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

• Measure breakthrough curve during a tracer test by a conductometer.
• Measure transient self-potential signals in electrodes inserted in a porous medium during a tracer test.
• Estimate longitudinal dispersivity by means of a coupled and uncoupled hydrogeophysical approach.
• Compare between longitudinal dispersivity estimates from solute concentrations and self-potential data.
• Self-potentials can be proxy for solute concentration tracer tests.

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.