Study of Time-Varying Laws of Stability and Wettability of SiO2–H2O Nanofluids with Different Particle Sizes

It has been proven that SiO2–H2O nanofluids have great application potential for water injection in coal seams. To explore the influences of the particle size on the stability and wettability of SiO2–H2O nanofluids, sedimentation observation of nanoparticles (NPs), viscosity tests, pH tests, surface tension tests, and contact angle tests were performed for SiO2–H2O nanofluids with different particle sizes. The research shows that the larger the particle size of SiO2 NPs, the more obvious the aggregation and sedimentation of NPs. The smaller the particle size of SiO2 NPs is, the lower the surface tension and contact angle of the SiO2–H2O nanofluids. As time goes on, SiO2–H2O nanofluids successively show time-varying characteristics in the low stability stage, moderate stability stage, and high stability stage. Therein, the low stability stage is the optimal period for enhancing the water injection in coal seams by nanofluids. The research provides theoretical support for using SiO2–H2O nanofluids to enhance water injection in coal seams.