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Source Rock Potential and Maturity Modeling in the Southern Adriatic Sea Area: Key Controls for Predicting Hydrocarbon Distribution

Carlo Caldarelli and D. Smith

One of the most significant offshore hydrocarbon provinces in Italy is located in the Southern Adriatic. Important discoveries in this area (Zone F) include the Rovesti discovery and Aquila field. Proven source rock in the area is the Late Triassic (Rhaetian, Norian) Burano Formation: a paralic carbonate source rock developed in a sabkha type environment. Due to the lack of deep Triassic penetrations in the area, organic rich facies have not been encountered in any well. However geochemical analyses indicate all the oils in the Southern Adriatic Sea area and Pre-Apulian zone (NW Greece) correlate with the Burano Formation in Central Italy.

The development of a new hydrocarbon maturity model indicates this source rock is probably fully mature within the Italian sector of the Southern Adriatic in both platform and basin areas. Long distance hydrocarbon migration from the Albanian Periadriatic Depression, as previously invoked by several authors, appears inadequate to describe the hydrocarbon distribution in this area. Paleogeographical reconstructions indicate progressive deepening of the Late Triassic (Rhaetian, Norian) facies towards Albania, implying unfavourable conditions for the deposition of organic matter associated with this type of source rock.

Maturity modelling indicates significant differences between the timing of hydrocarbon generation within the basin and in the Apulian platform domain. Large volumes of hydrocarbons within the platform are likely to have been expelled prior to the deposition of seals (Late Tertiary), thus explaining the unsuccessful exploration activities in the offshore Apulian platform domain. Furthermore Cretaceous marly intervals within the Apulian platform may have acted as a vertical barrier to fluid migration and are probably associated with shaly levels of limited source rock potential. Waxy oil traces interpreted to be a late charge have been encountered in one well drilled on the shelf edge, indicating a terrestrial input, which is also suggested by the oleanane biomarker (derived from angiosperms), constraining the age of this source rock to the Cretaceous or Tertiary.

Hydrocarbon generation and migration within the basin likely occurred from the Middle-Late Miocene to Post-Pliocene, subsequent to the formation of hydrocarbon traps in most cases. Migration is thought to have occurred mainly through faults with sealing intervals being the Maiolica Fm. (Early Cretaceous) and Late Tertiary marly sequences. Gas potential is associated with calcarenitic levels within the Tertiary marly sequence as proven by biogenic gas discoveries in the area and geochemical analyses of Tertiary sequences.

The integration of source rock potential, basin modelling, and the development of a new geological model for platform to basin transition is playing a key role in the evaluation of the remaining prospectivity in the Southern Adriatic.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013