A thickening agent for oil well fracturing and its preparation method

Abstract

The present invention relates to the technical field of thickeners, and specifically discloses a novel thickener for oil well fracturing and a preparation method thereof. The preparation method of the novel thickener for oil well fracturing includes: preparing modified hydroxyethyl methacrylate; preparing a gradient-branched polymer solution; preparing a sulfonic acid-boric acid double-modified montmorillonite powder; preparing a colloidal solution; centrifuging, spray-drying, and sieving the colloidal solution to obtain the novel thickener for oil well fracturing. The novel thickener for oil well fracturing prepared by the present invention has the characteristics of temperature resistance, salt resistance, and self-healing performance. In practical applications, it can quickly thicken and carry proppants during the low-temperature pumping stage, trigger the self-healing performance after entering the high-temperature formation, and partially dissociate the dynamic network to reduce the viscosity during backflow, providing a reliable technical support for the development of deep shale gas and tight oil.

Description

Technical Field

[0001] The present invention relates to the technical field of thickeners, and particularly to a thickener for oil well fracturing and a preparation method thereof. Background Art

[0002] With the continuous growth of global energy demand, the development of oil and gas resources has gradually expanded to deep sea, deep layer and unconventional oil and gas reservoirs. Under these complex reservoir conditions, oil well fracturing technology has become one of the key means to improve oil and gas recovery. As an important component of fracturing fluid, the performance of thickeners directly affects the effect and economic benefits of fracturing operations. However, existing thickeners still have some limitations in practical applications, especially in terms of salt resistance, temperature resistance and self-healing performance.

[0003] In terms of salt resistance, the salinity of oil well formation water is usually high, containing a large amount of salt ions. These salt ions will interact with the functional groups in the thickener molecules, resulting in a decrease in the viscosity of the thickener or even failure. For example, traditional polyacrylamide-based thickeners are prone to salting out in high-salt environments and lose their thickening effect. Although some modified polyacrylamides and supramolecular thickeners have improved salt resistance by introducing hydrophobic groups or supramolecular structures, they still have problems such as high cost and poor rapid solubility.

[0004] In terms of temperature resistance, the temperature of deep oil wells is usually high, requiring the thickener to maintain a stable viscosity and structure in a high-temperature environment. However, many traditional thickeners are prone to degradation under high-temperature conditions, resulting in a decrease in viscosity and deterioration of performance. For example, for some polyacrylamide-based thickeners in a high-temperature environment above 150 °C, their molecular chains will break and lose their thickening ability. Although some new high-temperature-resistant thickeners have improved temperature resistance by introducing high-temperature-resistant monomers and crosslinking agents, they still have problems with insufficient shear resistance.

[0005] In terms of self-healing performance, during the fracturing process, the thickener will be subjected to high-speed shear and mechanical wear, resulting in damage to its structure and a decrease in viscosity. Although some supramolecular thickeners have achieved self-healing functions by introducing dynamic bonds, they still have problems such as low repair efficiency in practical applications. In addition, the self-healing performance of some self-healing thickeners is also limited in high-temperature and high-salt environments.

[0006] In summary, existing thickeners for oil well fracturing still have certain limitations in terms of salt resistance, temperature resistance and self-healing performance, and it is difficult to meet the actual needs under complex reservoir conditions. Therefore, developing a new type of thickener with excellent salt resistance, temperature resistance and self-healing performance is of great significance for improving the efficiency and economic benefits of oil well fracturing operations. Summary of the Invention

[0007] The object of the present invention is to solve the deficiencies existing in the prior art, and a preparation method of a thickening agent for oil well fracturing is proposed.

[0008] A preparation method of a novel thickening agent for oil well fracturing comprises the following steps:

[0009] S1. Under nitrogen protection, hydroxyethyl methacrylate and phenylboronic acid are added to ethanol, sealed, stirred, cooled, and subjected to vacuum distillation to obtain modified hydroxyethyl methacrylate;

[0010] S2. A four-arm polyethylene glycol chain transfer agent, modified hydroxyethyl methacrylate, acrylamide, and hydroxyethyl methacrylate are dissolved in deionized water, and stirred at a constant temperature of 48 - 52 °C for 1.8 - 2.2 h at a stirring speed of 480 - 520 rpm. Ammonium persulfate is added, and the mixture is stirred at a constant temperature of 58 - 62 °C for 2.8 - 3.2 h at a stirring speed of 280 - 320 rpm. Ammonium persulfate is added, and the mixture is stirred at a constant temperature of 68 - 72 °C for 0.8 - 1.2 h at a stirring speed of 180 - 220 rpm. Ammonium persulfate is added, hydroquinone is added, cooled, and filtered to obtain a gradient-branched polymer solution;

[0011] S3. Montmorillonite and 3-aminopropyltriethoxysilane are added to ethanol, sealed, stirred, sulfosuccinic anhydride is added, stirred, and the pH value of the system is adjusted to 7.2 - 7.8 with 0.1 mol / L sodium hydroxide solution. Phenylboronic acid is added, stirred, centrifuged, washed, and dried to obtain sulfonic acid-boric acid double-modified montmorillonite powder;

[0012] S4. The sulfonic acid-boric acid double-modified montmorillonite powder is dispersed in deionized water, sonicated, the gradient-branched polymer solution is added, stirred, and the pH value of the system is adjusted to 8.3 - 8.7 with 0.1 mol / L sodium hydroxide solution, and allowed to stand to obtain a colloidal solution;

[0013] S5. The colloidal solution is centrifuged, spray-dried, and sieved to obtain a novel thickening agent for oil well fracturing.

