Shell reveals risk ratings of Brent Spar disposal techniques

At Shell Expro's request, DNV has published its assessment of the seven solutions for disposal of the Brent Spar. The report assesses technical and safety risks and environmental impact, as well as verifiying the projected prices of each approach. Input will be used by Shell in its own assessment of the Best Practical Environmental Option, which it is then likely to discuss with the UK government towards the end of this year. The government may then sanction a final abandonment plan.

At Shell Expro's request, DNV has published its assessment of the seven solutions for disposal of the Brent Spar. The report assesses technical and safety risks and environmental impact, as well as verifiying the projected prices of each approach.

Input will be used by Shell in its own assessment of the Best Practical Environmental Option, which it is then likely to discuss with the UK government towards the end of this year. The government may then sanction a final abandonment plan.

In terms of cost, Shell's original option, deepsea disposal in UK waters, remains by far the lowest, at £4.7 million, and also the safest, according to DNV, in terms of potential loss of life calculations. However, it is the worst as regards NOx emissions and equal worst for sulphur dioxide emissions.

Of the six land-based recycling options, all would achieve a re-use rate of 96-97%, but two are considered superior in terms of minimal waste disposal:

  • McAlpine/Doris/Able's idea is to up-end the Spar using compressed gas, tow it to a drydock, and re-use the hull to build a quay wall at the dock.
  • Wood-GMC's proposal is to raise the Spar vertically using jacked cables, cut the hull into rings, then use these to extend a quayside in Norway, scrapping the topsides onshore.
Amec's idea, to use the cleaned hull slices to build a coastal defense barrier in Norfolk, eastern England, presents the highest risk because of the rock placement involved. The highest priced solution, at £48 million, is Brown and Root's scheme to upend the Spar at its mooring in Norway using compressed gas, then tow it to the company's yard in Nigg, Scotland for onshore scrapping.

Best solutions for limiting carbon dioxide emissions were Kvaerner Seaway Spar Alliance's idea to tow the Spar to a Norwegian yard, raise it vertically using compressed gas or raising and rotate it to the horizontal, prior to scrap or recycling. Thyssen-Aker's notion is to partly raise the Spar using compressed air, tow it to a site in Norway where it would be fully raised with jacked cables, and then scrapping it.

Shell has also drawn up a shortlist of contractors for a less contentious disposal job, the SALM buoy that formerly served the Fulmar, Auk, Clyde and Gannet fields. The cylindrical buoy has been anchored in a fjord north-east of Stavanger since being taken out of service in 1994. It weighs 5,150 tons, including 2,450 tons of hematite and treated water ballast which is in a sealed compartment at the base. The SALM is 85 meters tall, up to 16 meters in diameter at the waterline, and floats vertically, with a draft of 62 meters. Draft and size restrict towing site locations, unless it is lifted onto a barge or rotated to the horizontal.

A contract for the disposal could be awarded early next spring. The six short-listed contractors are Able McAlpine Doris, Aker Saipem, Brown and Root, HeereMac, Kvaerner Seaway Alliance and Wood-GMC. Ideas include pulling the SALM ashore using winches and dismantling it vertically in inshore waters.

In other North Sea sectors, Statoil submitted its plans for Tommeliten shutdown, due to be undertaken August 1, 1998. Statoil plans to re-use the template and two flowlines that currently carry wellstream to Phillips' Edda platform 11 km distant. Edda itself is being readied for abandonment as the new Ekofisk II field center comes onstream.

NAM has initiated abandonment of wells on its K/11 gas production platform in the Dutch sector, and has been examining options for removal to shore of the 1,000-ton steel platform.

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