Effects of capillary pressures on two-phase flow of immiscible carbon dioxide enhanced oil recovery in fractured media

Abstract

CO2-EOR in a geological formation not only increases oil production but also ensures geological sequestration of CO2. The capillary pressure is an essential factor during the process of immiscible CO2-EOR in fractured media. Two classical capillary pressure models are adopted to investigate the effects systematically based on a unified pipe-network method. The identical capillary pressures in fractures and the rock matrixes have little effect on the fluid flow and saturation distribution of CO2. This implies that the capillary pressure can be neglected in this condition. The effect cannot be ignored when different capillary pressures are assigned for fractures and rock matrixes. The saturation of CO2 reaches its highest value at the fracture outlet tip if the capillary pressure in a fracture is smaller than that in the rock matrix. The phenomenon of saturation concentration of CO2 at the fracture tip is caused by the capillary pressure difference. For non-connected fractures, the saturation concentration causes CO2 to enter the adjacent fractures more easily. Thus, the capillary pressure difference enlarges the effect of fractures on the CO2 flow, and shorten the breakthrough time of CO2. Hence, both the storage amount of CO2 and the production of oil in geological media are reduced.