NMR well logging method using optimised rephasing pulse sequence

An NMR well logging method uses a variation of the CPMG pulse sequence in order to improve measured signal amplitude and cancel ringing caused by the initial tipping pulse. In a first embodiment, refocusing pulses R with spin tip angles substantially less than 180{ are used, which have a greater bandwidth than conventional 180{ pulses, thus exciting a greater proportion of excited spins in a region of interest. This increases the measured echo signal amplitude. There is also a power saving since shorter duration refocusing pulses are used. In a second embodiment, the wait time ts between the 90{ tipping pulse and first refocusing pulse R is reduced to less than the Can-Purcell inter-echo time tcp, which also serves to increase the amplitude of the received echo signals. In a third embodiment, a forced recovery pulse T' 260 for realigning the spins parallel to the static field may be provided at the end of the pulse sequence. This may reduce the wait time W needed between sequences. This recovery pulse may also be used to cancel the ringing caused by the initial 90{ tipping pulse.