Purpose Current surveying techniques used by port authorities to estimate the nautical depth are limited in depth resolution and temporal resolution. Because of this, certain heavily occupied quay walls cannot be optimised in terms of utilisation. Therefore, a permanent continuous measuring system with a higher depth resolution is needed to optimise the occupation at these quay walls. We show how this could be achieved with distributed acoustic sensing (DAS) using fibre-optical cables. Materials We analyse recordings from a dual-frequency echo-sounder source along a standard communication optical fibre coiled vertically around a PVC pipe to represent vertical seismic profiling. This PVC pipe is placed inside a transparent plastic cylindrical tank which is partly filled with water and mud. This allows us to track the water-mud interface visually. We use a Silixa iDAS v2 and a Febus A1 DAS interrogator to convert the optical fibre into a seismic sensor. We use a wave generator to select the source frequency and an amplifier to amplify the output of the wave generator to a SIMRAD 38/200 COMBI C dual-frequency echo-sounder. Results We identify standing waves and use them to make accurate depth estimates of the water-mud interface inside the column we measure. Due to the high apparent velocity, the standing waves are easy to identify in the time domain. Due to the constructive interference, standing waves also show the water-mud interface in a power spectral density plot. We demonstrate that these standing waves could be used with an on-demand permanent continuous measuring system using ambient noise sources. Conclusion Our laboratory experiment showed that DAS could be used to estimate the water-mud interface. In addition, we showed the potential for on-demand monitoring in ports and waterways using DAS. Furthermore, due to the low cost of optical fibres, and the possibility of utilising ambient noise sources, DAS could be used for continuous depth monitoring purposes in ports and waterways.@en

Monitoring the nautical depth is vital for the safe passage of water transport. Port authorities worldwide have different navigable depth criteria and use various methods to ensure the safe navigability and manoeuvrability of ships in ports and waterways. These measurements often require a surveying vessel and are limited in repeatability and accuracy. Often, it is challenging to survey at heavily occupied quay walls; this may hinder economical activities. Additionally, because the current monitoring techniques depend on a surveying vessel's availability, monitoring significant changes in the nautical depth after, for instance, storms, is challenging, especially over large areas. Reliable continuous depth measurements could therefore help to optimise ships’ docking operations in heavily occupied areas. We show how the nautical depth can be measured and demonstrate the potential for estimating shear stresses using distributed acoustic sensing. Our laboratory study and our field test show that the acoustic energy differs for non- Newtonian fluids with different shear strength. For our laboratory experiment, we use natural and synthetic sediment suspensions for measuring the difference in acoustic attenuation with an optical fibre wrapped around a polyvinyl chloride (PVC) pipe. Our first acoustic measurement conducted one hour after mixing has a shear strength of 17 Pa and shows very high attenuation. The second laboratory test recorded 24 hours after mixing, with the shear strength of 48 Pa, reveals a tremendous signal-attenuation decrease and thus amplitude increase. In our field experiment, we observe a similar increase in amplitude with increased shear strength when recording propeller noise from passing vessels for frequencies < 60 Hz. We also observe a reverse trend for frequencies > 100 Hz. This difference in amplitude with depth might be related to a difference in fibre coupling and a difference in attenuation of acoustic waves. Additionally, our field experiment shows the potential to use Distributed Acoustic Sensing for continuous depth measurements. @en

This work shows the potential of using DAS for continuous water-depth monitoring by using the difference in acoustic energy in water and mud. The advantage over conventional methods is that our method can be used continuously and remotely, given that there is traffic nearby. Due to the low cost of fibres and the far-reaching dynamic range of interrogators, DAS could be a very attractive alternative for water-depth monitoring using propeller noise in shallow marine environments, ports and waterways.@en

With the development of several CO₂ storage operations in the North Sea, there is a clear need to better characterise the seismic hazard and stress state in the region. Faults and associated fracture sets can act as hydraulic pathways for unintended CO₂ migration, ill-defined stress states can lead to numerous operational difficulties, and induced seismicity will be a clear risk as CO₂ is injected into subsurface reservoirs. Seismicity can reveal the location and extent of faults and fractures, and can be used to invert for the state of stress. Both operators and regulators therefore need a clear understanding of the rate of natural seismicity, to identify and distinguish induced events from natural, and to assess the likelihood of induced fault reactivation. This requires a dedicated, site specific background monitoring programme, as well as a high-quality seismic catalogue for the region around any CO₂ storage operation. Our study has produced the first dedicated seismic catalogue of the North Sea, based on all available data from each of the relevant seismological agencies. This dataset fosters further studies into seismic hazard, leakage risk, and stress state in a region that will be vital for European CO₂ storage efforts in the coming decades.@en

We conducted laboratory experiments using large-scale samples (height: 0.47, diameter: 0.39 m) of basalt and marble coiled with telecommunication fibre. The fibre optical cable was converted to an array of densely spaced receivers (0.01 m) using distributed acoustic sensing (DAS) technology, and the source was placed on top of the samples. We demonstrate with an active acoustic setup how we can capture both the natural and artificial fracture responses. Therefore, this work investigates the applicability of the DAS method for seismic imaging on the lab scale for further technological advancement of vertical seismic profiling using DAS.@en

