On the flow of buoyant fluid injected into an aquifer with a background flow

Abstract

AbstractWe study the dispersal of a plume of incompressible buoyant fluid injected into a confined inclined aquifer in which there is a background flow. We assume that, to prevent pressure buildup in the system, there is an outflow from the aquifer, with flux equal to the injection flux, through a producing well. Using the method of characteristics, we identify that the trajectory of the plume of injected fluid depends on the magnitudes of both the injection flux ${Q}_{I} $ and the background aquifer flux ${Q}_{A} $ relative to the buoyancy-driven exchange flow of injected and original fluid within the aquifer ${Q}_{E} $, on the direction of the background aquifer flow, and on whether the producing well lies upslope or downslope from the injecting well. We find the values of the controlling parameters ${Q}_{I} / {Q}_{E} $ and ${Q}_{A} / {Q}_{E} $ for which all injected fluid flows up-dip, for which the injected fluid partitions into a component moving up-dip and a component moving down-dip, and for which all injected fluid flows down-dip. A key learning from the analysis is that there may be very different plume trajectories when a buoyant fluid is injected into a confined, inclined aquifer, and prediction of the trajectory depends on knowledge of the background flow as well as the injection rate and location of the producing wells. In the process of ${\mathrm{CO} }_{2} $ sequestration, this range of initial plume geometries can inform analysis of longer-term geological storage and assessment of the risk of activating different possible leakage pathways to the surface.