CNPC and Chevron have started building gas production capacity at the Chuandongbei gas field in southwestern Sichuan province, the top Chinese oil and gas firm said on Thursday, more than three years after they inked a cooperation deal.

CNPC, parent of PetroChina, entered a 30-year product sharing contract in December 2007 to develop the high-sulphur gas field using technology from Chevron, which will be the operator of the field.

The Chuandongbei block, covering 1,970 square kilometres, has proven gas reserves of 176 billion cubic metres (bcm) and the companies said in 2007 that they planned to process the gas at two plants with total capacity of 740 million cubic feet per day, or 7.6 bcm a year.

Yan Cunzhang, head of the foreign cooperation department under CNPC, said in June last year that they expected to see first production at the end of 2011.