The decline in crude oil prices means output from China's inland Daqing oil field will start to drop off beginning next year, an official at PetroChina said.

Maturation of the Daqing field, the largest inland field of its kind in China, is strained further by the low price of crude oil, off more than 40 percent from its June highs above $100 per barrel. A staff member told the official Xinhua News Agency on condition of anonymity the field's production should be in a free fall by next year.

The field has produced more than 15 billion barrels since operations began in 1960. Last year's annual production was around 290 million barrels, though that should fall to around 234 million barrels by 2020, the employee at PetroChina said in an interview published Sunday.

The field's production rate as of this year represents about a quarter of China's total annual oil production.

The expected rate of decline from Daqing comes as data show Chinese apparent oil demand, a reflection of how much oil goes into domestic refineries combined with net oil product imports, increased in November by 3.5 percent.

Demand is driven largely by economic factors. Last week, the Chinese National Bureau of Statistics said it estimated the economy was 3.4 percent larger last year than previously estimated, adding about $9.6 trillion to the world's second-largest economy.

Chinese President Xi Jinping said the Chinese economy was entering a "new normal" where qualitative growth is favored over quantitative growth.