Supramolecular micro-nano bubble fracturing fluid and preparation method thereof

Abstract

The application discloses a kind of supramolecular micro-nano bubble fracturing fluids and preparation method thereof, it is related to oil exploitation field.The supramolecular micro-nano bubble fracturing fluid is mixed after micro-nano bubble water is sealed and stirred with supramolecular polymer drag reducer, then modified nano silicon dioxide is added and mixed, and is prepared.Therein, modified nano silicon dioxide bridges micro-nano bubble water and supramolecular polymer drag reducer by electrostatic interaction and hydrogen bond interaction, under the synergistic effect of modified nano silicon dioxide, micro-nano bubble water and supramolecular polymer drag reducer, so that the supramolecular micro-nano bubble fracturing fluid prepared has excellent drag reduction rate, temperature resistance and shear resistance, sand carrying capacity and the like.

Description

Technical Field

[0001] This invention relates to the field of oil extraction, specifically to a supramolecular micro / nano bubble fracturing fluid and its preparation method. Background Technology

[0002] Shale and tight oil reservoirs are typical unconventional tight reservoirs, generally characterized by poor porosity, permeability, and biomass, and strong microscopic heterogeneity, with significant differences in reservoir quality between vertical and horizontal directions. Currently, the mainstream development method for these reservoirs is horizontal well volumetric fracturing. However, due to the small pore throats and complex structure of the reservoirs, they are extremely sensitive to fracturing fluids. During fracturing operations, problems such as water-locking damage, clay mineral expansion, and pore throat microparticle blockage easily occur, significantly impairing the reservoir's permeability. Furthermore, the strong heterogeneity of the reservoirs leads to vastly different activation effects across different sections of the horizontal well. High-permeability sections can be effectively activated, while low-permeability tight sections are difficult to activate effectively, resulting in an uneven contribution of production capacity across sections and an overall low level of reservoir activation.

[0003] Fracturing fluid, used in fracturing technology, is a heterogeneous and unstable chemical system composed of various additives in specific proportions. It is the working fluid used to fracture and stimulate oil and gas reservoirs. Its main function is to transfer the high pressure generated by surface equipment to the formation, causing it to fracture and transport proppant along the fractures. The percolators in fracturing fluid are usually surfactants, which can reduce the interfacial activity and surface activity of oil and water, improve capillary self-adsorption, and synergistically displace crude oil into high-permeability fractures, thereby carrying the crude oil out during waterflooding. However, these percolators have poor salt resistance, are prone to hydrolysis and failure, and have insufficient resistance to formation temperatures, resulting in significant formation adsorption losses and limiting the performance of the fracturing fluid.

[0004] Therefore, how to develop a fracturing fluid with superior performance to meet the needs of high-salt and high-temperature formation environments in oil extraction is a question worth exploring further. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a supramolecular micro / nano bubble fracturing fluid and its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A supramolecular micro / nano bubble fracturing fluid, the preparation method of which includes the following steps:

[0008] Step (1): Heat and stir the hydrophobic functional monomer, add OP-10 and n-butanol, continue stirring, add deionized water dropwise, and after the addition is complete, shear at high speed and then perform high pressure homogenization to obtain a mixed emulsion;

[0009] Step (2): Heat deionized water, add 2-acrylamido-2-methylpropanesulfonic acid, stir, add acrylamide, continue stirring, cool, adjust the pH of the system, introduce protective gas, add initiator solution, seal, heat and stir, cool down, add mixed emulsion dropwise, add initiator solution again, stir evenly, add hydroquinone, cool, extrude through a sieve, dry, grind, sieve, and obtain supramolecular polymer drag reducer;

[0010] Step (3): Cool the compressed air, filter it, pass it through a hollow fiber membrane for membrane separation, then heat it, and then react it with hydrogen in the Pd / Al2O3 catalyst layer to remove oxygen. Finally, dehydrate it to obtain oxygen-reduced air.

[0011] Step (4): Mix water and AOS surfactant, stir, introduce oxygen-reduced air, continue stirring, then homogenize, let stand, pump into microchannel reactor for reaction, control the discharge temperature, let stand, and obtain micro-nano bubble water.

[0012] Step (5): Stir the micro-nano bubble water in a closed container, add the supramolecular polymer drag reducer, and continue stirring; adjust the stirring speed, stir evenly, add modified nano silica, disperse and stir by ultrasonication; let stand to obtain supramolecular micro-nano bubble fracturing fluid.

[0013] A supramolecular micro / nano bubble fracturing fluid, the preparation method of which includes the following specific steps:

[0014] Step (1): Heat the hydrophobic functional monomer to 55-60℃, stir for 5-10 min, add OP-10 and n-butanol, continue stirring for 10-15 min, add deionized water at 44-46℃ dropwise over 20-25 min, after the addition is complete, shear at high speed for 5-7 min, and then homogenize under high pressure at 150-200 bar for 6-8 min to obtain a mixed emulsion;

[0015] Furthermore, the hydrophobic functional monomer is obtained by mixing octadecyl acrylate and octadecyl methacrylate in a mass ratio of 1-3:1; the ratio of hydrophobic functional monomer, OP-10, n-butanol, and deionized water is 5-10g:0.3-0.5g:5-7g:65-75mL.

[0016] Step (2): Heat deionized water to 40-45℃, add 2-acrylamido-2-methylpropanesulfonic acid, stir for 5-10 min, add acrylamide, continue stirring for 30-40 min, cool, adjust the pH of the system to 7.0-7.5, introduce protective gas, add initiator solution, seal, stir at 48-52℃ and 60-80 rpm for 2-2.2 h, cool to 43-45℃, add mixed emulsion dropwise, the mixed emulsion is added dropwise within 40-50 min, then add initiator solution, stir at 150-200 rpm for 3-3.2 h, add hydroquinone, cool, extrude through a sieve, dry, grind, and sieve to obtain supramolecular polymer drag reducer;

[0017] Furthermore, the ratio of deionized water, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, initiator solution, mixed emulsion, and hydroquinone is 80-85 mL: 4-6 g: 10-15 g: 1-1.5 mL: 30-35 mL: 0.10-0.12 g; the initiator solution is prepared by mixing ammonium persulfate and deionized water at 0-5℃ in a ratio of 1 g: 5-7 mL, and the initiator solution is added in two equal volumes.

