A super-low-temperature nano-silica dispersion system, its preparation method and application

Abstract

The present invention belongs to the technical field of drilling fluids, and particularly relates to an ultra-low temperature nano-silica dispersion system and a preparation method and application thereof. The present invention provides a preparation method for an ultra-low temperature nano-silica dispersion system, which comprises the following steps: mixing a nano-silica particle suspension and a non-ionic surfactant for the first time and performing a dehydration reaction to obtain modified nano-silica particles; the non-ionic surfactant includes one or more of fatty alcohol polyoxyethylene ether, fatty alcohol polyoxypropylene polyoxyethylene ether, isomeric tridecyl alcohol polyoxyethylene ether, and coconut oil amide polyoxyethylene ether; mixing the modified nano-silica particles and an oil phase for the second time to obtain the ultra-low temperature nano-silica dispersion system. The nano-silica dispersion system obtained by the preparation method provided by the present invention can maintain appropriate viscosity and stable rheological properties in an ultra-low temperature environment of 25 to -22 °C, and thus can be applied to ultra-low temperature drilling operations such as deep water, polar regions, and permafrost layers.

Description

Technical Field

[0001] The present invention belongs to the technical field of drilling fluids, and particularly relates to a super-low temperature nano-silica dispersion system, a preparation method thereof, and an application thereof. Background Art

[0002] Deep waters, polar regions, and permafrost areas contain rich mineral and oil and gas resources. However, due to the low temperatures on the seabed and the polar surface, drilling and development work faces huge challenges. First, it is necessary to ensure that the drilling fluid has good rheological properties at ultra-low temperatures. If the viscosity of the drilling fluid is too low, it is not conducive to carrying drill cuttings or ice chips at the bottom of the hole, and it seriously scours the hole wall, easily causing hole wall instability. If the viscosity of the drilling fluid is too high, the flow resistance is large, the pump pressure is high, and complex drilling accidents are likely to occur. Commonly used polar drilling fluids are oil-based drilling fluids (mainly aviation kerosene-based drilling fluids) and ester-based drilling fluids, etc. However, these drilling fluids have poor viscosity increasing and shear strengthening properties at low temperatures. In conventional oil-based drilling fluids, organophilic clay is usually used as a viscosity increasing and shear strengthening agent to increase the viscosity and shear force of the system. However, the viscosity of this type of drilling fluid increases sharply when the temperature drops, greatly limiting its application at ultra-low temperatures.

[0003] US Patent US9562146 modified clay minerals with quaternary ammonium salts with branched alkyl chains to prepare a new type of organophilic clay, and used it to formulate an oil-based drilling fluid. The rheological properties of this drilling fluid are stable in the range of 4 - 49°C. MI-SWACO Company used organophilic clay and a flow pattern regulator together to increase the viscosity and shear force of the drilling fluid, achieving constant rheological properties of the drilling fluid in the range of 4 - 65°C. However, there are few reports on viscosity increasing and shear strengthening agents for drilling fluids in ultra-low temperature (-5°C or even lower) environments such as deep sea, polar regions, and permafrost areas. Chinese Patent CN115159536 prepared an ultra-low temperature (-35°C) drilling fluid using a composite modifier of double-chain alkyl quaternary ammonium salt and caprolactam, and used an organophilic clay type shear strengthening agent. However, the proportions of the two modifiers and the proportion of the composite modifier to montmorillonite need to be strictly controlled during preparation. Therefore, it is urgent to develop a new type of ultra-low temperature drilling fluid shear strengthening agent and construct an ultra-low temperature drilling fluid system to improve drilling efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a super-low temperature nano-silica dispersion system, a preparation method thereof, and an application thereof. The nano-silica dispersion system obtained by the preparation method provided by the present invention can maintain an appropriate viscosity and stable rheological properties in an ultra-low temperature environment.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a super-low temperature nano-silica dispersion system, comprising the following steps:

[0007] First, mix the nano-silica particle suspension and the non-ionic surfactant, and carry out a dehydration reaction to obtain modified nano-silica particles; the non-ionic surfactant includes one or more of fatty alcohol polyoxyethylene ether, fatty alcohol polyoxypropylene polyoxyethylene ether, isomeric tridecanol polyoxyethylene ether, and coconut oil amide polyoxyethylene ether;

[0008] Second, mix the modified nano-silica particles and the oil phase to obtain the ultra-low temperature nano-silica dispersion system.

