Composition containing nano silicon dioxide, preparation method of composition and fracturing fluid

Abstract

The invention relates to a fracturing technology, in particular to a composition containing nano silicon dioxide, a preparation method of the composition and fracturing fluid. The composition contains modified nano silicon dioxide and a solvent, based on the total amount of the composition, the content of the modified nano silicon dioxide is 30-50 wt%, the molecular aggregate hydrodynamic diameter D50 of the composition is 90-150 [mu] m, the molecular aggregate hydrodynamic diameter D90 is 180-300 [mu] m, and the adsorption force is 0.3-0.4 mN. The preparation method of the composition comprises the following steps: hydroxylating gas-phase nano silicon dioxide in a solvent, contacting the hydroxylated gas-phase nano silicon dioxide with a monomer A in the presence of an initiator, and mixing the obtained product with a fluorocarbon surfactant. The invention also provides an application of the composition in a fracturing fluid and the fracturing fluid containing the composition. The composition can promote the fracturing fluid to rapidly flow back to the reservoir and reduce the damage to the reservoir.

Description

Technical Field

[0001] The present invention relates to a fracturing technology, in particular to a composition containing nano-silicon dioxide, a preparation method thereof and a fracturing fluid containing the composition as a plugging agent. Background Art

[0002] With the continuous advancement of oil and gas resource development, tight sandstone reservoirs have gradually become a key target for oil and gas exploration and development. Fracturing is a key measure for increasing reservoir production. It uses pressure to compress the formation to form conductive fractures, thereby reducing fluid flow resistance. Fracturing fluid is a key technology in the fracturing process. This is especially true for normal-pressure and low-pressure tight sandstone reservoirs, which are characterized by low porosity, low permeability, and strong heterogeneity. Adding sand during fracturing is difficult, and the technical requirements for fracturing fluids are higher.

[0003] Currently, polymer-based variable-viscosity fracturing fluids, such as polyacrylamide-based variable-viscosity fracturing fluids, are primarily used in fracturing stimulation. These fracturing fluids can cause significant damage to the reservoir core matrix, with damage rates exceeding 30%. This leads to difficulties in post-process fluid flowback and unsatisfactory gas production in some wells. The main factors causing matrix damage include adsorption and retention of polymer fracturing fluids, as well as water lock damage. Adsorption and retention damage, caused by the thickener in the fracturing fluid accumulating within the porous rock medium, accounts for over 60% of the total reservoir damage. Water lock damage, caused by the penetration of fracturing fluid into the reservoir, makes fluid flowback difficult and results in low flowback rates, inevitably impacting post-fracturing production.

[0004] To address the major reservoir-damaging effects of fracturing fluids, both domestic and international approaches have typically sought to mitigate these reservoir damages by adding drainage aids and water-locking agents. However, these efforts have been less than ideal, particularly with regard to improving the flowback efficiency of the fracturing fluid. Therefore, there is an urgent need to develop a key treatment agent that can both reduce adsorption and water-locking damage, while also promoting rapid flowback, to address the demands of fracturing treatment technologies for more low-permeability, tight gas reservoirs. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems in the prior art of adsorption retention and water lock damage of fracturing fluid to the reservoir, and low backflow efficiency after fracturing. A composition containing nano-silica, a preparation method thereof, and a fracturing fluid are provided. The composition can promote the rapid return of fracturing fluid from the reservoir and reduce damage to the reservoir.

[0006] In order to achieve the above object, the present invention provides a nano-silica-containing composition in the first aspect, wherein the composition comprises modified nano-silica and a solvent, wherein the content of the modified nano-silica is 30-50% by weight based on the total amount of the composition, and the hydrodynamic diameter D of the molecular aggregates of the composition is 50 =90-150μm, D90 =180-300μm, adsorption force is 0.3-0.4mN.

[0007] A second aspect of the present invention provides a method for preparing a composition containing nano-silica, the method comprising: hydroxylating gas-phase nano-silica in a solvent, contacting the mixture with a monomer A represented by formula (II) in the presence of an initiator, and mixing the resulting product with a fluorocarbon surfactant;

[0008] Among them, R I 、R II 、R III Each is independently hydrogen or a C1-C5 alkyl group, m is an integer of 0-5, and the benzene ring of the monomer A may have a substituent.

[0009] The third aspect of the present invention provides a nano-silicon dioxide-containing composition obtained by the above-mentioned preparation method.

[0010] A fourth aspect of the present invention provides use of the above-mentioned nano-silica-containing composition in a fracturing fluid.

[0011] A fifth aspect of the present invention provides a fracturing fluid containing the above-mentioned nano-silica-containing composition.

[0012] Through the above technical solution, the beneficial effects of the present invention are as follows: when the composition provided by the present invention is applied to the fracturing fluid system, it has good suspension and dispersibility in the fracturing fluid and is easily adsorbed on the surface of the reservoir rock, while significantly reducing the adsorption force of the fracturing fluid system, reducing the adsorption retention and water lock damage caused by the liquid to the reservoir; further, the composition provided by the present invention has a surface tension of no more than 25mN / m, which can effectively promote the rapid return of the fracturing fluid from the reservoir and improve the return rate of the fracturing fluid. DETAILED DESCRIPTION

[0013] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0014] The first aspect of the present invention provides a composition containing nano-silica, wherein the composition contains modified nano-silica and a solvent, wherein the content of the modified nano-silica is 30-50% by weight based on the total amount of the composition, and the hydrodynamic diameter D of the molecular aggregates of the composition is 50=90-150 μm, specifically 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, or any value between the above two values, preferably 90-120 μm; D 90 =180-300μm, specifically 180μm, 210μm, 240μm, 270μm, 300μm, or any value between the above two values, preferably 190-250μm; the adsorption force is 0.3-0.4mN, specifically 0.3mN, 0.32mN, 0.34mN, 0.36mN, 0.38mN, 0.4mN, or any value between the above two values.

[0015] The inventors of the present invention unexpectedly discovered during the research and development process that the hydrodynamic diameter of the molecular aggregates of the composition containing nano-silica and solvent is controlled within D 50 =90-150μm, D 90 =180-300 μm, and the adsorption force is controlled within the range of 0.3-0.4 mN. When applied to a fracturing fluid system, it can be suspended and dispersed relatively evenly in the fracturing fluid, and can achieve multi-scale plugging of reservoirs of different sizes during fracturing. It has a high degree of matching with the pore throats of tight sandstone reservoirs and can adapt to the fracturing transformation technology requirements of more low-permeability tight gas reservoirs. The composition is easily adsorbed on the surface of the reservoir rock, and at the same time significantly reduces the adsorption force of the fracturing fluid system, reduces the adsorption retention and water lock damage of the liquid to the reservoir, and can reduce the core damage rate of the fracturing fluid system to below 15%.

