Temperature-resistant and salt-resistant thickening agent for fracturing and preparation method thereof

Abstract

The invention relates to the technical field of thickeners, in particular to a temperature-resistant and salt-resistant thickener for fracturing and a preparation method thereof, the temperature-resistant and salt-resistant thickener for fracturing comprises the following raw materials: an acrylamide hydrophilic monomer, a sodium acrylate hydrophilic monomer, a salt-resistant monomer, an association monomer and a functional monomer, the preparation method comprises the following steps: mixing and dissolving a required amount of acrylamide hydrophilic monomer, sodium acrylate hydrophilic monomer, salt-resistant monomer, associated monomer and functional monomer in water to obtain a mixed solution, adjusting the pH value of the mixed solution, refrigerating the mixed solution, adding a required amount of low-temperature composite initiator, and carrying out a polymerization reaction to obtain a colloidal product, and cutting, sieving and drying the colloid product to obtain the product. The temperature-resistant and salt-resistant thickening agent has the advantages that the temperature-resistant and salt-resistant performance of the temperature-resistant and salt-resistant thickening agent for fracturing can be greatly improved by the aid of triple effects of'intrinsic strengthening, association promotion and electrostatic holding ';

Description

Technical Field

[0001] The invention relates to the technical field of thickeners, in particular to a temperature-resistant and salt-resistant thickener for fracturing and a preparation method thereof. Background Art

[0002] Fracturing and production increase is an important technical means to achieve the scale and efficiency development of unconventional resources such as tight oil and gas. Fracturing fluid is a chemical working fluid that must be used in the process of fracturing and production increase. The quality of its performance will significantly affect the final transformation effect and oil and gas recovery rate to a large extent. As an important main agent of fracturing fluid, the temperature and salt resistance of thickeners are particularly critical to ensure the drag reduction and sand carrying properties of fracturing fluid systems. Due to its high drag reduction, strong thickening ability, good gel breaking performance, low residue content, and insensitivity to bacteria, synthetic polymers have gradually become one of the mainstream directions for the research and application of fracturing fluid thickeners.

[0003] With the continuous advancement of reservoir transformation and the continuous expansion of its scale, fracturing production is advancing into deep oil and gas with greater burial depth, higher temperature and formation mineralization. At the same time, the urgent need to use flowback fluid to repeatedly prepare fracturing fluid on site also poses a great challenge to the salt resistance of fracturing fluid thickeners. At present, conventional polyacrylamide polymers are the most mature synthetic polymers, but the temperature and salt resistance of this type of polymer is very limited. Under high temperature and high mineralization conditions (especially the presence of high-valent ions), the viscosity loss is obvious and even flocculation and precipitation occur, and the overall viscoelasticity and sand carrying capacity are significantly reduced.

[0004] A Chinese patent document with publication number CN105646772A discloses a hydrophobic associating polymer and a preparation method thereof, wherein a hydrophobic associating polymer is prepared by using one or more of allyl alkyl quaternary ammonium salt, acrylamide alkyl sulfonic acid and its sulfonate, alkylphenol polyoxyethylene acrylate and polyoxyethylene alkyl acrylate as hydrophobic monomers. Under the conditions of a mineralization degree of 50000 mg / L (calcium and magnesium ions 2000 mg / L) and 90°C, the viscosity of the 0.2% polymer is 40 mPa·s.

[0005] A Chinese patent document with publication number CN113402660A discloses a polymer for oil recovery in high-temperature, high-salt and high-hardness reservoirs, as well as a preparation method and application thereof. The polymer introduces organic carboxylic acid monomer units containing acrylimide groups, acrylamide monomer units, N-alkyl substituted acrylamide sulfonic acid monomer units and polyol monomer units containing vinylaniline groups. Under the conditions of a mineralization degree of 40,000 mg / L (calcium and magnesium ions 2000 mg / L) and 90°C, the viscosity of the 0.2% polymer is greater than 35 mPa·s.

[0006] A Chinese patent document with publication number CN109705834A discloses a composition, a heat-resistant and salt-resistant fracturing fluid thickener prepared using the composition, and a preparation method thereof. The heat-resistant and salt-resistant fracturing fluid thickener is prepared by copolymerizing a composition of acrylamide, acrylic acid, a hydrophobic monomer, 2-acrylamide-2-methylpropane sulfonic acid, a rigid monomer, a surfactant and a shielding agent. Under the conditions of a mineralization degree of 50,000 mg / L (calcium and magnesium ions 3500 mg / L) and 160°C, the viscosity of 0.35% polymer after aging for 2 hours is greater than 70.5 mPa·s.

[0007] A Chinese patent document with publication number CN110540618A discloses a method for preparing a heat-resistant and salt-resistant copolymer. The heat-resistant and salt-resistant copolymer is prepared by copolymerizing polyacryloyloxyethyltrimethylammonium chloride or polymethacrylamidepropyltrimethylammonium chloride as a template, a sulfonic acid derivative containing a terminal olefin group and its sulfonate derivative as a functional monomer with acrylamide. Under the conditions of a mineralization degree of 55000 mg / L (calcium and magnesium ions 5000 mg / L) and 100°C, the viscosity of 0.2% polymer is greater than 15 mPa·s.

[0008] Liu Tongyi and others from Southwest Petroleum University prepared a fracturing fluid thickener by copolymerizing acrylamide, N-hydroxymethyl acrylamide (NMA) and hydrophobic cationic monomers. Under the conditions of 1% KCl and 100°C, the viscosity of 0.35% polymer was greater than 53 mPa·s (Liu Tongyi, Synthesis and Evaluation of an Aluminum Cross-linked Fracturing Fluid Thickener, Petrochemical Engineering, 2018, 47(2)).

[0009] Tang Tang from Southwest Petroleum University prepared a thickener for high suspension sand ratio and low damage fracturing fluid by copolymerization of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, alkyl dimethyl allyl ammonium chloride and N,N-methylenebisacrylamide. Under the conditions of 1% KCl and 90°C, the viscosity of 0.4% polymer was greater than 57.44 mPa·s (Tang Tang, Research on a high suspension sand ratio and low damage fracturing fluid, Southwest Petroleum University, 2018).

