There are movements — shifts, even — under way in the global energy market, and one of the elements disrupting the old balance is shale gas. Disruption is precisely the right word, because it is gas extracted from porous rock through drilling or hydraulic fracturing (fracking).

Read also: What is fracking (hydraulic fracturing)

Shale gas — natural gas, predominantly methane — is contained in shale rock, clays and porous rock. American engineers were the first to recognise the potential of this resource. In 2000, shale gas accounted for 2 per cent of natural gas production in the United States. By the end of 2012, that figure had reached 40 per cent. Using horizontal drilling and multi-stage hydraulic fracturing (fracking) technologies, natural gas is extracted at low cost. Both techniques can be applied to new wells as well as — at even lower cost — to old ones. Within just a few years, the development of these unconventional resources promises to give the United States energy independence, with repercussions across all global energy markets through lower energy costs and a shift in import-export axes.

Just a few days ago came the news of Obama's authorisation for the export of fracking gas abroad, particularly to Asia. It is considered an unconventional gas because it is trapped in low-permeability rock formations that must be "fractured" in order to extract it.

Hydraulic fracturing involves injecting a high-pressure fluid into the reservoir. The process creates new micro-fractures in the rock and connects pre-existing ones, opening an escape route for the gas towards the well. The technique is, however, under scrutiny in many states due to risks of environmental damage and groundwater contamination. Shale gas, together with tight gas (compact sands) and coalbed methane (coal), accounts for approximately 60% of technically recoverable onshore reserves using these new methods in the United States, according to estimates from the US Department of Energy. Shale gas reserves could potentially meet American demand for the next 30 years.

There are four major shale gas deposits in the United States: the Barnett in Texas, which accounts for 50 per cent of total output, the Haynesville in Louisiana and Texas, the Fayetteville in Arkansas, and the Marcellus in Pennsylvania and several neighbouring states.

In Europe, shale gas has yet to see the development recorded in the United States due to several factors, including high population density and perhaps a greater regard for the precautionary principle. Poland and Ukraine are the countries that appear to be investing in it most, though recently the United Kingdom and France have also been drawing up exploitation plans. In Germany, an intense debate is currently under way. The exploitation of shale gas is not without its critical points.

There are four concerns associated with hydraulic fracturing operations: groundwater contamination, environmental and landscape impact, the risk of triggering seismic events, and the greenhouse effect.

With regard to water, proponents argue that rock reservoirs are generally located below the groundwater aquifers used by humans, which should therefore not be affected, and that the risk of leaks in the shallower sections of wells can be reduced by lining them with cement.

With regard to environmental and landscape impact, the areas where fracking is carried out are disrupted and disfigured: in America, the affected zones appear to also suffer from desertification.

The increase in low-intensity earthquakes (magnitude no greater than 3) recorded in many parts of the United States could, according to many geologists, be directly attributable to the 35,000 active fracking wells, and the US Senate has already launched an inquiry into the potential seismicity induced by energy technologies.

Finally, the heated debate over shale gas's contribution to the greenhouse effect has grown because during the early stages of production a portion of the extracted gas is released into the atmosphere, and methane has an extremely high climate-altering potential — six times greater than CO2. Technologies specifically aimed at limiting these leaks are currently being developed, though they will in any case always affect at least 1% of a well's total production.