Petrology and Diagenetical Processes in the Hawaz
Formation, a Middle Ordovician Clastic Reservoir of
the Murzuq
Barsó, Dolors1, David
Gómez-Gras2,
Mariano Marzo1, Emilio Ramos1, Khairi
Tawenki3, Nestor Bolatti4 (1) University of Barcelona,
Barcelona, Spain (2) Universitat Autònoma
de Barcelona, Bellaterra, Spain (3) REMSA, Trípoli, Libya (4) Repsol YPF,
Spain
The Hawaz Formation is a Llanvirnian-Llandeilian aged oil bearing detritic unit which constitutes a part of the Paleozoic
sedimentary infill in the Murzuq and Kufrah basins, in Central and
The Hawaz Formation sandstones are
fine to medium grained, well sorted and subrounded
with low matrix contents. Compositionally, these sandstones are mainly quartzarenites made up of quartz grains and minor amounts
of K-feldspar, plagioclase, mica and metamorphic rock fragments. Primary
porosity is mostly intergranular and ranges from 0 to
22.5 % having the highest values towards the lower part of the Formation.
Secondary porosity is uncommon. Diagenetic processes
promote the reduction of initial intergranular
porosity via precipitation of authigenic minerals and
chemical and mechanical compaction.
The diagenetic sequence starts with
the precipitation of early quartz and minor Kfeldspar
overgrowths prior to the development of mechanical and chemical compaction.
Ferruginous coatings precipitated subsequently to this compaction, followed by
the neoformation of clay minerals (illite-smectite and kaolinite).
Finally, dolomite cement filled the residual porosity. However, the main
reduction of the primary porosity was produced by chemical and mechanical
compaction. The highest compaction values have been measured in the middle and
upper parts of the Formation.