[0014] Preferably, in step S1, the weight ratio of hydroxyethyl methacrylate, phenylboronic acid, and ethanol is 100 - 140:70 - 80:480 - 520.

[0015] Preferably, in step S1, after adding hydroxyethyl methacrylate and phenylboronic acid to ethanol, it is stirred at a constant temperature, the constant temperature is 77 - 79 °C, the stirring time is 5 - 6 h, and the stirring speed is 200 - 300 rpm.

[0016] Preferably, in step S1, for vacuum distillation, the distillation temperature is 55 - 65 °C and the pressure is 0.08 - 0.12 MPa.

[0017] Preferably, in the step S2, the weight ratio of the four-arm polyethylene glycol chain transfer agent, modified 2-hydroxyethyl methacrylate, acrylamide, 2-hydroxyethyl methacrylate, deionized water, ammonium persulfate, and hydroquinone is 22-26: 100-140: 340-380: 2-5: 900-1100: 4-8: 0.3-0.7.

[0018] Preferably, in the step S2, the weight ratios of the three additions of ammonium persulfate are 2-4: 1-2: 1-2 in sequence.

[0019] Preferably, in the step S2, filter through a 180-220 mesh sieve.

[0020] Preferably, in the step S3, the weight ratio of montmorillonite, 3-aminopropyltriethoxysilane, ethanol, sulfosuccinic anhydride, and phenylboronic acid is 55-65: 10-20: 280-320: 9-10: 5-7.

[0021] Preferably, in the step S3, add montmorillonite and 3-aminopropyltriethoxysilane to ethanol and then stir at a constant temperature. The constant temperature is 79-81 °C, the stirring time is 3-4 h, and the stirring speed is 350-450 rpm.

[0022] Preferably, in the step S3, after adding sulfosuccinic anhydride, stir at a constant temperature. The constant temperature is 55-65 °C, the stirring time is 1.5-2.5 h, and the stirring speed is 200-300 rpm.

[0023] Preferably, in the step S3, after adding phenylboronic acid, stir at a constant temperature. The constant temperature is 55-65 °C, the stirring time is 1.5-2.5 h, and the stirring speed is 200-300 rpm.

[0024] Preferably, in the step S3, dry at 55-65 °C.

[0025] Preferably, in the step S4, the weight ratio of the sulfonic acid-boric acid dual-modified montmorillonite powder, deionized water, and the gradient-branched polymer solution is 55-65: 180-220: 1200-1400.

[0026] Preferably, in the step S4, perform ultrasonic treatment. The ultrasonic treatment time is 20-40 min, and the ultrasonic frequency is 40-60 kHz.

[0027] Preferably, in the step S4, after adding the gradient-branched polymer solution, stir at a constant temperature. The constant temperature is 55-65 °C, the stirring time is 5-6 h, and the stirring speed is 200-300 rpm.

[0028] Preferably, in the step S4, let it stand. The standing temperature is 55-65 °C, and the standing time is 10-14 h.

[0029] Preferably, in the step S5, for spray drying, the feeding rate is 20 mL / min, the inlet temperature is 170 °C, and the outlet temperature is 80 °C.

[0030] Preferably, in the step S5, for sieving, a 200-mesh sieve is used.

[0031] A novel thickening agent for oil well fracturing is prepared by using the preparation method of the novel thickening agent for oil well fracturing described in any one of the above.

[0032] Beneficial effects:

[0033] Through functional synergy and structural design at the molecular level, the present invention has developed a novel thickening agent suitable for high-temperature and high-salinity oil well environments, and systematically solved the problems of easy salting out and viscosity loss of traditional thickening agents in high salinity formations, easy failure in high-temperature environments, and difficult repair of shear damage. Compared with the prior art that relies on a single anti-salt group or simple physical blending modification, this solution starts from the molecular structure, and through dynamic bond design of monomers, gradient polymerization function distribution, and montmorillonite interface synergistic enhancement, forms a performance closed-loop of "anti-salt - temperature resistance - self-repair", significantly improving the comprehensive performance of the thickening agent.

[0034] Specifically, firstly, through the directional modification of phenylboronic acid and 2-hydroxyethyl methacrylate, the dynamic borate bond introduced into the monomer molecule can be reversibly broken and recombined at high temperature, effectively repairing the network damage caused by shear or thermal degradation, and breaking through the limitation of irreversible failure of the traditional static crosslinked network. Secondly, a four-arm initiator is used to guide the gradient polymerization of acrylamide and functional monomers, and the growth direction of the molecular chain is controlled in stages to form a functional partition structure of "dynamic repair core - transition layer - thickening shell", so that the dynamic bonds are concentrated in the core to achieve long-term self-repair, and the pure acrylamide chain segments of the shell quickly absorb water and thicken, taking into account the establishment of the initial viscosity and long-term stability. Further, by performing dual-functional modification on the surface of montmorillonite, the sulfonic acid group shields the attack of salt ions through strong charge repulsion, solving the problem of salting out and viscosity loss in high salinity formations; the boronic acid group forms a reversible network with the polymer hydroxyl group as a dynamic anchor point, combined with the physical enhancement of montmorillonite nanosheets, significantly improving the shear resistance and temperature resistance limit.

