Reservoir Characterization for Isolated Porosity from Multi-Frequency Dielectric Measurements

Abstract

Due to processes of geological diagenesis, pores in rocks can be isolated from the rest of the connected pore networks. The amount and spatial distribution of isolated pores can have direct effect on petrophysical properties and performance of the reservoir. This paper introduces a new methodology to quantify the isolated porosity of heterogeneous reservoirs from multi-frequency (dispersion) dielectric measurements. Based on numerical simulation studies, digital rock physics techniques are used to generate rock models with different isolated porosities. 3D dielectric dispersion modeling is then performed on the models to obtain the dispersion of rock’s dielectric constant. Dielectric dispersion behaves differently as the pore connectivity changes due to increase in isolated porosity. Dielectric constant is sensitive to frequency when pores are isolated, while insensitive to frequency when pores are connected. Variation of dielectric constant is strongly related to the amount of isolated pores. For rocks having the same total porosity, their dielectric constant increases as the isolated porosity increases. This enhancement of dielectric constant is attributed to the increase in pore network tortuosity, resulting in increased accumulations of electric charges at the interfaces between solid and pores. Analytical relationships are developed to correlate isolated porosity with the rate of permittivity change and/or the permittivity ratio, derived from the dispersion of dielectric constants. The validity and applicability of the established method are demonstrated by the agreement of predicted isolated porosity with the true values used in building the rock models. Potentially, this method can be used for enhancing reservoir characterization with modern multifrequency dielectric logs.