From Thrust-and-Fold Belt to Foreland Basins: Hydrocarbon Exploration in Italy

Cazzola, Anna L.¹; Fantoni, Roberto ¹; Franciosi, Roberto ¹; Gatti, Valter ¹; Ghielmi, Manlio ¹; Pugliese, Alfredo ¹
(1)Eni E&P, San Donato Milanese, Italy.

The Italian peninsula and its surrounding marine areas underwent a very complex geological evolution due to the superimposition of several tectono-stratigraphic cycles, which, starting from the end of the Paleozoic, modelled the region in several different shapes. The South-Alpine and Apennine thrust/fold belts and their foredeep basins are the results of this evolution.

A remarkable tectono-sedimentary variability, at regional and local scales, gives evidence of the complexity of the geological processes involved. In this framework several petroleum systems have developed, some of which are of paramount economic importance.

These petroleum systems can be associated with three main tectono-stratigraphic systems: biogenic gas in the terrigenous Plio-Quaternary foredeep wedges, thermogenic gas in the thrusted terrigenous Tertiary foredeep wedges and oil and thermogenic gas in the carbonate Mesozoic succession.

Biogenic gas has been discovered in the Plio-Quaternary foredeep basins of the Apennines (from north to south: Po Plain, Adriatic sea, Bradanic Plain and Sicily channel). Traps are commonly structural. In the inner basin margins they consist of thrusted anticlines, in the foreland they are related to draping on the relative highs of the carbonate substratum. Stratigraphic traps are also present, represented by sand terminations along the basin flanks. Nowadays exploration for biogenic gas is mature and is limited to the search for small accumulations near the existing fields.

Thermogenic gas can be found in the Paleogene foredeep basins of the Southern Alps and of the Apennines, in sediments tectonically involved in the accretionary prisms of the two chains. The exploration of this play is made difficult by the structural complexity of the geologic framework. Traps are usually small and the quality of the reservoirs is sometimes poor.

Oil and thermogenic gas have been discovered in the Mesozoic carbonate units in the Po Plain foreland (Villafortuna field), in the Southern Apennines (Monte Alpi giant field) and in Sicily foreland (Gela field). They are related to three different petroleum systems, associated to the main phases of the Tethyan crustal stretching (Middle Triassic, Late Triassic/Early Jurassic and Early Cretaceous)

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.