DW rigs maintain station (staying positioned over the wellhead location on the seafloor, within an operationally defined radius) by using either a mooring system or a dynamic positioning system.
Source: API RP 96, Deepwater Well Design and Construction, First Edition, March 2013. Global Standards
System capable of limiting the excursions of a floating structure within prescribed limits.
Source: ISO 19901-7:2013, Petroleum and natural gas industries – Specific requirements for offshore structures – Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units. Global Standards