When drilling in shallow waters a pure Dynamic Positioning (DP) station keeping solution may not be sufficient for the small offset requirements, hence to increase the station keeping capacity a mooring system is required. In ice infested waters, with extreme ice conditions, the ability to quickly disconnect the mooring system and leave the location, as well as a short reconnection time, is of great importance for safety and productivity.
To meet the industry need for exploration drilling in shallow water in the Arctic, an attachable turret mooring system for drillships, ATMOS (attachable mooring system), has been developed. Combining the ATMOS with a drillship´s DP system creates a thruster assisted mooring system and significantly increases the station keeping capacity of the drillship.
This paper presents a drillship mooring system that has been designed specifically to meet the challenges of drilling in Arctic regions but also for operation in open water and/or harsh environment in both deep and shallow waters. Stena has spent a number of years developing and refining the ATMOS concept for use with an Arctic 6th Generation drillship. The development process has included engineering, concept approval by Class, and both open water and ice model testing.