Improved Model for Characterization of Fractal Features of the Pore Structure in a High-Rank Coalbed Methane Formation

Abstract

In this paper, we propose a theoretically derived improved model for characterizing the fractal features of coalbed methane reservoirs, and we compare with previously published models for conventional reservoirs. The model was verified by mercury intrusion porosimetry. The results have shown that there is no linear relationship between the normalized wetting phase saturation, wetting phase saturation, or mercury saturation vs. the capillary pressure on a log-log plot. Therefore existing models are inapplicable for a high-rank CBM formation, which is characterized by low permeability and porosity. The improved model lets us calculate the multi-interval fractal features characterizing the physical properties of the formation. We show that higher fractal dimensions mean poorer physical properties of the formation.