The Petroleum Prospectivity of Reinga Basin, NW New Zealand

Abstract

The Reinga Basin is a large (c. 170,000 km²), deep water (up to 2000 m), sedimentary basin that lies northwest of New Zealand. In 2009, a wide-spaced (c. 40 km) seismic reflection survey acquired MCS data over most of the basin, and in 2013, a survey collected MBES data and dredge samples from 37 sites, including samples from the adjacent Aotea Basin. These data have formed the basis of a comprehensive review of the stratigraphy, providing age and lithologic constraints to seismic units, as well as providing information about potential source, reservoir and seal rocks in the region. We present the results of seismic mapping and sample analyses and their implications to the petroleum prospectivity of the region. Prior to the Late Cretaceous, the NW portion of Zealandia was in a convergent setting at the Gondwana margin. Late Cretaceous extension and rifting was followed by thermal subsidence and burial until Eocene time when contraction related to subduction in the northeast affected the region, and persisted until Middle Miocene time. The Late Miocene to Recent is mostly characterised by quiescence and regional subsidence. Paleontologic dating of dredge samples indicates a range of mid-Cretaceous to Recent sediments are present. The most prospective source rocks are likely to be Late Cretaceous equivalents to the Pakawau Group in the Taranaki Basin. Results from several 1-D basin models indicate that where source rocks are present the top of the oil expulsion window lies between 3.5 km and 4.5 km, depending on heat flow scenarios. Possible reservoir facies include non-marine and shallow marine quartzose feldspathic and lithic sandstones deposited on the flanks of paleo-highs of Late Cretaceous to early Cenozoic age, possible Eocene carbonate reefs (uncommon), basin-floor fans and channels of Late Eocene to Neogene age. Much of the Late Cretaceous to Eocene succession is likely to be mud- and/or carbonate-rich and be suitable seal rocks. Based on the dredged samples, they appear to be similar to the Whangai Formation and Amuri Limestone in other parts of New Zealand. Petroleum plays include possible traps at rift basin margins, horst blocks, compressional structures, carbonate reefs, submarine fans and channels. The wide-spaced seismic data coverage, sparse geological samples and the lack of nearby wells to constrain interpretations means that petroleum plays cannot be analysed in detail.

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