The hydrocarbon source potential of the Paleozoic rocks of Ghadamis Basin Northwestern Libya

Abstract

Ghadamis Basin is an intracratonic sag basin and is considered as an important hydrocarbon province in the North African continent. In Libya, the Ghadamis Basin is located in the western part of the country and filled by Palaeozoic sediments and overlying thin Mesozoic-Tertiary sequences. The Palaeozoic rocks range from Cambrian to Carboniferous with a maximum thickness of about 12, 000 feet. They consist of alternating transgressive and regressive marine sandstones, shales, siltstones and, locally limestones. The present study, based on the ditch cuttings shale samples, investigate the bulk organic geochemistry, kerogen microscopy and thermal maturity. The geochemical results demonstrated the presence of various organic-rich zones within the Palaeozoic sequences. The Mamuniyat, the lower ‘hot’ Tanezzuft and the Awaynat Wanin formations are considered to have a good to excellent potential source and are particularly prospective hydrocarbon generation in the study area. The Tanezzuft formation is divided into an upper ‘cool’ shale and lower ‘hot’ shale based on the basis of high gamma-ray response in wireline logs and high organic carbon content (TOC). Generally, the Palaeozoic sequence has TOC values ranging from 0.5 to 21.4 wt%. Maturity data indicate that the Devonian shale samples are immature to marginally mature and that the Silurian and the Ordovician shale samples are mostly middle to late mature. Visual Kerogen examination showed that organic matter is comprised mainly of amorphous and palynomorphs components (Type II Kerogen) oil prone with some phytoclasts materials (Type III), gas prone.