Bohao Wu

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

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.

CO2/water two-phase flow in a two-dimensional micromodel of heterogeneous pores and throats

Gas–liquid two-phase flow in porous media is highly relevant to numerous geological engineering processes. Pore network micromodeling is able to provide an effective way to experimentally observe the gas–liquid displacement phenomena. However, micromodel experiments were rarely conducted in heterogeneous conditions, which may significantly affect the displacement process. In this study, CO2/water displacement experiments were conducted at 25 °C and ambient pressure conditions in an etched glass micromodel with heterogeneous pores and throats. The experiments were performed in both vertical and horizontal directions with the CO2 injection rates ranging from 0.2 ml h−1 to 6.0 ml h−1. Dynamic displacements were detected in real time by a digital single lens reflex camera. Based on the experimental results, a detailed discussion about the instability of CO2 front and CO2 saturation variation was conducted. It is found that the displacements become more and more unstable with an advancing CO2 front. Small fingerings can be collapsed by capillary pressure. Micro-scale heterogeneity significantly influenced the flow pattern at both the microscale and macroscale. Moreover, we created a new evaluation parameter Seval to characterise CO2 saturation variations and the transformation of Seval agrees well with our experimental results of CO2 saturation.

Characterization of dissolution process during brine injection in Berea sandstones: an experiment study

A clear understanding of the mass transfer properties during fluid injection into porous media is of importance to the safety of CO2 storage. In this study, several experiments were conducted to elucidate the displacement and dissolution processes of gaseous and supercritical CO2 in Berea sandstones using the X-ray CT technology. The initial CO2 distribution before brine injection was related to the pore structure of the sandstones. Transient images during brine injection at different flow rates showed a transformation from displacement to dissolution, and the dissolution fronts were affected by the core heterogeneity and flow rates. Then, the CO2 saturation was determined by imaging analysis. Both supercritical and gaseous CO2 saturation decreased sharply, meaning that dissolution dominated the flow process. The dissolution time could be correlated in terms of the flow rate, initial gas saturation and heterogeneity of the sandstone. The relationships between CO2 volume content and specific surface area were verified to qualitatively predict the influence of heterogeneity. The dynamic concentration and mass transfer coefficient were obtained, which gave the information for the mass transfer rate during CO2 storage.