Partners at the giant Kashagan oil field are expected to ask the government of Kazakhstan for an extension for their 2013 first oil deadline, a source said.Partners at the Kashagan oil field -- Royal Dutch Shell, Total, Exxon Mobil, Italy's Eni and Kazakh state oil company KMG -- have struggled to get oil products out of the field.Partners had pitched plans to get at least 50,000 barrels of oil per day onshore by going around an artificial island housing a processing plant that isn't finished yet, but that plan was rejected at the last minute.A source at an oil services company in the country told The Daily Telegraph newspaper in London on condition of anonymity the Kashagan consortium needs an extension to the 2013 deadline."Our people went to a workshop 10 days ago, and were told that the partners had rejected the 'early oil' concept because it was not sufficiently worked out, and so they now had a brief to go back and ask for an extension to their 2013 deadline," he said.Kashagan was the largest oil discovery in 30 years when its reserve estimate of at least 9 billion barrels of oil was first announced in 2000.