2 APPROACHES TO MODELING UNSTABLE FLOW AND MIXING OF VARIABLE-DENSITYFLUIDS IN POROUS-MEDIA

Density variation of aqueous phase fluids flowing in a porous medium, resulting from spatial and temporal variation of solute concentration, often gives rise to unstable flow, and therefore has a significant ef fect on solute transport. Studies on simulating unstable how and mixin g of variable density fluids in seemingly homogeneous porous media are rare. In this study, a three-dimensional (3-D) and a one-dimensional (1-D) model were developed to simulate unstable flow and mixing in a v ertical, nominally 1-D system. In the 3-D model, the fluid flow and so lute transport equations were solved numerically with a very fine spat ial discretization. The 1-D numerical model was derived from a theoret ical model to simulate the flow and mixing of fluids with variable den sity and viscosity at the field scale. To evaluate the models, simulat ed results were compared with experimental data from displacement expe riments in a vertical sand column. The results show that the 1-D model provides fairly good prediction of breakthrough curves and that the 3 -D model is able to qualitatively simulate breakthrough curves for hig hly unstable flow and mixing.