Characterization of Coalbed Methane Reservoirs at Multiple Length Scales: A Cross-Section from Southeastern Ordos Basin, China

Coalbed methane (CBM) reservoirs are notoriously difficult to characterize for the existence of heterogeneity at several length scales. These length scales affect processes of desorption at the grain scale (1000 nm) and meso (100-1000 nm) pores shows an apparent decrease with an increase in coal burial depth, which is also confirmed by transverse relaxation time (TO spectra from NMR analyses. The water saturating the macropores is generally removable, while the water in the mesopores is only partially removable, and the abnormal increase in centrifuged T-2 amplitudes reflects poor connectivity between pores. Three kinds of N-2 adsorption/desorption (BET) curves are recovered and interpreted to be slit-like/plate-like pores, narrow slit-like pores, and ink-bottle (narrow throat and wide body) pores (similar to 10 nm). Results, using the same source samples throughout, show strong heterogeneity at the microscopic scale for the pore distribution characteristics, even for a single coal seam, and emphasize the utility of using multiple methods of characterization to infer heterogeneity and the textures and connectivity of pore structures.