Pulsed nuclear magnetism tool for formation evaluation while drilling

摘要

A permanent magnet of a pulsed nuclear magnetic resonance (NMR) device is positioned within a drill collar for evaluating earth formations. In this way, the torsional and bending strengths of the drill collar are maximized with relatively little sacrifice of the magnetic moment of the permanent magnet. The resulting tool makes NMR measurements while the formation is being drilled. An antenna for producing and detecting an oscillating RF field in the earth formation is either located in a groove in the outer surface of the drill collar, or in an alternative embodiment, the drill collar itself serves as an RF antenna.