Predicting streaming potential in reactive media: the role of pore geometry during dissolution and precipitation

Dissolution and precipitation processes modify the structure of the
porous media at microscale which significantly affects the macroscopic
properties of the media. These variations in the pore geometry result
in changes in the hydraulic properties that control the groundwater
flow and also in the electrokinetic properties associated to the
displacement of electrical charges carried by the flow. Therefore the
evolution of the streaming potential during dissolution and
precipitation can be estimated from the changes in the electrokinetic
properties. Under the hypothesis of a uniform dissolution or
precipitation of the pores and based on the effective excess charge
density approach, we developed a physically-based theoretical model
for estimating the effective excess charge density as function of
time. The model is derived based on the assumption that the pore
structure can be represented by an ensemble of capillary tubes with a
smooth periodic variation of their radius and a fractal pore size
distribution. The analytical expressions obtained to describe the
effective excess charge density also depend on chemical parameters of
the fluid and on petrophysical properties and geometrical parameters
of the medium. In addition, the periodic variations assumed in the
pore geometry allow us to include the hysteresis phenomenon on the
electrokinetic properties. The expressions of the proposed model have
been compared against available experimental laboratory data.