Application of Nanosilica in Glycerol-Based Drilling Fluid for Shale Formations

Abstract

In this study, we perform several tests to develop a formula of glycerol-based drilling fluid that is suitable for shale formations with severe wellbore instability problems. Drilling fluids with varying combinations of nanosilica, glycerol, sodium carboxymethyl cellulose (Na-CMC), and xanthan gum (XG) in organic soil glycerol-based slurry are tested, and the effects of nanosilica on the swelling of shale samples and the lubricity of drilling fluids are also investigated to verify the feasibility of designed drilling fluids. The experimental investigations reveal that the values of apparent viscosity (AV), plastic viscosity (PV), and yield value (YP) of the optimal formulation meet the rheological parameters required for the drilling of shale formations. The AV and PV values of drilling fluid with 55:45 glycerol/water ratio are lower than those of drilling fluids with other glycerol/water ratios. A higher XG content means higher YP value in the experiment and 0.4% XG is suitable for the glycerol-based drilling fluid to prevent the collapse of the shale wellbore. There is a critical nanosilica content threshold (0.5%), and the filtration loss (FL) increases gradually when this threshold is exceeded due to the agglomeration of nanosilica. The nanosilica coated on clay particles in shales because of the formation of hydrogen bonds results in a decrease in permeability of shale formations. The swelling of shale through hydration is greatly reduced by 37% and the sticking coefficient of drilling fluid is reduced by 28% when 0.5% nanosilica is added. The addition of nanosilica to glycerol-based drilling fluid is significant to deal with the wellbore instability problems in troublesome shale formations.