Nuclear magnetic resonance apparatus and method for geological applications

摘要

The present invention provides a nuclear magnetic resonance ("NMR") tool for determining geological properties of formations surrounding a borehole when said tool is traversed in the borehole. One embodiment of the NMR tool includes at least one permanent magnet that is disposed substantially parallel to a longitudinal axis of the tool to generate a static magnetic field at a known distance in the formation. Radio frequency magnetic field in the zone of interest is generated by passing current at a radio frequency through a linear electrical conduction path along the longitudinal axis of the tool. The frequency may be swept during operation of the tool. The return path for the RF current is through the formation. A receiver detects signals from the formation responsive to the induced radio frequency magnetic field, which are processed to provide information about a formation parameter such as the formation porosity, hydrocarbon saturation and permeability of the zone of interest. A plurality of symmetrically arranged permanent magnets may be utilized instead of a single permanent magnet. An alternative embodiment utilizes a plurality of permanent magnets to produce a static magnetic field that is substantially radial in the zone of interest.