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Depth Control

Length Calibration

Stretch Characteristics

Stretch Regimes
& Relative Stretch

Depth Determination

Depth Accuracy

Procedures While
Logging

Worked Depth
Control Example

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DEPTH CONTROL

WIRELINE LENGTH CALIBRATION

The wireline is accurately measured in set lengths at a defined horizontal tension. Each length is 'marked' on the cable by locally magnetizing the steel armor wires. The lengths used are typically 25 m or 100 ft intervals, and the tension used for OH logging cables is typically 1000 lbs (300 lbs for CH slim cables).

The reason for using 25 m or 100 ft lengths is that this sort of interval provides convenient benchmarks against which accurate subdivision can be based, and yet are far enough apart to retain individual identity. The 1000 lbs tension represents a tension which can be accurately controlled, represents a reasonable minimum tension encountered in average logging operation and is consistent with the manufacturer definition stretch correction charts. The entire wireline, or that length of wireline which can reasonably expected to be used in any series of operation, is marked at these constant intervals while subject to the constant tension. This marking procedure can either be conducted by hand (requiring stringent consistency, accuracy and quality control) or, as is now more widespread, using an automatic marking device.

METRIC versus ENGLISH DEPTH

Exactly the same principles are applicable in-English as in-Metric depth measurement. The only difference are the measurement units, meters and kilograms in Metric and feet and lbs. in English. The examples cited are given in meters depth and lbs. tension

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