Water-soluble hydrophobic associating polymer, process for its preparation and use thereof

Abstract

The present application relates to the technical field of oil and gas exploitation, and particularly relates to a water-soluble hydrophobic associating polymer, a preparation method and application thereof. The method comprises the following steps: mixing a hydrophilic monomer, a monomer containing a ketone carbonyl group and a hydrophobic monomer, and performing a copolymerization reaction to obtain a copolymer; mixing the copolymer and a crosslinking agent containing a hydrazine group, and performing a crosslinking reaction under an acidic condition to obtain a water-soluble hydrophobic associating polymer. The present application starts from the design of a molecular structure, and solves the bottleneck of poor stability, fast performance attenuation and non-recoverability of a traditional polymer thickener in a high-temperature, high-salt and high-shear environment by innovatively constructing a double-network structure of hydrophobic association and dynamic covalent bond crosslinking. The prepared water-soluble hydrophobic associating polymer has excellent comprehensive performance, provides an innovative solution for preparing a high-performance fracturing fluid suitable for harsh reservoir conditions, and has important significance for improving the recovery rate of crude oil.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, and in particular to a water-soluble hydrophobic associative polymer, its preparation method, and its application. Background Technology

[0002] As a key foundation of modern industrial systems and energy supply, the efficient extraction of petroleum plays a vital role in ensuring energy security and supporting economic development. With the continuous growth of global energy demand and the decreasing availability of conventional oil and gas resources, the focus of extraction is gradually shifting to complex oil and gas reservoirs that are deep, high-temperature, and highly salinized. These reservoirs present harsh environments, placing higher demands on extraction technologies, especially hydraulic fracturing. Fracturing fluid, as the core medium in fracturing operations, directly affects reservoir stimulation and ultimate recovery. Thickeners are a key component in fracturing fluid systems, increasing the viscosity of the displacement fluid and expanding the swept volume. Early thickeners widely used were natural plant gums, such as guar gum. However, these thickeners have significant drawbacks in practical applications, such as incomplete gel breaking leading to residues that can clog reservoir pores and pipelines, and limited temperature resistance, making them unsuitable for deep, high-temperature environments.

[0003] To overcome the aforementioned problems, polymer-synthesized thickeners have gradually become a focus of research and application. Among them, partially hydrolyzed polyacrylamide (HPAM) and its modified products, prepared using acrylamide (AM) as a monomer, have become the most widely used water-soluble polymers in the field of tertiary oil recovery due to their mild polymerization conditions, low cost, and ease of obtaining high molecular weights. However, these products face certain limitations in high-temperature, high-salinity formations: on the one hand, the amide groups in their molecular chains are prone to hydrolysis under high temperature or extreme acid and alkaline conditions, leading to polymer degradation; on the other hand, in the presence of high concentrations of metal ions, the electrostatic shielding effect generated by the ions causes the polymer molecular chains to coil, reducing the hydrodynamic volume and thus significantly reducing the solution's thickening capacity. To maintain the oil displacement effect, field operations are often forced to significantly increase the polymer concentration, which directly leads to a sharp increase in extraction costs.

[0004] To improve the temperature and salt resistance of polymers, the concept of hydrophobic associative polymers (HPAMs) has been proposed and studied. These polymers introduce a small number of hydrophobic groups into a hydrophilic backbone, relying on the physical association between these hydrophobic groups to form a reversible three-dimensional network structure in aqueous solution, thereby increasing the system viscosity. Studies have shown that hydrophobic association can resist the compression of molecular chains by salt ions to a certain extent, exhibiting superior performance compared to traditional HPAMs. However, this network structure built based on hydrophobic association still has inherent defects: First, hydrophobic association is essentially a weak physical interaction such as van der Waals forces, with low bond energy, resulting in insufficient strength and stability of the formed network structure; second, under harsh conditions such as high temperature and high shear, the hydrophobic microdomains are easily destroyed, leading to network dissociation and a sharp drop in viscosity; more importantly, this physical association is static and lacks active repair capabilities. Once the network structure is damaged by external forces, its performance is difficult to recover, thus limiting its long-term effectiveness and reliability in complex and variable reservoir environments. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing a water-soluble hydrophobic associative polymer, its preparation method, and its application. By constructing a dual-network structure of "hydrophobic associative physical network - dynamic covalent bond chemical network", the structural stability and environmental adaptability of the polymer are synergistically enhanced.

[0006] To achieve the above objectives, the present invention provides a method for preparing a water-soluble hydrophobic associative polymer, comprising the following steps: S1. A copolymer is obtained by mixing a hydrophilic monomer, a ketone-containing carbonyl monomer, and a hydrophobic monomer and performing a copolymerization reaction. S2. The copolymer and a crosslinking agent containing hydrazide groups are mixed and crosslinked under acidic conditions to obtain a water-soluble hydrophobic associative polymer.

