Geochemical Effects of Primary Migration of Petroleum and Their Relevance with Respect to Mechanisms and Efficiencies of Expulsion

D. Leythaeuser, B. Horsfield, R. Littke, M. Radke, R. G. Schaefer

Geochemical analysis of the petroleum residing in the pore system of source rocks after primary migration has occurred holds the key to better understanding the mechanisms and efficiencies of expulsion processes. Indeed, the detailed recognition of migration phenomena and quantification of their effects have been made by a combined approach which (1) examines the composition variation of residual oil within individual bodies of source rocks and its relationship to, inter alia, petroleum in juxtaposed reservoir rocks and (2) makes a material balance of petroleum-related chemical species.

This approach has been applied in three separate case studies, two of which address the economically most important source rock units of central and northwest Europe: the Lower Jurassic Toarcian shales from the Hils syncline area (Federal Republic of Germany) and the Upper Jurassic Kimmeridge Clay Formation from the Brae field area, North Sea (U.K. Sector). The third study is of a series of coals and interbedded sediments of Late Carboniferous age from the Ruhr area (Federal Republic of Germany).

A synthesis of results has revealed some fundamental differences in migration mechanisms and efficiencies which are strongly linked to organic richness, kerogen quality, and source rock fabrics. These differences concern especially the degree of microfracturing and the role of gas as transport agents.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.