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- Bergmann, Peter, et al.
(author)
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Combination of seismic reflection and constrained resistivity inversion with an application to 4D imaging of the CO2 storage site, Ketzin, Germany
- 2014
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In: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 79:2, s. B37-B50
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Journal article (peer-reviewed)abstract
- A combination of seismic and geoelectric processing was studied by means of a structurally constrained inversion approach. Structural constraints were interpreted from the seismic data and integrated into the geoelectric inversion through a local regularization, which allowed inverted resistivities to behave discontinuously across defined boundaries. This arranged seismic processing and constrained resistivity inversion in a sequential workflow, making the generic assumption that the petrophysical parameters of both methods change across common lithostructural boundaries. We evaluated the approach using a numerical example and a real data example from the Ketzin CO2 pilot storage site, Germany. The latter demonstrated the efficiency of this approach for combining 4D seismic and surface-downhole geoelectric data. In consistence with the synthetic example, the constrained resistivity inversions produced clearer delineated images along the boundary between caprock and reservoir formation. Near the CO2-flooded reservoir, the seismic and geoelectric time-lapse anomalies correlated well. At some distance to the downhole electrodes, however, the geoelectric images conveyed a notably lower resolution in comparison to the corresponding seismic images. Both methods confirm a northwesterly trend for the CO2 migration at the Ketzin site, although a rather northerly direction was initially expected. The results demonstrate the relevance of the presented approach for the combination of both methods for integrated geophysical CO2 storage monitoring.
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- Bergmann, Peter, et al.
(author)
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Review on geophysical monitoring of CO2 injection at Ketzin, Germany
- 2016
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In: Journal of Petroleum Science and Engineering. - : Elsevier BV. - 0920-4105. ; 139, s. 112-136
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Journal article (peer-reviewed)abstract
- Geophysical monitoring activities were an important component of the CO2 injection program at the Ketzin site, Germany. Here we report on the seismic and electrical resistivity tomography (ERT) measurements performed during the period of the site development and CO2 injection. Details on the site geology, the history of the CO2 injection operation, and petrophysical models relevant for the interpretation of the geophysical data are presented. The seismic measurements comprise 2D and 3D surface seismic surveys, vertical seismic profilings, and crosshole measurements. Apart from the measurements, results from advanced processing methods, such as impedance inversion and full-waveform inversion are also presented. In addition, results from crosshole ERT and surface-downhole ERT are presented. If operational efforts are taken into consideration we conclude that a combination of several geophysical methods is preferable given the demands of a spatiotemporally comprehensive monitoring program. We base this conclusion on that the different imaging characteristics and petrophysical sensitivities of different methods can complement each other. An important finding is, based on signal quality and reduced operational costs, that the use of permanent installations is promising. Generally, specific monitoring layouts will depend on site-specific characteristics, such as reservoir depth, availability of wells, petrophysical characteristics, and accessibility of surface locations. Given the comprehensive range of methods applied, the reported results are not only relevant to the operation of CO2 storage sites, but are also of interest to other monitoring projects dealing with fluid injection or production.
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- Bergmann, Peter, et al.
(author)
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Time-lapse processing of 2D seismic profiles with testing of static correction methods at the CO(2) injection site Ketzin (Germany)
- 2011
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In: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 75:1, s. 124-139
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Journal article (peer-reviewed)abstract
- The Ketzin project provides an experimental pilot test site for the geological storage of CO(2). Seismic monitoring of the Ketzin site comprises 2D and 3D time-lapse experiments with baseline experiments in 2005. The first repeat 2D survey was acquired in 2009 after 22 kt of CO(2) had been injected into the Stuttgart Formation at approximately 630 m depth. Main objectives of the 2D seismic surveys were the imaging of geological structures, detection of injected CO(2), and comparison with the 3D surveys. Time-lapse processing highlighted the importance of detailed static corrections to account for travel time delays, which are attributed to different near-surface velocities during the survey periods. Compensation for these delays has been performed using both pre-stack static corrections and post-stack static corrections. The pre-stack method decomposes the travel time delays of baseline and repeat datasets in a surface consistent manner, while the latter cross-aligns baseline and repeat stacked sections along a reference horizon. Application of the static corrections improves the S/N ratio of the time-lapse sections significantly. Based on our results, it is recommended to apply a combination of both corrections when time-lapse processing faces considerable near-surface velocity changes. Processing of the datasets demonstrates that the decomposed solution of the pre-stack static corrections can be used for interpretation of changes in near-surface velocities. In particular, the long-wavelength part of the solution indicates an increase in soil moisture or a shallower groundwater table in the repeat survey. Comparison with the processing results of 2D and 3D surveys shows that both image the subsurface, but with local variations which are mainly associated to differences in the acquisition geometry and source types used. Interpretation of baseline and repeat stacks shows that no CO(2) related time-lapse signature is observable where the 2D lines allow monitoring of the reservoir. This finding is consistent with the time-lapse results of the 3D surveys, which show an increase in reflection amplitude centered around the injection well. To further investigate any potential CO(2) signature, an amplitude versus offset (AVO) analysis was performed. The time-lapse analysis of the AVO does not indicate the presence of CO(2), as expected, but shows signs of a pressure response in the repeat data.
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- Huang, Fei, 1987-, et al.
(author)
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Preliminary Seismic Time-lapse Results from the First Post-injection Survey at the Ketzin Pilot Site
- 2016
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Conference paper (peer-reviewed)abstract
- Since the CO2SINK project start in April 2004, different methods involving seismics, geoelectrics andpressure-temperature monitoring have been applied at the Ketzin pilot site to map geological structuresand assess CO2 distribution and movement. One 3D baseline seismic survey prior to CO2 injection andtwo 3D repeat seismic surveys during CO2 injection have proven that the 3D time-lapse surface seismicmethod is an effective tool for providing good quality images of the CO2 plume. In the autumn of 2015, athird 3D repeat seismic survey, serving as the first post-injection survey, was acquired. The preliminaryresults show that the predominant westward trend of the CO2 migration is in agreement with the previousresults. No CO2 migration upwards through the caprock was detected. The decrease in the size of CO2plume may be related to ongoing dissolution into the saline formation water.
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