[0035] The present invention realizes performance upgrade through the synergy of monomer - polymer - interface enhancement. The dynamic bond design lays the foundation for self-repair, the gradient polymerization optimizes the function distribution, and the dual modification of montmorillonite simultaneously undertakes anti-salt and interface crosslinking. In practical applications, this thickening agent quickly thickens and carries proppants during the low-temperature pumping stage, triggers self-repair of the core dynamic bond after entering the high-temperature formation, montmorillonite enhances the network stability, and the dynamic network partially dissociates during backflow to reduce the viscosity, providing reliable technical support for the development of deep shale gas and tight oil. Specific embodiments

[0036] The present invention will be further illustrated below in conjunction with specific embodiments.

[0037] Example 1

[0038] A preparation method of a novel thickening agent for oil well fracturing includes the following steps:

[0039] S1. Under nitrogen protection, 100 g of 2-hydroxyethyl methacrylate and 70 g of phenylboronic acid are added to 480 g of ethanol, sealed, and stirred at a constant temperature of 77 °C for 5 h at a stirring speed of 200 rpm. After cooling to room temperature, vacuum distillation is carried out at 55 °C and 0.08 MPa to obtain modified 2-hydroxyethyl methacrylate (esterification of the hydroxyl group of 2-hydroxyethyl methacrylate with phenylboronic acid to form a dynamic borate bond);

[0040] S2. 22 g of tetra-arm polyethylene glycol chain transfer agent, 100 g of modified 2-hydroxyethyl methacrylate, 340 g of acrylamide, and 2 g of 2-hydroxyethyl methacrylate are dissolved in 900 g of deionized water, stirred at a constant temperature of 48 °C for 1.8 h at a stirring speed of 480 rpm, 2 g of ammonium persulfate is added, stirred at a constant temperature of 58 °C for 2.8 h at a stirring speed of 280 rpm, 1 g of ammonium persulfate is added, stirred at a constant temperature of 68 °C for 0.8 h at a stirring speed of 180 rpm, 1 g of ammonium persulfate is added, 0.3 g of hydroquinone is added, cooled, and filtered through a 180-mesh sieve to obtain a gradient-branched polymer solution (the tetra-arm initiator regulates the staged polymerization of acrylamide and modified 2-hydroxyethyl methacrylate to form a functionalized molecular chain);

[0041] S3. 55 g of montmorillonite and 10 g of 3-aminopropyltriethoxysilane are added to 280 g of ethanol, sealed, and stirred at a constant temperature of 79 °C for 3 h at a stirring speed of 350 rpm (condensation of 3-aminopropyltriethoxysilane with the surface silanol groups of montmorillonite to introduce amino groups), 9 g of sulfosuccinic anhydride is added, and stirred at a constant temperature of 55 °C for 1.5 h at a stirring speed of 200 rpm (reaction of sulfosuccinic anhydride with amino groups to graft sulfonic acid groups to enhance the salt resistance synergistic effect). The pH value of the system is adjusted to 7.2 with 0.1 mol / L sodium hydroxide solution, 5 g of phenylboronic acid is added, and stirred at a constant temperature of 55 °C for 1.5 h at a stirring speed of 200 rpm (reaction of phenylboronic acid with the surface hydroxyl groups of montmorillonite to fix boronic acid groups as dynamic crosslinking anchor points), centrifuged, washed, and dried at 55 °C to obtain sulfonic acid-boric acid dual-modified montmorillonite powder (reaction of the hydroxyl groups of montmorillonite with the amino groups of 3-aminopropyltriethoxysilane, sulfosuccinic anhydride, and phenylboronic acid);

[0042] S4. Disperse 55 g of sulfonic acid-boric acid dual-modified montmorillonite powder in 180 g of deionized water, ultrasonically treat it for 20 min at an ultrasonic frequency of 40 kHz, add 1200 g of gradient-branched polymer solution, stir at a constant temperature of 55 °C for 5 h with a stirring speed of 200 rpm, adjust the pH value of the system to 8.3 using 0.1 mol / L sodium hydroxide solution, and let it stand at a constant temperature of 55 °C for 10 h (under the condition of pH 8.5, the borate group of the sulfonic acid-boric acid dual-modified montmorillonite powder forms reversible borate ester bonds with the hydroxyl groups of the polymer, and these dynamic bonds break and recombine at high temperatures, endowing self-healing ability) to obtain a colloidal solution;

[0043] S5. Centrifuge the colloidal solution and spray-dry it with a feeding rate of 15 mL / min, an inlet temperature of 165 °C, and an outlet temperature of 75 °C, and pass it through a 180-mesh sieve to obtain a novel thickening agent for oil well fracturing.

[0044] Example 2

[0045] A preparation method of a novel thickening agent for oil well fracturing, comprising the following steps:

[0046] S1. Under nitrogen protection, add 140 g of 2-hydroxyethyl methacrylate and 80 g of phenylboronic acid to 520 g of ethanol, seal it, stir at a constant temperature of 79 °C for 6 h with a stirring speed of 300 rpm, cool to room temperature, and perform vacuum distillation at 65 °C and 0.12 MPa to obtain modified 2-hydroxyethyl methacrylate;

[0047] S2. Dissolve 26 g of tetraarm polyethylene glycol chain transfer agent, 140 g of modified 2-hydroxyethyl methacrylate, 380 g of acrylamide, and 5 g of 2-hydroxyethyl methacrylate in 1100 g of deionized water, stir at a constant temperature of 52 °C for 2.2 h with a stirring speed of 520 rpm, add 4 g of ammonium persulfate, stir at a constant temperature of 62 °C for 3.2 h with a stirring speed of 320 rpm, add 2 g of ammonium persulfate, stir at a constant temperature of 72 °C for 1.2 h with a stirring speed of 220 rpm, add 2 g of ammonium persulfate, add 0.7 g of hydroquinone, cool, and pass it through a 220-mesh filter to obtain a gradient-branched polymer solution;

