Laboratory simulations of self-potential signals to assist groundwater studies

We present a brief history of experimental simulations with electrokinetic potential signals observed when common porous geological media are subjected to water flow regimes. The laboratory simulations at Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG) of the Universidade de São Paulo (USP) had to overcome several challenges over years of research work, by developing experimental design, choice of materials, and software development to guide real data interpretation and definition of acquisition procedures to be implemented in practice. In this commemorative issue honouring the IAG/USP graduate program, we discuss some of our former results, including a set of original data for two laboratory experiments developed. The first experiment characterizes electrokinetic signals under controlled pumping regimes to illustrate the sensitivity of such potentials to structures with contrasting properties. The second study discusses model response for discrete fractures to guide field data interpretation to determine the hydraulic head in unconnected fractured systems by monitoring the variation of the electrokinetic potential after a borehole is pumped. In both cases, the experimental simulations are useful to understand the electric potentials of electrokinetic origin, pointing out their advantages in characterizing the subsurface hydraulic conditions when a borehole is pumped.