A laboratory study of complex resistivity spectra for predictions of reservoir properties in clear sands and shaly sands

To investigate the effect of the application of complex resistivity logging in sand-shale reservoirs, measurements of complex resistivity are performed on core plugs obtained from artificial clear sand samples and shaly sand samples with different clay types and contents in a frequency range of 40 Hz to 15 MHz. This paper discusses the relationship between the complex resistivity values of samples and their porosity, water saturation, salinity, ion type, clay content, and temperature using the Cole-Cole model to fit complex resistivity curves and obtain the model parameters R0 and tau, which represent the resistivity at zero frequency and the time constant respectively. The results show that tau has the same trend as R0 i.e., it decrease as porosity, water saturation, salinity, clay content and temperature increase. Based on the Archie model and Waxman-Smith model, the saturation evaluation model of tau is built. This study also extracts the slope of the real part of complex resistivity and explores the correlation between the slope and permeability. A model of slope can be used to predict permeability, and the model parameters are different for clear sand samples and different shaly sand samples. This study provides strong support for studies of the rock complex resistivity mechanism and the application of complex resistivity logging in oil and gas evaluation.