Experimental Study of Electrical Monitoring of Foam Propagation in Porous Media: Spectral Induced Polarization (SIP) and Time Domain Reflectometry (TDR) Measurements in a 2D Tank

Monitoring subsurface processes during soil remediation is crucial for optimizing environmental restoration techniques. Geophysical tools, such as Spectral Induced Polarization (SIP) and Time Domain Reflectometry (TDR), offer non-invasive methods for tracking these processes. This study focuses on the electrical monitoring of foam propagation in saturated porous media to enhance remediation strategies for hydrocarbon-polluted aquifers.

Aqueous foam, consisting of gas bubbles dispersed in a liquid phase containing surfactants, is widely used in soil remediation due to its high viscosity and ability to act as a blocking, mobilizing, or vectorizing agent. Understanding the electrical properties of foam propagation is essential for evaluating its effectiveness in remediation processes.

Our experiments were conducted in a 2D tank packed with 1 mm glass beads and saturated with tap water (400 µS/cm) Figure 1. The foam was generated using an anionic surfactant (SDS) and injected into the tank at a gas fraction (quality) of 85% and a constant flow rate of 8 mL/min. The SIP method was employed to measure complex electrical resistivity across frequencies ranging from 1.46 Hz to 187 Hz, while the TDR method was used to assess relative permittivity and electrical conductivity at this frequency of 70MHz. Additionally, image monitoring was utilized to convert optical densities into foam saturation values (S_f), providing a means to validate the geophysical measurements.

The results, (Figure 1, Figure 2), show that foam propagation causes significant changes in dielectric permittivity and resistivity in regions affected by foam injection. For the central zone, Probe 13, the dielectric permittivity decreases by 63% (from ~19 to ~7), while resistivity increases up to 6000% (~85 Ω.m to ~5100 Ω.m). In contrast, Near-Center zones, e.g. probe 12, show moderate changes (~33% permittivity decrease, ~120% resistivity increase). Probes in the edge zones, such as Probe 11, show no significant changes in permittivity or resistivity, as the foam propagation did not reach these areas. This lack of variation validates that foam impact is confined to the central and intermediate zones. The observed foam saturation from image analysis validates the geophysical measurements, with higher foam saturation (up to 90%) in the central zone correlating with greater electrical property changes. Additionally, we observe higher phase shifts in Probe 13, Figure 3. We are further analyzing the phase-frequency variation (1.46 Hz to 20 kHz) to better understand the polarization effects induced by foam.

These findings highlight the potential of SIP and TDR methods for monitoring foam flow in porous media and provide valuable insights into the complex interactions between foam and electrical properties. This study underscores the importance of integrating geophysical techniques with image-based analysis to improve the understanding and effectiveness of soil remediation processes.