A betaine-containing hydrophobically associating polymer, its preparation method and use

Abstract

The present application relates to the technical field of oil exploitation aids, in particular to a hydrophobic associating polymer containing betaine structure and a preparation method and application thereof.The hydrophobic associating polymer containing betaine structure (PADA) provided by the present application is composed of acrylamide structural units, diacetone acrylamide structural units and hydrophobic monomer ANMSC-16 structural units with sulfobetaine structure, and exhibits excellent salt thickening performance.It is tested that the PADA provided by the present application exhibits excellent temperature resistance and shear strength in sodium chloride solution, magnesium chloride solution and calcium chloride solution.Because of the reversibility of the associated structure, the polymer exhibits excellent shear recovery performance in the above salt solutions, and the viscoelasticity increases with the increase of the salt solution concentration.Therefore, the hydrophobic associating polymer containing betaine structure provided by the present application can be used as a temperature-resistant and salt-resistant thickening agent, and has important potential in enhanced oil recovery in oil and gas fields.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction additives technology, and in particular to a betaine-containing hydrophobic associative polymer, its preparation method, and its application. Background Technology

[0002] To cope with the ever-increasing energy demand and the depletion of traditional resources, the focus of oil and gas field development has shifted from conventional reservoirs to ultra-deep (burial depth > 4500 meters) and unconventional reservoirs. These reservoirs generally possess complex geological conditions such as high temperature, high salinity, and ultra-low permeability, which impose stringent requirements on the performance of chemical agents used in extraction operations.

[0003] Polyacrylamide (PAM) is widely used in key processes of oil and gas extraction, such as hydraulic fracturing and enhanced oil recovery (EOR). However, it degrades under high temperature and high salinity conditions, accompanied by problems such as intensified hydrolysis and charge shielding effects, which severely limit its suitability for complex reservoir development.

[0004] The synthesis of hydrophobic associative water-soluble polymers (HAWSPs) involves embedding a small amount of hydrophobic monomers into the backbone of a hydrophilic polymer. When the concentration exceeds the critical association concentration (CAC), the hydrophobic groups spontaneously aggregate through van der Waals forces, forming intermolecular associations and constructing a three-dimensional network structure. Compared to traditional polyacrylamides, these polymers exhibit significantly improved temperature and salt resistance. However, in extreme reservoir environments, especially under high temperature and high salinity conditions, HAWSPs still face the dual challenges of charge shielding effects and ion-induced crosslinking, which may lead to a significant loss of polymer solution viscosity or even polymer precipitation, severely compromising their performance stability.

[0005] In existing technologies, sulfonic acid groups are introduced into HAWSPs through directional modification. Although the charge shielding effect can be reduced within a specific salinity range by forming a hydration layer, thereby enhancing salt resistance to some extent, its performance will still decrease significantly under high salinity conditions. Summary of the Invention

[0006] The purpose of this invention is to provide a betaine-containing hydrophobic associative polymer, its preparation method, and its application, in order to solve the defects of HAWSPs such as severe viscosity loss and unstable performance under high temperature and high salinity environments.

[0007] To achieve the above objectives, the present invention provides a hydrophobic associating polymer containing a betaine structure, wherein the structural formula of the hydrophobic associating polymer containing a betaine structure is as follows: ; Where x, y, and z are the molar percentage ranges of the structural units, x is 65%-70%, y is 29%-34%, and z is 1%, where x+y+z=100%.

[0008] The betaine-containing hydrophobic associative polymer has a molecular weight of 1.0 × 10⁻⁶. 6 g / mol ~ 1.5 × 10 6 g / mol, preferably 1.39 × 10 g / mol. 6 g / mol.

[0009] This invention also provides a method for preparing the above-mentioned betaine-containing hydrophobic associative polymer, comprising the following preparation steps: S1. Sodium N-methyltaurate, hexadecane bromo, triethylamine, and ethanol are mixed and refluxed to obtain NMSC-16; S2. Mix NMSC-16, allyl chloride, and ethanol solution, and react to obtain ANMSC-16; S3. After mixing ANMSC-16 with water, an ANMSC-16 solution is obtained. Acrylamide and diacetone acrylamide are added to the ANMSC-16 solution to obtain a mixed solution. The solution is purged with nitrogen, and then azobisisobutylamidine hydrochloride is added. The reaction is carried out under sealed conditions to obtain a hydrophobic associative polymer containing a betaine structure.

