Abstract: Organic Petrography and Geochemistry of Oil Shales

Adrian Hutton

Organic matter in oil shales is derived from terrestrial plants, lacustrine algae, marine algae, acritarchs and dinoflagellates. As such, it is best described using maceral terminology, originally devised for coal, with modification to include a revision of the algal-derived organic matter. Many apparently anomalous properties of oil shales can be explained if the maceral composition is known.

Liptinite macerals are the dominant precursors of shale oil and, therefore, the type and abundance of liptinite and environment of deposition can be used to divide oil shales into three primary groups: terrestrial oil shales, lacustrine oil shales and marine oil shales. If a further subdivision is made, six oil shales can be recognized: cannel coal, torbanite, lamosite, marinite, tasmanite and kukersite. Oil shales within each group generally have similar properties.

Geochemical properties of the parent oil shale and the derived shale oil are determined by the type and abundance of liptinite macerals. Organic matter derived from algae, and the derived oils, have high hydrogen to carbon ratios, whereas those derived from terrestrial precursors have lower ratios. Alginite-dominated oil shale such as torbanite and lamosite tends to produce aliphatic oils containing homologous alkene/alkane pairs, whereas oil shale containing abundant vitrinite and liptinite derived from terrestrial sources, such as cannel coal, produce more aromatic oils.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994