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:
- 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.
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