We have developed the first experimental acoustic properties measurement during gas-hydrate formation and dissociation in crushed bituminous coal samples. We also compare the results with acoustic properties measurements during freezing and thawing water in the same samples. The results show a more complicated behavior that differs from similar experiments with sand. For the samples with adsorbed water, it does not freeze at anticipated temperatures, but acoustic velocities gradually increase with the decreasing negative temperatures. It is caused by complicated pore surface structures causing partial formation of ice/hydrate from bound water at different temperatures. We also observe that, for the same samples, the acoustic properties change significantly, becoming stronger during gas-hydrate formation than during freezing. We explain it by competitive sorption of methane and water in the coal pore space; methane under pressure replaces part of the adsorbed water from micropores so that this water can easily form hydrate. The difference in the acoustic properties of frozen and hydrate-bearing coal samples is important for developing seismic methods for geophysical characterization of coal seams.

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含水合物煤样品的声学特性取决于温度和水饱和度类型

我们已经开发出了第一个实验性的声学特性测量方法，用于在压碎的烟煤样品中形成天然气水合物和使其分解。我们还将结果与相同样品在冻结和解冻水过程中的声学特性进行了比较。结果显示出更复杂的行为，与类似的沙子实验不同。对于带有吸附水的样品，它不会在预期的温度下冻结，但是声速会随着负温度的降低而逐渐增加。这是由于复杂的孔表面结构导致在不同温度下由结合水部分形成冰/水合物而引起的。我们还观察到，对于相同的样品，声学特性发生了显着变化，在气体水合物形成过程中比在冷冻过程中变得更强。我们通过煤孔隙空间中甲烷和水的竞争性吸附来解释它。压力下的甲烷替代了微孔中吸附的部分水，因此该水很容易形成水合物。冷冻和含水合物煤样品的声学特性差异对于开发地震方法进行煤层地球物理表征很重要。