POROSITY AND CONSOLIDATION LIMITS OF SEDIMENTS AND GASSMANNS ELASTIC-WAVE EQUATION

The elastic framework properties of sediments relate to porosity. Poro sity relates to the state of consolidation of sediments. The full rang e of quasi-static, elastic moduli vs porosity behavior can be incorpor ated into Gassmann's [1951] equations. I review the Atterberg [1911] l imits to establish a basis for discussing the precompaction porosity, phi0, which corresponds approximately to the Atterberg plastic limit. This porosity is about 0.36-0.40 for sands and sandstones. The ratio o f the dry-frame moduli to the effective mineral moduli is (1-phi/phi0) . 1 incorporate this ratio into Gassmann's equations, which operate fr om 0 less-than-or-equal-to phi less-than-or-equal-to phi0, when sedime nts have a solid elastic frame. For phi > phi0, when sediments no long er have a solid elastic frame, Gassmann's equations reduce to Reuss' [ 1929] isostress average for the solid-fluid mixture.