Biot Bulk Coefficient and the Micro-inhomogeneity Parameter

The Biot bulk coefficient and the effective pressure coefficient for the bulk volume are important deformation parameters of porous rocks. There are different ways to measure these coefficients using quasi-static deformation experiments in the laboratory. However, only if the rock deforms in a self-similar manner then these two coefficients should coincide. In the presence of micro-inhomogeneities, one can expect that these two coefficients differ. We interpret laboratory measurements where such a difference has been reported and link the difference to the micro-inhomogeneity parameter. The latter is a measure for the deviation from the Biot-Gassmann rock behavior wherein self-similar deformation is assumed.