[0018] Step (3): Start the oil-free screw air compressor to generate compressed air of 0.8-1.0MPa. After being cooled by a refrigerated dryer, the air passes through a three-stage filter and then enters a hollow fiber membrane for membrane separation. The air after membrane separation enters a heat exchanger and is heated to 120-130℃. Then it passes through a Pd / Al2O3 catalyst layer and hydrogen is added to the catalyst layer. After being dehydrated by a molecular sieve adsorption tower, oxygen-reduced air is obtained.

[0019] Furthermore, the filtration employs a three-stage filter, which consists of a first-stage filter, a second-stage filter, and a third-stage filter, with filtration accuracies of 1μm, 0.1μm, and 0.01μm, respectively.

[0020] Furthermore, the hydrogen flow rate satisfies the hydrogen to oxygen volume ratio of 2.5-3:1; the gas space velocity through the catalyst bed is 800-1000 h⁻¹. -1 .

[0021] Furthermore, the Pd / Al2O3 catalyst was prepared according to the preparation process of Example 1 of the invention patent with publication number CN102626618B.

[0022] Step (4): Mix water and AOS surfactant, stir for 5-7 minutes, introduce deoxygenated air, continue stirring for 20-30 minutes, transfer to a high-speed homogenizer, homogenize for 3-5 minutes, let stand for 2-4 minutes, and then enter the microchannel reactor through a high-pressure ceramic plunger pump. React for 1.8-2.2 seconds, start the plate heat exchanger to control the discharge temperature to 28-32℃, and let stand for 5-7 minutes to obtain micro-nano bubble water;

[0023] Furthermore, the volume ratio of water to deoxygenated air is 9:1-1.2; the mass ratio of AOS surfactant to the total volume of water and deoxygenated air is 0.1-0.3g:100mL; the bubble diameter of the micro-nano bubble water is ≤500nm, the stability time is ≥48h, and the Zeta potential is ≤-7mV.

[0024] Step (5): At room temperature, stir the micro-nano bubble water at 300-400 rpm in a closed container for 5-7 minutes. While maintaining the closed stirring state, add the supramolecular polymer drag reducer in 5 portions, with the same mass of supramolecular polymer drag reducer added each time, every 30-40 seconds. After adding the supramolecular polymer drag reducer, continue stirring for 20-25 minutes. Adjust the stirring speed to 200-250 rpm and stir for 5-7 minutes. Add the modified nano silica, disperse it ultrasonically and stir for 35-45 minutes. Let it stand for 3-5 minutes to obtain the supramolecular micro-nano bubble fracturing fluid.

[0025] Furthermore, the ratio of micro-nano bubble water, supramolecular polymer drag reducer, and modified nano silica is 100mL: 0.05-0.10g: 0.15-0.20g.

[0026] Furthermore, the modified nano-silica is prepared by the following steps:

[0027] Step A1: N-methylimidazole, 8-bromooctanol and anhydrous ethanol are mixed, stirred, cooled and allowed to stand, filtered, washed and dried under vacuum to obtain product 1;

[0028] Step A2: Adjust the pH of the ethanol aqueous solution, add KH560, stir, add nano silica dispersion, heat and stir, cool, filter, wash, and vacuum dry to obtain product 2;

[0029] Step A3: Mix product 2 and acetonitrile aqueous solution, disperse and stir by ultrasonication, adjust the pH of the system, add product 1, heat and stir to react, cool, filter, wash, and vacuum dry to obtain modified nano silica.

[0030] Furthermore, the preparation method of modified nano-silica includes the following specific steps:

[0031] Step A1: Mix N-methylimidazole, 8-bromooctanol and anhydrous ethanol, stir for 12-13 h, cool to 0-5℃ and stand for 3-4 h, filter, wash and vacuum dry to obtain product 1;

[0032] Furthermore, the ratio of N-methylimidazole, 8-bromooctanol, and anhydrous ethanol is 4.5-5g: 10.5-11g: 35-40mL.

[0033] In step A1, N-methylimidazole reacts with 8-bromooctanol at 20-25°C to generate a primary alcohol containing an imidazole quaternary ammonium salt, i.e., product 1.

[0034] Step A2: Adjust the pH of the ethanol aqueous solution to 5-5.5, add KH560, stir for 0.5-1 h, add nano silica dispersion, heat to 55-60℃, stir for 4-5 h, cool, filter, wash, and vacuum dry to obtain product 2;

[0035] Furthermore, the ratio of the amount of ethanol aqueous solution, KH560, and nano silica dispersion is 100-105 mL: 0.4-0.6 g: 105-110 mL.

[0036] Furthermore, the ethanol-water solution is obtained by mixing ethanol and water in a volume ratio of 8-9:1-2; the volume fraction of ethanol is 95%.

[0037] Furthermore, the nano-silica dispersion is obtained by mixing nano-silica and anhydrous ethanol at a ratio of 10-11g:200mL, stirring for 5-10min, and then ultrasonically dispersing for 20-25min.

[0038] In step A2, KH560 modifies the surface of nano-silica to obtain nano-silica with epoxy groups on the surface, i.e., product 2.

[0039] Step A3: Mix product 2 and acetonitrile aqueous solution, disperse by ultrasonication and stir for 10-15 min, adjust the pH of the system to 7.5-8.5, add product 1, heat to 65-70℃, stir and react for 7-7.5 h, cool, filter, wash, and vacuum dry to obtain modified nano silica;

[0040] Furthermore, the ratio of product 2, acetonitrile aqueous solution, and product 1 is 7-8g: 190-200mL: 1-1.5g; the acetonitrile aqueous solution is obtained by mixing anhydrous acetonitrile and deionized water in a volume ratio of 8-9:1.

[0041] In step A3, the epoxy group in product 2 undergoes a ring-opening reaction with the primary alcohol hydroxyl group in product 1 to obtain nano-silica containing hydroxyl groups and imidazole quaternary ammonium salt, i.e., modified nano-silica.

