Reinjection water instant hydrophobic association polymer for fracturing and preparation method thereof

Abstract

The invention relates to the technical field of oilfield chemistry, and provides a reinjection water instant hydrophobic association polymer for fracturing and a preparation method thereof. The preparation method comprises the following steps: preparing a polymerizable hydrophobic association micelle from a hydrophobic functional monomer and a nonionic polarity regulator, mixing the polymerizable hydrophobic association micelle solution with a conventional monomer aqueous solution, regulating the molecular weight of the copolymer by a molecular weight regulator, reacting, granulating, drying and crushing to obtain the reinjection water instant hydrophobic association polymer. By comprehensively utilizing the synergistic effect of multi-element supramolecular force of a ternary hydrophobic functional monomer, the stability of associated micelles is regulated and controlled, and a salt-resistant polymer three-dimensional network structure with a dense association network and a strong association effect is obtained; a polarity regulator containing a nonionic hydrophilic structure is introduced, a hydration layer is formed on the surface of associated micelles by utilizing a self-assembly effect, a water phase aggregation effect and an ion shielding effect of a hydrophobic structure are weakened, stretching of a molecular chain in a water phase is facilitated, online mixing instant efficiency of reinjection water is obtained, and high salt resistance and strong sand-carrying performance are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield chemistry, and more specifically, to a rapidly soluble hydrophobically associating polymer for reinjected water in fracturing and a preparation method thereof. Background Art

[0002] With the gradual progress of shale gas development, large-scale horizontal well fracturing technology has become the main technical means for shale gas exploitation. For the huge water resource consumption, the fracturing fluid system faces the dual challenges of online mixing and rapid dissolution of reinjected water with high salinity (TDS > 10,000 mg / L) and high salt tolerance performance requirements. Traditional thickeners for fracturing fluids mostly use linear polyacrylamide, which shows a significant drop in performance in a high-salt environment due to the excessive curling of molecular chains and the destruction of the solvation layer. On the one hand, the shear thinning index decreases significantly, making it difficult for the fracturing fluid to maintain effective turbulence suppression ability during pipeline flow, resulting in a 30 - 40% reduction in drag reduction efficiency; on the other hand, the elastic modulus of the dynamic network structure decays rapidly, causing insufficient suspension ability for proppants and severely restricting the formation of fracture conductivity.

[0003] By enhancing the hydrophobicity of associating monomers and increasing the size of hydrophobic microdomains, the salt tolerance of polymers can be greatly improved. Although the large-size micelle system constructed with strongly hydrophobic monomers can form a high-strength fluid structure with a crosslinked network through hydrophobic association, the excessive content of hydrophobic groups in its molecular chain segments will significantly reduce the hydration and dissolution performance of the polymer. This phenomenon is particularly prominent in saline systems, mainly due to the synergistic effect of two aspects: (1) The salting-out effect caused by high-concentration electrolytes exacerbates the aggregation state transformation of hydrophobic chain segments, resulting in a further increase in micelle size; (2) The charge screening effect of counterions in the solution causes the molecular chain to contract, forming a denser core-shell structure, thus hindering the penetration and diffusion process of water molecules into the interior of polymer particles. This dissolution kinetic retardation phenomenon leads to the problem that traditional hydrophobically associating polymers are difficult to dissolve rapidly in online mixing processes.

[0004] The Chinese invention patent with the patent number CN106190088B developed a seawater-based salt-resistant instant polymer. When mixed with seawater, its complete dissolution time reaches 7 minutes, which cannot meet the mixing requirements for large-scale fracturing. The salt-resistant and high-temperature-resistant polymer proposed in the Chinese invention patent with the patent number CN118496448A adopts a multi-monomer cooperation method, introducing monomers containing salt-resistant sulfonic acid groups, high-temperature-resistant two-dimensional planar structures, and strong hydrophilic groups into the macromolecular backbone of the associative thickener, simultaneously improving the high-salt resistance, high-temperature resistance, and instant solubility of the associative thickener. However, to achieve a more suitable sand-carrying performance, the concentration of this thickener is relatively high, lacking economy in large-scale hydraulic fracturing. In addition, in some technical routes, excessive hydrophilic groups are introduced to improve the dissolution performance. This method weakens the strength of the associative effect, resulting in an obvious network structure dissociation phenomenon in the fracturing fluid system under high-temperature and high-salt conditions. In summary, based on the existing technical means, there is still a large room for exploration to obtain a fracturing fluid thickener that meets the requirements of online instant mixing of high-salinity reinjected water for large-scale hydraulic fracturing, and at the same time has low dosage, temperature and salt resistance, and high drag reduction and strong sand-carrying ability. Summary of the Invention

[0005] The purpose of the present invention is to provide a reinjected water instant hydrophobic associative polymer for fracturing. Through the structural design of hydrophobic functional monomers and the optimization of the hydration layer on the surface of hydrophobic associative micelles, the polymer can be instantaneously dissolved in high-salinity water and simultaneously exhibit excellent salt resistance.

