Sedimentology and 3D architecture of a bioclastic calcarenite complex on Favignana, southern Italy

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.