Disposal of Offshore Platforms (1985) / Chapter Skim
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3. Engineering and Cost of Platform Removal
3. Engineering and Cost of Platform Removal
Pages 14-30
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From page 14... ...
The jacket has been lifted of f the bottom using temporary, clamped-on buoyancy tanks for it to go to deeper water for ocean dumping, or, for one structure, to enable it to be moved to another area to serve as a fishing reef. A few platforms that were to be reused have been lifted or winched back onto launch barges, then relaunched at another location.
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From page 15... ...
It may be necessary for an offshore derrick barge to accompany the salvaged components to shore for offloading, or special skidding arrangements must be developed. Onshore, the small equipment items and components can be transEerrad directly to a commercial salvage yard.
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From page 16... ...
For example, a different procedure would be used if the jacket is to be cut off below the waterline and the upper sections floated with auxiliary buoyancy to deep water for ocean dumping. Unless the final disposition of the structure is known when the structure is designed, the development of a detailed removal procedure during the design and approval phase of a project is probably a waste of effort.
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From page 17... ...
The design and construction of offshore platforms has been a rapidly advanc ing technology. Des igns have improved as a result of increased knowledge of the marine environment and consequent enhanced understanding of des ign loads .
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From page 18... ...
While it is true that structures with sufficient reserve buoyancy or with buoyancy tanks attached can be towed to shore, to an ocean dump-site, or to an artificial reef site, there is a definite risk of loss of buoyancy during the tow, especially if the structure is old. Moreover, buoyancy tanks as well as the entire towing operation are expensive (see discussion of cost in next section)
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From page 19... ...
Figure 6 shows a comparison of jacket weight versus water depth for typical Gulf of Mexico drilling-production structures. Figure 7 employs the platform population data and life expectancy estimates presented in the previous chapter to estimate the number of structures in each category to be removed each year.
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From page 20... ...
Since the water depth of these structures is also relatively shallow, they are not likely to be treated as structures to be cut off at some point below the waterline with the bottom section left in place. For purposes of preparing an overall estimate, typical removal procedures ware developed for a structure of this category.
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From page 21... ...
An unpublished, detailed cost study, prepared by an owner of one of these structures several years ago, estimated the removal cost at over $70 million. At the present time, this estimate would probably range from $90 million to $100 million.
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From page 22... ...
22 TABLE 2 Number of Structures to be Removed and Estimated Removal Costs in the Gulf of Mexico Time of Category Cos t Removal I IT III TV V Total (millions ) 1985 27 5 32 9 1986 3S 5 40 11 1987 26 21 41 24 1988 34 22 56 26 1989 48 18 66 25 1990 68 24 92 34 1991 92 34 1 127 49 1992 85 41 5 131 63 1993 68 36 2 106 49 994 86 50 12 148 83 1995 74 60 9 143 84 1996 IS 57 4 136 73 1997 7 7 62 5 144 80 1998 61 40 18 5 124 129 1999 54 26 19 11 110 1 77 2000 59 30 26 8 123 163 2001 56 46 25 3 130 125 2002 59 36 29 18 142 2 73 2003 59 29 23 9 120 167 2004 37 15 12 9 73 131 2005 63 24 18 23 128 295 2006 60 30 18 28 136 3 50 2001 44 46 20 17 1 128 294 2008 65 53 36 29 3 186 532 2009 103 4 7 28 20 1 1 99 3 5 1 2010 89 56 35 19 2 201 398 2011 7 9 68 3 7 1 2 2 1 98 340 2012 101 63 28 1 2 209 35 5 2013 132 67 14 8 2 223 271 2014 105 S3 16 5 2 181 226 201 S 105 53 14 7 1 180 203 2016 105 63 19 10 2 199 290 2017 105 65 25 13 4 212 412 2018 105 65 30 14 4 218 431 2019 105 65 30 20 4 224 491 2020 105 65 30 20 4 224 491 Totals 2, 746 1, 786 588 328 34 5, 482 $7, 505 Previ ous ly removed 95 246 5 346
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From page 23... ...
Onshore dismantling and disposal costs represent about 20 percent of total removal costs. bThese costs assume complete removal and transportation of j acket to a deep-water s i te for di sposal wi th the deck taken to shore.
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From page 24... ...
Onshore di smantl ing and di sposal costs represent about 20 percent of total removal costs. bThese costs assume complete removal and transportation of jacket to a deep-water s i te for di sposal wi th the deck taken to shore .
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From page 25... ...
~ Estimated differences in costs for several removal options are shown in Table 5. Tax implications to the owner or the government are not included in Table S.~ ENGINEERING AND COST OF REMOVAL OF OTHER PLATFORM TYPES As the industry moves into deeper water' other types of offshore platforms may be the technology of choice as a result of performance The extent of the government's financial interest in offshore development can possibly influence the government's choice among alternative platform dispositions.
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From page 26... ...
These may include compliant structures such as guyed towers or tension-leg platforms (see Figures 9 and 10) , or subsea well completion structures coupled with floating storage systems.
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From page 27... ...
. _ ~ '~ p~3 a_ FIGURE 10 Tension leg platform (aster depth 485 feet)
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From page 28... ...
Alternatives to complete removal, beyond the obvious approach of leaving the structure intact on the seafloor, would include destruction in place by explosives, leaving structural debris scattered over a small area. The dumping of rock or other fill material to cover low profile bottom structures could also be considered.
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From page 29... ...
29 FIGURE 11 Concrete gravi ty-base platform -- North Sea (water depth 520 feet)
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From page 30... ...
One option would be to use explosives to reduce the base to rubble. Off Norway where there are some IS huge concrete gravity-base platforms, the Norwegian Petroleum Directorate requires that for each such platform, a complete Manual for Removal be developed, fully engineered, and approved prior to issuance of a permit for construction.
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