London (Platts)--8Nov2012/725 am EST/1225 GMT

The UK's largest oil field Buzzard is taking more time than expected to return to its full production rate of 220,000 b/d after restarting following two months of scheduled maintenance last week, traders said Thursday.

The field resumed output last weekend and was heard to be producing at a rate of 170,000 b/d earlier in the week, or around 77% of total capacity, but traders said production had fallen to 140,000 b/d Wednesday.

They added that output would likely stay at that level Thursday before ramping up further thereafter. The reason for the lower production isn't yet clear, they said.

Nexen, the operator of the field, wasn't immediately available for comment on the matter.

"Buzzard is coming back at a lower rate than we're used to...it was at 140,000 b/d yesterday [Wednesday} and will be today," said one trader.

Traders said the slower-than-expected ramp-up in Buzzard production would likely result in some Forties cargo deferrals this week.

Buzzard is the single largest stream feeding into the UK's Forties blend. --Olivier Lejeune, olivier_lejeune@platts.com --Edited by James Leech, james_leech@platts.com