Nanoscale Morphology of Kerogen and In Situ Nanomechanical Properties of Green River Oil Shale

Abstract

Oil shale is an important energy resource that is immensely underutilized due to the cost of extraction of crude oil from oil shale as a result of limited scientific understanding of the locking of kerogen, the precursor to crude oil in the oil shale. Here, nanomechanical properties of in situ kerogen surrounded by minerals in oil shale are evaluated for the Green River Formation oil shale of Colorado Piceance Basin. Electron microscopy and energy dispersive spectroscopy experiments indicate that the sizes of kerogen-rich phases in the oil shale samples are of the scale of 10–50 nm. Comparison of nanoindentation experiments on light- and dark-colored oil shale regions indicates that light oil shale has softer regions arising from higher kerogen content. There do not appear to be significant differences between light- and dark-colored oil shale in orientation parallel and perpendicular to the bedding plane. The elastic modulus values of dark- and light-colored oil shale from nanomechanical experiments indicate that the elastic modulus and hardness of kerogen are ∼5 to 11 and ∼1 GPa, respectively. The pressure environment experienced by kerogen, its proximity to minerals, and its orientation within the shale could play an important role in oil extraction from shale. These results describe important nanomechanical characteristics of the kerogen and its spatial dimension. The enhanced mechanical behavior of the kerogen is illustrative of role of mineral proximity on kerogen structure, conformation, and morphology, and thus physical properties.