Sequence Stratigraphy of the Darai Limestone Megasequence in the Gulf of Papua, Papua New Guinea

Morgan, Glenn D.¹, Shane S. Schofield², Tony L. Allan³ (1) The University of NSW, Kensington, NSW, Australia (2) Oil Search Limited, Sydney, NSW, Australia (3) CSIRO Petroleum, North Ryde, NSW, Australia

A sequence stratigraphic study was conducted on the Darai Limestone Megasequence in the foreland area of the Papuan Basin in Papua New Guinea. It enhanced the understand­ing of the structure, depositional architecture, basin morphology, and petroleum potential of the limestone. The study integrated seismic, wireline log, well core and cuttings, strontium isotope age and biostratigraphic data.

Ten third-order sequences were delineated within the Darai Limestone Megasequence. Seven depositional facies were interpreted across these sequences, namely: shelf; backreef; reef; shoal; forereef; basinal; and submarine fan facies. Each facies was differentiated according to seismic character and geometry, well core and cutting descriptions and its position in the depositional framework of the sequence.

Deposition of the Darai Limestone Megasequence commenced during the Upper Oligocene in response to oblique rifting of the Omati Trough in a back-arc setting. Sedimentation was initially restricted to the Omati Trough and comprised deep-water shelfal limestones. Regional subsidence associated with the back-arc extension led to the develop­ment of an extensive carbonate platform across the Gulf of Papua. Carbonate reef growth commenced along palaeo-highs during the Lower Miocene, and led to the establishment of a rimmed carbonate platform margin. The carbonate platform and reef margin kept pace with relative sea-level fluctuations until the Upper Miocene, when carbonate sedimentation was terminated by prograding clastic sediments from the uplifted northern parts of the Papuan Basin. New play fairways were identified within the Darai Limestone Megasequence. These were associated with slope and basin floor fan development, and stratigraphic traps in the Omati Trough.