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The AAPG/Datapages Combined Publications Database
AAPG Special Volumes
Abstract
R. Swennen, F. Roure, and J. W. Granath, eds., Deformation, fluid flow, and reservoir appraisal in foreland fold and thrust belts: AAPG Hedberg Series, no. 1, p.
DOI:10.1306/1025702H1854
Tectonic Setting of the Petroleum Systems of Sicily
James W. Granath,1 Piero Casero2
1Granath and Associates, Houston, Texas, U.S.A.
2Consultant, Rome, Italy
ACKNOWLEDGMENTS
J. W. Granath thanks Forest Oil International for providing the opportunity to become familiar with the geology of Sicily, Luigi Albanesi for his mentorship in Italian petroleum exploration, and A. W. Bally for his thoughtful review of an early form of the manuscript. Both of us thank the conveners of the conference Deformation, Fluid Flow, and Reservoir Appraisal in Foreland Fold and Thrust Belts held in Palermo in May 2002 for requesting this contribution to the proceedings volume.
ABSTRACT
Petroleum systems in Sicily are divided between the Neogene fold and thrust belt of the Sicilian accretionary prism and its foreland. By far, more production has been established in the foreland on the Ragusa platform, where generally heavy oil from Triassic and Jurassic source
rocks
has been trapped in similarly aged fractured carbonate mound
reservoirs
. Traps are structures recurrently rejuvenated since the Cretaceous. Although models of
source
maturation and migration history emphasize PlioceneāPleistocene charge related to subsidence in the foreland, occurrences of light oil and exploration data suggest intermittent periods of charge since the
Mesozoic
. Hydrocarbon deposits in the immediate vicinity of the thrust front, in the narrow foredeep depression, are also heavy and have characteristics in common with those more remote in the foreland from the front; they do not appear to have been significantly influenced by or mixed with oils from within the fold belt, although variations in their chemistry have yet to be investigated in terms of
source
correlation. Thrust sheets in the fold and thrust belt carry similar
Mesozoic
stratigraphy to the foreland, namely, a series of carbonate platforms and
basins
with potentially similar
source
rocks
, and can reasonably be expected to have undergone a similar pre-Neogene history.
Commercial hydrocarbons in the fold belt, however, are limited to thermo- and biogenic gas-charged Tertiary reservoirs
and questionably Tertiary-sourced oil offshore to the west. These all currently are viable exploration plays. Numerous seeps and tar deposits indicate that at least one petroleum system was active in the fold belt, but only one tar occurrence links that system to the
Mesozoic
carbonate section. Recent structural studies have indicated that a two-phase history of thrust emplacement and its redeformation by duplexing on lower detachments characterizes much of the Sicilian fold and thrust belt and affords exploration targets that have yet to be satisfactorily tested. Furthermore, structural petrological and fluid-inclusion studies in Neogene-thrusted
rocks
of the lower portions of the frontal fold belt indicate that a light hydrocarbon system used Neogene detachment surfaces as a preferential migration route in at least part of the accretionary prism.
Insofar as the foreland may give an insight into the early history of the fold belt platforms and basins
, a general sense of the hydrocarbon migration history in the fold belt might include the following: (1) early maturation and migration of a variety of oils into carbonate mound
reservoirs
during a long period of time in the latter half of the
Mesozoic
and Paleogene (like in the foreland plays), bolstered by (2) a charge of immature oil generated during rapid depression in the foredeep immediately adjacent to the moving thrust front (yet to be demonstrated), and (3) generation of higher maturity oil and gas in the thrust wedge during stacking of thrust sheets and remigration and mixing with the earlier generated fluids (an untested play).
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