CO2 Mineral Trapping Potential of Carbonates: A Numerical Investigation

Abstract

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.