Polymeric surfactant, fracturing fluid based on polymeric surfactant as well as preparation method and application of fracturing fluid

Abstract

The invention relates to a polymer surfactant, a fracturing fluid based on the polymer surfactant and a preparation method and application of the fracturing fluid, and belongs to the technical field of oil and gas development. The poly-surfactant provided by the invention is obtained by carrying out copolymerization reaction on three monomer raw materials, namely 2-acrylamide-2-methylpropanesulfonate, acrylamide and long-chain alkyl maleamic acid salt, and the fracturing fluid prepared by compounding the poly-surfactant and an anionic surfactant has excellent comprehensive properties such as high temperature resistance, high salt resistance and shear resistance; after the fracturing fluid is used for fracturing construction operation, the stratum permeability can be effectively improved, so that the recovery ratio of an oil-gas well is greatly improved.

Description

A polymer surfactant, a fracturing fluid based on the polymer surfactant, its preparation method and application Technical Field

[0001] This invention relates to a fracturing agent, a fracturing fluid based on the fracturing agent, and its preparation method and application, belonging to the field of oil and gas development technology. Background Technology

[0002] Fracturing technology is a crucial method for modifying oil and gas reservoirs and increasing oil and gas production. Its principle involves injecting fracturing fluid into the reservoir, creating fractures and supporting them to construct oil and gas flow channels, thereby increasing oil and gas production. In fracturing, the core role of the fracturing fluid is to create a network of flow channels through high-pressure fracture creation and to carry proppant to maintain long-term fracture conductivity. Therefore, fracturing fluid is key to fracturing technology, and its performance directly affects the fracturing effect. Developing high-performance fracturing fluid systems is of significant practical importance for improving oil and gas development efficiency.

[0003] Commonly used fracturing fluids are mainly prepared by adding long-chain surfactants to the system to form a viscoelastic colloidal solution, or by adding polymers to the fracturing fluid system to thicken it, in order to meet the performance requirements of the fracturing fluid. Chinese patent document CN104710974 A discloses an oligomeric surfactant-based cleaning fracturing fluid, which obtains a viscoelastic solution by compounding oligomeric quaternary ammonium salt surfactants with counterions; CN121086774 A discloses a modified polyacrylamide polymer fracturing fluid, which improves the performance of the fracturing fluid in high temperature and high salt environments by using modified polyacrylamide dry powder thickener as the core component, thereby ensuring effective proppant carrying and fracture propagation in fracturing operations; CN117903014 A discloses the preparation of a fracturing fluid containing polymerizable monomers and polymer thickeners. The copolymer formed by polymerizing zwitterionic polymerizable monomers with other monomers has significant anti-polyelectrolyte effect and good salt resistance by utilizing intermolecular hydrogen bonding and electrostatic interaction, and can be used as a thickener for fracturing fluid under high salinity conditions.

[0004] However, existing fracturing fluid systems still fall short of meeting the reservoir characteristics of coal-rock gas reservoirs, which are characterized by low permeability, strong adsorption, easy production of coal dust, and high water sensitivity. Polyacrylamide polymer fracturing fluids have a high residue content after gel breaking, and the residual fluid can easily cause secondary damage to the reservoir, clog coal and rock pores, and its adsorption with coal dust can easily lead to wellbore blockage. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a polymeric surfactant, a fracturing fluid based on the polymeric surfactant, its preparation method, and its application. The polymeric surfactant provided by this invention is obtained through a copolymerization reaction of three monomeric raw materials: 2-acrylamide-2-methylpropanesulfonate, acrylamide, and long-chain alkyl maleamic acid salt. The fracturing fluid prepared by compounding this surfactant with an anionic surfactant possesses excellent comprehensive properties such as high-temperature resistance, high-salt resistance, and shear resistance. When used in fracturing operations, this fracturing fluid can effectively improve formation permeability, resulting in a significant increase in oil and gas well recovery.

[0006] The technical solution of the present invention is as follows: Explanation of terms: Polymer surfactant: that is, polymer surfactant.

[0007] A surface-modifying agent, wherein the surface-modifying agent is a compound of formula i:

[0008] In Formula i, x, y, and z are the mole fractions of the structural unit, x = 68%~80%, y = 20%~30%, z = 0.3%~1.2%, x+y+z=100%, and R is one of alkyl laurate, alkyl palmitate, alkyl monostearate, alkyl oleate, dodecylphenyl, and hexadecylphenyl.

