Effects of Temperature and Rate-Dependent Mud Cake Buildup on Wellbore Stability in Multi-Permeability Formations

Abstract

AbstractIn this work, we use the theory of multi-porosity multi-permeability porothermoelasticity to derive the analytical solutions of pore pressure and stresses for an inclined wellbore, accounting for a rate-dependent mud cake buildup on the wellbore wall. The solutions are further combined with the Hoek-Brown shear failure criterion and a tensile failure criterion to calculate the critical collapse and fracturing mud weights. We choose a naturally fractured rock formation as an example to demonstrate the coupled effects of temperature, mud cake, and the formation's dual-porosity dual-permeability on wellbore stability. We show that drilling mud with a lower temperature than the rock formation results in differential contraction of the solid and pore fluid constituents and leads to significant alteration of pore pressure and stress distributions. Additionally, a low-permeability and thin mud cake can considerably increase effective tangential stress. Natural fractures also alter the pore pressure and effective stress distributions because of fractures’ higher permeability than the rock matrix. Both wellbore cooling and filter cake buildup decrease the collapse mud weight. Natural fractures have significant weakening effects, increasing the collapse mud weight and decreasing the fracturing mud weight. This work provides the first solutions for wellbore stability analysis, considering together the time-dependent filter cake buildup, thermal effects, and formation's multi-porosity multi-permeability.