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3D seismic traveltime tomography imaging of the shallow subsurface at the CO2SINK project site, Ketzin, Germany
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. (Geophysics)
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2009 (English)In: Geophysics, ISSN 0016-8033, Vol. 74, no 1, G1-G15 p.Article in journal (Refereed) Published
Abstract [en]

A 3D reflection seismic survey was performed in 2005 at the Ketzin carbon dioxide (CO2) pilot geological-storage site (the CO2SINK project) near Berlin, Germany, to image the geological structure of the site to depths of about 1 km. Because of the acquisition geometry, frequency limitations of the source, and artefacts of the data processing, detailed structures shallower than about 150 m were unclear. To obtain structural images of the shallow subsurface, we applied 3D traveltime tomography to data near the top of the Ketzin anticline, where faulting is present. Understanding the shallow subsurface structure is important for long-term monitoring aspects of the project after CO2 has been injected into a saline aquifer at about 650-m depth. We used a 3D traveltime tomography algorithm based on a combination of solving for 3D velocity structure and static corrections in the inversion process to account for artefacts in the velocity structure because of smearing effects from the unconsolidated cover. The resulting velocity model shows low velocities of 800 1200 m/s in the uppermost shallow subsurface of the study area. The velocity reaches about 1800 m/s at a depth of 60-80 m. This coincides approximately with the boundary between Quaternary units, which contain the near-surface freshwater reservoir and the Tertiary clay aquitard. Correlation of tomographic images with a similarity attribute slice at 150 ms (about 150-m depth) indicates that at least one east-west striking fault zone observed in the reflection data might extend into the Tertiary unit. The more detailed images of the shallow subsurface from this study provided valuable information on this potentially risky area.

Place, publisher, year, edition, pages
2009. Vol. 74, no 1, G1-G15 p.
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97520DOI: 10.1190/1.3026553ISI: 000264521900017OAI: oai:DiVA.org:uu-97520DiVA: diva2:172500
Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2017-01-25Bibliographically approved
In thesis
1. 2D and 3D Seismic Surveying at the CO2SINK Project Site, Ketzin, Germany: The Potential for Imaging the Shallow Subsurface
Open this publication in new window or tab >>2D and 3D Seismic Surveying at the CO2SINK Project Site, Ketzin, Germany: The Potential for Imaging the Shallow Subsurface
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Seismic traveltime inversion, traveltime tomography and seismic reflection techniques have been applied for two dimensional (2D) and three dimensional (3D) data acquired in conjunction with site characterization and monitoring aspects at a carbon dioxide (CO2) geological storage site at Ketzin, Germany (the CO2SINK project). Conventional seismic methods that focused on investigating the CO2 storage and caprock formations showed a poor or no image of the upper 150 m. In order to fill this information gap, an effort on imaging the shallow subsurface at a potentially risky area at the site is the principal goal of this thesis.

Beside this objective, a seismic source comparison from a 2D pilot study for acquisition parameter testing at the site found a weight drop source suitable with respect to the signal penetration, frequency content of the data and minimizing time and cost for 3D data acquisition.

For the Ketzin seismic data, the ability to obtain high-quality images is limited by the acquisition geometry, source-generated noise and time shifts due to near-surface effects producing severe distortions in the data. Moreover, these time shifts are comparable to the dominant periods of the reflections and to the size of structures to be imaged. Therefore, a combination of seismic refraction and state-of-the-art processing techniques, including careful static corrections and more accurate velocity analysis, resulted in key improvements of the images and allowed new information to be extracted. The results from these studies together with borehole information, hydrogeologic models and seismic modeling have been combined into an integrated interpretation. The boundary between the Quaternary and Tertiary unit has been mapped. The internal structure of the Quaternary sediments is likely to be complicated due to the shallow aquifer/aquitard complex, whereas the heterogeneity in the Tertiary unit is due to rock alteration associated with fault zones. Some of the major faults appear to project into the Tertiary unit. These findings are important for understanding the potentially risky anticline crest and can be used as a database for the future monitoring program at the site.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 80 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 550
Keyword
Inversion, Traveltime tomography, 3D seismic surveys, Seismic velocity, Seismic source, CO2SINK project
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-9273 (URN)978-91-554-7276-4 (ISBN)
Public defence
2008-10-07, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00
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Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2016-05-13Bibliographically approved

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Tryggvason, AriJuhlin, Christopher

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