About onshore natural gas
Natural gas from coal seams is a form of naturally occurring gas extracted from coal seams. Natural gas from coal seams was formed approximately 200 – 280 million years ago at the same time that coal was formed. The gas is trapped in the tiny cracks between the coal seams under pressure. Natural gas is odourless, colourless and usually 95% pure methane.
About natural gas
Natural gas can be sourced from coal seams, oil sands or from shale formations. More than 20% of the world's energy consumption currently comes from natural gas, providing much of the electricity powering homes and businesses.
Natural gas is odourless, colourless and usually 95% pure methane. It is non-toxic and lighter than air.
Natural gas produces about 20% less carbon dioxide than oil when burnt to create the same amount of energy. In addition, electricity generated from gas produces up to 70% less greenhouse gas emissions than current coal-fired generation facilities.
Gas is used for cooking, heating and cooling. It is used to create fertilisers and supply power plants that generate electricity for commercial and domestic users. The fuel is also used in manufacturing glass, steel, plastics, paint, fabrics and can power trains, cars, buses and trucks.
Natural gas from coal seams was formed approximately 200 – 280 million years ago at the same time that coal was formed. The gas is trapped in the tiny cracks between the coal seams under pressure.
Queensland has been producing gas from coal seams for over a decade and today it makes up about 80% of the state's natural gas supplies.
How we produce gas
QGC produces natural gas from wells drilled into coal seams in the Surat Basin in Queensland.
How a QGC gas well works:
Natural gas is held in the coal by groundwater pressure. When the water is released, gas flows from the seams.
Most of the production wells we drill are between 300 and 800 metres deep in the Walloon Coal Measures of the Surat Basin.
Gas and water are separated at the well site and the gas is transferred at low pressure through underground gathering pipelines to field compression stations. Water is transferred to treatment plants and later made available to farmers, irrigators and other consumers.
The natural gas produced from the Surat Basin is about 98% methane and requires minimal processing.
The onshore gas value chain
Typically, the following process is undertaken from first discovery of gas reserves through to providing gas to consumers.
Historical data, satellite images, aerial photographs and ground activities – such as seismic surveys and exploration or appraisal wells – scope out the size, location and commercial viability of gas reserves.
After gas is discovered, production wells are drilled using a series of mechanical rigs. Gas and associated water are extracted via the well.
The gas and water are separated. The water is transferred to a water treatment facility and made available for beneficial use. The gas is transferred to a nearby field compression station for compression. Several field compression stations are linked to a central processing plant facility where impurities and remaining water are removed and the gas is compressed further for transportation.
Meeting domestic gas supply commitments under long-term contracts is our first priority for production. These contracts are with power stations, industrial users and gas retailers throughout Australia. Gas for export markets is transported to a liquefaction plant on Curtis Island via a 540 kilometre pipeline.
At a liquefaction facility, the gas is cooled to -162°C, which reduces it to a liquid 600 times smaller than its original volume. This process also removes impurities and allows it to be stored and transported safely and economically in large vessels. The gas is now referred to as LNG.
Know more about QGC LNG Plant
The LNG is transported to purpose-built tankers which can carry between 138,000 and 174,000 cubic metres of LNG – enough to power a city of over two million people for two and a half weeks. The LNG is then shipped to overseas energy markets.
Read more about the LNG Shipping
On reaching its destination, the LNG tanker will offload its cargo at a regasification terminal. The LNG is then pumped to onshore storage tanks where the liquefaction process is reversed and the LNG is returned back to a gaseous state.
At the destination, the gas is processed or converted into electricity at a power station and is now ready for use by households and industry.