Formation and Extraction

Once a potential source of natural gas or oil has been identified, extensive studies are undertaken to assess the viability of the oil and gas reserves, seismic surveys are undertaken, and test wells are drilled in the area of interest to test the quality of the gas resource.

Conventional Gas

Conventional gas is found in porous sandstone formations capped by impermeable rock and often trapped at high pressure.

Coal Seam Gas

Coal is a sedimentary rock from the compressed remains of organic material such as plants. Increases in heat and pressure created coal and gas becomes trapped amongst the water in the coal seams.

Shale Gas

Shales are fine-grained sedimentary rocks, formed from the compaction of silt and mud. Gas can become trapped amongst the shale.

Tight Gas

‘Tight’ rocks are typically limestone and sandstone. Both shale and ‘tight’ rocks have very low levels of permeability and are found deep underground.

Types of gas wells [infographic]

Types of Gas Wells

Coal Seam Gas

Coal seam gas (CSG) reserves are generally shallower than other natural gas reserves, while shale and tight gas reserves are deeper underground.

If a gas field is found to be commercially viable, then production can commence.

Production usually involves drilling multiple wells to access the gas reserves. These wells are either vertically or horizontally drilled, depending on where the gas reserves lie within the coal seam, shale or tight sandstone.

Coal seams store both water and gas. When a well is drilled, the water and gas are pumped out.

Shale and Tight Gas

Shale and tight gas wells are drilled to depths below the surface of between 2 and 5 kilometres and generally require hydraulic fracturing to extract the resource. Shale and tight gas wells are drilled vertically during an exploration and appraisal program.

Depending on the structure of the target formation some development wells are drilled horizontally, which allows for operators to minimise surface impact.

Conventional oil and gas

Conventional gas is obtained from reservoirs that largely consist of porous sandstone formations capped by impermeable rock, with the gas trapped by buoyancy. The gas can generally move to the surface through the gas wells without the need to pump.