[0010] The above existing Chinese patent documents and journal documents are mainly prepared by copolymerizing acrylamide short-chain alkyl sulfonic acid or sulfonate or (and) rigid monomers containing unsaturated double bonds, and acrylamide long-chain alkyl sulfonic acid or sulfonate or long-chain alkyl quaternary ammonium salt containing unsaturated double bonds or long-chain alkyl acrylamide with self-association ability to prepare temperature-resistant and salt-resistant thickeners. The temperature-resistant, salt-resistant and shear-resistant abilities are very limited. For example, under the conditions of 50000mg / L (calcium and magnesium ions 5000mg / L) mineralization and 120°C, 0.15% to 0.2% thickener can resist heat and salt in 170s. -1 After 2 hours of shearing, the viscosity is difficult to reach 25 mPa·s or above. Summary of the invention

[0011] The present invention provides a heat-resistant and salt-resistant thickener for fracturing and a preparation method thereof, which overcomes the deficiencies of the above-mentioned prior art and can effectively solve the problem that the existing thickener has poor heat-resistant, salt-resistant and shear-resistant capabilities.

[0012] One of the technical solutions of the present invention is achieved through the following measures: a heat-resistant and salt-resistant thickener for fracturing, the raw materials including acrylamide hydrophilic monomer, sodium acrylate hydrophilic monomer, salt-resistant monomer, associative monomer and functional monomer in a mass ratio of 1: (0.15 to 0.3): (0.02 to 0.2): (0.004 to 0.06): (0.00004 to 0.0005).

[0013] The following is a further optimization and / or improvement of one of the above-mentioned technical solutions:

[0014] The above-mentioned salt-resistant monomer is one or more of acrylamide short-chain alkyl sulfonic acid / sulfonate salt-resistant monomer and rigid salt-resistant monomer containing unsaturated double bonds, and the associative monomer is one or more of acrylamide long-chain alkyl sulfonic acid / sulfonate associative monomer.

[0015] The acrylamide short-chain alkyl sulfonic acid / sulfonate salt-resistant monomer has the structural formula:

[0016]

[0017] Here, n is 1 to 3.

[0018] The above-mentioned rigid salt-resistant monomer containing unsaturated double bonds has the structural formula:

[0019]

[0020] The acrylamide long-chain alkyl sulfonic acid / sulfonate associative monomer has the structural formula:

[0021]

[0022] Wherein, n is 11 to 19.

[0023] The functional monomer is a modified graphene oxide functional monomer containing unsaturated double bonds.

[0024] The modified graphene oxide functional monomer containing unsaturated double bonds is obtained by the following method:

[0025] The first step is to add a required amount of graphene oxide to an ethanol aqueous solution with a mass concentration of 95% under stirring, and then add a required amount of a silane coupling agent containing an unsaturated double bond, and reflux the mixture at 65° C. to 90° C. for 2.5 h to 4.5 h to obtain a reaction mixture; wherein the mass ratio of graphene oxide to the silane coupling agent containing an unsaturated double bond is 1:(3 to 5);

[0026] In the second step, the reaction mixture is cooled and allowed to stand for 12 hours, then washed with acetone, vacuum filtered, and dried at 70° C. to 90° C. for 12 hours to obtain a modified graphene oxide functional monomer containing an unsaturated double bond.

[0027] In the first step, the vinyl-containing silane coupling agent is one or more of vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane, methacryloxyethyltrimethoxysilane, methacryloxyethyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, allyltrimethoxysilane and allyltriethoxysilane.

[0028] The above-mentioned heat-resistant and salt-resistant thickener for fracturing is obtained by the following method:

[0029] S1, mixing and dissolving required amounts of acrylamide hydrophilic monomer, sodium acrylate hydrophilic monomer, salt-resistant monomer, associative monomer and functional monomer in water to obtain a mixed solution;

[0030] S2, after adjusting the pH of the mixed solution, refrigerate the mixed solution, add the required amount of low-temperature composite initiator to cause polymerization reaction, obtain a colloidal product, cut, sieve and dry the colloidal product to obtain a heat-resistant and salt-resistant thickener for fracturing.

[0031] In the above step S1, the mass concentration of the solute in the mixed solution is 20% to 30%.

[0032] In the above step S2, the pH value of the mixed solution is adjusted to 7 to 9 with sodium bicarbonate solution, the refrigeration time is 30 min to 40 min, and the polymerization reaction temperature is 0°C to 25°C.

[0033] In the above step S2, the low-temperature composite initiator is a mixture of sodium persulfate, sodium bisulfite and azobisisobutylamidine hydrochloride in a volume ratio of 1:1:0.5, and the volume ratio of the low-temperature composite initiator to the mixed solution is 1:200.

[0034] The second technical solution of the present invention is achieved by the following measures: A method for preparing a heat-resistant and salt-resistant thickener for fracturing is carried out according to the following method:

[0035] S1, mixing and dissolving required amounts of acrylamide hydrophilic monomer, sodium acrylate hydrophilic monomer, salt-resistant monomer, associative monomer and functional monomer in water to obtain a mixed solution;

[0036] S2, after adjusting the pH of the mixed solution, refrigerate the mixed solution, add the required amount of low-temperature composite initiator to cause polymerization reaction, obtain a colloidal product, cut, sieve and dry the colloidal product to obtain a heat-resistant and salt-resistant thickener for fracturing.

[0037] The present invention integrates heat-resistant and salt-resistant acrylamide short-chain alkyl sulfonic acid / sulfonate salt-resistant monomers or rigid salt-resistant monomers containing unsaturated double bonds, self-association acrylamide acrylamide long-chain alkyl sulfonic acid / sulfonate associating monomers, and thermally stable, two-dimensional planar structured modified graphene oxide functional monomers containing unsaturated double bonds into a polymer skeleton, and utilizes the triple effects of "intrinsic reinforcement + association promotion + electrostatic support" to greatly improve the heat-resistant and salt-resistant performance of the heat-resistant and salt-resistant thickener for fracturing of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the infrared spectrum of the modified graphene oxide containing unsaturated double bonds prepared in Example 16 of the present invention.

[0039] Figure 2 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 16 of the present invention with a concentration of 0.15% and the heat-resistant and shear-resistant thickener in Comparative Example 1.

[0040] Figure 3 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 27 of the present invention with a concentration of 0.15% and the heat-resistant and shear-resistant thickener in Comparative Example 3.

