Reactive Transportmodelling and Long Term Behaviour of CO2Sequestration in Saline Aquifers

Geological sequestration of CO2 in deep saline aquifers may offer numerous opportunities for the mitigation of greenhouse gas emissions. In order to ensure good containment, a correct understanding of the evolution of such systems after a massive injection of CO2 is compulsory. For this purpose, coupled reactive transport modelling can provide useful information, by simulating chemical reactions likely to occur in the system coupled to reactive transport, at large time and space scales.This study aimed at investigating the possible benefits of reactive transport modelling in the context of CO2 sequestration. Two deep saline aquifers have been chosen to test the performance and limitationsof the codes: the carbonated aquifer of the Dogger (Paris Basin) and the sandstone aquifer of the Bunter (North Sea). The aquifers, with contrasting behaviours, have been chosen to illustrate the main expected phenomena: CO2 dissolution in the carbonated aquifer, carbonate mineral precipitation in the sandstone aquifer. The simulations highlight the performance of the reactive transport codes, particularly the possibility to represent in detail a source (or sink) term with the dissolution of the CO2 bubble (or the precipitation of carbonated minerals), coupled to the transport of the dissolved CO2. Furthermore, flux assessment at various points of the system illustrates the storage capacity of the systems. However, several shortages have been identified: a lack of data on the aquifers and on the reactivity of CO2 under sequestration conditions. Finally, developments are advisable to better estimate the transport, dissolution and reactivity of the supercritical CO2: This involves a two-phase coupled reactive transport code, and a coupling with the exchange between phases.