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Vega, the largest single oil field in the Mediterranean Sea, is located between the southeastern coast of Sicily and the Island of Malta. The field lies entirely in Italian waters. Its discovery in October 1980 was based on interpretation of a very poor-quality seismic survey which, nevertheless, roughly outlined a relatively small structure. A limestone and dolomite fractured reservoir of the Inici, or Siracusa Formation, of Late Jurassic age, may contain in excess of 1 billion bbl of heavy crude (15.5 API) within a productive area of approximately 10,000 acres (4,000 ha.). Reservoir properties are excellent, with permeabilities in darcys. The field extends northwest-southeast for 8.5 mi (14 km) and averages 1.7 mi (3 km) in width, according to the 3D seismic survey (2,0 0 km) shot soon after the discovery well was drilled. The gross oil column reaches approximately 820 ft (250 m). The southeasternmost part of the Vega structure is not yet completely defined, and an additional 3D seismic survey is in progress. Should the new seismic results confirm expectations, the Vega structure could extend over 10 mi (17 km).
The deepest formation reached by wells in the Ragusa basin is the Taormina Formation (dolomite of Middle to Late Triassic age) to which the Ragusa, Gela, Ponte Dirillo, and Piano Lupo oil fields are linked. The overlying Streppenosa Formation (Late Triassic to Early Jurassic age) is represented by bituminous shale with limestone development at the bottom (basal Streppenosa or Noto Member), which produces in the Mila and Irminio fields.
The overlying Inici reservoir consists of dolomite and underlain by limestone in the southwestern part of the basin, and entirely of limestone in the northwestern portion of the basin. The Inici Formation represents the platform facies of the open-sea Villagonia and Giardini sediments. The Cammarata-Pozzillo (discovered in 1959), Perla (1979), Vega (1980), and Prezioso (1983) heavy crude oil fields are related to this formation.
The Vega structure lies across the edge of the Inici carbonate platform. The northeastern flank appears to be controlled mainly by the facies variation between the Inici and Villagonia Formations. The southwestern flank seems, rather, to be controlled by dip.
The potential for discovery of other fields similar to Vega in the Ragusa basin is excellent.
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