[0048] S3. Add 65 g of montmorillonite and 20 g of 3-aminopropyltriethoxysilane to 320 g of ethanol, seal it, stir at a constant temperature of 81 °C for 4 h with a stirring speed of 450 rpm, add 10 g of sulfosuccinic anhydride, stir at a constant temperature of 65 °C for 2.5 h with a stirring speed of 300 rpm, adjust the pH value of the system to 7.8 using 0.1 mol / L sodium hydroxide solution, add 7 g of phenylboronic acid, stir at a constant temperature of 65 °C for 2.5 h with a stirring speed of 300 rpm, centrifuge, wash, and dry at 65 °C to obtain sulfonic acid-boric acid dual-modified montmorillonite powder;

[0049] S4. Disperse 65 g of sulfonic acid-boric acid dual-modified montmorillonite powder in 220 g of deionized water, perform ultrasonic treatment for 40 min at an ultrasonic frequency of 60 kHz, add 1400 g of gradient-branched polymer solution, stir at a constant temperature of 65 °C for 6 h with a stirring speed of 300 rpm, adjust the pH value of the system to 8.7 using 0.1 mol / L sodium hydroxide solution, and let it stand at a constant temperature of 65 °C for 14 h to obtain a colloidal solution;

[0050] S5. Centrifuge the colloidal solution and perform spray drying with a feeding rate of 25 mL / min, an inlet temperature of 175 °C, and an outlet temperature of 85 °C, and pass through a 220-mesh sieve to obtain a novel thickening agent for oil well fracturing.

[0051] Example 3

[0052] A preparation method of a novel thickening agent for oil well fracturing, comprising the following steps:

[0053] S1. Under nitrogen protection, add 120 g of 2-hydroxyethyl methacrylate and 75 g of phenylboronic acid to 500 g of ethanol, seal, stir at a constant temperature of 78 °C for 5.5 h with a stirring speed of 250 rpm, cool to room temperature, and perform vacuum distillation at 60 °C and 0.1 MPa to obtain modified 2-hydroxyethyl methacrylate;

[0054] S2. Dissolve 24 g of tetra-arm polyethylene glycol chain transfer agent, 120 g of modified 2-hydroxyethyl methacrylate, 360 g of acrylamide, and 3.5 g of 2-hydroxyethyl methacrylate in 1000 g of deionized water, stir at a constant temperature of 50 °C for 2 h with a stirring speed of 500 rpm, add 3 g of ammonium persulfate, stir at a constant temperature of 60 °C for 3 h with a stirring speed of 300 rpm, add 1.5 g of ammonium persulfate, stir at a constant temperature of 70 °C for 1 h with a stirring speed of 200 rpm, add 1.5 g of ammonium persulfate, add 0.5 g of hydroquinone, cool, and pass through a 200-mesh filter to obtain a gradient-branched polymer solution;

[0055] S3. Add 60 g of montmorillonite and 15 g of 3-aminopropyltriethoxysilane to 300 g of ethanol, seal, stir at a constant temperature of 80 °C for 3.5 h with a stirring speed of 400 rpm, add 9.5 g of sulfosuccinic anhydride, stir at a constant temperature of 60 °C for 2 h with a stirring speed of 250 rpm, adjust the pH value of the system to 7.5 using 0.1 mol / L sodium hydroxide solution, add 6 g of phenylboronic acid, stir at a constant temperature of 60 °C for 2 h with a stirring speed of 250 rpm, centrifuge, wash, and dry at 60 °C to obtain sulfonic acid-boric acid dual-modified montmorillonite powder;

[0056] S4. Disperse 60 g of sulfonic acid-boric acid dual-modified montmorillonite powder in 200 g of deionized water, ultrasonically treat for 30 min at an ultrasonic frequency of 50 kHz, add 1300 g of gradient-branched polymer solution, stir at a constant temperature of 60 °C for 5.5 h at a stirring speed of 250 rpm, adjust the pH value of the system to 8.5 using 0.1 mol / L sodium hydroxide solution, and let it stand at a constant temperature of 60 °C for 12 h to obtain a colloidal solution;

[0057] S5. Centrifuge the colloidal solution and spray-dry it at a feed rate of 20 mL / min, an inlet temperature of 170 °C, and an outlet temperature of 80 °C, and pass through a 200-mesh sieve to obtain a novel thickening agent for oil well fracturing.

[0058] Comparative Example 1

[0059] The difference between Comparative Example 1 and Example 3 is that in step S1, phenylboronic acid is not added, resulting in the absence of dynamic borate bonds and the inability to self-heal at high temperatures, and the molecular chain breakage is irreversible.

