Effect of the Orientation of Beddings on the Distribution of Stress around the Borehole in Anisotropic Shale Formation

Abstract

Summary The far-field stresses will be concentrated near a borehole existing in any geological formations. If the magnitudes of the concentrated stresses are sufficiently large, the formation rocks near the borehole yields or even fails. In isotropic formations, the solution of the stress concentration near a borehole is solved in two-dimensions by Kirsch (1898) and three-dimensions by Hiramatsu and Oka (1962) (see also Schmitt et al., 2012). However, many formation rocks, for example shales, are elastically anisotropic due to their oriented mineralogical textures or micro-fractures at many scales. In anisotropic formations, a closed form of the solution is established by Lekhnitskij (1963) and Amadei (1983) . In isotropic cases, the magnitude of the concentrated σθθ on the contour of the borehole equals three times that of the far-field horizontal principal stress ( Kirsch, 1898 ). This conclusion is not suitable for anisotropic formations, such as shale formations. In this research, we study the effect of the orientation of beddings on the concentration of stress by a borehole in anisotropic shale formations.