Gas extraction from shale requires hydraulic fracturing of the rock, known as fracking, to release the gas.
The fracking process injects a mixture of water, sand and chemicals into the rock. This requires very high pressure and happens deep below the Earth's surface.
This opens up cracks and fractures within the rock, releasing the gas. The sand grains keep the cracks open.
Each gas well uses a vertical drillhole into the shale rock, with a horizontal well drilled off the main vertical shaft. Each horizontal well is then ‘fracked’ and the gas then flows to the surface.
Figure 3 shows a geological cross section schematic of a shale gas well.
A typical horizontal well is fracked in stages. Contemporary horizontal wells may require 30-40 fracturing stages.
Water use is around 1–2 million litres (ML) for well drilling, and 1–2 ML for each hydraulic fracturing stage. Up to 50% of the injected water returns to the surface as flowback water. This flowback water is either reused or transported and treated offsite for safe disposal.
The Beetaloo’s rock formations and the distance between the shale resources and groundwater provide natural barriers. This makes it highly unlikely that there will be any movement of the petroleum resource into groundwater systems. In addition, the casing of wells through the aquifers provide further barriers between the recovery of petroleum resources and the groundwater systems.