Page 181 - Well Logging and Formation Evaluation

CHAPTER 12

HOMING-IN TECHNIQUES

Homing-in techniques are used when the position of one borehole rel-
ative to another needs to be known. Reasons why relative positions may
be important are:

• In relief well drilling for blowouts, it may be necessary to intersect one
borehole with another to enable the blowout well to be killed.
• Where survey data are unreliable, there may be a need to avoid col-
lision between boreholes or to pinpoint the location of one well in
relation to another.
• Some production/injection schemes require wells to be a fixed distance
apart.

The principal methodology available for homing in comprises electro-
magnetic and magnetostatic techniques. While there has been research in
the past on acoustic homing-in techniques, these have not been found to
be successful.

12.1 MAGNETOSTATIC HOMING IN

Magnetostatic homing-in techniques use the fact that steel placed in a
borehole usually has some remnant magnetization that causes a distur-
bance to the local magnetic field of the Earth. By running a sensitive mag-
netometer in open hole in a well close to another that has steel in it, this
magnetic disturbance may be detected. Interpretation of the magnetic field
detected as a function of depth can, in some cases, yield an accurate esti-
mate of the distance and direction of the target well. Basic limitations on
the usefulness of such methods are the generally short range over which

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