Industrial & Engineering Chemistry Research, Vol.59, No.11, 5158-5166, 2020
Quantitative Characterization of Foam Transient Structure in Porous Media and Analysis of Its Flow Behavior Based on Fractal Theory
Foam fluid is widely used in petroleum industry, so the behavior of the foam fluid flow in porous media directly affects the application effect of foam. However, the foam flow pattern in porous media is difficult to be established because of its dynamic change of interface structure and unpredictable boundary condition. In this work, the transient structural changes of the foam fluid in porous media are quantitatively characterized, and the flow behavior is analyzed based on fractal theory and visual experiments. First, the foam fractal characteristics are verified, and the fractal dimension is calculated. Results show that the foam fractal dimension is between 1.5 and 2.0, and the foam flow can be divided into three stages: gas-liquid two-phase flow, foam unstable flow stage, and foam stable flow stage. In addition, the evaluation indices of foam performance in porous media are proposed to evaluate the influencing factors, namely, the fractal dimension in stable stage Dfoam-s, and the time needed to reach stability T-s. The analysis shows that the larger concentration of the surfactant and the lower permeability correspond to smaller Dfoam-s and the larger temperature corresponds to larger Dfoam-s and Dfoam-s of the nitrogen foam is smaller than that of the carbon dioxide foam. T-s is the opposite. Last, the relationship between fractal dimension, pressure, and gas saturation is discussed. Qualitative analysis shows that the larger the displacement pressure, the smaller the foam fractal dimension and the higher the gas saturation, the smaller the foam fractal dimension. This paper provides a new method to explore the flow behavior of foam flow in formation, which has a certain significance for guiding the field application of the foam fluid.