[0010] In this invention, the molar volume ratio of sodium N-methyltaurate, hexadecane bromo, triethylamine, and ethanol in S1 is 45-55 mmol: 45-55 mmol: 45-55 mmol: 80 mL, preferably 50 mmol: 50 mmol: 50 mmol: 80 mL.

[0011] In this invention, the preferred form of N-methyl taurate sodium salt in S1 is an aqueous solution of N-methyl taurate sodium salt.

[0012] In this invention, the temperature of the reflux reaction in S1 is 75-85°C, preferably 80°C, and the reflux reaction time is 10-14h, preferably 12h.

[0013] In this invention, after the reflux reaction in S1 is completed, the reaction system is cooled to 25°C, filtered, and the precipitate obtained by filtration is washed with acetone and then recrystallized with ethanol solution to obtain a white flaky crystal product. The white flaky crystal product is placed in an oven and dried under vacuum at 50°C for 12 hours to obtain NMSC-16.

[0014] In this invention, the molar volume ratio of NMSC-16, allyl chloride, and ethanol solution in S2 is 25-35 mmol: 30-40 mmol: 100 mL, preferably 30 mmol: 35 mmol: 100 mL.

[0015] In this invention, the reaction temperature in S2 is 50-60°C, preferably 55°C, and the reaction time is 20-26 hours, preferably 24 hours.

[0016] In this invention, after the reaction in S2 is completed, the reaction system temperature is cooled to 25°C, filtered, and the precipitate obtained by filtration is placed in ethanol for recrystallization to obtain a white powder. The white powder is placed in an oven and vacuum dried at 50°C for 12 hours to obtain ANMSC-16.

[0017] In this invention, the reaction process of ANMSC-16 is as follows: .

[0018] In this invention, the molar ratio of acrylamide, diacetone acrylamide, and ANMSC-16 in S3 is 65-70:29-34:1, preferably 69.3:29.7:1.

[0019] In this invention, in the mixture solution described in S3, the total mass concentration of ANMSC-16, acrylamide, and diacetone acrylamide is 22%-28%, preferably 25%; the total mass concentration is the ratio of the total mass of ANMSC-16, acrylamide, and diacetone acrylamide to the volume of the mixture solution. The mass of azobisisobutylamidine hydrochloride accounts for 0.03%-0.07% of the total mass of ANMSC-16, acrylamide, and diacetone acrylamide, preferably 0.05%.

[0020] In this invention, the reaction temperature in S3 is 40-50°C, preferably 45°C, and the reaction time is 4-6 hours, preferably 5 hours.

[0021] In this invention, after the reaction in S3 is completed, a light white gel is obtained. The light white gel is placed in ethanol for purification (to remove unreacted monomers and products with low molecular weight). After purification, it is dried to obtain a hydrophobic associative polymer containing a betaine structure.

[0022] This invention also provides the application of the above-mentioned betaine-containing hydrophobic associative polymer in petroleum extraction agents.

[0023] The present invention has the following beneficial effects: This invention provides a betaine-containing hydrophobic associative polymer (PADA), composed of acrylamide structural units, diacetone acrylamide structural units, and ANMSC-16 structural units with a sulfobetaine structure, exhibiting excellent salt thickening properties. Testing shows that the PADA provided by this invention exhibits excellent temperature resistance and shear strength in sodium chloride, magnesium chloride, and calcium chloride solutions. Furthermore, due to the reversibility of its associative structure, this polymer exhibits excellent shear recovery properties in the aforementioned salt solutions.

