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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Fei, Huang, 1987-, et al.
(författare)
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DMO processing on the Ketzin 3D seismic data
- 2014
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Konferensbidrag (refereegranskat)abstract
- The Dip-moveout (DMO) correction is a process which attempts to make the finite offset data closer to zero offset data after the normal-moveout (NMO) correction. The NMO correction is then dip independent and reflections with different dips will stack coherently. DMO plays a critical role in seismic processing by enhancing the final image quality of the seismic data. In this study, we apply 3D Squeezing DMO (Hale and Artley, 1993) to seismic data from the Ketzin pilot CO2 site after NMO to study the impact of DMO on time-lapse seismic imaging and to investigate if it enhances the CO2 seismic monitoring technique. This 3D DMO method is based on an integral approach and incorporates Hale and Artley’s (1993) modifications for variable velocity with time. A constant velocity algorithm is used with a gamma correction function which depends on the velocity function. An anti-alias velocity of 3000 m/s is used for the DMO. After DMO the data are stacked and F-XY deconvolution is applied. Finally, 3D finite-difference migration using the final smoothed NMO velocities is performed for each data set.We then apply a time-lapse analysis to the 3D seismic data sets and compare the results with and without DMO processing. The most important aspect of the DMO processing is determining the velocity field for the NMO step. This is done by using the initial smoothed velocity field obtained from the conventional velocity analysis before DMO as a first estimate. The data are input into the DMO process and then inverse NMO is applied. These data are then subjected to a new velocity analysis and the velocity field is updated and used as input for the NMO process. A number of iterations are generally required until the velocity field does not need further updating. In this study velocities were picked at every 20th CDP in the inline and crossline directions. Compared to the velocity spectrum without DMO processing, the velocity trend is improved and the ambiguity in the velocity picks is eliminated after DMO correction. The improved accuracy of velocity picking makes it easier to interpret the velocity spectrum and obtain correct interval velocities. Considering the stacked section, DMO suppresses the random noise to a greater extent and thus the signal-to-noise ratio is enhanced. From the comparison of the amplitude difference horizon at the reservoir level, the shape of the anomaly observed in the data with DMO processing is similar to that observed in the data without DMO processing. However, the amplitude anomalies of the former are stronger than those of the latter, especially close to the injection well. In addition, one stronger amplitude anomaly in the DMO time-lapse horizon indicates a preferred trend of the CO2 migration in WNW direction due to the reservoir heterogeneity.
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| 3. |
- Fei, Huang, 1987-, et al.
(författare)
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Integration of Reservoir Simulation with 3D Reflection Seismic Time-lapse Data at Ketzin
- 2014
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Konferensbidrag (refereegranskat)abstract
- In this study we integrate reservoir simulation with 3D reflection seismic time-lapse data from the Ketzin CO2 storage pilot site using density and velocity models, a porosity model and a fluid flow simulation model. To simulate the seismic response corresponding to the real data, detailed density and velocity models are properly generated from the stratigraphic model and available borehole logging data. The reservoir simulation model providing the spatial CO2 saturation in the reservoir based on numerical simulations history-matched to the site monitoring data is used to calculate the bulk densities and compressional wave velocities of the rock after CO2 injection using a fluid substitution method. 3D synthetic seismic data are generated by convolving the density and velocity models with two different sources to study the change in seismic response after CO2 injection and to investigate the impact of the different source types on CO2 monitoring. Our results provide estimates of the time-lapse anomalies caused by CO2 injection and demonstrate that the choice of source type is a critical factor for time-lapse seismic monitoring to assess the distribution of injected CO2. The same source type should be used in the baseline and repeat surveys for site operation.
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| 4. |
- Huang, Fei, 1987-
(författare)
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3D Time-lapse Analysis of Seismic Reflection Data to Characterize the Reservoir at the Ketzin CO2 Storage Pilot Site
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 5. |
- Huang, Fei, 1987-, et al.
(författare)
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Application of seismic complex decomposition on thin layer detection of the CO2 plume at Ketzin, Germany
- 2015
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Konferensbidrag (refereegranskat)abstract
- The seismic complex decomposition technique is a spectral decomposition method using inversion strategies to decompose a seismic trace into its constituent frequencies and corresponding complex coefficients. This method has high time-frequency resolution and it is not necessary to select a signal window in comparison to conventional spectral decomposition methods. The thickness of the reservoir at the Ketzin pilot site is relatively thin, making it difficult to resolve seismically due to the band-limited seismic spectrum. This study presents an application of seismic complex decomposition to the time-lapse 3D seismic datasets at the Ketzin pilot site for estimating the temporal thickness of the injected CO2 within the thin reservoir via frequency tuning. Quantitative analysis for CO2 thickness and mass is investigated. Comparison between the real recorded data and the estimates shows that our results are reliable in assessing the amount of the CO2 in the plume at the Ketzin pilot site.
