Reduction of Nonmagnetic Drill Collar Length Through Magnetic Azimuth Correction Technique

Abstract

ABSTRACT Traditional compass-type surveying instruments with their ability to sense only the direction of the local magnetic field vector must be used in conjunction with appropriate lengths of nonmagnetic drill collar to ensure that the local magnetic field vector is uncorrupted by drillstring magnetization. It is now possible to compensate for the effects of drill-string magnetization and, hence, utilize much shorter nonmagnetic drill collars by using solid-state surveying instruments which use gravity and magnetic transducers. Measurements in different bottom hole assemblies show that the required nonmagnetic collar lengths can be reduced in most situations using this compensation technique. This ability to run with shorter collars has significant impact on the use of MWD tools because it allows greater flexibility in the configuration of the bottom hole assembly as well as allowing the directional sensor and other MWD sensors to be positioned closer to the bit.