Nanoscale imaging of pore‐scale fluid‐fluid‐solid contacts in sandstone

Direct observations of oil‐water‐rock contacts are key for improving our understanding of multiphase flow phenomena in mixed‐wet reservoir rocks. In this study we imaged pore‐scale fluid‐fluid‐solid contacts in sandstone with nanometer resolution using cryogenic broad ion‐beam polishing in combination with scanning electron microscopy and phase identification by energy‐dispersive X‐ray analysis. We observed, as expected, the nonwetting oil phase separated from quartz surfaces by a thin brine film, but also direct contacts between oil and rock at asperities and clay aggregates, which act as pinning points and cause discontinuous motion of the oil‐water‐solid contact line. For the rare classical configuration of a three‐phase contact the microscopic contact angle has been determined by serial sectioning. Our results call for improvements in models of multiphase pore‐scale flow in digital rocks.