Rock‐physics model for deep‐sea shallow calcareous sediment with porous grains

Abstract

We offer an effective‐medium model for estimating the elastic properties of high‐porosity marine calcareous sediment. This model treats this sediment as a pack of porous elastic grains. The effective elastic moduli of the porous grains are calculated using the differential effective medium model (DEM) where the ellipsoidal inclusions have a fixed aspect ratio and are filled with sea water. Then the elastic moduli of a pack of these spherical grains are calculated using a modified (scaled to the critical porosity) upper Hashin‐Shtrikman bound above critical porosity (ϕc) and a modified lower Hashin‐Shtrikman bound below critical porosity. We find that the best match between the model‐predicted compressional and shear‐wave velocity and ODP data from three wells is achieved for the grain‐aspect‐ratio 0.5. This model assigns finite non‐zero values to the shear modulus of high‐porosity marine sediment unlike the suspension model commonly used in such depositional setting. Unlike other existing models, this new model accurately predicts the S‐wave velocity.