A new method for calculating volumetric sweep efficiency in a water-flooding oilfield

On the basis of Zhang Jinqingʹs water drive characteristic curve and the basic principle of material balance, and using displacement efficiency expressions of water flooding, volumetric sweep efficiency expressions of water drive and the relationship between average water saturation and exit-end water saturation, this paper deduce the theoretical relationship formulae between displacement efficiency, volumetric sweep efficiency and water cut in a water-flooding oilfield, and puts forward a new method to calculate displacement efficiency and volumetric sweep efficiency with dynamic data in a water-flooding field. A case study shows when water cut is 100%, the volumetric sweep efficiency calculated with Zhangʹs water drive characteristic curve is 99.7%, and that calculated with Sipachevʹs water drive characteristic curve is 100%, which proves that the method with Zhangʹs water drive characteristic curve can more accurately reflect the actual field situation, and is more rational. Study shows the method is simpler, more efficient and cost-saving than conventional core test, reservoir engineering and numerical simulation methods, moreover, it overcomes the narrow application scope of the aforementioned methods.