A Study of Rock-Solution Interaction and Its Effect on Archie´s Law

The electrical conductivity (¿) of cylindrical cores of 25.4-mm diameter and length Pictured Cliffs sandstone (permeability range, 7 × 10-4 × 10-1 millidarcy (md); porosity range, 3.8-4.9 percent) was measured at a frequency of 1 kHz under ambient conditions after saturation in tap water. Kinetics of rock-water interaction and the effect of Soxhlet extraction on the ¿ of the rock were also investigated. Formation factors (F) and the ¿ display time-dependent behavior up to 4500 h. Smooth asymmetrical conductivity maxima occur for all samples at times which increase with increasing porosity. The observed timedependence of F in Archie´s Law (F = ¿-1, ¿ = porosity, n = a parameter) is influenced by the kinetics of ion transport between the Pictured Cliffs sandstone and the aqueous pore fluid. Soxhlet extraction lowers F, but does not significantly change its time dependence.