The occurrence of a secondary zone of coal-bed methane in the southern part of the Upper Silesian Coal Basin (southern Poland): Potential for methane exploitation

Coal-bed methane (CBM) exploitation in the Upper Silesian Coal Basin has, in spite of earlier failures, again aroused investor interest. Carboniferous coal seams at depths of 200–500 m are characterized by coal permeability values (estimated at 27–230 mD) and degrees of methane saturation (almost 100%) that suggest future successful exploitation. Based on the results of geological surveys archived in the Polish Geological Institute, the shallow CBM zone is defined as a gas horizon distinct from a deep CBM zone. The disposition of the shallow zone follows the topography of the Upper Carboniferous paleorelief, and, is deemed the most important factor controlling methane distribution within this zone. The most favorable places for CBM accumulation within the shallow coal seams are erosional highs and the slopes of Upper Carboniferous ridges associated with fault zones. The thickness of the zone (> 200 m) and methane contents (> 8 m3/t coal daf) are highest in these places. The nearly-full saturation of the coal seams with methane reflects the involvement of two genetic types of gas — indigenous late-stage microbial methane and thermogenic methane derived from the deeper coals. The favorable geological characteristic of this shallow CBM zone is a potential source of energy for Upper Silesia.

Research Highlights
► A shallow CBM zone occurs in uppermost-Carboniferous coal-bearing strata.
► The topography of the Carboniferous surface controls the distribution of CBM.
► That zone probably comprises a mixture of microbial and thermogenic methane.
► The estimated high permeability of the coals makes that zone an attractive prospect.