U.S. NAVY SALVAGE REPORT DEEPWATER HORIZON ... - ESSM

SECTION A: Technical Approach:
Background
A review of past oil skimming approaches developed during/after the Bravo and
Ixtoc blowouts 1,2,3 revealed the following characteristics:
1. Crude oil spills initially form large thin layers which are best cleaned by
large barriers towed slowly to prevent the oil from becoming entrained deep
into the water column where it can flow by the barrier. Furthermore, higher
speeds can form instabilities in the water/oil interface of the pool of oil that
forms in the “bucket” of the barrier which can lead to more loss of oil.
2. VOCs in the oil rapidly evaporate and within a few weeks highly viscous
strips of water-in-oil often called “chocolate Mousse” which spread out over
large areas. These “stringers” will have a total volume an order of
magnitude greater than the thin blue sheens of oil, and consequently their
collection presents the greatest potential benefit.
3. Skimmers typically use inflatable booms, with each leg pulled by a vessel or
by a single vessel with an outrigger or paravane. Oil is concentrated into the
bucket region (vertex of the caternary) and skimmed into a collection ship.
NOFI’s OceanBuster 4 technology has been particularly effective, because the
boom arms funnel the oil into a separate collection zone known as the Pocket. The
boom arms thus remain straighter and a plastic sheet submerged “shelf” in the
collection zone helps retain the oil once it is funneled in; hence the OceanBuster is
capable of collecting oil at speeds approaching 5 knots.
Problems
As the spill matures and more strings form and spread out, single skimmer
operations will be necessary. The following issues will still need to be addressed:
1. In using only a single skimmer per vessel, encounter width is reduced.
2. In traditional dual-towed skimming systems, skimming operations are
limited by the smaller vessel’s sea-handling capabilities.
3. As the oil ages and progresses nearer to shore, the bucket region of towed
barrier, or Pocket in the case of the NOFI technology, will collect significant
debris which can foul the operation of the skimmer or pump
Proposed Solution
The technical approach proposed below is a result of a recent brainstorming
session, at ICP Houma, Louisiana, led by Captain Patrick Keenan (SUPSALV) and
Ms. Stephanie Brown of NAVSEA and attended by Prof. Alexander Slocum of
MIT, Mr. Dag Nilsen of NOFI, and ICP Houma Operations Section personnel.
1 The Bravo Blowout, IKU Report NO 90, Assignment NO 71, Norwegian Information Publishers A/S
2 1977 Oil Spill Conference Proceedings, Library of Congress Catalog No. 75-4161
3 Jerome Milgram, “The Cleanup of Oil Spills from Unprotected Waters”, Index, Volume 20 (1977), pp 86-94
4 http://www.nofi.com/
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