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Introduction

Terms
Specifications

Cable
Construction

Portable Marking
Unit

Stationary Drum
1 Capstan

Stationary Drum
2 Capstan

Steps to Good
Cable Care

Calculating
Pull-Out Point

Rehead Strenght
Calculations

Specific Gravity
Weight and Pressure
Table

Calculating
Stuck Point

When Tool or
Cable is Stuck

Steps to Find
Stuck Point

Eliminating Errors

Things to check

Back to Manual Menu

CABLE CARE

Calculating Pull-Out Point:

We need to know (calculate) the strength of each and every rehead we do. There are two basic reasons why we must calculate our rehead strength: a) we want the maximum strength possible in the head to retrieve stuck tools and b) we must be able to pull the rope socket into or part the tension link without over straining and damaging the cable. Without knowing the amount of strain it will take to pull out of the head we may pull out at much less or much greater strain than expected. In fact at times too much strength in the cable head has caused us to permanently damage cables.

• Deep wells require lesser head strengths because of the heavier loads applied by cable weight.
    

• Smaller diameter cables require lesser head strengths because their lower cable breaking strength.
    

• Worn cables require lesser head strength because of their weakened conditions.
    

• The end result, the reason to calculate and know your rehead strength is to be able to pull out of the head (when necessary) without causing permanent, irreparable damage to the cable.

To be able to calculate the correct rehead strength, we must have some information about our cable. The First thing we will need to know is exactly what kind and type of cable is on the unit. Then it is a simple matter of checking the manufactures data chart for data needed. The information needed from the manufactures data sheet is:

1. Cable total breaking strength.
     

2. Individual strand breaking strength.
     

3. Cable weight per thousand feet.

We also need to know, tool string weight and total depth of the well that we will be running the rehead in.

After gathering the needed information, the next step is to determine the percentage for the cables' elastic limit. The elastic limit of a cable is, maximum amount of strain the cable can withstand without suffering permanent, irreparable damage. Elastic limit is a certain value that can be calculated from the cables total breaking strength. For all calculations we will use 60% of Cable Total Breaking Strength.

To calculate the elastic limit of a particular cable find the cable's total breaking strength and multiply by 60%.

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