Offshore Operations

Offshore operations encompass such activities as seismic survey, exploration drilling, facilities installation and materials transfer.

The principal metocean requirements for these activities may be itemised as follows:

Seismic Survey

  • ambient winds and waves (affecting safety of operations and background noise levels)
  • surface currents (affecting orientation of seismic lines and potential requirement for infill if ‘feathering’ of hydrophones becomes a problem
  • water level prediction (to facilitate accurate depth determinations)
  • swell prediction (to assess the need for heave compensation).

Exploration Drilling Studies

Decisions to be made prior to commencement of exploration drilling include:

  • What type of rig to use
  • Anchoring/footing (tidal current, wind-wave directional divergences);
  • Riser design
  • Likely operability/downtime
  • Insurance/regulatory requirements
  • Oil Spill Contingency plans and
  • Drilling cuttings disposal

Studies which might facilitate these decisions may include:

  • Ambient wind, wave and current conditions;
  • Extreme wind, wave, current and water level predictions;
  • Downtime analyses;
  • Oil spill trajectory studies; and
  • Drilling cuttings dispersion estimates

During this phase, potential deficiencies in metocean knowledge should be identified, and reconnaissance measurement programmes for rectifying these deficiencies should be scoped, costed and presented.

Installation/Commissioning

As more sophisticated facility installation options are being adopted, tighter specification of installation ‘weather windows’ is required.

Studies might typically address:

  • short return wind non-cyclonic winds and waves
  • tidal currents
  • tide height variation
  • long period swell non-exceedence persistence
  • joint occurrence of winds, waves and currents
  • sea state transformation