Patent ID: 7075298

Claim:
An improved logging method using nuclear magnetic resonance including generating a static magnetic field near a wellbore using at least one long magnet having a direction of magnetization passing predominantly perpendicular to a longitudinal axis of the long magnet, generating an excitation radio frequency field in a region in a direction perpendicular to the longitudinal axis of the long magnet and to the static magnetic field, and receiving nuclear magnetic resonance signals, the improvement comprising: wherein the long magnet used in the step of generating the static magnetic field is made of a conducting rare-earth material; and generating a separate radio frequency field which compensates for the excitation radio frequency field in the area of the long magnet by a coil mounted on the long magnet wherein said step of generating the separate radio frequency field which compensates for the excitation radio frequency field in the area of the long magnet comprises generating the separate compensating radio frequency field in a manner directed toward and equal in strength to the generated radio frequency field in the area of the long magnet.