A Novel Multifrequency Dielectric Technique for Analyzing Foam Flow in Porous Media for Enhanced Oil Recovery and CO₂ Sequestration

Foam has been widely used to control gas mobility during subsurface oil displacement processes, mitigating challenges such as reservoir heterogeneity, gas channeling, and gravity override. Its applications extend to enhanced oil recovery (EOR) and CO₂ storage, where foam improves sweep efficiency and reduces gas leakage. However, the thermodynamic instability of foam necessitates a reliable evaluation of its quality and stability before field deployment. This work introduces a novel multifrequency dielectric technique for characterizing both bulk foam and foam flow in porous media. This study presents the first application of a multifrequency dielectric technique for foam characterization, validated against conventional foam analyzer measurements of quality and stability. In the first part of the study, dielectric properties (permittivity and conductivity) were measured for bulk foams generated with sodium dodecyl sulfate (SDS) surfactant at two concentrations (0.1 wt% and 0.3 wt%) using deionized water (DW) and seawater (SW). Measurements were performed across a 1-MHz to 3-GHz frequency range using an open-ended coaxial probe connected to a Keysight impedance analyzer, and results were compared with those from a standard foam analyzer. The findings showed that conductivity increased with frequency due to ion polarization, particularly at low to intermediate frequencies. Foams generated with SDS in DW exhibited lower permittivity than bulk water, reflecting the reduced polarization caused by air bubbles and surfactant molecules interfering with water’s electric field. Conductivity increased slightly with SDS concentration, correlating with improved foam stability. In the second part, the dielectric response was measured along core samples under different conditions, including dry, brine-saturated, surfactant-saturated, and foam-filled states, to characterize foam flow in porous media. The dielectric profiles defined clear upper and lower boundaries corresponding to brine-saturated and dry-rock conditions, respectively. Stable and high-quality foams exhibited permittivity and conductivity values closer to surfactant-saturated profiles, while poor foams are closer to the dry-rock behavior. Foam flooding experiments were performed under both high-and low-pressure conditions to investigate foam stability and potential disruption during dielectric measurements. The results demonstrate that dielectric properties can be used to quantitatively assess foam distribution, texture, and gas/liquid saturation within the pore structure. The study further discusses the polarization mechanisms governing dielectric behavior at low frequencies to capture interfacial polarization related to gas/liquid and rock/fluid interactions, while high frequencies reflect dipolar polarization within the bulk foam. The observed decline in dielectric constant over time corresponds to foam drainage, gas expansion, and bubble coalescence. Overall, the multifrequency dielectric technique provides a new approach for foam evaluation, capable of quantifying foam quality, stability, and propagation in both bulk and porous systems. The proposed method enhances the understanding of foam/rock/fluid interactions and offers a foundation for real-time monitoring and optimization of foam-based EOR and carbon dioxide (CO₂) storage operations.