An anti-fouling cross-linked polymer fracturing fluid and a preparation method thereof

Abstract

The application discloses an anti-fouling cross-linking polymer fracturing fluid and a preparation method thereof, and relates to the technical field of fracturing fluids. In the preparation of the anti-fouling cross-linking polymer fracturing fluid, ethylenediamine is sequentially reacted with methyl acrylate, mercaptoethylamine and vinyl phosphoric acid to obtain an over-branched scale inhibitor; polyvinyl alcohol is reacted with (4-formylphenyl) prop-2-enate to obtain modified polyvinyl alcohol; 1-alkenylimidazole is reacted with bromododecane to obtain an alkenylimidazole salt monomer; acrylamide, acrylic acid, the alkenylimidazole salt monomer and 3-butene-1-amine are polymerized to obtain functionalized polyacrylamide; and the functionalized polyacrylamide, the functionalized polyvinyl alcohol, the over-branched scale inhibitor and deionized water are uniformly mixed to obtain the anti-fouling cross-linking polymer fracturing fluid. The anti-fouling cross-linking polymer fracturing fluid prepared by the application has the advantages of excellent anti-fouling performance, good temperature resistance and self-cross-linking.

Description

Technical Field

[0001] This invention relates to the field of fracturing fluid technology, specifically to a scale-inhibiting cross-linked polymer fracturing fluid and its preparation method. Background Technology

[0002] With advancements in petroleum exploration technology, oil and gas resource development is expanding into deeper areas, leading to increasingly deeper wells and consequently, higher reservoir temperatures requiring fracturing. Therefore, to match the fracturing performance of high-temperature reservoirs, higher demands are placed on the temperature and shear resistance of fracturing fluids. Currently, most polymer fracturing fluids utilize multivalent metals such as... , as well as These metal ions can crosslink with polymers, but the bonds formed between them and the polymer are chelate bonds, which are easily broken under high temperature or high shear conditions. This reduces the temperature and shear resistance of the polymer fracturing fluid system, making it unable to meet the requirements for fracturing fluids in construction. Furthermore, these metals cause some degree of environmental pollution, and the residual metal ions in the fracturing flowback fluid increase the difficulty of flowback fluid treatment.

[0003] On the other hand, during fracturing operations, the formation environment, including temperature, formation pressure, and dissolved gases, undergoes a series of changes. The water source used for fracturing fluid is typically water from non-oil / gas reservoirs, which is continuously injected into the oil / gas reservoir. This practice can disrupt the original ion balance of the reservoir water. Because the injected water and the reservoir water contain different scale-forming ions, coupled with the thermodynamic instability and chemical incompatibility of water, inorganic scale such as calcium carbonate and calcium sulfate easily form, blocking the channels for oil and gas flow. Over time, this blockage gradually reduces the reservoir's conductivity, causing significant damage.

[0004] Based on the above problems, it is essential to invent a fracturing fluid with superior temperature and shear resistance and scale inhibition performance. Summary of the Invention

[0005] The purpose of this invention is to provide an anti-scaling cross-linked polymer fracturing fluid and its preparation method, so as to solve the problems existing in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A scale-inhibiting crosslinked polymer fracturing fluid, by mass parts, mainly comprises: 5-6 parts of functionalized polyacrylamide, 2.8-3.2 parts of functionalized polyvinyl alcohol, 1.8-2.2 parts of hyperbranched scale inhibitor, and 1000 parts of deionized water.

[0008] The functionalized polyacrylamide is prepared by polymerizing acrylamide, acrylic acid, alkenyl imidazole salt monomer, and 3-butene-1-amine.

[0009] The alkenylimidazolium salt monomer is prepared by reacting 1-alkenylimidazolium with bromododecane.

[0010] The functionalized polyvinyl alcohol is prepared by reacting polyvinyl alcohol with (4-formylphenyl)prop-2-enoate.

[0011] The hyperbranched scale inhibitor is prepared by reacting ethylenediamine with methyl acrylate, mercaptoethylamine and vinyl phosphoric acid in sequence.

[0012] The vinyl phosphoric acid is prepared by reacting 2-vinylpropane-1,3-diol and phosphorus pentoxide.

