helios

Helicopter services have been used by the offshore industry for decades. Traditionally the offshore production platforms were fixed. For drilling, installation and work-over large and stable semi submersibles were deployed. Helicopter operations could be conducted on such platforms, which are hardly affected by wave induced motions.

The current deepwater and marginal field developments and the available technology have resulted in the use of floating production units such as FPSO’s, TLP’s and Spars as well as moderately sized mono hull vessels for support services such as installation, well intervention, seismic and survey work or other sub-sea activities. All these floating units exhibit wave induced motions, which can be severe due to resonant roll (noheading control), swells or high seas.

As the activities of these vessels require permanent station keeping or tracking for extended periods, logistics of crew, equipment and stores heavily depend on helicopter transport. This implicates that helicopters have to approach, maintain position on deck and depart from vessels exhibiting wave induced motions. Helicopters are also providing emergency services in case of casualties and evacuations (e.g. hurricanes in the GoM). If for some reason a helicopter cannot be operated the vessel has to rely on ship to ship transits or has to stop its operation and go to shore. Therefore heli-operations are crucial for the safety and economy of these offshore floaters and vessels.

In countries around the North Sea, Civil Aviation Authorities (CAA) and helicopter operators have agreed on limits for safe operation of helicopters to floating offshore vessels. In Norway, the helicopter operators (CHC and Norsk Helicopter) are operating under a strict regime; for “small” vessels; helicopters are only allowed to land and remain on deck if pitch and roll angles are less than 2o and the average heave rate of the largest wave is less than 1m/s for the last 20 minutes. Since the introduction of this regime, no major helicopter deck accidents have occurred offshore Norway. At the same time it is noted that this restriction is limiting several offshore operations in terms of logistics and planning. In the UK the landing limits currently in use are based on a maximum heave value of 5m double amplitude but operators have argued for the introduction of heave rate based limits such as the “Norwegian Method”. The criteria currently in use are based on old empirical data and not supported by scientific work.

Often helicopter services cannot be deployed and are delayed for several days to the point that the vessel has to stop offshore operations and go into harbour herself for crew changes and supplies.

In the coming decades offshore energy production will become more and more dependent on helicopter operations. Not only will oil and gas production be more and more based on floaters, these floaters will also be deployed in more remote harsh and even arctic conditions (Snøvit, Shtokman). At the same time for offloading, installation, early well-testing & workover relative small vessels will be used. For offshore wind turbine parks access by helicopter will be essential for maintenance and inspection.

As mentioned, since the introduction of this regime in Norway no major helicopter accidents have occurred. On the other hand the criteria used are lacking rational basis; critical parameters such as helideck accelerations and cross-wind components are not included in the regulations. Therefore the current criteria are not necessarily conservative from a safety point of view. A workability analysis for an 80 m light well intervention vessel operating offshore Norway, showed that the downtime for helicopter operations in winter time assuming good visibility varied between 70 and 90% depending on the relative wave direction. This is unacceptable for an economic operation of this vessel as it requires the vessel to disconnect riser systems and go to port herself on a regular basis.