Simultaneous spectral induced polarization and X-ray µCT imaging to investigate pore-scale dynamics and geoelectrical responses during stepwise drainage–imbibition experiment in porous media

SUMMARY

Understanding the interplay between pore-scale fluid distribution and bulk electrical properties is critical to improving petrophysical models of partially saturated porous media. This study introduces and evaluates a novel experimental setup that enables joint spectral induced polarization (SIP) and X-ray microcomputed tomography (µCT) under dynamic saturation conditions. A custom-designed flow cell was developed to enable simultaneous high-resolution µCT imaging and accurate SIP acquisition. It includes retracted, non-polarizable potential electrodes placed in agar-filled channels, which minimize electrode polarization and preserve signal integrity during measurement. Using this setup, we conducted a drainage–imbibition experiment on an unconsolidated sand sample. High-resolution µCT images captured the water-phase distribution at successive equilibrated saturation states, while co-acquired SIP data provided complementary information on bulk resistivity and aqueous phase connectivity. We extracted the fluid distribution in the pore network from segmented images and computed both geometric and electrical tortuosity to investigate how pore-scale and transport parameters are related. A pore network model, extracted from the dry µCT scan, was used to simulate resistivity index trends, allowing for direct comparison between experimental and modelled values. Results show that saturation history significantly impacts both resistivity and tortuosity, with notable differences between drainage and imbibition. The µCT data confirm that trapped gas phases and connectivity losses are key drivers of marked resistivity increases. While the tested sample exhibited limited polarization, the experimental platform proved effective in linking microstructure to geoelectrical response. The combined SIP–µCT method offers a promising route for refining petrophysical models and holds potential for future studies involving more complex, polarization-prone materials and biogeochemical processes.