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Fine-scale Characterisation of an Active Gas Chimney within the Quaternary Sediments of the Central North-Sea; using Acoustic Full Waveform Inversion

Authors

Jedari-Eyvazi,  Farid
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Plessix,  Rene-Edouard
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Bayrakci,  Gaye
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Minshull,  Timothy A.
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Bull,  Jonathan M.
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

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Citation

Jedari-Eyvazi, F., Plessix, R.-E., Bayrakci, G., Minshull, T. A., Bull, J. M. (2023): Fine-scale Characterisation of an Active Gas Chimney within the Quaternary Sediments of the Central North-Sea; using Acoustic Full Waveform Inversion, XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) (Berlin 2023).
https://doi.org/10.57757/IUGG23-4379


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5021810
Abstract
Integrity of overburden formations to the underlying reservoir rocks plays a vital role in permanent storage of CO2 within geological traps. Focused fluid escape structures (also known as chimney and pipe structures) are highly permeable (sub-)vertical geological features within the sedimentary rocks that can represent a substantial risk to geological CO2 storage projects. Despite the importance of such structures to the subsurface hydraulic system, their internal structures and fluid flow properties are poorly constrained to date. In this study, we examined the internal structure of a representative gas chimney underlying the Scanner Pockmark Complex in the North Sea, where methane is currently leaking to the seabed. We recovered an acoustic velocity model of the chimney structure and the host formations, using 3-D full waveform inversion (FWI) technique. The inverted data consists of ~125000 seismic traces from 23 ocean bottom seismometers (OBS) covering an area of 66 km2. We set the FWI scheme to include only diving waves at offsets of 1300-4600 m, corresponding to incident angles of about 60º to 80º respectively at the maximum well-resolved depth of 700 mbsl. The inverted model, at the maximum frequency of 7 Hz, revealed a complex fluid escape structure with an indirect vertical gas migration pathway that manifested itself as a simple gas pipe structure on a coinciding seismic reflection image. In addition, integration of the recovered velocity structures with a calibrated Gassmann model suggested a patchy gas saturation within the area.