query: How is oil shale made?
passage: Oil shale
Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced, called shale oil (not to be confused with tight oil—crude oil occurring naturally in shales). Shale oil is a substitute for conventional crude oil; however, extracting shale oil from oil shale is more costly than the production of conventional crude oil both financially and in terms of its environmental impact.[1] Deposits of oil shale occur around the world, including major deposits in the United States. A 2016 estimate of global deposits set the total world resources of oil shale equivalent of 6.05 trillion barrels (962billion cubic metres) of oil in place.[2]
passage: Oil shale reserves
Oil shale reserves refers to oil shale resources that are economically recoverable under current economic conditions and technological abilities. Oil shale deposits range from small presently economically unrecoverable to large potentially recoverable resources. Defining oil shale reserves is difficult, as the chemical composition of different oil shales, as well as their kerogen content and extraction technologies, vary significantly. The economic feasibility of shale oil extraction is highly dependent on the price of conventional oil; if the price of crude oil per barrel is less than the production price per barrel of shale oil, it is uneconomic.