25th International Meeting on Organic Geochemistry IMOG 2011

P-081
Geochemical evidence for two sources of oils in the Papuan
Basin, Papua New Guinea
Manzur Ahmed 1 , Herbert Volk 1 , David Holland 2 , Tony Allan 1
1 CSIRO Earth Science and Resource Engineering, North Ryde, Australia, 2 InterOil, Cairns, Australia
(corresponding author:manzur.ahmed@csiro.au)
Two major groups of hydrocarbons, Family A and
Family B, can be distinguished by detailed organic
geochemical assessment of 34 oils/condensates,
inclusion oils and solid bitumens from the Eastern
Papuan Basin (EPB) and the Western Papuan Basin
(WPB) (Fig. 1). Both groups of oils/condensates could
be further divided into two subgroups based on minor
variations in source facies. Family A2 samples in the
EPB were generated at peak to late oil-window
maturities from a clay-rich marine source rock
containing predominantly terrestrial higher plant
derived organic matter deposited in suboxic to anoxic
environments. Biomarker signatures are related to the
crude oils from the WPB Fold Belt region, and similar
to those oils (Family A1), this family was probably
generated from the Late Jurassic Imburu Formation.
Family B samples were also generated at peak to late
oil-window maturities, but from a clay-poor, possibly
calcareous marine source rock, richer in prokaryotic
organic matter, and deposited in suboxic to anoxic
environments. This is indicated by higher abundances
of C29 �� hopane,�C35 homohopanes and
2��methylhopanes. Oleanane±lupane and the
distributions of nordiacholestanes and norcholestanes
suggest that the Family B oils/condensates were
derived from Cretaceous or younger source rock(s).
Hydrocarbons in the Elk-Antelope gas-condensate
field, a significant recent discovery in the EPB, cluster
in Family B. The molecular and isotopic signatures of
thermogenic gases in this field show very little
variation and are also consistent with marine source
rocks. The presence of two major groups of
oils/condensates in the EPB is consistent with the two
families of solid bitumens and an inclusion oil from the
Aure Scarp area (George et al., 2007), and different
types of oils and inclusion oils in the WPB region
(George et al., 1997).
Although the exact origin of Family B hydrocarbons is
unclear, source rock intervals may be hosted in
Cretaceous or Palaeogene strata, e.g. in the
Cretaceous Ieru or Chim Formations. New total
organic carbon and Rock Eval pyrolysis data indicate
that the Late Jurassic / Early Cretaceous Tubu and
Maril Shales in the Papuan Gulf region are also
potential source rocks.
Figure 1. Dendrogram of hierarchical cluster analysis of 13
source-specific biomarker parameters showing genetic
groups of oil/condensates in the Papuan Basin. Data for
solid bitumens; Puri-1 and Bwata-1 oils/condensates are
1.0
P'nyang-2X 1922 m FI oil
Iagifu-7X 2615 m FI oil
Iagifu-7X 2564 m FI oil
Triceratops-1-1805 m oil show
Triceratops-1-1844 m oil show
CN405 Family B solid bitumen
ELK-2 oil show
CN360 Family B solid bitumen
Moose-2 513 m oil show
0.8 0.6 0.4 0.2 0.0
Elk-1 oil/condensate
CN540 Family B solid bitumen
CN409 Family B solid bitumen
Yawiyo seep sample-1
Family B1
CN457 Family B solid bitumen
Bwata-1 oil/condensate
North Ox seep
Moose-2 753 m oil show
Moose-2 634 m oil show
Family B
Antelope-1 DST-11 oil/condensate
Antelope-1 DST-12 oil/condensate
Antelope-1 DST-14 oil/condensate
Antelope-1 DST-13 oil/condensate
from George et al. (2007), and Western Fold Belt
oils/inclusion oils are from George et al. (1997). Sample
names in black for the Eastern and in red for the Western
Papuan Basin.
References
Elk-4 oil-condensate
Antelope-1 1747 oil/condensate
Antelope-1 D-8 oil/condensate
Iagifu-7X DST-1 crude oil
Iagifu-7X DST-3 crude oil
Iagifu-7x DST-5 crude oil
Iagifu-7X DST-2 crude oil
Pangia seep
CN415 Family A solid bitumen
CN383 Family A solid bitumen
Puri-1 oil/condensate
CN381 Family A solid bitumen
Similarity value
Family A1
Family B2
Family A
Family A2
[1] George, S.C., Krieger, F.W.,Eadington, P.J., Quezada,
R.A., Greenwood, P.F., Eisenberg, L.I., Hamilton, P.J. and
Wilson, M.A., 1997. Geochemical comparison of oil–bearing
fluid inclusions trapped in quartz grains and live oil from the
Toro Sandstone, Papua New Guinea. Organic Geochemistry
26, 155-173.
[2] George, S.C., Volk, H., Ahmed, M., Pickel, W., and Allan,
T., 2007. Biomarker evidence for two sources for solid
bitumens in the Subu wells: implications for the petroleum
prospectivity of the East Papuan Basin. Organic
Geochemistry, 38, 609-642.
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