Depositional and Diagenetic Evolution of a Papua New Guinean Onshore Carbonate Reservoir during the Change from a Rifted Margin to Fold and Thrust Belt Setting

Wilson, Moyra E.¹; Holland, David²; Yogi, Okaro³; Allan, Tony⁵; Hombo, Louise⁴; Goldberg, Adrian²
¹Applied Geology, Curtin University, Perth, WA, Australia.
²Interoil, Cairns, QLD, Australia.
³SPI Ltd, Port Moresby, Papua New Guinea.
⁴National Petroleum Company PNG, Port Moresby, Papua New Guinea.
⁵CSIRO, Sydney, NSW, Australia.

In active tectonic basins the location, sequence development, internal variability, demise and diagenesis of carbonate platforms are often strongly impacted by differential subsidence/uplift, faulting and tectonically-driven subsurface fluid flow. Here, we evaluate depositional and diagenetic changes across an Australasian subsurface buildup during its initiation in a rifted margin setting and subsequent development then demise in a fold and thrust belt. The Elk and Antelope system is a major recent gas discovery hosted in

Tertiary reefal, platformal and associated deepwater carbonates in the present day foothills region of the Fold and Thrust Belt in the Gulf Province of Papua New Guinea. A full suite of FMI logs (> 2000 m), > 250 thin sections (mainly from sidewall cores and cuttings) and additional diagenetic data (cathodoluminescence, fluid inclusion, SEM and stable isotopes) from both platform margin and shallow water deposits were evaluated during this study. An additional core, petrographic (>150 thin sections) and geochemical study of 16 onshore and offshore wells mostly from the adjacent Gulf of Papua Foreland Basin was undertaken to further understand controls on regional carbonate development.

A series of rift related structural highs strongly controlled the location of initial, and subsequent, carbonate development. Tectonic subsidence provided the accommodation space for thick carbonate successions. Early Paleogene platforms are dominated by non-framework building biota including foraminifera, coralline algae and echinoderm debris that typically did not build to sealevel and experienced significant post-depositional compaction. Plate tectonic drift through climatic belts, paucity of eustatic fluctuations, oceanography and lack of early cements were all controlling influences. By the late Paleogene and into the Miocene reefal development was common, with many buildups affected by repeated suaerial exposure. There were significant variations in facies and early cements across shelves and buildups. Active faulting, significant differential uplift and subsidence and regional compactional driven subsurface fluid flow associated with formation of the fold/thrust belt and foreland basin all impacted sequence development, platform margin collapse and/or demise and regional diagenetic trends.

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