Patent ID: 6268726
Filing Date: 2001-07-31
Classification: G01N,G01V

Abstract:
A nuclear magnetic resonance (NMR) logging tool for conducting measurements of a ground formation surrounding a borehole having an axis, comprising:(a) a permanent magnet producing a static magnetic field in the formation, the direction of the magnetic field being substantially perpendicular to the borehole axis;(b) a drill collar made of nonmagnetic metal, said drill collar enclosing the magnet;(c) an antenna mounted on the outside of said non-magnetic drill collar; and(d) one or more ferrite elements installed in proximate relationship with the antenna, said ferrite elements shaping radio frequency (RF) fields generated by the antenna and compensating the magnetic field of the permanent magnet as to provide a combined magnetic field the magnitude of which being substantially rotationally symmetric within the measurement volume of the tool.