Computer-linked nuclear magnetic logging tool and method having a sham

Abstract

The present invention decreases the time needed between collection cycles of a NML tool located in a wellbore penetrating an earth formation by zeroing the effect of prior-in-time residual polarization via a surprising change in the operations, viz., using a sham polarizing cycle wherein the coil circuits permitted to ring at a Q' value higher than normal. Result: previously non-precessing components of the residual polarization undergo precession and can be subsequently scattered by the next-in-time field. Since the sham field as well as the next-in-time polarizing field are both provided with slow-rising amplitude vs. time turn-on segments, the resulting polarization existing at the start of the buildup of the fields can be easily scattered. Ultimately, all aspects of the residual polarization are destroyed whereby cyclic NML logging speed can be greatly improved.