[0007] Preferably, in S1, the hydrophilic monomer is selected from acrylamide; the monomer containing a ketone carbonyl group is selected from diacetone acrylamide; and the structural formula of the hydrophobic monomer is [insert structural formula here]. .

[0008] Preferably, the method for preparing the hydrophobic monomer includes the following steps: (1) Sodium N-methyltaurate, bromododecane, triethylamine and solvent are mixed and reacted to obtain an intermediate product; (2) Mix the intermediate product, solvent and chloropropylene and react to obtain a hydrophobic monomer.

[0009] Preferably, in S1, the molar ratio of hydrophilic monomer, ketone-containing carbonyl monomer, and hydrophobic monomer is 7.5-8.5:1.5-2.5:0.05-0.15.

[0010] Preferably, in S1, the copolymerization reaction temperature is 40℃-50℃ and the time is 3.5h-5.5h.

[0011] Preferably, in S2, the crosslinking agent containing an acylhydrazine group is selected as azidodiacid hydrazine.

[0012] Preferably, in S2, the acidic conditions are achieved by adding acetic acid to adjust the pH of the system to 4-6.

[0013] Preferably, in S2, the crosslinking reaction temperature is 20-30℃ and the time is 23-25h.

[0014] The present invention also provides a water-soluble hydrophobic associating polymer, which is prepared according to the preparation method of the water-soluble hydrophobic associating polymer.

[0015] The present invention also provides the application of the aforementioned water-soluble hydrophobic associating polymer as a thickener in the formulation of fracturing fluids for oil and gas development.

[0016] The beneficial effects of this invention are as follows: (1) This invention provides a method for preparing a water-soluble hydrophobic associative polymer, comprising the following steps: mixing a hydrophilic monomer, a ketone carbonyl-containing monomer, and a hydrophobic monomer, and performing a copolymerization reaction to obtain a copolymer; mixing the copolymer with a crosslinking agent containing an acylhydrazine group, and performing a crosslinking reaction under acidic conditions to obtain a water-soluble hydrophobic associative polymer. This invention innovatively introduces dynamic covalent bonds (acylhydrazone bonds) for chemical crosslinking based on hydrophobic association, forming a dual-network structure. In this structure, the dynamic covalent bonds provide high-strength, stable crosslinking points, serving as the rigid framework of the network and enhancing the overall mechanical strength and thermal stability of the polymer structure; simultaneously, the hydrophobic association, as a reversible physical crosslinking point, endows the network with a certain degree of flexibility and responsiveness. The synergistic effect of the two networks enables the polymer to better withstand the intensified molecular chain thermal motion caused by high temperatures and the electrostatic shielding effect induced by high concentrations of salt ions, thereby maintaining excellent and stable thickening properties under extreme reservoir conditions.

[0017] (2) Based on the synergistic stabilizing effect of the above-mentioned dual-network structure, the polymer prepared by the present invention has excellent temperature resistance and salt resistance. Among them, the chemical cross-linking network composed of dynamic covalent bonds can effectively lock the extended conformation of the molecular chain, thereby suppressing chain curling at high temperature and chain collapse caused by high salt ions, making it suitable for the complex oil and gas reservoir exploitation environment of deep, high temperature and high mineralization.

[0018] (3) This dual-network structure endows the polymer with excellent viscoelastic characteristics: the chemically cross-linked network provides a solid elastic basis and improves the polymer's storage modulus; while the hydrophobic associative physical network contributes the viscous component and works with the chemical network to dissipate energy. This structure enables the polymer solution to buffer shear stress at high shear rates through reversible dissociation of physical association points and rearrangement of dynamic covalent bonds, thereby exhibiting good resistance to shear dilution and structural integrity.

[0019] (4) Acylhydrazone bonds, as a type of dynamic covalent bond, can undergo reversible breakage and recombination under specific conditions. Thanks to this property, it has been successfully introduced into polymer crosslinking networks, giving the material a unique self-healing function. When the network is locally damaged by external forces such as high-intensity shear, the dynamic covalent bonds can recombine under mild conditions and synergize with the simultaneously restored hydrophobic association to jointly drive the self-repair and performance recovery of the network structure. This mechanism ensures that the polymer can maintain its long-lasting thickening effect during intermittent construction or long-term formation residence, thereby improving the long-term effectiveness of the fracturing fluid system.

