Following the massive damage to the Deepwater Horizon drill platform in the Gulf of Mexico, a rescue mission has been carried out using new untested methods and technologies. Drill ships including the Discoverer Enterprise and the Discoverer Clear Leader have been employed to carry out works, operating in water depths up to 1,500m.

The deepwater drill ships utilise special N-line tensioner systems to compensate for the vertical drill ship motion between the surface and the ocean bed, which is due to the ocean’s surface swell, and thereby maintain constant tension in the drill string and riser. The N-line tensioner systems employ special hydraulic cylinders produced by Hunger Hydraulik, a company based in Lohr am Main, in Germany. We are able to accommodate drill pipes, which are up to 7km long, and to compensate for wave motion at the same time.

Using this compensation system has made the completion of the top kill trials possible and subsequently also to drill the relief wells to an accuracy of less than 0.5m diameter of the damaged drill hole at a depth of over 5,000m. Furthermore, with the help of a containment dome installed over the well, tens of thousands barrels of leaking oil and gas have been recovered on a daily basis.

Even though the N-line tensioner cylinders have an effective stroke of over 15m, the drill works were forced to be suspended for over a week in July due to hurricane Bonnie. Finally, the technically demanding and long process to drill the relief wells and to seal the damaged drill hole succeeded – with the help of special hydraulic cylinders from Hunger Hydraulik.