Effect of Surfactant Partitioning on Mobility Control During CO2 Flooding

Abstract

Summary This paper presents a systematic study of the effect of surfactant partitioning between supercritical carbon dioxide (SCCO2) and water on surfactant transport and foam propagation during a two-phase flow. A series of corefloods was conducted on Silurian dolomite cores with different nonionic and anionic surfactants that represent respective wide ranges of partition coefficients and solubility in SCCO2. Foam robustness (i.e., rate of foam development) and displacement efficiency were related to these surfactant properties. Coreflood results and all measured surfactant properties were used in a commercial reservoir simulator to determine the variation of the surfactant-partitioning effect from laboratory to field scale. The optimization of the surfactant-partition coefficient for field-scale foam process was performed with different injection strategies. The results from this study enable us to tailor the properties of CO2-soluble surfactants (i.e., partition coefficients) to a wide range of reservoir conditions and optimal injection strategies. The understanding of the surfactant-partitioning effect is also important in overcoming technical challenges encountered in the injection of surfactant in CO2. The partition between CO2 and water phases was much more sensitive to surfactant structure than temperature and pressure. Strong foam development was observed for all nonionic and anionic surfactants, whereas an increase in surfactant-partition coefficient lowered the rate of foam propagation. Field-scale foam simulations indicate that foam performance and surfactant transport are governed not only by constrained injection strategies, but also by a surfactant-partition coefficient. This novel CO2-soluble-surfactant concept diversifies injection strategies with respect to operational constraints, thus broadening the application of foam process. For a given injection strategy, a surfactant-partition coefficient could be optimized to improve injectivity and sweep efficiency. The optimal partition of the surfactant between the CO2 and aqueous phases minimizes the wasting of expensive surfactant in water that never comes in contact with CO2.