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The present work addresses the validity of no-slip condition for water-based bentonite drilling muds. The mud used for the investigation was a suspension of 10% solid (bentonite) concentration and its wall slip effects was explored using viscometric techniques. A concentric-cylinder viscometer (model Fann SOC) was used for this purpose. Flow curves obtained using two bobs with different radii indicates that the viscosity measured is a function of the gap distance between the inner and outer cylinders confirming that slip has indeed occurred for this particular mud. A simple technique was
explained which enables correcting the flow curve for the slip effects thus resulting in true viscosity function for the test fluid. Experimental results obtained show that slip
velocity scales with wall shear stress inferring that for this particular fluid, wall slip effects are less sever as compared to other nonNewtonian fluids such as polymer melts and solutions.