:为解决煤层气排采效率低的问题,提高煤储层渗透率,采用CT扫描的精细观测手段,对煤样进行钻孔注液氮实验,并分析其致裂过程与增透效果.研究结果表明:在冷冲击收缩应力与孔隙压力的双重作用下,煤岩注液氮钻孔周围发生了破裂,其孔隙率增加量随与钻孔距离增大呈负指数衰减.煤岩钻孔注液氮致裂效果随着与钻孔距离增加而减弱;增透效果在邻近钻孔的位置增加,由于碎胀作用,在远离钻孔的位置反而降低.液氮冷冲击对煤岩孔隙结构的影响与原始孔隙率之间具有一定相关性:即在原始孔隙率较低的区域,孔隙率增加较为明显,而在原始孔隙率较高的区域,孔隙率增加不明显甚至略有降低.研究结果证明注氮可以实现煤储层增透、提高煤层气排采产量.%In order to increase gas drainage efficiency of coal seam and improve the permeability of coal reservoir,the coal sample was drilled to inject liquid nitrogen and scanned by CT,so that the fracturing process and the permeability effect were analyzed.The results of study show that affected by double action of the cold shock shrinkage stress and the pore pressure,the fractures appear around the boreholes which has been injected liquid nitrogen,the porosity variation of coal has a negative exponential decrease with the increase of the distance from the borehole.With the increasing distance from the borehole,the fracturing effect of liquid nitrogen injection on coal weakened;due to the broken expansion,the area near the borehole has a better effect of permeability improving,while the effect on the area far from the hole is converse.There were some correlations between the fracturing effect on the coal sample and its original porosity:in the area of lower original porosity,the porosity increases more obviously,while in the area of higher original porosity,the increasing of porosity is not obvious or even decreased.The results show that nitrogen injection can improve the permeability of coal reservoir and increase the output of coalbed methane production.
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