Investigation on Characteristics and Affecting Factors of Water Cut in Planar Thief Zone

Abstract

During exploitation of unconsolidated sandstone reservoir, thief zones form because of heterogeneity and long-term water flooding, causing injection water dashing, production well flooded and inefficient development of reservoir. In order to prevent or limit the formation of thief zones and improve the efficiency of the oil field, it is necessary to identify and describe thief zones between production wells and injection wells. Summarizing present identification method of thief zones, firstly, based on well test theory, dimensionless time is defined and derivation of water cut is made, then, characteristics of water cut as well as its derivative in the presence of thief zone are investigated, and finally, affecting factors are analyzed. The results indicate that there are two peaks on the derivative curve of water cut when thief zone forms; otherwise, there is only one peak on the curve. The morphology of derivative curve of water cut is influenced by permeability and width of thief zone, boundary, formation dip, and so on. Different factors can make a different impact on derivative curve of water cut. The investigation has great reference value because it pioneers the utilization of derivative of dynamic parameters in addition to pressure, and its results can provide guidance for the establishment of a new approach to realize thief zone identification and description.