Tampen, the highest gas flaring region in the North Sea: distribution, characterization and fluid migration mechanisms

The Norwegian Continental Shelf (NCS) is a region with 100,000s of active and extinct natural occurring methane seeps (NOMS) that are sustaining oases of unique ecosystems. These emissions are sourced from thermogenic and microbial methane. In addition, vigorous seafloor gas emissions (i.e., gas flares) are also found at, or in the vicinity of numerous wells (i.e. WAMS: well-associated methane seep). The NCS hosts ~10.000 wells, ~2,000 of these are already plugged and abandoned, and 2,245 operating wells heading for decommissioning in the next decades. Here we integrate the results of a multidisciplinary surveys conducted in the Tampen area (western Norwegian Channel) where the highest NOMS and WAMS and related gas flare concentration has so far been observed.

We combine a large (800 km²) multibeam and water column survey with high resolution seismic profiles and gas geochemistry analyses from active seepage sites. A complete mapping of the area reveals the presence of nearly 2000 flares, 175 of which are WAMS. The highest density is observed in the western side of the Tampen region where up to 20 flares per km² can be mapped. Geochemical analyses show that methane is the main seeping gas with a microbial signature (d¹³C_CH4 as low as -91 ‰) and pore water profiles (sulfate and dissolved inorganic carbon-DIC concentrations and d¹³C_DIC) in gravity cores indicated intense anaerobic oxidation of dissolved methane in the shallow subsurface at 2-4 m bsf. Sediment incubations showed a widespread potential for aerobic and anaerobic MO as well as methane production in the top 20 cm, which was further confirmed by molecular biological analyses. We infer a shallow origin of the gas trapped in the glaciogenic wedge of the west shoulder of the Norwegian Channel. This shallow gas charge has also been observed on the reflection seismic data. Selected profiles have been used to trace back the potential fluid migration pathways from deeper units where reservoirs are sited. We suggest that deeper-sited tectonic discontinuities, clinoforms, and sedimentary interfaces promote the vertical and lateral fluid migration, respectively.

These findings are relevant to understanding the environmental impact of gas flare activity, future CO₂ and hydrogen storage planning in depleted reservoirs, and mitigation strategies for gas seepage on the NCS.