The Arafura Basin contains a sequence of Palaeozoic rocks
lying north-east of Darwin, and which extends from onshore
Australia, to perhaps as far as the Irian Jaya mainland. There are
over 9 km of Palaeozoic rocks preserved along the southern bounding
fault of a major graben (the Arafura Graben) located in the
southern part of the basin. In the uplifted centre of the graben,
there is less than 3 km of the Palaeozoic section preserved. The
basin is underlain by a Middle to Late Proterozoic sequence which
thickens to the east, and is probably equivalent to the onshore
McArthur Basin. Overlying the Arafura Basin is the Mesozoic Money
Shoal Basin, which is approximately 1 km thick over the central
parts of the graben, thickening rapidly to the west and thinning
to the east and north.
The structural cross-section that has been drawn is
located entirely offshore. It has been compiled using modern
seismic and well control. It runs from south-east of Tasman 1 in
a general north and north-east direction tying with Torres 1 and
Arafura 1. It passes through the central and north-eastern parts
of the graben, and the north-eastern part of the basin. Two-way
time to depth conversions were based on the velocity surveys from
the wells within the graben, but were modified locally outside the
graben. The structural analysis presented is largely based on the
evidence found along the line of the section. A more complete
structural analysis would require a regional examination of the
entire seismic network. Information from the recently published
Petroleum Basin Study on the Arafura Basin (Northern Territory
Geological Survey) has been incorporated into this report, although
there are major differences between some of their findings and the
interpretations presented here.
To date the major risk in hydrocarbon exploration has
been finding adequate reservoir conditions and seal. Contradictory
interpretations are present between the maturation and structural
modelling of the graben. Untested plays include possible Permian
and Triassic sediments (up to 5 km thick) which exist along the
flanks of the graben and which will probably contain good source
potential and improved reservoir conditions. To the north outside
the graben, there are poorly explored areas where it is speculated
that there are thick Palaeozoic and Proterozoic sequences.
