Scientific Discipline: Geophysics
Research Area: Hikurangi Margin, North Island, New Zealand
Research Vessel/Equipment: RV Tangaroa
PI Name and Affiliation: Dr Joerg Bialas, GEOMAR Helmholtz Center for Ocean Research Kiel
Date: 21 - 31 March 2023
Citation from PI: Eurofleets+ Program Oceans provides access to research vessels for small projects that would otherwise be difficult to undertake on regional or ocean class vessels. Engaged program managers at all engaged offices helped a lot to realise the project.
Abstract & Main objectives: The overarching motivation of this cruise is to move towards much improved estimations of gas and gas hydrate distribution and concentration in a typical active subduction margin. Estimates of the global gas hydrate reservoir vary widely as do geophysics-based estimations of hydrate saturation at local-scale gas hydrate reservoirs. The first aim is to test the hypothesis that: The co-existence of gas and gas hydrate within gas hydrate accumulations is the reason for the discrepancy in predicting hydrate saturation from seismic-based and CSEM (controlled source electromagnetic) -based methods. The converted S-wave data will be acquired using a high-frequency source (150 cu-in GI airgun), short shot intervals (⁓10 m) and closely spaced OBS nodes (100 m spacing). The second aim is to determine the dominant mechanism(s) driving concentrated gas hydrate formation within an accretionary wedge setting. The hypothesis that concentrated deposits are formed by free gas being injected into the gas hydrate stability zone (GHSZ) by “long-range” gas migration rather than by “short-range” methane migration will be investigated. Existing seismic reflection data show indications of gas injection, but seismic resolution limitations in those data make it unclear how free gas is distributed and whether “tuning effects” partially cause the seismic reflectivity observed.