Optimizing CO2 trapping in saline aquifers under geological uncertainty: A case study of the Rio Bonito Formation, Brazil

Abstract

Saline aquifers in subsurface geologic structures have the potential for permanent CO₂ storage. Injecting CO₂ into such formations; however, does not ensure safe storage because CO₂ could leak to the surface or pollute the formation water. The current study presents the methodology used to study structural, residual, and solubility trapping to propose an operational strategy for efficient CO₂ storage in the sandstone saline aquifers in the Paraná basin, Brazil. Three models were developed from various sections of the Rio Bonito Formation, each characterized by different depths and distinct reservoir properties. In the optimization process, geological uncertainties were addressed by using representative samples obtained from a set of unconditional realizations. In addition, robust optimization aimed to find an optimal solution across uncertainties for WAG and brine production. Preliminary findings suggest that brine production enhances reservoir injectivity, while WAG injection alters trapping mechanisms, increasing dissolved and residual trapping by around 15%. Moreover, WAG injection decreases the vertical migration of the CO₂ plume and reduces the reliance of the process on structural trapping. Robust optimization significantly increases cumulative CO₂ trapping by adjusting the water and gas injection periods and water production and injection rates. Sensitivity analysis indicates that increasing the gas injection period boosts cumulative trapping but lowers the trapping ratio, whereas increasing the water injection period has the opposite effect. Based on the cost analysis, shallow depths offer the lowest levelized cost and reinjection cost, making them the most economically viable option for CO₂ storage. To the authors' knowledge, this research marks a novel contribution to dynamic simulations of CCS projects, focusing specifically on the Rio Bonito Formation, Brazil. It offers a thorough examination of trapping processes, capacity estimation, management approaches, uncertainty assessments economic analysis and geochemical modelling, creating a valuable foundation for future studies.