المجلة الدولية للعلوم والتقنية

The Nubian Sandstone Formation (Pre-Upper Cretaceous) in the Sirte Basin, Libya is considered an important reservoir for hydrocarbons. It is subdivided into three stratigraphic members, the Lower Nubian Sandstone, the Middle Shale and the Upper Nubian Sandstone. Generally, the oil wells which have been drilled by Waha Oil Company in A-Pool, NC98 Block, Eastern Sirt Basin, Libya are producing from the Upper Nubian Sandstone reservoir. The main trapping systems in APool-NC98 Block are structural and stratigraphic combination traps, comprising of at least two major NW-SE trending tectonic blocks, with each block being further broken up with several more Pre-Upper-Cretaceous faults. Four wells have been selected to conduct the formation evaluation of the Upper Nubian Sandstone reservoir which lies at a depth of between 14,000 and 15,500 feet. This study is an integration approach using the petrophysical analysis and integrating the sedimentology and petrography from core. The geological and petrophysical evaluation were done using the Techlog software. The clay minerals identification was carried out using the Potassium (K) versus Thorium (Th) concentration cross-plot technique. The main clay minerals identified were; Kaolinite and Chlorite, in agreement with the Petrographical analysis on samples from well A4-NC98. The Petrophysical analysis clearly shows that the Upper Nubian Sandstone is a good reservoir in wells A3, A4 and A5, whereas low reservoir quality in well A6.