[0042] The supramolecular micro-nano bubble fracturing fluid prepared by the above-mentioned method is a supramolecular micro-nano bubble fracturing fluid.

[0043] The beneficial effects of this invention are:

[0044] This invention provides a supramolecular micro / nano bubble fracturing fluid and its preparation method. The supramolecular micro / nano bubble fracturing fluid is prepared from micro / nano bubble water, a supramolecular polymer drag-reducing agent, and modified nano-silica as raw materials. The micro / nano bubble water is prepared using water, AOS surfactant, and oxygen-reduced air as raw materials through high-pressure microchannel multiphase flow nanotechnology. Its Zeta potential is ≤-7mV, indicating that the surface of the micro / nano bubble water is negatively charged. The supramolecular polymer drag-reducing agent is obtained by polymerizing acrylamide as the main monomer, combined with a hydrophobic functional monomer (obtained by mixing octadecyl acrylate and octadecyl methacrylate) and an anionic monomer (2-acrylamido-2-methylpropanesulfonic acid) under the action of an initiator. This supramolecular polymer drag-reducing agent has a negatively charged surface and exhibits high drag reduction and high viscoelasticity.

[0045] This invention first reacts N-methylimidazolium and 8-bromooctanol to generate a primary alcohol containing imidazolium quaternary ammonium salt, i.e., product 1; then, the surface of nano-silica is modified with KH560 to obtain nano-silica with epoxy groups on the surface, i.e., product 2; then, under conditions of pH 7.5-8.5 and catalysis of the imidazolium quaternary ammonium salt in product 1, the hydroxyl groups of the primary alcohol in product 1 undergo a ring-opening reaction with the epoxy groups of product 2 to obtain nano-silica containing hydroxyl groups and imidazolium quaternary ammonium salt, i.e., modified nano-silica. The ether bond formed by the ring-opening reaction of the hydroxyl groups of the primary alcohol in product 1 and the epoxy groups of product 2 has strong hydrolysis resistance and is more suitable for the long-term immersion environment of fracturing fluid. Modified nano-silica is not prone to agglomeration and has good dispersibility in fracturing fluid. Furthermore, the imidazole quaternary ammonium salt on its surface is positively charged, which can bridge supramolecular polymer drag reducers and micro / nano bubble water through electrostatic interaction, thereby improving the stability of micro / nano bubble water and forming a stable and homogeneous fracturing fluid. Its hydroxyl groups can form hydrogen bonds with supramolecular polymer drag reducers to build a dense and stable cross-linked network. Through the synergistic effect of supramolecular polymer drag reducers, micro / nano bubble water, and modified nano-silica, the drag reduction effect, bubble stability, and proppant carrying capacity of fracturing fluid can be improved. It can still maintain excellent performance under conditions such as formation temperature, high salinity, and long-term well stagnation. Detailed Implementation

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Example 1

[0048] The preparation method of modified nano-silica includes the following steps:

[0049] Step A1: Mix N-methylimidazole, 8-bromooctanol, and anhydrous ethanol, stir at room temperature for 12 h, cool to 0 °C and stand for 3 h, filter, wash the filter cake twice with anhydrous ethanol at 5 °C, and vacuum dry at room temperature for 12 h to obtain product 1; the ratio of N-methylimidazole, 8-bromooctanol, and anhydrous ethanol is 4.5 g: 10.5 g: 35 mL.

[0050] Step A2: Adjust the pH of the ethanol-water solution to 5 with a 10% acetic acid solution, add KH560, stir at room temperature for 0.5 h, add nano-silica dispersion, heat to 55℃, stir for 4 h, cool to room temperature, filter, wash three times with anhydrous ethanol, and vacuum dry at 45℃ for 13 h to obtain product 2; the volume ratio of ethanol-water solution, KH560, and nano-silica dispersion is 100 mL: 0.4 g: 105 mL; the ethanol-water solution is obtained by mixing ethanol and water in a volume ratio of 8:1; the volume fraction of ethanol is 95%; the nano-silica dispersion is obtained by mixing nano-silica (supplier: Wuhan Kemike Biomedical Technology Co., Ltd., 50 nm) and anhydrous ethanol in a volume ratio of 10 g: 200 mL, stirring at room temperature for 5 min, and then ultrasonically dispersing at 300 W for 20 min.

[0051] Step A3: Mix product 2 and acetonitrile aqueous solution, ultrasonically disperse and stir for 10 min at room temperature and 100 W power, adjust the pH of the system to 7.5 with 5% ammonia aqueous solution, add product 1, heat to 65℃ at a rate of 1℃ / min, stir and react for 7 h, cool to room temperature, filter, wash three times with anhydrous acetonitrile, and vacuum dry at 40℃ for 16 h to obtain modified nano silica; the ratio of product 2, acetonitrile aqueous solution and product 1 is 7 g: 190 mL: 1 g; the acetonitrile aqueous solution is obtained by mixing anhydrous acetonitrile and deionized water in a volume ratio of 8:1.

[0052] Example 2

[0053] The preparation method of modified nano-silica includes the following steps:

[0054] Step A1: N-methylimidazole, 8-bromooctanol, and anhydrous ethanol were mixed and stirred at room temperature for 12.5 h. The mixture was then cooled to 3 °C and allowed to stand for 3.5 h. After filtration, the filter cake was washed twice with anhydrous ethanol at 5 °C and dried under vacuum at room temperature for 12 h to obtain product 1. The ratio of N-methylimidazole, 8-bromooctanol, and anhydrous ethanol was 4.8 g: 10.8 g: 37 mL.

[0055] Step A2: Adjust the pH of the ethanol-water solution to 5.3 with a 10% acetic acid solution, add KH560, stir at room temperature for 0.8 h, add nano-silica dispersion, heat to 58℃, stir for 4.5 h, cool to room temperature, filter, wash three times with anhydrous ethanol, and vacuum dry at 45℃ for 13 h to obtain product 2; the volume ratio of ethanol-water solution, KH560, and nano-silica dispersion is 103 mL: 0.5 g: 107 mL; the ethanol-water solution is obtained by mixing ethanol and water in a volume ratio of 8.5:1.5; the volume fraction of ethanol is 95%; the nano-silica dispersion is obtained by mixing nano-silica (supplier: Wuhan Kemike Biomedical Technology Co., Ltd., 50 nm) and anhydrous ethanol in a volume ratio of 10.5 g: 200 mL, stirring at room temperature for 8 min, and then ultrasonically dispersing at 300 W for 23 min.

