The mechanised drilling method developed by Herrenknecht and Deme to install foundations for large-diameter monopiles was used for the first time at the St Nazaire wind farm in 2021 and 2022.
OFD makes it possible to install foundations for wind turbines and other coastal infrastructure even in rocky seabed.
For the new wind farm, Deme will used OFD to drill boreholes for 61 monopiles in the rocky Atlantic seabed between the islands of Noirmoutier and Yeu. Each monopile has a 7m diameter and will provide the foundation for one of the more than 200m-high wind turbines.
The geology is mostly rock with hardness between 25MPa and 120MPa max and the water depth is up to 36m.
Deme and Herrenknecht jointly developed the drilling and installation method and are continuing their collaboration on the Noirmoutier wind farm. Herrenknecht supplies the drilling technology and specialised drilling personnel who work in shifts on board the installation vessel.
Deme is responsible for the installation of the monopiles and the MODIGA (monopile offshore drilling installation and grouting aid). This serves as a drilling template and enables controlled lowering using a liner, which also stabilises the borehole.
The drilling will be carried out with the 350-tonne OFD machine also used for St Nazaire, where 73 drilled foundations were required. The OFD machine has a drilling diameter of 7,700mm and will drill at depths of 15-27m.
It has been overhauled by Herrenknecht, subjected to extensive functional tests with comprehensive test documentation and then transported to Vlissingen, the home port of the installation vessel Innovation.
In addition to overhauling the machines and reusing them in new projects, Herrenknecht’s sustainability concept includes using OFD drilling technology to keep the seabed largely intact and reduce noise emissions that are harmful to underwater fauna.
The monopiles will be loaded onto the installation vessel in the port of La Rochelle. After the drilling process, the monopile is inserted into the lowered liner, creating the foundation for a wind turbine.
The Noirmoutier windfarm will have a total output of 496MW and generate around 1,900GW hours of electricity per year.
