Abstract: To address time-dependent rock deformation in deep coalbed methane development, high-temperature and high-pressure triaxial creep experiments were performed to reveal the creep mechanical properties and energy evolution mechanisms of deep coal rocks. The results indicate that during the creep process of deep coal rocks, the volumetric deformation exhibits a transition from shrinkage to expansion, and the axial, circumferential, and volumetric strain increments all increase with rising temperature. Moreover, high temperature can lead to a decrease in elastic modulus and an increase in Poisson’s ratio, significantly weakening the coal rock structure. The underlying mechanism of coal-rock radial expansion and volumetric expansion is that the deviatoric stress elevation triggers the weakening of radial constraints and the propagation of internal cracks, while high temperature amplifies deformation and damage effects through a triple mechanism including degradation of rock strength, induction of thermal damage, and acceleration of creep accumulation. CT-based 3D fracture reconstruction reveals that the combined high-temperature and high-pressure treatments enhance the coal porosity by 89.73 %, while increasing the proportion of pores larger than 150 μm in diameter. The simultaneous increase in both fractal dimension and tortuosity reveals the formation mechanism of complex fracture networks. Energy evolution analysis shows that dissipated energy exhibits the highest correlation with creep failure, and its increment decreases first and then increases with the creep stages. Additionally, the higher the deviatoric stress and temperature, the faster the accumulation of dissipated energy, the greater the creep rate, and the more prone the coal sample is to instability. The SEM results demonstrate that higher temperatures result in larger crack openings.

Key words: deep coalbed methane, high temperature and high pressure triaxial creep, mechanical properties, dissipative energy, damage evolution

摘要： 针对深层煤层气开发中的岩体时效变形问题,通过高温高压三轴蠕变实验,揭示了深层煤岩的蠕变力学特性与能量演化规律。结果表明,深层煤岩蠕变过程中,体积变形呈现从收缩到扩容的转变,轴向、环向及体积应变增量均随温度升高而增大,且高温会导致弹性模量降低、泊松比增大,显著弱化煤岩结构。煤岩径向膨胀与体积扩容的本质是偏应力增大引发径向约束减弱及内部裂纹扩展,而高温通过弱化强度、诱发热损伤、加速蠕变累积三重机制放大变形与损伤效应。CT三维裂隙重构结果表明,高温高压耦合作用使煤样孔隙度增加89.73%,大于150 μm孔径范围的孔隙占比增加,分形维数与迂曲度同步增长揭示了复杂裂隙网络的形成机制。能量演化分析表明,耗散能对蠕变破坏敏感性最高,其增量随蠕变级别先减后增,且偏应力与温度越高,耗散能累积越快,蠕变速率越大,煤样越易失稳。扫描电镜测试结果表明,更高的温度产生的裂纹开度更大。

关键词: 深层煤层气, 高温高压三轴蠕变, 力学特性, 耗散能, 损伤演化