Methane

Marsh gas, fart gas, sewage gas, landfill gas, biogas, coal seam gas, CSG, coal bed methane, CBM, CSM, LNG, CNG, or, natural gas. It is all methane. It is everywhere. 

Cows produce methane when they burp. Their droppings produce methane when it decomposes without air. Above is diagram of dog droppings being used to light a lamp in Cambridge MA USA.

Most sewage treatment plants collect the methane from the anaerobic digestion process to run the plant.

Measured over 25 years it is 70-130 times worse than CO2 as a greenhouse gas.

If you bury organic wastes underground they will produce methane and start turning to coal. Most landfill rubbish tips have laid gas pipes to collect methane for power generation.

Coalification - Lignin to coal

If you look at lignin which makes up one third of wood, and compare it to coal, you can see that when lignin is compressed underground, the benzene rings have been squeezed together and the CH4 has been squeezed out.

At first this is done biologically, then,  as it is all buried deeper, heat and pressure take over the same task.

The coal has small pores, and natural cracks called cleats, and methane clings to these and internal surfaces. Methane is held there by water pressure.

It can be removed by reducing the pressure, or by being replaced by CO2 which is preferentially adsorbed. It can also be flushed out with nitrogen because this lowers the partial pressure.

It is quite conceivable that flue gas cold be pumped through a coal bed to remove the CO2 while flushing out more methane.

Coal mine gas

Coal mining has always been dangerous work due to the risk of methane explosion.

Methane was first extracted from mines in the 90s as a safety measure, it was called methane drainage. Nowadays it is used to generate power.

Before that it was released to the atmosphere and wasted and produced something like 10% of our greenhouse emissions.

Fracking

To extract the methane from un-minable coal seams, a bore hole is drilled and high pressure water and sand is pumped into the coal,. The water pressure widens the cleats, and the sand keeps them open so the methane can flow along the cleats. There are also various chemicals pumped in and these have caused harm to the water quality.

There is great controversy on this. The companies claim they are safe, yet many wells have poisoned the underground water. Very few people know exactly what is in each batch of chemicals, and this has fuelled suspicion.

Extraction

To recover this gas, the underground water is removed, the methane will be released from the surfaces. This is the reason the water table must be lowered for methane extraction.

Typical half-life of a CBM well has  been 13 years. The standard method removes about half the methane.

However it could do tens, hundreds, or even in some cases, thousands of years damage to the artesian basin.

Methane can be removed by reducing the pressure. This can be achieved by removing the water, or flushing with nitrogen which reduces the partial pressure. 

The other way is to replace it with CO2 which is preferentially absorbed by the coal surface.

It will not be long before someone builds a gas fired power station on a CSG well and pumps the flue gas back into the coal bed. This would carry out the capture and storage all in one step, and be quite cheap. Watch this space

Ref... Page 15

A good summary of Australian coal and gas

Map of CSG reserves and wells - Getup

How much coal seam gas?

Australia has an estimated 4,800 million tonnes of CSG. (235 trillion cu ft)

Chemicals used in fracking - fraccing

It is difficult to get the facts on this topic. The miners say there is nothing harmful, and the activists are seeing cancer in every chemical.

The best lists seem to those published by governments who require the chemicals to be known.Methane info

Fracking chemicals  

Also, the effects of various chemicals: http://art-metal.ca/hazardous-substances-overview/

Working with hazardous chemicals:  http://www.safeworkaustralia.gov.au/sites/swa/whs-information/hazardous-chemicals/pages/hazardous-chemicals-other-substances

Working with substances hazardous to health
http://www.hse.gov.uk/pubns/indg136.pdf

Using flue gas to flush out methane and capture CO2

Enhanced Coal Bed Methane (ECBM) and CO2

This excellent CSIRO report gives a very clear picture of methane from coal (Coal seam methane CSM).

It looks at how flue gas which is a mixture of CO2 and nitrogen can be used to flush out more methane. The coal seam will be able to absorb 2 molecules of CO2 for every one molecule of CH4 (methane) flushed out.

The total CO2 storage capacity in unmineable coal seams: 

in NSW is 4.1 billion tonnes, and

in Qld is 1.7 billion tonnes.

A similar report has been produced in USA:

CO2 Sequestration in Deep “Unmineable” Coal Seams

Greenhouse emissions impact

Gas is no better than coal if the gas must be converted into and back from a liquid before it can be burnt. This happens with CSG shipped overseas. But burning domestic gas instead of coal avoids the liquefaction step, and consequently produces less greenhouse gas emissions overall. 

Full report

Industry claims a 70 per cent reduction in greenhouse gas emissions from burning CSG instead of black coal. With no leakage this would be the case. However there is leakage.  A recent NSW Parliamentary Inquiry concluded that CSG emissions are, at worst, likely to equal those from coal.

Environmental impact of CSG - report

Summary from this report:

Natural gas — various forms

‘Natural gas’, ‘coal seam gas’, ‘shale gas’ and ‘tight gas’ are
four types of naturally occurring combustible mixtures of
hydrocarbon gases. They are predominately methane with
varying proportions of heavier hydrocarbons and other gases
such as carbon dioxide. These natural gases are formed when
organic matter is altered by organisms in biogenic processes,
often in shallow geological sediments, or by high temperatures
and pressures known as thermogenic processes, usually deeper
in the earth’s crust.
Natural gas (also called ‘conventional gas’), which is piped to
homes and businesses across Australia, has accumulated over
millennia in pressurised subsurface reservoirs in sandstone,
onshore and offshore. It can readily be produced (extracted) by
conventional and uncontroversial drilling methods. Conventional
gas can be almost pure methane (‘dry’) or associated with
ethane, propane, butane and condensate (‘wet’). Dry gas has
less energy content than wet gas.  Conventional gas can also be
found with oil in oil fields.
Coal seam gas (CSG), shale gas and tight gas occur in
‘unconventional’ deposits, such as coal beds (coal seam gas),
or in shales (shale gas), or in other fine-grained rock types and
low quality reservoirs (tight gas), or as gas hydrates. These gases
cannot be extracted by conventional drilling. They are dispersed
through rock strata and are held in place by water or other
pressures which must be relieved to release the gas.
Typically, in Australian sedimentary basins, CSG is extracted from
coal seams at depths of a few hundred metres to 1 kilometre,
while shale gas and tight gas are found at greater depths.
Dewatering can be necessary to release CSG. This process can
entail bringing large volumes of water to the surface where it
may need treatment before use in, say, agriculture, or it must be
stored in ponds or otherwise disposed of. For shale and tight gas
production, dewatering is not required.
Hydraulical fracturing (see box on ‘fraccing’, page 8) is typically
needed to release shale gas and tight gas from their host rocks;
horizontal drilling also is increasingly being applied. By contrast,
not all coal seams need fraccing to release CSG.

© John Williams Scientific Services Pty Ltd,
and the Australian Council of Environmental Deans and Directors, 2012

 

Does gas produce less warming?

Most researchers who have looked into the gas industry claims of methane being less damaging have found there is no advantage because of methane's greater greenhouse warming potential.

The Conversation

Grass roots organisations:

Coal seam gas and regulation - what you should know about the law

National Toxics Network

According to Geosciences Australia, as at December 2008 the proven and probable (2P) reserves of coal seam gas (CSG, or coal bed methane as it is known elsewhere in the world) in Australia were 16,179 Petajoules, an 116% increase over the 2007 reserves.

Coal and coal seam gas in NSW

CSG future production

T​he Great Artesian Basin

Many are worried the Great Artesian Basin will be polluted by mining in the recharge areas,where the rainwater sinks into the ground.

Source: CSIRO