Reservoir characterization by push–pull tests employing kinetic interface sensitive tracers – Quantification of residual trapping in geological storage of carbon dioxide

• The KIS tracing method is proposed to quantify the interfacial area between brine and residually trapped scCO 2 . • At a small Péclet number, the measurement is unaffected by the scCO 2 architecture or the storage time. • Simple solutions for the interpretation of the breakthrough curves are demonstrated. Kinetic interface-sensitive (KIS) tracing is a recently developed methodology to monitor the change in fluid–fluid interfacial area (FIFA) in the context of geological storage of supercritical CO 2 in saline aquifers. Previous studies have demonstrated the applicability of KIS tracers at the scCO 2 injection stage, while its application at the storage stage when the tracked scCO 2 is residually trapped has not yet been studied. The main challenges that impede tracer application at the storage stage are the unknown concentration of the reacted tracer accumulated in the measurement region, resulting from the persistent interfacial reaction that occurs at the scCO 2 / brine interface with the KIS tracer injected by the scCO 2 , as well as the effects of the spatial distribution and shape of residual scCO 2 blobs. A “water push–pull” method is proposed here, enabling the application of the KIS tracer at the storage stage. This study applies pore-scale and field-scale numerical simulations to study the KIS tracer reactive transport during the “water push–pull” experiments. It is found that the measurement is not affected by the residual scCO 2 architecture, when the Péclet number is smaller than 5. The measurement relies on the steady-state concentration distribution formed in the measurement region, resulting from the equilibrium between the reaction production and the tracer removal due to the freshwater injection. The tracer breakthrough curves (BTCs) are not affected by the initial concentration nor a change in flow rate, and correlation functions between the FIFA and the slope of the BTCs are found.