Numerical optimization of duration time for the gravitational sedimentation process of produced water in oilfield

Abstract

Following water flooding, polymer flooding and alkali/surfactant/polymer (ASP) flooding have become the main measures to enhance oil recovery in mature oilfields. However, it is the fact that the development of mature oilfields has continuously entered the ultra-high water cut stage, the amount of produced water has increased year by year. The characteristics of water quality have become increasingly complex, posing challenges for green and efficient separation. Taking China's mature oilfield, Daqing Oilfield, as an example, gravitational sedimentation is a basic process for produced water treatment before filtration. The duration time has always been determined based on standardized design parameters, and the adjustment of duration time depends on experience. This paper distinguishes the characteristics of produced water, and the relationship between treatment performance and production conditions is comprehensively considered. The numerical simulation method is employed to optimize the duration time for gravitational sedimentation of produced water. For produced water with different characteristics of water flooding, polymer flooding and ASP flooding, the reasonable duration time for primary sedimentation is 5 h, 12 h and 14 h respectively, and the reasonable duration time for secondary sedimentation is 3 h, 8 h and 10 h respectively. This recommendation has been validated by experiments.