With the help of offshore mooring and anchoring specialist Todd Veselis, a senior project manager with InterMoor, Bill Clewes looks at the arguments surrounding the use of preset moorings for deepwater drilling rigs.
OE, May 2010
Why would you want to preset independent mooring lines to secure a mobile drilling rig equipped with a purpose-designed mooring system; and, moreover, one that you have already paid for? It’s a reasonable question. A few years ago, there would have been a perfectly simple answer: depth.
In the dash to develop oil and gas reserves in ever-deeper water, preset moorings provided a convenient means of overcoming the depth limitations of the available drilling rigs. It did not take long for the rig companies to catch up with field developers’ needs, however, and simply extending the depth capability of a drilling rig is now rarely the prime reason for opting to preset its mooring system.
So, why have presets continued to gain favour in recent years among operators in various parts of the world? More pertinently, in what sort of situation, under what conditions, is presetting likely to offer the best mooring solution?
According to InterMoor’s Todd Veselis, there are a number of factors to consider nowadays when deciding if it is going to be worthwhile to preset the mooring system for a drilling rig. Depth remains one of those factors, but lots of others come into play: the condition of the seabed; the presence of existing infrastructure; the environmental conditions; the local availability of mooring system components and anchor handling vessels; rig and vessel rates; and, not least, the nature of the planned drilling activities.
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