A multiple-depth-of-investigation electromagnetic wave resistivity sensor: Theory, experiment, and field test results

This paper presents theoretical, experimental, and field results for a multiple-depth-of-investigation, measurement-while-drilling (MWD), electromagnetic wave resistivity (EW) sensor. The sensor has four different transmitter/receiver antenna spacings with a phase difference and amplitude ratio at each spacing. The resultant logs provide information on the resistivity radial profile and an accurate R t evaluation. Comparisons of field logs with wireline logs and with theoretical and experimental results show that this type of sensor can offer an extra-shallow, shallow, medium, and deep investigation depth under most logging conditions