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A feasibility and efficiency study of seismic waveform inversion for time-lapse monitoring of onshore CO2 geological storage sites using reflection seismic geometry
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.
Vibrometric Oy, Finland.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The monitoring of the CO2 distribution at depth is very important for onshore geological storage of CO2. Seismic methods are effective monitoring tools during and after the injection process, but are generally expensive and time consuming to perform. In this paper we perform a series of synthetic experiments in order to compare the seismic waveform inversion method with conventional seismic monitoring methods for time-lapse monitoring at CO2 geological storage sites. We mainly focus our study on seismic data sets with typical reflection acquisition geometries, that is far offset data is limited. Three synthetic seismic data sets (consisting of one baseline and two repeats) were generated by a third party 2D forward modeling code to compare the waveform inversion method with the conventional method. The area into which CO2 is injected is on the order of a few hundred meters wide and a few 10s of meters high and can be considered as a leak. We compare the waveform inversion results and conventional time-lapse results to determine how sparse spatial sub-sampling affects the results by successively increasing both the shot and receiver spacing. Aside from testing the influence of the shot and receiver spacing on the results, we also use a coarse starting model and increase the starting frequency to make the test more realistic. Our results show that, under certain conditions concerning noise, it may be possible to use a combination of sparse spatial sampling geometries and seismic waveform inversion to monitor CO2 injection sites. Regardless, seismic waveform inversion may be a good complement to standard CDP processing when monitoring CO2 injection.

Keyword [en]
CO2 monitoring, CO2 sequestration, time lapse, seismic waveform inversion
National Category
Earth and Related Environmental Sciences Geophysics
Identifiers
URN: urn:nbn:se:uu:diva-187138OAI: oai:DiVA.org:uu-187138DiVA: diva2:573803
Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2013-02-11
In thesis
1. Quantifying the Seismic Response of Underground Structures via Seismic Full Waveform Inversion: Experiences from Case Studies and Synthetic Benchmarks
Open this publication in new window or tab >>Quantifying the Seismic Response of Underground Structures via Seismic Full Waveform Inversion: Experiences from Case Studies and Synthetic Benchmarks
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Seismic full waveform inversion (waveform tomography) is a method to reconstruct the underground velocity field in high resolution using seismic data. The method was first introduced during the 1980’s and became computationally feasible during the late 1990’s when the method was implemented in the frequency domain. This work presents three case studies and one synthetic benchmark of full waveform inversion applications. Two of the case studies are focused on time-lapse cross-well and 2D reflection seismic data sets acquired at the Ketzin CO2 geological storage site. These studies are parts of the CO2SINK and CO2MAN projects. The results show that waveform tomography is more effective than traveltime tomography for the CO2 injection monitoring at the Ketzin site for the cross-well geometry. For the surface data sets we find it is difficult to recover the true value of the velocity anomaly due to the injection using the waveform inversion method, but it is possible to qualitatively locate the distribution of the injected CO2. The results agree well with expectations based upon conventional 2D CDP processing methods and more extensive 3D CDP processing methods in the area. A further investigation was done to study the feasibility and efficiency of seismic full waveform inversion for time-lapse monitoring of onshore CO2 geological storage sites using a reflection seismic geometry with synthetic data sets. The results show that waveform inversion may be a good complement to standard CDP processing when monitoring CO2 injection. The choice of method and strategy for waveform inversion is quite dependent on the goals of the time-lapse monitoring of the CO2 injection. The last case study is an application of the full waveform inversion method to two crooked profiles at the Forsmark site in eastern central Sweden. The main goal of this study was to help determine if the observed reflections are mainly due to fluid filled fracture zones or mafic sills. One main difficulty here is that the profiles have a crooked line geometry which corresponds to 3D seismic geometry, but a 2D based inversion method is being used. This is partly handled by a 3D to 2D coordinate projection method from traveltime inversion. The results show that these reflections are primarily due to zones of lower velocity, consistent with them being generated at water filled fracture zones.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 62 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1005
Keyword
full waveform inversion, waveform tomography, CO2 monitoring, CO2 sequestration, time lapse seismic, Inversion
National Category
Earth and Related Environmental Sciences Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-187142 (URN)978-91-554-8562-7 (ISBN)
Public defence
2013-02-01, Hambergsalen, Geocentrum, Villavagen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2013-01-10 Created: 2012-12-03 Last updated: 2013-02-11Bibliographically approved

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