LAUSR

Abstract Accurate rheological measurements of barite-weighted ultrahigh density water-based drilling fluids with a rotational viscometer may be hindered by the wall slip effect. This paper describes a correction method that is based on the principle of flow curves gap dependence. A two-stage Tikhonov regularization numerical strategy was developed to obtain the true viscous behavior and wall slip of barite-weighted drilling fluids containing a high particle fraction. The proposed approach does not depend on the narrow gap assumption or the prescribed form of rheological models. The results show that barite-weighted ultrahigh density drilling fluids start to slip after reaching a small value of critical shear stress, and the wall slip velocity increases linearly as a function of shear. There are significant discrepancies between the slip-corrected rheological models and the apparent models. Curve fitting results show that the slip-corrected flow curves are linear as would be expected for Bingham plastic fluids, while the uncorrected apparent flow curves are nonlinear as one would expect for yield power law fluids. Failing to correct for the wall slip effect would result in seriously underestimating the bulk viscosity of barite-weighted ultrahigh density water-based drilling fluids.