Gas seeps in the Barents Sea – how does the geology influence the natural and well related seeps?

Abstract

This thesis examined gas flares found in the Cruise log 20-2 from CAGE and correlated them to subsurface seismic data in south of Barents Sea. The cruise log passed several hydrocarbon discoveries/fields such as Goliat, Caurus/Langlitinden, Norvarg and Wisting/Hanssen. The aim of the thesis is to investigate the relationship between shallow geology and the observed gas flares and seabed leakages. Multibeam echosounder data and Water Column Imaging (WCI) is used to hunt the flares along the cruise, 12 flare locations are detected mostly over the hydrocarbon discoveries/fields. Well data is also used to investigate if or how some of the flares might be connected to the drilling activities. However, not all amplitude anomalies in the WCI are gas flares, thus a protocol to define gas flares in WCI is applied. Tectonic movements and uplift in the study area cause faulting and fault reactivation, which open migration pathways from reservoir levels and fluids escape towards the seabed. Additionally, erosion and removal of as much as 2km sediments reduce the overburden pressure, causing the reservoir fluids to expand and escape. Repeated glaciation events during the last ice age formed an unconformity surface (URU) where many potential shallow gas accumulations locate. Shallow accumulation/seismic anomaly along the URU is the main target of this thesis. Some of the observed gas flares are closely related to hydrocarbon wells in the study area, gas might migrate through well-induced fractures along the wellpath. The relationship between deeper gas accumulations, hydrocarbon wells, shallow gas accumulation and potential leakage of gas into the water column is not straight forward. More empirical data and investigations needs to be applied to increase the knowledge of these interrelated and complicated processes