[0024] The betaine-containing hydrophobic associative polymer provided by this invention exhibits a viscoelasticity in the polymer solution that increases with increasing salt concentration, consistent with its salt resistance. Overall, this invention experimentally demonstrates that PADA can be used as a temperature- and salt-resistant thickener, showing significant potential for enhancing oil and gas recovery in oil and gas fields.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 This is the infrared spectrum of the present invention; in, Figure 1 (a) in the image is the infrared spectrum of ANMSC-16. Figure 1 (b) in the image is the infrared spectrum of PADA; Figure 2 This is the proton NMR spectrum of this invention; Figure 2 (a) in the image is the 1H NMR spectrum of ANMSC-16. Figure 2 (b) in the image is the hydrogen nuclear magnetic resonance spectrum of PADA; Figure 3 The η in the PADA solution of this invention sp / C r With C r Relationship diagram; Figure 4 This is a graph showing the test results of the critical association concentration (CAC) of this invention; Figure 4 (a) shows the fluorescence spectrum of PADA aqueous solution in the concentration range of 0.2–1.0 wt%. Figure 4 (b) represents the I1 / I3 ratio and apparent viscosity of PADA aqueous solutions in the concentration range of 0.2 to 1.0 wt%. Figure 5 These are the salt resistance test results of this invention; Figure 5 (a) in the figure shows the trend of apparent viscosity of PADA solution as a function of salt solution concentration. Figure 5(b) shows the effect of different types of salts on the viscosity of PADA; Figure 6 These are the temperature and shear strength test results of this invention; Figure 6 In Figure (a), the viscosity of PADA aqueous solution is a function of temperature. Figure 6 (b) shows the viscosity of PADA in sodium chloride solution as a function of temperature. Figure 6 (c) in the figure shows the viscosity of PADA in calcium chloride solution as a function of temperature. Figure 6 (d) in the figure represents the viscosity of PADA in magnesium chloride solution as a function of temperature. Figure 7 These are the shear recovery test results of this invention; Figure 7 (a) in the figure shows the shear recovery test results of PADA in sodium chloride solution. Figure 7 (b) shows the shear recovery test results of PADA in calcium chloride solution. Figure 7 (c) in the figure shows the shear recovery test results of PADA in magnesium chloride solution; Figure 8 These are the test results of the viscoelasticity of this invention; Figure 8 (a) shows the test results of viscoelasticity in PADA aqueous solution and various salt solutions at 100 g / L. Figure 8 (b) shows the viscoelasticity test results of PADA in a sodium chloride solution of 20-100 g / L. Figure 8 (c) shows the viscoelasticity test results of PADA in 20-100 g / L calcium chloride solution. Figure 8 (d) represents the viscoelasticity test results of PADA in a magnesium chloride solution of 20-100 g / L; Figure 9 This is an analysis diagram of the thickening mechanism of betaine-containing hydrophobic associating polymer salts provided by the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0028] The following raw material parameters were used: sodium N-methyltaurate (NMS, 62-66% aqueous solution), hexadecane bromide (BHD, 97%), triethylamine (TEA, AR, 99.0%), allyl chloride (AC, 98%), acrylamide (AM, AR 99.0%), diacetone acrylamide (DAAM, 99%), azobisisobutylamidine hydrochloride (AIBA, AR 98%), sodium chloride (NaCl, AR 99.5%), magnesium chloride (MgCl2·6H2O, AR 98%), and calcium chloride (CaCl·2H2O, AR 98%). All raw materials were purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). All water used was deionized water (DI).

[0029] Example 1 A method for preparing hydrophobically associating polymers containing betaine structures includes the following preparation steps: S1. Add 50 mmol of sodium N-methyltaurate (NMS), 50 mmol of hexadecane bromide (BHD), 50 mmol of triethylamine (TEA), and 80 mL of ethanol to a three-necked flask and reflux at 80 °C for 12 h. After the reflux reaction is completed, allow the reaction system to cool to 25 °C, filter, wash the precipitate obtained by filtration with acetone, and then recrystallize with ethanol solution to obtain a white flaky crystalline product. Place the white flaky crystalline product in an oven and vacuum dry at 50 °C for 12 h to obtain NMSC-16. S2. Add 30 mmol of NMSC-16, 35 mmol of allyl chloride (AC), and 100 mL of ethanol solution to a three-necked flask and react at 55 °C for 24 h. After the reaction is complete, let the reaction system cool to 25 °C, filter, and recrystallize the precipitate in ethanol to obtain a white powder. Place the white powder in an oven and dry it under vacuum at 50 °C for 12 h to obtain ANMSC-16. S3. 1 mmol of ANMSC-16 was mixed with water to obtain an ANMSC-16 solution. 69.3 mmol of acrylamide (AM) and 29.7 mmol of diacetone acrylamide (DAAM) were added to the ANMSC-16 solution to obtain a mixture solution with a total mass concentration of 25%. The mixture was transferred to a three-necked flask and purged with nitrogen for 20 min. Then, 0.05% of the total mass of the reactants (the sum of the masses of ANMSC-16, acrylamide, and diacetone acrylamide) of azobisisobutylamidine hydrochloride (AIBA) was added. The three-necked flask was sealed, and the reaction was carried out at 45 °C for 5 h under sealed conditions to obtain a light white gel. The light white gel was purified in ethanol and dried after purification to obtain a hydrophobic associative polymer containing a betaine structure, denoted as PADA.

