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Comparison of surface seismic sources at the CO2SINK site, Ketzin, Germany
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
GeoForschungsZentrum (GFZ), Potsdam, Germany.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
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2009 (English)In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 57, no 1, 125-139 p.Article in journal (Refereed) Published
Abstract [en]

In 2004 three seismic surface sources (VIBSIST, accelerated weight drop and MiniVib) were tested in a pilot study at the Ketzin test site, Germany, a study site for geological storage of CO2 (EU project CO2SINK). The main objectives of this pilot study were to 1) evaluate the response of the Ketzin site to reflection seismics, especially at the planned injection depth, 2) test different acquisition parameters and 3) use the results to guide the planning of the 3D survey. As part of these objectives, we emphasize the source performance comparison in this study. The sources were tested along two perpendicular lines of 2.4 km length each. Data were acquired by shooting at all stations (source and receiver spacing of 20 m) on both lines, allowing common-midpoint stacked sections to be produced. The sources' signal characteristics based on signal-to-noise ratio, signal penetration and frequency content of raw shot records were analysed and stacked sections were compared. The results show that all three surface sources are suitable for reflection seismic studies down to a depth of about 1 km and provide enough bandwidth for resolving the geological targets at the site, i.e., the Weser and Stuttgart Formations. Near surface conditions, especially a thick weathering layer present in this particular area, strongly influence the data quality, as indicated by the difference in reflectivity and signal-to-noise ratio of the two common-midpoint lines. The stacked sections of the MiniVib source show the highest frequency signals down to about 500 ms traveltime (approximately 500 m depth) but also the shallowest signal penetration depth. The VIBSIST source generates signals with the highest signal-to-noise ratio and greatest signal penetration depth of the tested sources. In particular, reflections below 900 ms (approximately 1 km depth) are best imaged by the VIBSIST source. The weight drop performance lies in between these two sources and might be recommended as an appropriate source for a 3D survey at this site because of the shorter production time compared to the VIBSIST and MiniVib sources.

Place, publisher, year, edition, pages
2009. Vol. 57, no 1, 125-139 p.
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97518DOI: 10.1111/j.1365-2478.2008.00737.xISI: 000261447600010OAI: oai:DiVA.org:uu-97518DiVA: diva2:172498
Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2017-12-14Bibliographically 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
Opponent
Supervisors
Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2016-05-13Bibliographically approved
2. Geological Structure and Time-Lapse Studies of CO2 Injection at the Ketzin Pilot Site, Germany
Open this publication in new window or tab >>Geological Structure and Time-Lapse Studies of CO2 Injection at the Ketzin Pilot Site, Germany
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

3D seismic time-lapse surveys (“4D seismics”) are an essential tool for large scale reservoir characterization. The target reservoir of the Ketzin pilot project for CO2 storage is a saline aquifer of the heterogeneous Stuttgart Formation (Upper Triassic) in the Northeast German Basin. The focus of this project is on testing and further developing monitoring CO2 storage technologies. For time-lapse seismic monitoring, three seismic surface sources were characterized with respect to S/N (signal to noise) ratios, signal penetration, and frequency content by analysis of raw shot gathers and stacked sections along two lines at the Ketzin site. Differences in reflectivity between these 2D lines reflect the differences in the nature of the sources tested and how they influence the signal bandwidth (resolution) and signal energy. All three sources image the target horizon. The weight drop source was recommended as the primary source for 3D surveys based mainly on logistics and cost. Results of processing, including equalization of a 4D (3D time-lapse) data set from the Ketzin site and cross-correlation, indicate that the injected CO2 can be monitored. The highly irregular amplitude response on the time-lapse data can be attributed to the reservoir heterogeneity. Time-lapse seismic processing, petrophysical measurements on core samples and geophysical logging of CO2 saturation levels allow for an estimate of the total amount of CO2 visible in the seismic data to be made. In spite of some uncertainty, the close agreement between the injected and observed amount is encouraging for quantitative monitoring of a CO2 storage site using seismic methods. By integrating seismic modeling and multiphase fluid flow simulations, the impact of the reservoir temperature on the 4D seismic data from Ketzin was estimated. The modeled time-lapse seismic differences for two temperature scenarios present in the reservoir are minor regarding the qualitative analysis. However, the influence of temperature on the volumetric estimation of the CO2 using the 4D seismic data is significant. Future issues to be considered include expanding the temperature range (34-38°C in this study) to be investigated and the resulting effects on the seismic response, as well as the role of the reservoir heterogeneity. In addition, it would be important to investigate the impact of temperature on the CO2 storage at other sites with favorable P-T conditions in the reservoir. Further seismic modeling using results of petrophysical experiments for estimating the effect of the CO2 injection at the Ketzin site on the AVA/AVO response on time lapse seismic data was performed. Two effects were considered: the CO2-saturation- and the pore-pressure-related effects. The results indicate that it is worth investigating if it is possible to discriminate between these effects on future 3D repeat surveys at the Ketzin site.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 96 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1026
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-196127 (URN)978-91-554-8613-6 (ISBN)
Public defence
2013-04-19, Hambergsalen, Villavagen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2013-03-27 Created: 2013-03-04 Last updated: 2016-07-20Bibliographically approved

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Ivanova, AlexandraJuhlin, Christopher

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