Coal seam gas

23 February 2015

Coal seam gas (CSG) is simply natural gas, which consists mainly of methane. It’s used every day to generate electricity, run home appliances, and fuel businesses and industries. In fact, CSG provides 90% of Queensland’s gas needs.

CSG is a a term used to describe the gas found in coal seams (areas of underground coal). These coal seams can be anywhere from 200 metres to 1,000 metres below the earth’s surface. The natural gas bonds to the surface of the coal as a thin film, and underground water pressure holds it in place.

How CSG was formed

The CSG we use today started forming millions of years ago as a by-product of decaying organic plant matter. Layers of sand and soil compressed the matter and over millions of years, this compression, combined with the earth’s heat, converted it into natural gas.


Coal seam gas extraction

Extracting and processing CSG is a multi-step process:

csg well illustration

1

Wells are drilled into the ground

CSG wells are about the size of a dinner plate. They are drilled into the ground until they reach the coal seams, and the surrounding area is lined with steel casing and a cement barrier to protect it.

First, some water is extracted from the well. This reduces the pressure in the underground coal seam and allows the gas to flow into the well and to the surface.

When in operation, the surface area of a fenced CSG well is generally around half the size of a netball court, and land uses, such as farming and grazing, outside the fenced area can continue. 

csg gas water separation illustration

2

The gas and water are seperated

Once the gas and water reach the surface, they are separated and flow along underground pipelines to nearby processing facilities. Water is sent to a treatment facility and gas is sent to a processing plant.

csg pressure valve illustration

3

The gas is put under pressure

Once the gas arrives at the processing plant, any remaining water is removed and the gas is compressed (put under pressure so it can flow) for distribution.

csg gas transport illustration

4

The gas is transported

The gas is transported along pipelines to either Australian residential and industrial customers or it’s sent to a facility to be turned into a liquid (liquefied natural gas, LNG), which makes it easier to export overseas.

csg gas cooling illustration

5

Gas is cooled to form LNG

LNG is liquefied natural gas, which is gas in liquid form. To create LNG, the CSG is cooled under pressure to a temperature of minus 161˚C. During the cooling process, any existing traces of carbon dioxide, water and other impurities are removed. Liquefaction shrinks CSG to 1/600th of its size making it easier to transport.2

csg gas export ship illustration

6

Storage, export and use overseas

The LNG is stored in tanks, before it is exported in purpose-built ships for export overseas. When it arrives, the LNG is turned back into gas and used to fuel power stations, homes, businesses or for electricity generation. 

csg well decommission illustration

7

Used wells are decommissioned

Once a CSG well is no longer being used, it is decommissioned (plugged with cement) and the area is returned to its natural environment

 


What is 'fraccing'?

Fraccing (or fracking) is a technique used in the extraction of coal seam gas (CSG).

Sometimes during the extraction process the CSG doesn’t flow freely through the natural underground pathways to reach the surface. That’s when the technique called hydraulic fracturing or ‘fraccing’ is used to help the gas flow to the surface.

The process involves pumping a fluid mixture under pressure into the well. The fluid mixture consists of around 99% water and sand, and about 1% of salts and other chemical additives, many of which are found in most homes.

The hydraulic pressure created by pumping the fluid into the well forces the fractures in the coal seams to open further, creating gaps up to about 10mm wide. The sand keeps the fractures open to create a better pathway for the gas to flow to the surface.

The additives in the fluid mixture improve the efficiency of the hydraulic fracturing. For example, guar gum, a thickener used in ice cream, thickens the water in the fluid mixture to suspend the sand, and acetic acid, which can be found in vinegar, balances the acidity in the fluid.

  1. Australia Pacific LNG 2014, LNG processing facility, Australia Pacific LNG.