What If the OWC Was Misplaced? Investigating the Mystery of OWC in the Intrasalt Carbonate Reservoir from South Oman Salt Basin

Stringer reservoirs in the south of Sultanate of Oman are isolated carbonate bodies encased within thick Ara salt formations. These unique geological settings present a range of pressure regimes from hydrostatic to lithostatic which pose considerable challenges in reservoir characterization and development. One of the most critical technical uncertainties in these reservoirs is the accurate determination of the oil-water contact (OWC), which directly impacts reserves estimation and development planning. In this study, the OWC was primarily interpreted using resistivity log responses across multiple wells. A notable anomaly was observed: one well indicated a shallower OWC compared to the oil-down-to (ODT) depth recorded in a nearby offset well. To investigate this inconsistency, a multi-scenario modelling approach was adopted. The study integrated geological, petrophysical, and fluid property data, utilizing structural interpretation and reservoir modelling tools to examine various scenarios, including potential compartmentalization and fluid distribution heterogeneity. Perched oil-water contacts (OWCs) are a common phenomenon in faulted fold structures, particularly those characterized by asymmetrical limbs with varying lengths and dips. During hydrocarbon migration, water is displaced on both sides of the fault. However, when a fault is present on the shorter limb of the fold, it can act as a barrier, trapping water on that side. Meanwhile, hydrocarbons continue to migrate and displace water on the opposite fold limb, resulting in the development of two distinct OWC levels. This study presents a novel interpretation of perched water in intrasalt stringer reservoirs and emphasizes the critical role of compartmentalization in influencing fluid distribution. Recognizing and correctly identifying perched water can significantly improve the accuracy of reserve estimates and inform more effective development strategies. By demonstrating the value of integrated, multidisciplinary analysis, this work contributes to reduce subsurface uncertainty and enhancing reservoir management in complex carbonate- salt systems.