Frequency‐Dependent Electric Properties of Microscale Rock Models for Frequencies from One Millihertz to Ten Kilohertz
Frequency‐Dependent Electric Properties of Microscale Rock Models for Frequencies from One Millihertz to Ten Kilohertz
复制标题
频率从 1 毫赫兹到 10 千赫兹的微尺度岩石模型的频率相关电特性
DOI：
10.2136/vzj2009.0162
复制
发表时间：
2010
影响因子：
2.8
通讯作者：
N. Klitzsch
中科院分区：
文献类型：
--
作者：
J. Volkmann;N. Klitzsch
为了更好地了解实际岩石微观结构和岩石孔隙中的电解质性质如何影响光谱模式，即岩石孔隙系统极化的特征弛豫时间和极化强度，本研究通过数值生成光谱诱导极化（SIP）光谱。利用频率相关的能斯特-普朗克-泊松（NPP）离子输运方程模拟了三维孔隙系统中载流子的动力学。主要研究了考虑双电层（EDL）的两种不同尺寸的交替堆叠柱的孔隙系统模型。假设在EDL内，由于这些阳离子在岩石-水界面上的吸附增加，导致阳离子迁移率降低。利用有限元法求解NPP方程，得到复电阻率相谱。随后，研究了孔隙结构性质和电解质电导率对岩石特征电阻率相最小值的幅度和频率位置的影响。结果表明：第一，在孔隙几何方面，相最小fmin的特征频率随大孔隙长度的增加而减小；其次，同时需要具有几个德拜长度半径的小孔隙和较大的孔隙，以确保可检测的相位振幅。第三，对于电解质浓度，相位振幅与浓度成反比，而fmin保持不变。由于所研究的模型并没有提供模拟电性与孔喉大小之间的直接和唯一联系，因此需要进一步研究以确定一种令人信服的SIP解释方法来改进渗透率估计。
In this study, spectral induced polarization (SIP) spectra were generated numerically to better understand how actual rock microstructure and electrolyte properties in rock pores affect the spectral pattern, i.e., the characteristic relaxation time of polarization as well as the polarization strength of a rock pore system. The dynamics of charge carriers in three‐dimensional pore systems were simulated using a frequency‐dependent formulation of the Nernst–Planck–Poisson (NPP) ion‐transport equations. Basically, a pore‐system model of alternating stacked cylinders of two different sizes was studied considering the electrical double layer (EDL). A reduced cationic mobility—resulting from increased adsorption of these cations at the rock–water interface—was assumed within the EDL. By solving the NPP equations using the finite element method, complex resistivity phase spectra were generated. Subsequently, the effect of pore structural properties and electrolyte conductivity on the magnitude and frequency position of the characteristic resistivity phase minimum of rocks was studied. The following results were found: First, regarding pore geometry, the characteristic frequency of the phase minimum fmin decreases with increasing pore length of the large pore. Second, both small pores having a radius of a few Debye lengths combined with larger pores are needed to ensure detectable phase amplitudes. Third, with regard to electrolyte concentration, the phase amplitude is inversely proportional to the concentration, whereas fmin remains constant. Because the studied model does not provide a direct and exclusive link between the simulated electrical properties and pore throat size, further research is needed here to specify a convincing SIP interpretation method for improved permeability estimation.