| 摘要 |
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 while guarding against the effects of tuning errors, viz., using a sham polarizing cycle wherein the coil circuit is permitted to ring at a Q' value higher than normal during the initial stages of the sham cycle followed by the establishment of a low Q thereafter. Result: the effect is as if sham ringing is at the higher Q' value, but without the consequences of slow cutoff of the decaying magnetic field introduced during ringing. Hence, the effects of error fields are minimized and previously non-precessing components of the residual polarization undergo precession and can be subsequently scattered by the next-in-time polarizing 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, any residual polarization precessing 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.
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