Robust optimization of CO₂ sequestration through a water alternating gas process under geological uncertainties in Cuu Long Basin, Vietnam

This study presents a robust optimization workflow to determine the optimal water alternating gas (WAG) process for CO₂ sequestration in a heterogeneous fluvial sandstone reservoir. As depicted in this study, WAG injection could enhance CO₂ residual and solubility trapping based on an integrated modeling workflow. First, continuous CO₂ injection and WAG were compared to demonstrate the efficiency of the WAG process for CO₂ trapping enhancement. To achieve this while highlighting the impact of reservoir heterogeneity, 200 geological realizations were generated considering a wide range of plausible geological conditions. The ranking of these realizations was performed by quantifying the CO₂ cumulative injection (P10, P50, and P90 realizations) that represent the overall geological uncertainties. Then, an innovative robust workflow was used Artificial Intelligence optimizer to determine the optimal solution for CO₂ trapping. For comparison, a nominal optimization workflow of P50 realization was also conducted. The proposed robust optimization workflow resulted in higher CO₂ trapping than the nominal optimization workflow. Thus, this study demonstrates a fast and reliable workflow that can accurately represent for optimization the cycle length injection in the WAG process under geological uncertainties.