Estimation of longitudinal dispersivity in a porous medium using self-potential signals

This paper presents several approaches to deduce the longitudinal dispersivity in a sand column during experiments oftracer tests, by measuring the output fluid concentration and the self-potential signals in the electrodes inserted into the sand. These signals have been used to obtain an estimate of longitudinal dispersivity through a coupled and an uncoupled hydrogeophysical approach. The first approach uses electrical current density and solute mass continuity equations simultaneously: the dispersivity is conditioned directly by the self-potential signals. Instead, the uncoupled approach firstly converts self-potential signals into concentration values using the Planck-Henderson equation and then estimates the dispersivity using only the transport equation. Longitudinal dispersivities calculated using self-potential signals by means of these two approaches were compared with those obtained using the concentration derived from a conductometer on the top of the column. The results show the goodness of the hydrogeophysical approaches.