Simulation of heave-induced pressure oscillations in Herschel-Bulkley muds

Abstract

Heave induces pressure oscillations when drilling offshore from floating rigs. A time-domain model is proposed to analyze and predict such pressure oscillations. The model considers the coupled dynamics of the mud and the drillstring, Herschel-Bulkley-type rheology, and realistic geometries. A computationally efficient method to evaluate friction as a nonlinear function of the mud-flow rate and drillstring velocity is discussed. In a simulation study, we illustrate several nonlinear phenomena that have important practical implications but were not included in previous, simpler models. In particular, muds with a yield point can increase the pressure amplitudes significantly, and severe downhole-pressure oscillations are not detectable from topside measurements in many cases.