From thrust-and-fold belt to foreland: hydrocarbon occurrences in Italy

Italy is the most hydrocarbon endowed country of southern Europe, with total discovered reserves (produced + remaining) of 1840 million barrels of oil and 30 trillion ft(3) of gas. The production of oil amounts to 43.2 million barrels per year, about 75% of which comes from the Val d'Agri Field in the southern Apennines. The production of gas is 340 billion ft(3) per year, most of it coming from the northern Adriatic Sea. Hydrocarbon occurrences derive from a variety of petroleum systems which are the result of a complex geological history. At least five important source rocks have been recognized which are distributed in age from Mesozoic through Pleistocene. Three of them were deposited during Mesozoic crustal extension and are mainly oil-prone. Hydrocarbon occurrences associated with these sources are usually found in complex carbonate structures along the Apennines thrust-and-fold belt and in the foreland. Villafortuna-Trecate (Po Plain), Val d'Agri/Tempa Rossa (southern Apennines) and Gela (Sicily) fields represent the largest oil accumulations pertaining to these systems. Two other important sources rocks were deposited in the foredeep terrigenous units of the foreland basins which formed during the Cenozoic orogenesis. The older source is thermogenic gas-prone and is found in the highly tectonized Oligo-Miocene foredeep wedges: gas occurrences associated with this source are mainly concentrated along the northern Apennines margin (e. g. Cortemaggiore Field), in Calabria (e. g. Luna Field) and Sicily (e. g. Gagliano Field). The younger source is biogenic gas-prone and is situated in the outer Plio-Pleistocene foredeeps. The most important gas fields of Italy, located in the eastern Po Plain and northern Adriatic sea (Barbara and other gas fields), have originated from this source. Hydrocarbon exploration in Italy is overall mature, especially for gas, whose residual potential is estimated to be 6.0 trillion ft(3) of reserves. The remaining potential of oil is estimated to be 800 million barrels.