Architecture and Reservoir Potential of Coastal to Nearshore Successions in Low-Accommodation, Continental Margin Settings: Examples from the Permian and Cenozoic of Eastern Australia
Christopher Fielding1, Jonathan P. Allen1, Patrick Ducey1, Kerrie Bann2,
Jonathon Trueman3, and J. Alexander4
1 University of Nebraska-Lincoln, Lincoln, NE
2 University of Alberta, Edmonton, AB
3 BP Exploration UK, Aberdeen, United Kingdom
4 University of East Anglia, Norwich, United Kingdom
Generic stratigraphic models for continental margins emphasize high-accommodation settings where sequences are thick, complete, and contain readily recognizable components of all the major systems tracts. In such settings, it may be possible to carry out sequence stratigraphic analysis from wireline logs, and to predict reservoir distribution away from wells. In low-accommodation areas, sequences and stacking patterns do not conform to the model predictions, and subsurface interpretation is more problematic. We compare the facies and sequence stacking patterns of three different coastal to near-shore successions of low-accommodation systems in northeastern Australia with the predicted patterns of published models. (1) The mid-Permian Freitag Formation in the Denison Trough is a gas producer from out-of-context Lowstand Systems Tract (LST) channel sandstones, which overlie regionally extensive sequence boundaries. The sequences are nonetheless dominated by the Transgressive (TST) and Highstand Systems Tracts (HST), and are <20 m thick. (2) The Late Permian Betts Creek Beds near the northeastern edge of the Galilee Basin contain a stack of sequences <10 m thick, each of which contains a fluvial LST overlain by a distinct but thin TST and a thin or erosionally truncated HST. Individual sequences can be resolved despite the basin-marginal location. (3) The Cenozoic Burdekin Delta succession comprises a stack of sequences typically <25 m thick each of which contains little or no LST, a mud-dominated TST and a sandy HST recording delta progradation. Sandstone bodies amalgamate in the up-dip direction. All three successions preserve a stack of thin, condensed, incomplete sequences with top-truncation. Highly variable reservoir potential among these successions, which would not be predicted by generic models, can be attributed to varying sand supply from up-dip fluvial dispersal systems.