Abstract

Between the Central New Guinea Mountain Ranges and the New Guinea Trench lies a terrane consisting of a hybrid, forearc basin and at least one, and possibly two, subduction-related accretionary prisms. Some authors refer to a sedimentary basin in this region as the Waropen Basin but we prefer to characterize a larger area as the "North Irian Basin". The prism we refer to as the "Niengo Basement Platform" appears to have formed coeval with the basin as a consequence of backthrust-subduction underplating of the Indo-Australian plate by a down-going slab of the Caroline-Pacific Plate. Subduction stopped and relative plate motion is now oblique. The plate boundary appears now to be marked by the Yapen Fault Zone, a sinistral wrench fault whose trace is marked on the mainland by a line of active mud volcanoes and extends westward along the northern coast of Yapen Island and may continue westward to connect to the Sorong Fault system.

The North Irian Basin contains over 25,000 feet of Tertiary-aged clastic and carbonate sediments in several localized depocenters or sub-basins, most notably the Waropen, Teer River and Waipoga "deeps" and an intermontane sub-basin known as the Meervlakte. Rapid subsidence has created asymmetric basin fills dominated by turbidites. Potential reservoir distribution across the depocenters appears to be problematical with good quality turbidite reservoirs being concentrated near depocenter margins. Large reef complexes are evident. There is evidence of ample terrigenous-derived kerogens to serve as a potential petroleum source. An apparent low thermal gradient of 1.67° F per 100 ft in the basin extends source maturity to considerable depth. Since the 1950's, 12 petroleum exploration wells, have been drilled including one stratigraphic test and resulted in four dry holes, two gas discoveries and one gas/oil discovery. Four were abandoned before reaching target depth due to encountering severe overpressure.