[0041] Figure 4 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 29 of the present invention with a concentration of 0.15% and that of Comparative Example 5.

[0042] Figure 5 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 31 of the present invention with a concentration of 0.15% and the heat-resistant and shear-resistant thickener in Comparative Example 7.

[0043] Figure 6 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 33 of the present invention with a concentration of 0.15% and the heat-resistant and shear-resistant thickener in Comparative Example 1.

[0044] Figure 7 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 35 of the present invention with a concentration of 0.15% and the heat-resistant and shear-resistant thickener in Comparative Example 1.

[0045] Figure 8 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 26 of the present invention with a concentration of 0.3% and the heat-resistant and shear-resistant thickener in Comparative Example 2.

[0046] Fig. 9 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 28 of the present invention with a concentration of 0.3% and the heat-resistant and shear-resistant thickener in Comparative Example 4.

[0047] Fig.10This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 30 of the present invention with a concentration of 0.3% and the heat-resistant and shear-resistant thickener in Comparative Example 6.

[0048] Fig.11 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 32 of the present invention with a concentration of 0.3% and the heat-resistant and shear-resistant thickener in Comparative Example 8.

[0049] Fig.12 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 34 of the present invention with a concentration of 0.3% and the heat-resistant and shear-resistant thickener in Comparative Example 2.

[0050] Fig.13 This is a comparison chart of the heat-resistant and salt-resistant thickener for fracturing prepared in Example 36 of the present invention with a concentration of 0.3% and the heat-resistant and shear-resistant thickener in Comparative Example 2.

[0051] Fig.14 The figure is a comparison diagram of the thixotropic energy of the heat-resistant and salt-resistant thickener for fracturing of the present invention at a concentration of 0.15%.

[0052] Fig.15 This is a comparison chart of the thixotropic energy of the heat-resistant and salt-resistant thickener for fracturing of the present invention at a concentration of 0.3%. DETAILED DESCRIPTION

[0053] The present invention is not limited by the following embodiments, and specific implementation methods can be determined according to the technical scheme of the present invention and actual conditions. Unless otherwise specified, the various chemical reagents and chemicals mentioned in the present invention are all known and commonly used chemical reagents and chemicals in the prior art; the percentages in the present invention are all mass percentages unless otherwise specified.

[0054] The present invention will be further described below in conjunction with embodiments:

[0055] Example 1: The heat-resistant and salt-resistant thickener for fracturing comprises raw materials of acrylamide hydrophilic monomer, sodium acrylate hydrophilic monomer, salt-resistant monomer, associative monomer and functional monomer in a mass ratio of 1:(0.15 to 0.3):(0.02 to 0.2):(0.004 to 0.06):(0.00004 to 0.0005).

[0056] Example 2: As an optimization of the above example, the salt-resistant monomer is one or more of acrylamide short-chain alkyl sulfonic acid / sulfonate salt-resistant monomers and rigid salt-resistant monomers containing unsaturated double bonds, and the associative monomer is one or more of acrylamide long-chain alkyl sulfonic acid / sulfonate associative monomers.

[0057] Example 3: As an optimization of the above example, acrylamide short-chain alkyl sulfonic acid / sulfonate salt-resistant monomer has the structural formula:

[0058]

[0059] Here, n is 1 to 3.

[0060] In the present invention, the acrylamide short-chain alkyl sulfonic acid / sulfonate salt-resistant monomer is one or more of 2-acrylamide-2-methylpropanesulfonate sodium, 2-acrylamide-2-ethylbutanesulfonate sodium, 2-acrylamide-2-propylpentanesulfonate sodium and 2-acrylamide-2-butylhexanesulfonate sodium.

[0061] Embodiment 4: As an optimization of the above embodiment, a rigid salt-resistant monomer containing an unsaturated double bond has the structural formula:

[0062]

[0063] In the present invention, the rigid salt-resistant monomer containing unsaturated double bonds is one or more of sodium p-acrylamidobenzenesulfonate, sodium p-vinylbenzenesulfonate and N-vinylpyrrolidone.

[0064] Example 5: As an optimization of the above example, acrylamide long-chain alkyl sulfonic acid / sulfonate associative monomer has the structural formula:

[0065]

[0066] Here, n is 11 to 19.

[0067] In the present invention, the acrylamide acrylamide long-chain alkyl sulfonic acid / sulfonate associative monomer is one or more of 2-acrylamido dodecyl sodium sulfonate, 2-acrylamido tetradecyl sodium sulfonate, 2-acrylamido hexadecyl sodium sulfonate, 2-acrylamido octadecyl sodium sulfonate and 2-acrylamido eicosyl sodium sulfonate.

[0068] Embodiment 6: As an optimization of the above embodiment, the functional monomer is a modified graphene oxide functional monomer containing unsaturated double bonds.

[0069] Example 7: As an optimization of the above example, a modified graphene oxide functional monomer containing an unsaturated double bond is obtained by the following method:

[0070] The first step is to add a required amount of graphene oxide to an ethanol aqueous solution with a mass concentration of 95% under stirring, and then add a required amount of a silane coupling agent containing an unsaturated double bond, and reflux the mixture at 65° C. to 90° C. for 2.5 h to 4.5 h to obtain a reaction mixture; wherein the mass ratio of the graphene oxide to the silane coupling agent containing an unsaturated double bond is 1:(3 to 5);

[0071] In the second step, the reaction mixture is cooled and allowed to stand for 12 hours, then washed with acetone, vacuum filtered, and dried at 70° C. to 90° C. for 12 hours to obtain a modified graphene oxide functional monomer containing an unsaturated double bond.

[0072] The modified graphene oxide functional monomer containing unsaturated double bonds prepared by the present invention has the structural formula:

[0073]

[0074] Example 8: As an optimization of the above example, in the first step, the vinyl-containing silane coupling agent is one or more of vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane, methacryloxyethyltrimethoxysilane, methacryloxyethyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, allyltrimethoxysilane, and allyltriethoxysilane.

[0075] Example 9: As an optimization of the above example, a heat-resistant and salt-resistant thickener for fracturing is obtained by the following method:

[0076] S1, mixing and dissolving required amounts of acrylamide hydrophilic monomer, sodium acrylate hydrophilic monomer, salt-resistant monomer, associative monomer and functional monomer in water to obtain a mixed solution;

[0077] S2, after adjusting the pH of the mixed solution, refrigerate the mixed solution, add the required amount of low-temperature composite initiator to cause polymerization reaction, obtain a colloidal product, cut, sieve and dry the colloidal product to obtain a heat-resistant and salt-resistant thickener for fracturing.

