Natural gas formation occurs in rock formations deep underground. Natural gas is also referred to as “non-associated” gas, when it is extracted from isolated gas fields. The alternative associated petroleum gas (APG) is found in oil fields with deposits of petroleum.

Natural gas is an established source of energy, which is more environmentally friendly than most hydrocarbon fuels, producing less carbon dioxide (CO2) per unit energy.

Natural gas is utilised in a range of applications to produce combined heat and power (CHP), using natural gas generators:

  • Commercial applications: office and retail centres, airports, hospitals
  • Industrial applications: food processing, mining, steel, glass, textiles, oil and gas, chemicals

Shale gas is natural gas, which is stored within shale formations and is trapped as free gas in low permeability, fine grained sandstone reservoirs . Shale gas differs from conventional natural gas in that conventional gas migrates from organic-rich formation environment into impermeable rock reservoir. 

Natural gas
Calorific value (CV) of natural gas is 35 - 43MJ/m3
Natural gas typical composition:
  • 70-90% Methane (CH4)
  • < 20% Ethane (C2H6), Propane (C3H8) and Butane (C4H10)
  • < 8% Carbon dioxide (CO2)
  • < 5% Nitrogen (N2)
  • < 5% Hydrogen sulphide (H2S)


Shale gas
Natural gas which is trapped within shale formations