What is onshore conventional gas?
Onshore gas is found very deep underground in sedimentary rocks. Gas supplied to consumers and industry in Western Australia is produced from offshore oil and gas fields under the seabed such as the North West Shelf as well as on land such as the Perth Basin.
Gas resources below the land are called ‘onshore gas’.
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 also vary.
Gas that flows freely into a well is called conventional gas. It occurs in sandstones and carbonate rocks that have higher permeability, such as those found in the offshore sedimentary basins of Western Australia’s North West Shelf and the conventional gasfields in the Perth Basin.
Conventional gas is stored in porous and permeable rock formations such as carbonates, sandstones, and siltstones, in a rock structure known as a trap. Impermeable or ‘solid’ rocks directly above the structure, trap the gas.
Conventional gas can flow freely from the rock formation when tapped by a well. This is because permeable rock formations have tiny interconnected cavities through them, similar to a sponge, which allow the gas to flow. A well drilled into the porous reservoir makes gas flow into the well where it is captured at the surface.
Gas is generated from source rock that has been buried and heated within the Earth’s crust. The gas moves into porous and permeable rocks and travels via these rocks into a trap.
The gas is held in structures like a dome or upside down dish. This is called a reservoir. Directly over the top of the reservoir is an impermeable layer of much finer grained rock (claystone) that seals and traps the gas.
Conventional gas has been used around the world and in Western Australia for many years. WA’s large LNG projects are based on conventional natural gas resources.
Bunbury Energy is working with stakeholders and communities in the region to provide information and understanding of onshore conventional gas exploration and develop an exploration programme that reflects community input.