[0006] Another purpose of the present invention is to provide a preparation method of a reinjected water instant hydrophobic associative polymer for fracturing. A ternary hydrophobic functional monomer containing multiple cooperative supramolecular forces is used to regulate the stability of associative micelles, obtaining a three-dimensional network structure of a salt-resistant polymer with a dense associative network and strong associative effect. By introducing a polar regulator containing a non-ionic hydrophilic structure, a hydration layer is formed on the surface of the associative micelles through self-assembly, weakening the aqueous phase aggregation effect and ionic shielding effect of the hydrophobic structure, facilitating the stretching of molecules in the aqueous phase, and thus obtaining the same dissolution efficiency as conventional polyacrylamide polymers.

[0007] To solve the above technical problems, the technical solutions adopted in this application are as follows: On the one hand, an embodiment of this application provides a reinjected water instant hydrophobic associative polymer for fracturing, and its molecular formula is shown in Formula 1: Formula 1; Among them, by mass fraction, i is 60 - 65%; j is 15 - 39%; k is 0 - 15%; l is 0 - 3%; m is 0 - 2%; n is 0 - 4%. R1 is a hydrophobic functional monomer 1, containing a non-ionic active group, a quaternary ammonium salt structure and a long carbon chain structure; R2 is a hydrophobic functional monomer 2, which is an alkylacrylamide-based mono- or poly-sulfonate; R3 is a hydrophobic functional monomer 3, containing a poly-non-ionic hydrophilic group and a hydrophobic carbon chain with a single unsaturated double bond; the weight-average molecular weight of the hydrophobic associative polymer is 5×10 6 - 8×10 6 .

[0008] Furthermore, the structural formula of the hydrophobic functional monomer 1 is as shown in Formula 2, wherein the double bond structure and the quaternary ammonium salt structure can be connected by a non-ionic polar group; Formula 2; In Formula 2, R4 can be , a is 1 - 4; or an active group containing an ester group, as shown in Formula 3: Formula 3; In Formula 3, b is 0 - 2, c is 0 - 2; or an active group containing an amide group, as shown in Formula 4: Formula 4; In Formula 4, d is 0 - 2, e is 0 - 2; or an active group containing an ethoxy group, as shown in Formula 5: Formula 5; In Formula 4, f is 0 - 2, g is 1 - 10, h is 0 - 2; In Formula 1, R5 is a straight-chain alkyl group with 8 - 22 carbon atoms.

[0009] Furthermore, the structural formula of the hydrophobic functional monomer 2 is as shown in Formula 6: Formula 6; In Formula 6, R6 and R7 can be -H, -OH, -COO - , -SO3 - , -SO4 - , -PO4 - one of them, and in the same molecule, at least has one anion structure; R8 is a straight-chain alkyl group with 8 - 14 carbon atoms.

[0010] Furthermore, the structural formula of the hydrophobic functional monomer 3 is as shown in Formula 7: Formula 7; In Formula 7, R9 is a polyvalent nonionic hydrophilic group, and its active groups are at least one of alcohol group, ether group, amine group, and carbonyl functional group; Further, the structure of R9 can be as shown in Formulas 8-10: Formula 8; or Formula 9; or Formula 10; R 10 The structural formula is as shown in Formula 11: Formula 11; In Formula 11, o is 4-12; p is 5-10; the spatial conformation of the carbon chain has a certain fold angle.

[0011] On the other hand, the embodiments of the present application provide a preparation method of a water-soluble hydrophobic associating polymer for fracturing reinjection water, including the following steps: S1. Add a hydrophobic functional monomer into water, and add a nonionic polar regulator to mix to obtain a polymerizable hydrophobic associating micelle solution. The hydrophobic functional monomer includes one or more of hydrophobic functional monomer 1, hydrophobic functional monomer 2, and hydrophobic functional monomer 3. S2. Add the polymerizable hydrophobic associating micelle solution into an aqueous solution of a conventional monomer. The total monomer system is composed of the hydrophobic functional monomer and the conventional monomer. Fix the mass of the total monomer to account for 65-75% of the total mass of the aqueous solution to obtain a mixed solution A. S3. Regulate the molecular weight of the copolymer in the mixed solution A with a molecular weight regulator to obtain a mixed solution B. S4. Add an initiator to the mixed solution B, keep warm and stand still for 2-4 h to complete the reaction, and obtain the hydrophobic associating polymer after granulation, drying, and pulverization.

