Shale oil is extracted primarily using two methods depending on the depth of the deposit, followed by a heating process called pyrolysis to convert the solid shale rock into usable liquid and gas fuels.
Primary Methods of Shale Oil Extraction
The chosen extraction method depends largely on the depth and location of the shale oil deposits.
Surface Mining
The most common method of extracting shale oil is by surface mining. This involves removing the layers of soil and rock above the oil shale deposit to access the rock. Once the oil shale rock is exposed, it is mined and transported to a processing facility.
In Situ Combustion
For deposits that are located far below the surface, where surface mining is not feasible or economical, the in situ combustion process is used. "In situ" means "in place." This method involves heating the oil shale deposit underground, often by injecting hot fluids or using electrical heaters, to extract the oil directly from the subsurface without mining the rock itself.
Processing Extracted Shale Oil
After the oil shale is extracted (either through surface mining or in situ methods), it undergoes a crucial processing step to yield useful products.
The extracted shale oil rock (or the heated underground deposit via in situ methods) is subjected to pyrolysis. This is a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen. The reference specifies this process occurs at temperatures between 842 to 932°F (450 to 500°C).
This heating process breaks down the solid organic matter (kerogen) within the shale rock into various forms of hydrocarbons.
Products of Pyrolysis
The pyrolysis of oil shale yields several valuable products:
- Oil Shale (Synthetic Crude Oil): This is the primary target product, a liquid hydrocarbon that can be further refined similarly to conventional crude oil. It is also known as syncrude or synthetic crude oil.
- Shale Gas: A gaseous mixture, primarily methane, which can be captured and used as natural gas.
- Residue (Solid): The remaining solid material, which includes spent shale and mineral matter.
Here's a simplified breakdown of the process:
| Step | Method/Process | Description | Temperature | Products |
|---|---|---|---|---|
| Extraction | Surface Mining | Removes rock from surface deposits | N/A | Raw Oil Shale Rock |
| In Situ Combustion | Heats rock underground for deep deposits | N/A | Oil/Gas released underground | |
| Processing (Post-Extraction) | Pyrolysis (for mined rock) | Heats extracted rock in processing facility | 842–932°F (450–500°C) | Synthetic Crude Oil, Shale Gas, Residue |
| Processing (Post-Extraction) | Pyrolysis (implicit in situ) | Heating process releases oil/gas from rock underground | Implied within In Situ process | Synthetic Crude Oil, Shale Gas, Residue (left underground) |
In summary, accessing shale oil involves either physically mining the rock from the surface or heating it underground, followed by a high-temperature process called pyrolysis to convert the solid kerogen into usable liquid synthetic crude oil, shale gas, and a solid residue.
