CO₂ Mineral Trapping Potential of Carbonates: A Numerical Investigation

During CO₂ geo-storage, mineral dissolution is considered as the safest trapping technique however it is the longest and the most complicated trapping mechanism involving geo-chemical reactions and physical forces like diffusion and advection. Many factors also influence the mineral trapping capacity of the geological formation e.g., mineralogy, temperature, pH, CO₂ fugacity, pressure of CO₂, salinity and composition of the brine. The scope of this study is to investigate the mineral trapping of CO₂ in Arabian carbonates reservoirs as a function of temperature, brine composition and pH of the subsurface systems. Numerical simulations are performed using the multi-phase simulator GEM-CMG. 2D and 3D models are developed to examine the mechanisms occurring during mineral trapping and how these affect its efficiency. The mineralogy of a carbonate field from an Arabian formation is used. Sensitivity analysis has been performed on the effect of temperature, pH and brine composition on CO₂ mineralization tendency and porosity. The results suggest that dissolution and precipitation of minerals occurred during and post CO₂ injection while pH had the major influence on mineral trapping. At basic pH conditions, pH=9, the highest amount of CO₂ was mineralized while at mid pH, precipitation of carbonates decreased remarkably. Changing the brine composition also highly affected the storage capacity e.g., divalent salt accelerated CO₂ mineralization. Moreover, temperature tends to promote the mineral activity during CO₂ storage. While a score of publications investigated CO₂ storage via structural, residual and dissolution trapping mechanisms, still the mineral trapping potential and its influencing factors have not been investigated much. This paper thus provides new insights into CO₂ sequestration by mineral trapping pertinent to Arabian carbonate rocks.