Streaming potential is a promising method for a variety of hydrogeophysical applications, including the characterisation of the critical zone, contaminant transport or saline intrusion. A simple bundle of capillary tubes model that accounts for realistic pore and pore throat size distribution of porous rocks is presented in this paper to simulate the electrokinetic coupling coefficient and compared with previously published models. In contrast to previous studies, the non-monotonic pore size distribution function used in our model relies on experimental data for Berea sandstone samples. In our approach, we combined this explicit capillary size distribution with the alternating radius of each capillary tube to mimic pores and pore throats of real rocks. The simulation results obtained with our model predicts water saturation dependence of the relative electrokinetic coupling coefficient more accurately compared with previous studies. Compared with previous studies, our simulation results demonstrate that the relative coupling coefficient remains stable at higher water saturations but vanishes to zero more rapidly as water saturation approaches the irreducible value. This prediction is consistent with the published experimental data. Moreover, our model was more accurate compared with previously published studies in computing the true irreducible water saturation relative to the value reported in an experimental study on a Berea sandstone sample saturated with tap water and liquid CO2. Further modifications, including explicit modelling of the capillary trapping of the non-wetting phase, are required to improve the accuracy of the model.
Bibliographical noteAuthor Contributions: J.V.: Conceptualisation, Formal analysis, Methodology, Software, Supervision, Writing—original draft and Writing—review and editing. R.H.: Data curation, Formal analysis, Software, Validation, Visualization, Writing—review and editing. D.J.: Conceptualisation, Formal analysis, Methodology, Supervision and Writing—review and editing. All authors have read and agreed to the published version of the manuscript.
- electrokinetic coupling coefficient
- zeta potential
- partial water saturation
- CO2 geo-sequestration
- bundle of capillary tubes model
- realistic capillary size distribution