New Zealand Journal of Geology and Geophysics abstracts
The Rank(Sr) scale: its basis and its applicability as a maturity index for
all coals
R. P. SUGGATE
Institute of Geological & Nuclear Sciences
P.O. Box 30368
Lower Hutt, New Zealand
Abstract A comprehensive revision of the basis of the 1959
Rank(S) scale of Suggate uses the van Krevelen diagram (axes of atomic O/C and
H/C), and a complementary diagram with axes of calorific value and volatile
matter, to demonstrate the progress of rank increase in coals of differing coal
types. Both type and rank (maturity) are significant in hydrocarbon generation.
The Late Cretaceous and Cenozoic New Zealand coals, which have an almost
complete rank range from peat to semi-anthracite, are used to exemplify medium
to high hydrogen coals, and Paleozoic coals from the Northern Hemisphere and
Australia provide data for lower hydrogen coals. A line of progressive
coalification of "average-type" coal, which typifies that of Type III kerogen,
is identified. Systematic analytical variation in isorank coals allows the
determination of the pattern of isorank lines on the diagrams. These lines are
then spaced to provide a scale of equal increments of rank increase, which is
accepted as being dependent on temperature at the time of maximum burial. The
1959 supposition that geothermal gradients did not vary widely between
subsiding basins is abandoned, and in its place it is now assumed that the
geothermal gradient in each basin was uniform with depth. The spacing of
isorank lines to provide the Rank(Sr) scale, which ranges from 0 in peat to
>20 in anthracite, follows study of individual sequences in deep coalfield
boreholes and in oil exploration wells.
Keywords coal analyses; coal rank; coal type; maturity;
Rank(Sr); New Zealand coals; Australian coals; Carboniferous coals;
Münsterland-1 well; Gironville well; Pie Rough borehole
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43:
521-553
0028-8306/00/4304-0521 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (2478K); (scanned from paper original: notes about this process)
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