煤岩变形破坏过程中渗流演化规律试验研究

高煤阶煤层气的开发主要采用压裂的方式进行增产。在压裂过程中,随着煤岩应力的不断变化,其孔隙结构和渗透特性发生变化,进而影响煤岩的力学破坏特征。以高阶煤为研究对象,开展不同围压作用下三轴渗流-应力耦合流变试验,研究煤岩变形和破坏过程中的应力、应变与渗透率之间的相互关系,分析了煤样应力、应变变化过程中渗透率随围压和体积应变的变化规律。试验结果表明:煤岩的应力-应变关系具有脆-塑性特征,煤岩体积应变经过压密和扩容阶段,环向应变能够比轴向应变更灵敏地反映出煤岩变形破坏的过程。煤岩渗透率在压缩过程中出现波浪状变化,在高应力作用下发生破裂后,其渗透率不一定比破裂前增加,相反有可能会减小。研究结果可为多场耦合下煤岩破裂模型的建立与分析、压裂施工参数设计和工艺的优化提供技术支撑。

Experimental study on seepage evolution during deformation and failure of coal rock

The fracturing is mainly used for high rank coalbed methane development. With the change of stress, the pore structure and permeability are changed during fracturing, in turn, will affect the mechanical fracture properties. By using three-axis seepage-stress coupled rheological tests under different confining pressures, the relationship between stress, strain and permeability in the process of deformation and failure of coal is studied The variation of permeability with the confining pressure and volume strain during strain change are analyzed. The experimental results show that the stress-strain relationship of coal has non-typical brittle characteristics. The volume strain goes through two stages with compacted and expanded. The circumferential strain can reflect the deformation and failure of coal more obviously than axial strain. There appear wave shape characters for permeability at the compaction. The permeability of coal is not higher than that before fracturing under the failure of high stress; otherwise the permeability may be reduced. The results can provide technical support for the establishment and analysis of rupture model with high rank coal under multi-field coupling, as well as the parameters and technical optimization of fracturing.