Decommissioning offshore wind – cutting and extracting the pile, not fighting it

The first generation of offshore wind was installed with the vessels and economics of its day, smaller, lighter spreads than the fleets installing today’s XXL monopiles. Those early sites are now reaching end of life, and removing them with today’s giant installation vessels is rarely the economic answer. Decommissioning this older inventory calls for methods built in the same spirit it was installed: innovative, but safe and matched to the asset rather than to the largest vessel on the market.

We are developing a pile-extraction concept that does exactly that, combining proven MintMech equipment with an integrated cutting technology to cut, free and recover a redundant foundation pile without a heavy-lift campaign. This is a concept we are actively developing and hold intellectual property in; the description below is the method, not an off-the-shelf system.

The idea: the pile-top drill becomes a numerically-controlled cutting and jacking machine

Our pile-top drill already carries the drive, the telemetry and the position awareness to know exactly where its bit is and what it is doing. That makes it the natural platform for precision cutting and controlled jacking, so instead of drilling a hole, the same machine becomes a numerically-controlled tool that works the pile itself.

• Cut the pile with an integrated water-jet tool – a very-high-pressure abrasive water-jet cutting tool (high-pressure water carrying an abrasive cutting medium) is integrated into the drill bit. Using the drill’s existing telemetry and bit positioning, the whole assembly behaves like a numerically-controlled machine: it cuts the pile cleanly through-wall, at a controlled level below the seabed and cuts the additional features the next step needs.
• Cut the jacking ports in the same operation – the same controlled cutting opens holes in the pile wall to receive high-load jacking cylinders. The cylinders are integrated into the drill bit assembly, so cutting and jacking happen from the one machine without a separate spread.
• Jack the upper pile out using the lower pile as the reaction – once the pile is severed, the integrated high-load jacking cylinders push the upper (redundant) section up out of the ground, reacting against the lower section that stays in the seabed. The principle is the same as a bi-directional load cell reacting against a buried lower section: the ground resistance of the buried section is far greater than the force needed to push the freed upper section out, so it makes a dependable reaction foundation.
• Guide the pile with a standard pile gate – one of our standard pile gate designs guides the pile as it comes up, keeping it located and controlled while the jacks drive it part-way clear.
• Switch to a semi-buoyant lift to surface it – once the pile is jacked far enough clear, we de-rig the drill and BHA, remove the jacks and switch the driving force to buoyancy. Pile bungs and grippers make the freed section semi-buoyant, recovering it the same way semi-buoyant lifts were used to install early foundations. The lift method is matched to the asset, not to a heavy-lift vessel.

Why it stands up: tried-and-tested parts, combined in a new way

The concept is deliberately not a leap into the unknown. It is an innovative combination of equipment we already design, build and commission, plus one integrated cutting technology:

• MintMech pile-top drills, drill bits, BHAs and drill string – the cutting and machining platform, already carrying the telemetry that turns it into a numerically-controlled tool. See pile top drill and large diameter drilling.
• Spoil management and airlifting – clearing arisings during cutting and freeing the pile. See airlifting.
• MintMech high-load jacking cylinders – the same engineering behind our jacking systems for jack-up barges and our subsea levelling systems, repurposed to push the pile from the ground.
• A standard pile gate – guiding and controlling the pile as it is jacked out. See pile gates.
• Pile bungs and grippers for the semi-buoyant lift – controlled buoyancy to surface the freed section.
• An integrated very-high-pressure cutting solution – one component we bring in and integrate into our drill bit rather than run as a separate cutting spread.

Each of these is established MintMech work; the innovation, and the IP, is in integrating them into one machine and one accountable method, so a redundant pile is cut, freed and recovered without mobilising a heavy-lift campaign sized for installing today’s foundations.

Where it fits

It targets the growing offshore wind decommissioning market, the ageing first-generation sites now reaching end of life and shares its toolset with our wider decommissioning drilling and large-diameter drilling work. The same thinking transfers to other end-of-life marine and foundation removal where pulling or heavy-lift extraction is uneconomic.