Effects of Rock Heterogeneity and Wettability on CO2 Mineralization During Storage in UAE Depleted Carbonate Gas Formations

Abstract

Abstract Anthropogenic CO2 emissions have accumulated significantly in the last few decades aggravating global warming. Mineral trapping is a key mechanism for the global energy transition during which injected CO2 is sequestered within the subsurface formations via dissolution/precipitation. However, the data of CO2 mineralization are extremely scarce, which limits our understanding of suitable candidate formations for mineral trapping. The aim of this study is to emphasize the impacts of wettability and rock heterogeneity on mineral trapping occurring during CO2 sequestration in carbonate formations. In this study, a numerical approach was followed by setting up one-spot pilot test-scale models of homogeneous and heterogeneous carbonate formations to predict the mineral trapping capacity of CO2 gas for two distinct wetting states: Strongly Water-Wet (SWW) and Intermediately Water-Wet (IWW). Accordingly, a 3D Cartesian base case model was created with upscaled petrophysical parameters to mimic the subsurface conditions of a representative carbonate formation from UAE. The study highlighted the relationship between carbonate wettability, rock heterogeneity, and fate of CO2 plume and mineralization potential. In this study, the effect of wettability and heterogeneity were analyzed in terms of CO2 mineralized after 1 year of injection and 200 years of storage. The mineral trapping capacities computed showed a monotonic increase as the wettability shifted from SWW to IWW irrespective of reservoir heterogeneity with different extents. Notably, after 115 years of storage, the heterogeneous formations started to sequester more CO2 attributed to permeability variance increase. In the same context, plume of CO2 extended upwardly and laterally further in case of intermediately water-wet compared to strongly water-wet, especially at earlier stages of storage duration. Classical trapping mechanisms such as solubility trapping gained more attention than mineralization. This is attributed to the time-dependency of mineralization with slow reaction rate scaling up to millennia. Thus, CO2 mineralization potential assessment is important to de-risk large-scale pilot tests. This work provides new insights into underpinning the effects of wettability and rock heterogeneity on CO2 storage capacity in carbonate formations. The findings suggest that mineralization within carbonate immobilizes CO2 and thus, assists in stable and long-term storage.