||Our experimental study relates to sandstones originating from different depths from a single tight gas field explored by GDF SUEZ. The aim is to characterize experimentally the petro-physical properties of these materials, in order to improve our knowledge on their gas recovery potential.
The initial characterization of these sandstones is performed in the dry and in the “as received” states: porosity, initial water saturation level, gas permeability at a confining pressure Pc=5MPa. For two different samples under increasing Pc, we have evaluated the water saturation threshold, above which no more gas passes through the porous network, due to hydraulic cut-off: it is at ca. 63-68%. Then, at intermediate saturation level (on the order of 40%), two different sample types have been identified, depending on whether their relative gas permeability is affected, or not, by Pc. For one sample of each type, poro-elastic experiments show that the variation in normalized matrix bulk modulus (Ks/Ks0) (due to confining pressure increase) may be attributed to the closure of portions of the connected pore network. Finally, to ascertain the above, a dedicated test was designed to measure the pore volume changes under confinement, simultaneously to volumetric strains. Whenever pore volume variation is significantly higher than volumetric strains, pore trapping is identified, otherwise microstructure changes are mainly attributed to crack closure.