Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/157

The Resources of the Niger Delta: Minerals component of natural gas is Methane, undoubtedly the product of the bacteria which are the agents of decay. Within professional geological circles, a debate continues about the definite sources of gas.

In addition to methane, natural gas sometimes contains Liquid Petroleum Gases (LPGs), such as propane, butane and pentane. Where LPGs are present the gas is referred to as Wet Natural Gas.

As already explained, most of the natural gas currently produced (and flared off into the atmosphere) in Nigeria is Associated Gas, that is associated with oil. Associated gas is generally, but not always, wet.

Natural gas is also found as Non-associated Gas which arises in three ways:
 * where the source rock is gas-prone, i.e. where is made up of a high percentage of deposits derived from plant remains as organic matter, i.e. bio-genic;
 * where the rock and/or oil is has been heated to above 150 degrees centigrade so that all the oil has been cracked to become gas, i.e. thermo-genic; or
 * where the gas has been able to migrate through permeable rock strata on its own. The non-associated gas fields are shown on map 5.

Non-associated gas is generally 'dry'; that is, low in LPGs.

In summary, therefore, there are generally four types of natural gas as follows:

According to an environmental impact assessment study undertaken for the Nigeria Liquefied Natural Gas project in 1995, Nigerian natural gas can "be roughly described as some:
 * 90% methane, with
 * 1.5 to 2.0% carbon dioxide,
 * 3.9 to 5.3% ethane,
 * 1.2 to 3.4% propane and
 * 1.4 to 2.4% heavier hydrocarbons."

Also Nigerian natural gas "is lean in Nitrogen (max. 0.3%) and has a low sulphur content (max. 30 mg/m³)". The same survey suggests trace elements in Nigerian natural gas as follows.

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