William R. Bryant
Texas A&M Univ., College Station, TX 77843
NRL, Stennis Space Center, MS 39529
Michael D. Richardson
Naval Res. Lab., Stennis Space Center, MS 39529
Permeability of fine-grained marine sediments is the most controversial and difficult variable to define for seismo-acoustics. Theoretical formulations of permeability are extremely complex for fine-grained sediments and usually bear small resemblances to real material. Values of permeability from consolidation tests and direct analysis of clayey marine sediments greatly differ from results determined by the Kozeny--Carman equation. These differences are not accountable by deviations from Darcy's law, electrokinetic coupling, or viscosity but are related to changes in microfabric. Porosities relationship to permeability presents natures largest range between cause and affect. In fine-grained marine sediments permeability changes at a rate from 2 to the 12th power of porosity. A 50% change in porosity, from a mud to mudstone, can result in a change in permeability of 10[sup -3] to 10[sup -12] cm/s, which is analogous of going from the speed of light to 60 mph. The effects of permeability on P-wave velocities of high porosity (85% to 70%) sediments, particularly Pacific red clays, appears minimal. A measured change of permeability from 7x10[sup -4] to 1.2x10[sup -7] cm/s has less of an effect on the velocity (average 1469 m/s) than does a density change from 1.25 to 1.36 g/cc. P-wave velocities of red clays, spanning an age of 45 m.y. with permeabilities of above, are essentially constant over a depth of 60 m while S-wave velocities of the same material increase from 5 to 180 m/s. The best relationship between permeability and porosity of marine clays for seismo-acoustic determinations is k=6.63x10[sup -9] (beta)[sup 8.1], where k=permeability (cm/s) and (beta)=decimal porosity.