Most carbonate reservoirs are heterogeneous in terms of pore distribution and the matrix is extremely low permeable, hindering the flow of oil, while highly permeable fractures are the primary flow conduit. This study presents the hybrid discrete fracture network (DFN) approach to represent fracture network, more realistically, which is a continuum approach equipped with local grid refinement (LGR). The LGR is adapted at the cells that fractures are passing through, in order to describe the fracture width less than 0.1 ft. In this approach, control volume of the well lying on the fracture is extremely small and thus, in this study, four-leg horizontal well concept substitutes the vertical well with the use of equivalent well radius for overcoming the numerical convergence problem. The hybrid DFN approach was applied for CO2-foam injection in fractured carbonate reservoirs to investigate the effect of conformance control. This foam injecting method yields more imbibition of CO2-foam into low permeable matrix, which contains most of the oil. From the numerical results, it shows that the foam controls CO2 velocity and this increases the contact time between CO2 and the rock matrix since CO2 mobility is controlled by foam, that decreases relative permeability of CO2 and increases its viscosity.
Key words: Carbonate, fracture, local grid refinement, CO2-foam, conformance control,discrete fracture network (DFN).
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