Micropore structure characteristics and water distribution in a coalbed methane reservoir.

Microscopic pore structure and water distribution are important and fundamental parameters for coalbed methane reservoir characterisation. These are closely related to the calculation/interpretation of other critical parameters, such as permeability and flow capacity. In this study, scanning electron microscopy, low-pressure nitrogen gas adsorption, nuclear magnetic resonance spectroscopy, and theoretical calculations were used to study the pore structure characteristics and water distribution of Zhaozhuang coal mine in the southeastern Qinshui Basin, PR China. The results show that the pore radius ranges from 2.066 to 594.045 nm, mainly classified as micropores and transitional pores. The micropores significantly contribute to the total pore volume. The adsorption pores (micropores and transitional pores) contribute the most to the total specific surface area. The T2 spectrum distributions of saturated water samples show two peaks. The first T2 spectrum peak is related to adsorption pores, whereas the second T2 spectrum peak is related to seepage pores. The seepage pores were not well developed as the adsorption pores. Most adsorption pores are saturated with irreducible water that could not be discharged by centrifugation, whereas the seepage pores are saturated with movable water that could be completely discharged by centrifugation. The T2 cutoff method was used to calculate the irreducible water saturation, and the irreducible water saturation of the sample was ≥90%. The irreducible water was mainly distributed in the micropores, and some of the irreducible water was distributed in the transitional pores. The irreducible water that remains in the pores can cause reservoir damage. [ABSTRACT FROM AUTHOR]