A new combined measurement method of the electromagnetic propagation resistivity logging

The electromagnetic propagation resistivity logging (EPRL) tool comprises one transmitter and a pair of receivers and measures the phase difference and the amplitude ratio (sometimes referred to as attenuation) across two receivers. Generally, the spatial response characteristics of the phase difference and the amplitude ratio can be summarized as follows: the amplitude ratio has large sensing volume and very low resolution than the phase difference. In this letter, a combined measurement method of the phase difference and the amplitude ratio (CPA) for EPRL is put forward by defining a new mathematical expression about the amplitude ratio. In this new mathematical expression, a so-called measure angle is introduced. By changing the measure angle, the CPA can provide a good tradeoff between the sensing volume and the resolution in the spatial response characteristics. Furthermore, the change of CPA curves that vary with the measure angle can be used to provide an alternative measurement which appears to be more applicable than the amplitude ratio.