[0078] The molecular weight of the heat-resistant and salt-resistant thickener for fracturing prepared by the invention is 5 million Daltons to 18 million Daltons.

[0079] Example 10: As an optimization of the above example, in step S1, the mass concentration of the solute in the mixed solution is 20% to 30%.

[0080] Example 11: As an optimization of the above example, in step S2, the pH value of the mixed solution is adjusted to 7 to 9 with sodium bicarbonate solution, the refrigeration time is 30 min to 40 min, and the polymerization reaction temperature is 0°C to 25°C.

[0081] Example 12: As an optimization of the above example, in step S2, the low-temperature composite initiator is a mixture of sodium persulfate, sodium bisulfite and azobisisobutyramidine hydrochloride in a volume ratio of 1:1:0.5, and the volume ratio of the low-temperature composite initiator to the mixed solution is 1:200.

[0082] Embodiment 13:

[0083] The modified graphene oxide functional monomer containing unsaturated double bonds is obtained by the following method:

[0084] The first step is to add a required amount of graphene oxide to an ethanol aqueous solution with a mass concentration of 95% under stirring, and then add a required amount of a silane coupling agent containing an unsaturated double bond (vinyltrimethoxysilane), and reflux the reaction at 65° C. for 2.5 hours to obtain a reaction mixture; wherein the mass ratio of graphene oxide to the silane coupling agent containing an unsaturated double bond is 1:3;

[0085] In the second step, the reaction mixture was cooled and allowed to stand for 12 hours, and then washed with acetone, vacuum filtered, and dried at 70° C. for 12 hours to obtain a modified graphene oxide functional monomer containing an unsaturated double bond.

[0086] The heat-resistant and salt-resistant thickener for fracturing comprises raw materials of acrylamide, sodium acrylate, salt-resistant monomer (sodium 2-acrylamide-2-methylpropane sulfonate), associative monomer (sodium 2-acrylamide dodecyl sulfonate) and functional monomer (modified graphene oxide functional monomer containing unsaturated double bonds) in a mass ratio of 1:0.15:0.02:0.004:0.00004, and is obtained by the following method:

[0087] S1, mixing and dissolving required amounts of acrylamide, sodium acrylate, salt-resistant monomer, associative monomer and functional monomer in water to obtain a mixed solution with a mass concentration of 20%;

[0088] S2, after adjusting the pH value of the mixed solution to 7 with sodium bicarbonate solution, the mixed solution is placed in a freezer for 30 minutes to cool the mixed solution to 0°C, and then the required amount of low-temperature composite initiator (a mixed solution of sodium persulfate, sodium bisulfite and azobisisobutylamidine hydrochloride in a volume ratio of 1:1:0.5) is added to cause a polymerization reaction, and the reaction is terminated when the temperature rises to the highest and then decreases without changing by more than 1°C to obtain a colloidal product. The colloidal product is cut, sieved and dried to obtain a heat-resistant and salt-resistant thickener for fracturing; wherein the volume ratio of the low-temperature composite initiator to the mixed solution is 1:200.

[0089] Embodiment 14:

[0090] The modified graphene oxide functional monomer containing unsaturated double bonds is obtained by the following method:

[0091] The first step is to add a required amount of graphene oxide to an ethanol aqueous solution with a mass concentration of 95% under stirring, and then add a required amount of a silane coupling agent containing an unsaturated double bond (methacryloxymethyltrimethoxysilane), and reflux the reaction at 90° C. for 4.5 hours to obtain a reaction mixture; wherein the mass ratio of graphene oxide to the silane coupling agent containing an unsaturated double bond is 1:5;

[0092] In the second step, the reaction mixture was cooled and allowed to stand for 12 hours, and then washed with acetone, vacuum filtered, and dried at 90° C. for 12 hours to obtain a modified graphene oxide functional monomer containing an unsaturated double bond.

[0093] The heat-resistant and salt-resistant thickener for fracturing comprises raw materials of acrylamide, sodium acrylate, salt-resistant monomer (sodium 2-acrylamide-2-ethylbutanesulfonate), associative monomer (sodium 2-acrylamide tetradecylsulfonate) and functional monomer (modified graphene oxide functional monomer containing unsaturated double bonds) in a mass ratio of 1:0.3:0.2:0.06:0.0005, and is obtained by the following method:

[0094] S1, mixing and dissolving required amounts of acrylamide, sodium acrylate, salt-resistant monomer, associative monomer and functional monomer in water to obtain a mixed solution with a mass concentration of 30%;

[0095] S2, after adjusting the pH value of the mixed solution to 9 with sodium bicarbonate solution, the mixed solution is placed in a freezer for 40 minutes to cool the mixed solution to 25°C, and then the required amount of low-temperature composite initiator (a mixed solution of sodium persulfate, sodium bisulfite and azobisisobutylamidine hydrochloride in a volume ratio of 1:1:0.5) is added to cause a polymerization reaction, and the reaction is terminated when the temperature rises to the highest and then decreases without changing by more than 1°C to obtain a colloidal product. The colloidal product is cut, sieved and dried to obtain a heat-resistant and salt-resistant thickener for fracturing; wherein the volume ratio of the low-temperature composite initiator to the mixed solution is 1:200.

[0096] Embodiment 15:

[0097] The modified graphene oxide functional monomer containing unsaturated double bonds is obtained by the following method:

[0098] The first step is to add a required amount of graphene oxide to an ethanol aqueous solution with a mass concentration of 95% under stirring, and then add a required amount of a silane coupling agent containing an unsaturated double bond (allyltriethoxysilane), and reflux the mixture at 80° C. for 3.5 hours to obtain a reaction mixture; wherein the mass ratio of graphene oxide to the silane coupling agent containing an unsaturated double bond is 1:4;

[0099] In the second step, the reaction mixture was cooled and allowed to stand for 12 hours, and then washed with acetone, vacuum filtered, and dried at 80° C. for 12 hours to obtain a modified graphene oxide functional monomer containing an unsaturated double bond.

