Study of the permeability in the Opalinus clay series (Mont Terri - Switzerland) using the steady state method in Hassler cell

Mont Terri rock laboratory located in the Northwestern Switzerland is an international platform for applied research in the field of radioactive waste disposal in clayrock formations. A borehole named BDB1 has been drilled in the Opalinus claystone in 2013 to assess its containment properties. Characterization of petrophysical and hydrogeological parameters in the Jurassic shale known as Opalinus Clay were performed by in situ experiments conducted in the rock laboratory of Jura Mountains and on borehole samples. This paper presents the results of laboratory measurements of permeability in a permeameter called Hassler cell by using the steady state method. The study is applied to core samples drilled perpendicular and parallel to the bedding, and involves gas and water permeability measurements. The Hassler cell is an experimental device that allows to put samples under a confining pressure reproducing the in situ one. In all, results were obtained for nine samples over sixteen for gas permeability measurements with values ranging between 6.9 x 10(-21) and 2.3 x 10(-19) m(2) and one sample for water permeability measurements with a value of 1.38 x 10(-20) m(2). Most of the results are in good agreement with previous studies obtained by in situ experiments and using the Poiseuille type law method. The usage of several methods to determine the permeability of the Opalinus clay unit helps to conclude about the accuracy, trueness and precision of the measurements.