Most Australian shale prospects are at least 2km beneath the ground – separated by thick impermeable layers of rock from freshwater aquifers, which are typically about 300 metres below the surface.
The transition from exploration to production involves installing production wells drilled into gas-bearing geological formations up to 4km below the surface.
Drilling and well construction are tightly regulated in Australia. The oil and gas industry has a strong understanding of the technologies involved as millions of wells have been drilled around the world in the last 160 years.
Drilling stops at regular intervals so that purpose-built steel pipes – or casing – can be installed.
The gap between the casing and borehole wall is filled with cement. The casing and the cement form a non-porous barrier that prevents cross-contamination between the petroleum-bearing rock formation and any overlying aquifers. The casing and cement are pressure-tested to ensure that they can tolerate higher pressures than those expected over the life of the well.
A wellhead – which contains barriers, valves, seals and a gas/water separator – is placed on the surface to maintain control of the well and the drilling rig is moved from the site.
In onshore drilling, an area is fenced off around the well, which is now ready for production. The size of this area varies. A typical shale gas well takes up about the same area as a two-car garage.
The drilling site is then rehabilitated.
When a well is no longer producing, it is permanently sealed off by a series of cement plugs designed for durability and withstanding high pressure.