Technical studies for offshore energy potential, geological and environmental mapping towards support of windfarm developers' decisions

Within the framework of Portuguese policy for the energy transition and economy decarbonisation, the Portuguese Institute for the Sea and the Atmosphere (IPMA) is carrying out project RP-C21-i07.01 – Technical studies for offshore energy potential. This project, funded with 42 M€ by the European Recovery and Resilience Plan, through the component C21-REPOWEREU of the Climate Transition dimension, aims to support Portugal’s ambitions regarding energy independence and ecological transition, in the context of new geopolitical and energy market challenges.

Led by the Marine Geology and Geophysics Laboratory (SEISLAB) team at IPMA, the projects is developing studies to provide detailed data on the geological, geophysical and geotechnical properties of the seafloor, as well to define an environmental baseline. The main objective is to support offshore wind farm developers regarding engineering and financial planning, thereby providing the basis for launching auctions in offshore areas designated for windfarm development in the Portuguese Allocation Plan for Offshore Renewable Energy (PAER).

This project started in early 2024, has a duration of 2.5 years and focuses on surveys in the PAER areas of Leixões and Figueira da Foz, totalling approximately 2000 km², located offshore the western Portuguese mainland coast, at water depths ranging from 120 m to 530 m.

Hydrographic and geophysical survey methodologies included multibeam echosounder (MBES), side scan sonar (SSS), magnetometer (MAG), two sub-bottom profilers (SBP) and multichannel ultra high-resolution seismic (UHRS) reflection data. Geotechnical methodologies included cone penetrating tests (CPT) and sedimentological and physical properties of sediments recollected with grabs and Vibrocoring (VC).

Preliminary works conducted in 2024 included desktop studies and exploratory surveys with the acquisition of approximately 2000 km of geophysical data (MBES, SBP, UHRS). Survey activities carried out in 2025 involved the acquisition of circa 15000 km of geophysical data (MBES, SSS, MAG, SBP, UHRS), 122 grabs samples, 71 VCs and 43 CPTs.

Seafloor surface characterisation relied on cartographic products derived from the MBES and SSS mosaic datasets, as well as on the identification of outcropping units from the seismo stratigraphic model calibrated with the geotechnical data. Seafloor features, including landforms and contacts were interpreted from the MBES and SSS data and validated against magnetic anomalies. These included anthropogenic features like shipwrecks, trawl marks and lost objects (e.g. fishing gear) and geological features like sorted bedforms, boulders, sinkholes and outcrops.

Sub-seafloor seismic data reveal a complex geological framework associated with the rifted margin and orogenic units. The upper units are dominated by unconsolidated sediments and polyphase channel complex events associated with sea level variations, while the lower units frequently display mass-transport deposits, extending for tens of kilometres, tectonic deformation and faulting.

Environmental analysis are based on water and sediment analytical work and on the characterisation of species communities, aiming to establish the biodiversity baseline and assess the environmental condition. Surveys were conducted in compliance with the Joint Nature Conservation Committee guidelines.

The thematic cartography resulting from these pioneering and unprecedented studies in Portugal constitutes a key asset for the development of the floating offshore wind industry, supporting the ongoing Portuguese energy transition