Drag reducing agent for shale gas reservoir fracturing and preparation method thereof

Abstract

The present invention belongs to the technical field of oil extraction, and specifically relates to a drag reducer for shale gas reservoir fracturing and a preparation method thereof. The preparation method is as follows: 5-allyl-3-methoxy salicylic acid methyl ester, methacryloylethyl sulfobetaine, 1-vinyl-3-methylimidazolium tetrafluoroborate, allyl dimethyl (4-methoxyphenyl) silane, OP-10, sodium dodecyl sulfate, buffer salt, deionized water are sequentially added to a reactor, and stirred to form a uniform emulsion; heating, adding an initiator to a high-level tank, keeping warm, heating, cooling, adjusting the pH value, and obtaining a viscous liquid; granulation to obtain a final product drag reducer. The present invention has the advantages of a wide source of raw materials, a simple synthesis process, and no by-products; at the same time, the present invention has the characteristics of high viscosity and high drag reduction rate, and the apparent viscosity at a concentration of 0.2wt% is ≥200mPa.s, and the drag reduction rate is ≥75%.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum extraction, relates to a high molecular polymer and a preparation method thereof, and particularly relates to a drag reducer for shale gas reservoir fracturing and a preparation method thereof. Background Art

[0002] Most of the domestic oil fields have entered the middle and late stages of water injection development. Due to the heterogeneity of the reservoir, the injected water easily breaks through and flushes along the high permeability layer, further increasing the permeability of the high permeability layer, and further expanding the heterogeneity of the reservoir, resulting in a large amount of water output from the oil wells, reduced production capacity, and poor economic benefits. Low-permeability and ultra-low-permeability reservoirs have gradually become the main body of oil field production succession. Due to the low pressure, low permeability, and imperfect development of natural fractures in low-permeability reservoirs, the development is difficult.

[0003] Hydraulic fracturing is a widely used reservoir transformation technology in the process of oil and gas field development. It can artificially form high-conductivity cracks around the wellbore, improve the flow environment of oil underground, slow down the interlayer and improve the utilization of oil layers, reduce the seepage resistance of the fluid near the wellbore, increase the oil leakage area of ​​the oil and gas well, and increase the production of oil and gas wells.

[0004] After the fracturing fluid is pressurized by the high-pressure pump injection equipment, it is pumped into the formation at high speed through the pipe string. Under high pressure and high speed conditions, the turbulence phenomenon of the fluid in the pipe is serious, and there is a large friction resistance between the fracturing fluid and the pipe wall. The friction resistance of the fluid limits the flow of the fluid in the pipeline, resulting in a decrease in pipeline output and an increase in energy loss. Therefore, it is necessary to add a drag reducing agent to the fracturing fluid to reduce the impact of friction resistance and improve construction efficiency.

[0005] CN103694984A discloses a shale gas acid fracturing drag reducer and a preparation method thereof. The present invention mixes monomer acrylic acid with 2-acrylamide-2-methylpropane sulfonic acid, dissolves in water, then adds acrylamide, and finally adds disodium ethylenediaminetetraacetate to prepare an aqueous phase; mixes and dissolves a composite surfactant with a base oil to form an oil phase; then performs inverse emulsion polymerization of the oil phase and the aqueous phase to prepare a shale gas acid fracturing drag reducer. A large amount of acid-resistant monomers are introduced into the drag reducer, which greatly improves the acid resistance of the drag reducer; the drag reducer has a milky white emulsion appearance, high stability, is non-flammable, non-explosive, and safe to transport and store; the drag reducer dissolves quickly in water, does not form fish eyes, and meets the requirements of continuous mixing of shale gas acid fracturing; the drag reducer aqueous solution with a mass fraction of 0.2% can achieve a drag reduction rate of more than 70%. The drag reducer formula of the invention contains a large amount of organic solvents. After being injected into the formation, this fracturing fluid drag reducer will cause groundwater pollution and harm the environment, making it difficult to promote on a large scale.

