Jack Signorelli

Finite-difference modeling of electromagnetic tool response for logging while drilling

This paper presents a 3D finite‐difference method for analyzing electromagnetic logging‐while‐drilling (LWD) tool response. The finite‐difference method is formulated with cylindrical coordinates, enabling accurate simulation of a cylindrical tool geometry. The algorithm allows the simulation of inhomogeneous media with arbitrary conductivity and magnetic permeability distributions. With the use of an irregular finite‐difference grid, a complex LWD antenna with cavities and slots is modeled accurately. Our results show that ferrite inserted in antenna slots increases the effective radiating length of the slots. The ferrite also helps reduce the eddy currents in the metal. However, it is unnecessary to use ferrite with a relative magnetic permeability greater than 200 for the particular antenna geometry considered. The slotted antenna exhibits azimuthal field variation that can be neglected for practical purposes because the variation is significant only within a few centimeters from the tools surface. Fo...