[0013] A method for preparing an anti-scaling crosslinked polymer fracturing fluid, the method comprising the following preparation steps:

[0014] (1) Ethylenediamine and methyl acrylate were added to methanol at a molar ratio of 1:(6~8) to 10~12 times the mass of ethylenediamine. The mixture was stirred at 30~40℃ and 300~500r / min for 20~24h under nitrogen protection. The mixture was then dried at 50~60℃ under vacuum for 8~10h to obtain intermediate 1. Intermediate 1 and mercaptoethylamine were added to methanol at a molar ratio of 1:(4~5) to 10~12 times the mass of intermediate 1. The mixture was stirred at 20~30℃ and 300~500r / min for 20~24h. The mixture was stirred and reacted for 20-24 hours, then dried at 50-60°C under vacuum for 8-10 hours to obtain intermediate 2. Intermediate 2 and vinyl phosphate were added to anhydrous ethanol at a molar ratio of 1:(4-4.2) to 12-14 times the mass of intermediate 2, and azobisisobutyronitrile was added at 0.04-0.06 times the mass of intermediate 2. The mixture was stirred and reacted at 60-70°C and 200-300 r / min for 6-8 hours, then dried at 50-60°C under vacuum for 10-12 hours to obtain a hyperbranched scale inhibitor.

[0015] (2) Polyvinyl alcohol, (4-formylphenyl)prop-2-enoate, and dimethyl sulfoxide are mixed evenly in a mass ratio of 1:(0.1~0.12):(8~10). 0.03~0.05 times the volume of p-toluenesulfonic acid is added to the mixture. The mixture is stirred at 40~50℃ and 200~300r / min for 18~20h. Then, 3~4 times the volume of acetone is added to the mixture and it is mixed evenly. The mixture is filtered and dried at 50~60℃ under vacuum for 12~14h to obtain functionalized polyvinyl alcohol.

[0016] (3) Acrylamide, acrylic acid, alkenyl imidazole salt monomer, and 3-butene-1-amine were added to deionized water at a molar ratio of 4:1:(0.6~0.8):(0.1~0.2) in 5~6 times the mass of acrylamide. The pH was adjusted to 7 with 30% sodium hydroxide aqueous solution. 2,2'-azobisisobutylamidine dihydrochloride was added at 0.05~0.07 times the mass of acrylamide. The mixture was stirred and reacted at 55~65℃ for 5~6h under nitrogen protection. The mixture was washed 3~5 times with anhydrous ethanol and dried at 50~60℃ for 12~14h under vacuum to obtain functionalized polyacrylamide.

[0017] (4) Take 5-6 parts of functionalized polyacrylamide, 2.8-3.2 parts of functionalized polyvinyl alcohol, 1.8-2.2 parts of hyperbranched scale inhibitor, and 1000 parts of deionized water by mass; mix the functionalized polyacrylamide, functionalized polyvinyl alcohol, hyperbranched scale inhibitor, and deionized water, and stir at 300-500 r / min for 20-30 min at room temperature to obtain the scale-inhibiting crosslinked polymer fracturing liquid.

[0018] As an optimization, the preparation method of vinyl phosphoric acid in step (1) is as follows: 2-vinylpropane-1,3-diol and phosphorus pentoxide are added to deionized water at a mass ratio of 1:(1.2~1.4) to 10~12 times the mass of 2-vinylpropane-1,3-diol. The mixture is stirred at 70~80℃ and 300~500r / min for 2~3h, filtered, and the filtrate is dried under vacuum at 50~60℃ for 8~10h to obtain vinyl phosphoric acid; the reaction process is shown below:

[0019] .

[0020] As an optimization, the reaction process of intermediate 2 in step (1) is as follows:

[0021] .

[0022] As an optimization, the reaction process of the hyperbranched scale inhibitor in step (1) is as follows:

[0023] ;

[0024] Where R is: .

[0025] As an optimization, the average molecular weight of the polyvinyl alcohol in step (2) is 20,000 to 50,000, and the degree of alcoholysis is 88%.

[0026] As an optimization, the CAS number of the (4-formylphenyl)prop-2-enoate ester described in step (2) is: 41704-79-4; the structural formula is: .

[0027] As an optimization, the preparation method of the alkenylimidazolium salt monomer in step (3) is as follows: 1-alkenylimidazolium and bromododecane are added to acetone at a molar ratio of 1:(1.2~1.4) in 10~12 times the mass of 1-alkenylimidazolium. The reaction is carried out under light-protected conditions at 50~54℃ and 300~500r / min for 10~12h. The reaction is then dried under vacuum conditions at 50~60℃ for 8~10h to obtain the alkenylimidazolium salt monomer.

