Shale gas exploration companies drill boreholes down into the gas-bearing shales, thousands of metres below the surface; drilling may also continue horizontally.
The borehole is lined with a steel and concrete casing.
A 'perforating gun' is lowered into the borehole to make small holes in the concrete casing at the depth of the shale target.
A mixture of water, chemicals and sand is pumped — at very high pressure — along the borehole and through the perforations that fracture the shale.
The water opens up cracks in the rock, and the sand grains lodge into the spaces and keep them open, allowing the released gas to flow out of the rocks and to travel back up the borehole casing.
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