As unconventional water-bearing rocks, the hydraulic conductivity of weakly cemented sandstones can increase by several orders of magnitude during drainages or pumping tests, posing great challenges to water prevention and control of coal mines in northwestern China. In this study, seepage experiments on Jurassic weakly cemented sandstones were performed and the hydraulic conductivity during the seepage process was analyzed. Combined with laboratory test and theoretical analysis methods, the relation between the permeability and micropore structures was studied, and the permeability evolution mechanism of the weakly cemented sandstones was eventually clarified. According to the experimental results, the seepage process can be divided into the saturated seepage stage, the stable seepage stage, and the seepage mutation stage. The hydraulic conductivity increases as the porosity and the mercury extrusion rate increase, but there is no obvious correlation between them that can be identified. In contrast, there is a linear positive correlation between the hydraulic conductivity and the average pore-throat radius. The variation trend of the pore-throat ratio can be used as the main reference indicator for judging whether the seepage mutation occurs in weakly cemented sandstone. Based on the correlation analysis of micropore structures and the hydraulic conductivity, a seepage model of straight capillary was constructed and the theoretical permeability equations of stable seepage stage and seepage mutation stage were proposed. It is concluded that the specific permeability of weakly cemented sandstones is directly proportional to porosity and the square of the average pore-throat radius. A theoretical equation to calculate the specific permeability during the latter two stages was also presented in this paper. Theoretical calculation results are roughly consistent with actual values obtained in the experiments.

中文翻译：

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水岩相互作用下侏罗系弱胶结砂岩渗流特性试验研究

弱胶结砂岩作为非常规含水岩体，在排水或抽水试验过程中，其导水率可提高几个数量级，给西北地区煤矿的防渗水带来巨大挑战。本研究对侏罗系弱胶结砂岩进行了渗流实验，分析了渗流过程中的导水率。结合室内试验和理论分析方法，研究了渗透率与微孔结构的关系，最终阐明了弱胶结砂岩渗透率演化机制。根据实验结果，渗流过程可分为饱和渗流阶段、稳定渗流阶段和渗流突变阶段。导水率随着孔隙度和压汞率的增加而增加，但它们之间没有明显的相关性可以识别。相比之下，水力传导率与平均孔喉半径呈线性正相关。孔喉比的变化趋势可作为判断弱胶结砂岩是否发生渗流突变的主要参考指标。在微孔结构与导水率相关性分析的基础上，构建了直毛细管渗流模型，提出了稳定渗流阶段和渗流突变阶段的渗透率理论方程。得出结论：弱胶结砂岩的比渗透率与孔隙度和平均孔喉半径的平方成正比。本文还提出了计算后两个阶段比渗透率的理论方程。理论计算结果与实验得到的实际值基本一致。