[0028] As an optimization, the dosage of functionalized polyacrylamide, functionalized polyvinyl alcohol, hyperbranched scale inhibitor, and deionized water in step (4) is as follows: 5-6 parts of functionalized polyacrylamide, 2.8-3.2 parts of functionalized polyvinyl alcohol, 1.8-2.2 parts of hyperbranched scale inhibitor, and 1000 parts of deionized water.

[0029] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0030] In preparing the anti-scaling crosslinked polymer fracturing fluid, the present invention first reacts 2-vinylpropane-1,3-diol and phosphorus pentoxide to obtain vinyl phosphoric acid; reacts ethylenediamine and methyl acrylate to obtain intermediate 1; reacts intermediate 1 and mercaptoethylamine to obtain intermediate 2; and reacts intermediate 2 and vinyl phosphoric acid to obtain a hyperbranched scale inhibitor. The hyperbranched scale inhibitor contains phosphate groups and amide bonds, which can chelate scale-forming metal cations in the solution, giving the fracturing fluid good anti-scaling properties.

[0031] Secondly, an alkenylimidazolium salt monomer was prepared by reacting 1-alkenylimidazolium with bromododecane; acrylamide, acrylic acid, alkenylimidazolium salt monomer, and 3-butene-1-amine were polymerized to prepare functionalized polyacrylamide; carboxyl groups, imidazolium salt cations, and amino groups were introduced into the side chains of the functionalized polyacrylamide; the introduced carboxyl groups can also chelate scale-forming metal cations in the solution, improving the scale prevention performance of the fracturing fluid; the alkenylimidazolium salt monomer contains both imidazolium salt cations and hydrophobic long chains. The imidazolium salt cations can form a cross-linking network by combining with the phosphate groups on the hyperbranched scale inhibitor and the carboxylic acid groups on the functionalized polyacrylamide through positive and negative charge bonding. At the same time, the hydrophobic long chains form hydrophobic microdomains in the aqueous solution, which are further cross-linked through intermolecular hydrophobic association, thereby significantly increasing the viscoelasticity of the polymer aqueous solution.

[0032] Finally, a partial aldol condensation reaction was carried out between the hydroxyl groups of polyvinyl alcohol and the aldehyde groups on (4-formylphenyl)prop-2-enoate to prepare functionalized polyvinyl alcohol. The carbon-carbon double bonds introduced on the functionalized polyvinyl alcohol can undergo Michael addition reaction with the amino groups introduced on the functionalized polyacrylamide at a certain temperature to form covalent crosslinks, which further improves the temperature resistance of the anti-scaling crosslinked polymer fracturing fluid.

[0033] This invention achieves cross-linking of scale-resistant cross-linked polymer fracturing fluid through hydrogen bonding, electrostatic bridging, and hydrophobic association, eliminating the need for additional metal cross-linking agents and offering advantages such as environmental friendliness and low pollution. Furthermore, covalent cross-linking is triggered during temperature increases, ensuring that the fracturing fluid retains sufficient viscosity and elasticity even at high temperatures. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1:

[0036] A method for preparing an anti-scaling crosslinked polymer fracturing fluid, the method comprising the following preparation steps:

[0037] (1) 2-Vinylpropane-1,3-diol and phosphorus pentoxide were added to deionized water at a mass ratio of 1:1.2 to 10 times the mass of 2-vinylpropane-1,3-diol. The mixture was stirred at 300 r / min for 3 h at 70 °C, filtered, and the filtrate was dried at 50 °C for 10 h under vacuum to obtain vinyl phosphoric acid. Ethylenediamine and methyl acrylate were added to methanol at a molar ratio of 1:6 to 10 times the mass of ethylenediamine. The mixture was stirred at 30 °C for 24 h under nitrogen protection and dried at 50 °C for 10 h under vacuum. Intermediate 1 was prepared; Intermediate 1 and mercaptoethylamine were added to methanol at a molar ratio of 1:4 to 10 times the mass of Intermediate 1, and the mixture was stirred at 20°C and 300 r / min for 24 h, and dried at 50°C under vacuum for 10 h to prepare Intermediate 2; Intermediate 2 and vinyl phosphate were added to anhydrous ethanol at a molar ratio of 1:4 to 12 times the mass of Intermediate 2, and azobisisobutyronitrile was added at 0.04 times the mass of Intermediate 2, and the mixture was stirred at 60°C and 200 r / min for 8 h, and dried at 50°C under vacuum for 12 h to prepare hyperbranched scale inhibitor;

[0038] (2) Polyvinyl alcohol, (4-formylphenyl)prop-2-enoate and dimethyl sulfoxide are mixed evenly in a mass ratio of 1:0.1:8. 0.03 times the amount of p-toluenesulfonic acid is added to polyvinyl alcohol. The mixture is stirred at 40°C and 200 r / min for 20 h. 3 times the volume of acetone is added to dimethyl sulfoxide and mixed evenly. The mixture is filtered and dried at 50°C for 14 h under vacuum to obtain functionalized polyvinyl alcohol.