[0009] Preferably, the mass percentage content of nano-silica particles in the nano-silica particle suspension is 1% - 10%, and the particle size is 10 - 40 nm.

[0010] Preferably, the mass ratio of the non-ionic surfactant to the nano-silica particles in the nano-silica particle suspension is 20% - 120%.

[0011] Preferably, the temperature of the first mixing is 30 - 90 °C, and the time is 1 - 4 h;

[0012] The first mixing method is stirring; the stirring speed is 500 - 1000 rpm.

[0013] Preferably, the temperature of the dehydration reaction is 100 - 150 °C, and the time is 10 - 24 h.

[0014] Preferably, the oil phase includes one or more of isododecane, isotetradecane, isohexadecane, kerosene, gas-to-liquid oil, and white oil;

[0015] The mass ratio of the modified nano-silica particles to the oil phase is 1% - 5%.

[0016] Preferably, the second mixing includes stirring and ultrasonic treatment in sequence.

[0017] Preferably, the stirring speed is 500 - 1200 rpm, and the time is 5 - 60 min;

[0018] The ultrasonic treatment is intermittent ultrasonic treatment; the power of the intermittent ultrasonic treatment is 200 - 600 W, the single time is 5 - 10 s, the interval time is 5 - 10 s, and the number of cycles is 20 - 60.

[0019] The present invention also provides an ultra-low temperature nano-silica dispersion system obtained by the preparation method described in the above technical solution.

[0020] The present invention also provides the application of the ultra-low temperature nano-silica dispersion system described in the above technical solution in drilling fluid or lubricating oil.

[0021] The present invention provides a method for preparing an ultra-low temperature nano-silica dispersion system, comprising the following steps: firstly, mixing nano-silica particle suspension and a non-ionic surfactant, and carrying out a dehydration reaction to obtain modified nano-silica particles; the non-ionic surfactant includes one or more of fatty alcohol polyoxyethylene ether, fatty alcohol polyoxypropylene polyoxyethylene ether, isomeric tridecyl alcohol polyoxyethylene ether, and coconut oil amide polyoxyethylene ether; then, mixing the modified nano-silica particles and an oil phase to obtain the ultra-low temperature nano-silica dispersion system. In the present invention, the non-ionic surfactant is stably adsorbed on the surface of nano-silica particles through the combined action of chemical and physical adsorption, preventing the desorption of the surfactant caused by temperature and pressure during the drilling process, thereby improving the dispersion stability of nano-silica particles in the oil phase under low temperature and high pressure. Moreover, the non-ionic surfactant contains both a hydrophobic alkyl chain and a hydrophilic polyoxyethylene chain, which can promote the moderate dispersion of nano-silica particles in the oil phase, construct a strong and stable network structure, endow the dispersion system with good rheological properties, and avoid the too low viscosity of the dispersion system caused by the over-dispersion of nano-silica particles and the instability of the system caused by particle aggregation. In addition, the polyoxyethylene chain on the non-ionic surfactant can inhibit the ordered arrangement of the alkyl chain on the particle surface in the oil phase during cooling, reduce the influence of temperature on the solvation of nano-silica particles, and further prevent the gelation of the dispersion system during cooling. Therefore, the nano-silica dispersion system obtained by the preparation method provided by the present invention can establish a relatively high viscosity at a relatively low nano-silica particle concentration, and maintain appropriate and stable rheological properties in an ultra-low temperature environment of 25~-22℃, so that it can be applied to ultra-low temperature drilling operations such as deep water, polar regions, and permafrost layers, solving the problems of poor rheological properties of drilling fluids at ultra-low temperatures and difficult drilling operations and non-recyclable drilling fluids caused by too high or too low viscosities. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0023] Figure 1 High-resolution O1s spectra of unmodified nano-silica and modified nano-silica particles prepared in Example 2 and Example 4;

[0024] Figure 2 Inverted physical pictures of samples of nano-silica dispersion systems prepared in Comparative Example 2, Example 2, Example 4, and Example 5 after being placed at 25℃ and -22℃ for 7 days;

[0025] Figure 3Curves showing the variation of the apparent viscosity of the nano-silica dispersion systems prepared in Comparative Example 1, Comparative Example 2, Example 2 and Example 5 with the shear rate. Detailed implementation mode

[0026] The present invention provides a method for preparing a nano-silica dispersion system at ultra-low temperature, comprising the following steps:

[0027] First mix the nano-silica particle suspension and a non-ionic surfactant, and carry out a dehydration reaction to obtain modified nano-silica particles; the non-ionic surfactant includes one or more of fatty alcohol polyoxyethylene ether, fatty alcohol polyoxypropylene polyoxyethylene ether, isomeric tridecanol polyoxyethylene ether, and coconut oil amide polyoxyethylene ether;

[0028] Second mix the modified nano-silica particles and an oil phase to obtain the nano-silica dispersion system at ultra-low temperature.

