INFLUENCE OF ANISOTROPIES IN BOREHOLE STABILITY

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 a three-dimensional stress analysis around an inclined borehole combined with a generalized three-dimensional anisotropic strength criterion for assessing shear fracturing. Parametric studies indicated that the stability of a wellbore is influenced significantly by rock anisotropy, rock strength anisotropy, and in-situ stress differentials when it is highly inclined and oriented in the direction parallel to the maximum horizontal in-situ stress. The influence of anisotropies is more pronounced on passive shear failure caused by wellborn pressurization.