Environmental documents show Woodside’s Browse LNG project will produce the same greenhouse emissions just to get gas to shore as the entire Gorgon project, one of the nation’s biggest polluters.

The proposed $US20.5 billion ($28 billion) Browse project about 400km north of Broome would on average emit the equivalent of 4 million tonnes of carbon dioxide a year for 50 years, with emissions peaking at 7 million tonnes a year.

In a filing with the Federal Environment Department, Woodside said most of the carbon dioxide would come from gas burnt to power two floating production vessels and pump the gas 900km to the North West Shelf’s Karratha gas plant.

In addition, 10 per cent of gas from the offshore project’s reservoirs would be made up of carbon dioxide, which would be vented to the atmosphere.

The Browse project is forecast to produce 10 million tonnes of LNG a year through the gas plant on the Pilbara’s Burrup Peninsula.

According to the filing, Woodside’s biggest growth project — planned for approval in 2020 — would have a so-called carbon intensity of 0.4 tonnes of greenhouse gases for each tonne of LNG, before the gas was processed onshore.

Chevron’s Gorgon, Australia’s largest LNG project, was planned to emit 6.1 million tonnes of greenhouse gases a year to produce 15.6 million tonnes of LNG, its greenhouse gas abatement program says.

This indicates LNG produced on Barrow Island has a carbon intensity of 0.4.

Gorgon planned to inject underground 80 per cent of the carbon dioxide in the reservoir gas, as required by Chevron’s agreement with the State Government.

Technical problems mean the injection system is yet to operate two-and-a-half years after Gorgon exported its first LNG cargo, giving the project a carbon intensity of 0.6 based on the abatement program figures.

If the NWS plant operates similarly to the Gorgon plant, then Browse would have a carbon intensity of 0.73 tonnes of carbon dioxide for each tonne of LNG produced.

The major difference between the two projects is that pressure in the reservoir is sufficient to drive gas to the Gorgon plant while powerful compressors are needed for Browse gas.

Gorgon’s emissions will increase in the future when gas from its Jansz-Io field requires compression to maintain flow rates.

Emission numbers include domestic gas production equivalent to 15 per cent of LNG production, as required by the State Government.

Greenhouse gas emissions from LNG plants are in practice not limited by any Federal regulation.

The Federal Government has a safeguard mechanism for large greenhouse gas emitters that sets a baseline based on historical emissions.

The baseline can be adjusted for expansions or natural variation in the resource.