Chevron Corp. and PetroChina Co. began long delayed gas production from the Luojiazhai onshore field in China’s southwestern regions of Sichuan and Chongqing, at the end of 2015, with an annual production capacity of 3bcm of gas, Bloomberg reported.

The Luojiazhai’s ‘A’ well production is the first phase of the $6.4b Chuandongbei project, which is a tricky sour gas development in the Sichuan basin that contains a high level of hydrogen sulphide, wrote Reuters. It carries higher operational risks and requires higher standards for technical processes. The project contains a 2,000 square km block and has proven reserves of 176bcm.

Initially, the production from the field was expected to start in 2010, according to a 30-year production-sharing agreement signed in 2007. Under the agreement, Chevron has become the Chuandongbei project operator with a 49% stake.