Mud as a porous medium

Abstract

Since marine mud supports shear waves, it must have an elastic, though fragile, frame. It is also saturated with seawater, therefore it could be modeled as a porous medium. It is an unusual porous medium for a number of reasons. The boundary between the skeletal frame and the pore fluid is difficult to define. The effective porosity of the skeletal frame is not the same as the bulk fluid fraction. The chemistry of mud suggests that a fraction of the water is an integral part of the skeletal frame. Similarly, a fraction of the solid particles may be suspended in the pore fluid. The structure of the skeletal frame is a function of several factors, including salinity of the water and mineralogy of the clay particles. Porous media have two main loss mechanisms: losses in the skeletal frame and viscous losses due to relative motion between the frame and the pore fluid. In the case of marine mud, the frame losses may be modeled as a relaxation process. The measurements from the Seabed Characterization Experiment show it has a spectrum of relaxation frequencies, consistent with a stationary creep process. [Work supported by ONR, Ocean Acoustics Program.]