Whilst past EU exploration and production of hydrocarbons, including of natural gas, have focused mainly on conventional resources, technological advances, in particular in the United States, have opened the possibility of extraction from unconventional resources, such as in particular shale gas.
Potential benefits as well as uncertainties and health and environmental risks associated with unconventional fossil fuels extraction practices, and in particular with hydraulic fracturing, have been highlighted. Potential risks will need to be carefully identified, assessed and mitigated.
The term unconventional refers to the characteristics of the geological reservoirs or rock formations containing these hydrocarbons. Shale gas, tight gas and coalbed methane are examples of unconventional natural gas, but also oil could potentially be extracted from unconventional reservoirs such as shales using hydraulic fracturing techniques.
Hydraulic fracturing 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.
Once the hydraulic fracturing process is completed, roughly 30% to 70% on average of the initial fracturing fluids, now mixed with fluids displaced from the geological formation, rises to the surface where it can be collected.