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Architecture of Buried Volcanoes as a Factor in Petroleum Systems Analysis: Cases from New Zealand Basins

Abstract

Petroleum systems analysis needs to account for coincident volcanism in many diverse situations around the world. New Zealand’s mainly offshore sedimentary basins, with extensive publicly-available seismic coverage and well data, contain numerous and widespread volcanic edifices and complexes - Miocene and younger arc related in the northwest (including the productive Taranaki Basin), and more widely, a late Cretaceous and younger intraplate basaltic suite. Volcanism introduces complexity to all aspects of petroleum systems analysis. Emplacement of magma beneath and/or within a sedimentary basin frequently causes domal, stratigraphic and paleogeomorphic traps, affects source rock maturation and hydrocarbon migration, and may either degrade or enhance reservoir quality, and give rise to lateral permeability barriers. Seismic interpretation of buried volcanic edifices within Taranaki and Canterbury basins reveals their architecture in terms of pre-, syn- and post-magmatic stages, and an assemblage of elements (geobodies) which can be ascribed petrophysical properties from an extensive analog data set. Where hydrocarbon maturation, expulsion and migration from pre-magmatic source formations results from post-magmatic burial, buried volcanic edifices, which are generally associated with structural doming, are important elements for migration and entrapment modelling. By mapping the fundamental architectural elements of buried volcanoes, the effects of their emplacement on coincident petroleum systems can be predicted. Detailed analog model inputs have been derived from 3D and 2D seismic data sets calibrated by exploration well data and further informed by outcrop analogs.