STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

MWD and LWD 903
Naturally for operating the tool, the seal must be maintained at the point
where the cable enters the drillstring:
a. either at the top of the drillpipes, in which case the logging tool is pulled
out every time a new drillpipe length is added on;
b. or through the drillpipe wall in a special sub placed in the drillstring as
near the surface as possible, in which case new lengths are added on
without pulling out the logging tool.
Figure 4-216 shows the typical operation of a steering tool for orienting the
drill bit. The electric wireline goes through a circulating head located on top
Circulatina Head
Tool
Figure 4-216. Typical operation of a steering tool for orienting the drill bit
using a circulating head on the swivel. (Courtesy SPE [loll.)