Seismic expression and geomorphology of igneous bodies: A Taranaki Basin, New Zealand, case study

Very little research has been done on volcanic rocks by the oil industry due to the misconception that these rocks cannot be good reservoirs. However, in the past two decades, significant quantities of hydrocarbons have been produced from volcanic rocks in China, New Zealand, and Argentina. In frontier basins, volcanic piles are sometimes misinterpreted to be hydrocarbon anomalies and/or carbonate buildups. Unlike clastic and carbonate systems, the 3D seismic geomorphology of igneous systems is only partially documented. We have integrated 3D seismic data, well logs, well reports, core data, and clustering techniques such as self-organizing maps to map two distinct facies (pyroclastic and lava flows), within a Miocene submarine volcano in the Taranaki Basin, New Zealand. Three wells; Kora-1-3 drilled the pyroclastic facies within the volcano encountering evidence of a petroleum system, whereas the Kora-4 well drilled the lava-flow facies, which was barren of hydrocarbons. By integrating results from geochemistry and basin modeling reports prepared for Crown Mineral, New Zealand, we concluded that the reason that Kora-4 was dry was due to a lack of source charge - not to the absence of reservoir quality. Moreover, the Kora-1 well drilled a thick sequence (> 1000 m) of pyroclastic flows in this submarine volcano by chance and found high peaks of gas in themudlogs near the top 25mof this sequence. A long-term test in this upper volcanic section resulted in 32 API oil flow of 668 barrels of oil per day for 254 h - a result that challenges the misconception that volcanic rocks cannot be good reservoirs.