The objective of this study is to evaluate CO2 storage potential of a small gas field located in Northern Oman using advanced reservoir simulation techniques. The field is to be used for CO2 storage in the future when this reservoir is depleted. The study includes the estimation of structural, residual, solubility and mineral trapping mechanisms, as well as determination of safe operating pressure limits for CO2 injection.

The study utilizes various reservoir simulation methods to investigate each trapping mechanism, taking into account the hydrodynamic, physical, and chemical conditions within the reservoir. Specifically, solubility trapping is analyzed using Henry's law, while residual trapping is modeled using the critical gas saturation via Corey correlations. To analyze risks of faults reactivation and leakage into overlying formations, the geomechanical analysis was applied in the study. At the end of the study, a sensitivity analysis is performed to assess the influence of uncertain parameters for each technical approach.

The results of the case study provided both quantitative and qualitative evaluations of each trapping mechanism for the gas field. Potential deformation and fracturing of the caprock trap were predicted to ensure it remains intact to prevent CO2 leakage. Additionally, the study demonstrated the practical application of various reservoir simulation techniques for modelling CO2 storage, adding further value to the study. In spite of the fact, that the gas field has been well studied during exploration and production periods, including previous reservoir simulations, a sufficient level of uncertainty still exists in reservoir description, fluid and rock properties and even was increased with adding CO2 storage approaches. This study took into account these uncertain parameters, and probabilities were calculated for the estimations of trapping mechanisms.

This case study presents a complete modelling cycle for CO2 storage within a depleted gas reservoir, employing a range of diverse reservoir simulation techniques. It serves as a valuable guide for those interested in modelling CO2 storage through the application of various reservoir simulation methods.

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