Physical Simulation of Temperature and Pressure Evolvement in Coal by Different Refrigeration Modes for Freezing Coring

Abstract

Reduction of gas desorption capacity by cooling coal samples seems a feasible way to improve the accuracy of gas in place estimation. To find an efficient refrigeration mode for the freezing coring technology, the freezing tests for coal containing gas (at 0, 1.09, and 2.15 MPa) are separately conducted based on the precalculation of dry ice dose. The evolvement of coal temperature and gas pressure shows that under the catalysis of ethanol, the average cooling rate of coal gradually accelerates with the increased amount of ethanol (from 0 to 600 mL) in the early stage. Additionally when charging gas into the coal canister, the cooling rate of coal at each subzero temperature accelerates with the increased adsorption pressure of gas, and the low temperature preservation time (<0 °C) of coal is also prolonged. There is a good linear relationship between gas pressure and coal temperature, which indicates that the CH4 adsorption and desorption in coal are basically reversible; but the desorption hysteresis is extensively observed, associated with the occurrence of numerous ink-bottle type micropores.