Effect of initial water saturation on crude oil recovery and water cut in water-wet reservoirs

Abstract

Crude oil recovery and water cut are key parameters in petroleum industry. Note that ‘crude oil’ was reduced to ‘oil’ for simplicity in many cases in the rest of this article. Both theoretical prediction and experimental results have shown that oil recovery could increase or decrease with initial water saturation at a core scale. However, there have been few studies on this once-considered peculiar phenomenon at a reservoir scale. Initial water saturation and its distribution in oil reservoirs depend upon oil-water capillary pressures. In this study, effect of initial water saturation on oil production, oil recovery, and water cut in reservoirs with bottom water was investigated numerically in horizontal wells. Distribution of initial water saturation as a function of reservoir height was either calculated using the oil-water capillary pressure or determined as constant values. The numerical simulation results were compared with experimental data. The results demonstrated that some of the numerical simulation results at a reservoir scale were consistent with the theoretical results from models derived at a core scale as well as the experimental data in the core samples, but the others were not. Experiments conducted in small core samples were often doubted because of the small size compared with the reservoir scale and the poor representation of large-scale reservoirs. The consistence of the results at both core and reservoir scales implies the importance of core analysis experiments and is of great significance in petroleum industry. Copyright © 2014 John Wiley & Sons, Ltd.