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Quantitative evaluation of thin-layer thickness and CO2 mass utilizing seismic complex decomposition at the Ketzin CO2 storage site, 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.
CNOOC Research Institute.
GFZ German Research Centre for Geosciences.
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(English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246XArticle in journal (Refereed) In press
Abstract [en]

Determining thin layer thickness is very important for reservoir characterization and CO2 quantification. Given its high time-frequency resolution and robustness, the complex spectral decomposition method was applied on time-lapse 3D seismic data from the Ketzin pilot site for CO2 storage to evaluate the frequency-dependent characteristics of thin layers at the injection level. Higher temporal resolution and more stratigraphic details are seen in the all-frequency and monochromatic reflectivity amplitude sections obtained by complex spectral decomposition compared to the stacked sections. The mapped geologic discontinuities within the reservoir are consistent with the preferred orientation of CO2 propagation. Tuning frequency mapping shows the thicknesses of the reservoir sandstone and gaseous CO2 is consistent with the measured thickness of the sandstone unit from well logging. An attempt to discriminate between pressure effects and CO2 saturation using the extracted tuning frequency indicates that CO2 saturation is the main contributor to the amplitude anomaly at the Ketzin site. On the basis of determined thickness of gaseous CO2 in the reservoir, quantitative analysis of the amount of CO2 was performed and shows a discrepancy between the injected and calculated CO2 mass. This may be explained by several uncertainties, like structural reservoir heterogeneity, a limited understanding of the complex subsurface conditions, error of determined tuning frequency, the presence of ambient noise and ongoing CO2 dissolution.

Keyword [en]
Inverse theory, Fourier analysis, Image processing, Computational seismology
National Category
Geophysics
Identifiers
URN: urn:nbn:se:uu:diva-300995DOI: 10.1093/gji/ggw274OAI: oai:DiVA.org:uu-300995DiVA: diva2:953159
Available from: 2016-08-17 Created: 2016-08-17 Last updated: 2016-09-02
In thesis
1. 3D Time-lapse Analysis of Seismic Reflection Data to Characterize the Reservoir at the Ketzin CO2 Storage Pilot Site
Open this publication in new window or tab >>3D Time-lapse Analysis of Seismic Reflection Data to Characterize the Reservoir at the Ketzin CO2 Storage Pilot Site
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

3D time-lapse seismics, also known as 4D seismics, have great potential for monitoring the migration of CO2 at underground storage sites. This thesis focuses on time-lapse analysis of 3D seismic reflection data acquired at the Ketzin CO2 geological storage site in order to improve understanding of the reservoir and how CO2 migrates within it.

Four 3D seismic surveys have been acquired to date at the site, one baseline survey in 2005 prior to injection, two repeat surveys in 2009 and 2012 during the injection period, and one post-injection survey in 2015. To accurately simulate time-lapse seismic signatures in the subsurface, detailed 3D seismic property models for the baseline and repeat surveys were constructed by integrating borehole data and the 3D seismic data. Pseudo-boreholes between and beyond well control were built. A zero-offset convolution seismic modeling approach was used to generate synthetic time-lapse seismograms. This allowed simulations to be performed quickly and limited the introduction of artifacts in the seismic responses.

Conventional seismic data have two limitations, uncertainty in detecting the CO2 plume in the reservoir and limited temporal resolution. In order to overcome these limitations, complex spectral decomposition was applied to the 3D time-lapse seismic data. Monochromatic wavelet phase and reflectivity amplitude components were decomposed from the 3D time-lapse seismic data. Wavelet phase anomalies associated with the CO2 plume were observed in the time-lapse data and verified by a series of seismic modeling studies. Tuning frequencies were determined from the balanced amplitude spectra in an attempt to discriminate between pressure effects and CO2 saturation. Quantitative assessment of the reservoir thickness and CO2 mass were performed.

Time-lapse analysis on the post-injection survey was carried out and the results showed a consistent tendency with the previous repeat surveys in the CO2 migration, but with a decrease in the size of the amplitude anomaly. No systematic anomalies above the caprock were detected. Analysis of the signal to noise ratio and seismic simulations using the detailed 3D property models were performed to explain the observations. Estimation of the CO2 mass and uncertainties in it were investigated using two different approaches based on different velocity-saturation models.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 73 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1407
Keyword
CO2 storage, 3D Time-lapse (4D), Reservoir characterization, Seismic simulation, Spectral decomposition, Wavelet phase, Tuning frequency, Thin-layer thickness, Seismic monitoring, Seismic processing, Quantitative interpretation
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-301003 (URN)978-91-554-9658-6 (ISBN)
External cooperation:
Public defence
2016-09-30, Hambergsalen, Geocentrum, Villavagen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2016-09-07 Created: 2016-08-17 Last updated: 2016-09-13

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