[0056] Step A3: Mix product 2 and acetonitrile aqueous solution, ultrasonically disperse and stir for 13 min at room temperature and 100 W power, adjust the pH of the system to 8.0 with 5% ammonia aqueous solution, add product 1, heat to 68℃ at a rate of 1.5℃ / min, stir and react for 7.3 h, cool to room temperature, filter, wash three times with anhydrous acetonitrile, and vacuum dry at 40℃ for 16 h to obtain modified nano-silica; the ratio of product 2, acetonitrile aqueous solution and product 1 is 7.5 g: 195 mL: 1.3 g; the acetonitrile aqueous solution is obtained by mixing anhydrous acetonitrile and deionized water in a volume ratio of 8.5:1.

[0057] Example 3

[0058] The preparation method of modified nano-silica includes the following steps:

[0059] Step A1: Mix N-methylimidazole, 8-bromooctanol, and anhydrous ethanol, stir at room temperature for 13 h, cool to 5 °C and stand for 4 h, filter, wash the filter cake twice with anhydrous ethanol at 5 °C, and vacuum dry at room temperature for 12 h to obtain product 1; the ratio of N-methylimidazole, 8-bromooctanol, and anhydrous ethanol is 5 g: 11 g: 40 mL.

[0060] Step A2: Adjust the pH of the ethanol-water solution to 5.5 with a 10% acetic acid solution, add KH560, stir at room temperature for 1 hour, add nano-silica dispersion, heat to 60°C, stir for 5 hours, cool to room temperature, filter, wash three times with anhydrous ethanol, and vacuum dry at 45°C for 13 hours to obtain product 2; the volume ratio of ethanol-water solution, KH560, and nano-silica dispersion is 105 mL: 0.6 g: 110 mL; the ethanol-water solution is obtained by mixing ethanol and water in a volume ratio of 9:2; the volume fraction of ethanol is 95%; the nano-silica dispersion is obtained by mixing nano-silica (supplier: Wuhan Kemike Biomedical Technology Co., Ltd., 50 nm) and anhydrous ethanol in a volume ratio of 11 g: 200 mL, stirring at room temperature for 10 minutes, and then ultrasonically dispersing at 300 W for 25 minutes.

[0061] Step A3: Mix product 2 and acetonitrile aqueous solution, ultrasonically disperse and stir for 15 min at room temperature and 100 W power, adjust the pH of the system to 8.5 with 5% ammonia aqueous solution, add product 1, heat to 70℃ at a rate of 2℃ / min, stir and react for 7.5 h, cool to room temperature, filter, wash three times with anhydrous acetonitrile, and vacuum dry at 40℃ for 16 h to obtain modified nano silica; the ratio of product 2, acetonitrile aqueous solution and product 1 is 8 g: 200 mL: 1.5 g; the acetonitrile aqueous solution is obtained by mixing anhydrous acetonitrile and deionized water in a volume ratio of 9:1.

[0062] Example 4

[0063] A supramolecular micro / nano bubble fracturing fluid, the preparation method of which includes the following specific steps:

[0064] Step (1): Heat the hydrophobic functional monomer to 55℃ and stir for 5 min. Add OP-10 and n-butanol, stir at 55℃ for 10 min, and add deionized water at 44℃ dropwise over 20 min. After the addition is complete, shear at 10000 rpm for 5 min, and then homogenize under high pressure at 150 bar and 55℃ for 6 min to obtain a mixed emulsion. The hydrophobic functional monomer is obtained by mixing octadecyl acrylate and octadecyl methacrylate in a mass ratio of 1:1. The ratio of hydrophobic functional monomer, OP-10, n-butanol, and deionized water is 5 g: 0.3 g: 5 g: 65 mL.

[0065] Step (2): Heat deionized water to 40℃, add 2-acrylamido-2-methylpropanesulfonic acid, stir at 40℃ for 5 min, add acrylamide, continue stirring for 30 min, cool to room temperature, add sodium bicarbonate to adjust the pH of the system to 7.0, purge with nitrogen, add initiator solution, seal, stir at 48℃ and 60 rpm for 2 h, cool to 43℃, add the mixed emulsion dropwise, the mixed emulsion is added dropwise within 40 min, then add initiator solution, stir at 150 rpm for 3 h, add hydroquinone. Cooled to 10°C in an ice-water bath at 0°C, extruded through a 2mm sieve, dried at 50°C for 12 hours, ground, and passed through an 80-mesh sieve to obtain a supramolecular polymer drag reducer; the ratio of deionized water, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, initiator solution, mixed emulsion, and hydroquinone was 80mL:4g:10g:1mL:30mL:0.10g; the initiator solution was prepared by mixing ammonium persulfate and 0°C deionized water at a ratio of 1g:5mL, and the initiator solution was added in two equal volumes.

[0066] Step (3): Start the oil-free screw air compressor to generate compressed air at 0.8 MPa. Cool the compressed air to -40°C using a refrigerated dryer, then pass it through a three-stage filter. The air then enters a hollow fiber membrane for membrane separation at an operating pressure of 0.75 MPa and a flow rate of 6 m / s. After membrane separation, the air enters a heat exchanger and is heated to 120°C. It then passes through a Pd / Al2O3 catalyst layer, to which hydrogen is added. The air is then dehydrated by a 4A-type molecular sieve adsorption tower to obtain oxygen-depleted air. The three-stage filter consists of a first-stage filter, a second-stage filter, and a third-stage filter. The filtration accuracies of the first-stage filter, second-stage filter, and third-stage filter are 1 μm, 0.1 μm, and 0.01 μm, respectively. The hydrogen flow rate satisfies a hydrogen to oxygen volume ratio of 2.5:1. The gas space velocity through the catalyst layer is 800 h⁻¹. -1 The Pd / Al2O3 catalyst was prepared according to the preparation process of Example 1 of the invention patent with reference to the announcement number CN102626618B.

