Computer-linked nuclear magnetic logging tool and method having sham polarizing cycles for rapidly dispersing components of residual polarization associated with a prior-in-time NML collection cycle

This patent describes a method for reducing the effects of both precessing and non-precessing residual polarization as well as tuning errors during ring down as in nuclear magnetic logging (NML) operations occur so that a series of collection cycles normalized to a common depth interval can be carried out more swiftly and accurately than in conventional NML operations. The common depth interval lies within an earth formation penetrated by a wellbore adjacent to NML polarizing and detection circuitry positioned within the wellbore under control of NML computerlinked controller and recording system at the earth's surface. Entrained fluids with the common depth interval are repetitively polarized with a polarizing field (B/sub rho/) of relatively high strength at an angle to the earth's field (B/sub e/), and after the polarizing field has been cutoff, NML signals from precessing protons of fluid nuclei within the formation are detected, comprising: establishing a series of alternative Q values associated with integers M/sub 1/, M/sub 2/,..., M/sub o/ where M/sub 1/ is 1 and M/sub 0/ is greater than two for a coil circuit of the polarizing and detection circuitry. The M/sub 1/ first Q value for the coil circuit is of value that maximizes NML response after termination of the polarizing field (B/sub rho/) and ring down of the coil circuit have occurred