Electrokinetic coupling in unsaturated porous media

Area of Science:

• Geophysics
• Physical Chemistry
• Fluid Dynamics

Background:

• Porous media saturated with immiscible fluids present complex transport phenomena.
• Understanding coupled fluid flow and electrical properties is crucial for subsurface applications.

Purpose of the Study:

• Derive macroscopic constitutive equations for electrical current density and multiphase flow in charged porous media.
• Investigate the dependence of streaming potential and electro-osmosis coupling coefficients on saturation and material properties.

Main Methods:

• Volume-averaging approach applied to Ampère's law, Nernst-Planck, and Stokes equations.
• Numerical simulation of primary drainage and imbibition experiments.
• Comparison of model predictions with experimental data from dolomite core samples.

Main Results:

• Macroscopic constitutive equations derived as functions of water saturation, electrical formation factor, and other key parameters.
• Demonstrated that streaming potential coupling coefficients depend on saturation, material properties, and saturation history.
• Excellent agreement found between model predictions and experimental measurements.

Conclusions:

• The developed volume-averaging model accurately describes coupled electrical and fluid transport in porous media.
• The study provides new insights into the factors influencing streaming potential and electro-osmosis.
• The findings validate the model's applicability for analyzing geophysical and reservoir engineering problems.