Nuclear magnetic resonance (NMR) microscopic simulation based on random-walk: Theory and parameters analysis

TAN Mao-jin(谭茂金)^{1, 2}, XU Jing-jing(徐晶晶)², ZOU You-long(邹友龙)², XU Chi-cheng(徐赤诚)³

(1. Key Laboratory of Geo-detection of Ministry of Education (China University of Geosciences),
Beijing 100083, China;
2. School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083; China;
3. Department of Petroleum & Geosystems Engineering, The University of Texas at Austin, TX 78712, USA)

Abstract:The microscopic response characteristics of nuclear magnetic resonance (NMR) are widely used for characterizing complex pore structures of rocks. Due to the prohibitive NMR experiment cost, numerical simulation was employed as an alternative approach to verify some theoretical aspects of NMR responses. Firstly, the basic principles of pore-scale NMR simulation based on random-walk method (RWM) were introduced. The RWM-simulated results were benchmarked with the analytical results for an ideal spherical pore model. Then, the effects of two numerical parameters, namely diffusion radius and walk numbers, were studied on the simulation accuracy. The simulation method is then applied to various pore models with different pore sizes and pore shapes filled with different fluids to study the microscopic NMR response characteristics. The numerical experiments are useful for understanding and interpreting NMR measurements and the simulation code provides a numerical tool to perform pixel-based digital rock analysis.

Key words:microscopic nuclear magnetic resonance; random-walk method; pore structure; parameters analysis