A review of the petroleum potential of Papua New Guinea with a focus on the eastern Papuan Basin and the Pale Sandstone as a potential reservoir fairway

Abstract

Abstract Substantial oil seeps were first reported from the eastern Papuan Basin in 1911, and oil has since been produced from the sub-surface, but not in commercial quantities. A significant discovery of gas in 1986 sparked an upsurge of activity within the adjacent western Papuan Basin. From 1986 to 1992, 13 new hydrocarbon discoveries were made, which included four major oil fields, and an oil pipeline for export purposes was then opened in 1992. This activity did not spread to the eastern Papuan Basin due to a perceived lack of good reservoir and the last well drilled there was over 30 years ago. In 1986, a potentially excellent reservoir, the Pale (Pah leh) Sandstone was discovered in outcrop in the eastern Papuan Basin. Thus the Papuan Basin as a whole remains an extremely prospective basin. However, due to high infrastructure costs most activity has recently been focussed on the already proven reservoir potential of the Late Jurassic Imburu and Toro Formations in the western section. The extent of the Imburu-Toro Formation reservoir in the western section of the Papuan Basin is well documented. It was deposited as several regressive episodes within an overall transgressive, passive-margin, clastic sequence. In the eastern section, the Late Cretaceous Pale Sandstone was deposited in a barrier island or strand-plain environment. Lateral equivalents of the Pale Sandstone and the potential for a new reservoir fairway have been documented for a strike length of approximately 400 km. This fairway is coincident with the northeast edge of the western Papuan Basin and on the northern edge of the Aure and Port Moresby Troughs of the eastern Papuan Basin. All the commercial oil accumulations and seeps found in the Papuan Basin before 1992 have been attributed to the Jurassic, with peak generation occurring in the Late Cretaceous prior to the formation of existing structures. In 1992 an oil seep was discovered which is geochemically very different to all the other oils found in the Papuan Basin. This was found to the north and east of the present discoveries that occur within the western Papuan Basin. The oil seep is indicative of undiscovered Tertiary source rock, which is currently at or near peak generation. However, most of this source rock in the north may be covered by overthrusted allochthonous terrain. The Aure Trough was a Late Cretaceous to Tertiary rift basin that later developed into an Oligocene to Mid-Miocene foreland basin depocentre occurring on the northern and eastern margin of the Papuan Basin. It is proposed in this paper that mature Tertiary source rocks which occur within this foreland basin and the Pale Sandstone reservoir may form a significant petroleum system on the northeastern rim of the western Papuan Basin and within the eastern Papuan Basin.