Novel approach for modeling kinetic interface-sensitive (KIS) tracers with respect to time-dependent interfacial area change for the optimization of supercritical carbon dioxide injection into deep saline aquifers

Abstract

Tracer methods represent techniques commonly used for the characterization and for the monitoring of transport processes in geo-reservoirs (e.g., CO2 storage). The current short communication addresses the development of a conceptual, mathematical and numerical model for a new tracer class (KIS tracers, Schaffer et al., 2013) useful for the characterization of fluid–fluid interfacial areas during supercritical CO2 injection into deep saline aquifers. This tracer type has the potential to quantify the amount of fluid–fluid interfacial areas, important for the quantification of reactions at the fluid interface, which can implicitly lead to optimized injection strategies, a better assessment of the extent of the CO2 plume and of the storage efficiency.The presented modeling approach overcomes the drawback of the current standard multiphase multicomponent models, which ignore kinetics of mass transfer over the interfacial area between the CO2 and brine and consider only the volumetric fraction of the fluids or their mass and molar fractions, respectively. In this model, the concept of a specific interfacial area obtained from pore network modeling is used to complement the constitutive relationships between capillary pressure and saturation. It is a two-phase four component flow and transport model with a kinetic mass transfer of tracers between the two fluids and taking the dissolution of CO2 in brine into account. Two numerical simulation scenarios are shown as examples for the design of experimental work in laboratory and eventually in the field. The modeling approach follows the assumptions of previous experimental work (Schaffer et al., 2013). Their implications are investigated by sensitivity analyses to narrow the physical range of reaction rates for further experiments and molecular tracer design. Both examples indicate that the tracer concentration is sensitive with respect to the interfacial area and, therefore, KIS tracer utilization both in the lab and in the field appear to be feasible for implementation.