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.@en

Carbon capture and storage (CCS) technology is essential to European decarbonisation efforts, and several offshore CO2 storage projects are being developed in the North Sea. Understanding the geomechanical response to CO2 injection is key to both the pre-characterisation and operation of a storage reservoir. A thorough assessment of seismicity gives critical insights into the stress field and faulting around reservoirs, both key controls on the geomechanical response to injection. Seismicity also illuminates potential hydraulic pathways for leakage, be it directly by revealing the extent of faults, or indirectly through fractures imaged by measurements of seismic anisotropy. High quality seismicity data is critical to underpin all of these methods of analysis. This paper presents the most complete catalogue of seismicity in the North Sea to date. The combined data are enabling revised assessments of seismic hazard and leakage risk in the North Sea, as well as a better understanding of faulting and stress. This study shows the value of unifying disparate seismicity data, allowing for more accurate seismological analyses. These lay the foundation for better management of risks for not only geologic CO2 storage, but other offshore industries and infrastructure.@en

Carbon capture and storage (CCS) technology is essential to European decarbonisation efforts, and several offshore CO2 storage projects are being developed in the North Sea. Understanding the geomechanical response to CO2 injection is key to both the pre-characterisation and operation of a storage reservoir. A thorough assessment of seismicity gives critical insights into the stress field and faulting around reservoirs, both key controls on the geomechanical response to injection. Seismicity also illuminates potential hydraulic pathways for leakage, be it directly by revealing the extent of faults, or indirectly through fractures imaged by measurements of seismic anisotropy. High quality seismicity data is critical to underpin all of these methods of analysis. This paper presents the most complete catalogue of seismicity in the North Sea to date. The combined data are enabling revised assessments of seismic hazard and leakage risk in the North Sea, as well as a better understanding of faulting and stress. This study shows the value of unifying disparate seismicity data, allowing for more accurate seismological analyses. These lay the foundation for better management of risks for not only geologic CO2 storage, but other offshore industries and infrastructure.@en

Carbon capture and storage (CCS) technology is essential to European decarbonisation efforts, and several offshore CO2 storage projects are being developed in the North Sea. Understanding the geomechanical response to CO2 injection is key to both the pre-characterisation and operation of a storage reservoir. A thorough assessment of seismicity gives critical insights into the stress field and faulting around reservoirs, both key controls on the geomechanical response to injection. Seismicity also illuminates potential hydraulic pathways for leakage, be it directly by revealing the extent of faults, or indirectly through fractures imaged by measurements of seismic anisotropy. High quality seismicity data is critical to underpin all of these methods of analysis. This paper presents the most complete catalogue of seismicity in the North Sea to date. The combined data are enabling revised assessments of seismic hazard and leakage risk in the North Sea, as well as a better understanding of faulting and stress. This study shows the value of unifying disparate seismicity data, allowing for more accurate seismological analyses. These lay the foundation for better management of risks for not only geologic CO2 storage, but other offshore industries and infrastructure.@en

Carbon capture and storage (CCS) technology is essential to European decarbonisation efforts, and several offshore CO2 storage projects are being developed in the North Sea. Understanding the geomechanical response to CO2 injection is key to both the pre-characterisation and operation of a storage reservoir. A thorough assessment of seismicity gives critical insights into the stress field and faulting around reservoirs, both key controls on the geomechanical response to injection. Seismicity also illuminates potential hydraulic pathways for leakage, be it directly by revealing the extent of faults, or indirectly through fractures imaged by measurements of seismic anisotropy. High quality seismicity data is critical to underpin all of these methods of analysis. This paper presents the most complete catalogue of seismicity in the North Sea to date. The combined data are enabling revised assessments of seismic hazard and leakage risk in the North Sea, as well as a better understanding of faulting and stress. This study shows the value of unifying disparate seismicity data, allowing for more accurate seismological analyses. These lay the foundation for better management of risks for not only geologic CO2 storage, but other offshore industries and infrastructure.@en

Carbon capture and storage (CCS) technology is essential to European decarbonisation efforts, and several offshore CO2 storage projects are being developed in the North Sea. Understanding the geomechanical response to CO2 injection is key to both the pre-characterisation and operation of a storage reservoir. A thorough assessment of seismicity gives critical insights into the stress field and faulting around reservoirs, both key controls on the geomechanical response to injection. Seismicity also illuminates potential hydraulic pathways for leakage, be it directly by revealing the extent of faults, or indirectly through fractures imaged by measurements of seismic anisotropy. High quality seismicity data is critical to underpin all of these methods of analysis. This paper presents the most complete catalogue of seismicity in the North Sea to date. The combined data are enabling revised assessments of seismic hazard and leakage risk in the North Sea, as well as a better understanding of faulting and stress. This study shows the value of unifying disparate seismicity data, allowing for more accurate seismological analyses. These lay the foundation for better management of risks for not only geologic CO2 storage, but other offshore industries and infrastructure.@en