Oil Shale, Shale oil and Shale gas

All the above terms may looks similar but are different. Let’s deep dive into them .

Oil Shale

Oil shale is a type of sedimentary rock that is rich in kerogen. Kerogen is a part of rock that breaks down and release hydrocarbon heated. Oil shale can be thought of as a precursor to oil and natural gas. With more pressure and over geological time kerogen would heat to it’s “oil window” or “gas window”.

“Oil shale is a rock from which shale oil is extracted”

• Lamosite and Torbanite are types of oil shales associated with lacustrine environment.
• Ex- The Barakar formation (oil bearing shale)

Shale Oil

Shale oil is similar to petroleum and can be refined into diesel, gasoline, LPG. Obtaining shale oil from oil shale involves heating kerogen in a process called Pyrolysis. It is a form of heating without using oxygen. The process can be done “In-situ” or “Ex-situ”

The petroleum trapped within the rocks are known as “tight oil” and is difficult to extract. Companies extracting tight oil often use hydraulic fracturing.

Shale Gas

Shale gas refers to natural gas that is trapped within shale formations. Shales are fine-grained sedimentary rocks that can be rich source of petroleum and natural gas. Gas can be stored in three ways in gas shales –

• Free gas : Gas within the rock pores and natural fractures
• Absorbed gas : The gas is absorbed on organic material and clay
• Dissolved gas : The gas is dissolved in organic materials

The combinations of hydraulic drilling and hydraulic fracturing has allowed access to large volumes of shale gas. The quality of shale gas is judged by the total amount of organic matter (organic shale = more than 2% organic matter) and it’s thermal maturity.

Environmental effects :

• Heating can release CO2 into atmosphere and carbon sequestration must be done.
• Enormous fresh water requirement for the drilling mining, generating powders. 8-9 liters of water per liter of oil and this water will be contaminated after use.