Impact of drilling fluid rheology and wellbore pressure on rock cuttings removal performance: Numerical investigation

Abstract

Drilling fluids exhibits non-Newtonian behavior that is generally described in the literature by two rheological models: Power Law and Herschel-Bulkley models. We have used Eulerian-Eulerian multiphase flow model to evaluate the drilling fluid flow patterns and filter cake formation patterns for both models for ultra-deep drilling conditions. Simulated drilling fluid flow patterns clearly show that the Herschel-Bulkley model exhibits fewer vortices around the drilling pipe, indicating better rock cuttings removal performance. In addition to mud rheology, we have analyzed the pressure drop variation with the filter cake formation on the wellbore during ultra-deep drilling process. We have shown that filter cake thickness at the wall linearly increases with differential pressure between the well and formation. This implies that the differential pressure needs to be optimized. Very thin filter cake may lead to excessive fluid seepage into the permeable subterranean vertical zone resulting in a loss of fluid circulation and hence in a loss of rock cuttings removal. Yet, very thick filter cake reduces the effective diameter of the hole, which may lead to a poor rock cuttings removal performance and stuck pipe. The mathematical model presented here needs to be experimentally validated when filter cake thickness data in deep drilling conditions become available. The model could be useful to provide drilling engineers insight on the filter cake formation and drilling fluid flow pattern and give guidelines to optimize the filter cake as field experimental data are scarce.