Geological factors on gas entrapment mechanism and prediction of coalbed methane of the no. 6 coal seam in the Jungar coalfield, northeast Ordos Basin, China

Low rank coal reservoirs of the no. 6 coal seam in the Jungar coalfield are characterised by low gas content but favourable porosity and permeability for recovery. The accumulation and enrichment of CBM is favoured by the presence of multiple (five seams) and thick (12.7–40.4 m) seams, adequate permeability (3.6–26 mD) and significant abundance of coal resource (5.44 × 10 10 tonnes), but hindered by low observed gas content (0.01–1.5 m 3 /t), which is shown to result from both shallow burial depth and high permeability of the seams. However, the sheer magnitude of the no. 6 coal resource offsets this shortcoming of low gas content and makes this a good prospect for exploration and exploitation. Conditions are most favourable in the southwest coalfield where a monoclinal structure and favourable hydrodynamic conditions have prevented gas escape. Areas of the no. 6 coal seam buried under the CH 4 weathering line ( > 860 m), with larger coal thickness ( > 10 m), and higher gas content ( > 1.2 m 3 /t) have the greatest potential for CBM enrichment.