The Dielectric Permittivity of Carbonate Formations With Different Porosity Types

Abstract

Abstract

The specific characteristic of carbonate formations is a complex pore space that includes small-scale primary pore system and large-scale secondary porosity represented by vugs, cracks and channels. We have studied the influence of the pore microstructure and saturation of pore systems on the dielectric permittivity of double-porosity formations. The calculations were carried out using the unified-model approach that is based on the simulation of different physical properties from the single microstructure model applying the symmetric variant of the effective medium approximation (EMA). A porous rock is considered as a composed material that consists of solid grains and fluid-filled pores of a small scale (primary porosity) that form a homogeneous isotropic matrix. Secondary pores of a large scale are represented by inclusions of different shapes placed in this matrix. Each component of the rock is approximated by a three-axial ellipsoid. The aspect ratios of grain and primary-pore ellipsoids are introduced as a function of porosity. The distribution of saturating immiscible fluids in a pore space is described by two models: (1) water (wetting component) is concentrated in a film attached to the pore walls while oil or gas (non-wetting component) occupies the central part of the pore; in this model a pore is considered as a layered ellipsoid with the wetting component in the outer layer; (2) the saturating fluid contains spherical drops of oil placed in the water. The results obtained for one-pore system media using the unified microstructure model, in which grain and pore shapes are functions of porosity, are in a good agreement with the experimental data and CRIM formula (Complex Refractive Index Method) for partially and 100% saturated carbonate formations. The effect of secondary pores depends on the pore shapes and values of primary and secondary porosities. However, this influence is less than in the case of electrical conductivity. In fully water-saturated formations cracks increase and vugs decrease the dielectric permittivity in comparison with a rock containing only primary porosity. The change of the dielectric permittivity due to the presence of secondary pores (vugs and cracks) increases with decreasing in total oil saturation. The results obtained demonstrate the feasibility of using the dielectric permittivity in the joint petrophysical inversion for the characterization of double-porosity carbonate formations.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016