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.
As source rocks for most conventional oil reservoirs, oil shale deposits are found in all world oil provinces, although most of them are too deep to be exploited economically. There are more than 600 known oil shale deposits around the world. Although resources of oil shale occur in many countries, only 33 countries possess known deposits of possible economic value.
Many deposits need more exploration to determine their potential as reserves. Well-explored deposits, which could ultimately be classified as reserves, include the Green River deposits in the western United States, the Tertiary deposits in Queensland, Australia, deposits in Sweden and Estonia, the El-Lajjun deposit in Jordan, and deposits in France, Germany, Brazil, China, and Russia. It is expected that these deposits would yield at least 40 liters (0.25 bbl) of shale oil per metric ton of shale, using the Fischer Assay.
A 2016 conservative estimate set the total world resources of oil shale equivalent to yield of 6.05 trillion barrels (962 billion cubic metres) of shale oil, with the largest resource deposits in the United States accounting for more than 80% of the world total resource. For comparison, at the same time the world’s proven oil reserves are estimated to be 1.6976 trillion barrels (269.90 billion cubic metres).
Oil shale geology
Oil shale formation takes place in a number of depositional settings and has considerable compositional variation. Oil shales can be classified by their composition (carbonate minerals such as calcite or detrital minerals such as quartz and clays) or by their depositional environment (large lakes, shallow marine, and lagoon/small lake settings). Much of the organic matter in oil shale is of algal origin, but may also include remains of vascular land plants. Three major type of organic matter (macerals) in oil shale are telalginite, lamalginite, and bituminite. Some oil-shale deposits also contain metals which include vanadium, zinc, copper, and uranium.
Most oil shale deposits were formed during Middle Cambrian, Early and Middle Ordovician, Late Devonian, Late Jurassic, and Paleogene times through burial by sedimentary loading on top of the algal swamp deposits, resulting in conversion of the organic matter to kerogen by diagenetic processes. The largest deposits are found in the remains of large lakes such as the deposits of the Green River Formation of Wyoming and Utah, USA. Oil-shale deposits formed in the shallow seas of continental shelves generally are much thinner than large lake basin deposits.
Definition of reserves
Estimating shale oil reserves is complicated by several factors. Firstly, the amount of kerogen contained in oil shale deposits varies considerably. Secondly, some nations report as reserves the total amount of kerogen in place, including all kerogen regardless of technical or economic constraints; these estimates do not consider the amount of kerogen that may be extracted from identified and assayed oil shale rock using available technology and under given economic conditions. By most definitions, “reserves” refers only to the amount of resource which is technically exploitable and economically feasible under current economic conditions. The term “resources”, on the other hand, may refer to all deposits containing kerogen. Thirdly, shale oil extraction technologies are still developing, so the amount of recoverable kerogen can only be estimated.
There are a wide variety of extraction methods, which yield significantly different quantities of useful oil. As a result, the estimated amounts of resources and reserves display wide variance. The kerogen content of oil shale formations differs widely, and the economic feasibility of its extraction is highly dependent on international and local costs of oil. Several methods are used to determine the quantity and quality of the products extracted from shale oil. At their best, these methods give an approximate value to its energy potential. One standard method is the Fischer Assay, which yields a heating value, that is, a measure of caloric output. This is generally considered a good overall measure of usefulness. The Fischer Assay has been modified, standardized, and adapted by the American Petroleum Institute. It does not, however, indicate how much oil could be extracted from the sample. Some processing methods yield considerably more useful product than the Fischer Assay would indicate. The Tosco II method yields over 100% more oil, and the Hytort process yields between 300% to 400% more oil.
Size of the resource
The size of the oil shale resources is highly dependent on which grade cut-off is used. A 2008 estimate set the total world resources of oil shale at 689 gigatons—equivalent to yield of 4.8 trillion barrels (760 billion cubic metres) of shale oil, with the largest reserves in the United States, which is thought to have 3.7 trillion barrels (590 billion cubic metres), though only a part of it is recoverable. According to the 2010 World Energy Outlook by the International Energy Agency, the world oil shale resources may be equivalent of more than 5 trillion barrels (790 billion cubic metres) of oil in place of which more than 1 trillion barrels (160 billion cubic metres) may be technically recoverable.
A 2016 conservative estimate by the World Energy Council set the total world resources of oil shale equivalent to yield of 6.05 trillion barrels (962 billion cubic metres). For comparison, at the same time the world’s proven oil reserves are estimated to be 1.6976 trillion barrels (269.90 billion cubic metres).
There is no comprehensive overview of oil shale geographical allocation around the world. Around 600 known oil shale deposits are diversely spread throughout the earth, and are found on every continent with the possible exception of Antarctica, which has not yet been explored for oil shale. Oil shale resources can be concentrated in a large confined deposit such as the Green River formations, which were formed by a large inland lake. These can be many meters thick but limited by the size of the original lake. They may also resemble the deposits found along the eastern American seaboard, which were the product of a shallow sea, in that they may be quite thin but laterally expansive, covering thousands of square kilometers.
At 301 billion metric tons, as estimated in 2005, the oil shale deposits in the United States are the largest in the world. There are two major deposits: the eastern US deposits, in Devonian-Mississippian shales, cover 250,000 square miles (650,000 km2); the western US deposits of the Green River Formation in Colorado, Wyoming, and Utah, are among the richest oil shale deposits in the world.
More recent studies by the United States Geological Survey estimate that the resource in the United States may be bigger than previously estimated. According to these studies, three largest oil-shale deposits — all are part of the Green River Formation — are the Piceance Basin with 1.525157 trillion barrels (2.424806×1011 cubic metres), the Greater Green River Basin with 1.444992 trillion barrels (2.297354×1011 cubic metres), and the Uinta Basin with 1.318964 trillion barrels (2.096985×1011 cubic metres) in-place shale oil resources. In 2010, it was estimated by the World Energy Council that the United States resource could be equal to 3.7 trillion barrels (590 billion cubic metres) of shale oil. In 2016, their estimation was that the resource may even consist of up to 6 trillion barrels (950 billion cubic metres) of shale oil.
In Canada 19 deposits have been identified. The best-examined deposits are in Nova Scotia and New Brunswick.