| Institution: | 1.School of Geosciences,China University of Petroleum (East China),Qingdao,China;2.Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology,Qingdao,China;3.CNPC Key Well Logging Laboratory,China University of Petroleum (East China),Qingdao,China;4.Suzhou Niumag Analytical Instrument Corporation,Suzhou,China;5.Shanghai Niumag Electronic Technology Co., Ltd,Shanghai,China |
| Abstract: | Nuclear magnetic resonance (NMR) plays a significant role in porous media analysis and petroleum exploration, but its response is significantly influenced by the internal magnetic field gradient in fluid saturated porous medium, which obviously limits the accuracy of rock core analysis and logging interpretation. The influential factors of the internal magnetic field gradient in formation and its influences on NMR response are studied in this paper, based on NMR mechanism through one- and two-dimensional core NMR experiments. The results indicate that the internal magnetic field gradient is positively correlated with the static magnetic field strength and the magnetic susceptibility difference between pore fluid and solid grains, while it presents negative correlation with pore radius. The internal magnetic field gradient produces an additional diffusion relaxation in hydrogen relaxation system and accelerates the attenuation of magnetization vector. As a result, T2 spectrum shifts to the left and NMR porosity and diffusion coefficient of the fluid could be inaccurate. This research sets a foundation for the NMR porosity correction and fluid distribution on T2-G maps based on the internal magnetic field gradient correction. |