[0100] The heat-resistant and salt-resistant thickener for fracturing comprises raw materials of acrylamide, sodium acrylate, a salt-resistant monomer (N-vinyl pyrrolidone), an associative monomer (sodium 2-acrylamidoarachidyl sulfonate) and a functional monomer (modified graphene oxide functional monomer containing unsaturated double bonds) in a mass ratio of 1:0.2:0.1:0.03:0.0002, and is obtained by the following method:

[0101] S1, mixing and dissolving required amounts of acrylamide, sodium acrylate, salt-resistant monomer, associative monomer and functional monomer in water to obtain a mixed solution with a mass concentration of 20% to 30%;

[0102] S2, after adjusting the pH value of the mixed solution to 8 with sodium bicarbonate solution, the mixed solution is placed in a freezer for 35 minutes to cool the mixed solution to 15°C, and then the required amount of low-temperature composite initiator (a mixed solution of sodium persulfate, sodium bisulfite and azobisisobutylamidine hydrochloride in a volume ratio of 1:1:0.5) is added to cause a polymerization reaction, and the reaction is terminated when the temperature rises to the highest and then decreases without changing by more than 1°C to obtain a colloidal product. The colloidal product is cut, sieved and dried to obtain a heat-resistant and salt-resistant thickener for fracturing; wherein the volume ratio of the low-temperature composite initiator to the mixed solution is 1:200.

[0103] Compared with the prior art, the present invention has the following beneficial effects:

[0104] The present invention integrates and introduces acrylamide short-chain alkyl sulfonic acid / sulfonate salt-resistant monomers or rigid salt-resistant monomers containing unsaturated double bonds with heat and salt resistance, acrylamide acrylamide long-chain alkyl sulfonic acid / sulfonate associating monomers with self-association ability, and modified graphene oxide functional monomers with unsaturated double bonds having strong thermal stability and a two-dimensional planar structure into a polymer skeleton, and utilizes the triple effects of "essential reinforcement + association promotion + electrostatic support" to greatly improve the heat and salt resistance of the heat-resistant and salt-resistant thickener for fracturing of the present invention, so that the heat-resistant and salt-resistant thickener for fracturing of the present invention is 0.15% to 0.30% under the conditions of 50000 mg / L mineralization (calcium and magnesium ion content 5000 mg / L) and 120°C. The thickener is 170s -1 After 2 hours of shearing, the viscosity reaches 25mPa·s to 55mPa·s, and the thixotropic energy reaches 1000Pa / s to 2300Pa / s.

[0105] Embodiment 16:

[0106] The modified graphene oxide functional monomer containing unsaturated double bonds is obtained by the following method:

[0107] The first step is to add 1 g of graphene oxide to 800 mL of 95% ethanol aqueous solution at a stirring speed of 500 r / min, and then add 3 g of a silane coupling agent containing an unsaturated double bond (vinyl triethoxysilane), and perform condensation reflux reaction at 80° C. for 2.5 hours to obtain a reaction mixture;

[0108] In the second step, the reaction mixture was cooled and allowed to stand for 12 h, then washed with 100 mL of acetone and vacuum filtered, and dried at 70° C. for 12 h to obtain a modified graphene oxide functional monomer containing an unsaturated double bond, which was labeled as MGO-1.

[0109] The heat-resistant and salt-resistant thickener for fracturing is obtained by the following method:

[0110] S1, mixing acrylamide, sodium acrylate, salt-resistant monomer (sodium 2-acrylamide-2-methylpropane sulfonate), associative monomer (sodium 2-acrylamide tetradecyl sulfonate) and functional monomer (modified graphene oxide functional monomer MGO-1 containing unsaturated double bonds) in a mass ratio of 1:0.15:0.02:0.004:0.00004 and dissolving in water to obtain a mixed solution with a mass concentration of 25%;

[0111] S2, after adjusting the pH value of the mixed solution to 8 with sodium bicarbonate solution, 1000 mL of the mixed solution was placed in a freezer for 30 to 40 min to cool the mixed solution to 0°C, and then 5 mL of a low-temperature composite initiator (a mixture of sodium persulfate, sodium bisulfite and azobisisobutylamidine hydrochloride in a volume ratio of 1:1:0.5) was added to cause a polymerization reaction, and an electronic thermometer was inserted to monitor the reaction temperature. The reaction was terminated when the temperature rose to the highest and then decreased without changing by more than 1°C to obtain a colloidal product. The colloidal product was cut into small particles of about 5 mm, sieved through an 80-mesh sieve, and dried at 95°C to obtain a heat-resistant and salt-resistant thickener for fracturing with a mesh number ≥80, which was marked as NTSP-1.

[0112] Comparative Example 1: The difference from Example 16 of the present invention is that, during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the modified graphene oxide functional monomer MGO-1 containing unsaturated double bonds was not added to the raw materials, and a heat-resistant and salt-resistant thickener for fracturing with a mesh number ≥ 80 was obtained, which was marked as DBP-1.

[0113] Example 17: The difference from Example 16 of the present invention is that, during the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the mass ratio of the raw materials in step S1 is changed to 1:0.3:0.02:0.004:0.00004, and the remaining steps are the same as in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥80 is obtained, which is marked as NTSP-2.

[0114] Example 18: The difference from Example 16 of the present invention is that, during the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the mass ratio of the raw materials in step S1 is changed to 1:0.15:0.2:0.004:0.00004, and the remaining steps are the same as in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥80 is obtained, which is marked as NTSP-3.

[0115] Example 19: The difference from Example 16 of the present invention is that, during the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the mass ratio of the raw materials in step S1 is changed to 1:0.15:0.02:0.06:0.00004, and the remaining steps are the same as those in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥80 is obtained, which is marked as NTSP-4.

[0116] Example 20: The difference from Example 16 of the present invention is that, during the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the mass ratio of the raw materials in step S1 is changed to 1:0.15:0.02:0.004:0.0005, and the remaining steps are the same as those in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥80 is obtained, which is marked as NTSP-5.

[0117] Example 21: The difference from Example 16 of the present invention is that, during the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the mass ratio of the raw materials in step S1 is changed to 1:0.3:0.2:0.004:0.00004, and the remaining steps are the same as those in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥80 is obtained, which is marked as NTSP-6.

[0118] Example 22: The difference from Example 16 of the present invention is that, during the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the mass ratio of the raw materials in step S1 is changed to 1:0.3:0.02:0.06:0.00004, and the remaining steps are the same as those in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥80 is obtained, which is marked as NTSP-7.

