冷加载作用下不同围压煤样结构损伤规律研究

Structural damage mechanism for cold loaded coal samples under different confining pressures

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 pore and fracture structure of coal sample are main factors that affect storage and percolation Capacity of Coalbed Methane(CBM). Structural damage of coal sample may improve permeability of CBM reservoir. To study the relationship between structural damage and confining pressure of coal samples under the effect of liquid nitrogen, we used the equipment for liquid nitrogen injection to drilled coal blocks to conduct confining pressures from 0 MPa to 7 MPa on coal samples, respectively, then the experiment of injecting liquid nitrogen into coal samples under different confining pressures is conducted to reveal structural damage mechanism of coal samples under different confining pressures. Several conclusions from the experiment are achieved. Firstly, structural damage degree of coal samples turned large as the confining pressure increased, and under 0 MPa confining pressure coal samples are more likely to be damaged or even destructed. Secondly, the changing rate of structure damage increases obviously when coal samples suffer 4 MPa confining pressure, but, the structure damage of coal samples is not obvious under 1 MPa. Thirdly, under the effect of temperature stress and confining pressure, the pore and fracture volume of coal samples expand along the vertical direction and this is obvious to coal samples with original fractures. Also, coal samples with confining pressures will develop structural damage under the effect of cold loading injected with liquid nitrogen.