[0006] CN103045226A discloses a drag reducing agent and a preparation method thereof, and a slickwater fracturing fluid using the drag reducing agent and a preparation method thereof. The drag reducing agent comprises 10% to 40% polyethylene oxide, 40% to 85% organic solvent, 0% to 10% nonionic surfactant, and 0% to 10% dispersant; the drag reducing agent comprises 0.05% to 0.2% drag reducing agent, 0.2% to 0.5% drainage agent, 1.0% to 3.0% anti-swelling agent, 0.1% to 0.3% bactericide, and the balance is clean water. The drag reducing agent of the invention can significantly reduce the friction resistance of the fracturing pipeline and near the wellbore, has low cost and good compatibility with formation water and other additives; the slickwater fracturing fluid using the drag reducing agent can maintain good drag reducing performance and thermal stability, and has a low drag reducing agent concentration, and has significant economic benefits for shale oil and gas reservoirs that require large-scale transformation. However, polyethylene oxide has poor shear resistance and will degrade during high-shear fracturing operations, resulting in decreased fracturing fluid viscosity and drag reduction performance. Summary of the invention

[0007] The present invention aims at the deficiencies of the prior art and provides a drag reducer for shale gas reservoir fracturing and a preparation method thereof. The present invention has the advantages of wide raw material sources, simple synthesis process and no by-products; at the same time, the present invention has the characteristics of high viscosity and high drag reduction rate, with an apparent viscosity of ≥200mPa.s at a concentration of 0.2wt%, and a drag reduction rate of ≥75%.

[0008] In order to achieve the above-mentioned object, one of the objects of the present invention is to disclose a drag reducer for shale gas reservoir fracturing, wherein the molecular structure of the drag reducer for shale gas reservoir fracturing is as follows:

[0009]

[0010] Where: a = 10000-100000;

[0011] b = 5000-100000;

[0012] c = 2000-40000;

[0013] d=2000-40000.

[0014] Preferably, the viscosity-average molecular weight of the drag reducer for shale gas reservoir fracturing is 10,000,000-20,000,000.

[0015] Another object of the present invention is to disclose a method for preparing the above-mentioned drag reducer for shale gas reservoir fracturing, and the specific steps of the preparation method are as follows:

[0016] (1) purging the reactor with nitrogen for 3-5 minutes, and slowly introducing nitrogen during the entire synthesis process to ensure that the reactants are isolated from oxygen as much as possible during the synthesis process; sequentially adding 5-allyl-3-methoxysalicylic acid methyl ester, methacryloylethyl sulfobetaine, 1-vinyl-3-methylimidazolium tetrafluoroborate, allyl dimethyl (4-methoxyphenyl) silane, OP-10 (nonylphenol polyoxyethylene ether), sodium dodecyl sulfate, buffer salt, and deionized water, stirring at high speed, the stirring speed is 1000-1200 rpm, until all the raw materials are completely formed into a uniform emulsion, and adjusting the pH to 7-8 with sodium hydroxide solution;

[0017] (2) adjusting the stirring speed of the reactor to 300-400 rpm, and slowly raising the temperature. After the temperature reaches 40-45°C, stop raising the temperature and continue stirring; adding the initiator to the high-level tank and slowly dripping it into the reactor. After the dripping is complete, keep the temperature for 0.5-1h, raise the temperature of the reactor to 70-75°C, continue stirring for 2-3h, cool it to 40-50°C, and adjust the pH to 7-8 with sodium hydroxide solution to obtain a viscous liquid;

[0018] (3) The viscous liquid is granulated with a granulator to obtain a final product, a drag reducer, with a particle size of 1-4 mm.

[0019] In the present invention, preferably, the molar ratio of methacryloylethyl sulfobetaine, 1-vinyl-3-methylimidazolium tetrafluoroborate, allyldimethyl(4-methoxyphenyl)silane and 5-allyl-3-methoxysalicylic acid methyl ester is 0.2-0.6:0.1-0.3:0.1-0.3:1.

[0020] Preferably, in step (1), the mass ratio of OP-10, sodium dodecyl sulfate and methyl 5-allyl-3-methoxysalicylate is 0.1-0.2:0.05-0.1:1.

[0021] Preferably, in step (1), the buffer salt is one of sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, and diammonium hydrogen phosphate, and the mass ratio of the buffer salt to methyl 5-allyl-3-methoxysalicylate is 0.05-0.1:1.

[0022] Preferably, in step (1), the mass ratio of deionized water to methyl 5-allyl-3-methoxysalicylate is 8-10:1.

[0023] In the present invention, preferably, in step (2), the initiator is a mixture of persulfate and reducing sulfur-containing salt, and the mass ratio of the initiator to methyl 5-allyl-3-methoxysalicylate is 0.1-0.3:1.

