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Abstract

(Begin page 233)

AAPG Bulletin, V. 86, No. 2 (February 2002), P. 233-256.

Copyright ©2002. The American Association of Petroleum Geologists. All rights reserved.

Source rock evaluation of Middle Jurassic coals, northeast Greenland, by artificial maturation: aspects of petroleum generation from coal

Henrik I. Petersen,1 Jorgen A. Bojesen-Koefoed,2 Hans P. Nytoft3

1Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark; email: [email protected]
2Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark
3Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark

AUTHORS

H. I. Petersen holds an M.Sc. degree in geology and a Ph.D. in organic petrology and geochemistry from the University of Aarhus, Denmark. He is a senior research geologist at the Geological Survey of Denmark and Greenland (GEUS) and works primarily with the depositional environments, source rock potential, and hydrocarbon generative characteristics of coals and terrestrial organic-rich rocks from the North Sea, Greenland, and Vietnam. He has also worked with suppression of vitrinite reflectance in relation to the determination of the thermal maturity of organic matter.

J. A. Bojesen-Koefoed is a senior research scientist at GEUS, where he has been employed since 1988. He works primarily with the application of organic geochemistry and petrography within petroleum exploration, and he has worked in the North Sea, Greenland, the Baltic countries, and various other areas. He holds an M.Sc. degree in geology from the University of Copenhagen, Denmark and a Ph.D. in geology and organic geochemistry from the Technical University of Denmark.

H. P. Nytoft received his M.Sc. degree in organic chemistry from the Technical University of Denmark in 1982. He worked in the chemical industry for nine years before joining GEUS in 1991, where he currently is a senior advisor. He works mainly with synthesis and gas chromatography-mass spectrometry analysis of biomarkers.

ACKNOWLEDGMENTS

This study received financial support from the Danish Energy Research Programme (EFP-98), grant no. 1313/98-0022. T. C. R. Pulvertaft (GEUS) improved the English, and J. Halskov (GEUS) prepared the figures. AAPG Bulletin reviewers J. B. Curtis and B. Horsfield are thanked for their constructive comments. This article is published with the permission of the Geological Survey of Denmark and Greenland (GEUS).

ABSTRACT

Paralic liptinite-enriched coals and carbonaceous mudstones in northeast Greenland constitute potential highly oil-prone source rocks, whereas the humic coals may be marginal source rocks. The liptinite-rich coals are dominated by resinite or fluorescing amorphous organic matter and alginite, resulting in hydrogen index (HI) values generally above 300 and reaching up to 728. During artificial maturation up to 330 degreesC/72 hr, the coals follow the maturation paths of kerogen types I and II on an HI vs. Tmax diagram, and calculations show that upon passage through the oil window, roughly 85% of their generation potential is realized. Activation energy (Ea) distributions with prominent principal Ea values centered around 60-62 kcal/mole and frequency factors from 5.855 x 1015 s-1 to 3.249 x 1016 s-1 strongly influence the generation characteristics from 300 to 330 degreesC/72 hr artificial maturation. Important changes include marked loss of liptinite fluorescence and increase in resinite reflectance; small change in Tmax; significant decrease in HI; pronounced increase in extract yields; increased generation of saturates; and generation of labile bitumen with low Ea values. These observations indicate significant bitumen/petroleum formation from the coals during a relatively narrow temperature range, which, together with the petrographic composition, may facilitate expulsion of a waxy crude oil. The coals demonstrate that under certain depositional conditions, highly prolific coal source rocks can form with the capacity not only to generate but also to expel liquid petroleum.

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