Structural and Stratigraphic Evolution of the Gulf of Papua, Papua New Guinea: New Insights from a Modern 3D Seismic Survey

Botsford, Andrew; Endebrock, Larry; Harrington, Amanda
PGS Reservoir, Petroleum Geo-Services, Singapore, Singapore.

The Gulf of Papua, part of the regional Papuan Basin, has undergone a complex and varied structural and stratigraphic evolution relating to its position on the NE edge of the Australian plate. Most PNG exploration to date has focussed on the onshore region of the Papuan fold belt where a number of commercial oil and gas discoveries have been made, highlighting the effective Jurassic source rock present across the region. There is now increasing focus on the offshore area where there are fewer wells but three significant gas and condensate discoveries.

PGS's recent acquisition and interpretation of 6,300 square kilometres of 3D seismic data has greatly improved imaging and mapping of the offshore area surrounding the Pasca gas condensate discovery and the NE-SW trending Pasca Ridge. A thick siliciclastic section has been deposited over the last 5 My. Beneath this section a carbonate reef provides the reservoir for the Pasca discovery. Reefs formed on palaeo-highs resulting from complex pre-Eocene tectonic events. The strata within the pre-carbonate section have been compressed to form NE-SW trending, SE verging anticlines. This section cannot be confidently tied to any well data, although the Pasca-C1 well (1968) encountered an undated quartzite immediately beneath the Tertiary carbonate section. Due to lack of well ties the age and lithology within the deformed section cannot be determined at present. Two hypotheses for the origin and age of these units are proposed: 1. A significant Early Tertiary (63-38 Ma) deformation event took place, resulting in uplift of Gondwana rift section and emplacement of the Pasca Ridge. 2. The Pasca Ridge was deformed prior to the deposition of Mesozoic section and the deformed strata are pre-rift Gondwana section.

An improved understanding of the age and origin of the Pasca Ridge allows better mapping of the proven Mesozoic source rock and, therefore, a better understanding of the petroleum potential of the region. If the deformed strata within the Pasca Ridge are Mesozoic, then it is highly likely the Pasca discovery was charged by simple vertical migration of hydrocarbons from this unit and the distribution of this source rock is also more widespread than previously thought. If the Pasca Ridge is completely composed of pre-Mesozoic material, then the Pasca discovery requires either a complex migration route from mature Mesozoic section to the NW, an undrilled Tertiary source or an unknown Paleozoic source.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012