Publication Name: The Sedimentary Basins of WA
Authors: E. Kopsen
Publication Volumne: 3
Date Published: December 2002
Number of Pages: 28
Reference Type: Book Section
Abstract:The Northern Carnarvon Basin and the Northern Basins (Browse and Bonaparte basins, including the Vulcan Sub-basin) within the Westralian Superbasin have each now been tested by around 400 new field wildcat wells. The PSO (proven and probable) reserves and resources in the Carnarvon currently amount to some 96 trillion cubic (TCF) of gas, 1.8 billion barrels (BBO) of oil and nearly 1.5 billion barrels (BBC) of condensate. In comparison, the Northern Basins presently account for around 61 TCF of gas, 1.6 BBC and just 1/2 a BBO.
A clear pattern of discoveries has been recognised over many years with huge gas/ condensate fields lying in the
outer basin platform areas bounding deep Mesozoic hydrocarbon kitchen areas and more liquids-prone fairways in inshore areas.
An important liquids-rich component of the resources occurs through the aborted Jurassic rift centre (Central
Fairway) and these areas are still quite under-explored. Further exploration through the Inner Fairway in the
Northern Basins and in the Central Fairway areas should yield significant liquid reserves additions. Important trends have emerged over the last decade, namely:
? New Northern Carnarvon Basin discoveries in reservoirs sealed by formations older than the Muderong Shale regional seal.
? The emergence of the Exmouth Sub-basin as a significant new oil province with surprisingly little gas reserves in the total hydrocarbon mix.
? New large gas/condensate discoveries made in the Central Fairway of the Browse Basin, details of which remain scant.
The industry is also confronted by anomalies in the exploration record that still remain unresolved:
? The commercially unsuccessful exploration track record in the Vulcan Graben where prime Upper Jurassic marine source rocks have expelled around nine billion barrels of oil from just two small grabens.
? Limited success of the Echuca Shoals petroleum system in the Northern Basins, particularly in the Browse
? No commercial production and few oil recoveries from offshore Palaeozoic reservoirs in the region, despite
frequent oil shows.
Nevertheless, the last decade has seen dramatic growth of hydrocarbon reserves and resources through exploration drilling on the Westralian Superbasin and the creaming curves for the region show no clear signs of "tailing-off". This is a healthy sign for future new field discoveries even though the discovery index, a measure of exploration success per metre drilled, has fallen away in the most mature basin, the Northern Carnarvon Basin.