Streaming potentials in two‐phase flow conditions

We report here, for the first time, the dependence of the streaming potential coupling coefficient of two consolidated rock samples (dolomite) in two‐phase flow conditions. We used two carbonate core samples characterized by image analysis and petrophysical measurements including porosity, formation factor, resistivity index at 1 kHz, and the critical water saturation determined from capillary pressure curves. In agreement with the results obtained recently by Guichet et al. 2003 , who used an unconsolidated sand, we observed that the relative electrokinetic coupling coefficient scales approximately with the reduced water saturation at capillary pressure equilibrium. This observation is explained with a new model, which makes a clear distinction between Stern and Gouy‐Chapman layer contributions to surface electrical conductivity. The streaming potential coupling coefficient becomes dependent on surface conduction in the Gouy‐Chapman layer where the pore space is not fully saturated.