North Morecambe, 25 miles west of Blackpool in the Irish Sea, was discovered in 1976. Three appraisal wells were drilled between 1978 and 1983, but the unusual composition of gas from the field made it too expensive to develop.
A field of North Morecambe's size would normally need a platform with a crew of 60. But the development of what British Gas says is the world's largest fully automated platform has cut operating costs to 25 per cent of those incurred on a manned installation.
Automatic processing systems at the terminal in Barrow- in-Furness, Cumbria, where the gas comes ashore, also means only six people are needed on each shift there: similar, non- automated terminals require 36. The high level of automation onshore and offshore has kept North Morecambe's operating costs down to pounds 10m a year, and the development should recover its pounds 600m capital cost in four years.
British Gas estimates the field's reserves at 1,060bn cubic feet - enough to fuel the central heating of every home in the North-west for 20 years. At its peak, the field will supply 4 per cent of national demand.
David Lane, the project manager, said incremental advances in several areas rather than giant leaps in technology had made North Morecambe the most technologically sophisticated field in Britain's offshore oil and gas industry.
'This project will give British Gas and other operators the ability and confidence to develop fields that were previously assessed to be uneconomic.'
Ironically, the unusual composition of the gas that made North Morecambe uneconomic was also the spur to build an automated platform. The gas contains 6 per cent carbon dioxide and 7 per cent nitrogen. The carbon dioxide not only makes the mixture of gas, liquid hydrocarbons and water that comes through the wellhead acidic (and thus corrosive) but also leads to the formation of hydrates as crystalline deposits that can block pipelines.
The nitrogen is inert and must be removed, because it reduces the calorific value of the gas. Removing these two gases requires large and complex processing plant. Incorporating them in the offshore platform would have involved huge expense, both in construction and operation.
So a decision was taken to process the gas onshore. This meant building a new terminal, rather than using the terminal that serves the adjoining South Morecambe field. The research and technology division of British Gas determined that adding methanol and a corrosion inhibitor to the wellstream would keep the gas in solution and prevent the acidic mixture from corroding the 19-mile pipeline between platform and terminal.
A separate, smaller pipeline takes the methanol mixture out to the platform, and when the gas is processed, the methanol is reclaimed and recycled.
Reducing the complexity of operations offshore enabled British Gas to automate the platform, controlling it from the nearby South Morecambe platform.
Another significant factor in reducing the costs of North Morecambe was the development of 'extended reach' drilling. This technique makes it possible to reach widespread target locations and bring all the wells into a central platform.
The whole project has been completed in three and a half years, rather than the four and half that would have been expected.
Mr Lane said that this was achieved against a background of changing legislation, with new safety and environmental rules coming into force.
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