[0020] (5) The preparation method of the present invention can effectively regulate the physical association strength and chemical crosslinking density in the polymer double network structure by controlling the ratio of hydrophilic monomer, ketone-containing carbonyl monomer and hydrophobic monomer, as well as the amount of crosslinking agent, thereby optimizing the final performance of the polymer for different reservoir conditions and giving it good application flexibility. Attached Figure Description

[0021] Figure 1 It is PADA-12 in Embodiment 1 of the present invention. 1 HNMR spectrum; Figure 2 These are the infrared spectra of PADA-12 and PADAH-12 in Embodiment 1 of the present invention; Figure 2 (a) in the image is the infrared spectrum of PADA-12. Figure 2 (b) in the image is the infrared spectrum of PADAH-12; Figure 3 This is a characterization diagram of PADAH-12 under different ADH addition amounts according to the present invention; Figure 4 This is a graph showing the change in apparent viscosity of PADAH-12 under different ADH addition amounts according to the present invention; Figure 5 This is a graph showing the G' and G'' curves of the PADA-12 solution of the present invention under different shear strains; Figure 6 This is a graph showing the G' and G'' curves of the PADA-12 solution of the present invention at different angular frequencies; Figure 7This is a graph showing the G' and G'' curves of the PADAH-12 solution of the present invention under different shear strains; Figure 8 This is a graph showing the G' and G'' curves of the PADAH-12 solution of the present invention at different angular frequencies; Figure 9 This is a viscosity-temperature curve diagram of different solutions of the present invention; Figure 10 This is a viscosity-shear rate curve of different solutions of the present invention; Figure 11 This is a shear recovery curve diagram of different solutions of the present invention. Detailed Implementation

[0022] This invention provides a method for preparing a water-soluble hydrophobic associating polymer, comprising the following steps: S1. A copolymer is obtained by mixing a hydrophilic monomer, a ketone-containing carbonyl monomer, and a hydrophobic monomer and performing a copolymerization reaction. S2. The copolymer and a crosslinking agent containing hydrazide groups are mixed and crosslinked under acidic conditions to obtain a water-soluble hydrophobic associative polymer.

[0023] In this invention, in S1, the hydrophilic monomer is selected from acrylamide; the monomer containing a ketone carbonyl group is selected from diacetone acrylamide; and the structural formula of the hydrophobic monomer is [insert structural formula here]. .

[0024] In this invention, the method for preparing the hydrophobic monomer includes the following steps: (1) Sodium N-methyltaurate, bromododecane, triethylamine and solvent are mixed and reacted to obtain an intermediate product; (2) Mix the intermediate product, solvent and chloropropylene and react to obtain a hydrophobic monomer.

[0025] In this invention, in step (1), the solvent is selected from ethanol; the molar ratio of sodium N-methyltaurate, bromododecane, and triethylamine is 45-55:45-55:45-55; the molar ratio of sodium N-methyltaurate to the volume of the solvent is 45-55 mmol:70-90 mL.

[0026] In this invention, in step (1), the reaction is: heated to reflux for 7-9 hours; after the reaction is completed, it is naturally cooled to room temperature, allowed to stand, filtered and dried to obtain the intermediate product.

[0027] In this invention, in step (2), the solvent is selected from at least one of ethanol and water.

[0028] In this invention, in step (2), the molar ratio of the intermediate product to allyl chloride is 1:1-1.5; the amount of solvent used is not specifically limited in this invention, as long as the reactants can be completely dissolved.

[0029] In this invention, in step (2), the reaction is carried out at 45-55℃ for 23-25h; after the reaction is completed, the solvent is removed by rotary evaporation to obtain the hydrophobic monomer.

[0030] In this invention, in S1, the molar ratio of hydrophilic monomer, ketone-containing carbonyl monomer and hydrophobic monomer is 7.5-8.5:1.5-2.5:0.05-0.15.

[0031] In this invention, in step S1, the monomer and water obtained by mixing are mixed at a mass ratio of 18-22:78-82 and stirred until completely dissolved. Then, nitrogen gas is introduced for 25-35 minutes to remove oxygen from the system. Subsequently, the mixture is heated to the copolymerization reaction temperature, and an initiator is added to carry out the copolymerization reaction. After the reaction is completed, the mixture is washed with ethanol, cut, dried and pulverized to obtain the copolymer.

[0032] In this invention, the initiator is selected from azobisisobutylamidine hydrochloride (AIBA); the number of ethanol washings is ≥2; and the drying temperature is 55-65℃.

[0033] In this invention, in S1, the temperature of the copolymerization reaction is 40℃-50℃ and the time is 3.5h-5.5h.

[0034] In this invention, the crosslinking agent containing an acylhydrazine group in S2 is selected as azidodiacid hydrazine.

[0035] In this invention, S2, mixing includes: preparing a copolymer aqueous solution with a mass concentration of 0.8-1.2%, and adding to the copolymer an aqueous solution of a crosslinking agent containing an acylhydrazine group with a mass concentration of 4.5-5.5% at a mass percentage of 0.6-2.0% of the solution.