[0030] Characterization tests: FTIR spectroscopy: The ANMSC-16 prepared in Example 1 and the betaine-containing hydrophobic associative polymer (PADA) were characterized at room temperature using a Nicolet 6700 FTIR spectrometer (Thermo, USA) via the potassium bromide pellet method, with a wavelength range of 4000 cm⁻¹. -1 ~400cm -1 The result is as follows Figure 1 As shown.

[0031] from Figure 1 It can be seen that in the infrared spectrum of ANMSC-16 ( Figure 1 (a) in the middle, 3081cm -1 and 3039cm -1 The peak at 2920 cm⁻¹ corresponds to the unsaturated CH stretching vibration. -1 and 2845cm -1 The strong peak at that point is the absorption peak of the saturated CH stretching vibration. -SO3 - The absorption peaks for symmetric and asymmetric vibrations are located at 1046 cm⁻¹. -1 and 1198cm -1 The CS vibration peak is located at 601 cm⁻¹. -1 .

[0032] In the infrared spectrum of PADA ( Figure 1 (b) of the middle section, 3438cm -1 and 3200cm -1 The peak at 1658 cm⁻¹ corresponds to the NH stretching vibration of the amide bond in acrylamide and diacetone acrylamide (DAAM). -1 The peak at 2972 ​​cm⁻¹ represents the C=O stretching vibration. The symmetric and asymmetric stretching vibration peaks of CH appear at 2972 ​​cm⁻¹, respectively. -1 and 2929cm -1 The CH bending vibration peak appears at 1546 cm⁻¹. -1 The CN bending vibration peaks are located at 1450 cm⁻¹. -1 and 1362cm -1 619cm -1 The peak at 1202 cm⁻¹ is the stretching vibration peak of the CS bond. -1 and 1154cm -1 The peak at that point represents the asymmetric stretching vibration of S=O in the sulfonate, indicating that the FTIR test results are consistent with the molecular structure of PADA.

[0033] 1H NMR spectrum ( 1¹H NMR: ANMSC-16 and PADA were measured using a Bruker AVANCE III HD 400 spectrometer (Bruker, Karlsruhe, Germany). ANMSC-16 was measured using dimethyl sulfoxide-d6 (DMSO-d6) as solvent, and PADA was measured using heavy water (D₂O) as solvent. The results are as follows: Figure 2 As shown.

[0034] from Figure 2 It can be seen that in AMNMS-16 1 H NMR spectrum ( Figure 2 In (a), the peaks at 0.85 ppm (a), 1.24 ppm (b), and 1.65 ppm (c) correspond to -CH3 and two types of -CH2 peaks of long alkyl chains. The peak at 2.94 ppm (d, e) represents -CH3 linked to a quaternary ammonium cation or -CH2- from a long alkyl chain. The peaks at 3.19 ppm (f) and 3.46 ppm (g) correspond to two -CH2 peaks in NMS. The peak at 3.95 ppm (h) corresponds to the -CH2- peak of AC; the peaks at 5.63 ppm (i) and 6.01 ppm (j) represent the -CH2 and -CH peaks of AC.

[0035] In PADA 1 H NMR spectrum ( Figure 2 In (b), the peak at 4.70 ppm is due to D2O. The peaks at 0.91 ppm (a) and 1.32 ppm (b) correspond to the proton signals of –CH3 and –CH2– in the long alkyl chain. The peak at 1.38–1.42 ppm (c) is related to the –CH3 group in DAAM. The peaks at 1.53–1.73 ppm (d) and 2.11–2.29 ppm (f) originate from the -CH2-CH- group in the PADA main chain. The peaks at 1.74–1.86 ppm (e) and 3.06 ppm (g) are attributed to the -CO-CH3 and -CH2-CO- groups in DAAM, respectively. The peaks at 3.12–3.33 ppm (h, i, j) are corresponding to the -N-CH2- and -N-CH3 groups in the ANMSC-16 structure. The peaks at 3.91–3.95 ppm (k, l) are attributed to the -CH2-CH2-SO3Na group in the ANMSC-16 structure.

