| 摘要 |
<p>An NMR logging tool (20) has a conducting permanent magnet (14) with its axis parallel to the borehole axis to produce a static field (32) in a portion of the formation surrounding a borehole that is parallel to the borehole axis. A dipole RF antenna (24) with the dipole axis orthogonal to the borehole axis is used to produce an RF magnetic field orthogonal to the static field. The same antenna is used to receive the echo signals from excited nuclei in the formation. A number of gapped ferrite strips (26a, 26b, 26c) on the permanent magnet shield the permanent magnet from the RF field and enhance the RF field. Another form of the tool may be used for making Measurement-While-Drilling measurements with the permanent magnet set in a recess on a drilling collar.</p> |
