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An Experimental Study of the Matrix-fracture Interaction During Miscible Displacement in Fractured Porous Media: A Micromodel Study

During miscible displacements in fractured porous media, one of the most important factors that plays a significant role in oil production is the matrix-fracture interaction. In this work, a series of hydrocarbon injection experiments have been performed on a fractured glass micromodel that was designed specifically to study matrix-fracture interaction. A high quality image analysis method was used to determine the fluid flow behavior, solvent front movement, and viscous fingering associated with solvent movement in matrix and fractures. Observations showed that in the case of unit viscosity ratio, the injection rate increased the slope of recovery curve and consequently improved the final oil recovery. However, when using a viscosity ratio of 65, the injection rate increased the oil recovery at earlier times due to the breakthrough and fracture drainage. At later times, diffusion and dispersion became dominant and oil recovery decreased. Studying the effect of molecular diffusion revealed that by using an optimum solvent the oil recovery at both early and late times increased. Fingering phenomena appeared in the matrix as fingers and in the matrix as channeling, which drained fracture in early times of the process. In higher viscosity ratios, dispersion dominantly takes place in an upward direction, however, in the lower viscosity ratio the effect of fracture in flooding decreased and dispersion takes place in a left-to-right direction. It can be concluded that during miscible displacement in fractured porous media dispersion in fracture is directly proportional to viscosity ratio while dispersion in matrix is inversely proportional to it. The results of this work are helpful in understanding the matrix-fracture interaction, the effect of injection rate, molecular diffusion, and viscous fingering behavior, which are crucial for accurate prediction of oil recovery in fractured reservoirs during miscible displacements.