Riser, mooring integrity critical to deepwater success

Offshore staff

KUALA LUMPUR, Malaysia -- Knowing the condition of riser and mooring systems is critical to successful production of deepwater fields. Frank Lim of 2H Offshore told attendees at the Offshore Asia Conference & Exhibition, "Riser and mooring failure can have potentially catastrophic consequences."

Deepwater poses particular challenges in riser performance, Lim said. "Riser systems become ever more challenging as the water gets deeper."

Lim talked about the difficulty in achieving a reliable riser design because of the many uncertainties that have to be taken into account. "Nothing is certain when designing riser systems," he said. "It is only when you are at full production that you know the parameters."

Lim listed a number of considerations that impact riser design, including current, direct wave loading, hydrostatic pressure, water temperature, vessel motion, seabed interaction, and vortex shedding. "There are a lot of things that can catch you up," he said.

Mooring systems are subject to the same failure issues as risers, Lim said. And moorings fail more often, sometimes even in calm weather, as a result of fatigue. The problem with mooring failures, Lim said, is that they often go undetected because the watch circle doesn't vary in calm conditions.

Lim pointed to monitoring as one means of contending with failure in both riser and mooring systems, noting that monitoring is often not considered until late in the game. "Most operators leave the monitoring system to the last," he said.

Lim said mooring system monitoring is just beginning, but he emphasized its importance in saving time and money for operators.

1/18/2007