An experimental study on the complex resistivity of fractured rock under different saturation conditions

The fracture can be a good channel for oil and gas migration, which has a great influence on the permeability of the reservoir. Therefore, it is of major significance to identify fractures and determine the characterization parameters and physical properties of fractured reservoirs. In this study, homogeneous sandstone was used to simulate different artificially fractured rocks. The fractured rock samples had different fracture widths, fracture numbers, and fracture dip angles. In addition, the complex impedance and weights of the rock samples were measured during the process of natural evaporation, and the relationships between the water saturation and the complex resistivity values at different frequencies were examined. The frequency range is 100 Hz–10 kHz. It was found that the influence effects of frequency on the resistivity, dielectric constant, and loss factor had differed among the homogeneous samples and the fractured rock sample. The fracturing had led to the resistivity index and the water saturation curves separating under the different frequencies, and the degree of the dielectric constant index and water saturation curve separation became larger. Furthermore, the influencing effects of the fracture widths, fracture numbers, and fracture dip angles mainly occurred in terms of three aspects. The first was the slope of the resistivity index and water saturation curves ( I R – S w ). The second was the slope of the dielectric constant index and water saturation curves ( I ε – S w ), and the third was the loss tangent D and water saturation S w curves.