Yield characteristics of caprocks: a criticial state mechanics approach

Summary The yield behaviour of both clay soils and reservoir materials can effectively be assessed using critical state mechanics. Nevertheless, this approach has been relatively unused, in relation to caprock materials and the shape of the yield envelope is poorly-constrained in comparison. In this study, we present experimental data on the hydromechanical behaviour of caprocks and their associated critical state yield envelopes. The degree of uncertainty in the form of the yield surface is considered, before the likely consequences of various stress path scenarios is examined. The potential for permeability enhancement versus reduction is also considered and the influence of stress history is found to be key. This approach demonstrates the potential for yield to be reached during some depletion scenarios, though this deformation is often compactive and permeability-reducing in nature. As such, the critical state approach represents an effective tool for assessing performance of caprocks under a range of potential stress paths.