This study employed a comprehensive approach utilizing X-ray diffraction, scanning electron microscopy (computed), computed tomography (CT) three-dimensional scanning, uniaxial compressive testing, acoustic emission (AE), and digital image correlation to investigate the micromorphology, mechanical properties, macro–microscopic fractal characteristics, failure modes, and mineral composition changes in acid–base coal samples from underground reservoirs. The findings from this study indicate that, in acidic environments, calcite undergoes acidolysis to form calcium chloride (CaCl₂), whereas kaolinite reacts with alkaline substances to produce albite (Na₂Al₂Si₂O₈). The average elastic modulus of the coal samples treated with strong acids or alkalis decreased by 51.08% and 38.17%, respectively, when compared to the naturally dried samples. After strong acid treatment (pH = 2), the post-peak modulus decreased to its lowest value of 1.78 GPa. The fracture threshold in the plastic phase of the acidic coal samples decreased by approximately 60% when compared to that of the naturally dried samples, with the cumulative AE energy reaching a maximum of 2.46 × 10¹⁰ aJ. CT image segmentation revealed that with higher H⁺ concentrations, the sliced fracture fractal dimension increased from 1.01 to 1.25, indicating enhanced fracture disorder. The evolution of the spatial and energy fractal dimensions of the AE, analyzed using the box-counting method and correlation dimension, showed that in strong acidic and alkaline environments, the spatial fractal dimension before the peak failure was higher, pre-disposing the formation of highly disordered and smaller-scale fractures. During the fracture development stage, the time-series energy correlation dimension of the acid–base coal samples experienced two significant fluctuations, with a rapid decrease before the peak, indicating a transition from disorderly expansion to orderly fracturing. In the final stage of fracturing, the strongly acidic samples predominantly developed microcracks. The stronger the acidity or alkalinity, the more likely it is that high-energy (greater than 10⁴ aJ) AE shear events will occur, with the mixed mode of tensile and shear failure tending to concentrate in the areas of high shear strain, thereby enhancing the macroscopic fragmentation orderliness. This research is crucial in regard to the safety assessment of dam bodies or coal pillars in acidic and alkaline coal mines in Northwestern China, particularly for predicting their stability.

本研究采用综合方法，利用 X 射线衍射、扫描电子显微镜（计算）、计算机断层扫描 (CT) 三维扫描、单轴压缩测试、声发射 (AE) 和数字图像相关性来研究微观形态、机械性能地下储层酸碱煤样的宏观-微观分形特征、破坏模式和矿物成分变化。这项研究的结果表明，在酸性环境中，方解石经历酸解形成氯化钙（CaCl ₂），而高岭石与碱性物质反应生成钠长石（Na ₂ Al ₂ Si ₂ O ₈）。与自然干燥的煤样相比，经过强酸或强碱处理的煤样的平均弹性模量分别下降了51.08%和38.17%。经过强酸处理（pH=2）后，峰后模量降至最低值1.78 GPa。与自然干燥样品相比，酸性煤样塑性相的断裂阈值降低了约60%，累积AE能量达到最大值2.46×10 ¹⁰  aJ。 CT图像分割显示，随着H ⁺浓度的升高，切片裂缝分形维数从1.01增加到1.25，表明骨折紊乱程度增强。利用盒数法和相关维数分析了AE的空间分形维数和能量分维数的演变，表明在强酸和强碱环境下，峰失效前的空间分形维数较高，有利于形成高度无序和较小规模的裂缝。在裂缝发育阶段，酸碱煤样的时间序列能量关联维数经历了两次显着波动，峰值前迅速下降，表明由无序扩张向有序裂缝转变。在压裂的最后阶段，强酸性样品主要发育微裂纹。酸性或碱性越强，越容易发生高能（大于10 ⁴  aJ）AE剪切事件，拉伸和剪切混合破坏模式往往集中在高剪切应变区域，从而增强宏观碎片有序性。这项研究对于西北地区酸性和碱性煤矿坝体或煤柱的安全评估，特别是预测其稳定性至关重要。