Mechanical damage and resultant permeability evolution during compaction of highly porous reservoir rocks have strong implications on the extraction of mineral and energy resources. Laboratory Experiments can be performed to quantify this effect; however, the effect of size on these processes and the information they provide need to be evaluated before any conclusion can be drawn. As part of this study, conventional triaxial compression tests under different confining pressures were carried out on large samples (30 mm diameter and 60 mm length). These experiments were compared to the same setup for small samples with 12.7 mm diameter and 25.4 mm length which allowed monitoring of the pore structure changes through the use of an X-ray transparent triaxial cell at constant confining pressure. Both scales showed a similar mechanical response. The large-scale experiments were used to investigate the transition from brittle to ductile deformation, and the small-scale experiments allowed detailed investigation of the microstructural changes affecting the permeability evolution. The permeabilities of the specimens were continually measured during the triaxial loading at both scales. At defined increasing axial strain levels, the small sample was imaged using X-ray computed tomography (XRCT) and internal structural changes were mapped. A series of digital rock analysis techniques and Pore Network Modelling allowed accurate analysis of the evolution of the microstructure and its effect on permeability evolution using Pore Network Models. An XRCT-based, microstructurally enriched, continuum model successfully describes the permeability evolution measured during triaxial testing. Self-organized criticality of the propagating front of compaction was also shown by R2 values > 0.95 for a double Pareto fractal scaling law. Both approaches, as well as the macroscale experiments, confirmed a phase change in permeability at ~ 5% axial strain which provided a solid basis for microstructurally enriched assessment of the dynamic permeability.

中文翻译：

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压实碳酸盐渗透率的动态演变：相变和临界点

高孔隙度储层岩石压实过程中的机械损伤和由此产生的渗透率演变对矿产和能源资源的开采具有重要意义。可以进行实验室实验来量化这种影响；然而，在得出任何结论之前，需要评估规模对这些过程及其提供的信息的影响。作为这项研究的一部分，在不同围压下对大样品（直径 30 毫米，长度 60 毫米）进行了常规三轴压缩试验。将这些实验与直径为 12.7 毫米、长度为 25.4 毫米的小样品的相同设置进行比较，这允许通过在恒定围压下使用 X 射线透明三轴池来监测孔隙结构的变化。两种量表都显示出相似的机械反应。大规模实验用于研究从脆性变形到韧性变形的转变，小规模实验用于详细研究影响渗透率演化的微观结构变化。试样的渗透率在两个尺度下在三轴加载期间连续测量。在定义的增加的轴向应变水平下，使用 X 射线计算机断层扫描 (XRCT) 对小样本进行成像，并绘制内部结构变化图。一系列数字岩石分析技术和孔隙网络建模允许使用孔隙网络模型准确分析微观结构的演变及其对渗透率演变的影响。基于 XRCT 的、微观结构丰富的连续模型成功地描述了三轴测试期间测量的渗透率演变。对于双帕累托分形标度定律，R2 值 > 0.95 也显示了压实传播前沿的自组织临界性。两种方法以及宏观实验都证实了约 5% 轴向应变下渗透率的相变，这为动态渗透率的微观结构丰富评估提供了坚实的基础。