The origins of methane

The origins of methane are examined in the context of the hazard that can result from its presence in unusual circumstances. Methane is shown to be a gas that can be encountered in a wide variety of geological environments and which should therefore be anticipated in any underground excavation.

The processes of methane generation are described in terms of the type of source organic matter and the subsequent changes that take place as a result of burial.

An important aspect of methane occurrence is the question of the origin of the gas. Various techniques for methane source evaluation are described including carbon isotope ratio, carbon 14 activity and the presence and relative abundance of higher hydrocarbons. Examples from various sources are given. Finally, the effects of migration on the parameters used in source identification techniques are examined.