G - Physics – 01 – V
Patent
G - Physics
01
V
324/1.2
G01V 3/32 (2006.01) G01R 33/20 (2006.01)
Patent
CA 1259656
ABSTRACT OF THE DISCLOSURE COMPUTER-LINKED NUCLEAR MAGNETIC LOGGING TOOL AND METHOD HAVING A SERIES OF SHAM POLARIZING CYCLES FOR RAPIDLY DISPERSING COMPONENTS OF RESIDUAL POLARIZATION ASSOCIATED WITH A PRIOR-IN-TIME NML COLLECTION CYCLE AS WELL AS REDUCE TUNING ERRORS DURING RING DOWN The present invention decreases the time needed between collection cycles of an NML tool located in a wellbore penetrating an earth formation by zeroing the effect of prior-in-time residual polarization via a sur- prising change in the operations, while guarding against the effects of tuning errors, viz., using a series of sham polarizing cycles wherein the coil circuit is permitted to ring at a Q' value higher than normal during the initial stages of each 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 conse- quences of slow cutoff of the decaying magnetic field introduced during ringing. Hence, the effect of error fields are minimized and previously non-precessing compo- nents of the residual polarization undergo precession and can be subsequently scattered by the next-in-time field. Since the sham fields as well as the next-in-time polariz- ing field are all provided with slow-rising amplitude v. 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 residual polarization are destroyed whereby cyclic NML logging speed can be greatly improved.
514986
Chevron Research And Technology Company
Sim & Mcburney
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