Dielectric logging has evolved from a single-frequency mandrel tool in the 1970's to a multifrequency fully-articulated pad tool in the 2000's. Dielectric dispersion, the frequency-dependent dielectric property of sedimentary rocks, provides an additional dimension to petrophysical evaluation over broad frequency up to about 1 GHz. However, the interpretation of dielectric dispersion can be particularly difficult in organic shale reservoirs, often due to a variety of polarization mechanisms across a broad frequency range, and considerable uncertainties caused by complex mineralogy and organic matter.
In this paper, we present an integrated workflow including dielectric core analysis, processing of dielectric dispersion logs, and petrophysical interpretation through core-log integration. We emphasize the need for accurate matrix permittivity determination for all current interpretation methods, and explore the possibility to determine matrix permittivity directly from dielectric well log. We use dielectric core analysis to validate interpretation model and calibrate dielectric well logs. For instance, matrix permittivity can be calibrated in the lab by optimizing the dielectric constant of each mineral and kerogen. This ensures that kerogen is lump-summed with matrix for more accurate estimation of hydrocarbon volume. Multifrequency dielectric well-log data are then fitted with an appropriate mixing law or dispersion model to obtain petrophysical parameters such as water-filled porosity, salinity, textural information, and flushed-zone resistivity. In addition, we propose a new method to solve complex refractive index mixing (CRIM) equation without having to know matrix permittivity. This new Complex-Domain Analysis (CDA) method provides a verification of chosen mixing law for interpretation, and a simple way to determine matrix permittivity directly from dielectric log without a need for calculating from mineralogy. The integrated dielectric interpretation workflow and Complex-Domain Analysis (CDA) are demonstrated in two case studies in organic shale reservoirs.