A review of experimental and numerical modeling of digital coalbed methane: Imaging, segmentation, fracture modeling and permeability prediction

Coalbed methane (CBM) is a form of natural gas that is extracted from coalbeds. Characterization of CBMs is very challenging mostly due to the very complex fracture system leading to ambiguous fluid and petrophysical properties. Among several important factors that control the performance of CBMs, permeability is the most crucial one, which summarizes the global fracture system, intensity, connectivity, and production ratio. As such, accurate characterization of CBMs is coupled with fracture delineation and permeability description, which resulted in the development of a wide range of methods. In this paper, all the necessary steps from imaging, segmentation, and modeling of the fractures to various methods of permeability evaluation are reviewed. This paper presents a critical review of all of the existing relevant and significant techniques and compares their performances with special reference to permeability prediction. Several practical and simplified computational methods for calculating permeability are thus reviewed and compared. Finally, this review paper summarizes the current challenges and possible future research.