Methane Associated with Coal Seams

Introduction

Methane is a natural product arising out of the decay of organic matter and as coal deposits were formed with increasing depths of burial, rising temperatures and rising pressures over geological time, a proportion of the methane produced was adsorbed by the coal.  Whereas in a natural gas reservoir such as sandstone the gas is held in the void spaces within the rock, methane in coal is retained on the surface of the coal within the micropore structure.  Such adsorption is maintained by the lithostatic and hydrostatic pressures and the release of these pressures allows methane to escape from the coal. 

Current or abandoned 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 giving rise to serious safety concerns if not managed properly.  Many explosions have occurred over the years leading to the development of “methane drainage” in mines where the gas is drained from the strata by pumping from boreholes drilled above the working face.  This practise often yields significant quantities of methane, which has on occasion been used to fire the colliery boilers or more recently generate electricity.

Methane can continue to emit from a mine after closure and the concept of collecting the gas from abandoned mines has been developed in recent years to provide an energy source which would otherwise be wasted.  In addition methane is 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 year time horizon.

The concept of utilising gas from working or closed mines is referred to as Coal Mine Methane (CMM) or Abandoned Mine Methane (AMM) and several projects have been completed by private sector operators in the UK with more being planned in the future.  These projects generally utilise the gas to generate electricity for local use or to be fed into the national grid.

There are over 900 former deep mines in the UK, which offer differing degrees of potential for exploitation of methane.  Projects can be developed using the existing mine shafts or adits, where these remain open, or by drilling from the surface into the abandoned workings.

The commercial exploitation of methane from coal mines has the potential, now well proven, of harnessing the gas safely and beneficially to generate electricity and can provide considerable benefits :-

• 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 available to local users, especially in cases where former colliery sites are developed for industry and commerce

Coal Bed Methane

In addition to exploiting methane from abandoned and existing coal mining operations, the opportunity also exists to exploit methane which is still locked into the vast reserves of coal and coal measures strata that remain unworked.  This concept is referred to as Coal Bed Methane (CBM) since it involves directly drilling into unworked coal and coal measures strata to release the methane adsorbed to the coal rather than utilising methane released as a result of mining activities. 

CBM offers a method of extracting methane from the coal without detrimentally affecting the physical properties of the coal.  This provides many benefits :-

• 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 with CMM/AMM which normally has a higher carbon dioxide content and as such is not suitable for direct introduction

There have been several pilot drilling schemes in the UK during the last few years but no large scale operational project has yet been developed (January 2007).  However companies are now utilising directional drilling techniques from the oil industry to try and make the exploitation of CBM a viable prospect in the UK.

The role of the Department for Business, Enterprise and Regulatory Reform (DBERR)

The 1994 Coal Industry Act clarified that the ownership of methane did not rest with the Coal Authority.  As a petroleum product, the crown owns the methane associated with coal and the rights to the gas are regulated by DBERR under the Petroleum Act 1998. 

DBERR Oil and Gas Division licence exploitation by means of onshore Petroleum Licences generally issued in “rounds”.  More information on this process and the location of existing licenses can be accessed on the DBERR web site at www.og.berr.gov.uk

In Energy Paper 67 (Clean Coal Technologies) issued in April 1999, the predecessors to DBERR, the Department of Trade and Industry, set out government policy on the aims, objectives and activities in relation to future exploitation of methane from coal.

The Role of the Coal Authority

Whilst DBERR is the licensing body for methane the consent of the Coal Authority is required before any works take place that intersect coal and/or coal mine workings (whether abandoned or not) vested in the Authority. 

The Authority grants Access Agreements to enter its property for coal methane exploitation and the process for applying for such an agreement can be found at :- http://www.coal.gov.uk/media//44430/GuidanceNotesforCBM2000.pdf   

The Coal Authority has a specific duty in the exercise and performance of its powers and duties with respect to its land and other property to have regard to the desirability of the exploitation, so far as that is economically viable of coal bed methane in Great Britain (Coal Industry Act 1994, Section 3(5)).  The Authority is therefore concerned to ensure that the situation with regard to methane is widely appreciated and understood, in particular its potential with regard to the energy needs of the nation.

October 2007