[0039] (3) 1-Alkenylimidazolium and bromododecane were added to acetone at a molar ratio of 1:1.2 in 10 times the mass of 1-alkenylimidazolium. The mixture was stirred at 300 r / min for 12 h at 50 °C under light protection. The mixture was then dried at 50 °C for 10 h under vacuum to obtain alkenylimidazolium salt monomer. Acrylamide, acrylic acid, alkenylimidazolium salt monomer and 3-butene-1-amine were added to deionized water at a molar ratio of 4:1:0.6:0.1 in 5 times the mass of acrylamide. The pH was adjusted to 7 with 30% sodium hydroxide aqueous solution. 2,2'-azobisisobutylamidine dihydrochloride was added at 0.05 times the mass of acrylamide. The mixture was stirred at 55 °C for 6 h under nitrogen protection. The mixture was washed 3 times with anhydrous ethanol and dried at 50 °C for 14 h under vacuum to obtain functionalized polyacrylamide.

[0040] (4) Take 5 parts of functionalized polyacrylamide, 2.8 parts of functionalized polyvinyl alcohol, 1.8 parts of hyperbranched scale inhibitor, and 1000 parts of deionized water by mass. Mix the functionalized polyacrylamide, functionalized polyvinyl alcohol, hyperbranched scale inhibitor, and deionized water, and stir at 300 r / min for 20 min at room temperature to obtain scale-resistant crosslinked polymer fracturing liquid.

[0041] Example 2:

[0042] A method for preparing an anti-scaling crosslinked polymer fracturing fluid, the method comprising the following preparation steps:

[0043] (1) 2-Vinylpropane-1,3-diol and phosphorus pentoxide were added to deionized water at a mass ratio of 1:1.3 to 11 times the mass of 2-vinylpropane-1,3-diol. The mixture was stirred at 75°C and 400 r / min for 2.5 h, filtered, and the filtrate was dried at 55°C under vacuum for 9 h to obtain vinyl phosphoric acid. Ethylenediamine and methyl acrylate were added to methanol at a molar ratio of 1:7 to 11 times the mass of ethylenediamine. The mixture was stirred at 35°C and 400 r / min for 22 h under nitrogen protection, and dried at 55°C under vacuum for 9 h to obtain vinyl phosphoric acid. Intermediate 1 was obtained; Intermediate 1 and mercaptoethylamine were added to methanol at a molar ratio of 1:4.5 in 11 times the mass of Intermediate 1, and the mixture was stirred at 25°C and 400 r / min for 22 h, and then dried at 55°C under vacuum for 9 h to obtain Intermediate 2; Intermediate 2 and vinyl phosphate were added to anhydrous ethanol at a molar ratio of 1:4.1 in 13 times the mass of Intermediate 2, and azobisisobutyronitrile was added at 0.05 times the mass of Intermediate 2, and the mixture was stirred at 250 r / min for 7 h, and then dried at 55°C under vacuum for 11 h to obtain a hyperbranched scale inhibitor;

[0044] (2) Polyvinyl alcohol, (4-formylphenyl)prop-2-enoate and dimethyl sulfoxide are mixed evenly in a mass ratio of 1:0.11:9. 0.04 times the volume of p-toluenesulfonic acid of polyvinyl alcohol is added. The mixture is stirred at 45°C and 250 r / min for 19 h. 3.5 times the volume of acetone of dimethyl sulfoxide is added and mixed evenly. The mixture is filtered and dried at 55°C for 13 h under vacuum to obtain functionalized polyvinyl alcohol.

[0045] (3) 1-Alkenylimidazolium and bromododecane were added to acetone at a molar ratio of 1:1.3 to 11 times the mass of 1-alkenylimidazolium. The mixture was stirred at 400 r / min for 11 h at 52 °C under light protection. The mixture was then dried at 55 °C for 9 h under vacuum to obtain alkenylimidazolium salt monomer. Acrylamide, acrylic acid, alkenylimidazolium salt monomer, and 3-butene-1-amine were added to deionized water at a molar ratio of 4:1:0.7:0.15 to 5.5 times the mass of acrylamide. The pH was adjusted to 7 with 30% sodium hydroxide aqueous solution. 2,2'-azobisisobutylamidine dihydrochloride was added at 0.06 times the mass of acrylamide. The mixture was stirred at 60 °C for 5.5 h under nitrogen protection. The mixture was washed 4 times with anhydrous ethanol and dried at 55 °C for 13 h under vacuum to obtain functionalized polyacrylamide.

