The streaming potential is that electrical potential which
develops when an ionic fluid flows through the pores of a rock.
It is an old concept that is recently being applied in many fields
from monitoring water fronts in oil reservoirs to understanding
the mechanisms behind synthetic earthquakes. We have carried
out fundamental theoretical modeling of the streaming-potential
coefficient as a function of pore fluid salinity, pH, and temperature
by modifying the HS equation for use with porous rocks
and using input parameters from established fundamental theory
(the Debye screening length, the Stern-plane potential, the zeta
potential, and the surface conductance). The model also requires
the density, electrical conductivity, relative electric permittivity
and dynamic viscosity of the bulk fluid, for which empirical
models are used so that the temperature of the model may be
varied. These parameters are then combined with parameters
that describe the rock microstructure. The resulting theoretical
values have been compared with a compilation of data for siliceous
materials comprising 290 streaming-potential coefficient
measurements and 269 zeta-potential measurements obtained
experimentally for 17 matrix-fluid combinations (e.g., sandstone
saturated with KCl), using data from 29 publications.
The theoretical model was found to ably describe the main features
of the data, whether taken together or on a sample by sample
basis. The low-salinity regime was found to be controlled by
surface conduction and rock microstructure, and was sensitive
to changes in porosity, cementation exponent, formation factor,
grain size, pore size and pore throat size as well as specific surface
conductivity. The high-salinity regime was found to be subject
to a zeta-potential offset that allows the streaming-potential
coefficient to remain significant even as the saturation limit is
approached