Geology, Hydrocarbon Potential Reservoirs and Age dating of the Ordovician Sequence Stages Ghadames and Murzuq Sedimentary Basins West Libya

الملخص

The Ordovician strata are mainly clastic, with palynological stage units identified in the Ghadames and Murzuq basins (F. Belhaj, 1996). Correlations are complicated by barren sections, inconsistent electric log markers, lateral lithological variations, facies changes, limited well control, and shallow penetration depths. Major unconformities correspond to the Sardinian and Taconian orogenic events, part of the broader Caledonian orogeny. The base of the Ordovician section is poorly defined in large areas of these regions, but Ordovician units are widespread. The sediments are categorized by a well-defined upper boundary unconformity, with the basal unconformity only partially known from a few wells and outcrops. Internal contact relationships among rock units are unclear, and while biostratigraphic analyses have identified several stages, their full extent is uncertain due to low palynomorph occurrence. Ordovician sandstones have excellent reservoir properties and significant hydrocarbon accumulations, with Tanezzuft Shales acting as the primary hydrocarbon system.

The clastic fill of the Ghadames and Murzuq Basins is complex due to varied depositional environments and their origins as erosional remnants of a thicker Paleozoic continental margin along Gondwana. Both basins have undergone significant erosion and sediment reworking, influenced by multiple tectonic events. Key formations along the Murzuq Basin's flanks include Tihemboka, Tibesti, Gargaf, and Atshan Sadale. They contain a substantial Paleozoic sedimentary succession of marine and transitional sediments overlying a Proterozoic to Precambrian basement, along with Mesozoic deposits. The Paleozoic sedimentation rate was low, with maximum infill exceeding 12,000 feet. The sedimentary records reveal multiple structural developments, with some faults showing north-south variations. The Paleozoic infill consists of six stages, representing five lithostratigraphic formations from the Cambro-Ordovician period: Hasawnah, Achabiyat, Hawaz, Melaz Suqran, Mamuniat, and Bir Tlacsin, with some rock units absent in both basins