Petroleum systems of Oman: Charge timing and risks

Abstract

After 35 years of exploration, creaming of the conventional plays in Oman is nearly complete, and consequently, the search has commenced for new, less obvious plays. Many of the new opportunities occur beyond the known hydrocarbon provinces and are considered to have significant charge risks. To define these risks, extensive basin modeling studies have been conducted in recent years. Modeling and empirical data show that Mesozoic and Cenozoic kitchen areas are restricted to western north Oman, the only areas currently buried at their maximum temperature. Large parts of north and central Oman depend on lateral migration from these kitchens for their charge. Progressive uplift of the east flank and basin inversion since the middle Paleozoic provides favorable conditions for long-distance migration in the post-Carboniferous interval. In central Oman, geochemical tracer molecules (benzocarbazoles) suggest that a north-south-trending, reactivated basement grain has funneled charge up to 300 km southeastward. Charge risks increase in the deeper sequence, in which eastward migrating hydrocarbons have to traverse the Ghaba salt basin, a pronounced syncline at depths greater than 3 km. The south Oman salt basin is currently cool because of shallow depths and hydrodynamic fluid-flow activity. The shallow post-Cambrian reservoirs rely on storage of early (Cambrian-Ordovician) charge by the Ara salt (Cambrian) sequence, followed by release of hydrocarbons as the salt edge retreats through time. Basin modeling has outlined the extent of the different petroleum systems and provided us with risk maps to guide our next exploration phase. It has revitalized some of the mature plays, for instance the Gharif Formation, where oil exploration is now focused along Late Cretaceous and Tertiary migration paths. Deeper sections are envisaged to have significant scope for gas.