(John Kemp is a Reuters market analyst. The views expressed are his own)
* Chart 1: http://tmsnrt.rs/2BfvjBG
* Chart 2: http://tmsnrt.rs/2AwX35m
LONDON, Dec 12 (Reuters) - Brent futures for delivery in nearby months have jumped to a big premium following the decision to shut the main pipeline bringing crude onshore from the UK North Sea for inspection and repairs.
The Forties pipeline system, which carries around 450,000 barrels per day and handles nearly a quarter of North Sea output, is likely to be shut for weeks, owner INEOS said.
Forties is the largest component of the Brent-Forties-Oseberg-Ekofisk-Troll (BFOE) complex of crudes that are the basis for the Brent futures contract.
Since the closure is expected to be extended but ultimately temporary, the main impact has been on nearby futures contracts for deliveries in February and March.
Brent futures prices for deliveries in February have surged by more than $2 per barrel since Friday while March is up by $1.60.
In contrast, prices for Brent futures with deliveries in June have risen by $1.25 and increases for later months are smaller.
The main impact from the shutdown has therefore been on the calendar spreads for nearby months rather than on outright or flat prices (http://tmsnrt.rs/2BfvjBG).
The calendar spread from February to March has more than doubled to 76 cents on Tuesday from 37 cents backwardation on Friday. The spread from March to April has similarly flared to 45 cents from 27 cents.
The longer the pipeline takes to be repaired, the more the tightness in the February-March and March-April calendar spreads is likely to bleed into later months.
A prolonged shutdown of the Forties system would accelerate the drawdown in global oil inventories and tightening of the oil market that is already underway.
For the moment, however, the price impact has been mostly confined to North Sea crudes, with prices rising against other light crudes as well as medium and heavy grades.
Futures prices for U.S. light crude delivered in February rose by less than $1 per barrel between Friday and Tuesday, suggesting traders see only a modest impact on global crude availability.
With the impact concentrated on the North Sea, Brent futures have jumped to a premium of more than $7 per barrel over WTI from under $5 at the start of last week (http://tmsnrt.rs/2AwX35m).
(Editing by David Evans)