Influence of size and surface acidity of silica nanoparticles on inhibition of the formation damage by bentonite-free water-based drilling fluids. Part I: nanofluid design based on fluid-nanoparticle interaction

The study aims to evaluate the effect of size and surface acidity of synthesised silica (SiO2) nanoparticles in a bentonite-free water-based drilling fluid (BFWBM) to minimise its impact on formation damage by filtration volume control and mudcake thickness reduction. Nanoparticles were synthesised through the sol-gel method, and the surfaces were modified through the incipient impregnation technique using acidic and basic treatments. The nanoparticles were characterised by dynamic light scattering (DLS), Fourier transforms infrared spectroscopy (FTIR) and zeta potential measurements. Drilling fluid properties in the presence and absence of nanoparticles were evaluated through the analysis of pH, density, solid content, rheology, and static filtration tests at high pressure and temperature. Drilling fluids were described as shear-thinning fluids under the rheological model of Herschel-Bulkley. The smallest nanoparticles (Si11) contributed to the highest filtration and mudcake thickness reduction. Hence, these were modified to obtain a different surface charge. Silica nanoparticles modified with the acidic treatment (Si11A) in drilling fluids showed the highest reduction of the filtration volume and mud cake thickness with values of -22% and -65%, respectively. Also, the filtration volume appeared to be a function of the zeta potential of nanoparticles that were investigated, for the highest zeta potential value, SiA -48.66 mV @ pH 10, the filtration volume is lower. SiO2 nanoparticles in a BFWBM reduce the filtration volume due to their nanometric size occupying empty spaces in the mudcake and promoting the repulsive forces avoiding the flocculation of the drilling fluid thanks to the anionic surface charge. This study provides a wider landscape about the role of the size and surface acidity of the SiO2 nanoparticles in the stability and dispersion of the BFWBM.