AN INVESTIGATION OF THE EXPONENT IN ARCHIE’S EQUATION:COMPARING NUMERICAL MODELING WITH LABORATORY DATA:TOWARDS CHARACTERISING DISTURBED SAMPLES FROM THECASCADIA MARGIN:- IODP EXPEDITION 311

摘要

Archie’s equation is used routinely in estimating thewater saturation of reservoirs, or for estimating a valuefor the reservoir water resistivity in the water leg. Weconsider experimental results from the laboratory for arange of samples exhibiting various grain-shapes, andmixtures of differently-shaped grains. These arecombined with a numerical modeling approach,considering 3D flow of electric current around ‘typical’grain shapes and is extended and applied to spheres andellipsoids.Numerical modelling, considering a single, sphericalgrain, led to values of Archie’s ‘m’ parameter inexcellent agreement with those obtained for largenumbers of sand-sized glass spheres deposited andcompacted in the laboratory. Similarly, for platy grainstheir orientation relative to the direction of flow ofelectric current is shown to be critical, in line with theefficiency concept proposed by Herrick and Kennedy(1993).Existing results for two-component mixtures ofdifferently-shaped grains, namely: quartz sands, glassspheres and shell fragments are considered. Predictionsmade of Archie’s ‘m’ parameter for such mixtures, onthe basis of their proportion and laboratory-determinedvalues of ‘m’ for each component, matched laboratoryderived values, suggesting the prospect of predictingArchie’s ‘m’ parameter on the basis of grain properties(e.g. shape) alone. Each individual sample, includingthese mixtures, obeyed Archie’s equation. Sampleshaving differently shaped grains, however, whenplotted together were better-described by Winsauer’sequation, although the values of ‘m’ derived fromArchie and Winsauer’s equations were quite different.Our approach is applied to estimating m from aknowledge of the grains themselves, even though asample may be highly disturbed and has been applied tosediment-hosted methane hydrate from the CascadiaMargin. Improving the possibilities for reservoircharacterization in loose sands and sediment hostedmethane hydrates.