Abstract
The heterogeneous effect of coal matrices on flow profiles in coal seam reservoirs was discussed in this paper. To this end the flow equations in cleats were formulated to couple with a new fracture (cleat)-matrix transfer function that incorporates the statistical details of the heterogeneity regarding the diverse matrix block's sizes. The resultant flow equations were then described by a set of integral-(partial) differential equations, and we developed a novel quatrature scheme to deal with them. An enhanced-coalbed-methane-recovery (ECBM) problem was taken as an excise example, where the statistical data measured for a coal sample from a literature was used. With this example we discussed the relative errors of the flow profiles that were predicted with and without considering the statistical variances relevant to the heterogeneous effect, respectively. These profiles discussed include the methane production rate, the carbon dioxide injection rate, and the pressure transient response at the bottomehole of the production well. The relative errors for the cleat methane recovery in the field were also examined. It was shown that, for the flowrates and the pressure response at the wells, considerable errors (around 5% to 60%) may be observed when the heterogeneous effect concerned is neglected, especially in earlier times of operations (e.g., 0 to 15 days), whilst large errors (e.g., over 50%) for the cleat methane recovery may still exist in some areas in the subsurface after a much longer time (e.g., 400 days).
