Core NMR experiments for low permeability reservoir and its field application

Key words:  low permeability reservoir  NMR experiment  reservoir parameter  porosity correction  acquisition parameter

Abstract:

Thanks to its obvious advantages in reservoir parameters calculating and fluid identification, the nuclear magnetic resonance (NMR) logging method is becoming popular in reservoir evaluation. In low permeability reservoirs with complicated lithology and pore structure, however, NMR logging faces problems of low signal-to-noise ratio signal and difficulty in parameter calculation of physical properties. A series of NMR simulations of samples with different fluid properties and lithologies are carried out under different acquisition parameters to recognize the characteristics and influencing factors of NMR response. An NMR porosity correction model, based on the lithology unit and simulation results, is established to improve the calculation efficiency of porosity. The results show that the NMR responses of low permeability rocks are apparently influenced by pore size, acquisition parameters such as the echo time and waiting time, as well as the fluid properties. The new calculation model of permeability, established based on the echo amplitude, does not need time-consuming inversion of the echo train, therefore greatly improves the efficiency of permeability calculation.