Compositional modeling with formation damage to investigate the effects of CO₂–CH₄ water alternating gas (WAG) on performance of coupled enhanced oil recovery and geological carbon storage

This study develops an integrative simulation model of a water alternating gas (WAG) process that co-injects carbon dioxide (CO₂) and methane (CH₄)–CO₂–CH₄ WAG—for formation damage caused by asphaltene deposition in an oil reservoir. The influences of CH₄ addition into the injection gas stream are analyzed in terms of enhanced oil recovery (EOR) and carbon capture and storage (CCS). Asphaltene precipitation and deposition mechanisms are examined by fluid modeling and compositional simulation, respectively. Fluid modeling is performed using Burke Oil 1 experimental data. Compositional simulation is conducted for a 13-year CO₂–CH₄ WAG case. Compared with 100% CO₂ WAG, addition of CH₄ decreases oil displacement efficiency due to reduced miscibility while mitigating asphaltene deposition. This relief of formation damage compensates for oil recovery. The CCS performance of CO₂–CH₄ WAG is investigated by residual and solubility trapping processes. The overall carbon storage effect of CO₂–CH₄ WAG is quantified using global warming potential. These results highlight the significance of CO₂–CH₄ co-injection to improve the performance of CCS-EOR and of integrative modeling with asphaltene for an accurate performance evaluation of CO₂–CH₄ WAG.