Dynamic prediction of coalbed methane well considering pseudo-steady state diffusion

Abstract

Dynamic prediction models combined with volume balance and pseudo-steady state diffusion were established in this study. Coal reservoir, coalbed methane (CBM), and formation water were taken into account in the volume balance equation, where the diffusion occurred as the gas travelled from the matrix system to the fracture system. Calculation results showed that diffusion could increase the maximum production of CBM. The findings also revealed that a larger diffusion coefficient would provide not only a higher maximum CBM production, but also a longer stable production time. Greater matrix shrinkage effect at the later stage of CBM production resulted in longer stable production time and gentler decline rate of production. Meanwhile, the time that production reached the maximum value was shorter. Also, the production was higher and the stable production time was shorter with greater reservoir permeability. Permeability had a more significant influence on stable production time.