Steel Catenary Riser for the Marlim Field FPS P-XVIII
Authors: Serta O.B. , Mourelle M.M. , Grealish F.W. , Harbert S.J. , Souza L.F.A. 
Published: October 2008

Steel catenary risers (SCRS) have been successfully deployed on the Shell Auger TLP in the Gulf of Mexico and will also be deployed on the Shell Mars TLP. There is considerable interest in using SCRS for other applications, in particular for semi-sub based FPS systems.

Petrobras is developing an SCR for installation on the PXVII I platform, located in the Marlim Field, Campos Basin, in a water depth of 910 meters. The riser will be a dead-ended prototype which will be monitored for a period of up to one year. Subsequently, it will be connected via flexible piping to the PXXVI platform, located approximately 5 kilometers from PXVH1.

This paper describes the design, materials, components, specification and installation of the Petrobras P-XVIII SCR. The static/dynamic design, VIV analysis and fatigue analysis methodologies are discussed in detail and results are presented.

Important aspects of the flex joint design and specification are discussed. This project represents the first application of SCRS to semi-sub based FPS systems. in addition, it is the first use of SCRS outside of the Gulf of Mexico.

Introduction

Petrobras uses flexible risers extensively in all of their FPS installations. However, there are technical and economic limitations for large diameter flexible risers in deep waters (normally used for oil and gas export by Petrobras). In the case of Petrobras XVIII (P-XVIII), it was necessary to use two 12 inch oil export flexible risers instead of a single 16 inch flexible line, due to technical limitations in manufacturing the bigger line, Steel Catenary Risers (SCRS) can provide a technically feasible alternative.

In addition to the manufacturing limitations mentioned above, significant potential savings may be achieved by deploying SCRS instead of flexible risers. This is due to the high procurement costs for flexible lines, which cannot compensate for their lower installation costs A recent cost estimate for the next five FPS platforms to be installed in the Marlim and Albacora Fields (which will require 17 export/import risers ranging from 8 inch to 16 inch ID) indicates a difference of around US$70 million in favor of the SCR solution,

Project Background

Currently there are only two installed SCRS, both on Shell's Auger TLP [I] (the SCRS for the Mars TLP will be installed in the first six months of 1996). The behavior of a semi submersible in terms of movements and displacements is significantly different from a TLP and implies a different operational environment for the riser. Because the static displacements are larger and the dynamic motions more severe, it is necessary to employ higher tension in the SCR, in order to reduce bending in the sag bend,

Therefore, for the case of the P-XVIII, a detailed evaluation was mandatory. Five different deep water scenarios in the Campos Basin were analyzed by the University of S50 Paulo [2], These studies concluded that an SCR installation was feasible and it was therefore decided to initiate detailed design of an SCR for the P-XVIII FPS.