[0067] Step (4): Mix water and AOS surfactant, stir in a closed container at 600 rpm for 5 min at room temperature, introduce deoxygenated air, continue stirring for 20 min, transfer to a high-speed homogenizer, homogenize at 9000 rpm for 3 min, let stand for 2 min, control the pressure to 30 MPa with a high-pressure ceramic plunger pump, and enter the microchannel reactor at a speed of 250 m / s. React for 1.8 s, start the plate heat exchanger to control the outlet temperature to 28 ℃, let stand for 5 min, and obtain micro-nano bubble water; the volume ratio of water to deoxygenated air is 9:1; the mass ratio of AOS surfactant to the total volume of water and deoxygenated air is 0.1 g: 100 mL; the bubble diameter of the micro-nano bubble water is 500 nm, the stabilization time is 48 h, and the Zeta potential is -7 mV.

[0068] Step (5): At room temperature, the micro-nano bubble water is stirred in a closed container at 300 rpm for 5 min. The stirring is maintained at 300 rpm. The supramolecular polymer drag reducer is added in 5 portions, with the same mass of supramolecular polymer drag reducer added each time, every 30 s. After adding the supramolecular polymer drag reducer, stirring is continued for 20 min. The stirring speed is adjusted to 200 rpm and stirred for 5 min. The modified nano silica obtained in Example 1 is added, and the mixture is ultrasonically dispersed at 200 W power and stirred at 250 rpm for 35 min. The mixture is allowed to stand for 3 min to obtain the supramolecular micro-nano bubble fracturing fluid. The ratio of the amount of micro-nano bubble water, supramolecular polymer drag reducer, and modified nano silica obtained in Example 1 is 100 mL: 0.05 g: 0.15 g.

[0069] Example 5

[0070] A supramolecular micro / nano bubble fracturing fluid, the preparation method of which includes the following specific steps:

[0071] Step (1): Heat the hydrophobic functional monomer to 58℃ and stir for 8 min. Add OP-10 and n-butanol, stir at 58℃ for 13 min, and add deionized water at 45℃ dropwise over 23 min. After the addition is complete, shear at 10000 rpm for 6 min, and then homogenize under high pressure at 180 bar and 58℃ for 7 min to obtain a mixed emulsion. The hydrophobic functional monomer is obtained by mixing octadecyl acrylate and octadecyl methacrylate in a mass ratio of 2:1. The ratio of hydrophobic functional monomer, OP-10, n-butanol, and deionized water is 8 g: 0.4 g: 6 g: 70 mL.

[0072] Step (2): Heat deionized water to 43°C, add 2-acrylamido-2-methylpropanesulfonic acid, stir at 43°C for 8 min, add acrylamide, continue stirring for 35 min, cool to room temperature, add sodium bicarbonate to adjust the pH of the system to 7.2, purge with nitrogen, add initiator solution, seal, stir at 50°C and 70 rpm for 2.1 h, cool to 44°C, add the mixed emulsion dropwise, the mixed emulsion is added dropwise within 45 min, then add initiator solution, stir at 180 rpm for 3.1 h, add hydroquinone. The mixture was cooled to 10°C in an ice-water bath at 0°C, extruded through a 2mm sieve, dried at 50°C for 12 hours, ground, and passed through an 80-mesh sieve to obtain a supramolecular polymer drag reducer. The ratio of deionized water, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, initiator solution, mixed emulsion, and hydroquinone was 83mL:5g:13g:1.3mL:32mL:0.11g. The initiator solution was prepared by mixing ammonium persulfate and deionized water at 3°C ​​in a ratio of 1g:6mL. The initiator solution was added in two equal volumes.

[0073] Step (3): Start the oil-free screw air compressor to generate compressed air at 0.9 MPa. Cool the compressed air to -40°C using a refrigerated dryer, then pass it through a three-stage filter. The air then enters a hollow fiber membrane for membrane separation at an operating pressure of 0.80 MPa and a flow rate of 7 m / s. After membrane separation, the air enters a heat exchanger and is heated to 125°C. It then passes through a Pd / Al2O3 catalyst layer, to which hydrogen is added. The air is then dehydrated by a 4A-type molecular sieve adsorption tower to obtain oxygen-depleted air. The three-stage filter consists of a first-stage filter, a second-stage filter, and a third-stage filter. The filtration accuracies of the first-stage filter, second-stage filter, and third-stage filter are 1 μm, 0.1 μm, and 0.01 μm, respectively. The hydrogen flow rate satisfies a hydrogen to oxygen volume ratio of 2.8:1. The gas space velocity through the catalyst layer is 900 h⁻¹. -1 The Pd / Al2O3 catalyst was prepared according to the preparation process of Example 1 of the invention patent with reference to the announcement number CN102626618B.

[0074] Step (4): Mix water and AOS surfactant, stir in a closed container at 600 rpm for 6 min at room temperature, introduce deoxygenated air, continue stirring for 25 min, transfer to a high-speed homogenizer, homogenize at 9000 rpm for 4 min, let stand for 3 min, control the pressure to 40 MPa with a high-pressure ceramic plunger pump, and enter the microchannel reactor at a speed of 300 m / s. React for 2.0 s, start the plate heat exchanger to control the outlet temperature to 30℃, let stand for 6 min, and obtain micro-nano bubble water; the volume ratio of water to deoxygenated air is 9:1.1; the mass ratio of AOS surfactant to the total volume of water and deoxygenated air is 0.2 g:100 mL; the bubble diameter of the micro-nano bubble water is 500 nm, the stabilization time is 48 h, and the Zeta potential is -7 mV.

[0075] Step (5): At room temperature, the micro-nano bubble water was stirred in a closed container at 350 rpm for 6 min. The stirring was maintained at 350 rpm. The supramolecular polymer drag reducer was added in 5 portions, with the same mass of supramolecular polymer drag reducer added each time, every 35 s. After the supramolecular polymer drag reducer was added, the stirring was continued for 23 min. The stirring speed was adjusted to 230 rpm and stirred for 6 min. The modified nano silica obtained in Example 2 was added and ultrasonically dispersed at 200 W power and stirred at 250 rpm for 40 min. The mixture was allowed to stand for 4 min to obtain the supramolecular micro-nano bubble fracturing fluid. The ratio of the amount of micro-nano bubble water, supramolecular polymer drag reducer, and modified nano silica obtained in Example 2 was 100 mL: 0.08 g: 0.18 g.

