Composition of natural gas consumed in France
Natural gas is a gaseous mix of hydrocarbons naturally trapped in porous rocks. Its composition and energetic value may change significantly depending on its origin.
Natural gas consumed in Europe is mostly non-associated conventional gas (i.e. it comes from a field independent from an oil reservoir). In France, it mainly comes from Norway, Russia, the Netherlands and Algeria.
Imports of natural gas (TWh HHV) per country of origin
Source: Chiffres clés de l’énergie 2015
Even if the natural gas injected in the network is composed of 80%, at least, of methane and of a combination of alkanes (ethane, propane, butane) and inert gases (carbon dioxyde, nitrogen). The gas calorific value is determined by its composition (i.e. the amount of energy it has): the greater the proportion of alkanes, the higher the calorific value. For example, according to the graph below, the quality of the Russian gas is greater than that of Dutch gas. Algerian gas stands out, as it is composed of a large proportion of alkanes, which explains its relatively high calorific value even if it as a relatively low proportion of methane.
It should be noted that in France, an odorous gas, the thiol, is added in order to identify leaks easily.
Composition of natural gas and biogas in accordance with its origin
Source: Société chimique de France, Biogaz Energie Renouvelable
Biogas is a natural gas produced from organic waste. It has great advantages: it is renewable and has a carbon balance that is almost neutral (CO2 emitted during its combustion would have been emitted in the atmosphere during the waste decomposition). However, it has less methane than conventional gas. Therefore, it has a lesser calorific value than conventional gas. In order to be injected in the network, its CO2 has to be removed to reach a percent of methane content comparable to the one of conventional gas.