Stratigraphic Trap in the Permian Unayzah Formation, Central Saudi Arabia

Abstract

The recent discovery in Central Saudi Arabia of Arabian Super Light oil in 'Usaylah-1 confirms stratigraphic trap potential of the Permian Unayzah Formation. The trap is an updip pinch-out of an upper Unayzah sandstone along the eastern flank of the north-south trending Hawtah anticline. The seal is the basal shales and siltstones of the Khuff and Unayzah formations and the source rock is the Lower Silurian Qusaiba Shale. The well encountered an oil column of 31 feet in an upper Unayzah eolian dune facies. The areal distribution of the prospect was mapped with a 3-D seismic survey. Seismic horizon slices and relative amplitude maps at the target reflection clearly delineate the trap. The oil-productive Unayzah sandstone is imaged as a high-amplitude reflection in an isolated area of approximately 8 square kilometers. Seismic isochron maps are proving effective in focusing future exploration to areas of similar stratigraphic trap potential in the region.