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The United States of America have pioneered the Shale Gas Revolution increasing production from 23 billion cubic meters (bcm) to 385 bcm by 2015. The USA is one of only four countries commercially producing gas from shale reservoirs and their production volumes far exceed those of Canada, China and Argentina, who reportedly produced 42 bcm, 4.5 bcm and 1.8 bcm of shale gas in 2015, respectively.
Exploitation of Shale Gas
Countries’ national interest in the development of and production of gas from unconventional reservoirs is attributable to a number of different reasons excluding employment and capital generation factors. For many European countries, with Poland as a prime example, shale gas exploitation is a way to reduce reliance on imported gas and improve the nation’s energy security. For other countries, where extraction of significant amounts of natural gas from conventional sources is well-established and where unconventional resources are known to be large, such as the USA and Canada, shale gas extraction is a way to make use of pre-existing infrastructure.
CO2 emissions from shale gas are approximately half that of coal for the same heat output and the USA’s transition from coal-fired power stations to gas-fired has caused a marked decrease in emissions. Natural gas-fired power stations, in comparison to coal-fired and nuclear power stations, are more easily adapted to utilize different fuel-sources, including renewables such as biomass. There also exists the potential for depleted shale gas reservoirs to be used for CO2 sequestration.
Challenges Faced in Shale Gas Extraction
Extraction of shale gas, performed by hydraulic fracturing or “fracking”, is plagued by a number of economic, environmental and social issues. Inefficient extraction remains a primary economic concern as knowledge of microstructural influences on gas-flow and transport in shale formations remains incomplete. Contamination of groundwater with hydrocarbons and fracking-fluid chemicals, particularly where fracking occurs close to drinking water or agricultural aquifers pose serious health risks.
Extraction of gas from shale reservoirs also carries the risk of human-induced seismicity. The state of Oklahoma in the USA has seen a surge in seismic activity in the last decade. Between 2008-2013, coinciding with the USA’s increased extraction of gas from shale reservoirs, Oklahoma became the most seismically active state in the USA for earthquakes exceeding magnitude 3. Thousands of injection wells have been drilled for fracturing of shale reservoirs, disposal of production brines and disposal of hydrofracture fluid. Between 2008 and 2013 the state experienced 154 seismic events exceeding magnitude 3.5. Prior to this, between 1880 and 2008 there were only 25 seismic events exceeding magnitude 3.5.
A study by Dr Jasmin Cooper, from Imperial College London’s Sustainable Gas Institute, and Dr Laurence Stamford and Professor Adisa Azapagic, from the University of Manchester’s School of Chemical Engineering and Analytical Science, determined the sustainability of exploiting UK shale gas for energy production in comparison to eight other electricity options; conventional gas, liquefied natural gas (LNG), coal, nuclear, hydroelectric, wind, solar and biomass.
Considered in the multi-criteria decision analysis were three sustainability aspects, these being the economic, environmental and social factors associated with shale gas extraction and energy production. The three economic factors consisted of the levelized cost i.e. total cost over the operations lifespan, capital cost and fuel cost. Environmental factors included global warming, eco-toxicity, human toxicity and ozone layer depletion. The four social factors consisted of direct employment, public support, injuries and fuel supply diversity.
When environmental, economic and social aspects all have equal importance shale gas is ranked seventh in terms of sustainability. In this instance wind and solar are the most sustainable options and the coal the least. Varying the importance of the sustainability aspects in realistic terms saw electricity generated form shale gas range between fourth and eighth in terms of its overall sustainability.
In order for electricity production from shale gas to be the most sustainable significant improvements would need to be made in terms of its environmental impact, requiring a 329-fold reduction in detrimental impacts, and a 16-fold increase in employment, coupled with massive changes, on the order of ten-thousand times, made to the importance of each criteria.
The overall indication from the study is that shale gas energy production, in the UK context at least, is not sustainable. The variability seen in the rankings provided by Dr Cooper, Dr Stamford and Prof Azapagic’s analysis indicate that what might be considered sustainable is dependent on the weighting assigned to each aspect of the gas-production and energy-generation chain.
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