Title: 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

Authors: Yongkai Qiu; Dameng Liu; Derek Elsworth; Yanbin Yao; Yidong Cai; Junqian Li

Addresses: Coal Reservoir Laboratory of National Engineering Research Center of CBM Development and Utilization, School of Energy Resources, China University of Geosciences, Beijing, 100083, China; G3 Center, EMS Energy Institute, Department of Energy and Mineral Engineering, Pennsylvania State University, University Park, PA 16801, USA ' Coal Reservoir Laboratory of National Engineering Research Center of CBM Development and Utilization, School of Energy Resources, China University of Geosciences, Beijing, 100083, China ' G3 Center, EMS Energy Institute, Department of Energy and Mineral Engineering, Pennsylvania State University, University Park, PA 16801, USA ' Coal Reservoir Laboratory of National Engineering Research Center of CBM Development and Utilization, School of Energy Resources, China University of Geosciences, Beijing, 100083, China ' Coal Reservoir Laboratory of National Engineering Research Center of CBM Development and Utilization, School of Energy Resources, China University of Geosciences, Beijing, 100083, China ' Coal Reservoir Laboratory of National Engineering Research Center of CBM Development and Utilization, School of Energy Resources, China University of Geosciences, Beijing, 100083, China

Abstract: 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 × 10¹⁰ tonnes), but hindered by low observed gas content (0.01-1.5 m³/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 CH₄ weathering line ( > 860 m), with larger coal thickness ( > 10 m), and higher gas content ( > 1.2 m³/t) have the greatest potential for CBM enrichment. [Received: January 21, 2014; Accepted: July 27, 2014]

Keywords: low rank coal reservoirs; coalbed methane; CBM; geological factors; gas entrapment mechanism; China; methane prediction; gas content; porosity; permeability.

DOI: 10.1504/IJOGCT.2014.066315

International Journal of Oil, Gas and Coal Technology, 2014 Vol.8 No.4, pp.449 - 467

Received: 25 Jan 2014
Accepted: 27 Jul 2014
Published online: 23 Dec 2014 *

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