Borehole Electromagnetics –Diffusive and Propagation Transients - Wave Propagation in Drilling, Well Logging and Reservoir Applications - page 344

8.2 Conductive Mud Effects in Wireline and MWD Logging
In the following simulations, the same homogeneous medium is taken
throughout, and contour plots for total electric field strength near the transmitter
plane are given. Figures 8.6a,b show results for “coil alone” and “coil with drill
collar” in the absence of borehole mud (note the “hole” left by the steel
mandrel). Figures 8.6c,d introduce very conductive mud, which severely
attenuates the produced field. Observe how the “red glow” in Figures 8.6a,b is
no longer evident in Figures 8.6c,d. Finally, in Figures 8.6e,f, we eccenter both
“coil alone” and “coil with collar” tools in our hole containing conductive mud.
These mud-dominated results show that receiver formation responses (which
measure azimuthal averages) arise mainly from one side of the hole, a dangerous
situation which is suggestive of incorrect well log interpretation.
Figure 8.6a. “Coil alone,” no mud.
Figure 8.6b. Steel mandrel, no mud.