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Energy from the prehistoric Natural gas through microorganisms
Natural gas was created millions of years ago when dead microorganisms, like algae and plankton, sank to the sea bed. Over time, they were covered by many layers of earth and rock, and were gradually converted into hydrocarbons. Under high pressure and temperatures and without oxygen, their organic elements were slowly converted into small gaseous hydrocarbons, particularly methane (CH4), the smallest hydrocarbon. The natural gas created in the bedrock rose slowly through porous layers of rock until it encountered an impermeable layer and collected to form reservoirs.
Mix of hydrocarbons
In contrast to crude oil, which is a mixture of different hydrocarbons with very different chemical properties, natural gas only contains a few elements. Natural gas is predominantly made up of methane (between 75% and 99%) with a small proportion of heavier elements: ethane (C2H6), propane (C3H8), butane (C4H10) and ethylene (C2H4).
If a higher proportion of these heavier hydrocarbons are present, the gas is described as “wet” because they can be turned easily into liquids under pressure. They are easily removed at the production site and processed for other uses. Butane and propane, for instance, are used as a fuel for camping stoves.
Natural gas from some sources contains hydrogen sulphide and carbon dioxide. This is described as sour” gas and has to be purified before it can be processed. Without this purification process, it would be heavily corrosive and damage pipes and production facilities. Sulphur is a by-product that results from this purification process, and can be used as a raw material in the chemicals industry. Some natural gas reservoirs also contain helium, which is a particularly valuable element. The production of natural gas is the most important source for acquiring helium.
Depending on the proportion of methane, we differentiate between H-gas (high calorific gas) and L-gas (low calorific gas). The energy-rich H-gas consists of 87-99% methane and is usually found in reservoirs in the North Sea and Russia. L-gas, found in Northern Germany consists of 80-87% methane and higher quantities of nitrogen and carbon dioxide. L-gas is cheaper than H-gas because its energy content is lower. The calorific value of L-gas is between eight and ten kilowatt hours per cubic meter, while the range for H-gas is between ten and twelve kilowatt hours.
Scouring the world for natural gas
Reservoirs must be discovered and extracted before natural gas can be supplied to consumers. This requires a great deal of effort and investment. Most natural gas deposits lie deep under the earth’s surface earth. The gas collects in saddle shaped impermeable traps that prevent it from rising, sometimes as deep as a few kilometres underground. Natural gas and crude oil are often found together in these reservoirs, with the light natural gas on top of the heavy crude oil. During production the gas is isolated from the oil and processed separately.
Unconventional natural gas reservoirs
In addition to the normal type of reservoirs, unconventional deposits of gas are playing an increasingly important role in gas production. Tight gas is stored in small pores in the sandstone that are poorly connected to each other so it cannot flow freely to the well. Shale gas is still trapped in the place it was formed in layers of clay, stuck to the surface of the rock particles and difficult to access. And the Coal Bed Methane (CBM) can be found in coal beds on the surface of the coal.
Many countries have large unconventional gas deposits, including the USA, Russia, China and Australia. According to estimates by the International Energy Agency (IEA) there is about 208 trillion cubic meters of shale gas, 76 trillion cubic meters of tight gas and 47 trillion cubic meters of CBM available worldwide, a total of more than 330 trillion cubic meters. Some sources estimate that unconventional gas deposits contain more than all the world’s proven and recoverable conventional gas reserves.