STRESS ANALYSIS AT THE BOREHOLE WALL IN TRANSVERSE ISOTROPIC FORMATIONS

Most of the existing models for borehole wall stress are based on isotropic rock. Thus, some errors may be generated under actual working conditions. In this research, according to the theory of mechanics of anisotropic materials, the bedded formation is simplified as transversely isotropic rock material, and a calculation model for stress around the borehole in anisotropic formations is developed. Based on the complex function solution of generalized plane strain elasticity problems, the circular-hole boundary conditions of the stress distribution, and the coordinate transformation, the stress distribution at the borehole wall in a transverse isotropic formation is investigated. A parametric study is carried out to investigate the effect of the elastic parameters, bedding plane inclination and orientation, ratio of horizontal in-situ stress, borehole deviation, and azimuth angle on the principal stress distribution. Results indicate that in the analysis of wellbore stability in bedding shale, special attention should be paid to the effect of bedding plane inclination, the in-situ stress ratio, and the borehole deviation parameters. The results are useful to construction site design before drilling.