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| 6. |
- Huang, Fei, 1987-, et al.
(författare)
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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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Konferensbidrag (refereegranskat)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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| 7. |
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| 8. |
- Huang, Fei, 1987-, et al.
(författare)
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Quantitative evaluation of thin-layer thickness and CO2 mass utilizing seismic complex decomposition at the Ketzin CO2 storage site, Germany
- 2016
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Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 207:1, s. 160-173
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Huang, Fei, 1987-, et al.
(författare)
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The first post-injection seismic monitor survey at the Ketzin pilot CO2 storage site : results from time-lapse analysis
- 2018
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Ingår i: Geophysical Prospecting. - : Wiley. - 0016-8025 .- 1365-2478. ; 66:1, s. 62-84
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Tidskriftsartikel (refereegranskat)abstract
- The injection of CO2 at the Ketzin pilot CO2 storage site started in June 2008 and ended in August 2013. During the 62 months of injection, a total amount of about 67 kt of CO2 was injected into a saline aquifer. A third repeat 3D seismic survey, serving as the first post-injection survey was acquired in 2015, aiming to investigate the recent movement of the injected CO2. Consistent with the previous two time-lapse surveys, a predominantly WNW migration of the gaseous CO2 plume in the up-dip direction within the reservoir is inferred in this first post-injection survey. No systematic anomalies are detected through the reservoir overburden. The extent of the CO2 plume west of the injection site is almost identical to that found in the 2012 second repeat survey (after injection of 61 kt), however there is a significant decrease in its size east of the injection site. Assessment of the CO2 plume distribution suggests that the decrease in the size of the anomaly may be due to multiple factors, such as limited vertical resolution, CO2 dissolution and CO2 diffusion, in addition to the effects of ambient noise. 4D seismic modelling based on dynamic flow simulations indicates that a dynamic balance between the newly injected CO2 after the second repeat survey and the CO2 being dissolved and diffused was reached by the time of the first post-injection survey. Considering the considerable uncertainties in CO2 mass estimation, both patchy and non-patchy saturation models for the Ketzin site were taken into consideration.
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| 10. |
- Ivandic, Monika, et al.
(författare)
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Monitoring CO2 saturation using time-lapse amplitude versus offset analysis of 3D seismic data from the Ketzin CO2 storage pilot site, Germany
- 2018
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Ingår i: Geophysical Prospecting. - : WILEY. - 0016-8025 .- 1365-2478. ; 66:8, s. 1568-1585
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Tidskriftsartikel (refereegranskat)abstract
- The injection of CO2 at the Ketzin pilot site commenced in June 2008 and was terminated in August 2013 after 67 kT had been injected into a saline formation at a depth of 630-650 m. As part of the site monitoring program, four 3D surface seismic surveys have been acquired to date, one baseline and three repeats, of which two were conducted during the injection period, and one during the post-injection phase. The surveys have provided the most comprehensive images of the spreading CO2 plume within the reservoir layer. Both petrophysical experiments on core samples from the Ketzin reservoir and spectral decomposition of the 3D time-lapse seismic data show that the reservoir pore pressure change due to CO2 injection has a rather minor impact on the seismic amplitudes. Therefore, the observed amplitude anomaly is interpreted to be mainly due to CO2 saturation. In this study, amplitude versus offset analysis has been applied to investigate the amplitude versus offset response from the top of the sandstone reservoir during the injection and post-injection phases, and utilize it to obtain a more quantitative assessment of the CO2 gaseous saturation changes. Based on the amplitude versus offset modelling, a prominent decrease in the intercept values imaged at the top of the reservoir around the injection well is indeed associated solely with the CO2 saturation increase. Any change in the gradient values, which would, in case it was positive, be the only signature induced by the reservoir pressure variations, has not been observed. The amplitude versus offset intercept change is, therefore, entirely ascribed to CO2 saturation and used for its quantitative assessment. The estimated CO2 saturation values around the injection area in the range of 40%-60% are similar to those obtained earlier from pulsed neutron-gamma logging. The highest values of 80% are found in the second seismic repeat in close vicinity to the injection and observation wells.
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