Spectro-Mechanical Characterizations of Kerogen Heterogeneity and Mechanical Properties of Source Rocks at 6 nm Spatial Resolution.

ABSTRACT

In situmeasurements of the chemical compositions and mechanical properties of kerogen help understand the formation, transformation, and utilization of organic matter in oil shale source rocks. However, the optical diffraction limit prevents attainment of nanoscale resolution using conventional spectroscopy and microscopy. Here, we developed peak force infrared (PFIR) microscopy for multimodal characterization of kerogen in organic shales. PFIR microscopy provides correlative infrared imaging, mechanical mapping, and broadband infrared spectroscopy capabilities with 6 nm spatial resolution within the frequency region of 2400-4000 cm-1. We have observed nanoscale heterogeneity in the chemical composition, aromaticity, and the level of maturity of the kerogens from source rocks obtained from the Eagle Ford shale play in Texas. The level of aromaticity of the kerogen positively correlates with the local mechanical moduli of the surrounding inorganic matrix, offering insights into the effect of kerogen heterogeneity on the nanoscale mechanical properties of the source rock. Our method and investigation advances the understanding toward the origin and transformation of kerogen in geological settings.