Self-potential (SP) signals that are generated under two-phase flow
conditions could be used to study vadose zone dynamics and to monitor
petroleum production. These streaming-potentials may also act as an
error source in SP monitoring of vulcanological activity and in
magnetotelluric studies. We propose a two-phase flow SP theory that
predicts streaming currents as a function of the pore water velocity,
the excess of charge in the pore water, and the porosity. The source
currents that create the SP signals are given by the divergence of the
streaming currents, and contributions are likely to be located at
infiltration fronts, at the water table, or at geological boundaries.
Our theory was implemented in a hydrogeological modeling code to
calculate the SP distribution during primary drainage. Forward and
inverse modeling of a well-calibrated 1D drainage experiment suggest
that our theory can predict streaming potentials in the vadose zone.