Joint Optimization of Economic Project Life and Well Controls

Abstract

Summary A new methodology for the joint optimization of optimal economic project life (EPL) and time-varying well controls is introduced. The procedure enables the maximization of net present value (NPV) subject to satisfaction of a specified modified internal rate of return (MIRR). Knowledge of the economic project life enables the operator to plan for infill drilling or some other type of field development in the case that the lease/contract duration is longer than the optimal project life. This will enable NPV to be maximized, and the hurdle rate to be honored, over the entire duration of the lease. The optimization is formulated as a nested procedure in which economic project life is optimized in the outer loop, and the associated well settings [time-varying bottomhole pressures (BHPs) in the cases considered] are optimized in the inner loop. The inner-loop optimization is accomplished by use of an adjoint-gradient-based approach, while the outer-loop optimization entails an interpolation technique. The successful application of this framework for production optimization for 2D and 3D reservoir models under waterflood is demonstrated. The tradeoff between maximized NPV and rate of return is assessed, as is the impact of discount rate on optimal operations. In the second example, we illustrate the advantages of initiating a new project (that satisfies the hurdle rate) once the EPL is reached. Taken in total, the results in this paper demonstrate the importance of explicitly incorporating both NPV and rate of return in production-optimization formulations.