Plume speed-up in layered porous media

The injection of CO₂ into porous subsurface reservoirs is a technological means for removing anthropogenic emissions, which relies on a series of complex porous flow properties. During injection of CO₂ small-scale heterogeneities, often in the form of sedimentary layering, can play a significant role in focusing the flow of less viscous CO₂ into high permeability pathways, with large-scale implications for the overall motion of the CO₂ plume. In these settings, capillary forces between the CO₂ and water preferentially rearrange CO₂ into the most permeable layers (with larger pore space), and may accelerate plume migration by as much as 200%. Numerous factors affect overall plume acceleration, including the structure of the layering, the permeability contrast between layers, and the relative importance of the other, gravitational and viscous, forces that act upon the flow. However, despite the sensitivity of the flow to these heterogeneities, it is extremely difficult to acquire field measurements at the ~10cm scale of the heterogeneities owing to the vast range of scales involved, presenting an outstanding challenge. As a first step towards tackling this uncertainty, we use a simple modelling approach, based on an upscaled thin-film equation, to create ensemble forecasts for many different types and arrangements of sedimentary layers. In this way, a suite of predictions can be made to elucidate the most likely scenarios for injection and the uncertainty associated with such predictions.