STRATIGRAPHIC CONCEPTS AND PETROLEUM POTENTIAL OF THE DENISON TROUGH, QUEENSLAND

Abstract

The Denison Trough in east central Queensland contains up to 4600m of both marine and non-marine, Permian and Triassic rocks. The sequence comprises thick mature source rocks interlayered and interfingering with thick sandstone intervals. Good to excellent sandstone reservoirs occur, though their distribution and development is sporadic and controlled by both despositional and diagenetic processes. This is the main limitation to the potential of the area. Source rocks appear to be gas or gas/condensate prone, although liquids generation cannot be discounted.

Exploration to date, comprising extensive seismic and the drilling of 39 exploration and 29 assessment wells, has led to the discovery of four small gas fields with combined reserves of approximately 850-1140m3 x 106. These reserves are insufficient to justify exploitation at this time. Apart from the fields, numerous gas shows and minor oil shows have been recorded throughout the Permian sequence, establishing beyond doubt that the trough is a hydrocarbon province.

The trough is assessed as having a high potential for the discovery of additional gas reserves, with a possible 15-55m3 x 109 being present both in deep structural plays and in shallower, essentially stratigraphic, plays. Further successful exploration will require both good quality structural control, particularly at depth and a sound understanding of the depositional processes controlling the development of reservoir sands. Since active exploration effectively ceased in the area in 1970, a great deal of stratigraphic information has become available. This has led to a better understanding of the stratigraphy than was previously possible. In addition, advances in seismic technology over the last decade have made available much more reliable exploration tools, with respect to achieving good quality, deep structural control and to stratigraphic interpretation and reservoir trend prediction.

The Denison Trough is considered to be one of the most prospective of Australia's onshore basins. It remains to be seen; however, if the application of present stratigraphic/depositional knowledge and new seismic technology will result in its potential being realised.