Abstract

The Papuan Basin is the largest sedimentary basin in Papua New Guinea. It is a mature basin with a long exploration history. The basin was initiated during Permo-Triassic rifting of the northern margin of Australia. Long lived passive margin sedimentation occurred until the Oligocene to Recent at which time the basin was compressionally inverted. This resulted in the formation of the present-day fold and thrust belt. Numerous hydrocarbon fields, including Iagifu-Hedinia, occur along the leading edge of the thrust belt.

Three petroleum systems have been identified in the Papuan Basin. The most important from a commercial standpoint is the Jurassic-Imburu system. The majority of significant hydrocarbon discoveries in the fold belt have been generated from this system. It is documented by positive oil-source correlations. A Cretaceous system has been tentatively identified through geochemical analysis of an oil seep from the Kagua area. A Tertiary petroleum system is inferred to exist based on the presence of significant quantities of oleanane in a seep from Goroka.

Basin modeling using a series of palinspastically-restored cross-sections helped to better define the pre-thrust basin geometry and help constrain the timing of hydrocarbon generation from the Jurassic-Imburu system. Two important scenarios were evaluated: 1) pre-thrust generation from local kitchens behind the present thrust belt, and 2) syn-thrust generation by loading of stacked thrust sheets within the fold belt. Fluid inclusion studies have shown that hydrocarbons migrated into present day structures very recently. While the generation-migration history of the Papuan Basin is undoubtedly complex, oil composition data in conjunction with basin modeling results have helped provide a better understanding of the relative importance of re-migration from pre-thrust traps vs. direct charging from recent hydrocarbon generation.