Coupling of TOUGHREACT-Geochemist Workbench (GWB) for Modeling Changes in the Isotopic Composition of CO2 Leaking from a CCS Storage Reservoir

Abstract

A novel coupled TOUGHREACT-Geochemist Workbench (GWB) model has been developed to predict changes of the isotopic composition of CO2 resulting from reactive transport during leakage of CO2 from a storage reservoir. In the TOUGHREACT environment, we created a simplified 2D radial multi-aquifer model with 50 vertical cells for the Shell Quest project site and simulated reactive transport processes that may occur during a hypothetical CO2 leakage event. Perl scripts were developed to take input and output data from TOUGHREACT and create input files for GWB for subsequent modeling of the isotopic composition of leaking CO2. Using this approach, we simulated the extent of changes of the isotopic composition of leaking CO2 at 1000 T/y and 100 Darcy permeability for the first 10 cells extending from the Basal Cambrian Sandstone to just above the overlying Winnipegosis. Initial results indicate that the leaking free gas phase had δ13C values of CO2 within 1 ‰ of that of the injected CO2. δ18O values of leaking CO2 showed more pronounced changes since they are controlled by oxygen isotope ratios of formation water and significant equilibrium isotope fractionation between CO2 and H2O. This suggests that ™13C values, but not ™18O values, of injected CO2 are a suitable tracer if they are sufficiently distinct from those of baseline carbon compounds.