Technical Study Assesses Geological Carbon Storage in Brazilian Brownfields

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 36184, “A Thorough Technical Assessment of Potential Sites for Geological Carbon Storage in Brazilian Brownfields,” by Tiago H.F. de Jesus, Marcos V.B. Machado, SPE, and Júnia Casagrande, Petrobras, et al. The paper has not been peer-reviewed. Copyright 2025 Offshore Technology Conference. _ This study assesses the technical feasibility of geological carbon storage in the operator’s Brazilian brownfields, focusing on mature oil fields and associated saline aquifers. The analysis includes geological characteristics, estimated storage capacities, and operational risks in each area. Overall, the findings support the development of regional carbon capture, use, and storage (CCUS) hubs and demonstrate Brazil’s technical readiness to deploy large-scale CCUS solutions. Introduction In alignment with strategic, logistical, technical, and economic considerations, the operator has prioritized the development of onshore mature fields and their associated saline aquifers near hard-to-abate industrial operations. While acknowledging the significant potential of offshore reservoirs, the operator also has initiated plans for the establishment of four CCUS hubs across Brazil. These include early-stage projects in the states of Rio de Janeiro, São Paulo, and Bahia (Recôncavo Basin), as well as a more-advanced initiative in the northern region of Espírito Santo. Additionally, the Cabiúnas pilot project in northern Rio de Janeiro is in the implementation phase. The northern Alagoas region also is under evaluation as a potential site. This study focuses on three strategically significant regions: Northern Espírito Santo, the Recôncavo Basin, and Alagoas. The first region is at a more-advanced stage of screening and evaluation, while the latter two are still in the early stages of assessment. The primary objective is to develop a comprehensive roadmap, establish benchmarks, and provide guidelines to support future evaluations and the implementation of CCUS solutions across Brazil’s onshore basins. While the complete paper contains detailed discussions of the first and third of these regions, this synopsis includes the evaluation of the Recôncavo Basin. Methodology When selecting oil and gas fields and their associated aquifers for CCUS, several critical criteria must be thoroughly evaluated. Foremost among these are storage capacity and containment. Adequate depth is another essential factor, because CO2 must be stored under conditions that roughly maintain it in a supercritical state. Transmissibility, which reflects the combined effect of formation permeability and thickness and is influenced by the geometry of gridblocks in reservoir simulations, also must be considered. Injectivity, shaped by factors such as reservoir permeability, fluid properties, well design, and near-wellbore conditions, plays a key role in determining the feasibility of CO2 injection. Finally, proximity to major CO2 emission sources offers a significant logistical advantage. In evaluating the carbon-storage potential of subsurface formations, two conceptual end-member models were used, open and closed-system storage resource estimates. These models represent extremes in terms of pressure behavior and containment dynamics during injection. In this context, storage efficiency (SE) serves as a multiplier that reflects the fraction of pore space that can be occupied realistically by CO2. In open systems, higher SE values typically are used because pressure dissipation through connected formations allows for more-extensive CO2 injection. Conversely, in closed systems, lower SE values are applied because of pressure buildup, which limits the volume of CO2 that can be injected and stored safely.