[0046] (4) Take 5.5 parts of functionalized polyacrylamide, 3 parts of functionalized polyvinyl alcohol, 2 parts of hyperbranched scale inhibitor, and 1000 parts of deionized water by mass; mix the functionalized polyacrylamide, functionalized polyvinyl alcohol, hyperbranched scale inhibitor, and deionized water, and stir at 400 r / min for 25 min at room temperature to obtain scale-resistant crosslinked polymer fracturing liquid.

[0047] Example 3:

[0048] A method for preparing an anti-scaling crosslinked polymer fracturing fluid, the method comprising the following preparation steps:

[0049] (1) 2-Vinylpropane-1,3-diol and phosphorus pentoxide were added to deionized water at a mass ratio of 1:1.4 to 12 times the mass of 2-vinylpropane-1,3-diol. The mixture was stirred at 80°C and 500 r / min for 2 h, filtered, and the filtrate was dried at 60°C under vacuum for 8 h to obtain vinyl phosphoric acid. Ethylenediamine and methyl acrylate were added to methanol at a molar ratio of 1:8 to 12 times the mass of ethylenediamine. The mixture was stirred at 40°C and 500 r / min for 20 h under nitrogen protection, and dried at 60°C under vacuum for 8 h to obtain vinyl phosphoric acid. Intermediate 1 was obtained; Intermediate 1 and mercaptoethylamine were added to methanol at a molar ratio of 1:5 to 12 times the mass of Intermediate 1, and the mixture was stirred at 30°C and 500 r / min for 20 h, and then dried at 60°C under vacuum for 8 h to obtain Intermediate 2; Intermediate 2 and vinyl phosphate were added to anhydrous ethanol at a molar ratio of 1:4.2 to 14 times the mass of Intermediate 2, and azobisisobutyronitrile was added at 0.06 times the mass of Intermediate 2, and the mixture was stirred at 70°C and 300 r / min for 6 h, and then dried at 60°C under vacuum for 10 h to obtain a hyperbranched scale inhibitor;

[0050] (2) Polyvinyl alcohol, (4-formylphenyl)prop-2-enoate and dimethyl sulfoxide are mixed evenly in a mass ratio of 1:0.12:10. 0.05 times the volume of p-toluenesulfonic acid of polyvinyl alcohol are added. The mixture is stirred at 300 r / min for 18 h at 50 °C. Then, 4 times the volume of acetone of dimethyl sulfoxide is added and mixed evenly. The mixture is filtered and dried at 60 °C for 12 h under vacuum to obtain functionalized polyvinyl alcohol.

[0051] (3) 1-Alkenylimidazolium and bromododecane were added to acetone at a molar ratio of 1:1.4 to 12 times the mass of 1-alkenylimidazolium. The mixture was stirred at 54°C and 500 r / min for 10 h under light-protected conditions. The mixture was then dried at 60°C under vacuum for 8 h to obtain alkenylimidazolium salt monomer. Acrylamide, acrylic acid, alkenylimidazolium salt monomer, and 3-butene-1-amine were added to deionized water at a molar ratio of 4:1:0.8:0.2 to 6 times the mass of acrylamide. The pH was adjusted to 7 with 30% sodium hydroxide aqueous solution. 2,2'-azobisisobutylamidine dihydrochloride was added at a molar ratio of 0.07 times the mass of acrylamide. The mixture was stirred at 65°C for 5 h under nitrogen protection. The mixture was washed 5 times with anhydrous ethanol and dried at 60°C under vacuum for 12 h to obtain functionalized polyacrylamide.

[0052] (4) Take 6 parts of functionalized polyacrylamide, 3.2 parts of functionalized polyvinyl alcohol, 2.2 parts of hyperbranched scale inhibitor, and 1000 parts of deionized water by mass. Mix the functionalized polyacrylamide, functionalized polyvinyl alcohol, hyperbranched scale inhibitor, and deionized water, and stir at 500 r / min for 30 min at room temperature to obtain the scale-inhibiting crosslinked polymer fracturing liquid.