[0016] In the present invention, the molecular aggregate hydrodynamic diameter refers to the apparent diameter of the molecular aggregate formed by the modified nano-silica in the aqueous solution. The test method is: using a Fritsch 22 laser particle size analyzer, refer to the liquid medium dispersion and measurement method in the standard GB / T 19077-2016 "Particle Size Analysis by Laser Diffraction Method" for wet testing; D 10 、D 50 and D 90 They respectively represent the particle sizes corresponding to when the cumulative particle size distribution of the sample reaches 10%, 50% and 90% (manually accumulate the percentages of all particle sizes before or after this particle size); its physical meaning is that the number of particles with a size smaller than this particle size accounts for 10%, 50% and 90% of the total number of particles.

[0017] In the present invention, the adsorption force test method is as follows: 5 μl of sample is dropped onto a glass slide (purchased from Xiangshan Tianqi (Pearl) Industry and Trade Co., Ltd., product model 7101) at room temperature (25±5°C), and the maximum weight (in mg) of the sample when peeled off from the glass slide is measured using a K100 mechanical tensiometer, and the gravitational acceleration is 9.80665 N / kg (m / s2 ) multiplied by the maximum action weight test data to obtain the adsorption force result.

[0018] According to the present invention, preferably, the molecular aggregate hydrodynamic diameter D of the composition is 10 The particle size is less than 5 μm, and the diameter is in the range of 2-250 μm. The inventors have found that under this preferred embodiment, the dispersion uniformity of the composition in the fracturing fluid system can be further improved, and the matching degree with the reservoir pore throat is higher, and the plugging effect is better.

[0019] According to the present invention, the surface tension of the composition preferably does not exceed 25 mN / m. The inventors have found that this preferred embodiment facilitates rapid return of the fracturing fluid from the reservoir and improves the return rate of the fracturing fluid. Further preferably, the surface tension of the composition is 20-23 mN / m, specifically 20 mN / m, 21 mN / m, 22 mN / m, 23 mN / m, or any value in between.

[0020] In the present invention, the surface tension is directly measured on the composition according to the method in Q / SHCG 69-2013 "Technical Requirements for Discharge Aids for Fracturing and Acidizing". The specific process is: the composition is measured at room temperature (25°C) according to the provisions of GB / T 5549, three parallel samples are made for each sample, and the arithmetic mean is taken as the measurement result. The difference between each measured value and the arithmetic mean is not greater than 1 mN / m. The numerical rounding of the test results is performed according to GB / T 8170.

[0021] The nano-silica composition provided by the present invention, when used in fracturing fluids, is preferably used as a plugging agent in the fracturing fluid, effectively reducing the adsorption capacity of the fracturing fluid system. Preferably, the composition reduces the adsorption capacity of a fracturing fluid composed of 0.1% thickener, 0.05% drainage aid, and 0.05% clay stabilizer, with an adsorption capacity of 0.52 mN, by 24.5-50%, further reducing adsorption, retention, and water lock damage to the reservoir caused by the fracturing fluid system.

[0022] The adsorption capacity reduction rate refers to the ratio of the change in adsorption capacity before and after the addition of the composition provided by the present invention (the addition amount of the composition is preferably 0.3-1% by weight) to the initial adsorption capacity of the fracturing fluid, and the calculation formula is shown in formula (I);

[0023]

[0024] Where:

[0025] ——Fracturing fluid adsorption reduction rate, %;

[0026] ——initial adsorption force of fracturing fluid, mN;

[0027] ——The adsorption capacity of the fracturing fluid after adding the composition provided by the present invention, mN.

[0028] In the present invention, the thickener can be any substance that can be used as a thickener in fracturing fluid, the drainage aid can be any substance that can be used as a drainage aid in fracturing fluid, and the clay stabilizer can be any substance that can be used as a clay stabilizer in fracturing fluid. For example, the thickener is an acrylamide homopolymer and / or a copolymer of acrylamide and another monomer, wherein the other monomer is selected from at least one of acryloyloxyethyltrimethylammonium chloride, sodium acrylate, and acrylic acid. Further preferably, the copolymer of acrylamide and another monomer is at least one of acrylamide-acryloyloxyethyltrimethylammonium chloride copolymer, acrylamide-sodium acrylate-acrylic acid copolymer, and acrylamide-acryloyloxyethyltrimethylammonium chloride-sodium acrylate-acrylic acid copolymer. The drainage aid is a polyoxyethylene amine ether and / or a polyoxyethylene fatty alcohol ether, preferably oleylamine polyoxyethylene ether and / or rosinamine polyoxyethylene ether, and the polyoxyethylene fatty alcohol ether is preferably at least one of polyoxyethylene lauryl alcohol ether, polyoxyethylene tetradecyl alcohol ether, polyoxyethylene cetyl alcohol ether, and polyoxyethylene octadecyl alcohol ether. The clay stabilizer is dimethylamine quaternary ammonium salt and / or polyquaternium salt, and the polyquaternium salt is preferably polyquaternium-126.

[0029] In the present invention, a fracturing fluid comprising a thickener, a drainage aid, and a clay stabilizer with an adsorption capacity of 0.52 mN can be formulated as follows: 0.1% by weight of an acrylamide homopolymer with a weight-average molecular weight of 18 million, 0.05% of oleylamine polyoxyethylene ether, and 0.05% of a dimethylamine quaternary ammonium salt. A fracturing fluid meeting these requirements can be, for example, a mixture of acrylamide homopolymer (thickener SPR-08), oleylamine polyoxyethylene ether (drainage aid SPR-201), and a dimethylamine quaternary ammonium salt (clay stabilizer SPR-103) produced by Dongying Shipurui Petroleum Engineering Technology Co., Ltd., in the aforementioned proportions.

[0030] According to the present invention, the modified nano-silica is preferably modified fumed nano-silica. The inventors have discovered that this preferred embodiment facilitates better control of the hydrodynamic diameter and adsorption capacity of the molecular aggregates of the composition within corresponding ranges, thereby improving the fracturing fluid flowback efficiency and reducing damage to the reservoir.

[0031] According to the present invention, preferably, the modified nano-silica contains a structural unit a represented by formula (I) with or without a substituent on the benzene ring,

[0032] Among them, R I 、RII 、R III Each is independently hydrogen or a C1-C5 alkyl group, for example, hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, cyclopropyl, cyclobutyl, cyclopentyl, etc.; m is an integer from 0 to 5, specifically 0, 1, 2, 3, 4, 5; the phenyl ring of the structural unit a may not have a substituent, or may have a substituent such as an alkyl group or an alkenyl group, for example, the phenyl ring may have a C2-C6 alkenyl group, specifically vinyl, n-propenyl, isopropenyl, n-butenyl, n-dibutenyl, isobutenyl, tert-butenyl, n-pentenyl, 1,3-pentadienyl, isopentenyl, n-hexenyl, 1,3-hexadienyl, cyclopropenyl, methylcyclopropenyl, ethylcyclopropenyl, cyclopentenyl, n-hexenyl, methylcyclopentenyl, cyclohexenyl, etc.

[0033] More preferably, R I 、R II 、R III The inventors have found that, in this preferred embodiment, the combination of nano-silica and structural unit a is more conducive to the composition playing a plugging role in the fracturing fluid, thereby reducing damage to the reservoir.

