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Oil shale

earth science Maturity 7-9 Next article →

Oil shale is an organic-rich, fine-grained sedimentary rock. It is not a standard fossil fuel like petroleum, but it contains a solid mixture of organic compounds called kerogen. This kerogen can be processed into liquid hydrocarbons. While the term "shale oil" is often used for both, scientists distinguish between oil shale and oil-bearing shales. Oil-bearing shales, such as the Bakken or Eagle Ford Formations, contain tight oil already inside the rock. In contrast, oil shale requires heating to release its liquid content.

OilShaleFossilsEstonia
OilShaleFossilsEstonia

To produce fuel, the rock undergoes a chemical process called pyrolysis. This process begins by heating the oil shale to a very high temperature. This heat causes the kerogen to transform into a vapor. Once the vapor is produced, it is allowed to cool down. As it cools, the vapor separates into two distinct parts: a liquid called shale oil and a combustible shale gas. The resulting shale oil acts as a substitute for conventional crude oil.

Oil shale extraction overview
Oil shale extraction overview

Geologists classify oil shales based on how they were originally deposited. This classification is often based on the environment where the original organic matter settled. Marine oil shales formed on the ocean floor. Lacustrine oil shales formed at the bottom of lakes. Terrestrial oil shales were deposited on land. This system was developed by Adrian C. Hutton to help estimate the yield and composition of extracted oil. Scientists also use the van Krevelen diagram to classify kerogen types based on hydrogen, carbon, and oxygen content.

Torbanite 2 oil shale
Torbanite 2 oil shale

Human history with oil shale stretches back to prehistoric times. Around 3000 BC, people in Mesopotamia used "rock oil" for road construction and building adhesives. During the Iron Age, Britons used tractable oil shales for burial cists or ornaments. The first patent for extracting oil from stone was granted in Britain in 1694. Modern industrial mining began in 1837 in Autun, France.

XXe - Mine des Télots - 02
XXe - Mine des Télots - 02

During the Industrial Revolution, Scotland became a major producer. By 1913, Scottish operations produced about 2% of the global petroleum supply. This was driven by the demand for kerosene and lamp oil.

Global oil shale resources are massive but vary in accessibility. A 2016 estimate set the total world resources at an amount equivalent to the yield of trillions of barrels of oil. The United States holds the largest share, containing more than 80% of the world's total resources. Most of this is found in the Green River Formation, which spans Colorado, Utah, and Wyoming. Other significant deposits exist in China, Russia, and Brazil. However, there is a difference between "resources" and "reserves." Resources are all known deposits, while reserves are those that can be extracted economically with current technology.

Extraction is a complex and expensive endeavor. Producing shale oil costs more financially than producing conventional crude oil. It also carries a significant environmental footprint. Mining and processing can lead to issues with land use and waste disposal. It also requires careful water use and wastewater management. Furthermore, the process can result in air pollution and greenhouse-gas emissions.

VKG Ojamaa kaevandus
VKG Ojamaa kaevandus

Despite these challenges, oil shale remains a key part of the energy conversation. Estonia and China have well-established industries that use oil shale for both oil and power generation. Other countries like Germany, Brazil, and Russia also utilize it to some extent. The industry has seen many ups and downs. For example, the 1973 oil crisis led to a production peak in 1980. Later, low oil prices caused major projects, like Exxon's Colony Shale Oil Project, to be canceled. As technology evolves, the potential of these vast organic-rich rocks continues to be studied.

Production of oil shale
Production of oil shale
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🖼️ Images & Media (8)
File:Tootuskihind läbilõige.jpg
Tootuskihind läbilõige.jpg
File:Torbanite 2 oil shale.jpg
Torbanite 2 oil shale.jpg
File:OilShaleFossilsEstonia.jpg
OilShaleFossilsEstonia.jpg
File:Production of oil shale.png
Production of oil shale.png
File:XXe - Mine des Télots - 02.jpg
XXe - Mine des Télots - 02.jpg
File:Shell insitu.gif
Shell insitu.gif
File:Oil shale extraction overview.png
Oil shale extraction overview.png
File:VKG Ojamaa kaevandus.jpg
VKG Ojamaa kaevandus.jpg
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