Horizontal Wellbore Collapse in an Anisotropic Formation

Abstract

ABSTRACT This paper discusses an anisotropic model for assessing the mechanical stability of a deep borehole subjected to an internal wellbore pressure and a far-field stress tensor. The model consists of the three-dimensional analysis of stress concentrations around an inclined borehole due to the far-field stress tensor, combined with internal wellbore pressurization, flow and thermally induced stresses to give an approximate non-coupled solution. The model utilizes a generalized three-dimensional anisotropic strength criterion for assessing borehole collapse which is one manifestation of shear failure. Parametric studies indicated that the stability of the wellbore is significantly influenced by high degrees of rock anisotropy, high in-situ stress differentials and excessive wellbore cooling. Pore pressure and porous elastic constant also affect the stability but these effects are less pronounced.