Method and apparatus for correcting ringing in NMR signals
AssigneeBaker Hughes Incorporated
InventorsDavid R. Beard, Daniel T. Georgi
Life of this patent
Estimating the term…
Abstract
Estimates of ringing produced by short recovery pulse sequences (CPMG or modified CPMG) are used to improve the effects of ringing in a conventional CPMG or modified CPMG sequences. This is an effective method for removal of ringing when the ringing is varying over a time interval that would be spanned by a phase alternated pair of conventional sequences. By use of frequency dithering, ringing due to the excitation pulse and the refocusing pulses can be removed.
Claims34
A method for correcting signals received from an earth formation using a Nuclear Magnetic Resonance (NMR) tool in a borehole in said earth formation, the method comprising:
- (a) exciting said earth formation with a first pulse sequence having a first recovery time;
- (b) exciting said earth formation with a plurality of additional pulse sequences having a second recovery time less than said first recovery time;
- (c) determining from spin echo signals resulting from said additional pulse sequences an estimate of a non-formation signal;
- and
- (d) correcting spin echo signals resulting from said first pulse sequence using said estimate.
An apparatus for conducting logging operations in a borehole in an earth formation, the apparatus comprising:
- (a) a magnet on a Nuclear Magnetic Resonance (NMR) tool which polarizes nuclear spins in a region of interest in the earth formation;
- (b) an antenna on the NMR tool which:
- (A) excites said earth formation with a first pulse sequence having a first recovery time;
- (B) excites said earth formation with a plurality of additional pulse sequences having a recovery time less than said first recovery time;
- (c) a processor which:
- (C) determines from spin echo signals resulting from said additional pulse sequences an estimate of a non-formation signal, and
- corrects spin echo signals resulting from said first pulse sequence using said estimate.
Dependencies are inferred from the claim text.