[0034] According to the present invention, preferably, the content of the structural unit a is 3-15% by weight based on the total weight of the composition. Specifically, the content of the structural unit a can be determined by H-NMR, C-NMR, and IR detection.

[0035] According to the present invention, preferably, the modified nano-silica surface is adsorbed with active groups containing fluorine-carbon chains. The inventors have found that under this preferred embodiment, it is beneficial to further reduce the adsorption force of the fracturing fluid system and control the surface tension of the composition.

[0036] According to the present invention, the reactive group of the fluorinated carbon chain is preferably a C4-C10 perfluoroalkyl group, a C4-C10 perfluoroalkoxy group, a substituted aromatic group containing a C4-C10 perfluoroalkyl group, or a substituted aromatic group containing a C4-C10 perfluoroalkoxy group; more preferably, it is a perfluorononenyloxyphenyl group and / or a perfluorooctyl group. The inventors have discovered that this preferred embodiment facilitates further control of the surface tension of the composition.

[0037] According to the present invention, the solvent is preferably water and / or an organic alcohol. The organic alcohol may be any aliphatic or aromatic alcohol, for example, methanol, ethanol, propanol, butanol, or pentanol, and the aromatic alcohol may be benzyl alcohol, phenylethyl alcohol, phenylpropanol, phenylbutanol, or phenylpentanol. The inventors have discovered that this preferred embodiment further reduces the damage caused by the fracturing fluid to the reservoir.

[0038] A second aspect of the present invention provides a method for preparing a composition containing nano-silica, the method comprising: hydroxylating gas-phase nano-silica in a solvent, contacting the mixture with a monomer A having a structure represented by formula (II) in the presence of an initiator, and mixing the resulting product with a fluorocarbon surfactant;

[0039] Among them, R I 、R II 、R III Each is independently hydrogen or a C1-C5 alkyl group, m is an integer of 0-5, and the benzene ring of the monomer A may have a substituent.

[0040] The preparation method of the nano-silica composition provided by the present invention is to contact the gas-phase nano-silica with the monomer A represented by formula (II) to react, and then use a fluorocarbon surfactant to modify and adsorb the active groups containing fluorocarbon chains on the surface of the nano-silica, so that the molecular aggregate hydrodynamic diameter D of the composition is 50 =90-150μm, D 90 =180-300 μm, and the adsorption force is 0.3-0.4 mN. When used in fracturing fluid, it can reduce the adsorption retention and water lock damage of the fracturing fluid, so that the fracturing fluid can be adapted to various fracturing transformation technologies of low-permeability and tight gas reservoirs. The preparation method is simple in process and easy to industrialize.

[0041] In the present invention, R I 、R II 、R III Each is independently hydrogen or C1-C5 alkyl, for example, hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, cyclopropyl, cyclobutyl, cyclopentyl, etc.; m is an integer from 0 to 5, specifically 0, 1, 2, 3, 4, or 5. Preferably, R I 、R II 、R III Each independently represents hydrogen or methyl; further preferably, monomer A is styrene and / or divinylbenzene. The phenyl ring of monomer A may have no substituents or may have substituents such as alkyl groups or alkenyl groups. For example, the phenyl ring may have C2-C6 alkenyl groups, specifically vinyl, n-propenyl, isopropenyl, n-butenyl, n-dibutenyl, isobutenyl, tert-butenyl, n-pentenyl, 1,3-pentadienyl, isopentenyl, n-hexenyl, 1,3-hexadienyl, cyclopropenyl, methylcyclopropenyl, ethylcyclopropenyl, cyclopentenyl, n-hexenyl, methylcyclopentenyl, cyclohexenyl, etc.

[0042] In the present invention, the hydroxylation process preferably comprises: mixing fumed nanosilica with an organic acid in the solvent for reaction I to obtain a first mixture; and mixing the first mixture with a diol for reaction II to obtain a second mixture. The inventors have discovered that this preferred embodiment facilitates the reaction efficiency of the fumed nanosilica with monomer A, controls the hydrodynamic diameter of the molecular aggregates of the resulting composition, and improves the dispersion uniformity of the composition in the fracturing fluid system.

[0043] Further preferably, the conditions of reaction I include: temperature of 70-90° C., time of 0.5-1.5 hours; the conditions of reaction II include: temperature of 70-90° C., rotation speed of 7500-8500 rpm, time of 0.5-1.5 hours.

[0044] According to the present invention, preferably, the solvent is water and / or an organic alcohol; the organic acid is selected from at least one of citric acid, malic acid and oxalic acid; the diol is preferably a C2-C6 aliphatic diol, for example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, more preferably ethylene glycol.

[0045] According to the present invention, preferably, the weight ratio of the fumed nano-silica, the organic acid and the diol is 1:0.5-1:2-3.

[0046] According to the present invention, preferably, the contact conditions include a temperature of 60-80°C, specifically 60°C, 65°C, 70°C, 75°C, 80°C, or any value therebetween; and a time of 2-8 hours, specifically 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or any value therebetween. The inventors have found that this preferred embodiment is conducive to improving the efficiency of the reaction.

[0047] According to the present invention, preferably, the initiator is an azo initiator, such as azobisisobutyronitrile, azobisisoheptanenitrile, azobisisobutyramidine hydrochloride, azobisisobutylimidazoline hydrochloride, etc. The inventors have found that under this preferred embodiment, it is beneficial to promote the addition reaction and improve the preparation efficiency of the composition.

[0048] According to the present invention, preferably, the molar ratio of nano-silica to monomer A is 1:2-5. The inventors have found that under this preferred embodiment, the dispersion uniformity of the prepared composition in the fracturing fluid system is further improved, the fluid loss during the fracturing process is reduced, and the compatibility with the reservoir pore throat is improved, resulting in a better plugging effect.

[0049] According to the present invention, fumed nano-silicon dioxide is an amorphous nano-silicon dioxide product, which is a nano-scale white powder generated by high-temperature hydrolysis of silicon halides in a hydrogen-oxygen flame. Preferably, the fumed nano-silicon dioxide used in the present invention has a particle size of 3-20nm and a specific surface area of 185-410m 2 / g, and the apparent density is 30-60g / L.

[0050] According to the present invention, preferably, the nano-silica contains a first particle size nano-silica and a second particle size nano-silica, the particle size of the first particle size nano-silica is 3-5nm, specifically 3nm, 3.5nm, 4nm, 4.5nm, 5nm, or any value between the above two values; the particle size of the second particle size nano-silica is 15-20nm, specifically 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, or any value between the above two values. The inventors found that under this preferred embodiment, it is beneficial to further improve the dispersion uniformity of the composition in the fracturing fluid system, reduce the filtration loss during the fracturing process, and have a higher matching degree with the reservoir pore throat. Further preferably, the molar ratio of the first particle size nano-silica to the second particle size nano-silica is 1:1-3. The inventors found that under this preferred embodiment, it is beneficial to better block the reservoir pore throat.

