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Late Jurassic To Early Cretaceous Sequence Stratigraphy, Northern Bonaparte Basin, Timor Sea.

Ceglar, Nathan

Honours Degree, 1999

University of Adelaide

Abstract

The potential for stratigraphic trap development in the syn-rift sediments of the Late Jurassic to Early Cretaceous interval (152 to 140 Ma) of the Northern Bonaparte Basin has stimulated a sequence stratigraphic analysis to help build a predictive regional depositional model. Sandstones in this interval, lithostratigraphically referred to as the ?Flamingo Formation?, provide a potential intraformational reservoir facies enveloped by shale of known source potential in the Nancar Trough and Sahul Syncline. The near syn-depositional relationship of these two lithologies combine to form the elusive ?Flamingo Formation Stratigraphic Play?.

Using a network of nine wells supported by biostratigraphic data, a regionally-consistent sequence stratigraphic framework was developed for the interval, based on regionally-significant key surfaces interpreted from the well logs. Sedimentary stacking patterns between key surfaces were analysed, resulting in the identification of eleven depositional sequences.

The major factors controlling sequence development appear to be two distinct orders of eustatic sea level cycles. These have significant implications for hydrocarbon exploration.

The potential for stratigraphic trap development exists mainly within the Nancar Trough and northernmost part of the Sahul Syncline. Stratigraphic plays within this area are likely to consist of stacked basin floor fans developed during the four lowstand systems tracts identified within the D.jurassicum palynozone (149 to 147 Ma). The extent of fan development is uncertain, however, interpretation of Nancar #1 suggests that the lowstand fans of the Nancar Trough/Sahul Syncline are sourced from the Londonderry High. The sand-rich nature of these fans is likely to restrict their radial extent, as sand-rich turbidity flow processes are relatively inefficient. Graben structures mapped at the Middle Jurassic level (~160 Ma) that are linked to the Londonderry High should be considered primary targets for future stratigraphic trap exploration. These structures are likely to have constrained turbidity flow and hence the probability of encountering lowstand basin-floor fans within them is greatly increased.

The potential for an alternative play exists within the Flamingo Syncline. The lack of bathymetric structures to channel turbidity flows has, however, downgraded the potential for economic trap development. Log interpretation suggests that where present, these basin floor fans are likely to broader and thinner than those of the Nancar Trough/Sahul Syncline.

The sequence stratigraphic framework developed in this study, once integrated with seismic data, will decrease the inherent risk associated with exploration for the Flamingo Formation Stratigraphic Play throughout the Northern Bonaparte Basin.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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