The effect of stress on limestone permeability and effective stress behavior of damaged samples - original data used for figures

The evolution of permeability and its effective stress behavior is related to inelastic deformation and failure mode. This was systematically investigated in Indiana and Purbeck limestones with porosities of 16% and 14%, respectively. High‐pressure compression tests were conducted at room temperature on water‐saturated samples. At relatively high confinement shear‐enhanced compaction was observed to initiate at a critical stress, accompanied by significant permeability reduction of up to a factor of ~3. Overall, the permeability reduction due to inelastic compaction in our limestones is smaller than that observed in sandstones. At relatively low confinement, dilatant failure was observed, which was accompanied by a decrease and increase of permeability in Indiana and Purbeck limestones, respectively. There seems to be a trend for the correlation between porosity and permeability changes to switch from positive to negative with increasing porosity. The void space of both limestones has significant proportions of macropores and micropores. The effective stress behavior of such a limestone with dual porosity has been documented to be different from the prediction for a microscopically homogeneous assemblage, in that its effective stress coefficients for permeability and pore volume change may attain values significantly >1. In contrast, our investigation of damaged samples consistently showed effective stress coefficients for both permeability and pore volume change with values <1. This suggests that the behavior in the damaged samples is akin to that of a microscopically homogeneous assemblage, possibly due to pervasive collapse of macropores that would effectively homogenize the initially bimodal pore size distribution.渗透率（permeability）的演化及其有效应力特性（effective stress behavior）与岩石的非弹性变形（inelastic deformation）及破坏模式（failure mode）紧密相关。本研究针对孔隙率分别为16%与14%的印第安纳石灰岩（Indiana limestone）和珀贝克石灰岩（Purbeck limestone）开展了系统探究。试验在室温条件下对饱水试样开展高压压缩试验：在较高围压（confinement）条件下，剪切增强压实（shear-enhanced compaction）会在临界应力（critical stress）下启动，伴随渗透率最高降低约3倍。总体而言，本研究中石灰岩因非弹性压实导致的渗透率降幅小于砂岩（sandstones）中观测到的结果。在较低围压条件下，试样发生扩容破坏（dilatant failure），其中印第安纳石灰岩的渗透率出现下降，而珀贝克石灰岩的渗透率则呈现上升趋势。似乎存在这样一种规律：随着孔隙率升高，孔隙率与渗透率变化之间的相关性会由正相关转为负相关。两类石灰岩的孔隙空间均包含占比可观的大孔隙（macropores）与微孔（micropores）。已有研究表明，这种具有双孔隙度（dual porosity）的石灰岩的有效应力特性与微观均匀集合体（microscopically homogeneous assemblage）的预测结果存在差异，其渗透率与孔隙体积变化（pore volume change）的有效应力系数（effective stress coefficients）可显著大于1。与之相反，本研究对受损试样（damaged samples）的测试结果始终显示，渗透率与孔隙体积变化的有效应力系数均小于1。这表明受损试样的力学特性趋近于微观均匀集合体，这可能是因为大孔隙发生了普遍坍塌，从而有效抹平了初始的双峰孔径分布（bimodal pore size distribution）。