[0119] Example 23: The difference from Example 16 of the present invention is that, during the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the mass ratio of the raw materials in step S1 is changed to 1:0.3:0.02:0.004:0.0005, and the remaining steps are the same as those in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥80 is obtained, which is marked as NTSP-8.

[0120] Example 24: The difference from Example 16 of the present invention is that, during the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the mass ratio of the raw materials in step S1 is changed to 1:0.3:0.2:0.004:0.00004, and the remaining steps are the same as in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥80 is obtained, which is marked as NTSP-9.

[0121] Example 25: The difference from Example 16 of the present invention is that, during the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the mass ratio of the raw materials in step S1 is changed to 1:0.3:0.2:0.06:0.00004, and the remaining steps are the same as in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥80 is obtained, which is marked as NTSP-10.

[0122] Example 26: The difference from Example 16 of the present invention is that, during the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the mass ratio of the raw materials in step S1 is changed to 1:0.3:0.2:0.06:0.0005, and the remaining steps are the same as in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥80 is obtained, which is marked as NTSP-11.

[0123] Comparative Example 2: The difference from Example 26 of the present invention is that, during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the modified graphene oxide functional monomer MGO-1 containing unsaturated double bonds was not added to the raw materials, and a heat-resistant and salt-resistant thickener for fracturing with a mesh number ≥80 was obtained, which was marked as DBP-2.

[0124] Example 27: The difference from Example 16 of the present invention is that during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the salt-resistant monomer is changed to sodium acrylamidobenzenesulfonate, and the remaining steps are the same as those in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥ 80 is obtained, which is marked as NTSP-12.

[0125] Comparative Example 3: The difference from Example 27 of the present invention is that, during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the modified graphene oxide functional monomer MGO-1 containing unsaturated double bonds was not added to the raw materials, and a heat-resistant and salt-resistant thickener for fracturing with a mesh number ≥ 80 was obtained, which was marked as DBP-3.

[0126] Example 28: The difference from Example 26 of the present invention is that during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the salt-resistant monomer is changed to sodium acrylamidobenzenesulfonate, and the remaining steps are the same as those in Example 26, to obtain a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥ 80, which is marked as NTSP-13.

[0127] Comparative Example 4: The difference from Example 28 of the present invention is that, during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the modified graphene oxide functional monomer MGO-1 containing unsaturated double bonds was not added to the raw materials, and a heat-resistant and salt-resistant thickener for fracturing with a mesh number ≥ 80 was obtained, which was marked as DBP-4.

[0128] Example 29: The difference from Example 16 of the present invention is that during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the salt-resistant monomer is changed to sodium p-vinylbenzenesulfonate, and the remaining steps are the same as those in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥ 80 is obtained, which is marked as NTSP-14.

[0129] Comparative Example 5: The difference from Example 29 of the present invention is that, during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the modified graphene oxide functional monomer MGO-1 containing unsaturated double bonds was not added to the raw materials, and a heat-resistant and salt-resistant thickener for fracturing with a mesh number ≥ 80 was obtained, which was marked as DBP-5.

[0130] Example 30: The difference from Example 26 of the present invention is that during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the salt-resistant monomer is changed to sodium p-vinylbenzenesulfonate, and the remaining steps are the same as those in Example 26, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥ 80 is obtained, which is marked as NTSP-15.

[0131] Comparative Example 6: The difference from Example 30 of the present invention is that, during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the modified graphene oxide functional monomer MGO-1 containing unsaturated double bonds was not added to the raw materials, and a heat-resistant and salt-resistant thickener for fracturing with a mesh number ≥ 80 was obtained, which was marked as DBP-6.

[0132] Example 31: The difference from Example 16 of the present invention is that during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the salt-resistant monomer is changed to N-vinyl pyrrolidone, and the remaining steps are the same as those in Example 16, and a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥ 80 is obtained, which is marked as NTSP-16.

[0133] Comparative Example 7: The difference from Example 31 of the present invention is that, during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the modified graphene oxide functional monomer MGO-1 containing unsaturated double bonds was not added to the raw materials, and a heat-resistant and salt-resistant thickener for fracturing with a mesh number ≥ 80 was obtained, which was marked as DBP-7.

[0134] Example 32: The difference from Example 26 of the present invention is that the salt-resistant monomer is changed to N-vinyl pyrrolidone, and the remaining steps are the same as Example 26, to obtain a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥ 80 mesh, which is marked as NTSP-17.

[0135] Comparative Example 8: The difference from Example 32 of the present invention is that, during the preparation of the heat-resistant and salt-resistant thickener for fracturing, the modified graphene oxide functional monomer MGO-1 containing unsaturated double bonds was not added to the raw materials, and a heat-resistant and salt-resistant thickener for fracturing with a mesh number ≥ 80 was obtained, which was marked as DBP-8.

[0136] Example 33: The difference from Example 16 of the present invention is that in the preparation process of the modified graphene oxide functional monomer containing unsaturated double bonds, the raw material unsaturated double bond silane coupling agent is changed to methacryloxypropyltrimethoxysilane, and the remaining steps are the same as Example 16. The obtained modified graphene oxide functional monomer containing unsaturated double bonds is marked as MGO-2, and the obtained temperature-resistant and salt-resistant thickener NTSP-18 for fracturing with a mesh number ≥80 mesh is obtained.

[0137] Example 34: The difference from Example 26 of the present invention is that in the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the raw material functional monomer is replaced by a modified graphene oxide functional monomer MGO-2 containing an unsaturated double bond, and the remaining steps are the same as Example 26, to obtain a heat-resistant and salt-resistant thickener for fracturing with a mesh size ≥ 80, which is marked as NTSP-19.

[0138] Example 35: The difference from Example 16 of the present invention is that in the preparation process of the modified graphene oxide functional monomer containing unsaturated double bonds, the raw material unsaturated double bond silane coupling agent is changed to allyltrimethoxysilane, and the remaining steps are the same as Example 16. The obtained modified graphene oxide functional monomer containing unsaturated double bonds is marked as MGO-3, and the obtained temperature-resistant and salt-resistant thickener NTSP-20 for fracturing with a mesh number ≥80 mesh is obtained.

