Nuclear magnetic resonance T2 spectrum: multifractal characteristics and pore structure evaluation
Yan Jian-Ping1,2, He Xu2, Geng Bin3, Hu Qin-Hong4, Feng Chun-Zhen5, Kou Xiao-Pan5, and Li Xing-Wen5
1. State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation (Southwest Petroleum University), Chengdu 610500, China.
2. School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China.
3. Institute of Exploration and Development, ShengLi Oil Field, SINOPEC, Dongying 257015, China.
4. Department of Earth and Environmental Science, University of Texas at Arlington, Texas, 76019, USA.
5. Changqing Division of PetroChina Logging Company, Xi’an 718500, China.
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.
. Nuclear magnetic resonance T2 spectrum: multifractal characteristics and pore structure evaluation[J]. APPLIED GEOPHYSICS, 2017, 14(2): 205-215.
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2017, Vol. 14 
