Åsgard subsea gas compression lowered into place
Published: 25 June, 2015
The installation of the modules that collectively constitute Åsgard subsea gas compression has commenced on the Åsgard field. ODEE report.
The new technology at a depth of 300 metres will create 282 million extra barrels from the Åsgard field. A total of 22 modules will be installed and connected. These comprise two identical compressor trains weighing 1500 tonnes each.
During the summer the new technology will be put in place in the large subsea frame that was installed in the field in summer 2013.
The installation work is being carried out by the North Sea Giant vessel, which was rebuilt for the purpose.
All the modules are provisionally stored at Vestbase in Kristiansund, from where they are shipped following commissioning and testing in Egersund.
Safety and efficiency
The modules comprising the subsea gas compression plant vary in size. The smallest modules are being installed via the vessel's so-called "moonpool", a large opening in the bottom of the hull through which the modules are lowered. Modules with a maximum weight of up to 70 tonnes can be installed in this way.
Several of the modules to be installed in the subsea plant are too large to be lowered through the ship's moonpool. Thus, the ship's crane system has been modified to incorporate a so-called special handling system (SHS).
This lifting system is designed to carry a load of up to 420 tonnes and can operate in up to nine-metre high waves. Each module is lowered into the sea via a crane and guided into place with a ROV and cables.
Project director, Torstein Vinterstø, commented: "This crane system makes the installation work safer and more efficient. To ensure quality at every stage of the process, all operational crew have practiced the operations in a specially designed simulator.
"We have also performed a number of sea trials prior to installation."
The installation sequence has been carefully planned so that start-up work can be carried out on the first compressor train while work to install modules on train 2 continues.
The operations organisation in Stjørdal, which will take over the plant once it has been completed on the project side, is closely following the installation work, which, thus far, has been carried out to a high level of quality and in accordance with the established schedule.
"I am very pleased that we have now commenced the installation work and that preparations for start up and operation are now underway”, commented Snorre Grande, senior vice president for Åsgard subsea gas compression in Field Development.
He added: "The ship fitted with the new crane system will also be a good tool for us once the system becomes operational.”
Facts
• Gas compression on the seabed will increase extraction from the Mikkel and Midgard reservoirs in the Åsgard field outside Trøndelag by around 282 million barrels of oil equivalents.
• Compression provides the driving force necessary to ensure a high gas flow and level of extraction.
• For the first time an operator uses compression on the seabed, instead of on a platform. The technology represents a quantum leap that can contribute to significant improvements both in the level of extraction and operational life of a number of gas fields.
• Subsea processing, and gas compression in particular, is an important technology for developing fields in deep water and in exposed areas.
