Water spectrum method of NMR logging for identifying fluids

摘要

A new fluid identification method by constructing water spectrum based on NMR logging was put forward after the limitations of existing nuclear magnetic resonance (NMR) fluid identification methods were analyzed. At present, differential spectrum method (DSM) and shifted spectrum method (SSM) of NMR logging are commonly used fluid identification methods. Due to the effects of fluid properties and pore structures, however, their coincidence rates of fluid identification are lower. A new fluid identification method named water spectrum construction method was developed in this study. Based on the existing acquisition mode of NMR logging, T 2 (transverse relaxation time) spectrum of long waiting time and long echo spacing in completely watered conditions was constructed from the T 2 spectrum which was measured in the mode of long waiting time and short echo spacing. And then, the types of fluids in reservoirs were identified by comparing the measured T 2 spectrum with the constructed water spectrum. This new method was applied in Nanpu sag, Bohai Bay Basin for identifying oil layers, oil-water layers, water layers, gas layers and low-resistivity oil layers. It is demonstrated that based on the water spectrum construction method, the coincidence rate of fluid identification caused by pore structures is increased and fluid identification capacity of NMR logging is improved. Water spectrum construction method is prospective for fluid identification and evaluation of complex reservoirs.