The Swire Appraisal and Early Development System (A&EDS) is based around a sub-surface riser buoy design with a spread mooring system and process suite located on deck. The Swire A&EDS is designed around a UT755L hull. Swire Pacific Offshore already owns a number of this class of Rolls Royce Marine dynamically positioned platform supply vessel. The vessel draws the riser buoy into a moonpool within the centre of the vessel and no swivel is included in the design. Well stream fluids, power and control signals from the geo-stationary riser(s) are transferred direct to the Swire A&EDS’ piping and cabling system via a riser buoy locked into a moonpool. The mooring system is of compliant design and permits adjustment and limited weathervaning around the centrally located moonpool through which the sub-surface riser buoy is mated to the vessel.

At the approach of a cyclonic storm or other potential adverse weather, the sub-surface buoy can be rapidly disconnected and lowered to support the riser system independently some 50 metres below the surface of the sea, while the Swire A&EDS vessel unmoors and seeks shelter. As monsoon conditions are usually associated with regions where cyclonic storms occur, the mooring is designed to orientate the vessel so that it lies head into the prevailing seasonal weather, with a planned re-orientation twice yearly at the change of each monsoon.

The merits of this system lie in the simplified riser system with no swivel and a mooring that is not only practical and effective under non-cyclonic conditions, but also includes a simple, quick-disconnect mechanism that enables the Swire A&EDS to leave its mooring without delay when infrequent severe cyclonic conditions are forecast.

The Swire A&EDS is also well suited to temporary production requirements, whereby an oil company can use the unit to continue producing from platforms shut down for topside maintenance. For a Swire A&EDS plugged into an existing export pipeline, there is no need for the storage tanker, as the oil would be exported via the existing line. A simpler four point mooring can be used, rather than the disconnectable nine point mooring which would be used on a stand-alone new field development.