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"We are delighted to have successfully completed such a demanding project. A world first of its kind, pushing the boundaries of technology. With the difficult winter conditions and remote location, we were thrilled with the team's commitment and overall quality of the installation. We wish Aquamarine Power every success in their Wave Energy Project and look forward to working with them again in the future."

Fiona O'Connell
Managing Director
Stockton Drilling Limited

Orkney - Aquamarine Power

Orkney - Aquamarine Power

600m twin drilled landfall

Project and Site Management

Two 600m horizontal directional drilled landfalls exiting on the seabed in 12m of water.

The Project

Aquamarine Power is developing the Oyster 2 wave energy project off the coast of Orkney. The Oyster 2 wave energy machine will be installed on the seabed and will pump water at pressures up to 140 bar through a 600m long pipeline up to a land based turbine. The Oyster 2 project is a closed loop system, using fresh water and requires a low pressure return pipeline back to the seabed wave energy machine to complete the circuit.

The Oyster 2 project required a 355mm diameter high pressure flow pipe and a 400mm diameter low pressure return pipe to be installed using HDD techniques from the Billia Croo turbine generator on the West Coast of Orkney, passing deep under the rocky shoreline, to exit 600m away on the seabed under 12m of water.

HDD

SDL utilised their 250 tonne HDD rig to drill and forward ream the two 600m long by 559mm diameter boreholes through the ancient Orcadian siltstone formation. Each bore followed a smooth 750m vertical radius to exit on the seabed under 12m of water. The installation of the high and low pressure lines had to be started in early January to ensure completion prior to the arrival of the Oyster 2 machine in early summer. The rough and unpredictable nature of the sea state and the ever changing Orcadian weather eliminated the possibility of performing a conventional pipe pull and instead, both pipelines had to be installed by pushing from land.

For this, SDL used a hydraulically powered pipe pushing machine, mounted on a purpose built frame. The pipe push was further complicated by two factors, firstly 2 x 60mm diameter steel umbilical pipes and a steel grout line had to be attached to the outside of the pipeline. Secondly there was insufficient available stringing space to weld either pipeline in a single string. This resulted in both pipelines being welded up in two off 300m sections. It took 24 hours to weld, inspect, and coat the final weld and to weld up and attach the bundle of umbilical and grout pipes to the outside of the pipeline. After recommencing the pipe push, push loads were lower than expected and both pipelines were successfully installed. Finally a complete string pressure test was performed prior to both pipelines being grouted in situ.

Design

SDL completed all the necessary design works for the installation of the pipes, including the pipe profile, the entry and exit point locations and the pipe push technique. Detailed designs of the pipe, bullnose and end flange construction were also undertaken.

Environment

It has been a real privilege to work in an area of outstanding natural beauty. We operated alongside a stunning coastline and were surrounded by the majestic siltstone cliffs, which are home to some of Britain's rarest flora and fauna. In order to preserve such a spectacular environment it was essential to avoid any disturbance and prevent any incidents during the construction works. In line with Stockton Environmental Policy, thorough environmental aspects, impacts and controls registers were completed, as part of an Environmental Management Plan. The entire drilling spread was located in the excavated area prepared for the Oyster 2 turbine generator, to minimise any visual impact on the environment. During pilot hole drilling and forward reaming works, all drilling fluid was recycled and contained within the HDD compound and borehole annulus. The use of super silent pumps and generator sets together with a clean site policy using enclosed skips for all waste materials minimised any impact on the environment.

Furthermore, Orkney's notorious temperamental weather presented additional challenges, particularly during the winter months. During January and February, horizontal hail and snow were the norm, with up to ten metre high waves crashing onto the beach directly in front of the drilling compound.

Because of the unpredictable nature of the sea state and weather on the west coast of Orkney, conventional pull reaming and pipeline installation by pulling was deemed unworkable. This was replaced with more technically demanding push reaming and one of the longest pipe installations by pushing from land ever attempted, however Stockton's team worked tirelessly to ensure that works were completed according to plan.

It has been very rewarding to be a part of Aquamarine's project, to supply the country with clean sustainable energy. It complements our efforts to ensure that we do our own part in combating climate change by minimising our own carbon emission as members of Achilles Carbon reduction scheme.

Project Summary

  • Full Project & Site Management
  • Installation Of One High Pressure 355.6mm X 648m Api 5l Erw, X52
  • Installation Of One Low Pressure 400mm X 648m Pn16/S-5/Sdr11, Pe100
  • Two 600m Horizontal Directional Drills
  • Operating In A Site Of Special Scientific Interest (SSSI)
  • Tight Environmental Controls


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Designed at B&W studio

HORIZONTAL DIRECTIONAL DRILLING