[0009] The preparation method of the above-mentioned polymer surface agent includes the following steps: (1) reacting long-chain fatty amines with maleic anhydride to synthesize long-chain alkyl maleamic acid; (2) mixing 2-acrylamido-2-methylpropanesulfonic acid and long-chain alkyl maleamic acid in a molar ratio of 20~30:0.3~1.2, dissolving in deionized water, controlling the total mass of the three monomer raw materials to account for 20%~30% of the total mass of the reaction solution, adding NaOH to adjust the pH of the system to 7.0~7.5, and generating a mixed solution of long-chain alkyl maleamic acid salt and 2-acrylamido-2-methylpropanesulfonic acid salt; (3) adding acrylamide to the mixed solution obtained in step (2) at 68%~80% of the total molar amount of the three monomer raw materials, stirring until completely dissolved; reacting in a polymerization reactor, purging with nitrogen to remove oxygen, heating the system to 40~60℃, adding an initiator and reacting for 4~6 hours to generate the polymer surface agent.

[0010] According to a preferred embodiment of the present invention, the long-chain fatty amine in step (1) is one of laurylamine, palmitamine, stearylamine, oleic acid amine, dodecylaniline, and hexadecylaniline.

[0011] According to a preferred embodiment of the present invention, the initiator in step (3) is ammonium persulfate and anhydrous sodium sulfite, the amount of initiator added is 0.2% to 0.3% of the total mass of the three monomer raw materials, and the molar ratio of ammonium persulfate and anhydrous sodium sulfite is 1:1.

[0012] A fracturing fluid based on a polymer surfactant, the composition of which includes: the aforementioned polymer surfactant, anionic surfactant, and water.

[0013] According to a preferred embodiment of the present invention, the fracturing fluid comprises, by mass percentage: 1.0% to 3.0% polymer, 0.5% to 1.5% anionic surfactant, and the balance being water.

[0014] According to a preferred embodiment of the present invention, the anionic surfactant is one or more of sodium fatty alcohol polyoxyethylene ether sulfate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and α-alkenyl sulfonate.

[0015] According to a preferred embodiment of the present invention, the fracturing fluid comprises, by mass percentage: 3.0% polymerizing agent, 1.5% anionic surfactant, and the balance being water; the polymerizing agent is a compound of formula i, wherein x, y, and z are the mole fractions of structural units, x=79%, y=20.6%, z=0.4%, x+y+z=100%, and R is an oleic alkyl group; the anionic surfactant is sodium fatty alcohol polyoxyethylene ether sulfate.

[0016] The preparation method of the above-mentioned fracturing fluid includes the following steps: dissolving a polymerizing agent and anionic surfactant in water to obtain the fracturing fluid.

[0017] A fracturing fluid system comprising the above-mentioned surfactant or the above-mentioned fracturing fluid.

[0018] Application of the above-mentioned fracturing agent, fracturing fluid, or fracturing fluid system in fracturing operations of low-permeability coal-gas reservoirs.

[0019] Beneficial Effects: The fracturing fluid provided in this application is formulated with a polymer surfactant and anionic surfactant. On one hand, the polymer surfactant contains multiple hydrophilic head groups and long hydrophobic chains. The presence of the hydrophilic groups induces electrostatic interactions between the polymer surfactant and the anionic surfactant, which helps maintain the extended state of the hydrophobic chains. On the other hand, the presence of the hydrophobic groups facilitates molecular bonding between the polymer surfactant and the anionic surfactant, which helps form larger aggregates in the fracturing fluid system. The polymer chains, like a "skeleton," are interwoven within the surfactant micelles, inducing the formation of larger "complex micelle structures." These polymer-induced micelles are more stable than simple VES (viscoelastic surfactant) micelles and can withstand higher temperatures. Simultaneously, the hydrophilic head groups contain multiple amino and hydroxyl groups that enhance hydrophilicity, resulting in a thicker hydration layer of the hydrophilic head groups and effectively strengthening the stability of the surfactant micelles.

