Direct measurement of the unjacketed pore modulus of porous solids

Abstract

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.