[0029] In the present invention, unless otherwise specified, all raw material components are commercially available products well-known to those skilled in the art.

[0030] In the present invention, the nano-silica particle suspension and the non-ionic surfactant are first mixed, and a dehydration reaction is carried out to obtain modified nano-silica particles.

[0031] In the present invention, the mass percentage content of nano-silica particles in the nano-silica particle suspension is preferably 1% to 10%, more preferably 2% to 8%, and most preferably 2% to 5%; the particle size is preferably 10 to 40 nm, more preferably 20 to 30 nm; the solvent is preferably deionized water.

[0032] In the present invention, the preparation process of the nano-silica particle suspension preferably includes the following steps: mixing nano-silica particles and deionized water to obtain the nano-silica particle suspension.

[0033] In the present invention, the temperature of the mixing is preferably room temperature; the mixing method is preferably stirring; the temperature of the stirring is preferably room temperature; the time is preferably 0.5 to 2 h, more preferably 1 to 1.5 h; the room temperature has the meaning well-known in the art and refers to 25 ± 5°C.

[0034] In the present invention, the non-ionic surfactant preferably includes one or more of fatty alcohol polyoxyethylene ether, fatty alcohol polyoxypropylene polyoxyethylene ether, isomeric tridecyl alcohol polyoxyethylene ether, and coconut oil amide polyoxyethylene ether, more preferably fatty alcohol polyoxyethylene ether and / or isomeric tridecyl alcohol polyoxyethylene ether, and most preferably fatty alcohol polyoxyethylene ether; when the non-ionic surfactant is more than two of the above specific types, the present invention has no special limitation on the ratio of the non-ionic surfactant; the carbon number of the alkyl chain in the aliphatic polyoxyethylene ether is preferably 8-18, more preferably 10-16, and most preferably 12-14; the number of ethoxy groups is preferably 3-9, more preferably 5-7.

[0035] In the present invention, the mass ratio of the non-ionic surfactant to the nano-silica particles in the nano-silica particle suspension is preferably 20% - 120%, more preferably 30% - 100%, and most preferably 50% - 80%.

[0036] In the present invention, the temperature of the first mixing is preferably 30 - 90°C, more preferably 40 - 80°C, and most preferably 50 - 70°C; the time is preferably 1 - 4 h, more preferably 2 - 3 h; the manner of the first mixing is preferably stirring; the rotation speed of the stirring is preferably 500 - 1000 rpm, more preferably 600 - 800 rpm.

[0037] In the present invention, the function of the first mixing is to make the nano-silica particle suspension reach a fluid state.

[0038] In the present invention, the temperature of the dehydration reaction is preferably 100 - 150°C, more preferably 110 - 140°C, and most preferably 120 - 130°C; the time is preferably 10 - 24 h, more preferably 12 - 20 h, and most preferably 14 - 18 h.

[0039] In the present invention, the temperature of the dehydration reaction is set within the above range to promote the dehydration reaction between the silanol groups on the particle surface and the alcohol hydroxyl groups on the non-ionic surfactant, so that the non-ionic surfactant is chemically grafted onto the surface of the nano-silica particles.

[0040] In the present invention, after the dehydration reaction, it preferably further includes first grinding, preparing a suspension, filtering, washing, drying, and second grinding in sequence.

[0041] In the present invention, the solvent for preparing the suspension is preferably anhydrous ethanol; the reagent for washing is preferably deionized water; the drying is preferably vacuum drying; the temperature of the vacuum drying is preferably 60-90 °C, and the time is preferably 4-24 h; the present invention has no other special limitations on the processes of preparing the suspension, filtration and washing, and the methods well-known to those skilled in the art can be adopted; the present invention has no other special limitations on the processes of the first grinding and the second grinding, and the modified nano-silica particles can be made without massive particles by the methods well-known to those skilled in the art.

