Complex Resistivity Dispersion Characteristics of Water-Bearing Coal Based on Double Cole-Cole Model

Reservoir fracture evaluation is an important research topic in the coalfield. In recent years, complex resistivity (CR) has been widely used in oil logging and achieved good results, such as permeability evaluation, water saturation (Sw) prediction, and aquifer identification. Therefore, the method has the potential to evaluate coal seam fracture. In the experiment, the real partRand imaginary partXof bituminous and anthracite coal with different Sw were measured by the impedance measuring instrument, then theDouble Cole-Colemodel was used to fit experimental data and analyze conductive mechanism. The main results are as follows: (1) the dispersion of CR parameters Reρand Imρis closely related to the metamorphism degree, frequency, and Sw; (2) induced polarization is the fundamental reason for the variation of coal samples’ complex resistivity parameters with frequency change; and (3) theDouble Cole-Colemodel agrees well with the experimental data, and the model parametersm₁andτ₂are strongly correlated with Sw. The parametersm₁andτ₂can be used to evaluate the Sw of fractures in coal seams and thus to evaluate the effect of hydraulic fracturing.

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