The expansion of Saudi Arabia's Khurais oilfield is expected to be delayed from the originally planned timeframe of 2017 and the start-up date is now unclear, industry sources said.

The sources said authorities had not given reasons for the delay. However, since global oil prices started to fall sharply last year, national oil giant Saudi Aramco has slowed some projects, shelving less important ones and asking for discounts on some contracts which it had awarded.

"The project is important because of the associated gas that comes with the expansion of the oilfield ... but Aramco has stretched the timeframe of the field. The picture will be much clearer in November or December," said one source who declined to be identified because of commercial sensitivities.

Contractors who have been awarded jobs on the field were asked to wait to finalise their contracts, suggesting start-up could be pushed beyond 2018, another source said.

Saudi Aramco did not respond to an emailed query for comment.

The Khurais expansion project is due to increase the field's output by 300,000 barrels per day (bpd) to 1.5 million bpd, and allow it to produce 143 million standard cubic feet per day of associated gas and 34,000 bpd of natural gas liquids.

In 2013, Aramco's former chief executive Khalid Al-Falih, now chairman of the company, said light sour crude output from two Saudi fields - Shaybah and Khurais - would increase by 550,000 bpd in 2016-2017, in order to rebalance the quality of Saudi crude production and extend the lifespan of mature fields.

Shaybah would come first, going online by the end of 2016 or early 2017, he said at that time.

The expansion of oil output at Shaybah will be ready for commissioning by the end of April 2016, an industry source told Reuters this week.

However, a major natural gas liquids project at Shaybah has been delayed because of a construction costs overrun. The liquids plant, which has two trains, is now due to be completed by the end of 2015 instead of the original completion date of end-2014. The first train is ready for commissioning while the second one could be ready by the end of this year.

When the expansion plans for Shaybah and Khurais were announced, officials said they would not add to Saudi Arabia's oil production capacity of 12.5 million bpd but merely compensate for declining and ageing oilfields.

This has not changed, an industry source said. -Reuters