Correlating Coal Petrology and Methane Adsorption Parameters of High-Volatile Bituminous Coals with P-Wave Velocity

The parameters of coal petrology and methane adsorption are significant to exploit coal and coalbed methane (CBM). Based on borehole core sampling, a new method using the P-wave velocity to predict coal maceral, coal face index, and Langmuir parameter of high-volatile bituminous coals was proposed. The results showed that the P-wave velocity correlated positively with coal skeletal density, apparent density, and ash yield with fitting coefficients (R ²) of 0.55, 0.57, and 0.57, respectively, but it negatively correlated with coal porosity and moisture content with R ² of 0.56 and 0.60, respectively. Vitrinite, ranging from 14.8 to 82.7% with an average of 53.8%, positively correlated with coal porosity due to more micropores in vitrinite and thus negatively correlated with the density and P-wave velocity. Inertinite content was in the range of 5.4 to 27.4% with an average of 11.0%, which correlated negatively with the coal porosity and thus positively with the density and P-wave velocity for most of the samples. Furthermore, the P-wave velocity was weakly positively correlated with mineral content, and a negative correlation was found between the P-wave velocity and vitrinite/inertinite ratio (V/I), gelification index (GI), and Langmuir volume (V _L). The porosity (Y ₁), vitrinite content (Y ₂), inertinite content (Y ₃), and V _L (Y ₄) of coals could be predicted based on the equations as follows: Y ₁ = 7842.4 e^-0.003 , Y ₂ = -0.0003X ² + 1.0731X - 924.09, Y ₃ = 0.0003X ² - 1.2797X + 1405, and Y ₄ = -0.04X + 101.24, where X is the P-wave velocity. Generally, P-wave velocity could be largely used to predict the variations of the coal maceral and methane adsorption capacity of high-volatile bituminous coals, providing a new and valuable approach for CBM exploration and gas prevention in coal mines.