According to the U.S. EPA (Environment Protection Agency), hydraulic fracturing:
“… produces fractures in the rock formation that stimulate the flow of natural gas or oil, increasing the volumes that can be recovered. Wells may be drilled vertically hundreds to thousands of feet below the land surface and may include horizontal or directional sections extending thousands of feet.
Hydraulic fracturing is a technique used in “unconventional” gas production. “Unconventional” reservoirs can cost-effectively produce gas only by using a special stimulation technique, like hydraulic fracturing, or other special recovery process and technology. This is often because the gas is highly dispersed in the rock, rather than occurring in a concentrated underground location.”
According to the EU Commission (DG ENVI – Environment Directorate-General), hydraulic fracturing:
“…, aka fracking is the process by which fracturing fluids – a mixture consisting primarily of water, sand and a small percentage of chemical substances (generally between 0.5% and 2%) are injected under high pressure into a geological formation that contains hydrocarbons so as to break the rock and to connect the pores that trap the hydrocarbons. As the injection pressure exceeds the rock strength, the process results in the opening or enlargement of fractures. Injected sand prevents these fractures from closing after the pumping pressure is released, thereby enabling natural gas and oil to flow from the geological formation into the well.”
What is conventional and unconventional gas and oil?
Gas and oil are neither ‘conventional’ nor ‘unconventional’. All oil and gas resources (fossil fuels) can be classified as hydrocarbons. ‘Unconventional’ does not refer to the characteristics or composition of the oil/gas. Instead it refers to the porosity, the permeability, the fluid trapping mechanism, or other characteristics of the geological reservoir or bearing rock formation from which oil and gas could be extracted. These characteristics result in the need to artificially alter the geological features of the reservoir or bearing rock formation using stimulation techniques such as hydraulic fracturing to extract the hydrocarbons.
Conventional fossil fuels refer to oil and/or gas which can be readily extracted from a high permeability and high energy content formation, usually porous, permeable sandstone, siltstone and carbonate (limestone) reservoirs, generally without requiring hydraulic fracturing stimulation. The oil and gas resources originate from another formation but have migrated upwards and were then trapped by an impermeable ‘cap’ rock. Conventional petroleum resources are extracted using traditional methods of drilling down through the ‘cap’ rock and allowing petroleum to flow up the well.
Unconventional fossil fuels refer to oil and gas produced from geological formations which are typically more difficult to access and require the use of specific stimulation techniques such as hydraulic fracturing to become productive. As described by the industry itself, “while conventional gas resources can be developed and produced without any special well completions, most unconventional gas production requires the rock to be hydraulically fractured or ‘stimulated’ to allow natural gas to escape from the low-permeability rock and flow through the wellbore to the surface“.
So-called ‘unconventional gas’ is thus the collective term used to describe for instance shale gas and tight gas. Other forms include coal bed methane, hydrates or geopressurized zones. Exploring for unconventional fossil fuels (such as shale gas/oil, tight gas/oil and coal bed methane) ultimately requires the use of some form of fracking.
- Shale gas: Natural gas that is tightly trapped in shale. It forms when black shale has been subjected to heat and pressure for millions of years, usually at depths of 1.500 to 4.500 metres. Its production requires hydraulic fracturing and is typically carried out with horizontal, multi-stage wells (i. e. multiple fracs).
- Tight gas: Natural gas trapped in impermeable rock and non-porous sandstone or limestone formations, typically at depths greater than 3,000 metres below the surface. The viability of sandstone reservoirs is determined by their porosity and permeability, or how easily fluid or gas moves through the rock. Because the capacity of these formations to allow gas migration is too limited for conventional production methods to be successful, horizontal hydraulic fracturing is used to optimize gas recovery.
- Tight oil: Light crude oil trapped in shale, limestone and sandstone formations. Like shale gas and tight gas, it is extracted by horizontal drilling and hydraulic fracturing.
- Coal bed methane (CBM): A form of natural gas trapped in coal reservoirs. Production may or may not require hydraulic fracturing. In the past wells usually were drilled vertically, but more recently horizontal and directional drilling is used. The reservoirs tend to be at shallow to moderate depths (approximately 610-1,830 meters) and well productivity varies widely.
Which extraction techniques exist and what is the problem with fracking?
- Well stimulation (also ‘hydrofracking’) is one extraction technique used to increase the recovery rate of oil and gas resources captured in easily accessible rocks (the so-called ‘conventional’ oil and gas). This has been used by the oil and gas industry since the late 1940-ies.
- High-Volume Horizontal Hydraulic fracturing (HVHF; also ‘modern fracking’) is a relatively young extraction method resulting from recent technological technical progress. It is supposed to make the extraction of unconventional oil and gas technically and economically feasable in some regions of the world. It was only in the last two decades that four different new technologies techniques have made it possible to fracture deep shale rock or clay formations 1 to 5 kilometres underground. They comprise:
- Directional drilling (wells that go down 1 to 5 km and then extend horizontally for another kilometre or more.
- Fracking (injection under very high pressure) of millions of litres of fracturing fluids including sand, water and toxic chemicals)
- Slick water (the use of gels and high fluid volumes at injection rates of 100 barrels a minute)
- Multi-well pad and cluster drilling (the drilling of six to twelve wells from one industrial platform)
The first horizontal shale gas well was drilled in 1991, the first slick watet fracturing took place in 1996, and the use of cluster drilling from one pad didn’t happen until 2007. What we call today ‘High-Volume Horizontal Hydraulic Fracturing’ – often mistakenly shortened to ‘fracking’ – is the result of the combination of these new techniques. In other words, it is wrong to state that this ‘modern fracking’ has been used in Europe since the 1960ies, as industry and politicians would like to make the world believe.
However, more than a decade of large-scale use of the fracking-technique in the US and in Canada has shown how harmful and destructive this extraction process can be, as confirmed and acknowledged by countless peer-reviewed scientific studies. Air pollution, ground and surface water contamination, radioactive releases, noise and light pollution, induced earthquakes, climate impact, competition for access-to-water, occupational health and safety hazards, and not to forget its proven negative consequences for human and animal health are some of the most imminent impacts and risks which are linked to the fracking technique.