Modeling Foam Displacement with the Local Equilibrium Approximation: Theory and Experiment Verification

Abstract

Abstract The gas mobility control aspects of foamed gas make it highly applicable for improved oil recovery. Gas bubble size, often termed as foam texture, determines gas flow behavior. A population balance model has been developed previously for modeling foam texture and flow in porous media. The model incorporates pore-level mechanisms of foam bubble generation, coalescence, and transport. Here, we propose a simplified foam model to reduce computational costs. The formulation is based on the assumption of local equilibrium of foam generation and coalescence and is applicable to high and low quality foams. The proposed foam model is compatible with a standard reservoir simulator. It provides a potentially useful, efficient tool to predict accurately foam flows at the field scale for designing and managing foamed-gas applications. There are three main contributions of this paper. First, the population balance representation of foam generation by gas-bubble snap off is modified to extend the capability of the population balance approach to predict foam flow behaviors in both the so-called high-quality and low-quality regimes. Second, a simplified population-balance model is developed and implemented with the local-equilibrium approximation. Third, foam displacement experiments in a linear sandstone core are conducted to verify the proposed model. A visualization cell is employed to measure the effluent foam bubble sizes for a transient flow as well as to estimate the in-situ foam bubble sizes along the length of the core during steady flow. Additionally, the evolution of aqueous phase saturation is monitored using X-ray computed tomography (CT) and the pressure profile is measured by a series of pressure taps. Good agreement is found between the experimental results and the predictions of the simplified model, with a minor mismatch in the entrance region.