Experimental study of two-phase flow properties of CO2 containing N2 in porous media

Abstract

In preliminary analyses, the co-injection of CO₂ with H₂S, SO₂ and N₂ impurities has been shown to reduce total carbon capture and storage (CCS) cost. The multiphase flow properties of impurities in the CO₂–brine system in porous media are the key to understanding the mechanisms and nature of geological CO₂ sequestration projects. In this study experiments were performed on the multiphase flow process of CO₂/N₂/brine system at conditions similar to aquifer pressure and temperature using the X-ray CT technique. Experiments at various rates of CO₂ injection that affect saturation and spatial distribution of injected gas were conducted in this experiment. The results indicate an strong relationship between gas saturation and porosity distribution in porous media, and the increasing capillary number leads to lower saturation in downward injection. Small capillary numbers and higher fractional flows in the gas phase both result in uniform saturation maps in the core. The CO₂ clusters seem larger at high capillary numbers and the high CO₂ collection regions extend based on the saturation distribution in the lower CO₂ fraction as the flow pattern stays similar as the same capillary number. CO₂ containing N₂ tends to retain more correlative relationships at different gas injection rates compared with the pure CO₂ stream. Even though both distribution and saturation are storage concerns, the N₂ component has little effect on gas distribution, whereas it brings about an overall increase in the saturation for most experiments. Thus the N₂ enhanced the storage performance of CO₂.