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

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