Prior to the test , its annual production was about 10,000 tons .
In April 2006 , PetroChina reported a successful test at the Changqing Oil Field ( Northwest China ) , first discovered in 1907 .
Prior to the test , PetroChina 's annual production was about 10,000 tons .
In April 2006 , PetroChina reported a successful test at the Changqing Oil Field ( Northwest China ) , first discovered in 1907 .