Shale gas and Shale oil are fossil fuels trapped in the deep and low porosity sedimentary rocks of shale, often located more than 3 km depth below earth surface. They are considered unconventional energy sources because the fuels are contained in difficult-to-produce reservoirs, which require special advanced technologies to achieve economic production. 

The great excitement about the shale gas is attributed to revolutionary methods of drilling using a combination of two technological processes: directional drilling and hydraulic fracturing also referred to as hydrofracturation, hydrofracking or fracking.

This technology is credited to have increased the proven reserves of natural gas for more than 700 Tcf in the USA over the last decades and made the country became now the number one gas producer in the World.

Directional drilling involves drilling vertically or on a specific direction first, then changing direction from a certain depth, and continuing horizontally in order to maximize the surface contact with the bedrock. 

Hydrofracking consists of creating fractures in the rocks by injecting a high pressure mixture of water, proppant or sand and a cocktail of chemicals. The proppant usually made of highly resistant ceramic grains maintain open fractures, causing a conductive path while the chemicals facilitate the circulation of fluid.

The identity and toxicity of those chemicals are not always disclosed by the oil & gas industry, which remain a major controversy for concerned citizens.