Dynamic response characteristics of water–gas–coal in freezing process of gas-bearing coal under water infiltration condition

Abstract

Rock cross-cut coal uncovering (RCCU) is susceptible to coal and gas outburst incidents, greatly impeding the safe extraction and miner safety. Freezing coal at low temperatures can enhance its mechanical properties and encourage gas adsorption. For the practical application of this method to prevent coal and gas outburst, water needs to be injected into the coal seam. However, the mutual dynamic response of the water–gas–coal combination during low-temperature freezing has not been sufficiently investigated, seriously restricting its application in disaster prevention. Therefore, this study investigates these characteristics using a low-temperature freezing experimental setup that was built for gas-bearing coal under conditions of water infiltration. The findings indicated that under low-gas-pressure conditions, the coal samples exhibited a larger degree of pore wettability. The improved Aronofsky index model was used to explain the relationship between the gas replacement quantity and time. Time required for the coal temperature to reach equilibrium showed a positive correlation with freezing temperature and gas pressure, respectively. As freezing temperature and gas pressure rise, respectively, freezing coal's thermal conductivity falls. The longitudinal strain of freezing coal rises with the drop in gas pressure and freezing temperature, respectively. Low-temperature freezing was conducive to the transformation of micropores and small pores into mesopores, macropores, and fractures. Based on these results, a collaborative measure of borehole methane drainage, coal seam water injection, and low freezing coal to prevent coal and gas outburst was proposed. The study lays a theoretical foundation for preventing coal and gas outbursts during RCCU.