OVERVIEW

Homing-in techniques are used when the position of one borehole relative 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 collision 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 electromagnetic 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 disturbance to the local magnetic field of the Earth. By running a sensitive magnetometer 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 estimate of the distance and direction of the target well. Basic limitations on the usefulness of such methods are the generally short range over which such disturbances may be detected (typically <15m) and the uncertain nature of the magnetization.

Since standard surveying tools, such as MWD (measurement while drilling), now possess accurate magnetometers, there...