[0036] Calculate the viscosity-average molecular weight M of PADA: The intrinsic viscosity [η] of PADA can be measured using an Ubbelohde capillary viscometer, specifically: First, a PADA solution with an initial concentration C0 = 0.009 g / mL was prepared using a 1.0 mol / L sodium chloride aqueous solution as the standard solvent. Then, the PADA solution was diluted to a series of different relative concentrations C0 using a dilution method. r (relative concentration C) r = Actual concentration C / Initial concentration C0). Before dilution, C r =1, diluted four times, the relative concentration C after each dilution is 1. r =2 / 3, 1 / 2, 1 / 3, and 1 / 4. C was measured using a Ubbelohde capillary viscometer. r The elution time t of samples with values ​​of 1, 2 / 3, 1 / 2, 1 / 3, and 1 / 4 at 30°C, and the elution time t0 of a 1.0 mol / L sodium chloride aqueous solution, are given. The relative viscosity η is calculated using the following formula. r and specific viscosity η sp ; ; ; Where t represents C r The elution times of samples with values ​​of 1, 2 / 3, 1 / 2, 1 / 3, and 1 / 4 are given, and t0 is the elution time of a 1.0 mol / L sodium chloride aqueous solution.

[0037] Next, with C r Let η be the x-axis. sp / C r and lnη r / C r Plot the relationship curve on the ordinate, and the result is as follows: Figure 3 As shown. From Figure 3 It can be seen that η sp / C r The curve exhibits a linear relationship, conforming to the trend of the Huggins equation, lnη r / C r The curves exhibit a linear relationship, conforming to the trend of the Kremer equation. The ordinate of the intersection point of the two straight lines (denoted as H) is used to calculate the intrinsic viscosity [η] of PADA.

[0038] Huggins equation: ; Where, η sp For specific viscosity, C is the actual concentration, [η] is the intrinsic viscosity, and k is the Huggins coefficient.

[0039] Kremer equation: ; Where, η rWhere η is the relative viscosity, C is the actual concentration, [η] is the intrinsic viscosity, and β is the Kremer constant.

[0040] It should be noted that, normally, the dilution method involves determining the actual concentration C of different samples, thus plotting two straight lines with different slopes. The ordinate value corresponding to the intersection of the lines represents the intrinsic viscosity [η]. However, for the sake of simplification, the relative concentration C is used instead. r To replace the actual concentration C (C r =actual concentration C / initial concentration C0), so the ordinate of the intersection point is marked as H, and then the intrinsic viscosity [η] is calculated through H.

[0041] ; Where C0 is the initial concentration and H is the ordinate value corresponding to the intersection point of the two straight lines.

[0042] Finally, the viscosity-average molecular weight M was calculated using the Mark-Houwink equation.

[0043] Mark-Houwink equation: ; Where [η] is the intrinsic viscosity.

[0044] Calculations show that the viscosity-average molecular weight of PADA is 1.39 × 10⁻⁶. 6 g / mol, which is much lower than the viscosity-average molecular weight of traditional HAWSP.

[0045] Critical association concentration (CAC) testing: The critical association concentration of hydrophobic polymers is a key parameter characterizing their aggregation behavior, and the process includes: Prepare PADA aqueous solutions with a concentration range of 0.2~1.0wt%, and determine the critical association concentration by combining fluorescence spectroscopy and rheological viscosity. When the viscosity of the PADA aqueous solution shows a significant abrupt change, the corresponding concentration is the critical association concentration.

[0046] Among them, fluorescence spectroscopy was performed using a Hitachi F-4500 fluorescence spectrophotometer, with pyrene as the fluorescent probe, an excitation wavelength of 335 nm, an emission wavelength of 350 nm to 550 nm, and a scan rate of 240 nm / min. The rheovis method was performed using an Anton Paar rheometer (MCR 302), with a cone-plate test and a shear rate set at 100 s⁻¹. -1 The test temperature is 30℃.

