Geologic Framework of Italian Petroleum Resources

Sedimentary sequences in Italy were deposited mostly on the African continental margin and in the contiguous ocean generated by Jurassic spreading. Triassic to Lower Cretaceous carbonates reflect the extensional tectonics that preceded and accompanied oceanic opening. Younger clastics formed in response to location and elevation of the source areas and to the tectonically controlled bathymetry of the basins. The major structural units of Italy are (1) island of Sardinia, a fragment of the European continental margin that escaped Alpine compressive tectonics; (2) Tyrrhenian Sea, a Miocene-Pliocene extensional area with oceanic crust; (3) southern Alps fold-thrust belt; (4) Apennine fold-thrust belt, with regional nappes; (5) foredeep; and (6) foreland. Gas reserves in Italy are primarily in Pliocene sand reservoirs of the external (outer) Apennines and the foredeep. The gas is biogenic, and the source is immature organic matter in coeval shales. The major part of the oil and part of the gas are thermogenic, derived mainly from black shales deposited in Middle Triassic, Upper Triassic, and lower Liassic basins. Petroleum generation began during the Mesozoic in the deepest parts of these basins, and heavy oil migrated into the adjacent Mesozoic carbonate reservoirs. Condensate and wet gas originated in the areas of major Cenozoic subsidence and migrated into Tertiary clastic reservoirs where tectonism was more intense. A minor part of the oil in Tertiary sand reservoirs may have been sourced by organic matter in shales of Miocene flysch. In 1984, gas and oil production in Italy supplied about 10% of the national energy demand. Although petroleum exploration has been heavy since 1950, plays with good potential still exist. They commonly depend on definition of rather deep structures, both onshore and offshore.