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(Rich Miller, Asjylyn Loder and Jim Polson 2012: p. 1) The breakthrough was made
possible by acombination of two new technologies: horizontal drilling and hydraulic
fracturing.
Horizontal drilling
Horizontal drilling involves creating awellbore that runs roughly parallel tothe surface
after reaching adesired vertical depth. This increases the subsurface space that is accessible
via one well, leading toareduction ofwells needed. Horizontal drilling was especially
advantageous for shale gas extraction due to two conditions often found in shales:
“(1) the presence of hydrocarbons in disjointed pockets rather than asacontinuous reservoir,
and (2) ahydrocarbon-bearing formation that isextensive but thin.” (Mauter,
Meagan S., Vanessa R. Palmer, Yiqiao Tang, and R. Patrick Behrer 2013: p. 8) With
this technology it’s possible to drill wells over 10kmaway from the surface location,
making drilling more profitable asthe amount of gas that can be drilled through one
wellhead increases sharply.
Hydraulic fracturing
The second technology essential for the extraction for shale gas was hydraulic fracturing,
or ‘fracking’. “Large volumes of fluid are pumped down the wellbore athigh pressures
to create anetwork of cracks inthe source rock, which are held open byaproppant
– typically sand – carried byadditional injected fluid.” (Mauter, Meagan S.,
Vanessa R.Palmer, Yiqiao Tang, and R. Patrick Behrer 2013: p. 8) The fluids most
commonly used for this process are water-based fracturing fluids mixed with frictionreducingadditives,
biocides, oxygen scavengers and acid. (ALL 2009: p.61)
It should be noted, however, that there are multiple concerns about the environmental
impact of hydraulic fracturing. One topic ofconcern is air pollution, caused bymethane
leaks originating from wells or by emissions from the diesel or natural gas powered
equipment such ascompressors, drilling rigs and pumps. (ALL 2009: p.56-66) The
second big topic ofconcern is water. Besides massive water consumption, the main
focus ofthe criticism lies onthe injected fluid and the flowback. (Anthony Andrews et
al. 2009: p. 7, 23) Furthermore, the danger that ground water may be contaminated by
methane isfeared as well as this would have anegative effect on water quality and in
extreme cases could lead to explosions. (Osborn, Stephen G.; Vengosh, Avner; Warner,
Nathaniel R.; Jackson, Robert B. 2011: p. 8172-8176)