[0051] According to the present invention, preferably, the mixing conditions include a temperature of 60-80°C, specifically 60°C, 65°C, 70°C, 75°C, 80°C, or any value between the above two values; and a time of 2-8 hours, specifically 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or any value between the above two values. The inventors have found that under this preferred embodiment, it is beneficial to better adsorb fluorine-containing groups on the surface of nano-silica, reduce the adsorption capacity of the fracturing fluid system, and improve the return efficiency of the fracturing fluid.

[0052] According to the present invention, preferably, the molar ratio of nano-silica to fluorocarbon surfactant is 1:1-2. The inventors have found that under this preferred embodiment, it is beneficial to control the surface tension of the composition and further improve the adsorption capacity of the fracturing fluid system.

[0053] According to the present invention, preferably, the molar ratio of fluorine element to carbon element in the fluorocarbon surfactant is 1-3:1;

[0054] Preferably, the fluorocarbon surfactant has an active group containing a fluorinated carbon chain, wherein the active group containing the fluorinated carbon chain is a C4-C10 perfluoroalkyl group, a C4-C10 perfluoroalkoxy group, a substituted aromatic group containing a C4-C10 perfluoroalkyl group, or a substituted aromatic group containing a C4-C10 perfluoroalkoxy group. More preferably, the fluorocarbon surfactant is perfluorononenyloxybenzenesulfonate and / or perfluorooctanesulfonate. The perfluorononenyloxybenzenesulfonate may be sodium perfluorononenyloxybenzenesulfonate, potassium perfluorononenyloxybenzenesulfonate, etc., and the perfluorooctanesulfonate may be sodium perfluorooctanesulfonate, potassium perfluorooctanesulfonate, etc. The inventors have found that under this preferred embodiment, it is beneficial to improve the adsorption effect of the fluorinated group on the surface of the nano-silica, reduce the surface tension of the composition, and promote the return of the fracturing fluid.

[0055] According to the present invention, when the fluorocarbon surfactant is perfluorononenyloxybenzenesulfonate and / or perfluorooctanesulfonate, the method for preparing the nano-silica composition preferably further comprises: subjecting the contact product to an activation reaction with urea before mixing with the fluorocarbon surfactant; and then mixing the activation reaction product with the fluorocarbon surfactant. The inventors have discovered that, under this preferred embodiment, the sulfonic acid groups of the fluorocarbon surfactant can chemically bond with amino groups on the surface of the activation reaction product, thereby improving the adsorption efficiency of the fluorine-containing groups on the nano-silica surface.

[0056] Further preferably, the activation reaction conditions include a temperature of 60-80°C, specifically 60°C, 65°C, 70°C, 75°C, 80°C, or any value therebetween; a time of 0.5-3 hours, specifically 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or any value therebetween. More preferably, the weight ratio of the urea to the nano-silica is 2.5-5:1.

[0057] The third aspect of the present invention provides a nano-silicon dioxide-containing composition obtained by the above-mentioned preparation method.

[0058] The composition provided by the present invention is applied to a fracturing fluid system, can be relatively evenly suspended and dispersed in the fracturing fluid, and is easily adsorbed on the surface of the reservoir rock. At the same time, it significantly reduces the adsorption capacity of the fracturing fluid system, promotes the rapid return of the fracturing fluid to the reservoir, reduces the adsorption retention and water lock damage of the liquid to the reservoir, and can reduce the core damage rate of the fracturing fluid system to below 15%. A fourth aspect of the present invention provides the use of the above-mentioned nano-silica-containing composition in a fracturing fluid.

[0059] According to the present invention, the nano-silica-containing composition is preferably used as a plugging agent in a fracturing fluid. During fracturing, it can achieve multi-scale plugging of reservoirs of varying sizes, highly compatible with the pore throats of tight sandstone reservoirs, and can meet the requirements of fracturing reformation technology for a wider range of low-permeability tight gas reservoirs.

[0060] A fifth aspect of the present invention provides a fracturing fluid containing the above-mentioned nano-silica-containing composition.

[0061] According to the present invention, preferably, the content of the composition containing nano-silica is 0.3-1% by weight, based on the total amount of the fracturing fluid. The inventors have found that under this preferred embodiment, the composition is conducive to better exerting the multi-scale plugging of reservoirs of different sizes, and effectively reduces the adsorption capacity of the fracturing fluid system, promotes the rapid return of the fracturing fluid to the reservoir, and reduces the damage of the liquid to the reservoir.

[0062] According to the present invention, preferably, the fracturing fluid further contains, based on the total amount of the fracturing fluid, 0.05-0.15 wt% of a thickener, 0.05-0.2 wt% of a drainage aid, and 0.05-0.2 wt% of a clay stabilizer. The fracturing fluid provided by the present invention, by adding the nano-silica and solvent composition provided above to an existing conventional fracturing fluid system, can significantly reduce the adsorption capacity of the fracturing fluid system compared to the initial fracturing fluid system, thereby improving the efficiency of fracturing fluid return and discharge from the reservoir and reducing damage to the reservoir caused by the fracturing fluid.

[0063] According to the present invention, preferably, the thickener is an acrylamide homopolymer and / or a copolymer of acrylamide and another monomer, wherein the other monomer is selected from at least one of acryloyloxyethyltrimethylammonium chloride, sodium acrylate, and acrylic acid. Further preferably, the copolymer of acrylamide and another monomer is at least one of an acrylamide-acryloyloxyethyltrimethylammonium chloride copolymer, an acrylamide-sodium acrylate-acrylic acid copolymer, and an acrylamide-acryloyloxyethyltrimethylammonium chloride-sodium acrylate-acrylic acid copolymer. Further preferably, the molecular weight of the acrylamide homopolymer is greater than 18 million, and the molecular weight of the copolymer of acrylamide and another monomer is greater than 18 million.

[0064] According to the present invention, preferably, the drainage aid is polyoxyethylene amine ether and / or polyoxyethylene fatty alcohol ether. Further preferably, the polyoxyethylene amine ether is oleylamine polyoxyethylene ether and / or rosin amine polyoxyethylene ether; and the polyoxyethylene fatty alcohol ether is at least one of polyoxyethylene lauryl alcohol ether, polyoxyethylene tetradecyl alcohol ether, polyoxyethylene cetyl alcohol ether, and polyoxyethylene stearyl alcohol ether.

[0065] According to the present invention, preferably, the clay stabilizer is dimethylamine quaternary ammonium salt and / or polyquaternium salt, and the polyquaternium salt is preferably polyquaternium-126.

[0066] The present invention will be described in detail below through examples.

[0067] In the following examples, the nano-silica raw material I is fumed nano-silica with a particle size of 3-5 nm and a specific surface area of 350-410 m 2 / g, with an apparent density of 30-40g / L, purchased from Shanghai Yuanjiang Chemical Co., Ltd., product model 10279-57-8; nano-silica raw material II is fumed nano-silica with a particle size of 15-20nm and a specific surface area of 185-350m 2 / g, with an apparent density of 40-60g / L, purchased from Shanghai Yuanjiang Chemical Co., Ltd., product model 262-373-8; the CAS number of sodium perfluorononenyloxybenzenesulfonate is 87-56-8; the CAS number of potassium perfluorooctanesulfonate is 2795-39-3.

