ABSTRACT: Some Critical Aspects of Foreland Exploration

Frank J. Picha

Forelands, positioned in front of and partly below the thin-skinned thrust belts, comprise over 80% of known oil reserves worldwide. Their productivity is affected by numerous factors. Two of them, formation and migration of foredeeps and the impact of preexisting structural highs, are discussed using examples from the Adriatic foreland.

The Miocene synorogenic flysch foredeeps and Pliocene postorogenic molasse foredeeps of the Adriatic are not continuous; rather, they consist of chains of depocenters whose geometry resulted from a combination of applied orogenic stresses and preexisting crustal strength. The rapid subsidence and deposition in depocenters enhanced generation of hydrocarbons from potential sources. As the front of deformation and the foredeeps moved toward the foreland, so did the hydrocarbon generation wave. In the process, most of the hydrocarbons formed during the early synorogenic phase were destroyed unless they had migrated far into foreland. On the other hand, the hydrocarbons generated during the late postorogenic phase tend to be preserved both in the frontal structures of orogenic belts and i the foreland.

The preexisting stable blocks (structural highs) within the foreland, such as the Apulian Platform, acted as buttresses with only limited development of foredeeps. Those blocks are only slightly deformed and/or partly overridden by thin-skinned thrust sheets. Hydrocarbons were generated late due to tectonic rather than depositional loading.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990