[0139] Example 36: The difference from Example 26 of the present invention is that, in the preparation process of the heat-resistant and salt-resistant thickener for fracturing, the raw material functional monomer is replaced with a modified graphene oxide functional monomer MGO-3 containing an unsaturated double bond, and the remaining steps are the same as Example 26, to obtain a heat-resistant and salt-resistant thickener for fracturing with a mesh number ≥ 80, which is marked as NTSP-21.

[0140] Example 37: The modified graphene oxide functional monomer containing unsaturated double bonds prepared in Example 16 of the present invention was characterized by Fourier transform infrared spectroscopy using the KBr pellet method. At the same time, the graphene oxide before modification was used as a control. The results are as follows: Figure 1 As shown by Figure 1 It can be seen that most of the absorption peaks corresponding to graphene oxide after modification have undergone blue shift to a certain extent, at 1396 cm -1 The hydroxyl bending vibration peak corresponding to 2920 cm -1 and 2847cm -1 At 1622cm -1 The absorption peak attributable to the carbon-carbon double bond (C=C) in MGO-1 red-shifts to 1613 cm -1 The results show that the vinyl-modified graphene oxide, i.e., modified graphene oxide functional monomer containing unsaturated double bonds, has been successfully prepared.

[0141] Example 38: The viscosity average molecular weight of the heat-resistant and salt-resistant thickener for fracturing of the present invention was measured using an Ubbelohde viscometer (0.55 mm capillary inner diameter) according to the method specified in GB / T 12005.10-1992 "Determination of Molecular Weight of Polyacrylamide". The results are shown in Table 2. It can be seen from Table 2 that the molecular weight of the heat-resistant and salt-resistant thickener for fracturing of the present invention ranges from 5 million Daltons to 18 million Daltons.

[0142] Example 39: The performance of the heat-resistant and salt-resistant thickener for fracturing of the present invention was tested, including the heat resistance, shear resistance and thixotropic energy.

[0143] Test method:

[0144] Solution preparation: The heat-resistant and salt-resistant thickener for fracturing of the present invention is placed in brine (total mineralization 50000 mg / L, wherein the calcium and magnesium ion content is 5000 mg / L), and dissolved evenly at room temperature and a stirring speed of 400±50 r / min to prepare a heat-resistant and salt-resistant thickener solution for fracturing with a concentration of 0.15% to 0.3% for standby use.

[0145] Temperature and shear resistance: RS6000 advanced rheometer PZ38 coaxial cylindrical rotor system was used at 120°C and 170s -1 The heat-resistant and salt-resistant thickener solution for fracturing was subjected to a heat-resistant and shear-resistant test, and the viscosity change curve over time and the final stable viscosity value were recorded. The duration from heating to the end of the test was 2 hours.

[0146] Thixotropic energy: Physica MCR301 advanced rheometer was used in rotation mode at 120°C for 0.01s -1 Up to 500s -1 Test from low shear to high shear within the shear rate range (stage 1, the resulting curve is an upward curve), 500s -1 Constant shear test 1min (2 stages), 500s -1 To 0.01s -1 From high shear to low shear test (3 stages, the obtained curve is a downward curve), the hysteresis area A of the thixotropic loop composed of the upward curve and the downward curve of the shear stress changing with the shear rate is calculated by the Hysteresis Area I model, and the thixotropic energy is obtained.

[0147] According to the above method, the heat resistance, shear resistance and thixotropic energy of the heat-resistant and salt-resistant thickeners for fracturing prepared in Example 16, Examples 26 to 36 and Comparative Examples 1 to 8 of the present invention were tested respectively.

[0148] Test results: The heat resistance and shear resistance of the heat-resistant and salt-resistant thickener for fracturing of the present invention are as follows: Figures 2 to 13As shown, the thixotropic energy of the heat-resistant and salt-resistant thickener for fracturing of the present invention is as follows: Fig.14 and Fig.15 As shown,

[0149] Depend on Figure 2 and Fig.14 It can be seen that in Example 16 of the present invention, after sodium 2-acrylamide-2-methylpropane sulfonate is used as the salt-resistant monomer and the raw material containing unsaturated double bonds modified graphene oxide MGO-1 is introduced, the heat-resistant and shear-stable viscosity and thixotropic energy of the obtained heat-resistant and salt-resistant thickener NTSP-1 for fracturing at an addition amount of 0.15% are 10.89 mPa·s and 391 Pa / s higher than those of the heat-resistant and salt-resistant thickener DBP-1 for fracturing obtained in Comparative Example 1 (without the introduction of MGO-1).

[0150] from Figures 3 to 7 and Fig.14 It can also be seen that after changing the salt-resistant monomer to sodium acrylamidobenzenesulfonate or sodium p-vinylbenzenesulfonate or N-vinylpyrrolidone, or changing the modified graphene oxide MGO-1 containing unsaturated double bonds to MGO-2 or MGO-3, the heat-resistant and shear-resistant stable viscosity and thixotropic energy of the obtained heat-resistant and salt-resistant thickener for fracturing at a dosage of 0.15% are 9.84mPa·s to 13.34mPa·s and 299Pa / s to 657Pa / s higher than those without the introduction of modified graphene oxide.

[0151] Likewise, from Figure 8 and Fig.15 It can be seen that in Example 26 of the present invention, after sodium 2-acrylamide-2-methylpropane sulfonate is used as the salt-resistant monomer and the unsaturated double bond-modified graphene oxide MGO-1 is introduced, the heat-resistant and salt-resistant thickener NTSP-1 for fracturing at a dosage of 0.3% has a heat-resistant and shear-resistant stable viscosity and thixotropic energy that are 13.3 mPa·s and 626 Pa / s higher than those of the thickener DBP-2 obtained in Comparative Example 2 (without the introduction of MGO-1).

[0152] from Figures 9 to 13 and Fig.15 It can also be seen that after changing the salt-resistant monomer to sodium acrylamidobenzenesulfonate, sodium p-vinylbenzenesulfonate, or N-vinylpyrrolidone, or changing the modified graphene oxide containing unsaturated double bonds to MGO-2 or MGO-3, the heat-resistant and shear-stable viscosity and thixotropic energy of the obtained heat-resistant and salt-resistant thickener for fracturing at a dosage of 0.3% are 11.46mPa·s to 15.66mPa·s and 495Pa / s to 805Pa / s higher than those without the introduction of modified graphene oxide.

