The relaxation phenomena observed in the electrical low-frequency range (approximately 1 MHz–10 kHz) of natural porous media such as sandstones are often assumed to be directly related to the dominant (modal) pore throat sizes measured, for instance, with mercury intrusion porosimetry. Attempts to establish a universally valid relationship between pore size and peak spectral induced polarization (SIP) relaxation time have failed, considering sandstones from very different origins and featuring great variations in textural and chemical compositions as well as in geometric pore space properties. In addition working with characteristic relaxation times determined in Cole-Cole or Debye decomposition fits to build the relationship have not been successful. In particular, samples with narrow pore throats are often characterized by long SIP relaxation times corresponding to long “characteristic length scales” in these media, assuming that the diffusion coefficients along the electrical double layer were constant. Based on these observations, three different types of SIP relaxation can be distinguished. We have developed a new way of assessing complex pore spaces of very different sandstones in a multimethodical approach to combine the benefits of mercury intrusion porosimetry, micro-computed tomography, and nuclear magnetic resonance. In this way, we achieve much deeper insight into the pore space due to the different resolutions and sensitivities of the applied methods to pore constrictions (throats) and wide pores (pore bodies). We experimentally quantify pore aspect ratios and volume distributions within the two pore regions. We clearly observe systematic differences between three SIP relaxation types identified previously, and we can attribute the SIP peak relaxation times to measured characteristic length scales within our materials. We highlight selected results for a total of nine sandstones. It seems that SIP relaxation behavior depends on the size difference of the narrow pore throats to the wide pore bodies, which increases from SIP type 1 to type 3.

中文翻译：

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更好地了解低频电弛豫-增强的孔隙空间表征

通常假定在天然多孔介质（如砂岩）的低频电气区域（大约1 MHz–10 kHz）中观察到的弛豫现象与测量的主要（模态）孔喉尺寸直接相关，例如，汞侵入孔隙率法。考虑到砂岩的来源非常不同，并且在结构和化学成分以及几何孔隙空间特性方面存在很大差异，试图在孔径和峰值光谱诱导极化（SIP）弛豫时间之间建立普遍有效的关系的尝试失败了。此外，使用Cole-Cole或Debye分解拟合确定的特征驰豫时间来建立这种关系还没有成功。尤其是，假设沿着双电层的扩散系数是恒定的，则具有窄孔喉的样品的特征通常是较长的SIP弛豫时间，对应于这些介质中的长“特征长度尺度”。基于这些观察，可以区分三种不同类型的SIP松弛。我们已经开发出一种新方法，可以通过多方法方法来评估非常不同的砂岩的复杂孔隙空间，以结合汞侵入孔隙率法，微计算机断层扫描和核磁共振的优势。这样，由于所应用方法对孔收缩（喉咙）和宽孔（孔体）的分辨率和敏感性不同，我们对孔空间有了更深入的了解。我们通过实验来量化两个孔隙区域内的孔隙长宽比和体积分布。我们清楚地观察到先前确定的三种SIP弛豫类型之间的系统差异，并且我们可以将SIP峰弛豫时间归因于材料中测得的特征长度尺度。我们突出显示了总共9个砂岩的选定结果。看起来SIP松弛行为取决于窄孔喉与宽孔体的尺寸差异，该差异从SIP类型1增加到类型3。