[0042] In the present invention, the functions of preparing the suspension, filtration and washing are to remove the excess surfactant.

[0043] After obtaining the modified nano-silica particles, the present invention mixes the modified nano-silica particles with the oil phase for the second time to obtain the ultra-low temperature nano-silica dispersion system.

[0044] In the present invention, the oil phase preferably includes one or more of isododecane, isotetradecane, isohexadecane, kerosene, gas-to-liquid oil and white oil, more preferably one or more of isohexadecane, kerosene and white oil, and most preferably isohexadecane and / or kerosene; when the oil phase is two or more of the above specific types, the present invention has no special limitations on the ratio of the oil phase; the mass ratio of the modified nano-silica particles to the oil phase is preferably 1%-5%, more preferably 2%-4%, and most preferably 3%-4%.

[0045] In the present invention, the reason for using the above specific types of oil phase is that they are all isoparaffins or contain a relatively high proportion of isoparaffins, the viscosity is less affected by temperature, and they have a low freezing point, which is beneficial to preparing a nano-silica dispersion system with stable rheological properties at ultra-low temperature (-22 °C), providing technical support for the construction of an ultra-low temperature drilling fluid system.

[0046] In the present invention, the second mixing preferably includes stirring and ultrasonic treatment in sequence.

[0047] In the present invention, the rotation speed of the stirring is preferably 500-1200 rpm, more preferably 800-1000 rpm; the time is preferably 5-60 min, more preferably 10-50 min, and most preferably 30-40 min.

[0048] In the present invention, the ultrasonic treatment is preferably intermittent ultrasonic treatment; the power of the intermittent ultrasonic treatment is preferably 200 - 600 W, more preferably 300 - 500 W, and most preferably 400 - 500 W; the single time is preferably 5 - 10 s, more preferably 5 - 8 s; the interval time is preferably 5 - 10 s, more preferably 5 - 8 s; the number of cycles is preferably 20 - 60, more preferably 30 - 50, and most preferably 40 - 50.

[0049] In the present invention, the non - ionic surfactant is stably adsorbed on the surface of nano - silica particles through the combined action of chemical and physical adsorption, preventing the desorption of the surfactant caused by temperature and pressure during drilling, thereby improving the dispersion stability of nano - silica particles in the oil phase under low temperature and high pressure. Moreover, the non - ionic surfactant contains both hydrophobic alkyl chains and hydrophilic polyoxyethylene chains, which can promote the moderate dispersion of nano - silica particles in the oil phase, construct a strong and stable network structure, endow the dispersion system with good rheological properties, and avoid the too - low viscosity of the dispersion system caused by the over - dispersion of nano - silica particles and the instability of the system caused by particle aggregation. In addition, the polyoxyethylene chains on the non - ionic surfactant can inhibit the ordered arrangement of the alkyl chains on the particle surface in the oil phase during cooling, reduce the influence of temperature on the solvation of nano - silica particles, and thus prevent the gelation of the dispersion system during cooling. Therefore, the nano - silica dispersion system obtained by the preparation method provided by the present invention can establish a high viscosity at a relatively low nano - silica particle concentration and maintain appropriate and stable rheological properties in an ultra - low temperature environment of 25 - -22°C, so that it can be applied to ultra - low temperature drilling operations such as deep - water, polar, and permafrost drilling, solving the problems of poor rheological properties of drilling fluids under ultra - low temperatures and difficult drilling operations and non - recyclable drilling fluids caused by too high or too low viscosities. At the same time, in the preparation method provided by the present invention, the preparation processes of the modified particles and the dispersion system are simple and easy to operate, without the need for compounding and strict control of raw material dosages. The raw materials used in the product are cheap, easy to obtain, and have low toxicity, so it has broad industrial application prospects.

[0050] The present invention also provides an ultra - low temperature nano - silica dispersion system obtained by the preparation method described in the above technical solution.

[0051] The ultra - low temperature nano - silica dispersion system provided by the present invention can maintain appropriate and stable rheological properties in the range of 25 - -22°C, with low temperature sensitivity, and has great application potential in fields such as lubricating oils, polar or deep - water drilling fluids that need to work in extreme environments.

[0052] The present invention also provides the application of the ultra - low temperature nano - silica dispersion system described in the above technical solution in drilling fluids or lubricating oils.

[0053] In the present invention, the drilling fluid is preferably a deep - water drilling fluid, a polar drilling fluid, or a permafrost drilling fluid.

