Investigation of organic-shale nanopores in the Lower Cambrian Niutitang Formation using low temperature N2 and CO2 adsorption: Multifractality and classification

Fractal Characteristics of Nanopores and Their Controlling Factors of the Lower Cambrian Shale in the Western Hubei Area, South China

“…The pores of shale reservoirs are mainly nanosized, and they are important reservoir spaces and migration channels of shale gas. − Therefore, the fine characterization of shale nanopore structure is vital to shale gas reservoir evaluation and development. − …”

“…Previous studies have shown that it was insufficient to study the porous media with complex pore systems (e.g., coals, tight sandstones, and shales) using traditional Euclidean geometry. ,− Recently, fractal theory has been applied to further study the pore heterogeneities of coals and shales, and some important understandings have been proposed. ,− For example, Wang et al found that the seepage and absorption pores of the coals increased with increasing of metamorphism using MICP experiments, and the pore surface and structure, respectively, became rougher and more complex due to coalification. Moreover, the fractal dimensions of large pores were higher than those of small pores.…”

Gas Desorption Behaviors in the In Situ Gas Desorption Test of Organic-Rich Shales: Implication of Monofractality and Multifractality

“…32 Combining CO 2 and N 2 nitrogen adsorption experiments, Tong et al demonstrated the multifractality of Niutitang shale nanopore distribution and classified nanopores based on pore heterogeneity and connectivity. 35 From the above literature reviews, it is evident that fractal theory provides a powerful advancement on the nonlinear time series analysis, but to the best of our knowledge, a monofractal or multifractal study on an in situ gas desorption curve has not been performed. In this study, shale cores from the Longmaxi Formation and the Wufeng Formation in northern Guizhou were collected and subjected to the in situ gas desorption test; subsequently, monofractal and multifractal theories were applied to quantitatively depict the characteristics of gas desorption behaviors, and finally, the relationships between monofractality, multifractality, and gas desorption behaviors were discussed.…”

“…The monofractal manifests as the similarity between local and overall signals, i.e., self-similarity, whereas the multifractal is the spatial entanglement of several monofractal, which is the extension of monofractal . A wide range of complex time series has been quantitatively characterized using monofractal and multifractal theories. − ,− Based on the multifractal detrended fluctuation analysis, Yan et al found that China’s over-the-counter stock market liquidity exhibits sustainability, long-range memory, and lower complexity than the large-cap market liquidity . Telesca et al studied the wind speed time series in Switzerland from the viewpoint of multifractal detrended fluctuation and revealed the multifractality at larger time scales and the monofractality at smaller time scales .…”

“…Combining CO 2 and N 2 nitrogen adsorption experiments, Tong et al. demonstrated the multifractality of Niutitang shale nanopore distribution and classified nanopores based on pore heterogeneity and connectivity . From the above literature reviews, it is evident that fractal theory provides a powerful advancement on the nonlinear time series analysis, but to the best of our knowledge, a monofractal or multifractal study on an in situ gas desorption curve has not been performed.…”