Fractal Characteristics of Shales Across a Maturation Gradient

Pore system in shales has attracted growing interest, given that gas storage capacity and gas producibility of shale reservoirs critically depend on shale porosity (Loucks et al., 2009; Bernard et al., 2012; Mastalerz et al., 2013). In spite of its importance, the investigation of pores in shale still remains challenging, owing to small pore sizes, wide pore size distributions, and, more importantly, highly heterogeneous pore structure (Loucks et al., 2012). The fractal dimension characterizes the geometric topography of the surface structure of solid materials (Lowell et al., 2004). This parameter expresses the degree of roughness of a surface or pore wall and can vary from a value of 2 for an ideally flat, smooth surface to 3 for a rough surface with irregular topography and more sorption sites for gases (Lowell et al., 2004). Fractal methods have recently been successfully used in the study of heterogeneous structures in coal (Yao et al., 2008; 2009). However, the fractal characterization of shales still remains scarce (Yang et al., 2014). This study aims to explore heterogeneous and fractal characteristics of pores in shales from N2 adsorption isotherms and discuss implications for gas adsorption capacity.