[0054] There is no special method for the application process of the ultra-low temperature nano-silica dispersion system in drilling fluid or lubricating oil, and the methods well-known to those skilled in the art can be adopted.

[0055] The ultra-low temperature nano-silica dispersion system provided by the present invention can significantly improve its applicability in extreme environments such as ultra-low temperature when applied to drilling fluid or lubricating oil, and has great application potential especially in the fields of polar or deep-sea drilling.

[0056] In order to further illustrate the present invention, the ultra-low temperature nano-silica dispersion system provided by the present invention, its preparation method and application will be described in detail below in conjunction with the drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0057] Example 1

[0058] Nano-silica particles with an initial particle size of 12 nm were uniformly dispersed in deionized water and stirred at high speed for 30 min at room temperature to obtain a nano-silica water suspension. The nano-silica particles accounted for 3% of the total mass of the suspension. The suspension was heated in a water bath to 60 °C and kept stable, and then a non-ionic surfactant fatty alcohol polyoxyethylene ether (AEO3) was added. AEO3 accounted for 20% of the mass of the nano-silica particles, and the mixture was stirred at 800 rpm at 60 °C for 2 h. After stirring, the water suspension was transferred to a glass dish, and then heat-treated at 120 °C for 12 h to graft AEO3 onto the surface of the nano-silica and obtain a dried modified nano-silica solid. In order to remove the excess AEO3, the above solid was ground into powder and redispersed in absolute ethanol, and the final modified nano-silica particles were obtained through rinsing, suction filtration, drying and grinding. The obtained modified nano-silica particles were added to kerosene, and the mass percentage of the nano-silica particles was 3%. The above system was stirred at 1000 rpm for 30 min, and then ultrasonicated 20 times at a power of 400 W, with each ultrasonic wave lasting for 5 s and an interval of 5 s, to obtain the final modified nano-silica dispersion system.

[0059] Example 2

[0060] Disperse nano-silica particles with an initial particle size of 12 nm evenly into deionized water, and stir at high speed for 30 min at room temperature to obtain a nano-silica aqueous suspension. The nano-silica particles account for 3% of the total mass of the suspension. Heat the suspension in a water bath to 60 °C and keep it stable, then add non-ionic surfactant AEO3, where AEO3 accounts for 50% of the mass of the nano-silica particles, and stir at 800 rpm at 60 °C for 2 h. After stirring is completed, transfer the aqueous suspension to a glass dish, and then perform high-temperature treatment at 120 °C for 12 h to graft AEO3 onto the surface of the nano-silica and obtain a dry modified nano-silica solid. To remove the excess AEO3, grind the above solid into powder and redisperse it in absolute ethanol, and obtain the final modified nano-silica particles through rinsing, suction filtration, drying, and grinding. Add the obtained modified nano-silica particles to kerosene, where the mass percentage of the nano-silica particles is 3%. Stir the above system at 1000 rpm for 30 min, and then perform ultrasonic treatment 20 times at a power of 400 W, with each ultrasonic treatment lasting 5 s and an interval of 5 s to obtain the final modified nano-silica dispersion system.

[0061] Example 3

[0062] Disperse nano-silica particles with an initial particle size of 12 nm evenly into deionized water, and stir at high speed for 30 min at room temperature to obtain a nano-silica aqueous suspension. The nano-silica particles account for 3% of the total mass of the suspension. Heat the suspension in a water bath to 60 °C and keep it stable, then add non-ionic surfactant AEO3, where AEO3 accounts for 80% of the mass of the nano-silica particles, and stir at 800 rpm at 60 °C for 2 h. After stirring is completed, transfer the aqueous suspension to a glass dish, and then perform high-temperature treatment at 120 °C for 12 h to graft fatty alcohol polyoxyethylene ether onto the surface of the nano-silica and obtain a dry modified nano-silica solid. To remove the excess AEO3, grind the above solid into powder and redisperse it in absolute ethanol, and obtain the final modified nano-silica particles through rinsing, suction filtration, drying, and grinding. Add the obtained modified nano-silica particles to kerosene, where the mass percentage of the nano-silica particles is 3%. Stir the above system at 1000 rpm for 30 min, and then perform ultrasonic treatment 20 times at a power of 400 W, with each ultrasonic treatment lasting 5 s and an interval of 5 s to obtain the final modified nano-silica dispersion system.

