Gas transport properties in argillaceous rocks are becoming an important issue within different contexts of energy-related geomechanics (disposal of radioactive waste, production of shale gas, CO₂ sequestration). The present investigation aims at describing the pathways generated on a deep Cenozoic clay during gas injection using different microstructural techniques. Mercury intrusion porosimetry results have allowed detecting fissures after gas injection tests that have not been observed on intact samples. The opening of these pressure-dependent fissures plays a major role on gas permeability. A complementary insight into the connectivity of these fissures has been quantified by micro-computed tomography.

Gas migration through a potential host clay formation for the geological disposal of radioactive waste in Belgium is experimentally investigated in the laboratory, and numerical modelling is performed to help in the interpretation of the results. Selected air injection tests under oedometer conditions on initially saturated Boom Clay samples with oriented bedding planes are presented. Priority in the experimental programme is given to the study of the deformation response along the injection and dissipation stages, as well as to the analysis of the pore network changes, which detect the opening of fissures that can act as preferential air pathways. The experimental results are simulated using a fully coupled hydro-mechanical finite element code, which incorporates an embedded fracture permeability model to account for the simulation of the gas flow along preferential pathways. The intrinsic permeability and the retention curve of the clay are assumed to be dependent on strains through fracture aperture changes. The numerical results could reproduce upstream/downstream pressures, outflow volume and soil volume change accurately. The experimental results, combined with the numerical simulation, provide good insight into the role of the volumetric response and of the bedding planes on the air transport properties of Boom Clay samples, confirming that fracture aperture occurs during gas injection, which eventually dominates further injection and pressure release stages.