Methane (CH4) is a natural gas compound produced out of the decay of organic matter. Over time, as coal deposits were formed with increasing depths of burial, rising temperatures and rising pressures over geological time, a proportion of the methane was absorbed by coal. When the coal and methane conversion process occurs such that the coal is saturated with water and methane is trapped within the coal, the result is “coal bed methane” (CBM).
There are over 900 former deep mines in the UK, which offer differing degrees of potential for exploration of methane. It should be noted that methane is still a greenhouse gas, which according to the Inter-governmental Panel on Climate Change has a global warming potential which is 21 times greater than that of carbon dioxide over a 100 years period.
Worked coal mines
The presence of significant amounts of methane in coal is familiar to coal miners as the gas is released due to the relaxation of pressure and fracturing of the strata during mining activity. Safety reasons have meant “methane drainage” often occurs in mines by pumping from boreholes drilled above the working services.
- An uncontrolled danger and potential surface hazard to individuals and property is harnessed and greatly reduced or removed altogether.
- Harmful ventilation to the atmosphere is reduced with a significant reduction of greenhouse gas emissions.
- Electricity is made available to local users, especially in cases where former colliery sites are developed for industry and commerce.
Un-worked coal mines
Opportunities exist to exploit methane still locked into the vast reserves of coal and coal measures strata that remain un-worked. It is this process which is generically referred to as CBM since it involves directly drilling into un-worked coal and coal measures strata to release the methane absorbed in the coal rather than utilising methane released as a result of mining activities.
- When carried out on its own it facilitates exploitation of the coal resource in areas where the coal would be unlikely to be worked by traditional mining methods.
- As the coal remains in the ground there is no surface subsidence.
- It facilitates extraction of gas from coal seams prior to mining the coal, thus reducing the potentially dangerous methane gas encountered when carrying out traditional mining methods.
- Methane quality is such that it has the potential to be fed directly into the gas distribution network. (This is one distinct difference relative to worked coal methane which normally has a higher carbon dioxide content and as such is not suitable for direct introduction.)
Is there a market for CBM and if so where?
There are already thriving CBM markets in various countries including the USA, where CBM provides around 10% of the domestic gas supply.
The largest resources of CBM are to be found in:
Significant resources also lie in:
- Southern Africa
In the UK, there is not yet a large CBM industry. Although there may not yet be an established market however, there have been a number of pilot drilling schemes for CBM materialising over recent years. A good example of a successful CBM pilot scheme is that of Composite Energy Limited and its test well in Falkirk.
Look out for our next article on CBM, which will look at certain legal issues surrounding CBM such as:
- property issues (both legal and practical) surrounding CBM projects in the UK specifically;
- the different regulatory bodies involved in a CBM project and the interaction between those bodies; and
- how CBM could be combined with other emerging carbon abatement technologies such as Carbon Capture and Storage (CCS) to mitigate climate change.