Abstract

The outer Browse Basin is a frontier area located outboard of the central Browse Basin, NW Australia, in water depths ranging from 500 to 3300m. It is believed to contain more distal extensions of the petroleum systems of the Browse Basin. In the latter, hydrocarbon discoveries can broadly be characterised as either large gas-condensate discoveries within Mesozoic Horst Blocks, reservoired in Jurassic deltaic sediments (Brecknock, Scott Reef and Brewster) or sub-commercial oil discoveries within Cretaceous sandstones structurally and stratigraphically trapped in drapes over Mesozoic horsts (e.g. Puffin) or basement highs (e.g. Cornea, Gwydion).

A joint venture consisting of BHP Billiton (operator), Kerr McGee and Chevron Texaco implemented an exploration programme designed to reduce the major petroleum systems risks; understanding the distribution of rift volcanics coincident with the Late Jurassic Plover Formation and presence of a generative source rock.

The three-year programme consisted of hyperspectral hydrocarbon seep detection, seabed coring, magnetic modelling and seismic interpretation. Several very large prospects were identified and the first well was drilled at Maginnis-1 in 2002. The well failed to encounter Jurassic reservoir and penetrated a thicker than anticipated volcanic section. Further work has been conducted using the Maginnis data to improve volcanic thickness predictions and improve the chance of encountering clastic reservoir. Several very large prospects remain to be tested including amplitude-supported targets in the Cretaceous interval overlying the volcanics.