Authors; Mr Scott Griffiths¹, Mr Michael Noel¹

Affiliation; ¹Kraken Robotics 

Summary; High voltage sub-seabed cables are becoming more common within seas around the world in the form of electrical interconnectors, offshore wind farm export and inter array cables.

This study focuses on the survey of the Viking Link interconnector cable between the UK and Denmark in the southern North Sea. Whilst an interconnector cable may not be directly linked to an offshore wind farm (OWF), the results of this study can be applied to OWF export and inter array cables. The Sub Bottom Imager™ (SBI) 3D acoustic profiler was used in conjunction with a Teledyne TSS 350 cable tracking system.

A 10 km comparison line was acquired to compare the TSS 350 top of product (ToP) data and the SBI ToP interpretation. The results of the comparison showed that the ToP from both systems had good alignment in both absolute depth and general cable trend.

Unlike an electromagnetic system, a 3D acoustic volume not only provides the position of the cable but also information on how the cable is interacting with the shallow soils. This can provide valuable information on why a cable has a varying burial depth and how to approach challenging shallow soils when it comes to trenching design.

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Authors; Ms Lieselot Noppe¹, Ms Dieuwertje Kuijpers², Ms Morgane Ravilly¹

Affiliations; ¹GEOxyz, ² Stema Systems

Summary; Stema Systems and GEOxyz have worked together on the development of a 3D detection method for buried cables. The abstract gives an extensive overview of the theory, the system components and hardware functionalities, and the processing and interpretation workflows. The system has been tested on several projects, giving both companies better understanding of the systems strengths and operational limits, understanding how geological, sedimentological and cable installation methods can influence the detection possibilities and quality of the data. Based on these experiences, and linking this to the theory of sub-seabed acoustics, a roadmap has been developed for further improvement of the system. This roadmap covers both improvements on processing methodologies, and hardware upgrades. 

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Authors; Ms Emma Le Gall¹, Mr Benjamin Durot¹, Mr Benjamin Bellwald²

Affiliations; ¹Eliis, ²NGI

Summary; Offshore wind farm development is a critical component in the transition towards decarbonized energy production. Studies prior to geo-engineering operations include geohazard assessment to avoid failure in foundations drilling and cable backfilling operations. 3D UHRS provides images with a fifty-centimetre resolution which combined with centimetre resolution CPTs logs form efficient tools in the detection of shallow geohazards in the first hundreds of meters below seafloor.
Located in the Dutch shelf of the North Sea, the TNW case study has shown a wide range of paleoenvironments due to Pleistocene glaciations. Resulting sea level fluctuations have led to the deposition of various types of sediments which were subsequently glaciotectonised.
An integrated study has been conducted to characterize the glacial geomorphology and spatial facies variability with the area of interest. CPTs logs were propagated to map static soil properties within a semi-automated and signal-driven Relative Geological Time (RGT) model. The use of semi-automated workflows in the Paleoscan™ software allowed for efficient handling of both geophysical and geotechnical datasets to better understand the glacial geomorphology and the location of geo-engineering hazards.

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Authors; Dr Gwenaëlle Salaün¹, Knud Ho Karkov², Dr Lluis Guasch³, Prof. Mike Warner³

Affiliations; ¹Ørsted, ² Formerly Ørsted, ³Imperial College London

Summary; In this study we present the results of a feasibility study on the application of Full Waveform Inversion of 2D UHR seismic data from an offshore wind farm.

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Authors; Dr Marijn van Cappelle¹, Mr Søren Mathiasen², Dr Bogusia Klosowska¹

Affiliations; ¹Fugro, ²Energinet

Summary; In the southern North Sea, Pleistocene sediments are within depths of interest for the foundations of wind turbine generators, offshore converter platforms and artificial islands. Pre-Pleistocene marine deposits are well studied, mainly using deep seismic data and wells from the oil and gas industry. However, relatively little is published on shallow (the upper 100 m) Pleistocene deposits. Here we present a large 2D ultra-ultra-high resolution (UUHR) seismic reflection dataset from the Energy Island offshore wind farm site in the Danish Sector of the North Sea, with a total line length of 6071 km covering an area of 1052 km2. The interpretation of 2D-UUHR data were supported by borehole data (269 seafloor CPTs and 58 sampling and CPT boreholes). Based on these data, three fluvial sand units were recognised, which were initially deposited on a coastal plain and were progressively restricted to relatively wide and shallow river valleys containing less fines (clay and silt) and more gravel. These three fluvial sand units are incised by two sets of relatively narrow and deep glacial tunnel valleys with an infill of poorly sorted clay, silt, sand and gravel.

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Authors; Dr Huub Douma¹, Ramón Parchen¹

Affiliation; ¹Quantairra Research And Development Services B.V.

Summary; We present a novel approximate linear fundamental-mode phase-velocity inversion method for Scholte and Stoneley waves to estimate the shallow shear-wave velocity underneath the ocean floor, for use in the context of Multi-channel Analysis of Surface Waves (MASW). The obtained model is accurate enough for many practical settings encountered in offshore wind-turbine construction, except in overly complex situations. In such situations it can be used as a starting model for a more sophisticated non-linear inversion to produce an improved model. The benefit of the presented method is that it is computationally efficient, that it needs no starting model and that minimal parameterization is required. As such it allows full automation and is therefore a good candidate for in-field real-time inversion during data acquisition as well as integration into the acquisition equipment itself. Using this method a shear-wave velocity model could be obtained while sailing over the area, allowing optimization of the geotechnical campaign in relation to minimizing the need for expensive CPTs. We verify the method using synthetic data and are working towards testing the method using field data.

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Author; Mr Ammar Ahmad¹

Affiliation; ¹SLB

Summary;

• Machine learning
• Ground Modeling
• Data Analytics
• Forward Stratigraphic Modeling
• Regression Analysis
• Offshore Wind Farms

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Authors; Mr Gabrio Rizzuti¹, Rob Telling¹, Ivan Vasconcelos¹

Affiliation; ¹Shearwater Geoservices

Summary; The quantitative characterization of the shallow subsurface for offshore windfarm sites is paramount to assess the load-bearing capacity of the soil. Seismic methods have the potential to greatly enhance and complement conventional geotechnical methods, but this requires processing steps that are not commonplace for UHR data. We present a comprehensive Bayesian framework for post-stack seismic inversion that describes the uncertainties related to acoustic impedance inversion. We rely on deeplearning tools, such as multiscale normalizing flows, that enable this type of approach at scale.

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