Stepping-up decommissioning

Alan Clifton

August 1, 2014

New specialist vessels have the potential to change the face of the decommissioning sector, but will they solve all the issues activity in this area continues to face? Alan Clifton takes a look.

The Pieter Schelte, at Daewoo Shipbuilding and Marine Engineering’s D-Quay, Korea, having its helideck installed. Image from Allseas. 

Decommissioning end-of-life offshore platforms is possibly the most unglamorous part of the oil and gas life-cycle. Understandably, operators do not welcome incurring the costs this work brings, but they do recognize the importance of disposing of their obsolete assets efficiently and with minimal environmental impact.

In some parts of the world, notably the Gulf of Mexico, local legislation allows for platforms to be cleaned and then sunk to create artificial reefs. Arguably, this is a sound environmental option, as new reefs become home to wildlife and the energy required for the disposal process is minimized.

However, in the North Sea, the Convention for the Protection of the Marine Environment of the Northeast Atlantic (OSPAR) requires that end-of-life installations are removed and disposed of.

One problem with removing these structures is that the equipment used in the industry, and the guidelines used for their use, has not really moved on in the 20-30 years since the platforms were installed. Techniques such as breaking the platform down into its original modules (employing a reverse installation process) or simply breaking-up the platform into small pieces, are the two methods most commonly used. These processes can be both inefficient and costly. In the recent past, some more innovative techniques have been tried—such as attaching buoyancy tank assemblies to the legs of a jacket, then de-ballasting and floating the jacket away. But these new techniques are the exception rather than the norm.

Single lifting

Another solution is the “single lift method,” much like a reversal of integrated platform installation. There have been many projects set-up to develop a single lift solution (MPU, Seametric, Excalibur) however, none have made it to operation, so far.

One “single lift” solution that has progressed, and offers a much anticipated step-change in the decommissioning process, is the impending delivery of the Allseas heavy lift vessel Pieter Schelte. This new class of vessel has the potential to reduce the lengthy offshore preparation process required by current removal techniques. Pieter Schelte will have a topsides lift capacity of 48,000-ton and a jacket lift capacity of 25,000-ton. Its design enables it to straddle a platform and take off the entire topside in a single lift. This will significantly reduce the amount of offshore vessel time required to dismantle a platform, although the time spent in shore-side preparation is likely to be similar. The vessel will also be used for deep-sea pipe-laying as well as installation activities and it is understood that a larger sister vessel could be delivered in 2020.

Challenges remain

Although specialist vessels like Pieter Schelte may change the face of offshore decommissioning removal operations, it will not solve a number of the associated risks and challenges that this activity continues to face. Once removed, the structures—either whole or in pieces—are moved to a shore-side facility for recycling. Independent operators invest large sums to ensure their facilities are safe and kind to the environment and clearly need to realize a commercial return as compensation. These reception facilities must be prepared and able to receive the removed items as delivered, which may add further cost to the project as a whole. With oil companies tending to delay the removal of their platforms, competition amongst recycling yards is fierce and some are beginning to struggle.

Rightly, platforms must be cleaned and all hazardous material removed or contained before the structure is moved. Often they are left unmanned for some considerable time before they are eventually taken away. A period of non-maintenance and the introduction of an external and unfamiliar cleaning team is not the optimum combination to ensure an efficient and safe operation—particularly if the associated documentation is incomplete or not up-to-date. Having to deal with structures and materials in common use 30 years ago also creates problems. Paint used in those days, for example, is much more toxic than today’s coatings and so must be dealt with in a way that does not harm the environment or the workforce.

Although unglamorous, decommissioning is an essential element of the offshore oil and gas industry but one that is clearly thought of as the poor-relation. Although the introduction of specialist vessels has the potential to change the face of the decommissioning sector, it will not solve all the issues that this activity continues to face.

Alan Clifton 
is a senior construction engineer and serves as the operations director for LOC in Norway. Clifton has acquired over 35 years’ experience in the offshore construction industry.