Journal of Petroleum Geology, Vol.14, No.4, pp. 429-444, 1991

©Copyright 2000 Scientific Press, Ltd.

VERTICAL HYDROCARBON MIGRATION: A MAJOR EXPLORATION PARAMETER

J.-C. Pratsch*

* 13711 Butterf1y Lane, Houston, Texas 77079, USA.

Abstract

Most oil- and gasfields result from the migration of hydrocarbons from the generating source bed to the reservoir and trap. Exceptions are producing source-bed formations (coal-bed gas, e.g. the Permian Spraberry Trend, West Texas). Where vertical hydrocarbon migration is active, oil/gas accumulations can be found in reservoirs of geological ages which are considerably different from those of the generating source beds. In such cases (e.g. the North Sea gas province, Louisiana offshore, Niger Delta, Vienna Basin), early recognition of vertical migration may well bring about the most effective exploration results. In many basins, vertical migration is less evident than lateral migration, leading to distinct, vertically-stacked hydrocarbon systems isolated from each other (e.g. the Po Valley, Powder River and Sirte Basins). Vertical migration from one source-bed level, or the mixing of hydrocarbons from different hydrocarbon systems, occurs where major faults or vertically-rising materials (salt, igneous rocks) create critical vertical pathways. In such cases, vertical migration can be an important factor in the location and existence of hydrocarbon accumulations.