[0012] Further, the above-mentioned conventional monomer is composed of one or more of acrylamide, sodium acrylate, and 2-acrylamido-2-methylpropanesulfonic acid sodium.

[0013] Further, the above-mentioned nonionic polar regulator is a small molecule active substance with a nonionic active group or a copolymer containing a nonionic active group; the addition amount of the nonionic polar regulator does not exceed 3 wt% of the total monomer.

[0014] Further, the above-mentioned small molecule active substance with a nonionic active group is composed of a hydrophobic chain part and a hydrophilic active group. The hydrophobic chain part is one or more of alkyl alcohol, alkylamine, and alkylphenol structures; the hydrophilic active group is one or more of polyoxyethylene block, glucoside group, polyglycerol group, and cyclodextrin group.

[0015] Further, the copolymer containing non-ionic active groups is copolymerized from one or more polymerizable monomers, with a degree of polymerization of 100 - 500. The polymerizable monomers consist of a hydrophobic chain part and a hydrophilic active group. The hydrophobic chain part is one or more of alkyl alcohol, alkylamine, and alkylphenol structures; the hydrophilic active group is one or more of polyoxyethylene block, glucosyl group, polyglycerol group, and cyclodextrin group.

[0016] Further, the above molecular weight regulator is one or more of sodium formate, sodium acetate, isopropyl alcohol, sodium hypophosphite, and urea, and the addition amount of the molecular weight regulator is 0.002 wt% - 0.004 wt% of the total monomers.

[0017] Further, in the above step S4, the initiator includes a first-stage initiator and a second-stage initiator. The first-stage initiator includes sodium formaldehyde sulfoxylate accounting for 0.01% - 0.025% of the total monomer system mass and ammonium persulfate accounting for 0.005% - 0.015% of the total monomer system mass; the second-stage initiator is azobisisobutyronitrile accounting for 0.05% - 0.08% of the total monomer system mass.

[0018] Further, in the above step S4, the crushing mesh number is 100 - 120 meshes.

[0019] Further, water is selected as the solvent. To achieve the effects of rapid dissolution and salt resistance of the polymer, the selected solvent can be brine containing cations such as Na + , K + , Ca 2+ , Mg 2+ , Cu 2+ , Fe 2+ , Fe 3+ , Pb 2+ , and Cr 2+ , or actual produced water with returned formation water salinity.

[0020] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: 1. The ternary hydrophobic monomer synergistic combination is adopted. Through the structural optimization of the hydrophobic functional monomer, the common actions of ionic force, hydrogen bond force, hydrophobic force, and spatial physical entanglement are balanced, obtaining a tight hydrophobic association structure and showing excellent salt resistance.

[0021] 2. Non-ionic active substances are incorporated into the hydrophobic association micelles, weakening the ionic effect, reducing the aggregation of the hydrophobic association structure, and facilitating the diffusion of water molecules into the interior, thus having rapid solubility in brine.

[0022] 3. Through the construction of a self-assembled hydrophobic association structure, a fracturing fluid with high drag reduction and high sand-carrying performance can be obtained. Description of the Drawings

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a schematic diagram of the preparation method process and principle of a quickly soluble hydrophobic associating polymer for reinjected water in fracturing provided by the embodiments of the present invention; Figure 2 It is a schematic diagram of the dissolution state of polymer particles after 2 minutes of dissolution in reinjected water in Embodiment 1 of the present invention; Figure 3 It is a schematic diagram of the dissolution state of polymer particles after 2 minutes of dissolution in reinjected water in Comparative Example 1 of the present invention; Figure 4 It is a comparison diagram of the particle size differences of monomer solutions in Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention. Detailed implementation manners

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can all be obtained as conventional products through commercial purchase.

[0026] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will refer to specific embodiments to detail the present invention.

