Design, operation and validation of a new fluid-sealed direct shear apparatus capable of monitoring fault-related fluid flow to large displacements

A new type of direct shear apparatus has been developed to allow for deformation of large and intact rock samples under fluid-sealed conditions. The sealed cell was specifically designed to monitor changes to fluid flow across the evolving rupture surface to large displacements (≤120 mm), and effective stress conditions up to 36 MPa. To maintain a seal for the pore fluid during deformation, a viscous and immiscible sealant fluid was injected at the interface between the rock specimen and the inner sample cell. Finite element modelling was conducted in parallel to verify the stress distribution in the specimen, notably the effect of geometrical constraints on the fault zone development and mechanical data. Results obtained from natural Castlegate sandstone, synthetically cemented sandstone and sandstone–clay composite blocks demonstrate the suitability of this equipment to investigating coupled fluid mechanical behaviour of a wide range of rock specimens. In particular, the test configuration is demonstrated to be capable of exploring fault-related fluid flow behaviour in reservoir–seal pair analogues with application for the hydrocarbon industry and the emerging field of carbon dioxide storage assessment.

► We developed a new direct shear cell to deform large rock samples under fluid-sealed conditions.
► Absolute displacement (up to 120 mm) is nearly an order of magnitude higher than previous models.
► Hydromechanical coupling can be studied from intact rock samples to very large strains.
► We demonstrate that the equipment is particularly suited to study the continuity of clay smears.