不同温度围压循环加卸载下砂岩渗透特性的试验研究

Experimental study on sandstone permeability under cyclic loading and unloading of temperature and confining pressure

  • 摘要: 为探索温度和围压周期性变化对深部岩石渗透特性的影响,采用Rock Top多场耦合试验仪,对25、50、75、90 ℃不同实时温度下砂岩开展了围压循环加卸载渗流试验,分析了围压循环加卸载过程中温度对砂岩渗透特性的影响,并探讨了不同温度下砂岩微观结构特征及其对渗透特性的影响。试验结果表明:(1)在不同温度或围压条件下,砂岩的渗透率损失随循环次数的增加而减少,且主要损失发生在初始加卸载阶段。(2)初始加载过程中,砂岩渗透率对温度变化的响应程度低于对围压变化的敏感性,而在后续加卸载阶段,岩石渗透率对温度的影响则超过了对围压的影响。(3)在较低温度(50、75 ℃)作用下,孔隙和微裂纹的密实程度较高,形成的新生裂纹较少;在较高温度(90 ℃)作用下,裂纹数量增加,出现明显的贯通裂纹,这是导致砂岩渗透率发生变化的根本因素。研究结果可为深部矿井工程的稳定性研究提供参考。

     

    Abstract: This study investigates the coupled effects of cyclic temperature and confining pressure variations on the permeability evolution of deep sandstone through a series of multi-physical field experiments conducted using the Rock Top multi-field coupling test system. Cyclic loading-unloading seepage tests were performed at real-time temperatures of 25, 50, 75, and 90 ℃ to systematically analyze the thermo-mechanical interactions governing permeability characteristics, alongside microscopic structural analysis to elucidate underlying mechanisms. Results show that under constant temperature conditions, sandstone permeability follows a consistent trend with confining pressure changes: permeability decreases as confining pressure increases and rises as confining pressure decreases. Moreover, within the same confining pressure loading-unloading cycle, permeability during loading is consistently higher than during unloading, with permeability and confining pressure exhibiting an exponential relationship. Under constant confining pressure, permeability initially decreases then increases with rising temperature, displaying a two-stage characteristic, and also follows an exponential function with temperature. Permeability loss diminishes with increasing confining pressure and reduces progressively with cycle number. Under varying confining pressures, permeability loss first decreases and then increases as temperature rises, while also decreasing over successive cycles. Additionally, regardless of temperature or confining pressure, permeability loss is mainly concentrated in the initial loading-unloading stage, accounting for approximately 60% of total loss. Under combined temperature and confining pressure variations, sandstone permeability loss steadily decreases with increasing loading-unloading cycles. The most significant reduction occurs during the first loading phase, driven by rapid pore compaction and microcrack closure, while subsequent cycles show diminishing permeability changes as the rock structure stabilizes. The permeability response reveals distinct sensitivities: during initial loading, confining pressure dominates permeability reduction through mechanical compression; in later cycles, temperature becomes predominant—with thermal expansion and microcrack propagation (notably above 75 ℃) mitigating compaction effects, leading to a transition from permeability reduction to potential recovery at 90 ℃ where interconnected crack networks form. Microstructural analysis via SEM and CT indicates that lower temperatures (50–75 ℃) mainly promote pore densification with limited new cracking, resulting in sustained permeability decline. Conversely, 90 ℃ induces extensive intergranular cracking and fracture coalescence, fundamentally altering flow pathways and increasing permeability despite cyclic loading. Further analysis under constant temperature confirms an exponential relationship between permeability and confining pressure. Due to hysteresis, permeability during loading consistently exceeds that during unloading at equal pressures. Under constant pressure, permeability exhibits a two-stage exponential response to temperature—initially decreasing (25–75 ℃) as thermal expansion closes microcracks, then increasing (≥90 ℃) as thermal cracking dominates. Quantitative data reveal permeability loss decreases with both increasing pressure and cycle number, with approximately 60% of total loss occurring in the first cycle. Pearson correlation coefficients verify the transition of controlling factors from confining pressure (early cycles) to temperature (later cycles). Microscopically, 50–75 ℃ reduces crack apertures to less than 1 μm via grain rearrangement, while 90 ℃ generates pervasive crack networks exceeding 10 μm in width, explaining permeability rebound. This study establishes quantitative relationships between thermo-mechanical conditions and permeability evolution, providing direct implications for stability evaluation in deep mining engineering involving temperature-pressure cycling—especially for ventilation design, water intrusion prevention, and support system optimization. The experimental methodology and identified temperature-pressure-permeability thresholds offer valuable references for similar sedimentary rocks in geoengineering applications. Future research should consider mineral composition effects and undertake larger-scale validation.

     

/

返回文章
返回