[0024] More preferably, the persulfate is one of potassium persulfate, ammonium persulfate and sodium persulfate, and the reducing sulfur-containing salt is one of sodium bisulfite, sodium sulfite and sodium thiosulfate.

[0025] More preferably, the concentration of the persulfate is 8-10 wt %, and the concentration of the reducing sulfur-containing salt is 3-5 wt %.

[0026] The reaction equation for the synthesis of the drag reducer for shale gas reservoir fracturing of the present invention is as follows:

[0027]

[0028] The drag reducer of the invention is a quaternary high molecular polymer with 5-allyl-3-methoxysalicylic acid methyl ester, methacryloylethyl sulfobetaine, 1-vinyl-3-methylimidazolium tetrafluoroborate and allyl dimethyl (4-methoxyphenyl) silane as monomers. Among them, 5-allyl-3-methoxysalicylic acid methyl ester has a certain lipophilicity, which can reduce the friction resistance during the migration of fracturing fluid. It contains a benzene ring in its molecule and has a certain shear resistance. Methacryloylethyl sulfobetaine is a typical amphoteric surfactant, which can reduce the oil-water interfacial tension and reduce the friction resistance during the migration of fracturing fluid. 1-vinyl-3-methylimidazolium tetrafluoroborate and allyl dimethyl (4-methoxyphenyl) silane are special fluorine-containing and silicon-containing surfactants, which have low surface tension and interfacial tension that ordinary surfactants cannot match, and can greatly reduce the friction resistance during the migration of fracturing fluid. The latter contains a benzene ring in its molecule and has a certain shear resistance. OP-10 and sodium dodecyl sulfate are conventional nonionic and anionic surfactants, which can improve the polymerization quality of the product, increase the molecular weight and uniformity, thereby increasing the viscosity of the product, and at the same time can further enhance the drag reduction effect.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] (1) The drag reducer for shale gas reservoir fracturing of the present invention is synthesized by a one-pot method, the synthesis process is simple, there are no by-products, and it is safe and environmentally friendly;

[0031] (2) The drag reducer for shale gas reservoir fracturing of the present invention has the characteristic of high apparent viscosity. Under the condition of temperature of 30°C, the apparent viscosity of 0.2wt% concentration is ≥200mPa.s;

[0032] (3) The drag reducing agent for shale gas reservoir fracturing of the present invention has a good drag reducing effect, and the drag reducing rate at a concentration of 0.3wt% is ≥75%. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0034] Example 1

[0035] (1) The reactor was purged with nitrogen for 3 min, and nitrogen was slowly introduced during the entire synthesis process to ensure that the reactants were isolated from oxygen as much as possible during the synthesis process. 0.5 mol 5-allyl-3-methoxysalicylic acid methyl ester, 0.1 mol methacryloylethyl sulfobetaine, 0.05 mol 1-vinyl-3-methylimidazolium tetrafluoroborate, 0.15 mol allyldimethyl (4-methoxyphenyl) silane, 11.1 g OP-10, 11.1 g sodium dodecyl sulfate, 5.6 g sodium dihydrogen phosphate, and 888 g deionized water were added in sequence, and stirred at a high speed of 1000 rpm until all the raw materials completely became a uniform emulsion, and the pH was adjusted to 7-8 with a 4 wt % sodium hydroxide solution.

[0036] (2) The stirring speed of the reactor was adjusted to 300 rpm, and the temperature was slowly raised. After the temperature reached 40°C, the temperature was stopped and the stirring was continued. 11.1 g of initiator was added to the high-level tank. The initiator was an aqueous solution containing 10 wt% potassium persulfate and 5 wt% sodium bisulfite. The initiator was slowly added dropwise to the reactor. After the addition was completed, the temperature was kept for 0.5 h. The reactor was heated to 71°C, and the stirring was continued for 2 h. The temperature was lowered to 45°C, and the pH was adjusted to 7-8 with 5 wt% sodium hydroxide solution to obtain a viscous liquid.

[0037] (3) The viscous liquid is granulated with a granulator to obtain a particle size of 1-4 mm to obtain the final product, drag reducer T1.