[0076] Example 6

[0077] A supramolecular micro / nano bubble fracturing fluid, the preparation method of which includes the following specific steps:

[0078] Step (1): Heat the hydrophobic functional monomer to 60℃ and stir for 10 min. Add OP-10 and n-butanol, stir at 60℃ for 15 min, and add deionized water at 46℃ dropwise over 25 min. After the addition is complete, shear at 10000 rpm for 7 min, and then homogenize under high pressure at 200 bar and 60℃ for 8 min to obtain a mixed emulsion. The hydrophobic functional monomer is obtained by mixing octadecyl acrylate and octadecyl methacrylate in a mass ratio of 3:1. The ratio of hydrophobic functional monomer, OP-10, n-butanol, and deionized water is 10 g: 0.5 g: 7 g: 75 mL.

[0079] Step (2): Heat deionized water to 45°C, add 2-acrylamido-2-methylpropanesulfonic acid, stir at 45°C for 10 min, add acrylamide, continue stirring for 40 min, cool to room temperature, add sodium bicarbonate to adjust the pH of the system to 7.5, purge with nitrogen, add initiator solution, seal, stir at 52°C and 80 rpm for 2.2 h, cool to 45°C, add the mixed emulsion dropwise over 50 min, then add initiator solution, stir at 200 rpm for 3.2 h, add hydroquinone. The mixture was cooled to 10°C in an ice-water bath at 0°C, extruded through a 2mm sieve, dried at 50°C for 12 hours, ground, and passed through an 80-mesh sieve to obtain a supramolecular polymer drag reducer. The ratio of deionized water, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, initiator solution, mixed emulsion, and hydroquinone was 85mL:6g:15g:1.5mL:35mL:0.12g. The initiator solution was prepared by mixing ammonium persulfate and deionized water at 5°C in a ratio of 1g:7mL. The initiator solution was added in two equal volumes.

[0080] Step (3): Start the oil-free screw air compressor to generate compressed air at 1.0 MPa. Cool the compressed air to -40°C using a refrigerated dryer, then pass it through a three-stage filter. The air then enters a hollow fiber membrane for membrane separation at an operating pressure of 0.85 MPa and a flow rate of 8 m / s. After membrane separation, the air enters a heat exchanger and is heated to 130°C. It then passes through a Pd / Al2O3 catalyst layer, to which hydrogen is added. The air is then dehydrated by a 4A-type molecular sieve adsorption tower to obtain oxygen-depleted air. The three-stage filter consists of a first-stage filter, a second-stage filter, and a third-stage filter. The filtration accuracies of the first-stage filter, second-stage filter, and third-stage filter are 1 μm, 0.1 μm, and 0.01 μm, respectively. The hydrogen to oxygen volume ratio is 3:1, and the gas space velocity through the catalyst layer is 1000 h⁻¹. -1 The Pd / Al2O3 catalyst was prepared according to the preparation process of Example 1 of the invention patent with reference to the announcement number CN102626618B.

[0081] Step (4): Mix water and AOS surfactant, stir in a closed container at 600 rpm for 7 min at room temperature, introduce deoxygenated air, continue stirring for 30 min, transfer to a high-speed homogenizer, homogenize at 9000 rpm for 5 min, let stand for 4 min, control the pressure to 50 MPa with a high-pressure ceramic plunger pump, and enter the microchannel reactor at a speed of 350 m / s. React for 2.2 s, start the plate heat exchanger to control the outlet temperature to 32℃, let stand for 7 min, and obtain micro-nano bubble water; the volume ratio of water to deoxygenated air is 9:1.2; the mass ratio of AOS surfactant to the total volume of water and deoxygenated air is 0.3 g:100 mL; the bubble diameter of the micro-nano bubble water is 500 nm, the stabilization time is 48 h, and the Zeta potential is -7 mV.

[0082] Step (5): At room temperature, the micro-nano bubble water was stirred in a closed container at 400 rpm for 7 min. The stirring was maintained at 400 rpm. The supramolecular polymer drag reducer was added in 5 portions, with the same mass of supramolecular polymer drag reducer added each time, every 40 s. After the supramolecular polymer drag reducer was added, the stirring was continued for 25 min. The stirring speed was adjusted to 250 rpm and stirred for 7 min. The modified nano silica obtained in Example 3 was added and ultrasonically dispersed at 200 W power and stirred at 250 rpm for 45 min. The mixture was allowed to stand for 5 min to obtain the supramolecular micro-nano bubble fracturing fluid. The ratio of the amount of micro-nano bubble water, supramolecular polymer drag reducer, and modified nano silica obtained in Example 3 was 100 mL: 0.10 g: 0.20 g.

[0083] Comparative Example 1

[0084] Compared with Example 6, 8-bromooctanol in the preparation process of modified nano silica was replaced with 8-bromooctanoic acid, and the rest was exactly the same as in Example 6, to prepare supramolecular micro-nano bubble fracturing fluid.

[0085] Comparative Example 2

[0086] Compared with Example 6, N-methylimidazole in the preparation process of modified nano silica was replaced with N,N-dimethylcyclohexylamine, and the rest was exactly the same as in Example 6, to prepare supramolecular micro-nano bubble fracturing fluid.

[0087] Comparative Example 3

[0088] Compared with Example 6, the oxygen-reducing air in the preparation process of supramolecular micro-nano bubble fracturing fluid was replaced with air, while the rest was exactly the same as in Example 6, and supramolecular micro-nano bubble fracturing fluid was obtained.

