Lessons Learned From the Evolution and Development of Multiple-Lines Hybrid RiserTowers for Deep Water Production Applications

摘要

The multiple-lines hybrid riser tower which was first applied inrnthe late 1980’s in the Gulf of Mexico, and more recently to deepwaterrnFPSO projects at the Girassol field in Angola, is nowrnstarting to be applied more widely on other deep water projects.rnThis paper presents the lessons learnt from the design of recentrnhybrid riser tower applied to meet the requirements of severalrndifferent deep water field developments. The paper specificallyrnaddresses the various changes made to the Hybrid Riser Towerrnrelating to the design, fabrication and installation. Thernperformance aspects are discussed along with informationrncovering the overall costs associated with the use of riser towersrnas opposed to other single riser line concept. The paper alsornconcludes on the possible future evolution of the HRT to meetrnthe future ultra deep-water developments.rnIntroduction:rnThe first generation of multiple-lines hybrid riser tower (HRT),rncalled FSPR (Free Standing Production Riser), was designed as arncost effective re-usable riser system by Cameron Iron Works inrn1983 and installed in 1988 by Placid on the Green Canyon fieldrnblock 29 (see reference 1). The structure was then upgraded andrnreinstalled on the deeper Garden Bank field (2096 feet waterrndepth) by Enserch in 1994 (see reference 2). This early conceptrnof HRT used the drilling technology to assemble the riser bundlernwith adequate buoyancy from a drilling rig; the riser tower footrnand spools were connected to a subsea base manifold and flexiblernjumpers at the top were connected to the rig. Refer to fig 1. Thernconcept proved to be cost effective and well adapted to operate inrnthe Gulf of Mexico environment.rnIn 1997 Total called for a design competition to define thernsubsea architecture of the Girassol field (1450m WD) discoveredrnin Angola. Stolt Offshore proposed three riser towers of what canrnbe considered the second generation of HRT after the firstrnexperience in the Gulf of Mexico. This technological choice wasrnmainly motivated by the stringent thermal insulation requirementrnimposed by the field operations and the layout (see reference 3).rnThis second-generation design of HRT was completely designedrnto accommodate the specific fabrication and installationrnrequirements associated with the Girassol field and itsrngeopolitical environment.rnThe AMG consortium consisting of Stolt Offshore (67%) andrnSaipem (33%) was awarded the contract for designing,rnfabricating and installing the Umbilical, Flowline and Riserrnsystem which included the three HRTs. The Girassol field, whichrnwas designed for a nominal production of 200,000 bbl/d has inrnpractice been capable of significantly higher production rates.rnThis success encouraged Stolt Offshore to further develop thernconcept and use the lessons learnt from the Girassol project tornimprove the HRT design and take it into the third generation ofrnHRT refer to Fig 2. The Greater Plutonio field operated by BP inrnAngola will be equipped with an HRT of the third generation.rnOther Contractors and Operators also consider the HRT for theirrndeep-water field development. This accumulation of experiencerncertainly allows to consider a possible design evolution towardsrnthe forth generation of ultra deep water HRT in beyond 2000mrnwater depth.