A model for investigating wellbore hydraulics of thermo-thixotropic drilling fluids

Abstract

In high-temperature drilling environments, accurate management of wellbore hydraulics is made more difficult due to complex fluid viscosity-temperature profiles. Although most of the fluid samples reported in the literature have monotonically decreasing viscosity with temperature, several studies have found the relationship much more complicated. This study investigates thermal effects on annular pressure loss and cuttings transport for fluids with non-monotonic viscosity-temperature profiles while modeling the thixotropic behavior of the drilling fluid. To this end, three fluid samples have been studied that have distinctly different viscosity-temperature profiles: monotonically decreasing, parabolic and inverted parabola. The mathematical framework is based on the drift flux approach and is numerically solved using the computational fluid dynamics (CFD) methodology. The recently proposed rheological algorithm by the authors has been extended to model thixotropy. The results are presented for different inclinations and eccentricities. It is observed that for fluids with parabolic or inverted parabolic viscosity-temperature profiles, annular pressure loss is highly non-linear, and a single equivalent density value cannot be ascribed to the wellbore. The annular pressure loss near the inlet is significantly higher than that near the outlet. The fluid with a monotonic decrease in viscosity yields the lowest pressure loss but worst cuttings transport whereas, the fluid with a parabolic viscosity-temperature profile has best cuttings transport but causes extremely high-pressure loss.