[0053] Comparative Example 1:

[0054] The preparation method of the anti-scaling crosslinked polymer fracturing fluid in Comparative Example 1 differs from that in Example 2 in that step (1) is omitted, and step (4) is modified as follows: 5.5 parts by mass of functionalized polyacrylamide, 3 parts by mass of functionalized polyvinyl alcohol, and 1000 parts by mass of deionized water are taken; the functionalized polyacrylamide, functionalized polyvinyl alcohol, and deionized water are mixed and stirred at 400 r / min for 25 min at room temperature to obtain the anti-scaling crosslinked polymer fracturing fluid. The remaining steps are the same as in Example 2.

[0055] Comparative Example 2:

[0056] The preparation method of the anti-scaling crosslinked polymer fracturing fluid in Comparative Example 2 differs from that in Example 2 in that step (2) is omitted, and step (4) is modified as follows: 5.5 parts by mass of functionalized polyacrylamide, 3 parts by mass of polyvinyl alcohol, 2 parts by mass of hyperbranched scale inhibitor, and 1000 parts by mass of deionized water are mixed with the functionalized polyacrylamide, functionalized polyvinyl alcohol, hyperbranched scale inhibitor, and deionized water, and stirred at 400 r / min for 25 min at room temperature to obtain the anti-scaling crosslinked polymer fracturing fluid. The remaining steps are the same as in Example 2.

[0057] Comparative Example 3:

[0058] The preparation method of the anti-scaling crosslinked polymer fracturing fluid in Comparative Example 3 differs from that in Example 2 only in step (3). Step (3) is modified as follows: Acrylamide, acrylic acid, and 3-butene-1-amine are added to deionized water at a molar ratio of 4:1:0.2, which is 6 times the mass of acrylamide. The pH is adjusted to 7 with a 30% sodium hydroxide aqueous solution. 2,2'-azobisisobutylamidine dihydrochloride is added at 0.07 times the mass of acrylamide. The mixture is stirred at 65°C for 5 hours under nitrogen protection. It is then washed 5 times with anhydrous ethanol and dried at 60°C for 12 hours under vacuum to obtain functionalized polyacrylamide. The remaining steps are the same as in Example 2.

[0059] Test Example 1

[0060] Scale inhibition performance test

[0061] Test method: Referring to standard Q / SY 17126-2019, the scale inhibition efficiency of calcium carbonate scale was tested in the example and comparative examples. The test was conducted three times and the average value was recorded. The results are shown in Table 1.

[0062] Table 1

[0063] ;

[0064] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-3 in Table 1 reveals that the scale-inhibiting crosslinked polymer fracturing fluid prepared in this invention exhibits excellent scale inhibition performance.

[0065] By comparison, the scale inhibition rate of calcium carbonate in Examples 1-3 is greater than that in Comparative Example 1. This indicates that the preparation of vinyl phosphoric acid by reacting 2-vinylpropane-1,3-diol and phosphorus pentoxide; the preparation of intermediate 1 by reacting ethylenediamine and methyl acrylate; the preparation of intermediate 2 by reacting intermediate 1 and mercaptoethylamine; and the preparation of hyperbranched scale inhibitor by reacting intermediate 2 and vinyl phosphoric acid are all possible. The hyperbranched scale inhibitor contains phosphate groups and amide bonds, which can chelate scale-forming metal cations in the solution, giving the fracturing fluid good scale prevention properties.

[0066] Test Example 2

[0067] Testing of apparent viscosity and high-temperature shear viscosity

[0068] Apparent viscosity test: Take 500 ml of the example and comparative examples and place them in a beaker. Incubate at room temperature for 170 seconds. -1 Its apparent viscosity was measured using a rotational viscometer at the shear rate.

[0069] Temperature shear viscosity test: Referring to SY / T 5017-2005, the examples and comparative examples were subjected to a temperature of 160℃ for 170 seconds. -1 The shear viscosity was measured after shearing at the specified shear rate for 90 minutes. The results are shown in Table 2.

[0070] Table 2

[0071] ;

[0072] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-3 in Table 2 reveals that the anti-scaling crosslinked polymer fracturing fluid prepared by the present invention has good thickening effect and temperature resistance.

