Matrix Dielectric Permittivity for Enhanced Formation Evaluation

Abstract

Modern dielectric tools are often run to obtain fundamental formation properties, such as remaining oil saturation, water-filled porosity, and brine salinity. Techniques to extract more challenging reservoir petrophysical properties like Archie m and n parameters are also emerging. The accuracy and representativeness of the obtained petrophysical parameters depend on the input parameter accuracy, such as matrix permittivity. In carbonates, matrix permittivity is known to vary over a wide range, for example, limestone matrix permittivity reported in the literature ranges from 7.5 to 9.2. The main objective of the current study is to reduce matrix dielectric permittivity uncertainty for enhanced formation evaluation in carbonate reservoirs. All dielectric measurements were conducted on 1.5 in. carbonate plug samples by means of a coaxial reflection probe with a range of frequency between 10 MHz and 1 GHz. To calculate matrix mineral dielectric permittivity, sample porosity must be obtained. Stress-corrected helium porosity from routine core analysis is used and samples mineralogy and chemical composition are measured by X-Ray diffraction. Dielectric system calibration is done by utilizing several well-characterized standards with known dielectric properties. Calcite and dolomite matrix permittivity are assessed by laboratory measurements. Results of this study and based on data from 180 core plugs allowed to assess the validity of the defined errors by statistical analysis, resulting in much reduced uncertainties in carbonate rock matrix dielectric permittivity; thus enhancing formation evaluation using dielectric measurements. The current study provides better control on dielectric permittivity values used in dielectric log interpretation for limestone formations. Such knowledge will provide better confidence in interpreted data such as water-filled porosity, flushed zone salinity and water phase tortuosity.