Natural gas is seen as a primary transition fuel to replace coal till renewable energies are able to replace fossils entirely for most energy requirements. But fracking is extremely damaging to the environment, with serious impacts on human health. It also releases methane, a powerful greenhouse gas, into the atmosphere.
Fracking is a vernacular term for 'hydraulic fracturing', the practice of increasing yield from fluid hydrocarbon seams by opening micro-fissures in rock by hydraulic pressure.
Hydraulic fracturing is a technique used since the 1940s to enhance the extraction of gas from deposits which would otherwise be unviable. In 'traditional' gas extraction, fossil methane gas is concentrated under pressure in oil-saturated rock strata. The gas is pressurised by the crust, and therefore exits under its own force when the retaining impermeable rock ceiling is punctured by a borehole. The effect is similar to the release of gas from the liquid when a champagne bottle is popped.
Many gas deposits, however, are not so conveniently structured. In these, the gas is dispersed throughout a rock formation, and will not exit by a simple process of releasing the pressure. In these cases, the gas needs to be encouraged to exit by special stimulation. The gas of this type is locked in rock formations such as shale and compacted sands, as well as coalbeds.
The fracking process
The land that lies above a gas reservoir needs to be purchased and cleared for easy access of drilling equipment. Access roads may also be built.
A wellbore is cut down through the top soil, aquifer, and intervening rock strata, down to the gas-bearing shale stratum. These wells are typically three or four kilometres deep, and are not necessarily always vertical.
- Concrete lining
The shaft is lined with concrete and a steel inner casing provides the structural strength to withstand the high pressures.
A series of explosions in the horizontal section fractures the shale, opening up fissures and micro-channels through which the gas may escape.
Fracking fluid, consisting of a mixture of chemicals and proppant (incompressible ceramic pellets or sand grains) and water, is injected under great pressure and causes the rock to shatter. The proppant enters the tiny fissures and holds them open afterwards. The amount of fluid can be typically 30,000 cubic metres, which is enough to fill 20 olympic size swimming pools.
The fracking fluid is withdrawn, bringing with it the methane gas. Typically only 25-50% of the fluid can be reclaimed.
The fracking fluid is stored on the surface. This may be in an open-air pit, till it is recycled or treated before disposal.
The fracking fluid cannot be stored indefinitely in surface pits and containers. It can be treated before being released into rivers, or pumped back underground after the well has ceased operation. Both of these processes have serious environmental concerns.
Economic advantages: energy resources and employment.
Of the fossil fuels, methane is the cleanest. When it burns it emits less pollution than oil and coal. This is because it burns more completely, giving more heat per amount of fuel, and also because gas has fewer impurities than oil and coal. Impurities like sulphur are responsible for acid rain.
By utilising the gas reserves that are still in the ground using HF (hydraulic fracturing), the energy crisis (when people need more energy than is available, causing a large increase in the price of energy) can be delayed till cleaner alternatives are found. Fossil fuels will never be clean, but solar, wind and other renewable energies can be clean or almost clean.
Environmental: fracking is very damaging to the environment through the liberation of metals from rock strata during extraction, and its product is a fossil fuel.
Very large quantities of a toxic mix is required for HF (hydraulic fracturing). The flowback of this fluid may escape containment during extraction or storage, and enter the water system. The chemicals and heavy metals it contains are harmful to humans and ecosystems. Most of the fluid cannot be reclaimed after injection, and will remain a hazard underground, slowly escaping into aquifers, for generations into the future.
Fossil fuels are the problem that causes global warming by the release of CO2, methane, and other greenhouse gases. Since they are the problem, they cannot be the solution. The word 'cleaner' does not mean 'clean'. The fact that gas burns cleaner than oil and coal does not mean it is good for the environment.
When the pressure is released, the pressure of the rock forces the gas in solution to rise to the surface, where it can be extracted.
- Substances known to be present in flowback:
- Heavy metals: arsenic, manganese
- VOCs: benzene, toluene, naphthalene, diesel fuel, 2-Butoxyethanol
- Chlorides and salts
The flowback is sometimes treated before being released to the hydrological cycle. The types and range of pollutants present in the flowback often exceed the capabilities of normal treatment plants, and can lead to pollutants entering the environment.
Flowback is often just pumped back underground after the well has been fully exploited for its methane. The fracturing of the rock may not be limited to impermeable strata, and may lead to migration of pollutants to water pathways.
There is evidence that the pumping of wastewater into fractured rock leads to an increase in earthquake activity. This is because the fluid acts as a lubricant to rock already under crustal stress.
Any disturbance to the natural world which will not repair itself in a reasonable time can be considered environmental damage. Pollution is the contamination of natural systems, such as ecosystems, with harmful substances, or unnatural alterations to water, air, and land bodies. A pollutant is a specific substance which causes environmental disturbance.
Hydraulic fracturing is of concern, because its wholesale use of toxic substances in the fracking fluid inevitably leads to their escape, as well as methane, into the ground, water and air. Fugitive methane has also been found in aquifer water many kilometers distant from the fracking operations. This water is used by humans in residential and agricultural areas, and will lead to serious health problems.
Fracking causes pollution of the air: it leads to the release of methane and, after combustion, of CO2. Both of these are greenhouse gases, contributors to global warming. Global warming is now generally accepted as a serious threat to human development and sustainable economies.
Natural gas is methane obtained from fossil deposits. These mostly date back as far as the Carboniferous Era, and most fossil fuel is as old as 100 million years. Humans are rapidly depleting all fossil fuels, and the carbon dioxide they release are causing an enhanced greenhouse effect, and the world is warming as a result. Natural gas burns cleaner and more efficiently than coal, so is the better choice. But it is still a fossil fuel.
In the USA, SO2 emissions have reduced over the past 20 years due to the large-scale application of flue-gas desulfurisation technlogy (FDG). In the decade 1994-2004 electricity generation from coal increased, but the use of lower sulphur content coal permitted a reduction by 79% in the SO2 emissions (11.7 Mt). However, in the decade 2004-214 the coal used had a higher sulphur content (subbituminous and lignite coals) so SO2 per kWh increases offset the fact that coal-powered electricity production decreased. The shift in coal quality added 2% to the sector's SO2 burden.
Period Avg. SO2 emissions from electric utilities (US) /Mt 1970 17.5 1975 18.1 1980 18.0 1985 16.7 1990 16.0 1994-5 14.9-12.0 1998-2000 13.5-12.0 2005 10.2 2010 6.0 2014 3.2
EIA, 2015a, 2016b, From graph in article by M.A.Brown et al.,The electricity Journal 30(2017)