The Kruja Platform in Albania: Characteristics and Prospectivity

Abstract

The Kruja carbonate platform outcrops in Albania and is considered to be the southward prolongation of the Adriatic carbonate platform (Italy, Slovenia, Croatia, Bosnia and Montenegro), connecting apparently to the Gavrovo platform (Greece). The outcropping shallow water carbonate succession ranges from Late Lower Cretaceous to Eocene, covered by flysch and molasses deposits. The pre-Late Lower Cretaceous succession is largely unknown, due to the absence of deep boreholes in the region. The outcropping succession is characterized by regular peritidal cycles, sometimes dolomitized, with scattered rudist floatstones. In the Dalit mountain, however, we identified some intraplatform basinal facies characterized by the presence of extensive slumpings and debris flow deposits, associated with metric-scale domal stromatolites. The outcropping Kruja carbonates forms a quite continuous ridge crossing Albania from northeast to southwest. In the Tirana area these outcrops are representing the uppermost structural units of a well-developed duplex, characterized at least by five/six stacked units. In order to develop such kind of geometry, we need to assume the presence of a detachment higher than the usual Upper Triassic evaporites, possibly invoking the presence of Upper Jurassic/Lower Jurassic evaporites. Such evaporites were found further north, in the Adriatic platform in Croatia and are called “Ravni Kotari Evaporites”: in Croatia they exceed 3.5 km of thickness and act as a major detachment horizon in the area south of Zadar. The estimated shortening in the Kruja platform exceeds 60%, with the original estimated width of the platform corresponding to more than 20/25 km. Several wells were drilled in this carbonate platform, but never with economic oil discoveries: usually they reached only the very first meters of the carbonates, often remaining in the Eocene portion. In the Kruja carbonates there were several oil shows, documented both on surface and subsurface and are quite problematic in terms of interpretation: the migration pathway from the Ionian basin source rocks is extremely difficult, as they are located at the footwall of the duplex. Some scattered geochemical data ( carbon isotopes) also indicate that there are some oils potentially of Cretaceous age rather than Early Jurassic, indicating the presence of another potential source rock in the region. The carbon isotope data are similar to the values of the oil seepages of Central Dalmatia (e.g. Vrgorac), indicating that potentially we could have a similar situation in terms of petroleum systems, opening new perspectives in the area. The migration pathway in this case is easier than invoking the Ionian basinal source rock, but adds more uncertainty in terms of charging capability of the reservoirs, as the source rock volumes are uncertain. We analyzed the wells in the region and we think they failed because they reached only the Eocene units and the bauxites separating the Eocene carbonates from the Cretaceous one could act as an internal seal. In addition to the, there is the possibility of a local erosion of the cap rock (Flysch) at the time of hydrocarbon migration, not allowing the development of an hydrocarbon accumulation: however, in the lower units of the duplex we expect to have the flysch still in place with more chance of finding hydrocarbons.

AAPG Datapages/Search and Discovery Article #90341 ©2019 AAPG Geoscience Technology Workshop, Exploration and Development of Siliciclastic and Carbonate Reservoirs in the Eastern Mediterranean, Tel Aviv, Israel, February 26-27, 2019