Modelling of Kinetic Interface Sensitive Tracers for Two-Phase Systems

This article presents a mathematical model for interface sensitive tracer transport used for the evaluation of the interface between two fluid-phases (i.e. CO

2

and brine) with general applicability in a series of engineering applications: oil recovery, vapour-dominated geothermal reservoirs, contaminant spreading, CO

2

storage, etc. Increasing the CO

2

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 CO

2

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 CO

2

and brine. The tracer is injected in the CO

2

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.