Weather! All of us talk about it at some point every day and, offshore it is a critical part of life, as many of Energy’s readers would know first-hand.
For us on the beach, it can be difficult to fully understand the challenges faced offshore, even though many of us saw the graphic pictures in the news showing the damage caused by high seas to parts of the UK during this past winter.
It really has been a tough winter in the North Sea, with platforms running short of fuel and water, tankers unable to access ports, and the evacuation of personnel from some installations because of high seas.
Marine forecasts are essential not only to operational planning offshore, but most importantly, to ensuring the safety of personnel.
But how bad has it really been offshore lately? And how can we tell?
Both technology and science have made huge leaps forward over the last 30 years. Companies have made significant investments in developing a network of offshore weather and wave measurement devices.
The data from these provide fully calibrated and accurate information in real-time, which is of great assistance to operational planning. This is a far cry from when I first started forecasting for the North Sea when only a few weather stations provided any measured data and I relied on weather ships in the Atlantic to provide clues on the waves heading towards the North Sea.
But weather science has since leapt forward.
In December 2012, a fierce storm struck the north-east of Scotland. I live in Stonehaven and saw at firsthand the damage the high seas caused to businesses and homes.
Met Office scientists had been alerted to the storm and the potential impact it may have on assets in the North Sea. Met Office research teams, utilising the wealth of measured data now available, assessed the storm identified and tested new science and methods to improve forecasting of waves. This new model has been rolled out and is now used in all forecasts provided to the marine community.
The research teams also calibrated the model, and have recalculated values going back over 30 years. This has been a huge exercise – and provides not just information on wave height, but on over 48 different elements (swell period and direction, for example) that go together to build what we call “sea-state”.
A key feature of the data-set is that it provides “homogenous” data, utilising the most up-to-date scientific assessment of marine conditions. This provides a valuable basis for planners looking at design and operational feasibility of offshore renewable energy schemes and, of course, North Sea oil and gas, from exploration through development, production, maintenance and modifications and eventual decommissioning.
I have looked at the percentage of time that the “significant wave height” was above 5.5m during the winter months of 2013/14 (December through February) for a location in the Northern North Sea. The results show that this percentage is the highest since 1980/81.
To help visualise, a 5.5m wave is about a metre higher than a double-decker bus, and each individual wave will be moving at around 35-40mph. And, just like a bus, waves don’t tend to come in ones!
The Five Worst Winters since 1980/81 (based on percentage of time when waves were above 5.5m)
1. 2013/14
2. 1992/93
3. 2003/04
4. 1983/84
5. 2011/12
Similar results are found in many waters around the UK.
In the Northern North Sea, the sheer number of storms as well as the dominance of south-easterly seas is interesting. We would normally expect to see the worst weather coming from the North Atlantic into the North Sea. Indeed a number of offshore assets are oriented because of this.
Seas do not discriminate. Any structure, vessel or device must be designed to operate as safely and efficiently as possible within whatever the envelope is; and in the North Sea/North Atlantic, that means sometimes extreme metocean conditions.
Indeed my work at the Met Office in providing wave and wind forecasts is vital to the efficient planning and delivery of projects. Based on a whole range of weather information, companies are able to make informed decisions to ensure cost efficiency and to protect personnel and property.
Events this winter have underlined the power of the sea. But look at it this way, it represents a considerable energy resource in its own right; the challenge is to harness it effectively.
John Mitchell is a metocean scientist at the Met Office Follow @MetOfficeMarine
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