Types of onshore gas
Onshore gas is found deep under the land surface in sedimentary rocks. The majority of gas supplied to Victorian consumers to date has been produced from offshore hydrocarbon fields under the seabed.
Onshore gas can be found in different sedimentary rocks known as tight sandstones (tight gas), shales (shale gas), coal seams (coal seam gas) or porous sandstones (conventional gas).
The main difference between tight gas, shale gas, coal seam gas and conventional gas is the type of rock that the gas is found in and the way in which the gas is stored. The methods used to produce gas from these different sources may also vary.
Tight gas is sourced from relatively low permeability and low porosity sedimentary reservoirs. The lack of permeability does not allow the gas to migrate out of the rock. In this case the method to extract gas may involve fracturing the rocks to create artificial porosity and permeability
Shale gas is sourced from very fine-grained sedimentary rocks that have low porosity and permeability and are organic-rich. The gas is held in organic matter in the rock, in tiny pores between grains and any fractures present in the rock. As for tight gas, fracturing the rocks to create artificial porosity and permeability will release the gas.
Coal seam gas, also called coal bed methane, refers to naturally occurring methane in coal seams. The gas is held on coal surfaces and trapped by water pressure in the gaps and cracks in the coal seams. In order to allow the gas to flow, water is drawn away from the seams to release the gas into a gas well.
Conventional gas is stored in porous and permeable sedimentary rocks such as sandstones or limestones in a geological structure known as a trap. Impermeable rocks directly above the structure trap the gas. A well drilled into the structure intersects the porous reservoir and gas flows into the well.
Currently there is no coal seam, tight or shale gas production in Victoria.
Diagram: types of natural gas
Where is it found?
Onshore natural gas is found around Australia including in New South Wales, Queensland, South Australia and the Northern Territory.
Conventional onshore gas has been produced from the Otway region in the past.
There is no onshore natural gas production in Victoria. Exploration of these gas types is at an early stage. It is unknown whether the State has any defined resources of natural gas in onshore areas that could be drawn on a commercial, basis. There has been a discovery of potential tight gas in Victoria, but the commerciality of this is yet to be determined.
The areas prospective for onshore gas in Victoria are shown in the map below.
Areas prospective for natural gas
Select the map to open a larger view.
For further information:
Please visit the CSIRO website.