The Effects Of High Pressure-High Temperature On Some Physical Properties Of Ocean Sediments

Abstract

A series of laboratory experiments was conducted with four ocean sediments, two biogenic oozes and two clays. Permeability and thermal conductivity were directly measured as a function of porosity and the testing program was designed to identify any dependence of these physical properties upon hydrostatic pressure and temperature. The results show no discernible effect of pressure, within the range of 2 to 60 MPa, upon the permeability of any of the samples. Temperature effects, from 22' to 220', upon this property are accounted for by applying a viscosity correction to the permeating seawater. Previous investigations have suggested the existence of a pressure-induced and/or a temperature-induced breakdown of the adsorbed water which surrounds clay particles, thereby promoting an increase in sediment permeability. Our experimental findings cannot confirm this phenomenon and fail to provide a satisfactory solution to the confiicting data which now exist between the pore water velocities inferred from non-linear thermal profiles of ocean sediments and those fluid velocities derived from Darcy's Law and laboratory permeability data. The effects of sizeable variations in pressure and temperature upon sediment thermal conductivity are found to closely refiect the behavior of the conductivity of the liquid phase alone under these same changes in environmental conditions. This is not surprising, due to the relatively narrow range of high porosities encountered in this study. Empirical equations are developed which allow sediment thermal conductivity to be calculated as a function of temperature and void ratio. A hydrostatic pressure correction term is also presented.