Abstract: Alpine Structure and Petroleum Geology of Bulgaria

GEORGIEV, GEORGE and CHRISTO DABOVSKI,

Parts of two major tectonic units may be traced in Bulgaria: the Balkan segment of the Alpine thrust belt and the Moesian platform. Both units evolved in the geodynamic setting of the Eurasian continental margin. The thrust belt is a system of stacked north verging thrust sheets that contain fragments of local, proximal and exotic paleogeodynamic units accreted to Eurasia during the closure of the Tethys. The thrust structure is a result of mainly Mid-Cretaceous and Mid-Eocene compressional events. Late Tertiary extensional basins cover large areas in the internal part of the belt.

The Moesian platform comprises a 4-13 km thick sequence of subhorizontal Paleozoic, Mesozoic and Neozoic sediments overlying a pre-Paleozoic metamorphic basement. Major unconformities have been drilled at the base of the Triassic, Lower Jurassic, Upper Cretaceous and Paleocene.

The known oil and gas fields in Bulgaria are located mainly in the southern periphery of the Moesian platform and the frontal part of the Alpine thrust belt. Hydrocarbons are related mainly to Middle Triassic carbonates (41.9% of the known recoverable reserves), Lower Jurassic sandstones (25%) and Valanginian carbonates (17.5%), less Commonly to Paleocene (8.6%) and Upper Triassic (6.9%) sediments. Stratigraphic trap reserves linked to unconformities dominate (73.3%) over anticlinal reserves (26.7%).

Future discovery expectations are directed mainly towards the Triassic-Jurassic sequences in the area of the platform margin and the autochthonous and allochthonous units of the thrust belt front. Devonian and Lower Carboniferous platform sediments are another prospective target.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria