不同温度应力下煤体蠕变中的渗流规律研究

Seepage evolution in coal creep under different temperatures and different stresses

煤层渗透性是决定煤层气开采效果的关键因素。在煤层气开采周期中,长期温度场及应力场作用使得煤体内渗流通道也不断发生演化。对不同温度应力下煤体蠕变过程中的渗流演化规律展开研究,结果表明,不同温度下分级蠕变过程中,各试样的渗流演化基本经历3个蠕变变形阶段:蠕变起始应力阈值前的压密硬化阶段、体积压缩的蠕变变形阶段和体积膨胀的蠕变变形阶段;试样渗透率表现为先逐渐降低再增加的趋势,且试样渗透率演化与体积时效变形存在较好一致性。温度升高,有助于煤体蠕变变形的发生,煤体蠕变的起始应力阈值减小,极限破坏强度降低,煤体渗透率由降低到升高的转折点应力值减小。温度较高时,煤体蠕变对渗透率降低的影响较大,煤体渗透率损失最大可达40.35%。研究结果可为煤层气的有效开采提供理论支持。

Coal permeability is the key factor determining the effectiveness of coal-bed methane(CBM) exploitation. In the CBM production cycle,the long-term high temperature and stress make the seepage paths in coal evolve with time. In this paper,the seepage evolution in coal creep under different temperatures and different stresses were studied,and the results shown that the creep of coal undergoes three phases:the hardening phase before the creep start stress threshold,the creep phase with compressive volume deformation and the creep phase with expanding volume deformation. In the whole process,the permeability of coal gradually decreases and then increases with the creep strains and there is a good consistency between the permeability evolution and time-dependent volumetric strain. The increasing temperature is helpful for the occurrence of coal creep strain,resulting in the decrease of the creep start stress threshold and the ultimate failure strength. At high temperature,the creep of coal shows a greater influence on the decrease of permeability,and the maximum loss of coal permeability can reach 40.35%. The results can provide theoretical support for the effective exploitation of CBM.