[0153] The above data results show that the heat-resistant and salt-resistant thickener for fracturing obtained by introducing modified graphene oxide containing unsaturated double bonds has greatly improved heat-resistant, salt-resistant and shear-resistant capabilities.

[0154] In summary, the present invention utilizes the triple effects of "essential strengthening + association promotion + electrostatic support" to greatly improve the heat and salt resistance of the heat-resistant and salt-resistant thickener for fracturing of the present invention, so that under the conditions of 50000 mg / L mineralization (calcium and magnesium ion content 5000 mg / L) and 120°C, the heat-resistant and salt-resistant thickener for fracturing of the present invention with a concentration of 0.15% to 0.30% can withstand 170s -1 After 2 hours of shearing, the viscosity reaches 25mPa·s to 55mPa·s, and the thixotropic energy reaches 1000Pa / s to 2300Pa / s.

[0155] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

[0156] Table 1

[0157]

[0158]

[0159] Table 2

[0160] Example Viscosity average molecular weight / ten thousand Example Viscosity average molecular weight / ten thousand Example 16 1800 Embodiment 31 1704 Embodiment 17 1720 Embodiment 32 568 Embodiment 18 1450 Embodiment 33 1685 Embodiment 19 1080 Embodiment 34 516 Embodiment 20 780 Embodiment 35 1729 Embodiment 21 950 Embodiment 36 534 Embodiment 22 815 Comparative Example 1 1912 Embodiment 23 753 Comparative Example 2 678 Embodiment 24 647 Comparative Example 3 1867 Embodiment 25 605 Comparative Example 4 634 Embodiment 26 565 Comparative Example 5 1829 Embodiment 27 1725 Comparative Example 6 603 Embodiment 28 500 Comparative Example 7 1854 Embodiment 29 1751 Comparative Example 8 632 Embodiment 30 548

Claims

1. A heat-resistant and salt-resistant thickener for fracturing, characterized in that The raw materials include acrylamide hydrophilic monomer, sodium acrylate hydrophilic monomer, salt-resistant monomer, associative monomer and functional monomer in a mass ratio of 1:0.15 to 0.3:0.02 to 0.2:0.004 to 0.06:0.00004 to 0.0005.

2. The heat-resistant and salt-resistant thickener for fracturing according to claim 1, characterized in that The salt-resistant monomer is one or more of acrylamide short-chain alkyl sulfonic acid / sulfonate salt-resistant monomers and rigid salt-resistant monomers containing unsaturated double bonds, and the associative monomer is one or more of acrylamide long-chain alkyl sulfonic acid / sulfonate associative monomers.

3. The heat-resistant and salt-resistant thickener for fracturing according to claim 2, characterized in that Acrylamide short chain alkyl sulfonic acid / sulfonate salt-resistant monomer, its structural formula is: Here, n is 1 to 3.

4. The heat-resistant and salt-resistant thickener for fracturing according to claim 2, characterized in that A rigid salt-resistant monomer containing an unsaturated double bond, the structural formula of which is:

5. The heat-resistant and salt-resistant thickener for fracturing according to any one of claims 1 to 4, characterized in that Acrylamide long chain alkyl sulfonic acid / sulfonate associative monomer, its structural formula is: Here, n is 11 to 19.

6. The heat-resistant and salt-resistant thickener for fracturing according to any one of claims 1 to 5, characterized in that The functional monomer is a modified graphene oxide functional monomer containing an unsaturated double bond, which is obtained by the following method: The first step is to add a required amount of graphene oxide to an ethanol aqueous solution with a mass concentration of 95% under stirring, and then add a required amount of a silane coupling agent containing an unsaturated double bond, and reflux the mixture at 65° C. to 90° C. for 2.5 h to 4.5 h to obtain a reaction mixture; wherein the mass ratio of graphene oxide to the silane coupling agent containing an unsaturated double bond is 1:3 to 5; In the second step, the reaction mixture is cooled and allowed to stand for 12 hours, then washed with acetone, vacuum filtered, and dried at 70° C. to 90° C. for 12 hours to obtain a modified graphene oxide functional monomer containing an unsaturated double bond.

7. The heat-resistant and salt-resistant thickener for fracturing according to claim 6, characterized in that In the first step, the vinyl-containing silane coupling agent is one or more of vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane, methacryloxyethyltrimethoxysilane, methacryloxyethyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, allyltrimethoxysilane, and allyltriethoxysilane.

8. The heat-resistant and salt-resistant thickener for fracturing according to any one of claims 1 to 7, characterized in that Obtained as follows: S1, mixing and dissolving required amounts of acrylamide hydrophilic monomer, sodium acrylate hydrophilic monomer, salt-resistant monomer, associative monomer and functional monomer in water to obtain a mixed solution; S2, after adjusting the pH of the mixed solution, refrigerate the mixed solution, add the required amount of low-temperature composite initiator to cause polymerization reaction, obtain a colloidal product, cut, sieve and dry the colloidal product to obtain a heat-resistant and salt-resistant thickener for fracturing.

9. The heat-resistant and salt-resistant thickener for fracturing according to claim 8, characterized in that In step S1, the mass concentration of the solute in the mixed solution is 20% to 30%; or / and, in step S2, the pH value of the mixed solution is adjusted to 7 to 9 with a sodium bicarbonate solution, the refrigeration time is 30 minutes to 40 minutes, and the polymerization reaction temperature is 0°C to 25°C; or / and, in step S2, the low-temperature composite initiator is a mixture of sodium persulfate, sodium bisulfite and azobisisobutyramidine hydrochloride in a volume ratio of 1:1:0.5, and the volume ratio of the low-temperature composite initiator to the mixed solution is 1:

200.

10. A method for preparing a heat-resistant and salt-resistant thickener for fracturing according to any one of claims 1 to 7 and 9, characterized in that Proceed as follows: S1, mixing and dissolving required amounts of acrylamide hydrophilic monomer, sodium acrylate hydrophilic monomer, salt-resistant monomer, associative monomer and functional monomer in water to obtain a mixed solution; S2, after adjusting the pH of the mixed solution, refrigerate the mixed solution, add the required amount of low-temperature composite initiator to cause polymerization reaction, obtain a colloidal product, cut, sieve and dry the colloidal product to obtain a heat-resistant and salt-resistant thickener for fracturing.

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