Apparatus including multi-wait time pulsed NMR logging method for determining accurate T2-distributions and accurate T1/T2 ratios and generating a more accurate output record using the updated T2- distributions and T1/T2 ratios

摘要

When a pulsed nuclear magnetic resonance (NMR) well logging tool is traversing a wellbore, a NMR well logging method includes magnetizing the hydrogen nuclei in a formation traversed by the tool with a static magnetic field, waiting for a first period of time W.sub.1, energizing the formation with oscillating RF pulses, collecting a first plurality of spin echo signals, waiting a second period of time W.sub.2 which is different from the first period of time W.sub.1, energizing the formation with oscillating RF pulses, collecting a second plurality of spin echo signals, waiting a third period of time W.sub.3 which is different from both the second period of time W.sub.2 and the first period of time W.sub. 1, energizing the formation with oscillating RF pulses, collecting a third plurality of spin echo signals, etc. The first, second and third, etc. plurality of spin echo signals corresponding to the different wait times are input to a signal processing apparatus disposed in the tool. Window sums of spin-echo signals are computed and transmitted uphole to a surface oriented signal processing apparatus. In response to the window sums, the surface signal processing apparatus determines an apparent formation T.sub.2 -distribution for each wait time in the multi-wait time pulse sequence. The apparent T.sub.2 - distributions are used to construct a cost function. When the cost function is minimized, the surface oriented signal processing apparatus determines estimates of the true T. sub.1 /T.sub.2 ratios and intrinsic T. sub.2 -distributions of the formations being logged. The surface signal processing apparatus uses the new T.sub.2 -distribution to generate new, more accurate, output record medium.