[0060] A preparation method of a thickening agent for oil well fracturing includes the following steps:

[0061] S1. Under nitrogen protection, add 120 g of 2-hydroxyethyl methacrylate and 9.5 g of sulfosuccinic anhydride to 500 g of ethanol, stir for 2.5 h at a stirring speed of 250 rpm, and perform vacuum distillation at 60 °C and 0.1 MPa to obtain a prefabricated material;

[0062] S2. Dissolve 24 g of tetra-arm polyethylene glycol chain transfer agent, 120 g of prefabricated material, 360 g of acrylamide, and 3.5 g of 2-hydroxyethyl methacrylate in 1000 g of deionized water, stir at a constant temperature of 50 °C for 2 h at a stirring speed of 500 rpm, add 3 g of ammonium persulfate, stir at a constant temperature of 60 °C for 3 h at a stirring speed of 300 rpm, add 1.5 g of ammonium persulfate, stir at a constant temperature of 70 °C for 1 h at a stirring speed of 200 rpm, add 1.5 g of ammonium persulfate, add 0.5 g of hydroquinone, cool, and pass through a 200-mesh filter to obtain a gradient-branched polymer solution;

[0063] S3. Add 60 g of montmorillonite and 15 g of 3-aminopropyltriethoxysilane to 300 g of ethanol, seal, stir at a constant temperature of 80 °C for 3.5 h at a stirring speed of 400 rpm, add 9.5 g of sulfosuccinic anhydride, stir at a constant temperature of 60 °C for 2 h at a stirring speed of 250 rpm, adjust the pH value of the system to 7.5 using 0.1 mol / L sodium hydroxide solution, add 6 g of phenylboronic acid, stir at a constant temperature of 60 °C for 2 h at a stirring speed of 250 rpm, centrifuge, wash, and dry at 60 °C to obtain sulfonic acid-boric acid dual-modified montmorillonite powder;

[0064] S4, disperse 60g of sulfonic acid-boric acid double-modified montmorillonite powder in 200g of deionized water, ultrasonically treat for 30min, the ultrasonic frequency is 50kHz, add 1300g of gradient branched polymer solution, stir at 60°C for 5.5h, the stirring speed is 250rpm, adjust the pH value of the system to 8.5 with 0.1mol / L sodium hydroxide solution, and keep it at 60°C for 12h to obtain a colloidal solution;

[0065] S5. Centrifuge the colloidal solution, spray dry it, and set the feed rate to 20 mL / min, the inlet temperature to 170° C., the outlet temperature to 80° C., and pass it through a 200-mesh sieve to obtain a thickener for oil well fracturing.

[0066] Comparative Example 2

[0067] The difference between Comparative Example 2 and Example 3 is that the staged polymerization is cancelled in step S2, and all reactions are performed at 60° C. at one time, resulting in no functional partitioning of the molecular chain and failure of the salt resistance and self-repair synergy.

[0068] A method for preparing a thickener for oil well fracturing comprises the following steps:

[0069] S1. Under nitrogen protection, add 120 g of hydroxyethyl methacrylate and 75 g of phenylboric acid to 500 g of ethanol, seal, stir at 78 ° C for 5.5 h, stirring speed is 250 rpm, cool to room temperature, add 9.5 g of sulfosuccinic anhydride, stir for 2.5 h, stirring speed is 250 rpm, and distill under reduced pressure at 60 ° C and 0.1 MPa to obtain modified hydroxyethyl methacrylate;

[0070] S2, dissolving 24g of four-arm polyethylene glycol chain transfer agent, 120g of modified hydroxyethyl methacrylate, 360g of acrylamide, and 3.5g of hydroxyethyl methacrylate in 1000g of deionized water, stirring at a constant temperature of 60°C for 6h, stirring at a speed of 300rpm, adding 6g of ammonium persulfate, adding 0.5g of hydroquinone, cooling, and filtering through a 200-mesh filter to obtain a polymer solution;

[0071] S3, add 60g montmorillonite and 15g 3-aminopropyltriethoxysilane to 300g ethanol, seal, stir at 80°C for 3.5h, stirring speed is 400rpm, add 9.5g sulfosuccinic anhydride, stir at 60°C for 2h, stirring speed is 250rpm, adjust the pH value of the system to 7.5 with 0.1mol / L sodium hydroxide solution, add 6g phenylboric acid, stir at 60°C for 2h, stirring speed is 250rpm, centrifuge, wash, and dry at 60°C to obtain sulfonic acid-boric acid double modified montmorillonite powder;

[0072] S4. Disperse 60 g of sulfonic acid-boric acid dual-modified montmorillonite powder in 200 g of deionized water, perform ultrasonic treatment for 30 min at an ultrasonic frequency of 50 kHz, add 1300 g of polymer solution, stir at a constant temperature of 60 °C for 5.5 h with a stirring speed of 250 rpm, adjust the pH value of the system to 8.5 using 0.1 mol / L sodium hydroxide solution, and let it stand at a constant temperature of 60 °C for 12 h to obtain a colloidal solution;

[0073] S5. Centrifuge the colloidal solution and spray-dry it with a feeding rate of 20 mL / min, an inlet temperature of 170 °C, and an outlet temperature of 80 °C, and pass it through a 200-mesh sieve to obtain a thickening agent for oil well fracturing.

[0074] Comparative Example 3

[0075] The difference between Comparative Example 3 and Example 3 is that in step S3, sulfosuccinic anhydride is not added, resulting in montmorillonite without sulfonic acid groups, and salt ions attack causing molecular chain aggregation and precipitation.

