Variations de la porosité et de la perméabilité le long d'un sondage géothermique. Relation avec la teneur en argiles

The petrophysical characteristics (porosity, gas and water permeability) and the salt and clay content of samples from a geothermal bore-hole have been studied. The gas permeability, the porosity and the mean size of the pores strongly decrease with increasing clay content. For a given sample, the water permeability has been continuously measured as a function of time. After an initial rapid drop, the permeability decreases more slowly and almost linearly as a function of time. The initial decrease is related to the motion of unconsolidated solid particules and to the physisorption of water on clays. The further linear decrease is attributed to a slow precipitation of silica-gel.