[0063] Example 4

[0064] Silica nanoparticles with an initial particle size of 12 nm were uniformly dispersed in deionized water and stirred at high speed for 30 min at room temperature to obtain a silica aqueous suspension. The silica nanoparticles accounted for 3% of the total mass of the suspension. The suspension was heated in a water bath to 60 °C and kept stable, and then a nonionic surfactant, fatty alcohol polyoxyethylene ether (AEO5), was added. AEO5 accounted for 50% of the mass of the silica nanoparticles, and the mixture was stirred at 800 rpm at 60 °C for 2 h. After stirring, the aqueous suspension was transferred to a glass dish and then heat-treated at 120 °C for 12 h to graft the fatty alcohol polyoxyethylene ether onto the surface of the silica nanoparticles and obtain a dried modified silica solid. To remove the excess surfactant, the above solid was ground into a powder and redispersed in absolute ethanol, and the final modified silica nanoparticles were obtained through rinsing, suction filtration, drying, and grinding. The obtained modified silica nanoparticles were added to kerosene, and the mass percentage of the silica nanoparticles was 3%. The above system was stirred at 1000 rpm for 30 min and then ultrasonicated 20 times at a power of 400 W, with each sonication lasting 5 s and an interval of 5 s, to obtain the final modified silica dispersion system.

[0065] X-ray photoelectron spectroscopy characterization was performed on the unmodified silica nanoparticles and the modified silica nanoparticles prepared in Example 2 and Example 4. The obtained high-resolution O 1s spectra are shown in Figure 1 .

[0066] As Figure 1 can be seen, the binding energy of the main peak was observed to be 533.6 eV in the O 1s spectrum of the unmodified particles, while the binding energies of the main peaks of the modified particles in Example 2 and Example 4 shifted to 532.6 and 532.7 eV, respectively. This is mainly attributed to the surface chemically bonded C-O bonds, because physically adsorbed C-O would shift the O 1s to a higher binding energy direction, indicating that the fatty alcohol polyoxyethylene ether was chemically adsorbed onto the particle surface. In addition, when performing peak fitting on the spectra, there was only one peak at 533.6 eV for the unmodified particles, and two peaks at 532.9 and 532.4 eV could be fitted for the modified particles prepared in Example 2, representing Si-O-Si and C-O-C / Si-O-C, respectively. The modified particles prepared in Example 4 had similar results, further indicating that the fatty alcohol polyoxyethylene ether was grafted onto the particle surface through the formation of the chemical bond Si-O-C.

[0067] Example 5

[0068] Silica nanoparticles with an initial particle size of 12 nm were uniformly dispersed in deionized water and stirred at high speed for 30 min at room temperature to obtain a silica nanoparticle aqueous suspension. The silica nanoparticles accounted for 3% of the total mass of the suspension. The suspension was heated in a water bath to 60 °C and kept stable, and then the nonionic surfactant fatty alcohol polyoxyethylene ether (AEO7) was added. AEO7 accounted for 50% of the mass of the silica nanoparticles, and the mixture was stirred at 800 rpm at 60 °C for 2 h. After stirring, the aqueous suspension was transferred to a glass dish and then heat-treated at 120 °C for 12 h to graft the fatty alcohol polyoxyethylene ether onto the surface of the silica nanoparticles and obtain a dried modified silica nanoparticle solid. To remove the excess AEO7, the above solid was ground into powder and redispersed in absolute ethanol, and the final modified silica nanoparticles were obtained through rinsing, suction filtration, drying, and grinding. The obtained modified silica nanoparticles were added to kerosene, and the mass percentage of the silica nanoparticles was 3%. The above system was stirred at 1000 rpm for 30 min and then ultrasonicated 20 times at a power of 400 W, with each ultrasonic treatment lasting 5 s and an interval of 5 s, to obtain the final modified silica nanoparticle dispersion system.

