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Towage and Marine Operations

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  • ombugge
    Originally posted by Steve.B View Post
    Ombugge, I have come to the conclusion that the word 'small' is not in your vocabulary!
    Oh yes, it does. just look at a post on the Fishing boat thread a few days ago.

    As for the boat inside the barrier, I think it is this one:

    Loa 32.3 m./106 ft. (Not sure, but look similar)

    I can assure you, I don't get involved in that type of operations any more. The pressure is tremendous and for younger people to deal with.

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  • Steve.B
    Ombugge, I have come to the conclusion that the word 'small' is not in your vocabulary!

    I love seeing these massive operations, and some of your photos really do out the size of some of this kit into perspective. For example, the photos of the Ekofisk Barrier, the ship inside really shows how big that thing is! Like you say, the ship looks like a toy boat! From the photo she looks similar to some of the older RFA ships.

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  • pilotdane
    Don't worry. Your post was read and I looked closely at each picture for a very long time trying to figure out what was happening. Your description was very good and you answered most of my questions as I read the post. And, I did not want to comment on the hair cuts in the barbeque picture .

    It is hard to provide too much information on this forum.

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  • ombugge
    Towage and Marine Operations

    As said on the new "Floating Crane" thread, the "Supply Ships" thread has been badly abused, mainly by me.
    I therefore take the liberty to propose starting a few new threads to separate the various Offshore Oil & Gas subjects for better clarity.

    To start it off I re-post about the Ekofisk Barrier tow and installation (previously posted in the "Supply ships" thread, post #121), which is probably the most complex Marine Operation ever performed. It didn't attract any comments earlier, but here is a bit of background info I found on the web, which may gain some interest:

    In 1984 the seabed around Ekofisk was found to be subsiding at a rate of about 0.5m per year and the total subsidence expected to reach 6.0 m. This subsidence made it necessary to protect the existing installations against severe wave action due to the fact that an increased part of the structures were submerged with consequently a reduced air gap.
    The field lay-out of the Ekofisk Complex is presented in Fig. 1.
    The topsides of all the jacket structures and all the bridges were raised 6 m in a jacking operation in summer 1987.
    However the design and lay-out of the concrete 2/4 Tank (see Fig. 2) including the two main decks at +90m and +100m above seabed level with all the modules and processing equipment did not allow for a jacking operation. As subsidence of this magnitude was not accomodated within the original design Phillips Petroleum Company Norway(PPCoN) and their partners investigated alternative solutions to protect the 2/4 Tank topsides and finally selected a Protective Barrier structure forming a complete ring around the existing 2/4 Tank. This is shown in Fig. 3. In February 1988 Peconor Ekofisk A/F was awarded the contract for the detailed design, procurement construction and installation of the Protective Barrier. Peconor Ekofisk A/F is a joint-venture of three Norwegian and two dutch companies. In Refs(l) and (2) a review is given of detailed design aspects of the structure and its foundation, whereas in Ref(3) information on hydrodynamic analysis and model testing programmes being part of the detailed design work is presented. A general review of the marine design work is outlined in Ref(4).

    Here is an abstract from a paper presented at OTC in 1990:
    Title : Transport and Installation of Protective Barrier Ekofisk 2/4 Tank
    Authors : P. Donoclift, Phillips Petroleum Co. Norway; T.G. Gijzel, Peconor Ekofisk/VSO; H.G. Hjelde, Peconor Ekofisk/AVECO; J.R. Veldkamp, Peconor Ekofisk/VSO
    Source: Offshore Technology Conference, 7 May-10 May 1990, Houston, Texas.
    Copyright 1990. Offshore Technology Conference

    After an engineering and construction period of sixteen months in June 1989 both halves of the Protective Barrier for the Ekofisk 2/4 Tank were ready for tow-out and installation. To enable installation of both halves immediately after each other both structures left the inshore construction site with approx. 1 day in between. Consequently two towing fleets had to be mobilized totalling 18 towing vessels with 2215 t bollard pull, the largest towing fleet ever assembled.

    At the Ekofisk Field during the approach to the 2/4 Tank the structures had to pass neighbouring installations with clearances down to 10 m. Arriving close to the 2/4 Tank clearances during manoeuvering reduced to 2 m, whereas the acceptable final positioning inaccuracy was less than 0.20 m, over the full height (84m)of the joints between the two halves.
    To enable this complex and critical operation in a fully operational Ekofisk Field (as a shut down was not acceptable), several installation systems and facilities were used, together with detailed preparation of the activities and training procedures of the responsible personnel.
    The installation was completed successfully and the required installation accuracies were met. The achieved position accuracy at the seabed was within 0.05 m of the target.
    This paper outlines several operational aspects of above described towing and installation and shows the feasibility of positioning large gravity structures with very high accuracies.
    Maybe an idea to move the following posts from the Supply Ships thread to this thread: # 108, # 109 & # 121, as they fit better under this title.

    I also propose to start a new thread for; "Rigs, Platforms and Oil Fields etc." to clean up the "old" thread. FPSO/FSO is a part of an Oil Field so they should also fit in here.

