NJG92-4-02
2012
Subsurface structures of the Longyearbyen CO2 Lab study area in Central Spitsbergen (Arctic Norway), as mapped by reflection seismic data
92
4
pp. 377-389
978-82-92-39476-2

The Longyearbyen CO2 Lab is a joint project between the University Centre in Svalbard and a consortium of partners. The project aims to investigate the possibilities of Carbon Capture and Storage (CCS) in the vicinity of Longyearbyen (Svalbard, Norway). In this contribution, seismic data from the Adventdalen area of Central Spitsbergen are combined with drillhole and outcrop data to give a thorough picture of the subsurface structural geometry close to the planned injection site of the Longyearbyen CO2 Lab. So far, 12 km of seismic data and one vertical seismic profile have been recorded, and four wells have been drilled, logged and cored to a maximum depth of 980 m. Several clear regional reflectors revealed from the snow-streamer seismic data correlate with boundaries within the lithological succession in drillcores retrieved from the boreholes.

This link between seismics and drillcore units allows the construction of a general velocity model for the Cretaceous to Upper Triassic succession, covering a 1000 m vertical section. Velocities in the bedrock succession are noticeably high, spanning from around 3500 m s-1 in the upper 200 m, to c. 4000 m s-1 between 200 and 650 m depth, and to 4200–4500 m s-1 below 650 m total depth. Geometrically, the open 2D seismic coverage shows no local physical closures/structures influencing the succession. Therefore, the potential reservoir rocks of the Upper Triassic De Geerdalen Formation, located at a depth of 672–980 m in drillhole Dh4 of Adventdalen, seem to follow the regional trend in that the constructed formation top surface dips gently to the southwest. Around 20 km to the northeast, this unit crops out in mountain sides. The seismic data also show one or more, laterally extensive, dolerite intrusions that are highly reflective, masking underlying reflectors. Thin (0.5 to 2.5 m) intrusions encountered in the basal part of the De Geerdalen Formation in drillhole 4 (Dh4) are, on the other hand, below seismic resolution. Locally, the intrusions could have an inverse saucer geometry, as possibly seen in outcrops. One of these reflective intrusions has its highest point some 50–100 m below the De Geerdalen Formation in Adventdalen

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