[0038] Example 2

[0039] (1) The reactor was purged with nitrogen for 5 min, and nitrogen was slowly introduced during the entire synthesis process to ensure that the reactants were isolated from oxygen as much as possible during the synthesis process. 0.5 mol 5-allyl-3-methoxysalicylic acid methyl ester, 0.3 mol methacryloylethyl sulfobetaine, 0.07 mol 1-vinyl-3-methylimidazolium tetrafluoroborate, 0.13 mol allyldimethyl (4-methoxyphenyl) silane, 14.2 g OP-10, 10.3 g sodium dodecyl sulfate, 7.8 g sodium dihydrogen phosphate, and 918 g deionized water were added in sequence, and stirred at a high speed of 1200 rpm until all the raw materials completely became a uniform emulsion, and the pH was adjusted to 7-8 with a 5 wt % sodium hydroxide solution.

[0040] (2) The stirring speed of the reactor was adjusted to 400 rpm, and the temperature was slowly raised. After the temperature reached 45°C, the temperature was stopped and the stirring was continued. 17.2 g of initiator was added to the high-level tank. The initiator was an aqueous solution containing 8 wt% potassium persulfate and 3 wt% sodium sulfite. The initiator was slowly added dropwise to the reactor. After the addition was completed, the temperature was kept for 0.6 h. The reactor was heated to 74°C, and the stirring was continued for 3 h. The temperature was lowered to 48°C, and the pH was adjusted to 7-8 with 3 wt% sodium hydroxide solution to obtain a viscous liquid.

[0041] (3) The viscous liquid is granulated with a granulator to obtain a particle size of 1-4 mm to obtain the final product, drag reducer T2.

[0042] Example 3

[0043] (1) The reactor was purged with nitrogen for 3 min, and nitrogen was slowly introduced during the entire synthesis process to ensure that the reactants were isolated from oxygen as much as possible during the synthesis process. 0.5 mol 5-allyl-3-methoxysalicylic acid methyl ester, 0.15 mol methacryloylethyl sulfobetaine, 0.09 mol 1-vinyl-3-methylimidazolium tetrafluoroborate, 0.12 mol allyldimethyl (4-methoxyphenyl) silane, 12.8 g OP-10, 9.6 g sodium dodecyl sulfate, 8.1 g sodium dihydrogen phosphate, and 939 g deionized water were added in sequence, and stirred at a high speed of 1000 rpm until all the raw materials completely became a uniform emulsion, and the pH was adjusted to 7-8 with a 6 wt % sodium hydroxide solution.

[0044] (2) The stirring speed of the reactor was adjusted to 350 rpm, and the temperature was slowly raised. After the temperature reached 45°C, the temperature was stopped and the stirring was continued. 15.4 g of initiator was added to the high-level tank. The initiator was an aqueous solution containing 10 wt% potassium persulfate and 3 wt% sodium thiosulfate. The initiator was slowly added dropwise to the reactor. After the addition was completed, the temperature was kept for 0.7 h. The reactor was heated to 75°C, and the stirring was continued for 2.5 h. The temperature was lowered to 47°C, and the pH was adjusted to 7-8 with 4 wt% sodium hydroxide solution to obtain a viscous liquid.

[0045] (3) The viscous liquid is granulated with a granulator to obtain a particle size of 1-4 mm to obtain the final product, drag reducer T3.

[0046] Example 4

[0047] (1) The reactor was purged with nitrogen for 5 min, and nitrogen was slowly introduced during the entire synthesis process to ensure that the reactants were isolated from oxygen as much as possible during the synthesis process. 0.5 mol 5-allyl-3-methoxysalicylic acid methyl ester, 0.2 mol methacryloylethyl sulfobetaine, 0.1 mol 1-vinyl-3-methylimidazolium tetrafluoroborate, 0.1 mol allyldimethyl (4-methoxyphenyl) silane, 15.4 g OP-10, 7.6 g sodium dodecyl sulfate, 11.1 g potassium dihydrogen phosphate, and 968 g deionized water were added in sequence, and stirred at high speed at a stirring speed of 1200 rpm until all the raw materials completely became a uniform emulsion, and the pH was adjusted to 7-8 with a 5 wt % sodium hydroxide solution.

[0048] (2) The stirring speed of the reactor was adjusted to 320 rpm, and the temperature was slowly raised. After the temperature reached 40°C, the temperature was stopped and the stirring was continued. 21.4 g of initiator was added to the high-level tank. The initiator was an aqueous solution containing 9 wt% ammonium persulfate and 4 wt% sodium bisulfite. The initiator was slowly added dropwise to the reactor. After the addition was completed, the temperature was kept for 1 hour. The reactor was heated to 72°C, and the stirring was continued for 2.3 hours. The temperature was lowered to 43°C, and the pH was adjusted to 7-8 with 5 wt% sodium hydroxide solution to obtain a viscous liquid.

