Paleozoic Sequence Stratigraphy and Hydrocarbon Accumulation Mode of the Ahnet Basin, North Africa

The purpose of the thesis is to establish, analyze the sequence stratigraphic evolution of the Paleozoic and hydrocarbon accumulation of Ahnet basin. The regional sequence stratigraphic framework of the Ahnet Basin has been established based on seismic stratigraphic geometries, regional well log correlation, previously studied outcrop information, reservoir core description. Episodes of regional structural movements and eustatic sea-level fluctuations are the underlying controls for the widespread transgressive-regressive cycles, numerous unconformities observed in the Paleozoic strata and hydrocarbon accumulation. The Cambrian to Carboniferous successions in the Ahnet Basin can be divided into five major tectonostratigraphic cycles and twelve second-order super-sequences related to regional tectonics and global sea level fluctuation, namely the Lower-Middle Cambrian( one second-order super-sequences: Lower-Middle Cambrian), Middle Cambrian to Middle Ordovician (Taconic orogeny)( three second-order super-sequences: Upper Cambrian, Lower Ordovician and Middle Ordovician), Middle to late Ordovician( one second-order super-sequences: Upper Ordovician), Silurian to Gedinnian( three second-order super-sequences: Silurian-1, Silurian-2 and Gedinnian), Siegenian to Namurian(four second-order super-sequences: Siegenian-Emsian-Couvinian, Givetian-Frasnian-Famennian, Strunian-Visean and Namurian). The best source rocks were deposited during early-middle Silurian regional transgressions. The major marine shale intervals in the Silurian also provide the best regional top seal for the Ordovician reservoir rocks. The major hydrocarbon accumulations are discovered in the sandstone reservoirs of Ordovician. The combined mode of “old accumulation with new sources, new accumulation with old sources” is the major accumulation mode for the Cambrian-Ordovician sandstone reservoirs. The secondary accumulation mode is the “old source with new accumulation” for the Lower Devonian reservoirs.