Calculating directional drilling tool face offsets

In a method for determining an offset angle between a directional tool reference point for tool face and a high side of a bent sub, including securing an instrument housing of the directional tool having a magnetometer onto a drill string, the improvement comprising:

• (a) placing a locater on the instrument housing to indicate a position of the magnetometer in the instrument housing;
• (b) placing a line on the instrument housing to mark an orientation of the high side of the bent sub;
• (c) positioning a magnetic source adjacent the magnetometer at a pre-selected angular orientation relative to the line;
• (d) measuring a magnetic induction using the magnetometer before and after the magnetic source is positioned according to step (c) and recording the magnetic induction readings;
• (e) processing the magnetic induction readings obtained in step (d) to determine the offset angle between the directional tool reference point and the high side of the bent sub;
• and
• (f) moving the magnetic source away from the magnetometer;
• and
• (g) adding the offset angle as a signed number to a sensor tool face to obtain a bent sub tool face.

In a method for determining an offset angle between a directional tool reference point for tool face and a high side of a bent sub for directional drilling of a well including securing an instrument housing of the directional tool having a magnetometer onto a drill string, the improvement comprising:

• (a) placing a marker on an outside of the instrument housing to indicate a position where the magnetometer is located;
• (b) drawing a line from the bent sub to the marker to mark an orientation of the high side of the bent sub;
• (c) positioning a magnetic source adjacent the magnetometer and orienting the magnetic source such that a magnetic field vector at the magnetometer is substantially aligned in a direction of a section line defined from the center of the instrument housing to the line drawn in step (b);
• (d) measuring a magnetic induction using the magnetometer before and after the magnetic source is positioned according to step (c) and recording the magnetic induction readings;
• (e) processing the magnetic induction readings obtained in step (d) to determine the offset angle between the directional tool reference point and the high side of the bent sub;
• and
• (f) adding the offset angle as a signed number to a sensor tool face to obtain a bent sub tool face.

A method for determining an offset angle between a directional sensor reference point for tool face and an orientational reference point including an instrument housing having a magnetometer, comprising:

• (a) positioning a magnetic source adjacent the magnetometer at a pre-selected angular orientation relative to the orientational reference point;
• (b) measuring a magnetic induction using the magnetometer before and after the magnetic source is positioned according to step (a) and recording the magnetic induction readings;
• and
• (c) processing the magnetic induction readings obtained in step (b) to determine an offset angle between the directional sensor reference point and the orientational reference point.