[0036] In this invention, in S2, the acidic condition is achieved by adding acetic acid to adjust the pH of the system to 4-6.

[0037] In this invention, in S2, the crosslinking reaction temperature is 20-30℃ and the time is 23-25h.

[0038] The present invention also provides a water-soluble hydrophobic associating polymer, which is prepared according to the preparation method of the water-soluble hydrophobic associating polymer.

[0039] The present invention also provides the application of the aforementioned water-soluble hydrophobic associating polymer as a thickener in the formulation of fracturing fluids for oil and gas development.

[0040] The following embodiments are provided to better understand the present invention and are not limited to the described embodiments. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0041] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0042] Example 1 This embodiment provides a method for preparing a water-soluble hydrophobic associative polymer, comprising the following steps: In a 250 mL flask equipped with a reflux condenser, 50 mmol of sodium N-methyltaurate (NMS), 50 mmol of dodecane bromide, 50 mmol of triethylamine (TEA), and 80 mL of anhydrous ethanol were added, and the mixture was heated to reflux for 8 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, allowed to stand, filtered, and dried to obtain the intermediate product (NMSC-12).

[0043] 20 mmol of NMSC-12 was placed in a flask, and a mixture of anhydrous ethanol and water (volume ratio of anhydrous ethanol to water 2:1) was added to completely dissolve it. Then, 22 mmol of allyl chloride was added dropwise, and the reaction was carried out at 50 °C for 24 h. After the reaction was completed, the solvent was removed by rotary evaporation to obtain the hydrophobic monomer. (ANMSC-12).

[0044] Acrylamide (AM), diacetone acrylamide (DAAM), and the synthesized ANMSC-12 (in a molar ratio of 8:2:0.1) were added to a 250 mL three-necked flask. Water was added at a mass ratio of 20:80 (total mass of AM + DAAM + ANMSC-12: mass of water), and the mixture was stirred until completely dissolved. Nitrogen gas was then purged for 30 min to remove oxygen from the system. The mixture was then heated to 45 °C, and the initiator azobisisobutylamidine hydrochloride (AIBA) was added. The reaction was carried out for 4.5 h. After the reaction was completed, the mixture was washed three times with ethanol, cut into small pieces, dried in a vacuum drying oven at 60 °C, and finally pulverized to obtain the copolymer (PADA-12).

[0045] PADA-12 was prepared into a 1% aqueous solution. Then, 0.8% of the solution was added to a 5% aqueous solution of adipic acid dihydrazide (ADH). Glacial acetic acid was then added dropwise to adjust the pH of the system to 5. The system was allowed to stand at 25°C for 24 hours to crosslink, resulting in a water-soluble hydrophobic associative polymer (PADAH-12).

[0046] Example 2 This embodiment provides a method for preparing a water-soluble hydrophobic associative polymer, which is basically the same as that in Example 1, except that "PADA-12 is prepared into an aqueous solution with a mass concentration of 1%, and an ADH aqueous solution with a mass concentration of 5% is added to it at a mass concentration of 0.6%".

[0047] Example 3 This embodiment provides a method for preparing a water-soluble hydrophobic associative polymer, which is basically the same as that in Example 1, except that "PADA-12 is prepared into an aqueous solution with a mass concentration of 1%, and an ADH aqueous solution with a mass concentration of 5% is added to it at a mass concentration of 1.0%".

[0048] Example 4 This embodiment provides a method for preparing a water-soluble hydrophobic associative polymer, which is basically the same as that in Example 1, except that "PADA-12 is prepared into an aqueous solution with a mass concentration of 1%, and an ADH aqueous solution with a mass concentration of 5% is added to it at a mass concentration of 1.2%".

[0049] Example 5 This embodiment provides a method for preparing a water-soluble hydrophobic associative polymer, which is basically the same as that in Example 1, except that "PADA-12 is prepared into an aqueous solution with a mass concentration of 1%, and an ADH aqueous solution with a mass concentration of 5% is added to it at a mass concentration of 1.4%".

[0050] Example 6 This embodiment provides a method for preparing a water-soluble hydrophobic associative polymer, which is basically the same as that in Example 1, except that "PADA-12 is prepared into an aqueous solution with a mass concentration of 1%, and an ADH aqueous solution with a mass concentration of 5% is added to it at a mass concentration of 1.6%".

[0051] Example 7 This embodiment provides a method for preparing a water-soluble hydrophobic associative polymer, which is basically the same as that in Example 1, except that "PADA-12 is prepared into an aqueous solution with a mass concentration of 1%, and an ADH aqueous solution with a mass concentration of 5% is added to it at a mass concentration of 1.8%".

