Modeling Reactive Transport in CO2 Geological Storage: Applications at the Site Scale and Near-Well Effects

The development of subsurface reactive transport modeling enables us to understand the behaviour of hydrogeological and hydrogeochemical systems under natural conditions or during various industrial operations (hydrocarbon extraction, gas storage, geothermal wells, etc.). As concerns CO2 geological storage, a considerable amount of modeling has been done since the concept was first developed in the 1990s. CO2 storage is considered to be one of the possible means of reducing greenhouse gas emissions and thus combatting climate change, much of which is caused by the atmospheric emission of carbon dioxide by industrial activity, increasingly fueled by coal and hydrocarbons. After several years of research, pilot sites were created in North America, Europe, Australia, Asia, and Africa. Of the many lines of research, the role of chemical reactivity on the behaviour, efficiency, and safety of a storage site has raised many questions. Indeed, carbon dioxide, once it has dissolved in water, produces carbonic acid, which might dissolve some of the minerals making up the reservoir rock into which the CO2 has been injected, the caprock that blocks all vertical buoyancy of the CO2 gas (supercritical), and the cement used to plug the injection wells or present in the storage complex. The EU's CCS Directive (2009) mentions the need to model the reactive transport of CO2 in order to understand, when characterizing the dynamic behaviour of storage sites, the reactive processes occurring notably with the minerals in the storage reservoir and the surrounding formations, the evolution with time of the chemical composition of the formation fluids, and any precipitation of secondary phases, all of these for timescales ranging from decades to millennia (EC Directive, 2009).