[0076] A preparation method of a thickening agent for oil well fracturing includes the following steps:

[0077] S1. Under nitrogen protection, add 120 g of 2-hydroxyethyl methacrylate and 75 g of phenylboric acid to 500 g of ethanol, seal it, stir at a constant temperature of 78 °C for 5.5 h with a stirring speed of 250 rpm, cool to room temperature, add 9.5 g of sulfosuccinic anhydride, stir for 2.5 h with a stirring speed of 250 rpm, and perform vacuum distillation at 60 °C and 0.1 MPa to obtain modified 2-hydroxyethyl methacrylate;

[0078] S2. Dissolve 24 g of tetra-arm polyethylene glycol chain transfer agent, 120 g of modified 2-hydroxyethyl methacrylate, 360 g of acrylamide, and 3.5 g of 2-hydroxyethyl methacrylate in 1000 g of deionized water, stir at a constant temperature of 50 °C for 2 h with a stirring speed of 500 rpm, add 3 g of ammonium persulfate, stir at a constant temperature of 60 °C for 3 h with a stirring speed of 300 rpm, add 1.5 g of ammonium persulfate, stir at a constant temperature of 70 °C for 1 h with a stirring speed of 200 rpm, add 1.5 g of ammonium persulfate, add 0.5 g of hydroquinone, cool, and pass it through a 200-mesh filter to obtain a gradient-branched polymer solution;

[0079] S3. Add 60 g of montmorillonite and 15 g of 3-aminopropyltriethoxysilane to 300 g of ethanol, seal it, stir at a constant temperature of 80 °C for 3.5 h with a stirring speed of 400 rpm, adjust the pH value of the system to 7.5 using 0.1 mol / L sodium hydroxide solution, add 6 g of phenylboric acid, stir at a constant temperature of 60 °C for 2 h with a stirring speed of 250 rpm, centrifuge, wash, and dry at 60 °C to obtain modified montmorillonite powder;

[0080] S4. Disperse 60 g of modified montmorillonite powder in 200 g of deionized water, perform ultrasonic treatment for 30 min at an ultrasonic frequency of 50 kHz, add 1300 g of gradient-branched polymer solution, stir at a constant temperature of 60 °C for 5.5 h at a stirring speed of 250 rpm, adjust the pH value of the system to 8.5 with 0.1 mol / L sodium hydroxide solution, and let it stand at a constant temperature of 60 °C for 12 h to obtain a colloidal solution;

[0081] S5. Centrifuge the colloidal solution and perform spray drying with a feeding rate of 20 mL / min, an inlet temperature of 170 °C, and an outlet temperature of 80 °C, and pass through a 200-mesh sieve to obtain a thickening agent for oil well fracturing.

[0082] Comparative Example 4

[0083] The difference between Comparative Example 4 and Example 3 is that in step S3, benzeneboronic acid is not added, resulting in montmorillonite without boronic acid groups, the lack of interfacial dynamic crosslinking, and insufficient physical entanglement shear resistance.

[0084] A preparation method of a thickening agent for oil well fracturing, comprising the following steps:

[0085] S1. Under nitrogen protection, add 120 g of 2-hydroxyethyl methacrylate and 75 g of benzeneboronic acid to 500 g of ethanol, seal, stir at a constant temperature of 78 °C for 5.5 h at a stirring speed of 250 rpm, cool to room temperature, add 9.5 g of sulfosuccinic anhydride, stir for 2.5 h at a stirring speed of 250 rpm, and perform vacuum distillation at 60 °C and 0.1 MPa to obtain modified 2-hydroxyethyl methacrylate;

[0086] S2. Dissolve 24 g of tetra-armed polyethylene glycol chain transfer agent, 120 g of modified 2-hydroxyethyl methacrylate, 360 g of acrylamide, and 3.5 g of 2-hydroxyethyl methacrylate in 1000 g of deionized water, stir at a constant temperature of 50 °C for 2 h at a stirring speed of 500 rpm, add 3 g of ammonium persulfate, stir at a constant temperature of 60 °C for 3 h at a stirring speed of 300 rpm, add 1.5 g of ammonium persulfate, stir at a constant temperature of 70 °C for 1 h at a stirring speed of 200 rpm, add 1.5 g of ammonium persulfate, add 0.5 g of hydroquinone, cool, and pass through a 200-mesh filter to obtain a gradient-branched polymer solution;

[0087] S3. Add 60 g of montmorillonite and 15 g of 3-aminopropyltriethoxysilane to 300 g of ethanol, seal, stir at a constant temperature of 80 °C for 3.5 h at a stirring speed of 400 rpm, add 9.5 g of sulfosuccinic anhydride, stir at a constant temperature of 60 °C for 2 h at a stirring speed of 250 rpm, adjust the pH value of the system to 7.5 with 0.1 mol / L sodium hydroxide solution, centrifuge, wash, and dry at 60 °C to obtain modified montmorillonite powder;

[0088] S4. Disperse 60 g of modified montmorillonite powder in 200 g of deionized water, perform ultrasonic treatment for 30 min at an ultrasonic frequency of 50 kHz, add 1300 g of gradient-branched polymer solution, stir at a constant temperature of 60 °C for 5.5 h at a stirring speed of 250 rpm, adjust the pH value of the system to 8.5 with 0.1 mol / L sodium hydroxide solution, and let it stand at a constant temperature of 60 °C for 12 h to obtain a colloidal solution;

[0089] S5. Centrifuge the colloidal solution and spray-dry it with a feeding rate of 20 mL / min, an inlet temperature of 170 °C, and an outlet temperature of 80 °C, and pass it through a 200-mesh sieve to obtain a thickening agent for oil well fracturing.

[0090] Comparative Example 5

[0091] The difference between Comparative Example 5 and Example 3 is that in step S4, the pH of the system is not adjusted, resulting in the inability of borate groups and hydroxyl groups to form dynamic bonds and an incomplete self-healing network.

