Streaming potential coupling coefficient and transport properties of unsaturated carbonate rocks

Our goal in this paper is to provide new experimental evidences for the dependence of the streaming potential coupling coefficient of carbonate rocks with the saturation, comparing our data with the predictive model developed by Revil et al. (2007), including the Corey or the van Genuchten exponent, often used to describe multi-phase flow in the vadose zone. We show that the relative permeability, the relative streaming potential coupling coefficient and the capillary pressure could be described in a consistent way for carbonates using the van Genuchten approach. We measured the streaming potential coupling coefficient of natural saturated and unsaturated carbonate rocks. Saturation was achieved with NaCl brines with salinities ranging from 2×10-3 Mol L-1 to 2.0 Mol L-1. The magnitude of the coupling coefficient increases with decreasing salinity similarly to the trend observed for sandstones. The permeability has a low impact on the values of the streaming potential coupling coefficient at high and low salinity. The zeta potential has been calculated at full saturation using a modified version of the Helmholtz-Smoluchowski equation that accounts for surface electrical conductivity.