Coal seam gas

Drilling for coal seam gas in the Surat Basin, southern Queensland.

Coal seam gas, sometimes shortened to CSG, occurs naturally.

It is produced over millions of years as coal is formed deep underground through heating and compressing plant matter.

The gas, which is mostly methane, is trapped in coal seams typically at depths of 300-600 metres. The coal seams are usually saturated with water and the pressure of this water holds the gas in place.

Coal seam gas is extracted by drilling wells into the coal seams. The water flows to the surface unaided or is pumped out if the pressure within the seam is low, releasing the gas from the coal.

The gas and water are separated at the wellhead and the gas is piped to a compression plant, where it is dried and compressed before it is transported through a pipeline to customers.

Advantage

An advantage of coal seam gas is that it leaves the coal intact for future extraction. Capturing the gas means it isn’t vented to the atmosphere as part of the mining process and can be put to good use.

In southern Queensland, water from coal seams is generally stored in evaporation ponds. QGC is committed to phasing out construction of new evaporation ponds and to investigating options for putting the water to beneficial use.

Coal seam gas in the Surat Basin of southern Queensland is typically more than 98% methane with only small amounts of nitrogen and carbon dioxide. As such, it requires relatively little treatment before it is turned into liquefied natural gas.