AN IMPROVED MEASURING PULSE SEQUENCE FOR NMR LOGGING

A new pulse sequence for the measurement of NMR logging is proposed in this article, based on the improvement of original CPMG pulse sequence. In the orig inal pulse sequence, after a CPMG pulse sequence, wait time (or T\-1 relay) is needed to allow the magnetization vector return to equilibrium, then the ne xt me asuring CPMG pulse sequence can be applied. The wait time is kept long and the l ogging speed is low in formations that contain long T\-1 components, since t he log ging apparatus is moving continuously along the bore hole. This is unfavorable b ecause the spin-latti ce relaxation time (T\-1) of oil and gas is always long . However, it's noti ced th at if a 90° pulse from the -x direction (or a 270° pulse from the x direction ) i s applied after the former CMPG pulse sequence, the long T\-1 components can be po larized more completely, then the wait time can be shortened and logging speed c an be improved. The advantage of the improved pulse sequence is proved by calcul ations and analyses.