The nature of stress state: numerical and laboratory experiments and some field observations

Abstract

AbstractSimulations of the stress state in a region of discontinuously fractured rock revealed a strongly heterogeneous, self-organized stress distribution displaying internally balanced strains and corresponding energy storage. The explicit simulations follow a sequence which may be inferred to be irreversible and strongly dependent on interaction between fractures, implying a time-dependency. The state of the simulated reservoir displays a sensitivity characteristic of marginal stability. These numerical observations are compared with new and previous laboratory and field experiments spanning a wide range of size, stress magnitude and stress difference. The characteristics of the state of the simulated reservoir, laboratory samples and field behaviour are found to be consistent with the numerical predictions. A stress memory is evident. This supports previous conclusions that the concept of stress state as uniform, constant and resulting from averaged values of stresses or displacements, presently applied at remote and artificial boundaries, is grossly oversimplified and flawed.