Shale oil extraction process is what may be classified as an unconventional oil extraction procedure. It predates crude oil extraction in practice and provides a synthetic form of crude oil, which is derived from a sedimentary rock type called oil shale. It is the prime alternative energy source, which is being targeted for extraction, throughout the world.
What is Oil Shale?
The sources of shale oil are fine-grained sedimentary rocks called oil shale. Oil is trapped in a solid state, inside these sedimentary deposits, in the form of significant quantities of 'Kerogen'. It is a solidified mixture of organic compounds, which releases crude oil and natural gas, on being heated inside the Earth's crust.
Kerogen is the precursor to crude oil and natural gas. When kerogen is not subjected to heat and deposited in high concentrations as sedimentation on Earth's surface, it forms oil shale rocks. The extraction technique mimics the formation of crude oil in the Earth's crust, by artificially subjecting the solid kerogen to heat and deriving oil and gas from it.
Large untapped deposits of oil shale have been found in the United States of America. It is estimated that there are 2.8 trillion to 3.3 trillion barrels of potentially recoverable oil in shale rock deposits, all over the world. This estimate exceeds the total proven reserves of crude oil, found around the world.
Countries like China, Estonia, Germany, Brazil, and Russia have well-established industries for refining of shale oil and make an extensive use of it, as a low-grade fuel.
Types of Processes Designed For Extraction
This process is different from crude oil extraction, which mostly boils down to oil drilling. After drilling into pockets of crude oil underground, it is extracted for refining and further use.
On the other hand, shale oil extraction is different, because solid rock deposits containing kerogen, need to be heated to yield an impure form of crude oil (shale oil), which needs to be further processed.
Reports of shale extraction date back to the tenth century. It took a back seat as an oil extraction process, after discovery of crude oil reserves, but has recently gained prominence at the beginning of 21stcentury. The reasons being the renewed realization of the limited crude oil reserves, which may get exhausted some day.
To put it simply, this technique involves processing of mined oil shale to extract the kerogen contained within and convert it into shale oil through pyrolysis, thermal dissolution, or hydrogenation. The extracted oil is further processed by hydrogenation and nitrogen, and sulfur deposits are removed.
The most common method is pyrolysis, which involves heating raw materials to convert the kerogen into shale oil vapors, through decomposition. The vapors are then collected through distillation and further refined.
The extraction processes come in many types. They can be classified by the type of method used for extraction, into pyrolysis, hydrogenation and thermal dissolution. They can also be broadly divided into two methods, which can be called 'Ex Situ' and 'In Situ' processes. Here is a brief overview of both methods.
Ex Situ Process
In ex situ type of processes, the oil shale is mined first and then transported to a processing plant for further action. Naturally, transport cost of raw materials, forms a big part of the total cost of these kinds of processes.
Some of the technologies used in ex situ extraction are called internal combustion, hot recycled solids, wall conduction, externally generated hot gas, and reactive fluid technologies.
In Situ Process
The in situ oil extraction processes involve heating the oil shale deposits on site and then extraction of shale oil through oil wells, as it rises out. Some of the processes used for in situ extraction are wall conduction, externally generated hot gases, Exxon Mobil electrofrac, and volumetric heating technologies.
There are environmental concerns about the air pollution caused, waste water disposal, and extensive water use, required by these processes. Besides that, these processes cost a lot more, compared to conventional crude oil extraction.
Research is on, to improve the processing methods and make it more economical and eco-friendly. Realizing the potential this oil extraction process has, many multinational companies are planning to set up plants worldwide. However, as of now, crude oil production remains a more viable and economical option, compared to shale extraction.