Research and application of the relationship between transverse relaxation time and resistivity index in tight sandstone reservoir

摘要

This paper discusses the relationship among capillary pressure (PC), nuclear magnetic transverse relaxation time (T-2) and resistivity index (I). The three parameters are related to the geometry of pore structure. We use the fractal concept to describe the relationship between T-2 and I. In addition, a new T-2-I model is established. 8 Cores from tight sandstone reservoir in China are selected to do experiments. The results reveal that the cores have continuous fractal dimension characteristics. Additionally, the fractal dimensions appear great differences in the different pore radius scales. Therefore, a piece-wise fitting method is adopted. We divided the pores into macropore, mesopore and micropore. Through the verification, our T-2-I model and piece-wise fitting method are feasible. An application example is also provided in this paper. Based on our researches, we adopt NMR logging data to obtain dynamic parameters of Archie's formula b and n for calculating water saturation in Tight Sandstone Reservoir. The comparison between our method and normal method demonstrated that our model is much better at matching the core water saturation.