[0027] To solve the problem of polymer salt tolerance, the present invention uses a ternary hydrophobic functional monomer containing multiple synergistic supramolecular forces. The three monomers are of cationic, anionic, and non-ionic structures respectively. Among them, hydrophobic functional monomer 1 and hydrophobic functional monomer 2 are mainly combined through ionic forces; hydrophobic functional monomer 3 is a hydrogen bond donor and combines with the other two monomers through hydrogen bond forces. Its hydrophobic tail chain has a bent conformation, enhancing the entanglement of hydrophobic chains inside the micelle. The combination of the ternary monomers realizes the regulation of the stability of associative micelles, thereby obtaining a three-dimensional network structure of an anti-salt polymer with a dense associative network and a strong associative effect. To solve the problem of quick dissolution in high salinity water, the present application introduces a polar regulator containing a non-ionic hydrophilic structure, and forms a hydration layer on the surface of the associative micelle through self-assembly, weakening the aqueous phase aggregation effect and ionic shielding effect of the hydrophobic structure, facilitating the stretching of molecules in the aqueous phase, and thus obtaining the quick dissolution efficiency of online mixing of reinjected water.

[0028] In the face of the problems that conventional linear polymers are not salt-resistant and the dissolution rate of hydrophobically associating polymers is slow or even insoluble in the blending of large-scale hydraulic fracturing reinjection water, through the structural design of hydrophobic functional monomers and the optimization of the hydration layer on the surface of hydrophobically associating micelles, the effects of rapid dissolution of the polymer in high salinity water and excellent salt resistance are simultaneously achieved.

[0029] As Figure 1 shown, based on the basic theoretical route concept of the present invention, a preparation method of a rapidly dissolving hydrophobically associating polymer for reinjection water in fracturing is proposed, including the following steps: S1. By mass, add 9 - 11 parts of acrylamide, 3 - 5 parts of sodium acrylate, and 1 - 2 parts of 2 - acrylamido - 2 - methylpropanesulfonic acid sodium to 18 - 22 parts of water, and adjust the pH to 6.5 - 7.5 to obtain an aqueous solution of conventional monomers; S2. Add the hydrophobic functional monomer to water, add a non - ionic polar regulator, the addition amount of the non - ionic polar regulator does not exceed 3% of the total monomer system mass. The non - ionic polar regulator is a small - molecule active substance with a non - ionic active group or a copolymer containing a non - ionic active group. Stir at 200 r / min for 24 h to obtain a polymerizable hydrophobically associating micelle solution. The hydrophobic functional monomer includes one or more of hydrophobic functional monomer 1, hydrophobic functional monomer 2, and hydrophobic functional monomer 3. The structural formula of hydrophobic functional monomer 1 is as shown in Formula 2: Formula 2; The structural formula of hydrophobic functional monomer 2 is as shown in Formula 6: Formula 6; The structural formula of hydrophobic functional monomer 3 is as shown in Formula 7: Formula 7; S3. Add the polymerizable hydrophobically associating micelle solution to the aqueous solution of conventional monomers. The total monomer system is composed of hydrophobic functional monomers and conventional monomers, and fix the mass of the total monomers accounting for 65 - 75% of the mass of water to obtain a mixed solution A; S4. Regulate the molecular weight of the copolymer in the mixed solution A with a molecular weight regulator. The molecular weight regulator is one or more of sodium formate, sodium acetate, isopropyl alcohol, sodium hypophosphite, and urea; the weight - average molecular weight of the copolymer after regulation is 5×10 6 - 8×10 6 , and the addition amount of the molecular weight regulator is 0.002% - 0.004% of the total monomer system mass to obtain a mixed solution B; S5. Add initiators to the mixed solution B. The initiators include a first-stage initiator and a second-stage initiator. The first-stage initiator includes sodium formaldehyde sulfoxylate accounting for 0.01% - 0.025% of the total monomer system mass and ammonium persulfate accounting for 0.005% - 0.015% of the total monomer system mass; the second-stage initiator is azobisisobutyronitrile accounting for 0.05% - 0.08% of the total monomer system mass. Keep warm and stand still for 2 - 4 h until the reaction is completed, then granulate, dry, and crush to 100 - 120 mesh to obtain the hydrophobically associating polymer.

[0030] The features and properties of the present invention will be further described in detail below in conjunction with the embodiments.

