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The 1st Edition of API RP 2SM — Recommended Practice for Design, Manufacture, Installation and Maintenance of Synthetic Fiber Ropes for Offshore Mooring — was released in March 2001. Prior to then, most of the actual synthetic fiber rope mooring applications were installed in Brazil by Petrobras. Since the publication of RP 2SM, polyester moorings have been used in other deepwater basins, including the Gulf of Mexico, for both temporary drilling MODUs and permanent FPSs. Much has been learned from the actual design, manufacture, installation and operation of these systems by other operators and contractors throughout the past decade. This work has created an extensive knowledge base in the areas of both synthetic fiber rope behavior and mooring system design. To best capture these new learnings, an API Task Group assembled to perform a major update in developing a 2nd Edition. API RP 2SM is the recognized standard for synthetic fiber offshore moorings in the Gulf of Mexico as well as other deepwater basins of the world. It is used in conjunction with API RP 2SK (Design and Analysis of Stationkeeping Systems for Floating Structures, 2005) and API RP 2I (In-Service Inspection of Mooring Hardware for Floating Structures, 2008) for the design, manufacture, installation and maintenance of both temporary and permanent synthetic fiber mooring systems. This paper will present the key changes in the update of this API RP. Reasons for the changes and significance on a synthetic fiber offshore mooring project will be discussed. Major changes in the RP include sections on elongation and stiffness testing, contact with the seafloor, creep rupture and axial tension compression fatigue. The new guidance in the RP will allow for improved synthetic fiber mooring systems design, installation and operation while also potentially reducing cost. Introduction In 1997, Petrobras installed a 12-point taut leg polyester mooring system on its P-27 semisubmersible floating production system in the Campos Basin, offshore Brazil. This installation was a first in the offshore industry, and since then Petrobras has installed more than 20 polyester mooring systems on semis, FSOs and FPSOs. In 2004, BP was the first to install a polyester mooring system in the Gulf of Mexico (GoM) on its Mad Dog spar. Anadarko followed shortly by installing a polyester system on its Red Hawk cell spar. Since then several other projects (Gomez, Tahiti, Blind Faith, Independence Hub, Thunder Hawk, Mirage and Perdido) have used polyester mooring systems in the GoM. Polyster moorings are planned for future GoM projects, including Petrobras's Chinook and Cascade development. Additionally, polyester has been used for the Kikeh spar moorings in Malaysia as well as several CALM buoy moorings and turret moorings throughout the world. Similarly on the MODU side, in 2001 both Shell and BP successfully performed a full scale field trial of polyester mooring systems from a MODU. Since then, such systems have become more commonly used. In particular, after the 2004 and 2005 hurricanes, the use of polyester mooring on the MODUs has greatly increased as a possible means to mitigate overload failure or damage to infrastructure on the seafloor should a mooring system failure occur and the MODU go adrift during a hurricane.

The subsea Coulomb field is a two-well gas/condensate development in 7500 fsw, tied back to the NaKika platform in the Gulf of Mexico via a single 27-mile, 8" bare flowline. First production was in June 2004. The design basis employed continuous injection of monoethylene glycol for hydrate inhibition along with a "wax-in-place strategy"; this assumed a low rate of wax deposition, controlled through the use of inhibitor, such that solids accumulation during field life would not constrain production. Fluids from one well are significantly waxier than the well used in the design basis, but this was not known until April 2004. Prior to startup, predictions of the most severe deposition rate in the absence of inhibitor suggested a steady increase in flowline ?P to 3500 psi after 20 years of production. However, in reality the Coulomb flowline experienced a rapid increase in pressure drop to ~4000 psi within the first month of production from the waxier of the two wells, ultimately resulting in the temporary shut-in of that well. Correlation of field observations, transient multiphase modeling and laboratory experiments eventually determined that the deterioration in flowline performance was most likely due to accumulation of a highly viscous material, either a wax/glycol/ condensate emulsion or a wax slurry, stable at ambient seafloor emperature. Further work strongly suggested that burying the flowline in order to improve heat retention by the produced fluids might mitigate this phenomenon. This paper discusses the evolution of the technical justification to bury the flowline and the ultimate impact of the burial with respect to re-establishing (and ultimately increasing) production from the two wells. Introduction The "Coulomb" subsea gas/condensate field is located in the deepwater Gulf of Mexico, at a water depth of approximately 7500 feet. Production from two subsea completions flows 27 miles along the seabed through a single, 8-inch subsea flowline, tied to the host platform by a steel catenary riser (Figure 1). The two wells, referred to as C-2 and C-3, produce fluids with significantly different condensate/gas ratios (CGRs); production from C-2 is rather leaner (65 bbl/MMscf) than that from C-3 (200 bbl/MMscf). Monoethylene glycol (MEG) is injected at the tubing head of each well to provide continuous hydrate inhibition throughout the subsea system. Shortly before production was started up, analysis identified that the fluids from the C-3 well contained a higher wax percentage than those from the C-2 well, which had been used to develop the design and operational philosophy for the field. Shortly after startup, a steady increase in pressure drop was observed in the flowline/riser system; the pressure gradient was approximately twice that predicted by steady-state multiphase flow models. The high ?P in the subsea flowline was attributed at first to wax deposition; the backpressure imposed on the flowing wells caused a reduction of some 30% in the total production capacity of the system. Attempts were made to identify an effective paraffin inhibitor that might reverse the phenomenon, however none was found.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. Abstract Hurricanes Ivan, Katrina and Rita in 2004 and 2005 resulted in twenty-one MODUs having suffered either complete mooring failures or partial mooring failure. The mooring work group under API SC2 was already actively working on the 3 rd Edition of API RP 2I, In-Service Inspection of Mooring Hardware for Floating Structures [1] prior to these hurricanes. However, after the hurricanes, the API RP 2SK, Design and Analysis of Station Keeping Systems for Floating Structures [2], work group was reactivated to explicitly address this issue. The API RP 2SM, Recommended Practice for Design, Manufacture, Installation and Maintenance of Fiber Ropes for Offshore Moorings [3], work group was also reactivated in early 2006. The need to revise 2SM largely lies in the experience gained since it was first issued. However, the work group addressed numerous items that also benefit moored MODUs, especially since the use of a fiber rope insert mooring system can enhance the MODU mooring performance and reliability.A summary of the major changes to API RP 2SK, 95F, Interim Guidance for Gulf of Mexico (GoM) MODU Mooring Practice -2007 Hurricane Season [4], 2I and 2SM recommended practices will be presented. Highlights will be given to code changes to these Recommended Practices (RP) that enable technology to address reliability and robustness challenges. This information will be helpful for people who analyze, design and install MODU moorings.