微波加热对煤层顶板砂岩微结构的影响

为从微观层面研究微波对煤层顶板砂岩的热作用,实验前对砂岩样品进行预处理,利用核磁共振技术(NMR)和扫描电镜(SEM)对微波辐射前后砂岩的微观结构进行了调查。研究结果表明:微波辐射对砂岩孔隙结构的改性作用包括扩大孔隙的分布范围、增加大孔隙的数量以及增强孔隙间的连通性;随着微波在样品中的传播,孔隙的改性行为明显减弱;砂岩中石英、长石颗粒受热膨胀及其附着黏土脱水的耦合作用产生的晶间断裂和晶内断裂是导致较大孔隙(T₂>10 ms)数量增加和孔隙体积增大的主要原因;工程中利用微波加热进行煤层脱气时,首先要对煤层取样分析,根据煤中碳酸盐类、硫化物类矿物和水分的含量来研判微波的脱气效果;此外,为避免微波注热煤层时对顶板岩石的损伤,作业时需根据煤层气的抽采范围选择合适波长的微波输出。

Effect of microwave heating on microstructure of sandstone in coal seam roof

To study the thermal effect of microwave on sandstone in coal roof at microscopic level, rock samples were pretreated before microwave experiment, and the microstructure before and after microwave radiation was investigated by nuclear magnetic resonance(NMR) and scanning electron microscopy(SEM). The results show that microwave radiation is very conducive to increase the pore number, enlarge the pore volume and enhance the pore connectivity. With the propagation of microwave, the pore modification is obviously weakened. The intergranular fractures and transgranular fractures appear in sandstone due to the coupled effect of thermal expansion of quartz and feldspar particles and dehydration of attached clay minerals, resulting in an increase in the number of larger pores(T;>10 ms) and pore volume. When the coal seam is degassed by microwave heating, the coal seam should be sampled and analyzed first, and the degassing effect of the coal seam by microwave heat injection is determined by the content of carbonate, sulfide and moisture in the coal. In addition, in order to avoid the damage of roof rock caused by microwave heating in coal seam, microwave output with appropriate wavelength should be selected according to the extraction range of coalbed methane.