C and D, monomer A is 55-75 mol%, monomer B is 15-25 mol%, monomer C is 1-10 mol%, and monomer D is 0.1-5 mol%.

7. The method according to claim 6, wherein, The alkyl groups in the alkylacrylamide and the alkylacrylic acid are each independently selected from H and alkyl groups having 1-3 carbon atoms.

8. The method according to claim 7, wherein, The alkyl groups in the alkylacrylamide and the alkylacrylic acid are each independently H and methyl.

9. The method according to claim 6, wherein, The alkyl group in the alkylphenol polyoxyethylene ether methacrylate is selected from alkyl groups with 6-10 carbon atoms.

10. The method according to claim 9, wherein, The alkyl group in the alkylphenol polyoxyethylene ether methacrylate is octyl.

11. The method according to claim 6, wherein, Based on the total molar amount of monomers A, B, C and D, monomer A is 70-75 mol%, monomer B is 15-25 mol%, monomer C is 4-9 mol%, and monomer D is 0.5-2 mol.

12. The method according to any one of claims 6-11, wherein, The monomer A is one or more of acrylamide, methacrylamide, ethylacrylamide, and propylacrylamide.

13. The method according to any one of claims 6-11, wherein, The monomer B is one or more of acrylic acid, methacrylic acid, ethylacrylic acid, and propylacrylic acid.

14. The method according to any one of claims 6-11, wherein, The monomer D is selected from one or more compounds of formula (3) where n=5, n=7, n=9, and n=10. Equation (3).

15. The method according to any one of claims 6-11, wherein, The initiator is one or more of azobisisobutyronitrile, azobisisovalerate, and azobisisobutyramidine hydrochloride.

16. The method according to claim 15, wherein, The amount of initiator used is 0.05-0.2% of the total weight of the monomers.

17. The method according to any one of claims 6-11, wherein, The solvent in the monomer solution is one or more of methanol, ethanol, diethyl ether, acetone, toluene, and xylene.

18. The method according to claim 17, wherein, The solvent in the monomer solution is one or more of ethanol, diethyl ether, and acetone.

19. The method according to any one of claims 6-11, wherein, The conditions for the polymerization reaction include: a polymerization temperature of 60-70℃ and a polymerization time of 7-8 hours.

20. The method according to any one of claims 6-11, wherein, In step 2), the halogenating agent is tribromomethane.

21. The method according to any one of claims 6-11, wherein, The amount of the halogenating agent is 3-8% of the weight of the polymer intermediate.

22. The method according to any one of claims 6-11, wherein, The conditions for the halogenation reaction include: a reaction temperature of 5-45℃ and a reaction time of 10-80 hours.

23. A fracturing fluid, characterized in that, The fracturing fluid contains the copolymer described in any one of claims 1-5.

24. The fracturing fluid according to claim 23, wherein, The content of the copolymer in the fracturing fluid is 0.1-1% by weight.

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