Response of tilted coil antennas in eccentric boreholes

Well-logging tools employing tilted coil antennas have been proposed to provide azimuthal sensitivity in borehole problems. This is particularly useful in instances such as deviated drilling for oilfield exploration. During the well-logging process however, the logging tool is often not perfectly aligned with the borehole due to mechanical vibrations and/or gravitational pull effects. This leads to an eccentric borehole problem. We extend a pseudo-analytical formulation originally developed for point sources (Lovell, J.R. and Chew, W.C., IEEE Trans. Geosci. Remote Sens., vol.25. no.6, p.850-8, 1987) and later to loop sources (Hagiwara, T. et al., SPE Annual Technical Conf. and Exhibition, 2003) in concentric boreholes, to study the response of logging tools employing tilted coil antennas in eccentric boreholes. This formulation is useful as a tool to assess, for example, the impact of the eccentricity on the geo-steering capabilities of well-logging directional resistivity tools (DRT) used in oilfield exploration. The results show very good agreement against brute-force 3D FDTD simulations.