Modeling anisotropic permeability of coal and its effects on coalbed methane reservoir simulation

In this study, an alternative permeability model was developed and compared with data from laboratory investigations. The model was further applied for reservoir simulation with several cases in order to evaluate the effects of the anisotropic permeability variation on the CO2-sequestration and CO2- sequestration enhanced coalbed methane (CO2-ECBM) recovery. The permeability model developed in this study is based on a discontinuum medium approach, in which coal is treated as a discontinuum medium containing anisotropic matrixes and cleats. The permeability variations and anisotropic permeability ratios under isotropic net stresses were tested with relatively large coal samples. The simulations show good agreements with the experimental data, revealing that the developed model is superior for describing stressand sorption-induced permeability variations in coals compared with models using constant values for stress-dependent parameters. The results from reservoir simulation incorporating the developed permeability model show the anisotropic permeability exhibit significant effect on CO2-ECBM recovery.