After extraction and processing, natural gas still suffers significant transportation costs. The construction of long-distance gas pipelines is a heavy investment. LNG shipments in the form of liquefied natural gas (LNG) are also very capital intensive, requiring the construction of a liquefaction plant at the point of export, the construction of a regasification plant near the point of consumption and the construction specialized vessels, LNG carriers. This is why small deposits of natural gas far from points of consumption are not necessarily exploited. In the absence of adequate transportation infrastructure, natural gas from oil deposits can be burned in situ in flares instead of being upgraded. Today, ecological concerns and the rise in the price of energy encourage gas players to act to avoid the use of flares.
The naming of unconventional gas includes different forms of natural gas requiring special operating techniques: the combination of horizontal drilling and hydraulic fracturing has made possible the exploitation of these gases, which until now required a lot of processes. too expensive to be extracted. While these gases are more difficult to exploit than conventional gases, the size of the reserves and new extraction methods explain why producers are increasingly interested in them. Conventional gases include, among others:
- the shale gas
- coal gas
- compact tank gas
Among the unconventional gas, it is certainly the gas that made the most talk about him. Also known as mother-rock gas or gas in Quebec, it is a natural gas that is found in marly or clay-rich rocks rich in organic matter. Unlike conventional gas, which is trapped in permeable rock, shale gas is contained in impervious rocks. Its exploitation, source of many polemics, is complex. The countries with the largest shale gas reserves are China, Argentina, Algeria and the United States. The latter are today the pioneers in the exploitation of shale gas, from the 2000s.
The extraction of shale gas poses a number of environmental problems:
- Heavy use of water to fracture rock;
- Pollution of groundwater;
- Increase in the number of earthquakes;
- Emission of greenhouse gases;
- Durability and surface of deposits.
These issues make shale gas a controversial resource. In France, a moratorium voted in 2013 prohibits both research and exploitation of shale gas in France. Other countries have similar legislation.
Coal gas is less well known. Its exploitation is much older: used as gas lighting until the end of the nineteenth century, it is then dethroned by electricity and gas. It comes from the transformation of coal into coke, a highly polluting fuel commonly used in Europe during the industrial revolution. Coal gas was extremely toxic to produce.
Compact tank gas
Compact tank gas, like shale gas, requires complex extraction techniques to be exploited, such as hydraulic fracturing of soils. It is stored in low permeability rocks, sandstone or limestone. These deposits are particularly different from the Schist gas in that the product has «migrated» out of its bedrock, and are contained in more porous rocks.