The Longyearbyen CO2 Lab of Svalbard, Norway - initial assessment of the geological conditions for CO2 sequestration

The aim of the Longyearbyen CO2 Lab pilot project in Spitsbergen has been to evaluate local geological conditions for subsurface storage of the greenhouse gas CO2 . Project activity included the drilling and logging of four slim-hole cored wells, acquisition of new seismic sections and a wide range of laboratory and field studies. The targeted reservoir is a marginal-marine sandstone succession of the Upper Triassic - Middle Jurassic Kap Toscana Group at ≥670 m depth, overlain by thick Upper Jurassic shales and younger shale-rich formations. The reservoir has a sandstone net/ gross of 25-30% and is intruded by thin dolerite sills and dykes. The reservoir and cap-rock succession rises at 1-3° towards the surface and crops out 14-20 km to the northeast of Longyearbyen.

Near the surface, all units are seemingly sealed by permafrost. The reservoir shows considerable underpressure, in the lower part equal to c. 30% of hydrostatic pressure, which indicates good initial sealing conditions. Core samples indicate a ‘tight’ reservoir, with sandstones of moderate porosity (5-18%) and low permeability (max. 1-2 mD). Rock fractures are important for fluid flow. Water-injection tests have indicated good injectivity in the lower part of the reservoir succession (870-970 m depth). The relatively more porous and permeable upper part (670-870 m depth) has only been partly tested. The injectivity increases with the increasing pressure, which suggests that the fractures gradually open and grow under injection. Reservoir pressure compartments indicate bedding-parallel permeability barriers, although these may gradually yield under a growing cumulative pressure. The reservoir storage capacity and its apparent connection with the surface remain to be fully evaluated. On the basis of its preliminary results, the project will proceed with a more advanced research programme.

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