[0047] The above test results are as follows Figure 4 As shown, from Figure 4It can be seen that when the concentration is 0.5 wt%, the I1 / I3 ratio decreases sharply, and the viscosity increases significantly. This indicates that as the concentration of PADA aqueous solution increases, the binding behavior of hydrophobic chains changes from intramolecular to intermolecular. The polarity around the pyrene probe changes from strong to weak, corresponding to a sharp increase in apparent viscosity and a significant decrease in the I1 / I3 ratio. The results show that when the concentration of PADA aqueous solution exceeds 0.5 wt%, hydrophobic aggregates are formed in the intermolecular region. Intramolecular hydrophobic groups combine to form aggregate structures. The formation of aggregates increases the fluid volume, thereby improving the viscosity-thickening properties of PADA aqueous solution.

[0048] Salt resistance test: At room temperature, PADA was placed in NaCl, CaCl2, and MgCl2 solutions of different concentrations to prepare corresponding 0.7 wt% PADA salt solutions. The viscosity under the cone plate was measured using an Anton Paar rheometer (MCR 302) at 30°C with a shear rate of 100 s⁻¹. -1 .

[0049] The above test results are as follows Figure 5 As shown, from Figure 5 It can be seen that PADA exhibits excellent salt-induced thickening properties. Specifically, Figure 5 (a) shows the viscosity of a 0.7 wt% PADA salt solution as the concentrations of sodium chloride (NaCl), calcium chloride (CaCl2), and magnesium chloride (MgCl2) increase from 1 × 10⁻⁶. 4 mg / L increased to 10×10 4 The viscosity of a 0.7 wt% PADA salt solution increased from 41.6 mPa·s, 43.9 mPa·s, and 43.7 mPa·s to 54.6 mPa·s, 67.4 mPa·s, and 63.9 mPa·s, respectively. These results indicate that the viscosity of the divalent cation (Ca) increases with mg / L. 2+ Mg 2+ ) compared to monovalent cations (Na) + This can more effectively enhance viscosity. This trend can be attributed to the stronger shielding effect of divalent ions, which, compared to monovalent ions, promote the formation of more extended configurations of PADA molecular chains in solution. With increasing valence state of salt ions, PADA exhibits enhanced salt-induced thickening properties due to its ability to form networks with other polymer molecules through chain extension. Furthermore, Figure 5 (b) shows the order of the effects of different types of salts on the viscosity of PADA: Ca 2+ >Mg 2+ Na + .

[0050] Temperature and shear strength: PADA was dissolved in 10 × 10⁻⁶ solution at room temperature. 4 mg / L NaCl solution, 10×10 4 mg / L CaCl2 solution, 10×10 4 Four 0.7 wt% PADA solutions were prepared using mg / L MgCl2 solution and water. Their temperature resistance and shear strength were determined using the high-temperature, high-pressure testing unit of an Anton Paar rheometer within a temperature range of 30–180 °C. Tests were conducted at a constant shear rate of 100 s⁻¹. -1 Continue for 50 minutes. Results are as follows: Figure 6 As shown.

[0051] from Figure 6 It can be seen that as the temperature increases, the intensified molecular thermal motion disrupts hydrophobic association, leading to a more disordered state in the system and a gradual decrease in solution viscosity. However, the viscosity remains stable at 180℃, which is attributed to the presence of thermosensitive DAAM side chains. These side chains readily aggregate at high temperatures, promoting self-assembly to form a three-dimensional network structure, thereby enhancing thermal stability. At a concentration of 10 × 10⁻⁶... 4 In NaCl, CaCl2, and MgCl2 solutions with concentrations of mg / L, the viscosities of PADA were 80.90 mPa·s, 92.72 mPa·s, and 98.04 mPa·s, respectively. These results indicate that the dynamic linear entanglement and hydrophobic association structure were maintained under prolonged shear stress. Figure 6 (b) to (d)). The above tests show that PADA exhibits strong temperature resistance and shear strength in various salt solutions. This performance improvement can be attributed to the introduction of cations, which not only induce an anti-polyelectrolyte effect in PADA solutions but also significantly increase the hydrodynamic volume, thereby promoting the conformational expansion of PADA molecules in salt solutions, thus enabling it to exhibit excellent thickening properties under high temperature and high salt conditions.

