Computer-linked nuclear magnetic logging tool and method for rapidly

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 operating parameters of the coil circuit while guarding against the effects of tuning errors in the latter, viz., using a higher Q value than normal or its equivalent for the coil circuit during the initial stages of ringing of the coil at the proton precession frequency followed by establishing a lower Q value for the latter stages. Result: the effect is as if ringing is at the higher Q' value with attendent zeroing of the residual polarization, but without the consequences of slow cutoff of the decaying magnetic field introduced during ringing. Hence, the effect of error fields associated with the latter is minimized.