Characteristics of Coal Matrix Compressibility: An Investigation by Mercury Intrusion Porosimetry

Coal matrix compressibility caused by a pressure change is an important parameter in evaluating the permeability change during coalbed methane production. In this study, the pressure-driven coal matrix compressibility for 21 coals in the rank range from high-volatile A bituminous (0.65% R-o,R-m) to low-volatile bituminous (1.77% R-o,R-m) was evaluated by combining the results from mercury intrusion porosimetry (MIP) with N-2 adsorption analysis. The pressure interval was chosen to be from 7.35 MPa to ensure that the compression is totally from the coal matrix. The calculated coal matrix compressibility shows a U-shaped relationship with increasing coal rank, and it obtains relatively low values at the medium-volatile bituminous coals. The coal matrix compressibility of high-volatile A bituminous coals is of 1.6398-2.9060 x 10(-4) MPa-1 and medium- and low-volatile bituminous coals have coal matrix compressibility of 0.3451-1.5519 x 10(-4) and 0.7625-2.5554 X 10(-4) MPa-1 respectively. Moreover, with the data of petrographic and proximate analyses, the porosity, moisture content, and macerals have influence on coal matrix compressibility.