Specifying and Testing Polyester Mooring Rope for the Barracuda and Caratinga FPSO Deepwater Mooring Systems

Abstract

Abstract Polyester rope is considered to be an attractive option for deepwater mooring systems. Polyester rope possesses many advantages over steel wire rope, however one of the major challenges in using polyester is an accurate understanding of the full scale physical properties. Further complicating this understanding is the variation in rope construction techniques employed by the rope manufactures. These differences may affect the individual performance and behavior of the polyester rope. This paper presents work done in addressing full scale design properties for the P-43 and P-48 FPSOs in the Barracuda and Caratinga fields, offshore Brasil in the Campos Basin in an average water depth of 800m and 1040m respectively. The paper discusses the initial characterization of the polyester rope properties for the engineering design of the mooring system and is based upon various data sources including industry data and Petrobras' past experience and testing. In addition, the paper examines the final development of the polyester rope specification and the resulting full scale qualification of four manufacturers based upon axial stiffness and minimum break load for their 1,250 tonne polyester rope design. Additionally, the recoverable and non-recoverable reep was determined for each manufacturer along with observations about the performance of the different rope constructions. Axial stiffness measurements are presented and compared with the data used during the mooring design and published formulations currently available in the public domain. Introduction Barracuda Field was discovered in June 1989, with the drilling of well 4-RJS-381 and the Caratinga Field in February 1994, with well 1-RJS-491. The Fields are located in central position in Campos Basin, two hundred (200) kilometers east of Macae, in a water depth varying from six hundred seventy (670) to one thousand two hundred (1200) meters and are separated by 12.5 kilometers. The Barracuda FPSO (P-43) is a Stena Concordia class VLCC converted into a FPSO unit with oil production capacity of 150,000 bopd, through 34 wells. The FPSO will be anchored in a nominal water depth of 800m at the Barracuda Field in Campos Basin offshore Brazil. The riser system consists of 81 production and export risers and umbilicals with the ability to accommodate an additional 26 future risers and umbilicals. The Caratinga FPSO (P-48) is also a Stena Concordia class VLCC converted into a FPSO unit with oil production capacity of 150,000 bopd, through 20 wells. The FPSO will e anchored in a nominal water depth of 1040m at the Caratinga field also in the Campos Basin offshore Brazil. The riser system consists of 51 production and export risers and umbilicals with the ability to accommodate an additional 26 future risers and umbilicals. The Caratinga FPSO is located twelve and a half kilometers southeast of the Barracuda FPSO. Each FPSO is spread moored by a taut leg mooring system using eighteen (18) mooring lines, ten (10) lines at the bow, and eight (8) at the stern for a twenty (20) year design life. The systems were designed to withstand the 100 yr storm condition according to API RP 2SK and ABS requirements as a permanent mooring system.