Mossel Bay, South Africa
The EM and satellite gas fields are situated 120km south-west of the Mossel Bay complex. They lie in the Bredasdorp Basin Block 9 and were discovered in 1984, when the well tested 10 million ft³/day in early Cretaceous sands. The porosity is typically 13% and permeability ranges from 5-200mD. Reserves are 600bcf. Development drilling is being carried out with the semisubmersible rig, South Seas Driller.
The development consists of three new production wells, tied back by a 450mm (18in) pipeline to Mossgas' production platform, on the FA field 49km to the east. Production is controlled by a buoy, overhead.
The field has been developed by the Bredasdorp Alliance between the owner, Mossgas, and the managing contractor, Dresser Kellogg. The US$387.5 million project first delivered gas to the onshore plant in April 2000. The new fields will supply Mossgas with feedstock until 2007.
The two-phase project involves the drilling of up to five subsea wells into the EM field. A single dual lateral was drilled into the EBF field immediately after the first two EM wells. The first phase was completed in April 2000 and the second phase will be completed in 2001.
A 346t reception-facilities module was installed on the FA platform, to receive hydrocarbons from EM as well as future fields in the area. It was built in Cape Town by SA Five Engineering, at a cost of 25 million rand. The module measures 14x7x17m. Its purpose is to ensure that the gas and condensate received from the new gas fields are compatible with the existing production facilities on the production platform. The module represents a world first, because hydrocyclones to separate condensate and MEG (monoethylene glycol) have never before been used on a commercial scale such as this.
A 55m-high buoy enables Mossgas to control new production wells from the FA platform.
The 34 million rand buoy is the second of its kind in the world. It weighs 331t and the lower hull's diameter is 8m. It is equipped with subsea control as well as UHF/VHF and satellite communication systems. Plus, a complete, self-contained power-generation system forms part of the equipment on-board.
The buoy carries diesel and other fluids required for the operation of the wells and pipelines. Maintenance personnel will periodically visit the buoy, which can take up to six people on board. For protection, the buoy has been painted with a paint above the waterline to the top of the mast. It is also equipped with a flashing marine warning light, a foghorn and a submarine pinger. The buoy has a design life of 25 years (100 year storm) and can serve up to ten production wells. It can be moved to other locations once the EM field is depleted.
J Ray McDermott (Middle East) Inc built the buoy at its Jebel Ali yard in Dubai. Fabrication commenced in August 1999 and it was shipped to Mossel Bay on 23 January 2000 aboard the Kamu, a Japanese vessel with a 450t crane on-board.
The buoy was anchored in Mossel Bay, before being towed out by two tugs to the EM site in late February 2000. It was then installed by the Seaway Discovery. It was tethered to a 2,000t concrete gravity base on the seabed, at a depth of 95m. This gravity base was constructed in Simonstown, near Cape Town.
Three double steel-wire tethers, each 80m long and 50mm in diameter, were used for this purpose.