[0020] On the other hand, the combination of the polymer surfactant and the anionic surfactant can produce a synergistic effect. The two can effectively combine through supramolecular interactions such as hydrogen bonding and hydrophobic association to form a complex micelle structure, which further improves the temperature resistance, salt resistance and shear resistance of the fracturing fluid. Thus, through the synergistic effect of the polymer surfactant and the anionic surfactant, the fracturing fluid is endowed with excellent high temperature resistance, high salt resistance and shear resistance.

[0021] Furthermore, the fracturing fluid of this application does not require the addition of an additional polymer thickener, thereby effectively avoiding problems such as damage to coal and rock reservoirs caused by polymer residues.

[0022] The fracturing fluid described in this application, based on a blend of polymeric surfactants and anionic surfactants, effectively enhances the association effect of each component during the formation of micelle structures by controlling the mass fraction ratio of each component. This results in better structural stability of the micelles, thereby endowing the fracturing fluid with superior high-temperature resistance, high-salt resistance, and shear resistance.

[0023] Based on the excellent properties of the fracturing fluid described in this application, its use in fracturing operations can effectively improve formation permeability, thereby significantly increasing the recovery rate of oil and gas wells. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 shows the shear viscosity curves of fracturing fluids PSF1-PSF6, P-PSF1, P-PSF2, and P-PSF3 provided in the embodiments of this application; Figure 2 shows the viscoelasticity curves of fracturing fluids PSF1-PSF6 and P-PSF1 provided in the embodiments of this application; Figure 3 shows the temperature resistance and shear strength curves of fracturing fluid PSF4 provided in the embodiments of this application; Figure 4 shows the viscosity curves of fracturing fluids PSF4', P-PSF1', P-PSF2', and P-PSF3' provided in the embodiments of this application under different salinity conditions. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0027] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0028] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: any one of a, b, and c, or ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0029] In the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0030] In the following description of embodiments of this application, numerical ranges should be understood to also specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within the scope of this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] In the following description of the embodiments of this application, the terminology used is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0032] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0033] In a first aspect, embodiments of this application provide a polymer surfactant, wherein the polymer surfactant is a compound of formula i:

[0034] In Formula i, x, y, and z are the mole fractions of the structural unit, x = 68%~80%, y = 20%~30%, z = 0.3%~1.2%, and x+y+z = 100%; R is alkyl laurate, alkyl palmitate, alkyl monostearate, alkyl oleate, dodecylphenyl, or hexadecylphenyl.

[0035] This application also provides a method for synthesizing the polymer surfactant. Taking R as alkyl lauryl acid as an example, the synthesis method preferably includes the following steps: Step 1: Dissolve laurylamine in acetone, add maleic anhydride according to the laurylamine:maleic anhydride molar ratio of 1:1.05, stir and react at 60°C for 10 h to obtain N-lauryl maleamic acid solution; remove the solvent by rotary evaporation to obtain N-lauryl maleamic acid.

[0036] Step 2: Mix 2-acrylamido-2-methylpropanesulfonic acid and N-lauryl maleamic acid at a molar ratio of 20~30:0.3~1.2, dissolve in deionized water, and control the total mass of the three monomer raw materials to account for 20%~30% of the total mass of the reaction solution. Add NaOH to adjust the pH of the system to 7.0~7.5 to generate a mixed solution of N-lauryl maleamic acid salt and 2-acrylamido-2-methylpropanesulfonic acid salt.

[0037] Step 3: Add acrylamide to the mixed solution obtained in Step 2 at 68%~80% of the total molar amount of the three monomer raw materials, and stir until completely dissolved; react in a polymerization reactor, purge with nitrogen to remove oxygen, heat the system to 40~60℃, add an initiator and react for 4~6 hours to generate the polymer surfactant shown in formula i, where x, y, and z are the molar fractions of structural units, x=68%~80%, y=20%~30%, z=0.3%~1.2%, x+y+z=100%; R is alkyl lauryl acid.

[0038] Of course, in the embodiments of this application, palmitamine, stearamine, oleic acid amine, dodecylaniline, hexadecylaniline and maleic anhydride can also be used to react with maleic anhydride to prepare the corresponding maleic acid, and then prepare the polymer surfactant represented by formula i, where R is palmitic alkyl, monostearate alkyl, oleic acid alkyl, dodecylphenyl, hexadecylphenyl.

[0039] Secondly, embodiments of this application provide a fracturing fluid based on a polymer surfactant, wherein the fracturing fluid comprises the aforementioned polymer surfactant, anionic surfactant, and water.

