Classification of the average capillary pressure function and its application in calculating fluid saturation

When reservoir heterogeneity is strong, there is a great error between the calculated oil saturation based on the J-function and the actual oil saturation interpreted by logging. Aimed at this problem, a reservoir quality index is proposed to classify the average mercury curves, and the reservoir quality index model and original oil saturation model are established, by experimental measurement and numerical simulation with an illustration of an oilfield in the Pearl River Mouth Basin. The oil saturation calculated with this method accords closely with that interpreted by logging, it is a reliable method to show the properties of strongly heterogeneous reservoirs. In addition, this paper proposes a comprehensive utilization of mercury curve and mercury-ejection curve fitting J-function in establishing the saturation model of bound water, movable water, residual oil, movable oil. Considering the influences of such factors as reservoir quality index and clay content on mercury-ejection efficiency, “mercury-ejection index” is used to classify the average mercury-ejection curves and a movable oil saturation model is established, which provides basis for the calculation of recoverable reserves and the research of residual oil distribution.