Three-Dimensional Imaging of Dissolution-Driven Convection in Simple Porous Media Using X-ray CT Scanning

Motivated by geological carbon dioxide (CO2) storage and the associated process of CO2 convective mixing in brine, we present an experimental method to visualize dissolution-driven convection in a three-dimensional porous medium. Owing to the difficulty of imaging the time-dependent convective process within an opaque medium, experiments so far have largely focused on two-dimensional systems. However, this imposes a strong restriction on the lateral spreading of the plumes. To explore the flow pattern within a three-dimensional medium, we present an experimental procedure employing X-ray computed tomography that enables the visualization of the spatial and temporal evolution of the mixing process non-invasively. To mimic the dissolution of CO2 in brine, we use potassium iodide (KI) in water. Here, we show the results with high spatial and temporal resolution for an experiment with a homogeneous packing of glass beads (Ra=5300). We discuss the evolution of the average solute mass fraction, compare it to numerical results of a purely diffusive process and report a strong enhancement of the dissolution process when convection dominates over diffusive mass transfer effects.