A full investigation of nonmagnetic drill collars was undertaken to check whether these collars induce significant errors in magnetic directional survey instruments which are positioned within the collar during measurement. Laboratory determinations of magnetic permeability and saturation remanence were made on samples taken from the collars, and field inspections were carried out on new and used nonmagnetic drill collars. Twenty per cent of all the nonmagnetic collars examined were found to be magnetised by differing amounts. Theoretical estimates of magnetic compass deviation due to 1. (a) the permeability of the nonmagnetic drill collar, and 2. (b) the permanent magnetisation of a section of the collar, are included in separate appendices. © 1979.
|Number of pages||13|
|Publication status||Published - Sep 1979|