Experimental deformation of shale: Mechanical properties and microstructural indicators of mechanisms

Abstract

The mechanical properties and deformation mechanisms of an illite-rich shale have been investigated in triaxial compression experiments at varying confining pressures (P c), temperatures (T), and strain rates (ϵ). Shale deforms by brittle processes at low P c and deforms by semi-brittle processes at high P c leading to the development of macroscopic fractures, semi-brittle shear zones, and kink bands. Differential stresses ( σ 1- σ 3) depend on P c as well as T and ϵ at high P c. The effects of P c are non-linear and those of T and ϵ at a selected P c may be described by an exponential dislocation glide law. The strength of shale depends on water content as well; loss of 2.1 weight % water from clay interlayers increases shale strength by 30%.