Reassessment of Exploration Risks in Taranaki Basin Related to Gondwana Margin Evolution and Establishment of an Active Plate Boundary in New Zealand Using Integrative 3-D Basin Modelling

Abstract

The discovery of the giant Maui gas-condensate field in 1969 initiated a long history of petroleum exploration in offshore Taranaki Basin. The large discovery was followed by many smaller finds but also by a very large number of dry wells through to present-day. Factors controlling prospectivity are still insufficiently understood despite 400 wells being drilled. Recent remapping of the southern Taranaki Basin as part of the GNS Science 4D Taranaki project has identified rapid changes in basin evolution and illustrated the structural complexity of the basin. Heterogeneities in the crust inherited from the Mesozoic Gondwana margin subduction system directly impact on heat flow and heat generation potential. The architecture of the crust was also affected by Late Cretaceous rifting related to the opening of the Tasman Sea as well as the initiation of the present-day convergent plate margin. These processes influenced the evolution of heat flow through time whilst increasing the thermal heterogeneity in the basin. In addition to heat flow, variability in source rock properties and a complicated petroleum plumbing system add further complexity. Although the capacity of the Late Cretaceous Rakopi Formation to charge the Maui Field as well as other accumulations has been demonstrated, the spatial variability of the source rock potential of the Rakopi Formation is not well known. The change from rifted to convergent margin has resulted in fragmentation and inversion of parts of the southern Taranaki Basin. Change in basin configuration has affected migration pathways and has likely compromised the integrity of several structures. Many factors such as crustal composition and heat generation potential are currently mapped only very broadly. We therefore choose a scenario-based basin modelling approach to illustrate risks to petroleum expulsion and charge of traps using PetroMod software. Instead of merely reproducing charge, which very often leads to overly optimistic predictions for untested prospects, we identify basin conditions that could prevent charge and assess their geological likelihood in the context of recent research on plate boundary evolution. We integrate thermal evolution and petroleum migration scenarios to better reflect the number of dry wells in the basin and to better understand exploration risks.

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