Reservoir characterization by push-pull tests employing kinetic interface sensitive tracers - a pore-scale study for understanding large-scale processes

Abstract

The kinetic interface-sensitive (KIS) tracer experiment is a newly developed method to quantify the fluid-fluid interfacial area (FIFA) during drainage processes. The concentration breakthrough curves, obtained by measuring reaction product concentration in brine/water samples after breakthrough, are interpreted with a specialized numerical model to determine the FIFA. However, this method has its own limitations since the volume of the usable water sample (after breakthrough), based on which the analysis takes place, is often insufficient. This happens because this volume strongly depends on the aquifer material, i.e. sand type and system parameters. An alternative is to employ KIS tracers in a “push-pull” experimental set-up, i.e. primary drainage is followed by a consequent main imbibition process, with the flow direction being reversed. This study applies a pore-scale numerical model to study the KIS tracer reactive transport during a push-pull experiment in a 2D porous medium. The advective-dispersive-reactive transport during both primary drainage and main imbibition processes is discussed. The concentration breakthrough curves show a non-linear descending trend with time, until reaching a constant concentration at the steady state. By analyzing the spatial concentration distribution and the concentration breakthrough curve, the macro-scale KIS tracer reactive transport model can be interpreted for the push-pull process. Finally, the new method is applied in a column experiment, where the determined specific interfacial area is found to be close to literature data.