Stress path constraints on veined rock deformation

Abstract

Although rock mechanical behaviour has a long record of study, attempts to understand the role of fractures on rock deformation still have unresolved issues. Due to technical and/or economic challenges, natural rock fractures are often dealt with crudely, without detailed consideration of fracture geometry and heterogeneity in many geoscience applications. Veined rocks that are ubiquitous in the upper Earth crust fall in that category where sustained efforts are needed to offer key information for rock mechanics and geomechanics applications. Following on from a recent study on the rupture of veined rocks (DOI: 10.1029/2019JB019052), we further examine stress path constraints on the deformation of veined rocks (i.e., stress-path-dependent behaviour of veined rocks) under polyaxial conditions. The Discrete Element Method is used to establish a calcite veined model where constant mean stress (σ_m) and constant least principal stress (σ₃) paths that are representative in the subsurface activities are considered. The results reveal the stress-path dependency of brittleness for models under different loading paths. Models tested under constant-σ_m conditions exhibit no brittleness, compared to cases where constant-σ₃ is applied. Sliding along the strike of an inclined vein is evident under constant-σ_m deformation, irrespective of the level of stress. Shear bands along the dominated (inclined) veins exhibit apparent particle trajectory anisotropy for the constant-σ_m deformations which is demonstrated by the evident colour contrast of the adjacent rock matrix and the displacement dispersion of the particles forming the shear bands. We envisage that the reactivation of veins is of relevance to Enhanced Geothermal Systems (EGS) development in terms of seismicity mitigation and multiphysics control of fracture and reservoir permeability.