Cenozoic Carbonate Deposition in the Eastern Papuan Basin

Abstract

Recent gas discoveries in Cenozoic carbonates demonstrate an active petroleum system in the onshore Eastern Papuan Basin (EPB) separate to that in the Western Papuan Basin; with synrift late Cretaceous to Early Tertiary sourced hydrocarbons charging the carbonate system. In parallel with exploration, knowledge of the age and general depositional facies of these carbonates has been advanced in a general study of the on and offshore EPB. This incorporates unpublished studies from recent discovery wells, reanalysis of samples from older wells, field studies, and published reports and regional maps. The study employed conventional petrographic facies analysis and a combination of Sr isotope and biostratigraphic age dating. The latter applied the T-Letter stages based on Sr isotopic calibration of index species to the geological timescale in the Western Papuan Basin. Middle to late Eocene and early Oligocene neritic calcarenites are present across the entire region, with both deeper water and redeposited shallow water facies at the Aure Scarp. In the late Oligocene - early Miocene (Te-lower Tf1-2; 28 to 17 Ma) fine deeper water “Puri limestone” was deposited across the basin. The youngest Puri of this age marks the end of continuous carbonate deposition preceding Aure Trough back arc clastic deposition in the northern fold belt. Redeposited coral-foram-algal debris including forereef talus is common in the Puri limestones of latest Oligocene to early Miocene (upper Te1-4 – lower Tf1-2) age. Similar shallow and deeper water carbonate deposition prevailed in the late early to middle Miocene (upper Tf1-2; 17 to 11 Ma) through much of the Pio-Purari and foreland area. Sites such as Antelope, Uramu, Ini and Iviri are shallow water accumulations of latest Oligocene to middle Miocene age. The middle Miocene minimum age of limestones at these locations is significant with respect to early porosity developed at eustatic sea level fall. Oligo-Miocene redeposited coral-foram-algal limestones exposed and penetrated in wells along the Pio-Purari axis constituted the “smoking gun” in the search for insitu shallow water accumulations validated by Antelope. Similarly, the late Oligocene to Middle Miocene (Te to Tf1-2) shallow water accumulations documented on the northern (Chimbu) and eastern margins (Kapau-Hells gate) suggest within the Aure trough area carbonates are an attractive untested potential reservoir play.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015