Reassessing historical gas occurrences considering CO2 geological storage, a case study of the Cuiabá Paulista occurrence, Brazil

• Historical gas site reassessed as a promising CO₂ geological storage target. • 3D electrofacies modeling refined reservoir and stratigraphic characterization. • Identified a saline aquifer reservoir with 930 Mt theoretical CO₂ capacity. • Highlighted EGR and tight gas potential coupled with CO₂ injection strategies. The Carbon Capture and Storage (CCS) technology encompasses integrated processes to prevent carbon dioxide (CO 2 ) emissions from reaching the atmosphere, including storage in deep geological formations. This technology supports international carbon reduction objectives, such as those established by the Paris Agreement. This study focuses on the Cuiabá Paulista natural gas occurrence, chosen for its proximity to one of Brazil's largest concentrations of CO 2 stationary emitters and its favorable geological attributes, which present future opportunities combining gas exploitation with CO 2 storage, besides tight gas potential, reassessing the historical gas occurrence that was previously considered subeconomic. This research aims to evaluate key geological parameters for CO 2 storage and to develop a 3D stratigraphic model based on lithological and petrophysical data from drilling wells, emphasizing the subdivision of formations into electrofacies to identify reservoirs with the potential for CO 2 storage. The analysis reveals that saline aquifer storage is a potential geological option, with a theoretical capacity of approximately 930 Mt of CO 2 . The key findings demonstrate that integrating geological, petrophysical, and reservoir data enables a robust reassessment of the Cuiabá Paulista gas occurrence as a potential CO₂ storage site, which implicates the broader applicability of an electrofacies-based capacity evaluation within a methodological workflow that can be replicated for other historical gas occurrences with limited data availability. The identified reservoir could function as a CO 2 sink not only for the local emitters but also as a regional hub, contributing to emission reduction efforts in the Southeast region of Brazil.