Summary North Sea subsurface structures provide prolific opportunities to reduce Europe's carbon footprint through permanently storing emitted CO2. In this paper we present a methodology to estimate resilience of manmade facilities and environment to potential induced seismicity during injection operations, based on historically observed regionally seismicity. This enables a robust design of a well informed risk management system that provides confidence to stakeholders while properly recognizing and establishing the right level of resilience to seismic events. The method is demonstrated by applying the assessment for offshore structures on the Norwegian shelf to address resilience to potential seismicity around the NorthernLights prospect. It appears that is likely an event with Moment Magnitude equal to 3.7 can be managed adequately. The method can be extension to other areas in the North Sea, such as the Dutch and UK sectors, and can also address for instance resilience of onshore domestic areas to offshore induced events.

Summary We present results and lessons learned from microseismic monitoring at megaton-scale CCS sites. The data examples allow the comparison of different network configurations and sensor technologies including surface, downhole, and DAS. Comparison of different sites reveals what information is most important to resolve, and at what scale, in order to be of value for storage operations. We can derive some basic criteria for network design aiming at obtaining this information in the most robust and cost-effective way.

Summary Distributed Acoustic Sensing (DAS) has emerged as a technology with many advantages over traditional borehole geophones for the long-term seismic monitoring of CCS fields. DAS can provide a much denser spatial sampling than a geophone string at a relatively low cost per sensor. However, current DAS systems have much higher noise floor than geophones meaning that small events may be harder to detect. Here we investigate the monitoring capabilities of downhole DAS compared to a nearly co-located geophone string at the Quest CCS Facility in Alberta, Canada. For high SNR events the dense spatial sampling and larger aperture provided by DAS offers a much more detailed image of the wavefield than can be provided by geophones. However, detection of smaller events can be a challenge as DAS has much lower (40 times smaller) SNR than geophones on a trace-by-trace comparison. Despite the lower SNR, event detection can be improved though advanced processing. Stacking over neighbouring channels increases SNR by a factor of two and boosts detectability from 33% to 44%. Finally, we present a DAS event detector based on coherent semblance stacking over expected moveouts which boosts the detection rates up to 53%, and shows potential for further improvements.

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2020Groningen gas field – Seismic monitoring using deep vertical arraysAuthors: E. FortierJ. VernierJ. TomicS. OatesE. FortierMagnitude-BakerhughesSearch for more papers by this author, J. VernierMagnitude-BakerhughesSearch for more papers by this author, J. TomicExxonMobilSearch for more papers by this author, and S. OatesShellSearch for more papers by this authorhttps://doi.org/10.1190/segam2020-3427486.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail AbstractGas production on Groningen field (Netherland) is inducind seismic activity since 30 years, with significant magnitudes. NAM (Nederlandse Aardolie Maatschappij) as the operator of the gas field, decided to implement a seismic network, including two deep vertical arrays with sensors at 3000m depth in the reservoir section. Due to strong velocities contrasts, recorded seismic signals were very complex to analyse, with refracted and reflected waves combining with direct arrivals. Seismic events location remains then a major challenge. Thanks to waveform modelling, phase identification, and location quality control, a consistent database was achieved with 880 events located. The event locations are mainly aligned on the fault systems, and allowed a better understanding of fault reactivation behaviour. Determining event depths and improving the sensitivity were part also part of the original objectives.Presentation Date: Tuesday, October 13, 2020Session Start Time: 9:20 AMPresentation Time: 10:35 AMLocation: Poster Station 4Presentation Type: PosterKeywords: wave propagation, sources, velocity analysis, acquisitionPermalink: https://doi.org/10.1190/segam2020-3427486.1FiguresReferencesRelatedDetails SEG Technical Program Expanded Abstracts 2020ISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2020 Pages: 3887 publication data© 2020 Published in electronic format with permission by the Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished Online: 30 Sep 2020 CITATION INFORMATION E. Fortier, J. Vernier, J. Tomic, and S. Oates, (2020), "Groningen gas field – Seismic monitoring using deep vertical arrays," SEG Technical Program Expanded Abstracts : 1349-1353. https://doi.org/10.1190/segam2020-3427486.1 Plain-Language Summary Keywordswave propagationsourcesvelocity analysisacquisitionPDF DownloadLoading ...

Summary After almost two years of monitoring of the Groningen reservoir in the Zeerijp area, Netherlands, the set of microseismic locations now enables to confirm at the local scale several properties of the seismic activity in the Groningen gas field. Events occur (i) mainly within the reservoir, (ii) along fault segments identified at the base Zechstein formation and (iii) have magnitude distributed according to a Gutenberg-Richter with a b-value of 0.82 ± 0.03. Our catalogue contains more than 500 events with M > −2.5 with a completeness level of 0.1. The period covered also underwent a significant rise in seismicity in relation to past activity levels, with the notable occurrence of four M > 2 events. Extrapolation of the Gutenberg-Richter law provides a 10 to 17 years return period for a M ≥ 3.9 in this area. The processing of such events proved to be particularly challenging due to the deployment of sensors within a low-velocity layer, leading to very complex waveform signatures. We had to develop a multi-phase location approach, in combination with comparison with synthetic waveforms to overcome this difficulty.