Shell U.K. Exploration & Production has revealed details of a comparative assessment of six shortlisted plans for disposal of the Brent spar, which will help determine the final choice.
The original plan to dump the spar off Northwest Britain also was included in the study-as a benchmark and because it remains the only plan approved by the U.K. government.
The comparison was made by Det Norske Veritas AS (DNV), Oslo, which was hired by Shell Expro to study technical feasibility, safety, environmental impact, and cost estimates for all the plans.
Shortlisted contractors are Brown & Root Energy Services, Kvaerner Stolt Seaway Alliance, McAlpine Doris JV, Thyssen-Aker, Wood-GMC, and AMEC Process & Energy.
They proposed a range of plans to remove the spar from the water either vertically or horizontally and then recycle or scrap its topsides and hull sections (OGJ, Jan. 20, 1997, p. 24).
Final choice considerations
Heinz Rothermund, managing director of Shell Expro, said that, while DNV had ranked the proposals according to a number of aspects, DNV was not asked to indicate a preferred solution."That's down to Shell," said Rothermund. "Now all key facts and figures regarding Brent spar have been put into the public domain. When we define the preferred solution, no one will have a surprise."
Eric Faulds, decommissioning manager at Shell Expro, said the technical feasibility of each proposal would be considered first, and if this is acceptable, environmental impact and safety aspects would be studied.
Elizabeth Harstad, head of safety, environmental, and quality services at DNV, said technical feasibility assessment was based on a proposal confidence assessment and on the risk of a major accident.
"For the proposal confidence assessment," said Harstad, "we looked at each contractor's experience of similar operations, and how systematic was their proposal and what was the quality of engineering in their proposal."
Harstad said three proposals stood out in this assessment: Brown & Root's upending and onshore scrapping scheme, Wood-GMC's slicing the hull as it is raised, and the deepwater dumping plan.
She added that as far as risk of major accidents went, four proposals did not document hazards sufficiently. Once again, the Brown & Root, Wood-GMC, and deepwater disposal plans stood out.
In its report on the comparisons, DNV said all but the Brown & Root, Wood-GMC, and deepwater disposal plans included intolerable risk levels in some part of the proposal.
While Harstad said these three options were better in terms of technical feasibility, Faulds was careful to point out that others scored better in terms of environmental impact and cost.
No clear winner
"No proposal is best in every category," said Faulds. "There is no clear winner so far, and no option has been ruled out. Now we will present DNV's work to the public in a series of seminars."Faulds said the key to the technical feasibility of disposing of the spar is stress levels during removal from the water: "Some of the proposals are outside the comfort zone for stresses."
He added that preference of disposal plan could also be determined by value judgments: "This is why the dialog seminars are being run. After the dialog, we hope to take our proposal to government around yearend."
Faulds said that once Shell Expro has submitted its plan to the Department of Trade and Industry, the department will most likely call for further consultations before granting or refusing a second disposal license. This is required under U.K. operating licenses.
Costs
Shell Expro said it will have spent £9 million in taking Brent spar disposal to the award-of-contracts stage. This does not include the abortive attempt to dump the structure at sea (OGJ, Nov. 27, 1996, p. 23).Under the revised estimates, the deepwater dumping cost falls to £4.7 million from the earlier estimated £11 million, because it will be cheaper to tow the structure from Norway to a disposal site and not from Brent field.
The other contractors' cost estimates are: AMEC £18.8 million ($30.1 million), plus a further £14 million ($22.4 million) for another contractor to raise the spar; Brown & Root £48 million ($76.8 million); Kvaerner Seaway £17.6 million ($28.2 million) for vertical removal or £11.4 million ($18.2 million) for horizontal; McAlpine Doris £19.6 million ($31.4 million); Thyssen-Aker £21.3 million ($34.1 million); and Wood-GMC £21.5 million ($34.4 million).
Although deepwater disposal came out well in many areas of the comparison, Shell Expro is not expected to choose it again. Rothermund said, "We reached our own conclusions on disposal last time without exposing our thinking first.
"We have learned it is not up to us to come up with conclusions without making sure these are shared by people from different backgrounds."
Copyright 1997 Oil & Gas Journal. All Rights Reserved.