[0092] A preparation method of a thickening agent for oil well fracturing includes the following steps:

[0093] S1. Under nitrogen protection, add 120 g of 2-hydroxyethyl methacrylate and 75 g of phenylboronic acid to 500 g of ethanol, seal it, stir at a constant temperature of 78 °C for 5.5 h at a stirring speed of 250 rpm, cool to room temperature, add 9.5 g of sulfosuccinic anhydride, stir for 2.5 h at a stirring speed of 250 rpm, and perform vacuum distillation at 60 °C and 0.1 MPa to obtain modified 2-hydroxyethyl methacrylate;

[0094] S2. Dissolve 24 g of tetraarm polyethylene glycol chain transfer agent, 120 g of modified 2-hydroxyethyl methacrylate, 360 g of acrylamide, and 3.5 g of 2-hydroxyethyl methacrylate in 1000 g of deionized water, stir at a constant temperature of 50 °C for 2 h at a stirring speed of 500 rpm, add 3 g of ammonium persulfate, stir at a constant temperature of 60 °C for 3 h at a stirring speed of 300 rpm, add 1.5 g of ammonium persulfate, stir at a constant temperature of 70 °C for 1 h at a stirring speed of 200 rpm, add 1.5 g of ammonium persulfate, add 0.5 g of hydroquinone, cool, and pass it through a 200-mesh filter to obtain a gradient-branched polymer solution;

[0095] S3. Add 60 g of montmorillonite and 15 g of 3-aminopropyltriethoxysilane to 300 g of ethanol, seal it, stir at a constant temperature of 80 °C for 3.5 h at a stirring speed of 400 rpm, add 9.5 g of sulfosuccinic anhydride, stir at a constant temperature of 60 °C for 2 h at a stirring speed of 250 rpm, adjust the pH value of the system to 7.5 with 0.1 mol / L sodium hydroxide solution, add 6 g of phenylboronic acid, stir at a constant temperature of 60 °C for 2 h at a stirring speed of 250 rpm, centrifuge, wash, and dry at 60 °C to obtain sulfonic acid-boric acid dual-modified montmorillonite powder;

[0096] S4. Disperse 60 g of sulfonic acid-boric acid double-modified montmorillonite powder in 200 g of deionized water, ultrasonically treat for 30 min at an ultrasonic frequency of 50 kHz, add 1300 g of gradient-branched polymer solution, stir at a constant temperature of 60 °C for 5.5 h at a stirring speed of 250 rpm, and let stand at a constant temperature of 60 °C for 12 h to obtain a colloidal solution;

[0097] S5. Centrifuge the colloidal solution and spray-dry it at a feeding rate of 20 mL / min, an inlet temperature of 170 °C, and an outlet temperature of 80 °C, and pass it through a 200-mesh sieve to obtain a thickening agent for oil well fracturing.

[0098] Performance test

[0099] Add the thickening agents prepared in Examples 1-3 and Comparative Examples 1-5 at a certain concentration to deionized water, stir for 30 minutes until completely dissolved, let stand at 25 °C for 2 hours to eliminate bubbles, adjust the pH value of the system to prepare a sample, and measure the initial viscosity V0 with a Brookfield DV3T viscometer.

[0100] Salt tolerance: According to the SY / T 5107-2016 standard, add CaCl2, stir at a constant temperature of 60 °C for 4 h, measure the viscosity V1 of the treated sample, and record the viscosity retention rate data. The results are shown in Table 1.

[0101] Calculation formula: Viscosity retention rate (%) 00%.

[0102] Temperature tolerance: According to the SY / T 5107-2016 standard, use a high-temperature and high-pressure rheometer (Haake MARS 60), set it at 150 °C, and continuously test the sample for 4 h at a shear rate of 170 s -1 and record the viscosity V2 data. The results are shown in Table 1.

[0103] Self-healing efficiency: Apply a shear of 1000 s -1 to the sample for 1 minute, let it stand for 10 minutes to recover; repeat 3 times, measure the final viscosity V3, and record the viscosity recovery rate data. The results are shown in Table 1.

[0104] Calculation formula: Viscosity recovery rate (%) = 00%.

[0105] Table 1 Performance test results

[0106]

[0107] Data analysis:

[0108] From the data of Examples 1 - 3 in Table 1, it can be seen that the novel thickening agent prepared by the present invention has the properties of temperature resistance, salt resistance and self - repair. Specifically, the average viscosity retention rate in the salt resistance test is 90%, and the highest can reach 90.5%; the average viscosity in the temperature resistance test is 48.2 mPa·s, and the highest can reach 48.5 mPa·s; the average viscosity recovery rate in the self - repair efficiency test is 94.6%, and the highest can reach 95.3%.

[0109] Compared with Example 3, in Comparative Example 1, the thickening agent prepared has a significant decline in terms of temperature resistance, self - repair ability and salt resistance. This is because phenylboronic acid is not introduced in step S1, and the dynamic borate bond is missing in the functional monomer. Only relying on physical entanglement to maintain the structure, the material cannot repair network damage through reversible cross - linking at high temperature, which also leads to a rapid attenuation of viscosity. Although sulfonic acid groups are still retained on the surface of montmorillonite to provide partial salt resistance, the lack of the synergistic effect of dynamic bonds still results in a decline in overall performance. In practical applications, this thickening agent is prone to viscosity loss in high - temperature well sections, unable to maintain the sand - carrying capacity for a long time, and also unable to reduce viscosity through the dissociation of dynamic bonds during backflow, indicating that the dynamic bond design is the core basis for temperature resistance and self - repair functions.