[0052] Example 8 This embodiment provides a method for preparing a water-soluble hydrophobic associative polymer, which is basically the same as that in Example 1, except that "PADA-12 is prepared into an aqueous solution with a mass concentration of 1%, and an ADH aqueous solution with a mass concentration of 5% is added to it at a mass concentration of 2.0%".

[0053] Experimental Example 1 The copolymer PADA-12 from Example 1 was subjected to proton nuclear magnetic resonance spectroscopy (NMR spectroscopy). 1 Characterized by ¹H NMR, the PADA-12 in Example 1 was obtained. 1 HNMR spectrum, such as Figure 1 As shown in the figure. The horizontal axis represents chemical shift (δ, ppm). The characteristic peaks are assigned as follows: the signal at 4.70 ppm originates from the deuterated solvent D2O; the peaks at 0.91 ppm (a) and 1.32 ppm (b) correspond to the protons of the -CH3 at the end of the hydrophobic long alkyl chain and the -CH2- within the chain, respectively; the peak at 1.38-1.42 ppm (c) belongs to the -CH3 group in the structure of diacetone acrylamide (DAAM); the peaks at 1.53-1.73 ppm (d) and 2.11-2.29 ppm (f) originate from the -CH3 group on the polymer backbone. 2- and -CH- protons; 1.74-1.86 ppm (e) and 3.06 ppm (g) correspond to the -CO-CH3 and -CH2-CO- groups in the DAAM unit, respectively; the peaks at 3.12-3.33 ppm (h, i, j) correspond to the -N-CH2- and -N-CH3 groups in the ANMSC-12 structure; the peaks at 3.91-3.95 ppm (k, l) belong to the -CH2-CH2-SO3Na group in the ANMSC-12 structure.

[0054] The copolymer PADA-12 and the water-soluble hydrophobic associative polymer PADAH-12 from Example 1 were characterized by Fourier transform infrared spectroscopy (FT-IR). The test was performed using the potassium bromide (KBr) pellet method: a small amount of dried sample was mixed and ground evenly with fully dried KBr powder in a mortar, and then pressed into a transparent sheet. A Fourier transform infrared spectrometer (model: WQF-510A) was used at 4000 cm⁻¹. -1 up to 400cm -1 Scan within the wavenumber range, with a resolution set to 4cm. -1 A total of 16 scans were performed to obtain a spectrum with a good signal-to-noise ratio.

[0055] The infrared spectra of PADA-12 and PADAH-12 in Example 1 are as follows: Figure 2 As shown; Figure 2 (a) in the image is the infrared spectrum of PADA-12. Figure 2 (b) shows the infrared spectrum of PADAH-12. Analysis of the spectrum confirmed the structure of the product. In the infrared spectrum of PADA-12 (a): 3438 cm⁻¹ -1 and 3200cm -1 The absorption peak at 3438 cm⁻¹ is attributed to the stretching vibration of the NH bond.-1 The location is free NH, 3200cm -1 The NH group at this position is hydrogen-bonded; 2972 ​​cm⁻¹ -1 and 2929cm -1 The absorption peaks at 1658 cm⁻¹ correspond to the asymmetric stretching vibrations of the methyl (CH₃) and methylene (CH₂) groups, respectively; -1 The strong absorption peak at 1546 cm⁻¹ is a characteristic peak of the stretching vibration of the carbonyl group (C=O); -1 The absorption peak at 1450 cm⁻¹ is attributed to the coupling of the in-plane bending vibration of NH and the stretching vibration of CN (amide II band); -1 and 1362cm -1 The absorption peaks at 1202 cm⁻¹ correspond to the asymmetric and symmetric bending vibrations of CH₃, respectively; -1 and 1154cm -1 The absorption peak at 619 cm⁻¹ can be attributed to the CN stretching vibration (amide III band) or the CO stretching vibration that may exist in the system; -1 The absorption peak at that location corresponds to the out-of-plane bending vibration of NH. In the infrared spectrum (b) of PADAH-12, structural changes due to the cross-linking reaction can be observed: at 1600-1700 cm⁻¹... -1 Within the range of 3300-3500 cm⁻¹, absorption peaks of the C=N structure appeared while retaining the carbonyl group (C=O); -1 A broad absorption band attributable to the stretching vibration of secondary amine NH appears within the range; furthermore, the absorption band at 1100-1200 cm⁻¹... -1 The absorption peak intensity of the CN bond in the amide structure within the range was significantly increased. These changes confirm that the ketone carbonyl group on the PADA-12 molecular chain successfully reacted with the acylhydrazine group of the crosslinking agent adipic acid dihydrazide, forming a crosslinked structure characterized by acylhydrazone bonds (-C=NN-).

