Impact of co-injected gases on CO2 storage sites: geochemical modeling of experimental results

At the end of a CO2 capture process the gas mixture composition can vary considerably incorporating components such as O-2, N-2, SOx, H2S, NyOx, H-2, CO, Ar at various concentration levels. These impurities, even if their concentrations are not significant from a health perspective, could lead to significant chemical reactivity towards reservoir or caprock minerals and well materials. Potential processes and impacts are not well documented yet. However, in the near future, it will be crucial for both operators and regulators to rely on numerical reactive-transport simulations able to model the behavior of these complex systems and consequently able to ensure the long-term stability of storage sites. Furthermore, numerous modeling studies have shown how limiting it could be to consider simple assumptions for gases such as dissolved gases only or infinite sources of gas, and also how important it is to correctly handle the gaseous phase. Recently, within the GAZ ANNEXES project funded by the ANR (French national research agency), we developed gas modules for both the geochemical code CHESS and the coupled reactive/transport code HYTEC. These advances make it now possible to simulate water/gas/rock interactions accurately. Within this project, some of the potential co-injected impurities were experimentally studied, highlighting their influence on the geochemical reactivity of some carbonate rocks involved in CCS. In this paper, the new gas module of CHESS is presented as well as its ability to reproduce these experimental results giving an important help to study both qualitatively and quantitatively the impact of co-injected gases. One key result for the experiments involving a gas mixture (82%mol CO2(g), 6% Ar-(g), 4% N-2(g), 4% SO2(g) and 4% O-2(g) which are the closest to real operations: both experiment -A and numerical results indicate a relative low reactivity of the rock. (C) 2013 The Authors. Published by Elsevier Ltd.