Abstract
Pore structure characteristics are important to oil and gas exploration in complex low-permeability reservoirs. Using multifractal theory and nuclear magnetic resonance (NMR), we studied the pore structure of low-permeability sandstone rocks from the 4th Member (ES4) of the Shahejie Formation in the south slope of the Dongying Sag. We used the existing pore structure data from petrophysics, core slices, and mercury injection tests to classify the pore structure into three categories and five subcategories. Then, the T2 spectra of samples with different pore structures were interpolated, and the one- and three-dimensional fractal dimensions and the multifractal spectrum were obtained. Parameters α (intensity of singularity) and f (α) (density of distribution) were extracted from the multifractal spectra. The differences in the three fractal dimensions suggest that the pore structure types correlate with α and f (α). The results calculated based on the multifractal spectrum is consistent with that of the core slices and mercury injection. Finally, the proposed method was applied to an actual logging profile to evaluate the pore structure of low-permeability sandstone reservoirs.
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We would also like to thank Hu Falong and Tan Maojin for the constructive suggestions that significantly improved the manuscript.
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This work was supported by the National Natural Science Foundation of China (Grant No. 41202110) and Open Fund of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University) (Grant No. PLN201612), the Applied Basic Research Projects in Sichuan Province (Grant No. 2015JY0200) and Open Fund Project from Sichuan Key Laboratory of Natural Gas Geology (Grant No. 2015trqdz07).
Yan Jian-Ping, associate professor, graduated in 2004 from China University of Petroleum (Hua Dong) with a degree in Exploration Technology and Engineering. Subsequently, he received his master’ s in Earth Exploration and Information Technology in 2007 and Ph.D. in Marine Geology from Tongji University in 2010. His research interests are rock physics and evaluation of unconventional reservoirs.
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Yan, JP., He, X., Geng, B. et al. Nuclear magnetic resonance T2 spectrum: multifractal characteristics and pore structure evaluation. Appl. Geophys. 14, 205–215 (2017). https://doi.org/10.1007/s11770-017-0614-0
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DOI: https://doi.org/10.1007/s11770-017-0614-0