Correlative nano-spectroscopic imaging of heterogeneity in migrated petroleum in unconventional reservoir pores

•Migrated petroleum may significantly hinder fluid flow in nanoporous rocks.•Nano-analyses record spatially registered information from petroleum in chalk.•Nano-scale IR spectroscopy results distinguish functional groups of oil and mineral.•Nano-scale mechanical data show heterogeneity of migrated oil in-situ in nanopores.•The spatial heterogeneity of oil may relate to intrinsic properties of the chalk. Low permeability unconventional oil and gas resources may experience formation damage due to the emplacement of viscous petroleum in narrow pore throats during petroleum migration and production. The composition of such pore-clogging molecules remains under-characterized, as standard analytical techniques in organic geochemistry either lack the desired nano-scale spatial resolution with simultaneous chemical specificity, or require extraction and therefore averaging of the suite of compounds that make up bulk crude oil. A new correlative imaging technique with high spatial resolution is demonstrated for migrated residual petroleum in nanopores of Niobrara chalk samples. Imaging combines Infrared scattering-Scanning Near-field Optical Microscopy (IR s-SNOM) with nano-mechanical atomic force microscopy to map both chemical and mechanical properties at ~30 nm spatial resolution. These correlative images demonstrate that heterogeneity exists within emplaced petroleum in situ on the scale of hundreds of nanometers, visualized as clusters of petroleum having distinct adhesive forces. The chemical composition of these clusters remains ambiguous, but their geometry and mechanical properties may imply that they are phase-separated asphaltene preferentially associated with petroleum-attractive nano-domains on calcite pore walls. Despite outstanding challenges, correlative IR s-SNOM and nano-mechanical imaging offer a promising and novel analytical approach to understanding fluid behavior in nanoporous reservoir rocks.