Yeltsov I.N.   Eltsov T.   Makarov A.   Nikitenko M.  

Effect of Dielectric Permittivity Distribution in Invaded Zone on Induction Log Data

Reporter: Yeltsov I.N.

The mud invasion process causes formation fluid displacement that results in changing of resistivity and dielectric permittivity distribution (electro-physical properties) of the near wellbore zone. To do a correct interpretation of electromagnetic logging data, it is necessary to take changing resistivity and dielectric permittivity parameters in the invaded area into account. The goal of this investigation is to show how near wellbore dielectric permittivity and resistivity distribution affects induction logging measurements. We simulate the process of mud invasion to obtain water saturation and salinity distributions that we use to compute distribution of electro-physical parameters in the near wellbore area. Then we estimate the influence of resistivity and dielectric permittivity on induction logging signals using induction logging data modeling. Buckley–Leverett equations for two-phase flow in porous media are used to carry out mud invasion simulation. Resistivity distributions are calculated using Archie’s equation. Dielectric permittivity distributions are calculated using the Complex Refractive Index Method (CRIM). Signals of an induction logging tool are computed using axisymmetric cylindrically layered earth model. Analysis of the computed induction tool signals shows that dielectric permittivity influence on magnetic field attenuation is higher than on magnetic field phase difference. High frequency (>1 MHz) measurements are significantly influenced by dielectric permittivity distribution of the invaded zone. The highest influence of dielectric permittivity on induction logging signals is observed in the case of low water saturation and high resistivity of drilling mud