The Prospectivity and Reservoirs Characteristics of the Triassic Depositional Systems of the North West Shelf, Australia: New Insights

Abstract

The Triassic is an important play on the NW Shelf of Australia, particularly in the Carnarvon Basin where source and significant reservoir rocks are present. Fluvial channel sandstones of various types represent the main exploration and development targets in the Mungaroo Formation reservoirs while distributary channel, mouth bar and inter-distributary bay deposits dominate within the Brigadier Formation. The predominance of relatively dry gas discoveries is generally considered to reflect the presence of non-marine Triassic source rocks. However, Late Triassic isolated carbonate build-ups have emerged as a new “oily” exploration play on the outer Exmouth Plateau of the North Carnarvon Basin. The presence of these carbonates in the Northern Carnarvon Basin has been known for many years from Exmouth Plateau well-based stratigraphy, seismic surveys and Ocean Drilling Programme wells on the Wombat Plateau. The seismic identification of numerous dome-shaped features in the outermost Exmouth Plateau, has helped confirm these domes as Upper Triassic reefs. The drilling of Tiberius 1 in WA-434-P, has advanced the understanding of this carbonate system. We show evidence of a more significant marine influence in distal parts of the Mungaroo than was previously understood and suggest that Kerogen type, controlled by depositional setting, may be more variable that previously thought. By developing an improved understanding of the regional Triassic paleogeography we show how source rock distribution can be de-risked. Implications for regional trends in reservoir type and quality will also be shown, helping us to develop an improved understanding of the Triassic play as whole.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015