Reversing a Line
Often an
operator will want to reverse a line end for end so that the unused portion on
the drum can be used as the outer end of the cable. This practice is not
recommended for the following reasons:
-
A
"reversed" cable can be very difficult to spool.
The reason for
the spooling difficulty lies in putting the smaller diameter section of the
cable on the drum first. This creates a bed layer with too many groves
for the unused larger diameter cable. The larger diameter unused section
just does not fit into the groves that are too close together to accommodate
it.
The used section
of the cable is typically .001"-.003" smaller in diameter than the
unused section of cable. The actual diameter difference depends on the
cable type, the severity of the usage, and the number of previous cable trips
into the hole.
-
The cable
weak point is no longer guaranteed to be at the cablehead.
The used
section of the cable may have wires that are weakened by abrasive wear and/or
by corrosion of borehole fluids. Reversing the cable is likely to put
this weakened section of cable near or at the highest field operational
tension point of the cable. This cable experiences its highest tension at the
top sheave in the derrick above the borehole. It is not a good idea to
place weakened line at this location during logging operations.
-
Corrosion
rate of the used portion is accelerated due to the unused portion not being
flexed during normal logging operation.
The winch bed
layer should never come off the drum during normal operating conditions.
If the section is cable that has been in a borehole is wound on the bed layer
of the winch, then that section of cable will have accumulated borehole fluids
have between the inner and outer armor layers. The corrosion rate of
these fluids on the armor plow steel is dramatically increased if there is no
movement between the inner and outer armor layers.
Experience
indicates that used cables, which are stored on shipping reels corrode at much
faster rates than cables that are used to log day after day. It is
believed that since there is no movement between the inner and outer armor
wires during storage that corrosion occurs continuously. Sometimes after
several months such stored cables will exhibit periodic (of drum circumference
period) cable bulges. Inspection of these bulges shows extreme rust
buildup.
-
Overlap of
previous tension-rotation profile with new tension-rotation profile.
As a new cable
is rotates depending more tension, the will have arrived put in use in the
field, its lower section on the tension to which it is subjected. The
more rotation. After 15-25 runs, the cable at a tension-rotation equilibrium.
If a cable is
reversed, the virgin section being used for the first time will acquire a
tension-rotation profile. If the logging depth is such that the previously
acquired and the new profiles overlap, there is a high likelihood that the
profiles will be different. At the intersection of the differing
tension-rotation profiles expect to experience bird caging, loose armor, and/or
high wires.
Any or all of
the above effects can be expected when a logging line is "reversed".
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