The future of oil: unconventional fossil fuels

Unconventional fossil hydrocarbons fall into two categories: resource plays and conversion-sourced hydrocarbons. Resource plays involve the production of accumulations of solid, liquid or gaseous hydrocarbons that have been generated over geological time from organic matter in source rocks. The character of these hydrocarbons may have been modified subsequently, especially in the case of solids and extra-heavy liquids. These unconventional hydrocarbons therefore comprise accumulations of hydrocarbons that are trapped in an unconventional manner and/or whose economic exploitation requires complex and technically advanced production methods. This review focuses primarily on unconventional liquid hydrocarbons. The future potential of unconventional gas, especially shale gas, is also discussed, as it is revolutionizing the energy outlook in North America and elsewhere.