NUCLEAR MAGNETIC RESONANCE TOOL WITH EXTERNAL MAGNETS

摘要

Methods and systems are provided that enable logging while drilling NMR measurements to be made with a tool having magnets with positions adjustable or movable relative to each other. Such movement can affect the depth of investigation of the NMR tool. A variety of moving assemblies can be used to effectuate the movement, which can be performed either at the surface or downhole. The tool also can include a magnetically permeable member to control the magnetic field gradient.