[0068] In the following examples, the test method for the hydrodynamic diameter of molecular aggregates is: a Fritsch 22 laser particle size analyzer is used to perform wet method testing in accordance with the liquid medium dispersion and measurement method in the standard GB / T 19077-2016 "Particle Size Analysis by Laser Diffraction Method".

[0069] The adsorption force test was conducted using a K100 mechanical tensiometer at room temperature (25±5°C). The specific steps for the test were as follows: ① Turn on the instrument and software and select the adsorption force test operation unit; ② Fix the adhesion accessory to the balance lock and use a pipette to add 5μL of sample; ③ Place the slide on the laboratory table and press the OK button to test the adhesion strength of the droplet product to it and measure the maximum effective weight (in mg) when the sample is peeled off from the slide; ④ After the test, the gravity acceleration of 9.80665N / kg (m / s 2 ) multiplied by the test data (maximum effective weight) to obtain the adsorption force result.

[0070] Adsorption force reduction rate The calculation formula is shown in formula (I);

[0071]

[0072] Where:

[0073] ——Fracturing fluid adsorption reduction rate, %;

[0074] ——initial adsorption force of fracturing fluid, mN;

[0075] ——The adsorption capacity of the fracturing fluid after adding the composition provided by the present invention, mN.

[0076] The surface tension is measured according to the method in Q / SHCG 69-2013 "Technical Specifications for Discharge Aids for Fracturing and Acidizing". The specific process is as follows: the composition is measured at room temperature according to the provisions of GB / T 5549. Three parallel samples are made for each sample, and the arithmetic mean is taken as the measurement result. The difference between each measured value and the arithmetic mean is not greater than 1mN / m. The numerical rounding of the test results is carried out according to GB / T 8170.

[0077] The content of modified nano-silica in the composition is detected by a drying method. The specific process is: the composition is placed in a pre-weighed container, and the solvent in the liquid is evaporated or volatilized by heating or vacuum drying to leave a solid substance. The mass of the solid substance is then weighed, and the weight of the solid substance is divided by the weight of the composition.

[0078] The contents of the structural unit a and the fluorocarbon chain in the composition are determined by nuclear magnetic hydrogen spectrum, nuclear magnetic carbon spectrum and infrared detection.

[0079] Example 1

[0080] 1) 2 g of fumed nanosilica (composed of 0.8 g of nanosilica raw material I with a particle size of 3-5 nm and 1.2 g of nanosilica raw material II with a particle size of 15-20 nm), 76.3 g of water, and 1.5 g of citric acid were added to a reactor equipped with a condenser in this order, mixed well, and reacted at 80° C. for 1 hour to obtain a first mixture;

[0081] 2) The first mixture was pumped into a high-speed shearing machine, 5.2 g of ethylene glycol was added, and the mixture was mixed uniformly. The mixture was sheared at 80° C. and 8000 rpm for 1 hour to obtain a second mixture containing modified fumed nanosilica.

[0082] 3) adding 12.15 g of styrene to the second mixture and mixing uniformly, and simultaneously adding 0.2 g of azobisisobutyronitrile, and reacting at 70° C. for 5 hours to obtain a third mixture;

[0083] 4) adding 10 g of urea to the third mixture, mixing well, and reacting at 70° C. for 1 hour to obtain a fourth mixture;

[0084] 5) 36.8 g of sodium perfluorononenyloxybenzenesulfonate was added to the fourth mixture, mixed evenly, and reacted at 70° C. for 5 hours to obtain a nano-silica-containing composition.

[0085] Example 2

[0086] 1) 2 g of fumed nanosilica (composed of 0.5 g of nanosilica raw material I with a particle size of 3-5 nm and 1.5 g of nanosilica raw material II with a particle size of 15-20 nm), 76.3 g of ethanol, and 1.5 g of oxalic acid were added to a reactor equipped with a condenser in this order, mixed well, and reacted at 70° C. for 1.5 hours to obtain a first mixture;

[0087] 2) The first mixture was pumped into a high-speed shearing machine, 5.2 g of ethylene glycol was added, and the mixture was mixed uniformly. The mixture was sheared at 70° C. and 8500 rpm for 1.5 hours to obtain a second mixture containing modified fumed nanosilica.

[0088] 3) adding 8.68 g of styrene to the second mixture and mixing uniformly, and simultaneously adding 0.2 g of azobisisoheptanenitrile, and reacting at 80° C. for 2 hours to obtain a third mixture;

[0089] 4) adding 10 g of urea to the third mixture, mixing well, and reacting at 80° C. for 0.5 hours to obtain a fourth mixture;

[0090] 5) Add 18 g of potassium perfluorooctane sulfonate to the fourth mixture, mix well, and react at 80° C. for 2.5 hours to obtain a nano-silica-containing composition.

[0091] Example 3

[0092] 1) 4 g of fumed nanosilica (composed of 2 g of nanosilica raw material I with a particle size of 3-5 nm and 2 g of nanosilica raw material II with a particle size of 15-20 nm), 120.5 g of water, and 1.5 g of malic acid were added to a reactor equipped with a condenser in this order, mixed well, and reacted at 90° C. for 0.5 hour to obtain a first mixture;

[0093] 2) The first mixture was pumped into a high-speed shearing machine, 5.2 g of ethylene glycol was added, and the mixture was mixed uniformly. The reaction was continued at a temperature of 90° C. and a rotation speed of 7500 rpm for 0.5 hour to obtain a second mixture containing modified fumed nanosilica;

[0094] 3) 8.67 g of styrene and 10.84 g of divinylbenzene were added to the second mixture and mixed evenly. 0.2 g of azobisisobutylamidine hydrochloride was added at the same time, and the mixture was reacted at 60° C. for 8 hours to obtain a third mixture;

[0095] 4) adding 10 g of urea to the third mixture, mixing well, and reacting at 60° C. for 3 hours to obtain a fourth mixture;

[0096] 5) Add 24 g of sodium perfluorononenyloxybenzenesulfonate and 17 g of potassium perfluorooctanesulfonate to the fourth mixture, mix well, and react at 60° C. for 8 hours to prepare a nano-silica-containing composition.

[0097] Example 4

[0098] A composition containing nano-silica was prepared according to the method of Example 1, except that citric acid in step 1) was replaced by acetic acid.

[0099] Example 5

[0100] A nano-silica composition was prepared according to the method of Example 1, except that 2 g of fumed nano-silica in step 1) was replaced by 1.5 g of nano-silica raw material I with a particle size of 3-5 nm and 0.5 g of nano-silica raw material II with a particle size of 15-20 nm.

[0101] Example 6

[0102] A nano-silica-containing composition was prepared according to the method of Example 1, except that the amount of styrene in step 3) was replaced with 5.2 g.

[0103] Example 7

[0104] A nano-silica-containing composition was prepared according to the method of Example 1, except that the amount of styrene in step 3) was replaced with 20 g.

[0105] Example 8

[0106] A nano-silica-containing composition was prepared according to the method of Example 1, except that azobisisobutyronitrile in step 3) was replaced by sodium sulfite.

