Geochemical tracers applied to reservoir simulation of the Weyburn CO2 EOR field

The results of integrating processes affecting selected geochemical tracers into a model of fluid flow and phase behaviour at the Weyburn CO2 EOR Field are presented. Flow patterns, and phase behaviours are obtained from a reservoir model, which had been history matched to fluid (oil and water) production rates as part of the IEA GHG Weyburn-Midale CO2 Monitoring and Storage Project. The reservoir model was updated by including tracer components with properties similar to those measured in produced fluids as part of the same project. The modelling results are compared with field values of chloride in produced water and the carbon isotope ratio of ethane, δ13C(C2H6), in produced gases. An accurate representation of the processes responsible for generating these, relatively simple, signals is a prerequisite for any future simulations incorporating reactive transport, such as would be needed to quantify rates of reactions between the injected CO2 and the host-rock. Modelling runs based on the previously developed history-matched single-porosity reservoir model failed to reproduce the variability seen in produced fluids for either a conservative major ion or δ13C(C2H6). Modifications incorporating fracture flow through use of a dual-porosity reservoir description lead to calculated chemical signals that were more compatible with the field observations.

► Single porosity geochemical simulations are incompatible with field observations.
► Dual porosity geochemical simulations are more compatible with field observations.
► Lack of injected fluid compositional data complicates produced water interpretation.