Experiment analysis and application on nuclear magnetic resonance logging

摘要

The transverse relaxation time (T2) distribution of nuclear magnetic resonance logging (NMR) can be used to study the pore structure of reservoir. A certain transforming relationship between the T2 distribution of NMR and the pore distribution exists in the presence of single-phase fluid. Longitudinal relaxation time (T1) and T2 tests of NMR to 33 core samples and T2 test of NMR to 6 core samples of high shale content in different echo times. Also differential spectrum analysis and shifted spectrum analysis were done to 4 core samples. The experiment shows that the relaxation time of shale bound water is rather short, and the shale bound water could be observed simultaneously or alone in the case of smaller echo spacing. The NMR signals could reflect the amount of clay bound water, and the obtained NMR porosity basically reflects the clay water signals. The NMR porosity there equals to the total porosity, which indicates that lithology hardly influences the core porosity determined by the NMR method indoors. The measured NMR porosity is smaller than the normal porosity when the shale content of the rock is high, and the deviation is related to the shale content, the higher shale content brings the bigger deviation. The diffusion effects of fluid molecules would become rather obvious along with the increasing of the echo spacing TE. The short relaxation components increase as the echo time decreases, illustrating the increasing of the detected amount of clay bound water.