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.

The experimental measurement of water retention curve in hydrate‐bearing sediments is critically important to understand the behavior of hydrate dissociation and gas production. In this study, tetrahydrofuran (THF) is selected as hydrate former. The pore habit of THF hydrates is investigated by visual observation in a transparent micromodel. It is confirmed that THF hydrates are not wetting phase on the quartz surface of the micromodel and occupy either an entire pore or part of pore space resulting in change in pore size distribution. And the measurement of water retention curves in THF hydrate‐bearing sediments with hydrate saturation ranging from Sh = 0 to Sh = 0.7 is conducted for excess water condition. The experimental results show that the gas entry pressure and the capillary pressure increase with increasing hydrate saturation. Based on the experimental results, fitting parameters for van Genuchten equation are suggested for different hydrate saturation conditions.

Gas bubbles can be naturally generated or intentionally introduced in sediments. Gas bubble migration and trapping affect the rate of gas emission into the atmosphere or modify the sediment properties such as hydraulic and mechanical properties. In this study, the migration and trapping of gas bubbles are simulated using the pore‐network model extracted from the 3D X‐ray image of in situ sediment. Two types of bubble size distribution (mono‐sized and distributed‐sized cases) are used in the simulation. The spatial and statistical bubble size distribution, residual gas saturation, and hydraulic conductivity reduction due to the bubble trapping are investigated. The results show that the bubble size distribution becomes wider during the gas bubble migration due to bubble coalescence for both mono‐sized and distributed‐sized cases. And the trapped bubble fraction and the residual gas saturation increase as the bubble size increases. The hydraulic conductivity is reduced as a result of the gas bubble trapping. The reduction in hydraulic conductivity is apparently observed as bubble size and the number of nucleation points increase.

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