Chapter 1 - Stresses and strains

Abstract

Basic rock mechanics concepts are introduced, including stresses and strains, normal and shear stresses, total and effective stresses, displacement and deformation, and normal and shear strains. The 2-D and 3-D Mohr circle representations of stresses are described, which can be used to interpret mechanical behaviors of rocks under stresses and depletion. Stress–strain governing equations are given for both elastic and poroelastic rocks with thermal effects. Rock anisotropic behaviors are investigated, and the constitutive equations for transversely isotropic and orthotropic rocks are presented. Considerations of anisotropy and poroelasticity play a very important role in understanding mechanical behaviors of rocks, particularly in shale oil and gas formations in which anisotropy and pore pressure are dominant characteristics. In situ stress equations accounting for anisotropy effects are also derived.