[0073] By comparison, the apparent viscosity of Examples 1-3 is greater than that of Comparative Examples 1 and 3, indicating that the alkenylimidazolium salt monomer is prepared by reacting 1-alkenylimidazolium and bromododecane; functionalized polyacrylamide is prepared by polymerizing acrylamide, acrylic acid, alkenylimidazolium salt monomer, and 3-butene-1-amine; carboxyl groups and imidazolium salt cations are introduced into the side chains of functionalized polyacrylamide; the alkenylimidazolium salt monomer contains both imidazolium salt cations and hydrophobic long chains. The imidazolium salt cations can form a cross-linking network with the phosphate groups on the hyperbranched scale inhibitor and the carboxylic acid groups on the functionalized polyacrylamide through positive and negative charge bonding. At the same time, the hydrophobic long chains form hydrophobic microregions in the aqueous solution, thereby significantly increasing the viscoelasticity of the polymer aqueous solution. Further cross-linking through intermolecular hydrophobic association improves the viscosity of the scale-inhibiting cross-linked polymer fracturing fluid.

[0074] By comparison, the temperature-resistant shear viscosity of Examples 1-3 is greater than that of Comparative Example 2, indicating that functionalized polyvinyl alcohol is prepared by undergoing aldol condensation reaction between some hydroxyl groups of polyvinyl alcohol and the aldehyde group on (4-formylphenyl)prop-2-enoate. The carbon-carbon double bonds introduced on the functionalized polyvinyl alcohol can undergo Michael addition reaction with the amino groups introduced on the functionalized polyacrylamide at high temperature to form covalent crosslinks, so that the fracturing fluid still has sufficient viscosity at high temperature.

[0075] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A scale-resistant cross-linked polymer fracturing fluid, characterized in that, By weight, it mainly includes: 5-6 parts of functionalized polyacrylamide, 2.8-3.2 parts of functionalized polyvinyl alcohol, 1.8-2.2 parts of hyperbranched scale inhibitor, and 1000 parts of deionized water. The preparation method of the functionalized polyacrylamide is as follows: Acrylamide, acrylic acid, alkenyl imidazole salt monomer, and 3-butene-1-amine are added to deionized water at a molar ratio of 4:1:(0.6~0.8):(0.1~0.2) in 5~6 times the mass of acrylamide. The pH is adjusted to 7 with a 30% sodium hydroxide aqueous solution. 2,2'-azobisisobutylamidine dihydrochloride is added at 0.05~0.07 times the mass of acrylamide. The mixture is stirred and reacted at 55~65℃ for 5~6h under nitrogen protection. The mixture is washed 3~5 times with anhydrous ethanol and dried at 50~60℃ for 12~14h under vacuum to obtain the functionalized polyacrylamide. The alkenylimidazolium salt monomer is prepared by adding 1-alkenylimidazolium and bromododecane in a molar ratio of 1:(1.2~1.4) to acetone in a volume of 10~12 times the mass of 1-alkenylimidazolium. The mixture is stirred at 50~54℃ and 300~500r / min for 10~12h under light-protected conditions, and then dried at 50~60℃ for 8~10h under vacuum conditions to obtain the alkenylimidazolium salt monomer. The preparation method of the functionalized polyvinyl alcohol is as follows: polyvinyl alcohol, (4-formylphenyl)prop-2-enoate, and dimethyl sulfoxide are mixed evenly in a mass ratio of 1:(0.1~0.12):(8~10), 0.03~0.05 times the volume of p-toluenesulfonic acid is added, and the mixture is stirred at 40~50℃ and 200~300r / min for 18~20h. Then, 3~4 times the volume of acetone is added to dimethyl sulfoxide and mixed evenly. The mixture is filtered and dried at 50~60℃ under vacuum for 12~14h to obtain the functionalized polyvinyl alcohol. The preparation method of the hyperbranched scale inhibitor is as follows: Ethylenediamine and methyl acrylate are added to methanol at a molar ratio of 1:(6~8) to 10~12 times the mass of ethylenediamine. The mixture is stirred at 30~40℃ and 300~500 r / min for 20~24 h under nitrogen protection. Then, it is dried at 50~60℃ under vacuum for 8~10 h to obtain intermediate 1. Intermediate 1 and mercaptoethylamine are added to methanol at a molar ratio of 1:(4~5) to 10~12 times the mass of intermediate 1. The mixture is stirred at 20~30℃ and 300~500 r / min for 20~24 h. The mixture was stirred at 0 r / min for 20-24 h, and dried at 50-60 °C under vacuum for 8-10 h to obtain intermediate 2. Intermediate 2 and vinyl phosphate were added to anhydrous ethanol at a molar ratio of 1:(4-4.2) to 12-14 times the mass of intermediate 2, and azobisisobutyronitrile was added at 0.04-0.06 times the mass of intermediate 2. The mixture was stirred at 200-300 r / min for 6-8 h at 60-70 °C, and dried at 50-60 °C under vacuum for 10-12 h to obtain hyperbranched scale inhibitor. The method for preparing the vinyl phosphoric acid is as follows: 2-vinylpropane-1,3-diol and phosphorus pentoxide are added to deionized water at a mass ratio of 1:(1.2~1.4) in 10~12 times the mass of 2-vinylpropane-1,3-diol. The mixture is stirred at 70~80℃ and 300~500r / min for 2~3h. After filtration, the filtrate is dried under vacuum at 50~60℃ for 8~10h to obtain vinyl phosphoric acid.

