Some of the highest HI (300-400 kg HC/t Corg) and lowest GOGI...

Some of the highest HI (300-400 kg HC/t Corg) and lowest GOGI (c. 0.4) values are associated with Late Cretaceous coals in Galleon-1 (Gibbons & Fry 1986), suggesting these coals are among the most oil prone. The fact that condensate was detected in the intervals 2532-2653 and 2821-2870 m bsf suggests that migrated liquid hydrocarbons could be present in the intervening interval, which would account for the high Sl/TOC value-, rather than needing to invoke unusually high expulsion thresholds for the Galleon-1 coals.

Coaly sediments of mid-Cretaceous age, similar to those
of the Taniwha Formation in the Taranaki Basin, are present
in the Great South Basin (Hoiho Group, Fig. 2). They are
also present in Clipper-1 in Canterbury Basin, where they
have been termed the Clipper Formation (Field & Browne
1989). Similar HI values are recorded for these sediments
in Kawau-IA and Toroa-1 wells (c. 100-200 kg HC/t Corg),
despite apparent differences in maturity. Rock-Eval Tmax
values are c. 450°C in Kawau-IA and c. 470°C in Toroa-1,
suggesting the peak of oil generation has already been
reached in Kawau-IA and passed in Toroa-1. In Clipper-1
these sediments are of slightly greater maturity than in Toroa-1 (Ro c. 1.2-1.3 cf. 1.15-1.2%) and residual HI values have declined to c. 100 kg HC/t Corg (Gibbons & Herridge 19841.