Modeling Aspects of Wellbore Stability in Shales

Abstract

Abstract Drilling problems associated with wellbore instability are normally aggravated when crossing shale layers. Instabilities in shales may be caused by a complex mechanism of shale-drilling fluid interaction and by the overstress of the rock formation. Wellbore stability models that include some aspects of this coupled phenomenon have already been developed. However, the use of these models without the knowledge of the associated simplifications may lead to wrong conclusions. The present paper discusses the modeling aspects of the coupled process. Three formulations are compared: an analytical elastic solution without the diffusion process, an analytical poroelastic solution and a numerical chemical-hydro-mechanical model. The objective is to analyze the applicability of each model.