Utilising spectral decomposition to determine the distribution of injected CO2 at the Snohvit field

Hydrocarbon gas extracted from the Snohvit gas field contains approximately 6% CO2. The gas is piped to shore 150 km away for processing before the extracted CO2 is returned by pipeline for injection. In this study, analysis of the Snohvit CO2 injection program relates to the period prior to the 2009 3D seismic monitoring survey. This followed the injection of 0.5 Mtons of CO2 over 16 months at the base of the Tubaen Formation, a fluvial to tidal sandstone deposit of approximately 100 m thickness. This formation, at a depth of 2565-2665 m below sea surface lies beneath the producing Snohvit gas field. The reservoir proved to be more complex than originally anticipated with significant permeability variations. These have been attributed to quartz cementation, fluvial channelling and the possibility of undetected faults in the formation hindering flow. Horizontal permeabilities range from mDarcies to several Darcies whilst porosity values between 8 % and 20 % are observed (Hansen et al., 2011). Log records confirm that the unit also contains four thin mudstone layers which appear to have hindered flow into the less permeable upper Tubaen.