HARBIN, April 11 (Xinhua) -- Daqing Oilfield, the largest oilfield run by PetroChina, produced 7.94 million tonnes of crude oil in the first quarter of this year, down 17.8 percent year on year.

With rising difficulties in extracting crude oil, the oilfield seeks to increase its natural gas output.

The oilfield produced 1.22 billion cubic meters of natural gas in the three months, up 13.3 percent year on year, the oil and gas producer said Wednesday.

The oilfield has set a target of selling 2.72 billion cubic meters of natural gas in 2018.

Discovered in 1959, Daqing Oilfield is located in northeast China's Heilongjiang Province. For many years, the oilfield had an annual output exceeding 50 million tonnes of crude oil, but output has shrank due to dwindling reserves.