Quantitative evaluation of thin-layer thickness and CO₂mass utilizing seismic complex decomposition at the Ketzin CO₂storage site, Germany

Abstract

S U M M A R YDetermining thin layer thickness is very important for reservoir characterization and CO 2 quantification. Given its high time-frequency resolution and robustness, the complex spectral decomposition method was applied on time-lapse 3-D seismic data from the Ketzin pilot site for CO 2 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 CO 2 propagation. Tuning frequency mapping shows the thicknesses of the reservoir sandstone and gaseous CO 2 is consistent with the measured thickness of the sandstone unit from well logging. An attempt to discriminate between pressure effects and CO 2 saturation using the extracted tuning frequency indicates that CO 2 saturation is the main contributor to the amplitude anomaly at the Ketzin site. On the basis of determined thickness of gaseous CO 2 in the reservoir, quantitative analysis of the amount of CO 2 was performed and shows a discrepancy between the injected and calculated CO 2 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 CO 2 dissolution.

Monitoring CO2 saturation using time‐lapse amplitude versus offset analysis of 3D seismic data from the Ketzin CO2 storage pilot site, Germany

“…The thickness of the sandstone channels in the upper part of the Stuttgart Formation obtained from complex spectral decomposition of the 3D time‐lapse seismic, ranges from 9.7 m to 17.4 m (Huang et al . ; Fig. ), which is consistent with the 9–20 m sandstone unit thickness obtained from well logs reports (Förster et al .…”

“…Temporal reservoir thickness obtained from complex spectral decomposition of the 3D time‐lapse seismic (Huang et al. ). The injection well is marked by a grey dot.…”

“…Furthermore, Huang et al . () used complex spectral decomposition of the 3D time‐lapse seismic data to discriminate between the anomalies generated by the reservoir pressure and gaseous CO 2 saturation. The resulting signatures show that the pressure effect is present, but is not significant and that the amplitude anomaly is almost entirely due to CO 2 saturation.…”

The first post‐injection seismic monitor survey at the Ketzin pilot CO2 storage site: results from time‐lapse analysis

“…; Huang et al . , ). It is desirable to remove these spurious changes in seismic attributes by performing cross‐equalisation of the time‐lapse seismic datasets.…”

Revising the Static Geological Reservoir Model of the Upper Triassic Stuttgart Formation at the Ketzin Pilot Site for CO2 Storage by Integrated Inverse Modelling

“…In this context, substantial efforts have been undertaken to integrate data from ongoing on-site field tests and continuous observations as well as laboratory experiments on the Stuttgart Formation reservoir rocks with numerical simulations [12,14,19,20,[22][23][24][25][26][27][28][29][30][31][32]. Recent activities especially focussed on integration of the 3D seismic survey data with other geophysical findings and numerical simulations [33][34][35][36], also in view of defining conformance criteria between geophysical monitoring and numerical model predictions to be considered in German and EU-wide regulations [37].…”