Predicting streaming potentials for various pore size distributions, comparison of numerical and analytical approaches.

Understanding streaming potential generation in porous media is of high interest forhydrological and reservoir studies as it permits to relate water fluxes to measurable electricalpotential distributions in geological media. This streaming potential generation results fromelectrokinetic coupling between water and electrical fluxes due to the presence of anelectrical double layer at the interface between the mineral and the pore water. Therefore, theporous medium’s pore size is expected to play an important role in this generation. We use inour study 2D pore network simulations to better understand the effect of the pore sizedistribution upon this electrokinetic mechanism. Our simulations in well-controlledconditions allow us to study in detail the influence of a large permeability range (from 10−16to 3 × 10−10 m2) for different ionic concentrations (from 10−4 to 1 mol L−1). Wethen use and compare two different approaches that have been used over the lastdecades to model and interpret the generation of the streaming potential: the classicalcoupling coefficient approach based on the Helmholtz-Smoluchowski equation and amore recent one based on the effective excess charge density. Our results show thatthe pore size distribution has a limited influence on the coupling coefficient forionic concentrations smaller than 10−3 mol L−1, while it completely drives thebehaviour of the effective excess charge density over several orders of magnitude. Then,we use these simulation results to test a recently proposed analytical model basedon a fractal pore size distribution. We show that this model predicts very well theeffective excess charge density for all the tested pore size distributions within itsintrinsic limitation, that is, for a thin electrical double layer compared to the pore size. [ABSTRACT FROM AUTHOR]