Publications

In this article, we describe the exploration activities for two frontier deepwater basins in Eastern Indonesia, undertaken over a period from 2006 to 2013. The two basins are the Kofiau Basin and Cendrawasih Bay (Waipoga) Basin, located respectively on the northwestern and eastern margins of the Bird’s Head terrane of West Papua. Significant datasets were acquired in both basins during the pre-tender stage (open area-joint study) and PSC operations stage. This included regional 2D seismic, gravity/magnetics, high resolution sea floor multi-beam, piston core geochemistry, and prospect-specific 2D and 3D seismic programs. Two deepwater exploration wells were subsequently drilled in Kofiau (Ajek-1 and Elit-1) and one well in Cendrawasih Bay (Elang-1). The two basins show some similarities in their stratigraphic architecture, but also some important differences in tectonic setting and structural evolution. The Kofiau basin is a northeast-southwest trending depocenter with two major episodes of basin formation, one in the early Pliocene, followed by a period of deformation and erosion, and another depositional period lasting from the mid Pliocene until Recent. The basin evolution is controlled by the Sorong Fault Zone, the main strike slip plate bounding fault between the Australian Plate and the Pacific Plate. Eocene to late Miocene carbonates of the New Guinea Limestone (NGL) comprise the effective basement of the Kofiau basin. The Kais limestone member at the top of NGL is likely to occur at drillable depths in the northern part of the basin, but is generally too deep to be of interest over much of the area. The Cendrawasih Bay (Waipoga) Basin belongs to a large Plio-Pleistocene post-collisional clastic.basin complex which extends across northern New Guinea. The northern margin is formed by the major east-west trending Sorong-Yapen Fault zone, to the west and southwest by the Bird’s Head and Lengguru Fold Belt, to the south by the Weyland mountain terranes, and to the east by the Waipoga Foldbelt. It contains Miocene to Pleistocene sequences which attain sediment thicknesses of at least 25,000 ft in the Waipoga Trough. Sea-floor piston cores revealed the presence of significant oil and gas seepage. Crude oil biomarkers and carbon isotopes showed that, in both basins, the oil was derived from a Tertiary source rock, most likely of the Klasafet Formation type (Late Miocene-Pliocene). Seepage of thermogenic and biogenic gases was also recorded, although the relative amounts of each differed between areas. Two exploration wells in Kofiau targeted Plio-Pleistocene sands in structural/stratigraphic traps, and showed the presence of good quality sands charged with mixed thermogenic-biogenic gas, although the pay sands at these locations were not sufficiently thick for commercial development. The exploration well in Cendrawasih Bay targeted a sedimentary package comprising carbonates and clastics of Tertiary age in a large four-way structural anticline. The well successfully encountered a moderately thick limestone section of Miocene to Eocene age, however the carbonate was tight and non-productive. No indications of thermogenic hydrocarbons were seen in the well. Reconciliation of the drilling results with evidence for active petroleum systems in both basins provides the impetus and direction for follow-up exploration activity.