Abstract: In the traditional rock mechanics analysis, the formation is always simplified to orthotropic and transverse isotropic. On the basis of detailed analyzing petroleum engineering background regarded to rock mechanics, the rock mechanics orthotropic experiment was done with the drilling core. The experimental results show that the anisotropy of the mechanical property in the plane perpendicular to the wellbore axis is existing. So in some extreme geologic environment, the degree of orthotropic is relatively obvious, the formation can not be simplified to transverse isotropic.

Key words: rock mechanics, orthotropic, experimental analysis