3D gas hydrate petroleum systems modelling at the New Zealand Hikurangi subduction margin

Abstract

Gas hydrate petroleum systems modelling is an approach that uses integrated thermogenic and microbial gas generation and migration modelling to predict gas hydrate formation and distribution. This approach has been used to predict gas hydrate formation along the New Zealand Hikurangi Margin, where the presence of gas hydrates has been established based on observed widespread bottom simulating reflectors (BSRs) and velocity anomalies suggesting the presence of free gas beneath concentrated hydrate deposits. To construct a 3D basin model using PetroModTM software, we have mapped key sedimentary horizons, BSRs, and the distribution of basin floor and channel sandstones across the basin. The thermal model has been calibrated to the mapped depth of the BSR. The modelled temperature history of the margin has been used to predict thermogenic gas generation from potential Cretaceous‒Paleogene source rocks and biogenic gas generation from Plio-Pleistocene sediments. The trench basin and the rapidly uplifting thrust anticlines represent ideal environments for gas hydrate accumulation. The trench basin has been filled rapidly during the Plio-Pleistocene with sediments distributed mainly by the Hikurangi Channel system. Older stacked channel deposits provide potential fluid migration pathways and high sedimentation rates enhance the generation of biogenic methane. In addition, we identify significant potential for generation of thermogenic gas from sediments originally deposited seaward of the Mesozoic subduction margin that are now subducted in the Modern margin, charging the gas hydrate system. Widespread gas hydrates at the base of the hydrate stability zone are predicted to be charged largely from biogenic gas generated underneath the base of hydrate stability. In addition, the model predicts three areas that are most likely to host concentrated gas hydrate accumulations consistent with strong BSR reflectivity. Concentrated hydrate accumulations in thrust anticlines are also predicted to be charged largely from biogenic gas, but with potential contributions of thermogenic gas. For the charge of structures seaward of the plate boundary, the presence of permeable carrier beds becomes more important. In this regard, the Hikurangi Margin is unique, as the modern plate boundary incorporates sediments deformed during Mesozoic subduction beneath Gondwana. Cretaceous structures are predicted to focus the migration of thermogenic, and to a lesser degree biogenic gas into deformed Neogene sediments and buried sandstones of the Hikurangi Channel system, where they form additional concentrated gas hydrate deposits.

AAPG Datapages/Search and Discovery Article #90348 © 2019 AAPG Asia Pacific Region Geosciences Technology Workshop, Gas Hydrates – From Potential Geohazard to Carbon-Efficient Fuel?, Auckland, New Zealand, April 15-17, 2019