Libya lies in the centre of the North African Margin and
has endured a polyphase tectono-stratigraphic history that
has been controlled by adjacent plate tectonic processes
since the Pan African Orogeny. The Palaeozoic Ghadames, Murzuq
and Kufra basins lie in central and southern Libya, while
the late Mesozoic to Cenozoic Sirte-Pelagian system and the
Cyrenaica Platform occupy the northern, coastal fringe.
Hydrocarbon Prospectivity
The Sirte Basin, Libya is regarded as a world-class Petroleum
Province, with the offshore Pelagian Platform that straddles
the Libya-Tunisia border forming an important component of
the regions prospectivity. These Mesozoic-Cenozoic systems
are sourced by Upper Cretaceous to Oligocene shales that
feed fractured basement and U. Cretaceous to Oligocene clastic
and carbonate reservoirs in tilted fault block, drapes, horst
and Palaeocene reef traps. However, there are also Palaeozoic
plays and recent discoveries have refocused attention from
the Ghadames to the Murzuq Basins. These are sourced from
the Silurian Tanezzuft and Acacus Fms that fill reservoirs
from Cambrian to Permo-Triassic in age in faulted anticlines,
fault blocks and stratigraphic traps on the basin margins.
The Kufra basin in SE Libya is presently thought to be a
high-risk venture, as is the Palaeozoic to Cenozoic aged
Cyrenaica Platform. Structure interpreted from the satellite
images has isolated structural prospects such as roll-over,
drape and transpressional-related folding and related them
to source, reservoir and seal within a plate tectono-stratigraphic
framework.
The Sirte Basin is a late Mesozoic to Cenozoic extensional
basin that was initiated in the late Jurassic. Many existing
discoveries are linked to tilted fault blocks and associated
folding on the eastern flank of the rift, carbonate shoals
and reefs that relate to low amplitude drapes developed above
deeper footwall blocks in the centre and western rift shoulders.
The faults that control the separate horst and graben and
the subtle drape folds above deeper targets are visible on
the imagery allowing the location of any stratigraphic
trap to be predicted.
The Cyrenaica Platform is part of the Western Desert domain
that occupies NW Egypt. Jebel Al Akhdar lies NW of the platform
and represents an inverted sub-basin in which Cretaceous
to Palaeocene muds accumulated prior to Syrian Arc-aged tectonism.
The extensional fault block style of the platform and the
inverted elements of the NE-SW trending Jebel are clearly
visible but the prospectivity of this region is in doubt
as the timing of inversion may have destroyed traps leading
to remigration and hydrocarbon loss.
The Murzuq basin was initiated during the Palaeozoic and
is separated from the Illizi basin, which lies mostly within
Algeria, by the N-S trending Themboka Arch. Several discoveries
during the Nineties have led to re-evaluation of the region.
The style of the underlying Pan African structure controls
the basin extent and reactivated lower Palaeozoic structural
trends. Hercynian tectonic events overprinted these forming
a second fundamental control on basin form. The fault patterns
seen at the present day surface show the effects of several
tectonic episodes during the Cretaceous, which were significant
trap creators in this region.
The Ghadames or Hamra Basin is contiguous with the basin
of the same name in Algeria and Tunisia. The basin content
is dominated by the Palaeozoic succession with a reported
thickness up to 3500 meters. The northern half of the basin
has the classic salt seal of the Triassic Province, further
west. The Ghadames is an intercratonic basin developed over
the site of major Pan-African Orogenic mobile belt. The basins
are buried under a northward thickening late Palaeozoic and
Mesozoic sedimentary section that deepens further over the
Djeffara-Nafusa Arch. Many faults suffered periodic reactivation
in the Triassic-Jurassic, Middle Cretaceous and Tertiary.
Fault activity continues and Neogene scarps are visible on
satellite imagery of the Hamada al Hamra'.
The basin is relatively under explored despite the number
of wells which have encountered only small accumulations
compared to farther west (150+ oil discoveries) suggesting
that current play models are inadequate. There are three
areas or fields currently in production: Hamra', Emgayet
and the "Z" field connected to Zawia on the coast
by a pipeline. There are another two or three fields capable
of production if pipelines were built. Reservoirs include
Devonian, Silurian, Cambro-Ordovician and Triassic sandstones.
There is no significant surface sand and the Palaeogene carbonate
surface present over much of the area presents few problems
(acoustic coupling may be a problem).
The Kufra basin is an intracratonic basin originally developed
within the Paleozoic margin of northern Africa. It has the
form of a shallow syncline orientated NE-SW. A little seismic
has defined the basin, and two wells have been drilled by
Agip, but no trace of hydrocarbons found. The Kufra is a
high-risk frontier area with lack of source rock or structural
trapping and uncertain maturation.
