Oil Shale - Extraction and Processing

Extraction and Processing

Most exploitation of oil shale involves mining followed by shipping elsewhere, after which one can burn the shale directly to generate electricity, or undertake further processing. The most common methods of surface mining involve open pit mining and strip mining. These procedures remove most of the overlying material to expose the deposits of oil shale, and become practical when the deposits occur near the surface. Underground mining of oil shale, which removes less of the overlying material, employs the room-and-pillar method.

The extraction of the useful components of oil shale usually takes place above ground (ex-situ processing), although several newer technologies perform this underground (on-site or in-situ processing). In either case, the chemical process of pyrolysis converts the kerogen in the oil shale to shale oil (synthetic crude oil) and oil shale gas. Most conversion technologies involve heating shale in the absence of oxygen to a temperature at which kerogen decomposes (pyrolyses) into gas, condensable oil, and a solid residue. This usually takes place between 450 °C (842 °F) and 500 °C (932 °F). The process of decomposition begins at relatively low temperatures (300 °C/570 °F), but proceeds more rapidly and more completely at higher temperatures.

In-situ processing involves heating the oil shale underground. Such technologies can potentially extract more oil from a given area of land than ex-situ processes, since they can access the material at greater depths than surface mines can.

Several companies have patented methods for in-situ retorting. However, most of these methods remain in the experimental phase. One can distinguish true in-situ processes (TIS) and modified in-situ processes (MIS). True in-situ processes do not involve mining the oil shale. Modified in-situ processes involve removing part of the oil shale and bringing it to the surface for modified in-situ retorting in order to create permeability for gas flow in a rubble chimney. Explosives rubblize the oil-shale deposit.

Hundreds of patents for oil shale retorting technologies exist; however, only a few dozen have undergone testing. As of 2006, only four technologies remained in commercial use: Kiviter, Galoter, Fushun, and Petrosix.