Carbonate Reservoir Characterization: Examples from the Upper Cretaceous to Eocene Strata of the Ionian Zone (Albania)

Nadège Vilasi¹, Rudy Swennen², and Francois Roure^3
1Institut Français du Pétrole, Rueil-Malmaison, France
²Katholieke Universiteit Leuven, N/A, Belgium
³Institut Français du Pétrole, France

Petroleum companies focus more often today on reservoirs in fold-and-thrust belts. In these complex areas, reservoir analogues are studied to decrease exploration risks, because they provide a direct access to 3D heterogeneities and fracturing features. The Ionian zone in Albania and Northern Greece consists of a thrust front zone, characterized by a complex geological evolution. Its main tectonic feature is a west-verging thrust with the Triassic evaporites as the main décollement level. In southern Albania, the Upper Cretaceous to Eocene deep marine carbonates represent the most important hydrocarbon bearing reservoir. Our objective is to better understand the fluid flow history and the deformation in several outcrop analogues adjacent to productive reservoirs. Petrographical observations as well as geochemical analyzes have been performed on veins and rock matrix to link the paragenetic history with the fluid flow evolution and the burial history of the studied areas. In a second step, basin modelling techniques (i.e. Thrustpack, Ceres tools) have been used to reconstruct the fluid, pressure and temperature evolution in the reservoirs. Results show that reservoir properties mainly relate to the existence of fractures or stylolites. During the pre-folding stages, complex textures such as crack-and-seal features most likely reflect the expulsion of overpressured fluids, especially in the eastern part of the Ionian zone. Moreover, several meteoric fluids episodes account for the occurrence of an earlier forebulge in the external Albanides. These paleofluids are enriched in strontium (up to 8000ppm), accounting for an interaction with the Triassic evaporites (e.g. diapirs). In contrast, the post-deformational stage is characterized by the migration of several exotic fluids, which help to remobilize the sulphates. Late fluids include hydrothermal fluids and finally meteoric fluids, which induced successive dolomitization and dedolomitization episodes, as well as a karstic network during the final emersion episode.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece