Gary Kirby

Seismic monitoring at the Sleipner underground CO2 storage site (North Sea)

Abstract The growing emissions of greenhouse gases, especially CO2, are seen worldwide as one of the major causes of climate change. International treaties like the Kyoto Protocol are supposed to contribute to reducing the emission of greenhouse gases. Underground sequestration has the potential to play an important role in keeping large volumes of CO2 from escaping into the atmosphere in the short term. The first case of industrial scale CO2 storage in the world (close to one million tonnes per year since 1996) is taking place at the Sleipner underground CO2 storage site in the North Sea offshore Norway. Careful monitoring of the behaviour of the storage facility is required to establish its safety. To this end, two time-lapse seismic surveys have been acquired; the first repeat survey was completed in October 1999 and the second in October 2001. The presence of CO2 beneath thin intra-shale layers within the reservoir has caused significant changes both in reflection amplitudes (up to a factor 10) and in travel time (more than 40ms) through the CO2 plume (the velocity push-down effect). Some aspects of the interpretation of these time-lapse seismic surveys will be presented here.

Review of monitoring issues and technologies associated with the long-term underground storage of carbon dioxide

Abstract Large-scale underground storage of CO2 has the potential to play a key role in reducing global greenhouse gas emissions. Typical underground storage reservoirs would lie at depths of 1000 m or more and contain tens or even hundreds of millions of tonnes of CO2. A likely regulatory requirement is that storage sites would have to be monitored both to prove their efficacy in emissions reduction and to ensure site safety. A diverse portfolio of potential monitoring tools is available, some tried and tested in the oil industry, others as yet unproven. Shallow-focused techniques are likely to be deployed to demonstrate short-term site performance and, in the longer term, to ensure early warning of potential surface leakage. Deeper focused methods, notably time-lapse seismic, will be used to track CO2 migration in the subsurface, to assess reservoir performance and to calibrate/validate site performance simulation models. The duration of a monitoring programme is likely to be highly site specific, but conformance between predicted and observed site performance may form an acceptable basis for site closure.

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.

The case for underground CO 2 sequestration in northern Europe

Abstract In northern Europe numerous industrial point sources of CO2 surround the North Sea Basin, which contains a number of viable underground sequestration opportunities. These include injection into depleted oil and gas fields and into major regional aquifers; the latter probably offering the greatest ultimate storage potential. At the Sleipner gas field, CO2 is being injected into the Utsira Sand, a large saline aquifer. More than 6 Mt of CO2 have currently been injected, with a projected final target of about 20 Mt. Time-lapse seismic reflection data are being used to monitor the operation and have provided clear images of the CO2 plume and its development with time. Moreover, CO2 volumetrics derived from the seismic data are consistent with the well injection figures. In conjunction with reservoir simulation studies, time-lapse seismic monitoring seems, therefore, to offer an effective means of predicting the future growth, migration and dispersion of the CO2 plume. Another important aquifer, the Bunter Sandstone, stretches from Britain to Poland. In the UK sector alone, the pore volume in structural closures is equivalent to about 350 years’ worth of current CO2 emissions from UK power generation. Industrial CO2 sources in northern Europe are well placed to exploit these major subsurface reservoirs and European countries are technically very well equipped to use and develop this emerging technology.

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).