Parallel simulation of three-dimensional convective mixing in long-term geological CO2 storage in saline aquifers

Mohammed Adil Sbai (1)

1 BRGM - Bureau de Recherches Géologiques et Minières

Accurate numerical modelling of the effective dissolution rate of aqueous CO2 solutions is important for analysis of long-term storage efficiency and risk assessments. Theoretical and field studies showed the possibility of switching from a diffusion-controlled mode of dissolution to a natural convection mode which is much more efficient for accelerating the dissolution mechanism. However, most of the previous investigations have been restricted to two-dimensional cross-section models similar to Elder (1947) problem. In this work, we developed a high resolution parallel simulator to investigate these mechanisms with grid blocks needed for accurate modelling of convective mixing in realistic three-dimensional configurations. The simulator sequentially couples groundwater flow and CO2 transport equations by density and viscosity contrasts. Density and viscosity of the aqueous CO2 solution is predicted by accurate equations of state module validated against previously published experimental data for a wide range of temperatures and pressures of interest. Numerical experiments show that two-dimensional modelling over-predicts the time to onset natural convection and under-predicts the time to achieve ultimate dissolution of the CO2-free phase in a homogeneous porous medium. The role of aquifer heterogeneity in further enhancing CO2 dissolution is illustrated for a generic case study. Heterogeneity leads to a disconnection of the otherwise continuous fingers to form CO2 blobs and ganglia, increasing the effective surface area between CO2-rich blobs and formation waters. Results suggest that high resolution three-dimensional modelling should be guided in CO2 storage projects to (a) estimate the onset of natural convection, (b) determine the size of convective instabilities when they occur, and (c) calculating the maximum mixing achieved.

Domaines: Sciences de la Terre

Mohammed Adil Sbai. Parallel simulation of three-dimensional convective mixing in long-term geological CO2 storage in saline aquifers. EGU General Assembly 2007 - European Geosciences Union, Apr 2007, Vienna, Austria. ⟨hal-00589919⟩