ملخص
Abstract
The Nubian Sandstone Formation is a significant hydrocarbon reservoir in the Concession 59D, Eastern Sirt Basin, Libya. This formation is underlain uncomfortably by granitic basement and/or by the Hercynian unconformity and overlain uncomfortably by Pre-Upper Cretaceous followed by an Early Upper Cretaceous Transition beds. The Nubian formation is a thick sequence comprises mainly of sandstone, siltstone and shale.The Nubian Formation in this area has been subdivided into three stratigraphic members; namely Lower Sandstone, Middle Shale and Upper Sandstone (main reservoir well be focus of this study).The Upper Sandstone is the upper most subdivision of the Nubian Sandstone sequence consists mainly of white, grey to brown sandstones, ranging from fine to medium, locally coarse grained, moderately cemented with straight to concavo convex or slightly sutured grain contacts. This reservoir is a complex of fluvial sands deposited in Braided and Meandering streams.The reservoir fluids are very rich retrograde condensate gas and waxy oil with pressure at slightly above the saturation pressure. Most of this hydrocarbon in this reservoir has been sourced from the Nubian Middle Shale Member, but the Upper Cretaceous shale and Evaporates belonging to the Transition beds sequence have a significant potential source. The trapping mechanism in the field is a combined structural and stratigraphic trap for the Nubian Sandstone with the southern closure against the tight Nubian facies and basement of the Gialo High. Reservoir properties across the North Gialo Study Area vary in terms of porosity, permeability fluid saturation. These variations are indicated through the porosity, permeability and saturation maps and charts based on well log analysis and lab core sample measurements. These properties are discussed in the reservoir characterization part of this thesis.