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- Bergmann, Peter, et al.
(författare)
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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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Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 79:2, s. B37-B50
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 75:1, s. 124-139
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Tidskriftsartikel (refereegranskat)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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- Ivanova, Alexandra, 1970-, et al.
(författare)
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Impact of temperature on CO2 storage at the Ketzin site based on fluid flow simulations and seismic data
- 2013
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836 .- 1878-0148. ; 19, s. 775-784
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Tidskriftsartikel (refereegranskat)abstract
- Temperature is one of the main parameters influencing the properties of CO2 during storage in saline aquifers since it along with pressure and co-constituents controls the phase behavior of the CO2/brine mixture. When the CO2 replaces brine as a free gas it is well known to affect the elastic properties of porous media considerably. In order to track the migration of geologically stored CO2 at the Ketzin site, 3D time-lapse seismic data were acquired by means of a baseline (pre-injection) survey in autumn 2005 and a first monitor survey in autumn 2009. During this period the temperature in the storage reservoir near the injection well was observed to have increased from 34 °C to 38 °C.This temperature increase led us to investigate the potential impact of temperature on the seismic response to the CO2 injection and on the CO2 mass estimations based on the Ketzin 4D seismic data. Two temperature scenarios in the reservoir (34 °C and 38 °C) were studied using multiphase fluid flow modeling. The simulations show that the impact of temperature on the seismic response is minor, but that the impact of the temperature on the CO2 mass estimations is significant and can, with the help of the multiphase fluid flow simulations, be explained mostly by the impact on the density of the CO2.
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| 10. |
- Ivanova, Alexandra, et al.
(författare)
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Seismic modeling of the AVO/AVA response to CO2 injection at the Ketzin site, Germany
- 2013
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Konferensbidrag (refereegranskat)abstract
- Over 64 kilotons of CO2 have been injected (May, 2013) into a heterogeneous sandstone reservoir (saline aquifer) at 630-650 m depth. 4D seismics have been applied to monitor CO2 at the Ketzin site. However, the obtained time-lapse seismic signals have been so far interpreted as being caused by fluid saturation changes only. Modeling of the AVO/AVA response allows us to study two kinds of effects: CO2-saturation- and pore-pressure-related effects. Our results indicate that it is rather infeasible to discriminate between both these effects at the Ketzin site dealing with the real seismic data with limited signal/noise ratios.
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