[0031] Example 1 This Example 1 provides a preparation method of a rapidly soluble hydrophobically associating polymer for fracturing injection water, including the following steps: S1. By mass, add 10.3 parts of acrylamide, 4.2 parts of sodium acrylate, and 1.8 parts of 2-acrylamido-2-methylpropanesulfonic acid sodium salt to 20 parts of water, and adjust the pH to 6.5 - 7.5 to obtain a conventional monomer aqueous solution. S2. Add 0.32 part of hydrophobic functional monomer 1 and 0.21 part of hydrophobic functional monomer 2 to 13 parts of clear water, add 0.36 part of non-ionic polar regulator, and stir at 200 r / min for 24 h until the liquid presents a homogeneous state to obtain a polymerizable hydrophobically associating micelle solution. Hydrophobic functional monomer 1 is 2-acrylamidotriethoxydimethyldodecylammonium chloride, and its structural formula is as shown in Formula 12: Formula 12; Hydrophobic functional monomer 2 is sodium 2-acrylamidododecanesulfonate, and its structural formula is as shown in Formula 13: Formula 13; The non-ionic polar regulator is dodecyl glucoside; S3. Add the polymerizable hydrophobically associating micelle solution to the conventional monomer aqueous solution. The total monomer system is composed of hydrophobic functional monomers and conventional monomers, and the total monomer mass accounts for 70% of the water mass to obtain a mixed solution A; S4. Add 0.0003 part of molecular weight regulator sodium hypophosphite, 0.0012 part of sodium formaldehyde sulfoxylate as the first-stage initiator, 0.0008 part of ammonium persulfate, and 0.005 part of azobisisobutyronitrile as the second-stage initiator to the mixed solution A; S5. Keep warm and stand still for 2 - 4 h until the reaction is completed to obtain a polymer block. Granulate, dry, and crush the obtained polymer block to 120 mesh to obtain the hydrophobically associating polymer.

[0032] Example 2 Example 2 provides a preparation method of a fast-dissolving hydrophobically associating polymer for reinjected water in fracturing, comprising the following steps: S1. By mass, add 10.3 parts of acrylamide, 4.2 parts of sodium acrylate, and 1.8 parts of 2-acrylamido-2-methylpropanesulfonic acid sodium salt to 20 parts of water, and adjust the pH to 6.5 - 7.5 to obtain an aqueous solution of conventional monomers; S2. Add 0.26 part of hydrophobic functional monomer 1, 0.12 part of hydrophobic functional monomer 2, and 0.21 part of hydrophobic functional monomer 3 to 13 parts of clear water, add 0.3 part of nonionic polar regulator, and stir at 200 r / min for 24 h until the liquid presents a homogeneous state to obtain a polymerizable hydrophobically associating micelle solution. Hydrophobic functional monomer 1 is ethyl acrylate dimethyldodecylammonium chloride, and its structural formula is as shown in Formula 14: Formula 14; Hydrophobic functional monomer 2 is 2-acrylamidododecane disulfonic acid sodium salt, and its structural formula is as shown in Formula 15: Formula 15; Hydrophobic functional monomer 3 is 2-acrylamidotriglycerol oleate, and its structural formula is as shown in Formula 16: Formula 16; The nonionic polar regulator is dodecyl glucoside; S3. Add the polymerizable hydrophobically associating micelle solution to the aqueous solution of conventional monomers. The total monomer system is composed of hydrophobic functional monomers and conventional monomers, and the total monomer mass accounts for 70% of the water mass to obtain a mixed solution A; S4. Respectively add 0.0003 part of molecular weight regulator sodium hypophosphite, 0.0012 part of sodium formaldehyde sulfoxylate as the first-stage initiator, 0.0008 part of ammonium persulfate, and 0.005 part of azobisisobutyronitrile as the second-stage initiator; S5. Keep warm and stand for 2 - 4 h until the reaction is completed to obtain a polymer block. Granulate, dry, and pulverize the obtained polymer block to 120 meshes to obtain a hydrophobically associating polymer.

[0033] Example 3 Example 3 provides a preparation method of a fast-dissolving hydrophobically associating polymer for reinjected water in fracturing, comprising the following steps: S1. By mass, add 10.3 parts of acrylamide, 4.2 parts of sodium acrylate, and 1.8 parts of 2-acrylamido-2-methylpropanesulfonic acid sodium salt to 20 parts of water, and adjust the pH to 6.5 - 7.5 to obtain an aqueous solution of monomers; S2. Add 0.55 parts of hydrophobic functional monomer 1 and hydrophobic functional monomer 3 to 13 parts of water, add 0.38 parts of nonionic polar regulator, and stir at 200 r / min for 24 h until the liquid presents a homogeneous state, obtaining a polymerizable hydrophobic association micelle solution. Hydrophobic functional monomer 1 is ethyl acrylate dimethyl hexadecyl ammonium chloride, and its structural formula is as shown in Formula 17: Formula 17; Hydrophobic functional monomer 3 is 2-acrylamido triethanolamine erucate, and its structural formula is as shown in Formula 18: Formula 18; The nonionic polar regulator is dodecyl glucoside; S3. Add the polymerizable hydrophobic association micelle solution to the conventional monomer aqueous solution. The total monomer system is composed of hydrophobic functional monomers and conventional monomers. Fix the total monomer mass to account for 70% of the water mass, obtaining mixed solution A; S4. Respectively add 0.0003 parts of molecular weight regulator sodium hypophosphite, 0.0012 parts of sodium formaldehyde sulfoxylate as the first-stage initiator, 0.0008 parts of ammonium persulfate, and 0.005 parts of azobisisobutyronitrile as the second-stage initiator; S5. Keep warm and stand for 2 - 4 h until the reaction is completed, obtaining a polymer gel block. Granulate, dry, and crush the obtained polymer gel block to 120 meshes to obtain a hydrophobic association polymer.

