Print this pageGeochemical 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.