Abstract
Based on the experiments of nitrogen gas adsorption (N2GA) and nuclear magnetic resonance (NMR), the multifractal characteristics of pore structures in shale and tight sandstone from the Chang 7 member of Triassic Yanchang Formation in Ordos Basin, NW China, are investigated. The multifractal spectra obtained from N2GA and NMR are analyzed with pore throat structure parameters. The results show that the pore size distributions obtained from N2GA and NMR are different, and the obtained multifractal characteristics vary from each other. The specific surface and total pore volume obtained by N2GA experiment have correlations with multifractal characteristics. For the core samples with the similar specific surface, the value of the deviation of multifractal spectra Rd increases with the increase in the proportion of large pores. When the proportion of macropores is small, the Rd value will increase with the increase in specific surface. The multifractal characteristics of pore structures are influenced by specific surface area, average pore size and adsorption volume measured from N2GA experiment. The multifractal characteristic parameters of tight sandstone measured from NMR spectra are larger than those of shale, which may be caused by the differences in pore size distribution and porosity of shale and tight sandstone.
Highlights
Shale oil resources are abundant in China and it is another hot spot in current exploration and development (Hu et al 2017)
The Chang 7 member has the characteristics of continuous development of organic shale and sandstone, and studying the pore structure characteristics of shale and tight sandstone is of great significance for the effective development of the Chang 7
Lai et al (2016) used high-pressure mercury intrusion (HPMI) and nuclear magnetic resonance (NMR) to study the pore structures of tight sandstone, and found that micropores play an important role in the heterogeneity of reservoir rocks and they can be quantitatively characterized by fractal dimension
Summary
Shale oil resources are abundant in China and it is another hot spot in current exploration and development (Hu et al 2017). Lai et al (2016) used HPMI and NMR to study the pore structures of tight sandstone, and found that micropores play an important role in the heterogeneity of reservoir rocks and they can be quantitatively characterized by fractal dimension. As the one of the main tight oil/gas reservoirs in China, the pore structures of tight sandstones in the Ordos Basin have been widely reported (Du and Shi 2019; Li et al 2016; Wang et al 2020). The multifractal characteristics of the pore structures of shale and tight sandstone core samples from the same exploration well located in the Chang 7 Member of the Ordos Basin are studied based on N2GA and NMR experiments. The differences of multifractal characteristics of shales and tight sandstones obtained from N2GA and NMR are compared and discussed
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