Pore-Scale Remaining Oil Characterization by Integrated Online NMR and Micro-CT

Abstract

An integrated online nuclear magnetic resonance (NMR) and microcomputed tomography (micro-CT) workflow was established to characterize remaining oil mobilization in water-flooded heavy-oil porous media at the pore scale. NMR enabled quantitative tracking of oil-phase depletion across distinct pore-throat intervals via a transverse relaxation time (T2)–pore-throat radius conversion relationship, while micro-CT provided direct spatial and morphological identification of remaining oil. For the investigated cores, the power-law calibration provided better agreement with the mercury-intrusion pore-throat distributions than the linear counterpart. Core permeability, oil viscosity, and displacement velocity collectively govern the extent and location of remaining oil mobilization. With increasing permeability, the dominant mobilized pore-throat interval shifts from small–medium throats, 1–20 μm, to medium–large throats, 20–40 μm and above. CT-derived oil displacement efficiencies showed trends generally consistent with the NMR-based evaluation and further revealed that extended high-pore-volume water flooding and late-stage flow acceleration could still mobilize a portion of the remaining oil, albeit with diminishing incremental recovery. This integrated approach bridges the gap between pore-size-resolved quantification and three-dimensional spatial evidence, offering a robust framework for evaluating remaining-oil potential after prolonged water flooding in heavy-oil reservoirs.