Inversion for Parameters of Mud as a Porous Medium

Abstract

In this article, the seven input parameters of a porous medium model for mud are defined and inverted for the New England Mud Patch. One distinguishing feature is that the skeletal frame may contain adsorbed water, and the pore water may contain suspended solid material. This means that the effective properties of the skeletal frame and pore water are different from that of the pure solid and pure seawater, and the effective porosity is not the same as the bulk water fraction. The model contains two loss mechanisms: creep and viscous loss due to relative motion between skeletal frame and pore water. It is demonstrated that the input parameters could be inverted from the wave speeds, attenuations, and reflection. The inversion from reflection loss exclusively is more difficult due to the relative insensitivity to shear properties. A partial solution is obtained by using a regression relationship to constrain the shear speed. A connection between the assumed shear speed and the inverted compressional wave attenuation is consistent with a recent finding by Godin. Regarding reflection loss from a half-space, for frequencies less than about 10 kHz, a homogeneous medium model is indistinguishable from a porous medium model, and for shear speeds less than 50 m/s, a fluid model would be adequate. The porous medium model does not suffer from these restrictions.