Natural gas

Natural gas is the only relatively clean fossil fuel because it has the highest ratio of hydrogen to carbon of any fossil fuel. It is mostly methane, CH4.

Throughout most of oil drilling history this gas was regarded as a dangerous nuisance and was simply flared off. The drillers attitude has been "burn the stuff because its too much trouble to sell". The consequence is that a prime, relatively non-polluting fuel was mainly used to enrich the carbon dioxide content of the atmosphere. It is only in the last four decades that anybody bothered to use it in place of coal-gas. Even then it was only used when the wells were relatively close to consumers and in areas where coal mining was expensive and/or the Government hated coal miners. Make a sentence containing the words "football" and "political".

The future of natural gas in the United Kingdom is pretty bleak despite the fact that in 2007 the UK was the third largest user of natural gas in the world. Now North Sea gas is almost used up and a dedicated port and gas storage depot has just been completed at Newhaven in West Wales, together with a pipeline connecting it to the national grid in Gloucestershire. 15 million tonnes of gas a year will be shipped from Qatar in a specially built supertanker fleet as a compressed and cooled liquid. On arrival an Newhaven it will be converted back to gas before being pumped into the national grid. The new pipeline will transport 20% of the natural gas used in the UK.

Natural gas has two main uses in the UK: for electricity generation and as a heat source. Using it for electricity generation is wasteful. This uses up a valuable, non-polluting fuel at an overall thermal efficiency of 40% at best, when it should be reserved only for direct heating and cooking. Used this way a thermal efficiency of up to 80% can be achieved. Every tonne used for direct heating rather than generation halves the amount imported as well as reducing the resulting carbon dioxide emissions.

Wait for the first tanker explosion in or near a port. At a guess that will release nearly as much energy as an atomic bomb and cause significant damage. Fortunately the confinement provided by ships and storage tanks is relatively poor so the result will be more a Woof! than a Bang, but I still wouldn't want to be in the vicinity. That sound will be matched by that of the public demanding that imports stop. Now. Because of the danger. Next thing you know they will be complaining about gas shortages.

If I remember correctly the USA is about on the verge of importing gas, but see below, and meanwhile Germany is building a pipeline from the Georgian gas fields.

Conventional natural gas sources are fairly limited. In 2010 the global reserves were estimated at 177.3 trillion cubic metres (tcm), or 59 years supply at the current consumption rate of 3 tcm/year. See New Scientist (12 June, 2010 p45, Wonderfuel gas). If we reckon a 5% annual consumption increase this will be used up in 28 years. In other words, it is likely to be used up at some point between 2038 and 2069.

Shale gas

Recent advances in horizontal drilling techniques, which allow boreholes to fan out from the bottom of a vertical bore, and hydraulic rock fracturing, which makes rock more permeable to gas, promise to allow natural gas to be extracted from shale deposits. Gas reserves in shale have been assessed at 456 tcm, which is equivalent to 152 years supply at current consumption rates or 45 years with a 5% annual growth in consumption. However, there are environmental concerns about hydraulic fracturing: it is said to require 17 million litres of water to fracture a new well. In addition, this water has to contain thickening agents and bacteriosides. Some 70% of the water can be recycled to fracture the next well - but only if this new well is nearby. Despite being in its infancy, hydrofracking is already causing widespread environmental contamination around Dimmock, PA and other parts of Pennsylvania, the Catskills region in New York state and near Fort Worth, Texas. This is described in Onshore Drilling Disasters Waiting to Happen, The Nation, 17 June 2010.

So, provided the shale reserves have been reliably estimated and the water use and recycling can be managed, shale gas should extend natural gas to 633 tcm, which would last just over 210 years at current consumption rates or a more realistic 51 years at a 5% annual growth rate. This means all known natural gas is likely to be used up some time between 2061 and 2220. Unless, of course, hydrofracking is banned because its environmental impact outweighs the extra gas it would tap.

Methane clathrates

Methane clathrates form under conditions in which water saturated with methane forms a stable cage structure that traps a methane molecule in a lattice of water molecules. The water molecules are held together by hydrogen bonds. This structure is favoured when the saturated aqueous methane solution is cold and under high pressure. These conditions are generally found in or on a section of sea bed which overlays a leaking source of methane.

Methane clathrates are found in the Arctic sea and on most continental shelves around the world with the exception of Antarctica. There is a huge amount of methane trapped in these structures: the US Geological Survey estimates that they contain twice as much energy as all the world's other fossil fuel reserves combined.

Clathrate deeposits are one of the cleanest energy sources known. They contain only water and pure methane, which is extracted by reducing the pressure on the clathrate, which lets the methane emerge as a gas. If the clathrate is beneath the seabed this can amount to little more than drilling down to it with oil drilling equipment and starting to pump. If it is on the seabed it can be dredged up using a large diameter suction pipe. The reduced pressure in the pipe and in the sealed header tanks connected to it will cause the methane to separate. The methane needs only to be dried before use while the water that formed the clathrate structure is uncontaminated and so can be simply returned to the sea.

Using methane clathrate as an energy source is in fact beneficial to the global climate because atmospheric methane is a potent greenhouse gas. Its use as an energy source has three benefits: