Kazakhstan's giant Kashagan oilfield will not be able to restart production before the end of 2013, said the chief executive of French oil company Total, one of the partners in the project.

Kazakhstan has been looking forward to revenues from Kashagan, which took nearly 13 years and about $50 billion to complete. It is the world's costliest oil project but also the biggest global oil find in decades - forecast to total 8 million tonnes next year, rising to 12 million tonnes in 2015. However, production was halted two weeks after its September launch when a gas leak was found. Another leak was found in October after a brief restart.

On Sunday Christophe de Margerie told a news conference in Abu Dhabi that Kashagan, in the Caspian Sea off western Kazakhstan, would not be able to start production again before the end of the year. "It's more than simply repairing pipes," he said, adding the consortium must be sure before restarting production that the whole piping system would operate safely over the long term.

The consortium operating the field includes Kazakh state oil firm KazMunaiGas, Italy's ENI, U.S. major ExxonMobil, Royal Dutch Shell and France's Total. Each own 16.81%. Japan's Inpex 1605.T owns 7.56%. China National Petroleum Corp CNPET.UL (CNPC) acquired a 8.33% stake this year.

Kazakhstan is the second-largest post-Soviet producer after Russia - which holds 3% of global recoverable oil reserves - and hopes Kashagan can help it join the world's superleague of oil producers. According to earlier comments by top Kazakh oil industry officials, the field's daily output before the second leak had exceeded 60,000 barrels per day (bpd). The field had been due to achieve commercial output of 75,000 bpd this month.

The deal, estimated to be worth $5 billion, followed Kazakhstan's decision in July to use its pre-emptive rights to buy an 8.40% stake from U.S. oil major ConocoPhillips COP.N in the field for a similar price.