Eccentricity of Normal Electric Borehole Sondes with Finite Geometry

A. Galsa, and M. Herein
Eötvös University
Budapest, Hungary

Numerical calculations have been carried out to quantify the effect of the eccentric position of normal electric borehole sondes on the current density distribution and the obtained specific resistivity. In the most calculations the distorting influence of the eccentricity (distance between the axis of the borehole and the sonde) on the specific resistivity is less than 2%, but in special cases (low resistivity clayey medium, small electrode distance) it can reach 50%.

The accuracy of the simulations was verified by comparison between the numerical and analytical solutions for eccentric point-wise electrodes and was found the deviation below 0.01%. The effect of finite geometry on the geometrical coefficient was appr. 0.2% and 1.5% in case of long and short normal sondes, respectively.