Opportunities and challenges for geologic CO2 sequestration in carbonate reservoirs: A review

Within the last three decades, there has been a remarkable increase in both the adoption and implementation of geologic CO2 sequestration, a mature and well-established method for reducing greenhouse gas emissions. Numerous research efforts have been geared toward subsurface engineering for effective containment and project scale-up in various types of geologic reservoirs, including sandstones, shales, carbonates, ultramafic, and basalts. However, only a handful of full-scale or pilot projects have been conducted in carbonate reservoirs despite their favorable petrophysical characteristics and wide prevalence across the globe. The principal challenge for CO2 sequestration in carbonate reservoirs includes concerns surrounding the effective containment of CO2 due to geologic complexities, such as high reactivity, petrophysical heterogeneity, structural compartmentalization, and mineralogical variability. Nonetheless, carbonate reservoirs are often characterized by porosity and permeability that are favorable for CO2 sequestration, and they frequently occur below low-permeability cap rock. Moreover, carbonate formations are prevalent in many geologic basins worldwide and in close proximity to anthropogenic CO2 sources. Thus, with proper engineering, carbonate formations will play a significant role in geologic CO2 sequestration to achieve the global emissions reduction target. This paper presents a comprehensive review of carbonate reservoirs in the context of geologic CO2 sequestration. We explore their unique opportunities and challenges, including their geology, global distribution, and natural CO2 accumulations. Insights are drawn from a wide range of sources, including experimental studies, numerical and reactive transport modeling, and pilot projects. We highlight the various factors that influence effective CO2 storage, providing recommendations for successful geologic CO2 sequestration.