Effect of capillary and viscous force on CO₂ saturation and invasion pattern in the microfluidic chip

Carbon dioxide sequestration into geological formations has been identified as an alternative to mitigate the global climate change. The CO₂ invasion pattern is dependent on various factors such as fluid viscosity, interfacial tension, injection rate, and the characteristics of porous media. Among these variables, we provide a systematic experimental study on the influence of the injection rate and the phase of CO₂ invading into a brine-saturated microfluidic chip in order to quantitatively assess the displacement ratio. Interfacial tension and contact angle are accurately measured under the temperature and pressure conditions relevant to in situ conditions. The injection rate varies 3 orders of magnitude for gaseous, liquid, supercritical CO₂, and CO₂-water foam invasion. The capillary number and the viscosity ratio are calculated for each experimental condition, and the displacement ratio (CO₂ saturation) is obtained after CO₂ invasion. The results show that the saturation of injected CO₂ is controlled by manipulating the injection rate and the phase of invading fluid, which can be used to optimize the in situ storage capacity. Especially, the CO₂-water foam displaces almost all brine out of the microfluidic chip, but the increase in CO₂ saturation is 23% ~ 53% compared to pure gaseous CO₂ injection due to the water initially mixed in the CO₂-water foam. The potential advantages of using CO₂-water foam in the geological CO₂ sequestration were also discussed.