[0049] (3) The viscous liquid is granulated with a granulator to obtain a particle size of 1-4 mm to obtain the final product, drag reducer T4.

[0050] Example 5

[0051] (1) The reactor was purged with nitrogen for 4 min, and nitrogen was slowly introduced during the entire synthesis process to ensure that the reactants were isolated from oxygen as much as possible during the synthesis process. 0.5 mol 5-allyl-3-methoxysalicylic acid methyl ester, 0.25 mol methacryloylethyl sulfobetaine, 0.12 mol 1-vinyl-3-methylimidazolium tetrafluoroborate, 0.09 mol allyldimethyl (4-methoxyphenyl) silane, 20.2 g OP-10, 8.2 g sodium dodecyl sulfate, 10.5 g diammonium phosphate, and 1042 g deionized water were added in sequence, and stirred at a high speed of 1100 rpm until all the raw materials completely became a uniform emulsion, and the pH was adjusted to 7-8 with a 6 wt % sodium hydroxide solution.

[0052] (2) The stirring speed of the reactor was adjusted to 360 rpm, and the temperature was slowly raised. After the temperature reached 42°C, the temperature was stopped and the stirring was continued. 24.7 g of initiator was added to the high-level tank. The initiator was an aqueous solution containing 10 wt% sodium persulfate and 4 wt% sodium sulfite. The initiator was slowly added dropwise to the reactor. After the addition was completed, the temperature was kept for 0.8 h. The reactor was heated to 73°C, and the stirring was continued for 2.6 h. The temperature was lowered to 42°C, and the pH was adjusted to 7-8 with 3 wt% sodium hydroxide solution to obtain a viscous liquid.

[0053] (3) The viscous liquid is granulated with a granulator to obtain a particle size of 1-4 mm to obtain the final product, drag reducer T5.

[0054] Example 6

[0055] (1) The reactor was purged with nitrogen for 3 min, and nitrogen was slowly introduced during the entire synthesis process to ensure that the reactants were isolated from oxygen as much as possible during the synthesis process. 0.5 mol 5-allyl-3-methoxysalicylic acid methyl ester, 0.15 mol methacryloylethyl sulfobetaine, 0.13 mol 1-vinyl-3-methylimidazolium tetrafluoroborate, 0.05 mol allyl dimethyl (4-methoxyphenyl) silane, 22.2 g OP-10, 6.3 g sodium dodecyl sulfate, 6.4 g disodium hydrogen phosphate, and 1068 g deionized water were added in sequence, and stirred at high speed at a stirring speed of 1050 rpm until all the raw materials completely became a uniform emulsion, and the pH was adjusted to 7-8 with a 4 wt % sodium hydroxide solution.

[0056] (2) The stirring speed of the reactor was adjusted to 380 rpm, and the temperature was slowly raised. After the temperature reached 43°C, the temperature was stopped and the stirring was continued. 25.9 g of initiator was added to the high-level tank. The initiator was an aqueous solution containing 8 wt% ammonium persulfate and 3 wt% sodium thiosulfate. The initiator was slowly added dropwise to the reactor. After the addition was completed, the temperature was kept for 0.6 h. The reactor was heated to 72°C, and the stirring was continued for 2.7 h. The temperature was lowered to 45°C, and the pH was adjusted to 7-8 with 4 wt% sodium hydroxide solution to obtain a viscous liquid.

[0057] (3) The viscous liquid is granulated with a granulator to obtain a particle size of 1-4 mm to obtain the final product, drag reducer T6.

[0058] Example 7

[0059] (1) The reactor was purged with nitrogen for 5 min, and nitrogen was slowly introduced during the entire synthesis process to ensure that the reactants were isolated from oxygen as much as possible during the synthesis process. 0.5 mol 5-allyl-3-methoxysalicylic acid methyl ester, 0.2 mol methacryloylethyl sulfobetaine, 0.14 mol 1-vinyl-3-methylimidazolium tetrafluoroborate, 0.07 mol allyl dimethyl (4-methoxyphenyl) silane, 17.9 g OP-10, 5.6 g sodium dodecyl sulfate, 7.1 g dipotassium hydrogen phosphate, and 1095 g deionized water were added in sequence, and stirred at high speed at 1150 rpm until all the raw materials completely became a uniform emulsion, and the pH was adjusted to 7-8 with 5 wt% sodium hydroxide solution.

