WEATHER WISE

A joint study by BP and the Met Office has identified some patterns of weather than may be of great significance to the offshore oil industry.

A study into conditions over a 12-month period at five offshore oil rigs has confirmed that the seas west of Shetland have some of the world's worst weather. Between July 1996 and June 1997, the west of Shetland experienced about 2,300 hours of waves more than 4m high, compared with 100 hours at a location in the South China sea. Stewart Wass, of the Met Office, said: "As loading operations are disrupted by the severest of weather, these figures are a good indication of just how many hours of work are lost on rigs and vessels."

The study has identified a pattern of ocean swells that may eventually lead to more accurate prediction of the sort of waves that cause the greatest problems to oil exploration in deep waters. Rigs are apparently especially exposed to a "bottleneck" of winds and high waves driving in from storms that may be anywhere from the mid-Atlantic to the east coast of America. Once generated, the swells travel along great circular routes, some of which take them past Shetland, others towards the exploration and production locations of Angola, west Africa. Such swells, previously unpredictable, can lead to some floating units bucking violently.