[0034] Example 4 This Example 4 provides a preparation method of a fast-dissolving hydrophobic association polymer for fracturing reinjection water, including the following steps: S1. By mass, add 10.3 parts of acrylamide, 4.2 parts of sodium acrylate, and 1.8 parts of 2-acrylamido-2-methylpropanesulfonic acid sodium to 20 parts of water, and adjust the pH to 6.5 - 7.5 to obtain a conventional monomer aqueous solution; S2. Add 0.32 parts of hydrophobic functional monomer 1 and 0.21 parts of hydrophobic functional monomer 2 to 13 parts of water, add 0.41 parts of nonionic polar regulator, and stir at 200 r / min for 24 h until the liquid presents a homogeneous state, obtaining a polymerizable hydrophobic association micelle solution. Hydrophobic functional monomer 1 is 2-acrylamido triethoxy dimethyl dodecyl ammonium chloride, and its structural formula is as shown in Formula 12 above. Hydrophobic functional monomer 2 is 2-acrylamido dodecyl sulfonic acid sodium, and its structural formula is as shown in Formula 13 above. The nonionic polar regulator is triethylamine polyoxyethylene ether with a polymerization degree of 150, and its structural formula is as shown in Formula 19: Formula 19; S3. Add the polymerizable hydrophobic associative micelle solution to the conventional monomer aqueous solution. The total monomer system consists of the hydrophobic functional monomer and the conventional monomer. Fix the mass of the total monomer at 70% of the mass of water to obtain the mixed solution A. S4. Add 0.0003 parts of the molecular weight regulator sodium hypophosphite, 0.0012 parts of sodium formaldehyde sulfoxylate as the first-stage initiator, 0.0008 parts of ammonium persulfate, and 0.005 parts of azobisisobutyronitrile as the second-stage initiator respectively. S5. Keep warm and stand still for 2 - 4 h until the reaction is completed to obtain the polymer gel block. Granulate, dry, and pulverize the obtained polymer gel block to 120 meshes to obtain the hydrophobic associative polymer.

[0035] Comparative Example 1 This Comparative Example 1 is basically the same as Example 1, except that the non-ionic polar regulator is not added to verify the beneficial effect of the non-ionic polar regulator on the rapid dissolution of the polymer. Analyze the solubility difference through the viscosity comparison of different dissolution times.

[0036] Comparative Example 2 This Comparative Example 2 is basically the same as Example 2, except that the hydrophobic functional monomer 2 and the hydrophobic functional monomer 3 are not added, and the addition amount of the hydrophobic functional monomer 1 is increased to 0.59 parts. Compare the difference in anti-salt performance between the synergistic effect of multiple hydrophobic monomers and the single hydrophobic functional monomer 1 to verify the high anti-salt effect of the hydrophobic association formed by the supramolecular action of the ternary hydrophobic monomers.

[0037] Comparative Example 3 This Comparative Example 3 is basically the same as Example 2, except that the hydrophobic functional monomer 1 is not added, and the addition amount of the hydrophobic functional monomer 2 is increased to 0.59 parts. Compare the difference in anti-salt performance between the synergistic effect of multiple hydrophobic monomers and the single hydrophobic functional monomer 2.

[0038] Comparative Example 4 This Comparative Example 4 is basically the same as Example 1, except that the hydrophobic functional monomer 1 and the hydrophobic functional monomer 2 are not added. Compare the solubility and anti-salt property of the polymer in the absence of hydrophobic monomers.

[0039] Test Example Use the produced water sample from the gas well as the water sample source for polymer performance testing. Its salinity is shown in Table 1. According to the principle of preparing the reinjected water on-site, mix the produced water sample and the clear water at a ratio of 4:1 to obtain the simulated reinjected water sample. Unless otherwise specified in the following text, the reinjected water is used to represent it.

