Experimental and Numerical Investigation on Stress Dependence of Sandstone Electrical Properties and Deviations from Archie's Law

Abstract

Resistivity Index (RI) of Fontainebleau and Bentheimer sandstones was investigated at ambient and reservoir pressures down to low water saturations using the porous plate method. The measurements compared with computations directly on high-resolution three-dimensional images of the pore space using Digital Rock Physics. The numerical computations are in reasonable agreement with the experimental measurements down to water saturations as low as Sw = 10 %. The RI measurements show that both sandstones display Archie behavior at elevated pressure. However, at ambient pressure the RI for Fontainebleau sandstone deviates from Archie behavior at low water saturations. The pore-space images suggest that the deviation from Archie behavior is due to the presence of conductive percolating grain contact regions. Bentheimer sandstone for which grain contacts do not percolate, displays Archie behaviour both at ambient and elevated pressures. The present study extends previous work on RI of clean sandstones using micro-CT based analysis to high confining pressures and shows that for such sandstones the RI at elevated pressure displays Archie behavior down to low water saturations.

A digital rock physics approach to effective and total porosity for complex carbonates: pore-typing and applications to electrical conductivity

“…Numerical capabilities to carry out electrical conductivity calculations directly on tomographic images were established [11][12][13][14][15] and morphological transforms applied to carry out resistivity index calculations [16][17][18]. Integrated approaches combining experiments with tomogram-based numerical modeling were presented for non-Archie behavior of clean sandstones [19][20][21] including for pressure-dependent return to Archie behavior of Fontainebleau sandstone at high confining pressures [21] and more recently also carbonates [22], where the effect of films on the RI behavior of dualporosity carbonate rock is assessed with network models derived from tomograms acquired via micro-CT.…”