[0040] The fracturing fluid provided in this application is formulated with a polymeric surfactant and anionic surfactant. On one hand, the polymeric surfactant contains multiple hydrophilic head groups and long hydrophobic chains. The presence of the hydrophilic groups induces electrostatic interactions between the polymeric and anionic surfactants, which helps maintain the extended state of the hydrophobic chains. On the other hand, the presence of the hydrophobic groups facilitates molecular bonding between the polymeric and anionic surfactants, which helps form larger aggregates in the fracturing fluid system. The polymer chains, like a "skeleton," are interwoven within the surfactant micelles, inducing the formation of larger "complex micelle structures." These polymer-induced micelles are more stable than simple VES micelles and can withstand higher temperatures. Simultaneously, the hydrophilic head groups contain multiple amino and hydroxyl groups that enhance hydrophilicity, resulting in a thicker hydration layer and effectively strengthening the stability of the surfactant micelles. On the other hand, the combination of the polymeric surfactant and the anionic surfactant can produce a synergistic effect. They can effectively combine through supramolecular interactions such as hydrogen bonding and hydrophobic association to form a complex micelle structure, further enhancing the fracturing fluid's temperature resistance, salt resistance, and shear resistance. Thus, through the synergistic effect of the polymeric surfactant and the anionic surfactant, the fracturing fluid is endowed with excellent high-temperature resistance, high-salt resistance, and shear resistance. Furthermore, the fracturing fluid of this application does not require the addition of an additional polymeric thickener, thereby effectively avoiding problems such as polymer residue damage to coal and rock reservoirs.

[0041] The preferred composition of the fracturing fluid by mass percentage is: 1.0%~3.0% polymer surfactant, 0.5%~1.5% anionic surfactant, and the balance being water.

[0042] It should be noted that, based on the compounding of polymer surfactant and anionic surfactant, the embodiments of this application effectively improve the association effect of each component in the process of forming micelle structure by controlling the mass fraction ratio of each component, resulting in better structural stability of the micelles, thereby giving the fracturing fluid better high temperature resistance, high salt resistance and shear resistance.

[0043] In the embodiments of this application, the anionic surfactant is preferably one or more of sodium fatty alcohol polyoxyethylene ether sulfate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and α-alkenyl sulfonate.

[0044] Thirdly, embodiments of this application provide a method for preparing the fracturing fluid of this application, preferably including the following steps: dissolving a polymeric surfactant and an anionic surfactant in water to obtain the fracturing fluid.

[0045] It should be noted that, in order to ensure that the polymeric surfactant and the anionic surfactant can be fully dissolved and interact, heating and ultrasonic-assisted dispersion can be applied.

[0046] Fourthly, embodiments of this application provide a fracturing fluid system, including the polymer surfactant or the fracturing fluid.

[0047] Fifthly, embodiments of this application also provide the application of the fracturing agent, fracturing fluid, or fracturing fluid system described in this application in fracturing operations in low-permeability coal and rock reservoirs.

[0048] Based on the excellent properties of the fracturing fluid in the embodiments of this application, its use in fracturing operations can effectively improve formation permeability and significantly enhance oil and gas well recovery.

[0049] The technical solution of this application will be further described below with reference to specific embodiments.

[0050] Example 1: A method for preparing a polymer surfactant, comprising the following steps: Step 1: Maleic anhydride and laurylamine are reacted at a molar ratio of 1.05:1. Specifically, 18.0 g of laurylamine is dissolved in 50 mL of acetone, and 10.0 g of maleic anhydride is added. The mixture is stirred at 60 °C for 10 h to obtain an N-lauryl maleamic acid solution. The solvent is removed by rotary evaporation to obtain N-lauryl maleamic acid.

[0051] Step 2: Dissolve 10.0 g of 2-acrylamide-2-methylpropanesulfonic acid and 0.45 g of N-lauryl maleamic acid in 60 mL of deionized water, add an appropriate amount of NaOH to adjust the pH of the system to 7.0~7.5, and obtain a mixed solution of 2-acrylamide-2-methylpropanesulfonic acid and N-lauryl maleamic acid.

