WELL LOGGING METHOD AND APPARATUS INVOLVING ELECTROMAGNETIC WAVE PROPAGATION PROVIDING VARIABLE DEPTH OF INVESTIGATION BY COMBINING PHASE ANGLE AND AMPLITUDE ATTENUATION

摘要

An electromagnetic wave propagation well logging system (Fig. 3) measuring dielectric constant and/or formation resistivity (conductivity) includes three transmitters (T1) and a pair or receivers (R1 and R2). The receiver pair (R1 and R2) is connected to circuitry that measures the amplitude ratio (60) between the receivers, as well as the phase angle difference (62) between the receivers. Signal representative of the detected amplitude ratio and of the detected phase angle difference are combined (84) in such a manner as to make the depth of investigation controllable. Methods are also disclosed for maintaining a common depth of investigation as the well logging instrument traverses the earth borehole.