Reservoir Characterisation of the East Coast and Pegasus basins, Eastern North Island, New Zealand

Abstract

This integrated study focuses on the reservoir characteristics of the East Coast and Pegasus basins, located on- and offshore eastern North Island, New Zealand. The compilation of existing GNS Science knowledge and data includes paleogeographic maps, seismic interpretations, petrophysical analysis of both conventional wireline and FMI image logs in exploration wells, poroperm analysis and reservoir potential of likely Neogene and Cretaceous formations, found in both onshore and offshore parts of the basins. Integration of onshore/outcrop analogues with subsurface data sets (e.g. wireline logs, seismic interpretation) is undertaken, with the aim of building a model for predicting reservoir distribution and quality in the region. Over 300 known onshore oil and gas seeps occur in eastern North Island, New Zealand, indicating an active petroleum system. Although more than 40 wells have been drilled onshore, only three have been drilled offshore, all with significant gas shows. Reservoir units mainly comprise Neogene clastic rocks, such as deepwater slope (channel and overbank) and basin floor fans. Shelfal sands have been identified as possible reservoirs onshore however they are not thought to be extensive offshore. Fractured reservoir potential is present locally in the form of Miocene limestones. Recent GNS Science seismic interpretation studies indicate that Cretaceous aged units are present offshore, although more data are needed to better understand their reservoir potential, given that offshore wells have not yet encountered rocks of this age. In addition, a promising gas hydrate province exists offshore, where widespread bottom simulating reflections corresponding to a hydrate layer are observed in seismic data, and where methane seep sites indicate focused fluid flow that may have created concentrated gas hydrate deposits. However, the perceived lack of quality reservoir facies may be hindering the unlocking of the region's petroleum potential.

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