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Well Conditions
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The Temperature Rating of Well Logging Cables

Temperature, Well Conditions, and Cable Dynamics

The Camesa temperature ratings are in excess of the recommended maximum temperatures specified by the plastic manufacturers. From years of operational experience with these cables we are confident that they can perform at the rated temperatures without loss of electrical insulation. However, it is important to understand how well conditions and type of service can influence performance of the cable.

In all contrahelically armored cables, as tension increases, so does the compressional force of the armor layers upon the core. The higher the tension, the higher the compressional force. The amount of space or gap between inner armor wires is a function of cable design and is usually chosen to be very small. The typical inner armor coverage in Camesa cables is around 98%. Therefore, the plastic is tightly contained within the inner armor package. At higher temperatures, plastic insulation softens and can more easily change shape or move outside of the core (through the small gaps in the inner armor wires.)

First, examine the stresses within a wireline cable that has been run to bottom in a typical well. At the greatest depth, well temperature is usually the highest and therefore plastic insulation is softest. But, the tension in the cable is at it's lowest point just above the cablehead and is a function of the weight of the logging tool or perforating gun plus the drag force added as it is pulled out of the well. This tension is typically 10-15% of the fixed ends breaking strength of the cable. Therefore, there is less compressional force to move the plastic outside the core, and less chance that an electrical short will occur.

At the same time in this well, the portion of the cable at the surface is under high tension. Tension at surface is a function of cable weight, logging tool weight, and total cable and tool drag. However, the temperature at surface is usually low, or approximately surface ground temperature. Therefore, the plastic is not soft, and despite the high compressional force of the armor layers, is not as likely to move outside the core and cause an electrical failure.

Therefore, cable maximum temperature can be rated at a higher value than that given by the plastic supplier, due to the fact that high cable tension and high well temperature do not always occur together, and cables are designed with high inner armor coverage.

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