SINGAPORE, Sept 19 (Reuters) - Asian crude prices are set to remain firm this week, including some Middle East grades at near record levels, as refiners accelerate purchases in a trading month that has seen buyers pick up cargoes faster than usual. Refiners across the continent are stocking up for peak winter heating demand, while the supply of arbitrage cargoes from the Atlantic Basin remains limited because of curtailed Libyan and North Sea production. Brent's premium over Dubai crude has remained above $5 a barrel despite expectations of resuming Libyan exports. "It should be supported because the Brent-Dubai spread has widened enough for refiners to look for more cargoes," a trader said. "Last week it was only the second week of September, just the beginning of the three-week trading window, and things moved very fast." MIDDLE EAST NEAR RECORDS * In the Middle East market, traders expect premiums of some heavy sour grades will continue near record levels, after Oman crude traded above $2 a barrel last week and Qatari al-Shaheen reached all-time peaks in Tasweeq's tender. * Wider-than-average refining margins have made it profitable for refiners to keep processing rates at high levels, raising crude demand at complex refineries that can process heavy sour crude into light fuels. * Buyers including Thailand's PTT and oil majors are likely to ramp up purchases of heay sour grades, while the lighter Middle East crude is likely to be supported by strong values for grades like Russian Sokol. ASIA-PACIFIC SEEKS SUPPLIES * In the Asia-Pacific markets, regional refiners are also chasing additional supplies. * Petral, the trading unit of Indonesian state-run energy firm Pertamina, is seeking light sweet crude for delivery in November in a second tender after skipping purchases in a previous one last week, a trading source said on Monday. * The company is seeking a 600,000-barrel cargo for arrival in November. The tender closes on Sept. 20 and remains valid until Sept. 21, the source said. * Malaysia's state oil firm Petronas raised the Tapis crude price alpha factor for September lifting to $6.25 per barrel, up by 35 cents from $5.90 for August, an industry source said on Monday. CONDENSATES MAY CLIMB * In the condensates market, traders will be looking at a tender by Qatar International Petroleum Marketing Co, or Tasweeq, to sell deodorised field condensate (DFC) and low-sulphur condensate (LSC) to be awarded by the end of the week. * Last month, Tasweeq sold fewer than usual October-loading DFC cargoes because of abundant term sales before Tasweeq's monthly tender and reduced otuput at Qatargas LNG trains in October. * Condensate values are likely to respond positively to a tighter market and higher values for Asian crude. * Attention will also be on a tender by Petronas to sell Labuan which closes later on Monday. (Reporting by Alejandro Barbajosa; Editing by Michael Urquhart)

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