EGU21-6407
https://doi.org/10.5194/egusphere-egu21-6407
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Susceptibility assessment of gas hydrate dissociation occurrence along European continental margins and adjacent areas. GARAH project (GeoERA)

Ricardo León1, Christopher Rochelle2, André Burnol3, Carmen Julia Giménez- Moreno1, Tove Nielsen4, John Hopper4, Isabel Reguera1, Margaret Stewart5, Miguel Llorente1, Pilar Mata1, and Silvia Cervel1
Ricardo León et al.
  • 1Instituto Geologico y Minero de España (IGME), Rios Rosas 23, 28003 Madrid, Spain (r.leon@igme.es; j.gimenez@igme.es; mi.reguera@igme.es; m.llorente@igme.es; p.mata@igme.es; s.cervel@igme.es))
  • 2British Geological Survey (BGS), Environmental Science Centre, Nicker Hill, Keyworth, Nottingham, NG12 5GG (caro@bgs.ac.uk)
  • 3Bureau de Recherches Géologiques et Minières (BRGM), Orléans, France (a.burnol@brgm.fr)
  • 4Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark (tni@geus.dk; jrh@geus.dk)
  • 5British Geological Survey (BGS), The Lyell Centre, Research Avenue South, Edinburgh, EH14 4AP, UK (mstewart@bgs.ac.uk)

The Pan-European gas-hydrate relate GIS database of GARAH project has allowed assessing the susceptibility of seafloor areas affected by hydrate dissociation. This study has been applied as a first step for the hydrate related risk assessment along the European continental margins. Several factors and variables have been taken into account. They have been defined by their relationship with the presence of hydrates below seafloor and weighted depending on the confidence of finding hydrates in this site. The maximum weight (or confidence) has been given to the recovered samples of gas hydrates or hydrate-dissociation evidences such as degassing or liquation structures observed in gravity cores. Seismic indicators of the presence of gas hydrate or hydrocarbon seabed fluid flow such as BSR, blanking acoustic, amplitude anomalies or the presence of geological structures of seabed fluid flow in the neighbouring of the GHSZ have been weighted with a lower value. The theoretical gas hydrate stability zone (GHSZ) for a standard composition for biogenic gas has been taken into account as another control factor and constrain feature. Seafloor areas out of the theoretical GSHZ have been excluded as potential likelihood to be affected by hydrate dissociation processes. The base of GHSZ has been classified as a critical area for these dissociation processes.

The proposed methodology analyses the geological hazard by means of the susceptibility assessment, defined by the likelihood of occurrence of hydrate dissociation, collapses, crater-like depressions or submarine landslides over seafloor. The baseline scenario is that gas hydrate occurrence is only possible in seafloor areas where pressure (bathymetry) and seafloor temperature conditions are inside the theoretical GHSZ. Inside GHSZ, the occurrence of gas hydrate is directly related to the presence of its evidences (direct samples of hydrates) or indicators (eg. pore water and velocity anomalies, BSR, gas chimneys, among others), as well as the occurrence of hydrocarbon fluid flow structures inside GHSZ. Finally, the likelihood of the seafloor to be affect gas hydrate dissociation processes will be major at the base of the GHSZ and in the neighbouring of the gas hydrate evidences and indicators. In order to proof this initial hypothesis, a susceptibility assessment has been carried out throughout map algebra in a GIS environment from a density map of evidences and indicators and the Pan-European map of the GHSZ over seafloor. Specifically, it has been conceived as a segmentation in three levels by quantiles resulting of the addition of the density map of evidences and indicators and the weighted map of the GHSZ over seafloor.

 

Acknowledgment

GARAH project. GeoERA - GeoE.171.002

How to cite: León, R., Rochelle, C., Burnol, A., Giménez- Moreno, C. J., Nielsen, T., Hopper, J., Reguera, I., Stewart, M., Llorente, M., Mata, P., and Cervel, S.: Susceptibility assessment of gas hydrate dissociation occurrence along European continental margins and adjacent areas. GARAH project (GeoERA), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6407, https://doi.org/10.5194/egusphere-egu21-6407, 2021.

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