[0056] Experiment Example 2 The water-soluble hydrophobic associative polymers PADAH-12 prepared in Examples 1-8 were characterized, and characterization diagrams of PADAH-12 with different ADH addition amounts were obtained, as shown in the figure. Figure 3 As shown. From Figure 3It can be seen that precipitation occurs when the crosslinking agent is used in excess. This is because when the amount of crosslinking agent is too high, the crosslinking reaction rate is too fast and the degree of crosslinking is too great. A large number of crosslinking points cause PADAH-12 molecules to form huge and insoluble crosslinked aggregates. The size of these aggregates exceeds the stable range of colloidal particles and cannot be stably dispersed in solution. At the same time, the excessive crosslinking agent disrupts the balance of intermolecular forces within the system. The solvation and intermolecular repulsion that originally maintained the stable dispersion of molecules are weakened under strong crosslinking. The internal interaction of the aggregates is much greater than its interaction with solvent molecules, resulting in poor compatibility between the aggregates and the solvent, thus inducing precipitation.

[0057] Further, the water-soluble hydrophobic associative polymer PADAH-12 prepared in Examples 1-5 was selected and tested using a rheometer (Anton Paar MCR302) at a temperature of 25°C and a shear rate of 7.34 s⁻¹. -1 The apparent viscosity of PADAH-12 was measured under the following conditions. Each sample was tested continuously for 120 seconds, with data points collected every 6 seconds, for a total of 20 data points. The arithmetic mean of these data points was taken as the final apparent viscosity of the sample. The changes in apparent viscosity of PADAH-12 under different ADH additions were obtained, as shown in the figure. Figure 4 As shown. Figure 4 The results showed that the viscosity of PADAH-12 initially increased and then decreased with increasing ADH dosage. This is mainly because when the ADH dosage is low, as its dosage increases, more ketone carbonyl groups on the PADAH-12 copolymer molecular chain react with the acylhydrazine groups of ADH, forming more acylhydrazone crosslinking points. The network structure constructed by dynamic covalent bonds between molecules becomes more complete, the interaction between molecular chains is enhanced, and the degree of entanglement and aggregation increases, which macroscopically manifests as a significant increase in solution viscosity. However, when the ADH dosage exceeds a certain range, excessive crosslinking leads to an overly dense network structure, severely restricting the degree of freedom of molecular chain movement. This may also cause local aggregation of macromolecular chains or even precipitation from the solution, resulting in a relative reduction in the polymer components that can effectively contribute to viscosity in the solution, which macroscopically manifests as a decrease in viscosity.

[0058] Experimental Example 3 To evaluate the changes in viscoelasticity of the polymer before and after crosslinking in Example 1, the following test solutions were prepared: (1) PADA-12 aqueous solution (PADA-12 mass concentration is 0.8%); (2) Salt solution obtained by dissolving PADA-12 in 40 g / L NaCl solution (PADA-12 mass concentration is 0.8%). (3) Salt solution obtained by dissolving PADA-12 in 40 g / L CaCl2 solution (PADA-12 mass concentration is 0.8%).

[0059] (4) Add 5% adipic acid dihydrazide (ADH) aqueous solution to (1)-(3) above, then add glacial acetic acid to adjust the pH of the system to 5, and let it stand at 25°C for 24 hours to crosslink, to obtain three PADAH-12 solutions (PADAH-12 mass concentration is 0.8%).

[0060] For example, (2) includes the following preparation process: preparing a NaCl aqueous solution with a concentration of 40 g / L, dissolving PADA-12 in the solution, and preparing a PADA-12 salt solution with a mass concentration of 0.8%.

[0061] Dynamic oscillatory shear tests were conducted on the above solutions using a rheometer at 25°C. First, amplitude scanning (shear strain range 0.01%-1000%) was performed to determine the linear viscoelastic region of each system. Based on the results, a 1% shear strain value was selected for subsequent frequency scanning tests. Subsequently, frequency scanning was performed within an angular frequency range of 0.1-100 rad / s, and the changes in storage modulus (G') and loss modulus (G'') with angular frequency were recorded to characterize the viscoelasticity of the material. Viscoelasticity is a key rheological property affecting the microscopic efficiency of oil displacement. Storage modulus (G') reflects the material's ability to store elastic deformation energy, corresponding to the reversible deformation of molecular chain segments; loss modulus (G'') reflects energy dissipation due to internal friction, corresponding to the irreversible slip and rearrangement of molecular chain segments. The G' and G'' curves of PADA-12 solution under different shear strains are shown below. Figure 5 As shown; G' and G'' curves of PADA-12 solution at different angular frequencies, as shown. Figure 6 As shown; G' and G'' curves of PADAH-12 solution under different shear strains, as shown. Figure 7 As shown; G' and G'' curves of PADAH-12 solution at different angular frequencies, as shown. Figure 8 As shown. From Figure 5-8 It can be seen that PADA-12 exhibits predominantly viscous properties in fresh water and predominantly elastic properties in brine, indicating that its viscoelasticity is enhanced in a saline environment. The PADAH-12 dual-network polymer constructed by introducing acylhydrazone chemical crosslinks shows significantly higher storage modulus (G') and loss modulus (G'') in both fresh water and brine than the uncrosslinked precursor PADA-12, and both exhibit predominantly elastic properties. This polymer exhibits excellent rheological properties dominated by elasticity in brine solutions, indicating that its chemically crosslinked network and hydrophobic associative network work synergistically in the presence of ions, forming a more stable and robust structure. These properties collectively demonstrate that the PADAH-12 dual-network structure possesses superior overall mechanical stability compared to a single physically associative network, which is of great significance for maintaining structural integrity and effectively driving crude oil under complex reservoir conditions with high temperature and high salinity.

