The main difference between natural gas and shale gas lies primarily in where they are found and how they are extracted, as shale gas is a form of natural gas.
Understanding the Relationship
Think of natural gas as the broader category, similar to "fruit," and shale gas as a specific type within that category, like "apple." Both are essentially the same substance – primarily methane (CH₄) – but they are located in different geological formations.
According to the reference:
- Shale gas is a form of natural gas (mostly methane), found underground in shale rock.
Conventional vs. Unconventional
The distinction arises from how easily the gas can be extracted, which is determined by the type of rock it's trapped in.
- Conventional Natural Gas: Found in more permeable rock formations such as sandstone, siltstone, or limestone. These rocks have connected pore spaces, allowing the gas to flow relatively easily towards a well. This is considered 'conventional' because it was the primary source historically extracted using standard drilling techniques.
- Shale Gas: Found in low-permeability shale rock. Shale formations are much tighter, meaning the gas is trapped in tiny, disconnected pores and doesn't flow easily. This makes it 'unconventional' to extract, requiring specialized techniques like hydraulic fracturing (fracking) and horizontal drilling to release the gas.
The reference explicitly states: It is classified as 'unconventional' because it is found in shale , a less permeable rock formation than sandstone, siltstone or limestone in which 'conventional' gas is found.
Key Differences Summarized
Here is a quick overview:
| Feature | Natural Gas (General Term) | Conventional Natural Gas | Shale Gas |
|---|---|---|---|
| Composition | Primarily Methane | Primarily Methane | Primarily Methane |
| Location | Found underground | Permeable rocks (sandstone, limestone) | Impermeable shale rock |
| Classification | N/A | Conventional | Unconventional |
| Extraction | Varies | Standard drilling methods | Requires advanced methods (fracking, etc.) |
| Distribution | Varies | Typically concentrated in specific traps | Generally distributed over a much larger area |
The reference also notes that shale gas is generally distributed over a much larger area compared to conventional deposits.
Why the Distinction Matters
The difference in geological location and permeability dictates the methods required for extraction. While conventional gas can often be retrieved using straightforward vertical wells, accessing shale gas requires more complex and resource-intensive techniques like horizontal drilling and hydraulic fracturing to create pathways for the gas to flow out of the dense shale rock. This has significant implications for:
- Technology: The development of advanced drilling and completion technologies was crucial for unlocking shale gas reserves.
- Cost: Extraction from shale formations can sometimes be more complex and costly than from conventional reservoirs.
- Environmental Considerations: The techniques used for shale gas extraction have associated environmental considerations that are widely discussed and studied.
In essence, while chemically similar, the term "shale gas" specifically refers to natural gas found within shale formations, highlighting its unconventional nature and the specific technologies needed to produce it.
