Geochemical Enhancement of Seismic Data Interpretations of Gas Hydrate Loadings; Proof of Concept Along the Eastern Coast of New Zealand

Abstract

Through world, coastal oceans there have been extensive surveys with the application of seismic data to predict deep sediment gas hydrate loading. Over the past 10 years comparisons of seismic data and geochemistry show there is a need to combine these data for a more thorough understanding of the deep sediment gas hydrate loading. Initial observations in predicting hydrate presence with integration of seismic and geochemistry data off the mid Chilean margin suggested gas hydrate loading could be greater at a location where seismic data showed moderate gas blanking. On the Atwater Valley in the Gulf of Mexico geochemical assessment showed a region with a strong vertical rise in the BSR to be a site where gas hydrate are likely not stable as a result of salt diapir intrusions creating gas hydrate instability and higher vertical methane advection. Here we present a series of data along the eastern coast of New Zealand that include seismic profiles, geochemistry, controlled source electromagnetics, and heatflow to assess gas hydrate loading. This comparison of locations shows remarkable inconsistencies in the data sets applied to gas hydrate predictions. Through these locations comparisons include: 1) The Porangahau Ridge in the Hikurangi Margin where geochemical profiles focusing anaerobic methane oxidation display moderate vertical gas migration in a region that strong seismic reflection, active heat flow, and controlled source electromagnetic data suggest deep gas hydrate loading and active fluid and gas advection. 2) Mahia Peninsula, located further south from the Porangahau Ridge show strong similarity in geochemical and seismic data for assessment vertical methane fluxes in two different transects. However porewater geochemical data from these transects compared to a location where seismic data indicates no gas hydrate loading are similar. A more in depth assessment of vertical fluid and gas migration in this area will be compared with porewater oxygen-18 stable isotope data. 3) Chatham Rise, a region where published seismic data was believed to contain gas hydrate loading was found to have a total absence of vertical methane migration. In this location, radiocarbon data of shallow sediment carbonate and organic carbon suggest a potential for carbon dioxide migration. This observation has resulted in plans for a paleo-geochemical study to understand vertical carbon dioxide migration over climate cycles.

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