Laboratory scale characterisation of brittleness and permeability enhancement due to rock failure

Abstract

In this study, the multi-stage triaxial compression testing method is adopted to obtain geomechanical parameters without heterogeneity effect. Using the geomechanical characterisation we calculate various brittleness indices previously suggested in the literature. Before the triaxial test and after the ultimate rock failure, we also measure the permeability enhancement ratio caused by rock failure with characteristic time obtained from pulse decay permeameter. Analysing the relationship between the various brittleness indices and the permeability enhancement, we assess the ability of the former to predict the latter. The results show that no unique brittleness index can completely explain the permeability enhancement, but those indices perform better which contain information on post-peak behaviour in direct or indirect manner. We conclude that at least three aspects of the failure behaviour are important and hence at least two indices are required to characterise the potential of permeability enhancement.