[0107] Example 9

[0108] A nano-silica-containing composition was prepared according to the method of Example 1, except that the reaction conditions in step 3) were replaced with a reaction at 60° C. for 10 h.

[0109] Example 10

[0110] A nano-silica-containing composition was prepared according to the method of Example 1, except that the amount of urea in step 4) was replaced with 3 g.

[0111] Example 11

[0112] A nano-silica-containing composition was prepared according to the method of Example 1, except that the amount of sodium perfluorononenyloxybenzenesulfonate in step 5) was replaced with 18 g.

[0113] Example 12

[0114] A nano-silica-containing composition was prepared according to the method of Example 1, except that the reaction conditions in step 5) were replaced with a reaction at 50° C. for 10 h.

[0115] Comparative Example 1

[0116] 1) 2 g of fumed nanosilica (composed of 0.8 g of nanosilica raw material I with a particle size of 3-5 nm and 1.2 g of nanosilica raw material II with a particle size of 15-20 nm), 76.3 g of water, and 1.5 g of citric acid were added to a reactor equipped with a condenser in this order, mixed well, and reacted at 80° C. for 1 hour to obtain a first mixture;

[0117] 2) The first mixture was pumped into a high-speed shearing machine, 5.2 g of ethylene glycol was added, mixed evenly, and sheared at 80° C. for 1 hour to obtain a second mixture containing modified fumed nanosilica;

[0118] 3) adding 10 g of urea to the second mixture, mixing well, and reacting at 70° C. for 1 hour to obtain a third mixture;

[0119] 4) 36.8 g of sodium perfluorononenyloxybenzenesulfonate was added to the third mixture, mixed evenly, and reacted at 70° C. for 5 hours to obtain a nano-silicon dioxide-containing composition.

[0120] Comparative Example 2

[0121] 1) 2 g of fumed nanosilica (composed of 0.8 g of nanosilica raw material I with a particle size of 3-5 nm and 1.2 g of nanosilica raw material II with a particle size of 15-20 nm), 76.3 g of water, and 1.5 g of citric acid were added to a reactor equipped with a condenser in this order, mixed well, and reacted at 80° C. for 1 hour to obtain a first mixture;

[0122] 2) The first mixture was pumped into a high-speed shearing machine, 5.2 g of ethylene glycol was added, mixed evenly, and sheared at 80° C. for 1 hour to obtain a second mixture containing modified fumed nanosilica;

[0123] 3) 12.15 g of styrene was added to the second mixture and mixed evenly. 0.2 g of azobisisobutyronitrile was also added and the mixture was reacted at 70° C. for 5 hours to obtain a nano-silica-containing composition.

[0124] Comparative Example 3

[0125] 1) 2 g of fumed nanosilica (composed of 0.8 g of nanosilica raw material I with a particle size of 3-5 nm and 1.2 g of nanosilica raw material II with a particle size of 15-20 nm), 76.3 g of water, and 12.15 g of styrene were mixed uniformly, and 0.2 g of azobisisobutyronitrile was added, and the mixture was reacted at 70° C. for 5 hours to obtain a first mixture;

[0126] 2) adding 10 g of urea to the first mixture, mixing well, and reacting at 70° C. for 1 hour to obtain a second mixture;

[0127] 3) Add 36.8 g of sodium perfluorononenyloxybenzenesulfonate to the second mixture, mix well, and react at 70° C. for 5 hours to obtain a nano-silica-containing composition.

[0128] Comparative Example 4

[0129] 2 g of fumed nano-silica (composed of 0.8 g of nano-silica raw material I with a particle size of 3-5 nm and 1.2 g of nano-silica raw material II with a particle size of 15-20 nm), 76.3 g of water, 1.5 g of citric acid, 5.2 g of ethylene glycol, 12.15 g of styrene, 0.2 g of azobisisobutyronitrile, 10 g of urea and 36.8 g of sodium perfluorononenyloxybenzenesulfonate were physically mixed.

[0130] Comparative Example 5

[0131] The commercially available fracturing aid produced by Dongying Shipurui Petroleum Engineering Technology Co., Ltd. was used as comparative example 3.

[0132] Test Example 1

[0133] The nano-silica-containing compositions prepared in Examples 1 to 12 and Comparative Examples 1 to 4, the content of modified nano-silica in the fracturing aid in Comparative Example 5, the content of structural unit a, and the content of fluorocarbon chains were tested. Nano-silica raw material I, an aqueous solution of titanium dioxide (10% by weight, purchased from Xuancheng Jingrui New Materials Co., Ltd., model VK-TA33), an aqueous solution of nano-silica (20% by weight, purchased from Xuancheng Jingrui New Materials Co., Ltd., model VK-Sp15W), and a nano-silica solution were used as controls. The results are shown in Table 1.

[0134] Table 1

[0135]

[0136]

[0137] Among them, the nano-silica in Comparative Examples 3 and 4 was not effectively modified, and there was no modified nano-silica.

[0138] The hydrodynamic diameter D of the molecular aggregates of the nano-silica compositions prepared in test examples 1 to 12 and comparative examples 1 to 4 and the fracturing aid in comparative example 5 is 10 、D 50 and D 90 , adsorption force and surface tension, and nano-silica raw material I, titanium dioxide solution, and nano-silica raw material II were used as controls. The results are shown in Table 2.

[0139] Table 2

[0140]

[0141]

[0142] Test Example 2

[0143] 1. Preparation of base liquid:

[0144] Step 1) Add 0.1 g of acrylamide homopolymer with a weight average molecular weight of 18 million (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model: thickener SPR-08) to 99.8 g of clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and adjust the speed at all times to ensure a vortex state until it is fully dissolved to form a uniform solution;

[0145] Step 2) While maintaining the stirring state, 0.05 g of dimethylamine quaternary ammonium salt (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model clay stabilizer SPR-103) was added to the solution obtained in step 1) and stirred evenly;

[0146] Step 3) Lower the stirring speed, add 0.05g of oleylamine polyoxyethylene ether (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model: drainage agent SPR-201) to the product obtained in step 2), stir evenly, and prepare the required base liquid.

[0147] After testing, the performance indicators of the base liquid are as follows: viscosity is 3-6mPa.s, and pH value is 6-7.

[0148] 2. Preparation of fracturing fluid

[0149] Step 4) 0.5 g of the nano-silica-containing composition prepared in Examples 1 to 12 was added separately to the above base fluid and stirred to obtain a fracturing fluid.

[0150] Test Example 3

[0151] Step 1) Adding 0.15 g of acrylamide-acryloyloxyethyltrimethylammonium chloride copolymer (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model: thickener SPR-06) with a weight average molecular weight of 18 million to 99.45 g of clean water, controlling the addition rate to prevent the formation of fish eyes and constantly adjusting the rotation speed to ensure a vortex state until the copolymer is fully dissolved to form a uniform solution, thereby preparing a first base liquid;

[0152] Step 2) While maintaining the stirring state, 0.2 g of polyquaternium-126 (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model SPR-102) was added to the first base liquid and stirred evenly to prepare a second base liquid;

[0153] Step 3) lowering the stirring speed, adding 0.2 g of polyoxyethylene cetyl alcohol ether (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model SPR-200) to the second base liquid, and stirring evenly to prepare a third base liquid;

[0154] Step 4) Add 1 g of the nano-silica-containing composition prepared in Example 1 to the third base fluid and stir to obtain the fracturing fluid.

