China’s largest oil field is expected to cut production by 1.5 million tonnes, or 10.95 million barrels, in 2015, Chinese state media reported, as a slump in oil prices puts pressure on margins for refining crude from the ageing field.

Production at the Daqing field in northeastern Heilongjiang province will shrink by an average 1.3 million tonnes, or 9.5 million barrels, a year, falling to an annual 32 million tonnes, or 234 million barrels, by 2020, according to state-owned China National Petroleum Corp (CNPC), the China Business News said.

Current production at the 54-year-old field is 40 million tonnes, or 292 million barrels, a year.

No immediate comment was available from Daqing Oilfield Company, a CNPC subsidiary.

With global oil prices losing almost half their value since June, profit margins for refining Daqing crude have disappeared. In November, losses averaged 124 yuan per tonne or $2.75 per barrel, according to China Oil, Gas & Petrochemicals (OGP), a newsletter published by the state-run Xinhua News Agency. Losses were 42 yuan per tonne higher than in October.