WEST TUNA I BREAM B: APPLICATION OF CONCRETE TECHNOLOGY OFFSHORE AUSTRALIA

Abstract

Esso/BHPP's West Tuna and Bream B Platforms are the first completed concrete-based platforms in Australia and are Exxon's first designed, built and operated concrete gravity structures (CGSs). Both platforms were towed to location, complete with commissioned topsides facilities, in fourth quarter 1996 and successfully installed in 61 m of water. They will add in excess of 45,000 BOPD (7200 kl/d) of oil production to Bass Strait volumes. West Tuna, with 48 well slots, will be Esso/BHPP's largest and most complex Bass Strait production facility, whereas Bream B will be an 18-slot, unstaffed minimum facility satellite platform with a 720-tonne topsides. By comparison, West Tuna's topsides weigh 7,300 tonnes.

Esso/BHPP chose the CGS concept for the two developments following extensive conceptual studies with selected North Sea designers. Because of rising derrick barge day rates in the early 1990s (required for steel pile jacket installations), coupled with the availability of a suitable casting basin near Sydney, the CGS concept was judged economically attractive, with savings estimated at 10 per cent of the total facilities capital expenditure relative to its steel pile jacket alternative.

The project saw a number of firsts, including the use of the world's largest land-based crawler cranes to lift and set the completed production modules over 75 m in the air onto the completed CGS structures. CGS fabrication productivity problems were experienced during the early phase of construction reflecting the complex nature of the construction, however implementation of a number of project management initiatives resulted in achievement of world-class productivity by completion of the works.