Influence of the observation scale on permeability estimation at local and regional scales through well tests in a fractured and karstic aquifer (Lez aquifer, Southern France)

Determination of permeability in fractured and karstic carbonate reservoirs is of great importance as reservoirs of this type represent a significant proportion of the aquifers and petroleum reservoirs in the world. In fact at a given scale the permeability values determined from the hydrodynamic response to a well test can vary dramatically from one observation well to another. In this study we investigate such permeability variations and their origins at both local and regional scales. Permeability values for a fractured and karstic carbonate aquifer (Lez spring hydrogeological catchment, Southern France) have therefore been analyzed from well tests conducted at local and regional scales: (i) interference tests at the field site scale, (ii) pulse tests at the reservoir scale. Analyzing and comparing the hydrodynamic responses to the pumping tests at both scales show that (i) mean estimated permeability values can increase with observation scale in this particular carbonate reservoir, (ii) at a given scale these values depend dramatically on the location of the observation well used for permeability estimations as the connectivity between the well and the high permeability flow path network depends on this location, and (iii) the water table level or the drilling depth of the observation well appear to be key parameters when estimating permeability values as they also control the connectivity between the well and the high permeability flow path network.