Influence of Pore Size Distribution on the Electrokinetic Coupling Coefficient in Two-Phase Flow Conditions

Jan Vinogradov,Damien Jougnot,Rhiannon Hill

doi:10.3390/w13172316

Abstract

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.

Highlights

Groundwater provides the main source of water for human consumption worldwide, and it is critically important for agriculture [1]
As Swirr increases towards 0.4, the krw curves of each of the three distribution functions gradually move closer together and begin to overlap. These results suggest that the distribution of capillary radii throughout the Bundle Of Capillary Tubes (BOCT)
Our model suggests that a more accurate New capillary size distribution (CSD) function should be used in BOCT models to capture the behaviour of Cr with water saturation

Summary

Introduction

Groundwater provides the main source of water for human consumption worldwide, and it is critically important for agriculture [1]. Poorly managed pumping schedules could potentially lead to contamination of boreholes, and in coastal aquifers, to the intrusion of saltwater [2]. To improve aquifer management requires accurate characterisation and modelling of subsurface water flow using available methods. Geophysical methods are non-intrusive and can be used for monitoring. Such methods are not yet routinely deployed, and their implementation, as well as interpretation of measured signals, still require improvements. There is a real need for a robust hydrogeophysical tool to monitor water flow in hydrosystems. One of the main challenges is to characterise the effects of partial water saturation in the upper part of the critical zone, i.e., the vadose zone: the near-surface compartment where water and gas (normally air) are present

Objectives

Methods

Results

Conclusion