The anisotropic mechanical characteristics of layered rocks under numerical simulation

Abstract

Layered rocks pose the challenge of wellbore stability in drilling engineering because of the anisotropic mechanical properties caused by the distinct weak planes. To understand the significant anisotropy of layered rocks in real formation condition, true triaxial compression tests are conducted by numerical simulation in this study. It is revealed that the mechanical responses of layered rocks are either controlled by the rock matrix or dominated by the weak plane and exhibit three different types associated with the orientations of the weak plane (including the dip direction α and dip angle β). When the orientations of the weak plane are α = 0°–90° and β = 0°, 60°–90°, the failure and strength properties of layered rocks depend entirely on the rock matrix, classified to the first type. Whereas the layered rocks with angle α ≤ 45° and β = 15°–45° fail by slipping failure along the weak plane, the relationship curves of rock strength versus the intermediate principal stress (σ2) are downward convex parabolas. In the last type, the mechanical behaviors of layered rocks with α > 45° and β = 15°–45°, involved in the changes of failure mode and the strength curve, are complex. Besides, the limitation of the simulation is discussed, and further studies on layered rocks are essential.