[0052] Step 3: Add 10.6 g of acrylamide to the above mixed solution and stir until completely dissolved; insert the vent tube below the liquid surface and purge with high-purity nitrogen for 30 min to remove oxygen. Use N2 as a protective gas in the polymerization reactor. Heat the system to 45°C and add 0.03 g of ammonium persulfate and 0.016 g of anhydrous sodium sulfite as initiators to carry out the polymerization reaction. After 6 h of reaction, the polymer surfactant shown in formula i is formed, where x, y, and z are the mole fractions of structural units, x=75%, y=24.2%, z=0.8%, x+y+z=100%; R is alkyl laurate.

[0053] Example 2: A method for preparing a polymer surfactant, comprising the following steps: Step 1: Maleic anhydride and palmitamine are reacted at a molar ratio of 1.05:1. Specifically, 23.4 g of palmitamine is dissolved in 50 mL of acetone, and 10.0 g of maleic anhydride is added. The mixture is stirred at 60 °C for 10 h to obtain an N-palmitoyl maleamic acid solution. The solvent is removed by rotary evaporation to obtain N-palmitoyl maleamic acid.

[0054] Step 2: Dissolve 11.2 g of 2-acrylamide-2-methylpropanesulfonic acid and 0.68 g of N-palmityl maleamic acid in 60 mL of deionized water, add an appropriate amount of NaOH to adjust the pH of the system to 7.0~7.5, and obtain a mixed solution of 2-acrylamide-2-methylpropanesulfonic acid and N-palmityl maleamic acid.

[0055] Step 3: Add 10.2 g of acrylamide to the above mixed solution and stir until completely dissolved; insert the vent tube below the liquid surface and purge with high-purity nitrogen for 30 min to remove oxygen. Use N2 as a protective gas in the polymerization reactor. Heat the system to 55°C and add 0.03 g of ammonium persulfate and 0.016 g of anhydrous sodium sulfite as initiators to carry out the polymerization reaction. After 5.5 h of reaction, the polymer surfactant shown in formula i is formed, where x, y, and z are the mole fractions of the structural units, x=72%, y=27%, z=1.0%, x+y+z=100%; R is alkyl palmitate.

[0056] Example 3: A method for preparing a polymer surfactant, comprising the following steps: Step 1: Maleic anhydride and stearylamine are reacted at a molar ratio of 1.05:1. Specifically, 26.1 g of stearylamine is dissolved in 50 mL of acetone, and 10.0 g of maleic anhydride is added. The mixture is stirred at 60 °C for 10 h to obtain an N-stearyl alkyl maleamic acid solution. The solvent is removed by rotary evaporation to obtain N-stearyl alkyl maleamic acid.

[0057] Step 2: Dissolve 8.83 g of 2-acrylamide-2-methylpropanesulfonic acid and 0.51 g of N-stearyl maleamic acid in 60 mL of deionized water, add an appropriate amount of NaOH to adjust the pH of the system to 7.0~7.5, and obtain a mixed solution of 2-acrylamide-2-methylpropanesulfonic acid and N-stearyl maleamic acid.

[0058] Step 3: Add 11.1 g of acrylamide to the above mixed solution and stir until completely dissolved; insert the vent tube below the liquid surface and purge with high-purity nitrogen for 30 min to remove oxygen. Use N2 as a protective gas in the polymerization reactor. Heat the system to 60°C and add 0.03 g of ammonium persulfate and 0.016 g of anhydrous sodium sulfite as initiators to carry out the polymerization reaction. After 4 h of reaction, the polymer surfactant shown in formula i is formed, where x, y, and z are the mole fractions of structural units, x=78%, y=21.3%, z=0.7%, x+y+z=100%; R is stearic acid alkyl.

[0059] Example 4: A method for preparing a polymer surfactant, comprising the following steps: Step 1: Maleic anhydride and oleic amine are reacted at a molar ratio of 1.05:1. Specifically, 26.0 g of oleic amine is dissolved in 50 mL of acetone, 10.0 g of maleic anhydride is added, and the mixture is stirred at 60 °C for 10 h to obtain an N-oleic alkyl maleamic acid solution; the solvent is removed by rotary evaporation to obtain N-oleic alkyl maleamic acid.

[0060] Step 2: Dissolve 8.54 g of 2-acrylamide-2-methylpropanesulfonic acid and 0.29 g of N-oleic alkyl maleamic acid in 60 mL of deionized water, and add an appropriate amount of NaOH to adjust the pH of the system to 7.0-7.5 to obtain a mixed solution of 2-acrylamide-2-methylpropanesulfonic acid and N-oleic alkyl maleamic acid.

