Analysis of a guided wave along a conducting structure in a borehole
S. Ebihara, M. Sato and H. Niitsuma
Journal name: Geophysical Prospecting
Issue: Vol 46, No 5, September 1998 pp. 489 - 505
Info: Article, PDF ( 5.49Mb )
A guided wave along a borehole is often observed in borehole radar measurements. These guided waves deform the antenna pattern and can cause artefacts in radar measurements. A water-filled borehole or a conducting logging cable can function as a waveguide for electromagnetic waves under some conditions. We describe the theoretical characteristics of such a guided wave in a borehole and compare them with our experiments. The measured signal discussed was obtained with a directional borehole radar. This radar uses a cylindrical conformal array antenna as receiver and is a model of a conducting structure in a borehole. The induced field around the borehole was compared with the theory. The most fundamental symmetrical and asymmetrical modes were TM01 and HE11, and they were identified in the measured signals using time–frequency distribution analysis and by observation of the azimuthal field distribution of the magnetic field.