Both the oil reservoir and gas reservoir are commercial in North Alwyn field, a rare attribute in the North Sea.
Oil production has passed its peak, gas is at peak, but there is plenty to come. Facilities can be used to produce other fields nearby.
In many ways North Alwyn is a good model for a typical North Sea field. Study it and you learn about the status of the U.K. sector.
Total Oil Marine plc is operator and holds 33.33% interest in Alwyn. Ste. Nationale Elf Aquitaine holds 66.67%. The field lies in 410 ft of water on Block 3/9. Reserves are 220 million bbl of oil and 940 bcf of gas.
Peak oil production was 94,000 b/d in 1990, with 279 MMcfd of gas. Output now is 88,000 b/d of oil and 283 MMcfd of gas.
VITAL PRODUCT
"Hydrocarbons are not our most important product," says Ian Dundas, the North Alwyn project manager. "Most crucial is the associated water used for injection, which is later treated prior to discharge. If the water system does not work, oil and gas cannot flow."
North Alwyn requires 137,000 b/d of water injection. Two chemists are employed full time to monitor water entering the wells and before discharge. A key task is to keep the field free of sulfate reducing bacteria.
By 1997, production will be 10,600 b/d of oil and 130 MMcfd of gas. By 2000, it will be 4,000 b/d and 35 MMcfd. Development of three fields nearby will keep North Alwyn facilities going well into the next century.
Dundas foresees 40% of hydrocarbons coming from subsea satellites. Earlier this year, North Alwyn Extension, a three well subsea cluster 3.3 miles south-southwest of the central platforms, was brought on stream. This will contribute 16,000 b/d of oil and 88 MMcfd of gas at plateau.
Fifteen miles south of Alwyn's platforms lie three accumulations on Blocks 3/14 and 3/15, where water depth is an average 475 ft.
SATELLITES
Dunbar reservoir, on Block 3/14, holds reserves of 120 million bbl of oil and 510 bcf of sales gas.
Grant field, also on Block 3/14, has reserves of 226 bcf of sales gas and 9 million bbl of condensate.
Ellon field, on Block 3/15, contains two reservoirs, a western one holding 140 bcf of sales gas and an eastern one with 45 bcf. Condensate reserves in both total 6 million bbl.
Dunbar will be developed via unmanned platform as a satellite to North Alwyn, with production scheduled to begin in late 1994. A semisubmersible will be used for tender assisted drilling.
Ellon and Grant will be developed as satellites to Dunbar. Six subsea wells will be tied back to Dunbar, coming on stream in early 1995.
"The development of Dunbar field shows what North Sea operators require: reliable and economical operation," said Claude Brice, managing director of Total Oil Marine. "Our approach will reduce capital and operating expenditures."
Copyright 1992 Oil & Gas Journal. All Rights Reserved.