    Offshore Construction, Pipe laying and related operations can be thrown in with the Crane Barges in the new Floating Crane thread, as most such operations are done with combined Derrick/Lay Barges (DLB). Floatels and Accommodation/Work Barges falls more or less into this same category, as they are used mainly during construction.

    That should pretty much cover the Offshore Industry.

    I can start the threads with some new posts over the next few days/weeks, but I don't know if I have the authority and knowledge to move posts between threads.

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  • ombugge
    Ekofisk Barrier - Tow and Installation in Field

    This is a continuation of the a post on the Heavy Lift Carrier thread a while ago. This cover the completion of the barrier at Aalfjord, tow to field, installation and present status:

    The two barrier halves were anchored in Aalfjord during the winter of 1989 and slipformed to their full height of 120 m. Some of the top walls were installed, but some had to be left out as we would have to bring the barrier into place under the existing bridges to/from Ekofisk Centre:

    That "toy boat" floating inside the tub is actually a full size vessel, just to illustrate the dimensions of this barrier.
    The little white "boxes" on the right is our "bridge" for the tow (top) and instrument rooms for etc. (All are 20' Containers)

    Before leaving we did a "Trail Mating" to make sure the two halves would fit together once we set the down on bottom in the field:

    They did.

    The first half leaving Aalfjord under tow by 9 tugs:

    It is mid-summer and near mid-night. Beautyful weather.

    For a photo oportunity the 9 tugs for the second half was arranged as if also towing and some were good aerial photoes were taken, but unfortunately I don't find any copies here. (Maybe somebody can find on the net?)
    This was the largest fleet of big tugs ever assambled for a single job and the spot market rate in the North Sea has never been higher then when this operation and the Gullfax C tow took plase nearly simultanuously.

    Weather en route was perfect, flat calm seas and over 20C. even at night. We had a barbeque on deck:

    Due to the draft of abt. 67-68 m. we could not take the direct route to Ekofisk Field. We had to skirt the "shallow" banks to the north by going into British sector and approach Ekofisk Field from the SW.
    This is the sight that met us on approach:

    The first half had already been positioned and the complex was going at full production. (350,000 Bbls/day C.O.+ Natural Gas for export to Germany)

    I don't have any pics of the actual installation process here, but it was the most complex Marine Operation ever performed, in my opinio. Tolarance of relative position between the two half was 7.5 cm., which we acheived

    Here is a pic of looking down between the Barrier and the Ekofisk Tank, once in position:

    This is a pic taken from the net, showing Ekofisk Centre with its protective barrier in place and completed:

    I had long left by that time.

    This is what it looks like today:

    The production equipment has been removed, but it would be too difficult and expensive to remove the 1 million tonnes Tank and the barrier, which is filled with sand dredged up in the vicinity and probably weigh about the same.
    (Weight on tow-out was abt. 230,000 m.t. for each half, of which about 50,000 t. was ballast)

    Does anybody have good idea for what to do with such a relic once the rest of the field is removed and only this "Island" is left? (Sorry, no Palm trees)

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  • ombugge
    Gyda Jacket Tow

    The second towage operation was in Sept. 1989, also from Vaerdal, but this time to the Gyda Field, offshore Norway. The same Barge (M-44) and the same Crane Vessel (M-7000) was involved. The lead tug this time was the British tug "Salvageman".
    The Gyda Jacket was abt. 8,500 m.t. with slings and spreaders and about 120 m. tall. It was loaded standing upright on the barge so it could be lifted and set on the seabed in one easy operation. Also a "first" and the heaviest lift ever done offshore until then. (That record did not last long, however. I don't know what is the record lift now, but I believe it is over 12,000 m.t.)
    Here is a pic of the M-45 with the Gyda Jacket on board:

    We followed the same route to Grip and again the weather forecast suddenly changed, so I had to seek shelter in Vartdalsfjorden. The pressure was tremendous, as M-7000 was standing by in the field and waiting, at a cost of USD 350,000/day (Now probably double that)
    When we eventually got good enough weather and forecast to proceed to sea, I was planning to take the inshore route for the first bit to save some time, until I realised that there was an electric cable across the Rovdefjord with "only" 120 m. free sailing height. I quickly changed my mind and went back the way we had come in.
    Once we go out in open water the barge behaved remarkable well, despite having a very tall "superstructure":

    When we got to the field the M-7000 was ready to lift but the weather window was very short, this being already late Sept. and the first few autumn storms had already passed.
    Here is the barge under the cranes, ready to lift:

    As soon as the jacket was lifted clear I moved the barge away and the jacket was lowered to seabed and positioned over the template:

    Within a few hours the next storm came through and I spent something like 18 hrs. on the barge before it was safe to transfer back to M-7000.

    Here is the Gyda Field now, operated by Canadian Oilco. Talisman:

    This was my last job for Micoperi as the went bankrupt and was eventually "sold" to Saipem, but we were then planning on lifting a 11,000 m.t. deck structure onto the Sleipner concrete platform while on DP and with both units floating. The tolerance of accuracy was 2 inch.
    And before you ask; no, it did not go bankrupt because of my delaying the tow in Vartdalsfjorden.
    Last edited by ombugge; October 9th, 2010, 11:04.

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