Gas migration from reservoirs towards the seabed is known to influence the local sedimentary regime, seabed morphology, seabed stability and the diversity and number of benthic organisms. Geological characterization by sediment coring and high-resolution 3D seismic imagery (tomography) in areas with seafloor expression of fluid flow above known gas hydrate reservoirs, as well as in control areas with no indication of such flow, are crucial to reach further knowledge on this task. Migration of gas from reservoirs to the seabed is known to have influenced the local sedimentary regime and the diversity and number of benthic micro-organisms. Such information is important in order to determine what these seabed structures reflect in terms of migration of gas as the microfossils are expected to bear the signature of the history seeping activities in the area. Knowledge on gas migration, and its rate, is therefore crucial for evaluation of prospects and geohazards, however so far few detailed studies on this topic have been carried out for cold water systems like the NBS margin. Geochemical information is needed for diagnostics of seep targets, assessment of migration pathways and characterization of sources of gaseous hydrocarbons. Knowledge of the source of the gases incorporated in the hydrates is crucial for developing precise quantitative models and understanding their origin. The molecular and isotopic composition of the gases will clearly indicate whether their origin is thermogenic, biogenic or mixed, since the microbial gas will be strongly dominated by methane while natural gas seeps contain the whole sequence of hydrocarbon gases. Carbon isotopic compositions and presence of CO₂ and acetate in the pore-waters are also important parameters, together with the monitoring of C15+oil hydrocarbons in the sediments. Analysis of water samples for hydrocarbon gas compositions which can be used as a proximity indicator for hydrate occurrence can be developed into a valuable diagnostic tool. Thus, the goals of this project were: (1) to study any gas migration along transects of known abundances of gas hydrates, and (2) to demonstrate the apparent relationship between subsurface gas hydrate reservoirs and seep features observed at the seabed.

Project led by Prof. Haflidi Haflidason (University of Bergen, Norway). The project was funded by The Research Council of Norway.