[0062] Experiment Example 4 The following solutions were selected for temperature resistance testing (the PADAH-12 used was the PADAH-12 prepared in Example 1): (1) PADAH-12 aqueous solution (PADAH-12 mass concentration is 0.8%); (2) Salt solutions obtained by dissolving PADAH-12 in 40 g / L or 80 g / L NaCl solution (PADAH-12 mass concentration is 0.8% respectively); (3) Salt solutions obtained by dissolving PADAH-12 in 40 g / L or 80 g / L CaCl2 solution (PADAH-12 mass concentration is 0.8% respectively).

[0063] The test was conducted using a rheometer in steady-state shear mode. The shear rate was set to 100 s. -1 The temperature program was as follows: starting from 30℃, the temperature was increased to 90℃ in a stepwise manner at a rate of 10℃ / 3min, and then held at seven temperature points between 30℃ and 90℃ for 1min at each point. The apparent viscosity of the solution at each temperature point was recorded, and viscosity-temperature curves were plotted to evaluate the temperature resistance of the polymer in different media. Viscosity-temperature curves for different solutions are shown below. Figure 9 As shown. From Figure 9 It can be seen that although the viscosity of all solutions decreases with increasing temperature, the viscosity of each system can still be maintained within the range of 100-200 mPa·s at 90℃. This indicates that the PADAH-12 polymer, through the synergistic effect of its hydrophobic associative physical network and acylhydrazone chemical network, can effectively suppress excessive coiling of molecular chains and network disintegration during heating, exhibiting good stability.

[0064] Experimental Example 5 The following solutions were selected for shear resistance testing (the PADAH-12 used was the PADAH-12 prepared in Example 1): (1) PADAH-12 aqueous solution (PADAH-12 mass concentration is 0.8%); (2) Salt solutions obtained by dissolving PADAH-12 in 40 g / L or 80 g / L NaCl solution (PADAH-12 mass concentration is 0.8% respectively); (3) Salt solutions obtained by dissolving PADAH-12 in 40 g / L or 80 g / L CaCl2 solution (PADAH-12 mass concentration is 0.8% respectively).

[0065] Steady-state shear rate sweep tests were conducted using a rheometer under isothermal conditions at 25°C. The shear rate was measured from 0.01 s⁻¹. -1linearly increased to 1000s -1 The total test duration was 300 seconds. The apparent viscosity versus shear rate curve was recorded to evaluate the polymer's shear resistance in different media. Viscosity-shear rate curves for different solutions are shown below. Figure 10 As shown. From Figure 10 It can be observed that PADAH-12 solutions often exhibit a slight increase in viscosity in the low shear rate region. This is attributed to the fact that under extremely low shear conditions, polymer molecular chains, hydrophobic associated microdomains, and dynamic covalent networks have ample time for structural rearrangement and reinforcing interactions, leading to an increase in instantaneous flow resistance. As the shear rate further increases, the mechanical force applied by the fluid is sufficient to disrupt these weak interactions and physical entanglements, causing the molecular chains to orient along the flow direction. The solution exhibits typical "shear thinning" behavior, i.e., the viscosity decreases significantly with increasing shear rate. Throughout the entire shear rate scan range, PADAH-12 exhibited continuous and smooth shear thinning curves in all test media, without any abrupt changes or breaks. Even at shear rates as high as 1000 s... -1 At shear rates of [specific shear rate], the solution remained homogeneous, with no phase separation or precipitation observed. This indicates that PADAH-12 possesses a synergistic and stable dual structure formed by its hydrophobic associative physical network and acylhydrazone chemical cross-linking network, effectively dissipating shear energy and preventing irreversible network damage under strong shear. Therefore, this polymer exhibits excellent shear stability and resistance to mechanical degradation in simulated reservoir shear environments.