[0089] Comparative Example 4

[0090] Compared with Example 6, the modified nano silica in step (5) of the preparation process of supramolecular micro-nano bubble fracturing fluid was mixed with micro-nano bubble water before the addition of supramolecular polymer drag reducing agent, and the rest was exactly the same as in Example 6, so as to obtain supramolecular micro-nano bubble fracturing fluid;

[0091] Specifically:

[0092] Step (5): At room temperature, the micro-nano bubble water is stirred in a closed container at 400 rpm for 7 min. The stirring speed is then adjusted to 250 rpm and stirred for 7 min. Modified nano silica is added, and the mixture is ultrasonically dispersed at 200 W and stirred at 250 rpm for 45 min. The mixture is stirred in a closed container at 400 rpm, and the supramolecular polymer drag reducer is added in 5 portions. The mass of the supramolecular polymer drag reducer added each time is equal, and the mixture is added every 40 s. After the supramolecular polymer drag reducer is added, the mixture is stirred for 25 min and allowed to stand for 5 min to obtain the supramolecular micro-nano bubble fracturing fluid. The ratio of the amount of micro-nano bubble water, supramolecular polymer drag reducer, and modified nano silica is 100 mL: 0.10 g: 0.20 g.

[0093] Comparative Example 5

[0094] Compared with Example 6, the modified nano-silica was replaced with unmodified nano-silica, and the rest was exactly the same as in Example 6, to prepare supramolecular micro-nano bubble fracturing fluid.

[0095] The supramolecular micro-nano bubble fracturing fluids prepared in Examples 4-6 and Comparative Examples 1-5 of this invention were further tested below, and the test results are shown in the figure.

[0096] Referring to SY / T 5107-2016 "Performance Evaluation Method of Water-Based Fracturing Fluids", the drag reduction rate was measured using a pipeline friction meter (10mm inner diameter, 4m length) at 25℃ and a flow rate of 15L / min. The calculation formula is as follows:

[0097] Drag reduction rate = (Stable pressure difference of water in the pipeline ΔP0 - Stable pressure difference of fracturing fluid in the pipeline ΔP) / Stable pressure difference of water in the pipeline ΔP0 × 100%.

[0098] A six-speed rotational viscometer was used to test the viscosity of the fracturing fluid under static, unsheared conditions, according to SY / T 5107-2016 "Performance Evaluation Method for Water-Based Fracturing Fluids". The viscosity was then measured for 170 seconds. -1 The high-temperature shear rate and viscosity at 120°C were used to evaluate the temperature resistance and shear strength.

[0099] Referring to SY / T 5107-2016 "Performance Evaluation Method of Water-based Fracturing Fluid", the static suspended sand method was used to evaluate the proppant carrying capacity of the fracturing fluid. 20-mesh quartz sand was used as the proppant, and the sand-to-fluid ratio was controlled at 30%. The proppant settling rate (cm / s) was calculated.

[0100] Referring to the NB / T 14022-2017 standard, the capillary sucking time (CST) was used to evaluate the anti-swelling performance. Shale powder was dried at 105℃ for 8 hours and pulverized through a 100-mesh sieve. 7.5g of shale powder was mixed with 50mL of fracturing fluid and a 3.0% KCl solution, and sheared at 5700r / min for 20s to obtain slurry. 3mL of slurry was injected into a CST tester, and the time required for the filtrate to diffuse 0.5cm (i.e., the CST value) was measured. The ratio of the CST value of the supramolecular micro-nano bubble fracturing fluid to the CST value of the 3.0% KCl solution was calculated. If the ratio was less than 1.0, the hydration inhibition ability was strong and the anti-swelling performance was excellent.

[0101] Referring to the SY / T 6376-2008 standard, the core displacement method was used for determination. The target reservoir core (φ25×50mm) was dried, saturated with formation water, and then loaded into a holder. Under conditions of formation temperature 85℃, confining pressure 25MPa, and back pressure 10MPa, 2PV supramolecular micro-nano bubble fracturing fluid was injected at a rate of 1mL / min. After 12 hours of well shut-in, nitrogen gas at 5MPa was used for displacement until no fluid flowed out. The cumulative flowback fluid volume was recorded, and the flowback rate was calculated using the formula: Flowback rate = Flowback fluid volume / Injected fracturing fluid volume × 100%.

[0102] The results are recorded in Table 1.

[0103] Table 1: Test Results of Supramolecular Micro / Nano Bubble Fracturing Fluid

[0104]

[0105] According to the data in Table 1, the supramolecular micro-nano bubble fracturing fluids prepared in Examples 4-6 of this invention have good drag reduction rate, temperature resistance and shear resistance, sand carrying capacity, anti-swelling performance and flowback rate.

[0106] Comparing Example 6 with Comparative Example 1, it can be seen that replacing 8-bromooctanol with 8-bromooctanoic acid in the preparation process of modified nano-silica indicates that the ring-opening reaction of the primary alcohol hydroxyl group of product 1 obtained by the reaction of 8-bromooctanol with the epoxy group of product 2 in this invention results in an ether bond with strong hydrolysis resistance, which is more suitable for the long-term immersion environment of fracturing fluid. The resulting fracturing fluid has better drag reduction, temperature resistance and shear resistance, sand carrying capacity, anti-swelling performance and flowback rate.

[0107] Comparing Example 6 with Comparative Example 2, it can be seen that replacing N-methylimidazole in the modified nano silica preparation process with N,N-dimethylcyclohexylamine indicates that the imidazole quaternary ammonium salt in Product 1 obtained by using N-methylimidazole in the reaction of the present invention has better autocatalytic performance for the reaction of Product 1 and Product 2, and is more conducive to the bridging effect of modified nano silica on supramolecular polymer drag reducer and micro-nano bubble water, thereby improving the drag reduction rate, temperature resistance and shear resistance, sand carrying capacity, anti-swelling performance and flowback rate of fracturing fluid.

[0108] Comparing Example 6 with Comparative Example 3, it can be seen that replacing the deoxygenated air in the preparation process of supramolecular micro-nano bubble fracturing fluid with air shows that the micro-nano bubble water prepared by the present invention using deoxygenated air has a better synergistic effect with the supramolecular polymer drag reducer and modified nano silica. The resulting fracturing fluid has better drag reduction rate, temperature resistance and shear resistance, sand carrying capacity, anti-swelling performance and flowback rate.

