Application and Evolution: 17.5Te, 85Te and 250Te to 3000 meters using a Drum Winch Approach, HMPE Fiber Rope and Efficient Offshore Vessels

Abstract

Abstract The experience gained from the utilization of the synthetic fiber, high modulus polyethylene (HMPE) to carry out specialist cargo recovery using in 3000 meters water depth, using an adapted 17.5Te drum winch, has lead to the development of a patented drum profile. This profile allows the fiber rope to be spooled evenly and prevents excessive flange loading and cutting in. It also minimizes heat generation in the fiber rope compared to alternative types of winch, as the fiber rope is put through fewer bend cycles. This enabling technology has been harnessed by Expro AX-S to deploy and recover its innovative light well intervention system capable of working down to 3000 mwd, using an 85Te actively heave compensated fiber rope drum winch operating from a 120m, DP2 monohull. The drum profile has also been incorporated into the established design of an offshore deck crane to deploy and recover 250Te to 3000 mwd. These developments have only be made possible by a combination of calculated risk taking, to be some of the first to use HMPE in deep water lifting application; backed by rigorous testing to further understand the nature and influencing factors that affect the working life of fiber rope; and the application of an integrated systems approach. The commercial goal is to open up deep and ultra deep water by providing safe, reliable and cost-effective means of deployment and recovery using readily available monohulls in combination with a synthetic alternative to steel wire rope that it weightless in water. Cargo Recovery in 3000 meters of water The global oil and gas industry has immense financial power, and yet it is often slow to adopt new technology, probably because it still makes the bulk of its revenue without having to do so. The salvage industry, however, is exactly the opposite. It can only achieve, especially in the niche activity of cargo recovery, by taking advantage of every new advance that will make its activities safer, cheaper and faster. This is why as far back as 2000 Deep Tek took the strategic decision to harness synthetic fiber for operation down to 3000 mwd, after experiencing the weight penalty of a wire wound umbilical in 1250 mwd. The properties of a wide range of fibers were investigated and HMPE was chosen, as it provided the best alternative for marine lifting application when compared to steel wire rope of the same diameter. A 3500 meter length of 28mm, 12×1 strand HMPE with standard urethane coating was purchased. A bespoke drum winch, designed to accommodate 1800 meters of 32mm diameter hoist umbilical was modified to take the extra capacity. Its Lebus grooving was made flush with a covering and new spooling gear was added in order lay on the rope in an open, crossing fashion; an idea that was taken directly from handling fiber rope on tug winches, in order to prevent ‘cutting in’. The result was the onsite proof that a drum winch could be successfully used to repeatedly deploy and recover varying loads down to 3000 meters water depth; undertaking many hundreds of cycles from the surface to the seabed and back again, and still remain within its original safe working load. The only drawback was the spooling pattern, which was uneven, was not deemed suitable for larger diameters of fiber rope for continued cycling. The quest therefore continued for a means of handling heavier loads.