VUCHEV, VASSIL, Bulgarian Academy of Sciences, Sofia, Bulgaria

ABSTRACT: Geological Prerequisites for Petroleum Potential of the Couple Moesian Platform and Fore-Balkan (Central Balkan Peninsula), Bulgaria

The Moesian platform and the Fore-Balkan are among the best developed structural elements in the Alpine morphostructure of the Balkans. Many authors considered them as foreland and fold belt, joined by an asymmetric, narrow foredeep.

Almost all Mesozoic sedimentary units are similarly developed on the platform and in the Fore-Balkan, where they are involved in predominantly small brachystructures and linear, often isoclinal and larger folds, respectively. Late Jurassic and Early Cretaceous sediments were deposited on the platform in carbonate facies and in the Fore-Balkan as a thick turbidite sequence. The peri-platform concept for the transitional foredeep is currently under review, and new approaches to the evaluation of its hydrocarbon potential are being developed.

Several small oil and gas fields have been found in the Fore-Balkan and the foredeep. Major discoveries have been made on the Moesian platform, where more than 20 small and medium fields are known. These pools are structurally or stratigraphically trapped in Middle to Upper Triassic carbonates and Early to Upper Jurassic clastics. Traps are related to the relief of the lower Kimmerian unconformity, straddling the Triassic-Jurassic boundary. Additional accumulations are contained in Upper Jurassic-Lower Cretaceous carbonates.

All sedimentary sequences contain disseminated organic matter and have reached maturity for the generation of hydrocarbons; however, no specific source rocks have been identified. Reservoirs are characterized by generally low intergranular and fracture porosity and permeability.

During the past decades, the concept of a thrusted Fore-Balkan, overriding the foredeep, was gradually developed on the basis of well results. With the acceptance of this concept, the oil exploration strategy had to be changed. Combined structural and stratigraphic/sedimentological studies are required to resolve the evolution of the Fore-Balkan and its foredeep and to assess their hydrocarbon potential.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.