Pore-Scale Study of the Wetting Behavior in Shale, Isolated Kerogen, and Pure Clay

Understanding the wetting behavior of nanopores in shale formations is crucial for the evaluation of gas adsorption and the prediction of the dynamic performance of fluid flow in their complex pore structures. Conventionally, the wetting behavior of a rock sample can be quantitatively characterized using a variety of laboratory measurements. However, the spatial heterogeneity of shale samples challenges the traditional wettability determination approaches, such as Amott-Harvey, US Bureau of Mines, and contact angle measurements. In this study, we proposed a novel approach to quantitatively analyze the wetting behavior of different nanopores in shale. Our results show that the wetting behavior of different nanopores in our studied illite-rich shale samples is controlled by geochemical and mineralogical compositions. The pores ranging from 2 to 17 nm in size, which are mainly formed within clay particles, exhibit an obvious water-wet behavior. By contrast, the nanopores larger than 17 nm, which are synchronically contributed by clays and organic matter (OM), show a mixed wettability behavior. The hydrophilic pores in shales are mainly attributed to clay pores, whereas a minority can be contributed by OM pores. Although OM pores are originally hydrophobic, some of them can be converted into water-wet as thermal maturity increases. This wettability conversion of OM pores tends to occur in larger pore sizes (>17 nm).