[0060] (2) The stirring speed of the reactor was adjusted to 350 rpm, and the temperature was slowly raised. After the temperature reached 44°C, the temperature was stopped and the stirring was continued. 30.2 g of initiator was added to the high-level tank. The initiator was an aqueous solution containing 9 wt% sodium persulfate and 4 wt% sodium bisulfite. The initiator was slowly added dropwise to the reactor. After the addition was completed, the temperature was kept for 0.9 h. The reactor was heated to 70°C, and the stirring was continued for 2 h. The temperature was lowered to 50°C, and the pH was adjusted to 7-8 with 5 wt% sodium hydroxide solution to obtain a viscous liquid.

[0061] (3) The viscous liquid is granulated with a granulator to obtain a particle size of 1-4 mm to obtain the final product, drag reducer T7.

[0062] Example 8

[0063] (1) The reactor was purged with nitrogen for 4 min, and nitrogen was slowly introduced during the entire synthesis process to ensure that the reactants were isolated from oxygen as much as possible during the synthesis process. 0.5 mol 5-allyl-3-methoxysalicylic acid methyl ester, 0.25 mol methacryloylethyl sulfobetaine, 0.15 mol 1-vinyl-3-methylimidazolium tetrafluoroborate, 0.08 mol allyldimethyl (4-methoxyphenyl) silane, 19.8 g OP-10, 7.3 g sodium dodecyl sulfate, 8.8 g diammonium hydrogen phosphate, and 1110 g deionized water were added in sequence, and stirred at high speed at a stirring speed of 1100 rpm until all the raw materials completely became a uniform emulsion, and the pH was adjusted to 7-8 with a 3 wt % sodium hydroxide solution.

[0064] (2) The stirring speed of the reactor was adjusted to 330 rpm, and the temperature was slowly raised. After the temperature reached 41°C, the temperature was stopped and the stirring was continued. 33.3 g of initiator was added to the high-level tank. The initiator was an aqueous solution containing 8 wt% sodium persulfate and 5 wt% sodium sulfite. The initiator was slowly added dropwise to the reactor. After the addition was completed, the temperature was kept for 0.7 h. The reactor was heated to 75°C and stirred for 3 h. The temperature was lowered to 40°C. The pH was adjusted to 7-8 with 4 wt% sodium hydroxide solution to obtain a viscous liquid.

[0065] (3) The viscous liquid is granulated with a granulator to obtain a particle size of 1-4 mm to obtain the final product, drag reducer T8.

[0066] Example 9 Apparent Viscosity Test

[0067] The apparent viscosity of the drag reducer of the present invention was tested at a concentration of 0.2 wt %, and the method was referred to 7.1 of SY / T 6376-2008 "General Technical Requirements for Fracturing Fluids". The apparent viscosity was compared with the drag reducer for fracturing produced by Zhengzhou Derong Technology Co., Ltd., and the test results are shown in Table 1.

[0068] It can be seen from Table 1 that the apparent viscosity of the drag reducers T1, T2, T3, T4, T5, T6, T7 and T8 of the present invention at a concentration of 0.2wt% is greater than 200mPa.s, among which T8 reaches a maximum of 218mPa.s, while the apparent viscosity of the comparative sample is 95mPa.s, which is significantly lower than that of the present invention.

[0069] Example 10 Drag reduction rate test

[0070] The drag reduction rate of the drag reducer of the present invention was tested at 0.1wt%, 0.2wt% and 0.3wt% concentrations, and the method was referred to 7.13.1 of SY / T 6376-2008 "General Technical Requirements for Fracturing Fluids". The drag reduction rate was compared with the fracturing drag reducer of Zhengzhou Derong Technology Co., Ltd., and the test results are shown in Table 1.