[0061] Step 3: Add 11.2 g of acrylamide to the above mixed solution and stir until completely dissolved; insert the vent tube below the liquid surface and purge with high-purity nitrogen for 30 min to remove oxygen. Use N2 as a protective gas in the polymerization reactor. Heat the system to 50°C and add 0.03 g of ammonium persulfate and 0.016 g of anhydrous sodium sulfite as initiators to carry out the polymerization reaction. After 5 h of reaction, the polymer surfactant shown in formula i is formed, where x, y, and z are the mole fractions of structural units, x=79%, y=20.6%, z=0.4%, x+y+z=100%; R is oleic acid alkyl.

[0062] Examples 5-10: At room temperature, polymer surfactants and anionic surfactants of different mass concentrations were ultrasonically dissolved in deionized water according to the composition and content of fracturing fluids shown in Table 1 (water to 100%), and fracturing fluids PSF1-PSF6 were prepared respectively.

[0063] Table 1. Composition and content (mass percentage) of fracturing fluids in Examples 5-10

[0064] The fracturing fluid is prepared according to the following steps: Polymer surfactants are prepared according to the preparation methods of Examples 1 to 4 respectively. The polymer surfactants and anionic surfactants are dissolved in deionized water according to the composition and content in Table 1 to obtain the fracturing fluid based on the polymer surfactant.

[0065] To ensure that the polymeric surfactant and the anionic surfactant can fully dissolve and interact, this embodiment applies heating and ultrasonic-assisted dispersion at a heating temperature of 50°C and an ultrasonic frequency of 30 Hz.

[0066] To illustrate the actual effects of the fracturing fluids in the embodiments described above, this application uses fracturing fluids PSF1 to PSF6 as test samples, and provides an explanation in conjunction with comparative examples 1 to 2.

[0067] Comparative Example 1: At room temperature, the oleic acid alkyl polystyrene prepared in Example 4 was ultrasonically dissolved in deionized water at a mass concentration of 3% to prepare fracturing fluid P-PSF1.

[0068] Comparative Example 2: At room temperature, oleamidopropyl betaine (an amphoteric surfactant) at a mass concentration of 3% and polyacrylamide (a thickener) at a mass concentration of 1.5% were ultrasonically dissolved in deionized water to prepare fracturing fluid P-PSF2.

[0069] Comparative Example 3: At room temperature, oleamidopropyl betaine at a mass concentration of 3% and sodium fatty alcohol polyoxyethylene ether sulfate at a mass concentration of 1.5% were ultrasonically dissolved in deionized water to prepare fracturing fluid P-PSF3.

[0070] Example 1: Propane Carrying Performance Test. The proppant carrying performance of fracturing fluids PSF4, P-PSF1, P-PSF2, and P-PSF3 was tested. During the test, each fracturing fluid was maintained at a specific temperature. A 30% mass ratio of ceramic proppant (70 / 140 mesh size) was gently placed on the surface of each fracturing fluid. The ceramic proppant was allowed to settle naturally under static conditions. The settling rate was calculated based on the settling height, and the results are shown in Table 2.

[0071] Table 2 Settling velocity of ceramic proppant in various fracturing fluids

[0072] Settling rate characterizes the viscosity change of fracturing fluid. Table 2 shows that as temperature increases, the settling rate of proppant in the fracturing fluid increases, indicating a decrease in fluid viscosity. At 100℃, the proppant has the fastest settling rate among all fracturing fluids, but it is still less than 0.5 cm / min in fracturing fluid PSF4, demonstrating that the PSF4 system has good proppant carrying capacity, and the fracturing fluid mainly relies on elastic proppant carrying. Compared to fracturing fluid PSF4, the settling rates of fracturing fluids P-PSF1, P-PSF2, and P-PSF3 increase significantly in the temperature range of 60–100℃, indicating a decrease in viscosity and proppant carrying capacity.

[0073] 2. Shear resistance test: The fracturing fluids PSF1~PSF6 and P-PSF1, P-PSF2, and P-PSF3 were subjected to shear resistance tests. The test method was as follows: at room temperature, the shear rate was tested from 0 to 100 s⁻¹. -1 The viscosity changes of various fracturing fluids at different times are shown in Figure 1. Figure 1 shows the shear viscosity curves of fracturing fluids PSF1~PSF6 and P-PSF1, P-PSF2, and P-PSF3.

