Unstable Density‐Driven Convection of CO2 in Homogeneous and Heterogeneous Porous Media With Implications for Deep Saline Aquifers

Abstract

AbstractDensity‐driven convection mixing has been identified to enhance CO2 trapping in deep saline aquifers storage. In this study, the dynamics of fingering instability and associated mass transfer caused by convection mixing between the movements of miscible analogue fluid pairs are investigated by magnetic resonance imaging (MRI). Two kinds of homogeneous porous media and six kinds of heterogeneous porous media with varying permeability permutations were used at ambient pressure and temperature. In homogeneous porous media, the detail analyses on the data of fingering pattern, finger number and distribution identify that the large finger sizes and high sinking velocities can be developed when the permeability up to 3.3 × 10−11 m2. In heterogeneous porous media, the sand layer first touched by downward fingers plays a dominant role in finger evolution, channeling and fingering convection mechanisms were found among these cases. Moreover, the dissolution rate characterized by Sherwood number (Shm) (enhance or inhibit fluid mixing, depending on the layout of the sand layer) was found to be independent of the local convection dissolution, such as vortex flow and finger splitting at the sand boundary with mutation permeability (enhanced fluid mixing, promoting CO2 dissolution in carbon storage). Finally, the total CO2 dissolution rate Shm in all cases was compared, Shm are at a range of 970–5,079 in homogeneous porous media, while are 190–688 in heterogeneous porous media.