Evaluation method of tight sandstone reservoir saturation based on frequency domain electrical dispersion measurement data

Abstract

The traditional Archie model, which is primarily applicable to medium-high porosity and permeability sandstones, often fails to accurately characterize the the resistivity-saturation relationship in tight sandstones, and it makes the saturation evaluation face great challenges. In this paper, complex resistivity spectrum measurements across 1 kHz to 10 MHz frequencies are performed on tight sandstone reservoir cores. Then, the percentage frequency effect (PFE) values are calculated from complex resistivity modulus at 1 kHz and interfacial polarization frequency under varied saturation states. Furthermore, a new quantitative saturation evaluation model based on the normalized PFE is developed by referring to the normalization method of the resistivity index in the classic Archie formula. The results demonstrate that a good linear correlation between the PFE of the tight sandstone reservoirs and water saturation, and the new saturation evaluation model effectively eliminates electrical differences between samples due to pore structures. Experimental data from tight sandstones shows that higher accuracy of the predicted water saturation by the new saturation evaluation model against measured values compared to the predicted water saturation by the Archie model, and the normalized PFE used in this model can quantitatively evaluate water saturation of tight sandstone reservoirs instead of the traditional Archie formula. The results provide a theoretical model and experimental reference for saturation evaluation in tight sandstone reservoirs.