Why Coal Bed Methane (CBM) Production in Some Basins is Difficult

Andrzej Olajossy and Jerzy Cieślik
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Andrzej Olajossy: Faculty of Mining and Geoengineering, AGH University of Science and Technology, 30-059 Kraków, Poland
Jerzy Cieślik: Faculty of Mining and Geoengineering, AGH University of Science and Technology, 30-059 Kraków, Poland

Energies, 2019, vol. 12, issue 15, 1-21

Abstract: The changes in the permeability of coal-bed reservoirs with methane, as associated with gas depletion, are the consequence of two opposing processes, namely geomechanical compaction that narrows down fractures, and matrix shrinkage, which, in turn, widens fractures. Many previous studies on the effects of these processes have emphasised, albeit not always, the circumstances and conditions that led to a greater coal permeability, with a natural decrease in the pore pressure of methane during its production, and, in consequence, to an increase in the cumulative volume of this gas. However, in some coal basins, there are beds where the methane production has failed to reach the appropriate level, whether in economic or engineering terms. This paper identifies some reasons for the failed attempts at well exploration of gas from such coal beds. Specifically, it describes seven parameters to be considered in relation to CBM, including geomechanical parameters such as Young’s modulus, Poisson’s ratio, and the initial porosity, which define coal cleat compressibility, a very important parameter, and parameters related to methane desorption, i.e., desorption-induced volumetric strain, the Langmuir pressure, and the initial pressure of gas within the bed. In addition to cleat compressibility, there are other, equally important parameters, such as the rebound pressure and recovery pressure, which are defined by the following parameters in order of importance: Young’s modulus, desorption-induced volumetric strain, initial pressure of methane, the Langmuir pressure, and Poisson’s ratio. To assess the impact of these parameters on changes in permeability, we used the Cui-Bastin model. The simulation results were analysed to allow us to present our findings.

Keywords: CBM; gas depletion; geomechanical compaction; matrix shrinkage; desorption (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2019
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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