Integrated petroleum systems and play fairway analysis in a complex Palaeozoic basin: Ghadames-Illizi Basin, North Africa

Abstract

The Ghadames-Illizi Basin system is a highly productive petroleum province with a long exploration history in Algeria, Libya and Tunisia (from the late 1950s to present day). Ongoing exploration success in all three countries suggests that it will continue to provide attractive exploration targets in the future. The basin has a long (Cambrian to Plio-Pleistocene) and complex geological evolution characterized by multiple phases of subsidence punctuated by significant regional uplift events. Two 'world-class' petroleum source rocks of different geological age are present (Lower Silurian and Upper Devonian) with similar depositional environments and geochemical characters. Both source horizons have generated significant volumes of oil and gas. Migration is strongly influenced by the stratigraphic architecture of the basin fill, notably distribution of regional seals and the complex patterns of subcrop and onlap across regional unconformities. Multiple reservoir-seal combinations are presented by Late Ordovician glaciogenic sediments and younger Silurian through to Carboniferous paralic sequences. Integrating the stratigraphic relationships with the complex burial history of the basin (timing of uplift, degree of tilting, amount of section removed by erosion) is not a trivial task, but is key to exploration success in such a complex basin. With the aid of 3D basin reconstruction and fluid flow modelling software, we can attempt to capture the stratigraphic and structural complexity and make exploration predictions. If basin modelling techniques are to be optimally applied in such settings, a fully integrated and geologically realistic approach involving sedimentologists, structural geologists, geophysicists and geochemists is required. A modelling approach, workflow and some results are presented.

From Neoproterozoic to Early Cenozoic: exploring the potential of older and deeper hydrocarbon plays across North Africa and the Middle East

“…The Taoudenni Basin was uplifted and eroded at this time and the resulting unconformity completely removes the Silurian succession in some areas of the basin (Dixon et al 2010). The thermal evolution of any potential Early Silurian Tannezuft Formation source rocks in the Taoudenni Basin is influenced strongly by burial prior to the Hercynian orogeny (Fig.…”

“…Its distribution is more restricted than that of the deeper Silurian 'hot' shales, due in part to the fact that it was deposited in an active foredeep (Dixon et al 2010) so it is best developed in the basin centre and thin to absent on the regional arches and local inversion structures, and partly due to the later effects of erosion at the Hercynian Unconformity. It is a key source interval in the Berkine and Illizi basins and also has an important role in the Palaeozoic petroleum system in the Ahnet and Reggane basins.…”

“…Dixon et al 2010). Present day, the Silurian source rock is overmature and the Frasnian source rock is in the gas window in the central part of the Ghadames Basin .…”

Glaciogenic reservoirs and hydrocarbon systems: an introduction

“…The Silurian shales also form the regional top-seal to the Ordovician glaciogenic play. The Late Ordovician glaciogenic sandstones are charged by upward migration from down-faulted Silurian Tannezuft shales, in some cases by downward migration from the Early Silurian source and, possibly, also by the underlying speculated Ordovician Hiswa source (Dixon et al 2010). Giant oil and gas fields with Activities associated with exploration, appraisal, development of and production from Ordovician glaciogenic reservoirs continue across the region.…”

“…Important changes in the geometry of the North African basins began in the Late Devonian and Early Carboniferous as a result of 'Hercynian' compression and regional uplift (Dixon et al 2010). In southeastern Algeria and southwestern Libya, the Illizi Basin and southern Ghadames Basin were uplifted by 1-2 km and the northwardtilted, Palaeozoic 'basin fill' was deeply eroded.…”