The Influence Of Micro-Geometry On The Hydraulic Permeability And The Induced Polarization Response Of Sandstones

Abstract

The transport properties of porous rocks and soils are of broad interest to many disciplines. An elusive goal in rock physics has been to develop a method of estimating permeability in-situ, and various models have been developed. These existing models characterize the porous media with parameters including porosity, hydraulic radius, grain packing, tortuosity, specific surface area, fractal surface dimension, grain size and grain size distribution. Induced polarization (IP) measurements are sensitive to many of the same variables associated with hydraulic permeability as well as with the pore fluid chemistry, and may be able to measure the parameters which make up the permeability models. A series of experiments were performed on five different sandstones. Hydraulic permeability and broadband (spectral) induced polarization measurements were made on several sandstone samples both parallel and perpendicular to bedding. lnteresting relationships are shown for the anisotropy data as a function of frequency. Porosity values were also determined for all of the sandstones. Permeability model parameters, including formation factor, porosity, specific surface area and surface fractal dimension were calculated using the IP data. Empirical models which relate the polarization/capacitance of the sample to the grain size, surface fractal dimension and the specific surface area were investigated. The results indicate that the surface fractal dimension is the key component of the model, and that the values determined from our experiments align extremely well with previously published data. Further investigation is being pursued in efforts to determine the fractal dimension solely from electrical measurements.