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Abstract

The island of Favignana provides an exceptional three-dimensional insight in the architecture of a Lower
Pleistocene bioclastic calcarenite complex. Due to the degree of quarrying, a large amount of outcrops is
available in the eastern part of the island. Two campaigns resulted in the logging of stratigraphic sections,
recording of sedimentary structures and palaeo-transport orientations, analysis of the fossil content and
the collection of samples in order to test the reservoir potential of the calcarenite — associated with
foramol skeletal grain types.

A correlation between palaeo-transport directions and the stratigraphic logs distributed over the whole
fieldwork area led to a conceptual geological model. Sediments were generated in the shallow temperate
water of the Mediterranean, and are subsequently transported and/or reworked by storm events. Deposition
on top of the middle to Upper Pliocene Trubi clay most likely took place in a topographic low between the
already existing mountainous structures of Favignana and the nearby Levanzo island. A system of large
scours characterised the depositional processes — which are described by three phases — significantly.
Propagation of the calcarenite complex was dominated by a southeastern direction, making the Favignana
calcarenite complex a rare example in the Mediterranean, as comparable deposits in the area propagate
on a shelf towards the open sea instead of towards a major land mass.

The use of a multi-point statistics algorithm, which is a suitable option when a large dataset and a good
conceptual model are available, led to the generation of a facies model. Based on the analysis performed
on the calcarenite samples, the reservoir potential is high, with porosity values of up to 0.65 bulk rock
fraction and a permeability of tens of darcy. Because the fieldwork area has never been buried to depth,
little diagenesis — such as cementation, compaction and fracturing — has taken place.

The Favignana calcarenite is believed to be a relevant and important analogue for a several carbonate
hydrocarbon fields in various regions of the world such as South America and Middle East. The detailed
understanding of sedimentary facies distribution, internal architecture and reservoir property variability
can therefore assist to guide and/or optimize the development of those reservoirs. In particular, the
Favignana calcarenite is thought to be a relevant analogue for the Perla gas field in Venezuela, a giant
reservoir consisting of foramol carbonates, and the reservoirs formed by the Asmari limestone in the
Zagros basin.

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