Measurements of complex resistivity spectrum for formation evaluation

Low resistivity reservoirs usually remain undetected when conventional electrical logging techniques are used (e.g. Dual laterolog, dual induction logging, etc.), causing huge economic losses to oil companies. Resistivity, low frequency permittivity, and characteristics of dispersion can be obtained using the novel logging method and complex resistivity spectrum logging; these measurements are useful in identifying low resistivity reservoirs. [Display omitted] •Relationships between water-filled porosity and the spectrum are presented.•Measurements of the spectrum can be achieved using an electrode array.•The spectrum can provide resistivity, permittivity and dispersion information.•Water saturation could be obtained from the spectrum in borehole.•The spectrum can be used to identify low resistivity reservoirs more effectively. Low resistivity reservoirs, which are important oil reservoirs with considerable productivity, cannot be easily identified through traditional electrical logging methods. In this paper, we introduced a new logging method for effective identification of low resistivity reservoirs. The complex resistivity spectrum of sandstone layers can be obtained using this method. This paper presents the electrode array for measurements in boreholes, and the relationships between the complex resistivity spectrum and petrophysical properties. A numerical simulation was performed to study the detection characteristics of this logging tool and field tests were conducted to verify the feasibility of this method. The results show that variations in water-filled porosity obtained from this tool agree well with the actual values. Finally, water saturation can be obtained for oil reservoirs. This logging method provides a more effective approach than existing methods for the characterization of low resistivity reservoirs.