[0110] Compared with Example 3, in Comparative Example 2, both the initial thickening speed and long - term stability are inferior to those of Example 3. This is because one - time polymerization leads to the random distribution of functional groups, and the dynamic bonds and thickening chain segments are mixed, unable to exert a long - term protective effect centrally. During actual pumping, the initial viscosity of the liquid is established slowly, and the dispersion of functional regions at high temperature leads to a reduction in self - repair efficiency. Gradient polymerization controls the growth direction of molecular chains in stages, realizing the precise distribution of functions with dynamic bonds concentrated in the core and thickening chain segments extending outwards. The homogeneous structure of Comparative Example 2 proves that functional zoning is a necessary strategy to balance rapid thickening and long - term stability.

[0111] The salt resistance of Comparative Example 3 decreases significantly, and its temperature resistance also weakens. This is because montmorillonite is not grafted with sulfonic acid groups, unable to form an interfacial synergistic effect, and the nanosheets are prone to aggregation due to insufficient surface charge, weakening the physical enhancement effect. In practical applications, this thickening agent is prone to salt precipitation and viscosity loss in a high - salt environment, proving that the sulfonation of montmorillonite is the key to salt - resistance synergy and dispersion stability.

[0112] The self - repair ability and temperature resistance of Comparative Example 4 are significantly reduced. This is because montmorillonite is not modified with boronic acid groups, unable to act as a dynamic anchor to bind with the polymer, only relying on physical entanglement to strengthen the network, lacking the ability of chemical cross - linking and recombination at high temperature, and the molecular chains are prone to slip and break. In the actual downhole shear environment, this thickening agent is difficult to maintain viscosity stability, proving that the boronic acid - based dynamic anchor is a necessary design for interfacial enhancement and self - repair.

[0113] The self-healing efficiency of Comparative Example 5 decreased significantly. This is because under neutral conditions, borate groups and hydroxyl groups cannot form a dynamic network, and it is difficult to construct a stable network relying only on physical mixing. At high temperatures, the free movement of molecular chains intensifies, and the viscosity rapidly decays. In practical applications, this thickener cannot trigger the self-healing function in high-temperature well sections, proving that pH regulation is a necessary condition for the formation of a dynamic crosslinked network.

[0114] Those of ordinary skill in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a thickener for oil well fracturing, characterized in that: The steps include: S1. Under nitrogen protection, hydroxyethyl methacrylate and phenylboric acid are added to ethanol, sealed, stirred, cooled, and distilled under reduced pressure to obtain modified hydroxyethyl methacrylate; S2, dissolving a four-arm polyethylene glycol chain transfer agent, modified hydroxyethyl methacrylate, acrylamide, and hydroxyethyl methacrylate in deionized water, stirring at a constant temperature of 48-52° C. for 1.8-2.2 h, with a stirring speed of 480-520 rpm, adding ammonium persulfate, stirring at a constant temperature of 58-62° C. for 2.8-3.2 h, with a stirring speed of 280-320 rpm, adding ammonium persulfate, stirring at a constant temperature of 68-72° C. for 0.8-1.2 h, with a stirring speed of 180-220 rpm, adding ammonium persulfate, adding hydroquinone, cooling, filtering, and obtaining a gradient branched polymer solution; S3, adding montmorillonite and 3-aminopropyltriethoxysilane to ethanol, sealing, stirring, adding sulfosuccinic anhydride, stirring, adjusting the pH value of the system to 7.2-7.8 with 0.1 mol / L sodium hydroxide solution, adding phenylboric acid, stirring, centrifuging, washing, and drying to obtain sulfonic acid-boric acid double-modified montmorillonite powder; S4, dispersing the sulfonic acid-boric acid double-modified montmorillonite powder in deionized water, ultrasonicating, adding the gradient branched polymer solution, stirring, adjusting the pH value of the system to 8.3-8.7 with 0.1 mol / L sodium hydroxide solution, and standing to obtain a colloidal solution; S5. Centrifuge the colloidal solution, spray dry it, and sieve it to obtain a thickener for oil well fracturing.

2. The method for preparing a thickener for oil well fracturing according to claim 1, characterized in that: In the step S1, the weight ratio of hydroxyethyl methacrylate, phenylboric acid and ethanol is 100-140:70-80:480-520.

3. The method for preparing a thickener for oil well fracturing according to claim 1, characterized in that: In the step S2, the weight ratio of the four-arm polyethylene glycol chain transfer agent, modified hydroxyethyl methacrylate, acrylamide, hydroxyethyl methacrylate, deionized water, ammonium persulfate, and hydroquinone is 22-26: 100-140: 340-380: 2-5: 900-1100: 4-8: 0.3-0.

7.

4. The method for preparing a thickener for oil well fracturing according to claim 1, characterized in that: In the step S2, the weight ratios of the three additions of ammonium persulfate are 2-4:1-2:1-2 respectively.

5. The method for preparing a thickener for oil well fracturing according to claim 1, characterized in that: In the step S3, the weight ratio of montmorillonite, 3-aminopropyltriethoxysilane, ethanol, sulfosuccinic anhydride and phenylboric acid is 55-65:10-20:280-320:9-10:5-7.

6. The method for preparing a thickener for oil well fracturing according to claim 1, characterized in that: In the step S4, the weight ratio of the sulfonic acid-boric acid double-modified montmorillonite powder, deionized water, and gradient branched polymer solution is 55-65:180-220:1200-1400.

7. The method for preparing a thickener for oil well fracturing according to claim 1, characterized in that: In the step S5, spray drying is performed with a feed rate of 20 mL / min, an inlet temperature of 170° C., and an outlet temperature of 80° C.

8. A thickener for oil well fracturing, characterized in that: The thickener is prepared by the preparation method of the thickener for oil well fracturing according to any one of claims 1 to 7.

Images