Characterizing pore-level oil mobilization processes in unconventional reservoirs assisted by state-of-the-art nuclear magnetic resonance technique

Rigorous characterizations of fluid contents, rock/fluid interactions, and pore-size distributions are crucial in the development of unconventional resources. As a nonintrusive and real-time tool, Nuclear Magnetic Resonance (NMR) draws increasingly attention for these applications. Herein, we first summarized the most intensively used NMR methods, T-2 (1D), T-1-T-2 and D-T-2 (2D) maps, and then performed a critical analyses of pore-scale oil mobilization characterization assisted by NMR, aiming to advance the understanding of unconventional reservoir exploitation. Numerous efforts have been made on presenting the oil mobilization process by 1D NMR. There, however, exists some controversial and even contradictory for similar research objects. Quantifying the interactions in place between gas and oil still needs further investigation. The 2D NMR technique is much more informative compared to the 1D NMR, whereas only limited qualitative analysis can be conducted and the accuracy of the measurement needs to be enhanced for clay mineral-rich reservoirs. Water and oil signals can be easily distinguished in 2D NMR maps with the increase of NMR frequency, which greatly help to identify the fluids in nano-size pores. Currently, all the NMR measurements are limited to the short core plug (length <= 10 cm); thus, future attention should be given to the development of NMR hardware. (C) 2021 Elsevier Ltd. All rights reserved.