On the flow of buoyant fluid injected into a confined, inclined aquifer

Abstract

We study the dispersal of a plume of incompressible buoyant fluid injected into a confined sloping aquifer which has an outflow at a single fault which may be up-dip (up-slope) or down-dip (down-slope) from the point of injection. We develop a long-time asymptotic solution for the motion of the injected fluid. We show that for the case in which the outflow fault is up-dip from the point of injection, there is a critical injection rate above which the injected fluid floods the full depth of the aquifer, and we show that for the case in which the outflow fault is down-dip from the point of injection, there is a critical injection rate below which all injected fluid initially flows up-dip. Our analysis leads to expressions for the lateral extent of the injected fluid as a function of time, and we consider the implications of the model for the dispersal of supercritical carbon dioxide injected into deep saline aquifers. The work also indicates that the geometry of the system may have a significant effect on (i) the total volume of carbon dioxide which it is possible to sequester in a faulted aquifer and (ii) the interpretation of the dispersed position of any injected tracers.