Reservoir Potential of Cretaceous-Paleocene Carbonate Turbidite Successions Adjacent to the Maiella Platform Margin, Italy

In the search for new carbonate plays, carbonate mass gravity flow deposits received new attention. The aim of this project is to assess the reservoir potential of Cretaceous-Tertiary carbonate turbidite successions along the slope and in the basin adjacent to the Maiella platform, Italy. Our analysis includes the sedimentological and petrophysical characterization of the re-deposited carbonates and the surrounding background sediment. Outcrops in the Abruzzi and an offshore core yielding coeval slope and basinal facies provide information for the assessment. The analysis shows that the Cretaceous redeposited carbonates are potentially better reservoirs than the Tertiary ones.

The Cretaceous-Paleocene slope and basin sections contain five re-deposited carbonate facies intercalated in the periplatform background sediment (Scaglia facies). These facies include (mega)breccias, slumps, carbonate turbidites, thin calcisiltite layers and beds with bi-directional cross-bedding. Each facies has different sedimentological properties such as composition, grain size, sedimentary structures and diagenetic fabrics. These properties are related to the type of gravity flow and turbidity current density.

The porosities and permeabilities of both the re-deposited carbonates and the background sediment vary in the Cretaceous and Tertiary sections. In the Cretaceous re-deposited beds porosity is about 15% and permeability can reach 500 mD. The porosity in the background sediment is 7.5 - 27% and permeability ranges from 0 - 522 mD. However, at a given porosity, the permeability of the re-deposited beds is generally higher than in the background sediment. The Tertiary sections have less porosity and permeability. Paleocene megabreccias in the subsurface core display up to 12% porosity while the Paleocene turbidites in outcrop range in porosity from 0 - 13%; permeability reaches a maximum of 100 mD. The background sediment of the Tertiary turbidite successions, however, is tight with permeability around 1 mD.

The better reservoir quality of the Cretaceous is related to the original mineralogy and the resultant diagenetic potential. During the Cretaceous, calcite was the predominant carbonate mineral, while in the Tertiary most carbonate production was aragonite. Metastable aragonite has a high diagenetic potential and is subject to dissolution and re-precipiation. This process produced more cement and tighter rocks.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California