Contractors must adapt to changing priorities for platform removal

For specialist contractors, this market could be worth between $20-50 billion, with prospects of work being sustained even beyond 2030. However, the emergence of new technologies for decommissioning could force contractors to re-establish their credentials in this sector, IMCA points out.

The association’s Decommissioning Workgroup, formed in mid-2004, also participates in the Decommissioning Technology Forum in Aberdeen, members of which include several majors. Among the subjects under discussion, and touched on in IMCA’s report, are:

• Fixed North Sea installations feature a wide range of designs. There is no single established removal technique applicable in all cases
• The available dive support/heavy lift crane vessel fleet is also aging, some being 25 years old or older. New vessels will be needed to serve the sector in the decades ahead
• Lack of decommissioning experience going forward, particularly if little or no decommissioning occurs over the next few years
• Relocation of redundant platform topsides. As the cost of fabricating new structures increases, more operators are considering this option for projects in West Africa and South-East Asia
• Survey of pipelines prior to decommissioning, taking into account the condition of the line in question, the planned removal method (i.e. fragmentation, reversed lay), and seabed characteristics along the route. Pipeline removal also requires access to data not normally listed for an inspection, repair and maintenance program, such as the presence of T-pieces, and localized areas of rock dump and sedimentation over the line.

Limited role models

Most experience to date in the North Sea relates to small platforms in the southern gas basin. Of the few large structures successfully taken out, only those on Odin and Froey in the Norwegian sector were “conventional” fixed platforms.

According to IMCA, issues needing further investigation include drill cuttings removal; pigging and cleaning of rough-bore pipes; managing “springing” caused by stored energy in the steel lattice after cutting; methods of capturing structures lifted and lowered onto barges, and subsequent sea-fastening; back-loading, and metrology.

Another concern for IMCA members is the trend of the past two decades to move risk for marine construction projects onto the contractor, and how this might be applied to decommissioning. A major worry is the risk of the structural status of items to be removed: it can be difficult obtaining as-built engineering drawings of offshore installations, and this can exacerbate the financial, as well as safety, risks where there are undocumented changes to a structure.

IMCA instances one contractor that encountered unexpected internal pipes while attempting to cut through a platform leg. On another occasion, a 400-ton drilling template lifted clear of the seabed was found to contain an additional 200-ton of materials such as grout and mud, which had to be disposed of after removal to shore - via 50 truck-loads. In such unforeseen scenarios, IMCA believes the commercial risk needs to be shared more equitably.

Finally, decommissioning seabed pipelines involves pigging, flushing and filling, followed by removal or abandonment in situ. The industry needs greater guidance on removal procedures, the report claims, particularly in cases where pipelines cross, or where concrete protection mattresses or pipeline bundles are in place.

Contractors could also use assistance concerning removal and safe disposal of paraffins and other waxy hydrocarbon substances, and handling emissions of hydrocarbons from pipes and flowlines taken to the surface from a high ambient pressure subsea environment.

For more information, contact IMCA:www.imca-int.com.