Direct measurement of the unjacketed pore modulus of porous solids

Pressure decline caused by the extraction of oil from deep sedimentary layers depends on the pore modulusKpp , a poroelastic parameter that characterizes the effect of pressure change on pore volume under constant mean stress. Measurement ofKpp is difficult, however, as it requires calibration to account for fluid compressibility and compliance of the testing system. Nevertheless, knowing the easily measurable drained pore modulusKp and adopting an assumption on the unjacketed pore modulusK s ″, it is possible to determineKpp because these pore moduli are related. Previous work on indirectly estimatingK s ″ claimed thatK s ″ is strongly dependent on Terzaghi effective pressureP′ and therefore not a constant; also,K s ″ might be different fromKs , the solid bulk modulus of the major mineral constituent. We overcome the limitations of the indirect approach by directly measuringK s ″. The experiments reveal thatK s ″ is indeed a constant and that for an ideal porous rock, the assumption ofK s ′ ′ = K s holds. Furthermore, a constantK s ″ implies thatKp andKpp are functions of Terzaghi effective pressure only. These results provide a framework to accurately determine the Skempton coefficientB .