Abstract

The Sepik and Ramu basins of Papua New Guinea contain several documented petroleum systems. It is worthwhile to compare these petroleum systems with the Salawati, North Coast and Meervlakte basins of Irian Jaya. Petroleum system analysis describes source rock, reservoir rock and seal rock, and integrates these building blocks into a temporal/kinetic framework that describes trap formation and source/carrier bed/reservoir geometry.

The Sepik Basin contains several deep extensional troughs formed during the Oligo-Miocene. These troughs remained sediment starved until the late Middle Miocene, and then underwent several pulses of structuring and rapid sedimentation. Sepik Basin exploration targets are Miocene Puwani carbonate build-ups which are analogous to the Miocene Kais reefal limestone in the Salawati Basin and the Nubai limestone of the Meervlakte Basin of Irian Jaya.

The Ramu Basin formed in response to Oligo-Miocene extension. Gravity data indicates a very thick (10km) pile of predominantly Pliocene sedimentary rocks in the southeastern Ramu Basin depocenter. This section is analogous to the thick Pliocene section of the Mamberamo Formation of the North Coast basin of Irian Jaya. The southeast terminus of the Ramu Basin is dominated by a 50 km long, northwest-southeast trending surface anticlinorium, termed the Banam Anticline. This feature hosts hundreds of gas seeps that have a biogenic source and appear analogous to the methane seeps in the North Coast Basin. The reservoir rocks in the Ramu Basin are late Miocene, quartz-rich clastics deposited in a nearshore marine environment.

The Sepik and Ramu basins are geologically complex. By integrating the various data sets from previous exploration programs and using the petroleum systems analysis approach, a clearer understanding of the risks and potential rewards of the northern margin of New Guinea Island is gained.