Pore Structure of Xujiahe Shale and Influencing Factors in the Sichuan Basin: Implication of Monofractality and Multifractality

The pore structures of shale gas reservoirs are intricately complex. In order to explore the dominant controlling factors of shale pore structure characteristics and the role of these factors on shale pore characteristics, six shale samples from the Triassic Xujiahe Formation in the northern Sichuan Basin were selected. We implemented mercury intrusion porosimetry (MIP) and low-temperature nitrogen adsorption (LTN2A) to characterize the structural characteristics of the pore of the shale qualitatively and quantitatively. Subsequently, monofractal and multifractal have been used to explain the heterogeneity and complexity of the pore. Finally, the controlling factors of shale affecting pore characterization are discussed. The results show that the sizes of Xujiahe shale pores are mainly mesopores and micropores. The sample pore size is characterized by a typical bimodal distribution. Through monofractal and multifractal analyses, we learned that the overall heterogeneity and complexity of the pores of shale samples are strong and varied. Through the correlation analysis between fractal and shale characterization parameters, we have obtained shale organic matter characteristics, major minerals have varying degrees of influence on the heterogeneity and complexity of shale pore space, and maceral groups such as vitrinite and sapropelinite also have important and opposing effects on these characteristics. The organic macerals, organic matter abundance, and maturity of shale affect the distribution and characteristics.