[0071] Table 1 Apparent viscosity and drag reduction test results

[0072]

[0073]

[0074] From Table 1 we can see that:

[0075] (1) The drag reduction rates of the drag reducers T1, T2, T3, T4, T5, T6, T7 and T8 of the present invention at a concentration of 0.1wt% are all greater than 50%, among which T8 has a maximum of 62%, while the drag reduction rate of the comparative sample is 40%, which is significantly lower than that of the present invention;

[0076] (2) The drag reduction rates of the drag reducers T1, T2, T3, T4, T5, T6, T7 and T8 of the present invention at a concentration of 0.2 wt% are all greater than 60%, with T8 reaching a maximum of 72%, while the drag reduction rate of the comparative sample is 49%, which is significantly lower than that of the present invention;

[0077] (3) The drag reduction rates of the drag reducers T1, T2, T3, T4, T5, T6, T7 and T8 of the present invention at a concentration of 0.3 wt% are all greater than 75%, among which T8 reaches a maximum of 82%, while the drag reduction rate of the comparative sample is 53%, which is significantly lower than that of the present invention.

[0078] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a drag reducer for shale gas reservoir fracturing, characterized in that: The specific steps of the preparation method are as follows: (1) The reactor was purged with nitrogen for 3-5 minutes, and nitrogen was slowly introduced during the entire synthesis process to ensure that the reactants were isolated from oxygen as much as possible during the synthesis process; 5-allyl-3-methoxysalicylic acid methyl ester, methacryloylethyl sulfobetaine, 1-vinyl-3-methylimidazolium tetrafluoroborate, allyl dimethyl (4-methoxyphenyl) silane, OP-10, sodium dodecyl sulfate, buffer salt, and deionized water were added in sequence, and stirred at a high speed of 1000-1200 rpm until all the raw materials were completely formed into a uniform emulsion, and the pH was adjusted to 7-8 with sodium hydroxide solution; (2) Adjust the stirring speed of the reactor to 300-400 rpm, and slowly increase the temperature. When the temperature reaches 40-45°C, stop increasing the temperature and continue stirring. Add the initiator to the high-level tank and slowly drip it into the reactor. After the dripping is complete, keep the temperature for 0.5-1h, heat the reactor to 70-75°C, continue stirring for 2-3h, cool it to 40-50°C, and adjust the pH to 7-8 with sodium hydroxide solution to obtain a viscous liquid. (3) Granulating the viscous liquid with a granulator to obtain a particle size of 1-4 mm to obtain a final product, a drag reducer; The molar ratio of methacryloylethyl sulfobetaine, 1-vinyl-3-methylimidazolium tetrafluoroborate, allyl dimethyl (4-methoxyphenyl) silane and 5-allyl-3-methoxysalicylic acid methyl ester is 0.2-0.6: 0.1-0.3: 0.1-0.3: 1; The molecular structural formula of the drag reducer is as follows: , Where: a=10000-100000; b=5000-100000； c=2000-40000； d=2000-40000； The viscosity average molecular weight of the drag reducer is 10,000,000-20,000,000.

2. The method for preparing a drag reducer for shale gas reservoir fracturing according to claim 1, characterized in that: The mass ratio of OP-10, sodium dodecyl sulfate and methyl 5-allyl-3-methoxysalicylate in step (1) is 0.1-0.2:0.05-0.1:

1.

3. The method for preparing a drag reducer for shale gas reservoir fracturing according to claim 1, characterized in that: The buffer salt described in step (1) is one of sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, and diammonium hydrogen phosphate, and the mass ratio of the buffer salt to 5-allyl-3-methoxysalicylic acid methyl ester is 0.05-0.1:

1.

4. The method for preparing a drag reducer for shale gas reservoir fracturing according to claim 1, characterized in that: The initiator described in step (2) is a mixture of persulfate and reducing sulfur-containing salt, and the mass ratio of the initiator to 5-allyl-3-methoxysalicylic acid methyl ester is 0.1-0.3:

1.

5. The method for preparing a drag reducer for shale gas reservoir fracturing according to claim 4, characterized in that: The persulfate is one of potassium persulfate, ammonium persulfate and sodium persulfate, and the reducing sulfur-containing salt is one of sodium bisulfite, sodium sulfite and sodium thiosulfate.

6. The method for preparing a drag reducer for shale gas reservoir fracturing according to claim 4, characterized in that: The concentration of the persulfate is 8-10wt%, and the concentration of the reducing sulfur-containing salt is 3-5wt%.

7. A drag reducer for shale gas reservoir fracturing, characterized in that: The molecular structural formula of the drag reducer is as follows: , Where: a=10000-100000; b=5000-100000； c=2000-40000； d=2000-40000。 8. The drag reducer for shale gas reservoir fracturing according to claim 7, characterized in that: The viscosity average molecular weight of the drag reducer is 10,000,000-20,000,000.

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