Modelling of localised gas preferential pathways in claystone

• 2D model of long-term injection gas test on initially saturated claystone is performed.
• Evidences of localised pathways through the sample are observed experimentally.
• An embedded pressure-dependent fracture is included within the model.
• The HM model yields a better description of the mechanisms governing gas flow.
• After the breakthrough the transport properties are invariants with deformation.

A long-term injection gas test on initially saturated claystone samples under isotropic confining pressure is modelled in a 2D hydro-mechanical framework, which includes the hydraulic anisotropy. Evidences of localised pathways through the sample have been observed experimentally, which are difficult to reconcile with standard two-phase flow models. The presence of an embedded pre-existing fracture is included in a continuum finite element model. A hydro-mechanical coupling between the fracture aperture, permeability and the retention properties along the fracture is included in the model. Due to the increase in permeability and the decrease of the air entry pressure induced by the rise in fluid pressure at constant mean total stress, the model provides good agreement with the experimental observations. The discussion offers additional insight into the fluid flow mechanisms into the sample and the processes involved in the development of localised gas pathways. This study allows conclusions to be drawn regarding the performance of the model and its practical limitations.