Colliery Gas

Coal-related gases: Rise of an energy fuel

Coalbed methane is a usual term for methane from coals. However, the term “coal-related gases” is much more accurate. The utilization of coal-related gases rises year on year. Because of a globally rising demand in energy, the production of coal-related gases is of economic interest. In 2007, already 6 % of the global production of natural gas came from coal-related gases. 45 Bill. m³ coal-related gas were produced 2007 (Figure 1). This volume represented an energy content of ca. 39 Mio. tce. Coal-related gases will remain to be available as energy source, as it is descending from coal and as the global coal supply from a geoscientific view is not critical until 2100 [1].

 

 

Figure 1: History of the global production of coal-related gases 1970 to 2007.

Gases from coals can be classified by origin and composition. Coal gases are subdivided into coalbed methane (CBM), coalseam methane (CSM), and coalmine methane (CMM, Figure 2). CBM is coal gas produced from boreholes in unworked coal-bearing rocks. CSM is coal gas released in active collieries, whereas CMM escapes or is produced from abandoned mines.  

 

Figure 2: Classification of coal-related gases. Depending on their origin these gases contain different concentrations of a number of components. From [2].

Coal-related gases occur in all of those coal deposits where coals have reached or exceed the coalification of high volatile bituminous B coal and Flammkohle (German), respectively. This led to substantial methane generation. If the subsidence history of a coal deposit allowed and allows gas storage, a gas reservoir of coalbed methane could be accumulated. Highest gas contents can be expected with bituminous coals. Due to their low coalification, lignite and brown coal deposits are not relevant for an utilization of coal-related gases.

Citations:

[1] Thielemann, T., Schmidt, S., Gerling, J.P. (2007, in German): Lignite and hard coal: Energy suppliers for world needs until the year 2100 An outlook. Glückauf, 143 (3): 116-123; Essen.

[2] Thielemann, T. (2002, in German): Coal-related gases in Germany. BGR Commodity Top News, 17: 4 pages; Hannover www.geozentrum-hannover.de