[0069] Example 6

[0070] Silica nanoparticles with an initial particle size of 12 nm were uniformly dispersed in deionized water and stirred at high speed for 30 min at room temperature to obtain a silica nanoparticle aqueous suspension. The silica nanoparticles accounted for 3% of the total mass of the suspension. The suspension was heated in a water bath to 60 °C and kept stable, and then the nonionic surfactant AEO3 was added. AEO3 accounted for 50% of the mass of the silica nanoparticles, and the mixture was stirred at 800 rpm at 60 °C for 2 h. After stirring, the aqueous suspension was transferred to a glass dish and then heat-treated at 120 °C for 12 h to graft AEO3 onto the surface of the silica nanoparticles and obtain a dried modified silica nanoparticle solid. To remove the excess AEO3, the above solid was ground into powder and redispersed in absolute ethanol, and the final modified silica nanoparticles were obtained through rinsing, suction filtration, drying, and grinding. The obtained modified silica nanoparticles were added to kerosene, and the mass percentage of the silica nanoparticles was 4%. The above system was stirred at 1000 rpm for 30 min and then ultrasonicated 20 times at a power of 400 W, with each ultrasonic treatment lasting 5 s and an interval of 5 s, to obtain the final modified silica nanoparticle dispersion system.

[0071] Example 7

[0072] Silica nanoparticles with an initial particle size of 12 nm were uniformly dispersed in deionized water and stirred at high speed for 30 min at room temperature to obtain a silica nanoparticle aqueous suspension. The silica nanoparticles accounted for 3% of the total mass of the suspension. The suspension was heated in a water bath to 60 °C and kept stable, and then non-ionic surfactant AEO3 was added, with AEO3 accounting for 50% of the mass of the silica nanoparticles. Stirring was carried out at 800 rpm at 60 °C for 2 h. After stirring was completed, the aqueous suspension was transferred to a glass dish, and then heat-treated at 120 °C for 12 h to graft AEO3 onto the surface of the silica nanoparticles and obtain a dried modified silica nanoparticle solid. To remove the excess AEO3, the above solid was ground into a powder and redispersed in absolute ethanol, and the final modified silica nanoparticle was obtained through rinsing, suction filtration, drying, and grinding. The obtained modified silica nanoparticles were added to isoparaffin (Isopar M), with the mass percentage of the silica nanoparticles being 3%. The above system was stirred at 1000 rpm for 30 min, and then ultrasonicated 20 times at a power of 400 W, with each ultrasonic treatment lasting 5 s and an interval of 5 s, to obtain the final modified silica nanoparticle dispersion system.

[0073] Comparative Example 1

[0074] To compare the contribution of the polyoxyethylene chain to the stability at ultra-low temperatures, a dispersion system of octadecyl-modified silica nanoparticles was prepared as follows: Silica nanoparticles with an initial particle size of 12 nm were uniformly dispersed in ethanol to obtain a silica nanoparticle suspension, with the silica nanoparticles accounting for 3% of the total mass of the suspension. Then, octadecyl dimethyl chlorosilane (accounting for 30% of the particle mass) was added dropwise to the above dispersion system, and stirring was carried out at 90 °C for 2 h in a nitrogen atmosphere. Solid particles were obtained by centrifugation (rotation speed 8000 rpm, time 10 min, centrifugation 3 times), and during this process, the particles were rinsed with ethanol to remove unreacted octadecyl dimethyl chlorosilane. Finally, the octadecyl-modified silica nanoparticles were placed in a vacuum drying oven (temperature 90 °C, time 24 h), and after drying, they were ground into a powder with a mortar. The obtained octadecyl-modified silica nanoparticles were added to kerosene, with the mass percentage of the silica nanoparticles being 3%. The above system was stirred at 1000 rpm for 30 min, and then ultrasonicated 20 times at a power of 400 W, with each ultrasonic treatment lasting 5 s and an interval of 5 s, to obtain the final octadecyl-modified silica nanoparticle dispersion system.

[0075] Comparative Example 2

[0076] Commercially available octyl-modified silica nanoparticles (R805, Degussa) were added to hydrogenated kerosene, with the mass percentage of the silica nanoparticles being 3%. The above system was stirred at 1000 rpm for 30 min, and then ultrasonicated 20 times at a power of 400 W, with each ultrasonic treatment lasting 5 s and an interval of 5 s, to obtain the final modified silica nanoparticle dispersion system.

[0077] Test example

[0078] Samples of the nano-silica dispersion systems prepared in Comparative Example 2, Example 2, Example 4, and Example 5 were placed at 25 °C and -22 °C for 7 days and then inverted. The physical pictures are shown in Figure 2 .

