OIL AND GAS ACCUMULATION CONDITIONS IN THE NEW FRONTIER DEEP WATER AREA OF TARANAKI BASIN, NEW ZEALAND

The Taranaki Basin is the only oil and gas producing basin in New Zealand. However, exploration activities and oil and gas discoveries are mainly concentrated in the land and shallow water areas, but deficient in the deep water area. There are some basic problems to be solved, such as, the tectonic and sedimentary evolution of the basin, the resource potential of oil and gas in the deep water area of the basin and so on. This paper is devoted the deep water hydrocarbon potential. It starts from the tectonic background and sedimentary evolution of the basin before the New Zealand plate drifted away from the eastern margin of Gondwana paleo-continent. The deep water stratigraphy is established based on seismic stratigraphic sequences. At the same time, combining geological together with geophysical methods, the potential of source rocks, reservoir-cap assemblages, traps, possible hydrocarbon accumulation models and exploration directions in the deep water area are studied. It is concluded that:①The tectonic and sedimentary evolution of the deep water area of the basin is different with that in the land and shallow water areas which are well known at present, and the deep water area depositional sequences and the filling history of the basin can be divided into four sequences; ②There exists a new petroleum-bearing system in the deep water area which is older than those found on the land and in the shallow water areas of the basin. There are two sets of hydrocarbon source beds of continental coal measures in the rifting stage and covered by transgressive mudstone in post-rifting stage. Gas generated in rifting period and oil in post rifting period, and the hydrocarbon-generating potential is high.③The main exploration targets of the deep water oil and gas reservoirs are delta sandstone and shallow marine littoral sandstone of Late Cretaceous. However, the volcanic drape structural traps could be the main exploration targets in the eastern uplift area.