Preventing Crushed Cables on Deep Logging Jobs, Electromechanical Cable

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Electromechanical Cable - Working Loads

When an electromechanical cable is pulled, all the components, (steel, plastic insulation and copper conductors) are stretched. As long as the elastic limit has not been exceeded, when the tension is released the cable will shrink back to its prestretched condition. However, copper has a much lower elastic limit then steel and its elastic limit will be exceeded at relatively low cable tensions.

In order to minimise problems caused by stretch of the copper conductors, we recommended that maximum working loads of Camesa electromechanical cables are kept below 50% of the breaking load of the cable.

If the cable is pulled over 50% of breaking load there is risk of overstretching the copper and causing 'Z' kinks in the conductor when the tension is relaxed. This problem is accentuated when the tension is released suddenly (such as pulling out of the cable head or shock loading associated with firing perforating guns) and 'Z' kinks are particularly likely to occur. The phenomenon of 'Z' kinks is made worse at higher temperatures because the plastic insulation is softer at elevated temperatures and this allows the copper to deform more readily.

To the best of my knowledge, no work has been done or data compiled on the effects on high frequency data transmission over cables that have been 'overstretched'. There is a possibility that the formation of 'Z' kinks or similar non-homogeneities over the length of the conductor may interfere with high speed communication. We will endeavor to monitor this as data is fed back to us from cable customers over the next few months and will let you know what problems, if any, are reported.

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Camesa, Inc · 1615 Spur 529 · P.O. Box 1048 · Rosenberg, Texas 77471 Phone: (281) 342-4494 · Fax: (281) 342-0531