What is coal seam gas?

Today we have Coal Seam Gas 101: what is coal seam gas and how do they get it out?

Coal seam gas (also known as natural gas) is methane which naturally occurs within the coal structure. Water also naturally occurs in coal and it is pressure from this water which holds the coal seam gas in place.

As part of the normal coal mining process, much of the coal seam gas escapes and can pose a safety and environmental hazard. In the past, coal seam gas has been ‘flared’ or burnt off.  More recently, the gas has been recognised as an energy source in its own right and deliberately mined, captured and processed.

Coal seam gas is extracted by drilling wells hundreds of metres into the ground and pumping the water from the coal seam. When the water pressure is reduced, gas escapes from fractures in the coal. Water and gas are pumped together and later separated for treatment, shown in the diagram below.

Sourced from DERM

To increase the flow rate of gas from the wells, a process called hydraulic fracturing, or ‘fraccing’ can sometimes be used. This is the part of the CSG process which dominates headlines. As I understand it, fraccing involves high pressure pumping of a liquid, which is primarily made up of water and sand, into the well to fracture the coal seam and help release gas (I will discuss other chemicals used in fraccing in later posts). The fraccing fluid is pumped back to the surface and disposed of.

An average coal seam gas well may operate for 10 to 20 years.

Next up: how much coal seam gas mining is there in QLD?


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