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Integrating Sedimentology, Sequence Stratigraphy and Ichnology for Improved Reservoir Prediction in the Bayu-Undan Field, Bonaparte Basin, NW Australia

Boyd, Ron 1; Krieger, Frank 1; Ryer, Mihaela 1; Mathers, Genevieve 2
1 ConocoPhillips Company, Houston, TX.
2 University of Wyoming, Laramie, WY.

The Bayu-Undan gas field in the Bonaparte Basin off NW Australia contains a Bathonian-Callovian pre-rift interval of reservoir rocks that exhibit limited subsidence and accommodation. Structural architecture during deposition of upper Plover and Elang Formation's reservoir rocks resulted in a restricted basin with limited wave fetch but enhanced tidal action. The large Plover fluvial system drained the Australian continent to the southeast and deposited a tide-dominated delta during a period of longer-term relative sea level rise.

A key to exploration and prediction in the Bayu-Undan field is the ability to identify tidal and marine influence in sediments using a combination of sedimentary structures, such as tidal mud drapes and couplets, with ichnological evidence identifying a range of marine influence. Restricted marine influence is indicated by low-diversity bioturbated caps on pervasively cross-bedded distributary sandstones containing tidal mud drapes and couplets. More open marine influence occurs in transgressive tidal flats and is characterized by erosionally-based regional sands pervasively burrowed by Teichichnus, Skolithos, Thalassinoides, Paleophycos and Ophiomorpha. Correlation of the low-diversity distributary caps enables the establishment of minor flooding surfaces of delta plain tidal flats, while correlation of the regional transgressive bioturbation events enables the determination of maximum flooding surfaces. Using these events for field-wide correlations, two complete sequences and their associated lowstand, highstand and transgressive systems tracts can be recognized in the upper Plover and Elang Formations, thus providing a method for distinguishing local facies change baffles from regional transgressive shale barriers in the reservoir.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009