What is oil shale?
Conventional oil and gas are produced from sediments which have been buried deeply enough to where the organic matter in the rock has gone through a process of thermal maturation to produce free gaseous and liquid hydrocarbons. Normally, the organic matter is concentrated in fine-grained rocks such as shales, from which the oil and gas have migrated into porous and permeable reservoirs from which they can be freely extracted. The concentration of organic matter within the source rocks is generally quite low, with values of 0.5 - 1.5% TOC (total organic carbon) considered as reasonably rich.
As these source rocks are buried deeply over time, the temperature will rise with increasing depth, and the organic materials will undergo the process of pyrolysis whereby they are converted into molecules of oil and gas. With increased burial, the hydrocarbon molecules will undergo change from oil, then to oil and gas, to gas and condensate until they end up as pure methane.
Note that in some cases, the generated oil and gas does not migrate into reservoir rocks, but remains trapped in the shale, often in minute natural fractures, and is now usually referred to a “shale gas” and “shale oil” by the industry. Although production of such tight oil and gas tends to be relatively expensive, large resources are being identified and developed as the technologies necessary for extraction of such oil and gas are developed.
In contrast, oil shales are sediments with much higher TOCs, usually in the order of 5% to over 40%, but which have never been buried deeply enough to undergo thermal maturation, and therefore do not contain any free oil. The organic matter in oil shales is referred to as kerogen, and most commonly is of algal origin, deposited in shallow marine basins (e.g. Julia Creek) or freshwater lakes (e.g. Stuart) where the lack of oxygen caused the kerogen to be preserved.
Deposits of oil shale are common throughout the world, notably in the western USA, Jordan, Brazil, Estonia, Russia and China, and total in-place resources are estimated at over 2.6 trillion barrels of oil, or much more than remaining resources of conventional oil. Commercial exploitation of these resources has been limited and is currently restricted to Estonia, Brazil and China.
The challenge for large scale production of synthetic crude oil from oil shale has always been the absence of an economically and environmentally viable processing technology.
Blue Ensign’s Rendall process offers the first realistic solution to this problem due its high efficiency, lack of environmental problems and ability to be scaled up to high production levels.