By Robert Gibbons
NEW YORK (Reuters) - Front-month Brent crude prices rose on Thursday after a power outage shut production at Britain's largest oilfield and as the August contract approached expiration.
U.S. crude futures settled lower after giving up gains reacting to data from industry intelligence firm Genscape showing higher crude inventories at the Cushing, Oklahoma, hub, traders said.
Expiring Brent August crude rose 46 cents to settle and go off the board at $57.51 a barrel, having reached $58.21.
September Brent crude fell 20 cents to settle at $56.92, off its $58 intraday peak.
August Brent moved to a premium to September and reached 75 cents intraday, the highest for front-month Brent to the nearby month since June 2014, according to Reuters data.
U.S. August crude fell 50 cents to settle at $50.91, having swung from $50.34 to $52.71.
"Another build at Cushing would be bearish for U.S. crude, and the Buzzard outage and contract expiration are supporting Brent," said Phil Flynn, analyst at Price Futures Group in Chicago.
Britain's Buzzard oilfield was closed after power supplies failed, traders said.
It normally pumps 170,000 to 180,000 barrels per day (bpd) but went down early on Thursday, traders said.
A spokeswoman for Buzzard operator Nexen, a unit of China's CNOOC Ltd, declined to comment.
Buzzard is the single biggest contributor to the Forties crude stream, one of four crude grades underpinning the price of over-the-counter Brent, which is linked to Brent futures.
In a potentially bearish development, an Iranian supertanker with 2 million barrels of oil headed to Asia after sitting in Iranian waters for months, the first vessel storing crude to sail after this week's agreement between global powers and Iran over Tehran's nuclear program.
Crude stocks at the Cushing, Oklahoma, delivery point for the U.S. crude contract have risen nearly 1 million barrels since last Friday, according Genscape data, trading sources said.
Last week total U.S. crude inventories fell 4.3 million barrels but stocks at Cushing rose 438,000 barrels, according to the Energy Information Administration (EIA) data released on Wednesday. [EIA/S]
Crude runs at U.S. refineries jumped 229,000 bpd last week to 16.83 million bpd, a record high, according to EIA data, as refiners reacted to strong gasoline demand.
But Olivier Jakob, head of Swiss energy consultancy Petromatrix, cautioned that the market might not be as well balanced when seasonal maintenance shuts some refineries in the fall.
(Additional reporting by Christopher Johnson in London and Henning Gloystein in Singapore; Editing by Marguerita Choy and Lisa Shumaker)