Ulrik Gregersen

Geological Characterization of CO2 Storage Sites: Lessons from Sleipner, Northern North Sea

Publisher Summary This chapter draws some generic conclusions on reservoir characterization based on the Sleipner operation where CO 2 is being injected into the Utsira Sand. Regional mapping and petrophysical characterization of the reservoir, based on 2D seismic and well data, enable gross storage potential to be evaluated. Site specific injection studies, however, require precision depth mapping based on 3D seismic data and detailed knowledge of reservoir stratigraphy. Stratigraphical and structural permeability barriers, which are difficult to detect prior to CO 2 injection, can radically affect CO 2 migration within the aquifer. The Sleipner sequestration operation is the focus of the SACS (Saline Aquifer CO 2 Storage) project, whose aims include monitoring and modeling the fate of the injected CO 2 and regional characterization of the Utsira reservoir and its caprock. This chapter describes some of the results of the investigations and draws out some generic aspects of geological reservoir characterization, which are particularly applicable to CO 2 injection into flat-lying aquifers of regional extent.

A contourite drift system on the Baffin Bay–West Greenland margin linking Pliocene Arctic warming to poleward ocean circulation

Terrestrial records from the Canadian Arctic Archipelago indicate that a temperate and moist climate prevailed during the Pliocene, i.e., before the intensification of Northern Hemisphere glaciations, but the controlling factors causing these conditions remains elusive. Here we present marine seismic reflection evidence of contiguous kilometer-scale sedimentary drifts, or contourites, buried below the West Greenland shelf, which relates high-latitude Pliocene warmth to intense geostrophic currents along the eastern Baffin Bay margin. Seismic to borehole correlation indicates that enhanced current-induced deposition began during the middle Miocene, ca. 17–15 Ma, and terminated during the late Pliocene onset of global cooling. The transition from along-slope sediment transport to trough-mouth fan progradation designates the onset of Greenland Ice Sheet glaciers advancing across the continental shelf and coincides with increasing iceberg productivity in Baffin Bay and the Nordic Seas from 3.3 to 2.7 Ma. Our results suggest that the Baffin Bay–West Greenland margin formed a late Neogene passageway for persistent ocean boundary currents, and we infer that the Pliocene high-latitude warmth was to a significant extent caused or enhanced by advection of subtropical heat and moisture to the Arctic regions. Attenuation of the poleward heat flux conveyed by the paleo–current system may have been critical for allowing glacial buildup in the Canadian Arctic and northern Greenland during the late Pliocene. We further surmise that vertical tectonic adjustments of the continental margin played a role in this attenuation, which eventually caused the demise of meridional ocean circulation through Baffin Bay.

The subtle play-potential of Upper Jurassic–Lower Cretaceous block-faulted turbidites in the Danish Central Graben, North Sea

Abstract The Gertrud Graben, in the Danish Central Graben, was formed during the Early Volgian by extensional block rotation. The basin was bounded by series of NW–SE trending normal faults, the resultant bathymetry of which controlled the depocenters of Volgian–Ryazanian turbidites in the Farsund Formation. Seismic correlation to basin marginal locations in the Jeppe-1 and Gwen-2 wells suggests that high amplitude horizons and high acoustic impedance values in the depocenters of the turbidites probably reflect accumulation of sand-rich turbidites. The high amplitude and impedance values, calculated from seismic inversion, are locally concentrated below minor closures. A short horizontal impedance horizon within the turbidite depocenter and below a closure possibly indicates hydrocarbon accumulation, adjacent to a well-known Jurassic source-rock the ‘Hot Unit’ (Bo member) in the Central Graben area. The turbidites seem to have been transported mainly from the north, possibly from positive areas in the southern Norwegian Central Graben area. Subsequent Late Ryazanian block faulting and local compressional tectonics caused erosional truncation of upper parts of the turbidites on footwall blocks, but preserved parts of the basin-axial turbidites from erosion in the hangingwall positions.

Regional Study of the Neogene Deposits in the Southern Viking Graben Area - a Site for Potential CO2 Storage

Since 1996 Statoil has injected CO2 separated from gas of the Sleipner Vest field into saline reservoir sands of the Utsira Forrnation in the central North Sea at a depth of approximately 900 m. This is the first case of industrial scale CO2 storage in the world (1 million tons per year). The Saline Aquifer CO2 Storage (SACS) project is conducted by a consortium of oil companies and research institutions. This paper presents regional geological interpretation in the southem Viking Graben area. Sands of the Mio-Pliocene Utsira Formation and the Nordland Shale have been identified and their stratigraphical architecture outlined from seismic sections and well-logs. Detailed geophysical and geological aspects at the injection site are treated in Arts et al. (this volume) and Brevik et al. (this volume).