[0074] As shown in Figure 1, the maximum shear viscosity of the fracturing fluids PSF1~PSF6 prepared in the embodiments of this application is on the order of 10. 4 Among the fracturing fluids, PSF4 exhibited the best apparent viscosity (mPa·s), and its shear viscosity changed systematically with shear rate. In contrast, fracturing fluids P-PSF1, P-PSF2, and P-PSF3 had lower maximum shear viscosities, which decreased to 10 mPa·s with increasing shear rate. 0 Pa·s below. This indicates that the fracturing fluid formulated with polymeric surfactants and anionic surfactants in this application possesses excellent shear resistance.

[0075] 3. Viscoelastic Performance Testing: Viscoelastic performance testing was conducted on fracturing fluids PSF1~PSF6 and P-PSF1. The testing method was as follows: At room temperature, frequency and stress scans were performed on the prepared fracturing fluids using the plate testing system of an Anton Paar rheometer. Within the linear frequency and linear stress range, the viscoelasticity of the system was evaluated by testing the quantitative relationship between the elastic modulus G' and the viscous modulus G". The results are shown in Figure 2. Figure 2 shows the viscoelastic curves of fracturing fluids PSF1~PSF6 and P-PSF1.

[0076] As shown in Figure 2, throughout the entire test range, the elastic modulus G' of the fracturing fluids in each embodiment is higher than the viscous modulus G", exhibiting obvious elastofluid characteristics. This indicates that the fracturing fluids in each embodiment have prominent elastic characteristics, which is beneficial for maintaining good shear resistance and proppant carrying properties. The elastic modulus G' and viscous modulus G'' of fracturing fluids PSF1~PSF6 are significantly higher than those of P-PSF1, indicating that the fracturing fluid provided by this invention has better viscoelasticity. However, the difference between the elastic modulus G' and viscous modulus G" of fracturing fluid P-PSF1 is smaller, indicating that its viscoelastic performance is weaker and cannot meet the core requirement of proppant carrying in fracturing fluids. In addition, the elastic modulus G' value of fracturing fluid PSF4 is higher than that of other fracturing fluids, proving that fracturing fluid PSF4 has more obvious viscoelasticity.

[0077] 4. Temperature and Shear Resistance Test: Since the comparative fracturing fluids P-PSF1, P-PSF2, and P-PSF3 have low viscosity and their viscosity decreases significantly at high temperatures, the fracturing fluid PSF4, which exhibits the best viscoelasticity, was subjected to a temperature and shear resistance test. The test method was as follows: At room temperature, the fracturing fluid PSF4 was tested using an Anton Paar rheometer at a shear rate of 170 s⁻¹. -1 The temperature was set from 30℃ to 95℃, and shearing was continued for 60 min to investigate the temperature and shear resistance of the fracturing fluid. The results are shown in Figure 3. Figure 3 is the temperature and shear resistance characteristic curve of fracturing fluid PSF4.

[0078] As shown in Figure 3, at a constant shear rate of 170 s... -1Under the given conditions, the apparent viscosity of fracturing fluid PSF4 showed an increasing trend with rising temperature, then a decreasing trend after the temperature reached 50℃, and finally exhibited a constant viscosity at 95℃. The final viscosity of fracturing fluid PSF4 was approximately 90 mPa·s, demonstrating that fracturing fluid PSF4 has excellent temperature resistance and shear strength.

[0079] 5. Salt resistance test: The fracturing fluids PSF4, P-PSF1, P-PSF2, and P-PSF3 were tested for salt resistance. The test method was as follows: Based on the composition of a simulated formation water, 163.89 g NaCl, 0.234 g Na2SO4, 4.60 g MgCl2·6H2O, and 31.28 g CaCl2·2H2O were added to 1 L of distilled water to prepare a mother solution with a salinity of 200,000 mg / L. This mother solution was then diluted to simulated formation water solutions with a salinity of 0~20 g / L. Based on the composition and content of fracturing fluids PSF4, P-PSF1, P-PSF2, and P-PSF3, simulated formation water solutions with different salinities were used to make up to 100%, and fracturing fluid systems PSF4', P-PSF1', P-PSF2', and P-PSF3' were prepared respectively. The viscosity of the fracturing fluid system was measured using an Anton Paar rheometer, and the results are shown in Figure 4.

