UK Stocks-Factors to watch on Sept 13

Sept 13 (Reuters) - Britain's FTSE 100 index is seen opening 7 points lower on Wednesday, according to financial bookmakers. * ROYAL DUTCH SHELL: Royal Dutch Shell is seeking to withdraw from Iraq's Majnoon oilfield and the oil ministry has started preparations to finalise its exit, according to an oil ministry letter and oil officials. * SABRE-IPO: British motor insurer Sabre is planning an initial public offering (IPO) that could value it at 600 million pounds ($800 millio