Borehole Measurements of the Complex-Resistivity Dispersion Spectrum: A New Logging Method to Identify Low-Resistivity Reservoirs

Identifying low-resistivity reservoirs, which are important oil reservoirs with considerable productivity, is a real challenge to conventional electrical resistivity logging methods. For this reason, this paper introduces a new spectrum logging method for effective identification of low-resistivity reservoirs. This method measures the complex-resistivity spectrum of formation, which is sensitive to water-lled porosity without the influence of low resistivity. This paper presents the relationships between the complex-resistivity spectrum and petrophysical properties based on laboratory data. The electrode array of the prototype for borehole testing is also described. A numerical simulation was performed to study the detection characteristics of this prototype and field tests were conducted to verify the feasibility of this method. The results show that variations in water-filled porosity obtained by this method show a good fit with the actual values. Further, water saturation can be obtained for oil reservoirs, especially for low-resistivity reservoirs. This logging method provides an approach to characterize oil reservoirs that is more effective than existing methods for the case of low-resistivity reservoirs.