Chevron has passed a milestone of one million tonnes of greenhouse gas emissions captured and stored underground at its Gorgon LNG plant in Western Australia as it works to ramp up its $2.5 billion-plus carbon capture and storage project to full capacity.

The start-up of the project, the largest carbon capture initiative worldwide, was delayed by more than two years due to technical setbacks incurred with water content in the greenhouse gases extracted from the gas flow.

"We continue to safely ramp up the system and are making good progress towards reaching full operation," Chevron Australia managing director Al Williams told AFR Weekend.

Once fully operational, the CO2 capture system will reduce Gorgon's greenhouse gas emissions by about 40 per cent, or more than 100 million tonnes over its life.

"Once fully operational, the system will reduce up to 4 million tonnes of CO2 per year – equivalent to more than a million electric vehicles."

Gas started to be buried underground at the Gorgon onshore site on Barrow Island last August, more than two years after the first LNG was exported from the project in March 2016. The second of three compression trains at the project started up in October, with the third expected within weeks.