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煤体孔隙、裂隙结构是影响煤层气存储能力和渗流能力的主要因素,煤体结构损伤可以提高煤层气储层的渗透性。为了研究液氮作用下煤样结构损伤与围压之间的关系,通过将液氮注入钻孔煤实验装置系统对煤样施加0~7MPa围压,开展液氮注入不同围压煤样实验,揭示了不同围压下煤样结构损伤的规律。结果发现:(1)围压大于1MPa时,煤样结构损伤程度随围压的增加而增大;无围压条件下,煤样更容易发生损伤甚至破坏;(2)4MPa~7MPa围压下煤样结构损伤变化速率明显增加,1MPa围压煤样结构损伤不明显;(3)在温度应力与围压作用下,煤样的孔隙、裂隙体积在垂直层理方向扩展明显;冷加载对于煤样原生裂隙扩展效果显著。本文结果表明液氮冷加载作用可以使带围压煤样结构发生损伤。
The porosity and fissure structure of coal seam are the main factors affecting CBM storage capacity and seepage capacity. The damage of coal mass structure can improve the permeability of CBM reservoirs. In order to study the relationship between structure damage and confining pressure under the action of liquid nitrogen, a confining pressure of 0 ~ 7MPa was applied to coal samples by injecting liquid nitrogen into borehole coal experimental device, Reveals the law of coal structure damage under different confining pressure. The results show that: (1) When the confining pressure is more than 1MPa, the damage degree of coal sample structure increases with the increase of confining pressure; under the condition of no confining pressure, the coal sample is more likely to be damaged or even destroyed; (2) The damage rate of coal sample structure obviously increases, the damage of 1MPa confining coal sample structure is not obvious; (3) Under the action of temperature stress and confining pressure, the pore volume and fracture volume of coal sample expand obviously in vertical bedding direction; Prototype crack expansion effect is obvious. The results of this paper show that the liquid nitrogen can cause the damage of the coal-like structure with confining pressure.