Matrix-fracture interactions during gas injection: A pore-scale experimental study

摘要: Fractured oil reservoirs represent a massive percentage of hydrocarbon formations in the world. Improvement in oil recovery from these reservoirs can be achieved by developing a better understanding of interactions between matrix and fracture and governing mechanisms at the pore level. X-ray micro-computed tomography (CT) imaging techniques can be employed to explore the underlying physics by mapping fluid pore occupancies in matrix and fracture during displacements. The main scope of the present study is to examine the possible beneficial role of spreading phenomena in transferring oil from matrix to fracture during gas injection.We systematically investigate pore-scale displacement physics of three-phase (ie, brine, oil, and gas) flow in fractured porous media and the effectiveness of interaction mechanisms between matrix and fracture using spreading oil. The study is performed based on comparing pore fluid occupancies at a wide range of oil saturations in the pore space established by injecting gas. Visualizing the pore configurations at different oil saturations in the medium reveals the substantial role of spreading layers in maintaining the hydraulic conductivity and the phase connectivity of oil from the matrix to the fracture during the displacement. This mainly takes place at higher gas flow rates where layer drainage in the presence of stable spreading oil layers is the dominant displacement mechanism. At lower gas flow rates, however, the oil displacement is primarily governed by the accessibility of the gas to pore elements adjacent to the fracture as well as threshold capillary pressure.