Modelling of kinetic interface sensitive tracers for two-phase systems

Abstract

This article presents a mathematical model for interface sensitive tracer transport used for the evaluation of the interface between two fluid-phases (i.e. CO2 and brine) with general applicability in a series of engineering applications: oil recovery, vapour-dominated geothermal reservoirs, contaminant spreading, CO2 storage, etc. Increasing the CO2 storage efficiency in brine deep geological formations requires better injection strategies to be developed which could be accomplished with better tools for quantification of the fluid-fluid interfaces. The CO2 residual and solubility trapping are highly influenced by the interfaces separating the phases. An increase in the interface area is expected to produce an increase in the solubility trapping. However, standard multi-phase models do not account for the specific fluid-fluid interface area. A new class of reactive tracers is used for the characterization of interfacial areas between supercritical CO2 and brine. The tracer is injected in the CO2 and migrates to the interface where it undergoes a hydrolysis reaction in contact with water. A mathematical model is constructed based on volume-averaged properties (saturation, porosity, permeability, etc.) at the macroscale. The fluid phases are described with an extended form of the Darcy equation based on thermodynamic principles and complemented with relations for relative permeability and saturation and a specific equation for interfacial area. The kinetic mass transfer effects between the two phases are highly dependent on the interface area, and are captured with an approach introduced by [1]. The mathematical model is tested with a simple numerical example. © Springer-Verlag Berlin Heidelberg 2013.