[0052] Shear recovery test: PADA was dissolved in 10 × 10⁻⁶ solution at room temperature. 4 mg / L NaCl solution, 10×10 4 mg / L CaCl2 solution, 10×10 4 Three 0.7wt% PADA salt solutions were prepared in a mg / L MgCl2 solution.

[0053] Using the high-temperature, high-pressure testing unit of an Anton Paar rheometer (MCR 302), shear degradation was simulated at 120°C by varying the shear rate, and the viscosity recovery of the above solution was tested. The shear rate was adjusted sequentially to 100 s. -1 75s -1 50s-1 25s -1 50s -1 75s -1 100s -1 Each time, the process lasts for 15 minutes, while monitoring changes in fluid viscosity.

[0054] The above test results are as follows Figure 7 As shown. From Figure 7 It can be seen that at 120℃, the shear rate is within 100s. -1 up to 25 s -1 After three cycles, the viscosities of the NaCl, CaCl2, and MgCl2 solutions remained at 128.95 mPa·s, 109.74 mPa·s, and 104.62 mPa·s, respectively. These results indicate that PADA exhibits excellent shear recovery properties under high-temperature conditions in a brine environment. This phenomenon is attributed to the reversible associative network structure formed by the hydrophobic chains between PADA molecules through van der Waals interactions. Under high shear stress, the hydrophobic association structure is disrupted, leading to a temporary decrease in the viscosity of the PADA salt solution. However, when the shear effect weakens, the physical cross-linking between PADA molecular chains is restored, and the viscosity recovers. Furthermore, under high-temperature conditions, the motion of water molecules and PADA chains becomes more vigorous, which further affects the recovery kinetics of the PADA salt solution.

[0055] Viscoelasticity test: PADA was dissolved in water and in 20-100 g / L NaCl, CaCl2, and MgCl2 solutions at room temperature to prepare various 0.7 wt% PADA solutions.

[0056] The viscoelastic behavior of the above-mentioned 0.7wt% PADA solutions was measured using an Anton Paar rheometer (MCR 302) cone-plate at 25°C. The specific procedure included: First, the linear viscoelastic region (LVR) of the system was determined through amplitude scanning experiments. Then, 1% strain within the LVR was selected as a fixed strain value, and frequency scanning tests were performed to examine the dynamic viscoelasticity (storage modulus G', loss modulus G'') of the various PADA solutions within the frequency range of 0.1–10 Hz. The results are as follows: Figure 8 As shown.

[0057] from Figure 8 It can be seen that, Figure 8 As shown in (a) of the figure, in the frequency range of 0.1–10 Hz, the loss modulus (G'', viscous modulus) of PADA aqueous solution formed in water is always greater than the storage modulus (G', elastic modulus), indicating that the PADA aqueous solution exhibits predominantly viscous behavior. PADA at 10 × 10⁻⁶ Hz...4 In a NaCl solution of mg / L, G' and G'' were slightly increased compared to the PADA aqueous solution system; while in a 10×10 mg / L solution... 4 mg / L CaCl2 solution and 10×10 4 In a mg / L MgCl2 solution, G' and G'' showed a significant increase, indicating that divalent salts are more effective than monovalent salts in promoting the formation of hydrophobic association structures. This enhancement effect stems from the fact that divalent salts strengthen the hydrophobic aggregation microregions of PADA, prompting the formation of more aggregates and acting as crosslinking points, thereby improving the viscoelasticity of the system.

[0058] exist Figure 8 As can be seen from (b) to (d) in the diagram, both G′ and G″ increase with the increase of various salt solution concentrations. This indicates that the effect of salt solution concentration on the elasticity of PADA is similar to its effect on viscosity, further demonstrating the salt-induced enhancement effect on the polymer network structure.

