Abstract: A method of directionally drilling a borehole makes use of a drilling assembly including an apparatus having an upper section with a longitudinal axis I, and a lower section having a central axis II and including at least part of a rotary drill bit, said sections being interconnected by a universal pivot mechanism. The method comprises rotating the assembly in such a manner that the upper section rotates about said longitudinal axis I and the lower section rotates about said central axis II. During at least part of the drilling operations said central axis II is tilted and rotated in an orbital mode relative to said longitudinal axis I such that a plane containing said two axes is maintained in a predetermined orientation relative to a reference direction.

Abstract: A method for eliminating the influence of drill string magnetization on an azimuth measurement made by a magnetometer package disposed in the drill string. The method comprises first eliminating the influence of the cross-axial components of the drill string magnetization by taking magnetometer readings at various angular orientations of the drill string and then eliminating the influence of the axial component of the drill string magnetization.