Natural gas that is economical to extract and easily accessible is considered “conventional.” Conventional gas is trapped in permeable material beneath impermeable rock.
Natural gas found in other geological settings is not always so easy or practical to extract. This gas is called “unconventional.” New technologies and processes are always being developed to make this unconventional gas more accessible and economically viable. Over time, gas that was considered “unconventional” can become conventional.
Biogas is a type of gas that is produced when organic matter decomposes without oxygen being present. This process is called anaerobic decomposition, and it takes place in landfills or where organic material such as animal waste, sewage, or industrial byproducts are decomposing.
Biogas is biological matter that comes from plants or animals, which can be living or not-living. This material, such as forest residues, can be combusted to create a renewable energy source.
Biogas contains less methane than natural gas, but can be refined and used as an energy source.
Deep Natural Gas
Deep natural gas is an unconventional gas. While most conventional gas can be found just a few thousand meters deep, deep natural gas is located in deposits at least 4,500 meters (15,000 feet) below the surface of the Earth. Drilling for deep natural gas is not always economically practical, although techniques to extract it have been developed and improved.
Shale
Shale gas is another type of unconventional deposit. Shale is a fine-grained, sedimentary rock that does not disintegrate in water. Some scientists say shale is so impermeable that marble is considered “spongy” in comparison. Thick sheets of this impermeable rock can “sandwich” a layer of natural gas between them.