Oil shale extraction is not, as of this writing, an economically feasible way of obtaining oil from these geological formations. However, this has not stopped countries like the United States and Estonia from capitalising on oil shale and processing it as an alternative to traditional petroleum products. The difference between the two types is that oil in shale exists as kerogen which is embedded in layers that have not been exposed to as high temperatures as petroleum. Chemicals, gases and solids are sometimes introduced during the retorting, or heating, process to extract oil from the shale.
Use refrigerant, such as chilled ammonia, to create a "freeze wall" surrounding the oil shale resource underground, as has been performed on oil shale "in situ," or in its original place, by Shell in Colorado. Pipe in the ammonia to freeze the groundwater and prevent it from coming into contact with the oil shale production area, which will be heated to 750 degrees Fahrenheit to release gas and liquid hydrocarbons.
Use another in situ extraction process for oil shale by heating carbon dioxide gas above ground, then injecting it into the shale. Heat the formation to assist in the circulation of the gas through the crevices. Condense the resulting shale oil vapors. Alternately, use hot recycled solids as the heat source to decompose oil shale particles. The solids may include hot ash derived from spent oil shale.
Extract oil from oil shale by using an electrically conductive substance, such as calcined petroleum coke, in what is known as an "electrofracking" process. Inject the material into the fissures in the formation. The fissures will be heated by parallel heating wells intersected by another horizontal well. Do this to administer opposing charges to each end.
Double the yield of oil from oil shale by using reactive fluid for oil shale with low hydrogen content. Introduce hydrogen gas or donor solvents -- chemicals contributing hydrogen to a reaction -- to the oil shale. The coke precursors in the oil shale will interact with the hydrogen under high pressure.