This paper presents a methodology to optimize the value of oil produced by adjusting the water injection rates in a mature field.

The reservoir is considered to be a multi-well input-output system with the injection rates as the inputs and production rates as the outputs. A simple capacitance model based on control volume of a given producer is fitted to total injection/production data obtained from a three dimensional reservoir simulator. A power law relationship models the instantaneous water-oil ratio as a function of the cumulative water injected. An optimization problem for oil production is formulated to optimize future performance, where oil production rates and water injection rates are optimized simultaneously based on the selling price of the oil produced and the cost of water injected or the disposal cost of water produced.

The simulation results show that the simple capacitance model satisfactorily captures the long-time behavior between injectors and producers. The solution of the constrained optimization problem for oil production using nonlinear programming can maximize the future economic return of the reservoir asset. Various patterns of optimal injection are followed under different revenue objectives. The optimal injection rates depend on the cost of water injected/disposed, which leads to some wells being shut in while other wells operate at their maximum values.

The proposed optimization method can be used for realtime production control and is appropriate for simultaneous optimization of well rates in a field where injectors are shut-in frequently.

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