Simulating in-zone chemistry changes from injection time to longer periods of CO2 storage

Geochemical reactions can play important role in the long-term geological storage of CO 2 in sites where the target formations have reactive minerals. Although the use of batch models (experimental or theoretical) is expedient, it leaves questions unanswered about how to interpret or predict field-scale injection over long time periods. In this study we present results of coupled multiphase, multicomponent reactive transport simulation using geochemistry data derived from Cranfield site, Mississippi, USA, a site that has long been used for carbon sequestration R&D activities. The simulation was performed using PFLOTRAN, an open-source parallel reactive transport code. The geochemical system consists of 22 primary or basis species, in situ CO 2 and O 2 gaseous components, and 5 minerals. In this model, there are 37 secondary elements with brine molality being 1.81. The fluid chemical compositions were measured from production fluids, and mineral composition of the formation was obtained from XRD analysis of core samples. Results show how brine chemistry changes in the reservoir and shed insights into the need to monitor the mobility of cations such as Mg, Ca, Al, Mn, Fe, Cu, Zn, Sr, Ba, and Cd. We delineate the reservoir volume that is affected in order to provide simultaneous potential mobile inventory of these metals in the storage formations and warn possible risks through leakage into overlying zone. It is found that during injection period considered in this study dissolved CO 2 can spread about 3.5 km 2 area around the injection well and, as a result, pH drops to as low as 3.3–5.5 at the farthest location affected. Among the metals considered, only concentrations of Ca and Al are increased by 1 and 2 orders, respectively. In longer periods, Al concentration can increase by orders of magnitude of EPA’s threshold limit. Compared to no reactions, the CO 2 plume’s extent area is 50 % less in 20 years; however, more CO 2 is trapped in solution.