PICHA, FRANK J., Chevron Overseas Petroleum Inc., San Ramon, CA

ABSTRACT: Exploration for Hydrocarbons Under Thrust Belts: A Challenging New Frontier in the Carpathians

The Carpathian thrust belt has been explored with mixed results. Large reserves of oil and gas have been found in Romania and the western Ukraine, while exploration in other areas has been disappointing. Deep drilling and seismic profiling, as well as better understanding of structure, however, has contributed to the opening of promising new plays beneath the allochthonous belt.

The thin-skinned Carpathian thrust belt is characterized by a long-range tectonic transport over the Neogene foredeep and the underlying European platform. The complex structure of the platform involves Caledonian and Variscan compressional deformation, Mesozoic extension, related to the development of the northern Tethyan margins, and Cenozoic normal faulting and wrenching associated with the Alpine orogeny. Elements of the platform were also detached and incorporated into the thrust belt proper. In addition to numerous structural plays, significant morphologic features, such as large Paleogene and Neogene buried valleys, have been found within the platform margins. Both the valley fill and the associated subsea fans and channels represent promising plays.

Generation of hydrocarbons from various source rocks within the platform was greatly enhanced by emplacement of the wedge-shaped Carpathian thrust belt. The low heat flow, typical for the subthrust setting, enabled generation and preservation of hydrocarbons at great depths. Although several oil and gas fields have been found in shallower parts of the platform, the deeper structures (below 5 km) remain mostly unexplored.

The complexity and diversity of subthrust geology offers a big challenge to exploration, but also provides an opportunity for finding significant oil and gas accumulations not only in the Carpathians, but elsewhere under thin-skinned thrust belts.

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