Method and device for determining the location of a rod fixing point

A method to determine a fixation point of a rod in a well, comprising:

• while applying a torque to the rod about a longitudinal axis of the rod, measuring the magnetic flux due to the Earth's magnetic field that passes through a first window attached to the rod at a first location and measuring the magnetic flux due to the Earth's magnetic field that passes through a second window attached to the rod at a second location, wherein the first and second locations are known with respect to a point of origin on the rod;
• while no torque is applied to the rod about the axis, measuring the magnetic flux due to the Earth's magnetic field that passes through at least one of the first or second windows or a third window attached to the rod at a third location;
• and,
• determining the fixation point of the rod relative to the point of origin as a function of the measurement of magnetic flux taken when no torque is applied to the rod and a difference between the measurements of the magnetic flux taken at the first and second locations.

A device, comprising:

• a sensor having a window for measuring magnetic flux passing through the window, the sensor being attachable to a rod situated in a well and movable to different locations along the rod;
• and,
• a processor programmed to:
• receive signals from the sensor to measure the magnetic flux due to the Earth's magnetic field that passes through the window while no torque is applied to the rod about a longitudinal axis of the rod,
• while a torque is applied to the rod about the axis, receive signals from the sensor to measure the magnetic flux due to the Earth's magnetic field that passes through the window at a first location and at a second location, wherein the first and second locations are known with respect to a point of origin on the rod, and
• determine a fixation point of the rod relative to the point of origin on the rod as a function of the measurement of magnetic flux taken when no torque is applied to the rod and a difference between the measurements of the magnetic flux taken at the first and second locations.