This paper presents a systematic study of the effect of surfactant partitioning between supercritical CO2 and water on surfactant transport and foam propagation during two-phase flow. A series of corefloods were conducted on Silurian dolomite cores with different non-ionic and anionic surfactants that represent respective wide ranges of partition coefficients and solubility in supercritical CO2. Foam robustness 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 surfactant partitioning effect from laboratory to field scale. Optimization of surfactant partition coefficient for field-scale foam process was performed with different injection strategies.

The results from this study enable us to tailor properties of CO2 soluble surfactants (i.e. partition coefficient) to a wide range of reservoir conditions and optimal injection strategies. The understanding of 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 non-ionic and anionic surfactants while an increase in surfactant partition coefficient lowers the rate of foam propagation. Field-scale foam simulations indicate that foam performance and surfactant transport was governed not only by constrained injection strategies, but also surfactant partition coefficient. For a given injection strategy, the latter could be optimized to improve injectivity and sweep efficiency.

The optimal partition of the surfactant between the CO2 and aqueous phases minimize wasting expensive surfactant in water that is never contacted with CO2. This novel CO2 soluble surfactant concept diversifies injection strategies with respect to operational constraints, broadening the application of foam process.

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