Consideration of an effect of interfacial area between oil and CO2 on oil swelling

Abstract

Oil swelling is an important phenomenon in CO2-EOR. According to various studies in the past, the degree of oil swelling depends on the partial pressure of CO2, temperature, and oil composition. However, we expect that other factors, such as oil saturation, capillary pressure, and grain size of reservoir rock must be also considered in evaluating oil swelling because they may influence the interfacial area between oil and CO2, which affects the dissolubility of CO2 in oil. Therefore, we had made clear the effect of the interfacial area on oil swelling in this study. Oil and CO2 were injected into a small see-through windowed high-pressure cell and oil swelling was observed under a microscope. The swelling factor increased with the increase of the specific interfacial area between oil and CO2. Moreover, oil swelling in porous media was observed using micro-models which had been made of two different diameter glass beads. Swelling factor in fine beads micro-model became larger than that in coarse beads micro-model whose interfacial area between oil and CO2 was smaller than that of fine beads micro-model. Therefore, the swelling factor is expected to be larger with an increase in the interfacial area in porous media. These results suggest that the oil swelling should be expressed as a function of oil saturation, capillary pressure, and grain size of reservoir rock which are related to the interfacial area as well as the partial pressure of CO2, temperature, and oil composition.