Journal of Petroleum Geology, Vol.12, No.4, pp. 465-476, 1989

©Copyright 2000 Scientific Press, Ltd.

ALUM SHALE BITUMEN MATURATION AND MIGRATION: IMPLICATIONS FOR GOTLAND'S OIL

J. Dahl*, R. T. Chen* and I. R. Kaplan*

* Department of Earth and Space Science and Institute of Geophysics and Planetary Physics, University of California at Los Angeles, Los Angeles, California 90024-1567, USA.

Abstract

Thermal maturation of Swedish Alum Shale kerogen and bitumen has been determined from core samples from Eastern and Central Sweden. In samples from Eastern Sweden (Öland and Gotland), the kerogen and bitumen are thermally immature with respect to petroleum generation. In some areas of Central Sweden (Närke, Östergötland, and Kinnekulle in Västergötland), the kerogen is immature, whereas the bitumen is marginally mature to mature. In other areas of Central Sweden (Halleberg-Hunneberg in Västergötland), the kerogen is super-mature and the bitumen mature. This suggests that bitumen from a mature source-rock has migrated into the Alum Shales of Central Sweden. Migration in Central Sweden is further evidenced by the occurrence of obviously-migrated bitumens in vugs and voids in the organic-poor Ordovician limestone overlying the Alum Shale in Central Sweden, and in concretions within the Alum Shale itself.