GEOCHEMICAL EVALUTION OF THE TANEZZUFT FORMATION IN THE JIFARAH TROUGH, NW LIBYA

Abstract

The study area (Jifarah Trough) is bound to the north by a coastal fault system. To the south the Jifarah Trough is bound by the east-west trending Al Aziziyah Fault System and to the southwest by the Telmzane Arch; the Nafusah Uplift defines its eastern limit. The region lies at the intersection of two major structures the NNW trending Tripoli-Tibisti Arch formed in Caledonian times and the E-W trending Jifarah Uplift formed during the Hercynian Orogeny. The best expected hydrocarbon source rock in the area is the lower hot shale member of the Tanezzuft Formation. Several reservoirs can be targeted as hydrocarbon traps such as the Ordovician quartzitic sandstone in Tunisia and the sandstone of the Silurian Acacus Formation in Libya. The objectives of this study are to assess the source rock potential, measure the thermal maturity of the source rock (Silurian Tanezzuft Formation), and to recognize the sources of organic matter and probable depositional conditions for this formation.A Rock-Eval 6 was used for bulk geochemical screening analysis. The analytical error of the system was assessed using an IFP standard sample. Seventeen samples were analysed by GC and GC/MS. The results gained during this study show that the TOC wt.%, S1 and S2 are high in the lower part of the formation and low in the upper part. Furthermore, all maturity parameters based on Rock-Eval, and biomarker maturity parameters give indicators to vertical variation of thermal maturity from late immature to early mature, although the aromatic hydrocarbons show higher ratios in the lower part than in the upper part of the Tanezzuft Formation. The Tanezzuft Formation is characterized by marine algae organic input with a bacterial contribution and that, dysoxic-anoxic conditions may be the most probable for the depositional environment of the lower Tanezzuft Formation with slightly more oxic conditions associated with some samples of the upper Tanezzuft Formation