Abstract

New Zealand is generally considered to be gas-prone as its source rocks are generally coaly. This is not the case in the East Coast Basin, where all known source rocks are of marine origin. Two source rocks considered for this study; Waipawa Formation and Whangai Formation are both mature across much of the region, giving rise to two active petroleum systems. The Waipawa Formation, Paleocene in age, is a black marine shale up to 50 meters thick with and average TOC of 5%. The Whakataki Formation is an early Miocene turbidite fan sand with a large lateral extent and up to 20% porosity. The Takiritini Sandstone is also early Miocence in ago. It is a littoral sandstone with a thickness of 1000 meters and roughly 20% porosity. The Paleogene was dominated by mudstones, claystones and marl including bentonites that act as seal in these petroleum systems. The Neogene was also mud dominated with plentiful turbidites and limestones. More than 300 known gas and oil seeps occur onshore along the East Coast. The Raukumara sub-basin is a 200 miligal low with 13 km of sedimentary fill of largely unknown geology however Neogene structures are present particularly in the East. Hawke Bay is a "pull-apart" basin that resulted from oblique subduction. Numerous structural traps are present in Hawke Bay. Direct hydrocarbon indications are seen along the top Middle Miocene reflector and above the crest of the Tawatawa Structure. This suggests that the regional seal is also leaky in this structure with migration pathways are likely along the thrust fault that formed the anticline. The Pegasus sub-basin is a 200 miligal low with thick sediments >10km, Cretaceous and Paleocene source rocks at depth and Neogence turbidites. The sedimentary section in New Zealand is very tick with known source, generation, reservoirs and seals. The key to understanding is in new high-quality seismic data.

Presented at: 2005 South East Asia Petroleum Exploration Society (SEAPEX) Conference, Singapore, 2005