[0079] From Figure 2 it can be seen that after standing at 25 °C for 7 days, the dispersion systems of Comparative Example 2, Example 2, Example 4, and Example 5 can flow when inverted, indicating that the systems all have appropriate fluidity. After standing at -22 °C for 7 days, the dispersion system of Comparative Example 2 has gelation and does not flow when inverted, indicating that the viscosity and gel strength of the system increase significantly at ultra-low temperatures; while the dispersion systems of Example 2, 4, and 5 do not have gelation and can flow after inversion, indicating that the dispersion system prepared by modifying silica with fatty alcohol polyoxyethylene ether is less affected by low temperatures and can maintain appropriate fluidity at ultra-low temperatures.

[0080] The rheological properties of the nano-silica dispersion systems prepared in Comparative Example 1, Comparative Example 2, Example 2, and Example 5 were tested at 25 °C, 5 °C, -5 °C, and -22 °C. The change curves of the apparent viscosity of the dispersion system with the shear rate are as Figure 3 shown, and the apparent viscosity values are shown in Table 1.

[0081] Table 1 Apparent viscosity values of the nano-silica dispersion systems prepared in Comparative Example 1, Comparative Example 2, Example 2, and Example 5

[0082]

[0083]

[0084] From Figure 3 and Table 1, it can be seen that the apparent viscosity of the dispersion system decreases with the increase of the shear rate at different temperatures, showing the characteristic of shear thinning. At the same shear rate, compared with the dispersion systems of Comparative Examples 1-2, the apparent viscosity of the dispersion systems in Examples 2 and 5 changes less with the decrease of temperature in the range of 25 °C to -22 °C, and the rheological properties can basically remain constant.

[0085] From the above examples, it can be known that the nano-silica dispersion system obtained by the preparation method provided by the present invention can establish a higher viscosity with a lower concentration of nano-silica particles, and maintain appropriate viscosity and stable rheological properties in an ultra-low temperature environment of 25 °C to -22 °C, so that it can be applied to ultra-low temperature drilling operations such as deep water, polar regions, and permafrost layers, and solve the problems of poor rheological properties of drilling fluids at ultra-low temperatures, difficult drilling operations caused by too high or too low viscosity, and inability to recycle drilling fluids.

[0086] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments can also be obtained based on this embodiment without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing an ultra-low temperature nano-silicon oxide dispersion system, characterized in that: The following steps are involved: The nano-silicon oxide particle suspension and the non-ionic surfactant are first mixed and subjected to a dehydration reaction to obtain modified nano-silicon oxide particles; the non-ionic surfactant is a fatty alcohol polyoxyethylene ether; the temperature of the dehydration reaction is 100-150° C.; the mass percentage of the nano-silicon oxide particles in the nano-silicon oxide particle suspension is 1%-10%, and the particle size is 10-20 nm; The mass ratio of the nonionic surfactant to the nano-silicon oxide particles in the nano-silicon oxide particle suspension is 50% to 80%; The carbon number of the alkyl chain in the fatty alcohol polyoxyethylene ether is 12 to 14; The dehydration reaction further includes first grinding, preparing a suspension, filtering, washing, drying and second grinding in sequence; The modified nano silicon oxide particles and the oil phase are mixed for a second time to obtain the ultra-low temperature nano silicon oxide dispersion system.

2. The preparation method according to claim 1, characterized in that: The first mixing temperature is 30 to 90° C. and the time is 1 to 4 hours; The first mixing method is stirring; the stirring speed is 500-1000 rpm.

3. The preparation method according to claim 1, characterized in that: The dehydration reaction time is 10 to 24 hours.

4. The preparation method according to claim 1, characterized in that: The oil phase includes one or more of isododecane, isotetradecane, isohexadecane, kerosene, gas-to-liquids and white oil; The mass ratio of the modified nano silicon oxide particles to the oil phase is 1% to 5%.

5. The preparation method according to claim 1, characterized in that: The second mixing includes stirring and ultrasonic treatment performed sequentially.

6. The preparation method according to claim 5, characterized in that: The stirring speed is 500-1200 rpm, and the time is 5-60 min; The ultrasonic treatment is intermittent ultrasonic treatment; the power of the intermittent ultrasonic treatment is 200-600W, the single time is 5-10s, the interval time is 5-10s, and the number of cycles is 20-60.

7. The ultra-low temperature nano-silicon oxide dispersion system obtained by the preparation method according to any one of claims 1 to 6.

8. Use of the ultra-low temperature nano-silicon oxide dispersion system according to claim 7 in drilling fluid or lubricating oil.

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