[0059] Salt and heat resistance mechanism: The above tests show that, compared with traditional copolymers, the PADA provided by this invention exhibits excellent "anti-polyelectrolyte" effect after the introduction of betaine-type zwitterionic groups. Figure 9 As shown, the sulfonate in betaine forms internal salt bonds with the quaternary ammonium structure in aqueous solution, leading to a coiled molecular conformation and a reduced hydrodynamic radius. The addition of salt disrupts these internal salt bonds, causing the molecular conformation to shift from a coiled to an extended state. This conformational change increases the hydrodynamic radius of the PADA solution and raises its viscosity. With increasing salt concentration, the ionic strength also increases, enhancing the shielding effect on the internal salt bonds. Under the condition of equal anion concentration, the ionic strength is proportional to the square of the cation charge. Therefore, with monovalent cations (Na+, Na ... + Compared to ), divalent cations (Ca) 2+ Mg 2+ The effect of salts is stronger, allowing molecular chains to acquire larger hydrodynamic radii and more extended conformations, thus exhibiting superior salt thickening properties. Furthermore, higher salt content can further enhance hydrophobic association, leading to further increases in viscosity.

[0060] In summary, the synergistic effect of increased hydrodynamic radius and enhanced hydrophobic association significantly improves the salt thickening properties of PADA (a betaine-type polymer). Simultaneously, the aggregation of heat-sensitive groups in the PADA side chains at high temperatures promotes molecular self-assembly into a three-dimensional network structure, thereby enhancing the thermal stability of the system.

[0061] 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 hydrophobically associating polymer containing a betaine structure, characterized in that, The structural formula of the betaine-containing hydrophobic associative polymer is: ； Where x, y, and z are the molar percentage ranges of the structural units, x is 65%-70%, y is 29%-34%, and z is 1%, where x+y+z=100%; The betaine-containing hydrophobic associative polymer has a molecular weight of 1.0 × 10⁻⁶. 6 g / mol ~ 1.5 × 10 6 g / mol.

2. The method for preparing a betaine-containing hydrophobic associative polymer according to claim 1, characterized in that, The preparation steps include the following: S1. Sodium N-methyltaurate, hexadecane bromo, triethylamine, and ethanol are mixed and refluxed to obtain NMSC-16; S2. Mix NMSC-16, allyl chloride, and ethanol solution, and react to obtain ANMSC-16; S3. After mixing ANMSC-16 with water, an ANMSC-16 solution is obtained. Acrylamide and diacetone acrylamide are added to the ANMSC-16 solution to obtain a mixed solution. The solution is purged with nitrogen, and then azobisisobutylamidine hydrochloride is added. The reaction is carried out under sealed conditions to obtain a hydrophobic associative polymer containing a betaine structure.

3. The method for preparing a betaine-containing hydrophobic associative polymer according to claim 2, characterized in that, The molar volume ratio of sodium N-methyltaurate, hexadecane bromo, triethylamine, and ethanol in S1 is 45-55 mmol: 45-55 mmol: 45-55 mmol: 80 mL.

4. The method for preparing a betaine-containing hydrophobic associative polymer according to claim 2, characterized in that, The reflux reaction temperature in S1 is 75-85℃, and the reflux reaction time is 10-14h.

5. The method for preparing a betaine-containing hydrophobic associative polymer according to claim 2, characterized in that, The molar volume ratio of NMSC-16, allyl chloride, and ethanol solution in S2 is 25-35 mmol: 30-40 mmol: 100 mL.

6. The method for preparing a betaine-containing hydrophobic associative polymer according to claim 2, characterized in that, The reaction temperature in S2 is 50-60℃, and the reaction time is 20-26h.

7. The method for preparing a betaine-containing hydrophobic associative polymer according to claim 2, characterized in that, The molar ratio of acrylamide, diacetone acrylamide, and ANMSC-16 in S3 is 65-70:29-34:

1.

8. The method for preparing a betaine-containing hydrophobic associative polymer according to claim 2, characterized in that, In the mixture solution described in S3, the total mass concentration of ANMSC-16, acrylamide, and diacetone acrylamide is 22%-28%; the mass of azobisisobutylamidine hydrochloride accounts for 0.03%-0.07% of the total mass of ANMSC-16, acrylamide, and diacetone acrylamide.

9. The method for preparing a betaine-containing hydrophobic associative polymer according to claim 2, characterized in that, The reaction temperature in S3 is 40-50℃, and the reaction time is 4-6 hours.

10. The application of the betaine-containing hydrophobic associative polymer of claim 1 in petroleum extraction agents.

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