Hydrocarbon prospectivity to the north-west of the assumood field, Sirt Basin, Libya

Abstract

The area of study covers parts of the Assumood Ridge and the Wadayat Trough in the Sirt Basin, onshore Libya. The area is surrounded on three sides by gas fields producing from the Lower Oligocene Arida Formation, the Middle Eocene Gialo Formation and the Bahi /Gargaf Formation. The DDDl-6 well was drilled in the study area in 1965 and tested gas at low rates from carbonates of the Upper Palaeocene Harash Formation. Re-evaluation of data from this well in 1996 confirmed the presence of untested gas intervals in the Upper Cretaceous Kalash Formation and in the Gialo Formation. The re-evaluation encouraged Sirte Oil Company to acquire more seismic data in 1998 and to interpret all available seismic data in the area. The study area is about 380 km(^2) and contains 1196 km of 2-D seismic data comprising 48 seismic lines. The data consist of eight vintages of seismic data from 1971 to 1998. Borehole data from 10 wells were utilised. Three time structure maps were generated in this study for the tops of the following carbonate formations: the Kalash Formation, the Upper Palaeocene-Lower Eocene Kheir Formation and the Gialo Formation. The Kheir Formation was mapped because direct mapping of the Harash carbonate is not possible as its contact with the overlying Harash/Kheir limestone beds is usually not seismically resolvable. Two structural closures were identified as prospective locations for the Kalash Formation, the first located south of the DDDl-6 well and the second located southwest of the ZZl-6 well. One structural closure for the Gialo Formation was identified, approximately at the same location as the first closure at the Top Kalash horizon. No prospective locations were identified for the Kheir Formation. The new prospective location located south of DDDl-6 well is particularly recommended for exploration drilling since the same well could test structural closures in both the Kalash and Gialo formations.