Direct measurement of the unjacketed pore modulus of porous solids

摘要

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.