5.2.3 Azimuth Error

Drillstring magnetisation affects the observed horizontal component of the local magnetic field. A magnetic compass detects the horizontal component of the Earth’s magnetic field. The drillstring induced error, ΔBz acts along the drillstring axis and this affects the east/west component of the observed field in proportion to (Sine Inclination x Sine Azimuth). This means that the compass error increases with inclination and with increased easterly or westerly azimuth of the wellbore