Basin Evolution and Hydrocarbon Plays in Albania

With Roland Barbullushi, Prize Reserves Management Ltd
6.30pm tonight, The Geological Society of London 

The geological structures in Albania form part of a foreland fold and thrust belt system that includes Mesozoic-Eocene carbonate sequences of the Ionian Basin. The sequences are incorporated into three major Tertiary thrust sheets verging towards Apulia foreland in the southwest and overlain by foreland basin deposits, part of which forms the Durresi Basin. The oil and gas fields are all concentrated onshore in western Albania in these two basins. This presentation discusses some important features that control tectonic history as a prerequisite for assessing the petroleum systems as well as the type and location of accumulations and plays.

A new geodynamic model based on structural and kinematic observations and presented here predicts that anticlockwise rotation of the Apulia foreland along with its uplifted promontory in the southwest of Albania provided a buffer stop for the incoming ‘train’ of the Ionian basin thrusts during the Oligocene to Pliocene. A regional shear couple was formed between the hinterland and the buffer stop which was accommodated by strain partitioning along the strike. The Ionian basin thrusts were uplifted and exhumed in the south as they buttressed towards the promontory, while propagating freely in the north towards the foreland and overlain by Durresi foredeep basin during the Miocene–Pliocene.

Such a geologic framework formed the natural setting for the formation of two petroleum systems, one in each basin. In the Ionian Basin, all source rocks have good to excellent potential for liquid hydrocarbon generation and are of types II and I. The highest maturation occurs in the Triassic and Jurassic source rocks of the Ionian Basin buried beneath the southern part of the Durresi Basin in central Albania. The beginning of oil generation from the source rocks is related to this Miocene and Pliocene burial. Oil accumulated in two types of reservoirs. The first type of accumulation relates to deep–water carbonates of Late Cretaceous – Eocene age. The reservoirs are fractured with predominantly vuggy porosity. The second type of accumulation relates to molasse deposits of the foreland basin. The oil is located in stratigraphic traps formed during the late Miocene. In the Durresi Basin, the source rocks consist of Tortonian turbidity sequences and Pliocene shales. A large volume of gas was generated by bacterial action. The reservoir is provided by the same Tortonian-Pliocene turbidity sequences and shales.

There are three main types of traps and possible complementary plays, all located onshore Albania: (i) a carbonate oil and gas play that comprises Upper Cretaceous – Eocene deep-water carbonate reservoirs of the Ionian Basin in fault-controlled anticlines sealed by Oligocene flysch and charged from the Mesozoic source rocks; (ii) a clastic oil play that comprises Tortonian-Messinian reservoirs of the Durresi Basin in Tortonian-Messinian sand pinch-outs and sand lenses sealed by intraformational Tortonian-Messinian shales charged by Mesozoic deep-water carbonate rocks of the Ionian Basin, and; (iii) a clastic gas play that comprises Tortonian-Messinian reservoirs in the Durresi Basin in Tortonian-Messinian sand pinch-outs and sand lenses sealed by intraformational Tortonian-Messinian shales charged by the terrigenous source rocks of the foreland basin.

The hitherto investigation of the petroleum systems in Albania suggests that future complementary oil and gas plays may still occur within the Ionian Basin. Some gas plays may still be found in the Durresi Basin. For both these plays, the HC charge is known, and the key risk lies mainly in the trap configuration and to a lesser degree on the timing of generation, migration, and accumulation.