Constraints on fluid flow pathways from shear-wave splitting in and around an active fluid-escape structure: Scanner Pockmark, North Sea
Constraints on fluid flow pathways from shear-wave splitting in and around an active fluid-escape structure: Scanner Pockmark, North Sea
Vertical fluid-escape structures observed in seismic reflection data represent an important class of potentially active fluid flow pathways. An understanding of the mechanism of fluid flow in these types of structures is needed to assess the risk of natural gas venting from potential subsurface carbon dioxide storage operations. The Scanner Pockmark Complex is a 22 m deep, 900 × 450 m seabed depression in the North Sea, which actively vents methane, and is underlain by a seismic chimney structure with horizontal dimensions of ∼300 × 600 m. Gas accumulation is evidenced by the presence of bright reflectors at the top of this seismic chimney, at a depth of ∼50 m below the seabed. Here, we analyse seismic anisotropy in these shallow sediments using shear wave splitting observed on ocean bottom seismographs (OBS). Anisotropy varies spatially, with a strength of ∼1-4 per cent, on several OBS located in and around the pockmark complex. By correlating these observations with calculated subsurface P- and S-wave velocities, we show that there is anisotropy present throughout the sediments through which the chimney passes, which are interpreted as relating to syn- and post-depositional glaciomarine processes. However, within the chimney itself the orientation of the fast direction is different to that outside the chimney and the degree of anisotropy is lower. We attribute this difference as indicating that the anisotropy observed within the chimney is associated with the formation and continued presence of the gas migration system, which overprints the background depositional anisotropy.
Controlled source seismology, Fracture and flow, Gas and hydrate systems, Seismic anisotropy
1164-1195
Robinson, Adam
f5aea908-d884-465b-bfc1-ed67ca16ed85
Bayrakci, Gaye
8717575b-4aa2-4046-9b6b-39b955c5a742
Macdonald, Calum
3f509a74-9552-4ff3-aef1-34b57cf1d9ec
Minshull, Timothy
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Chapman, Mark
4f8c8192-9dd1-49f1-8e50-379357ccb1b0
Henstock, Timothy
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Callow, Ben
15166203-d3e6-4b28-8369-e99e1bd00240
1 November 2022
Robinson, Adam
f5aea908-d884-465b-bfc1-ed67ca16ed85
Bayrakci, Gaye
8717575b-4aa2-4046-9b6b-39b955c5a742
Macdonald, Calum
3f509a74-9552-4ff3-aef1-34b57cf1d9ec
Minshull, Timothy
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Chapman, Mark
4f8c8192-9dd1-49f1-8e50-379357ccb1b0
Henstock, Timothy
27c450a4-3e6b-41f8-97f9-4e0e181400bb
Callow, Ben
15166203-d3e6-4b28-8369-e99e1bd00240
Robinson, Adam, Bayrakci, Gaye, Macdonald, Calum, Minshull, Timothy, Bull, Jonathan, Chapman, Mark, Henstock, Timothy and Callow, Ben
(2022)
Constraints on fluid flow pathways from shear-wave splitting in and around an active fluid-escape structure: Scanner Pockmark, North Sea.
Geophysical Journal International, 231 (2), .
(doi:10.1093/gji/ggac197).
Abstract
Vertical fluid-escape structures observed in seismic reflection data represent an important class of potentially active fluid flow pathways. An understanding of the mechanism of fluid flow in these types of structures is needed to assess the risk of natural gas venting from potential subsurface carbon dioxide storage operations. The Scanner Pockmark Complex is a 22 m deep, 900 × 450 m seabed depression in the North Sea, which actively vents methane, and is underlain by a seismic chimney structure with horizontal dimensions of ∼300 × 600 m. Gas accumulation is evidenced by the presence of bright reflectors at the top of this seismic chimney, at a depth of ∼50 m below the seabed. Here, we analyse seismic anisotropy in these shallow sediments using shear wave splitting observed on ocean bottom seismographs (OBS). Anisotropy varies spatially, with a strength of ∼1-4 per cent, on several OBS located in and around the pockmark complex. By correlating these observations with calculated subsurface P- and S-wave velocities, we show that there is anisotropy present throughout the sediments through which the chimney passes, which are interpreted as relating to syn- and post-depositional glaciomarine processes. However, within the chimney itself the orientation of the fast direction is different to that outside the chimney and the degree of anisotropy is lower. We attribute this difference as indicating that the anisotropy observed within the chimney is associated with the formation and continued presence of the gas migration system, which overprints the background depositional anisotropy.
Text
Robinson_etal_ScannerSWS_accepted
- Accepted Manuscript
More information
Accepted/In Press date: 24 May 2022
Published date: 1 November 2022
Additional Information:
Funding Information:
This work was funded by the Natural Environment Research Council (CHIMNEY; NERC Highlight Topic; NE/N016130/1 and NE/N015762/1) and the European Union s Horizon 2020 research and innovation programme under grant agreement No. 654462 (STEMM-CCS). We would like to thank all those involved in the planning and acquisition of data during RRS James Cook cruise JC152, including the officers, engineers and crews, the scientific parties, and all seagoing technicians and engineers. OBSs were supplied by the UK Ocean Bottom Instrumentation Facility (Minshull et al. 2005).We are also grateful for the support of Applied Acoustics Ltd during sparker data acquisition. We thank Ross Haacke (CGG) for advice on the design of the CHIMNEY seismic surveys and for providing codes for rotation of OBS data and Giuseppe Provenzano for work processing of the seismic reflection data. We thankMartha Savage, Sunny Singhroha and editor Jenny Collier for their helpful reviews. The final accepted version of this manuscript is available through ePrints Soton (eprints.soton.ac.uk).
Publisher Copyright:
© 2022 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society.
Keywords:
Controlled source seismology, Fracture and flow, Gas and hydrate systems, Seismic anisotropy
Identifiers
Local EPrints ID: 457738
URI: http://eprints.soton.ac.uk/id/eprint/457738
ISSN: 0956-540X
PURE UUID: 5aa87a63-40c6-45c6-affb-3d178b16bdde
Catalogue record
Date deposited: 16 Jun 2022 00:28
Last modified: 12 Nov 2024 03:02
Export record
Altmetrics
Contributors
Author:
Gaye Bayrakci
Author:
Calum Macdonald
Author:
Mark Chapman
Author:
Ben Callow
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics
