The pore pressure oscillation method as a proven tool for determining the hydraulic properties of low-permeability rocks

Abstract

Abstract. In the context of selecting and designing a future repository site for nuclear waste, a proper understanding of the host rock's physical behavior is required. One of the fundamental characteristics is the hydraulic diffusivity of the host rock, i.e., the ratio between permeability and storativity. For low-permeability rocks, however, determination of these properties is technically challenging and often time consuming. Among various steady-state and transient methods, the pore pressure oscillation technique has been proven to be an advantageous method for the simultaneous measurement of permeability and storativity for potential host rocks on a laboratory scale. In this contribution, we will introduce the methodological approach and highlight the advantages and disadvantages compared to other methods. Furthermore, we will demonstrate the applicability of this method for clay-rich rocks by presenting our experimental results. Carefully chosen boundary conditions allow us to constrain dependencies of the properties on, e.g., effective stress or bedding orientation with respect to the fluid flow direction. Additionally, this method is practical for measuring the damage-induced changes of permeability and storativity due to differential loading.