High resolution continuous depth positioning in a well bore using persistent casing properties

1. A method of deriving measurement indicia between casing collars of at least one pipe segment of a casing in a well bore, comprising:

obtaining intermediate characteristic signals along the length of the pipe segment between the casing collars by sensing variations in innate, persistent and unaltered characteristic properties of the one pipe segment existing continuously along its length between the casing collars;

distinguishing the intermediate characteristic signals from other signals created by intentionally introduced physical alterations in the pipe segment between the casing collars; and

using the intermediate characteristic signals as indicia of the length of the one pipe segment between the casing collars.

2. A method as defined in claim 1 , further comprising:

dividing the length of the one pipe segment into divisions; and

correlating the intermediate characteristic signals to the divisions.

3. A method as defined in claim 1 , used to position a downhole tool at a desired location between the casing collars of the one pipe segment, further comprising:

selecting a predetermined aspect of the intermediate characteristic signals which corresponds to the desired location; and

moving the downhole tool to the desired location by reference to the predetermined aspect of the intermediate characteristic signals.

4. A method as defined in claim 3 , further comprising:

moving the downhole tool while sensing the variations in the characteristic properties of the one pipe segment to obtain the intermediate characteristic signals which include the predetermined aspect.

5. A method as defined in claim 3 , used to perform a downhole function at the desired location, further comprising:

moving the downhole tool to the desired location using the predetermined aspect of the intermediate characteristic signals; and

performing the downhole function with the downhole tool at the desired location by reference to the predetermined aspect of the intermediate characteristic signals.

6. A method as defined in claim 5 , wherein the intermediate characteristic signals include amplitude variations occurring along the length of the one pipe segment and the predetermined aspect constitutes a selected amplitude variation of the intermediate characteristic signals.

7. A method as defined in claim 5 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.

8. A method as defined in claim 3 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.

9. A method as defined in claim 1 , used with a base cased hole log that establishes locations within the casing including a desired location along the one pipe segment between the casing collars, further comprising:

correlating a predetermined aspect of the intermediate characteristic signals to the desired location described in the base cased hole log.

10. A method as defined in claim 9 , further comprising:

creating a continuous indicia depth measurement log from the intermediate characteristic signals obtained along the length of the one pipe segment between the casing collars; and

correlating predetermined aspects of the intermediate characteristic signals of the continuous indicia depth measurement log to depth locations of the base cased hole log along the length of the one pipe segment.

11. A method as defined in claim 10 , further comprising:

correlating at least one predetermined aspect of the intermediate characteristic signals of the continuous indicia depth measurement log to the desired location described by the base cased hole log at which one of a downhole tool is to be positioned or a downhole function is to be performed.

12. A method as defined in claim 11 , wherein:

the variations in the characteristic properties are variations the magnetic permeability of the one pipe segment.

13. A method as defined in claim 9 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.

14. A method as defined in claim 10 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.

15. A method as defined in claim 14 , further comprising:

using a computer executing software instructions to automatically correlate the depth locations of the base cased hole log and the intermediate characteristic signals of the continuous indicia depth measurement log.

16. A method as defined in claim 1 , used to perform a downhole function at a desired location in the casing which is described by a previously-existing base cased hole log, further comprising:

correlating a predetermined aspect of the intermediate characteristic signals to the desired location described in the base cased hole log.

17. A method as defined in claim 16 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.

18. A method as defined in claim 1 , wherein the casing is described by a base cased hole log that establishes locations along the casing including a desired location between the casing collars of the one pipe segment, further comprising:

performing a first downhole function at the desired location by reference to the base cased hole log;

waiting for a predetermined time to lapse after performing the first downhole function;

obtaining the intermediate characteristic signals after the time lapse;

correlating a predetermined aspect of the intermediate characteristic signals to the desired location in the base cased hole log; and

performing a second downhole function after the time lapse at the same location where the first downhole function was performed by reference to the predetermined aspect of the intermediate characteristic signals.

19. A method as defined in claim 18 , further comprising:

creating a continuous indicia depth measurement log from the intermediate characteristic signals; and

performing subsequent downhole functions at the same desired location where the first and second downhole functions were performed by reference to the predetermined aspect of the intermediate characteristic signals of the continuous indicia depth measurement log.

20. A method as defined in claim 18 , further comprising:

performing the first downhole function as a plurality of first gravity measurements at a corresponding plurality of the desired locations which are spaced apart along the length of the one pipe segment;

identifying each of the plurality of the desired locations of the first gravity measurements by respectively different predetermined aspects of the intermediate characteristic signals obtained after the time lapse; and

performing the second downhole function as a plurality of second gravity measurements at the plurality of the desired locations by reference to the respective predetermined aspects of the intermediate characteristic signals obtained after the time lapse.

21. A method as defined in claim 20 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.

22. A method as defined in claim 18 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.

23. A method as defined in claim 1 , used to perform first and second downhole functions at the same desired location, further comprising:

obtaining a first set of intermediate characteristic signals;

performing a first downhole function within the one pipe segment at a desired location identified by a predetermined aspect of the first set of intermediate characteristic signals;

waiting for a predetermined time to lapse after performing the first downhole function;

obtaining a second set of intermediate characteristic signals after the time lapse, the first set of intermediate characteristic signals constituting earlier-obtained intermediate characteristic signals and the second set of intermediate characteristic signals constituting later-obtained intermediate characteristic signals;

identifying the predetermined aspect of the later-obtained intermediate characteristic signals which correlates to the predetermined aspect of the earlier-obtained intermediate signals; and

performing the second downhole function at the same desired location as the first downhole function by reference to the predetermined aspect of the later-obtained intermediate characteristic signals.

24. A method as defined in claim 23 , further comprising:

creating a continuous indicia depth measurement log from the earlier-obtained intermediate characteristic signals; and

moving a downhole tool and performing the second downhole function with the downhole tool at the desired location by reference to the predetermined aspect of the intermediate characteristic signals of the continuous indicia depth measurement log.

25. A method as defined in claim 23 , further comprising:

creating a first continuous indicia depth measurement log from the earlier-obtained intermediate characteristic signals;

creating a second continuous indicia depth measurement log from the later-obtained intermediate characteristic signals; and

correlating the first and second continuous indicia depth measurement logs.

26. A method as defined in claim 25 , further comprising:

using the predetermined aspect of the first continuous indicia depth measurement log to perform the first downhole function at the desired location; and

using the correlated predetermined aspect of the second continuous indicia depth measurement log to perform the second downhole function at the same desired location where the first downhole function was performed.

27. A method as defined in claim 25 , further comprising:

using a computer executing software instructions to automatically correlate corresponding predetermined aspects of the first and second continuous indicia depth measurement logs.

28. A method as defined in claim 25 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.

29. A method as defined in claim 23 , further comprising:

performing the first downhole function as a plurality of first gravity measurements at a plurality of desired locations which are spaced apart along the length of the one pipe segment;

identifying each of the plurality of desired locations of the first gravity measurements by respectively different predetermined aspects of the earlier-obtained intermediate characteristic signals; and

performing the second downhole function as a plurality of second gravity measurements at a plurality of desired locations which are identical in position to the desired locations of the plurality of first gravity measurements by reference to corresponding predetermined aspects of the earlier-obtained and later-obtained intermediate characteristic signals.

30. A method as defined in claim 29 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.

31. A method as defined in claim 23 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.

32. A method as defined in claim 1 , wherein:

the variations in the characteristic properties are variations in the magnetic permeability of the one pipe segment.