Evaluating large-scale saline aquifers: Unlocking CO₂ storage in the Santos Basin through consistent multiscale analysis
M.J. Kreutz Erdtmann (Petróleo Brasileiro S.A. (Petrobras), TU Delft - Reservoir Engineering)
F. Silva Lira (TU Delft - Applied Geology, Petróleo Brasileiro S.A. (Petrobras))
S. Geiger (TU Delft - Geoscience and Engineering)
H. Hajibeygi (TU Delft - Reservoir Engineering)
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Abstract
Regional-scale saline aquifers are promising candidates for geological CO2 storage but present significant modeling challenges due to their vast extent, heterogeneity, and limited subsurface data. This study introduces a multiscale modeling framework that was applied to assess CO2 storage in the Ponta Aguda saline aquifer (Santos Basin, Brazil, 40,000 km2 area). Consistency of the multiscale models is checked by combining boundaries conditions for pressure match and verification of trapping mechanisms representativity. Four different methods were evaluated regarding the trapping mechanisms accuracy in coarse models: Local Grid Refinement, Effective Values, and Algebraic Dynamic Multilevel. Compositional simulations conducted with CMG-GEM and DARSim2 demonstrate that coarse-scale models systematically overestimate CO2 trapping due to numerical artifacts, particularly in solubility and hysteresis behavior. These artifacts arise from mismatched CO2/brine volumes in large cells, leading to artificially enhanced trapping efficiency. Among the evaluated methods, Algebraic Dynamic Multilevel delivers the most reliable predictions, providing a general solution that aligns closely with fine-scale reference simulations while remaining computationally feasible. The results show the importance of scale-consistent modeling approaches for accurate CO2 storage assessment and highlight the risks of relying on overly simplified coarse models in the design and optimization of carbon storage projects in large saline aquifers.