Effects of Wettability, Pore Geometry and Stress on Electrical Conduction in Fluid Saturated Rocks

This paper summarizes the experimental and theoretical work conducted at the University of Texas investigate the effects ofwettability, pore geometry, and stress on electrical conduction in partially saturated porous media. Experiments conducted on both glass-bead packs and Berea cores show that wettability has a profound effect on the saturation exponent, consistent with theoretical predictions based on a network representation ofthe porous medium. The effect of wettability is most pronounced when the pores are poorly connected. The influence of stress is substantially smaller than the effect of wettability in the relatively simple low-clay content intergranular-porosity systems considered here. Small increases in the formation factor were observed for the cores and the water-wet beads, whereas larger increases were observed with the compressible asphaltene-coated oil-wet beads. A small degree of hysteresis was observed in the measured R, and n values during drainage and imbibition. The implications of the above observations for resistivity logs and for core measurements are discussed. Log interpretations based on measurements in the flushed zone (R,) and the virgin formation (R,) must be carefully evaluated.