[0155] Test Example 4

[0156] Step 1) Adding 0.12 g of acrylamide homopolymer with a weight average molecular weight of 18 million (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model: thickener SPR-08) to 99.72 g of clean water, controlling the addition speed to prevent the formation of fish eyes, and constantly adjusting the speed to ensure a vortex state, until it is fully dissolved to form a uniform solution, to prepare a first base liquid;

[0157] Step 2) While maintaining the stirring state, 0.08 g of polyquaternium-126 (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd.) was added to the first base liquid and stirred evenly to prepare a second base liquid;

[0158] Step 3) Lower the stirring speed, add 0.08 g of polyoxyethylene cetyl alcohol ether (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model SPR-200) to the second base liquid, and stir evenly to prepare a third base liquid;

[0159] Step 4) Add 0.4 g of the nano-silica-containing composition prepared in Example 1 to the third base fluid and stir to obtain a fracturing fluid.

[0160] Test Example 5

[0161] A fracturing fluid was prepared according to the method of Test Example 2, except that the amount of the nano-silica-containing composition prepared in Example 1 in step 4 was replaced with 1.5 g.

[0162] Test Example 6

[0163] A fracturing fluid was prepared according to the method of Test Example 2, except that the amount of the nano-silica-containing composition prepared in Example 1 in step 4 was replaced with 0.2 g.

[0164] Comparative test example 1

[0165] A fracturing fluid was prepared according to the method of Test Example 2, except that 0.5 g of the nano-silica-containing composition prepared in Example 1 was replaced with 0.5 g of the nano-silica-containing composition prepared in Comparative Example 1 in step 4).

[0166] Comparative test example 2

[0167] A fracturing fluid was prepared according to the method of Test Example 2, except that 0.5 g of the nano-silica-containing composition prepared in Example 2 in step 4) was replaced by 0.5 g of the nano-silica-containing composition prepared in Comparative Example 2.

[0168] Comparative test example 3

[0169] A fracturing fluid was prepared according to the method of Test Example 2, except that 0.5 g of the nano-silica-containing composition prepared in Example 2 in step 4) was replaced by 0.5 g of the nano-silica-containing composition prepared in Comparative Example 3.

[0170] Comparative test example 4

[0171] A fracturing fluid was prepared according to the method of Test Example 2, except that 0.5 g of the nano-silica-containing composition prepared in Example 2 in step 4) was replaced by 0.5 g of the nano-silica-containing composition prepared in Comparative Example 4.

[0172] Comparative test example 5

[0173] A fracturing fluid was prepared according to the method of Test Example 2, except that 0.5 g of the nano-silica-containing composition prepared in Example 4) was replaced with 0.5 g of the fracturing aid in Comparative Example 5.

[0174] Comparative Test Example 6

[0175] The fracturing fluid was prepared according to the method of Test Example 2, except that 0.5 g of the nano-silica-containing composition prepared in Example 4) was replaced with 1 g of the fracturing drainage agent in Comparative Example 5.

[0176] Comparative Test Example 7

[0177] A fracturing fluid was prepared according to the method of Test Example 2, except that 0.5 g of the nano-silica-containing composition prepared in Example 4) was replaced with 2.6 g of ethylene glycol.

[0178] Comparative test example 8

[0179] A fracturing fluid was prepared according to the method of Test Example 2, except that 0.5 g of the nano-silica-containing composition prepared in Example 4) was replaced with 10 g of urea.

[0180] Comparative test example 9

[0181] A fracturing fluid was prepared according to the method of Test Example 2, except that 0.5 g of the nano-silica-containing composition prepared in Example 4) was replaced with 5 g of sodium perfluorononenyloxybenzenesulfonate.

[0182] Comparative test example 10

[0183] The fracturing fluid was prepared according to the method of Test Example 2, except that 0.5 g of the nano-silicon dioxide-containing composition prepared in Example 4 was not added. The fracturing fluid prepared in Comparative Test Example 10 was used as the original fracturing fluid.

[0184] The adsorption capacity of each fracturing fluid prepared in Test Examples 2-6 and Comparative Test Examples 1-10 was measured, and the adsorption capacity of the original fracturing fluid was used as the The adsorption reduction rate is calculated according to formula (I): See the results

[0185] Table 3;

[0186]

[0187] Where:

[0188] ——Fracturing fluid adsorption reduction rate, %;

[0189] ——initial adsorption force of original fracturing fluid, mN;

[0190] —The adsorption capacity of the fracturing fluid after adding the composition provided by the present invention, the fracturing drainage agent, ethylene glycol, urea, or sodium perfluorononenyloxybenzenesulfonate, in mN.

[0191] The fracturing fluids prepared in Test Examples 2-6 and Comparative Test Examples 1-10 were respectively used in a core displacement device to conduct a tight sandstone core damage performance evaluation experiment in accordance with the standard SY / T 5107-2016 "Water-based Fracturing Fluid Performance Evaluation Method", specifically as follows: the fracturing fluids of each test example were added to a high-temperature and high-pressure filter loss tester, the temperature was set to 80°C and the pressure was set to 3.5 MPa, and 300 mL of filtrate was obtained. Natural tight sandstone cores with permeabilities of the same order of magnitude were selected, and the permeabilities of the cores before and after filtrate damage were measured. The reduction rate of the core permeability after filtrate damage compared to the core permeability before damage (i.e., the core damage rate) was calculated. The results are shown in Table 3.

[0192] The fracturing fluids prepared in Test Examples 2-6 and Comparative Test Examples 1-10 were subjected to permeability recovery rate (flowback efficiency) evaluation experiments as follows: natural tight sandstone cores with permeabilities of the same order of magnitude were selected, 20,000 mg / L standard brine (containing 2 wt% KCl + 5.5 wt% NaCl + 0.45 wt% MgCl2 + 0.55 wt% CaCl2) was used to establish an initial water saturation of 40 wt%, and the initial permeability of the cores was measured by gas measurement; 0.02 wt% of the solution was added to each fracturing fluid sample. The ammonium persulfate was used to break the gel for 180 minutes to obtain a breaking fluid. The breaking fluid was heated to 80°C and then added to the intermediate container. The fluid was pressurized to 3.5 MPa by a pressure source and then squeezed into the core from the other end of the core holder. The time for displacing the damaged fluid with the breaking fluid was 180 minutes. The gas-tested core permeability was measured 24 hours after being damaged by the breaking fluid for 180 minutes. The ratio of the gas-tested core permeability 24 hours after damage to the initial permeability before damage was calculated to obtain the permeability recovery rate of the fracturing fluid (24-hour flowback efficiency). The results are shown in Table 3.

