Reactive Surface Area in Geochemical Models - Lessons Learned from a Natural Analogue

Many uncertainties exist in geochemical modeling. Mineral reactive surface area is one of the uncertain parameters. QEMSCAN analyses are performed on sandstone samples from a Dutch CO2 natural analogue to determine reactive surface areas. Geochemical modeling is performed using QEMSCAN surface areas and surface areas which are conventionally used in modeling. The model predicts that the QEMSCAN reactive surface areas result in higher reaction rates and faster equilibration of the sandstones with CO2. The fact that reactions are predicted to occur in a sandstone which has been in contact with CO2 for geological times suggests that the reservoir mineralogy is not yet in equilibrium with CO2. This would indicate that, even if mineral reactive surface areas are determined in detail, geochemical models strongly overestimate reaction kinetics. Other uncertain parameters which can affect kinetics, like mineral nucleation and ion diffusion, should be evaluated in order to be able to better predict long-term CO2-mineral reactions and storage integrity.