[0040]

[0041] The polymers obtained from the above examples and comparative examples were dissolved in reinjected water at a concentration of 0.1%. A 500 mL beaker was taken, 400 mL of reinjected water was added, and mechanical stirring was started until 500 r / min. Subsequently, the polymer was added to the water within 10 s. The viscosity at different time points was measured by a six-speed rotational viscometer to obtain the dissolution rate relationship of the polymer. The results are shown in Table 2:

[0042] For Examples 1-4, when the polymer was formulated with reinjected water, the viscosity release rate reached over 65% within 30 s and the complete release state could be achieved within 2 min, realizing the rapid dissolution effect during the formulation with reinjected water. However, for Comparative Example 1, since no non-ionic polar regulator was used for optimization, its viscosity was only 6 mPa·s at 10 min, far lower than that of Example 1. This was because the polymer did not dissolve within the specified dissolution time and all presented swollen particle states. For example, the polymer in Example 1 was basically completely dissolved after 2 min and there were no obvious particles on the beaker wall, as Figure 2 shown; while for Comparative Example 1, after 2 min of dissolution, a large number of granular polymer swellings were presented, as Figure 3 shown. This comparison shows that the optimization of micelle polarity regulation is the key step to achieve the rapid dissolution of the polymer in reinjected water. During the dissolution process of Comparative Examples 2-4 in reinjected water, it was observed from the experiment that the polymer was basically dissolved at 10 min and there were no large amounts of swollen particles on the wall. However, their viscosities were still low, which was because the self-assembled large-size hydrophobic association structure was not obtained, so the salt resistance was poor. Even though the polymer was dissolved, its viscosity was still much lower than that of Example 1. At the same time, for Comparative Example 4, since it did not contain hydrophobic monomers, the viscosity was released within 1 min and it had a more significant rapid solubility than the hydrophobic associating polymer. However, Examples 1-4 could still be dissolved within 1-2 min and had the rapid dissolution effect for on-line mixing.

[0043] The polymer obtained from Example 1 was dissolved in reinjected water with different dilution ratios of produced water to obtain simulated reinjected water with different salinities. The rheology, viscoelasticity, drag reduction property, and static sand-carrying property of the obtained solution were tested according to the standard "SY / T 7627-2021 Technical Requirements for Water-Based Fracturing Fluids". The results are shown in Table 3:

[0044] At a low viscosity (6 mPa·s), the drag reduction rate of the liquid was 78%. When the viscosity increased to 30 mPa·s, its drag reduction rate was 72%, and it had significant elastic characteristics and could keep 70 / 140 quartz sand proppants completely suspended without sedimentation; as the salinity of the reinjected water increased, the elastic modulus could reach 5.65 Pa at the corresponding dosage, and it could still keep the proppants in a fully suspended state.

[0045] The polymerizable hydrophobic functional monomer solutions obtained in step S2 of Example 1, and the corresponding polymerizable hydrophobic functional monomer solutions of Comparative Example 1 and Comparative Example 2 were configured at different concentrations, and their average particle sizes were measured. The results are as Figure 4 shown. The hydrophobic functional monomer micelles obtained in Example 1 reached the maximum size at 300 mg / L, with an average of 318 nm, which was larger than those of Comparative Example 1 and Comparative Example 2. The larger micelle size is beneficial for forming a more compact associative cross-linked structure, thus significantly enhancing the salt resistance of the polymer.

[0046] According to the test results of the above examples, it is demonstrated that the polymer proposed in this application has the ability to achieve online mixing and rapid dissolution in reinjected water, and at the same time, it has excellent salt resistance. The fracturing fluid prepared in high salinity water has outstanding advantages in drag reduction and sand carrying.

[0047] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

Claims

1. A rapid-dissolving hydrophobic associating polymer for reinjected water in fracturing, characterized in that, The molecular formula is shown in Formula 1: Formula 1; Among them, by mass parts, i is 60 - 65%; j is 15 - 39%; k is 0 - 15%; l is 0 - 3%; m is 0 - 2%; n is 0 - 4%; R1 is a hydrophobic functional monomer 1, containing a nonionic active group, a quaternary ammonium salt structure and a long carbon chain structure; R2 is a hydrophobic functional monomer 2, which is an alkylacrylamide-based mono- or poly-sulfonate; R3 is a hydrophobic functional monomer 3, containing a polyhydric nonionic hydrophilic group and a hydrophobic carbon chain with a single unsaturated double bond; the weight average molecular weight of the hydrophobic associative polymer is 5×10 6 - 8×10 6 .

