Well Stimulation vs. Damage: Operational Implications for WAG and CO2 Storage Projects

Abstract Near-wellbore conditions play a central role in controlling the performance of CO2-WAG injection in carbonate reservoirs such as those found in the Brazilian Pre-Salt. Skin factor, which represents the degree of damage or stimulation around the well, directly influences injectivity and can alter the hydraulic and geochemical evolution of the system. This study assesses how variations in skin affect long-term WAG behavior using a heterogeneous reservoir model with properties representative of Pre-Salt formations. A compositional and geochemical framework was implemented to capture fluid–rock interactions induced by CO2-rich injection cycles over a thirty-one-year period. The results show that negative skin improves water injectivity by reducing bottom-hole pressures and increasing the cumulative water volume injected, thereby promoting a more efficient displacement front. Positive skin produces the opposite effect and increases the pressure required for injection. Although stimulation enhances operational performance, its effect on ultimate oil recovery and CO2 storage is moderate. However, in very large reservoirs such as those in the Pre-Salt province, even modest percentage differences in recovery can translate into substantial financial impact due to the enormous production volumes involved. Gas saturation distributions remain similar across skin cases, indicating that large-scale reservoir dynamics dominate CO2 mobility. Geochemical responses, however, are sensitive to skin: stimulated wells exhibit stronger early carbonate dissolution and greater long-term calcite precipitation, while damaged wells show more buffered chemical behavior. Overall, the findings indicate that injector stimulation provides operational advantages and moderate changes on WAG efficiency in Pre-Salt settings. The study also highlights that accurate representation of skin is essential for reliable forecasting, since small deviations in assumed values can lead to significant differences in injectivity, pressure evolution, and mineral reactions. Incorporating realistic skin conditions into WAG design improves predictive robustness and supports better operational decision-making in CO2-driven recovery and storage projects.