Buoyancy‐Driven Flow at Reservoir Conditions

Abstract Quantifying the transition between viscous‐ and buoyancy‐dominated flow during injection is essential for predicting plume migration and evaluating storage efficiency in saline aquifers. While previous studies have examined the interaction of viscous, gravitational, and capillary forces, the precise definition of buoyancy‐dominated flow remains unclear. In this study, we use fractional‐flow theory to show that there is a transition in the flow profiles below a threshold flow rate. Below the threshold flow rate, the saturation profile is only a shock with no spreading wave—we posit that this is the signature for buoyancy‐dominated flow. We perform high‐pressure CT core‐flood experiments and find that at high flow rates there is a spreading wave, and at low flow rates there is little or no spreading wave. These findings establish a quantitative threshold for the transition between flow regimes and provide a robust framework for scaling laboratory –brine displacements to field‐scale storage systems.