[0109] Comparing Example 6 with Comparative Example 4, it can be seen that mixing the modified nano-silica in step (5) of the preparation process of supramolecular micro-nano bubble fracturing fluid with micro-nano bubble water before adding the supramolecular polymer drag reducer indicates that the present invention uses micro-nano bubble water to first mix with the supramolecular polymer drag reducer, and then adds modified nano-silica to prepare supramolecular micro-nano bubble fracturing fluid. This helps the modified nano-silica bridge the micro-nano bubble water and the supramolecular polymer to form a composite network, thereby improving the drag reduction rate, temperature resistance and shear resistance, sand carrying capacity, anti-swelling performance and flowback rate of the fracturing fluid.

[0110] Comparing Example 6 with Comparative Example 5, it can be seen that replacing the modified nano-silica with unmodified nano-silica shows that the modified nano-silica used in this invention has better dispersibility and is more conducive to bridging the supramolecular polymer drag reducer and micro-nano bubble water through hydrogen bonding and electrostatic interaction. This is more conducive to improving the drag reduction rate, temperature resistance and shear resistance, sand carrying capacity, anti-swelling performance and flowback rate of the fracturing fluid.

[0111] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a supramolecular micro / nano bubble fracturing fluid, characterized in that: Includes the following steps: Step (1): Heat and stir the hydrophobic functional monomer, add OP-10 and n-butanol, continue stirring, add deionized water dropwise, and after the addition is complete, shear at high speed and then perform high pressure homogenization to obtain a mixed emulsion; Step (2): Heat deionized water, add 2-acrylamido-2-methylpropanesulfonic acid, stir, add acrylamide, continue stirring, cool, adjust the pH of the system, introduce protective gas, add initiator solution, seal, heat and stir, cool down, add mixed emulsion dropwise, add initiator solution again, stir evenly, add hydroquinone, cool, extrude through a sieve, dry, grind, sieve, and obtain supramolecular polymer drag reducer; Step (3): Cool the compressed air, filter it, pass it through a hollow fiber membrane for membrane separation, then heat it, and then react it with hydrogen in the Pd / Al2O3 catalyst layer to remove oxygen. Finally, dehydrate it to obtain oxygen-reduced air. Step (4): Mix water and AOS surfactant, stir, introduce oxygen-reduced air, continue stirring, then homogenize, let stand, pump into microchannel reactor for reaction, control the discharge temperature, let stand, and obtain micro-nano bubble water. Step (5): Stir the micro-nano bubble water in a closed container, add the supramolecular polymer drag reducer, and continue stirring; adjust the stirring speed, stir evenly, add modified nano silica, disperse and stir by ultrasonication; let stand to obtain supramolecular micro-nano bubble fracturing fluid.

2. The method for preparing a supramolecular micro / nano bubble fracturing fluid according to claim 1, characterized in that: In step (1), the hydrophobic functional monomer is obtained by mixing octadecyl acrylate and octadecyl methacrylate in a mass ratio of 1-3:1; the ratio of the amount of the hydrophobic functional monomer, OP-10, n-butanol and deionized water is 5-10g:0.3-0.5g:5-7g:65-75mL.

3. The method for preparing a supramolecular micro / nano bubble fracturing fluid according to claim 1, characterized in that: In step (2), the ratio of deionized water, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, initiator solution, mixed emulsion, and hydroquinone is 80-85 mL: 4-6 g: 10-15 g: 1-1.5 mL: 30-35 mL: 0.10-0.12 g; the initiator solution is obtained by mixing ammonium persulfate and deionized water at 0-5℃ in a ratio of 1 g: 5-7 mL, and the initiator solution is added in two equal parts.

4. The method for preparing a supramolecular micro / nano bubble fracturing fluid according to claim 1, characterized in that: In step (3), the hydrogen flow rate satisfies a hydrogen to oxygen volume ratio of 2.5-3:1; the gas space velocity through the catalyst layer is 800-1000 h⁻¹. -1 .

5. The method for preparing a supramolecular micro / nano bubble fracturing fluid according to claim 1, characterized in that: In step (4), the volume ratio of water to deoxygenated air is 9:1-1.2; the ratio of the mass of AOS surfactant to the total volume of water and deoxygenated air is 0.1-0.3g:100mL; the micro-nano bubble water has a bubble diameter ≤500nm, a stability time ≥48h, and a Zeta potential ≤-7mV.

6. The method for preparing a supramolecular micro / nano bubble fracturing fluid according to claim 1, characterized in that: In step (5), the ratio of the amount of micro-nano bubble water, supramolecular polymer drag reducer, and modified nano silica is 100mL: 0.05-0.10g: 0.15-0.20g.

7. The method for preparing a supramolecular micro / nano bubble fracturing fluid according to claim 1, characterized in that: The modified nano-silica is prepared by the following steps: Step A1: N-methylimidazole, 8-bromooctanol and anhydrous ethanol are mixed, stirred, cooled and allowed to stand, filtered, washed and dried under vacuum to obtain product 1; Step A2: Adjust the pH of the ethanol aqueous solution, add KH560, stir, add nano silica dispersion, heat and stir, cool, filter, wash, and vacuum dry to obtain product 2; Step A3: Mix product 2 and acetonitrile aqueous solution, disperse and stir by ultrasonication, adjust the pH of the system, add product 1, heat and stir to react, cool, filter, wash, and vacuum dry to obtain modified nano silica.

8. The method for preparing a supramolecular micro / nano bubble fracturing fluid according to claim 7, characterized in that: In step A1, the ratio of N-methylimidazole, 8-bromooctanol, and anhydrous ethanol is 4.5-5g: 10.5-11g: 35-40mL.

9. The method for preparing a supramolecular micro / nano bubble fracturing fluid according to claim 7, characterized in that: In step A2, the ratio of the amount of the ethanol aqueous solution, KH560, and nano silica dispersion is 100-105 mL: 0.4-0.6 g: 105-110 mL; in step A3, the ratio of the amount of the product 2, acetonitrile aqueous solution, and product 1 is 7-8 g: 190-200 mL: 1-1.5 g; the acetonitrile aqueous solution is obtained by mixing anhydrous acetonitrile and deionized water in a volume ratio of 8-9:

1.

10. A supramolecular micro-nano bubble fracturing fluid prepared by the method of any one of claims 1-9.

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