2. The instant-soluble hydrophobic associating polymer for reinjected water in fracturing according to claim 1, wherein The structural formula of the hydrophobic functional monomer 1 is shown in Formula 2, wherein the double bond structure and the quaternary ammonium salt structure can be connected by a nonionic polar group; Formula 2; In Formula 2, R4 can be , a is 1 - 4; Or an active group containing an ester group, as shown in Formula 3: Formula 3; In Formula 3, b is 0-2 and c is 0-2; Or an active group containing an amide group, as shown in Formula 4: Formula 4; In Formula 4, d is 0-2 and e is 0-2; Or an active group containing an ethoxy group, as shown in Formula 5: Formula 5; In Formula 4, f is 0-2, g is 1-10, and h is 0-2; In Formula 1, R5 is a straight-chain alkyl group with 8-22 carbon atoms.

3. The instant-soluble hydrophobic associating polymer for reinjection water in fracturing according to claim 1, wherein The structural formula of the hydrophobic functional monomer 2 is shown in Formula 6: Formula 6; In Formula 6, R6 and R7 can be -H, -OH, -COO - , -SO3 - , -SO4 - , -PO4 - , and in the same molecule, it has at least one anionic structure; R8 is a straight-chain alkyl group with 8 to 14 carbon atoms.

4. The instant-soluble hydrophobic associating polymer for reinjection water in fracturing according to claim 1, wherein, The structural formula of the hydrophobic functional monomer 3 is shown in Formula 7: Formula 7; In Formula 7, R9 is a polyvalent nonionic hydrophilic group, and R 10 is a hydrophobic carbon chain containing a single unsaturated double bond. The structural formula of R9 is shown in Formulas 8 - 10: Formula 8; or Formula 9; or Formula 10; R 10 The structural formula is as shown in Formula 11: Formula 11; In Formula 11, o is 4-12; p is 5-10; the carbon chain spatial conformation has a kink.

5. The preparation method of an instantaneously soluble hydrophobically associating polymer for reinjected water in fracturing according to any one of claims 1-4, characterized in that, It includes the following steps: S1. Add the hydrophobic functional monomer into water, and add a nonionic polar regulator and mix to obtain a polymerizable hydrophobic associative micelle solution. The hydrophobic functional monomer includes one or more of the hydrophobic functional monomer 1, the hydrophobic functional monomer 2, and the hydrophobic functional monomer 3; S2. Add the polymerizable hydrophobic associative micelle solution into the conventional monomer aqueous solution. The total monomer system is composed of the hydrophobic functional monomer and the conventional monomer. Fix the total monomer mass to account for 65-75% of the total mass of the aqueous solution to obtain a mixed solution A; S3. Regulate the molecular weight of the copolymer in the mixed solution A with a molecular weight regulator to obtain a mixed solution B; S4. Add an initiator to the mixed solution B, keep warm and stand still for 2-4 h until the reaction is completed, granulate, dry, and pulverize to obtain a hydrophobic associative polymer.

6. The preparation method of a rapid-dissolving hydrophobic associating polymer for reinjection water in fracturing according to claim 5, characterized in that, The nonionic polar regulator is a small molecule active substance with a nonionic active group or a copolymer containing a nonionic active group.

7. The preparation method of a water-soluble hydrophobic associating polymer for reinjection water in fracturing according to claim 5, characterized in that, The small molecule active substance with a nonionic active group is composed of a hydrophobic chain part and a hydrophilic active group. The hydrophobic chain part is one or more of an alkyl alcohol, an alkylamine, and an alkylphenol structure; the hydrophilic active group is one or more of a polyoxyethylene block, a glucoside group, a polyglycerol group, and a cyclodextrin group.

8. The preparation method of a rapid-dissolving hydrophobic associating polymer for reinjection water in fracturing according to claim 5, characterized in that, The copolymer containing a nonionic active group is copolymerized from one or more polymerizable monomers, with a degree of polymerization of 100-500. The polymerizable monomer is composed of a hydrophobic chain part and a hydrophilic active group. The hydrophobic chain part is one or more of an alkyl alcohol, an alkylamine, and an alkylphenol structure; the hydrophilic active group is one or more of a polyoxyethylene block, a glucoside group, a polyglycerol group, and a cyclodextrin group.

9. The preparation method of a water-soluble hydrophobic associating polymer for reinjected water in fracturing according to claim 5, characterized in that, The molecular weight regulator is one or more of sodium formate, sodium acetate, isopropyl alcohol, sodium hypophosphite, and urea.

10. The preparation method of a rapidly soluble hydrophobic associating polymer for reinjected water in fracturing according to claim 5, characterized in that, The conventional monomer is composed of one or more of acrylamide, sodium acrylate, and 2-acrylamido-2-methylpropanesulfonic acid sodium.

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