Heating shale to high temperatures liquefies solid hydrocarbons contained in the shale, which allows processing or pumping equipment to then sieve liquid hydrocarbons from shale for refinement into oil. This heating process, referred to as retorting, extracts oil from shale.
Surface processing, also known as surface retorting, constitutes the most common form of shale oil extraction. In this method, mined shale undergoes the retorting and refinement process in above-ground facilities. Surface retorting requires large amounts of water for the purposes of mining, refinement and waste shale disposal. The land impact caused by mining shale, along with the significant quantities of water required for mining waste disposal, serves as the primary disadvantage of surface retorting. Alternative mining methods to mitigate the land impact of mining, such as Room-and-Pillar mining, extract shale at extremely inefficient rates and leave behind approximately one-third of the usable resources in a deposit.
The other primary method of shale oil extraction, in-situ retorting, eschews the need for mining shale by heating up underground deposits of shale directly instead. This releases solid hydrocarbons into liquid and gaseous states suitable for pumping in a manner similar to crude oil reservoirs. In-situ retorting alleviates the problems associated with mining, processing and disposing of oil shale materials while also dramatically reducing the land impact of oil shale extraction.