Oil drilling, though difficult, is pretty simple when compared to oil shale extraction. Getting oil shale, solidified oil trapped inside rock, to the surface is currently more expensive and environmentally harmful than conventional drilling. How much do you know about this potential fuel source trapped beneath the Earth's crust?
Pyrolysis, the application of extreme heat without the presence of oxygen, produces a chemical change in the rock that forces oil out.
Kerogen, the fossil fuel trapped inside the rock, emerges at extreme temperatures.
It takes two barrels of water to produce each barrel of oil shale liquid. The water discharge from oil shale refining increases the surrounding water's salinity.
After a barrel of oil is removed from shale, about 1.5 tons (1.36 metric tons) of rock get left behind.
Shell Oil's In Situ Conversion Process involves extracting oil trapped in shale by lowering heaters into the Earth, eliminating the need for mining and rock extraction. However, oil shale refining is still considerably more expensive than conventional drilling.
Green River Formation, a 17,000-square-mile (44,030-square-kilometer) deposit, is located in the western United States and covers parts of Wyoming, Utah and Colorado.
Green River Formation's reserves can produce an estimated 1.5 to 1.8 trillion barrels of crude oil -- that's three times more than what Saudi Arabian reserves currently hold.
The United States consumes about 21 million barrels of oil a day, and the country imports about 10 million of those.
To loosen the trapped oil, extreme heat is applied. The kerogen begins to liquefy and separate from the rock it's trapped inside when the temperature hits between 650 and 700 degrees Fahrenheit (343 and 371 degrees Celsius).
Some oil analysts and researchers think humans have already reached peak oil, and that from here on out, the amount of available oil will only decrease.