Pressure dependence of permeability and spectral induced polarisation (SIP)

对砂岩孔隙中载流子的输运有一个基本的认识，是利用电数据（谱激极化）推导砂岩水力输运参数的必要前提。离子在孔隙流体中的迁移将受到与岩石基质相互作用引起的极化的阻碍。相互作用的程度由许多参数控制，如盐度、孔隙流体的化学性质、矿物组成、孔隙空间的内表面和粘土矿物的阳离子交换能力。因此，电化学双层（DL）中载流子的输运在Stern层和扩散层中存在显著差异，而这两种传导过程对总电导率的贡献取决于化学参数和孔隙度、渗透率、内表面、孔隙半径分布等孔隙特有的岩石物理性质。这些参数之间相互作用的详细知识对于建立公共模型概念至关重要，这将允许将电传输参数分配给测量的SIP签名。之前在不同类型的砂岩上进行的SIP测量存在一个问题，即基本的电化学和岩石物理参数的确定非常精确，但由于砂岩的孔隙几何形状不同，无法建立与渗透率的一般相关性。因此，不同的研究小组使用不同的模型方法解释SIP光谱。这些都是根据一般的信息价值进行检验的，但是，到目前为止还不能确定一种一般的关系。但是，测量SIP的压力依赖性可以帮助解决这个基本问题，因为在这些测量中，系统岩石/孔隙流体的总化学性质将是恒定的，而变量是压力引起的孔隙度和渗透率的变化，特别是孔隙系统的互连程度。因此，只有电化学双层（EDL）的斯特恩部分和扩散部分的电荷输运的贡献会改变。因此，SIP测量的复合电导率虚部（正交分量）的变化可以与独立测量的压力相关渗透率的变化相关联。

An essential precondition for a derivation of hydraulic transport parameters of sandstones from electric data (spectral induced polarization, SIP) are a basic understanding of the transport of charge carriers in the pore space of sandstones. The mobility of ions in the pore fluid, will be hampered by polarizations caused by interaction with the rock matrix. The degree of interaction is controlled by numerous parameters like salinity, chemistry of the pore fluid, the mineralogical composition, the inner surface of the pore space and the cation exchange capacity of the clay minerals. The transport of charge carriers in the electrochemical double layer (DL) is thus in the Stern layer and the diffuse part of the double layer significantly different, whereas the contributions of the two conduction processes to the total conductivity are determined by chemical parameters and pore-specific petrophysical properties such as porosity, permeability, inner surface, pore radius distribution, etc.. A detailed knowledge of the interactions of these parameters with each other are essential to establish common model concepts, which would allow to assign the electrical transport parameters to measured SIP signatures. The problem to interpret the previously performed SIP measurements that were performed on different types of sandstones, is that the fundamental electrochemical and petrophysical parameters were determined very precise, but due to the different pore geometries of the sandstones a general correlation with the permeability could not be created. Thus various groups interpreted the SIP spectra using different model approaches. These were tested with respect to a general informational value, however, a general relationship could not be established so far. But measurement of the pressure dependence of the SIP can contribute to solve this fundamental problem, since the total chemistry of the system rock/pore-fluid will be constant in these measurements, while variables are the pressure induced changes in porosity and permeability, especially the degree of interconnection of the pore system. Consequently only the contributions of the charge transport in the Stern- and the diffuse part of the electrochemical double layer (EDL) will be changed. Thus the change in the imaginary part of the complex conductivity (quadrature component) of the SIP measurement can then be correlated with the independently measured change of the pressure-dependent permeability.