Research On The Synthesis Of Superhydrophobic/Amphiphobic Nanofluids And Their Self-Cleaning Properties On Core Surface

With the further exploration and development of conventional oil and gas reservoirs,the oil and gas reserves of conventional oil and gas reservoirs are decreasing day by day,and it is becoming increasingly difficult to meet the growing demand of oil and gas.Unconventional oil and gas,especially shale oil and gas,has gradually become the main field of oil and gas exploration and development,but its characteristics of dense pore throats,deep reservoir burial and high formation pressure pose new challenges to the "efficient,safe,environmentally friendly and economical" goal of unconventional oil and gas drilling.Therefore,the required performances of drilling fluids,which are indispensable in unconventional oil and gas drilling,have been increasing.In this paper,superhydrophobic nanofluids suitable for water-based drilling fluids and superamphiphobic nanofluids suitable for oil-based drilling fluid were synthesized from the perspective of changing surface chemical energy,and amphiphobic nanofluids with a special "pearls chain" structure were synthesized from the perspective of changing the surface physical structure.All these three kinds of nanofluids can improve the self-cleaning properties of rock surface.In addition,superhydrophobic nanofluids can enhance the inhibition performance of water-based drilling fluids,superamphiphobic nanofluids can enhance the emulsion stability and borehole wall stability of oil-based drilling fluids,amphiphobic nanofluids can improve the shear and iubrication performance of water-based drilling fluids,and the mechanisms of these three nanofluids were analyzed.In this paper,the fluoride-free superhydrophobic nanofluids were synthesized in one step by sol-gel method through imitating the self-cleaning performance of lotus leaf surface.Superhydrophobic nanofluids can reverse the wettability of rock surface to superhydrophobic,and the wettability is not affected by temperature,salt solution and p H=5-11,the surface self-cleaning property was improved,and the capillary force in aqueous phase was reversed,but it not resistant to friction.Through the evaluation of inhibition performance,it was found that the superhydrophobic nanofluids have good inhibition performance.Superhydrophobic nanofluids can reduce viscosity and filter loss of the water-based drilling fluids,and its treatment effect was better than traditional inhibitors,such as potassium chloride and polyetheramine.In order to further enhance the oleophobicity of the core surface,the superamphiphobic nanofluids were synthesized by modifying fluorinated groups on the nano-silica surface in this paper.The superamphiphobic nanofluids enlarge the oil contact angle greater than 150 °,achieving superamphiphobic wettability of the core surface,further improving the surface self-cleaning characteristics,and simultaneously reversing the capillary forces of the capillary in oil phase and water phase,decreasing the liquid value of spontaneous imbibition,and ensuring that the rock will not be eroded by liquid which will resulted in strength reduction,so as to stabilize the wellbore.At the same time,superamphiphobic nanofluids can reduce the oil-water interfacial tension,so as to maintain the stability of the oil-water emulsion.According to the performance evaluation of superamphiphobic nanofluids in the oil-based drilling fluids,superamphiphobic nanofluids can increase the demulsification voltage and reduce the high-temperature and high-pressure filtration loss of the drilling fluids.Through imitating the special nano-micro multi-level structure on the nature plants surfaces,the amphiphobic nanofluids were synthesized by mixing nanometer-diameter nano-silica and micrometer-length multi-walled carbon nanotubes and grafting a small amount of fluorinated groups on surface.This article proposed for the first time that a special "pearls chain" structure can effectively increase the rock surface roughness,reverse the wettability of rock surface to amphiphobic and improve the self-cleaning of the rock surface.At the same time,the amphiphobic nanofluids can improve the shear and lubrication performance of water-based drilling fluids.The field application proved that the high performance water-based drilling fluids formed with amphiphobic nanofluids as the core agent had greatly reduced the occurrence of complex conditions downhole.