2. A method for preparing a scale-resistant cross-linked polymer fracturing fluid, characterized in that, The preparation method of the anti-scaling crosslinked polymer fracturing fluid includes the following preparation steps: (1) Add 2-vinylpropane-1,3-diol and phosphorus pentoxide to deionized water at a mass ratio of 1:(1.2~1.4) in 10~12 times the mass of 2-vinylpropane-1,3-diol. Stir at 300~500 r / min for 2~3 h at 70~80 °C. Filter and dry the filtrate at 50~60 °C under vacuum for 8~10 h to obtain vinyl phosphoric acid. Add ethylenediamine and methyl acrylate to methanol at a molar ratio of 1:(6~8) in 10~12 times the mass of ethylenediamine. Stir at 30~40 °C at 300~500 r / min for 20~24 h under nitrogen protection. Dry at 50~60 °C under vacuum for 8~10 h to obtain intermediate... Intermediate 1; Intermediate 1 and mercaptoethylamine were added to methanol at a molar ratio of 1:(4~5) in 10~12 times the mass of Intermediate 1, and stirred at 300~500 r / min for 20~24 h at 20~30℃, and dried at 50~60℃ under vacuum for 8~10 h to obtain Intermediate 2; Intermediate 2 and vinyl phosphate were added to anhydrous ethanol at a molar ratio of 1:(4~4.2) in 12~14 times the mass of Intermediate 2, and azobisisobutyronitrile was added at 0.04~0.06 times the mass of Intermediate 2, and stirred at 200~300 r / min for 6~8 h at 60~70℃, and dried at 50~60℃ under vacuum for 10~12 h to obtain hyperbranched scale inhibitor; (2) Polyvinyl alcohol, (4-formylphenyl)prop-2-enoate, and dimethyl sulfoxide are mixed evenly in a mass ratio of 1:(0.1~0.12):(8~10). 0.03~0.05 times the volume of p-toluenesulfonic acid is added to the mixture. The mixture is stirred at 40~50℃ and 200~300r / min for 18~20h. Then, 3~4 times the volume of acetone is added to the mixture and it is mixed evenly. The mixture is filtered and dried at 50~60℃ under vacuum for 12~14h to obtain functionalized polyvinyl alcohol. (3) Add 1-alkenylimidazolium and bromododecane in a molar ratio of 1:(1.2~1.4) to acetone in a volume 10~12 times the mass of 1-alkenylimidazolium. React under light-protected conditions at 50~54℃ and 300~500 r / min for 10~12 h with stirring. Dry under vacuum at 50~60℃ for 8~10 h to obtain the alkenylimidazolium salt monomer. Add acrylamide, acrylic acid, alkenylimidazolium salt monomer, and 3-butene-1-amine in a molar ratio of 4:1:(0.6). ~0.8):(0.1~0.2) was added to deionized water at 5~6 times the mass of acrylamide, and the pH was adjusted to 7 with 30% sodium hydroxide aqueous solution. 2,2'-azobisisobutylamidine dihydrochloride at 0.05~0.07 times the mass of acrylamide was added. The mixture was stirred and reacted at 55~65℃ for 5~6h under nitrogen protection. The mixture was washed 3~5 times with anhydrous ethanol and dried at 50~60℃ for 12~14h under vacuum to obtain functionalized polyacrylamide. (4) Take 5-6 parts of functionalized polyacrylamide, 2.8-3.2 parts of functionalized polyvinyl alcohol, 1.8-2.2 parts of hyperbranched scale inhibitor, and 1000 parts of deionized water by mass; mix the functionalized polyacrylamide, functionalized polyvinyl alcohol, hyperbranched scale inhibitor, and deionized water, and stir at 300-500 r / min for 20-30 min at room temperature to obtain the scale-inhibiting crosslinked polymer fracturing liquid.