Introduction to Natural Gas

Definition of natural gas:

      Natural Gas is one of the principle sources of energy for many of our day-to-day needs and activities. Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons (primarily ethane). It is found associated with other hydrocarbon fuel, in coal beds, as methane catharses, and is an important fuel source and a major feedstock for fertilizers. Before natural gas can be used as a fuel, it must undergo processing to remove almost all materials other than methane. The by-products of that processing include ethane, propane, butanes, pentanes, and higher molecular weight hydrocarbons, elemental sulfur, carbon dioxide, water vapor, and sometimes helium and nitrogen 

Natural gas classification:

·  based on reserve:

1. Natural gas reservoir : Consists of methane (85%) while ethane is found of(10-12%)based on dry gases i.e.it is assumed that the LPG which are propane and butane have been removed.
2. Condensate reservoir: Consists of heavier hydrocarbons and lighter ones (C1-C2) are less content.
3. Crude oil reservoir: Consist of higher 5% of heavier hydrocarbons and   less% of lighter ones than two mentioned types.

The petroleum gases classified based on the source of the gas:

·   refinery gas ;

·  distillate gas

·  other process

· Natural gas

        Types of natural gas

1. Wet gas: which is vital for processing operations? Contains some condensable         hydrocarbon molecules.

2. Dry gas:   indicates that the fluid does not contain enough of heavier hydrocarbon molecules to form a liquid at surface conditions.

3. Lean gas: doesn't contain water vapor.

4. Sour gas: contain H2S and other sulfur compound, co2.

5. Sweet gas: doesn’t contain H2S and other sulfur compound_.

 Composition of Natural gas:

     Because natural gas is petroleum in a gaseous state, it is always accompanied by oil that is liquid petroleum. There are three types of natural gases: nonassociated gas, associated gas, and gas condensate. Nonassociated gas is from reservoirs with minimal oil. Associated gas is the gas dissolved in oil under natural conditions in the oil reservoir. Gas condensate refers to gas with high content of liquid hydrocarbon at reduced pressures and temperatures. Natural gas as recovered from underground deposits contains mainly methane (CH4), but it also contains heavier gaseous hydrocarbons such as ethane (C2H6), propane (C3H8) and butane (C4H10). Other gases such as CO2, nitrogen and hydrogen sulfide (H2S) are also often present. Natural gas also contains small amounts of helium, and is the main source of helium. Small amounts of mercury may be present. The exact composition varies from one field to another. Sulfur compounds must be removed before distribution. Small amounts of odorant are added to assist in leak detection. Mercury if present is removed

Methane(CH4)	70- 90%
Ethane(C2H6)	0- 20%
Propane (C3H8)
Butane (C4H10)
Carbon Dioxide (CO2)	0- 8%
Oxygen (O2)	0- 0.2%
Nitrogen (N2)	0- 5%
Hydrogen sulphide	0- 5%
Rare gases	trace