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We present the results of a systematic pore-scale experimental investigation of two-phase oil/brine flow through a miniature water-wet, fractured sandstone core sample. X-ray microtomography is employed to generate three-dimensional fluid occupancy maps within a rough-walled fracture and its neighboring rock matrix during drainage and imbibition flow experiments. Several different imbibition flow conditions were created by changing brine flow rate, fracture aperture field, and interfacial tension between the fluids. These maps along with steady-state pressure drop data are then used to shed light on the dominant flow mechanisms and preferential flow paths through the matrix and fracture domains as well as fluid transfer between them during the imbibition processes. Depending on the fracture aperture properties and the magnitude of the local capillary pressures that are established under varying flow conditions, transport of the wetting phase across the hybrid matrix-fracture medium is governed by flow through wetting layers of brine on fracture walls (fracture layer flow), center of the fracture (fracture bulk flow), and brine-filled pores within the matrix. The hydraulic conductivity through these conduits is regulated by the medium as it identifies a combined flow path with minimum pressure drop from the inlet to the outlet of the system. The resulting balance determines the magnitude of fluid transfer experienced by the neighboring matrix and ultimate oil recovery as a result.

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