Influence of in-situ bitumen on the generation of gas and oil in New Zealand coals.pdf

Organic Geochemistry 39 (2008) 1606–1619
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Organic Geochemistry
journal homepage: geochem
Influence of in-situ bitumen on the generation of gas and oil in
New Zealand coals
Vu Thi Anh Tiem a,*, Brian Horsfield a, Richard Sykes b
a GeoForschungsZentrum Potsdam, Section , Telegrafenberg, B221, D-14473 Potsdam, Germany
b Institute of Geological & Nuclear Sciences, PO Box 30368, Lower Hutt 5040, New Zealand
article info abstract
Article history: New Zealand coals of peat to high volatile bituminous rank have been studied in order to
Received 3 April 2008 assess the effect of in-situ bitumen (soluble in a methanol:acetone:chloroform azeotrope),
Received in revised form 1 July 2008 on petroleum potential during progressive maturation. Both non-extracted and extracted
Accepted 8 July 2008
coals, as well as the extracted bitumen itself, were analyzed using Rock-Eval and pyrolysis
Available online 22 July 2008
gas chromatography. The difference in yields between non-extracted and extracted coals,
attributable to the influence of bitumen, pared with direct measurements made
on the bitumen itself. positional changes in pyrolysis products were seen when
the bitumen was finely dispersed throughout the kerogen matrix. Notably, second-order
reactions between kerogen and bitumen during pyrolysis reduce primary gas yield and
enhance both oil yield and potential secondary gas yield. The stabilization of free radicals,
and prevention of bination/repolymerization processes have been attributed to the
presence of the dispersed in-situ bitumen. These results demonstrate that petroleum for-
mation in coals likely proceeds via intermolecular interactions and not simply first order
cracking. mon procedure of employing solvent extraction prior to pyrolysis is
clearly not appropriate when assessing the petroleum potential of coal.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction 1988; Powell, 1988; Hunt