Paper submitted to EAGE Annual 2026
Summary
Before the construction of an offshore wind farm (OWF) geophysical and geotechnical site characterisation surveys are undertaken. One of the main aims of these surveys is to enable an integrated interpretation to characterise the structure and properties of key soil units, identify hazards and enable reliable and safe foundation or anchoring systems to be selected and designed appropriately. However, these geophysical & geotechnical site characterization surveys can take multiple years because of both structural and technical reasons. One reason is that prior to final investment decision project funding is limited & expenditure on site characterization must be carefully managed. A key technical reason is that geophysical data is required to both plan and derisk geotechnical surveys. A sequential and iterative survey strategy is sub-optimal and ultimately unsustainable with the growing scale of offshore wind developments, ambition to develop projects rapidly, and need to reduce the levelized cost of energy. Also, many seismic surveys that are undertaken are 2D and multiple surveys may be undertaken with increasingly fine line spacing as the project progresses. Nevertheless, even after this kind of multiyear campaign there can be uncertainty about the spatial variability of key subsurface units and properties, as well as lack of flexibility in the placement of infrastructure such as wind turbine generators (WTG). Such uncertainties – and the need to mitigate risk – contribute to conservatism and over-engineering of structures such as WTG foundations e.g. using more steel than is necessary. Moving from 2D to 3D seismic methods reduces subsurface risk and uncertainty but it must be both necessary and cost-effective (see e.g. Catterall et al. 2025). Using a case study from a recent project in Northern Europe we show that an integrated geophysical and hydrographic survey incorporating ultra high resolution (UHR) 3D seismic data – utilizing advanced processing and imaging methods - to characterize the seabed & shallow subsurface is a viable way to both optimize the OW site characterization process and reduce the overall duration & cost. This survey strategy will decrease the number of geophysical surveys undertaken, whilst honouring site complexity and subsurface heterogeneity across at spatial scales ranging from meters to hundreds of square kilometres (see McKay et al. 2025).