[0193] Table 3

[0194]

[0195]

[0196] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A composition containing nano-silica, the composition containing modified nano-silica and a solvent, characterized in that: Based on the total amount of the composition, the content of modified nano-silicon dioxide is 30-50% by weight, and the hydrodynamic diameter D of the molecular aggregate of the composition is 50 =90-150μm, D 90 =180-300μm, adsorption force is 0.3-0.4mN.

2. The composition according to claim 1, wherein The molecular aggregate hydrodynamic diameter D of the composition 10 Less than 5μm, with diameters ranging from 2-250μm.

3. The composition according to claim 1 or 2, wherein The surface tension of the composition does not exceed 25 mN / m, preferably 20-23 mN / m.

4. The composition according to any one of claims 1 to 3, wherein The adsorption reduction rate of the composition to the fracturing fluid composed of 0.1 weight percent of a thickener, 0.05 weight percent of a drainage aid, and 0.05 weight percent of a clay stabilizer and having an adsorption force of 0.52 mN is between 24.5% and 50%.

5. The composition according to any one of claims 1 to 4, wherein The modified nano-silica contains a structural unit a represented by formula (I) with or without a substituent on the benzene ring. Among them, R I 、R II 、R III Each is independently hydrogen or C1-C5 alkyl, and m is an integer from 0 to 5; Preferably, based on the total amount of the composition, the content of the structural unit a is 3-15 wt%.

6. The composition according to any one of claims 1 to 5, wherein The modified nano-silica surface is adsorbed with active groups containing fluorine-carbon chains; Preferably, the active group of the fluorine-containing carbon chain is a C4-C10 perfluoroalkyl group, a C4-C10 perfluoroalkoxy group, a substituted aromatic group containing a C4-C10 perfluoroalkyl group, or a substituted aromatic group containing a C4-C10 perfluoroalkoxy group; more preferably, it is a perfluorononenyloxyphenyl group and / or a perfluorooctyl group; Preferably, based on the total amount of the composition, the content of the fluorocarbon chain is 7-20 wt%.

7. The composition according to any one of claims 1 to 6, wherein The solvent is water and / or organic alcohol.

8. A method for preparing a composition containing nano-silicon dioxide, characterized in that: The method comprises: hydroxylating gas-phase nano-silica in a solvent, contacting the gas-phase nano-silica with a monomer A represented by formula (II) in the presence of an initiator, and mixing the obtained product with a fluorocarbon surfactant; Among them, R I 、R II 、R III Each is independently hydrogen or a C1-C5 alkyl group, m is an integer of 0-5, and the benzene ring of the monomer A may have a substituent.

9. The preparation method according to claim 8, wherein The hydroxylation process includes: reacting the fumed nano-silica with an organic acid in the solvent in step I, and then reacting with a diol in step II; Preferably, the conditions of reaction I include a temperature of 70-90° C. and a time of 0.5-1.5 hours; the conditions of reaction II include a temperature of 70-90° C., a rotation speed of 7500-8500 rpm, and a time of 0.5-1.5 hours; Preferably, the solvent is water and / or an organic alcohol, the organic acid is selected from at least one of citric acid, malic acid and oxalic acid, and the diol is a C2-C6 aliphatic diol, more preferably ethylene glycol; Preferably, the weight ratio of the fumed nano-silica, the organic acid and the diol is 1:0.5-1:2-3.

10. The preparation method according to claim 8 or 9, wherein The contact conditions include a temperature of 60-80°C and a time of 2-8 hours; The initiator is an azo initiator; Preferably, the molar ratio of the nano-silica to the monomer A is 1:2-5.

11. The preparation method according to any one of claims 8 to 10, wherein The nano-silicon dioxide has a particle size of 3-20 nm and a specific surface area of 185-410 m 2 / g, the apparent density is 30-60g / L; Preferably, the fumed nano-silica contains nano-silica of a first particle size and nano-silica of a second particle size, wherein the particle size of the nano-silica of the first particle size is 3-5 nm, and the particle size of the nano-silica of the second particle size is 15-20 nm; Preferably, the molar ratio of the first particle size nano-silicon dioxide to the second particle size nano-silicon dioxide is 1:1-3.

12. The preparation method according to any one of claims 8 to 11, wherein The mixing conditions include a temperature of 60-80° C. and a time of 2-8 hours.

13. The preparation method according to any one of claims 8 to 12, wherein: The molar ratio of the nano-silica to the fluorocarbon surfactant is 1:1-2.

14. The preparation method according to any one of claims 8 to 13, wherein: The molar ratio of fluorine element to carbon element in the fluorocarbon surfactant is 1-3:1; Preferably, the fluorocarbon surfactant has an active group containing a fluorinated carbon chain, and the active group containing a fluorinated carbon chain is a C4-C10 perfluoroalkyl group or a C4-C10 perfluoroalkoxy group, a substituted aromatic group containing a C4-C10 perfluoroalkyl group, or a substituted aromatic group containing a C4-C10 perfluoroalkoxy group; more preferably, the fluorocarbon surfactant is perfluorononenyloxybenzenesulfonate and / or perfluorooctanesulfonate.

15. A composition containing nano-silicon dioxide obtained by the preparation method according to any one of claims 8 to 14.

16. Use of the nano-silica-containing composition according to any one of claims 1 to 7 and claim 15 in a fracturing fluid, preferably as a plugging agent.

17. A fracturing fluid comprising the nano-silica-containing composition according to any one of claims 1 to 7 and claim 15.

18. The fracturing fluid according to claim 17, wherein: Based on the total amount of the fracturing fluid, the content of the composition containing nano-silicon dioxide is 0.3-1% by weight.

19. The fracturing fluid according to claim 17 or 18, wherein: The fracturing fluid also contains, based on the total amount of the fracturing fluid, 0.05-0.15 weight percent of a thickener, 0.05-0.2 weight percent of a drainage aid, and 0.05-0.2 weight percent of a clay stabilizer; Preferably, the thickener is an acrylamide homopolymer and / or a copolymer of acrylamide and other monomers, wherein the other monomers are selected from at least one of acryloyloxyethyltrimethylammonium chloride, sodium acrylate, and acrylic acid; further preferably, the copolymer of acrylamide and other monomers is at least one of acrylamide-acryloyloxyethyltrimethylammonium chloride copolymer, acrylamide-sodium acrylate-acrylic acid copolymer, and acrylamide-acryloyloxyethyltrimethylammonium chloride-sodium acrylate-acrylic acid copolymer; Preferably, the drainage aid is polyoxyethylene amine ether and / or polyoxyethylene fatty alcohol ether; Preferably, the polyoxyethylene amine ether is oleylamine polyoxyethylene ether and / or rosin amine polyoxyethylene ether; The polyoxyethylene fatty alcohol ether is at least one of polyoxyethylene lauryl alcohol ether, polyoxyethylene tetradecanol ether, polyoxyethylene cetyl alcohol ether and polyoxyethylene stearyl alcohol ether; Preferably, the clay stabilizer is dimethylamine quaternary ammonium salt and / or polyquaternium salt.

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