[0080] As shown in Figure 4, when the salinity increased from 0 g / L to 20 g / L, the apparent viscosity of the fracturing fluid system PSF4' decreased from 142 mPa·s to 84 mPa·s, with a viscosity retention rate of 59.2%, indicating that the fracturing fluid has good salt resistance. Throughout the entire salinity range, the apparent viscosity of the fracturing fluid system PSF4' was consistently significantly higher than that of P-PSF1', P-PSF2', and P-PSF3'. When the salinity increased to 15 g / L, the apparent viscosities of P-PSF1', P-PSF2', and P-PSF3' decreased to below 60 mPa·s, indicating that PSF4' has higher salt resistance than P-PSF1', P-PSF2', and P-PSF3'.

[0081] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0082] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A polymer surfactant, characterized in that, The polymer surfactant is a compound of formula i: In Formula i, x, y, and z are the mole fractions of the structural unit, x = 68%~80%, y = 20%~30%, z = 0.3%~1.2%, x+y+z=100%, and R is one of alkyl laurate, alkyl palmitate, alkyl monostearate, alkyl oleate, dodecylphenyl, and hexadecylphenyl.

2. The method for preparing the polymer surfactant according to claim 1, characterized in that, The process includes the following steps: (1) reacting long-chain fatty amines with maleic anhydride to synthesize long-chain alkyl maleamic acid; (2) mixing 2-acrylamido-2-methylpropanesulfonic acid and long-chain alkyl maleamic acid in a molar ratio of 20~30:0.3~1.2, dissolving in deionized water, controlling the total mass of the three monomer raw materials to be 20%~30% of the total mass of the reaction solution, adding NaOH to adjust the pH of the system to 7.0~7.5, and generating long-chain alkyl maleamic acid salt and 2-acrylamido-2-methylpropanesulfonic acid. (2) Add 68% to 80% of the total molar amount of the three monomer raw materials to the mixed solution obtained in step (2), and stir until completely dissolved; react in a polymerization reactor, purge with nitrogen to remove oxygen, heat the system to 40 to 60°C, add an initiator and react for 4 to 6 hours to generate the polymer surface agent; preferably, the long-chain fatty amine in step (1) is one of laurylamine, palmitamine, stearylamine, oleic acid amine, dodecylaniline, and hexadecylaniline.

3. The preparation method according to claim 2, characterized in that, The initiator mentioned in step (3) is ammonium persulfate and anhydrous sodium sulfite. The amount of initiator added is 0.2% to 0.3% of the total mass of the three monomer raw materials, and the molar ratio of ammonium persulfate and anhydrous sodium sulfite is 1:

1.

4. A fracturing fluid based on a polymer surfactant, characterized in that, The fracturing fluid comprises: the polymerizing agent as described in claim 1, anionic surfactant, and water.

5. The fracturing fluid as described in claim 4, characterized in that, The fracturing fluid comprises, by mass percentage: 1.0%~3.0% polymer, 0.5%~1.5% anionic surfactant, and the balance being water.

6. The fracturing fluid as described in claim 4, characterized in that, The anionic surfactant is one or more of the following: sodium fatty alcohol polyoxyethylene ether sulfate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and α-alkenyl sulfonate.

7. The fracturing fluid as described in claim 4, characterized in that, The fracturing fluid comprises, by mass percentage: 3.0% polymerizing agent, 1.5% anionic surfactant, and the balance being water; the polymerizing agent is a compound of formula i, where x, y, and z are the mole fractions of structural units, x=79%, y=20.6%, z=0.4%, x+y+z=100%, and R is an alkyl oleate; the anionic surfactant is sodium fatty alcohol polyoxyethylene ether sulfate.

8. The method for preparing the fracturing fluid according to any one of claims 4 to 7, characterized in that, The process includes the following steps: dissolving a polymerizing agent and anionic surfactant in water to obtain the fracturing fluid.

9. A fracturing fluid system, characterized in that, Includes the fracturing agent as described in claim 1 or the fracturing fluid as described in any one of claims 4 to 7.

10. The application of the fracturing agent of claim 1, the fracturing fluid of any one of claims 4 to 7, or the fracturing fluid system of claim 9 in fracturing operations in low-permeability coal-gas reservoirs.

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