Originally Posted by
Gabriel
They drill the wellbore first, insert a metal casing into the well bore and cement it in place. They then load up these "sleds" with shaped/directional explosives and detonate them inside the wellbore to perforate the casing and to create the starts for the cracks that are then expanded with water pressure in the actual hydraulic fracturing phase. The whole length of the wellbore that lies within the shale formation is perforated every 5-15 cm in multiple directions section by section. When the perforation "gun" is removed from the well they will pump the fracturing fluid into the wellbore at huge pressures so that the cracks created by the perforation charges will expand due to the pressure. The proppants (usually sand or small glass/ceramic beads) get into the cracks that were expanded by the water pressure and will hold the cracks open once the water pressure in the wellbore goes down. The majority of the tracking fluid is not recovered in the flowback phase of the operation.
Most of methane/oil leaks are not due to the cracks going up to the ground water layer, but due to faulty seals in the piping close to the surface. Gas wells opened with hydraulic fracturing techniques also lose some 3% of the life time production of gas of the well in the flowback phase, compared to wells opened with conventional drilling that lose only about 0,01% of the lifetime production in the opening phase.