Apparatus and Methods for Well-Bore Proximity Measurement While Drilling

An apparatus for determining a distance between a first borehole and a second borehole during drilling of the second borehole, comprising:

• a magnet on a drilling tool that rotates in the second borehole to induce a primary magnetic field in a magnetic object in the first borehole;
• a substantially stationary sensor on the drilling tool that detects a secondary magnetic field from the magnetic object responsive to the induced primary magnetic field;
• and
• a controller that determines the distance between the first borehole and the second borehole from the detected magnetic field.

A method of determining a distance between a first borehole and a second borehole, the method comprising:

• inducing a primary magnetic field in a magnetic object in the first borehole using a magnet in the second borehole rotating at a first rotational speed;
• detecting a secondary magnetic field from the magnetic object responsive to the induced primary magnetic field using a magnetometer in the second borehole rotating at same rotational seed;
• and
• determining the distance between the first borehole and the second borehole from the detected magnetic field.

An apparatus for determining a distance between a first borehole and a second borehole, the method comprising:

• a drilling tool having a magnet configured to rotate at a first rotating speed for inducing a primary magnetic field from the second borehole into a magnetic object in the first borehole;
• a sensor on the drilling tool rotating at a second rotating speed for detecting a secondary magnetic field from the magnetic object responsive to the induced primary magnetic field, wherein the first rotational speed and second rotational speed are different;
• and
• a controller that determines the distance between the first borehole and the second borehole from the detected magnetic field.