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ABSTRACT: Offshore frontier basins of southern New Zealand

Sutherland, Rupert , Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand

Oil and gas shows from exploration wells and onshore seeps confirm models that suggest the region has significant hydrocarbon accumulations. Technological advances for drilling in moderate water depths now make the region highly prospective.

Canterbury and Great South basins cover > 150,000 km2, have 0-2000 m. water depths, and contain 8 km of sediment. 12 offshore wells have been drilled and > 50,000 km of seismic lines acquired. Six wells had shows, including promising comments such as "bleeding thick black oil" in well logs. Two condensate discoveries were tested. Source rocks include Cretaceous-Paleocene marine and lacustrine shales, including black shales (TOC 8%), and coals. Reservoirs are terrestrial clastic sediments, shallow-marine sands, or deep-water clastic fans. Structures are associated with normal-faulted basement and overlying drapes, or gentle Cenozoic folds. Modeling suggests all components of a viable petroleum system were in place before the critical moment and significant volumes of hydrocarbons were trapped. The large size of prospects and potential discoveries offset moderate risk associated with remoteness.

The Solander Basin covers 20,000 km2 with 0-2000 m water depths. There are > 5,000 km of seismic lines and 2 wells, one of which had an oil show. Onshore, the region is prospective and known from geological mapping and 6 exploration wells. The Cenozoic geology is more complex than that of the Great South or Canterbury basins, because it has been astride an active plate boundary since 40 Ma. This increases the variety of possible petroleum systems, but means structures are only of moderate size ( < 50 km2). Although exploration cost is higher offshore, structures are larger and erosional unconformities less common.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia