TROBRIAND BASIN EXPLORATION, PAPUA NEW GUINEA

Abstract

Regional studies suggested that the Solomon Sea would be underlain by upper Tertiary sediments inluding possible Miocene reef carbonates similar to those found in the Gulf of Papua and Irian Jaya. As the Trobriand area of the Solomon Sea lies in a zone of interaction between the Australian and Pacific tectonic plates, it was considered likely that Tertiary basins prospective for petroleum would be present. In 1969 the East Papua aeromagnetic survey revealed a magnetic low which was interpreted as a basin, here named the Trobriand Basin. A sedimentary section of some 3000 m, situated under shallow water was indicated.

Amoco, Australian Oil & Gas and Southern Pacific Petroleum made application for and were granted exploration permit PNG/15P in June, 1971. The Group initially undertook field geological, aerial photographic and hydrographic surveys which revealed the presence of numerous Pliocene to Recent coral reefs throughout the permit and also indicated the likely nature of economic basement. Between April 1972 and May 1973, three marine seismic surveys by Western Geophysical produced 2250 km of reflection profiles. The seismic data suggest that the Trobriand Basin is an east-west trending graben filled with up to 5000 m of probable Miocene and younger sediments. Positive structures, of which several were interpreted as mid-Miocene reefs, were mapped.

Two subsidised exploratory wells, Goodenough No. 1 and Nubiam No. 1, were drilled in 1973. Only minor and questionable hydrocarbon shows were encountered and both wells bottomed in Miocene volcaniclastics. The wells penetrated immature upper Tertiary sediments with low present and palaeo-geothermal gradients and consequently the sediments might be considered an unfavourable environment for petroleum generation. Nevertheless, the Trobriand Basin has not been adequately explored for hydrocarbon accumulations as only a portion of the Tertiary section has been evaluated in two widely-spaced wells.