5 huge MWA structures of 90t - moored with Dynamica Tethers

The 5 MWA structures measuring 12.5m x 14m, manufactured by National Oilwel Varco (NOV) and installed by Havfram (former Ocean Installer) at Balder field. The installation required each of the MWA's to be pulled down by a system of Dynamica MWA Tethers. This enabled connection to the preinstalled suction mid-water arch foundation anchors, consisting of a 140t clump weight.

Dynamica Tethers are reliable synthetic subsea mooring systems that secure risers, umbilical and mid-water arches connected to production systems, ensuring smooth flow of oil to processing facilities.

Well over 90km of flowlines and nearly 2,000t of structures have been installed in the process of re-developing the Balder field. Meanwhile offshore mooring pile and bottom chain installation operations have been completed.

We designed the complicated tethering system, in matched pairs, with very exact lengths using the latest CAD technology in close cooperation with our customer.

Tethers were produced with high-performance fibres with very little creep, even after being subject to millions of cycles over 20-30 years life span.

Fibre Tethers were equipped with multiple layers of flexible laminated and PU-coated jackets eliminating any chance of particle ingress into the load-bearing core.

The design of MWA Tethers was chosen in order to achieve the best possible long-term performance under dynamic subsea load conditions.

The installation went smoothly, as the tethers were designed with minimal length tolerances in pairs, down to below 0,1% between matched pairs and redundant sub-tethers.

“The project deployed more than 1 million man-hours and well over 1,000 vessel days” 

Havfram

Balder is a field in the central part of the North Sea, discovered in 1967. The water depth is 125 meters, while the reservoir lies at a depth of 1700 m. The oil is transported by tankers. Excess gas from Balder is exported from the Jotun FPSO through the Statpipe system to Kårstø in Norway and from there on to continental Europe. The field has been developed with subsea wells tied-back to the Balder production, storage and offloading is done by a vessel (FPSO).

Photo credit ‘Havfram’