[0066] Experimental Example 6 To evaluate the structural recovery ability of the polymer after shearing, the following solutions were selected for shear recovery performance testing (the PADAH-12 used was the PADAH-12 prepared in Example 1): (1) PADAH-12 aqueous solution (PADAH-12 mass concentration is 0.8%); (2) Salt solution obtained by dissolving PADAH-12 in 80 g / L NaCl solution (PADAH-12 mass concentration is 0.8%). (3) Salt solution obtained by dissolving PADAH-12 in 80 g / L CaCl2 solution (PADAH-12 mass concentration is 0.8%).

[0067] Using a rheometer, a three-stage shearing program was executed under constant temperature conditions of 25℃: Phase 1: At a low shear rate (0.01 s⁻¹) -1 First stage: initial shearing for 60 seconds; second stage: instantaneously increase the shearing rate to 1000 seconds. -1 The condition was maintained for 60 seconds to simulate high shear failure conditions; the third stage involved restoring the shear rate to 0.01 s. -1The solution was subjected to shear for 180 seconds, and the viscosity change over time was observed and recorded. Shear recovery curves for different solutions were obtained, as shown below. Figure 11 As shown. From Figure 11 As can be seen, under the high shear rate in the second stage, the viscosity of the samples decreased sharply. This is because the strong shear force disrupted the physical entanglements, hydrophobic microregions, and even some dynamic covalent networks in the polymer solution, forcing the molecular chains to orient and reducing flow resistance. When the flow rate was switched back to low in the third stage, the viscosity of each solution recovered to varying degrees. This indicates that the cross-linked network inside PADAH-12, especially the dynamically reversible acylhydrazone bonds and the hydrophobic associations that can be rebuilt after shearing, can rearrange and recombine after the shear force is removed or weakened, partially repairing the damaged network structure, thereby restoring the macroscopic viscosity of the solution.

[0068] Therefore, this invention employs the aforementioned water-soluble hydrophobic associating polymer, its preparation method, and its applications. Starting with molecular structure design, it innovatively constructs a dual-network structure of hydrophobic association and dynamic covalent cross-linking, synergistically solving the bottlenecks of traditional polymer thickeners' poor stability, rapid and irreversible performance degradation under high temperature, high salt, and high shear environments. The prepared water-soluble hydrophobic associating polymer exhibits excellent comprehensive performance, providing an innovative solution for formulating high-performance fracturing fluids suitable for harsh reservoir conditions, and is of great significance for improving oil recovery.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a water-soluble hydrophobic associative polymer, characterized in that, Includes the following steps: S1. A copolymer is obtained by mixing a hydrophilic monomer, a ketone-containing carbonyl monomer, and a hydrophobic monomer and performing a copolymerization reaction. S2. The copolymer and a crosslinking agent containing hydrazide groups are mixed and crosslinked under acidic conditions to obtain a water-soluble hydrophobic associative polymer.

2. The method for preparing the water-soluble hydrophobic associative polymer according to claim 1, characterized in that, In S1, the hydrophilic monomer is selected from acrylamide; the monomer containing the ketone carbonyl group is selected from diacetone acrylamide; the structural formula of the hydrophobic monomer is... .

3. The method for preparing the water-soluble hydrophobic associating polymer according to claim 2, characterized in that, The preparation method of hydrophobic monomers includes the following steps: (1) Sodium N-methyltaurate, bromododecane, triethylamine and solvent are mixed and reacted to obtain an intermediate product; (2) Mix the intermediate product, solvent and chloropropylene and react to obtain a hydrophobic monomer.

4. The method for preparing the water-soluble hydrophobic associating polymer according to claim 1, characterized in that, In S1, the molar ratio of hydrophilic monomer, ketone-containing carbonyl monomer, and hydrophobic monomer is 7.5-8.5: 1.5-2.5: 0.05-0.

15.

5. The method for preparing the water-soluble hydrophobic associating polymer according to claim 1, characterized in that, In S1, the copolymerization reaction temperature is 40℃-50℃ and the time is 3.5h-5.5h.

6. The method for preparing the water-soluble hydrophobic associating polymer according to claim 1, characterized in that, In S2, the crosslinking agent containing an acylhydrazine group is selected as azidodiacid hydrazine.

7. The method for preparing the water-soluble hydrophobic associating polymer according to claim 1, characterized in that, In S2, acidic conditions are achieved by adding acetic acid to adjust the pH of the system to 4-6.

8. The method for preparing the water-soluble hydrophobic associating polymer according to claim 1, characterized in that, In S2, the cross-linking reaction is carried out at a temperature of 20-30℃ for 23-25 ​​hours.

9. A water-soluble hydrophobic associative polymer, characterized in that, The water-soluble hydrophobic associative polymer was prepared according to any one of claims 1-8.

10. The application of the water-soluble hydrophobic associating polymer of claim 9 as a thickener in the formulation of fracturing fluids for oil and gas development.

Images