Mega oil and gas reservoirs have been discovered in deep and ultra-deep offshore Brazil. These Pre-Salt discoveries are remotely located at water depths ranging from 2200m (~7,200 ft) to 2600 m (~8,500 ft). Offshore Brazil has unique metocean conditions with long swell periods which present challenges on floating platforms such as Spars and Semis. In addition, the remoteness of location and the associated high cost of vessel mobilization add further pressure on economics and risk. Quayside integration is thus a desired feature of the hull concept in order to eliminate offshore mating and the associated risk to cost and schedule.
To explore these pre-salt complicated ultra-deepwater reservoirs usually require large drilling rig and drilling variable payload which result in very large topsides in both size and weight. Spars and TLPs are the only two proven dry tree hull forms in deep and ultra-deep waters in the GOM. However the TLP becomes cost prohibitive if the water depth is beyond 1,524 m (5,000 ft). For large payload systems requiring a large drilling rig, a suitable Spar size creates a challenge for transportation and installation. The semi-submersible hull form is known to offer advantages over Spars such as larger deck space and quayside integration which are essential to reducing offshore commissioning time and risk as well as cost and schedule.
Maturation of the dry tree semi-submersible solution in GoM ultra-deepwater (2,400m) had been undertaken by RPSEA and dry tree Paired Column Semisubmersible (PC Semi) platform, developed by Houston Offshore Engineering, was selected by the RPSEA committee in 2009. Extensive wind tunnel tests and wave basin model tests including 1,000-year central GoM hurricanes were successfully completed in 2010. PC Semi hull configuration, TTR stroke, the analytical results and simulation tools had been fully validated.
This paper presents validation analysis results of a dry tree PC semi developed with conventional RAM style tensioners, in 2,400m ultra-deepwater of Offshore Brazil Pre-Salt carrying same topsides payloads as RPSEA. The validation analysis was performed by the correlated analysis tools and established analysis procedures. The design efficiencies including payload, steel weight and production efficiencies of PC Semis for BPS and central GoM are addressed and discussed. Highly efficient PC Semi for BPS has been developed, validated and became "market ready".
