LONDON (Reuters) - Oil held above $63 on Monday, as dense fog delayed crude imports to refiners in the world's largest energy consumer the United States.OPEC's plan to deepen oil output curbs from February also lent support.U.S. crude traded down 28 cents at $63.15 a barrel at 1052 GMT, after rising 92 cents on Friday to the highest close in two weeks. Tankers struggled for the fourth consecutive day on Sunday to deliver oil supplies to refineries in Houston and Texas City, which between them account for nearly 12 percent of U.S. refining capacity.The refineries also supply crude oil to pipeline systems for refineries in other parts of the country.The bad weather has caused intermittent delays along the 53- mile (85-km) Houston Ship Channel, although forecasters said the fog should lift early this week.Fog also affected imports to other refining centers along the U.S. Gulf of Mexico coast.Some refiners have warned that they may need to slow fuel production due to the delays, but none so far have announced output reductions.OPEC CUTThe shipping disruptions could hit relatively high U.S. crude inventories, which may also soon start to show the effect of a 1.2 million barrels per day (bpd) supply cut by the Organization of the Petroleum Exporting Countries (OPEC), effective from Nov 1. OPEC last week decided to make a second output cut of 500,000 bpd, to start from February, to prevent stockpiles rising again after the northern hemisphere winter.OPEC's deal struck a balance between price hawks concerned about inventories, and others who worried that an immediate cut could leave markets short at the height of winter.A Reuters survey shows OPEC only met about two-thirds of its November cutbacks, so some analysts question whether fresh limits will be effective in supporting prices that have slid about 20 percent from a record over $78 in July."I'm not convinced OPEC's production cuts were enough to turn this market around," said Christopher Bellew, broker at Bache Financial in London.U.S. crude oil stocks fell a sharper-than-expected 4.3 million barrels last week, but still stand at their highest since 1998 for this time of year.Supplies of crude from Nigeria, already down by about a fifth because of militant attacks, have been further trimmed by gunmen who seized an oil platform operated by Royal Dutch Shell (RDSa.L: Quote, Profile , Research) in the Niger Delta, shutting its 12,000 bpd oil output, the company said on Saturday.Mild weather continues to limit the need for heating fuel in the United States. Temperatures in the U.S. Northeast were expected to remain above average for at least the next five days, according to private forecaster DTN Mete