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 modulus K _pp , a poroelastic parameter that characterizes the effect of pressure change on pore volume under constant mean stress. Measurement of K _pp 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 modulus K _p and adopting an assumption on the unjacketed pore modulus K _s , it is possible to determine K _pp because these pore moduli are related. Previous work on indirectly estimating K _s claimed that K _s is strongly dependent on Terzaghi effective pressure P and therefore not a constant; also, K _s might be different from K _s , the solid bulk modulus of the major mineral constituent. We overcome the limitations of the indirect approach by directly measuring K _s . The experiments reveal that K _s is indeed a constant and that for an ideal porous rock, the assumption of K _s = K _s holds. Furthermore, a constant K _s implies that K _p and K _pp are functions of Terzaghi effective pressure only. These results provide a framework to accurately determine the Skempton coefficient B.