Lazy-Wave Steel Rigid Risers for Turret-Moored FPSO

Abstract

The free-hanging SCR (Steel Catenary Riser) was adopted by Petrobras as a cost-effective alternative for oil and gas export lines on deepwater fields, where large diameter flexible risers present technical and economic limitations. It is considered an available technology for semi-submersible application. There was interest in applying SCR’s attached to FPSO (Floating, Production, Storage and Offloading) units due to the trend of using these units for exploration and production in Brazilian deep waters. This alternative has to be carefully studied due to the high offsets and heave motions imposed by the vessel on the top of the riser. This work presents the approach and methodology adopted in Petrobras to study the structural integrity and feasibility of a lazy-wave SCR attached to a bow turret-moored FPSO at a water depth of 1290 m. The analysis was performed using the Petrobras’s in-house computer codes ANFLEX and POSFAL developed and implemented as part of projects from CENPES with “COPPE/UFRJ - The Engineering Post-Graduating Coordination of the Federal University of Rio de Janeiro”. For VIV (Vortex Induced Vibration) fatigue damage calculation SHEAR7 was used.

Vessel relocation strategy for multiple steel catenary riser fatigue damage mitigation

“…The objective function values at the feasible design points can be obtained by evaluating them at 𝐗 𝐅𝐃𝐒 as shown in equation ( 13). The corresponding feasible set of index systems, 𝐈 𝐅𝐃𝐒 , which is a subset of 𝐈 is expressed in equation (14).…”

“…These solutions include the SCR configuration change, alternative riser pipe material application, increased understanding of riser soil interactions, decoupled SCRs, upset pipe end, hydrodynamic dampers, vessel relocation, etc. SCR configuration can be changed to obtain steel lazy wave risers (SLWR) and shaped risers [10][11][12][13][14][15]. This will require the installation of buoyancy modules on the section of the SCR.…”

Steel Catenary Riser Design and Analysis for Petrobras Roncador Field Development

“…There was a work carried out at CENPES that focused in considering two peak sea states and with environmental data bringing concomitant occurrence of wave, current and wind , [12,13,14]. .…”

Influence of Fatigue Issues on the Design of SCRs for Deepwater Offshore Brazil

“…To minimize this impact, one solution adopted was to develop a statistical treatment procedure in order to reduce the database to a reasonable number of representative loading cases to be used in fatigue damage verification [8] [7]. Nevertheless, riser design schedule may be impacted mainly if random time domain analysis is used.…”