Study On Division Method Of Effective Flow Unit And Oil-Water Distribution

Most of oil fields in China have been at the middle-late stage of development when water-oil dominant channel exists due to long-term water flooding. Reservoir heterogeneity results in intensified high water cut and complex remaining oil distribution at late stage of development. Based on fluid dynamics, mathematical statistics and oil-water two-phase flow theory, division principles and method of effective flow unit are established, in order to investigate oil-water distribution at different stages of development and to reveal mechanism of remaining oil. Numerical simulations were carried out of flow units division and remaining oil distribution in an actual reservoir.First of all. concepts of the Contribution Rate of Flow. Non-uniform Flow Distribution Curve and Difference Coefficient of Flow Intension were proposed based on mathematical statistics and streamline cluster equation. According to the concept, flow units could be divided into high-velocity flow area and low-velocity flow area. Mathematical model for average water saturation of each streamline during water flooding with constant rate was established based on Dacry’s Law. According to the principle of water and electricity similarity, three-dimensional two-phase model was established by production split. According to the concept of limit water cut, the effective and ineffective flow area could be divided. Consequently, reservoir flow units could be categorized into four types:type I high velocity ineffective flow, type Ⅱ high velocity effective flow, type III low velocity ineffective flow, type IV low velocity effective flow. Divided principle and method of effective flow units have been established. Using static and dynamic data from Block BSX-S212 in Daqing oil field in China, numerical simulations were carried out of effective flow units division and oil-water distribution after water and polymer flooding respectively in homogeneous reservoir. Mechanism of oil recovery enhancement by polymer flooding was simulated and revealed, introducing threshold value with production contribution degree per unit of flow area. For thick oil layer with high water cut. contribution degree per unit of flow area of type IV flow units is larger than 1. indicating that most of oil production is displaced from low velocity effective flow area. Contribution degree per unit of flow area of type Ⅱ grows during polymer flooding with gradual decrease of growth rate. Therefore, effect of polymer flooding is water control in type Ⅰ flow units and oil recovery enhancement in effective flow units.Subsequently, mathematical models were derived for division of effective flow units and oil-water saturation distribution in heterogeneous reservoir, considering permeability heterogeneity, inter-bed and shelter development. Effects of horizontal and vertical permeability heterogeneity were analyzed. Simulation results show that stronger heterogeneity of reservoir leads to earlier occurrence and larger area of high-velocity ineffective flow units. Based on the above mathematical models, division principle and method was verified to be capable of describing oil-water distribution in reservoir and revealing mechanism of remaining oil in BSX-S212 reservoir of Daqing. and put forward potential exploitation measures. The investigation in the thesis provides new insight and theoretical basis of rational adjustment of oil development.