Nuclear magnetic resonance experimental study on gas adsorptioncharacteristics of deep low rank coal

This paper presents the results of a gas adsorption experimental study on adsorption characteristics of deep low rank coal gas using low field nuclear magnetic resonance (NMR) technique. The coal samples used in the experiment are low rank coal collected from the Aiweigou mine in Xinjiang. The spectral integral area (dimensionless) of the nuclear magnetic resonance T2 (transverse) is used to quantify the adsorbed gas contents. The experimental results show that there are three characteristic peaks (adsorption peak, free peak, and free gas peak) in the T2 spectrum of deep low rank coal gas adsorption process. Under different gas pressures, both total gas adsorption and gas adsorption capacity increase as the adsorption time increases at the beginning and then remain stable. The gas adsorption rate increases at beginning and then decreases with the increases of adsorption time. The adsorption gas volume correlates with the gas pressure by a hyperbolic function. The higher gas pressure is associated with longer time for the gas in the low rank coal to reach adsorption equilibrium. This research provides an important guidance to exploration and development of deep low rank coalbed methane and gas drainage.